The development of trenches and pits is carried out mainly in a mechanized way. Selection of equipment for execution earthworks depends on the volume of foundation pits, the type of soil and is provided for by the project for the production of works (Table 1). This type of work includes: excavation; unloading soil onto the curb or vehicles; transportation of soil to the place of storage; storage in a dump or embankment; development of slopes, cleaning and leveling of the bottom; fastening the walls of trenches and pits; backfilling of trenches.
|
Transportation distance, km |
Carrying capacity of dump trucks (t) with excavator bucket capacity (m 3) |
||||||
Places of development of trenches, ditches and ditches are protected from surface water runoff by installing temporary or permanent drainage systems (protective embankment, drainage ditches, planning that provides drainage, etc.).
Trenching and ditching work should be started from the lower side, and in places with low marks if groundwater arrange pits for their collection and pumping. When making excavations in loess soils, it is necessary to take additional measures against stagnant water during work.
Development of soil in trenches and pits in cases of their intersection by any underground communications is allowed only with the written permission of the operating organization. At the same time, in the immediate vicinity of communications, the soil must be developed manually (1 m above the pipe, cable, etc.). In case of an unexpected (not indicated in the design) discovery of underground utilities, earthworks should be suspended and representatives of the relevant organizations should be called to the place.
The need to fasten the vertical walls of trenches and ditches or excavation of the soil with the device of slopes is justified by the project (Table 2).
Table 2. The steepest slopes of trenches and ditches
|
The greatest steepness of slopes at a depth of excavation (m), up to |
||||||
|
The angle between the direction of the slopes and the horizontal, ° |
The ratio of the slope height to its inception |
The angle between the direction of the slopes and the horizontal, ° |
The ratio of the slope height to its inception |
|||
|
Bulk |
||||||
|
Sandy and gravel wet (saturated) |
||||||
|
Clay: sandy loam, loam, clay |
||||||
|
Loess and dry loesslike |
||||||
|
Moraine: sandy, sandy loam, loamy |
||||||
If the project provides for the fastening of trenches, it should be installed immediately after the excerpts. Strengthening of the soils and walls of the pit is performed in unbound soils, where there is a threat of collapse of the side walls. This is done using horizontal planks 40-60 mm thick, installed in the form of formwork and resting on vertical beams using spacers. The formwork walls are additionally reinforced with horizontal struts installed between the walls.
Digging of pits and trenches with vertical walls without fastening can be carried out in sandy and coarse-grained soils to a depth of 1 m, in sandy loams - 1.25 m, in loams and clays - 1.5 m, and in very strong loams and clays - 2 m. the need for people to work in a trench with vertical walls, the smallest clear distance between the side surfaces or attachment shields should be at least 0.7 m.When installing trenches for pipelines, their width along the bottom, excluding attachment, is taken according to table. 3.
Table 3. Pipeline trench width
|
Pipeline laying method |
The smallest width of a trench with vertical walls along the bottom (m) excluding fastening |
||
|
Steel and plastic |
Socket cast iron, concrete and asbestos-cement |
Concrete on couplings and rebates, ceramic |
|
|
With lashes or separate sections with the outer diameter (D) pipes, m: |
|||
|
D + 0.3, but not less than 0.7 |
|||
|
Separate pipes with an outer diameter D, m: |
|||
|
1.6-3.5 (common sewers) |
|||
Trenches with laid pipelines are filled up in the following order: pits and sinuses are filled with soft soil and pits and sinuses simultaneously from both sides, and then the trench is covered with the same soil 0.2 m above the top of the pipes, while the soil is compacted layer by layer with manual and mounted electric rammers. For ceramic, asbestos-cement and polyethylene pipelines, the height of the backfill layer above the pipe should be 0.5 m. Subsequent backfilling is performed mechanically after testing the pipelines with any soil without large inclusions. Backfilling of trenches and pits at intersections with existing roads, driveways, squares, etc. should be carried out to the full depth with low-compressible soils (sand, pebble, gravel, crushed stone screenings, etc.) with thorough layer-by-layer compaction.
Backfilling of trenches and pits, to which additional loads are not transferred (except for the mass of soil), can be performed without compaction, but with filling an earthen roller equal in volume to the subsequent natural shrinkage of the soil.
The width along the bottom of pits and trenches for strip and free-standing foundations should be determined taking into account the width of the foundation structure, waterproofing, formwork and fastening with the addition of 0.2 m. The bottom of the pit must be flat and horizontal. If construction is carried out on a slope, the bottom may consist of horizontal and vertical sections at an angle of 45 °. In this case, it is not recommended to make vertical transitions, in which cracks can form when laying foundations.
Trenches and ditches in non-rocky soils should be developed without disturbing the natural structure of the soil at the base with a shortage (Table 4).
Places of overpasses in rocky soils should be filled with clay, sandy or gravelly soil with careful compaction. Surveys in non-rocky soils (except for boulder and block) are not allowed (Table 5).
Table 4. Allowable shortages in non-rocky soils
|
Work equipment excavator |
Allowable shortfalls with an excavator with a bucket capacity, m 3 |
||||
|
reverse |
|||||
|
Dragline |
|||||
Table 5. Permissible values \u200b\u200bof overkill in rocky soils
Depending on the condition of the soil, one of the methods of strengthening it can be applied, designed to increase the bearing capacity. Most often, such a need arises when erecting buildings of two or more floors. Construction practice has many methods of artificial soil strengthening. The need for artificial soil strengthening can be determined by the project.
Soil compaction is performed by rolling with various rollers, transport and earth-moving machines, mechanical or electric rammers, vibration. Weak or especially weak soils are fixed.
