7.8.1 Before the beginning earthworks on the slope above the upper edge of the developed excavation, upland drainage ditches should be arranged to prevent the possibility of water flow along the slope into the excavation being developed.
7.8.2 To ensure the stability of the embankment, backfilled on the slope, ledges 2-3 m wide should be cut on the area of the foot of the embankment before it is backfilled by a bulldozer with a rotary blade moving longitudinally parallel to the road axis, starting from the lower ledge.
After cutting the lower ledge, the soil from the cut overlying ledge, transferred to the finished lower ledge, is distributed in an even layer and compacted before the next layer of embankment is filled. If the slope soil collapse is possible, the development can be started from the upper ledge with the soil moving down the slope.
On gentle slopes with a steepness of less than 20 °, instead of cutting ledges, it is allowed to loosen with a multi-furrow plow.
7.8.3 Excavations on gentle slopes with a steepness of less than 20 ° should be developed by bulldozers with a rotary blade, passages at an angle of 45 ° to the road axis. In this case, the soil moves into the embankment, starting from its lower part, and its layer-by-layer leveling and compaction is ensured.
On slopes with a steepness of more than 20 °, the excavation and backfilling of the soil into the embankment is carried out by bulldozers with universal dumps with passages parallel or at an angle of less than 45 ° to the axis.
Earthworks using hydromechanization
7.9.1 The use of hydraulic mechanization is effective with fairly large concentrated volumes of earthworks (at least 50,000 m 3 per kilometer of embankment), conveniently located sand and dry pits sandy soils, the possibility of using industrial electricity to power the ground pine and hydromonitor installations.
7.9.2 Works on hydraulic filling of subgrade highways should be carried out by specialized production organization. Preparatory work on hydraulic filling of the embankment can be carried out by a road construction organization. Such works include uprooting forests and other
The intensity of alluvium into the embankment should ensure the return of water from the soil. Depending on the type of soil to be washed, it should be within the range of values given in Table 7.7.
Table 7.7 - Intensity of alluvium into the embankment
7.9.3 A drainage well should be arranged in the center of the "map". The cross section of the well should be designed for the maximum flow rate of the pulp supplied to the "card".
To drain water from the well, an adit is arranged with a bottom slope of at least 5% to the downstream side; the adit and the drainage well must have walls made of waterproof materials, and also must not let water into the junction points.
Embankments must be washed with a margin for settlement, taken at 1.5% of the height of the embankment when alluvium from mixed soils and 0.75% - when alluvium from sandy soils.
7.9.4 In order to reduce labor costs for preparatory work, laying slurry pipelines, dike, as well as to reduce the cost of timber, it is recommended to use a non-trestle end method of alluvium when filling in an embankment with a height of more than 2 m (Figure 7.10). The use of this technology of alluvial subgrade is feasible when mandatory application machines to perform all auxiliary work and. first of all, for the device of a dike and re-laying of pipes.
1 - working slurry pipeline; 2- cream with a carrying capacity of 2.5 tons (specific pressure on the ground 0.017 MPa); 3 - catchment wells; 4 - switch 5 - subsequent positions of the slurry pipeline; 6 - the position of the slurry pipeline when moving "forward"; 7 - the position of the slurry pipeline when moving "back". Q - the direction of movement of the pulp
a - plan, b - cross section
Figure 7.10 - Scheme of the non-trestle end method of alluvial subgrade
The use of trestle or non-trestle methods of soil reclamation must be justified in the design of the organization of work by appropriate technical and economic calculations.
When acquiring approaches to large bridge structures using a non-trestle method, it is necessary to prevent the possibility of pulp spreading along a long slope at the junction with the abutments, for which various delay devices should be created at the abutment (side and end openings-walls, dikes, etc.).
7.9.5 The hydraulic filling of the subgrade should be linked to the process of building an artificial structure through a water barrier.
7.9.6 If, according to local conditions, it is not possible to develop a pioneer trench or a pioneer pit with filling with water from a watercourse and then putting a dredger afloat into the face, then the development of a quarry is advisable using hydraulic monitors.
If at the point where the route crosses the water barrier, the shore is sandy and it is necessary to cut it off or arrange a jet-directing embankment, then hydraulic monitors should also be used to wash out the shore with pumping the pulp from the receiving sump by suction dredgers.
By its size, the sump should ensure uninterrupted operation of the dredger for 1-2 minutes in the event of a break in the supply of pulp.
7.9.7 To develop excavations with hydromonitors, water is supplied under pressure.
When operating hydraulic monitors, the following should be used:
Direct water supply - in cases where the source has a flow rate equal to or greater than the flow rate of water monitors;
Water supply with reuse - in cases where more water is required than the source can provide; Waste water must be clarified in a settling basin for reuse.
SOIL COMPACTION
8.1.1 The compaction of soils from which the subgrade is constructed is a technological process, as a result of which the design strength, stability and stability of the road structure are achieved.
The construction of embankments without layer-by-layer compaction of soils (rollers, rammers, etc.) is allowed in special cases: in swamps (below the surface of the swamp), in reservoirs (underwater); by the hydraulic method. In the listed cases, the project should indicate which method, instead of layer-by-layer compaction, ensures the required stability of the bulk soil.
8.1.2 Soil density is estimated by the compaction factor ( To s). In the subgrade of highways, the soil compaction coefficient should not be lower than the values \u200b\u200bgiven in TCP 45-3.03-19 (Appendix L).
Soil filling into the embankment is carried out, as a rule, from the edges to the middle of the entire width of the canvas, including the sloping parts. In order to compact the soil in the edge parts adjacent to the slope, the width of the poured layer may be 0.3-0.5 m more than the design outline of the embankment on each side. Immediately before the start of work to strengthen the slope, the excess soil is removed when planning the slopes and moved to fill up the roadsides, the arrangement of congresses, and the reclamation of the road strip. If, after removal of excess soil, undercompaction of the soil on the slope is detected, then additional compaction is carried out in accordance with 8.5.3-8.5.5. the sufficiency of which is determined by repeated measurements.
The embankment is not widened when backfilling from coarse-grained and sandy soils that do not significantly change the volume during compaction, as well as when constructing high embankments or embankments with slopes of 1: 2 or more gentle. For these cases, slope compaction should be provided as a separate operation.
8.1.3 Each layer is leveled taking into account the longitudinal slope of the embankment surface. In cross section, the surface of the layer is planned for a single-pitched or double-pitched profile with a slope of 20% to the crest for sandy soils. 40% o - for clay. The surface of each layer must be leveled so that after compaction there are no depressions or elevations of more than 50 mm on it and that puddles do not form during rain. The evenness of the surface of the layers is checked by viziers or leveling.
8.1.4 Each subsequent pass of the compacting machine on one track should not be done until then. until the entire width of the subgrade is blocked by the traces of the previous pass of the compacting machine (on embankments with a width of more than 20 m, a longitudinal division of the grips is allowed). Special attention should be given to compaction of the soil in the sections of the exits and entrances to the road (over a length of 15 - 20 m on both sides) and in the end sections, at their junction with the areas filled during concentrated work.
8.1.5 For compaction of cohesive soils, it is advisable to use rollers on pneumatic tires, cam and lattice trailed rollers; for compaction of non-cohesive soils, vibration and vibro-impact machines, rollers on pneumatic tires should be used.
Compaction of loose, especially clayey, soils should be carried out with two types of rollers: preliminary compaction (rolling) - weighing 6-12 tons and final compaction - weighing more than 25 tons.
During pre-compaction with lighter rollers, up to 30%-40% of the total required number of passes should be performed.
8.1.6 The highest density of the soil can be achieved by using rollers that provide the maximum allowable contact pressure on the surface of the layer (Table 8.1), which is permissible under the conditions of the strength of this soil (Table 8.1). The contact pressure throughout the compaction process should be close to the tensile strength of the soil. If the strength limit of the soil is exceeded, phenomena of local softening may occur (wave formation in front of the wheels of the rollers, extrusion of the soil to the sides during compaction). With insufficient contact pressure, high density can also not be achieved either by reducing the layer thickness or by increasing the number of repeated loads.
Table 8.1 - Soil strength limits
8.1.7 The required density of soils can be achieved with a moisture content that differs from the optimum by no more than indicated in Table 8.2.
8.1.8 If the humidity is less than acceptable (see Table 8.2), non-cohesive and slightly cohesive soils are recommended to be moistened in the backfilled layer shortly before compaction. Cohesive soils, in which the redistribution of moisture is slower, are recommended to be moistened at the development site (in a quarry, excavation, reserve) after they have been loosened.
