Construction of pits: digging, slopes, fastening. Fastening the walls of trenches and pits Fastening the walls of the pit with inventory panels
Formation of pit slopes
Construction company BEST-STROY (Moscow) performs full cycle pit installations: excavation work, digging, slopes, fastening walls, installing a spacer system or ground anchors, pile foundation.
On construction site Marking is carried out in accordance with the technological map of the pit: the perimeter, access roads for soil removal and the place where rock is stored for backfilling. Special equipment is transported to the site: excavators, bulldozers, loaders. All buildings, external and hidden communications located on the site are subject to relocation or demolition in agreement with the relevant organizations. Tree cutting and site planning are also being carried out.
Excavation
After completing the preparatory actions, the special equipment proceeds to the main excavation work on a pit. Highly efficient mechanized excavation allows you to excavate the full volume of the pit in the shortest possible time. The excavated soil partially remains within the construction site For backfill sinuses during the construction phase of the building. The volume of rock left behind is known from calculations previously carried out for the project. The remaining volume is transported by dump trucks to the disposal site.
Excavation and tongue-and-groove excavation walls using pipes and boards
Calculation of pit volume and soil removal
When calculating rock excavation, the loosening effect during digging is taken into account. The density of sedimentary rocks compacted for centuries is disturbed when digging with an excavator and when moving it to a dump or to the back of a dump truck. Depending on the type or types of soil being developed, a correction factor of 20-30% is given. Thus, for example, if the length of a pit is 70 m, width 30 m and depth 5 m with straight tongue-and-groove walls on a planned area, then calculating the volume of the pit gives us a value of 10,500 cubic meters. But for soil removal, you need to calculate the volume to be at least 20% larger: 70x30x5x1.2 = 12600 cubic meters. Making slopes increases the volume of the excavation and excavated soil, but this same amount often goes into backfill and is therefore not transported outside the construction site.
Walls and slopes of the pit
IN favorable conditions If the soil is particularly dense and the depth is up to 2 meters, dig a pit with vertical walls without fastening. If the soil is clayey - up to a depth of 1.5 meters, sandy loam and loam - up to 1.25 meters, bulk and sandy - up to 1 meter.
If necessary, construct a pit to a depth of 5 meters, above the level groundwater- the SNiP table comes to the aid of the designer, showing the dependence of the angle of repose (the ratio of height to foundation) on the type of soil and the depth of the pit.
Table 1. Steepness of pit slopes
| Types of soils | Slope steepness (ratio of its height to foundation) at excavation depth, m, no more | ||
| 1,5 | 3 | 5 | |
| Bulk uncompacted | 1:0,67 | 1:1 | 1:1,25 |
| Sand and gravel | 1:0,5 | 1:1 | 1:1 |
| Sandy loam | 1:0,25 | 1:0,67 | 1:0,85 |
| Loam | 1:0 | 1:0,5 | 1:0,75 |
| Clay | 1:0 | 1:0,25 | 1:0,5 |
| Loess and loess-like | 1:0 | 1:0,5 | 1:0,5 |
In the case of nearby structures, groundwater and the need for dewatering, soils with an uneven structure, a pit depth of more than 5 meters, it is necessary individual calculation angle of slopes or wall fastenings.
Fastening the pit walls
Fastening vertical walls performed during the construction of pits in loose and water-saturated soils. The fastening not only protects against the collapse of the excavation walls, but also prevents the soil from shifting under the weight of neighboring buildings, and protects their foundations from deformation.
The following wall strengthening technologies are used:
- Sheet piling - sheet piling from rolled metal:
- from pipes, with or without board pick-up,
- rolled profile, with or without pick-up,
- specialized Larsen tongue and groove.
- Reinforced concrete structures:
- drilled tangential and drilled secant piles,
- wall in the ground.
All of the above technologies are applied before digging a pit. The fencing is deepened along the perimeter of the excavation strictly in accordance with technological map. Under certain conditions, preliminary drilling of wells is carried out: ensuring vertical immersion, reducing vibration effects through the soil on the bases of nearby structures during driving.
Sheet piling made of pipes with a rolled metal band
The most resource-saving method is immersion of sheet piles from pipes. This material is cheap and has high turnover, that is, the possibility of repeated use. Pipe driving is carried out by driving with a pile driver with a diesel hammer or a hydraulic pile driver, as well as using a vibratory loader. An alternative method is immersion using a pile drilling rig using the push-in and screw-in method.
Picking up is carried out in case of critical spillage of rock between the sheet piles, from a board 40-50 mm thick.
Larsen sheet pile fencing
If water reduction measures are necessary, sheet piling made from Larsen sheet piles is used. Each of these tongues has a trough-shaped strong profile and locking grooves for rigid connection with each other. In this way it is possible to form a strong and sealed wall of any length. Immersion is carried out by driving or vibration immersion. Larsen sheet pile, as well as pipes and rolled profiles, are usually removed after completion of construction, backfilling, and reused at other sites. Sometimes it is not removed, and then the fence is made from a special profile that is left behind.
Fastening the pit walls reinforced concrete structures provides high mechanical and waterproofing properties of the future foundation of structures. They can also serve as the foundation and at the same time the walls of the underground part of the building.
Fastening the pit walls with secant piles and ground anchors
Drilled tangential and drilled secant piles are made by drilling, reinforcement and concreting with a diameter of 400 to 1500 mm and a depth of up to 45 m. First, a foreshaft is prepared along the perimeter of the pit - a small reinforced conductor trench. Odd-numbered wells are drilled in it with a step of 0.9 diameters between the lateral edges of the wells. Fill in concrete mixture. By the time they start drilling even-numbered wells, the concrete has already set and the drilling rig’s auger cuts two adjacent odd-numbered piles, making a well for the even-numbered one between them. Then a pre-prepared reinforcing frame, welded from a special reinforcing rod and wire, is immersed in the well and concreted. As a result, after the concrete hardens, a very strong monolithic reinforced concrete wall is obtained. At the next stage, a pit is dug with a ready-made reinforced concrete fastening wall.
Technological diagram of the construction of a wall in the ground, and the subsequent development of a pit
The “Wall in the Ground” technology provides high-strength fencing and fastening of pit walls with a thickness of 300 to 1200 mm, and a depth of up to 60 m. Complex special equipment is used - a grab installation. The grab is a narrow, wall-width, two-bucket earth-moving tool, immersed in the ground on a rigid rod or suspension, with a hydraulic or pulley drive. The trench being developed is protected from collapse with a clay bentonite solution. Upon reaching the design depth, the reinforced frame is immersed in it and concrete is poured, which displaces the clay solution, which in turn is collected in a reserve tank for further use. Development is carried out in sections (occupations) one at a time. The second burst breaks the intermediate grips and receives monolithic wall. After the concrete gains strength, you can dig a pit.