Siliconization provides for the strengthening of fine and dusty sands and quicksands with one-solution or two-solution compositions based on water glass. With a single-solution composition, sodium silicate is used - water glass and sodium aluminate. In two-solution - in the second composition, calcium chloride is used instead of sodium aluminate. The solutions are injected with injectors under a pressure of 3-6 atmospheres, fixing the soil in a radius of 0.3-1 m. By means of silicatization, it is possible to fix individual areas, as well as whole soil masses. With the solid consolidation of the soil massif, the injectors are staggered with a distance between the rows equal to 1.5 of the radius of fastening by one injector.
Cementation is performed with special injectors (perforated pipes), usually to strengthen sandy (less often clay) soils. Cement mix grade 400 at a ratio of 0.8: 1 (water: cement) fills all the voids in the soil under pressure. After the injector is removed from the soil, the well is also filled with a solution.
Electrosilication accelerates the pace and quality of work by passing DC current through the injectors.
All of the listed methods of soil strengthening provide for the presence special equipment and can be performed by organizations with the necessary technology.
As a result of earthworks, earthworks are created, which are classified according to a number of characteristics.
According to the purpose and duration of operation, earthen structures are divided into permanent and temporary.
Permanent structures are designed for long term use. These include canals, dams, dams, planned sites for residential quarters, industrial complexes, stadiums, airfields, excavations and embankments of the roadbed, water bodies, etc.
Temporary earthen structures are those that are erected only for the period of construction. They are intended for the placement of technical equipment and the performance of construction and installation work on the construction of foundations and underground parts of buildings, the laying of underground communications, etc.
A temporary excavation that is up to 3 m wide and significantly longer than the width is called a trench. A recess, the length of which is equal to the width or does not exceed ten times its value, is called a pit. Pits and trenches have a bottom and side surfaces, inclined slopes or vertical walls.
The division of earthen structures into permanent and temporary is necessary, since different requirements are imposed on them with respect to the stability of the slopes, the thoroughness of their compaction and finishing, and ensuring the watertightness of the excavation body.
According to the location of earthworks relative to the surface of the earth, there are: cuts - depressions formed by the development of soil below the surface level; embankments - elevations on the surface, erected by backfilling of previously developed soil; cavaliers - embankments formed when filling unnecessary soil, as well as for temporary storage of soil, backfilling of trenches and foundations.
The most typical profiles and elements of earthworks are shown in Fig. 1.1.
Figure: 1.1. Types of earthworks:
I - transverse profile of the notches: a - rectangular trench;
b - pit (trench) of trapezoidal shape;
in - permanent cut profile; 1 - the edge of the slope; 2 - slope; 3 - berm;
4 - the base of the slope; 5 - the bottom of the recess; 6 - banquet;
7 - Upland ditch; II - section of underground workings;
r - round; d - rectangular; III - embankment profiles;
e - temporary embankment; f - constant; IV - backfilling;
s - pit sinuses; and - trenches
Temporary excavations, closed from the surface and arranged for the construction of transport and utility tunnels and other purposes, are called underground workings.
After device underground parts of buildings, the soil from the dump (cavalier) fits into the so-called "sinuses" - the spaces between the side surface of the structure and the slopes of the excavation (trench). If the dumping of soil from the dump is used to completely close the underground part of the building or utilities, it is called backfilling.
Compliance with the purpose and reliability in the operation of earthen structures is ensured by compliance with a set of requirements for design and construction. All earthen structures must be stable, durable, capable of withstanding the design loads, withstand climatic influences (precipitation, freezing temperatures, weathering, etc.), have the configuration and dimensions in accordance with the design and keep them during operation. Requirements for earthworks in specific conditions are established by the project in accordance with the building design standards.
Determination of the volume of excavated soil
For the main production processes, the volumes of the excavated soil are determined in cubic meters in a dense body. For some preparatory and auxiliary processes (plowing the surface, grading slopes, etc.), volumes are determined in square meters of the surface.
Counting the volumes of the excavated soil is reduced to determining the volumes of various geometric shapes that determine the shape of a particular earthen structure. It is assumed that the volume of soil is limited by planes and individual irregularities do not affect the accuracy of the calculation.
In the practice of industrial and civil construction, it is necessary mainly to calculate the volumes of pits, trenches (and other extended structures) and the volume of excavations and embankments in the vertical layout of sites.
Determination of volumes during the development of pits and trenches
The pit is an obelisk from a geometric point of view. (figure 3.12), the volume of which Vcalculated by the formula: V \u003d H / (2a + a1) b + (2a1 + a) b1 / 6,
where H- the depth of the pit, calculated as the difference between the arithmetic mean mark of the top of the pit in the corners (marks of the terrain on the section of the planning embankment and the design on the section of the planning excavation) and the mark of the bottom of the pit; a, b- the lengths of the sides of the pit (taken equal to the dimensions of the lower part of the foundation at the base with a working gap of about 0.5 m on each side), a \u003d a "+ 0.5 * 2, b \u003d b" + 0.5 * 2; a ", b"- dimensions of the bottom of the foundation; a1, b1- the lengths of the sides of the pit on top, a1 \u003d a + 2H · m; b1 \u003d 2H · m; m- slope coefficient (standard value according to SNiP).
Figure 3.12. Determination of the volume of the pit:
a- geometric scheme for determining the volume of the pit; b- section of the foundation pit permanent (slope 1: 2) and temporary (slope 1: 1); 1 - the volume of the excavation; 2 - backfill volume
To determine the volume of backfilling of the pit sinuses, when its volume is known, it is necessary to subtract the volume of the underground part of the structure from the volume of the pit Vob.z \u003d V - (a "· b") · Н.
