Verification method for biased foundation pit support using internal support

Abstract

The present invention relates to the technical field of engineering construction, and discloses a verification method for biased foundation pit support using internal support, comprising the following steps: S1, analyzing the foundation pit environment, obtaining the active pressure side and the passive pressure side of the foundation pit, so as to determine the deformation direction of the foundation pit; S2, obtaining the height of the retaining member and the height of the cross section of the internal support member; S3, obtaining the stiffness of the soil reaction elastic support; S4, obtaining the horizontal load of the retaining member; S5, using the plane bar structure elastic fulcrum method to establish a structural analysis model, and calculating the internal force per linear meter of the retaining member and the internal support member and the overall deformation of the analysis model; S6, according to the soil reaction force standard value and the passive soil pressure standard value, checking whether the retaining member and the internal support member meet the requirements; S7, according to the overall deformation of the analysis model calculated in step S5, checking whether the deformation of the foundation pit support structure meets the requirements. The present invention can verify the overall safety of the foundation pit support structure, so as to facilitate the subsequent reasonable analysis and design.

Description

Technical Field

[0001] The invention relates to the technical field of engineering construction, and in particular to a calibration method for biased foundation pit support using internal supports. Background Art

[0002] During the excavation of the foundation pit, when the terrain, water level, overload and other factors on both sides of the foundation pit are inconsistent, the horizontal loads of the retaining components on both sides of the foundation pit will be unequal. If the foundation pit support structure uses internal support to transmit horizontal force at this time, a bias phenomenon will occur: the soil on the back of the retaining component on the side with greater active earth pressure still maintains a downward trend, while the displacement trend of the soil on the back of the retaining component on the other side changes to upward sliding, and the soil pressure on the back of the retaining component becomes passive earth pressure, causing the entire support structure to move to the same side as a whole. Therefore, the internal force and deformation of the overall support structure of the foundation pit in this case are quite different from those of the symmetrical foundation pit.

[0003] At present, the Technical Code for Building Foundation Pit Support (JGJ120-2012) recommends the use of the plane bar structure elastic support method for analysis, but it only stipulates the design method of the plane bar structure elastic support method for the single-sided support structure, and does not clearly propose a design method suitable for the biased foundation pit. In addition, the mainstream foundation pit design software has not proposed a modeling design method suitable for the biased foundation pit. Therefore, the existing technology lacks a verification method for the biased foundation pit support using internal support, especially how to verify the overall safety of the foundation pit support structure. Summary of the invention

[0004] The present invention provides a verification method for biased foundation pit support using internal supports, which can verify the overall safety of the foundation pit support structure to facilitate subsequent reasonable analysis and design.

[0005] In order to solve the above technical problems, the present invention provides a calibration method for biased foundation pit support using internal support, comprising the following steps:

[0006] S1. Analyze the foundation pit environment and obtain the active pressure side and passive pressure side of the foundation pit to determine the deformation direction of the foundation pit;

[0007] S2, obtaining the height of the retaining member and the height of the cross section of the inner support member;

[0008] S3, obtain the stiffness of the soil reaction elastic support;

[0009] S4. Obtain the horizontal load of the retaining member;

[0010] S5. According to the height of the retaining member, the height of the cross section of the inner support member, the stiffness of the soil reaction elastic support and the horizontal load of the retaining member, a structural analysis model is established by using the plane bar structure elastic fulcrum method to calculate the internal force per linear meter of the retaining member and the inner support member and the overall deformation of the analysis model;

[0011] S6. Check whether the retaining member and the inner support member meet the requirements according to the standard value of soil reaction force and the standard value of passive earth pressure;

[0012] S7. According to the overall deformation of the analysis model calculated in step S5, check whether the deformation of the foundation pit support structure meets the requirements.

[0013] Preferably, in the step S2, the retaining member and the inner supporting member are simplified into elastic rods, and the height of the retaining member and the height of the cross section of the inner supporting member are determined according to the principle of equal stiffness per meter.

