RU2310039C2 - Method and device for ground testing by rod punch - Google Patents

Abstract

FIELD: investigation of foundation soil in situ, particularly quick ground testing by applying static load thereto in prospecting shafts drilled in building under reconstruction and in construction pitches.

SUBSTANCE: method involves embossing die made as rod preferably having diameter d of 5-20 mm and provided with dynamometer in upper part thereof in ground under the action of static load applied thereto by operator's hand; recording depth of rod immersion in ground and die immersion force. Operator presses upon double-console arm secured to dynamometer. It has been found experimentally that at a given rod die cross-sections specific clay ground adherence or the square of internal sand friction angle tangent φ are proportional to depth h of die immersion and immersion force in clay ground F_c and in sand ground F_s generated as a result of rod die embossing. F_c=k₁·h·c, F_s=k₂·h²·tg²φ, where k₁ and k₂ are dimensional experimentally determined proportionality coefficients. Deformational ground characteristics are determined from experimentally established conditions, which fix that sand stress-strain modulus E_s is proportional to square of internal sand friction angle tangent φ and clay stress-strain modulus E_c is proportional to specific clay ground adhesion c. E_s=B·tg²φ, E_c=D c. It can be tolerated that B=60 MPa for sand, D=800 for loam and D=400 for clay at any sand particle size and porosity and at any clay ground consistence.

EFFECT: possibility to estimate ground deformability by stress-strain modulus determining by express-method.

3 cl, 6 dwg

Description

The invention relates to tests of soils by a static load in the pits of reconstructed buildings and in construction pits by the express method.

The method of testing with a rod stamp is that (see Fig. 1) a stamp in the form of a rod 1 (mainly with a diameter of d from 5 to 20 mm) is pressed into the ground by a static load developed by the hand of the tester by pressing on the rod located at the upper end of the rod 1 dynamometer 2 through the handle 3, with simultaneous fixation of the indentation force and the value of the immersion of the rod in the ground (see figure 2).

It was experimentally established that for a given cross-sectional size of the core stamp, the force F developed as a result of its indentation (below the upper layer of loosened soil) is proportional to the depth of immersion of the stamp h and the specific adhesion from clay soils or the square of the tangent of the angle of friction φ of sand (see Fig. 3 )

where: k ₁ and k ₂ are proportionality coefficients (the dimensionality of the coefficients arises due to the need to take into account the stamp cross-sectional dimension and the specific gravity of soil particles, that is, quantities whose values are, in principle, practically constant).

Both sandy and clay soils are dispersed (discrete) media consisting of separate disparate particles interacting only by their contacts. In sands, this interaction of particles is similar to the interaction of polyhedra (including spherical) under the action of friction forces resulting from a spread, under the influence of soil weight and transmitted load, and in clays, it is similar to the interaction of plates attracted by molecular forces. It is thanks to this interaction that the soil is resisted by external loads, and condition (1) can be approximately confirmed theoretically. For these reasons, soil compression should also be considered as the process of overcoming and restoring the ultimate equilibrium of soil particles at the micro level, occurring inside the soil, accompanied by the appearance of defects and their healing with a decrease in soil porosity. Therefore, the deformation characteristics of soils, called deformation modules, are actually a function of their strength characteristics. This is well confirmed by a comparison of the strength and deformation characteristics of soils.

Figure 4 shows the dependence of the deformation modulus of the sand E on the square of the tangent of the angle of their internal friction φ, obtained from the corresponding processing of the values of these experimentally established characteristics used in the current design standards.

The figure shows that such a dependence can be described with a high degree of certainty by the equation

where: B is the deformation parameter of the strength of the sand, equal to 60 MPa.

It is very important that the parameter B = 60 MPa has a constant value for all types of sand (from dusty to gravelly) at any density (porosity coefficients from 0.45 to 0.75), and therefore is a parameter of the sand particle system .

The deformation modulus of clay soils can likewise be expressed as a function of their basic strength characteristics — specific adhesion, according to FIG. 5, where such a relationship is constructed.

where: D is the deformation parameter of the strength of clay soils with water-colloidal bonds, equal for clays D = 400, and for loams D = 800.

The established ratios of the modulus of deformation of clay soils and their adhesion, as well as in sands, are valid for a wide range of changes in soil porosity (from 0.35 to 1.05) and yield index (0≤J _L <0.75), i.e., practically for any types of clay soils characterized by the presence of water-colloidal bonds and most often (80% or more) used as the bases of buildings and structures.

According to the claimed invention, the design of a stamp in the form of a rod, as established by experimental data, allows us to model the soil deformation process with its lateral surface and determine their deformation modulus by the data of its loading with a static load. The indicated feature of the invention is confirmed by the experimental data of figures 3, 4 and 5, as well as the dependencies (1), (2) and (3) obtained from them.

Since the working body of a stamp in the form of a rod according to the claimed invention is its lateral surface, an essential element is its development, that is, an increase in its area with a reduced cross-sectional area of the rod, which is realized through the use of a stamp rod with a diameter of 5 ... 20 mm, with a length 80 times the indicated cross-sectional size.

In order to increase operational reliability, the core stamp can be performed with a broadened head part, which provides a more rigid attachment of a mechanical spring dynamometer to it and creates a stop for removing the rod from the soil after testing.

