A checking calculation method for the anti-heave stability of the bottom of a narrow foundation pit

Abstract

The present application discloses a method for checking the anti-heave stability of the bottom of a narrow foundation pit in saturated cohesive strata when the embedment depth of the retaining member is relatively small. The method includes: obtaining the undrained shear strength of the soil layer at the foundation pit site, calculating the critical foundation pit width, and determining whether the foundation pit is a narrow foundation pit based on the comparison result between the actual foundation pit width and the critical foundation pit width. When it is determined to be a narrow foundation pit, the width of the sinking soil mass is inversely calculated from the actual foundation pit width, and the anti-heave safety factor under the foundation bearing capacity mode of the narrow foundation pit is calculated. Then, it is compared with the anti-heave safety factor of the circular arc sliding mode, and the smaller value is taken as the anti-heave safety factor of the bottom of the narrow foundation pit to judge the anti-heave stability of the bottom. Thus, the technical problems in the related art, such as the unreasonable judgment of narrow foundation pits and the selection of slip surfaces, the unclear preconditions for design and checking calculations of narrow foundation pits, and the lack of a calculation method for the anti-heave safety factor of narrow foundation pits under the foundation bearing capacity mode, are solved.

Description

Technical Field

[0001] This application relates to the technical field of geotechnical engineering, and particularly to a method for checking the anti-heave stability of the bottom of a narrow foundation pit in a saturated cohesive stratum. Background Art

[0002] The method for checking the stability and deformation of a foundation pit has always been an important topic in foundation pit engineering. The heave of the bottom of the foundation pit is a plastic heave deformation of the bottom soil that occurs during the excavation of the foundation pit due to the removal of the overlying pressure of the bottom soil and the action of the gravity of the soil outside the pit. The heave of the bottom of the pit can cause the ground around the foundation pit to collapse, endanger the safety of adjacent existing buildings and other facilities, seriously damage the bearing stratum of the foundation of the proposed building, and may also lead to the failure of the support system and the collapse of the foundation pit. Therefore, the check of the anti-heave of the bottom of the foundation pit is an important content of the foundation pit support design.

[0003] The current industry regulations mainly check the anti-heave problem of the bottom of the foundation pit based on the failure mode based on the failure of the foundation bearing capacity and the failure mode based on the circular arc slip surface. However, in recent engineering practices, it has been found that there are deficiencies in the current check method for the anti-heave of the bottom of the foundation pit in the industry regulations. Although the calculation method of the safety factor for the anti-heave problem of the bottom of the wide foundation pit involved in the regulations has been improved, neither the method in the regulations nor the improved method considers the influence of the foundation pit width, that is, it is only applicable to the check of the anti-heave stability of large-width foundation pits.

[0004] The anti-heave stability of the foundation pit is affected by various factors such as the width of the foundation pit, the depth of the foundation pit, the strength of the retaining member, and the depth of the embedded section. At present, common foundation pits such as subway stations, utility tunnels, and underground pipelines often have a small width. When they undergo heave failure, the slip surface is often restricted by the width of the foundation pit and is different from that of a wide foundation pit. Such foundation pits belong to the category of narrow foundation pits. The anti-heave safety factor of the bottom of a narrow foundation pit is generally higher than that of a wide foundation pit. Designing a narrow foundation pit with the traditional design check method for a wide foundation pit will underestimate the anti-heave safety factor and result in an overly conservative design.

[0005] In related technologies, the methods for checking the anti-heave stability of a narrow foundation pit may include the following several methods:

[0006] 1. Determine the anti-heave stability safety factor of the bottom of the pit according to the calculation method in the current specifications, including the check based on the foundation bearing capacity and the check based on the circular arc sliding mode. However, as mentioned above, this method is not applicable to narrow foundation pits.

[0007] 2. In related technologies, the uplifted sliding surface of the foundation pit can be approximated as a combined sliding surface of a circular arc surface and a vertical surface. The essence of this is to move the rotation center of the circular sliding surface downward, so that the arc passing through the lower end of the embedded section of the retaining member is reduced, so that the width of the narrow foundation pit can accommodate this circular sliding surface. However, whether analyzed from the perspective of mechanical principles or verified through numerical simulation calculations, the part of the retaining member above the assumed rotation center in this technology will also move significantly into the pit, that is, the entire embedded section rotates around the fulcrum of the lowest support.

[0008] 3. Other related technologies determine whether a pit is narrow based solely on whether the pit width can accommodate the arc sliding surface calculated based on a wide pit. If not, the pit is narrow. The center of the arc is then assumed to be movable so that the sliding surface does not extend beyond the opposite pit wall. For multiple potential arc sliding surfaces corresponding to different center points, the ratio of the corresponding anti-slip torque to the sliding torque is calculated using the strip method as a trial safety factor. The sliding surface corresponding to the minimum value is considered the most unfavorable sliding surface, and the corresponding safety factor is used as the safety factor for the pit verification.

[0009] However, the above-mentioned related technologies all have defects:

[0010] 1. The calculation model in Related Technology 1 does not consider the influence of the width of the foundation pit on the size of the uplift and failure slip surface at the bottom of the pit, and implicitly assumes that the width of the foundation pit is very large. Therefore, it is only applicable to foundation pits with a sufficiently large width, but not to narrow foundation pits. For narrow foundation pits, a relatively small safety factor will be given.

[0011] Secondly, the safety factor of pit bottom uplift calculated under the arc sliding mode will be seriously excessive when the embedment depth of the retaining member is small, and the maximum embedment depth (critical embedment depth) corresponding to the arc sliding mode is not taken into account.

[0012] Third, the specification recommends that the strength index of saturated clay be calculated using the consolidated undrained strength index, but in fact it is more reasonable to use the unconsolidated undrained shear strength index.

[0013] Fourth, the calculation method of the foundation bearing capacity verification method is too conservative when the embedment depth is small, because the shear force between the sunken soil outside the pit and the stable soil is ignored, and an item related to the foundation width in the foundation bearing capacity formula is ignored; and when the embedment depth is large, because it is still assumed that the embedded section will not be damaged by kicking and rotation, the calculated safety factor will be too large.

[0014] 2. In related technology 2, whether a foundation pit is narrow is determined based on the relative size of the embedded section depth and the foundation pit width. However, because it ignores the failure mode corresponding to the foundation bearing capacity verification, the judgment of the narrow foundation pit is not accurate. When the embedded depth of the retaining member is small, the narrow foundation pit will be judged as a wide foundation pit.

[0015] Secondly, the position of the center of the circular arc sliding failure surface is specified at the embedded section of the retaining member, rather than at the fulcrum position of the lowermost support. Thereafter, both the anti-heave moment and the heave moment are calculated based on this artificially specified center. However, in fact, the retaining member should rotate around the fulcrum position, and this assumption does not conform to the mechanical principle.

[0016] Thirdly, the verification is not carried out for saturated cohesive strata.

