In modern megacities, there is an increasing trend towards a more rational use of space and building compaction. These circumstances dictate certain conditions to construction companies. There are fewer and fewer free sites on the surface, which forces developers to resort to the construction of underground structures. Among other things, there are some objects that are more rational to build underground. These include large warehouses, shopping and entertainment complexes, as well as garages. But underground construction is a rather laborious process, which requires certain experience and appropriate equipment from construction companies.
The solution of the problem described above can be further complicated by the fact that the soil is very heterogeneous, it can contain voids of various sizes, underground water currents. Sometimes, when examining a territory for building, it turns out that the rocks are rather weak. It happens that underground there are all kinds of tunnels of engineering systems that are not mapped. It is enough to workoften in cramped conditions, as the foundations of neighboring buildings are located quite close to the construction site, and the walls of high-rise buildings do not allow crane booms to fully deploy.
Solving the issue of construction of underground structures
Depending on the hydrogeological characteristics of the area and how deep the premises will be, underground construction can be done in one of several ways. The most common are the "wall in the ground", the method of the fall well, as well as the open method. The first technology in modern realities is quite common and still continues to rapidly gain popularity, because with its help you can solve the problem in cramped conditions without bothering the foundations of buildings located nearby.
Technology principle
The wall in the ground is built according to a fairly simple principle, which involves preparing a trench and excavating the soil. Further, enclosing structures are constructed in the formed voids, for this, as a rule, reinforced concrete is used. Under the protection of the resulting systems, internal structures are equipped, such as the floor and other elements.
Varieties of method
Technology "wall in the ground" can be divided into several subspecies, such as: trench and pile. The first is the use of cast-in-situ concrete and reinforced concrete sections, with the help of which a single wall is formed. pilethe method involves the installation of bored supports, which are located in a continuous row. They allow you to form a solid enclosing structure. Whichever technology is used, it is more promising than alternative methods of building underground structures. It is advisable to use it in the reconstruction of existing buildings for any purpose.
Scope of application
The wall in the ground can be used when there is a need to build impervious curtains, subway tunnels, garages, warehouses, underpasses, reservoirs, all kinds of sedimentation tanks, road interchanges, as well as the foundations of buildings for various purposes.
Wet and dry methods
Considering the strength of the soil and its level of moisture, builders can choose a wet or dry construction method. The latter is not so expensive, because it does not need to prepare a clay solution. However, it can be resorted to only when there is confidence in the strength of the soil and the absence of underground currents. Wet technology is an ideal solution for the construction of large objects in water-saturated unstable soils. If the construction is accompanied by the described conditions, then sometimes it becomes necessary to additionally strengthen the walls of the trench. The end result is a strong and secure space.
Thixotropy
Whena wall is being built in the ground, the technology may involve the use of a wet method, in which such a concept as thixotropy is important. This property is inherent in the clay solution, which has the ability to restore its original shape without mechanical impact. Due to this, a properly selected suspension will gain strength during the construction phase and liquefy from vibrational influences. This allows you to insure the walls of the trench from deformation. The highest thixotropic qualities are characteristic of bentonite clays.
If we consider the additional characteristics of such solutions, then you should pay attention to their water-repellent quality. After the suspension has hardened, hydrostatic pressure will act on the surface of the walls, which contributes to the formation of a waterproof film. Its thickness can vary from 1.5 to 5 millimeters, which is enough to protect the structure from water. Wall cladding allows saving on water reduction of sheet pile driving. This is one of the many advantages of the described technology.
Applied equipment
When a wall is created in the ground, the technology involves the use of appropriate equipment. It allows you to dig a trench. For this, a continuous device is most often used. Similar results can be demonstrated by the cyclical approach. To form a trench, earthmoving machines are usually used, namely: bucket, plow, milling machines, draglines,drilling rigs for rotary and percussive drilling, grabs, as well as backhoes. The listed equipment will be quite enough to obtain a wall in the ground, which can be deepened by 100 meters. The conditions for this can be completely different. The "wall in the ground" method most often assumes that the width of the trench will be equal to the limit from 1 to 1.5 meters. In some cases, projects are drawn up in which the width reaches 2 meters.
