RU2750919C1 - Method for testing ground foundation with pile - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention relates to construction, namely to methods for testing piles with static load. The method for testing the ground foundation with a pile includes the application of a pressing force continuously increasing at a constant speed to the model pile, synchronous registration of the pressing force, the time of its application and the pile sediment with a step of 0.005 mm of the pile sediment. As a model pile, a natural bored pile is used in the foundation of the structure. At the lower end of the model pile, a ground pressure sensor is placed. On the side surface of the model pile, meters of vertical ground deformation relatively to the side surface of the pile are placed. At the levels of the meters, depth marks are placed along a closed contour in the plan with a radius of 1-2 of the pile diameter from the pile axis in the directions from the axis of the model pile to neighboring working piles in this pile foundation. Vertical ground deformation relatively to the side surface of the pile, vertical movements of depth marks, ground pressure under the lower end of the pile, which is synchronous to registering pile sediment with a step of 0.005 mm of pile sediment, are additionally registered. After reaching the final value of the indentation force at its constant value, until the model pile sediment is stabilized according to the condition of 0.005 mm/h, the pile sediment, the time of its registration, the vertical ground deformations relatively to the side surface of the pile and the vertical movements of the depth marks at all levels of their placement and the ground pressure under the lower end of the pile, which is synchronous to the pile sediment with a step of 0.005 mm of the pile sediment, are synchronously recorded. According to the measurement data, the cycles of changes in the pile sedimentation rate are distinguished. The values of vertical ground deformations relatively to the side surface of the pile and vertical movements of the depth marks are distinguished, which are synchronous to the bursts of the pile sedimentation rate. The lengths of the projections of the traces of shear and separation cracks on the horizontal plane are calculated and taken as the horizontal dimensions of the pile base. Additionally, the position of the beginning of the shear and ground separation crack is determined. The directions of the greatest slopes of the surfaces of the depth marks movement are determined. Based on the obtained data, the increments of elastic and plastic deformation of the ground base are calculated in each cycle of changes in the sedimentation rate of the model pile. The increments of the resistance of the ground base to the immersion of the working pile and the corresponding increments of elastic and plastic deformations of the ground base in the entire range of the pressing force are determined. The load-bearing capacity of the working pile is determined by the condition of limiting its precipitation. The increments of the vertical and horizontal components of the elastic reaction of the ground base for the working pile are calculated at distances equal to the horizontal dimensions of the base.

EFFECT: increasing reliability and accuracy of determining the load-bearing capacity of the working pile in the foundation of the structure, the resistance of the ground base to the immersion of the pile, determining the size of the ground base of the pile at different levels along the length of the pile and the forces exerting influence from the tested pile to neighboring piles in this pile foundation.

1 cl, 3 dwg

Description

The invention relates to construction, and in particular to methods for testing piles with a static load.

There is a known method for measuring soil deformations near a micro-model pile, including measuring the settlement of a micro-model pile and vertical displacements of deep marks in the soil located at the same depth from the day surface of the soil massif, and the vertical load is transferred to the pile in steps, and the settlement of the micro-model pile and the movement of soil marks are simultaneously measured after stabilization of their movement [Ponomarev AB, Golubev KV. Distribution of stresses and deformations in the active zone of the model of a single micromodel pile with widening at the end when it is loaded with a static vertical load // Urban agglomerations in landslide territories. Mater. III Int. scientific. Conf. dedicated to the 75th anniversary of building, education in Volgograd December 14-16, 2005, Volgograd. Part II. - S. 9-15].

The disadvantages of this method are:

- the mode of applying an indentation load by steps with holding until the settlement of the micro-model pile stabilizes does not correspond to the mode of loading the piles in the foundation during the construction of structures, in which the load increases almost constantly [see. Yu.V. Rossikhin, A.G. Bitainis Precipitation of structures under construction. - Riga: Zinatne, 1980. - 339 p.] And does not allow to associate it with the loading mode of the pile in the foundation of the structure and to strictly substantiate their similarity;

- the lack of measurements of vertical soil deformations relative to the lateral surface of the micro-model pile does not allow to correctly describe the soil deformations in the place of its direct interaction with the pile: continuity or rupture of vertical soil displacements relative to the pile, as well as to reveal the appearance of shear and separation cracks in the soil.

There is a known method of testing a soil foundation by a pile, which includes the application of an indentation force to a model pile, continuously increasing at a constant speed, determined depending on the diameter of the pile and the physical properties of the soil, synchronous registration of the indentation force, the time of its application and settlement of the pile with a step of 0.005 mm of settlement of the pile, dividing the graph of the dependence of the rate of settlement of the pile on the pressing force into three sections according to the average rate of settlement of the pile in each of them and calculating the bearing capacity of the working pile by the value of the pressing force at the end of the 2nd section of the graph and by the coefficients of similarity of the model pile [Patent for invention of the Russian Federation No. 2502847, E02D 33/00. Method for determining the bearing capacity of a model pile / Denisenko V.V., Lyashenko P.A. et al. // Inventions. Utility Models, 2013, No. 36. - (prototype)].

The disadvantages of this method are:

- does not ensure the similarity of loading of the model and working piles in the foundation of the structure and, accordingly, the reliability of the results obtained for the working pile;

- the lack of measurements of the vertical deformations of the soil relative to the lateral surface of the pile and in the active zone of the soil foundation does not allow assessing the deformations of the soil foundation around the pile shaft caused by settlement of the pile and the formation of shear and shear cracks, the position of the places of formation of shear cracks and separation and to obtain a spatial idea of the shape of the base of the pile along its entire length, about the asymmetry of the base at its different levels in the process of loading the pile [see. Lyashenko P.A., Denisenko V.V., Marinichev M.B. Research of the work of the foundations of bored piles // Construction: New technologies - new equipment, 2019, No. 7, pp. 18-23];

- the lack of connection between the parameters of the placement of depth marks in the plan around the trunk of the model pile reduces the reliability of the assessment of the mechanical effect of the working pile on the adjacent piles in the foundation;

- the lack of data on the size and location in the soil base of the shear and separation cracks during pile loading does not allow determining the size of the base and the zone of its influence on adjacent piles in the pile foundation;

- the lack of soil pressure measurement directly under the lower end of the model pile makes it difficult to assess the distribution of the resistance of the model pile between the lower end and the lateral periphery of the pile base;

- the formulation of similarity conditions does not take into account significant changes in the parameters of the foundation resistance during the loading of the pile.

