RU2324788C2 - Method of compressing soil and device for its implementation - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention pertains to the field of construction, more specifically to the technology and equipment of compressing soil during construction of buildings and during renovation and reconstruction of already existing structures on dispersive binding or non-cohesive soil, as well as on piled (industrial) soil and slide slopes. The engineering problem of this invention is broadening of features due to compression of not only dispersed binding soil - clay, loam soil, sandy loam, but also non-cohesive dispersed soil - sand, as well as piled (industrial) soil due to the mode of infusion of mortar into soil with a chosen quality characteristic of the mortar, providing for its high penetrative capability, as well as use of media, providing for constructing soil structures reinforced by a common frame made from hardened mortar. In this case, there is increased bearing strength of the soil, effective holding in the soil structure of slide slopes with formation of a frame in it, as well as increased rate of production. This is achieved by that, the technique of compressing soil involves infusion of cement mortar through injectors in the form of perforated pipes with simultaneously opening caps on the perforations, achieved through a concrete slab on non-cohesive soil in the form of a tightening weight or tightening weights mounted on it, with hydraulic fracturing of the soil at hydraulic fracturing pressure between 3.0 and 20.0 atm. After hydraulic fracturing of the soil using cement mortar, there is compression of the soil by way of widening the fractures of the hydraulic fracturing due to infusion of the cement mortar. Infusion of the cement mortar for widening the fractures from hydraulic fracturing can be achieved continuously in pulsed mode. When installing injectors, distance between their longitudinal axes is chosen in the range 2.0-4.0 m at with an injection depth of 3.0-8.0 m. In case of compressing argillaceous water-bearing or water-logged loam soil and sandy loam, there is change, at least in one category, of their consistency due to compression and taking out the water in them. The injectors are laid out in series, while infusion of cement mortar into those series is done from the centre to the periphery, preferably in spiral form, successively in each injector or in steps after 1-3 injectors. A possible alternative is laying out the injectors in series, and infusion of the cement mortar is done successively from the centre to the periphery, preferably in radial form, successively in each injector or in steps after every 1-3 injector in radial form or with alternation between adjacent injectors in adjacent radial directions. In the device for implementing the above described technique, the engineering problem is solved based on that, the device for infusion of cement mortar is in the form of a pipe whose lateral surfaces are perforated. The perforations are covered by simultaneously opening caps at a given pressure of the cement mortar. The caps are in the form of overlapping perforation straps, located in spiral form or in form of a ring. The strap can be made of an adhesive layer, inverse to the perforated pipe, and the caps can be made from several layers of straps, the number of which is defined by the given value of pressure of hydraulic fracturing in the soil. In the device for infusion of cement mortar, the perforated tube is equipped with a non-destructible lower end cap at the hydraulic fracturing pressure.

EFFECT: design of a device for soil compression.

11 cl, 2 dwg, 2 ex

Description

The invention relates to the field of construction, and in particular to technology and means of compaction of soils during the construction of buildings and structures or during the repair and reconstruction of existing buildings and structures on dispersed bound or unbound soils, as well as on bulk (technogenic) soils and landslide slopes.

The closest known are the method and device for compaction of bound dispersed soils to create the foundations of buildings and structures by supplying a hardening mortar in the form of a sand-cement mixture, in which the solution is supplied at a pressure of 2-10 atm through injectors located in increments of 2-3 m in the form of perforated pipes immersed to the depth of the core (RU No. 2059044 C1, E02D 3/12, 1996).

Known technical solutions provide soil compaction on dispersed bonded soils, which limits the scope of their application, and the use of cement-sand mixture reduces the penetration of the solution, which negatively affects the bearing capacity of the compacted soil.

The technical task of the present invention is to expand the functionality by compaction of not only dispersed bound soils - clays, loams, sandy loams, but also unbound dispersed soils - sands, as well as bulk (man-made) soils due to the mode of pumping the solution into the soil when choosing a quality solution , providing its high penetrating ability, as well as the use of tools to create an array of soil reinforced with a single frame of hardened mortar. This ensures an increase in the bearing capacity of the soil, effective fixing in a single massif of landslide slopes with the formation of a skeleton in it, a decrease in the material consumption for the technological process, as well as an increase in the rate of work.