Installation of a pit expansion system
Despite all the engineering tricks, sometimes, especially for deep pits in difficult soil conditions and dense urban areas, sheet piling may not be strong enough to withstand the pressure of the soil mass.
At the last stage of pit construction, 2 fencing fastening technologies come to the rescue.
View of the expansion pit system near the highway and neighboring buildings
The first of them is the spacer system. A rolled metal strapping belt is installed around the perimeter, evenly distributing the load over the entire belt. Spacers rest against the belt - both between opposite walls and between the bottom. All structures are carried out in accordance with precise mechanical calculations and are outlined in the work plan (work plan).
But the spacer system steals inner space recess, which was arranged specifically for free maneuver in the process construction work. Particularly loaded structures of spacer systems create incredibly cramped conditions for builders. This reduces productivity and lengthens the delivery time.
Installation of ground anchors (anchors)
The BEST-STROY company recommends the use of and fastens sheet piling walls with ground anchors that take on the pulling load from the rock mass. This method is not much more labor-intensive and slightly more complicated than installing spacers, but in the end it provides unlimited operational space and results in significant resource savings, increased productivity and a reduction in construction time.
Ground anchor installation diagram
Based on the results of carefully carried out survey and calculation work, wells are drilled in the walls of the pit, an “anchor” is made, the rod is secured, and it is fixed to the anchored sheet pile. It is important to take into account the location of the foundations of nearby structures and buildings.
During production earthworks have to produce whole line side work, without which development is impossible. These works are called auxiliary.
The most common auxiliary works during excavation work include:
- installation of fastenings for trenches and pits;
- drainage (removal of water from pits);
- construction of temporary roads, entrances to and exits from the mine face for transporting soil during its development.
We must always strive to ensure that all auxiliary work is carried out by special workers and that the performance of auxiliary work does not delay or interfere with the main work.
Pit fastening device
As already indicated in, not every soil can support vertical slopes when digging. The magnitude of the required pit slope is equal to the magnitude of the angle of natural repose of the soil. This slope is the most reliable.
However, digging pits and trenches at great depths with gentle slopes is considered uneconomical, as it causes a significant amount of unnecessary excavation work. Even at shallow depths, natural slopes are sometimes impossible to achieve, for example, if buildings are located nearby. In those cases when the bottom of a pit or trench is under water, free slopes are completely unacceptable, since they are not protected in any way from soaking by water and destruction.
This is why in most cases, when constructing pits and trenches, it is necessary to arrange various kinds temporary fastenings. In addition, as indicated above, a special type of fastening (sheet piling) serves to reduce the influx of groundwater into the pits.
Fastening trenches and pits with wooden spacers
The simplest fastenings to the walls of pits and trenches up to 2 m deep are arranged as follows.
Along the walls of the trenches, 4 boards 50 mm thick are laid with spacers between them, placed every 1.5-2 m along the length of the trenches (Fig. 38);
Spacers are made from short logs or pipes 10-12 cm thick. This type of fastening is used for dense, dry soils that can hold a vertical slope for some time and are not washed away by rain (dense clay, dense loam). In this case, the slopes can be either vertical or with a slight slope (1/10).
At greater depths (up to 4 m) for dry soils that give rise to local sliding within a short period of time after lifting, a so-called horizontal fastening is installed. It is arranged like this: a series of thrust posts made of boards up to 6 cm thick or plates are installed over the entire depth of the pit at a distance of 2 to 3 m, depending on the depth of the pit (Fig. 39). Behind these posts, a fence is laid from horizontal rows of boards 4-5 cm thick, staggered or continuous, depending on the ground. Wooden or steel spacers are used to hold the posts in place. The spacers should have a length slightly greater than the distance between the opposite walls. When installing a spacer, this circumstance makes it possible to “start” the spacers with blows of a sledgehammer or hammer, and thereby tightly press the posts and fence against the walls of the pit or trench.
To prevent the spacers from falling (Fig. 40), short pieces (bobs) made from scrap boards 4-5 cm thick are placed under their ends. The short pieces are nailed to the posts with 125 mm nails.
The distance between the spacers in height depends on the depth of the trench. As the depth increases, the pressure of the soil on the fastenings increases, so spacers are placed at the bottom more often than at the top, namely: at the top - after 1.2 m and at the bottom - after 0.9 m in height. The upper horizontal board is placed slightly higher than the edge of the trench so that the soil from the edge does not fall into the trench. To transfer the soil, shelves made of boards are laid on spacers.
For loose and wet soils, as well as crumbling soils, vertical fastening is used, which differs from horizontal in that the horizontal boards in it are replaced by vertical ones, and the racks are replaced by horizontal pressure bars. The pressure bars are pushed apart by spacers from the knurl, forming spacer or pressure frames (Fig. 41).
Pressure frames with vertical mounting to a depth of 3 m they are made of half-edged boards 6 cm thick, and the spacers are made of knurling or plates. At a depth of up to 6 m, the thickness of the pressure boards, as well as the spacer, should be increased to 10 cm.
In addition to the inner board, the upper clamping frame must also have an outer board 6 cm thick. This board cuts into the trench wall to its full thickness.
The height distance between individual clamping frames made of boards is 0.7 - 1.0 m, and with frames made of plates and beams - 1.0 - 1.4 m.
At a depth of up to 5.0 m, the number of spacers for each frame made of boards 6.5 m long is 4 pcs., at greater depths - 5 pcs.
For both vertical and horizontal fastening, the trench walls must be plumb. With inclined walls, the spacers can pop up under the pressure of the earth.
The lower clamping bars and spacers for fastening water supply and sewer trenches must be positioned in such a way that there is a gap between them and the bottom of the trench sufficient for unhindered laying of pipes.
There are often cases (weak soil, presence of water) when fastenings are necessary before digging begins. In these cases, the fastenings are more complex.
Such fastenings include:
Bottomhole fastening
In small but deep pits and pits, the so-called downhole fastening is used (Fig. 42).
It is arranged as follows: on the surface of the earth at the location of the pit or pit, a horizontal cobblestone frame is laid according to the size of the pit. This frame is buried flush into the ground, after the frame a row of boards is driven in slightly at an angle. Then they begin to dig a pit under the protection of the walls formed by boarded boards. When the excavation approaches the lower ends of the forgotten boards, a second frame is placed between them. To ensure that the upper frame does not fall down as the soil is excavated, short bars made of bars that are gradually lengthened are placed under it. When the second frame is installed, bars are installed between it and the upper frame, which support the upper frame. Next, another row of slightly sloping boards is nailed along the outer edge of the bottom frame. Between the upper and lower rows of the fence, wedges for greater stability of the upper fence are driven in.