Table 8.2 - Permissible soil moisture during compaction
| soils | Permissible humidity (W add) in fractions of the optimal (W 0) at the required soil compaction coefficient | |||
| St. 1.0 | 1,0 – 0,98 | 0,95 | 0,90 | |
| The sands are silty; sandy loam, light, large; sandy loam, light and silty; sandy loam, heavy, silty; light and light silty loams Heavy and heavy silty loams, clays | 0,85 – 1,30 0,85 – 1,20 0,90 – 1,10 0,90 – 1,00 | 0,80 – 1,35 0,80 – 1,25 0,85 – 1,15 0,90 – 1,05 | 0,75 – 1,60 0,75 – 1,35 0,80 – 1,30 0,85 – 1,20 | 0,75 – 1,60 0,70 – 1,60 0,75 – 1,50 0,80 – 1,30 |
| Notes 1 When building embankments from non-silty sands in summer conditions, the permissible humidity is not limited. 2 These restrictions do not apply to embankments built by hydraulic fill. 3 When embankments are erected in winter conditions, soil moisture should not, as a rule, be more than 1.3W 0 for sandy and non-silty sandy loamy, 1.2W 0 for sandy loamy silty and light loams and 1.1W 0 for other cohesive soils. 4 The value of the permissible soil moisture can be specified taking into account the technological capabilities of the specific sealing agents available in accordance with TKP 059. |
Watering machines can be used to moisten the soil, pouring water in several steps. When irrigating in situ, the upper moistened layer should be mixed until compacted by loosening or transshipment with a motor grader or bulldozer.
8.1.9 With intense short-term rains, leading to waterlogging of soils,. dumping and compaction of cohesive soils should be stopped before they dry out. In this case, measures are taken to accelerate the drying of soils (loosening, transshipment by graders, bulldozers, etc.). It is allowed to remove the upper layer of soil, waterlogged after rain, into a dump with its subsequent use in other places.
Before a break in work, the surface and slopes of embankments should be compacted and planned so as to prevent waterlogging of soils from stagnant water on the surface of an unfinished embankment. In case of waterlogging in some places, the soil must be dried before the resumption of work or replaced with soil of optimal moisture.
8.1.10 When widening the subgrade of existing highways by adjoining the newly erected part of the embankment to the old one, it is necessary to first remove the vegetable soil from the slope and the sole, fill in the old cuvettes and compact the freshly poured soil in layers in order to avoid subsequent subsidence of the carriageway due to the unevenness of the subgrade in density. The degree of compaction of the backfill of old ditches and other workings should not be less than the degree of compaction of the widened part of the embankment at a given level from the surface.
8.1.11 The thickness of the backfill layer should be set in accordance with the technical parameters of the compacting machines, based on the requirement of a constant density of the soil over the depth of the layer. The layer thickness can be preliminarily assigned according to Table 8.3 with subsequent refinement based on the results of the test soil compaction in accordance with Appendix M.
8.1.12 The results of trial rolling (Appendix M) are included in the technological maps for the construction of the subgrade.
The use of test rolling allows, in some cases, to replace operational control by instrumental measurements of density and moisture technological control, which includes determining the conformity of indicators of the composition and condition of soils and monitoring compliance with the layer thickness, the number of passes and the uniformity of the distribution of passes. Acceptance of the compacted layer must be carried out by instrumental methods in accordance with 13.
Rolling
8.2.1 A layer of loose soil is recommended to be compacted in two stages. First, in order to avoid shifts and the formation of soil waves in front of the working bodies of the compacting machine, it is necessary to perform rolling with a light roller weighing from 6 to 12 tons, and then the main rolling with a heavier roller weighing 25 tons or more.
8.2.2 Pre-rolling is not required when the soil layer is backfilled with the regulation of the movement of transport and earthmoving vehicles across the entire width of the embankment. Earth-carrying transport performs the first stage of rolling to a density of about 0.9 of its maximum value according to standard compaction. In this case, compacting machines are immediately used. heavy type. A clear organization of the joint work of earthmoving-transport and soil-compacting machines makes it possible to ensure complete and uniform soil compaction across the entire width of the subgrade at minimal cost.
Table 8.3 - Data for setting the thickness of the poured layers
| The thickness of the soil layer in a dense body, cm | The method of filling the subgrade | Name of compacting machine | Number of passes (strokes) of the compacting machine | Recommended combination of compacting machines | ||||||||||||||
| Pre-compaction | final compaction | |||||||||||||||||
| Sealing agent | Cohesive soils | Cohesive soils | Sealing agent | Required compaction factor | Cohesive soils | Cohesive soils | ||||||||||||
| Weight, t | Type of | Weight, t | Type of | Cohesive soils | Cohesive soils | |||||||||||||
| 0,95 | 0,98 | 1,00 | 1,02 | 0,95 | 0,98 | 1,00 | 1,02 | |||||||||||
| 20-40 | dump trucks | 12-15 | BUT | 2-3 | 1-2 | I | 3-5 | 5-7 | 7-9 | 10-12 | 5-7 | 7-9 | 9-11 | 12-14 | A and I B and I | A and I B and I | ||
| - | - | - | - | 9-18 | II | - | - | - | - | 6-8 | 8-10 | 10-12 | 13-15 | - | II | |||
| - | - | - | - | 6-18 | III | 1-2 | 2-4 | 4-6 | 7-9 | - | - | - | - | III | - | |||
| Trailed lattice roller | 14-15 | B | 2-3 | 2-3 | 25-30 | IV | 3-5 | 5-7 | 7-9 | - | 5-7 | 7-9 | 9-11 | - | IV | IV | ||
| 20-40 | Scrapers | Pneumatic tire roller trailed or semi-trailed | - | - | - | - | I | 3-5 | 5-7 | 7-9 | 10-12 | 5-7 | 7-9 | 9-11 | 12-14 | I | I | |
| Trailed or combined cam roller | - | - | - | - | 9-18 | II | - | - | - | - | 5-7 | 7-9 | 9-11 | 12-14 | - | II | ||
| Roller vibratory trailed or combined | - | - | - | - | 6-18 | III | 1-2 | 2-4 | 4-6 | 7-9 | - | - | - | - | III | - | ||
| 40-50 | dump trucks | 12-15 | BUT | 3-4 | 2-3 | 40-50 | V | 4-6 | 6-8 | 8-10 | 11-13 | 6-8 | 8-10 | 10-12 | 14-16 | A and V B and V | A and V B and V | |
| 40-50 | dump trucks | Cam roller | 5-9 | AT | - | 3-4 | - | - | - | - | - | - | - | - | - | - | ||
| Lattice roller | 14-15 | B | 3-4 | 2-3 | 25-30 | IV | 4-6 | - | - | - | 6-8 | - | - | - | IV | IV | ||
| Vibratory roller | - | - | - | - | 8-18 | VI | 3-4 | 4-6 | 6-8 | 9-11 | - | - | - | IV | - | |||
| rammer | - | - | - | - | VII | 1-2 | 2-3 | 3-4 | 4-6 | 1-2 | 2-3 | 3-4 | 4-6 | VII | VII | |||
| 70-80 | dump trucks | Roller with pneumatic tires | 12-15 | BUT | 4-5 | 3-4 | 40-50 | V | 6-8 | 8-10 | 10-12 | - | - | - | - | - | A and V B and V | - |
| Lattice roller | 14-15 | B | 3-4 | - | - | - | - | - | - | - | - | - | - | - | - | - | ||
| Trailed vibratory roller | - | - | - | - | 10-18 | VIII | 4-6 | 6-8 | 8-10 | - | - | - | - | - | VIII | - | ||
| 100-120 | dump trucks | Trailer vibrating roller (semi-trailer) | 3-6 | G | 2-3 | - | 15-18 | IX | 6-8 | 8-10 | 10-12 | - | - | - | - | - | B and IX | - |
8.2.3 Rollers on pneumatic tires are the most versatile means of soil compaction. A gradual increase in specific pressure is one of the main requirements for the compaction of cohesive soils, which ensures that a dense and strong soil structure is obtained throughout the entire thickness of the layer. The pressure in the tires of the rink at the initial stage of compaction of cohesive soils should not exceed 0.2-0.3 MPa. final stage compaction should correspond to the compaction of sandy loam 0.3 - 0.4 MPa, loam - 0.6 - 0.8 MPa. When compacting sands, the tire pressure at all stages of compaction should not exceed 0.2-0.3 MPa.
8.2.4 When pre-compacting the soil with a lighter roller, the load on each wheel should be approximately 2 times less than the load on the wheel of the main, heavier roller.
The first and last passes along the rolling strip should be made at a low speed of the roller (2-2.5 km/h); intermediate passes - at high speed (8-12 km / h).
8.2.5 To achieve uniform soil compaction, the pressure in all tires of the roller wheels must be the same. The most uniform density of the compacted layer of the embankment is provided by sectional rollers, in which pneumatic wheels with separate sections for ballast have an independent suspension.
8.2.6 Padfoot compaction is effective in cohesive soils where the soil is loose or lumpy at the start of compaction.
Sandy loams are heavy silty, light loams - from 0.7 to 1.5;
Light silty loams, heavy loams - from 1.5 to 4.0;
Heavy silty loams, clays - from 4.0 to 6.0.
