CN106777648A - Pile foundation anti-seismic analysis method considering soil liquefaction - Google Patents

Abstract

The invention relates to a pile foundation anti-seismic analysis method considering soil liquefaction, which is characterized in that liquefaction effect analysis is carried out on liquefied foundation soil as fluid, a fluid mechanics constitutive model describing the hole pressure thixotropy of the liquefiable foundation soil is established, viscous shearing force acting on a pile body structure during liquefaction of the liquefiable foundation soil is mainly determined by the shear strain rate of the soil around a pile and the apparent viscosity representing the fluid characteristics of the soil, and a mathematical formula is more intuitive; the existing method considers the horizontal inertia force of the pile top and the nonlinearity of the foundation, but ignores the movement effect of the soil layer. The method for analyzing the earthquake resistance of the pile foundation by considering the liquefaction of the soil body can well consider the influence of soil layer rigidity, the flow effect of the liquefied soil body and the pore pressure development, which is not possessed by the traditional method.

Description

A Method for Seismic Analysis of Pile Foundation Considering Soil Liquefaction

technical field

The invention relates to an anti-seismic analysis method of a pile foundation considering soil liquefaction, and belongs to the technical field of geotechnical engineering and pile foundation.

Background technique

Pile foundations are widely used in high-rise buildings, highway bridges, ports and wharfs due to their characteristics of large bearing capacity, good stability, and small settlement value. The damage is severe under the earthquake load, which leads to the collapse and destruction of the superstructure. Therefore, the seismic performance of pile foundations in liquefiable sites has become a hot research topic in geotechnical earthquake engineering.

As an important means to evaluate the seismic performance of pile foundations in liquefiable sites, model tests cannot be widely used due to high cost and long time consumption. Numerical methods such as finite element and finite difference have become important methods for seismic analysis of pile foundations in liquefiable sites. However, due to the complexity of numerical modeling, these methods have great limitations in practical engineering applications. Regarding the calculation of pile body stress under the action of horizontal force, the m method is often used in my country. The m method considers the influence of stiffness by adjusting the value of m, but the m method cannot reflect the stress on the pile body at the interface of the soil layer. The reasons are: In liquefied sites, the effect of earthquakes on piles is equivalent to the sum of the horizontal inertial force at the top of the pile and the movement of the soil layer, while the m-method only considers the horizontal inertial force at the top of the pile and ignores the influence of soil layer movement during earthquakes. Although the P-y curve method considers the nonlinearity of the foundation, it does not consider the influence of the flow effect of liquefied soil, and sometimes it cannot accurately describe the pile-soil interaction response, such as the development of pore pressure and the movement effect of the soil layer. Liquefied soil has a strong rate correlation and pore pressure correlation. The existing methods do not take into account the flow effect of liquefied soil and the influence of pore pressure development on the pile foundation response.

Contents of the invention

The technical problem to be solved by the present invention is to provide a pile foundation seismic analysis method considering soil liquefaction that can efficiently evaluate the seismic performance of pile foundation structures in liquefaction sites, and is effectively used in the analysis of pile-soil interaction problems in liquefaction sites.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions: the present invention designs a pile foundation seismic analysis method considering soil liquefaction, and performs seismic stability analysis for pile foundations passing through liquefiable foundation soil, including the following steps:

Step 001. For the liquefiable foundation soil, use equivalent linearity instead of dynamic nonlinear characteristics to analyze the seismic response of a one-dimensional free liquefiable site, obtain the shear strain time history γ when the liquefiable foundation soil liquefies, and calculate the first-order Derivative, to obtain the shear strain rate when the liquefiable foundation soil liquefies

Step 002. Measure the effective confining pressure σ _c of the liquefiable foundation soil and the vibration pore pressure u during liquefaction, and determine the degree of difficulty of liquefaction of the liquefiable foundation soil according to the effective confining pressure σ _c and the compactness of the liquefiable foundation soil parameter α _u ; at the same time, obtain the apparent viscosity η ₀₁ of the liquefiable foundation soil entering the complete liquefaction stage;

Step 003. According to the pore pressure thixotropic fluid constitutive model shown below:

Obtain the viscous shear stress τ acting on the pile body when the liquefiable foundation soil liquefies;

Step 004. According to the viscous shear stress τ acting on the pile body when the liquefiable foundation soil liquefies, obtain the lateral load ΔP acting on the contact pile body when the liquefiable foundation soil liquefies, and at the same time, obtain the horizontal seismic inertial force of the pile body E;

Step 005. According to the sum of the lateral load ΔP acting on the contacted pile body when the liquefiable foundation soil liquefies, and the horizontal seismic inertial force E of the pile body, obtain the total side of the pile body that acts on the liquefiable foundation soil when it liquefies to the load P;

Step 006. According to the total lateral load P acting on the contacted pile body when the liquefiable foundation soil is liquefied, obtain the pile body bending moment and lateral displacement, and realize the seismic stability analysis of the pile foundation.