This is achieved by the fact that the method of compaction of the soil involves pumping cement mortar through injectors in the form of perforated pipes with simultaneously destructible perforation plugs, carried out through or under a concrete slab in the form of a load or placed on it with a load to ensure hydraulic fracturing of the soil at hydraulic fracture pressure 3.0-20.0 atm. In this case, after hydraulic fracturing of the soil with cement mortar, soil compression is performed by expanding hydraulic fractures due to the supply of cement mortar. The supply of cement mortar to expand hydraulic fractures can be carried out continuously in a pulsating mode. When injectors are installed, the distance between their longitudinal axes is selected from a range of 2.0–4.0 m with an injection depth of 3.0–8.0 m. In the case of compaction of clay flooded soils or water-saturated loams and sandy loams, a change of at least one category, their consistency by squeezing and draining the water contained in them. In the method of compacting the soil, the injectors in the plan are arranged in rows, as an option, and the cement mortar in their rows is supplied from the center to the periphery, preferably in a spiral plan, sequentially into each injector or in increments of 1-3 injectors. It is possible, as another option, the arrangement of injectors in the plan in rows, and when applying cement in their rows, carried out sequentially from the center to the periphery, preferably in a radial direction in the plan, sequentially in each injector or in increments of 1-3 injectors in the radial direction , or alternating between adjacent injectors in adjacent radial directions.

In the device for implementing the method of soil compaction described above, the task is achieved in that the device for injecting cement mortar is made in the form of a perforated pipe on the side surface, the perforation holes of which are plugged at the same time with plugs that are destructible at a given cement mortar pressure, made in the form of a tape covering the perforation hole, located in a spiral or in the form of rings. In this case, the tape can be made with an adhesive layer facing the perforated pipe, and the plugs can be formed by several layers of tape, the amount of which is determined by a given value of hydraulic fracturing pressure in the soil. In the device for injecting cement mortar, the perforated pipe is provided with a bottom end cap that is not destructible at fracturing pressure.

Figure 1 shows an injector with a perforated side surface, the openings of which are closed with destructible plugs (a variant of the spiral arrangement of the tape is the upper part and the variant of the ring arrangement of the tape is the lower part);

figure 2 presents the layout of the injectors in the plan and the direction of supply of the solution A in them - radially, B - in a spiral.

The method of compaction of the soil includes the injection of cement through injectors 1 in the form of pipes with holes (perforations) 2 on the side surface. Holes 2 are blocked by destructible plugs 3. The pressure providing hydraulic fracturing of the soil - 3.0-20.0 atm is determined in accordance with the expanded categories of soil and the features of fixing it on the slopes. A decrease in pressure does not lead to hydraulic fracturing, and an increase negatively affects economic performance, requiring high performance equipment and increasing the flow rate of the solution. The supply of cement mortar to expand hydraulic fractures can be carried out continuously in a pulsating mode. When installing injectors, the distance between their longitudinal axes is selected from the range of 2.0–4.0 m, which is due to work on various categories of soil with an injection depth of 3.0–8.0 m, which in some cases requires an extension of the injector in length. When compaction of clay flooded soils or water-saturated loams and sandy loams, the water contained in them is pressed and drained. With this compaction of the soil, the injectors in the plan are arranged, as an option, in rows, and the cement mortar in their rows is supplied from the center to the periphery, preferably in a spiral in plan (Fig. 2 - B), sequentially into each injector or in increments of 1- 3 injectors. Perhaps, as another option (figure 2 - A), the location of the injectors in the plan in rows, and when applying cement in their rows, carried out sequentially from the center to the periphery, preferably in a radial direction in the plan, sequentially into each injector or in steps of 1-3 injectors in the radial direction, or alternating between adjacent injectors in adjacent radial directions. The simultaneous destruction of the plugs ensures the formation of hydraulic fracturing in the soil in all directions. The plugs 3 are made in the form of an overlapping hole 2 of the perforation of the tape located in a spiral (figure 1) or in the form of rings. The tape of the plugs 2 is made with a sticky layer facing the perforated pipe. The plugs 2 are formed, as a rule, by several layers of tape, the amount of which is determined by a given value of hydraulic fracture pressure in the soil. In the lower part of the pipe, the lower end cap 4, which is not destroyed under hydraulic fracturing pressure, is placed.