The specified values of specific pressures refer to soils of optimal moisture content.
8.2.7 Trailed lattice rollers are most effective in compacting coarse and gravelly soils with frozen clods, as they provide crushing and uniform density throughout the entire thickness of the compacted layer. However, heavy duty rollers with pneumatic tires and vibratory rollers should be used for final compaction.
8.2.8 Soil compaction with trailed cam and lattice rollers is carried out by circular passages along the working area. Rolling is carried out from the edges of the embankment to its middle (Figure 8.1) with the overlap of the compaction strips by 0.15-0.23 m. 0.3 m
1-8 - sequence of passes;
h is the thickness of the soil layer; b - width of the rolled strip
a - a diagram of the movement of a tractor with cam rollers; b - cross section;
c - overlapping of rolling strips
Figure 8.1 - Scheme of trailed cam rollers
When rolling the upper layers of the embankment with a height of more than 1.5 m with trailed rollers on pneumatic wheels, the first and second passes should be carried out at a distance of 2 m from the edge of the embankment, and then, shifting the moves by 1/3 of the width of the roller towards the edge, compact the edges of the embankment (Figure 8.2). After that, rolling is continued in circular passes from the edge to the middle of the embankment.
1-10 - sequence of passes
Figure 8.2 - Scheme of operation of a trailed roller on pneumatic tires
The approach of the working bodies of compacting machines to the edge of the embankment closer than 0.3 m (Figure 8.3) is not allowed for safety reasons with any compaction methods (except for mounted rammers).
Figure 8.3 - Scheme of compaction of the embankment, taking into account safety regulations
8.2.9 For the operation of trailed rollers, the optimal dimensions of the grip should be at least 200 m across the entire width of the embankment. An increase in the rolling front increases the productivity of trailed rollers. However, with an increase in the length of the section prepared for rolling, it should be borne in mind that in dry and hot weather there is an intense loss of soil moisture.
8.2.10 With the intensification and increase in the rate of construction of the subgrade, soil compaction can be carried out by the same rollers, but moving at a speed of 10-15 km/h. This requires more powerful (by 50% -70%) basic or traction means, a decrease in the thickness of the poured layers by 30% -40% and an increase in the number of passes along one track by at least 1/3.
tamping
8.3.1 Compaction is used to compact soils of natural foundations when additionally compacting existing embankments without dismantling them, in cramped places. In this way, it is possible to compact soils in layers of large thickness in one or two passes of the machine. The tamping method makes it possible to obtain a density of soils significantly higher than the maximum standard density, to compact soils when moisture content is above and below the permissible limits. Compaction can be used to compact solid cloddy soils, including coarse-grained ones.
8.3.2 When choosing a compacting machine, continuous self-propelled machines should be preferred. Tamping plates suspended from the excavator-crane can be used if there are no other machines (Figure 8.4).
When compacting layers of large thickness from 1 to 2 m, to compact soils of low humidity, as well as to achieve soil density above the standard maximum density, tamping plates freely falling from a height of 2-3 to 5-6 m are used, weighing from 2-3 to 12- 15 tons, which are suspended from the boom of an excavator-crane of the appropriate carrying capacity. For a slab weighing 2-3 tons, an excavator with a bucket capacity of at least 0.5-0.7 m 3 is required, for a slab of 12-15 g - at least 1.25 m 3. In this case, the thickness of the compacted soil layer is approximately equal to the diameter of the slab base.
Specification of technological parameters of ramming is carried out according to the test compaction data.
1 - spring shock absorber; 2 - rammer; 3-compacted soil layers; 4-sealed strip;
W- step of moving the excavator (the arrow shows the direction of the working stroke of the excavator
Figure 8.4 - Scheme of operation of a heavy (weighing 12-15 tons) tamping plate suspended from an excavator boom
In order to reduce dynamic loads on the excavator and prevent premature wear of its main mechanisms, a spring suspension is installed between the tamper plate and the lifting rope.
8.3.3 The operating speed of a rammer with free-falling plates on a backhoe crane depends on the type and moisture content of the soil, as well as on the thickness of the compacted layer. Soil with optimal moisture and a layer thickness approximately equal to the diameter of the sole of the slab is recommended to be compacted in one pass of the machine at a speed of about 150 m/h.
8.3.4 When using tamping plates on excavator cranes, the width of the compaction strip should be taken within no more than 1.5 of the radius of the boom.
Compaction of loose clay soil is carried out in two stages: preliminary and main compaction. It is expedient to carry out preliminary compaction by reducing the mass of the rammer by a factor of 2 or by reducing the fall height by a factor of 4. Preliminary compaction of the soil, in which no more than two or three blows are applied on one track, is carried out simultaneously on three or four strips over their entire width. until the specified number of strokes has been made on each strip. During ramming, it is necessary to maintain a constant lifting height of the rammer at the moment of dropping. You can only move to a new compaction strip after compacting the previous strip.
When choosing the operating mode of tamping plates, preference should be given to dropping plates of a larger mass from a lower height. For excavators with buckets with a capacity of 0.5 to 1 m 3, this height is usually 2 to 4 m.
8.3.5 Upon completion of compaction, the top layer of soil 10-15 cm thick, loosened by ramming, should be compacted with light ramming blows from a height of 0.5 miles by rolling with rollers.
Part 1
Bulldozers perform operations as follows. Layered development and movement of materials produced at a transportation distance of 50 ... 150 m. Large travel distances are economically beneficial for heavy bulldozers. In the surface development of soils and minerals, the shuttle movements of the machine are characteristic, alternating the working stroke and the departure back empty. It is advisable to collect and transport the soil in one pass with the formation of side rollers, in a trench way, in paired operation of bulldozers, and in the formation of several prisms. In light soil conditions, additional interchangeable bulldozer equipment (openers, expanders, extensions) is used.
Elevation of embankments carried out in two ways: transverse passages from the reserve (Fig. 137, I) and longitudinal one-way movements of the machine (Fig. 137, II).
Rice. 137. Basic excavation bulldozer work
When transversely moving soil from reserves, it is advisable to use the trench method of developing materials and the paired operation of several machines. The first prisms are fed into the center of the embankment, the next - closer to its edges.
Drawing prisms are placed in a clamp. The slopes of the embankment, along which the soil is supplied, should not exceed 30%. With large elevations of the embankment, the work is inefficient.
By longitudinal movements of the bulldozer in the direction of the longitudinal axis of the embankment, it is advisable to feed the soil down the slope. The height of the embankment in this case can be up to 4 ... 5 m.
Development of recesses produce longitudinal bilateral passages (Fig. 137, III) and transverse moves (Fig. 137, IV). Longitudinal double-sided method provides greater productivity of bulldozers. It is used for small excavations and in cases where the soil excavated from the excavation is completely laid in adjacent embankments. The transverse excavation method is used when excess soil is laid in cavaliers along the future roadbed.
Extraction of canals, irrigation facilities, trenches, pits produce transverse strokes of the bulldozer with a gradual displacement of the machine along the structures (Fig. 137, V). The soil is laid in cavaliers along the entire length of the channels, creating earth ramparts on both sides. Soil is developed in parallel trenches with a depth not exceeding the overall height of the machine. The distance between the trenches is up to 0.4 ... 0.6 m. After the excerpt, the inter-trench bridge is destroyed. In this case, the group operation of machines with paired parallel strokes is effective.
planning work carried out on a flat surface, cutting off small bumps and filling up depressions, pits, ravines. Large depressions fall asleep from neighboring slopes with longitudinal passages (Fig. 137, VI). The last passes are made with an offset of 3/4 of the blade width to eliminate the appearance of side ridges. After a rough front layout (see Fig. 130, G) it is advisable to finish the surface when the bulldozer is reversing (see Fig. 130, in) and the "floating" position of the blade. For greater accuracy, it is advisable to use mutually perpendicular passages of bulldozers.
Rice. 130. The main types of work performed by bulldozers: a- development of trenches, pits, channels with backfilling of soil into caves, embankments, b- cutting slopes and backfilling of recesses, in- removal of the fertile layer or waste rock, G- forward planning d- forward leveling, e- rear layout and- backfilling of trenches, h- pushing scrapers when filling the bucket with soil, and- loading soil into transport from a flyover, to- loading materials into transport from the tray, l- felling trees m- uprooting of stumps, n- cutting bushes and small forests, about- snow removal works; 1 - initial position of the bulldozer, 2 - cutting and transporting soil, 3 - bulldozer on the embankment, 4 - embankment or cavalier, 5 - trench, 6 - slope, 7 - excavation, 8 - fertile layer or waste rock, 9 - minerals and Construction Materials, 10 - scraper, 11 - overpass, 12 - vehicles, 13 - loading tray
Punching of terraces and shelves on slopes carried out by bulldozers with fixed and rotary blades. The most efficient and safest way to move soil from a slope to a semi-mound is by the transverse passages of the machine downhill (Fig. 138, I). It is used on gentle slopes of slopes. At large slope angles, the longitudinal method is used (Fig. 138, II). In this case, the dozer blade, mounted at an angle, punches first pass 1, then 2, 3, 4, and 5. Working with longitudinal passes is more productive, but special care must be taken, as the machine may slide sideways or tip over the slope. Therefore, for the safety of work, the transverse stability of the bulldozer is taken into account.
