RU2502847C1 - Method to determine bearing capacity of pile - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: continuously rising impressing load at a model pile is applied with permanent speed, and its value is accepted depending on diameter of the model pile, moisture, limits of plasticity and coefficient of soil porosity under a lower end of an experimental pile, based on the formula. Registration of the impressing load and settling of the model pile is carried out continuously with error of 100-200 N for the impressing load and 0.005-0.010 mm for pile setting. According to the data of registration of the impressing load and setting of the model pile, a curve is built for dependence of model pile setting speed on the impressing load, which is broken into three sections - 1st section with the permanent linear speed of model pile setting, 2nd section with non-linearly increasing speed of model pile setting that is 5-10 times higher than on the 1st section, and the 3rd section with the speed of model pipe setting that is 5-10 times higher than on the 2nd section, and the bearing capacity of the natural pile in the structure foundation is calculated using the data of the curve of dependence of model pile setting speed on the impressing load according to the formula.

EFFECT: higher validity and accuracy of determination of bearing capacity of a natural pile in a structure foundation and reduced labour costs.

1 tbl, 2 dwg

Description

The invention relates to the field of engineering surveys and is intended, in particular, to determine the bearing capacity of natural piles in the foundation of structures.

A known method of determining the bearing capacity of piles [GOST 5686-94. Soils. Field test methods by piles. - M.: Publishing. Standards, 1996], which includes application of a pressing load on a model pile with steps with each holding in time until the pile is conditionally stabilized. For the bearing capacity of the piles take the value of the pressing load of the last stage, after which there is a continuous increase in the pile upset [SP 24.13330.2011 Pile foundations. Updated version of SNiP 2.02.03-85. - M .: 2011. - 85 p.].

The method has the following disadvantages:

- the mode of applying the pressing load in steps with holding until stabilization of the pile upset does not correspond to the loading mode of the piles in the foundation during the construction of structures, in which the load increases almost constantly [Rossikhin Yu.V., Bitainis AG Precipitation of buildings under construction. - Riga: Zinatne, 1980. - 339 p.];

- indefinite duration of tests, as before the start of the tests, the number of stages and the exposure time of each stage of the load to stabilize the pile upset are not known;

- for the bearing capacity of a natural pile in the foundation of the structure, the value of the pressing load is taken, at which continuous settlement of the pile occurs and, accordingly, the loss of its bearing capacity;

- low reliability and accuracy of determining the bearing capacity of piles of natural piles in the foundation of the structure.

Closest to the claimed invention is a method for determining the bearing capacity of driven piles [Auth. USSR for invention No. 505769 E02D 3/00, E02D 33/00 and G09B 25/00, BI No. 9, 1976 (prototype)], including the application on a model pile of a continuously increasing load until it moves at a speed of 0.02-0, 03 m / min. The load corresponding to this speed is taken as the ultimate carrier and is modeled on a real (natural) pile according to the formula

$$P_P=P_M\frac{U_P}{U_M},\left(\mathrm{one}\right)$$

where P _P is the bearing capacity of a real (natural) pile;

P _M - ultimate load on a model pile;

U _P and U _M are the perimeters of sections, respectively, of real and model piles.

This method has the following disadvantages:

- immersion of a model pile in the soil is made by a continuously increasing load without taking into account its size and properties of the tested soils [Denisenko VV, Lyashenko PA, Snezhkin BA Features of the behavior of clay soils under compression with an ever-increasing load // Sat. scientific Tr. Hydroproject, 1990, issue 143. - S.161-166] with an arbitrary speed before the movement of the pile at a speed of 0.02-0.03 m / min, which eliminates the possibility of consolidation of the soil around the pile and reduces the value of its bearing capacity;

- when determining the bearing capacity of real (natural) piles, the ratio of the lengths of model and real piles is not taken into account; Estimated loading times of model piles and real piles in the foundation of the structure; the maximum permissible value and the rate of settlement of a real pile in the foundation of the structure, taken from the building code, depending on the structure of the building or structure;

- for the bearing capacity of a real (natural) pile in the foundation of the structure, the value of the pressing load is taken, at which continuous pile settlement occurs at a speed of 0.02-0.03 m / min and, accordingly, the loss of its bearing capacity;

- low reliability and accuracy of determining the bearing capacity of a real pile in the foundation of the structure.