The inclusion of sand and industrial soils in the field of application became possible due to the formation of hydraulic fractures, as without fracturing, the cement slurry penetrated into the pores of the sandy soil without compacting it. Pumping is carried out if there is a foundation plate and several (2-3) floors of the building over the fortified array. The base plate is a screen that prevents the solution from leaving the massif of soil, and the presence of several floors creates a load that allows you to create pressure, because in the absence of a slab and a load, the injection of a compacting solution leads to a rise (swelling) of the soil stratum above the injection point and sometimes to a breakthrough of the cement mortar to the surface. In order to ensure the formation of hydraulic fractures, the injectors are wrapped in tape, for example with adhesive tape, in several layers. The number of layers of adhesive tape depends on the required pressure at which fractures are formed. As a result of injection, the pressure in the hoses and the injector rises to the hydraulic fracturing pressure characteristic of this type of soil, and after the adhesive tape ruptures, the solution instantly enters the soil mass and forms hydraulic fractures. The pitch and depth of the location of the injectors depend on the properties of the soil stratum, the loads from the structure and the power of the compressible stratum. The injection volumes depend on the porosity of these soils and the load of a particular structure. If the finely dispersed cement mortar is too liquid, then hydraulic fractures do not form in sandy soils, but cement milk penetrates into the soil pores according to the principle of classical cementation. If the solution is too viscous, hydraulic fractures do not form at all and the walls of the well expand and the soil around the well becomes denser.

It is carried out as follows.

The foundation pit is opened to the level of the foundation plate. Standard concrete preparation is being arranged. After hardening of concrete preparation, leader wells are drilled from it. Injectors (a perforated pipe) with a diameter of 30-50 mm are lowered into the leader wells in increments of 2.5 × 2.5-3.0 × 3.0 meters to the depth of propagation of soft soils within the compressible zone. The connection of the injector and concrete preparation is varnished with a special cement mortar. The release of the injector above the foundation slab is 5-10 cm. After that, the reinforcing cage is knitted according to the design of the foundation slab. After arranging the foundation plate through the reinforcing cage, the injectors are built up with blind pipes so that the injectors rise 10-20 cm above the future foundation plate and the foundation plate is poured with concrete. Before lowering, the injector is wrapped with tape to create hydraulic fracturing pressure. After arranging the base plate, 2-3 floors of the building are erected to create the necessary load, because otherwise, the injection of the sealing solution will not lead to soil compaction, but to the rise of the building. The injection of cementitious cement slurry is carried out at a fracturing pressure characteristic of this type of soil. As a result, hydraulic fractures form 2-3 meters long in the most weakened areas of the soil mass. The compaction solution, which continues to enter the fractures, expands them and the expanding crack begins to work as an intramuscular jack, compacting an array of soil around itself. When compacting clay flooded and water-saturated loams and sandy loams, water is squeezed out and, accordingly, their consistency changes. The consistency of clay soils changes into 2 categories, i.e., if the soils were fluid plastic, they become stiff, and if soft, they are semi-hard. Frozen sealing solution in hydraulic fractures, which are interconnected, forms a single reinforced frame. After the injection process is completed, the valve installed on the injector is closed, because otherwise, the elastic deformations of the soil mass will be pushed out by the sealing solution through hydraulic fractures and the injector and the compaction will only partially occur. The valve remains closed until the sealing solution has set. After hardening of the sealing solution, the injector is cut flush with the foundation plate.

As a result of the actions taken, the following occurs:

- Dispersed soils are compacted, while clay dispersed soils at the same time change their texture to harder categories. As a result, all physical and mechanical properties are improved 1.5-2 times.