Rice. 138. Development of slopes with a bulldozer
backfilling trenches produced by bulldozers with fixed (Fig. 139, a) or a rotary blade (Fig. 139, b). This operation is performed by straight passages perpendicular to the axis of the trench, or by oblique movements at some angle to it.
Rice. 139. Backfilling trenches with bulldozers: a- with non-rotating blade, b- with a rotary dump; 1 - soil embankment, 2 - trench
A bulldozer with a fixed edge grabs some of the soil from the embankment and moves it into the trench. If the depth of the trench is 1.5 m or more, then the soil is poured through one or two prisms in order to prevent the walls of the trench from collapsing and the bulldozer sliding into it. After the first pass, the bulldozer shifts in reverse and the operation is repeated.
For a bulldozer with a swivel (wider) blade, it is installed at an angle to the right to the longitudinal axis of the machine and the soil is pushed into the trench with oblique moves at an angle of 30 ... 40 °. The use of bulldozers with a rotary blade in this work is more effective, since the soil is partially shifted to the side when pushed.
Scraper pushing(see fig. 130, h) are carried out by bulldozers when collecting soil and exiting a loaded scraper from a face with a large slope of access roads.
Loading soil into transport from a flyover(see fig. 130, and) are predominantly produced in sand pits. The overpass is arranged in a trench dug by a bulldozer. With longitudinal strokes, the bulldozer moves the material to the trestle bunker and loads dump trucks. The bulldozer works through one or two prisms so as not to cause the overpass to collapse. Loading soil into transport from the tray is shown in fig. 130, to.
felling trees(see fig. 130, l) is carried out by focusing the maximum raised blade into the trunk.
Stump uprooting(see fig. 130, m) can be carried out with a straight blade or a blade with a skew. First, by deepening the blade with medium or angled knives, the roots of the stump are cut and swayed by repeated engagements of the clutch. Then, with the simultaneous translational movement of the machine and the lifting of the working equipment, the stump is uprooted. Similarly, large stones and boulders, partially located on the surface, are removed from the ground.
Shrub and undergrowth cutting(see fig. 130, n) is produced with a direct blade lowered into the ground to a depth of 10 ... 20 cm, with the entire bulldozer moving forward. As heaps of bushes, roots, small trees accumulate, they are moved away from the track being cleared in a rotary motion.
snow plow(see fig. 130, about) are performed to keep roads in good condition. The most effective in this case is a bulldozer with a rotary blade with an oblique working body.
Bulldozers perform operations as follows. Layer-by-layer development and movement of materials produced at a transportation distance of 50 ... 150 m. Large travel distances are economically beneficial for heavy bulldozers. In the surface development of soils and minerals, the shuttle movements of the machine are characteristic, alternating the working stroke and the departure back empty. It is advisable to collect and transport the soil in one pass with the formation of side rollers, in a trench way, in paired operation of bulldozers, and in the formation of several prisms. In light soil conditions, additional interchangeable bulldozer equipment (openers, expanders, extensions) is used.
Elevation of embankments carried out in two ways: by transverse passages from the reserve and by longitudinal one-way movements of the machine.
When transversely moving soil from reserves, it is advisable to use the trench method of developing materials and the paired operation of several machines. The first prisms are given to the center of the embankment, the subsequent ones are closer to its edges.
Drawing prisms are placed in a clamp. The slopes of the embankment, along which the soil is supplied, should not exceed 30%. With large elevations of the embankment, the work is inefficient.
Rice. 137. Basic excavation bulldozer work.
See also:
By longitudinal movements of the bulldozer in the direction of the longitudinal axis of the embankment, it is advisable to feed the soil downhill. The height of the embankment in this case can be up to 4 ... 5 m.
Development of recesses produced by longitudinal double-sided passages and transverse passages . The longitudinal double-sided method provides greater productivity for bulldozers. It is used for small excavations and in cases where the soil excavated from the excavation is completely laid in adjacent embankments. The transverse excavation method is used when excess soil is laid in cavaliers along the future roadbed.
Extraction of canals, irrigation facilities, trenches, pits produced by transverse strokes of the bulldozer with a gradual displacement of the machine along the structures . The soil is laid in cavaliers along the entire length of the channels, creating earth ramparts on both sides. Soil is developed in parallel trenches with a depth not exceeding the overall height of the machine. The distance between the trenches is up to 0.4 ... 0.6 m. After the separation, the inter-trench bridge is destroyed. In this case, the group operation of machines with paired parallel moves is effective.
planning work carried out on a flat surface, cutting off small bumps and filling up depressions, pits, ravines. Large depressions fall asleep from neighboring slopes with longitudinal passages . The last passes are made with an offset of V4 of the blade width in order to exclude the appearance of side ridges. After a rough front layout, it is expedient to carry out surface finishing with the rear of the bulldozer and the "floating" position of the blade. For greater accuracy, it is advisable to use mutually perpendicular passages of bulldozers.
Punching of terraces and shelves on slopes carried out by bulldozers with fixed and rotary blades. The most efficient and safest way is to move soil from a slope to a semi-mound with the transverse passages of the machine down the slope. It is used on gentle slopes of slopes. At large angles of inclination of slopes, a longitudinal method is used . In this case, the bulldozer blade, installed with a skew, punches first passage 1, then 2, 3, 4 and 5. Working with longitudinal passages is more productive, but special care must be taken, as it is possible to cross-slide or tip the machine down the slope . Therefore, for the safety of work, the transverse stability of the bulldozer is taken into account.
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Rice. 140. Soil loosening schemes:
a- longitudinal-annular, b - spiral, c - shuttle-night with offset, d - longitudinal-transverse.
The choice of loosening scheme depends on the strength and nature of the rocks being developed.
When loosening soils of category IV and strong rocks, it is advisable to organize the operation of machines according to longitudinal-ring and spiral schemes, since they provide the highest productivity of the machine. Shuttle and longitudinal-transverse schemes are used for loosening rocks and permafrost soils. The latter scheme is used when it is necessary to obtain loosened rock of smaller sizes. It is additionally crushed by tractor tracks.
Areas of frozen soils are developed in layers to the maximum possible depth.
With a depth of freezing of rocks of 50 ... 70 cm, it is possible to loosen the array with three teeth. If the depth of the development of rocks is greater, then with one tooth in two or three passes with a loosening depth of 30 ... 40 cm for each cycle. When working on frozen rocks, the traction force of the machine is reduced by 35 ... 45% due to a decrease in the coefficient of adhesion of the undercarriage to the ground.
Soils are loosened on the working gear of the tractor at a speed of 0.9 ... 2.7 km / h. At the end of the working cycle, the ripper is dug out and the presence of a removable tip is checked. If the tip is lost, the toe of the rack can be damaged and it will not hold the tip. In this case, the rack is replaced.
Rice. 141. Methods for the development of soils and the extraction of minerals:
a-trench with feed into vehicles by a loader, b - downhill with loading from a stack into transport by an excavator, with - two bulldozers-rippers with backfilling and from the dump into vehicles by a loader;
1 - bull-dozer-ripper; 2 - loader, 3 - vehicles, 4 - excavator.
Loose soils and rocks are removed by earth-moving vehicles. The most effective development of strong, frozen rocks and minerals is by a bulldozer-ripper.
There are several rational schemes for organizing the work of a bulldozer-ripper in combination with loaders and excavators.
When developing an array in a trench way, the bulldozer-ripper 1 loosens the rock in layers at the bottom of the trench. Then, with bulldozer equipment, with the ripper raised, the rock is moved into the stack by shuttle movements of the machine. From the stack with a single-bucket loader 2, the crushed material is loaded into vehicles 3 and transported to the place of storage or processing.
A more rational scheme for loosening and cleaning rocks with a bulldozer downhill. A stack of material is formed at the bottom of the slope. From the pile, an excavator or loader loads the rock into vehicles. The performance of the unit in this case is higher.
To match the performance of the loading equipment, sometimes two bulldozers-rippers are used, which first loosen the bottom of the trench with longitudinal-transverse strokes, and then one bulldozer delivers the material to the storage site, and the other pushes it into the pile, from which the loader picks up breed and fills vehicles.
When mining open way they use a complex detachment of machines, which includes 3 ... 5 bulldozers, rippers, an excavator or loader, and several dump trucks. To avoid downtime, one bulldozer-ripper 3 only loosens the site. Several bulldozers 2 in parallel move the loosened waste rock 4 into a pile, from which the excavator 1 loads it into vehicles 4 and transports it to the dump. After harvesting the waste rock, minerals are developed in a similar way.
