CN110093951B - Virtual soil pile model-based friction pile longitudinal vibration analysis method - Google Patents
Virtual soil pile model-based friction pile longitudinal vibration analysis method Download PDFInfo
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Abstract
The invention discloses a friction pile longitudinal vibration analysis method based on a virtual soil pile model, which adopts a Kelvin model and a virtual soil pile model, assumes that an entity pile and a virtual soil pile are both homogeneous and circular visco-elastic bodies with equal cross sections, and the interface of the entity pile and the virtual soil pile has continuous displacement and balanced stress; the soil around the pile and the soil at the bottom of the pile are all isotropic linear viscoelastic bodies, and the soil material damping adopts viscous damping; the upper surface of the pile surrounding soil layer is a free boundary without normal stress and shear stress, and the bottom of the pile substrate soil layer is a rigid substrate; establishing a longitudinal vibration control equation of a pile bottom soil body and a pile periphery soil body under the condition of vertical axis symmetry according to a viscoelastic dynamics theory, establishing a longitudinal vibration control equation of a virtual soil pile and a solid pile according to an Euler-Bernoulli rod member theory, and solving the vibration control equation by using Laplace transformation to obtain a time domain speed response function of any exciting force acting on the pile top so as to analyze the longitudinal vibration of the friction pile.
Description
Technical Field
The invention relates to the field of civil engineering, in particular to a friction pile longitudinal vibration analysis method based on a virtual soil pile model.
Background
In terms of pile-pile soil interface interaction, various methods have been studied to simplify the pile-soil interface interaction. A series of discrete Winkler spring-damper models study the longitudinal vibration characteristics of a rigid foundation. Although this method is simple, the parameter values depend on experience. On the basis of improvement, a plane strain analysis model is provided for considering the stress strain continuity of the soil body along the circumferential direction of the pile, and the model has a certain theoretical basis but cannot consider the change of the soil around the pile along the depth. Based on the consideration, a three-dimensional continuous medium model of soil around the pile is developed, and the model can consider the change of soil displacement and stress components along the depth, ignore the radial displacement of the soil and study the longitudinal vibration characteristic of the pile. Then, the influence of vertical and radial displacement of the soil body is considered at the same time, and a three-dimensional continuous medium model of soil around the pile is improved. The research is based on the assumption that the pile soil is completely contacted, and the assumption can exaggerate the constraint effect of the soil body on the pile body. Therefore, a plurality of students adopt a pile end rigid support model and consider the longitudinal vibration characteristic of the pile under the condition of relative slippage of a pile-soil interface. However, the pile tip rigid support model is used, and the fluctuation effect of the pile bottom soil is ignored. In the past, numerous scholars simplify the interaction of the pile and the pile bottom soil, for example, the pile bottom soil is simplified into a spring, a damper and an elastic half-space model, but the two methods have respective limitations, and on the basis, the poplar and winter English propose a virtual soil pile model, strictly consider the fluctuation effect of the pile bottom soil, and can simulate the engineering conditions of pile end sediment, pile end soil compaction and the like. However, a method for considering the longitudinal vibration characteristics of the pile foundation caused by the relative slip of the pile-soil interface and the pile bottom soil fluctuation effect is still lack of disclosure.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a friction pile longitudinal vibration analysis method based on a virtual soil pile model.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a friction pile longitudinal vibration analysis method based on a virtual soil pile model is characterized by comprising the following steps
S1: the following assumptions are introduced to establish a friction pile longitudinal vibration analysis model based on a virtual soil pile model: assuming that the solid pile and the virtual soil pile are homogeneous, round and uniform-section sticky elastomers, and the solid pile and the virtual soil pile have continuous displacement and balanced stress at the interface; assuming that the soil around the pile and the soil at the bottom of the pile are all isotropic linear viscoelastic bodies, and the soil material damping adopts viscous damping; assuming that the upper surface of the pile surrounding soil layer is a free boundary without normal stress and shear stress, and the bottom of the pile substrate soil layer is a rigid substrate;
s2: establishing a longitudinal vibration control equation of a pile bottom soil body and a pile periphery soil body under the condition of vertical shaft symmetry according to a viscoelastic dynamics theory;
establishing a virtual soil pile and solid pile longitudinal vibration control equation according to the Euler-Bernoulli rod piece theory;
pile-soil boundary conditions are established according to the assumption in step S1.
S3: and (4) solving the vibration equations of the soil body at the bottom of the pile and the soil body around the pile in the step S2 by using Laplace transformation, solving a control equation of longitudinal vibration of the virtual soil pile and the solid pile, and obtaining a time domain speed response function of any excitation force acting on the pile top so as to analyze the longitudinal vibration of the friction pile.