The objective of the invention is the approximation of the test conditions of the model pile to the working conditions of a natural pile in the foundation of the structure.

The technical result of the invention is to increase the reliability and accuracy of determining the bearing capacity of a natural (real) pile in the foundation of the structure and reduce labor costs.

The technical result is achieved by the fact that in the method for determining the bearing capacity of a pile, including applying to the model pile a continuously increasing pressing load until the loss of its bearing capacity, recording the pressing load and draft of the pile and calculating the bearing capacity of the natural pile in the foundation of the structure:

a continuously increasing pressing load on the model pile is applied at a constant speed, and its value is taken depending on the diameter of the model pile, humidity, ductility limits and soil porosity coefficient under the lower end of the model pile according to the formula

$$U_m=\mathrm{0,048}{\mathrm{<figure-callout\; id="2"\; label="D\; m"\; filenames="00000020.png"\; state="\{\{state\}\}">D\; </figure-callout>}}_m^{}{10}^{0.106+8.60/I_P-\mathrm{1,1}W/W_L+1.01e}\left(2\right)$$

where 0,048 is an empirical coefficient, kPa / min;

U _m is the speed of continuously increasing pressing load, kN / min;

D _m is the diameter of the model pile, m;

I _P is the number of soil plasticity under the lower end of the model pile;

W and W _L - natural humidity and moisture at the yield strength, respectively, of the soil under the lower end of the model pile;

e is the coefficient of porosity of the soil under the lower end of the model piles,

registration of the pressing load and draft of the model pile is carried out continuously with an error of 100-200 N for the pressing load and 0.005-0.010 mm for draft of the pile,

according to the registration data of the pressing load and draft of the model pile, a graph is plotted of the rate of draft of the model of the pile on the pressing load, which is divided into three sections - to the 1st section with a constant linear speed of draft of the model pile, to the 2nd section with a non-linearly increasing rate of draft of the model piles are 5-10 times larger than in the 1st section, and in the 3rd section with a model pile settlement rate of 5-10 times greater than in the 2nd section, and the bearing capacity of a natural pile in the foundation of the structure is calculated with used eat a graph of data rate precipitation model piles are pressed by the load by the formula

$$F_n={\alpha }_f{F}_m,\left(3\right)$$

where f _n - the bearing capacity of a natural pile in the foundation of the structure;

F _m is the bearing capacity of the model pile, defined as the value of the pressing load at the end of the 2nd section of the graph of the deposition rate of the model pile on the pressing load;

α _f - the coefficient of similarity of the bearing capacity of the model piles and natural piles in the foundation of the construction of piles

$${\alpha }_f={\left(\frac{L_n}{L_m}\right)}^2\frac{D_n}{D_m}\frac{t_n}{t_m}{\left(\frac{S_n}{S_m}\right)}^{-\mathrm{one}}{\left(\frac{V_n}{V_m}\right)}^2$$

where L _m and L _n are the lengths of the model pile and natural pile in the foundation of the structure, respectively;

D _m and D _n - respectively, the diameters of the model piles and natural piles in the foundation of the structure;

t _m and t _n are the calculated duration of the test model piles and loading of natural piles in the foundation of the structure;

S _m - increment of draft of the pile on the 2nd plot of the graph of the rate of draft of the pile on the pressing load before the exhaustion of the bearing capacity of the model pile;

S _n - the maximum draft of natural piles in the foundation of the structure, taken from the building code, depending on the structure of the building or structure;

V _m is the average sedimentation speed of the model pile in the 2nd plot of the graph of the dependence of the sedimentation speed of the model pile on the pressing load;

V _n - the permissible settlement rate of natural piles in the foundation of the structure, taken depending on the structure of the building or structure (see table).

Table Limit values of the strain rate of the foundations of foundations, depending on the type and design features of buildings and structures [Rossikhin Yu.V., Bitainis AG Precipitation of buildings under construction. - Riga: Zinatne, 1980. - 339 p.] Type of construction Permissible pile upsetting speed, V _n , cm / year (mm / hour) Residential and public high-rise buildings: - panel and frame-panel with L / B≥7 20 (0,023) - the same, for 4 <L / B <1 30 (0,034) - with load-bearing walls of large blocks and bricks (masonry without reinforcement) with L / B> 7 30 (0,034) - the same, for 4 <UB <1 40 (0,045) - the same, reinforced with stiffening belts, located not less than one floor 40 (0,045) Full-frame multi-story industrial buildings 30 (0,034) Note: L is the length and B is the width of the building.