Rice. 142. Open pit mining with preliminary loosening:
1 - excavator or loader, 2 - bulldozers, 3 - bulldozer-ripper, 4 - waste rock, 5 - vehicles, 6 - minerals.
The choice of excavation method depends on the properties of the soil, the amount of work, the type of earthworks, hydrogeological conditions and other factors. The technological process of excavation consists of excavation, transportation, laying in a dump or embankment, compaction and leveling. For the mechanization of earthworks, single-bucket construction excavators are used with flexible and rigid suspension of working equipment in the form of a front and back shovel, dragline, grab, earth-moving, planning, planning and loading devices; continuous excavators, which include chain bucket, chain scraper, rotary bucket and rotary bucketless (milling); bulldozers, scrapers, graders (trailed and self-propelled), graders-elevators, rippers, drilling machines. The set of machines for mechanized soil excavation, in addition to the leading earth-moving machine, also includes auxiliary machines for transporting soil, cleaning the bottom excavation, compacting the soil, finishing slopes, preliminary loosening the soil, etc., depending on the type of work.
Soil excavation with single-bucket excavators
In industrial and civil construction, excavators with a bucket with a capacity of 0.15 to 4 m3 are used. When performing large volumes of earthworks in hydraulic engineering, more powerful excavators with a bucket capacity of up to 16 m3 or more are used.
Wheeled excavators are recommended to be used when working on soils with high bearing capacity with dispersed scopes of work, when working in urban areas with frequent relocations; caterpillar excavators are used for concentrated scopes of work with rare relocations, when working on soft soils and excavating rocks; mounted excavators on pneumatic wheeled tractors - with dispersed scopes of work and when working in off-road conditions.
Soil excavation by single-bucket excavators is carried out by penetrations. The number of penetrations, faces and their parameters are provided in the projects and technological maps of earthworks for each specific object in accordance with the parameters of earthworks (according to working drawings) with the optimal working dimensions of excavator equipment.
Single-bucket excavators are cyclical machines. The working cycle time is determined by the sum of the individual operations: the duration of filling the bucket, turning to unload, unloading and turning to the face. The least time spent on the execution of the working cycle is provided under the following conditions:
- the width of penetrations (faces) is taken in such a way as to ensure the operation of the excavator with an average turn of no more than 70 degrees;
- the depth (height) of the faces should not be less than the length of the soil chips required to fill the bucket with a cap in one digging step;
- the length of the penetrations is taken into account, taking into account the possibly smaller number of inputs and outputs of the excavator into and out of the face.
The face is the working area of the excavator. This zone includes the site where the excavator is located, part of the surface of the developed array and the installation site. Vehicle or a site for laying the developed soil. The geometric dimensions and shape of the face depend on the equipment of the excavator and its parameters, the size of the excavation, the types of transport and the adopted soil development scheme. AT technical specifications excavators of any brand, as a rule, their maximum indicators are given: cutting radii, unloading, unloading height, etc. In the production of earthworks, optimal operating parameters are taken, which are 0.9 of the maximum passport data. The optimal height (depth) of the face should be sufficient to fill the excavator bucket in one scoop, it should be equal to the vertical distance from the excavator parking horizon to the level of the pressure shaft, multiplied by a factor of 1.2. If the height of the face is relatively small (for example, when developing a planning cut), it is advisable to use an excavator together with a bulldozer: the bulldozer develops the soil and moves it to the excavator's workplace, then earths up the soil, while ensuring a sufficient face height. The excavator and vehicles should be located so that the average angle of rotation of the excavator from the place where the bucket is filled to the place where it is unloaded is minimal, since up to 70% of the working time of the excavator cycle is spent on turning the boom.
As the soil is developed in the face, the excavator moves, the worked out areas are called penetrations. In the direction of movement of the excavator relative to the longitudinal axis of the excavation, longitudinal (with a frontal or end face) and transverse (lateral) methods of development are distinguished. The longitudinal method consists in developing a recess with penetrations, the direction of which is chosen along the largest side of the recess. Frontal slaughter is used when developing a congress into a pit and when digging the beginning of an excavation on steep slopes. With a frontal face, the soil is developed for the entire width of the penetration. End face is used in the development of excavations below the level of the excavator parking, while the excavator, moving in reverse on the surface of the earth or at a level located above the bottom of the excavation, develops the end of the excavation. Sidewalls are used for excavation with a straight shovel, while the paths of vehicles are arranged parallel to the axis of movement of the excavator or above the bottom of the face. With the lateral method, the full width of the penetration can be obtained by successively developing a number of penetrations. In a transverse (lateral) way, excavations are developed with soil filling in a direction perpendicular to the axis of the excavation. The transverse method is used in the development of extended narrow excavations with backfilling of cavaliers or in the construction of embankments from lateral reserves.
Some types of cuts (for example, planning) can be developed by sidewall with traffic on the same level with the excavator. Sometimes, in order to move to development with a side face, it is first necessary to tear off the so-called pioneer trench, which the excavator begins to develop by descending to the bottom of the face along the ramp. If the excavator unloading height is greater than or equal to the sum of the excavation depth, the height of the side of the dump truck and the “cap” above the side (0.5 m), the pioneer trench is developed with a side face when vehicles move on the day surface at a distance of at least 1 m from the edge of the excavation. With a significant size of the excavation, it is developed by transverse penetrations along the smaller side, while ensuring the minimum length of the pioneer trench, which allows organizing the most productive ring traffic. Excavations, the depth of which exceeds the maximum depth of the face for this type of excavator, are developed in several tiers. At the same time, the lower tier is developed similarly to the upper one, and the cars are fed to the excavator so that the bucket is on the back of the body. The route of the car in this case should be parallel to the axis of the excavator penetration, but directed in the opposite direction.
A backhoe equipped with a backhoe is used when excavating soil below the level of the parking lot and is most often used when digging trenches for laying underground utilities and small pits for foundations and other structures. When working with a backhoe, face or side slaughter is also used. It is most advisable to use a backhoe excavator for excavation of pits with a depth of no more than 5.5 m and trenches up to 7 m. The rigid attachment of the backhoe bucket makes it possible to dig narrow trenches with vertical walls. The depth of the developed narrow trenches is greater than the depth of the pits, since the excavator can lower the boom with the handle to the lowest position, while maintaining stability.
An excavator with dragline working equipment is used in the development of large and deep pits, in the construction of an embankment from reserves, etc. The advantages of a dragline are a large radius of action and a digging depth of up to 16-20 m, the ability to develop faces with a large influx of groundwater. Dragline develops recesses with end or side penetrations. For end and side penetrations, the organization of dragline work is similar to that of a backhoe. At the same time, the same ratio of the maximum depth of cut is maintained. The dragline usually travels 1/5 of the length of the boom between stops. The development of soil by dragline is most often carried out in a dump (one-sided or two-sided), less often - for transport.
Excavators tear off pits and trenches to a depth slightly less than the design one, leaving the so-called shortfall. The shortfall is left in order to avoid damage to the base and prevent overshooting the soil, it is usually 5-10 cm. To increase the efficiency of the excavator, a scraper knife mounted on a bucket is used. This device allows you to mechanize operations for cleaning the bottom of pits and trenches and conduct them with an error of no more than plus or minus 2 cm, which eliminates the need for manual modifications.
Soil excavation by continuous excavators is carried out in the absence of stones, roots, etc. in the soil. Before starting work along the trench route, a bulldozer plans a strip of earth with a width not less than the width of the caterpillar track, then the trench axis is broken and fixed, after which it begins to be cut from the side of low marks (for water flow). Bucket excavators develop trenches of limited dimensions and, as a rule, with vertical walls.
Soil excavation by earth-moving machines
The main types of earth-moving machines are bulldozers, scrapers and graders, which develop the soil in one cycle, move it, unload it into the embankment and return to the face empty.
Excavation work with bulldozers
Bulldozers are used in construction to develop soil in shallow and extended excavations and reserves to move it in embankments at a distance of up to 100 m (when using more powerful machines, the distance of soil movement can be increased), as well as in clearing the territory and planning work, and cleaning up foundations under embankments and foundations of buildings and structures, when arranging access roads, excavating soil on slopes, etc.
Rice. 7. :
a - conventional cutting; b - comb cutting
In the practice of earthworks, there are several ways to cut the soil with a bulldozer (Fig. 7):
- conventional cutting - the knife first deepens to the maximum depth for a given soil and gradually rises as it is loaded, as the drag prism resistance increases, which consumes the tractor's traction;
- comb cutting - the dump is filled with several alternating indentations and uplifts.
The comb scheme allows you to reduce the length of cut by increasing the average chip depth. In addition, with each penetration of the knife, the soil is chipped off under the drag prism and the already cut soil is compacted on the blade. This reduces cutting time and increases the volume of soil on the blade.
