RU2379419C2 - Method of increasing bearing strength of piling - Google Patents

Abstract

FIELD: building.

SUBSTANCE: method of increasing bearing strength of piling involves two-stage forced feed of a hardening solution in a ground. At first the hardening solution is fed around the periphery of the secured piles. At the first stage, injectors are poled in a ground in parallel piles around the periphery of the secured piles at 0.5-2 m intervals, at a depth of projected impaction. Then through the injectors, the hardening solution is pressurised to ensure hydraulic fracturing of the ground. The feed is continued until adjacent impaction areas close up to form after hardening around the peripheral outline of the secured piles, a durable screen with broken ground structure reinforced by the hardening solution. The second stage involves feed of the hardening solution into the area within the peripheral contour including an interpile space which is ensured with using the pressurised injectors enabling for leak-free conditioning of the ground in the formed screen and in the closed-up piling field. The ground is transformed into a solid mass throughout all sites, including in the interpile space. The near-pile ground is treated as well.

EFFECT: higher efficiency of securing the pile base, increased degree of impaction and ground pressure on a lateral surface of the pile with simplified execution of works.

3 cl, 2 dwg

Description

The present invention relates to construction and can be used to strengthen the existing pile foundation in the reconstruction of buildings and structures, as well as to increase the bearing capacity of the newly constructed pile foundation.

A known method of construction of a pile foundation (AS USSR No. 1193239, publ. 11/23/1985, bull. No. 43), including separate deepening in the soil of the foundation elements to a part of the design depth, and then their joint immersion to full length.

The disadvantage of this method is the dependence of its effectiveness on the depth of the processed material in the process of driving the pile head. Therefore, an increase in bearing capacity is achieved by compaction of the soil only on a limited length of the upper part of the pile. The remaining length of the pile is compressed only by the soil pressure created when driving the pile. Thus, this method provides the effect of increasing the specific load only for short piles and is ineffective when using long piles.

There is also a method of strengthening the pile foundation (AS USSR No. 1162900, publ. 06/23/1985, bull. No. 23), including the separation of at least one pile from the grillage, and after separation, the application of horizontal alternating loads to her head with simultaneous supply of water to the annular funnel formed around the pile. After adding piles in the known method, the funnel is filled with a hardening solution.

The disadvantage of the method as. USSR No. 1169200 is a decrease in soil compaction with increasing depth and limitation of the compaction itself by the bending strength of piles. In addition, there is a complete loss of contact interaction of the side surface of the pile with the soil, which, even when using a hardening mortar, it is practically impossible to restore to the previous level due to the small amount of clearance formed when the pile is swayed.

The disadvantages of this method also include the complexity of the work while strengthening the pile foundation. The near-pile soil in such a foundation is not compacted enough, therefore, its resistance to the side surface of these piles is less than that of driven piles. After filling with a hardening solution, the piles become compressed only by natural pressure.

Closest to the proposed method is a method of increasing the bearing capacity of piles (RF patent No. 2275470, publ. 2006.04.27). The known method includes the filing in the soil between the piles and the base of the piles, the hardening solution soil is first under gradually increasing pressure until the formation of fracture cavities around each injector, and then under constant pressure.

The disadvantage of the method according to the patent of Russian Federation No. 2275470 is the low efficiency of compaction of the soil around the pile. This disadvantage is explained by the following reason. Since the soil around the driven pile is always more compacted, during hydraulic fracturing due to changes in the stress state, the crack path will bend and bend around this obstacle when approaching the compaction zone, finding weaker sections. In this situation, the soil around the pile may remain intact even if slotted directional injectors are used as tools. In the trajectory of least resistance, a crack with a subsequent increase in pressure can generally leave the compaction zone of the near-pile soil, that is, the process becomes ineffective and uncontrolled. Moreover, it is known that a multi-slit injector can work well only in isotropic homogeneous soils.

The technical problem solved in the present invention is to increase the efficiency of strengthening the pile foundation by increasing the degree of compaction and at the same time increasing the pressure of the soil on the side surface of the pile while simplifying the work.

The problem is solved in that in the method of increasing the bearing capacity of the pile foundation by supplying a hardening mortar under pressure into the soil, the solution is supplied in two stages: first, along the peripheral contour of the group of reinforced piles with a step of 0.5-2 m until a continuous curtain is formed, and then - to the area limited by the contour.

The proposed sequence of operations will allow creating around the piles an array of soil with desired properties due to the pressure value and the amount of solution supplied.

On soft soils, it is advisable to supply the solution through non-directional injectors, which are a pipe with a lost tip.

In denser soils, it is possible to drill wells both on the periphery of the group of reinforced piles and in the inter-pile space, into which a hardening solution is supplied under pressure in the same sequence.