- The soil mass contains a hardened compacting solution, which forms a single reinforced cage, which increases (due to the presence of hard inclusions) indicators of physical and mechanical properties by another 1.3-1.5 times.

- Injectors, monolithic in the foundation plate, from which hard inclusions of the compacting mortar solidified in the hydraulic fractures are turned into root piles, which take part of the load. At the same time, experiments conducted to assess the bearing capacity of root piles show that their bearing capacity is at least 7-8 tons.

Thus, the resulting pile-frame system in a compacted mass of soil works as a whole and significantly increases the bearing capacity and reliability of the base as a whole.

The use of this particular pile-frame system in a compacted soil mass makes it possible, at lower material costs, to obtain a reliable and efficient-functioning base. Savings are achieved by increasing the pitch of the location of the injectors and reducing the injection volume. Reliability and efficiency are enhanced by the operation of root piles.

Example 1

In an array of weak soft-plastic loams, soil was strengthened under the foundations of the building under construction with a step of 3.5 m × 3.5 m to a depth of 5 meters. Through 160 injectors, a weakly viscous (liquid) solution was injected under the hydraulic fracturing pressure characteristic of these soils (12 atm). As a result, hydraulic fractures formed, which, with further injection, expanded and compacted soft-plastic loams. The hardened cement mortar formed a reinforcing cage in a compacted and improved soil mass.

Example 2

On a landslide-hazardous slope, folded with loose and refractory clay loams of natural composition, injectors are immersed with a step of 4 × 4 m to a depth of 3 to 8 meters and through them a low-viscosity cement mortar is pumped under a hydraulic fracture pressure of 7 atm. Further injection of cement mortar through hydraulic fractures leads to compaction of the soil and the formation of a single reinforcing cage, the presence of which will completely eliminate the possibility of a landslide.

Claims (11)

1. A method of compaction of the soil, including the injection of cement through injectors in the form of perforated pipes with simultaneously destructible perforation plugs, carried out through or under a concrete slab in the form of a load or placed on it with a load to ensure hydraulic fracturing of the soil at a fracture pressure of 3, 0-20.0 atm. 2. The method of compaction of soil according to claim 1, in which after hydraulic fracturing of the soil with a cement mortar, the soil is compressed by expanding the fractures of the hydraulic fracturing due to the supply of cement mortar. 3. The method of compaction of soil according to claim 2, in which the supply of cement for expansion of hydraulic fractures is carried out continuously in a pulsating mode. 4. The method of compaction of soil according to claim 1, in which the distance between the longitudinal axes of the injectors is selected from a range of 2.0-4.0 m with an injection depth of 3.0-8.0 m 5. The method of compaction of soil according to claim 2, in which when compaction of clay watered soils or water-saturated loams and sandy loams, they change at least one category of their consistency by squeezing and draining the water contained in them. 6. The method of compaction of soil according to claim 1 or 5, in which the injectors in the plan are arranged in rows, and the cement mortar in their rows is supplied from the center to the periphery, preferably in a spiral plan, sequentially into each injector or in increments of 1-3 injectors . 7. The method of compaction of soil according to claim 1 or 5, in which the injectors are arranged in rows in a row, and the cement mortar in their rows is supplied sequentially from the center to the periphery, preferably in a radial direction, sequentially into each injector or in steps of 1- 3 injectors in the radial direction or alternating between adjacent injectors in adjacent radial directions. 8. The device for injecting cement mortar by the method according to claim 1, made in the form of perforated along the side surface of the pipe, the perforation holes of which are plugged at the same time as plugs that are destructible at a given cement mortar pressure, made in the form of a spiral overlaying perforation tape located in a spiral or in the form of rings . 9. The device for injecting cement mortar according to claim 8, in which the tape is made with an adhesive layer facing the perforated pipe. 10. A device for injecting a cement mortar according to claim 8 or 9, in which the plugs are formed by several layers of tape, the amount of which is determined by a given value of the fracturing pressure in the soil. 11. The device for injecting cement mortar according to claim 1, in which the perforated pipe is provided with a bottom end cap that is not destructible at fracturing pressure.

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