The objective of the invention is to increase the reliability and accuracy of determining the bearing capacity of the working pile in the foundation of the structure, the resistance of the soil base to the immersion of the pile, determining the dimensions of the soil base of the pile at different levels along the length of the pile and the forces that affect the neighboring piles in this pile foundation from the test pile.

The technical result of the invention is achieved by the fact that in the method of testing the soil base with a pile, including the application of an indentation force on a model pile, continuously increasing at a constant speed, determined depending on the diameter of the pile and the physical properties of the soil, synchronous registration of the indentation force, the time of its application and settlement of the pile with a step of 0.005 mm of pile settlement, dividing the graph of the dependence of the settlement rate of the model pile on the pressing force into three sections according to the average rate of settlement of the pile in each of them and calculating the bearing capacity of the working pile by the value of the pressing force at the end of the second section of the graph and by the similarity coefficients model pile, according to the invention, a natural bored pile is used as a model pile in the foundation of the structure, a soil pressure sensor is placed at the lower end of the model pile, meters of vertical soil deformation relative to the lateral surface of the pile are placed on the side surface of the model pile at levels the middle of each geotechnical element, composed of clay soil, in which the resistance to immersion of the probe at a speed of 5 mm / min during static sounding changes cyclically, and at the same levels depth marks are placed, at least 4, along a closed contour in the plan with a radius of 1 -2 diameters of the pile from the axis of the pile in directions from the axis of the model pile to adjacent working piles in the given pile foundation and fix their coordinates in plan relative to the pile, while additionally registering vertical deformations of the soil relative to the lateral surface of the pile, vertical displacements of depth marks and soil pressure under the lower end of the pile synchronously records the settlement of the pile with a step of 0.005 mm of the settlement of the pile, and after reaching the final value of the pressing force at its constant value until stabilization of the settlement of the pile according to the condition 0.005 mm / h, the settlement of the pile, the time of its observation, and vertical deformations of the soil relative to the lateral surface are synchronously recorded piles and vertical strips The placement of depth marks at all levels of their placement and the soil pressure under the lower end of the pile is synchronous with the settlement of the pile with a step of 0.005 mm of the settlement of the pile, and according to the measurements, the acceleration g _l , mm / kPa ² , the settlement of the pile is calculated by the formula:

where ƒ _l is the rate of settlement of the pile, mm / kPa;

s _l and P _l - I-th values of pile settlement, mm, and pressing force, kPa;

I - registration number of the pile settlement value;

на нисходящей ветви цикла скорости осадки сваи при g<0, максимальное значение скорости осадки сваи

на восходящей ветви цикла скорости осадки сваи при g≥0 и значения вертикальных деформаций грунта относительно боковой поверхности сваи и вертикальных перемещений глубинных марок, синхронные всплескам скорости осадки сваи, определяемым по условиямthe cycles of change in the rate of settlement of the pile are distinguished, setting their boundaries according to the last value of the acceleration of settlement of the pile g at g <0 in each i-th cycle of change in the rate of settlement of the pile, where i is the number of the cycle of change in the rate of settlement of the pile, determine the minimum value of the rate of settlement of the pile

on the descending branch of the cycle, the rate of settlement of the pile at g <0, the maximum value of the rate of settlement of the pile

on the ascending branch of the cycle, the settlement rate of the pile at g≥0 and the values of vertical deformations of the soil relative to the lateral surface of the pile and vertical displacements of depth marks, synchronous to bursts of the rate of settlement of the pile, determined by the conditions

м, в каждом уровне в направлениях от измерителя вертикальной деформации грунта относительно боковой поверхности сваи на каждую глубинную марку по формулам:the first surge in the settlement rate of the pile is taken as the beginning of the second section of the graph of the dependence of the rate of settlement of the pile on the pressing force and as the beginning of the formation of the first shear and separation crack in the soil base, and subsequent bursts in the rate of settlement of the pile are taken as the beginning of the formation of other shear and separation cracks in clayey base soils and calculate the horizontal dimensions of the subgrade

m, in each level in the directions from the meter of the vertical deformation of the soil relative to the lateral surface of the pile for each depth mark according to the formulas:

- расстояние глубинной марки до j-ого измерителя вертикальной деформации грунта относительно боковой поверхности сваи в уровне его размещения, м;Where

- the distance of the depth mark to the j-th meter of the vertical deformation of the soil relative to the lateral surface of the pile at the level of its placement, m;

и

- вертикальные перемещения глубинной марки и вертикальные деформации грунта относительно боковой поверхности сваи в j-ом уровне размещения, соответственно, синхронные всплескам значений скорости осадки сваи на восходящей ветви i-ого цикла скорости осадки сваи, принимаемые положительными, если их направление совпадает с направлением осадки сваи, мм,

and

- vertical displacements of the depth mark and vertical deformations of the soil relative to the lateral surface of the pile at the j-th level of placement, respectively, synchronous to the bursts of the values of the settlement rate of the pile on the ascending branch of the i-th cycle of the settlement rate of the pile, taken positive if their direction coincides with the direction of settlement of the pile , mm,

и

- вертикальные перемещения глубинной марки и вертикальные деформации грунта относительно боковой поверхности сваи в j-ом уровне размещения, соответственно, синхронные всплескам значений скорости осадки сваи на нисходящей ветви i-ого цикла скорости осадки сваи, принимаемые положительными, если их направление совпадает с направлением осадки сваи, мм,Where

and

- vertical displacements of the depth mark and vertical deformations of the soil relative to the lateral surface of the pile at the j-th level of placement, respectively, synchronous to the bursts of the values of the settlement rate of the pile on the descending branch of the i-th cycle of the settlement rate of the pile, taken positive if their direction coincides with the direction of settlement of the pile , mm,

additionally determine the position of the beginning of each shear and tear-off crack on the lateral surface of the pile by the inequality

where H is the depth of the upper boundary of the engineering-geological element, in the middle of which a meter is installed for the vertical deformation of the soil relative to the lateral surface of the pile, m;

- глубина точки начала трещины сдвига и отрыва на боковой поверхности сваи, м;

