Safety assessment method for quick-drop flash support foundation pit retaining structure

Abstract

The present invention relates to the technical field of foundation pit deformation assessment, and in particular to a method for safety assessment of a quick-drop flash support foundation pit retaining structure, comprising the following steps: establishing a foundation pit model; simulating the excavation of the first layer of earthwork, pouring the first concrete support, and performing the first calculation; simulating the excavation of the next layer of earthwork twice, one normal excavation, and the other over-excavation of 0.6m and using a flash-drop servo support, performing simulation calculations on the two simulation processes respectively, and recording the deformation and bending moment of the foundation pit retaining structure; extracting the maximum value of the deformation during the two simulation processes, and calculating the deformation control effectiveness index of the flash-drop servo support; extracting the maximum value of the bending moment during the two simulation processes, and calculating the bending moment control effectiveness index of the flash-drop servo support; judging whether it is the last layer of earthwork excavation, if so, ending the calculation, if not, repeating the above steps. The present invention objectively reflects the control effect of the flash-drop servo support on the deformation and bending moment of the foundation pit retaining structure through evaluation indicators.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit deformation assessment, and in particular to a safety assessment method for a quick-fall flash support foundation pit retaining structure. Background Art

[0002] The flash-down servo steel support is a new deep foundation pit construction technology. After the foundation pit is excavated, a temporary pre-support is quickly set up in a short period of time with the help of a vertical sliding module, and the pre-support force is applied to the retaining wall through the hydraulic jack servo module. Finally, the concrete support is quickly poured on the pre-support, which effectively controls the deformation of the support structure by greatly shortening the exposure time of the foundation pit. In the design process, the traditional design method faces some challenges. This is because the sliding support will inevitably cause over-excavation of the foundation pit during use, and the active support effect of the flash-down servo support can effectively control the deformation of the retaining structure and improve the bending moment of the retaining structure. However, there is currently a lack of a scientific and systematic evaluation method to evaluate the control effect of the flash-down servo support system on the deformation of the foundation pit retaining structure under over-excavation. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a method for safety assessment of a quick-drop flash support foundation pit retaining structure, so as to solve the problem that there is no scientific and systematic assessment method in the prior art to evaluate the control effect of the flash-drop servo support system on the deformation of the foundation pit retaining structure under over-excavation.

[0004] The technical solution to achieve the above purpose is: The present invention provides a method for safety assessment of a quick-fall flash support foundation pit retaining structure, comprising the following steps: S1: Establish a foundation pit model according to the project conditions, and set the number of earth excavation layers for the established foundation pit model; S2: simulate the excavation of the first layer of earthwork, simulate the pouring of the first concrete support in the foundation pit model, and perform the first calculation of the deformation of the foundation pit retaining structure; S3: simulate the excavation of the next layer of earthwork twice. The first simulation is to perform normal excavation of the next layer of earthwork, and the second simulation is to over-excavate the next layer of earthwork by 0.6m and use a flash-down servo support. The two simulation processes are simulated and calculated respectively, and the corresponding deformation and bending moment of the foundation pit retaining structure are recorded; S4: Extract the maximum value of the deformation of the foundation pit retaining structure during the two simulations respectively, and calculate the deformation control effectiveness index of the flash-down servo support; S5: Extract the maximum value of the bending moment of the foundation pit retaining structure during the two simulations respectively, and calculate the effectiveness index of the bending moment control of the flash-down servo support; S6: Determine whether it is the last layer of earth excavation. If so, end the calculation. If not, repeat steps S3 to S5.

[0005] A further improvement of the safety assessment method of the quick-drop flash support foundation pit retaining structure of the present invention is that in step S4, the deformation control effectiveness index of the flash-drop servo support is calculated by the following formula: Formula 1, In formula 1, is the effectiveness index of deformation control of the flash-down servo support. is the maximum deformation of the foundation pit retaining structure under normal excavation conditions, It is the maximum deformation of the foundation pit retaining structure when over-excavation is 0.6m and flash-down servo support is used.