The application on a model pile of a continuously increasing pressing load at a constant speed and the determination of this speed taking into account the diameter of the model pile, humidity, plasticity limits and the coefficient of porosity of the soil under the lower end of the model pile using formula (2) more accurately models the working conditions of a natural pile in the foundation of the structure at testing a model pile and thus increases the reliability of determining the bearing capacity of a natural pile in the foundation of the structure.

Continuous recording of the pressing load and draft of the model pile with an error of 100-200 N for the pressing load and 0.005-0.010 mm for pile driving allows you to build a detailed graph of the dependence of the draft speed of the pile on the pressing load and select three sections on it - the first section with a constant as a whole, by the linear settlement rate of the model pile, the 2nd section with a non-linearly increasing settlement rate of the model pile, generally 5-10 times greater than in the 1st section, and the 3rd section with the settlement rate of the model pile in 5-10 times greater than on the 2nd section, and then for the bearing capacity of the model pile to take the value of the pressing load at the end of the 2nd section of the graph, i.e. the value of the pressing load before the loss of the bearing capacity of the model pile, etc. increases the accuracy and reliability of determining the bearing capacity of a natural pile in the foundation of the structure.

Determination of the bearing capacity of a natural pile in the foundation of a structure according to formula (3) with a similarity coefficient of the bearing capacity of a model pile and natural pile in the foundation of a pile structure, determined by formula (4) and taking into account the lengths and diameters of the model pile and natural pile in the foundation of the structure, calculated durations tests of a model pile and loading of a natural pile in the foundation of the structure, increment and average settlement rate of a model pile in the 2nd section of the graph of the dependence of the settlement speed of a model pile on airborne overload before exhausting the bearing capacity of the model pile, the maximum draft and the permissible speed of the natural pile in the foundation of the structure, increases the accuracy and reliability of determining the bearing capacity of the natural pile in the foundation of the structure.

Modeling of piles under load is based on the principles of similarity theory. The loss of the bearing capacity of the pile occurs due to the onset of the ultimate state of the soil under the lower end of the pile. At this point, a zone of extreme equilibrium of the soil is formed. Based on the work [Grigoryan A.A. Calculation of the foundations of pile foundations in the light of solving the problems of soil mechanics // Transactions of International Scientific and Practical Conf. on problems of soil mechanics, foundation engineering and transport construction. T.1, Perm, 2004, p.200-205; Lyashenko P.A., Ostapenko A.I. Laboratory modeling of injection piles // b Scientific journal Kub-GAU [Electronic resource]. - Krasnodar: KubSAU, 2011. - No. 02 (66). S.245-260. http://ej.kubagro.ru/201 l / 02 / par723.pdf], the zone of limit equilibrium can be schematically represented as a 4-sided pyramid flattened from the sides, the base of which serves as the sole of the conditional foundation at the time of destruction of its base.

Under the assumptions made, the work of the resistance force of the pile is determined by the speed of the compacted soil under the lower end of the pile and the duration of movement of the pile at a constant speed.

Then the work of the resistance forces of the model pile is expressed by formula (5), and the resistance forces of a natural pile in the foundation of the structure by formula (6):

$$F_m{S}_m=Q_{m}g{V}_m{t}_m,\left(5\right)$$

$$F_m{S}_m=Q_{n}g{V}_n{t}_n,\left(6\right)$$

where Q _m and Q _n are the masses of the compacted soil area under the lower end of the pile before exhausting its bearing capacity, respectively, of the model pile and natural pile in the foundation of the structure;

g is the acceleration of gravity,

the remaining notation is given in formulas (3) and (4).