- the depth of the point of the beginning of the shear and separation crack on the lateral surface of the pile, m;

- глубина точки размещения на боковой поверхности сваи j-го измерителя вертикальной деформации грунта относительно боковой поверхности сваи, м,

- the depth of the point of placement on the lateral surface of the pile of the j-th meter of vertical soil deformation relative to the lateral surface of the pile, m,

build maps of displacements of marks for their values, synchronous with bursts of values of the rate of settlement of the pile, and calculate the values of the gradient of displacements of depth marks at the points of their placement

- вертикальные перемещения глубинной марки, синхронные всплескам значений скорости осадки сваи, мм,Where

- vertical displacements of the depth mark, synchronous to the bursts of the values of the settlement rate of the pile, mm,

and determine the directions of the greatest slopes of the displacement surfaces of depth marks by the values of the gradients of their vertical displacements

- градиент перемещений глубинных марок в точке размещения глубинной марки в j-ом уровне размещения, д. е.;Where

- gradient of displacements of depth marks at the point of placement of the depth mark in the j-th level of placement, f .;

- наибольший уклон поверхности перемещений глубинных марок в точке размещения глубинной марки в j-ом уровне размещения, д. е.,

- the greatest slope of the surface of displacements of depth marks at the point of placement of the depth mark in the j-th level of placement, i.e.,

и на восходящей ветви

и соответствующие им приращения вдавливающей силы

и

в каждом i-ом цикле изменения скорости осадки модельной сваи, рассчитывают приращения упругой деформаций грунтового основания

на приращении вдавливающей силы

и пластической деформаций грунтового основания

на приращении вдавливающей силы

в каждом i-ом цикле изменения скорости осадки модельной сваи по формулам:determine the increments of settlement of the model pile on the descending branch

and on the ascending branch

and the corresponding increments of the pressing force

and

in each i-th cycle of change in the rate of settlement of the model pile, the increments of elastic deformations of the soil foundation are calculated

on the increment of the pressing force

and plastic deformations of the soil base

on the increment of the pressing force

in each i-th cycle of changing the settlement rate of the model pile according to the formulas:

and determine the increments of the resistance of the soil base to the immersion of the working pile and the corresponding increments of elastic and plastic deformations of the soil base in the entire range of the pressing force according to the formulas:

- соответственно приращения упругих и пластических деформаций грунтового основания в каждом i-ом цикле изменения скорости осадки рабочей сваи, мм, и соответствующие им приращения вдавливающей силы, кН;Where

- respectively, the increments of elastic and plastic deformations of the soil base in each i-th cycle of change in the rate of settlement of the working pile, mm, and the corresponding increments of the pressing force, kN;

- коэффициенты подобия рабочей и модельной свай;

- coefficients of similarity of working and model piles;

- соответственно диаметр рабочей и модельной сваи, м;

- respectively, the diameter of the working and model piles, m;

- соответственно скорость нагружения рабочей и модельной сваи, кН/ч;

- respectively, the loading rate of the working and model piles, kN / h;

- длительность восходящей части цикла изменения скорости осадки модельной сваи, с;

- the duration of the ascending part of the cycle of changing the rate of settlement of the model pile, s;

- параметры ползучести грунтового основания, с и мм, соответственно, определяемые из уравнения

- parameters of the soil base creep, s and mm, respectively, determined from the equation

then the bearing capacity of the working pile is determined according to the condition of limiting its settlement

сумма приращений осадки рабочей сваи, мм;Where

the sum of the increments of the slump of the working pile, mm;

s _u - the limiting value of the settlement of the foundation of the structure, mm,

на расстояниях, равных горизонтальным размерам основания

в каждом j-м уровне размещения измерителя вертикальной деформации грунта относительно боковой поверхности сваи, по формулам:and additionally calculate the increments of the vertical and horizontal components of the elastic reaction of the soil base for the working pile

at distances equal to the horizontal dimensions of the base

in each j-th level of placement of the vertical soil deformation meter relative to the lateral surface of the pile, according to the formulas:

- расчетные приращения вертикальной и горизонтальной составляющих упругой реакции грунтового основания, кН, на расстояниях

от оси модельной сваи;Where

- calculated increments of the vertical and horizontal components of the elastic reaction of the soil foundation, kN, at distances

from the axis of the model pile;

- длина части модельной сваи ниже j-ой трещины, испытывающая на боковой поверхности упругое сопротивление грунтового основания, м; G_e - упругая постоянная грунта, кПа;Where

- the length of a part of the model pile below the j-th crack, experiencing the elastic resistance of the soil foundation on the lateral surface, m; G _e - elastic soil constant, kPa;

- приращение вдавливающей силы в циклах изменения скорости осадки модельной сваи на участке испытания после j-го всплеска до (j+1)-го всплеска скорости ее осадки, кН;

- increment of the pressing force in the cycles of change in the settlement rate of the model pile in the test area after the j-th burst before the (j + 1) -th burst of the settlement rate, kN;

- приращение упругой осадки грунтового основания на нисходящей части циклов изменения скорости осадки модельной сваи на участке испытания после j-го всплеска до (j+1)-го всплеска скорости ее осадки, мм;

- increment of elastic settlement of the soil foundation on the descending part of the cycles of changing the settlement rate of the model pile in the test area after the j-th burst before the (j + 1) -th burst of the settlement velocity, mm;

- приращение упругой осадки грунтового основания на восходящей части циклов изменения скорости модельной осадки сваи на участке испытания после j-го всплеска до (j+1)-го всплеска скорости ее осадки, мм;

- increment of elastic settlement of the soil foundation on the ascending part of the cycles of changing the rate of model settlement of the pile in the test area after the j-th burst before the (j + 1) -th burst of the rate of its settlement, mm;

- приращение сопротивления грунта основания под нижним концом модельной сваи, синхронное приращению упругой осадки грунтового основания

кН.

- the increment of the soil resistance of the base under the lower end of the model pile, synchronous with the increment of the elastic settlement of the soil base

kN.

