RU2561093C2 - Method to determine bearing capacity of needle pile - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: method to determine bearing capacity of a needle pile includes manufacturing of at least two needle piles in accordance with the accepted design technology. In order to reduce labour intensiveness and to increase accuracy of bearing capacity determination, they perform in series several cycles of well pressurising at the pressure of at least 4 kg/cm² with duration of 10-12 minutes. After each cycle of pressurising the cement-sand mortar is added until full saturation of the well. At the same time the radius of the needle pile is determined by measurement of the entire volume of added mortar during all cycles of pressurising, using the given dependence. Accordingly, the bearing capacity of the needle pile with account of well walls expansion is determined using the given dependence.

EFFECT: increased accuracy of determination of bearing capacity of a needle pile, reduced labour intensiveness.

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Description

The invention relates to the field of construction, and in particular to the determination of the bearing capacity of a bored pile.

A known method for determining the bearing capacity of injection piles [1] according to the formula, the calculation of which adopted the radius of the piles equal to the radius of the well.

The disadvantage of this method is the significant inaccuracy in determining the bearing capacity of a bored pile.

The closest solution to the proposed is a method for determining the bearing capacity of piles [2] according to the results of static tests.

The disadvantage of this method is the significant complexity. The purpose of the invention is to reduce the complexity, improving the accuracy of determining the bearing capacity of the injection piles.

The specified goal in the proposed method is achieved by the fact that before starting the main work on the installation of injection piles according to the adopted design technology, at least two wells are drilled, a reinforcing cage is installed in the wells, the wells are filled from the bottom up with cement-sand mortar through an injector, followed by the installation of a sealing device at the wellhead, after which several pressure testing cycles are performed at a pressure of at least 4 kg / cm ² lasting 10-12 minutes, at the end of each about the pressure test cycle, cement-sand mortar is topped up to complete saturation of the wells, then the smallest radius of the injection pile is found according to the formula (1) according to the measurement of the added volume of the solution for all cycles of pressure testing:

Where:

R _St - radius of the pile, m;

R _SLE - well radius, m;

L - well depth, m;

V _dol - the total volume of the poured solution, m ³ ;

Ρ - pressure of pressure testing, m water;

Ε -module of soil deformation, tf / m ^2;

µ is the coefficient of transverse expansion of the well at pressure (P) crimping:

for sands: µ = l-sinφ / 2;

for sandy loam: µ = 0.15 (1 + I _L );

for clay soils: µ = 0.1 (1 + 3I _L );

where: φ is the angle of internal friction of the soil (25-40 °);

ε is the porosity coefficient;

α is the coefficient of pore filling with cement-sand mortar, we find from table.№1;

The bearing capacity of the injection pile, taking into account the expansion of the walls of the well, is determined by the formula (2):

Where:

F _d - bearing capacity of piles, hardware;

R is the calculated soil resistance under the lower end of the pile, tf / m ² , according to the tables SNiP 2.02.03-85 or SP50-102-2003 "Design and construction of pile foundations";

A _R is the bearing area of the pile, taken equal to the cross-sectional area of the injection pile, is located through the radius R _s , m ² ;

u _R - pile shaft perimeter, defined by the radius R of the pile _binding, m;

γ _c is the coefficient of pile working conditions in the soil, taken equal to γ _c = 1, regardless of the type of soil;

γ _cr is the coefficient of the working conditions of the piles under the lower end of the pile, taken equal to γ _c = 0.8, regardless of the type of soil;

γ _cf — coefficient of working conditions of the i-th soil layer on the lateral surface, taken equal to γ _cf = 0.9, regardless of the type of soil;

f _i is the calculated resistance of the i-th soil layer on the side surface of the trunk, taken according to the tables SNiP 2.02.03-85 or SP50-102-2003 "Design and construction of pile foundations";

h _i - the thickness of the i-th soil layer in contact with the side surface of the pile, m

The proposed method can significantly reduce the complexity and improve the accuracy of determining the bearing capacity of the injection piles.

Information sources

1. SNiP 2.02.03. Pile foundations. Gos. Com USSR for construction. M., 1986. Determination of the bearing capacity of injection piles is made according to the formula (7.11).

2. SP 50-102-2003 "Design and construction of pile foundations." Section (7.3). Determination of bearing capacity of injection piles according to static tests.

Claims (1)

A method for determining the bearing capacity of a bored injection pile, comprising producing at least two bored injection piles according to the design technology adopted, characterized in that in order to reduce the labor intensity and improve the accuracy of determining the bearing capacity, several cycles of pressing a well under pressure at least 4 kg / cm ² lasting 10 -12 minutes, after each cycle of crimping, cement-sand mortar is topped up to complete saturation of the well, while measuring the entire volume of dolitog about the solution for all cycles of crimping determine the radius of the injection piles according to the formula (1):
Where:

Where:
R _St - radius of the pile, m;
R _SLE - well radius, m;
L - well depth, m;
V _dol - the total volume of the poured solution, m ³ ;
Ρ - pressure test, m water. st .;
Ε - soil deformation modulus, tf / m ² ;
µ is the coefficient of transverse expansion of the well at pressure (P) crimping:
where: φ is the angle of internal friction of the soil (25-40 °);
ε is the porosity coefficient;
α is the coefficient of pore filling with cement-sand mortar,
and accordingly, the bearing capacity of the injection pile, taking into account the expansion of the walls of the well, is determined by the formula (2):

Where:
F _d - bearing capacity of piles, hardware;
R is the calculated soil resistance under the lower end of the pile, tf / m ² , according to the tables SNiP 2.02.03-85 or SP50-102-2003 "Design and construction of pile foundations";
A _R is the bearing area of the pile, taken equal to the cross-sectional area of the injection pile, is located through the radius R _s , m ² ;
u _R - pile shaft perimeter, defined by the radius R of the pile _binding, m;
γ _s is the coefficient of pile working conditions in the soil, taken equal to γ _s = 1, regardless of the type of soil;
γ _сR — coefficient of the working conditions of the pile under the lower end of the pile, taken equal to γ _c = 0.8, regardless of the type of soil;
γ _сf - coefficient of working conditions of the i-th soil layer on the lateral surface, taken equal to γ _сf = 0.9, regardless of the type of soil;
f _i is the calculated resistance of the i-th soil layer on the lateral surface of the trunk, taken according to the tables SNiP 2.02.03-85 or SP50-102-2003 "Design and construction of pile foundations";
h _i - the thickness of the i-th soil layer in contact with the side surface of the pile, m