[0017] 3. In Related Art 3, when checking the circular arc sliding surface corresponding to the embedded depth of the retaining member according to the wide foundation pit, the ratio of the size of the circular arc sliding surface to the width of the foundation pit is used as the judgment standard for the width and narrowness of the foundation pit. When the embedded depth of the retaining member is small, a narrow foundation pit may be judged as a wide foundation pit because the failure mode at this time is very likely not the circular arc sliding surface mode.

[0018] Secondly, it is considered that the possible center position of the circular arc sliding surface moves within the horizontal plane where the lowermost support is located, and the constructed possible circular arc sliding surface is less reasonable. Because as mentioned above, the analysis according to the mechanical principle shows that the deformation of the retaining member rotates around the fulcrum of the lowermost support.

[0019] Thirdly, this technical solution searches for the sliding surfaces corresponding to the centers in both the horizontal plane where the lower support is located and the horizontal plane of the top surface of the foundation pit at the same time, but it does not consider the actual possible foundation bearing capacity failure mode, nor does it consider the possible critical embedded depth problem.

[0020] Fourthly, this technical solution also does not clearly specify the selection of the unconsolidated undrained strength index when checking saturated cohesive soil, and there are defects in the calculation of the strength of saturated cohesive soil.

[0021] In summary, there are problems in the related technologies such as the unreasonable judgment standard for narrow foundation pits and the selection of sliding surfaces, the unclear preconditions for design and verification of narrow foundation pits, and the lack of a calculation method for the anti-heave safety factor under the failure mode of foundation bearing capacity failure for narrow foundation pits, which need to be improved. Summary of the Invention

[0022] This application is made based on the inventor's recognition and discovery of the following problems:

[0023] For the anti-heave stability verification of narrow foundation pits, the following aspects need to be considered:

[0024] 1. For the judgment standard of narrow foundation pits, in the related technologies, the relative size of the foundation pit width and the embedded depth of the foundation pit retaining member is used to determine whether the foundation pit is a narrow foundation pit, that is, to judge according to whether the foundation pit width can accommodate the arc slip surface corresponding to the actual embedded depth. However, such a judgment standard is not applicable to the case where the embedded depth of the foundation pit retaining member is small. For example, when the embedded depth of the foundation pit is less than the foundation pit width, considering the arc slip surface, the foundation pit width will not affect the stability safety factor. But in fact, when the embedded depth of the retaining member is small, the failure mode of the bottom heave of the pit is likely to be the foundation bearing capacity failure mode rather than the arc slip mode. At this time, the relatively narrow foundation pit width will limit the slip surface of the foundation bearing capacity failure mode, thereby affecting the anti-heave stability, resulting in the related technologies being unable to correctly identify narrow foundation pits, and naturally unable to make a reasonable anti-heave stability check according to the actual situation.

[0025] 2. In the related technologies, based on the arc slip surface method in the wide foundation pit checking method, the rotation center position of the embedded section of the retaining member is moved to calculate the safety factor of the anti-heave stability of the narrow foundation pit. However, arbitrarily moving the position of the rotation fulcrum of the retaining member does not conform to the mechanical principle, and when the embedded depth is small, the failure slip surface should be closer to the failure mode of the foundation bearing capacity failure rather than the arc slip surface, which leads to a difference between these methods and the actual situation of the narrow foundation pit, and there will be a large error in the results.

[0026] 3. For the foundation pits in cohesive soil sites, the undrained shear strength index of the soil is used for checking. Usually, in saturated cohesive soil sites, the problem of bottom heave of the foundation pit is more prominent. For the design and checking of foundation pits in saturated cohesive soil sites, the correct soil strength index should be selected according to the undrained condition. At present, in the domestic geotechnical industry, the consolidated undrained strength index combined with the total stress method is mostly used for checking, and this method will have a large error. A more reasonable and accurate method is to use the undrained shear strength of the soil, that is, to calculate with the undrained shear strength of the undisturbed soil sample consolidated under the effective self-weight stress. Therefore, it is necessary to give a checking method for the anti-heave stability of narrow foundation pits using the undrained shear strength index.

[0027] In summary, how to determine that a foundation pit is a narrow foundation pit, especially in the case where the embedded depth is less than the foundation pit width; how to check according to the failure mode of the foundation bearing capacity failure; how to consider the undrained shear strength index of the soil are the problems that need to be solved urgently in the current checking of the bottom heave resistance of narrow foundation pits.

[0028] The present application provides a method for checking the anti - heave stability of the bottom of a narrow foundation pit, aiming to solve the technical problems in the related art, such as the unreasonable judgment criteria and the selection of slip surfaces for narrow foundation pits, the unclear pre - conditions for design and checking calculations of narrow foundation pits, and the lack of a calculation method for the anti - heave safety factor under the failure mode of foundation bearing capacity for narrow foundation pits. Thus, for the foundation pit in the case of "small embedment depth" where the embedment depth calculated from the bottom - most strut is less than the actual width of the foundation pit, a method for accurately identifying narrow and wide foundation pits is given, solving the problem in the related art that the foundation pits in the case of "small embedment depth" are still classified as wide foundation pits and lacking the corresponding checking methods for narrow and wide foundation pits, and a calculation method for the anti - heave safety factor corresponding to the failure mode of foundation bearing capacity of narrow foundation pits is proposed.

[0029] In the first - aspect embodiment of the present application, a method for checking the anti - heave stability of the bottom of a narrow foundation pit is provided, which is applied to the checking of the stability of a narrow foundation pit in a saturated cohesive soil layer. The method includes the following steps: obtaining the actual width of the foundation pit and the undrained shear strength of the soil layer on the site; calculating, based on the undrained shear strength index, the width of the first subsiding soil mass corresponding to the failure mode of the bearing capacity of a wide foundation pit, and calculating the critical width of the foundation pit based on the width of the first subsiding soil mass and the first width calculation coefficient; comparing the actual width of the foundation pit and the critical width of the foundation pit to obtain the type of the foundation pit, and when the type of the foundation pit is a narrow - foundation - pit type, calculating the width of the second subsiding soil mass corresponding to the failure mode of the bearing capacity of the narrow - foundation - pit based on the actual width of the foundation pit; calculating the safety factor of the failure mode of the bearing capacity of the narrow - foundation - pit based on the width of the second subsiding soil mass; calculating the safety factor of the circular - arc sliding mode of the foundation pit, and by comparing the safety factor of the failure mode of the bearing capacity of the narrow - foundation - pit and the safety factor of the circular - arc sliding mode of the foundation pit, taking the smaller value between the safety factor of the failure mode of the bearing capacity of the narrow - foundation - pit and the safety factor of the circular - arc sliding mode as the anti - heave safety factor of the bottom of the narrow foundation pit, so as to judge the anti - heave stability of the bottom of the foundation pit based on the anti - heave safety factor of the bottom of the narrow foundation pit.