In the production of earthworks with bulldozers, a method of cutting downhill is successfully used, based on rational use traction force of the tractor. Its essence is that when the tractor moves downhill, part of the traction force is released, which is necessary to move the machine itself, due to which the soil can be destroyed with a thicker layer. When the bulldozer works downhill, soil chipping is facilitated, the resistance of the drag prism is reduced, which moves partially under its own weight. In the absence of a natural slope, it can be created by the first penetrations of the bulldozer. When working under a slope of 10-15 degrees, productivity increases by about 1.5-1.7 times.
Rice. eight. :
a - single-layer cutting; b - trench cutting. The numbers indicate the order of cutting
The bulldozer works according to the schemes shown in fig. 8. With a single-layer cutting with overlapping strips of 0.3-0.5 m, the vegetation layer is removed. Then the bulldozer moves the soil into the dump or intermediate shaft and returns to the place of the new cutting without turning, in reverse (shuttle pattern), or with two turns. Trench development is carried out leaving 0.4 m wide cofferdams in cohesive soils and 0.6 m in loose soils. The depth of the trenches is assumed to be 0.4-0.6 m. The lintels are developed after the passage of each trench.
Production of earthworks with scrapers
The operational capabilities of the scrapers make it possible to use them for excavating pits and leveling surfaces, for arranging various excavations and embankments. Scrapers are classified:
- according to the geometric volume of the bucket - small (up to 3 m3), medium (from 3 to 10 m3) and large (over 10 m3);
- according to the type of aggregation with a tractor - trailed and self-propelled (including semi-trailers and saddles);
- according to the method of loading the bucket - loaded due to the traction force of the tractor and with mechanical (elevator) loading;
- according to the method of unloading the bucket - with free, semi-forced and forced unloading;
- according to the method of driving the working bodies - hydraulic and cable.
Scrapers are used to develop, transport (the range of soil transportation ranges from 50 m to 3 km) and lay sandy, sandy loam, loess, loamy, clay and other soils that do not have boulders, and the admixture of pebbles and crushed stone should not exceed 10%. Depending on the category of soil, it is most effective to cut them on a straight section of the path when driving down a slope of 3-7 degrees. The thickness of the developed layer, depending on the power of the scraper, ranges from 0.15 to 0.3 m. The scraper is unloaded in a straight section, while the soil surface is leveled with the bottom of the scraper.
Rice. 9. :
a - with filling the ladle with chips of constant thickness; b - with filling the ladle with chips of variable cross section; c - comb method of filling the ladle with shavings; g - filling the bucket by pecking
There are several ways to cut chips during the operation of the scraper (Fig. 9):
- chips of constant thickness. The method is used in planning work;
- shavings of variable cross section. In this case, the soil is cut off with a gradual decrease in the thickness of the chips as the bucket is filled, i.e., with a gradual deepening of the scraper blade towards the end of the set;
- comb way. In this case, the soil is cut off with alternate deepening and gradual lifting of the scraper bucket: at different stages, the thickness of the chips varies from 0.2-0.3 m to 0.08-0.12 m;
- pecks. The filling of the bucket is carried out by repeatedly deepening the scraper knives to the greatest possible depth. The method is used when working in loose loose soils.
Depending on the size of the earthen structure, the relative position of the cuts and embankments, various schemes scraper work. The most common is the ellipse pattern. In this case, the scraper rotates in one direction each time.
Rice. ten. :
a - trench-comb; b - ribbed chess
When working in wide and long faces, the filling of the scraper bucket is carried out by trench-comb and ribbed-staggered methods. With the trench-comb method (Fig. 10), the development of the face is carried out from the edge of the reserve or excavation in parallel strips of a constant depth of 0.1-0.2 m, the same in length. Between the strips of the first row, strips of uncut soil are left - ridges, equal in width to half the width of the bucket. In the second row of passages, soil is taken to the full width of the bucket, cutting off the ridge and forming a trench under it. The thickness of the chips in this case in the middle of the bucket is 0.2-0.4 m, and along the edges 0.1-0.2 m.
With the ribbed-staggered method (Fig. 10), the development of the face is carried out from the edge of the excavation or reserve in parallel strips so that between the scraper penetrations there are strips of uncut soil equal in width to half the width of the bucket.
The second row of penetrations is developed, retreating from the beginning of the first row by half the length of the penetration of the first row. The work of the scraper should be combined with the work of the bulldozer, using them to develop elevated areas and move soil over short distances to low places.
Excavation work by graders
Graders are used in planning the territory, slopes of earthworks, cleaning the bottom of pits and extracting ditches up to 0.7 m deep, in the construction of extended embankments up to 1 m high and the lower layer of higher embankments from the reserve. Motor graders profile the roadbed, driveways and roads. It is most effective to use motor graders with a driving length of 400-500 m. Dense soils are loosened before being developed by a grader. During the construction of the embankment from the developed reserve, the inclined knife shifts the cut soil towards the embankment. With the next grader penetration, this soil moves even further in the same direction, so it is advisable to organize work with two graders, one of which cuts, and the other moves the cut soil.
When erecting embankments and a profiled roadway, cutting the soil starts from the inner edge of the reserve and is carried out in layers: first, triangular chips are cut out, then until the end of the layer, the chips are rectangular. When developing wide reserves in soils that do not require preliminary loosening, cutting starts from the outer edge of the reserve and is carried out in layers, with all passes of triangular chips; another way is possible: in this case, the chips are triangular and quadrangular in shape.
When performing various operations, the grader's inclination angles change within the following limits: gripping angle - 30-70 degrees, cutting angle - 35-60 degrees, inclination angle - 2-18 degrees. In construction practice, several methods of laying soil are used:
- the soil is laid in layers, pouring it from the edge to the axis of the road (profiling work at zero marks with an embankment height not exceeding 0.1-0.15 m);
- rollers are placed one next to the other with their contact only with their bases (filling embankments 0.15-0.25 m high);
- each subsequent roller is partially pressed against the previously laid one, overlapping it with the base by 20-25%; the crests of these two rollers are located at a distance of 0.3-0.4 m from one another (filling embankments up to 0.3-0.4 m high);
- each subsequent roller is pressed against the previously laid without any gap; a new roller is moved with a dump close to the previously laid one with its capture by 5-10 cm; one wide dense shaft is formed above the first roller by 10-15 cm (filling of embankments up to 0.5-0.6 m high).
Development of frozen soils
Frozen soils have the following main properties: increased mechanical strength, plastic deformation, heaving and increased electrical resistance. The manifestation of these properties depends on the type of soil, its humidity and temperature. Sandy, coarse-grained and gravel soils, lying in a thick layer, as a rule, contain little water and almost do not freeze at low temperatures, so their winter development is almost the same as summer. During the development of pits and trenches in winter in dry loose soils, they do not form vertical slopes, do not heave and do not give subsidence in the spring. Dusty, clayey and wet soils significantly change their properties when freezing. The depth and speed of freezing depends on the degree of soil moisture. Earthworks in winter are carried out by the following methods:
- by the method of preliminary preparation of soils with their subsequent development by conventional methods;
- the method of pre-cutting frozen soils into blocks;
- soil development method without preliminary preparation.
Preliminary soil preparation for development in winter consists in protecting it from freezing, thawing frozen soil and preliminary loosening of frozen soil. The easiest way to protect the soil surface from freezing is to insulate it with thermal insulation materials; for this, peat fines, shavings and sawdust, slag, straw mats, etc. are used, which are laid in a layer of 20-40 cm directly on the ground. Surface insulation is used mainly for small recesses.
To insulate large areas, mechanical loosening is used, in which the soil is plowed with tractor plows or rippers to a depth of 20-35 cm, followed by harrowing to a depth of 15-20 cm.
Mechanical loosening of frozen soil at a freezing depth of up to 0.25 m is carried out by heavy rippers. When freezing up to 0.6-0.7 m, when extracting small pits and trenches, the so-called splitting loosening is used. Impact permafrost breakers work well at low soil temperatures, when it is characterized by brittle deformations that contribute to its splitting under impact. For loosening the soil at a large freezing depth (up to 1.3 m), a diesel hammer with a wedge is used. The development of frozen soil by cutting consists in cutting mutually perpendicular furrows with a depth of 0.8 of the freezing depth. The block size should be 10-15% smaller than the size of the excavator bucket.
Thawing of frozen soil is carried out using hot water, steam, electric current or fire. Defrosting is the most complex, time-consuming and expensive method, so it is resorted to in exceptional cases, for example, during emergency work.
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Construction of subgrade in highly rugged and mountainous terrain
Experimental work on the complex mechanization of the construction of the subgrade was carried out by DORNII not only in flat and slightly rugged areas, but also in mountainous and highly rugged terrain.
The relief of the area where the work was carried out has a typical mountainous character, since the roads in it are designed mainly along steep slopes and ravines with serpentines, partly with retaining walls and using drilling and blasting in some places.