Inappropriate Methods
Undoubtedly, the described technology has many advantages, but it is possible to single out situations where the use of the method is inappropriate. The construction of a "wall in the ground" is not carried out if there are strong underground currents in the soil, with loose soil, as well as when there is dilapidated masonry on the site. The technology should not be used when there are metal islands, as well as large fragments of concrete. When there are voids and cavities in the soil, you should also not start work on the described technology.
Anti-filtration curtains
Manipulations to create impervious curtains can be considered as simple as possible. They are performed using heavy and hard clays, as well as monolithic concrete. The purpose of curtains is to protect the object from water. Most often, such elements are used in the equipment of dams and digging pits. In the latter case, curtains are necessary to prevent the penetration of water into the cavity. The workers will not face the task of lowering the level of groundwater, which is a rather laborious procedure. If ato compare the air curtain with reducing installations, then the latter operate temporarily while work is underway. Structures with curtains will not be afraid of the most powerful groundwater flows.
Grip Options
Before the foundation "wall in the ground" is built, it is necessary to calculate the length of the grip. This parameter will be influenced by some factors, among them:
- trench stability;
- design features and functional purpose of the structure;
- a kind of technique that is used to develop a trench;
- calculated intensity of concreting.
Work technology
The construction of a wall in the ground begins with drilling a well, after which trenches are prepared, which are simultaneously filled with mortar. The next step will be the installation of reinforcing cages, as well as a concrete pipe. The final manipulations involve the displacement of the clay solution by supplying the concrete mixture through a vertically movable pipe. Trenches can be developed in full length or in separate sections. Reinforcing cages are based on corrugated steel rods. The resulting system should be less than 12 centimeters compared to the width of the trench. Elements are wetted with water prior to installation as this reduces the volume of sticky clay and increases adhesion to concrete.
Concreting
The construction of a wall in the ground involves concreting, which is carried out using the method of a movable pipe. The latter has a diameter ranging from 270 to 300 millimeters, whilewall thickness is 10 mm. Given the volume of the pipe, the neck is selected, and the wads can be made of burlap.
Cuff limiters
The construction of a wall in the ground may involve deepening the trench 15 meters or less. In this case, pipes should be used, the diameter of which is 50 millimeters less than the width of the trench. 5 hours after concreting, the elements must be removed, and the resulting cavities are filled with a mixture. If the depth of the trench is greater than the mentioned parameter, then there will be a need to install a limiter. Its task is performed by a metal sheet, which is strengthened to the reinforcing cage. The canvas can be strengthened by welding beams to it.
Increased productivity
When the "wall in the ground" method is used in the construction process of a fairly large object, and the length of the grip is more than 3 meters, it may be necessary to supply large volumes of concrete mix. In this case, it enters through pipes, and for faster and easier installation, the plasticity of the solution is increased by plasticizers. The composition is poured in such a way that its surface overlaps the entire structure by 10 centimeters. This is required in order to be able to subsequently remove the contaminated layer of concrete, because it will have a large amount of clay. Compaction will need to be done using special equipment, which is fixed on a concrete pipe. If its length is more than 20 meters, then it is recommended to use two vibrators.
Those pipes that will be on the border of the grips are always removed. Important rightdetermine the extraction time. If this is done too early, the edges of the shell may be damaged. If the pipe is removed too late, it may become stuck between the concrete and the ground. In order to exclude such processes, sheet iron is often used instead of a pipe, with which you can create non-removable strong jumpers. They must be welded to the reinforcing cages. To protect the mouth of the trench from deformation and shedding, it is necessary to equip the foreshaft, which is the head of the trench.
About ground pressure
If you need to know what is the soil pressure on the wall at depth z, then you can use the following formula: PR=PS + PQ, where PS is the intensity of the lateral pressure at the indicated depth from its weight of the soil, taking into account the stratification of layers, action water, as well as effective adhesion; PQ is the intensity of the lateral pressure at the mentioned depth from surface loads. If, according to the project, the fore-mine is located on a specially formed dump above the surface of the earth, then the value is taken with a minus sign.