[0014] Preferably, in step S3, the soil reaction elastic bearing is a horizontal elastic bearing that is only subjected to pressure and is arranged on the side where passive earth pressure is generated.

[0015] Preferably, in the step S3, the cohesion c and internal friction angle required for calculating the stiffness of the soil reaction elastic support are: The values ​​are taken from the geotechnical test parameters of the soil on the passive earth pressure side of the retaining element.

[0016] Preferably, in the step S4, the horizontal load of the retaining member includes water and soil load and overload on the back side of the retaining member.

[0017] Preferably, in the step S5, the initial distributed soil reaction force p of the soil with an upward sliding tendency on the back side of the retaining member is s0 Ignore the resistance caused by cohesion

[0018] Among them, p s0 --initial soil reaction strength;

[0019] c i --cohesion of the i-th soil layer (kPa);

[0020] K a,i --Active earth pressure coefficient of the i-th soil layer.

[0021] Preferably, in step S5, the structural analysis model is established using structural calculation software, and the height of the retaining member, the height of the cross-section of the internal support member, the stiffness of the soil reaction elastic support and the horizontal load of the retaining member are input into the structural calculation software to obtain the internal force per linear meter of both the retaining member and the internal support member and the overall deformation of the analysis model.

[0022] Preferably, in the step S6, when the soil reaction force standard value is greater than the passive earth pressure standard value, the retaining member and the inner support member do not meet the requirements.

[0023] Preferably, in step S6, the values ​​of the soil reaction force and the passive earth pressure are the soil reaction force and the passive earth pressure from the lateral displacement zero point upward on the back side of the retaining member and the soil reaction force and the passive earth pressure from the lateral displacement zero point downward on the side opposite to the back side of the retaining member.

[0024] Preferably, in steps S6 and S7, if the overall deformation of the retaining member, the internal support member and the foundation pit support structure does not meet the requirements, the requirements are met by adjusting the horizontal stiffness of the retaining member and the internal support member, the embedding depth of the retaining member and reinforcing the soil on the back of the retaining member.

[0025] Compared with the prior art, the calibration method of the biased foundation pit support using the internal support of the present invention has the following beneficial effects:

[0026] The present invention adopts the elastic fulcrum method of plane bar structure to establish a structural analysis model, conducts technical analysis on the eccentric foundation pit with internal support, obtains the structural deformation and stress conditions of the retaining components and the internal support components, and uses this to verify the overall safety of the eccentric foundation pit support structure and components, filling the gap in the existing technology in the verification method of eccentric foundation pit support with internal support. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of the steps of the present invention;

[0028] Figure 2 It is a schematic diagram of the installation of the retaining member and the inner supporting member of the present invention;

[0029] Figure 3 is a schematic diagram of a structural analysis model of the present invention;

[0030] Figure 4 This is a schematic diagram of the calculation depth of the soil reaction elastic support when there is a slope or foundation pit excavation on the soil layer on the passive earth pressure side;

[0031] Figure 5 It is a schematic diagram of the horizontal load of the present invention.

[0032] In the figure,

[0033] 1. Retaining member, 2. Internal supporting member, 3. Elastic bearing for soil reaction, 4. Zero point of horizontal displacement of retaining member. DETAILED DESCRIPTION

[0034] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0035] In the description of the present invention, it is necessary to understand that the orientations or positional relationships indicated by terms such as “upper”, “lower”, “left”, “right”, “top” and “bottom” are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0036] The biased foundation pit support structure with internal support of the present invention comprises a soil retaining member 1, an internal support member 2 and a soil reaction elastic support 3.