Preferably, the control equation of the longitudinal vibration of the soil at the bottom of the pile and the soil around the pile under the axial symmetry condition in the step S2 is
Wherein r is an axial coordinate, the zero point of the axial coordinate is positioned at the center of the circle of the section of the pile, z is a longitudinal coordinate, the zero point of the longitudinal coordinate is positioned on the free surface and is positive downwards, t is a time coordinate,the displacement is the longitudinal displacement of the soil body,is the Lame constant of the soil body and has Modulus of elasticity of the respective soil body
The poisson ratio, the viscous damping coefficient and the density correspond to the parameters of the soil at the bottom of the pile when j is 1, and correspond to the parameters of the soil around the pile when j is 2.
Preferably, the control equation of the longitudinal vibration of the soil pile in the step S2 is
The control equation of the longitudinal vibration of the solid pile is
In the formula, r is an axial coordinate, the zero point of the axial coordinate is positioned at the center of a circle of the section of the pile, z is a longitudinal coordinate, the zero point of the longitudinal coordinate is positioned on the free surface and is positive downwards, and t is a time coordinate; u. ofSPAnd uPRespectively the longitudinal displacement of the virtual soil pile and the solid pile,is the sectional area of pile body, r0Is the radius of the cross section of the pile,respectively the modulus of elasticity, viscous damping coefficient and density of the soil-deficient pile, EP、ηP、ρPThe elastic modulus, viscous damping coefficient and density of the solid pile are respectively.
Preferably, in step S2, the pile-soil boundary conditions include pile bottom soil boundary conditions, pile soil boundary conditions, boundary conditions of solid piles and soil deficiency piles, and pile soil coupling conditions, which are respectively
Pile bottom soil boundary conditions:
boundary conditions of soil around the pile:
boundary conditions of the solid pile and the deficient soil pile are as follows:
uSP|z=H=0 (6b)
pile-soil coupling conditions:
in the formula, r is an axial coordinate, the zero point of the axial coordinate is positioned at the center of a circle of the section of the pile, z is a longitudinal coordinate, the zero point of the longitudinal coordinate is positioned on the free surface and is positive downwards, and t is a time coordinate; hPThe soil layer around the pile is thickDegree HSPIs thick in the pile foundation layer, H is HP+HSPThe total thickness of the soil layer on the bedrock; q (t) any exciting force acts on the pile top;is the sectional area of pile body, r0Is the pile section radius; k is a radical ofSIs the dynamic stiffness of the distributed spring between the soil around the pile and the soil layer at the bottom of the pile, cSThe damping coefficient of the distributed damper between the soil around the pile and the soil layer at the bottom of the pile is shown; k is a radical offIs the elasticity coefficient of Kelvin model at the boundary between solid pile and soil around the pile, cfThe coefficient of a Kelvin model damper at the boundary between the solid pile and the soil around the pile is obtained; f. ofSP(z, t) is unit side frictional resistance of pile bottom soil to the deficient soil pile,the shear stress of the pile bottom soil at the interface of the pile bottom soil and the virtual soil pile is defined; f. ofP(z, t) is unit side friction resistance of soil around the pile to the solid pile,is the shear stress of the soil around the pile at the interface of the soil around the pile-the solid pile,the longitudinal relative slippage between the solid pile and the soil around the pile,the relative slip speed between the solid pile and the soil around the pile is obtained; u. ofSPAnd uPRespectively the longitudinal displacement of the virtual soil pile and the solid pile,respectively the modulus of elasticity, viscous damping coefficient and density of the pile bottom soil, EP、ηP、ρPRespectively the elastic modulus, viscous damping coefficient and density of the solid pile;is the longitudinal displacement of the soil body of the pile bottom soil,is the Lame constant of the soil body of the pile bottom soil and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the pile bottom soil;is the longitudinal displacement of the soil body of the soil around the pile,is the Lame constant of the soil around the pile, and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the soil around the pile;
preferably, in the step S3, the solving includes the following steps
Step S31: let j be 1, perform laplace transform on the control equation of the pile bottom soil longitudinal vibration under the axisymmetric condition in the formula (1), and perform laplace transform on the boundary condition formulas (4a) and (4b), to obtain a longitudinal displacement function of the pile bottom soil as
And the shear stress of the pile bottom soil at the pile bottom soil-deficient soil pile interface is
Step S32: let j be 2, perform laplace transform on the control equation of the longitudinal vibration of the soil around the pile under the axisymmetric condition in the formula (1), perform laplace transform on the boundary condition formulas (5a) and (5b), and obtain a longitudinal displacement function of the soil around the pile as
And the shear stress of the soil around the pile at the soil-solid pile interface around the pile is
