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 sheet pile, which is installed before or parallel to the excavation and secured with horizontal spacers 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. Maybe anchorage tongue and groove;
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 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 inflow groundwater. 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, according to 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. Facing vertical walls OK excavation with horizontal tongue and groove is used in cases where two parallel walls of the excavation are slightly removed 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 of a large number of transverse struts;
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 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 - transverse 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 using 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. Can be used instead of wood metal cladding from profiled elements. 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 the structure for fastening the walls of a trench for laying a pipeline, made of boards. Design solutions for the construction of an inspection well at the end of a narrow trench are shown in Fig. 3.3.
When laying pipelines, the distance between the lower tier of spacers and the bottom of the trench is often insufficient. 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 spacer. In this case, in addition to the usual short racks, long ones are additionally installed almost to the entire height of the wall mounting vertical racks, having greater strength, and the lower struts are attached at a greater height from the bottom of the trench.
In Fig. 3.5 shown constructive solution fastening the trench walls 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 excavated in a pit with slopes, after which the soil that lies at the base of the slope is excavated and subsequently secured with cladding, which is secured to the 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.

The geometric dimensions of the trenches are determined based on the depth of the pipelines, the required width of the trenches along the bottom (along the bottom) and the configuration of the walls.

The width of the trench along the bottom consists of the size of the pipelines and technological gaps that ensure all construction work is carried out. The width of the trench along the bottom b (m) depending on the outer diameter of the pipeline D (m) is taken equal to:
b = D + (0.5...0.6) m with D ≤0.5 m;
b = D + (0.8...1.2) m at D > 0.5 m.

The width of the trench along the bottom can be specified in the work plan, but should not be less than 0.7 m.

Trenches are dug with sloping or vertical side walls. Trenches with vertical walls are more economical. However, due to the danger of soil collapse, their greatest depth in dense soils without special calculations and fastening the walls should not exceed 2 m. Therefore, trenches with slopes (with inclined walls) are mainly used, the greatest steepness of which in soils natural humidity ranges from 1: 0.25 to I: 1.25 (Table 5.3).

In waterlogged clayey and dry sandy soils The steepness of the slopes should be taken as for bulk soils. In all cases, in the work project it is necessary to check the stability of the slopes, taking into account specific hydrogeological conditions and the presence of a temporary load on the collapse prism.

Trenches with slopes, due to their large width at the top, can only be developed in undeveloped areas. In cramped conditions, trenches with vertical reinforced walls are mainly used. Depending on the depth of the trench, soil and hydrogeological conditions, the type (Table 5.4) and design parameters of fastening are selected.

Most widespread During the construction of drains, embedded fasteners are found that are installed in the trench as the soil is excavated. They consist (Fig. 5.9) of a pick-up, risers and spacers. Horizontal or vertical scaffolding is made from boards 4 cm thick, installed close to one another or with gaps (with gaps) equal to the width of the board.

Rice. 5.9. Embedded trench fastenings
a - horizontal staggered; b - vertical solid; c - inventory; 1 - pick-up boards; 2 - risers; 3 - spacers; 4 - bosses; 5 - runs; 6 - wooden boards; 7 - tubular frames; 8 - screw spacers

Horizontal intake boards (Fig. 5.9a) are supported by vertical risers, pressed against the walls of the trench by spacers. Risers made of boards at least 5-6 cm thick or pipes are installed at a distance of 1.5-2 m along the length of the trench. Spacers made of logs with a diameter of 12-18 cm or pipes are placed at 0.6-0.75 m 410 to the depth of the trench. In continuous vertical mounts(Fig. 5.9.6) the pick-up boards are united every 0.7-1.4 m by horizontal belts (purlins) pressed against the walls of the trench with spacers.

Inventory fastenings consist of standard, most often plank panels and metal tubular frames with screw spacers (Fig. 5.9c). These are prefabricated fastenings, so they are less labor-intensive and material-intensive compared to the considered wooden fastenings.

The development of trenches during the construction of a drainage network is carried out, as a rule, by single-bucket excavators equipped with a backhoe or dragline with a bucket volume of 0.25-1 m 3. A backhoe excavator provides higher productivity and digging accuracy, but has limitations on the size of the face. Therefore, when the trenches are large and deep, a dragline is used. To develop trenches with vertical reinforced walls, excavators with grab equipment are used.

Excavators continuous action have the highest productivity, but can only develop relatively narrow trenches with vertical walls, so their use is limited to separate installations, mainly cable networks.

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 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 2.8d)
Loose soils in deep trenches and soils with layers of quicksand	Vertical-solid (Figure 2.8e)

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 Development of excavations in soils, saturated with water(quicksands), should be carried out according individual projects, providing safe ways execution of works - artificial dewatering, sheet piling, etc.

2.8.11 Fastenings of pits and trenches should be dismantled from bottom to top, as backfill soil and simultaneously remove no more than two or three boards 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.

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 earthworks on the 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 backfilling of the cavities 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 using plank and sheet piling fencing (for example, using inventory boards for fastening 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.

Board 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.

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.