The possibility of implementing the claimed invention with the implementation of its purpose is confirmed by the manufacture of its prototype (figure 2) and its practical application in Moscow and Kemerovo.

A prototype core stamp was made with a diameter of 11.2 mm (stamp area 1 cm ² ) and equipped with spring dynamometers 2 kN. The values of k ₁ and k ₂ were assigned in relation to the size of its cross section selected in the manufacture of the core stamp, taking into account the experimental corrections k ₁ = 0.9ω; k ₂ = 0.9ωγ (where ω is the perimeter of the cross section, γ is the specific gravity of the soil).

The performance of the manufactured core stamp can be illustrated by the example of evaluating the characteristics of soils in the pits of a house under construction in Krasnogorsk. In this case, the dipping of the stamp was carried out in various parts of the pit, the soils of which were visually different. Figure 6 shows the results of the most characteristic dependencies of the emerging force of indentation of the stamp on the depth of its immersion in the clay soils of these pits. The processing of these dependencies in accordance with formulas (1), (2) and (3) showed that the prevailing soils at the level of the base of the foundation plate of a house being built can be estimated as having specific adhesion from 14 to 18 MPa and a strain modulus E of 11 on average MPa Based on the materials of the performed surveys (including those with compression and shear tests) on the territory of this building, these characteristics are determined for adhesion of 12 ... 17 kPa and a deformation modulus of ~ 12 MPa.

Comparison of the data obtained when testing soils with a rod stamp with the survey data indicates their good convergence.

The technical result achieved by the claimed invention is the express method (method) and a device for its implementation, which allows to evaluate the deformability of soils by determining the modulus of their deformation. The specified device as a result of replacing standard flat type dies with a stamp in the form of a rod allows static soil loading to be carried out directly due to the strength of the hand of the tester. The claimed invention for the first time provides the creation of a convenient portable device for determining the module of soil deformation in the field.

The prototype of this invention can be considered described below previously published invention.

1. A known method of testing soil with static load [1]. This invention relates to tests of soils by static load during engineering surveys in construction, mainly by the express method, using flat and screw dies, as well as a shift meter and inventory piles. The indicated method of testing the soil with static load consists in screwing a screw pile spaced from the test point into the soil, moving the drilling rig to the axis of the rotator at the test point, drilling the well to a predetermined depth, and lowering it to the bottom of the well on the pipe string corresponding to the specified method test the working tip, after which on the upper end of the pipe string install a headband, a hydraulic jack, and then install a reference system and measuring instruments - indicator Ators and test the soil with the necessary number of load steps.

2. A known installation for testing soils with static loads [1], according to which a stamp with a stand is installed on the bottom of the pit, screw anchor piles are screwed into an undisturbed array (or leader wells). A hydraulic cylinder is installed on top of the rack. Then establish a benchmark system and begin testing. To do this, set the calibrated load corresponding to the first stage of the load. After the soil test is completed by the first stage of the load, another calibrated load corresponding to the second stage is installed on the site. Further loading is repeated to a predetermined value.

The previously proposed proposals on methods for field testing of soils with dies in pits and pits are very cumbersome and do not meet the requirements of express methods. The present invention aims to eliminate this disadvantage.

Information sources

1. Patent of the Russian Federation RU (11) 2212494 (13) С1 (51) Е02D 1/00 (54) “Method for testing soil with static load” dated September 20, 2003 Bull. Number 26.

2. USSR author's certificate (19) SU 1622506 A1 (51) 15 G02D 1/100 “Installation for testing soil static. load "from 23.01.1991, bull. Number 3.

Claims (3)

1. The method of testing soils with a rod stamp, which means that a rod stamp is made on the soil surface, made in the form of a rod of constant cross section along its entire working length with a dynamometer with a handle rigidly fixed at its upper end, then the stamp is pressed through the handle of the dynamometer into the ground and record the readings pressing force f _n and f with clay _n for sandy soils of a dynamometer, and the depth h of immersion of the stamp risks coated on its side surface, whereupon n Based on these indications empirically established relationships F _r = k ₁ · h · c; F _p = k ₂ · h ² · tg ² φ, determine the angle of internal friction φ of sandy soils and specific adhesion from clay soils, and the deformation moduli of sands E _p and clay soils E _g according to the formulas E _p = B · tg ² φ, E _g = D · c, where k ₁ , k ₂ , are the proportionality coefficients; In - deformation parameter of soil strength equal to 60 MPa, D is the deformation strength parameter of clay soils with water-colloidal bonds, equal to 400 MPa for clay and 800 MPa for loam. 2. The core stamp for soil testing by the method according to claim 1, in which the core stamp to ensure the accuracy of the results and facilitate its manual immersion is made in the form of a cylindrical rod with a diameter of 5 ... 20 mm, and the handle of the stamp in the form of a two-console element is mounted on a dynamometer crosswise at an angle of 90 ° with respect to the stem of the stamp. 3. The core stamp according to claim 2, characterized in that the core of the stamp is made with a broadened head, providing a more rigid attachment to it of a mechanical spring dynamometer and creating a stop for removing the core from the soil after testing.

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