Step S33: laplace transformation is carried out on the control equation (2) of the longitudinal vibration of the virtual soil pile and the boundary condition (7a), and the longitudinal vibration displacement function of the virtual soil pile is obtained on the basis of the shearing stress (9a) of the pile bottom soil at the virtual soil pile interface, which is obtained in the step S31
Performing Laplace transformation on the control equation (3) of the longitudinal vibration of the solid pile and the boundary condition (7c) to obtain a longitudinal vibration displacement function of the solid pile
Step S34: performing Laplace transformation on the boundary condition formula (4b) to obtain a complex impedance function at the interface of the virtual soil pile and the solid pile
Carrying out Laplace transformation on the boundary condition formulas (6c and 6d) to obtain a displacement impedance function of the pile top of the solid pile
Step S35: obtaining the complex stiffness of the pile top of the solid pile as
Kd=ZP=Kr+iKi (12)
Step S36: obtaining a pile top displacement function of (11b) according to the displacement impedance function of the pile top of the solid pile
Step S37: according to the pile top displacement function (13), obtaining a pile top speed frequency response function
Step S38: obtaining the time domain response of the unit impulse excitation using a Fourier transform from the pile-top velocity frequency response function (14)
Step S39: according to the convolution theorem, the time domain response of the pile top speed under the action of any exciting force q (t) is obtained as
g(t)=q(t)*h(t)=IFT[Q(iω)·Hv(iω)] (16)
When the exciting force is half-sine pulse excitationWhen T is pulse width, the time domain half-analysis of the pile top is solved into
In the above-mentioned steps, the step of,
z′=z-HPthe vertical coordinate is a local longitudinal coordinate, the zero point of the vertical coordinate is the top of the soil body at the bottom of the pile, and the direction is positive downwards; i ω is a laplace transform constant, i is an imaginary number unit, and ω is an excitation load frequency; n is a subscript;is the sectional area of pile body, r0Is the pile section radius; q (t) is an arbitrary excitation force;
for longitudinal displacement of the soil under the pile(ii) a laplace transform of;for longitudinal displacement of soil around pile(ii) a laplace transform of; u shapeSP(z', s) is the displacement of the pile body of the deficient soil pile, uSP(z', t) laplace transform; u shapeP(z, s) solid pile shaft displacement uP(z, t) laplace transform; q (i ω) is the fourier transform of any excitation force Q (t);
K0(·)、K1(.) is a zero-order and first-order second-class imaginary vector Bessel function respectively;
IFT [ ] is to perform Fourier transform operation
One-dimensional compression wave velocity of the deficient soil pile;is a solid pile oneThe wave velocity of the compression wave is measured;
EP、ηP、ρPrespectively the elastic modulus, viscous damping coefficient and density of the solid pile;
A1nis a constant determined by the coupling condition (7b) of the pile bottom soil and the deficient soil pile and the shear stress (9a) of the pile bottom soil at the interface of the pile bottom soil and the deficient soil pile; a. the2nIs a constant determined by the coupling conditions (7c, d) of the soil around the pile and the solid pile and the shear stress (9b) of the soil around the pile at the soil-solid pile interface;
β1n(n-1, 2, 3 …) is an equation of transcendence Middle beta 11The solution of (a) is to be solved,wherein k isSIs the dynamic stiffness of the distributed spring between the soil around the pile and the soil layer at the bottom of the pile, cSIs the damping coefficient of the distributed damper between the soil around the pile and the soil layer at the bottom of the pile,is the Lame constant of the soil body of the pile bottom soil and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the pile bottom soil;
β2n(n-1, 2, 3 …) is an equation of transcendenceMiddle beta2The solution of (a) is to be solved,wherein k isSIs the dynamic stiffness of the distributed spring between the soil around the pile and the soil layer at the bottom of the pile, cSIs between the soil around the pile and the soil layer under the pileThe damping coefficient of the distributed damper of (2),is the Lame constant of the soil body of the pile bottom soil and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the pile bottom soil;
MSP,NSPfor the coefficient to be determined, the following relationship is satisfied
MP,NPFor the coefficient to be determined, the following relationship is satisfied
The above steps also include the following symbol definitions
According to the technical scheme, the friction pile longitudinal vibration dynamic impedance algorithm system based on the virtual soil pile model adopts the Kelvin model and the virtual soil pile model, can simultaneously consider the relative slippage of a pile soil interface and the fluctuation effect of pile bottom soil, carries out rationalization analysis on factors influencing the pile foundation longitudinal vibration characteristic (such as the rigidity coefficient and the damping coefficient of the pile soil interface, the thickness of the pile bottom soil, the shear wave speed and the like), is suitable for the friction pile longitudinal vibration characteristic research, and can provide theoretical guidance and reference for pile foundation dynamic detection.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a model schematic of the present invention.