в каждом уровне в направлениях от измерителя вертикальной деформации грунта относительно боковой поверхности сваи на каждую глубинную марку по формулам (4-6), дополнительно определяют положение начала каждой трещины сдвига и отрыва на боковой поверхности сваи по неравенству (7), строят карты перемещений марок для их значений, синхронных с всплесками значений скорости осадки сваи, и рассчитывают значения градиента перемещений глубинных марок в точках их размещения по формуле (8) и определяют направления наибольших уклонов поверхностей перемещений глубинных марок по значениям градиентов их вертикальных перемещений по уравнению (9), определяют приращения осадки модельной сваи на нисходящей ветви

и на восходящей ветви

и соответствующие им приращения вдавливающей силы

в каждом i-ом цикле изменения скорости осадки модельной сваи, рассчитывают приращения упругой деформаций грунтового основания

на приращении вдавливающей силы

и пластической деформаций грунтового основания

на приращении вдавливающей силы

в каждом i-ом цикле изменения скорости осадки модельной сваи по формулам (10-12) и определяют приращения сопротивления грунтового основания погружению рабочей сваи и соответствующие им приращения упругих и пластических деформаций грунтового основания во всем диапазоне вдавливающей силы по формулам (13-17), затем определяют несущую способность рабочей сваи по условию ограничения ее осадки

по формуле (18) и дополнительно рассчитывают приращения вертикальной и горизонтальной составляющих упругой реакции грунтового основания для рабочей сваи

на расстояниях, равных горизонтальным размерам основания

в каждом j-м уровне размещения измерителя вертикальной деформации грунта относительно боковой поверхности сваи, по формулам (19-23).The novelty of the proposed technical solution is due to the fact that in the inventive method of testing a soil base with a pile, a natural bored pile is used as a model pile in the foundation of a structure, a soil pressure sensor is placed at the lower end of the model pile, meters of vertical soil deformation relative to the lateral surface are placed on the lateral surface of the model pile piles at the levels of the middle of each engineering-geological element, composed of clay soil, in which the resistance to immersion of the probe at a speed of 5 mm / min during static sounding changes cyclically, and at the same levels depth marks are placed, at least 4, along a closed loop in plan with a radius of 1-2 pile diameters from the axis of the pile in directions from the axis of the model pile to the adjacent working piles in the given pile foundation and fix their coordinates in the plan relative to the pile. In the process of applying the pressing force, the vertical deformation of the soil relative to the lateral surface of the pile, the vertical displacements of the depth marks, the soil pressure under the lower end of the pile are recorded synchronously with the registration of the pile settlement with a pitch of 0.005 mm of the pile settlement. After reaching the final value of the indentation force at its constant value until the settlement of the model pile stabilizes according to the condition of 0.005 mm / h, the settlement of the pile, the time of its observation, vertical deformations of the soil relative to the lateral surface of the pile and vertical displacements of depth marks at all levels of their placement, soil pressure are recorded synchronously under the lower end of the pile synchronously with the pile settlement with a pitch of 0.005 mm of the pile settlement. According to the measurement data, the acceleration g _{7 of the} pile settlement is calculated according to the formulas (1-2), the cycles of change in the rate of settlement of the pile are distinguished, setting their boundaries according to the last value of the acceleration of the settlement of the pile g at g <0 in each i-th cycle of the change in the rate of settlement of the pile, determine the minimum value of the pile settlement rate on the descending branch of the pile settlement rate cycle at g <0, the maximum value of the pile settlement rate on the ascending branch of the pile settlement rate cycle at g≥0 and the values of vertical soil deformations relative to the lateral surface of the pile and vertical displacements of deep marks synchronous to bursts the settlement rate of the pile, determined according to conditions (3), the first burst of the settlement rate of the pile is taken as the beginning of the 2nd section of the graph of the dependence of the rate of settlement of the pile on the pressing force and as the beginning of the formation of the first shear and separation crack in the soil base, and the subsequent bursts of the settlement rate of the pile the base is taken as the beginning of the formation of other shear cracks and separation in clay soils and calculate the horizontal dimensions of the subgrade

in each level in the directions from the meter of vertical soil deformation relative to the lateral surface of the pile for each depth mark according to the formulas (4-6), additionally determine the position of the beginning of each shear crack and tearing on the lateral surface of the pile according to inequality (7), build maps of displacement marks for their values, synchronous with the bursts of the pile settlement rate, and calculate the values of the gradient of displacements of depth marks at the points of their placement according to formula (8) and determine the directions of the greatest slopes of the surfaces of displacements of deep marks according to the values of the gradients of their vertical displacements according to equation (9), determine the increments settlement of the model pile on the descending branch

and on the ascending branch

and the corresponding increments of the pressing force

in each i-th cycle of change in the rate of settlement of the model pile, the increments of elastic deformations of the soil foundation are calculated

on the increment of the pressing force

and plastic deformations of the soil base

on the increment of the pressing force

in each i-th cycle of changing the settlement rate of the model pile according to the formulas (10-12) and determine the increments of the resistance of the soil base to the immersion of the working pile and the corresponding increments of elastic and plastic deformations of the soil base in the entire range of the pressing force according to the formulas (13-17), then the bearing capacity of the working pile is determined according to the condition of limiting its settlement

according to the formula (18) and additionally calculate the increments of the vertical and horizontal components of the elastic reaction of the soil foundation for the working pile

at distances equal to the horizontal dimensions of the base

in each j-th level of placement of the meter of vertical soil deformation relative to the lateral surface of the pile, according to formulas (19-23).

The use of a natural bored pile in the foundation of a structure as a model pile makes it possible to test the pile in real conditions of its operation in the foundation and, accordingly, provides an increase in the reliability of the results of registering vertical soil deformations relative to the lateral surface of the pile and vertical displacements of depth marks at all levels of their placement.

Placing a soil pressure sensor at the lower end of the model pile and recording the soil pressure under the lower end of the pile synchronously with the settlement of the pile with a pitch of 0.005 mm of the settlement of the pile ensures the measurement of the actual soil pressure under the lower end of the pile in real conditions of its operation in the foundation and ensures an increase in the accuracy and reliability of recording the pressure soil under the lower end of the pile.

The use of meters for vertical soil deformations relative to the lateral surface of the pile provides data on continuous or discontinuous soil deformation with concrete near the lateral surface of the pile.

The use of depth marks provides data on the vertical deformation of the soil in the active zone of the subgrade around the pile.

