Development and fastening of trenches. Fastening the walls of the trenches Fastening the walls of the trenches with inventory boards

Formation of slopes of the pit

Construction company BEST-STROY (Moscow) performs a full cycle excavation devices: excavation, digging, slopes, wall fastening, arrangement of a spacer system or ground anchors, pile foundation.

On the construction site marking is carried out in accordance with the technological map of the excavation: the perimeter, access roads for the removal of soil and the place of storage of rock for backfilling. Transportation of special equipment to the site is carried out: excavators, bulldozers, loaders. All buildings, outdoor and hidden communications located on the territory of the site are subject to transfer or demolition in agreement with the relevant organizations. Tree felling and site planning are also carried out.

Excavation

After the completion of the preparatory actions, the special equipment proceeds to the main earthworks at the pit. Highly efficient mechanized allows you to excavate the full volume of the pit in as soon as possible. Excavated soil partially remains within the construction site for backfill sinuses during the construction phase of the building. The volume of rock to be left is known from previous calculations for the project. For the rest of the volume, the soil is transported by dump trucks to the disposal site.

Earthworks and sheet piling of excavation walls with pipes with board pick-up

Calculation of the volume of the pit and removal of soil

When calculating the excavation of rock, the effect of loosening during digging is taken into account. The density of centuries-old compacted sedimentary rocks is disturbed when digging with an excavator and when moving to a dump or to a dump truck. Depending on the type or types of developed soils, a correction factor of 20-30% is given. Thus, for example, if the length of the pit is 70 m, the width is 30 m and the depth is 5 m with straight grooved walls on a planned area, then the calculation of the volume of the pit gives us a value of 10500 cubic meters. But for the removal of soil, it is necessary to calculate the volume more, at least by 20%: 70x30x5x1.2 = 12600 cubic meters. The implementation of slopes increases the volume of the pit and excavated soil, but the same amount often goes into backfilling, so it is not taken out of the construction site.

Walls and slopes of the pit

In favorable conditions, if the soil is especially dense and the depth is up to 2 meters, they dig a pit with vertical walls without fastening. If the soil is clayey - up to a depth of 1.5 meters, sandy loam and loam - up to 1.25 meters, bulk and sandy - up to 1 meter.

If necessary, a pit device to a depth of 5 meters, above the level ground water- the SNiP table comes to the aid of the designer, giving the dependence of the slope angle (height to foundation ratio) on the type of soil and the depth of the pit.

Table 1. The steepness of the slopes of the pits

In the case of nearby structures, groundwater and the need for dewatering, soils with an uneven structure, a pit depth of more than 5 meters, it is necessary individual calculation angle of slopes or wall fixings.

Fixing the walls of the pit

Fastening vertical walls performed during the construction of pits in loose and water-saturated soils. The fastening protects not only from the collapse of the excavation walls, but also prevents the soil from shifting under the weight of neighboring buildings, protects their foundations from deformation.

The following wall strengthening technologies are used:

• Sheet piling - sheet pile from rolled metal:
  • from pipes, with a pick-up from a board or without it,
  • rolled profile, with or without pick-up,
  • specialized sheet pile Larsen.
• Reinforced concrete structures:
  • tangent and secant piles,
  • wall in the ground.

All of the above technologies are applied before digging a pit. The deepening of the fence is carried out along the perimeter of the excavation strictly in accordance with technological map. Under certain conditions, pre-drilling of wells is carried out: ensuring the verticality of immersion, reducing vibration effects through the ground on the bases of closely spaced structures during driving.

Sheet piling made of pipes with a strapping belt made of rolled metal

The most resource-saving method is the immersion of pipe piles. This material is cheap and has a high turnover, that is, the possibility of repeated use. Pipes are plunged by driving with a diesel hammer or hydraulic pile driver, as well as using a vibratory driver. Alternative way- immersion using a pile drilling rig using the indentation and screwing method.

A pick-up is arranged in case of critical spillage of rock between sheet piles, from a board 40-50 mm thick.

Fencing of the excavation from the Larsen sheet pile

If necessary, dewatering measures are used sheet piling from Larsen sheet pile. Each of these sheet piles has a trough-shaped strong profile and lock grooves for rigid connection with each other. Thus, it is possible to form a strong and sealed wall arbitrarily long. Immersion is performed by driving or vibration immersion. Larsen sheet piling, as well as pipes and rolling profile, are usually removed after construction is completed, backfilled, and reused at other sites. Sometimes it is not removed, and then the fence is arranged from a special left profile.

