A method for determining surface deformation of CFG pile composite foundation under reverse fault dislocation

Abstract

The present invention provides a method for determining the surface deformation of a CFG pile composite foundation under reverse fault dislocation. Combined with the fault rupture mode in the site cover layer, a method for analyzing the site stress of the fault rupture zone and a calculation formula are given to solve the problem of calculating the deformation of a vertical reinforced composite foundation adjacent to or across a strong earthquake surface rupture zone in an actual engineering project. (1) Combined with the fault rupture mode in the site cover layer, determine the calculation range of the site's surface uneven deformation, 1, 2, 3, j...n; (2) Calculate the deformation D of the surface point j caused by the bedrock dislocation j ; (3) Calculate the deformation of the composite foundation under the load of the building itself#imgabs0#(4) Calculate the foundation deformation S when the soil of the composite foundation is broken due to strong earthquake dislocation jQ ; (5) Calculate the total deformation T of the surface at point j j The present invention provides a parameter basis for the anti-fracture design of composite foundations of buildings on engineering sites across fault rupture zones, and provides basic research data for the safe use and toughness requirements of buildings in strong earthquake rupture zones.

Description

Technical Field

[0001] The invention relates to the field of deformation calculation and analysis of CFG pile composite foundation in construction engineering, and in particular to a method for determining surface deformation of a CFG pile composite foundation under reverse fault movement. Background Art

[0002] As one of the main treatment methods for strengthening the foundation of urban high-rise buildings, composite foundation has a wide range of engineering applications. Considering the applicability and economy of actual projects, the use of vertical reinforcement CFG pile composite foundation is more common. At the same time, earthquakes under fault structures occur frequently in my country, and the strong earthquake surface ruptures caused by earthquakes are the direct culprits of the destruction of surface buildings near active faults (fractures) at home and abroad in recent years. Due to factors such as active fault detection technology and engineering land restrictions, the study of the anti-fracture of buildings in the strong earthquake surface rupture zone has been applied to engineering design. Combined with earthquake damage analysis, it is shown that the uneven deformation of the building surface is an important design parameter that affects the safe use of the building.

[0003] Therefore, in order to quantify the degree of damage caused by fault rupture to the surface building site, the present invention takes the reverse fault as an example to calculate the uneven deformation of the surface, that is, to provide a method for determining the surface deformation of the CFG pile composite foundation under reverse fault dislocation. Summary of the invention

[0004] In view of this, the present invention provides a method for determining the surface deformation of a CFG pile composite foundation under reverse fault dislocation, so as to solve the problem of calculating the deformation of a vertically reinforced composite foundation adjacent to or across a strong earthquake surface rupture zone in actual engineering projects.

[0005] The specific technical solution is:

[0006] A method for determining the surface deformation of a CFG pile composite foundation under reverse fault dislocation is proposed. Combined with the fault rupture mode in the site cover layer, a site stress analysis method and calculation formula for the fault rupture zone are given to solve the problem of calculating the deformation of the vertical reinforced composite foundation adjacent to or across the strong earthquake surface rupture zone in actual engineering projects. The specific steps include:

[0007] (1) Combined with the fault rupture mode in the site cover layer, determine the calculation range of the site surface uneven deformation, 1, 2, 3, j···n;

[0008] (2) Calculate the deformation D of point j on the ground surface caused by bedrock dislocation j ;

[0009] (3) Calculation of composite foundation deformation under the load of the building itself

[0010] (4) Calculation of foundation deformation S when the soil of composite foundation under strong earthquake dislocation breaks jQ ;

[0011] (5) Calculate the total surface deformation T at point j j .

[0012] Combined with the fault rupture mode in the site cover layer, the cover layer produces two typical fault rupture zones under the action of reverse faults. The left side is a tensile rupture zone developed from the surface downward (the influence of uneven deformation of the surface is negligible), and the right side is a fan-shaped main rupture zone developed at the bedrock dislocation and penetrating to the surface. The present invention uses the fan-shaped rupture zone on the right side as the calculation background to calculate the uneven deformation of the surface of the fault rupture zone.