Placement of meters for vertical soil deformation relative to the lateral surface of the pile and depth marks:

- in engineering-geological elements, composed of clay soil, in which the resistance to immersion of the probe at a speed of 5 mm / min during static probing, carried out before testing the pile, changes cyclically, and, accordingly, their elastic-plastic destruction with the formation of shear cracks and separation is possible [see: 1) Nadai A. Plasticity and fracture of solids. In 2 volumes. T. 1. - M .: Publishing house of IL, 1954. - 647 p .; 2) Lyashenko P.A., Denisenko V.V., Marinichev M.B. Scheme of work under load of bored piles in clayey soils // Construction: new technologies - new equipment, 2019, No. 8. - S. 34-40], provides data for determining the size of these cracks;

- at the level of the middle of engineering-geological elements, composed of clay soil, guarantees registration of the moment of formation of shear and separation cracks in the soil base of the pile, increases the accuracy of determining their dimensions in the direction of depth marks and, accordingly, increases the accuracy of determining the horizontal dimensions of the soil base of the pile in these levels.

The placement of depth marks at the levels of the vertical soil deformation meters relative to the lateral surface of the pile at least four along a closed contour in the plan with a radius of 1-2 pile diameters from the pile axis in directions from the model pile axis to adjacent working piles in the given pile foundation provides data on vertical deformations of the soil in the active zone of the soil foundation around the pile and improving the accuracy of determining the forces influencing the test pile on the adjacent piles in the given pile foundation.

The placement of depth marks at a distance of 1–2 diameters of the pile from its axis provides the possibility of their immersion into the subgrade next to the pile and guarantees their location in the active zone of the subgrade around the pile.

Synchronous registration of pile settlement, time of its observation, vertical deformations of the soil relative to the lateral surface of the pile and vertical displacements of depth marks at all levels of their placement and soil pressure under the lower end of the pile synchronously with the settlement of the pile with a pitch of 0.005 mm of settlement of the pile, and after reaching the final value of the pressing force at its constant value until the settlement of the model pile stabilizes according to the condition of 0.005 mm / h, it provides data for assessing the creep of the soil under the lower end of the pile and increases the reliability of the results.

Building maps of depth marks displacements for their values synchronous with bursts of pile settlement rates, calculating the value of the gradient of displacements of depth marks at the points of their location and determining the directions of the greatest slopes of the surfaces of displacements of depth marks according to the values of the gradients of their vertical displacements make it possible to refine the shape of shear and separation cracks arising at different levels.

Thus, the totality of these distinctive features is the essence of the invention, providing its novelty, inventive step and industrial applicability.

Explanations for the inventive method for testing the soil base with piles are shown in:

fig. 1 - an example of a layout scheme with respect to a pile of vertical soil deformation meters relative to the lateral surface of the pile, a soil pressure sensor and depth marks at the levels of the middle of each engineering-geological element, composed of clay soil, the outer contours of shear cracks and separation at these levels that have arisen in the soil base due to pile settlement: Go - soil foundation; Tr is a crack in the ground; I - technogenic soil; II - hard loam; III - hard-plastic loam; IV - medium density sand; V - hard-plastic loam; VI - dense sand;

fig. 2 is a schematic diagram of a system for testing a subgrade with a pile: Go - subgrade; Tr is a crack in the ground; H - the depth of the upper boundary of the engineering-geological element, in the middle of which is installed a meter 2 of the vertical deformation of the soil relative to the lateral surface of the pile; h ^(G) is the depth of the point of placement on the lateral surface of the pile of the meter 2 of the vertical deformation of the soil relative to the lateral surface of the pile; l ^(M) - distance from depth mark 3 to meter 2 of vertical soil deformation relative to the lateral surface of the pile; h _cr - the depth of the point of the beginning of the shear crack and separation on the lateral surface of the pile; L _cr is the horizontal size of the soil base in the direction from the meter 2 of the vertical deformation of the soil relative to the lateral surface of the pile to a depth mark 3;

fig. 3 - an example of a scheme for placing depth marks in one of the engineering-geological elements, folded by clay soil, and a map of displacements of depth marks, reflecting the location relative to pile 1 of traces of 17 shear and tearing cracks, meter 2 of vertical soil deformation relative to the lateral surface of the pile, depth marks 3 , lines of the outer contour 18 of the shear and separation crack, lines 19 of equal displacement values of depth marks and vectors 20 of gradients of displacements of depth marks U ^(M) (section A-A).

To implement the method for testing the soil base with a pile, a system is used that consists of a model bored concrete pile 1, meters 2 of the vertical deformation of the soil relative to the lateral surface of the pile, depth marks 3, a soil pressure sensor 4, a device 5 for applying an indentation force, a sensor 6 of the magnitude of an indentation force, a sensor 7 settlement of the pile, sensors 8 of vertical soil deformation relative to the pile, sensors 9 of vertical displacements of depth marks, thrust structure 10, control unit 11 and benchmark 12.

Meters 2 are designed to measure the vertical deformation of the soil relative to the lateral surface of the pile. Each meter 2 is a housing 13 with a lateral longitudinal through groove, from which a rotary element 14 protrudes, connected through a transfer rod 15 with a sensor 8 of vertical soil deformation relative to the pile [see. // Positive decision of July 28, 2020 on the application for invention of the Russian Federation No. 2010105074 of February 3, 2020 A device for measuring shear deformations of the soil relative to the surface of a concrete structure / Lyashenko P.A., Denisenko V.V., Marinichev M.B. .].

Depth marks 3 are designed to measure ground movements at the base. Each depth mark 3 is a hard round stamp with a diameter of 20-25 mm, connected through a transfer rod 16, placed in a cylindrical body 17, with a vertical displacement transducer 9 of the depth mark. As a depth mark 3, a probe of a static sensing installation with a retractable core can be used, in which the conical tip (indenter) is replaced by a cylindrical one [see. RF patent №2398210, G01N 3/42. Method of soil testing by static sounding / Denisenko V.V., Lyashenko P.A. // Inventions. Utility Models, 2010, No. 24].

The soil pressure sensor 4 is designed to measure the value of the soil pressure under the lower end of the pile in the process of applying the pressing force.

The device 5 is designed to apply a pressing force on the pile, continuously increasing at a constant speed, and can have any drive: hydraulic, pneumatic or mechanical.

Sensor 6 is designed to measure the applied pressing force with a measurement step of no more than 100-200 N and can be made, for example, in the form of a compression dynamometer with a raster photoelectric linear displacement transducer.