When calculating the volumes of trenches and other linear-extended structures, longitudinal and transverse profiles should be presented as part of their projects. The longitudinal profile is divided into sections between the break points along the bottom of the trench and the day surface. For each such section, the volume of the trench is calculated separately, after which they are summed up. The trench, long cut and embankment in the area between points 1 and 2 represent a trapezoidal prismatoid (Figure 3.13), the volume of which can be determined approximately:
V1-2 \u003d (F1 + F2) L1-2 / 2(overpriced),
V1-2 \u003d Fср L1-2(understated),
where F1, F2- the cross-sectional areas at the corresponding points of the longitudinal profile, defined as F \u003d aH + H2m; Fav- cross-sectional area at the middle of the distance between points 1 and 2.
Figure: 3.13. Trench volume determination scheme
A more accurate value of the volume of a prismatoid is found by the formulas:
V1-2 \u003d Fav + L1-2,
V1-2 \u003d L1-2.
Calculation of the volume of planning workproduced either by the method of triangular prisms, or by the mean mark of the squares.
In the first method, the planned site is divided into squares with a side (depending on the terrain) of 25-100 m; the squares are divided into triangles, at the vertices of which they write out the working marks of the layout (Figure 3.14, a).
If the marks (Н1, Н2, Н3) have the same sign (cut or embankment),
the volume of each prism (Figure 3.14, b) is determined by the formula:
V \u003d a² / 6 · (H1 + H2 + H3).
With different signs of working marks (Fig. 3.14, c), the calculation according to this formula gives the total volume of filling and excavation; the split volumes can be obtained by subtracting the volume of the pyramid ABCD from the total volume of the ADHYGE prism.
Figure: 3.14. Volume counting scheme
earthworks way
triangular prisms:
a- a breakdown of the site (numbers in circles - numbers of prisms; numbers on the
section lines - working marks);
b- triangular prism with working
marks of one sign; in- also with different marks 
Average mark method
squares, planning volumes are calculated using a plan with contours in 0.25–0.5 m for flat and 0.5–1 m for mountainous terrain.
A grid of squares with a side of 10-50 m and a line of boundaries of embankments and excavations are applied to the plan. The volume of the layout of each square is calculated based on the average working marks of the layout over the square.
The volume of embankments and excavations of linear structures(roads, canals) on straight-line sections of a structure is usually determined according to auxiliary tables.
For structures with curvilinear axis(Fig. 3.15) you can use the Gulden formula: V= (F⋅π⋅ r⋅α) / 180º;
where V- the volume of the earthen structure, m3, F- cross-sectional area of \u200b\u200bthe cross section, m2,
r- radius of curvature of the body axis of the earth structure, m,α- central angle
turning the extreme profiles that limit the curved section, hail.
Counting the volume of earthen conesat artificial structures:
With the same steepness of the slope of the subgrade and the slope of the cone - according to the formula:
V \u003dπ H / 24;
where V1- the volume of both cones, m3, N- the height of the embankment in the section along the edge of the foundation, m, b- web width, m, b1- abutment width, m, m- slope indicator
subgrade and cones,
Figure: 3.15. Linear earthen structure with Figure 3.16. Subgrade slopes
Curvilinear axisat the bridge cones.
With different steepness of the slope of the subgrade and the slope of the cone (Fig. 3.16)
- according to the formula: V 1= π H / 6· [ 3(b- b1) / 2· (x-α ) + 1.5 ( b- b1) / 2· nH +1.5 (x-α)· mH + mnH² ;
where n- indicator of the slope of the cone, x- the full value of the entry of the roadbed -
on standing at the level of the edge, m,α - the amount of entry of the straight part
subgrade, m.
Notes:
1. When bedding different types soil, the slope steepness for all layers is assigned according to the weaker type of soil.
2. Bulk soils include soils that have lain in dumps for less than 6 months. and not subjected to artificial compaction (passage, rolling, etc.).
3. The steepness of slopes of excavations with a depth of more than 5 m in all cases and a depth of less than 5 m under unfavorable hydrogeological conditions and with soils not provided for in the table is established by the project.
Territory planning, cutting of plant soil and backfilling of soil are carried out with a bulldozer with a capacity of 80-130 liters. from. The movement of the soil is carried out at a distance in accordance with the PIC.
The excavation of soil in pits and trenches is carried out by a single-bucket excavator with various replaceable equipment and different bucket capacities. Excavators with a bucket capacity of 0.15-0.4 m3 are used to carry out small volumes of earthworks (low-rise construction, laying of engineering networks). In mass housing and civil construction, excavators with a bucket capacity of 0.5-0.65 m 3 are usually used for earthworks. During the construction of large residential, public and industrial buildings, excavation is carried out by excavators with a bucket capacity of 0.8-1.2 m 3.
When excavating excavations, some of the excavated soil can be used for backfilling. The rest of the soil is taken to the landfill. In this case, the following options for the production of work are possible:
1. If there is a place at the construction site for storing soil, the volume of soil required for backfilling is developed by an excavator into a dump, the rest is loaded into dump trucks and taken to the soil dump.
2. If it is impossible to store the excavated soil at the construction site, the soil for backfilling is taken to a temporary dump. In this case, the entire volume of excavation is accepted with loading into dump trucks, but the transportation of soil is provided for different distances: for backfilling - to a temporary storage site, the rest - to a landfill.
3. The excavated soil is not suitable for backfilling. All soil is mined with loading into dump trucks and taken to the landfill. For backfilling, conditioned soil is brought in (backfilling with soil replacement).
The scope of work in the mechanized development of pits and trenches during the construction of buildings (structures) is determined by design data minus the amount of soil shortfall.