[0013] According to the relationship between bedrock dislocation and strong earthquake surface rupture zone, and combined with the rupture mode of soil in the thickness of the overburden, the uneven deformation of the surface of the construction project includes the surface deformation caused by bedrock dislocation D j , deformation of composite foundation under the load of the building itself Foundation deformation S when soil of composite foundation with dislocation breaks due to strong earthquake jQ It consists of three parts.

[0014] The calculation formula of the uneven deformation of the surface of the CFG pile composite foundation at point j in the i-th layer is as follows:

[0015]

[0016] in,

[0017]

[0018]

[0019] Among them, T j The rise of each j point on the surface of the rupture zone; S j D is the deformation of point j on the ground surface after soil compression caused by building load and fault dislocation load; j is the surface deformation at point j caused by the vertical displacement of the bedrock of the earthquake fault; S ji is the deformation of the i-th layer at point j; Q ji is the additional stress of the bedrock of the i-th layer at point j on the overlying soil layer; ji is the effective bulk density of the soil in the i-th layer at point j; Z ji is the soil depth of the i-th layer at point j; E spji is the calculated composite foundation compression modulus of the i-th layer of soil at point j; p 0j Add pressure to the building base; is the i-th layer of soil Z at point j ji The average additional stress coefficient of the base at depth.

[0020] According to the calculation formula of the surface deformation of the CFG pile composite foundation in the fracture zone of the construction site, the method for determining the deformation of each point on the surface of the specific construction site is as follows:

[0021] Determine the calculation range of uneven surface deformation of the construction site, 1, 2, 3, j...n, that is, the surface deformation corresponding to the red zone of the rupture zone. The deformation of each point in the calculation range of uneven surface is calculated and connected with a smooth curve to obtain the surface deformation.

[0022] It should be noted that 1 is the projection point of the upper and lower plate dislocation points of the bedrock to the surface, and point n is the intersection of the fault dislocation angle θ and the horizontal surface after extension. θ is the fault bedrock dislocation angle, and the vertical amount of the earthquake fault bedrock dislocation is D. Assuming that the left hanging plate is a rigid body, the left horizontal surface also rises by a distance D after the bedrock is lifted, that is, D j = D. The pile diameter of the CFG pile composite foundation is R, and the pile spacing is l.

[0023] Calculate the deformation of the i-th layer below the j-th point of the CFG pile composite foundation of the building site under the earthquake action across the reverse fault. The calculation method is as follows:

[0024] (1) Determine and calculate the site cover thickness Z based on the geotechnical engineering investigation report of the construction site n If there is bedrock, take the thickness of the soil layer overlying the bedrock of the site.

[0025] (2) Calculate the additional pressure P of the building site foundation at point j 0j , take the sum of the load F transferred to the foundation by the superstructure and the foundation load G divided by the foundation area A′, and subtract the self-weight stress value of the soil within the foundation burial depth d.

[0026]

[0027] where γ m is the weighted average density of soil within burial depth d.

[0028] (3) Calculate the self-weight stress σ of the soil under the site cji :

[0029] σ cji =∑γ ji Z ji

[0030] (4) Calculate the compression modulus E of the composite foundation of the soil at the selected site at point j and layer i spji ;

[0031] According to the difference between the surface point and the calculated layer, the soil in the red zone of the rupture zone under point j takes the rupture compression modulus E′ of the CFG pile composite foundation spji The conventional compression modulus E of the CFG pile composite foundation is taken from the foundation outside the fracture zone. spji, the calculation of the compression modulus of the composite foundation soil layer is selected as follows:

[0032] Site modulus of composite foundation outside the rupture zone:

[0033] E spji =mE pji +(1-m)E sji ;

[0034] Where E pji 、E sji They represent the compression modulus of the reinforcement (CFG pile) and soil (matrix) outside the rupture zone respectively.