[0006] A further improvement of the safety assessment method for the quick-drop flash support foundation pit retaining structure of the present invention is that in step S5, the moment control effectiveness index of the flash-drop servo support is calculated by the following formula: Formula 2: In formula 2, is the moment effectiveness index of the flash-down servo support. is the maximum bending moment of the foundation pit retaining structure under normal excavation conditions, It is the maximum bending moment of the foundation pit retaining structure when over-excavation is 0.6m and flash-down servo support is used.

[0007] A further improvement of the safety assessment method of the rapid-fall flash support foundation pit retaining structure of the present invention is that in step S3, the elastic foundation beam method is used to perform simulation calculations on the two simulation processes respectively.

[0008] A further improvement of the safety assessment method of the quick-fall flash support foundation pit retaining structure of the present invention is that the elastic foundation beam method is used to perform simulation calculations on two simulation processes respectively, including the following steps: The retaining structure of unit width is taken as a vertical elastic foundation beam. The support or anchor rod and the soil act on the foundation beam by a series of springs. Instead, the foundation beam is subjected to each spring force Under the action, the displacement coordination equation at each spring support point is: Equation 1, In equation 1, Indicated in Under the effect is the displacement of the foundation beam, is the flexibility coefficient, i ranges from 1 to n, and j ranges from 1 to n-1; is the vertical distance from the action point to the origin, and the value of i ranges from 1 to n; is the horizontal displacement of the beam at the origin; is the rotation angle of the beam at the origin; is the displacement of the beam under the action of external force, and the value of i ranges from 1 to n; Combined with the following force balance equation, equation 2 indicates that the sum of the horizontal components of the external force acting on the foundation beam is 0, and equation 3 indicates that the bending moment vector acting on the foundation beam is 0. ; Equation 2, ; Equation 3, In equation 2 and equation 3, represents the horizontal component of the external force acting on the beam, represents the bending moment acting on the beam; The coefficient matrices in equations 2 and 3 are abbreviated as I and Y, and the equations to be solved are as follows: Equation 4, This can be solved , , …, , and The bending moment and shear force at any section of the foundation beam can be obtained by the section method; the bending moment M of the retaining structure is approximately equal to the bending moment M of the foundation beam. 0 , under normal excavation conditions, the maximum value of the bending moment of the foundation beam section is taken as ; When the over-excavation is 0.6m and the flash-down servo support is used, the maximum value of the bending moment of the foundation beam section is ; The displacement of the foundation beam at any spring is: Equation 5, In equation 5, represents the displacement of the foundation beam at any spring, represents the soil spring stiffness at any spring point, and the deformation of the retaining structure δ n Approximately equal to the displacement of the foundation beam Δ n , under normal excavation conditions, the maximum displacement of the foundation beam is taken as ; When the over-excavation is 0.6m and the flash-down servo support is used, the maximum displacement of the foundation beam is .

[0009] The beneficial effects of the safety assessment method of the quick-fall flash support foundation pit retaining structure of the present invention are: The present invention provides a safety assessment method for a quick-drop flash support foundation pit retaining structure. By introducing the assessment method into the traditional design method, the control effect of the flash-drop servo support on the deformation and bending moment of the foundation pit retaining structure can be objectively reflected through the assessment index. And through the effectiveness index, problems that may occur during the excavation process can be discovered in advance and corresponding measures can be taken to improve the safety of the foundation pit project. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The present invention is a flow chart of the safety assessment method of the rapid-fall flash support foundation pit retaining structure.

[0011] Figure 2 It is a deformation diagram of the foundation pit retaining structure under normal excavation conditions in the safety assessment method of the rapid-fall flash support foundation pit retaining structure of the present invention.

[0012] Figure 3 This is the deformation diagram of the foundation pit retaining structure when over-excavation is 0.6m and flash-drop servo support is used in the safety assessment method of the quick-drop flash-support foundation pit retaining structure of the present invention.

[0013] Figure 4 It is the bending moment diagram of the foundation pit retaining structure under normal excavation conditions in the safety assessment method of the rapid-fall flash support foundation pit retaining structure of the present invention.