In the figure, 1 is soil around the pile, 2 is soil at the bottom of the pile, 3 is rigid foundation, 4 is solid pile, 5 is virtual soil pile, 6 is interface between soil around the pile and soil at the bottom of the pile, 7 is interface between soil around the pile and solid pile
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
In the following detailed description of the embodiments of the present invention, in order to clearly illustrate the structure of the present invention and to facilitate explanation, the structure shown in the drawings is not drawn to a general scale and is partially enlarged, deformed and simplified, so that the present invention should not be construed as limited thereto.
In the following detailed description of the present invention, reference is made to FIG. 1, which is a flow chart of the method of the present invention. As shown in the figure, the first and second,
a friction pile longitudinal vibration analysis method based on a virtual soil pile model is characterized by comprising the following steps:
s1: the following assumption is introduced to facilitate the establishment of a friction pile longitudinal vibration analysis model based on the virtual soil pile model.
1) Assuming that the solid pile and the virtual soil pile are homogeneous, round and uniform-section sticky elastomers, and the solid pile and the virtual soil pile have continuous displacement and balanced stress at the interface;
2) assuming that the soil around the pile and the soil at the bottom of the pile are all isotropic linear viscoelastic bodies, and the soil material damping adopts viscous damping;
3) the upper surface of the pile soil layer is assumed to be a free boundary without normal stress and shear stress, and the bottom of the pile soil layer is a rigid substrate.
A friction pile longitudinal vibration analysis method based on a virtual soil pile model is characterized by comprising the following steps
S1: the following assumptions are introduced to establish a friction pile longitudinal vibration analysis model based on a virtual soil pile model: assuming that the solid pile and the virtual soil pile are homogeneous, round and uniform-section sticky elastomers, and the solid pile and the virtual soil pile have continuous displacement and balanced stress at the interface; assuming that the soil around the pile and the soil at the bottom of the pile are all isotropic linear viscoelastic bodies, and the soil material damping adopts viscous damping; assuming that the upper surface of the pile surrounding soil layer is a free boundary without normal stress and shear stress, and the bottom of the pile substrate soil layer is a rigid substrate;
s2: and establishing a longitudinal vibration control equation of the soil body at the bottom of the pile and the soil body around the pile under the condition of vertical axis symmetry according to a viscoelastic dynamics theory.
The control equation of the longitudinal vibration of the pile bottom soil and the pile surrounding soil under the condition of axial symmetry is
Wherein r is an axial coordinate, the zero point of the axial coordinate is positioned at the center of the circle of the section of the pile, z is a longitudinal coordinate, the zero point of the longitudinal coordinate is positioned on the free surface and is positive downwards, t is a time coordinate,the displacement is the longitudinal displacement of the soil body,is the Lame constant of the soil body and has The elastic modulus, the Poisson ratio, the viscous damping coefficient and the density of the soil body are respectively, the parameters correspond to the parameters of the soil at the bottom of the pile when j is 1, and the parameters correspond to the parameters of the soil around the pile when j is 2.
And establishing a control equation of the longitudinal vibration of the virtual soil pile and the solid pile according to the Euler-Bernoulli rod member theory. The control equation of the longitudinal vibration of the virtual soil pile is
The control equation of the longitudinal vibration of the solid pile is
In the formula, r is an axial coordinate, the zero point of the axial coordinate is positioned at the center of a circle of the section of the pile, z is a longitudinal coordinate, the zero point of the longitudinal coordinate is positioned on the free surface and is positive downwards, and t is a time coordinate; u. ofSPAnd uPRespectively the longitudinal displacement of the virtual soil pile and the solid pile,is the sectional area of pile body, r0Is the radius of the cross section of the pile,respectively the modulus of elasticity, viscous damping coefficient and density of the soil-deficient pile, EP、ηP、ρPThe elastic modulus, viscous damping coefficient and density of the solid pile are respectively.
Pile-soil boundary conditions are established according to the assumption in step S1.