Fastening pits with piles with a wooden fence between them
Fastening pits with piles with a wooden fence is used when weak soils, preventing the excavation of a pit to full depth. In addition, the installation of transverse struts when fastening a pit is often undesirable, since it complicates the work in the pit. If the pit is large or its shape is complex, it is generally impossible to install spacers. Therefore, in all such cases, they resort to fastening with piles with wooden filling between them. This type of fastening is as follows: before digging begins, wooden and sometimes steel (iron) piles, the so-called lighthouse piles, are driven into the ground at a distance of 1.5-2 m from each other, depending on the depth of the pit (Fig. 43) ; Between these piles, as the excavation deepens from the side of the slope, separate fastening boards are laid. Piles are driven to a depth somewhat greater than the depth of the pit, so that until the end of digging the pit, the pile remains sufficiently stable. To enhance the stability of lighthouse piles, their upper ends are anchored in the slope or supported by struts, resting the latter on the piles driven into the bottom of the pit.
Fastening pits with piles with a fence can also be installed in pre-dug pits, if it is undesirable to have spacers in the pit, and the soil allows digging without pre-installed fastenings.
Fastening with sheet piles
To secure pits in soils saturated with water (slurry and quicksand), the so-called sheet piling is used. Sheet piling consists of a continuous row of vertically installed sheet piling pipes or boards (in which a tongue-and-groove is made on one edge and a ridge on the other), pressed against the walls of a trench or pit by horizontal frames with spacers (Fig. 44). Everything that has been said about spacers in vertical fastening applies entirely to sheet piling fencing; the thing is that with sheet piling, the sheet pile is first driven in, and then a trench is dug with the spacer frames being gradually installed; in a vertical fastening, a trench or foundation pit is first dug, and then a fastening is installed, which is gradually lowered down as the soil is further excavated. The sheet pile boards are driven to a depth slightly greater (0.2-0.5 m) than the depth of the trench or pit, so that after digging is completed, their lower ends cannot be moved by the pressure of the soil.
Wooden tongue and groove is made from boards 6-7 cm thick or from beams 10x20 cm (Fig. 45). A tongue and groove are installed in each sheet piling (pile). When driving piles, the ridge of one fits into the groove of the other. The cutting of the lower end of the pile is made in the form of a wedge with acute angle from the groove side. With this type of driving, the piles fit tightly to each other when driving, which is very important in wet soils, when water seeps under pressure into the cracks of loose sheet piles. Sheet piles must be made from raw, freshly cut wood. If they are made from wood that has been lying in the air for some time, then before driving they must be placed in water for 10-15 days so that they have time to swell. This is done because the sheet piling row, driven from dried piles, swells in wet soil and, due to the increase in the volume of the piles, the row bends; individual piles are turned out, forming cracks, and the row becomes unusable. the work of driving piles begins with the installation of a row of so-called lighthouse piles exactly along the line of the future, 2 m apart from each other (Fig. 43).
These piles are driven first and frame beams are attached to them on both sides. In the spaces between the lighthouse piles and the frame beams that serve as guides, the remaining piles of the sheet piling row are driven. Each subsequent pile must be adjacent to the one already driven into the groove, and the ridge must remain free, otherwise the grooves will become heavily clogged with earth, and it will be difficult to achieve a tight row. Driving is done with a mechanical piledriver, and at shallow depths and weak soil it can also be done manually using wooden poles.
Dismantling the fastenings of the sheet piling of the pit
Dismantling of fasteners should be done starting from the bottom, as the trenches are filled.
Horizontal fastenings are disassembled one board at a time in weak soils, and in very dense soils - no more than 3-4 boards. In this case, the vertical posts are sawed at the bottom to the desired height. Before sawing the posts, the spacers must be moved above the sawing point. The rearrangement of the spacers is done as follows: first, a new spacer is installed on top of the undercut, and then the bottom one is knocked out.
With vertical fastening and sheet piling, the spacers and pressure bars are removed gradually as backfilling proceeds, starting from the bottom: sheet piles and vertical boards are pulled out at the end of backfilling using a lever (Fig. 46). The engagement of the piles is done according to one of the methods shown in Fig. 47.
Dismantling of fastenings on piles with a wooden fence is carried out by gradual sawing as the fence boards are filled, starting from the bottom; You need to remove the fence one board at a time. The piles are removed after all backfilling has been completed in the same way as when dismantling sheet piling fastenings.
Currently in use steel fencing: Larsen tongue, steel pipes used with diameter: from 159 to 426 mm.
Lining pits and trenches can be done as follows:
a) vertical cladding, consisting of a system of vertical load-bearing posts, the space between which is sheathed with horizontally located elements. The fastening is installed after excavating soil from a pit or trench without first securing the walls;
b) vertical retaining structures. The fastening consists of a vertically positioned tongue and groove, which is installed before or parallel to the excavation and secured with horizontal struts or special pile attachments;
c) load-bearing sheet pile walls. They are constructed from vertical load-bearing sheet pile elements, which are driven into the ground before it is excavated, and then secured with horizontal struts. Anchor fastening of tongue and groove is possible;
d) fastening with special plates. The walls of the pits are lined with specially manufactured large-size slabs, installed immediately after excavation. They are secured by vertical or horizontal load-bearing elements, which can be additionally secured with spacers.
When constructing deep pits with vertical walls in residential, industrial and agricultural construction before installation load-bearing structures the walls must be lined with protective elements coated with various film materials.
In accordance with the above classification, their areas of application are distributed as follows:
a) for small and medium-sized pits;
b) limited width of the construction site;
c) close location of construction soil;
d) in conditions that exclude the possibility of shocks. The types of cladding described in this chapter are used only
in conditions of limited groundwater flow. The groundwater level must be located below the bottom of the pit. If necessary, dewatering should be carried out in a closed manner.
3.1. FASTENING PIT WALLS WITH HORIZONTAL ELEMENTS
The method of fastening the walls of pits appeared a long time ago and is still widely used in the construction of small and complex objects. It is used when ground conditions the height of the loose part of the wall should not exceed 0.5 m, and the mark of the bottom of the pit is above the groundwater level. Lining the vertical walls of pits with horizontal tongue and groove is used in cases where two parallel walls of the pit are slightly spaced from each other. The design of such walls consists of:
horizontal - wooden, metal or reinforced concrete elements;
vertical posts made from round wooden racks or steel beams;
horizontal or inclined struts made of round timber or beams, steel beams or screw struts for narrow trenches;
elements providing local rigidity of the structure, consisting of additional posts and struts.
The following advantages of fastening racks with horizontal elements can be mentioned:
possibility of constructing pits of complex configuration;
small mass of individual building elements;
possibility of repeated use of fastening structures.
However, this solution has several disadvantages: restrictions on the use of machines for laying pipelines and performing other types of work due to the presence large number cross braces;
the need to re-ensure stability when disassembling and reassembling the struts;
the possibility of loss of stability of the walls when removing spacers during construction work.