[0014] Figure 5 This is the bending moment diagram of the foundation pit retaining structure when over-excavation is 0.6m and flash-drop servo support is used in the safety assessment method of the fast-drop flash-support foundation pit retaining structure of the present invention. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0016] See also Figure 1 The present invention provides a method for safety assessment of a quick-drop flash support foundation pit retaining structure, which is used to solve the problem that traditional design methods cannot accurately assess the deformation and bending moment control effect of the foundation pit retaining structure under the action of the flash-drop servo support. The present invention uses the "elastic foundation beam method" to accurately calculate the deformation and bending moment of the foundation pit retaining structure under normal excavation and over-excavation and the use of the flash-drop servo support, establish an evaluation index system, and scientifically and systematically evaluate the effectiveness of the flash-drop servo support, objectively reflecting the control effect of the flash-drop servo support system on the deformation and bending moment of the foundation pit retaining structure. The method for safety assessment of a quick-drop flash support foundation pit retaining structure of the present invention is described below in conjunction with the accompanying drawings.

[0017] See also Figure 1 , showing a flow chart of the safety assessment method of the quick-drop flash support foundation pit retaining structure of the present invention. Figure 1 , the safety assessment method of the rapid-fall flash support foundation pit retaining structure of the present invention is explained.

[0018] like Figure 1 As shown, the safety assessment method of the quick-fall flash support foundation pit retaining structure of the present invention comprises the following steps: S1: Establish a foundation pit model according to the engineering situation; according to the specific engineering situation, determine the basic engineering information such as excavation depth, retaining structure design parameters, layer parameters, and establish a basic model of the foundation pit; set the number of earthwork excavation layers for the established foundation pit model, and the set number of earthwork excavation layers can be m, where m is a positive integer greater than 1; S2: simulate the excavation of the first layer of earthwork, simulate the pouring of the first concrete support in the foundation pit model, and perform the first calculation of the deformation of the foundation pit retaining structure; S3: simulate the excavation of the next layer of earthwork twice. The first simulation is to perform normal excavation of the next layer of earthwork, and the second simulation is to over-excavate the next layer of earthwork by 0.6m and use a flash-down servo support. The two simulation processes are simulated and calculated respectively, and the corresponding deformation and bending moment of the foundation pit retaining structure are recorded; S4: Extract the maximum value of the deformation of the foundation pit retaining structure during the two simulations respectively, and calculate the deformation control effectiveness index of the flash-down servo support; S5: Extract the maximum value of the bending moment of the foundation pit retaining structure during the two simulations respectively, and calculate the effectiveness index of the bending moment control of the flash-down servo support; S6: Determine whether it is the last layer of earthwork excavation (i.e., determine whether it is the mth layer of earthwork excavation). If so, end the calculation; if not, repeat steps S3 to S5.

[0019] Furthermore, after the calculation is completed, the effectiveness indicators of the flash-down servo support on the deformation and bending moment control of the foundation pit retaining structure are statistically analyzed and evaluated.

[0020] Furthermore, in step S4, the deformation control effectiveness index of the flash-down servo support is calculated by the following formula: Formula 1, In formula 1, is the effectiveness index of deformation control of the flash-down servo support. is the maximum deformation of the foundation pit retaining structure under normal excavation conditions, It is the maximum deformation of the foundation pit retaining structure when over-excavation is 0.6m and flash-down servo support is used.

[0021] By calculating the deformation effectiveness index, the influence of using flash-down servo support on the deformation of foundation pit retaining structure under over-excavation can be evaluated scientifically and effectively.

[0022] Furthermore, in step S5, the moment control effectiveness index of the flash-down servo support is calculated by the following formula: Formula 2: In formula 2, is the moment effectiveness index of the flash-down servo support. is the maximum bending moment of the foundation pit retaining structure under normal excavation conditions, It is the maximum bending moment of the foundation pit retaining structure when over-excavation is 0.6m and flash-down servo support is used.

[0023] By calculating the bending moment effectiveness index, the influence of using flash-down servo support on the bending moment of foundation pit retaining structure under over-excavation condition can be evaluated scientifically and effectively.

