Fixing the walls of the trenches. Pit device: digging, slopes, fastening The volume of the inventory board for fastening the walls of trenches

After excerpts, trenches and pits are prone to rapid destruction. Therefore, their walls must be further strengthened. This, firstly, keeps the shape of the notch for a while further work, and secondly, it protects workers from accidents due to landslides. Most often, the walls of the trench are fastened with inventory boards, boards or tongues. In what cases are such measures necessary and how exactly is soil strengthening carried out?

When is it necessary to fix the walls of trenches and pits?

In preparation for the construction or laying of communications, recesses without slopes, with vertical walls, are usually preferred. Such trenches have a number of advantages:

• they are more economical in execution, because attachments excavators are mainly designed to create vertical walls OK;
• pits and trenches without slopes occupy a smaller area, which is very important when digging in conditions of dense buildings or natural landscape, which is undesirable to destroy;
• the presence of a slope can complicate further construction works on a dug trench or in a pit.

But recesses with vertical walls are prone to collapse and shedding. Therefore, without additional reinforcement, you can only dig pits and trenches of small depth:

• on bulk, sandy and coarse soils - up to 1 m;
• on sandy loam - up to 1.25 m;
• on loams, clays, loess-like soils - up to 1.5 m;
• on especially dense soils, for the development of which it is necessary to use crowbars, picks and wedges - up to 2 m.

When digging at a greater depth, it is necessary to fasten the walls of the trench with special devices. In addition, it is necessary to strengthen the walls even at shallow depths if the soil is oversaturated with moisture, and the excavation can “float”.

Attention! The need to strengthen the walls of pits and trenches is spelled out in normative documents. This requirement cannot be ignored. Soil collapse can lead to the destruction of construction sites, landslides and accidents. The presence of workers in excavations without slopes or reinforced vertical walls is strictly prohibited!

Ways to strengthen the walls of the trench

Most often, the slopes of the recesses are strengthened in the following ways:

• inventory boards and spacers;
• sheet piles;
• boards.

The method and design parameters of strengthening are selected depending on the type and condition of soils, height ground water, depth and purpose of the excavation. At the same time, the fastening of the slopes of the trench is performed small areas, as it digs. As a rule, this process follows the excavator, at a safe distance from the excavation site. With a large digging depth, the structures are installed from top to bottom, after excavating the excavation to a depth of no more than 0.5 m.

The upper part of all fasteners must protrude at least 15 cm above the edge of the trench. During backfill wall reinforcements are usually dismantled. The exception is cases when the dismantling of structures is technically impossible or may cause deformation (destruction) of the construction object. The fasteners should be disassembled from the bottom up, as the excavation is backfilled.

Strengthening trenches with inventory shields

This is the most popular way of fastening the walls today:

• it is convenient in execution and safe;
• requires less labor and materials than the use of plank and sheet piling fencing (for example, using inventory boards for fixing trenches is 3-4 times cheaper than building reinforcing fences from boards).

Also, inventory fasteners are indispensable when extracting recesses with a ditcher. Indeed, in this case, the width of the excavation is so small that the installation of reinforcing structures is possible only from above.

Inventory fastening for trenches consists of:

• metal screw spacer frames;
• wall fencing shields.

The spacer frame is a simple fixture of two stops and a screw that connects them. With the help of a screw, the stops are moved apart to the desired width and press the elements of the trench fence against its walls.

Inventory shields for fixing trenches are made from different materials. It could be:

• waterproof plywood;
• bituminized cardboard;
• wavy sheet metal and etc.

The types of shields are selected based on working conditions and economic feasibility.

Installation inventory fasteners pretty simple. First, two already assembled spacer frames are lowered into the trench. Then, shields are placed in the gaps between their posts and the walls of the recess. After that, it remains only to push the stops to fix the fence.

Take off inventory fences in the process of backfilling the trench. Spacers are removed as the backfilled soil reaches their lower ends. The shields are removed after removing the uppermost struts. Since by this time they are already covered with soil, crane equipment is required to lift them.