The pile-soil boundary conditions comprise pile bottom soil boundary conditions, pile soil boundary conditions, solid pile and deficient soil pile boundary conditions and pile soil coupling conditions which are respectively
Pile bottom soil boundary conditions:
boundary conditions of soil around the pile:
boundary conditions of the solid pile and the deficient soil pile are as follows:
uSP|z=H=0 (6b)
pile-soil coupling conditions:
in the formula, r is an axial coordinate, the zero point of the axial coordinate is positioned at the center of a circle of the section of the pile, z is a longitudinal coordinate, the zero point of the longitudinal coordinate is positioned on the free surface and is positive downwards, and t is a time coordinate; hPIs the thickness of the soil layer around the pile, HSPIs thick in the pile foundation layer, H is HP+HSPThe total thickness of the soil layer on the bedrock; q (t) any exciting force acts on the pile top;is the sectional area of pile body, r0Is the pile section radius; k is a radical ofSIs the dynamic stiffness of the distributed spring between the soil around the pile and the soil layer at the bottom of the pile, cSThe damping coefficient of the distributed damper between the soil around the pile and the soil layer at the bottom of the pile is shown; k is a radical offIs the elasticity coefficient of Kelvin model at the boundary between solid pile and soil around the pile, cfThe coefficient of a Kelvin model damper at the boundary between the solid pile and the soil around the pile is obtained; f. ofSP(z, t) is unit side frictional resistance of pile bottom soil to the deficient soil pile,the shear stress of the pile bottom soil at the interface of the pile bottom soil and the virtual soil pile is defined; f. ofP(z, t) is unit side friction resistance of soil around the pile to the solid pile,is the shear stress of the soil around the pile at the interface of the soil around the pile-the solid pile,the longitudinal relative slippage between the solid pile and the soil around the pile,the relative slip speed between the solid pile and the soil around the pile is obtained; u. ofSPAnd uPRespectively the longitudinal displacement of the virtual soil pile and the solid pile,respectively the modulus of elasticity, viscous damping coefficient and density of the pile bottom soil, EP、ηP、ρPRespectively the elastic modulus, viscous damping coefficient and density of the solid pile;is the longitudinal displacement of the soil body of the pile bottom soil,is the Lame constant of the soil body of the pile bottom soil and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the pile bottom soil;is the longitudinal displacement of the soil body of the soil around the pile,is the Lame constant of the soil around the pile, and has The elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the soil around the pile are respectively.
S3: and (4) solving the vibration equations of the soil body at the bottom of the pile and the soil body around the pile in the step S2 by using Laplace transformation, solving a control equation of longitudinal vibration of the virtual soil pile and the solid pile, and obtaining a time domain speed response function of any excitation force acting on the pile top so as to analyze the longitudinal vibration of the friction pile.
The solution includes the following steps
Step S31: let j be 1, perform laplace transform on the control equation of the pile bottom soil longitudinal vibration under the axisymmetric condition in the formula (1), and perform laplace transform on the boundary condition formulas (4a) and (4b), to obtain a longitudinal displacement function of the pile bottom soil as
And the shear stress of the pile bottom soil at the pile bottom soil-deficient soil pile interface is
Step S32: let j be 2, perform laplace transform on the control equation of the longitudinal vibration of the soil around the pile under the axisymmetric condition in the formula (1), perform laplace transform on the boundary condition formulas (5a) and (5b), and obtain a longitudinal displacement function of the soil around the pile as
And the shear stress of the soil around the pile at the soil-solid pile interface around the pile is
Step S33: laplace transformation is carried out on the control equation (2) of the longitudinal vibration of the virtual soil pile and the boundary condition (7a), and the longitudinal vibration displacement function of the virtual soil pile is obtained on the basis of the shearing stress (9a) of the pile bottom soil at the virtual soil pile interface, which is obtained in the step S31
Performing Laplace transformation on the control equation (3) of the longitudinal vibration of the solid pile and the boundary condition (7c) to obtain a longitudinal vibration displacement function of the solid pile
Step S34: performing Laplace transformation on the boundary condition formula (4b) to obtain a complex impedance function at the interface of the virtual soil pile and the solid pile
Carrying out Laplace transformation on the boundary condition formulas (6c and 6d) to obtain a displacement impedance function of the pile top of the solid pile
Step S35: obtaining the complex stiffness of the pile top of the solid pile as
Kd=ZP=Kr+iKi (12)
Step S36: obtaining a pile top displacement function of (11b) according to the displacement impedance function of the pile top of the solid pile