[0035] Site modulus of composite foundation in the rupture zone:

[0036] E′ spji =mE′ pji +(1-m)E′ sji ;

[0037] Where E′ pji , E′ sji They represent the compression modulus of the site reinforcement (CFG pile) and soil (matrix) in the rupture zone respectively.

[0038] Where m is the CFG pile area replacement rate, and the replacement rate formula is

[0039] Compression modulus E of the reinforcement body (CFG pile body) outside the fracture zone pji , compression modulus E of soil (matrix) sji The pile specimen and the original soil specimen were selected for triaxial test calculation. The vertical pressure and confining pressure applied in the test are generally recommended to be K0γ ji z ji , K0 is the static lateral pressure coefficient of the soil (determined by static triaxial consolidation test). The test method for selecting the compression modulus of the site reinforcement body (CFG pile body) and soil body (matrix) in the fracture zone is the same as above. The vertical pressure and confining pressure applied in the test are generally recommended to be:

[0040]

[0041] (5) Calculation of α ji , according to the i layer, the average additional stress coefficient α in the range is given ji ;

[0042] Additional stress factor The value of is selected according to the type of foundation of the building project and the corresponding average additional stress coefficient is selected in the "Code for Design of Building Foundations" sheet.

[0043] (6) Calculate the additional stress value Q of the site bedrock on the overlying soil layer ji ;

[0044] Assuming that the shear force and pressure on the left vertical surface and the right inclined surface are negligible, a simplified force calculation model of the overlying soil layer on the bedrock is obtained, and the formula is derived and calculated.

[0045]

[0046] W is the force acting on the bottom of the active plate of the bedrock, A is the area of ​​the bottom action surface of the bedrock, G1 and G2 are the gravity of the overall uplift section and the rupture zone section of the calculation model, respectively, X is the width of the surface rupture zone, which is selected according to the width experience value of the rupture zone earthquake damage statistics, and the overall uplift section width is empirically taken as 10 times X, and B is the longitudinal length of the calculation site range. mZn It is the weighted average density of soil within the range of cover layer thickness Zn.

[0047] (7) Calculate the deformation S at point j of the site ji ;

[0048] The deformation S of the i-th layer at point j on the ground surface after soil compression caused by fault dislocation load jiQ :

[0049]

[0050] Deformation of the i-th layer at point j on the ground surface after soil compression caused by building load

[0051]

[0052] The deformation of layer i under point j of the covering layer,

[0053] (8) The deformation of point j on the ground surface after soil compression due to building loads and fault dislocation loads.

[0054]

[0055] (9) Calculate the total surface deformation T at point j j

[0056] T j =D j -S j

[0057] The vertical displacement of the bedrock of the earthquake fault is D. Assuming that the left hanging wall is a rigid body, the horizontal surface on the left side also rises by a distance D after the bedrock is lifted, that is, D j= D. The vertical amount of bedrock dislocation of the earthquake fault is selected according to the existing empirical formula based on the type of fault, magnitude, rupture length, etc.

[0058] (10) Determine the calculation range of uneven surface deformation of the construction site

[0059] The surface deformation corresponding to the red area of ​​the rupture zone can be obtained by calculating the deformation of each point 1, 2, 3, j...n on the surface and connecting them with a smooth curve to obtain the surface deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a diagram of the rupture pattern of the overburden soil under the influence of the earthquake fault at the project site;

[0061] Figure 2 It is a schematic diagram of the calculation of uneven deformation of the surface of the CFG pile composite foundation across the reverse fault;

[0062] Figure 3 It is the additional stress distribution diagram of soil layer for deformation calculation of CFG pile composite foundation across reverse fault;

[0063] Figure 4 This is a simplified model diagram for deriving additional stress in soil compression caused by fault dislocation;

[0064] Figure 5 This is a diagram of the steps for calculating surface deformation at a construction site across a fault rupture zone. DETAILED DESCRIPTION

[0065] In order to make the specific implementation steps and calculation formula application of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Based on the embodiments of the present invention, it is only used to describe the specific calculation formula and method of the present invention, and is not used to limit the scope of the present invention.