Plank and sheet piling wall reinforcements

Fastening the trench with boards is done in different ways. There are four main types:

• vertical solid;
• horizontal solid;
• horizontal with a gap;
• horizontal frame.

AT different occasions boards are located on the walls of the trench vertically or horizontally, solid or with gaps through one board. For their fixation, spacers, tongues and other additional elements are used.

Fastening the trench with a tongue is used in difficult cases:

1. In areas with a strong influx of groundwater, when soil particles can be carried out by water and the walls of the excavation are washed out. For example, a solid fence made of Larsen's trough-shaped sheet piles makes it possible to hold even swampy, spreading, water-saturated soils and withstands a sharp rise in groundwater.
2. With very deep development.
3. If the trench runs close to the foundation of the building.

Sheet piling can be solid or with boards. Depending on the depth and width of the trench or pit, wooden, steel or reinforced concrete sheet piles of various profiles (flat, trough-shaped, tubular) are used. They are hammered in before the start of excavation and, if necessary, additionally fixed with anchor braces.

Standard inventory fasteners for the walls of trenches and pits are used at a development depth of up to 3 m. If the excavation needs to be dug deeper, the reinforcing structures are developed individually and approved by the project.

2.8.1 Development of trenches and pits with vertical walls in soil natural humidity without fastening can be carried out at a depth of:

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 especially dense soils. At the same time, work should be carried out immediately after excavation of trenches and pits.

2.8.2 If the specified depths are exceeded, digging trenches and pits is allowed only if vertical walls are fixed or slopes of acceptable steepness are arranged (Figure 2.7).

Figure 2.7 - Determining the steepness of the slope

The maximum allowable 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 ground all rocks, with the exception of dry sandy, can be carried out with vertical walls without fastenings to the entire depth of their freezing. When deepening below the freezing level, fastening should be carried out.

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 slopes or with a wall fastening device.

2.8.5 Digging trenches and pits in warmed (thawed) soils should be carried out with the necessary steepness of the slopes or with the device for fastening walls in those cases (or places) when the depth of the warmed area exceeds the dimensions indicated in Table 2.4.

Table 2.4 - Maximum allowable steepness of slopes of trenches and pits

2.8.6 At intersections with railway or tram tracks, it is necessary to develop trenches and pits with the obligatory fastening of their walls. Tracks should be fastened with rail packages only in cases provided for by the project agreed with the maintenance service for these tracks.

2.8.7 Types of fastening of pits and trenches with vertical walls are shown in Figure 2.8 and Table 2.5.

a) horizontal-frame mounting;
b) fastening horizontally solid;
c) horizontal fastening with gaps;
d) mixed fastening: horizontal, solid and tongues;
e) vertical-frame fastening;
f) vertical-solid fastening

Figure 2.8 - Ways of fastening the walls of trenches and pits

Table 2.5 - Types of fastening of pits and trenches with vertical walls

2.8.8 As a rule, trenches and pits up to 5 m deep should be fixed with inventory devices. Inventory metal screw struts (Figure 2.9) are used to reduce the consumption of forest materials.

Figure 2.9 - Screw struts for fixing 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, the details of fastening trenches and pits must be made on site in compliance with the following requirements:

a) for fixing 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. Boards should be laid vertical racks close to the ground with reinforcement struts;

b) fastening posts should be installed at least every 1.5 m;

c) the vertical distance between the struts should not exceed 1 m. The struts are fixed with a stop;

d) the upper boards should protrude at least 15 cm above the brows;

e) the attachment points on which the shelves for transferring the soil rest must be made reinforced. Shelves are protected by side boards with a height of at least 15 cm.

2.8.10 The development of excavations in soils saturated with water (quicksand) should be carried out according to individual projects providing safe ways works - artificial dewatering, sheet piling, etc.

2.8.11 Pit and trench fastenings should be dismantled from the bottom up, as the soil is backfilled and at the same time remove no more than two or three boards in normal soil, 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 the old struts may only be removed after the installation of new ones; fasteners must be dismantled in the presence of a responsible contractor. In places where the dismantling of fasteners can cause damage to structures under construction, as well as in quicksand soils, it is possible to partially or completely leave fasteners in the ground.