Step S37: according to the pile top displacement function (13), obtaining a pile top speed frequency response function
Step S38: obtaining the time domain response of the unit impulse excitation using a Fourier transform from the pile-top velocity frequency response function (14)
Step S39: according to the convolution theorem, the time domain response of the pile top speed under the action of any exciting force q (t) is obtained as
g(t)=q(t)*h(t)=IFT[Q(iω)·Hv(iω)] (16)
When the exciting force is half-sine pulse excitationWhen T is pulse width, the time domain half-analysis of the pile top is solved into
In the above-mentioned steps, the step of,
z′=z-HPthe vertical coordinate is a local longitudinal coordinate, the zero point of the vertical coordinate is the top of the soil body at the bottom of the pile, and the direction is positive downwards; i ω is a laplace transform constant, i is an imaginary number unit, and ω is an excitation load frequency; n is a subscript;is the sectional area of pile body, r0Is the pile section radius; q (t) is an arbitrary excitation force;
for longitudinal displacement of the soil under the pile(ii) a laplace transform of;for longitudinal displacement of soil around pile(ii) a laplace transform of; u shapeSP(z', s) is the displacement of the pile body of the deficient soil pile, uSP(z', t) laplace transform; u shapeP(z, s) solid pile shaft displacement uP(z, t) laplace transform; q (i ω) is the fourier transform of any excitation force Q (t);
K0(·)、K1are each of zero orderAnd a first order, second class imaginary vector Bessel function;
IFT [. cndot ] is to perform Fourier transform operation;
one-dimensional compression wave velocity of the deficient soil pile;the wave velocity of one-dimensional compression waves of the solid pile is obtained; eP、ηP、ρPRespectively the elastic modulus, viscous damping coefficient and density of the solid pile;
A1nis a constant determined by the coupling condition (7b) of the pile bottom soil and the deficient soil pile and the shear stress (9a) of the pile bottom soil at the interface of the pile bottom soil and the deficient soil pile; a. the2nIs a constant determined by the coupling conditions (7c, d) of the soil around the pile and the solid pile and the shear stress (9b) of the soil around the pile at the soil-solid pile interface;
β1n(n-1, 2, 3 …) is an equation of transcendenceMiddle beta1The solution of (a) is to be solved,wherein k isSIs the dynamic stiffness of the distributed spring between the soil around the pile and the soil layer at the bottom of the pile, cSIs the damping coefficient of the distributed damper between the soil around the pile and the soil layer at the bottom of the pile,is the Lame constant of the soil body of the pile bottom soil and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the pile bottom soil;
β2n(n1, 2, 3 …) is an equation of transcendenceMiddle beta2The solution of (a) is to be solved,wherein k isSIs the dynamic stiffness of the distributed spring between the soil around the pile and the soil layer at the bottom of the pile, cSIs the damping coefficient of the distributed damper between the soil around the pile and the soil layer at the bottom of the pile,is the Lame constant of the soil body of the pile bottom soil and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the pile bottom soil;
MSP,NSPfor the coefficient to be determined, the following relationship is satisfied
MP,NPFor the coefficient to be determined, the following relationship is satisfied
The above steps also include the following symbol definitions
In summary, the friction pile longitudinal vibration dynamic impedance algorithm system based on the virtual soil pile model can simultaneously consider the fluctuation effect of the soil body at the pile bottom and the relative slip of the pile soil interface by adopting the virtual soil pile model and the kelvin model, can be suitable for the longitudinal vibration problem when the pile soil interface of the friction pile slides relatively, and can provide theoretical guidance and reference for pile foundation dynamic detection.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (3)
1. A friction pile longitudinal vibration analysis method based on a virtual soil pile model is characterized by comprising the following steps
S1: the following assumptions are introduced to establish a friction pile longitudinal vibration analysis model based on a virtual soil pile model: assuming that the solid pile and the virtual soil pile are homogeneous, round and uniform-section sticky elastomers, and the solid pile and the virtual soil pile have continuous displacement and balanced stress at the interface; assuming that the soil around the pile and the soil at the bottom of the pile are all isotropic linear viscoelastic bodies, and the soil material damping adopts viscous damping; assuming that the upper surface of the pile surrounding soil layer is a free boundary without normal stress and shear stress, and the bottom of the pile substrate soil layer is a rigid substrate;
s2: establishing a longitudinal vibration control equation of a pile bottom soil body and a pile periphery soil body under the condition of vertical shaft symmetry according to a viscoelastic dynamics theory;
establishing a virtual soil pile and solid pile longitudinal vibration control equation according to the Euler-Bernoulli rod piece theory;