As a preferred technical solution of the present invention: in the step 002, a liquefiable soil sample having the same compactness as the liquefiable foundation soil is prepared, and an indoor undrained cycle triaxial test is carried out on the liquefiable soil sample, Obtain the shear stress τ ₀ and shear strain rate of the liquefiable soil sample after initial liquefaction Calculate the apparent viscosity of the liquefied soil sample entering the complete liquefaction stage That is, the apparent viscosity η ₀₁ of the liquefiable foundation soil entering the complete liquefaction stage can be obtained.

As a preferred technical solution of the present invention: in the step 004, according to the viscous shear stress τ acting on the pile body when the liquefiable foundation soil is liquefied, the following model is passed:

Obtain the lateral load ΔP acting on the contacting pile body when the liquefiable foundation soil liquefies, where d represents the diameter of the pile, L represents the length of the pile body in contact with the liquefiable foundation soil, and θ represents a point on the side of the pile and the center of the pile body section The angle formed by the connection line of , and any straight line passing through the center of the cross-section of the pile.

As a preferred technical solution of the present invention: in the step 004, the following model is adopted:

E＝α _h ξG _E α/g

Obtain the horizontal seismic inertia force E of the pile body; among them, α _h represents the horizontal acceleration of the seismic load, ξ represents the effect reduction coefficient of the earthquake action, G _E represents the gravity of the pile foundation, α represents the dynamic distribution coefficient of the seismic inertial force, and g represents acceleration of gravity.

Compared with the prior art, a pile foundation seismic analysis method considering soil liquefaction according to the present invention has the following technical effects: the pile foundation seismic analysis method considering soil liquefaction designed in the present invention will liquefy The foundation soil is regarded as a fluid to analyze the liquefaction effect, and a hydromechanical constitutive model is established to describe the thixotropy of the pore pressure of the liquefiable foundation soil. The shear strain rate of the soil is determined by the apparent viscosity that characterizes the fluid properties of the soil, and the mathematical formula is more intuitive; although the existing methods consider the horizontal inertial force at the top of the pile and the nonlinearity of the foundation, they ignore the soil layer. Motion effect, the seismic analysis method of pile foundation considering soil liquefaction designed in the present invention not only considers the attenuation effect of pore pressure development on soil stiffness, but also can well consider the stiffness of soil layer and the flow effect of liquefied soil and pore pressure The impact of development, which is not available in traditional methods.

Description of drawings

Fig. 1 is the flow chart of the pile foundation seismic analysis method that the present invention design considers soil liquefaction;

Fig. 2 is a schematic diagram of the lateral load calculation acting on the pile body when the liquefiable foundation soil is liquefied in the present invention;

Fig. 3 is a simplified analysis model of pile-soil interaction in the present invention.

detailed description

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

For the pile foundation in liquefiable foundation soil, the lateral load acting on the pile may not be the same under the condition of the same pile-soil relative displacement, which is due to the accumulation of soil pore pressure under the continuous seismic load. Although the existing simplified analysis methods for pile-soil interaction in liquefiable sites take into account the attenuation effect of pore pressure development on soil stiffness, they do not take into account the flow effect of liquefied foundation soil and the influence of apparent viscosity. The invention establishes a constitutive model of liquefiable foundation soil pore pressure thixotropic fluid, regards the liquefied foundation soil as a fluid to analyze the liquefaction effect, and replaces the side of the pile with the viscous shear force generated by the relative movement of the fluid with a certain viscosity and the pile Earth pressure, and the pile-soil interaction is analyzed by a pseudo-static calculation method.