2.8.12 The walls of pits and trenches developed by earth-moving machines must be fastened with ready-made shields, which are lowered and burst apart from above (workers are prohibited from descending into an unsecured trench). The development of trenches by earth-moving machines without fasteners must be carried out with slopes.

When carrying out earthworks, it is necessary to arrange the fastening of the walls of trenches and pits to prevent soil shedding. The walls are usually fastened with shields with spacers, which are placed along the length of the trench at least every 2 meters at a depth of up to 3.75 meters in dry and loose soils and at least 1.5 meters in loose, wet and wet soils at a depth of more than 3, 75 meters. How is the fastening of the walls of trenches and pits in practice?

How should spacers be placed?

Spacers in height (in tiers) should be placed at least every 1.2 meters at all depths, regardless of the nature of the soil. The presence of wall fastening elements imposes its own requirements on the width of the trenches. The width of the trenches should be divided with the calculation of the width of the base of the foundation, adding 15-20 centimeters on both sides for fastening. The width of trenches for pipelines is broken down based on the width of the outer diameter of the pipes plus 0.6 meters for fastening.

Wooden or metal shields

Shields that serve to fix the soil in trenches and pits are made of wood or metal. For loose and floating soils, solid shields are used, and for dense soils in trenches up to 3 meters deep, shields can be assembled with gaps from boards up to 200 millimeters wide. In this case, the width of the gaps between the boards of the shield should not exceed the width of the boards themselves.

For fixing the walls of trenches of medium width, inventory can be used. metal mounts ladder type. Inventory fastenings from steel pipes are made in trenches with vertical walls 0.8-1.8 meters wide, while pipes with a diameter of about 60 millimeters and up to 3 meters long are used (for longitudinal elements of ladder fastening).

The transverse struts of inventory fasteners have threaded sections, by turning the screws on which you can increase the length of the struts, thereby pressing the racks to the shields. While inventory bracing is more expensive than timber bracing, it will pay for itself in the long run with multiple uses.

Sheet piling of walls

With loose and fluid soils (quicksand), the walls of trenches and pits are fastened with a sheet pile, which is a continuous fastening of lighthouse piles and sheet piles. tongue and groove serves simultaneously as a fence for conducting drainage works.

The device of a wooden sheet pile is as follows: screw piles are driven in, guide boards are attached to them, between which the tongue is driven. Fully clogged spans fasten at the top special nozzle, which has slots with sockets.

The nozzle is attached to the piles with brackets. To prevent the earth from destroying the sheet piling in the trenches with a two-sided device, spacers are made in the places where the sheet piles are stuffed. In construction, metal and reinforced concrete sheet piles are also used, the device of which differs from wooden ones only in manufacturing technology.

With a one-sided sheet piling, struts are arranged in the pit, and spacers are placed in the pits in the direction perpendicular to the sheet piling. The sheet piling can be built as a permanent fence or as a temporary one.

Lighthouse pile driving

When installing sheet piling, the most time-consuming work is driving lighthouse piles and the sheet pile itself. If the amount of work is insignificant and the sheet piling is driven in light soils, then it is advisable to use simple devices such as a tripod. The tripod is arranged as follows: a metal hammer - a “woman” weighing 200-250 kg on a cable with a folding hook is suspended on a block through which the cable passes to the winch. As a result of the rotation of the winch, the woman rises up to a height of 0.5-1 meters.

During the reverse free running of the winch drum, it falls down and clogs the sheet pile or pile with its weight. For a small amount of work, simple wooden or steel-rolled copra are used, equipped with hand winches and a woman weighing up to 1 ton.

Mechanical pile drivers

For large volumes of pile work, mechanical pile drivers are used, which include those operating with the help of compressed air hammers and diesel hammers. They operate on the same principle, for impact they use the free fall force of the hammer or the pressure force of compressed air. With the use of mechanized pile drivers in 10-15 minutes, a pile can be driven to a depth of 6-8 m, which significantly speeds up the arrangement of sheet piles for fixing walls of trenches and pits in comparison with manual sheet pile installation.