Comparing formulas (6) and (5), we obtain the similarity condition for a model pile and a natural pile in the foundation of a structure

$${\alpha }_f={\mathrm{<figure-callout\; id="2"\; label="\alpha \; L"\; filenames="00000020.png"\; state="\{\{state\}\}">\alpha \; </figure-callout>}}_L^{}{\alpha }_D{\alpha }_t{\alpha }_S^{-\mathrm{one}}{\mathrm{<figure-callout\; id="2"\; label="\alpha \; V"\; filenames="00000020.png"\; state="\{\{state\}\}">\alpha \; </figure-callout>}}_V^{},\left(7\right)$$

- коэффициент подобия несущей способности модельной сваи и натуральной сваи в фундаменте сооружения;Where $${\alpha }_f=\frac{F_n}{F_m}\left(8\right)$$

- the coefficient of similarity of the bearing capacity of the model piles and natural piles in the foundation of the structure;

- коэффициент подобия длины модельной сваи и натуральной сваи в фундаменте сооружения; $${\alpha }_L=\frac{L_n}{L_m}\left(9\right)$$

- the coefficient of similarity of the length of the model piles and natural piles in the foundation of the structure;

- коэффициент подобия диаметров модельной сваи и натуральной сваи в фундаменте сооружения; $${\alpha }_D=\frac{D_n}{D_m}\left(10\right)$$

- the coefficient of similarity of the diameters of the model piles and natural piles in the foundation of the structure;

- коэффициент подобия скоростей осадки сваи перед исчерпанием несущей способности модельной сваи и натуральной сваи в фундаменте сооружения; $${\alpha }_V=\frac{V_n}{V_m}\left(\mathrm{eleven}\right)$$

- the coefficient of similarity of the pile upsetting speeds before exhausting the bearing capacity of the model pile and natural pile in the foundation of the structure;

- коэффициент подобия расчетных длительностей осадки сваи перед исчерпанием несущей способности модельной сваи и нагружения натуральной сваи в фундаменте сооружения; $${\alpha }_t=\frac{t_n}{t_m}\left(12\right)$$

- the coefficient of similarity of the estimated duration of pile upset before exhausting the bearing capacity of the model pile and loading of natural pile in the foundation of the structure;

- коэффициент подобия приращение осадки сваи перед исчерпанием несущей способности модельной сваи и натуральной сваи в фундаменте сооружения. $${\alpha }_S=\frac{S_n}{S_m}\left(13\right)$$

- the similarity coefficient, increment of pile upset before exhaustion of the bearing capacity of the model pile and natural pile in the foundation of the structure.

From equation (8) we obtain equation (3), substituting equations (8) - (13) in equation (7), we obtain equation (4).

A method for determining the bearing capacity of a pile is realized, for example, using a device consisting of a model pile, a thrust system, a node for continuously increasing the pressing load, a node for continuously recording the pressing load, and a node for continuously recording the pile upset.

Explanations of the proposed method for determining the bearing capacity of piles and one of the design options of the device for implementing this method are schematically shown in the drawing,

where figure 1 is a schematic block diagram of a device for implementing a method for determining the bearing capacity of piles;

figure 2 is a graph of the dependence of the speed of upsetting piles from the pressing load.

A device for implementing the method for determining the bearing capacity of a pile consists of a model pile 1, a thrust system 2, a node for applying a continuously increasing pressing load 3, a node for continuously recording a pressing load 4, and a node for continuously recording a pile upset 5.

The method of determining the bearing capacity of piles is as follows.

A continuously increasing pressing load is applied to the model pile at a constant speed, and its value is taken depending on the diameter of the model pile, humidity, ductility limits and soil porosity coefficient under the lower end of the model pile according to formula (2).

In the process of indentation of the model pile, the indentation load and draft of the model pile are continuously recorded with an error of 100-200 N for the pressing load and 0.005-0.010 mm for the pile upsetting.

According to the registration of the pressing load and draft model piles, a graph of the dependence of the draft rate of the test pile on the pressing load is constructed (see Fig. 2) and it is divided into three sections:

, в целом, мала, и осадка увеличивается линейно, т.е. пропорционально вдавливающей силе Р_m;- 1st section (plot FD-1), in which the average draft rate of the experimental pile $$V_m^{\left(\mathrm{one}\right)}$$

, in general, is small, and the sediment increases linearly, i.e. in proportion to the pressing force P _m ;

существенно увеличивается по сравнению с 1-м участком (участком FD-1), т.е. $$V_m^{\left(2\right)}\ge \left(5÷10\right)V_m^{\left(1\right)}$$