The invention is illustrated by drawings, where in Fig.1 shows a diagram of the forces acting on the pile, and in Fig.2 is a diagram of the implementation of the method.

It is known that hanging piles with their lower end do not reach solid soil. They are held in soft soil by the forces of its resistance, applied to the side surface of piles and their soles. If the piles are surrounded on the side by weak soil, they usually tend to be deepened to a strong, slightly compressible soil. However, with a fixed pile length, the bearing capacity of such a foundation may be insufficient, for example, under conditions of increasing pressure during the reconstruction of the building.

Figure 1 shows such a pile. It cuts through soft soil and with its sole rests on the solid ground below. The vertical load applied to it is balanced by the reaction of the soil acting on the pointed part of the lower end of the pile and its resistance distributed over the lateral surface of its trunk τ = tgφ * σ (Coulomb friction proportional to the coefficient of friction and normal compression in the case of a granular medium). From this expression it follows that the pile can work well if the necessary compaction is created in weak surrounding soil, which increases the coefficient of friction on the contact surface and normal lateral pressure. Thus, an effective increase in the bearing capacity of a pile surrounded by soft soil can be achieved by increasing both components simultaneously.

Figure 2 shows the arrangement of piles and injectors for supplying a hardening solution.

The proposed method is as follows.

In the soil 1 parallel to the piles 2 along the periphery of the reinforced piles 2, injectors 3 are driven into the depth of the intended compaction in increments of 0.5-2 m. Then through the injectors 3 serves a hardening solution under pressure, causing hydraulic fracturing of the soil. The flow of the solution is continued until the adjacent areas of the seal 4 are closed with each other. In this case, hydraulic fracturing occurs in the soil with compaction and elimination of weak areas. Since the injectors 3 are located around the pile field, and their principle of operation is non-directional, compaction around each of them is carried out in a radial direction more or less evenly, forming soil compaction zones 4, similar in shape to cylindrical. After the solution has hardened along the peripheral contour of the reinforced piles, a reliable curtain is formed with a contaminated soil structure reinforced with a compacting solution. The second stage consists in supplying the solution to the area limited by the contour, including the inter-pile space, which is carried out using injectors 5. The formed curtain around the pile field allows the solution to be injected under high pressure. The maximum pressure is determined by the technical capabilities of the high-pressure pumps used, which are currently capable of developing a pressure of up to 20 atmospheres and the required magnitude of the increase in bearing capacity. The created curtain allows you to increase the bearing capacity of both pile bushes and free-standing piles.

In denser soils, wells are first drilled around the periphery of the reinforced piles and in the intra-pile space. And then the hardening mortar is supplied under pressure in the same sequence - first a curtain is formed, and then the solution is fed into the intrapile space. The solution can be supplied by means of non-directional injectors lowered into pre-drilled wells.

The injection injected under high pressure without leakage in a closed pile field is able to work out the soil in all its sections. The pressure value and the amount of injected hardening solution allows you to turn the entire inter-pile space, including near-pile soil, into an array with the properties we set.

As can be seen, the proposed method of increasing the bearing capacity of the pile foundation in comparison with the known ones along with the simplicity of its implementation has great potential for strengthening both by compaction of the near-pile soil and by increasing lateral compression with the same pressure over the entire depth of compaction. If it is necessary to increase the bearing capacity of the pile both along the lateral surface and at its lower ends, the injectors are driven to a depth exceeding the length of the pile by the calculated value of the soil gain. In the case of the construction of a new foundation on suspended piles using the proposed method, instead of long piles, it is possible to use shorter ones.

Claims (3)

1. A method of increasing the bearing capacity of a pile foundation, including feeding into the soil in two stages of a hardening mortar under pressure, first hardening the solution is carried out on the periphery of the reinforced piles, characterized in that at the first stage in the soil parallel to the piles along the periphery of the reinforced piles in increments 0.5-2 m injectors are driven into the depth of the intended compaction, then a hardening solution is injected through the injectors under pressure, causing hydraulic fracturing of the soil, while the flow of the solution is continued until the bottom compaction zones will not close with each other, to form a solid curtain with a variable soil structure reinforced by a hardening mortar after the hardening of the solution along the peripheral contour of the reinforced piles, the hardening mortar is fed into the zone limited by the peripheral contour, including the inter-pile space which is carried out with the help of injectors under pressure, providing the opportunity to work out the soil in the created curtain and in a closed pile field without leakage, turning it into a mass willows in all areas, including space mezhsvaynom and okolosvayny ground. 2. The method according to claim 1, characterized in that the solution is supplied through non-directional injectors. 3. The method according to claim 1, characterized in that previously, at the periphery of the group of reinforced piles and inside the inter-pile space, wells are drilled into which a hardening solution is supplied under pressure.

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