During the earthworks, a number of side works have to be carried out, without which development is impossible. These jobs are called auxiliary.

The most common ancillary activities in earthworks include:

• fixing trenches and pits;
• dewatering (removal of water from pits);
• arrangement of temporary roads, entrances to the face and exits from the face for the transportation of 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 fixing device

As already mentioned in, not every soil can hold vertical slopes when digging. The value of the required slope of the pit is equal to the value of the angle of repose of the soil. This slope is the most reliable.

However, digging pits and trenches at great depths with gentle slopes is not considered economical, as it causes a significant amount of unnecessary excavation. Even at shallow depths, natural slopes are sometimes impossible to implement, for example, if buildings are located nearby. In cases where the bottom of the pit or trench is under water, free slopes are completely unacceptable, since they are not protected from water soaking and destruction.

That's why, in most cases, when arranging pits and trenches, you have to arrange various kinds of temporary fasteners. In addition, as mentioned above, a special type of fastening (sheet piling) serves to reduce the inflow of groundwater into the pits.

Fastening trenches and pits with wooden struts

The simplest fastening of 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 rains (dense clay, dense loam). Slopes in this case can be both vertical and with a slight slope (1/10).

At greater depths (up to 4 m), for dry soils that give local creep after a short period of time after the passage, the so-called horizontal fastening is arranged. It is arranged as follows: for the entire depth of the pit, a series of thrust posts are installed from boards up to 6 cm thick or plates at a distance of 2 to 3 m, depending on the depth of the pit (Fig. 39). For these racks, a fence is laid from horizontal rows of boards 4-5 cm thick, staggered or completely, depending on the soil. Wooden or steel spacers are used to hold the posts in place. The spacers should be slightly longer than the distance between opposite walls. When setting the strut, this circumstance makes it possible to “start” the struts with blows of a sledgehammer or hammer, and thereby tightly press the posts and the fence to the walls of the pit or trench.

In order to prevent the spacers from falling (Fig. 40), shorties (bosses) are placed under their ends from scraps of boards 4-5 cm thick. The shorties are nailed to the racks with 125-mm nails.

The distance between the struts in height depends on the depth of the trench. With increasing depth, the pressure of the soil on the fasteners increases, so the struts 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 above the edge of the trench so that the soil from the edge does not crumble into the trench. To transfer the soil, shelves from boards are laid on spacers.

With loose and wet soils, as well as in crumbling soils, a vertical fastening is used, which differs from the horizontal one in that the horizontal boards in it are replaced by vertical ones, and the racks are replaced by horizontal clamping bars. The clamping bars are bursting with knurled spacers, forming spacer or clamping frames (Fig. 41).

Clamping frames for vertical mount to a depth of up to 3 m, they are made of semi-edged boards 6 cm thick, and the spacers are made of knurled or plates. At a depth of up to 6 m, the thickness of the pressure boards, as well as the spacer, must be increased to 10 cm.

The upper clamping frame must have, in addition to the inner board, an outer board 6 cm thick. This board cuts into the trench wall to its full thickness.

The height distance between individual pressure frames made of boards is 0.7 - 1.0 m, and with frames made of plates and beams - 1.0 - 1.4 m.

With a depth of up to 5.0 m, the number of spacers for each frame of boards 6.5 m long is placed in 4 pieces, with a greater depth - 5 pieces.

Both vertical and horizontal mount trench walls should be sheer. With inclined walls, the spacers under the pressure of the earth can jump up.

The lower clamping bars and struts of fastenings of water and sewer trenches should be located in such a way that there is a gap between them and the bottom of the trench, sufficient for unhindered laying of pipes.

Often there are cases (weak soil, the presence of water) when fastening is necessary before digging. In these cases, the fasteners are more complex.