Table 3
Soil shortages during the operation of single-bucket excavators:
The volume of the shortfall and the method of its development are taken in accordance with the construction organization project.
The development of soil shortages, as a rule, is carried out in a mechanized way. When cleaning the bottom of the pits with bulldozers, excavators with special scraper buckets or other leveling machines, the remaining shortfall to the design level should not exceed 5 cm, which is manually finalized at the places where the foundations are installed.
When determining the costs of manually reworking pits and trenches developed by a mechanized method, the estimated norms and prices of the section "Development of soil manually" are used with a coefficient of 1.2.
When developing soils with a high level of groundwater, drainage is used. In the estimate, the cost of drainage works during the development of soil is calculated only for the volume of soil lying below the design level of groundwater. When draining from pits with an area of \u200b\u200bup to 30m 2 along the bottom or trenches with a width of up to 2m along the bottom, the norms for 100m 3 of wet soil should be applied. In case of drainage from pits with an area of \u200b\u200bmore than 30 m2 along the bottom or from a trench with a width of more than 2 m along the bottom, a calculation is made based on the design data on the strength of the water inflow, the duration of the drainage works and the drainage means used.
Determination of the size of pits and trenches.
To determine the volume of excavation work in the development of pits and trenches, you need to know their basic dimensions: depth (H), width (B) and length (L).
The depth of development of pits and trenches is taken according to design data: from the "black" mark of the earth's surface to the mark of the foundation for foundations or an underlying layer for floors and decreases onthe thickness of the crop soil cut if the cut volume is calculated separately.
When determining the dimensions in plan (width and length) of a pit or a trench with vertical walls, the dimensions of the basement and foundations are taken into account, including the thickness of the waterproofing, the thickness of the formwork and fasteners, the distance on all sides between the structure and the wall of the pit (trench) is 0.2 m, and if it is necessary to lower people into the pit - not less than 0.7 m.
For a pit, with slopes, the dimensions of the pit are determined at the bottom and top: width (B) and length (L).
The dimensions to the bottom (B, L) are determined by the dimensions of the structure, taking into account the distance between the structure and the foot of the slope (at least 3 m). The dimensions on top are determined taking into account the steepness of the slopes:
V in \u003d V n + 2V open
where:
In open - width (laying) of the slope, m.
The steepness of the slope is characterized by the slope ratio - the ratio of the excavation depth to the slope:
k open \u003d H / B open
In open \u003d H / k open
B in \u003d B n + 2 H / k open
The volume of earthworks (V) in the development of pits with slopes is determined by the formulas:
§ for the pit rectangular
V to \u003d H / 6 * (S n + S in + (B n + B in) * (L n + L in))
S n and S in - pit area, respectively, bottom and top, m 2;
§ for a square pit
V to \u003d H / 3 * (S n + S in + (S n * S in) * 0.5)
§ for a pit round in plan
V к \u003d πH / 3 * (R 2 + r 2 + Rr)
R and r - the radii of the upper and lower base of the excavation;
§ for a pit shaped like a polygon
V to \u003d H / 6 * (S n + S in + 4 S av)
S Wed - cross-sectional area in the middle of its height, m \u200b\u200b2. The formulas given are suitable for determining the volumes of small pits (less than 15 m wide). In this case, they can be developed by an excavator located on the ground (dragline and backhoe).
When the pit is more than 15 m wide, excavation is carried out with a shovel excavator, which must be lowered to the bottom of the pit.
If the pit is being developed by an excavator with a front shovel, then the volume of excavation must be added to the volume of the pit for the device of entrances to it.
The number of entrances should be provided for by the construction organization project, and the volume of one entry is calculated using the formula:
V in \u003d (6 + 1.5 H) ∙ 4 H 2
H- pit depth.
In cases where the pit is developed from above (with a dragline excavator or a backhoe), and the excavation is cleaned with a bulldozer, the volume of excavation should be added to the volume of the pit for the entry of the bulldozer. The number of entries is determined by the construction organization project, and the volume of entry is calculated using the formula:
V in \u003d (4 + H) * 2 H 2
The dimensions of the trenches are determined depending on the size of the foundations, the diameter of the pipes to be laid, and the method of work. The distances between the structures and the walls of the trenches at the bottom are taken in the same order as for the pits.
Open methods for the construction of underground water supply and sewerage networks
Explanatory note to the course project
Checked: Associate Professor of the Department of OSB, Ph.D. A.A. Kuzmenkov
Petrozavodsk 2011
Initial data
2. The sequence of work.
Demolition of asphalt
Development of foundation pits for cameras
Development of a trench for a pipeline
Trench wall fastening device
Installation of cameras
Arrangement of pits for pipe joints
Laying pipes with joints
Connecting pipes to chambers
Arrangement of trays in chambers
Partial backfilling of pipes
Preliminary testing of pipelines
Disassembly of the trench wall mountings
Backfilling of trenches and pits with soil with layer-by-layer compaction
Arrangement of hatches of chambers with blind areas
Pipeline test
Asphalt pavement restoration
II ENVIRONMENTAL PROTECTION AND SAFETY RULES
III Determination of labor costs and machine time. Payroll preparation.
IV APPENDICES TECHNOLOGICAL MAP (TC)
Initial data
1.purpose of the pipeline: drainage
2.pipe material: fiberglass
3 pipeline diameter 1600 mm, total length 644.7 m, wall thickness 27.1 mm
4.type of connection: coupling
5. working conditions: urban
6. pipeline laying depth: at the beginning 2.30 m; in the middle 2.69 m; at the end 3.07 m
7.type and type of soil: sandy loam
8.ground water table: 6.6 m
9. sewer chambers (4 pieces), their dimensions: length 1.9 m, width 2.1 m; reinforced concrete trays
10.pipe: pipe length 12 m, pipe weight 253.2 kg / lm.