Sensor 7 is designed to measure the settlement of a pile with a measurement step of 0.005 mm, sensors 8 are designed to measure vertical deformations of the soil relative to the lateral surface of a pile with a measurement step of 0.005 mm, and sensors 9 are designed to measure vertical displacements of depth marks with a measurement step of 0.005 mm. Sensors 7, 8 and 9 can have the same design, for example, in the form of a raster photoelectric linear displacement transducer.

The structure 10 is intended to create a stop for the device 5 for applying the pressing force and the sensor 6 of the magnitude of the pressing force. Any structure can be used as a thrust structure 10, for example, a device for testing soil with static loads [see. Auth. USSR No. 1366602, E02D 33/00. Device for testing pounds with static loads / Denisenko V.V., Baikov O.N., Antropov V.A. and others // Discovery. Inventions, 1988, No. 2].

The control unit 11 is intended for: setting a constant rate of increasing the pressing force; turning on the device 5 applying a pressing force; indicating on the display and registering in the electronic memory of the control unit 11 the value of the applied pressing force, the time of its application, the amount of settlement of the pile from the sensor 7, the values of the vertical deformations of the soil relative to the lateral surface of the pile from the sensors 8 and the values of the vertical displacements of the depth marks from the sensors 9.

The method for testing the soil base with a pile is as follows.

In the soil base, a model bored concrete pile 1 is made, at the lower end of which a soil pressure sensor 4 is placed. Along the length of the pile, place meters 2 of the vertical deformation of the soil relative to the lateral surface of the pile at the levels of the middle of each engineering-geological element, folded with clay soil, in which the resistance to immersion of the probe at a speed of 5 mm / min during static probing, carried out before testing the pile, changes cyclically, and at the same levels, depth marks 3 are placed, placing at least four of them along a closed contour in the plan with a radius of 1-2 diameters of the pile from the pile axis and fixing their coordinates in the plan relative to the pile.

Each meter 2 of vertical soil deformation relative to the lateral surface of the pile is placed in the corresponding engineering-geological element so that its body 13 with the transfer rod 15 comes out on the day surface and does not interfere with another meter of vertical soil deformation relative to the lateral surface of the pile, located in another engineering-geological element.

Depth marks 3 are placed in directions from the axis of the model pile 1 to adjacent working piles in this pile foundation.

Each depth mark 3 is immersed in the soil base at a speed of up to 1.5 m / min by the cylindrical body 17 of the static sounding probe [see. RF patent №2398210, G01N 3/42. Method of soil testing by static sounding / Denisenko V.V., Lyashenko P.A. // Inventions. Utility Models, 2010, No. 24], first 5-6 cm above the design level h ^(G) , and then using the core 16, the depth mark 3 is immersed at a speed of no more than 5 mm / min, to prevent disturbance of the natural composition of the soil, to the design level h ^(G) , coinciding with the level of the position of the rotary element 14 of the meter 2 of the vertical deformation of the soil relative to the lateral surface of the pile.

Each depth mark 3 in the corresponding level is placed so that its cylindrical body 17 with the transfer rod 16 comes out to the day surface and does not interfere with another depth mark placed in another level.

A device 5 for applying a pressing force with a sensor 6 of the magnitude of the pressing force is installed on the pile 1 and a thrust structure 10 is mounted.

A sensor 7 of the pile settlement is brought to the end of the pile 1, a sensor 8 of the vertical deformation of the soil relative to the pile is brought to each transfer rod of the meter 2 of the vertical deformation of the soil relative to the lateral surface of the pile, and a sensor 9 of the vertical displacement of the depth mark is supplied to each core 16. All sensors 7 and 9 are installed on one benchmark 12, and all sensors 8 - on meters 2 of vertical soil deformation relative to the lateral surface of the pile.

The device 5 for applying the pressing force, the sensor 6 of the magnitude of the pressing force, the sensor 7 of the settlement of the model pile, the sensor 4 of the soil pressure, the sensors 8 of the vertical deformation of the soil relative to the pile and the sensors 9 of the vertical displacement of the depth marks are connected to the control unit 11.

In the control unit 11, the rate of constant increase in the pressing force is set, which is determined depending on the diameter of the pile and the physical properties of the soil [see. RF patent №2502847, E02D 33/00. Method for determining the bearing capacity of a model pile / Denisenko V.V., Lyashenko P.A. et al. // Inventions. Utility Models, 2013, No. 36].

Then the device 5 for applying the pressing force is turned on and the pressing force is applied to the pile 1 at a predetermined continuously increasing at a constant speed. In the process of applying the pressing force on the pile 1, the following values are indicated on the display of the control unit 11 and recorded in the electronic memory of the control unit 11 with a step of 0.005 mm synchronously with the settlement of the pile: the pressing force applied to the pile 1, the time of its application, the soil pressure under the lower end of the pile 1 , settlement of the pile 1, vertical deformations of the soil relative to the lateral surface of the pile 1 from each sensor 8 and vertical displacements of depth marks 3 from each sensor 9.

After reaching the final value of the pressing force at its constant value, the settlement of the model pile is recorded until the settlement of pile 1 is stabilized according to the condition of 0.005 mm / h, the time of its observation, vertical deformations of the soil relative to the lateral surface of the pile and vertical displacements of depth marks 3 at all levels of their placement and pressure soil under the lower end of the pile synchronously with the pile settlement with a pitch of 0.005 mm of the pile settlement.