[0066] like Figure 1 The figure shows the fracture mode of the soil within the thickness of the overburden layer. The main fault fan-shaped fracture zone extends from the bedrock dislocation point to the surface. The depth range of the soil layer calculation at the project site is determined by the geotechnical engineering investigation report of the construction site. n .like Figure 2 This is a case diagram of a reverse fault rupture zone with a dip angle of θ across a CFG pile composite foundation at a construction site. A specific analysis of the uneven surface deformation of the site is as follows:

[0067] The specific calculation and analysis steps of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. The present invention provides a calculation formula and method for the uneven deformation of the surface of a CFG pile composite foundation under the action of reverse fault earthquakes with different inclination angles. Specifically, the following steps are included:

[0068] Step 1: According to the relationship between bedrock dislocation and strong earthquake surface rupture zone, see Figure 2 , Figure 3 , and combined with the rupture mode of the soil within the thickness of the overburden layer, the calculation boundary area of ​​the deformation zone is determined. The projection point of the bedrock dislocation point to the overburden surface is taken as the starting point 1 of the calculation range, and the intersection point of the extended line of the bedrock dislocation point and the surface is taken as the end point n of the calculation range, which is used as the calculation range of surface uneven deformation (1, 2, 3, j···n).

[0069] Step 2, according to Figure 2 The calculation range of the uneven deformation zone of the surface is determined in the calculation range, and the overburden layer under the calculation range is layered, with the thickness of each layer Z ji -Z j(i-1) The specific stratification can be calculated by various parameters in the geotechnical engineering survey report of the site, different compression moduli, groundwater levels, composite foundation depth ranges, etc. Select the j point on the surface of the calculation range and calculate the uneven deformation of the i-th layer.

[0070] Step 3: Through the site conditions and force analysis, it can be known that the uneven internal deformation of the site surface is mainly affected by the following factors. The uneven deformation of the construction project surface includes the surface deformation caused by bedrock dislocation D j , deformation of composite foundation under the load of the building itself Foundation deformation S when soil of composite foundation with dislocation breaks due to strong earthquake jQ It consists of three parts.

[0071] Step 4: Assuming that the left upper plate is a rigid body, select the vertical amount of bedrock dislocation of the earthquake fault on the site according to the existing empirical formula, D, based on the type, magnitude, and rupture length of the fault on the building site. j =D.

[0072] Step 5: Calculate the deformation of the composite foundation under the load of the building itself

[0073] Calculate the additional pressure P of the building site foundation at point j 0ji :

[0074]

[0075] According to the foundation type of the building project, select the corresponding average additional stress coefficient in the "Code for Design of Building Foundations"

[0076] Compression modulus E sp , obtained by taking the pile sample of layer i at point j and the original soil sample for triaxial test calculation.

[0077] The deformation of the composite foundation under the load of the building itself is obtained:

[0078]

[0079] Step 6: Calculate the foundation deformation S when the soil of the composite foundation is broken due to strong earthquake dislocation jiQ The bottom force W is calculated by using a simplified force calculation model of the overlying soil layer on the bedrock:

[0080]

[0081] Calculate the additional stress Q of bedrock on the overlying soil layer:

[0082]

[0083] Calculate the self-weight stress σ of layer i at point j cji :

[0084]

[0085] The foundation deformation when the soil of the composite foundation under strong earthquake dislocation breaks is obtained:

[0086]

[0087] Step 7: Calculate the deformation of layer i at point j

[0088]

[0089] Step 8: Calculate the deformation S of point j on the site j ,

[0090] Step 9: Calculate the total surface deformation T at point j j , T j =D j -S j

[0091] The above descriptions of the embodiments are not limitations of the solutions of the present invention. Therefore, the scope of protection of the present invention is not limited to the above embodiments. Any modifications and improvements that are merely formal but not substantial and made based on the concept of the present invention should be deemed to fall within the scope of protection of the rights of the present invention.