[0037] Combination Figure 1 The embodiment of the present invention provides a verification method for biased foundation pit support using internal support, comprising:

[0038] S1. Analyze the foundation pit environment and obtain the active pressure side and passive pressure side of the foundation pit to determine the deformation direction of the foundation pit;

[0039] S2, obtaining the height of the retaining member 1 and the height of the cross section of the inner support member 2;

[0040] S3, obtaining the stiffness of the soil reaction elastic support 3;

[0041] S4, obtaining the horizontal load of the retaining member 1;

[0042] S5. According to the height of the retaining member 1, the height of the cross section of the inner support member 2, the stiffness of the soil reaction elastic support 3 and the horizontal load of the retaining member 1, a structural analysis model is established by using the plane bar structure elastic fulcrum method to calculate the internal force per linear meter of the retaining member 1 and the inner support member 2 and the overall deformation of the analysis model;

[0043] S6. Check whether the retaining member 1 and the inner support member 2 meet the requirements according to the standard value of soil reaction force and the standard value of passive earth pressure;

[0044] S7. According to the overall deformation of the analysis model calculated in step S5, check whether the deformation of the foundation pit support structure meets the requirements.

[0045] Based on the above technical scheme, the present invention adopts the elastic fulcrum method of plane bar structure to establish a structural analysis model, conducts technical analysis on the eccentric foundation pit with internal support, obtains the structural deformation and stress conditions of the retaining member 1 and the internal support member 2, and verifies the overall safety of the eccentric foundation pit support structure and components, filling the gap in the existing technology in the verification method of eccentric foundation pit support with internal support.

[0046] Combination Figure 2 -5. Preferably, in step S2, the retaining member 1 and the inner supporting member 2 are simplified into elastic rods, and the height of the retaining member 1 and the height of the cross section of the inner supporting member 2 are determined according to the principle of equal stiffness per meter.

[0047] Preferably, in step S3, the soil reaction elastic bearing 3 is a horizontal elastic bearing that is only subjected to pressure and is arranged on the side where the passive earth pressure is generated.

[0048] Preferably, in step S3, the cohesion c and internal friction angle required for calculating the stiffness of the soil reaction elastic support 3 are: The value should be taken from the geotechnical test parameters of the soil on the passive earth pressure side of the retaining member 1. Specifically, the stiffness calculation formula of the soil reaction elastic support 3 used in the structural analysis model of the present invention refers to 4.1.4-4.1.7 of the "Technical Code for Building Foundation Pit Support" (JGJ120-2012). The calculation depth of the stiffness of the soil reaction elastic support 3 should take into account the influence of the terrain, such as Figure 4 As shown, the required soil cohesion c and internal friction angle are calculated. The value should be taken as the geotechnical test parameter of the soil on the passive earth pressure side of retaining element 1.

[0049] Preferably, in step S4, the horizontal load of the retaining member 1 includes the water and soil load and overload on the back of the retaining member. Specifically, the horizontal load of the retaining member 1 of the present invention is implemented in accordance with the "Technical Code for Building Foundation Pit Support" (JGJ120-2012), and the short-term covering is calculated as overload; for the situation where there is a slope or excavated foundation pit on the back of the support structure, it can also refer to the Guangdong Province "Technical Code for Building Foundation Pit Engineering" (DB / T 15-20-2016) and other local standards for implementation; at the same time, the initial distributed soil reaction force p of the soil body with an upward sliding trend on the back of the retaining member 1 s0 (For details, see Formula 4.1.4-1 on page 16 of the Technical Code for Construction Foundation Pit Support (JGJ120-2012)) Ignore the resistance generated by cohesion (For details of relevant parameters, please refer to Formula 3.4.2-1 on page 11 of the Technical Code for Construction Foundation Pit Support (JGJ120-2012)), where p s0 --initial soil reaction strength; c i --cohesion of the i-th soil layer (kPa); K a,i --The active earth pressure coefficient of the i-th layer of soil, the calculation diagram is as follows Figure 5 shown.