As shown in Figure 1, the present invention designs a pile foundation seismic analysis method considering soil liquefaction, and performs seismic stability analysis for pile foundations passing through liquefiable foundation soil. In the actual application process, it specifically includes the following steps :

Step 001. For the liquefiable foundation soil, the equivalent linearity is used to replace the dynamic nonlinear characteristics, and the one-dimensional free liquefiable site seismic response analysis is carried out by PROSHAKE software, and the shear strain time history γ when the liquefiable foundation soil is liquefied is obtained, and the time history Calculate the first derivative to obtain the shear strain rate when the liquefiable foundation soil liquefies

Step 002. Measure the effective confining pressure _σc of the liquefiable foundation soil and the vibration pore pressure u during liquefaction, and determine the liquefaction difficulty parameter of the liquefiable foundation soil according to the effective confining pressure _σc and compactness of the liquefiable foundation soil α _u ; at the same time, obtain the apparent viscosity η ₀₁ of the liquefiable foundation soil entering the complete liquefaction stage.

Among them, for the apparent viscosity η ₀₁ of the liquefiable foundation soil entering the complete liquefaction stage, the specific method is as follows: prepare a liquefiable soil sample with the same compactness as the liquefiable foundation soil, and carry out indoor Undrained cyclic triaxial test to obtain the shear stress τ ₀ and shear strain rate of the liquefiable soil sample after initial liquefaction Calculate the apparent viscosity of the liquefied soil sample entering the complete liquefaction stage That is, the apparent viscosity η ₀₁ of the liquefiable foundation soil entering the complete liquefaction stage can be obtained.

Step 003. According to the pore pressure thixotropic fluid constitutive model shown below:

The viscous shear stress τ acting on the pile body when the liquefiable foundation soil liquefies is obtained.

As shown in Figure 2, during the interaction process between the pile body and the liquefied foundation soil, the viscous shear stress acts on the surroundings of the pile foundation and is affected by the flow effect of the soil layer, but the viscous shear stress on the pile on the back soil surface is more The direction of the soil surface should be small. For the convenience of analysis and simplified calculation, the following assumptions are made: 1) The liquefied foundation soil is an ideal linear fluid; 2) The motion of the liquefied foundation soil is an incompressible irrotational motion; The viscous shear stress is evenly distributed along the tangential direction of the pile circumference, and based on the load action mode for the pile foundation as shown in Figure 2, the following step 004 is performed.

Step 004. According to the viscous shear stress τ acting on the pile body when the liquefiable foundation soil liquefies, pass the following model:

The lateral load ΔP acting on the contacting pile body when the liquefiable foundation soil liquefies is obtained, where d represents the diameter of the pile, L represents the length of the pile body in contact with the liquefiable foundation soil, and θ represents a point on the side of the pile and the section of the pile body The angle formed by the line connecting the center of the circle and any straight line passing through the center of the pile section.

In order to explore the dynamic response of the pile, the pile is regarded as an Euler-Bernoulli beam, which assumes that: 1) the plane section of the vertical beam centerline before deformation is still a plane after deformation; 2) the plane of the cross section after deformation is still the same as the deformation The rear axis is perpendicular. Based on the above assumptions, the pile-soil interaction analysis is carried out, and the simplified analysis model is shown in Figure 3. The seismic action analysis of the pile foundation is carried out, and the horizontal seismic inertia force along the height of the pile body is obtained.

That is, at the same time, through the following model:

E＝α _h ξG _E α/g

Obtain the horizontal seismic inertia force E of the pile body; among them, α _h represents the horizontal acceleration of the seismic load, ξ represents the effect reduction coefficient of the earthquake action, G _E represents the gravity of the pile foundation, α represents the dynamic distribution coefficient of the seismic inertial force, and g represents acceleration of gravity.

Step 005. According to the sum of the lateral load ΔP acting on the contacted pile body when the liquefiable foundation soil liquefies, and the horizontal seismic inertial force E of the pile body, obtain the total side of the pile body that acts on the liquefiable foundation soil when it liquefies to the load P.

Step 006. According to the total lateral load P acting on the contacted pile body when the liquefiable foundation soil is liquefied, obtain the pile body bending moment and lateral displacement, and realize the seismic stability analysis of the pile foundation.