Claims

1. A method for determining surface deformation of a CFG pile composite foundation under reverse fault dislocation, characterized in that: Combined with the fault rupture mode in the site cover layer, the site stress analysis method and calculation formula of the fault rupture zone are given to solve the deformation calculation problem of the vertical reinforcement composite foundation adjacent to or across the strong earthquake surface rupture zone in actual engineering projects. The specific steps include: (1) Combined with the fault rupture mode in the site's covering layer, determine the calculation range of the site's surface uneven deformation. The projection point of the bedrock dislocation point onto the covering layer surface is taken as the calculation range starting point 1, and the intersection point of the extended line of the bedrock dislocation point and the surface is taken as the calculation range end point n, which are used as the surface uneven deformation calculation ranges 1, 2, 3, j...n; (2) Calculate the deformation D of point j on the ground surface caused by bedrock dislocation j ; (3) Calculation of composite foundation deformation under the load of the building itself The specific method of step (3) is as follows: the deformation of the composite foundation under the load of the building at point j and layer i is p 0j Add pressure to the building base; is the i-th layer of soil Z at point j ji The average additional stress coefficient of the base at depth; (4) Calculation of foundation deformation S when the soil of composite foundation under strong earthquake dislocation breaks jQ ; The specific method of step (4) is as follows: the foundation deformation S of the composite foundation soil body at the point j and layer i when the strong earthquake dislocation is broken jiQ : Q ji is the additional stress of the bedrock of the i-th layer at point j on the overlying soil layer; ji is the effective bulk density of the soil in the i-th layer at point j; W is the force acting on the bottom of the active plate of the bedrock; A is the area of ​​the bottom action surface of the bedrock; G1 and G2 are the gravity of the overall uplift section and the gravity of the rupture zone section of the calculation model respectively; X is the width of the surface rupture zone, which is selected according to the width empirical value of the rupture zone earthquake damage statistics, and the width of the overall uplift section is empirically taken as 10 times X; B is the longitudinal length of the calculation site range; (5) Calculate the total deformation T of the surface at point j j ; The specific method of step (5) is: Calculate the deformation of layer i at point j: Deformation S of point j in the building site j : The uplift of the rigid body on the upper wall of the reverse fault is D, and the total deformation of each j point on the surface of the rupture zone is T j , T j =D j -S j .

2. The method for determining surface deformation of CFG pile composite foundation under reverse fault dislocation according to claim 1 is characterized in that: The specific method of step (1) is to determine the calculation range of uneven surface deformation of the building site according to the relationship between bedrock dislocation and strong earthquake surface rupture zone, combined with the rupture mode of the covering layer thickness soil, 1, 2, 3, j...n, that is, the surface deformation corresponding to the red zone range of the rupture zone, and calculate the deformation of each point in the surface uneven calculation range and connect them with a smooth curve to obtain the surface deformation amount.

3. The method for determining surface deformation of CFG pile composite foundation under reverse fault dislocation according to claim 1 is characterized in that: The specific method of step (2) is as follows: the left hanging wall is assumed to be a rigid body. After the bedrock is lifted, the horizontal surface on the left side also rises by a distance D. The vertical amount of bedrock dislocation of the specific earthquake fault is selected according to the type, magnitude, and rupture length of the fault according to the existing empirical formula. The deformation D of the surface point j is j =D.

4. The method for determining surface deformation of CFG pile composite foundation under reverse fault dislocation according to claim 1 is characterized in that: The compression modulus E of the soil composite foundation of layer i at point j spji According to the difference between the surface point and the calculation layer, the corresponding parameters are selected for calculation. The calculation formulas for the composite foundation site modulus outside and inside the rupture zone are: HAVE BEEN spji =mE pji +(1-m)E sji , HAVE BEEN' spji =mE′ pji +(1-m)E′ sji ; Where E pji 、E sji and E′ pji , E′ sji They represent the compression modulus of the reinforcement body on the outside and inside of the rupture zone, i.e., the CFG pile body, and the soil body, i.e., the matrix, respectively. m is the area replacement rate of the CFG pile. The replacement rate formula is:

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