[0024] Furthermore, in step S3, the elastic foundation beam method is used to perform simulation calculations on the two simulation processes respectively.

[0025] Furthermore, the elastic foundation beam method is used to simulate the two simulation processes respectively, including the following steps: The retaining structure of unit width is taken as a vertical elastic foundation beam. The support or anchor rod and the soil act on the foundation beam by a series of springs. Instead, the foundation beam is subjected to each spring force Under the action, the displacement coordination equation at each spring support point is: Equation 1, In equation 1, Indicated in Under the effect is the displacement of the foundation beam, is the flexibility coefficient, i ranges from 1 to n, and j ranges from 1 to n-1; is the vertical distance from the action point to the origin, and the value of i ranges from 1 to n; is the horizontal displacement of the beam at the origin; is the rotation angle of the beam at the origin; is the displacement of the beam under the action of external force, and the value of i ranges from 1 to n; Combined with the following force balance equation, equation 2 indicates that the sum of the horizontal components of the external force acting on the foundation beam is 0, and equation 3 indicates that the bending moment vector acting on the foundation beam is 0. ; Equation 2, ; Equation 3, In equation 2 and equation 3, represents the horizontal component of the external force acting on the beam, represents the bending moment acting on the beam; The coefficient matrices in equations 2 and 3 are abbreviated as I and Y, and combined with the displacement coordination equation (i.e. equation 1), the solution equation is as follows: Equation 4, This can be solved , , …, , and , the bending moment at any section of the foundation beam and shear It can be obtained by the cross-section method; the retaining structure bending moment M is approximately equal to the foundation beam bending moment M 0 , under normal excavation conditions, the maximum value of the bending moment of the foundation beam section is taken as ; When the over-excavation is 0.6m and the flash-down servo support is used, the maximum value of the bending moment of the foundation beam section is ; The displacement of the foundation beam at any spring is: Equation 5, In equation 5, represents the displacement of the foundation beam at any spring, represents the soil spring stiffness at any spring point, and the deformation of the retaining structure δ n Approximately equal to the displacement of the foundation beam Δ n , under normal excavation conditions, the maximum displacement of the foundation beam is taken as ; When the over-excavation is 0.6m and the flash-down servo support is used, the maximum displacement of the foundation beam is .

[0026] In a specific example, Figures 2 to 5 As shown in the figure, by comparing the effectiveness index of the flash-down servo support on the deformation and bending moment control of the foundation pit retaining structure, it can be seen that over-excavation of 0.6m will lead to increased deformation and bending moment of the foundation pit retaining structure, which will have an adverse effect on the foundation pit. The comparison results of the deformation and bending moment of the foundation pit retaining structure are summarized in Tables 1 and 2 below: Table 1: Summary of comparison results of foundation pit retaining structure deformation.

[0027]

[0028] Table 2: Summary of comparison results of bending moments of foundation pit retaining structures.

[0029]

[0030] In the early stage of excavation, over-excavation has a great adverse effect on the deformation and bending moment of the foundation pit retaining structure; however, as the foundation pit excavation progresses, the active support effect of the flash-drop servo support gradually reduces this adverse effect, and the relative increase in the deformation and bending moment of the foundation pit retaining structure is significantly reduced; after the foundation pit excavation is completed, the flash-drop servo support effectively reduces the deformation and bending moment of the foundation pit retaining structure, improves the working condition of the foundation pit retaining structure, and improves the safety of the foundation pit.

[0031] The present invention is described in detail above in conjunction with the embodiments of the accompanying drawings. A person skilled in the art can make various variations of the present invention according to the above description. Therefore, certain details in the embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention shall be the scope defined by the attached claims.