Fixing the walls of the pit 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 walls of the pit with secant piles and ground anchors

Tangent and bored secant piles are made by drilling, reinforcing and concreting with a diameter of 400 to 1500 mm and a depth of up to 45 m. First, a forest shaft is prepared along the perimeter of the pit - a small reinforced trench-conductor. Odd wells are drilled in it with a step of 0.9 diameter between the side edges of the wells. fill concrete mix. By the time the even-numbered holes start to be drilled, the concrete has already set and the auger of the drilling rig cuts two adjacent odd-numbered piles, making a hole for the even-numbered one between them. Then, a pre-prepared reinforcing frame, welded from a special reinforcing rod and wire, is immersed in the well and concreted. As a result, after the concrete hardens, a very strong monolithic reinforced concrete wall is obtained. At the next stage, the digging of the pit takes place with the finished w-b fastening wall.

Technological scheme of the construction of the wall in the ground, and the subsequent development of the pit

The "Wall in the ground" technology provides high-strength fencing and fastening of the walls of the pit with a thickness of 300 to 1200 mm and a depth of up to 60 m. Complex special equipment is used - a clamshell installation. The grapple is a narrow, wall-width, two-bucket earth-moving tool, immersed in the ground on a rigid rod or suspension, with a hydraulic or chain hoist drive. The developed trench is protected from collapse by clay bentonite mortar. Upon reaching the design depth, the reinforcement 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 (captures) through one. The second queue breaks the intermediate grips and get monolithic wall. After the concrete has gained strength, you can dig the pit.

The device of the spacer system of the pit

Despite all the engineering tricks, sometimes, especially for deep excavations in difficult soil conditions and dense urban development, sheet piling may not be strong enough to hold the pressure of the soil mass.

On the last step erecting a pit, 2 technologies for fixing fences come to the rescue.

View of the expansion system of the excavation near the highway and neighboring buildings

The first of these is the spacer system. A strapping belt made of rolled metal is installed along the perimeter, which evenly distributes 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 the exact mechanical calculation and are set out in the PPR (work plan).

But the spacer system steals inner space recess, which was arranged specifically for free maneuver in the process construction works. Particularly loaded structures of spacer systems create incredibly cramped conditions for builders. This reduces productivity and lengthens the delivery time of the facility.

The device of ground anchors (anchors)

The BEST-STROY company recommends the use and fastens sheet pile walls with ground anchors that take on the pull-out load from the rock mass. This method is not much more laborious and slightly harder device struts, but in the end gives unlimited operational space, turns into significant savings in resources, increased productivity and reduced construction time.

Ground anchor mounting scheme

As a result of carefully conducted research and settlement work wells are drilled in the walls of the pit, the “anchor” is made, the traction is fixed, and it is fixed on the anchored sheet pile. It is important to take into account the location of the bases of nearby structures and buildings.

Facing pits and trenches can be done as follows:
a) vertical facings, consisting of a system of vertical bearing posts, the space between which is sheathed with horizontally arranged elements. The fastening is installed after excavation of the soil from the pit or trench without first fixing the walls;
b) vertical retaining structures. The fastening consists of a vertically placed sheet pile, which is installed before or parallel to the excavation and secured with horizontal braces or special pile nozzles;
c) load-bearing sheet pile walls. They are constructed from vertical load-bearing sheet piles, which are driven into the ground until it is excavated, and then unfastened by horizontal struts. Pole anchoring is possible;
d) fastening with special plates. The lining of the walls of the pits is carried out with specially made large-sized slabs, installed immediately after excavation. Their fastening is carried out by vertical or horizontal bearing elements, which can be additionally secured with spacers.
When constructing deep pits with vertical walls in residential, industrial and agricultural construction before installation load-bearing structures the walls must be lined with protective elements coated with various film materials.
In accordance with the above classification, their areas of application are distributed as follows:
a) for small and medium-sized pits;
b) limited width of the construction site;
c) the proximity of the building soil;
d) in conditions that exclude the possibility of concussions. The types of claddings described in this chapter are only applicable
in conditions of limited inflow of groundwater. The groundwater level should be below the bottom of the pit. If necessary, dewatering should be carried out in a closed way.