11.the depth of soil freezing 1 m
Work sequence.
1. Preparatory work: dismantling asphalt
2. Development of foundation pits for cameras
3. Development of a trench for a pipeline
4. Arrangement of fasteners for the walls of the trench
5. Installation of cameras
6. Preparation of foundations for pipelines
7. Arrangement of pits for pipe joints
8. Laying pipes with a joint device
9. Connection of pipes with chambers
10. Partial backfilling of pipes
11. Preliminary testing of pipelines
12. Disassembly of the trench wall mountings
13. Backfilling of trenches and pits with soil with layer-by-layer compaction
14. Arrangement of trays in chambers
15. Arrangement of hatches of chambers with blind areas
16. Testing the pipeline
17. Removal of surplus soil
18. Restoration of asphalt pavement
Demolition of asphalt
For such purposes, jackhammers of the MO-6P brand are used (striker impact energy 36 J, impact frequency 22 s)
Milling of the old asphalt concrete pavement is carried out with a thickness of 5 cm with the removal of chips.
Trench width B
B \u003d D + 2 * a, where D is the pipe diameter 1600 mm, a is the distance from the pipe to the edge of the trench 0.3 m
B \u003d 1.6 + 2 * 0.3 \u003d 2.2 m
Chamber dimensions: 1.9 x 2.1 m
Pit for a well: length L \u003d 1.9 + 2 * 0.2 \u003d 2.3 m, width B \u003d 2.1 + 2 * 0.2 \u003d 2.5 m
The length of the section is 650 m.
The area of \u200b\u200bthe removed asphalt F asf:
F asf \u003d F asf. tr + F asf. boiler-tr \u003d 1820 + 2.76 \u003d 1822.76 m 2
F asph. tr \u003d L tr * B tr \u003d 1820 m 2 - the area of \u200b\u200bthe removed asphalt under the trench
F asph. boiler-tr \u003d n boiler * L boiler * (B boiler -B tr) \u003d 4 * 2.3 (3.1- 2.8) \u003d 2.76 m 2 - the area of \u200b\u200bthe removed asphalt for the pit
Breakdown of pits and trenches on the ground.
To stake out the main alignment lines at the construction site, first create a alignment network with side sizes of 50, 100, 200 m.
The main alignment axes are fixed with geodetic marks in the form of a metal rod with a length of 57 cm, driven by 50 cm.
The construction organization ensures the safety of all geodetic marks during earthworks. For this purpose, it breaks down the contours of structures and fixes the main axes.
Before the commencement of earthworks, representatives of the construction organization, together with representatives of the customer, check the correctness of the breakdown in kind and draw up an appropriate act, with the attachment to it of breakdown diagrams.
The breakdown of the pit on the ground begins with the fixing of its edges and the bottom with stakes, using for this the mutually perpendicular, extreme or central main axes of the structure according to the geodetic layout and the geometric dimensions of the pit. After that, castoffs are installed around the future foundation pit, consisting of metal or wooden racks dug into the ground and attached to them strictly on one level of slats-boards. The axles are placed on the upper edge of the boards and fixed with axles or risks. Periodically pulling the axial wires along the cast, using plumb lines, they control the accuracy of the excavation pit, then the axial wires are used to construct the foundation of the structure.
Trenching for laying pipelines is carried out on the basis of a geodetic alignment scheme, longitudinal and transverse profiles. Anchoring the axis of the route on the ground is carried out with milestones (length 2-2.5 m), driven into the ground after 10 m on straight lines and 5 m on curved sections, as well as at the turning angles of the route and the locations of wells. In the process of excerpts, the level of the bottom of the trench between adjacent rags is controlled using a walking sight.
Calculation of the volume of earthworks.
For the main production processes, the volumes of excavated soil are determined in m 3 in a dense body. For some preparatory processes (leveling slopes, etc.), volumes are determined in m2 of surface. Counting the volumes of the excavated soil is reduced to determining the volumes of various geometric shapes that determine the shape of the earthen structure. It is assumed that the volume of soil is limited by planes and individual irregularities do not significantly affect the accuracy of the calculation.
2. Development of foundation pits for cameras.
The development of the soil by an excavator with a front shovel is largely predetermined by the features of its design. The excavator moves along the bottom of the excavation, digs "away from itself" from the bottom up with loading the excavated soil onto vehicles. The recess formed by one stroke of the excavator is called penetration. When driving frontally, the excavator moves along the axis of the excavation and develops the soil in front of itself and on both sides of the axis.
When the depth of the excavation (pit) exceeds the optimal height of the face, the soil is worked out in tiers (ledges) in the sequence determined by the profile of the excavation.
Pits are being developed for 4 chambers
∑V boiler\u003d V boiler av * 4 \u003d 16.91 * 4 \u003d 67.64 m 3 - the volume of soil from the pits
V boiler av \u003d L tr * B tr * H cp, m 3 where is the volume of soil from 1 pit
h av - pit depth + 0.2 m under the pit
V boiler av \u003d 2.3 * 2.5 * 2.94 \u003d 16.91 m 3
3. Development of trenches for pipelines.
The excavation is carried out with a front shovel excavator, brand EO-5111A, with a bucket capacity of 1 m 3.
The complete profile of the trench is developed in one run of the mechanism.