[0030] Optionally, in an embodiment of the present application, the step of comparing the actual width of the foundation pit and the critical width of the foundation pit to obtain the type of the foundation pit further includes: if the type of the foundation pit is a wide - foundation - pit type, calculating the safety factor of the bearing - capacity mode check according to the wide foundation pit; comparing the safety factor of the circular - arc sliding mode of the foundation pit and the safety factor of the bearing - capacity mode check, and taking the smaller value between the safety factor of the circular - arc sliding mode of the foundation pit and the safety factor of the bearing - capacity mode check as the anti - heave safety factor of the bottom of the wide foundation pit, so as to judge the anti - heave stability of the bottom of the foundation pit based on the anti - heave safety factor of the bottom of the wide foundation pit.

[0031] Optionally, in an embodiment of the present application, calculating the corresponding critical foundation pit width based on the width of the first subsided soil mass includes: obtaining foundation pit parameters and retaining member parameters, and obtaining the undrained shear strength of the soil mass at the bottom end of the retaining member based on the foundation pit parameters and the retaining member parameters; using the width of the first subsided soil mass, the undrained shear strength of the soil mass at the bottom end of the retaining member, and the soil strength parameters to obtain a first dimensionless parameter, and obtaining a first width calculation coefficient based on the first dimensionless parameter; multiplying the first width calculation coefficient and the width of the first subsided soil mass to obtain the critical foundation pit width.

[0032] Optionally, in an embodiment of the present application, the calculation formula for the first width calculation coefficient is:

[0033]

[0034] where η1 is the first width calculation coefficient and k1 is the first dimensionless parameter.

[0035] Optionally, in an embodiment of the present application, the calculation formula for the first dimensionless parameter is:

[0036]

[0037] where c 01 is the undrained strength of the soil mass at the bottom end of the retaining member, c inc is the growth rate of the undrained strength of the soil mass with depth, and B1 is the width of the first subsided soil mass.

[0038] Optionally, in an embodiment of the present application, the calculation formula for the width of the second subsided soil mass is:

[0039] B2 = B / η2,

[0040]

[0041]

[0042] where B is the actual foundation pit width, η2 is the second width calculation coefficient, k2 is the second dimensionless parameter, and B2 is the width of the second subsided soil mass.

[0043] Optionally, in an embodiment of the present application, the calculation formula for the safety factor of the failure mode of the bearing capacity of the narrow foundation pit is:

[0044]

[0045] where K b is the safety factor of the failure mode of the bearing capacity of the narrow foundation pit, β2 is the bearing capacity correction coefficient, and Zmax,2 is the depth of the slip surface at the failure of the foundation bearing capacity, F Q is the resultant force of the shear force of the vertical slip surface, γ' and γ w are the buoyant unit weight of the soil mass and the unit weight of water respectively, H is the depth of the excavation, and q0 is the surface surcharge load.

[0046] The embodiment of the present application can obtain the unconsolidated undrained shear strength index of the soil layer at the foundation pit site and the actual width of the foundation pit, avoiding the large errors that may be caused by directly checking and calculating using the consolidated undrained strength index. Based on the undrained shear strength index, the width of the first subsiding soil mass corresponding to the failure mode of the bearing capacity of the wide foundation pit is calculated, and then the corresponding critical foundation pit width is calculated. By comparing the sizes of the critical foundation pit width and the actual foundation pit width, the type of the foundation pit is obtained, solving the problem of difficult judgment of wide and narrow foundation pits. When the type of the foundation pit is a narrow foundation pit type, the width of the second subsiding soil mass is inversely obtained based on the actual foundation pit width, and then the safety factor of the failure mode of the bearing capacity of the narrow foundation pit is calculated. By comparing with the safety factor of the circular arc sliding mode, the safety factor of the bottom heave resistance of the narrow foundation pit is obtained, and the stability of the bottom heave resistance of the narrow foundation pit is judged. Among them, when calculating the safety factor in the foundation bearing capacity mode, the influence of the width of the subsiding soil mass needs to be considered. In the case of a narrow foundation pit, the width of the subsiding soil mass is inversely obtained from the actual foundation pit width according to the proportional relationship between the foundation width and the width of the slip surface in the foundation bearing capacity problem, with clear and correct physical concepts, and the calculated safety factor is more accurate than the existing technical solutions. Thus, it solves the technical problems in the related art, such as the unreasonable judgment standard for narrow foundation pits and the selection of the slip surface, the unclear preconditions for design checking and calculation of narrow foundation pits, and the lack of a calculation method for the safety factor of bottom heave resistance in the failure mode of the bearing capacity of narrow foundation pits according to the foundation bearing capacity.

[0047] The additional aspects and advantages of the present application will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present application. Brief Description of the Drawings

[0048] The above and / or additional aspects and advantages of the present application will become obvious and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0049] Figure 1 is a flowchart of a method for checking the stability of the bottom heave resistance of a narrow foundation pit provided according to an embodiment of the present application;

[0050] Figure 2 is a schematic diagram for calculating the safety factor in the failure mode of the bearing capacity of the wide foundation pit according to a specific embodiment of the present application;

[0051] Figure 3Schematic diagram for calculating safety factor according to the failure mode of foundation bearing capacity with reference to a specific embodiment of the present application;

[0052] Figure 4 Schematic diagram for calculating safety factor of failure mode of foundation bearing capacity by back-calculating the width of the subsiding soil mass according to the width of a narrow foundation pit in a specific embodiment of the present application;

[0053] Figure 5 Flow chart of the checking method for the anti-heave stability of the bottom of a narrow foundation pit according to a specific embodiment of the present application;

[0054] Figure 6 Schematic diagram of the relationship between the safety factor and the width of the subsiding soil mass when calculating the safety factor according to the checking of a wide foundation pit in a specific embodiment of the present application. Detailed implementation manners

[0055] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, but should not be construed as a limitation to the present application.

[0056] The following describes a method and device for checking the anti - heave stability of the bottom of a narrow foundation pit according to an embodiment of the present application. In view of the technical problems in the related art mentioned in the above - mentioned background technology, such as the unreasonable judgment criteria for narrow foundation pits and the selection of slip surfaces, the unclear pre - conditions for design and checking according to narrow foundation pits, and the lack of a calculation method for the anti - heave safety factor under the failure mode of foundation bearing capacity for narrow foundation pits, the present application provides a method for checking the anti - heave stability of the bottom of a narrow foundation pit, which is applied to the stability check of narrow foundation pits in saturated cohesive soil layers. In this method, the unconsolidated undrained shear strength index of the soil layer at the foundation pit site and the actual width of the foundation pit can be obtained, avoiding large errors that may be caused by directly using the consolidated undrained strength index for checking. Based on the undrained shear strength index, the width of the first subsiding soil mass corresponding to the failure mode of the bearing capacity of the wide foundation pit is calculated, and then the corresponding critical foundation pit width is calculated. By comparing the critical foundation pit width with the actual foundation pit width, the type of the foundation pit is obtained, solving the problem of difficult judgment of narrow and wide foundation pits. When the type of the foundation pit is a narrow foundation pit type, the width of the second subsiding soil mass is inversely obtained based on the actual foundation pit width, and then the safety factor of the failure mode of the bearing capacity of the narrow foundation pit is calculated. By comparing it with the safety factor of the circular arc sliding mode, the anti - heave safety factor of the bottom of the narrow foundation pit is obtained, and a judgment on the anti - heave stability of the bottom of the narrow foundation pit is made. Among them, when calculating the safety factor in the foundation bearing capacity mode, the influence of the width of the subsiding soil mass needs to be considered. In the case of a narrow foundation pit, the width of the subsiding soil mass is inversely obtained from the actual foundation pit width according to the proportional relationship between the foundation width and the slip surface width in the foundation bearing capacity problem, with clear and correct physical concepts, and the calculated safety factor is more accurate than the existing technical solutions. Thus, the technical problems in the related art, such as the unreasonable judgment criteria for narrow foundation pits and the selection of slip surfaces, the unclear pre - conditions for design and checking according to narrow foundation pits, and the lack of a calculation method for the anti - heave safety factor under the failure mode of foundation bearing capacity for narrow foundation pits, are solved.