establishing pile-soil boundary conditions according to the assumption in step S1; the control equation of the longitudinal vibration of the soil at the bottom of the pile and the soil around the pile under the axial symmetry condition in the step S2 is
Wherein r is an axial coordinate, the zero point of the axial coordinate is positioned at the center of the circle of the section of the pile, z is a longitudinal coordinate, the zero point of the longitudinal coordinate is positioned on the free surface and is positive downwards, t is a time coordinate,the displacement is the longitudinal displacement of the soil body,is the Lame constant of the soil body and has Respectively representing the elastic modulus, the Poisson ratio, the viscous damping coefficient and the density of a soil body, wherein j is 1 and corresponds to a pile bottom soil parameter, and j is 2 and corresponds to a pile surrounding soil parameter; the control equation of the longitudinal vibration of the deficient soil pile in the step S2 is
The control equation of the longitudinal vibration of the solid pile is
In the formula, r is an axial coordinate, the zero point of the axial coordinate is positioned at the center of a circle of the section of the pile, z is a longitudinal coordinate, the zero point of the longitudinal coordinate is positioned on the free surface and is positive downwards, and t is a time coordinate; u. ofSPAnd uPRespectively the longitudinal displacement of the virtual soil pile and the solid pile,is the sectional area of pile body, r0Is the radius of the cross section of the pile,respectively the modulus of elasticity, viscous damping coefficient and density of the soil-deficient pile, EP、ηP、ρPRespectively the elastic modulus, viscous damping coefficient and density of the solid pile; f. ofSP(z, t) is unit side frictional resistance of pile bottom soil to the deficient soil pile; f. ofP(z, t) is unit side frictional resistance of soil around the pile to the solid pile;
s3: and (4) solving the vibration equations of the soil body at the bottom of the pile and the soil body around the pile in the step S2 by using Laplace transformation, solving a control equation of longitudinal vibration of the virtual soil pile and the solid pile, and obtaining a time domain speed response function of any excitation force acting on the pile top so as to analyze the longitudinal vibration of the friction pile.
2. The analysis method according to claim 1, wherein in step S2, the pile-soil boundary conditions include pile subsoil boundary conditions, solid pile and soil deficiency pile boundary conditions, and pile-soil coupling conditions
Pile bottom soil boundary conditions:
boundary conditions of soil around the pile:
boundary conditions of the solid pile and the deficient soil pile are as follows:
uSP|z=H=0 (6b)
pile-soil coupling conditions:
in the formula, r is an axial coordinate, the zero point of the axial coordinate is positioned at the center of a circle of the section of the pile, z is a longitudinal coordinate, the zero point of the longitudinal coordinate is positioned on the free surface and is positive downwards, and t is a time coordinate; hPIs the thickness of the soil layer around the pile, HSPIs a pile bottomThickness of soil layer, H ═ HP+HSPThe total thickness of the soil layer on the bedrock; q (t) any exciting force acts on the pile top;is the sectional area of pile body, r0Is the pile section radius; k is a radical ofSIs the dynamic stiffness of the distributed spring between the soil around the pile and the soil layer at the bottom of the pile, cSThe damping coefficient of the distributed damper between the soil around the pile and the soil layer at the bottom of the pile is shown; k is a radical offIs the elasticity coefficient of Kelvin model at the boundary between solid pile and soil around the pile, cfThe coefficient of a Kelvin model damper at the boundary between the solid pile and the soil around the pile is obtained; f. ofSP(z, t) is unit side frictional resistance of pile bottom soil to the deficient soil pile,the shear stress of the pile bottom soil at the interface of the pile bottom soil and the virtual soil pile is defined; f. ofP(z, t) is unit side friction resistance of soil around the pile to the solid pile,is the shear stress of the soil around the pile at the interface of the soil around the pile-the solid pile,the longitudinal relative slippage between the solid pile and the soil around the pile,the relative slip speed between the solid pile and the soil around the pile is obtained; u. ofSPAnd uPRespectively the longitudinal displacement of the virtual soil pile and the solid pile,respectively the modulus of elasticity, viscous damping coefficient and density of the pile bottom soil, EP、ηP、ρPRespectively the elastic modulus, viscous damping coefficient and density of the solid pile;is the longitudinal displacement of the soil body of the pile bottom soil, is the Lame constant of the soil body of the pile bottom soil and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the pile bottom soil;is the longitudinal displacement of the soil body of the soil around the pile,is the Lame constant of the soil around the pile, and has The elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the soil around the pile are respectively.