3.1. FASTENING PIT WALLS WITH HORIZONTAL ELEMENTS

The method of fastening the walls of pits appeared a very long time ago and is still widely used in the construction of small and complex objects. It is used when, according to soil conditions, the height of the loose part of the wall should not exceed 0.5 m, and the elevation of the bottom of the pit is above the groundwater level. Facing the vertical walls of the pits with a horizontal sheet pile is used in cases where two parallel walls of the pit are slightly removed from each other. The design of such walls consists of:
horizontal - wooden, metal or reinforced concrete elements;
vertical posts made of round wooden posts or steel beams;
horizontal or inclined braces wooden round timber or beams, steel beams or screw struts for narrow trenches;
elements providing local rigidity of the structure, consisting of additional racks and struts.
The following advantages of fastening racks with horizontal elements can be called:
the possibility of arranging pits of complex configuration;
small mass of individual building elements;
possibility of multiple 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 a large number cross struts;
the need to re-stability during disassembly and reassembly of struts;
the possibility of loss of stability of the walls when removing the spacers in the process of construction work.

Rice. 3.6. Fastening the vertical walls of a wide pit
a - driving a guide trench; b - the device of the bearing element with its anchoring; c - support of the walls of the pit on load-bearing element; d - top view of the anchor fastening; 1 - anchor made of round steel; 2 - spacers; 3 - metal bearing racks; 4 - racks; 5 - sheathing; 6 - traverse; 7- cross beam; 8 - wedges

3.1.1. Trench linings.
When implementing a structure 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 sheathing must be at least 50 mm;
wooden posts with a 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;
wooden stud diameter round section must be at least 100 mm and have a chamfer at the ends.
For sheathing the walls of trenches, boards are usually used 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. For each individual section of the sheathing, it is allowed to use boards of only 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 braces 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 at least two spacers to be placed along their length. On fig. 3.2 shows the design of the fastening of the walls of the trench for laying the pipeline, made of boards. Structural solutions for the construction of a manhole 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 racks that can absorb large bending moments. On fig. 3.4 shows a solution that eliminates the need for a bottom brace. In this case, in addition to the usual short racks, long vertical racks, having greater strength, and the lower struts are attached at a greater height from the bottom of the trench.
On fig. 3.5 shown constructive solution fixing the walls of the trench for laying a steel pipeline with a diameter of 800 mm. Racks for fixing the horizontal cladding are made of metal profiles. Metal tubular spacers with a diameter of 60 mm and a wall thickness of 4 mm are laid in the base (Fig. 3.5, a) and two wooden spacers are installed in the upper part of the trench. This provides the space needed for the pipeline installation work. For the installation of individual sections of the pipeline, sections 6 m long were provided, on which spacers were not installed. Pipes were laid in a trench in these places and then stretched to the installation site.
On fig. 3.5,c shows a plan of the site on which the lowering of individual pipe sections is carried out. After excavation, special metal frames are installed in the trench, eliminating the possibility of wall collapse.
Served as the bottom brace concrete base trenches into which the lower ends of the racks were brought.
If the edge of the trench provides for the movement of vehicles or construction mechanisms, the vertical fastening of the walls of the trenches must be strengthened.
In this case, the upper struts should be located at a depth of not more than 0.5 m from the ground surface, and if the road for transport 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. Fixing 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 structures described above with horizontal cladding elements. Fixing the walls of the pit is carried out by two methods:
1) a slit-like trench is constructed along the perimeter of the future pit, the walls of which are fixed by 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 is excavated, which lies at the base of the slope, its subsequent fixation with sheathing, which is unfastened to the existing structure (Fig. 3.7).
On fig. 3.8 shown phased implementation works according to the first option during the construction of a railway bridge in conditions of incessant traffic. Initially, two slit-like slots were developed with their fastening by horizontal skin. After completing this stage of work, numerous wooden struts were installed. Durable 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. On fig. 3.9 shows the structural solution of 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 pipelines and technological gaps that ensure all construction work. 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 for D > 0.5 m.

The width of the trench along the bottom can be specified in the project for the production of works, but should not be less than 0.7 m.

The trenches are torn off with inclined or vertical side walls. Vertical wall trenches are more economical. However, due to the danger of soil collapse, their greatest depth in dense soils without special calculations and fastening of the walls should not exceed 2 m. Therefore, trenches with slopes (with inclined walls) are mainly used, the greatest steepness of which is 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, it is necessary to check the stability of the slopes in the project for the production of works, taking into account specific hydrogeological conditions and the presence of a temporary load on the collapse prism.