[0057] Specifically, Figure 1 FIG. is a schematic flow chart of a method for checking the anti - heave stability of the bottom of a narrow foundation pit provided by an embodiment of the present application.

[0058] As Figure 1 shown, the method for checking the anti - heave stability of the bottom of the narrow foundation pit is applied to the stability check of narrow foundation pits in saturated cohesive soil layers, and the method includes the following steps:

[0059] In step S101, obtain the actual width of the foundation pit and the unconsolidated undrained shear strength of the soil layer at the site.

[0060] In the actual implementation process, the unconsolidated undrained shear strength index c of the soil layer at the foundation pit site can be obtained through a geological exploration report in an embodiment of the present application u, in the embodiments of the present application, c can be directly obtained through an unconsolidated undrained test or an in-situ undrained test on the undisturbed soil sample after consolidation under self-weight stress u , where c u can increase approximately linearly with depth.

[0061] c u = c0 + c inc z,

[0062] , where c0 is the value of the undrained shear strength at the top of the soil layer, and c inc is the increase rate of the undrained shear strength with depth, that is, c0 and c inc are the undrained strength parameters of the soil mass, and z is the depth.

[0063] When the unconsolidated undrained test data is lacking, the embodiments of the present application can also use the results of the consolidated undrained test to estimate c0 and c inc . By adopting the unconsolidated undrained strength index, the embodiments of the present application can be more in line with the engineering characteristics of the foundation pit in the saturated cohesive soil site, thus avoiding the large errors that may be caused by directly checking and calculating using the consolidated undrained strength index.

[0064] Further, the embodiments of the present application should obtain the actual foundation pit width B for subsequent judgment of the type of the foundation pit.

[0065] In step S102, based on the undrained shear strength index, the first width of the subsiding soil mass corresponding to the failure mode of the bearing capacity of the wide foundation pit is calculated, and based on the first width of the subsiding soil mass and the first width calculation coefficient, the critical foundation pit width is calculated.

[0066] As a possible implementation manner, the embodiments of the present application can, according to the principle of the minimum safety factor, based on the shear strength index, obtain through trial calculation the width of the subsiding soil mass corresponding to the most unfavorable (minimum safety factor) slip surface, which is the first width of the subsiding soil mass in the failure mode of the bearing capacity of the wide foundation pit, and based on the first width of the subsiding soil mass, calculate the critical foundation pit width by using the proportional relationship between the width of the subsiding soil mass and the width of the slip surface.

[0067] Specifically, the embodiments of the present application can, based on the principle of the minimum safety factor, solve for the first width of the subsiding soil mass B1 that can make the safety factor K b1 take the minimum value in the case of the wide foundation pit, where the safety factor K b1 and the first width of the subsiding soil mass B1 can satisfy the following formula:

[0068]

[0069] , where the assumed failure slip surface in the above formula can be as Figure 2As shown, D is the depth of the fixed section, H is the depth of the pit, γ′ and γ w are the buoyant unit weight of the soil and the unit weight of water respectively, and F Q = c0(H + D)+0.5c inc (H + D) 2 , which is the resultant force of the shear force of the vertical slip surface, is the depth of the slip surface when the foundation bearing capacity fails, is the bearing capacity correction coefficient, λ1 = 2c inc B1 / c 01 , which is the first dimensionless parameter required for calculating the foundation bearing capacity, c 01 = c0 + c inc (H + D), which is the undrained strength of the soil at the bottom of the retaining member.

[0070] In the process of solving the above formula, the embodiment of the present application can solve it by iterative search and trial calculation. For example, the embodiment of the present application can calculate K by inputting B1 = 1m b1 , and then gradually increase the value of B1 until the minimum value of K b1 is found, that is, when B1 increases, the safety factor no longer decreases, and the safety factor when the foundation bearing capacity fails is obtained. At the same time, the corresponding width of the subsiding soil body is obtained, that is, the first width of the subsiding soil body B1.

[0071] Optionally, in an embodiment of the present application, calculating the corresponding critical foundation pit width based on the first width of the subsiding soil body includes: obtaining the foundation pit parameters and the retaining member parameters, and obtaining the undrained shear strength of the soil at the bottom of the retaining member based on the foundation pit parameters and the retaining member parameters; using the first width of the subsiding soil body, the undrained shear strength of the soil at the bottom of the retaining member, and the soil strength parameters to obtain the first dimensionless parameter, and obtaining the first width calculation coefficient based on the first dimensionless parameter; multiplying the first width calculation coefficient and the first width of the subsiding soil body to obtain the critical foundation pit width.

[0072] It can be understood that when the foundation bearing capacity fails, the proportional relationship between the foundation width and the slip surface width can be represented by a width calculation coefficient. It should be noted that there is no prior art to study this proportional relationship. In fact, there is no prior art attempting to use the foundation pit width to inversely calculate the width of the subsiding soil body. Through summarizing the numerical test results of a large number of saturated clay foundation bearing capacity problems, the embodiment of the present application can obtain that the value range of this width calculation coefficient is between [0,1], and it is related to the soil strength parameters and the foundation width. The calculation formula of this width calculation coefficient is:

[0073]

[0074] where η is the calculation coefficient representing the proportional relationship between the foundation width and the slip surface width in the bearing capacity problem (such as Figure 3as shown); k is a dimensionless parameter, c 0,0 is the undrained shear strength of the soil at the depth where the base of the foundation is located, and c inc,0 is the growth rate of the soil shear strength with depth, and B0 is the foundation width. Through conceptual analysis and verification with a large number of numerical tests, the dimensionless parameter can comprehensively characterize the influence of the soil strength parameters c 0,0 and c inc,0 and the foundation width B0, and the calculation coefficient η can be uniquely determined by the dimensionless parameter k. In the foundation bearing capacity check for the anti-heave stability at the bottom of the pit, the foundation width B0 should be determined by the width of the soil mass that sinks outside the pit, and c 0,0 and c inc,0 should be determined according to the properties of the soil at the bottom of the retaining member.

[0075] Thus, the embodiment of the present application can, based on the above formula, based on the undrained strength c 01 and c inc of the soil at the bottom of the retaining member, combine with the width B1 of the first sinking soil mass to calculate the first dimensionless parameter k1, and based on the first dimensionless parameter, obtain the first width calculation coefficient η1, and then multiply the first width calculation coefficient η1 by the width B1 of the sinking soil mass to obtain the critical foundation pit width B'.