D pipeline 1600 mm
The calculation of the volume of soil removed is summarized in Table 1:
Table 1 Calculation of the volume of excavated soil
| Plot No. | trench depth, m | width tran. along the bottom, m | cross. cross-sectional area, m 2 | F cp, m 2 | dist-e, m | volume, m3 | |
| 2,50 | 2,2 | 5,28 | |||||
| 5,5 | 197,7 | 1087,35 | |||||
| 2,70 | 2,2 | 5,72 | |||||
| 6,05 | 197,7 | 1196,08 | |||||
| 3,00 | 2,2 | 6,38 | |||||
| 6,56 | 247,7 | 1624,91 | |||||
| 3,27 | 2,2 | 6,75 | |||||
| Total: 3908.34 |
∑V tr\u003d 3908.34 m 3
4. Arrangement of fasteners for the walls of the trench.
Ensuring the stability of earthworks is the most important requirement for them.
Fastening type - spacer. They consist of boards, posts, sliding screw spacers or frames.
The norms provide for the device of fasteners as the soil is excavated and the corresponding cleaning of the walls of trenches, pits and pits.
In soils resistant to natural moisture, the installation of the first fastening is when excavating the soil in a layer to a depth of 0.6-1.2 m. Subsequently, it is planned to install the fastening as it deepens to a depth of 0.4-0.8 m.
Replacement of temporary anchorage racks with permanent ones is provided during the development of trenches or foundation pits.
Work composition
1Procurement of fasteners with sawing and tinkering. 2. Supply of fastening elements into a trench, foundation pit or pit. 3. Installation of temporary fastening elements with their replacement with permanent ones (re-fastening); with cutting off irregularities on the walls and filling voids with soil behind the fastening boards. 4. Lifting the elements of temporary fastening to the surface.
Calculation of the area F of the fastenings of the trench walls:
F crepe \u003d (l 1 * h cp 1) + (l 2 * h cp 2) + (l 3 * h cp 3)
F crepe \u003d (197.7 * 2.5) + (197.7 * 2.7) + (247.7 * 2.94) \u003d 1756.3 m 2
Calculation of the volume of soil for fastening the walls.
V crepe \u003d F crepe * b \u003d 1756.3 * 0.04 \u003d 70.26 m 3
Installation of cameras
An observation chamber is a shaft located above a sewer pipe or collector, inside which the pipe or collector is replaced by an open tray.
Inspection chambers on sewer networks are provided at the points of connection, in places where the direction of slopes and diameters of pipelines changes, on straight sections at distances convenient for operation.
Depending on the purpose, manholes are divided into linear, rotary, nodal and control. In addition, wash, drop and special wells are used.
Rectangular chambers are assembled from precast concrete wall panels; the shapes and sizes of prefabricated elements allow them to be manufactured in factory conditions and at landfills. The height of the wall panels is accepted as 600, 900 and 1800 mm.
The maximum weight of precast concrete elements is taken from the conditions for the use of mobile cranes with a lifting capacity of up to 6.3 tons, usually used in the construction of sewer networks. Reinforced concrete floor slabs of wells are made of concrete of grade 300, and all other elements - of concrete of grade 200; for packing trays, concrete of grade 200 is used.
The chambers are covered with reinforced concrete slabs and necks with hatches and second covers are installed.
Inspection chambers consist of a base, a working chamber, a ceiling or transitional part, a neck and a hatch with a cover.
Installation is carried out using a boom crane KS-2161AHL, with a lifting capacity of up to 6.3 tons.
Extension of brick necks of wells and chambers
1. Submitting materials. 2. Preparation of cement mortar. 3. Cleaning the base. 4. Brickwork neck.
Work composition
1 Arrangement of crushed stone preparation for the base of wells with cleaning the bottom of the excavation, feeding the rubble into the excavation, leveling and compaction. 2. Laying of bottom slabs with sealing of joints and grouting of the surface with cement mortar. 3. Installation of wells 4 Installation of ladders and brackets with fixing. 5. Laying of floor slabs with sealing of seams. 6. Install the support ring and hatch to lock in place.
Preparation of foundations for pipelines
An artificial base is made in the form of a crushed stone cushion with a layer of 0.20 m on pre-compacted soil.
According to SNiP, the base for the pipelines must be accepted by the customer and drawn up by an act for hidden works... With a gravel-crushed stone base, the thickness of its individual sections is measured.
Work composition
1. Layout of the bottom of the trench or foundation pit according to the line of sight. 2. Installation of side boards and lighthouse pegs. 3. Submission of materials to a trench or foundation pit using cranes with their intake from dump trucks. 4. Leveling and compaction of materials with line inspection.
Crushed stone 200 mm
Crushed stone volume:
V u \u003d L pipes * B tr * h u \u003d 644.7 * 2.2 * 0.2 \u003d 283.67 m 3
7. Arrangement of pits for pipe joints.
Coupling connection.
The length of 1 pipe is 12 m, the distance for the coupling is 180 mm.
Total number of pipes: 55 pieces.
Calculation of the volume of soil removed.
Pit: length 1 m, width 2.1 m, height 0.3 m
V pr \u003d l * b * h * n connection \u003d 1 * 2.1 * 0.3 * 52 \u003d 32.76 m 3
When organizing water supply at home, after purchasing the necessary equipment and a reliable pump, the question arises of bringing communications directly to the dwelling. Typically, in our harsh environment, pipes are laid in the ground. The article discusses the correct methods of organizing such work.
Trenches for laying pipelines are of three types: rectangular section with sheer walls, trapezoidal section with inclined walls and mixed type (Fig. 1).
Rectangular trenches
Rectangular trenches with steep walls have a minimum amount of excavation, a small width in plan, which makes it easier to work within street driveways. The disadvantages of such trenches include the need for a wall attachment device that prevents the walls from collapsing and ensures the safety of people working in the trench.