[0050] Preferably, in step S5, a structural analysis model is established using structural calculation software, and the height of the retaining member 1, the height of the cross-section of the internal support member 2, the stiffness of the soil reaction elastic support 3, and the horizontal load of the retaining member 1 are input into the structural calculation software to obtain the internal force per linear meter of both the retaining member 1 and the internal support member 2 and the overall deformation of the analysis model.

[0051] Preferably, in step S6, when the soil reaction force standard value is greater than the passive earth pressure standard value, the retaining member 1 and the inner support member 2 do not meet the requirements. Specifically, the calculation results should be reviewed according to the requirements of relevant specifications. The Technical Code for Building Foundation Pit Support (JGJ120-2012) 4.1.4 requires the comparison of the soil reaction force standard value of the embedded section with the passive earth pressure standard value of the embedded section. At this time, the force on the back of the retaining member 1 from the lateral displacement zero point to the upper part can be compared. The soil reaction force standard value is Figure 5 P ak1 The calculation of the standard value of passive earth pressure can refer to the attached Figure 4 .

[0052] Preferably, in steps S6 and S7, if the overall deformation of the retaining member 1, the inner support member 2 and the foundation pit support structure does not meet the requirements, the requirements are met by adjusting the horizontal stiffness of the retaining member 1 and the inner support member 2, the embedding depth of the retaining member 1 and reinforcing the soil on the back of the retaining member 1. Specifically, if the requirements of the specification are not met, the design scheme should be adjusted, such as increasing the embedding depth of the retaining member 1, adjusting the horizontal stiffness of the retaining member 1, increasing the ground overload on the back of the retaining member 1 on the passive earth pressure side, reinforcing the back soil, and locally reducing the slope and load on the back of the retaining member 1 on the active earth pressure side. The deformation control standard of the support pit support structure should be specifically formulated according to the specifications and surrounding environmental conditions.

[0053] It should be noted that the retaining member 1 is generally a reinforced concrete structure, and is simplified to a cross-sectional height that is consistent with its thickness per linear meter of equal stiffness. When the retaining member 1 is a member of uniform thickness such as a ground-connected wall, its cross-sectional height is the thickness of the retaining member 1; when the retaining member 1 is a member of non-uniform thickness such as a row of piles, it should be replaced by a method that the horizontal stiffness per linear meter along the foundation pit side is equal.

[0054] Figure 3 In the figure, the horizontal displacement zero point 4 of the retaining member is the "inflection point" of the retaining member 1.

[0055] In addition, the soil reaction elastic support 3 is an elastic support that is only subjected to pressure. A soil reaction elastic support 3 is set at intervals of 0.5m or 1m from the ground. The direction of the soil reaction elastic support 3 is consistent with the horizontal displacement direction of the retaining member 1. The stiffness value of the soil reaction elastic support 3 is the same as the horizontal reaction coefficient ks in 4.1.5-4.1.7 of the Technical Code for Building Foundation Pit Support (JGJ120-2012). The calculation depth of the elastic support is as follows: Figure 4 Za (corresponding to point a) and Zb (corresponding to point b) in the calculation of the cohesion c and internal friction angle used to calculate the value of "m" The geotechnical test value of the soil on one side of the passive earth pressure of retaining element 1 should be used;

[0056] The inner support member 2 is generally a reinforced concrete structure or a steel structure, and is used to transfer the horizontal force between the retaining members 1 on both sides.

[0057] An embodiment of the present invention provides a verification method for an eccentric foundation pit support using internal supports. The method refers to the "Technical Code for Building Foundation Pit Support" (JGJ120-2012), and the calculation adopts the elastic fulcrum method of the plane bar structure. It is suitable for the internal force and deformation calculation of the eccentric foundation pit support using internal supports. The calculation results can be used to verify the safety of the support structure under the eccentric stress state and to optimize the support structure scheme.

[0058] In summary, the embodiments of the present invention have the following beneficial effects:

[0059] 1. A simplified rod that is only subjected to axial force is used to simulate the inner support member 2 subjected to axial force, and the horizontal force is transmitted through the inner support member 2.