[0076] Optionally, in an embodiment of the present application, the calculation formula for the first width calculation coefficient is:

[0077]

[0078] where η1 is the first width calculation coefficient and k1 is the first dimensionless parameter.

[0079] Specifically, the embodiment of the present application can use the width B1 of the first sinking soil mass, the undrained strength c 01 of the soil at the bottom of the retaining member, and the soil strength parameter c inc to obtain the first dimensionless parameter k1, and based on the first dimensionless parameter k1, obtain the first width calculation coefficient η1, where the first width calculation coefficient η1 refers to the ratio of the width of the slip surface in the failure mode of the foundation bearing capacity failure to the width of the sinking soil mass; multiply the first width calculation coefficient η1 by the width B1 of the sinking soil mass to calculate the corresponding critical foundation pit width B'. As Figure 2 shown, the width B' of the slip surface in the failure of the foundation bearing capacity of the wide foundation pit can be regarded as the critical foundation pit width. Among them, the calculation formula is as follows:

[0080] B = η1B1,

[0081]

[0082] Among them, η1 is the ratio between the width of the failure slip surface of the foundation bearing capacity of the wide foundation pit and the width of the first subsiding soil mass, and η1 should be related to the soil strength parameters c 01 and c inc and the width B1 of the first subsiding soil mass.

[0083] Optionally, in an embodiment of the present application, the calculation formula of the first dimensionless parameter is:

[0084]

[0085] Among them, c 01 is the undrained strength of the soil at the bottom end of the retaining member, c inc is the growth rate of the undrained strength with depth, and B1 is the width of the first subsiding soil mass.

[0086] The first dimensionless parameter k1 can comprehensively characterize the influence of the undrained strength parameters c 01 and c inc of the soil at the bottom end of the retaining member and the width B1 of the first subsiding soil mass.

[0087] In step S103, compare the actual foundation pit width and the critical foundation pit width to obtain the type of the foundation pit, and when the type of the foundation pit is the narrow foundation pit type, inversely calculate the width of the second subsiding soil mass corresponding to the failure mode of the narrow foundation pit foundation bearing capacity based on the actual foundation pit width.

[0088] In some embodiments, in the embodiment of the present application, compare the actual foundation pit width B and the critical foundation pit width B′ to obtain the type of the foundation pit. When B < B′, it can be determined that the type of the foundation pit is the narrow foundation pit type.

[0089] When the type of the foundation pit is the narrow foundation pit type, the embodiment of the present application can solve the width B2 of the subsiding soil mass corresponding to the maximum failure slip surface of the foundation bearing capacity that can be accommodated with the actual foundation pit width B, that is, the width B2 of the second subsiding soil mass.

[0090] Optionally, in an embodiment of the present application, the calculation formula of the width of the second subsiding soil mass is:

[0091] B2 = B / η2,

[0092]

[0093]

[0094] Among them, B is the width of the foundation pit, η2 is the second width calculation coefficient, k2 is the second dimensionless parameter, and B2 is the width of the second subsiding soil mass.

[0095] Such as Figure 4As shown, the embodiment of the present application can calculate the width B2 of the second subsiding soil mass corresponding to the failure mode of the bearing capacity of the narrow foundation pit based on the actual width B of the foundation pit, and the calculation formula can be as follows:

[0096] B2 = B / η2,

[0097]

[0098]

[0099] where η2 is the second width calculation coefficient, which is related to the variable B2 to be solved. Therefore, B2 can be solved by the iteration method through the above formula.

[0100] In step S104, based on the width of the second subsiding soil mass, calculate the safety factor of the failure mode of the bearing capacity of the narrow foundation pit.

[0101] In the actual execution process, the embodiment of the present application can calculate the safety factor K of the failure mode of the bearing capacity of the foundation pit in the case of a narrow foundation pit b .

[0102] As Figure 4 shown, the embodiment of the present application can use the safety factor calculation formula of the preset failure mode of the bearing capacity of the narrow foundation pit, that is, calculate the anti-heave safety factor K of the corresponding failure mode of the bearing capacity of the foundation pit in the case of a narrow foundation pit through the reduction strength method b .

[0103] Optionally, in an embodiment of the present application, the safety factor calculation formula of the failure mode of the bearing capacity of the narrow foundation pit is:

[0104]

[0105] where K b is the safety factor of the failure mode of the bearing capacity of the narrow foundation pit, β2 is the bearing capacity width calculation coefficient, Z max,2 is the depth of the slip surface at the time of the failure of the bearing capacity of the foundation, F Q is the resultant force of the shear force of the vertical slip surface, γ' and γ w are the buoyant unit weight of the soil and the unit weight of water respectively, H is the depth of the foundation pit, and q0 is the surface surcharge.

[0106] Furthermore, as Figure 4 shown, based on the failure slip surface for calculation, the derivation process of the safety factor calculation formula of the failure mode of the bearing capacity of the narrow foundation pit can be as follows:

[0107] When solving, the embodiment of the present application can calculate the bearing capacity p with the width B2 of the second subsiding soil mass, the reduced undrained strength parameters of the soil mass, and the foundation pit parameters u, calculate the shear force F of the vertical slip surface using the reduced undrained strength parameters of the soil mass Q , and calculate the downward load p1, then calculate the safety factor K by solving the following formula b :

[0108]

[0109] where p u (K b ) means that p u is a function of K b .

[0110] The bearing capacity p u can be written as after considering the reduction of soil strength:

[0111]

[0112] where D is the depth of the embedded section, H is the depth of the excavation, is the depth of the slip surface for the failure of the foundation bearing capacity, is the correction coefficient for calculating the bearing capacity, λ2 = 2c inc B2 / c 02 , is the dimensionless parameter required for calculating the foundation bearing capacity, and this dimensionless parameter does not change with the simultaneous reduction of the strength parameters c 01 、c inc . c 01 = c0 + c inc (H + D), is the undrained strength of the soil at the bottom of the retaining member. And the resultant force of the shear force of the vertical slip surface can be:

[0113] F Q = c0(H + D) + 0.5c inc (H + D) 2 ,

[0114] The load caused by the soil settlement outside the excavation and the surface surcharge q0 is:

[0115] p1 = γ'(H + D) + γ w H + q0,

[0116] In summary,

[0117]

[0118] Since there is only one unknown K b in the above formula, it can be sorted out as:

[0119]

[0120] Thus, the calculation method of the safety factor for the instability mode of the foundation bearing capacity applicable to narrow excavations is obtained.

[0121] In step S105, calculate the safety factor of the circular arc sliding mode of the foundation pit. By comparing the safety factor of the failure mode of the foundation bearing capacity of the narrow foundation pit and the safety factor of the circular arc sliding mode of the foundation pit, take the smaller value between the safety factor of the failure mode of the foundation bearing capacity of the narrow foundation pit and the safety factor of the circular arc sliding mode as the bottom heave resistance safety factor of the narrow foundation pit, so as to judge the bottom heave resistance stability of the foundation pit based on the bottom heave resistance safety factor of the narrow foundation pit.