The seismic analysis method of pile foundations designed in the above technical scheme considering soil liquefaction regards the liquefied foundation soil as a fluid to analyze the liquefaction effect, and establishes a hydromechanical constitutive model describing the thixotropy of liquefiable foundation soil pores. The liquefiable foundation soil The viscous shear force acting on the pile structure during soil liquefaction is mainly determined by the shear strain rate of the soil around the pile and the apparent viscosity that characterizes the fluid properties of the soil. The mathematical formula is more intuitive; although the existing methods consider The horizontal inertial force at the top of the pile and the nonlinearity of the foundation ignore the movement effect of the soil layer. The seismic analysis method of the pile foundation considering the liquefaction of the soil designed in the present invention not only considers the attenuation of the stiffness of the soil layer by the development of pore pressure It can well consider the stiffness of the soil layer and the influence of the flow effect of liquefied soil and the development of pore pressure, which is not available in traditional methods.

The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and can also be made without departing from the gist of the present invention within the scope of knowledge possessed by those of ordinary skill in the art. Variations.

Claims (4)

1. A pile foundation seismic analysis method considering soil liquefaction, for passing through the pile foundation of liquefiable foundation soil, carries out seismic stability analysis, it is characterized in that, comprises the steps: Step 001. For the liquefiable foundation soil, use equivalent linearity instead of dynamic nonlinear characteristics to analyze the seismic response of a one-dimensional free liquefiable site, obtain the shear strain time history γ when the liquefiable foundation soil liquefies, and calculate the first-order Derivative, to obtain the shear strain rate when the liquefiable foundation soil liquefies Step 002. Measure the effective confining pressure σ _c of the liquefiable foundation soil and the vibration pore pressure u during liquefaction, and determine the degree of difficulty of liquefaction of the liquefiable foundation soil according to the effective confining pressure σ _c and the compactness of the liquefiable foundation soil parameter α _u ; at the same time, obtain the apparent viscosity η ₀₁ of the liquefiable foundation soil entering the complete liquefaction stage; Step 003. According to the pore pressure thixotropic fluid constitutive model shown below: $\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}$ Obtain the viscous shear stress τ acting on the pile body when the liquefiable foundation soil liquefies; Step 004. According to the viscous shear stress τ acting on the pile body when the liquefiable foundation soil liquefies, obtain the lateral load ΔP acting on the contact pile body when the liquefiable foundation soil liquefies, and at the same time, obtain the horizontal seismic inertial force of the pile body E; Step 005. According to the sum of the lateral load ΔP acting on the contacted pile body when the liquefiable foundation soil liquefies, and the horizontal seismic inertial force E of the pile body, obtain the total side of the pile body that acts on the liquefiable foundation soil when it liquefies to the load P; Step 006. According to the total lateral load P acting on the contacted pile body when the liquefiable foundation soil is liquefied, obtain the pile body bending moment and lateral displacement, and realize the seismic stability analysis of the pile foundation. 2. A kind of pile foundation seismic analysis method considering soil liquefaction according to claim 1, is characterized in that: in described step 002, prepare the liquefiable soil sample that has the same compactness as liquefiable foundation soil, and for The liquefiable soil sample was subjected to an indoor undrained cyclic triaxial test to obtain the shear stress τ ₀ and shear strain rate of the liquefiable soil sample after initial liquefaction Calculate the apparent viscosity of the liquefied soil sample entering the complete liquefaction stage That is, the apparent viscosity η ₀₁ of the liquefiable foundation soil entering the complete liquefaction stage can be obtained. 3. A pile foundation seismic analysis method considering soil liquefaction according to claim 1, characterized in that: in the step 004, according to the viscous shear stress τ acting on the pile body when the liquefiable foundation soil is liquefied, by The following model: $\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\mathrm{<span\; class="notranslate">\; \&tau;</span>}\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}$ Obtain the lateral load ΔP acting on the contacting pile body when the liquefiable foundation soil liquefies, where d represents the diameter of the pile, L represents the length of the pile body in contact with the liquefiable foundation soil, and θ represents a point on the side of the pile and the center of the pile body section The angle formed by the connection line of , and any straight line passing through the center of the cross-section of the pile. 4. A kind of pile foundation seismic analysis method considering soil liquefaction according to claim 1, is characterized in that, in described step 004, by following model: E＝α _h ξG _E α/g Obtain the horizontal seismic inertia force E of the pile body; among them, α _h represents the horizontal acceleration of the seismic load, ξ represents the effect reduction coefficient of the earthquake action, G _E represents the gravity of the pile foundation, α represents the dynamic distribution coefficient of the seismic inertial force, and g represents acceleration of gravity.