3. The analysis method according to claim 2, wherein in the step S3, the solving includes the following steps
Step S31: let j be 1, perform laplace transform on the control equation of the pile bottom soil longitudinal vibration under the axisymmetric condition in the formula (1), and perform laplace transform on the boundary condition formulas (4a) and (4b), to obtain a longitudinal displacement function of the pile bottom soil as
And the shear stress of the pile bottom soil at the pile bottom soil-deficient soil pile interface is
Step S32: let j be 2, perform laplace transform on the control equation of the longitudinal vibration of the soil around the pile under the axisymmetric condition in the formula (1), perform laplace transform on the boundary condition formulas (5a) and (5b), and obtain a longitudinal displacement function of the soil around the pile as
And the shear stress of the soil around the pile at the soil-solid pile interface around the pile is
Step S33: laplace transformation is carried out on the control equation (2) of the longitudinal vibration of the virtual soil pile and the boundary condition (7a), and the longitudinal vibration displacement function of the virtual soil pile is obtained on the basis of the shearing stress (9a) of the pile bottom soil at the virtual soil pile interface, which is obtained in the step S31
Performing Laplace transformation on the control equation (3) of the longitudinal vibration of the solid pile and the boundary condition (7c) to obtain a longitudinal vibration displacement function of the solid pile
Step S34: performing Laplace transformation on the boundary condition formula (4b) to obtain a complex impedance function at the interface of the virtual soil pile and the solid pile
Carrying out Laplace transformation on the boundary condition formulas (6c and 6d) to obtain a displacement impedance function of the pile top of the solid pile
Step S35: obtaining the complex stiffness of the pile top of the solid pile as
Kd=ZP=Kr+iKi (12)
Step S36: obtaining a pile top displacement function of (11b) according to the displacement impedance function of the pile top of the solid pile
Step S37: according to the pile top displacement function (13), obtaining a pile top speed frequency response function
Step S38: obtaining the time domain response of the unit impulse excitation using a Fourier transform from the pile-top velocity frequency response function (14)
Step S39: according to the convolution theorem, the time domain response of the pile top speed under the action of any exciting force q (t) is obtained as
g(t)=q(t)*h(t)=IFT[Q(iω)·Hv(iω)] (16)
When the exciting force is half-sine pulse excitationWhen T is pulse width, the time domain half-analysis of the pile top is solved into
In the above-mentioned steps, the step of,
z′=z-HPthe vertical coordinate is a local longitudinal coordinate, the zero point of the vertical coordinate is the top of the soil body at the bottom of the pile, and the direction is positive downwards; i ω is a laplace transform constant, i is an imaginary number unit, and ω is an excitation load frequency; n is a subscript;is the sectional area of pile body, r0Is the pile section radius; q (t) is an arbitrary excitation force;
for longitudinal displacement of the soil under the pile(ii) a laplace transform of;for longitudinal displacement of soil around pile(ii) a laplace transform of; u shapeSP(z', s) is the displacement of the pile body of the deficient soil pile, uSP(z', t) laplace transform; u shapeP(z, s) solid pile shaft displacement uP(z, t) laplace transform; q (i ω) is the fourier transform of any excitation force Q (t);
K0(·)、K1(.) is a zero-order and first-order second-class imaginary vector Bessel function respectively;
IFT [. cndot ] is to perform Fourier transform operation;
one-dimensional compression wave velocity of the deficient soil pile;the wave velocity of one-dimensional compression waves of the solid pile is obtained;
EP、ηP、ρPrespectively the elastic modulus, viscous damping coefficient and density of the solid pile;
A1nis a constant determined by the coupling condition (7b) of the pile bottom soil and the deficient soil pile and the shear stress (9a) of the pile bottom soil at the interface of the pile bottom soil and the deficient soil pile; a. the2nIs a constant determined by the coupling conditions (7c, d) of the soil around the pile and the solid pile and the shear stress (9b) of the soil around the pile at the soil-solid pile interface;
β1n(n-1, 2, 3 …) is an equation of transcendenceMiddle beta1The solution of (a) is to be solved,wherein k isSIs the dynamic stiffness of the distributed spring between the soil around the pile and the soil layer at the bottom of the pile, cSIs the damping coefficient of the distributed damper between the soil around the pile and the soil layer at the bottom of the pile,is the Lame constant of the soil body of the pile bottom soil and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the pile bottom soil;
β2n(n-1, 2, 3 …) is an equation of transcendenceMiddle beta2The solution of (a) is to be solved,wherein k isSIs the dynamic stiffness of the distributed spring between the soil around the pile and the soil layer at the bottom of the pile, cSIs the damping coefficient of the distributed damper between the soil around the pile and the soil layer at the bottom of the pile,is the Lame constant of the soil body of the pile bottom soil and has Respectively the elastic modulus, Poisson's ratio, viscous damping coefficient and density of the soil body of the pile bottom soil;
MSP,NSPfor the coefficient to be determined, the following relationship is satisfied
MP,NPFor the coefficient to be determined, the following relationship is satisfied
The above steps also include the following symbol definitions
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