Rice. 3.6. Fastening the vertical walls of a wide pit
a - driving a guide trench; b - arrangement of the load-bearing element with its anchoring; c - supporting the walls of the pit on the load-bearing element; d - top view of the anchorage; 1 - round steel anchor; 2 - spacers; 3 - metal supporting racks; 4 - racks; 5 - casing; 6 - traverse; 7 - cross beam; 8 - wedges
3.1.1. Trench lining.
When implementing a design with horizontal elements to protect the walls of trenches when laying pipelines (Fig. 3.1), the following design solutions are used:
the thickness of the boards used for cladding must be at least 50 mm;
wooden posts with a cross-section of at least 100x140 mm must support at least four horizontal elements or boards along the length;
when used metal racks their cross-section must be at least 10;
diameter of wooden posts round section must be at least 100 mm and have a chamfer at the ends.
For lining the walls of trenches, boards with a length of 4.0 to 4.5 m, a width of 200 to 300 mm and a thickness of 50 to 70 mm are usually used. For each individual section of the cladding, it is allowed to use boards only of the same length, since it is not allowed to extend them along the length. Instead of wood, metal cladding made of profiled elements can be used. Under normal conditions, the length of the posts and spacers is from 1.5 to 2.5 m. The posts should be located at a distance of no more than 200 mm from the end of the horizontal board. Boards 2.5 long; 4.5 m are attached to three posts. The length of the vertical posts is at least 1 m, this allows you to place at least two spacers along their length. In Fig. Figure 3.2 shows a design for fastening the walls of a trench for laying a pipeline, made of boards. Constructive decisions when constructing an inspection well at the end of a narrow trench are shown in Fig. 3.3.
When laying pipelines, the distance between lower tier spacers and the bottom of the trench. This leads to the need to install stronger and longer posts that can withstand large bending moments. In Fig. 3.4 shows a solution that allows you to do without the lower strut. In this case, in addition to the usual short racks, long vertical racks that have greater strength are additionally installed almost at the entire height of the walls, and the lower struts are attached at a greater height from the bottom of the trench.
In Fig. 3.5 shows a design solution for fastening the walls of the trench for laying steel pipeline with a diameter of 800 mm. The racks for securing the horizontal cladding are made of metal profiles. Metal tubular struts with a diameter of 60 mm with a wall thickness of 4 mm are laid in the base (Fig. 3.5, a) and two wooden struts are installed in the upper part of the trench. This provides the space necessary for pipeline laying work. For the installation of individual sections of the pipeline, sections of 6 m in length were provided, where spacers were not installed. The pipes were laid in a trench in these places and then pulled to the installation site.
In Fig. 3.5c shows a plan of the area where individual sections of pipes are lowered. After excavating the soil, special metal frames are installed in the trench to prevent the walls from collapsing.
Served as a lower strut concrete base trench into which the lower ends of the racks were inserted.
If traffic or construction machinery is intended to move along the edge of the trench, the vertical fastening of the trench walls must be strengthened.
In this case, the upper struts should be located at a depth of no more than 0.5 m from the ground surface and if the road for vehicle access is located at a distance of less than 1 m from the edge of the trench, their number should be doubled.
3.1.2. Fastening the walls of pits.
When constructing wide pits with vertical walls in conditions that exclude the possibility of ground shaking, it is possible to use the above-described structures with horizontal cladding elements. The walls of the pit are secured in two ways:
1) a slot-shaped trench is constructed along the perimeter of the future pit, the walls of which are secured using the method described above, after which the main soil of the pit is excavated (Fig. 3.6);
2) first, the main part of the soil is developed in a pit with slopes, after which the soil that lies at the base of the slope is excavated, its subsequent securing with casing, which is secured to existing structure(Fig. 3.7).
In Fig. 3.8 shown phased implementation work according to the first option during the construction of a railway bridge in conditions of continuous traffic. Initially, two slot-like slots were developed and secured with horizontal cladding. After this stage of the work was completed, numerous wooden spacers were installed. Long-term spacers and their heads were made of metal. In parallel with the excavation, the wooden struts were gradually replaced with metal ones and the lining of the trench walls was installed. In Fig. 3.9 shows the design solution for the bridge crossing support.
2.8.1 The development of trenches and pits with vertical walls in soils of natural moisture without fastening can be carried out at a depth:
no more than 1 m - in bulk, sandy and gravelly soils;
no more than 1.25 m - in sandy and loamy soils;
no more than 1.5 m - in clay soils;
no more than 2 m - in particularly dense soils. In this case, the work should be carried out immediately after the excavation of trenches and pits.
2.8.2 If the specified depths are exceeded, digging trenches and pits is permitted only if vertical walls are fastened or slopes of acceptable steepness are constructed (Figure 2.7).
Figure 2.7 - Determination of slope steepness
The maximum permissible steepness of slopes of trenches and pits in soils of natural moisture should be determined according to Table 2.4.
2.8.3 Digging trenches and pits in frozen soils All rocks, with the exception of dry sand, can be built with vertical walls without fastenings to the entire depth of their freezing. When deepening below the freezing level, fastening must be done.
2.8.4 Trenches and pits in dry (loose) sandy soils, regardless of the degree of their freezing, should be developed to ensure the established steepness of the slopes or with a device for fastening the walls.
2.8.5 Digging trenches and pits in heated (thawed) soils should be carried out by ensuring the required steepness of slopes or installing wall fastenings in those cases (or places) when the depth of the heated area exceeds the dimensions indicated in Table 2.4.
Table 2.4 - Maximum permissible slope slopes of trenches and pits
| Priming | Steepness of slopes at depth of trenches and pits, m | |||||
| trenches | pits | |||||
| up to 1.5 | from 1.5 to 3 | from 3 to 5 | ||||
| & | ON | & | ON | & | ON | |
| Bulk natural humidity | 76° | 1:0,25 | 45° | 1:1,00 | 38° | 1:1,25 |
| Sandy and gravelly wet but not saturated | 63° | 1:0,50 | 45° | 1:1,00 | 45° | 1:1,00 |
| Clayey natural humidity: - sandy loam loam - clay |
76° | 1:0,25 | 56° | 1:0,67 | 50° | 1:0,85 |
| 90° | 1:0,00 | 63° | 1:0,50 | 53° | 1:0,75 | |
| 90° | 1:0,00 | 76° | 1:0,25 | 63° | 1:0,50 | |
| Loess-like dry | 90° | 1:0,00 | 63° | 1:0,50 | 63° | 1:0,50 |
| & is the angle between the direction of the slope and the horizontal, the ratio of the height of the slope H to its location A. Note - For excavation depths greater than 5 m, the steepness of the slope is given in the project |
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2.8.6 At intersections with railway or tram tracks, it is necessary to develop trenches and pits with mandatory fastening of their walls. Tracks should be secured with rail packages only in cases provided for by the project, agreed upon with the service for the operation of these tracks.