Digging trenches without fixing sheer walls is permissible in soils of natural moisture and in the absence of groundwater. In this case, the depth of the excavation should not exceed:
- in bulk, sandy and gravelly soils - 1 m;
- in sandy and loamy soils - 1.25 m;
- in clayey soils - 1.5 m.
Figure: 1. Cross-sections of trenches:
A - rectangular;
B - trapezoidal;
B - combined
The choice of the type of trench fastening depends on the nature and condition of the soil, the depth and width of the trench, the proximity to the trench of certain underground and aboveground structures, possible shocks from the dynamic load and the method of excavation. It must always be borne in mind that the stability of the same soils can vary depending on a number of conditions.
For example, clay soils of normal moisture are quite stable, but, being wetted with water, they create a large load on the trench fastenings. Trenches in rocky soils can be excavated to a considerable depth without any anchorage. However, rocky soils can be hazardous in the presence of inclined foreign layers located at an angle of more than 30 ° to the horizon.
Dry gravelly and sandy soils easily crumble inside the trench even through small cracks in the mount, forming dangerous voids and caverns behind them. This dictates the need for careful fastening of the sides of the trench and does not allow deepening the trench in loose soil without immediate appropriate fastening.
From all of the above, it is easy to conclude that timely and correct loosening of the trench walls is an extremely important factor in preventing emergencies and requirements for safe work. The fastening structures, depending on the depth of the trench and the nature of the soil, are shown in the table.
Fastening structures, depending on the depth of the trench and the nature of the soil
Trench horizontal fastening
It is used in dense soils and consists of horizontal boards installed with gaps of 25-30 cm or more (depending on the stability of the soil and local conditions) (Fig. 2).
Figure: 2. Horizontal mount at random:
1 - horizontal boards;
2 - gaps;
3 - vertical risers;
4 - cross braces
Horizontal boards are fastened with vertical risers from boards and transverse spacers. For fastening, boards with a thickness of 40-50 mm are used. The length of horizontal boards is usually 4.5-6.5 m. For deep trenches, it is more convenient to use boards with a length of 4.5 m, since lowering the longer boards into the trench takes a long time and can cause the walls to collapse before they are unfastened. The length of the cross-braces supporting the fastening should ensure that the boards are tightly pressed against the walls of the trench.
Solid horizontal fastening is used in weak crumbling soils or when trenches with critical structures are located close. When fastened horizontally, the top board should protrude above the ground to prevent stones, clods of soil, etc. from entering the trench. To protect the struts from skewing and falling out after their installation, bosses are sewn under them to the risers. Driving the spacer boards will be greatly facilitated if chamfers are removed from their ends.
Figure: 3. Solid vertical mount:
1 _ boss;
2 - spacer;
3 - boards 50 mm thick;
4 - pad;
5 - nails
It is used when developing deep trenches in soft loose soils or near critical aboveground or underground structures (fig. 3). Solid vertical fastening consists of vertically placed planks 50 mm thick, pressed against the walls of the trench with cobblestone or plank frames using spacers.
In this case, the trench is dug with the simultaneous settling of vertical boards. As the trench deepens, additional frames are installed inside, the vertical distance between which depends on the soil and local conditions and averages 1.2 m.
To prevent the frames from sinking, bosses are sewn under them, or short racks of boards or logs are installed, the length of which is equal to the distance between the frames. Multi-tiered vertical anchorage is used when excavating deep trenches in soft soils.
Slope trenches
Sloped trenches do not require fastening and allow extensive use of mechanization of earthworks. Excavation volume per one running meter sloped trenches are greatly increased. In addition, this type of trench requires a considerable land strip, given their large width on top. When carrying out work within the limits of roadways with a road surface, excavation of trenches with slopes may be economically unprofitable due to the large amount of work on dismantling and restoration of road surfaces. A significant volume of excavated soil with small dimensions of the passage makes it difficult to place it in the dump and may require a partial temporary removal of soil with a return transportation for backfill. Therefore, in cramped urban conditions, trenches with steep walls are most often used. The width of the slope depends on the density of the soil.
Mixed type of trenches
A mixed type of cross-section of trenches is used when excavating soil at great depths and in the presence of groundwater, the level of which is higher than the design marks of the bottom of the trench. In this case, the upper part of the trench to the groundwater level is dug with slopes, and the lower part, within the groundwater, with sheer walls. This type of trench may be useful in the presence of wide unpaved passages, free of underground structures.
Trench width
The width of the trench is taken based on the conditions of the minimum volume of work, depending on the diameter of the pipeline being laid, the depth of its laying, geological conditions and the adopted method of work. The width along the bottom of the trench (excluding fastening) should be taken according to the specifications. The smallest clear width of trenches between the fastening boards, as well as between the bases of the slopes, should be at least 0.7 m, and in the case of mechanized excavation of trenches - correspond to the dimensions of the cutting edge of the working body of the earthmoving machine.
Trench depth
The minimum pipe laying depth, taking into account the dynamic load from the ground (when moving vehicles), is approximately 1.0 m to the top of the pipe. When determining the depth of laying pipes, first of all, they are guided by the experience of operating the water supply system. Typically, the depth of the water supply networks should be slightly greater than the depth of soil freezing in a given area.
For rough calculations, the depth water pipes with a diameter up to 500 mm you can take:
H \u003d Hpr + 0.3 m,
where Нпр - depth of soil freezing in meters.
For the northern regions of the Russian Federation, the depth of laying metal pipes take approximately 3-3.5 m; for the middle strip 2.5-3 m; for the southern regions - 1.25-1.3 m to the bottom of the pipe.