в каждом уровне в направлениях от измерителя 2 вертикальной деформации грунта относительно боковой поверхности сваи 1 на каждую глубинную марку 3 по формулам (4-6), дополнительно определяют положение начала каждой трещины сдвига и отрыва на боковой поверхности сваи 1 по неравенству (7), строят карты перемещений глубинных марок 3 в каждом уровне их размещения по известной методике [см. Марфенко С.В. Геодезические работы по наблюдению за деформациями сооружений. Учебное пособие. - М: МИИГАиК, 2004. - 36 с.] для их значений, синхронных с всплесками значений скорости осадки сваи, и рассчитывают значения градиента перемещений глубинных марок 3 в точках их размещения по формуле (8) и определяют направления наибольших уклонов поверхностей перемещений глубинных марок 3 по значениям градиентов их вертикальных перемещений по уравнению (9), определяют приращения осадки модельной сваи на нисходящей ветви

и на восходящей ветви

и соответствующие им приращения вдавливающей силы

в каждом i-ом цикле изменения скорости осадки модельной сваи, рассчитывают приращения упругой деформаций грунтового основания

на приращении вдавливающей силы

и пластической деформаций грунтового основания

на приращении вдавливающей силы

в каждом i-ом цикле изменения скорости осадки модельной сваи по формулам (10-12) и определяют приращения сопротивления грунтового основания погружению рабочей сваи и соответствующие им приращения упругих и пластических деформаций грунтового основания во всем диапазоне вдавливающей силы по формулам (13-17), затем определяют несущую способность рабочей сваи по условию ограничения ее осадки

по формуле (18) и дополнительно рассчитывают приращения вертикальной и горизонтальной составляющих упругой реакции грунтового основания для рабочей сваи

на расстояниях, равных горизонтальным размерам основания

в каждом j-м уровне размещения измерителя 2 вертикальной деформации грунта относительно боковой поверхности сваи, по формулам (19-23).According to the obtained measurement data, the acceleration g _{l of the} settlement of pile 1 is calculated according to the formulas (1-2), the cycles of changes in the rate of settlement of the pile are distinguished, setting their boundaries according to the last value of the acceleration of the settlement of the pile g at g <0 in each i-th cycle of the change in the rate of settlement of the pile , determine the minimum value of the settlement rate of the pile on the descending branch of the cycle of the rate of settlement of the pile at g <0, the maximum value of the rate of settlement of the pile on the ascending branch of the cycle of the rate of settlement of the pile at g≥0 and the values of vertical deformations of the soil relative to the lateral surface of the pile 1 and vertical displacements of deep marks 3, synchronous to the bursts of the pile settlement rate determined by the conditions (3), the first burst of the pile settlement rate is taken as the beginning of the 2nd section of the graph of the dependence of the pile settlement rate on the pressing force and as the beginning of the formation of the first shear and separation crack in the soil foundation, and the subsequent bursts in the rate of settlement of the pile are taken as the beginning of the formation of other shear cracks and separation into clay base soils and calculate the horizontal dimensions of the subgrade

in each level in the directions from the meter 2 of the vertical deformation of the soil relative to the lateral surface of the pile 1 for each depth mark 3 according to the formulas (4-6), additionally determine the position of the beginning of each shear crack and tearing on the lateral surface of the pile 1 according to inequality (7), build maps of displacements of depth marks 3 in each level of their placement according to a well-known technique [see. S.V. Marfenko Geodetic work to monitor the deformation of structures. Tutorial. - M: MIIGAiK, 2004. - 36 p.] For their values, synchronous with bursts of values of the pile settlement rate, and calculate the values of the gradient of displacements of depth marks 3 at the points of their location according to the formula (8) and determine the directions of the greatest slopes of the surfaces of displacements of depth marks 3 according to the values of the gradients of their vertical displacements according to equation (9), determine the increments of the settlement of the model pile on the descending branch

and on the ascending branch

and the corresponding increments of the pressing force

in each i-th cycle of change in the rate of settlement of the model pile, the increments of elastic deformations of the soil base are calculated

on the increment of the pressing force

and plastic deformations of the soil base

on the increment of the pressing force

in each i-th cycle of changing the settlement rate of the model pile according to the formulas (10-12) and determine the increments of the resistance of the soil base to the immersion of the working pile and the corresponding increments of elastic and plastic deformations of the soil base in the entire range of the pressing force according to the formulas (13-17), then the bearing capacity of the working pile is determined according to the condition of limiting its settlement

according to the formula (18) and additionally calculate the increments of the vertical and horizontal components of the elastic reaction of the soil foundation for the working pile

at distances equal to the horizontal dimensions of the base

in each j-th level of placement of the meter 2 of the vertical deformation of the soil relative to the lateral surface of the pile, according to the formulas (19-23).

The invention allows:

- to increase the reliability and accuracy of determining the dimensions of the soil base of the pile, the sizes of shear cracks and tearing in the soil by directly measuring soil deformations at different levels of the soil base;

- to divide the settlement of the base of the model pile into elastic and plastic parts for further calculations of the resistance and deformations of the foundations of the working piles and the foundation as a whole;

- rigorously justify the use of the tested pile as a model of working piles in the same foundation;

- to obtain data for assessing the ratio of soil resistance forces around the pile shaft and under its lower end by separately measuring these values;

- to obtain data for assessing the interaction of adjacent piles in the foundation of the structure by calculating the reaction of the soil at the periphery of the foundation of the pile;

- use the tested pile to monitor the base of the foundation during the construction and operation of the structure;

- to determine the parameters of soil deformation anisotropy at the base of the pile along the greatest slopes of the surfaces of soil displacement caused by the movement of the pile.

Claims (61)

A method for testing a soil base by a pile, including applying a pressing force to a model pile, continuously increasing at a constant speed, determined depending on the diameter of the pile and physical properties of the soil, synchronous registration of the pressing force, the time of its application and settlement of the pile with a step of 0.005 mm of settlement of the pile, splitting the graph of the dependence of the rate of settlement of the model pile on the pressing force into three sections according to the average rate of settlement of the pile in each of them and the calculation of the bearing capacity of the working pile by the value of the pressing force at the end of the 2nd section of the graph and by the coefficients of similarity of the model pile, characterized in that in as a model pile, a natural bored pile is used in the foundation of the structure, a soil pressure sensor is placed at the lower end of the model pile, meters of vertical soil deformation relative to the lateral surface of the pile are placed on the lateral surface of the model pile at the levels of the middle of each engineering-geological element, folded by clay soil, in which the resistance to immersion of the probe at a speed of 5 mm / min during static sounding changes cyclically, and at the same levels depth marks are placed, at least 4, along a closed contour in the plan with a radius of 1-2 diameters of the pile from the axis of the pile in directions from the axis of the model pile to adjacent working piles in a given pile foundation and fix their coordinates in plan relative to the pile, while additionally registering vertical deformations of the soil relative to the lateral surface of the pile, vertical displacements of depth marks and soil pressure under the lower end of the pile synchronously registering the settlement of the pile with a step of 0.005 mm, the settlement of the pile, and after reaching the final value of the pressing force at its constant value until the settlement of the pile is stabilized according to the condition of 0.005 mm / h, the settlement of the pile, the time of its registration, vertical deformations of the soil relative to the lateral surface of the pile and vertical displacements of depth marks in all levels of their placement and yes The emergence of the soil under the lower end of the pile is synchronous with the settlement of the pile with a step of 0.005 mm of the settlement of the pile, and according to the measurements, the acceleration g _l , mm / kPa ² , the settlement of the pile is calculated by the formula