2.8.7 Types of fastening pits and trenches with vertical walls are shown in Figure 2.8 and Table 2.5.
a) horizontal frame mounting;
b) horizontal-solid fastening;
c) horizontal fastening with gaps;
d) mixed fastening: horizontal, solid and tongue-and-groove;
e) vertical frame mounting;
e) vertical-solid fastening
Figure 2.8 - Methods of fastening the walls of trenches and pits
Table 2.5 - Types of fastening pits and trenches with vertical walls
| Ground conditions | Types of fastening |
| Dry soils capable of maintaining vertical walls at a depth of up to 2 m | Horizontal frame (Figure 2.8a) |
| Sliding soils, dry and dense soils (if trenches or pits remain open for a long period of time) | Horizontal-solid (Figure 2.8b) |
| Bound dry soils in the absence of groundwater at a development depth of no more than 3 m | Horizontal with gaps (Figure 2.8c) |
| Water-saturated soils | Mixed: horizontal, solid and tongue-and-groove (Figure 2.8d) |
| Bound dry soils in the absence of groundwater | Vertical frame (Figure 2.8d) |
| Loose soils in deep trenches and soils with layers of quicksand | Vertical-solid (Figure 2.8f) |
2.8.8 Trenches and pits up to 5 m deep should, as a rule, be secured using equipment. Inventory metal screw spacers (Figure 2.9) are used to reduce the consumption of forest materials.
Figure 2.9 - Screw spacers for securing trenches
At a depth of more than 3 m, fastenings must be made according to separate projects approved by the management of the construction organization
2.8.9 In the absence of inventory devices, fastening parts for trenches and pits must be manufactured on site in compliance with the following requirements:
a) for fastening soils of natural moisture (except sandy), boards with a thickness of at least 40 mm should be used, and for soils high humidity- not less than 50 mm. The boards should be laid behind vertical posts close to the ground and reinforced with spacers;
b) fastening posts must be installed at least every 1.5 m;
c) the vertical distance between the spacers should not exceed 1 m. The spacers are secured with a stop;
d) the top boards must protrude at least 15 cm above the edges;
e) the fastening units on which the shelves for transferring soil rest must be reinforced. The shelves are fenced with side boards no less than 15 cm high.
2.8.10 The development of excavations in soils saturated with water (quicksands) should be carried out according to individual projects, providing for safe methods of performing work - artificial dewatering, sheet piling, etc.
2.8.11 The fastenings of pits and trenches should be dismantled from the bottom up, as the soil is backfilled, and at the same time no more than two or three boards should be removed in normal soil, and no more than one board in quicksand. Before removing the boards of the lower part of the fastening, temporary oblique struts must be installed above, and old struts must be removed only after installing new ones; fastenings must be disassembled in the presence of the responsible performer of the work. In places where dismantling the fastenings can cause damage to structures under construction, as well as in quicksand soils, it is possible to leave the fastenings partially or completely in the ground.
2.8.12 The walls of pits and trenches excavated by earth-moving machines must be secured with ready-made shields, which are lowered and pushed out from above (workers are prohibited from descending into an unsecured trench). The development of trenches using earth-moving machines without fastenings must be carried out with slopes.
In cramped conditions, as well as in the presence of groundwater, quicksand and other difficult hydrogeological conditions, when it is impossible to ensure the required slopes, it is necessary to fasten pits and trenches.
The permissible excavation depth, i.e. the maximum (critical) depth at which the slope of cohesive soil is held in a vertical position without fastening the walls, is determined by calculation. Approximate values of the critical depths of excavations made with vertical walls: 1.0 m in bulk, sandy and gravelly soils of natural moisture; 1.25 m - in sandy loam; 1.5 - in loams and clays; 2.0 - in particularly dense non-rocky soils.
The need for fastenings is determined by the project. The installation of fastenings for the vertical walls of pits and trenches requires significant costs manual labor, therefore, fastening is carried out only when it is economically feasible or when it is not possible possible device slopes.
Depending on the type of soil, width and depth of excavations and service life, apply different kinds fastenings. Temporary support can be made in the form of wooden or metal sheet piles, wooden panels with support posts, panels with spacer frames. The design of any fastening includes a fence made of boards, beams or panels that directly absorb soil pressure. Purlins, spacers and other elements are used to hold the pick-up in a vertical position. A distinction is made between horizontal fastening, when the boards or beams of the pick-up are placed horizontally behind the posts, and vertical, when the pick-up boards are installed vertically and secured with horizontal purlins with spacers.
For narrow trenches 2-4 m deep in dry soils, a horizontal frame fastening is used, consisting of racks, horizontal boards or boards (solid and not solid) and spacers that press the boards or boards to the walls of the trench. Spacers are installed along the length of the trench at a distance of 1.5-1.7 m from one another and at a height of 0.6-0.7 m.
Vertical fastening is most often used if the fastenings are placed in one row. The backfill is made continuous if the soils are unstable and have high humidity, or with gaps (openings) if sufficiently stable cohesive soils of normal moisture are attached. In difficult hydrogeological conditions, when there are highly water-saturated, flowing soils, a continuous fence made of wooden or metal sheet piling is used.
To hold the pick-up in a vertical position, there are three types of fastenings: spacer, cantilever and strut. The spacer type of fastening is the most common due to its ease of assembly. In this case, the racks are freely installed at the bottom of the excavation and pressed against the intake with horizontal spacers installed at several levels according to calculations. The width of the recess with spacer fastening is limited. The spacer fastening is installed in the following sequence: after cutting off a section of the trench, two frames are lowered into it and installed on the bottom 2 m from each other, temporarily secured with guy ropes, then horizontal boards or panels are inserted from above into the gap between the uprights of the frames along both walls, after then push the spacer frames all the way.
In cases where the possibility of installing spacers is excluded (for example, when developing wide pits), anchor or strut fastenings are used. Strut fastenings consist of plank boards installed along the slopes of the racks, which are held by the struts, and stops driven into the base of the struts. However, such fastening, despite its structural simplicity, suffers from some disadvantages: such fastening constrains work inside the pit, in addition, driving in thrust anchors leads to disruption of the soil structure at the bottom of the pit.