Ensuring the slope of trenches
Plumbing and sewer pipes laid with a certain slope indicated in the project on the longitudinal profile. The slope of the pressure water pipelines is given such that it remains possible to empty them. With the correct slope of the pipeline, it becomes impossible for air to accumulate in its internal cavities. Sewer pipes are gravity-flowing and the slope with which they are laid is a very important factor for their operation. Depends on the slope throughput sewer pipeline and ensuring its self-cleaning, that is, preventing precipitation from flowing waste liquid. Of particular importance is the implementation of the design slopes for areas with flat relief, where the slopes have to be designed very small.
In case of inaccurate production of work, areas with zero and even reverse slopes may occur, which creates great difficulties in the operation of the sewer network. To ensure the correctness of the slopes of the pipelines being laid, it is of great importance to perform high-quality work on leveling the bottom of the trench according to the design marks. To control the slope of the bottom of the trench, after the end of the excavator's work, castoffs are installed on the trench. The strip is a 40-50 mm thick board, embedded and firmly sewn to the posts dug in on the sides of the trench. A shelf bar is firmly sewn to the cast-off, from its lower side. The upper edge of this block is level in a strictly horizontal position. Castoffs are usually arranged over observation wells, the distance between which is sewer network usually does not exceed 50 m.
When laying collectors with small slopes, the distance between the castoffs should be no more than 25-30 m. Knowing the mark of the castoff flange and the design mark of the trench bottom under the castoff (from the working profile), determine the value of h2, which is measured from the upper edge of the flange. In this case, the design mark of the bottom of the trench under this cast-off is obtained. Between the design points under the cast-offs, every 2-3 m, pegs are driven in with the help of sighting devices, the top of which is at the design marks.
When developing a trench, the quality of the preparation of the base on which the pipes are laid plays an important role. In water supply systems, pipelines are laid on a natural or artificial foundation. The type of foundation is chosen depending on the hydrogeological conditions, the size and material of the pipes to be laid, the design of the butt joints, the depth of the laying, transport loads and local conditions. With a natural foundation, pipes are laid on the soil of an undisturbed structure, providing the transverse and longitudinal profile of the foundation according to the project.
In this case, along the entire length of the pipe must fit snugly to the base. In order to avoid unacceptable subsidence, the strength of the foundation must be sufficient to balance the active forces, that is, external loads acting on the pipe. With the bearing capacity of soils less than 0.1 MPa (1 kgf / cm2), it is necessary to arrange an artificial foundation. To increase the density of base soils, the compaction method is widely used.
The load-bearing capacity of pipes largely depends on the nature of their support on the base. So, pipes laid in a soil bed with a coverage angle of 120 ° can withstand a load 30-40% greater than pipes laid on flat bases. When laying pipes on an artificial base with a coverage angle of 120e load bearing capacity pipes increase by 1.7 times or more compared to laying on a flat soil base. Thus, it is easy to conclude that the base arrangement is one of the main factors ensuring the durability and reliability of pipelines.
With an increase in the diameter of pipelines, this condition becomes even more important, since the cost of such structures increases. To create artificial foundations of a gravel-crushed stone type, a layer of dry crushed stone or gravel is scattered along the bottom of the trench, leveled, and after laying the pipes, the sinuses are lined with crushed stone or gravel, arranging the required bed along the diameter of the pipe. In the process of preparing the base, it is necessary to check the compliance with the design data of the longitudinal and transverse slopes. To do this, level the bottom of the trench. The depth and angle of the bed must be checked with a template.
Backfilling of trenches
In winter and spring, backfilling of the lower part of the trench to a height of 30-40 cm is carried out immediately after laying the pipes. Backfilling of the lower part of the trench to a height of at least 0.5 m should be carried out exclusively with thawed soil with careful compaction of the sinuses. Backfilling of the upper part of the trench when it is located within road crossings with a road surface should also be done with thawed soil to prevent subsequent sediment of the road surface. When backfilling the upper part of the trench passing through unsubstituted passages, frozen soil is allowed to be laid in an amount of no more than 15% of the total backfill volume.
Before backfilling, the trench must be cleared of snow. An important point is backfilling the lower part of the trench where the pipeline is laid. In the process of backfilling, it is necessary to take measures to preserve butt joints, isolate the laid pipes from damage by the dumped soil. Backfilling of the lower part of the trench to a height of 0.25-0.30 m must be done manually.
With shallow trenches, the soil is dropped from above carefully and not onto the pipes themselves, but from the side, into a corner, so that the impact falls on the walls of the trench. When backfilling deep trenches to protect the laid pipes from damage by stones and clods of caked soil, boards covering the pipes are laid on the lower tier of spacers.
The soil for backfilling the lower part of the trench must be free of stones, clods and other impurities. Backfilling of the lower part of the trenches should be carried out simultaneously from both sides of the laid pipeline in layers of 0.15-0.20 m, since one-sided backfilling can move the pipeline. To compact the soil in the sinuses of the trench, wooden or pneumatic rammers are used.
After backfilling and compaction of the soil in the sinuses of the trench, further backfilling 0.25-0.30 m above the pipe sheath can be done without compaction (except in cases where it is urgently required to restore the roadway bed).
Mechanization of backfilling of trenches without compaction can be carried out using a bulldozer or excavator. When laying pipelines on paved street passages, backfilling should be done in layers with careful compaction of the soil to prevent subsequent subsidence of the road surface. The horizontal fastening of the trench is disassembled gradually as the soil is backfilled, starting from the bottom.
The number of simultaneously removed boards in height should not exceed three, and in loose or unstable soils - one. When disassembling the mount, the through risers are sawn off each time to the width of the Board being removed. The vertical and sheet piling are removed after backfilling the trench.