[0060] 2. By setting a soil reaction elastic support 3 with a certain stiffness, the soil reaction force distribution on the side where the soil displacement trend is upward sliding is simulated.

[0061] 3. According to the deformation of the overall support structure and the stress condition of the retaining member 1, the overall safety of the foundation pit support structure is verified and the design scheme of the foundation pit support structure is optimized.

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A method for verifying biased foundation pit support using internal support, characterized in that: The following steps are involved: S1. Analyze the foundation pit environment and obtain the active pressure side and passive pressure side of the foundation pit to determine the deformation direction of the foundation pit; S2, obtaining the height of the retaining member and the height of the cross section of the inner support member; S3, obtain the stiffness of the soil reaction elastic support; S4. Obtain the horizontal load of the retaining member; S5. According to the height of the retaining member, the height of the cross section of the inner support member, the stiffness of the soil reaction elastic support and the horizontal load of the retaining member, a structural analysis model is established by using the plane bar structure elastic fulcrum method to calculate the internal force per linear meter of the retaining member and the inner support member and the overall deformation of the analysis model; S6. Check whether the retaining member and the inner support member meet the requirements according to the standard value of soil reaction force and the standard value of passive earth pressure; S7, according to the overall deformation of the analysis model calculated in step S5, checking whether the deformation of the foundation pit support structure meets the requirements; In the step S6, when the soil reaction force standard value is greater than the passive earth pressure standard value, the retaining member and the inner support member do not meet the requirements; In the step S6, the values ​​of the soil reaction force and the passive earth pressure are the soil reaction force and the passive earth pressure of the back side of the retaining member from the lateral displacement zero point to the upper part and the soil reaction force and the passive earth pressure of the side opposite to the back side of the retaining member from the lateral displacement zero point to the lower part; In steps S6 and S7, if the overall deformation of the retaining members, internal support members and foundation pit support structure does not meet the requirements, the requirements are met by adjusting the horizontal stiffness of the retaining members and the internal support members, the embedding depth of the retaining members and reinforcing the soil on the back of the retaining members.

2. The calibration method for biased foundation pit support using internal support according to claim 1 is characterized in that: In the step S2, the retaining member and the inner supporting member are simplified into elastic rods, and the height of the retaining member and the height of the cross section of the inner supporting member are determined according to the principle of equal stiffness per meter.

3. The calibration method for biased foundation pit support using internal support according to claim 1 is characterized in that: In the step S3, the soil reaction elastic bearing is a horizontal elastic bearing that is only subjected to pressure and is arranged on the side where passive soil pressure is generated.

4. The calibration method for biased foundation pit support using internal support according to claim 3 is characterized in that: In the step S3, the soil reaction elastic support stiffness calculation required cohesion c, internal friction angle The values ​​are taken from the geotechnical test parameters of the soil on the passive earth pressure side of the retaining element.

5. The calibration method for biased foundation pit support using internal support according to claim 1 is characterized in that: In the step S4, the horizontal load of the retaining member includes the water and soil load and the overload on the back side of the retaining member.

6. The calibration method for biased foundation pit support using internal support according to claim 1 is characterized in that: In the step S5, the initial distributed soil reaction force p of the soil with an upward sliding tendency on the back side of the retaining member is s0 Ignore the resistance caused by cohesion Among them, p s0 --initial soil reaction strength; c i -- cohesion of the i-th soil layer; K a,i --Active earth pressure coefficient of the i-th soil layer.

7. The calibration method for biased foundation pit support using internal support according to claim 6 is characterized in that: In the step S5, the structural analysis model is established using structural calculation software, and the height of the retaining member, the height of the cross-section of the inner support member, the stiffness of the soil reaction elastic support and the horizontal load of the retaining member are input into the structural calculation software to obtain the internal force per linear meter of both the retaining member and the inner support member and the overall deformation of the analysis model.

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