Cantilever fastenings are characterized by the fact that the racks (wooden piles) are held by pinching the lower part into the ground. Racks, piles, rails, rolled steel, pipes, etc. are driven into the bottom of the excavation to a depth of 2.2-3.3 m. Horizontal pick-up boards are placed either behind the racks or inserted between the I-beam flanges. Cantilever fastening is carried out in the following order: along the trench laid out on the ground, racks are driven in at a calculated pitch to a depth below the bottom of the future pit. After this, the soil is developed. If the soil is unstable, horizontal collection elements are installed simultaneously as the trench is deepened. In this case, each subsequent board is brought from below under the previously installed one - they are grown. In sufficiently stable soils that are capable of maintaining a vertical slope for at least a short time, trenches are torn out in sections 3-4 m long to the design depth, and the pick-up boards are installed by lowering them from above - by building them up. Wooden or steel tongue and groove fastenings are widely used; with non-thrust fastening, the posts are positioned at a certain pitch, and with tongue-and-groove fastening they are driven in without intervals.
Cantilever non-thrust fastening is used for pits and wide trenches up to 4.7 m deep. If it is necessary to tear off deeper pits, additional fastening of the upper part of the racks with anchors is arranged. The anchor consists of one or two driven anchors and guys. Anchors should be driven to a depth of about 3 m and at a considerable distance from the edge (equal to approximately one and a half depth of the excavation), in order to position them outside the destruction prism. The distance between the anchors is determined by calculation. The disadvantage of this method is that the installation of anchors requires a significant free area along the excavation and, in addition, guy ropes interfere with work in this area, so sometimes guys are installed in trenches 0.5 m deep opened for this purpose.
When constructing deep pits with sheet piling, first a steel sheet pile is driven along the perimeter of the future pit 4-5 m below the bottom, then anchors are installed, after which the soil is torn off. Hanging mounts most often used for fastening pits rectangular section depth up to 2-5 m depending on the purpose; they have horizontal elements that act as thrust girders, which are suspended from a support frame laid on the surface of the excavation.
Rice. 6. :
a - console; b - anchor; c - cantilever-spacer; g - spacer; d - braced; e - suspended; 1 - shields (boards); 2 - racks (piles); 3 - anchors; 4 - spacers; 5 - struts; 6 - stops (anchors); 7 - support; 8 - ring
In loose and unstable soils, spacer or log fastenings made of plates and beams are installed. In viscous soils and with a strong influx of water, enclosing sheet pile walls made of boards or beams, reinforced with spacers, are hammered in. A wooden block frame is laid on the surface of the ground according to the dimensions of the well, and then boards 1.5-2 m long with a slight slope are driven in from the outer sides of the frame bars, close to them, and a pit is dug under the protection of the driven boards. After deepening to 1-1.5 m, a second frame of the same type is installed at the bottom of the well and a second row of boards is driven in. Work continues in the same order until the required depth is reached (Fig. 6).
The development of trenches with vertical walls using rotary and trench excavators in cohesive soils (loams, clays) is allowed without fastening to a depth of no more than 3 m. Work on the construction of foundations, laying utility networks etc. in trenches with vertical walls without fastenings should be carried out immediately after the excavation of soil to avoid its shedding or sliding.
© 2000 - 2009 Oleg V. site™
During excavation work, it is necessary to carry out a number of side works, without which development is impossible. These works are called auxiliary.
The most common auxiliary works during excavation work include:
- installation of fastenings for trenches and pits;
- drainage (removal of water from pits);
- construction of temporary roads, entrances to and exits from the mine face for transporting soil during its development.
We must always strive to ensure that all auxiliary work is carried out by special workers and that the performance of auxiliary work does not delay or interfere with the main work.
Pit fastening device
As already mentioned, not every soil can support vertical slopes when digging. The magnitude of the required pit slope is equal to the magnitude of the angle of natural repose of the soil. This slope is the most reliable.
However, digging pits and trenches at great depths with gentle slopes is considered uneconomical, as it causes a significant amount of unnecessary excavation work. Even at shallow depths, natural slopes are sometimes impossible to achieve, for example, if buildings are located nearby. In those cases when the bottom of a pit or trench is under water, free slopes are completely unacceptable, since they are not protected in any way from soaking by water and destruction.
This is why, in most cases, when constructing pits and trenches, it is necessary to arrange various kinds of temporary fastenings. In addition, as indicated above, a special type of fastening (sheet piling) serves to reduce the influx of groundwater into the pits.
Fastening trenches and pits with wooden spacers
The simplest fastenings to the walls of pits and trenches up to 2 m deep are arranged as follows.
Along the walls of the trenches, 4 boards 50 mm thick are laid with spacers between them, placed every 1.5-2 m along the length of the trenches (Fig. 38);
Spacers are made from short logs or pipes 10-12 cm thick. This type of fastening is used for dense, dry soils that can hold a vertical slope for some time and are not washed away by rain (dense clay, dense loam). In this case, the slopes can be either vertical or with a slight slope (1/10).
At greater depths (up to 4 m) for dry soils that give rise to local sliding within a short period of time after lifting, a so-called horizontal fastening is installed. It is arranged like this: a series of thrust posts made of boards up to 6 cm thick or plates are installed over the entire depth of the pit at a distance of 2 to 3 m, depending on the depth of the pit (Fig. 39). Behind these posts, a fence is laid from horizontal rows of boards 4-5 cm thick, staggered or continuous, depending on the ground. Wooden or steel spacers are used to hold the posts in place. The spacers should have a length slightly greater than the distance between the opposite walls. When installing a spacer, this circumstance makes it possible to “start” the spacers with blows of a sledgehammer or hammer, and thereby tightly press the posts and fence against the walls of the pit or trench.
To prevent the spacers from falling (Fig. 40), short pieces (bobs) made from scrap boards 4-5 cm thick are placed under their ends. The short pieces are nailed to the posts with 125 mm nails.
The distance between the spacers in height depends on the depth of the trench. As the depth increases, the pressure of the soil on the fastenings increases, so spacers are placed at the bottom more often than at the top, namely: at the top - after 1.2 m and at the bottom - after 0.9 m in height. The upper horizontal board is placed slightly higher than the edge of the trench so that the soil from the edge does not fall into the trench. To transfer the soil, shelves made of boards are laid on spacers.
In loose and wet soils, as well as in crumbling soils, a vertical fastening is used, which differs from the horizontal in that the horizontal boards in it are replaced by vertical ones, and the racks by horizontal pressure bars. The pressure bars are pushed apart by spacers from the knurl, forming spacer or pressure frames (Fig. 41).
Pressing frames for vertical fastening to a depth of up to 3 m are made of semi-edged boards 6 cm thick, and spacers are made of knurling or plates. At a depth of up to 6 m, the thickness of the pressure boards, as well as the spacer, should be increased to 10 cm.
In addition to the inner board, the upper clamping frame must also have an outer board 6 cm thick. This board cuts into the trench wall to its full thickness.
The height distance between individual clamping frames made of boards is 0.7 - 1.0 m, and with frames made of plates and beams - 1.0 - 1.4 m.
At a depth of up to 5.0 m, the number of spacers for each frame of 6.5 m long boards is 4 pcs., at greater depths - 5 pcs.