where ƒ ₁ - pile settlement rate, mm / kPa;

s _l and P _l - I-th values of pile settlement, mm, and pressing force, kPa; I - registration number of the pile settlement value; the cycles of change in the rate of settlement of the pile are distinguished, setting their boundaries according to the last value of the acceleration of settlement of the pile g at g <0 in each i-th cycle of change in the rate of settlement of the pile, where i is the number of the cycle of change in the rate of settlement of the pile, determine the minimum value of the rate of settlement of the pile

on the descending branch of the cycle, the rate of settlement of the pile at g <0, the maximum value of the rate of settlement of the pile

on the ascending branch of the cycle, the settlement rate of the pile at g≥0 and the values of vertical deformations of the soil relative to the lateral surface of the pile and vertical displacements of depth marks, synchronous to bursts of the rate of settlement of the pile, determined by the conditions

the first surge in the settlement rate of the pile is taken as the beginning of the second section of the graph of the dependence of the rate of settlement of the pile on the pressing force and as the beginning of the formation of the first shear and separation crack in the soil base, and subsequent bursts in the rate of settlement of the pile are taken as the beginning of the formation of other shear and separation cracks in clayey base soils and calculate the horizontal dimensions of the subgrade

m, in each level in the directions from the meter of the vertical deformation of the soil relative to the lateral surface of the pile for each depth mark according to the formulas

Where

- the distance of the depth mark to the j-th meter of the vertical deformation of the soil relative to the lateral surface of the pile at the level of its placement, m;

and

- vertical displacements of the depth mark and vertical deformations of the soil relative to the lateral surface of the pile at the j-th level of placement, respectively, synchronous to the bursts of the values of the settlement rate of the pile on the ascending branch of the i-th cycle of the settlement rate of the pile, taken positive if their direction coincides with the direction of settlement of the pile, mm,

Where

and

- vertical displacements of the depth mark and vertical deformations of the soil relative to the lateral surface of the pile at the j-th level of placement, respectively, synchronous to the bursts of the values of the settlement rate of the pile on the descending branch of the i-th cycle of the settlement rate of the pile, taken positive if their direction coincides with the direction of settlement of the pile, mm, additionally determine the position of the beginning of each shear and tear-off crack on the lateral surface of the pile by the inequality

where H is the depth of the upper boundary of the engineering-geological element, in the middle of which a meter is installed for the vertical deformation of the soil relative to the lateral surface of the pile, m;

- the depth of the point of the beginning of the shear and separation crack on the lateral surface of the pile, m;

- the depth of the point of placement on the lateral surface of the pile of the j-th meter of vertical soil deformation relative to the lateral surface of the pile, m, build maps of displacements of marks for their values, synchronous with bursts of values of the rate of settlement of the pile, and calculate the values of the gradient of displacements of depth marks at the points of their placement

Where

- vertical displacements of the depth mark, synchronous to the bursts of the values of the settlement rate of the pile, mm, and determine the directions of the greatest slopes of the surfaces of displacements of depth marks by the values of the gradients of their vertical displacements

Where

- gradient of displacements of depth marks at the point of placement of the depth mark in the j-th level of placement, f .;

- the greatest slope of the surface of displacements of depth marks at the point of placement of the depth mark in the j-th level of placement, i.e., determine the increments of settlement of the model pile on the descending branch

and on the ascending branch

and the corresponding increments of the pressing force

and

in each i-th cycle of change in the rate of settlement of the model pile, the increments of elastic deformations of the soil foundation are calculated

on the increment of the pressing force

and plastic deformations of the soil base

on the increment of the pressing force

in each i-th cycle of changing the settlement rate of the model pile according to the formulas

and determine the increments of the resistance of the soil base to the immersion of the working pile and the corresponding increments of elastic and plastic deformations of the soil base over the entire range of the pressing force according to the formulas

Where

and

and

- respectively, the increments of elastic and plastic deformations of the subgrade in each i-th cycle of change in the rate of settlement of the working pile, mm, and the corresponding increments of the pressing force, kN;

- coefficients of similarity of working and model piles;

and

- respectively, the diameter of the working and model piles, m;

and

- respectively, the loading rate of the working and model piles, kN / h;

- the duration of the ascending part of the cycle of changing the rate of settlement of the model pile, s;

and

- parameters of soil base creep, s, and mm, respectively determined from the equation

then the bearing capacity of the working pile is determined according to the condition of limiting its settlement

Where

the sum of the increments of the slump of the working pile, mm; s _u - the limiting value of the settlement of the foundation of the structure, mm, and additionally, the increments of the vertical and horizontal components of the elastic reaction of the soil base for the working pile are calculated

and

at distances equal to the horizontal dimensions of the base

in each j-th level of placement of the vertical soil deformation meter relative to the lateral surface of the pile, according to the formulas

Where

and

- calculated increments of the vertical and horizontal components of the elastic reaction of the soil foundation, kN, at distances

from the axis of the model pile;

Where

- the length of a part of the model pile below the j-th crack, which experiences elastic resistance of the soil foundation on the lateral surface, m; G _e - elastic soil constant, kPa;

- increment of the pressing force in the cycles of change in the settlement rate of the model pile in the test area after the j-th burst before the (j + 1) -th burst of the settlement rate, kN;

- increment of elastic settlement of the pound base on the descending part of the cycles of variation of the settlement rate of the model pile in the test area after the j-th burst before the (j + 1) -th burst of the settlement velocity, mm;

- increment of elastic settlement of the soil foundation on the ascending part of the cycles of changing the rate of model settlement of the pile in the test area after the j-th burst before the (j + 1) -th burst of the rate of its settlement, mm;

- the increment of the soil resistance of the base under the lower end of the model pile, synchronous with the increment of the elastic settlement of the soil base

kN.

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