Claims

1. A method for safety assessment of a quick-fall flash support foundation pit retaining structure, characterized in that: The steps include: S1: Establish a foundation pit model according to the project conditions, and set the number of earth excavation layers for the established foundation pit model; S2: simulate the excavation of the first layer of earthwork, simulate the pouring of the first concrete support in the foundation pit model, and perform the first calculation of the deformation of the foundation pit retaining structure; S3: simulate the excavation of the next layer of earthwork twice. The first simulation is to perform normal excavation of the next layer of earthwork, and the second simulation is to over-excavate the next layer of earthwork by 0.6m and use a flash-down servo support. The two simulation processes are simulated and calculated respectively, and the corresponding deformation and bending moment of the foundation pit retaining structure are recorded; S4: Extract the maximum value of the deformation of the foundation pit retaining structure during the two simulations respectively, and calculate the deformation control effectiveness index of the flash-down servo support; S5: Extract the maximum value of the bending moment of the foundation pit retaining structure during the two simulations respectively, and calculate the effectiveness index of the bending moment control of the flash-down servo support; S6: Determine whether it is the last layer of earth excavation. If so, end the calculation. If not, repeat steps S3 to S5.

2. The safety assessment method for the rapid-fall flash support foundation pit retaining structure according to claim 1 is characterized in that: In step S4, the deformation control effectiveness index of the flash-down servo support is calculated by the following formula: Formula 1, In formula 1, is the effectiveness index of deformation control of the flash-drop servo support. is the maximum deformation of the foundation pit retaining structure under normal excavation conditions, It is the maximum deformation of the foundation pit retaining structure when over-excavation is 0.6m and flash-down servo support is used.

3. The safety assessment method for the rapid-fall flash support foundation pit retaining structure according to claim 1 is characterized in that: In step S5, the moment control effectiveness index of the flash-down servo support is calculated by the following formula: Formula 2: In formula 2, is the bending moment effectiveness index of the flash-down servo support. is the maximum bending moment of the foundation pit retaining structure under normal excavation conditions, It is the maximum bending moment of the foundation pit retaining structure when over-excavation is 0.6m and flash-down servo support is used.

4. The safety assessment method for the rapid-fall flash support foundation pit retaining structure according to claim 1 is characterized in that: In step S3, the elastic foundation beam method is used to perform simulation calculations on the two simulation processes respectively.

5. The safety assessment method for the rapid-fall flash support foundation pit retaining structure according to claim 4 is characterized in that: The elastic foundation beam method is used to simulate the two simulation processes separately, including the following steps: The retaining structure of unit width is taken as a vertical elastic foundation beam. The support or anchor rod and the soil act on the foundation beam by a series of springs. Instead, the foundation beam is subjected to each spring force Under the action, the displacement coordination equation at each spring support point is: Equation 1, In equation 1, Indicated in Under the effect is the displacement of the foundation beam, is the flexibility coefficient, i ranges from 1 to n, and j ranges from 1 to n-1; is the vertical distance from the action point to the origin, and the value of i ranges from 1 to n; is the horizontal displacement of the beam at the origin; is the rotation angle of the beam at the origin; is the displacement of the beam under the action of external force, and the value of i ranges from 1 to n; Combined with the following force balance equation, equation 2 indicates that the sum of the horizontal components of the external force acting on the foundation beam is 0, and equation 3 indicates that the bending moment vector acting on the foundation beam is 0. ; Equation 2, ; Equation 3, In equation 2 and equation 3, represents the horizontal component of the external force acting on the beam, represents the bending moment acting on the beam; The coefficient matrices in equations 2 and 3 are abbreviated as I and Y, and the equations to be solved are as follows: Equation 4, This can be solved , , …, , and The bending moment and shear force at any cross section of the foundation beam can be obtained by the cross section method; the bending moment M of the retaining structure is approximately equal to the bending moment M0 of the foundation beam. Under normal excavation conditions, the maximum value of the bending moment of the foundation beam cross section is taken as ; When the over-excavation is 0.6m and the flash-down servo support is used, the maximum value of the bending moment of the foundation beam section is ; The displacement of the foundation beam at any spring is: Equation 5, In equation 5, represents the displacement of the foundation beam at any spring, represents the soil spring stiffness at any spring point, and the deformation of the retaining structure δ n Approximately equal to the displacement of the foundation beam Δ n , under normal excavation conditions, the maximum displacement of the foundation beam is taken as ; When the over-excavation is 0.6m and the flash-down servo support is used, the maximum displacement of the foundation beam is .

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