These fasteners include:

Downhole fastening

In small in size, 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 block 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 hammered slightly obliquely. Then they start digging a pit under the protection of the walls formed by the clogged boards. When the excavation approaches the lower ends of the forgotten boards, a second frame is laid between them. In order for the upper frame not to fall down as the soil is worked out, short pieces of bars are placed under it, gradually lengthened. When the second frame is installed, between it and top frame install bars that support the upper frame. After that, another row of slightly inclined boards is hammered along the outer edge of the lower frame. Between the upper and lower rows of the fence, wedges of greater stability of the upper fence are hammered.

Fixing pits with piles with a wooden fence between them

The fastening of pits with piles with a wooden fence is used when soft soils that do not allow digging a pit to the full depth. In addition, often the device of transverse struts when fixing the pit is undesirable, since it makes it difficult to work in the pit. With a large width of the pit or its complex shape, spacers cannot be installed at all. Therefore, in all such cases, they resort to a device for fastening with piles with wooden driving between them. This type of fastening is as follows: before digging, 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 slightly greater than the depth of the pit, so that the pile remains sufficiently stable until the digging of the pit is completed. To enhance the stability of lighthouse piles, their upper ends are anchored in a slope or supported by struts, resting the latter against the piles hammered at the bottom of the pit.

Pit fastenings with piles with a fence can also be arranged in pre-dug pits, if it is undesirable to have spacers in the pit, and the soil allows digging without pre-installed fasteners.

Sheet piling fastening

For fixing 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 in one edge, and a ridge on the other), pressed against the walls of the 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, in that with sheet piling, the sheet pile is first driven in, and then the trench is digged with the gradual installation of spacer frames; in a vertical mount, a trench or pit is first dug, and then a mount is installed, gradually lowering down as the soil is further developed. The sheet pile boards are driven to a depth somewhat greater (by 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.

A wooden sheet pile is made from boards 6-7 cm thick or from bars 10x20 cm (Fig. 45). In each sheet pile (pile), a ridge and a groove are arranged. When driving piles, the crest of one enters the groove of the other. The cutting of the lower end of the pile is done in the form of a wedge with acute angle from the groove side. With such a fit, the piles fit snugly against each other during driving, which is very important in wet soils, when water seeps under pressure into the cracks of loose sheet piles. Sheet piles should be made from raw, freshly cut wood. If they are made from wood that has already lain in the air for some time, then before driving them they must be put in water for 10-15 days so that they have time to swell. This is done later that the sheet piling row, hammered from dried piles, swells in wet soil and, due to the increase in the volume of piles, the row is bent; individual piles turn out, forming cracks, and the row becomes unusable. pile driving begins with the installation exactly along the line of the future row of so-called lighthouse piles 2 m apart (Fig. 43).

These piles are driven first, and frame bars are attached to them on both sides. In the intervals between the lighthouse piles and the frame beams serving as guides, the rest of the sheet piles are driven. Each subsequent pile must be adjacent to the already clogged groove, and the crest must remain free, otherwise the grooves are heavily clogged with earth, and it will be difficult to achieve a dense row. Driving is done with a mechanical pile driver, and at shallow depths and weak soil it can also be done manually with wooden broads.

Dismantling of fastenings of the sheet piling of the excavation

Dismantling of fasteners should be carried out, starting from the bottom, as the trenches are backfilled.

Horizontal mounts are dismantled one by one for weak soils, and for very dense soils - no more than 3-4 boards. In this case, the vertical racks are sawn down to desired height. Before sawing the posts, the spacers must be moved above the sawing point. The spacer is rearranged as follows: first, a new spacer is installed on top of the notch, and then the lower one is knocked out.

With vertical fastening and sheet piles, the spacers and clamping bars are removed gradually as the filling is done, starting from the bottom: sheet piles and vertical boards are pulled out after filling is completed using a lever (Fig. 46). In this case, the engagement of piles is done according to one of the methods shown in Fig. 47.

Dismantling of fastenings with piles with a wooden fence is carried out by gradual sawing as the fence boards are backfilled, starting from the bottom; it is necessary to remove the fence one by one. The piles are removed after the entire backfilling is completed in the same way as when disassembling the sheet piles.

AT this moment time use steel railings: Larsen sheet pile, steel pipes Bu diameter: from 159 to 426 mm.