[0122] As a possible implementation manner, the embodiment of the present application can calculate the second safety factor K of the circular arc sliding mode c and compare it with the safety factor of the foundation bearing capacity mode, and take the smaller value to obtain the bottom heave resistance safety factor of the narrow foundation pit, so as to judge the bottom heave resistance stability of the foundation pit based on the bottom heave resistance safety factor of the narrow foundation pit.

[0123] Among them, the calculation formula of the safety factor of the circular arc sliding mode is:

[0124]

[0125] Among them, K c is the safety factor of the circular arc sliding mode, D is the embedded section depth, l0 is the distance from the lowest support to the bottom of the pit, c 02 is the undrained shear strength of the soil layer at the plane of the lowest support, θ1 = arcsin(l0 / (D + l0)), and M0 is the ultimate flexural strength of the retaining member.

[0126] Optionally, in an embodiment of the present application, compare the actual foundation pit width and the critical foundation pit width to obtain the type of the foundation pit, and further include: if the type of the foundation pit is a wide foundation pit type, calculate the safety factor of the foundation bearing capacity mode verification according to the wide foundation pit; compare the safety factor of the circular arc sliding mode of the foundation pit and the safety factor of the foundation bearing capacity mode verification, and take the smaller value between the safety factor of the circular arc sliding mode of the foundation pit and the safety factor of the foundation bearing capacity mode verification as the bottom heave resistance safety factor of the wide foundation pit, so as to judge the bottom heave resistance stability of the foundation pit based on the bottom heave resistance safety factor of the wide foundation pit.

[0127] Further, the embodiment of the present application can compare the actual foundation pit width B and the critical foundation pit width B' corresponding to B1. When B ≥ B', the embodiment of the present application can judge that the type of the foundation pit is a wide foundation pit type.

[0128] At this time, the embodiment of the present application can calculate the safety factor of the foundation bearing capacity verification by checking according to the failure mode of the wide foundation pit foundation bearing capacity, and this safety factor is the minimum value of K b1 calculated in step S102.

[0129] In the embodiments of the present application, the safety factor of the arc sliding mode and the safety factor of the foundation bearing capacity mode verification can be compared, and the smaller value is taken to obtain the anti - heave safety factor of the bottom of the wide foundation pit, so as to judge the anti - heave stability of the bottom of the foundation pit based on the anti - heave safety factor of the bottom of the wide foundation pit.

[0130] Combined with Figures 2 to 6 As shown, the checking calculation method for the anti - heave stability of the bottom of the narrow foundation pit in the embodiments of the present application will be elaborated in detail with an example.

[0131] As Figure 5 shown, the embodiments of the present application may include the following steps:

[0132] Step S501: Obtain the unconsolidated undrained shear strength index of the soil layer of the foundation pit site and the actual width of the foundation pit. In the embodiments of the present application, the unconsolidated undrained shear strength index c of the soil layer of the foundation pit site can be obtained through the geological exploration report. u In the embodiments of the present application, c can be directly obtained through the unconsolidated undrained test or in - situ undrained test after the undisturbed soil sample is consolidated under its own gravity stress. u Among them, c u can increase approximately linearly with depth.

[0133] c u = c0 + c inc z,

[0134] Among them, c0 is the value of the undrained shear strength at the top surface of the soil layer, c inc is the increase rate of the undrained shear strength with depth, that is, c0 and c inc are soil strength parameters, and z is the depth.

[0135] When the unconsolidated undrained test data is lacking, in the embodiments of the present application, the results of the consolidated undrained test can also be used to estimate c0 and c inc By adopting the unconsolidated undrained strength index, the embodiments of the present application can be more in line with the engineering characteristics of the foundation pit in the saturated cohesive soil site, thus avoiding the large errors that may be caused by using the consolidated undrained strength index.

[0136] Furthermore, the embodiments of the present application should obtain the actual width B of the foundation pit for subsequent judgment of the type of the foundation pit.

[0137] Step S502: Obtain the width of the first subsiding soil mass corresponding to the failure mode of the bearing capacity of the wide foundation pit. In the embodiments of the present application, based on the principle of the minimum safety factor, the width B1 of the first subsiding soil mass that can make the safety factor K b1 take the minimum value in the case of the wide foundation pit is solved. Among them, the safety factor K b1 and the width B1 of the first subsiding soil mass can satisfy the following formula:

[0138]

[0139] Among them, the assumed failure slip surface in the above formula can be as Figure 2 shown, where D is the depth of the embedded section, H is the depth of the pit, γ′ and γ w are the buoyant unit weight of the soil and the unit weight of water respectively, and F Q = c0(H + D) + 0.5c inc (H + D) 2 , which is the resultant force of the shear force of the vertical slip surface, is the depth of the slip surface at the time of foundation bearing capacity failure, is the calculation width calculation coefficient, λ1 = 2c inc B1 / c 01 , which is the first dimensionless parameter required for calculating the foundation bearing capacity, c 01 = c0 + c inc (H + D), which is the undrained strength of the soil at the bottom of the retaining member.

[0140] In the process of solving the above formula, the embodiments of the present application can solve by iterative search and trial calculation. For example, the embodiments of the present application can calculate K by inputting B1 = 1m b1 , and then gradually increase the value of B1 until the minimum value of K b1 is found, that is, when B1 increases, the safety factor no longer decreases, and the safety factor at the time of foundation bearing capacity failure is obtained, and at the same time, the corresponding width of the sinking soil body, that is, the first width of the sinking soil body B1, is obtained.

[0141] Step S503: Calculate the critical foundation pit width based on the first width of the sinking soil body. As Figure 2 shown, B′ is the slip surface corresponding to the wide foundation pit. The embodiments of the present application can calculate the first dimensionless parameter k1 based on the undrained strength parameters c 01 and c inc , in combination with the first width of the sinking soil body B1, and obtain the first width calculation coefficient η1 based on the first dimensionless parameter. Multiply the first width calculation coefficient η1 by the width of the sinking soil body B1 to obtain the critical foundation pit width B′. Among them, the calculation formula can be as follows:

[0142] B′ = η1B1,

[0143]

[0144]

[0145] Among them, η1 is the ratio between the width of the failure slip surface of the foundation bearing capacity of the wide foundation pit and the first width of the sinking soil body, and η1 should be related to the soil strength parameters c 01 , c inc and the first width of the sinking soil body B1.

[0146] Step S504: Compare the actual foundation pit width with the critical foundation pit width. If the actual foundation pit width is less than the critical foundation pit width, go to Step S505; if the actual foundation pit width is greater than or equal to the critical foundation pit width, go to Step S507.

[0147] Step S505: The type of the foundation pit is the narrow foundation pit type, and find the width of the second subsiding soil mass. In the embodiment of the present application, the type of the foundation pit can be obtained by comparing the actual foundation pit width B with the critical foundation pit width B'. When B < B', the embodiment of the present application can determine that the type of the foundation pit is the narrow foundation pit type.