Sloped trenches, 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 the design parameters of the fastening are selected.

The most widespread in the construction of gutters are embedded fasteners installed in the trench as the soil is developed. They consist (Fig. 5.9) of a pick-up, risers and spacers. A horizontal or vertical fence is made of boards 4-6 cm thick, installed close to one another or with gaps (with gaps) equal to the width of the board.

Rice. 5.9. Embedded trench fasteners
a - horizontal apart; b - vertical solid; in - inventory; 1 - pickup boards; 2 - risers; 3 - spacers; 4 - bosses; 5 - runs; 6- wooden shields; 7 - tubular frames; 8 - screw struts

The horizontal boards of the pickup (Fig. 5.9, a) are supported by vertical risers pressed against the walls of the trench by spacers. Risers made of boards with a thickness of at least 5-6 cm or pipes are installed at a distance of 1.5-2 m along the length of the trench. Spacers from logs with a diameter of 12-18 cm or pipes are placed through 0.6-0.75 m 410 in the depth of the trench. In continuous vertical fastenings (Fig. 5.9.6), the pick-up boards after 0.7-1.4 m are combined with horizontal belts (runs) pressed against the walls of the trench by struts.

Inventory mounts consist of standard, most often plank shields and metal tubular frames with screw struts (Fig. 5.9, c). These are collapsible fasteners, so they are less labor-intensive and material-intensive compared to the considered wooden fasteners.

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. The backhoe excavator provides more high performance and digging accuracy, but has limitations on the size of the face. Therefore, with a large width and depth of trenches, a dragline is used. For the development of trenches with vertical reinforced walls, excavators with clamshell 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 laying, mainly cable networks.

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 fasteners from steel pipes they are made in trenches with vertical walls 0.8-1.8 meters wide, while pipes with a diameter of about 60 millimeters and a length of up to 3 meters are used (for longitudinal elements of ladder fastening).

Cross braces inventory fasteners have threaded sections, by turning the screws on which it is possible to increase the length of the spacers, 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. So that the earth does not destroy the sheet piling in the trenches with a two-sided device, spacers are made in the places where the sheet piles are packed. 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. With a small amount of work, simple wooden or steel-rolled copras 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 in them is the force of free fall of the hammer or the force of pressure 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.

Scope of work: 1. Arrangement and dismantling of trench fastenings inventory shields.

Meter: 100 m2 fixtures

Fastening with inventory boards of trench walls up to 2 m wide in soils:

1-171-1 unstable and wet

1-171-2 resistant

Table 311 - Group 171 Codes 1 to 2

Group 172 Fastening the walls of pits and trenches with boards

Scope of work: 1. Fastening the walls of pits and trenches with boards, cleaning the walls and preparing fasteners. 2.Disassembly of fasteners.

Meter: 100 m2 fixtures

Fastening with boards the walls of pits and trenches with a width of more than 2 m, a depth of up to 3 m, in soils:

1-172-1 unstable

1-172-2 resistant

1-172-3 wet

The same, with a depth of more than 3 m, in soils:

1-172-4 unstable

1-172-5 resistant

1-172-6 wet

Table 312 - Group 172 Codes 1 to 3

Table 313 - Group 172 Codes 4 to 6

Group 173 Drainage

Scope of work: 1. Drainage from pits with an area of ​​up to 30 m 2. Drainage from trenches up to 2 m wide along the bottom for strip foundations for buildings and structures, as well as for intra-factory and yard [intra-quarter] communications.

Meter: 100 m3 of wet soil

1-173-1 Drainage from trenches

1-173-2 Drainage from pits

Table 314 - Group 173 Codes 1 to 2

Development of seasonally frozen soils

Group 187 Snow removal from construction sites and roads

Scope of work: 1. Snow removal by mechanisms. 2.0 manual cleaning of places that are inaccessible to mechanisms, with snow transfer to a distance of up to 3 m, or loading onto vehicles[norms 5,6].

Meter: 1000 m3 of snow

Snow removal from construction sites and roads:

1-187-1 auger snow blowers

1-187-2 snow plows on a tractor

1-187-3 bulldozers with a distance of up to 20 m

1-187-4 bulldozers with movement for each subsequent 10 m, over 20

1-187-5 manually, loose snow

1-187-6 manually, dense snow

Table 315 - Group 187 Codes 1 to 3

Table 316 - Group 187 Codes 4 to 6