The soil conditions in this area are characterized by the predominance of heavily gravelly soils of III and IV categories, interspersed with individual sections of rocks (limestones). The conditions for the mechanization of earthworks in this region differ sharply from the usual conditions of flat and slightly rugged areas; the use of grader-elevators under these conditions is completely excluded, and the use of graders and motor graders is possible only in the most limited size for finishing work. The main machines suitable for working in mountainous conditions are: a straight shovel excavator without transport, a bulldozer and a scraper. The main type of subgrade in mountainous areas is a semi-fill-floor at a recess on slopes, often cut by ravines, in which artificial structures (pipes) are located with approaches in the form of relatively high and short embankments. Thus, the whole complex of works on the construction of the subgrade under these conditions consists of:
a) the development of relatively gentle slopes into a hyulun-fill-semi-dredging,
b) the development of steep slopes,
c) arrangement of embankments in ravines for approaches to artificial structures.
In the construction area, this complex of works was complicated by the fact that all slopes were covered with dense deciduous forest.
Rice. Fig. 25. Scheme of felling the forest with uprooting using a tension cable: 1-tractor, 2 - cable Felling the forest from below
The use of excavators and bulldozers for slope-mountain work makes it possible in many cases to get rid of a number of the most difficult preparatory work - uprooting stumps and combing out the root system from the upper layers of the soil of the road strip. Mandatory in all cases of building a canvas in a mountainous terrain in the presence of a forest is the work of felling the forest and clearing the strip of bushes. Felling of the forest can be carried out simultaneously with uprooting, which is quite cost-effective in mountainous conditions. The terrain conditions at slopes with a steepness of 35° and above often do not allow delivering mechanization equipment directly to the route of the road under construction and force them to be located below or above the road route on existing temporary roads.
Let's analyze these cases.
When the temporary road is located below the main road (Fig. 25), it is advantageous to fell the forest together with uprooting, capturing 10-15 trees at the same time with the uprooting cable, as shown in Fig. 26. In this case, after felling the forest from the root, no more preparatory work will be required, since the whips of felled trees are removed from the road lane at one time with felling and uprooting. When the temporary access road is located above the route (Fig. 26), it is impractical and very difficult to cut the forest with a straight pull with a cable upwards. In such cases, the use of a block and an anchor stump located below the route is required, as indicated in fig. 26. As in the first case, uprooting with simultaneous felling is more profitable here, since it requires only a tractor and a cable. A separate felling of the forest with electric saws, obviously, in these cases, from the organizational point of view, will be unprofitable, since it will require, on the one hand, the delivery of a power plant and saws to the work site, and on the other hand, it will necessitate an extra operation to remove fallen trees from the road strip, which in conditions mountainous terrain will create additional organizational difficulties. With gentle slopes, the above method of simultaneous felling and uprooting of the forest can also be used. Separate felling of the forest with saws can only be profitable when the growing forest consists of trees so large and thick that it will be difficult to uproot them with a tractor.
Rice. 26. Scheme of felling forest with uprooting using a tension cable:
1 - tractor; 2 - cable, 3 - block, 4 - anchor Forest felling from above
After harvesting the fallen tree trunks from the work strip, you can begin to carry out the main excavation work. The development of gentle slopes with a steepness of up to 20 ° should be carried out mainly by bulldozers, since the use of excavators for it is unprofitable, because the latter will have to work mainly in low-height faces, which will reduce their output. The development of gentle slopes in the presence of bulldozers of a rotary type can be carried out according to two fundamentally different main schemes of work.
The first scheme can be used with rotary bulldozers D-161 or D-149. It consists in the preliminary development of the slope in layers with the gradual movement of the soil from the excavation to the embankment.
Subsequent passes are cut with the right edge of the knife 30-50 cm from the line of each previous cut. After 3-4 cuttings, a mass of soil is formed that is sufficient for a full-fledged passage to move the soil into the embankment without cutting. When developing each gouging layer, the first pass is usually not quite complete.
The length of the treated area should be as long as possible in order to reduce the number of blade changes during the reverse stroke. On average, each permutation takes about 1 minute.
This scheme has a number of significant disadvantages, which are as follows.
1. The scheme can be implemented only with rotary bulldozers. Conventional bulldozers cannot work according to this scheme.
2. The scheme requires multiple ground movements before being placed in place in multiple passes. As a result of this scheme, each soil particle moves not only in the transverse, but also in the longitudinal direction. Therefore, the design features of bulldozers are used insufficiently expediently and their productivity is reduced.
3. At the beginning of work, the rotary bulldozer should work with a relatively large skew in relation to its longitudinal axis.
With a slope of more than 12-15%, such a misalignment can cause the caterpillars to come off the tractor. With a slope of 18%, work with a warp becomes completely impossible due to the frequent departure of the tractor from the tracks.
Rice. Fig. 27. Scheme of development of a slope with a slope of 20°
4. The scheme requires frequent permutations of the blade grip angle (with each turn of the machine), which also negatively affects the rational use of machines.
All these negative sides Such a scheme of work allows us to consider it inappropriate for widespread use in production, despite the fact that it is recommended by some authors.
The second scheme is applicable in the development of slopes with a steepness of up to 20 and even 25 ° (with an experienced operator) and lies in the fact that the development of the slope is carried out from the very first pass by transversely moving the soil with a bulldozer. The procedure for developing a slope according to this scheme is shown in a specific example.
Having placed the bulldozer perpendicular to the axis of the road, so that its knife is located 5 m from the transition point of the half-cut to the half-fill, we will make the first cut. Having moved the bulldozer back another 5 m, we will make a second cutting, which, together with the first one, in this case, will cover the entire surface of the slope to be developed into a half-cut.
The following (3,4 and 5) cuts will be made in the same order. Obviously, the cutting marked in Fig. 27 No. 6, it is impossible to make a bulldozer, since a steep step was formed between the surface of the slope outside the half-cut and the soil surface in the half-cut after the first cuts were made. Therefore, cutting the soil in sections 6, 8, 10, etc. will have to be done with a grip angle of 67 ° with the left end of the knife or a motor grader. Thus, the final development of the slope for the side ditch can be made by the joint operation of the bulldozer and only partially rotary bulldozer and motor grader; the cuvette device is carried out by a number of additional passes of the motor grader in the process of finishing the already rough subgrade. This scheme is devoid of most of the disadvantages of the first scheme and can be recommended for wide application.
If the balance of earthen masses allows the development of a slope with a more gentle slope of the half-cut (up to 25 °), the scheme can be greatly simplified and all the main work done by a bulldozer without the participation of more complex machines such as D-149 or D-161.
In many cases, the development of reserves for the arrangement of approaches to artificial structures on the slopes of the Road at the places where it is crossed by ravines is difficult, and it becomes necessary to prepare reserves in the process of developing the slopes. As a particular solution to this problem, a method can be proposed for developing a slope with a widened ditch used as a reserve for backfilling pipes in ravines.
On slopes overgrown with forest, the first passages of the bulldozer near the felling of the forest are made specifically for the purpose of uprooting the remaining stumps and cleaning the upper vegetation cover. Thus, when developing gentle slopes, a set of machines should be used, consisting of tractors for uprooting, bulldozers, a scraper, a D-162 ripper (for loosening dense soils before scraping) and a motor grader for finishing work.
The development of steep slopes cannot be carried out with bulldozers alone, since bulldozers cannot work on large slopes either in the direction of the slope, and even more so, in the direction along the slope due to the inevitable departure of tractors from the tracks.
Among the available machines, the most suitable for the development of steep slopes are front shovel excavators with a bucket capacity of 0.5 to 1.0 m3. In experimental work in 1948, the development of steep slopes was carried out mainly by excavators with a bucket capacity of 0.5 m3. Excavators with a bucket capacity of 1 m3 can work not only in soils of III, IV and V categories, but also in previously loosened soils of the highest category. The performance of these excavators is almost twice that of excavators with a bucket capacity of 0.5 m3, but their lower mobility construction site, and when transferred from object to object, it greatly reduces the effectiveness of their use in linear road works.
The development of steep slopes cannot be completed by excavators. In the best case, only 50-60% of the excavation work on the slope is put into place by an excavator, the rest of the work must be done by bulldozers or their varieties (D-149 and D-161), and partly by other machines. Thus, in the development of steep slopes, even more than in other relief conditions, the complex work of a number of machines that make up the mechanized link is required. The development of the slope begins with the preparation of the site, from which the pioneer trench begins, which is necessary for the excavator to enter the mark of the future subgrade (Fig. 28).