For both vertical and horizontal fastening, the trench walls must be plumb. With inclined walls, the spacers can pop up under the pressure of the earth.
The lower clamping bars and spacers for fastening water supply and sewer trenches must be positioned in such a way that there is a gap between them and the bottom of the trench sufficient for unhindered laying of pipes.
There are often cases (weak soil, presence of water) when fastenings are necessary before digging begins. In these cases, the fastenings are more complex.
Such fastenings include:
Bottomhole fastening
In small but deep pits and pits, the so-called downhole fastening is used (Fig. 42).
It is arranged as follows: on the surface of the earth at the location of the pit or pit, a horizontal cobblestone frame is laid according to the size of the pit. This frame is buried flush into the ground, after the frame a row of boards is driven in slightly at an angle. Then they begin to dig a pit under the protection of the walls formed by boarded boards. When the excavation approaches the lower ends of the forgotten boards, a second frame is placed between them. To ensure that the upper frame does not fall down as the soil is excavated, short bars made of bars that are gradually lengthened are placed under it. When the second frame is installed, bars are installed between it and the upper frame, which support the upper frame. Next, another row of slightly sloping boards is nailed along the outer edge of the bottom frame. Between the upper and lower rows of the fence, wedges for greater stability of the upper fence are driven in.
Fastening pits with piles with a wooden fence between them
Fastening pits with piles with a wooden fence is used in weak soils that do not allow digging a pit to its full depth. In addition, the installation of transverse struts when fastening a pit is often undesirable, since it complicates the work in the pit. If the pit is large or its shape is complex, it is generally impossible to install spacers. Therefore, in all such cases, they resort to fastening with piles with wooden filling between them. This type of fastening is as follows: before digging begins, wooden and sometimes steel (iron) piles, the so-called lighthouse piles, are driven into the ground at a distance of 1.5-2 m from each other, depending on the depth of the pit (Fig. 43) ; Between these piles, as the excavation deepens from the side of the slope, separate fastening boards are laid. Piles are driven to a depth somewhat greater than the depth of the pit, so that until the end of digging the pit, the pile remains sufficiently stable. To enhance the stability of lighthouse piles, their upper ends are anchored in the slope or supported by struts, resting the latter on the piles driven into the bottom of the pit.
Fastening pits with piles with a fence can also be installed in pre-dug pits, if it is undesirable to have spacers in the pit, and the soil allows digging without pre-installed fastenings.
Fastening with sheet piles
To secure pits in soils saturated with water (slurry and quicksand), the so-called sheet piling is used. Sheet piling consists of a continuous row of vertically installed sheet piling pipes or boards (in which a tongue-and-groove is made on one edge and a tongue on the other), pressed against the walls of a trench or pit by horizontal frames with spacers (Fig. 44). Everything that has been said about spacers in vertical fastening applies entirely to sheet piling fencing; the thing is that with sheet piling, the sheet pile is first driven in, and then a trench is dug with the spacer frames being gradually installed; in a vertical fastening, a trench or foundation pit is first dug, and then a fastening is installed, which is gradually lowered down as the soil is further excavated. The sheet pile boards are driven to a depth slightly greater (0.2-0.5 m) than the depth of the trench or pit, so that after digging is completed, their lower ends cannot be moved by the pressure of the soil.
Wooden tongue and groove is made from boards 6-7 cm thick or from beams 10x20 cm (Fig. 45). A tongue and groove are installed in each sheet piling (pile). When driving piles, the ridge of one fits into the groove of the other. The cutting of the lower end of the pile is made in the form of a wedge with an acute angle on the groove side. With this type of driving, the piles fit tightly to each other when driving, which is very important in wet soils, when water seeps under pressure into the cracks of loose sheet piles. Sheet piles must be made from raw, freshly cut wood. If they are made from wood that has been lying in the air for some time, then before driving they must be placed in water for 10-15 days so that they have time to swell. This is done because the sheet piling row, driven from dried piles, swells in wet soil and, due to the increase in the volume of the piles, the row bends; individual piles are turned out, forming cracks, and the row becomes unusable. the work of driving piles begins with the installation of a row of so-called lighthouse piles exactly along the line of the future, 2 m apart from each other (Fig. 43).
These piles are driven first and frame beams are attached to them on both sides. In the spaces between the lighthouse piles and the frame beams that serve as guides, the remaining piles of the sheet piling row are driven. Each subsequent pile must be adjacent to the one already driven into the groove, and the ridge must remain free, otherwise the grooves will become heavily clogged with earth, and it will be difficult to achieve a tight row. Driving is done with a mechanical piledriver, and at shallow depths and weak soil it can also be done manually using wooden poles.
Dismantling the fastenings of the sheet piling of the pit
Dismantling of fasteners should be done starting from the bottom, as the trenches are filled.
Horizontal fastenings are disassembled one board at a time in weak soils, and in very dense soils - no more than 3-4 boards. In this case, the vertical posts are sawed at the bottom to the desired height. Before sawing the posts, the spacers must be moved above the sawing point. The rearrangement of the spacers is done as follows: first, a new spacer is installed on top of the undercut, and then the bottom one is knocked out.
With vertical fastening and sheet piling, the spacers and pressure bars are removed gradually as backfilling proceeds, starting from the bottom: sheet piles and vertical boards are pulled out at the end of backfilling using a lever (Fig. 46). The engagement of the piles is done according to one of the methods shown in Fig. 47.
Dismantling of fastenings on piles with a wooden fence is carried out by gradual sawing as the fence boards are filled, starting from the bottom; You need to remove the fence one board at a time. The piles are removed after all backfilling has been completed in the same way as when dismantling sheet piling fastenings.
At this point in time, steel fences are used: Larsen sheet piles, used steel pipes with a diameter of 159 to 426 mm.
Construction of pits and trenches with fastening
For pits and trenches up to 3 m deep, as a rule, inventory fastenings made according to standard projects. The choice of fastening type (Table 5.3) for excavation depths of up to 3 m depends on the type of soil and its moisture content.
Table 5.3
For excavations with a depth of more than 3 m, fastenings are installed according to individual designs approved by the chief construction engineer in accordance with the PPR. Structural solutions for securing the soil are shown in Fig. 5.2.
