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 production auxiliary works did 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 sometimes it is impossible to implement, for example, if there are buildings 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 inflow into the pits groundwater.

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.

The upper clamping frame must have, in addition to internal board also an outer board 6 cm thick. This board cuts into the wall of the trench 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.

Both with vertical and with horizontal mounting The walls of the trenches must be vertical. 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 in 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 a device for fastening 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

For fastening pits in soils, saturated with water(slurry and quicksand), the so-called sheet piling is used. A sheet piling fence 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. Wherein vertical racks are filed down at the bottom 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 occurs, starting from the bottom: sheet piles and vertical boards are pulled out at the end of the backfill 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 with piles 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.

IN this moment time use steel fencing: Larsen tongue, steel pipes used with diameter: from 159 to 426 mm.

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.

Markings are carried out at the construction site in accordance with the technological map of the pit: the perimeter, access roads for soil removal and the location for storing rock 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 with pipes and pick-up from 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, it is given correction factor 20-30%. 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 it is necessary to construct a pit to a depth of up to 5 meters, above the groundwater level, the SNiP table comes to the aid of the designer, which shows 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 water reduction, soils with an uneven structure, or a pit depth of more than 5 meters, an individual calculation of the slope angle or wall fastening is necessary.

Fastening the pit walls

Fastening of vertical walls is carried out 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 fencing 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. Alternative way- immersion using a pile drilling rig using the pressing and screwing 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, you can form a strong and airtight 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 has hardened, a very strong monolithic structure is obtained. reinforced concrete wall. On next stage a pit is being 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.

On last stage When constructing a pit, 2 technologies for fastening fences 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 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 during construction work. Particularly loaded structures of spacer systems create incredibly cramped conditions for builders. This reduces productivity and lengthens the delivery time of the project.

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.

After excavation, trenches and pits are prone to rapid destruction. Therefore, their walls need to be further strengthened. This, firstly, maintains the shape of the excavation for the duration of further work, and secondly, protects workers from accidents due to ground collapses. Most often, fastening the trench walls with inventory panels, boards or tongues is used. In what cases are such measures necessary and how exactly is soil strengthening carried out?

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

When preparing for construction or laying communications, preference is usually given to excavations without slopes, with vertical walls. Such trenches have a number of advantages:

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

But excavations with vertical walls are prone to collapses and collapses. 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 loams - up to 1.25 m;
• on loams, clays, loess-like soils - up to 1.5 m;
• on particularly dense soils, for the development of which it is necessary to use crowbars, picks and wedges - up to 2 m.

When digging at greater depths, trench walls must be secured 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 may “float”.

Attention! The need to strengthen the walls of pits and trenches is prescribed in regulatory documents. This requirement cannot be ignored. Ground 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!

Methods for strengthening trench walls

Most often, excavation slopes are strengthened in the following ways:

• inventory panels and spacers;
• tongues;
• boards.

The method and design parameters of strengthening are selected depending on the type and condition of the soil, the height of groundwater, the depth and purpose of the excavation. In this case, the fastening of the trench slopes is carried out in small areas, as it digs. As a rule, this process follows the excavator, at a safe distance from the excavation site. For large digging depths, structures are installed from top to bottom, after digging the excavation to a depth of no more than 0.5 m.

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

Strengthening trenches with inventory shields

This is the most popular method of attaching walls today:

• it is easy to use and safe;
• requires less labor and materials than the use of board and sheet piling fencing (for example, using inventory panels to secure trenches is 3-4 times cheaper than building reinforcing fences from boards).

Also inventory fastenings indispensable when excavating excavations with a ditch digger. Indeed, in this case, the width of the excavation is so small that installation of reinforcing structures is possible only from above.

Inventory fastening for trenches consists of:

• metal screw spacer frames;
• wall fencing panels.

The spacer frame is a simple device consisting of two stops and a screw that connects them. Using a screw, the stops are moved apart the required width and press the trench fencing elements against its walls.

Inventory panels for fastening 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 operating conditions and economic feasibility.

Installing inventory mounts is quite 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 this, all that remains is to move the stops apart to secure the fence.

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

Boardwalks and sheet piling fortifications walls

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.

IN different cases the boards are placed on the walls of the trench vertically or horizontally, solidly or with gaps through one board. To fix them, spacers, tongues and other additional elements are used.

Fastening the trench with tongue and groove 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 can be washed away. For example, a continuous fence made of Larsen trough-shaped sheet piles allows you to retain 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 fences 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 digging the excavation and, if necessary, additionally secured with anchor guys.

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

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

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 of all types, with the exception of dry sand, can be carried out 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

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 2.8e)
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 fastening 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 safe ways execution of works - 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.