;- 2nd section (plot FD-2), on which the draft of the test pile increases non-linearly to the pressing force, and the average value of the draft rate of the test pile $$V_m^{\left(2\right)}$$

significantly increases in comparison with the 1st section (section FD-1), i.e. $$V_m^{\left(2\right)}\ge \left(5÷10\right)V_m^{\left(\mathrm{one}\right)}$$

;

;- the 3rd section (plot FD-3), on which the sedimentation rate of the experimental pile significantly increases compared to the 2nd plot (plot FD-2), i.e. $$V_m^{\left(3\right)}\ge \left(5÷10\right)V_m^{\left(2\right)}$$

;

At the beginning of the 3rd section (section FD-3), the increase in the pressing load P _{m is} stopped, and the value of the pressing load at the end of the 2nd section is taken as the value of the bearing capacity of the model pile Ф _m and the bearing capacity of the natural pile in the foundation of the structure Ф _{n is} calculated according to formula (3).

The inventive method for determining the bearing capacity of piles allows you to increase the reliability and accuracy of determining the bearing capacity of a natural pile in the foundation of the structure, reduce labor costs during testing and thus create a certain practical and economic effect.

Claims (1)

A method for determining the bearing capacity of a pile, including applying to the model pile a continuously increasing pressing load until the bearing capacity of the pile is lost, registering the pressing load and draft of the pile and calculating the bearing capacity of the natural pile in the foundation of the structure, characterized in that a continuously increasing pressing load on the model pile is applied with constant speed, and its value is taken depending on the diameter of the model pile, humidity, ductility limits and porosity coefficient g Unt beneath the lower end of the pile experimental formula:
$$U_m=\mathrm{0,048}{D}_m^2{10}^{0.106+8.60/I_P-\mathrm{1,1}W/W_L+1.01e}$$

,
where U _m is the speed of a continuously increasing pressing load;
D _m is the diameter of the model pile;
I _P is the number of soil plasticity under the lower end of the model pile;
W and W _L - natural humidity and moisture at the yield strength, respectively, of the soil under the lower end of the model pile;
e is the coefficient of porosity of the soil under the lower end of the model piles,
registration of the pressing load and draft of the model pile is carried out continuously with an error of 100-200 N for the pressing load and 0.005-0.010 mm for draft of the pile, according to the registration of the pressing load and draft of the model pile, a graph is plotted of the rate of draft of the pile from the pressing load, which is divided into three sections - on the 1st section with a constant linear rate of settlement of the model pile, on the 2nd section with a nonlinearly increasing rate of settlement of the model pile 5-10 times greater than on the 1st section, and on the 3rd section with sk growth precipitation model piles 5-10 times greater than at the 2nd section and the bearing capacity of foundation piles in the natural structures calculated using data generated depending on rainfall rate model piles are pressed by the load from the formula:
Ф _n = α _ф + Ф _m ,
where f _n - the bearing capacity of a natural pile in the foundation of the structure;
F _m is the bearing capacity of the model pile, defined as the value of the pressing load at the end of the 2nd section of the graph of the deposition rate of the model pile on the pressing load;
α _f - the coefficient of similarity of the bearing capacity of the model piles and natural piles in the foundation of the construction of piles
$${\alpha }_f={\left(\frac{L_n}{L_m}\right)}^2\frac{D_n}{D_m}\frac{t_n}{t_m}{\left(\frac{S_n}{S_m}\right)}^{-\mathrm{one}}{\left(\frac{V_n}{V_m}\right)}^2$$

,
where L _m and L _n are the lengths of the model pile and natural pile in the foundation of the structure, respectively;
D _m and D _n - respectively, the diameters of the model piles and natural piles in the foundation of the structure;
t _m and t _n are the calculated duration of the test model piles and loading of natural piles in the foundation of the structure;
S _m - increment of draft of the pile on the 2nd plot of the graph of the rate of draft of the pile on the pressing load before the exhaustion of the bearing capacity of the model pile;
S _n - the maximum draft of natural piles in the foundation of the structure, taken from the building code, depending on the structure of the building or structure;
V _m is the average sedimentation speed of the model pile in the 2nd plot of the graph of the dependence of the sedimentation speed of the model pile on the pressing load;
V _n is the permissible settlement rate of natural piles in the foundation of the structure, taken depending on the structure of the building or structure.

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