Rice. 5.2. Constructive solutions for ground support:
a) fastening with spacers (1 - stand, 2 - bosses 3 - spacer), b) anchor fastening (1 - stand, 2 - fastening boards, 3 - screed, 4 - anchor) c) anchor fastening (1 - stand; 2 - fastening boards 3 - bosses 4 - struts) d) tongue-and-groove fastening (1 - wooden tongue-and-groove 2 - purlins) e) device for fastening trenches (1 - stand, 2 - guide 3 - sliding struts 4 - braces, 5 - steel panels) g ) device for fastening trench walls (1 - enclosing panels, 2 - spacers 3 - rod 4 - spreader blocks 5 - hinges;) h) fastening trench walls when laying pipelines (1 - wooden shield, 2 - spacer frame 3 - sector support, 4 - a pipe that is lowered, 5, 6 - hinged struts) f) temporary fastening when laying pipelines (1 - anchor elements 2 - soil is removed 3 - panels 4 - racks, 5 - bracket, 6 - hook)
Advantages inventory fastenings: assembly of elements, the possibility of installing them from above without descending into a trench, the possibility of mechanizing installation and disassembly, calculating all elements for strength and stability.
Let's consider the basic labor safety requirements when making pits and trenches. The fastenings must be installed downwards as the excavation is developed to a depth of no more than 5 m (in unstable soils 0.2-0.25 m). When installing fasteners top part they should protrude above the edge of the excavation by at least 15 cm. Installation of non-inventory wooden fastenings trenches up to 3 m deep must meet the following requirements: for fastening soils of natural moisture, except sandy ones, use boards with a thickness of at least 4 cm, and for sandy soils and soils of high humidity - at least 5 cm, which are laid behind vertical posts close to the ground with strengthening spacers. The fastening posts are installed at least every 1.5 m, the fastening spacers are placed at a distance of no more than 1 m, and finally the spacers are driven into the bosses. When throwing out soil from excavations more than 1.8 m deep, it is necessary to install shelf-flooring on spacers, which must be protected with side boards at least 15 cm wide. When installing fasteners fastening material needs to be fed into the recess mechanized way. It is prohibited to dump it into trenches or pits. The condition of the fastenings must be systematically monitored. Fastenings installed in winter are inspected especially carefully and, if necessary, strengthened. Fill the holes in parts. In this case, the fastening is dismantled from the bottom up, removing simultaneously no more than three boards in stable soils, and no more than one in unstable soils. When removing boards, the spacers must be adjusted accordingly. Dismantling of fastenings is carried out under the supervision of a foreman or foreman. When constructing underground structures in loose and water-saturated soils, there is no need to dismantle the fastenings, as this can lead to an accident. Usually, the recesses are filled in without dismantling the fastenings, and a corresponding report is drawn up about this.
Place in dry and low-moisture stable soils.
If the height of the pit hk ≤5 m, then the slope position (ratio h to /b) is determined from the tables depending on the type of soil.
If the height hk >5 m, then calculation of the steepness of the slope is necessary.
Such pits are the simplest, but the volume of excavation work increases sharply, especially with deep pits. In addition, in the natural conditions of the city, excavation of a pit with a natural slope is not always possible (closely located buildings)
2.2.B Pits with vertical walls
can be: - with fastening
Without fastening
Without fastening it is allowed only in dry and low-moisture stable soils for a short period of time. The depth of such pits should not exceed:
in sands up to 0.5 m
in sandy loams up to 1.0 m
in loams and clays up to 3 m
The design of the foundation pits is selected depending on the following conditions:
pit depth;
soil properties;
fastening service life.
Depending on these conditions, the following fastening designs are selected:
embedded fastenings;
anchor or strut fastenings;
sheet pile fencing.
2.2.V. Mortgage fastenings
They are installed at a pit depth of up to 2...4 m in dry and low-moisture soils (Fig. 14.2 a, b). The embedded fastening consists of racks, spacers and horizontal boards (removals), which are inserted behind the racks from below as the pit or trench is deepened, and the racks are gradually replaced with longer ones, carefully securing them with spacers.
Rice. 14.2. Fastening the vertical walls of the recesses:
a, b – mortgage; c – anchor; g – braced; 1 – stand; 2 – boards; 3 – spacer; 4 – pile; 5 – screed; 6 - strut
A more convenient fastening, which does not require replacement of the posts as the excavation deepens, consists of I-beams of steel pre-hammered into the ground, behind the flanges of which boards are gradually laid.
2.2.G. Anchor and strut fastenings
Suitable in cases where the possibility of installing spacers is excluded (wide pit, also if spacers interfere with the construction of the foundation).
For device anchor(Fig. 14.2 c) for fastenings along the wall of the pit, inclined piles are driven in, which are connected by anchor rods to the fastening posts.
In a braced fastening (Fig. 14.2d), the walls are held by struts that transmit shear forces to a stop driven into their base.
2.2.D. Sheet piling
They are used for fastening the vertical walls of a pit at a depth of more than 4 meters, as well as at any depth, but when the groundwater level is above the bottom of the pit.
Sheet piling fences consist of individual elements (sheet piling), which are immersed in the ground even before the pit is excavated and form a solid wall that prevents the soil from sliding and the penetration of water into the pit.
Rice. 14.3. Wooden sheet piling fencing:
a – from boards; b – from beams; c – the lower end of the wooden tongue and groove
Dowels can be made from:
→ Wooden sheet piling is used for fastening shallow pits (3...5 m) (Fig. 14.3) can be:
Plank (thickness up to 8…10cm)
Pavement (t from 10 to 24 cm)
Rice. 14.4. Rolled steel sheet pile profiles:
a – flat; b – trough; V -Z-shaped
The length of the sheet piles is determined by the depth of their immersion, but, as a rule, does not exceed 8 m, since longer ones are not expensive and are in short supply.
To completely close the tongues, they are provided with a ridge or groove, and the lower end is made with a one-sided sharpening, due to which the immersed tongue is pressed against the already immersed one, which makes the wall more dense.
The gradual swelling of the wood in water also contributes to additional compaction of the tongue joint.
Wooden sheet piling fencing is easy to manufacture, but there are limitations to its use:
Impossibility of driving sheet piles into dense soils;
Short length of sheet piles (6...8 m);
And relatively low strength.
→ Metal Sheet piles are used at depths of more than 5...6 m. Due to its design (Fig. 14.4), it has great strength and rigidity.
It consists of a rolled profile l=8...24 m.
Korytnoy;
) at large bending moments
Z-shape The connection between the sheet piles is carried out vertically using “ castles
" The design of the locks ensures a tight and durable connection between the tongues and grooves. The remaining gaps in the locks are quickly filled and the metal sheet pile wall becomes almost waterproof. Reinforced concrete
sheet piles are used in the construction of embankments, quays and hydraulic structures, or in cases where sheet piles are subsequently used as part of the structure.
Reinforced concrete tongue and groove
Continuous reinforced concrete row of piles (driven or bored)
Permitted row of piles in clay soils.
Sheet piling wall structures:
Without fastenings (cantilever);
With spacer fastening;
With ground anchors.
Rice. 14.5. Sheet piling schemes:
a – console; b – with spacer fastening; c – with anchor fastening; 1 – sheet pile wall; 2 – spacer; 3 – harness; 4 – anchor pile; 5 – anchor rod.