Rice. 28. Beginning of the development of a pioneer trench by an excavator with a bucket with a capacity of 0.5 m3
The pioneer trench is usually passed with a rise of up to 10-12%; it is developed with a straight shovel to the width necessary for the excavator to pass, i.e., 2.5-3.5 m. After the excavator reaches the subgrade mark, it must begin to develop the main trench, laying soil from the lower side of the slope. The width of the developed trench should not exceed 4.5-5 m in order to increase the output of the excavator along the length of the road. In experimental work in 1948, in some cases, Stakhanovite excavators (comrades Efimenko and Gavryushin) achieved output up to 100 running meters. m per working day with a productivity of up to 500 m3 per shift, which was about 200% of the norm. After the excavator, the development of the shaft he poured was carried out by bulldozers, and the development of the latter by leveling the shaft and expanding the trench made by the excavator was several times higher than in linear meters. m production excavator. Thus, in order to more evenly load the machines participating in the slope development team, one should strive to reduce the width of the trench being developed by the excavator in order to increase its output along the length of the road and at the same time to load the bulldozers more. Experience has shown that one bulldozer can easily serve the work of 2-3 excavators, even with some margin of time for independent work on the development of less steep sections of the slope.
With a slope of less than 30 °, the development of a slope in this way is possible with the construction of a subgrade in a half-fill-semi-dredging without a retaining wall, but with the obligatory arrangement of at least one ledge to stop the soil of the half-fill. In the experimental works of 1948, ledges were arranged manually, which, of course, should not be allowed in the future with complex mechanization of work. It must be borne in mind that ledges can also be made mechanized using small excavators with a bucket capacity of 0.25 m3. On fig. 29 shows the location of the ledges: the main one - for the roadbed and the auxiliary one, produced by a small excavator, - for the stop of the slope of the embankment.
With slopes steeper than 33°, it is impossible to construct a semi-fill-semi-dredging without retaining walls if it is required to withstand one and a half laying of the slope of the semi-fill.
If the construction of a retaining wall, according to estimates, turns out to be not economical, and if we take into account that when determining the technical and economic indicators of the construction of a retaining wall, it is necessary to reckon with a decrease in the degree of mechanization and output per worker in natural terms, then the development of the slope should be carried out without a half-fill, so that the entire shelf The roadbed was located on the mainland in a recess (Fig. 30). In this case, all the soil produced by the excavator and after it by the bulldozer will go down the slope of the slope for ejection without registering it as a cavalier.
Rice. 29. Scheme of the location of ledges for ground support during slope work
It is necessary to make a reservation that when building roads in mountains made of massive rocks, in many cases, the construction of retaining walls can be much more profitable than expanding excavations, since working in dense rocky soils requires a significant amount of relatively expensive and labor-intensive drilling and blasting. In recent years, in the practice of the Ministry of Railways and other departments, mass explosions to eject cuts and half-cuts have often been used. Since these works are of a specific nature and in road conditions require special equipment, specialists, explosive materials, etc., this issue is not considered in this work, especially since a fairly extensive literature is devoted to drilling and blasting in the construction of communication lines.
Rice. 30. Cross profile of the road on the slope in the recess
Rice. 31. Development of a trench for lowering an excavator into a ravine
Let us now turn to the issue of arranging crossings over ravines along a mountain road routed along the slopes of steep slopes. It has already been mentioned that in many cases the laying of special reserves for the construction of these embankments is hampered by local conditions. In particular, the impossibility of laying individual reserves took place at almost all intersections of ravines along the mountain road, which was built in 1948.
The development of slopes at the approaches of the road route to the ravine can be organized in such a way as to create a reserve of soil on the road route itself so that later it can be fed into the embankment by scrapers with a longitudinal wagon. This can be achieved by developing a slope at the approach to the ravine at elevations higher than for the designed road bed.
Having determined in advance, by appropriate calculation, the volume of soil required for the formation of an embankment, the development of the slope when approaching the ravine should be carried out from a certain calculation of the place above the design mark to the very descent into the ravine. Approaching the descent, a pioneer trench should be developed for lowering the excavator into the ravine and crossing it from below (Fig. 31). On the other side of the ravine, the beginning of the development of the slope also begins from a higher elevation. In cross section, the ratio of the design diameter of the road and the actual one developed by the excavator when approaching the ravine is shown in Fig. 32.
Rice. Fig. 32. Scheme of the ratio of the design diameter of the road and the diameter actually developed by the excavator when approaching the ravine: 1 - soil shaft developed by the bulldozer downhill, 2 - full embankment, 3 - reserve for the scraper, h - trench lifting height, I - excavator trench slope
All the soil that was not taken up by the excavator in height with this method of developing the slope is easily fed into the embankment by a bulldozer and a scraper (Fig. 33). The bulldozer feeds the soil shaft developed by the excavator down the ravine and softens the descent to the limits at which the scraper can be put into operation.
The work of bulldozers in the development of steep slopes is carried out according to schemes that are somewhat different from those used in flat and slightly rugged areas. It consists in leveling the relatively high shafts of soil, previously developed by an excavator, in preparing the front for the work of scrapers and, where possible, sites for installing excavators into the face.
The most common operation carried out by bulldozers in the development of steep slopes is moving downhill and leveling the shafts of the soil poured by the excavator in order to expand the ledge punched by it to the width of the roadway required by the project.
Rice. 33. Development by a scraper of shafts of soil, poured by an excavator
From this table it can be seen that with a slope of up to 12 °, the excavator puts in place only about 10% of the soil it produces. Thus, in low-slope slopes, up to 90% of the excavator output requires recycling, which indicates the obvious disadvantage of using excavators in the development of gentle slopes.
With slope slopes of 24 ° and above, the excavator puts in place already about 30-35% of the soil it has worked out. The cross-sectional area of the trench developed by him, depending on the steepness of the slope, ranges from 8.5 to more than 20 m2, and the dimensions of the shaft to be further processed by a bulldozer reach 17 m3 per linear meter. m road. To complete the work done by the excavator in 1 hour, it is required to spend from 0.17 to 0.27 machine hours of the bulldozer.
Therefore, on average, one bulldozer can serve the work of 4 excavators. It is obvious that with an increase in the capacity of the excavator bucket to 1 m3, the number of excavators serviced by one bulldozer decreases to an average of 2. In addition, these data also indicate that a decrease in the section of the trench produced by the excavator will increase the speed of construction of the subgrade in lin. m and more fully load bulldozers.
The development of shafts poured by an excavator can be carried out by bulldozers D-157 or D-161. The work of the rotary bulldozer is more efficient and in working conditions more convenient, since its operations require a smaller trench width (for the operation of the D-157 bulldozer, it is necessary to provide a trench width of about 6 m, and for the D-161, 4.5 m is enough). The bulldozer begins development with a raised knife and pushes the soil forward (Fig. 34). At this moment, the soil above the bulldozer's blade falls down. It turns out the development of the shaft by digging. A bulldozer knife is lowered onto the soil that has fallen down. In one or two passes, the soil falls downhill, and the trench developed by the excavator expands. From Table. 18 shows how great the productivity of bulldozers is at this job. To develop a shaft with a volume of 57.4 m3 in a loose body (with an average loosening coefficient of 1.3), only 0.23 machine hours are required. bulldozer operation, i.e. the productivity of the bulldozer is about 140 m3 per hour of net work, and for the development of a shaft with a volume of 50.6 m3 - 0.2 machine-hours, i.e. the productivity in this case will be 115 m3 / hour. On average, the productivity of bulldozers D-157 and D-161 when processing shafts downhill will be about 1200 m3 per shift.
In cases where it is required to dump the shaft not down a slope, but to advance it along the slope to backfill any depression, the development of the shaft should be carried out in two steps: with the first step, the bulldozer, rising from the end side to the crest of the shaft, slightly smoothes and expands the upper part shaft, so that a tractor with a scraper can subsequently climb on it for further longitudinal transportation of the soil.
Therefore, the task of the bulldozer operator is not only to smooth the crest of the shaft with its expansion on top of at least 3 m, but also to position the entrance and exit from the shaft to create a convenient work front for the scraper.
In cases where the length of the longitudinal movement of the soil is small, the bulldozer can independently perform the work of moving the soil into place. With high and relatively narrow shafts, this work is done by digging with the installation of a knife during the first pass approximately in the middle of the height of the shaft - to shed the soil, and then the knife is buried in the soil by half or a third of its length, to the entire height of the blade and moves with the soil along the axis of the road .
Rice. 34. Movement of shafts poured by an excavator or bulldozers
The productivity of a bulldozer with such a development of shafts is also very high and, with a travel distance of 30-40 m, is from 800 to 1000 m3 per shift.
Thus, the composition of the detachment for the construction of a road in the mountains was determined: the main machine of this detachment is an excavator. When working on steep slopes, it is better to work with one excavator with a bucket capacity of 1 m3 on the main shelf and one small excavator with a bucket capacity of 0.25 m3g included in the detachment specifically for the construction of ledges.
To service such a small detachment, it is necessary to assign only one bulldozer, but even it will not be fully loaded.
Therefore, it is advisable to make up a detachment of two excavator links (4 excavators), serviced by one bulldozer and one scraper.
Such a detachment should include a D-162 ripper (to ensure the operation of scrapers in heavy stony soils) and a supply of cable for felling trees.
The front of the work of such a detachment should be at least 1-1.5 km, and the excavator units should work with a gap of at least 1 km between them in order to avoid frequent transfers of these heavy machines.
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