[0148] When the type of the foundation pit is the narrow foundation pit type, in the embodiment of the present application, with the actual foundation pit width B, the width B2 of the subsiding soil mass corresponding to the maximum slip surface that the actual foundation pit width can accommodate when the foundation bearing capacity fails and collapses can be solved, that is, the width B2 of the second subsiding soil mass.

[0149] As Figure 4 shown, in the embodiment of the present application, B2 can be obtained by back-calculating with B through solving the following formula:

[0150] B2 = B / η2,

[0151]

[0152]

[0153] where B is the foundation pit width, η2 is the second width calculation coefficient, k2 is the second dimensionless parameter, and B2 is the width of the second subsiding soil mass.

[0154] Step S506: Calculate the safety factor of the foundation bearing capacity failure mode in the case of a narrow foundation pit. As Figure 4 shown, in the embodiment of the present application, the safety factor calculation formula for the foundation bearing capacity failure mode of the preset narrow foundation pit can be used, that is, the anti-heave safety factor K of the foundation bearing capacity failure mode corresponding to the narrow foundation pit case is calculated by the reduction strength method. b .

[0155] Further, based on the failure slip surface for calculation, the derivation process of the safety factor calculation formula for the foundation bearing capacity failure mode of the narrow foundation pit can be as follows:

[0156] When solving, in the embodiment of the present application, the bearing capacity p can be calculated with the width B2 of the second subsiding soil mass, the reduced undrained shear strength parameter of the soil mass, and the foundation pit parameters. u The shear force F of the vertical slip surface is calculated with the reduced undrained shear strength parameter of the soil mass. Q , and the downward pressure load p1 of the subsiding soil mass, and then the safety factor K is calculated by solving the following formula. b :

[0157]

[0158] Among them, p u (K b ) means that p u is a function of K b .

[0159] The bearing capacity p u can be written as after considering the reduction of soil strength:

[0160]

[0161] Among them, D is the depth of the embedded section, H is the depth of the excavation, c 01 = c0 + c inc (H + D), which is the undrained strength of the soil at the bottom of the retaining member, is the depth of the slip surface for the failure of the foundation bearing capacity, is the correction coefficient for calculating the bearing capacity, λ2 = 2c inc B2 / c 01 , which is the dimensionless parameter required for calculating the foundation bearing capacity. Note that this dimensionless parameter does not change with the simultaneous reduction of the strength parameters c 01 and c inc . The resultant force of the shear force of the vertical slip surface can be:

[0162] F Q = c0(H + D) + 0.5c inc (H + D) 2 .

[0163] The load caused by the soil settlement outside the excavation and the surface surcharge q0 is:

[0164] p1 = γ'(H + D) + γ w H + q0,

[0165] In summary,

[0166]

[0167] Since there is only K b one unknown in the above formula, it can be sorted out as:

[0168]

[0169] Thus, the calculation method of the safety factor for the instability mode of the foundation bearing capacity applicable to narrow excavations is obtained.

[0170] Step S507: The type of the foundation pit is a wide foundation pit type, and the safety factor of the foundation bearing capacity check is calculated according to the checking method of the wide foundation pit foundation bearing capacity mode. In the embodiment of the present application, the actual foundation pit width B can be compared with the critical foundation pit width B' corresponding to B1. When B≥B', the embodiment of the present application can determine that the type of the foundation pit is a wide foundation pit type.

[0171] At this time, the embodiment of the present application can obtain the safety factor of the foundation bearing capacity check by checking according to the failure mode of the wide foundation pit foundation bearing capacity. This safety factor is the K b1 obtained by calculation in step S502.

[0172] Step S508: Calculate the safety factor of the circular arc sliding mode, and obtain the final bottom heave resistance safety factor of different foundation pits based on the type of the foundation pit.

[0173] Among them, the calculation formula for the safety factor of the circular arc sliding mode is:

[0174]

[0175] Among them, K c is the safety factor of the circular arc sliding mode, D is the embedded depth section, l0 is the distance from the lowest support to the bottom of the pit, c 02 is the undrained shear strength of the soil layer at the plane of the lowest support, θ1 = arcsin(l0 / (D + l0)), and M0 is the ultimate flexural strength of the retaining member.

[0176] Next, the effectiveness of the embodiment of the present application will be verified with an example.

[0177] The embodiment of the present application can be verified with a narrow foundation pit in a saturated clay site. The embedded depth of the foundation pit support structure is only 1.5 m, which is applicable to the situation proposed in the embodiment of the present application. The soil layer parameters of the site, the parameters of the foundation pit and the support structure can be shown in Table 1 and Table 2. Among them, Table 1 is the table of soil layer parameters of the site, and Table 2 is the table of parameters of the foundation pit and the support structure.

[0178] Table 1

[0179] <![CDATA[c0 / kPa]]> <![CDATA[c inc / kPa]]> <![CDATA[γ / kN / m 3 > 25 2.0 18

[0180] Table 2

[0181] Depth of pit H / m Width of pit B / m Embedded depth D / m <![CDATA[q0 / kPa]]> <![CDATA[M p / (kNm / m)]]> 15 5 1.5 0 1000

[0182] Step S1: The embodiment of the present application can obtain the unconsolidated undrained strength parameters of the saturated clay through the geological exploration report. Among them, c0 = 25 kPa, c inc = 2.0 kPa / m.

[0183] Step S2: Based on the principle of the minimum safety factor, solve for the first width B1 of the subsiding soil mass that can minimize the safety factor K corresponding to the wide foundation pit situation, where the safety factor K b1 and the first width B1 of the subsiding soil mass satisfy the formula: b1

[0184] Furthermore, as Figure 6 shown, B1 and the safety factor K that satisfy the above formula for different groups b1 are visible, and it can be seen that the B1 that minimizes the safety factor is B1 = 12.5m.

[0185] Step S3: Calculate the corresponding critical foundation pit width B′ based on the first width B1 of the subsiding soil mass. The calculation formula can be as follows:

[0186] B’ = η1B1,

[0187]

[0188]

[0189] Obtain

[0190] Step S4: Compare the actual foundation pit width B and the critical foundation pit width B′. Since B = 5m is less than the critical foundation pit width B′, the type of this foundation pit is a narrow foundation pit type.

[0191] Step S5: Inversely calculate the second width B2 of the subsiding soil mass through the actual foundation pit width B. At this time, substitute it into the formula:

[0192] B2 = B / η2,

[0193]

[0194]

[0195] It can be obtained and the solution is B2 = 5.61m.

[0196] Step S6: Calculate the first safety factor K of the failure mode of the foundation bearing capacity in the case of a narrow foundation pit b , based on the formula to obtain K b = 1.55.

[0197] Step S7: Based on the formula to obtain K c = 1.73. It can be seen that the first safety factor K b is smaller. Therefore, select the first safety factor K b as the final safety factor of this foundation pit.​

[0198] By calculating the safety factor of the embodiment of the present application with the finite element limit analysis software OPTUM G2, it can be known that its safety factor is 1.553, and at the same time, its failure slip surface is close to the failure mode of bearing capacity failure. It can be seen that the method of the embodiment of the present application has a high accuracy. On the other hand, when the foundation pit in the embodiment of the present application is checked by the circular arc sliding method, the width of the foundation pit can accommodate the slip surface, and the influence of the width of the foundation pit may not be considered in the calculation of the safety factor of the circular arc sliding method; but for the actual sliding mode that plays a role - the sliding mode of bearing capacity failure of the foundation, the influence of the width of the foundation pit must be considered, that is, this foundation pit should be calculated as a narrow foundation pit, which shows that the method of the embodiment of the present application can reasonably and correctly identify the narrow foundation pit and give the correct checking result.

[0199] According to the checking method for the bottom heave stability of a narrow foundation pit proposed in the embodiment of the present application, which is applied to the checking of the stability of a narrow foundation pit in a saturated cohesive stratum, the undrained shear strength index of the soil layer of the foundation pit site and the actual width of the foundation pit can be obtained, avoiding the large errors that may be caused by directly using the consolidated undrained strength index for checking, and based on the undrained shear strength index, the width of the first subsiding soil mass corresponding to the failure mode of bearing capacity failure of a wide foundation pit is calculated, so as to calculate the corresponding critical foundation pit width. By comparing the sizes of the critical foundation pit width and the actual foundation pit width, the type of the foundation pit is obtained, solving the problem of difficult judgment of wide and narrow foundation pits. When the type of the foundation pit is a narrow foundation pit type, the width of the second subsiding soil mass is inversely obtained based on the actual width of the foundation pit, so as to calculate the safety factor of the failure mode of bearing capacity failure of the narrow foundation pit, and by comparing with the safety factor of the circular arc sliding mode, the bottom heave safety factor of the narrow foundation pit is obtained, and a judgment is made on the bottom heave stability of the narrow foundation pit. Among them, when calculating the safety factor in the bearing capacity mode, the influence of the width of the subsiding soil mass needs to be considered, and in the case of a narrow foundation pit, the width of the subsiding soil mass is inversely obtained from the actual width of the foundation pit according to the proportional relationship between the width of the foundation and the width of the slip surface in the bearing capacity problem of the foundation, with clear and correct physical concepts, and the calculated safety factor is more accurate than the existing technical solutions. Thus, the technical problems in the related art, such as the unreasonable judgment standard for narrow foundation pits and the selection of slip surfaces, the unclear preconditions for design and checking according to narrow foundation pits, and the lack of a calculation method for the bottom heave safety factor of narrow foundation pits in the failure mode of bearing capacity failure, are solved.

[0200] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or N embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0201] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of this application, the meaning of "N" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0202] Any process or method description depicted in a flowchart or otherwise described herein can be understood to represent a module, segment, or portion of code including one or N executable instructions for implementing a customized logical function or process, and the scope of the preferred embodiments of this application includes additional implementations, where the functions can be executed in a substantially simultaneous manner or in a reverse order according to the functions involved, rather than in the order shown or discussed, which should be understood by those skilled in the art to which the embodiments of this application pertain.

Claims

1. A checking calculation method for the anti-heave stability of the bottom of a narrow foundation pit, characterized in that The method is applied to the stability verification of a narrow foundation pit in a saturated viscous substratum, wherein the method comprises the following steps: Obtain the actual width of the foundation pit and the unconsolidated undrained shear strength of the site soil; Based on the undrained shear strength index, a first sinking soil width corresponding to a wide foundation pit bearing capacity failure mode is calculated, and based on the first sinking soil width and a first width calculation coefficient, a critical foundation pit width is calculated; Comparing the actual foundation pit width with the critical foundation pit width to obtain the type of the foundation pit, and when the type of the foundation pit is a narrow foundation pit type, inversely calculating the second subsidence soil width corresponding to the narrow foundation pit foundation bearing capacity failure failure mode based on the actual foundation pit width; Calculating the safety factor of the narrow foundation pit foundation bearing capacity failure mode based on the width of the second sunken soil mass; The safety factor of the circular sliding mode of the foundation pit is calculated, and by comparing the safety factor of the bearing capacity failure mode of the narrow foundation pit foundation and the safety factor of the circular sliding mode of the foundation pit, the smaller value between the safety factor of the bearing capacity failure mode of the narrow foundation pit foundation and the safety factor of the circular sliding mode is taken as the anti-uplift safety factor of the pit bottom of the narrow foundation pit, so as to judge the anti-uplift stability of the pit bottom of the foundation pit based on the anti-uplift safety factor of the pit bottom of the narrow foundation pit.

2. The method according to claim 1, wherein The comparing the actual foundation pit width and the critical foundation pit width to obtain the type of the foundation pit includes: If the foundation pit is a wide foundation pit type, the safety factor of the foundation bearing capacity model is calculated based on the wide foundation pit; Compare the safety factor of the circular sliding mode of the foundation pit with the safety factor of the foundation bearing capacity mode test, and take the smaller value between the safety factor of the circular sliding mode of the foundation pit and the safety factor of the foundation bearing capacity mode test as the anti-uplift safety factor of the pit bottom of the wide foundation pit, so as to judge the anti-uplift stability of the pit bottom of the foundation pit based on the anti-uplift safety factor of the pit bottom of the wide foundation pit.

3. The method according to claim 1, characterized in that The calculating of the corresponding critical foundation pit width based on the width of the first sunken soil body includes: Acquiring foundation pit parameters and retaining member parameters, and obtaining the undrained shear strength of the soil at the bottom end of the retaining member based on the foundation pit parameters and the retaining member parameters; Obtaining a first dimensionless parameter using the width of the first sunken soil mass, the undrained strength of the soil mass at the bottom end of the retaining member, and the growth rate of the undrained strength of the soil mass with depth, and obtaining a first width calculation coefficient based on the first dimensionless parameter; The critical foundation pit width is obtained by multiplying the first width calculation coefficient and the first sunken soil width.

4. The method according to claim 3, wherein The calculation formula of the first width calculation coefficient is: ， Among them, is the first width calculation coefficient, is the first dimensionless parameter.

5. The method according to claim 4, characterized in that, The calculation formula of the first dimensionless parameter is: ， Among them, is the undrained strength of the soil at the bottom end of the retaining member, is the growth rate of the undrained strength of the soil with depth, is the width of the first subsiding soil mass.

6. The method according to claim 1, characterized in that The calculation formula for the width of the second subsided soil body is: ， ， ， in, B is the actual foundation pit width, Calculate the coefficient for the second width, is the second dimensionless parameter, is the width of the second sunken soil body.

7. The method according to claim 1, characterized in that The safety factor calculation formula for the narrow foundation pit bearing capacity failure mode is: ， Among them, is the safety factor of the failure mode of the bearing capacity of the narrow foundation pit, is the bearing capacity correction factor, is the depth of the slip surface at the time of the failure of the bearing capacity of the foundation, is the resultant force of the shear force of the vertical slip surface, 、 are respectively the buoyant unit weight of the soil and the unit weight of water, H is the depth of the pit, is the surface surcharge.

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