Method for calculating overall stability of narrow foundation pit

Abstract

The invention discloses a method for calculating the overall stability of a narrow foundation pit, and belongs to the technical field of geotechnical engineering. The method comprises the steps that overall stability calculation is conducted on a foundation pit according to a standard method, and the most unfavorable sliding surface position is obtained; judging the type of the foundation pit according to the position, if the intersection point of the most unfavorable sliding surface and the bottom surface of the foundation pit is within the width range of the foundation pit, determining that the foundation pit is a common foundation pit, and calculating according to a standard method; if the most unfavorable sliding surface intersects with the opposite side supporting structure or penetrates through the lower portion of the opposite side supporting structure, the foundation pit is a narrow foundation pit. For a narrow foundation pit, when a sliding surface intersects with a supporting structure, considering the reactive force contribution of the supporting structure to a soil body, and adopting a corresponding formula to calculate the overall stability; when the sliding surface passes through the lower part of the supporting structure, considering the anti-sliding contribution of the soil body above the pit bottom on the outer side of the supporting structure, and calculating the overall stability by adopting a corresponding formula.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, specifically to a method for calculating the overall stability of narrow foundation pits. Background Technology

[0002] In the design and calculation of foundation pit support structures, anchored, cantilevered retaining structures and double-row piles should undergo overall sliding stability verification according to the requirements of Article 4.2.3 of the "Technical Specification for Foundation Pit Support" JGJ120-2012. The verification method used is the circular arc sliding strip method. This circular arc sliding strip method implicitly assumes that the foundation pit is a semi-infinite body, and its sliding surface will slide out from the bottom of the foundation pit and is not affected by the opposite side support structure. This assumption is relatively consistent with the actual situation of building foundation pits, because the planar dimensions of building foundation pits are usually relatively large, which can meet the assumption of a semi-infinite body. The results calculated using this method are relatively close to the actual situation.

[0003] However, in actual engineering construction, there are many municipal foundation pits that are long and narrow, such as those for integrated utility tunnels, power tunnels, underground pedestrian passages, and various water supply and drainage pipelines. The narrow width of these municipal foundation pits clearly fails to meet the semi-infinite body assumption required by the circular sliding strip method, rendering the traditional circular sliding strip method of calculation and analysis inapplicable. Furthermore, numerous engineering practice cases have demonstrated that if traditional calculation and analysis methods are continued to be used for the overall stability calculation and support structure design of these narrow municipal foundation pits, the design of the foundation pit support structure will inevitably be overly conservative, resulting in dimensions and material usage exceeding actual engineering requirements, thus leading to a waste of engineering resources and costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calculating the overall stability of narrow foundation pits, which solves the problem that the traditional circular arc sliding strip method is not applicable to narrow foundation pits because it assumes that the foundation pit is a semi-infinite body, and that continuing to use this method will lead to overly conservative design of narrow foundation pits, resulting in waste.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for calculating the overall stability of a narrow foundation pit includes the following steps:

[0007] The overall stability of the foundation pit was calculated according to the standard method to obtain the location of the most unfavorable sliding surface.

[0008] Based on the location of the most unfavorable sliding surface, the foundation pit is determined to be a normal foundation pit or a narrow foundation pit. If the intersection of the most unfavorable sliding surface and the bottom surface of the foundation pit is within the width of the foundation pit, the foundation pit is determined to be a normal foundation pit. If the most unfavorable sliding surface intersects with the opposite side support structure or passes under the opposite side support structure, the foundation pit is determined to be a narrow foundation pit.

[0009] If the excavation pit is a typical excavation pit, the overall stability calculation of the excavation pit shall be performed according to the standard method. The formula for calculating the overall stability of the excavation pit according to the standard method is as follows: ;

[0010] If the foundation pit is a narrow foundation pit, the overall stability calculation of the foundation pit is completed by using the corresponding calculation method based on the relative position of the most unfavorable sliding surface and the opposite side support structure.

[0011] In one possible implementation, when the excavation pit is determined to be a narrow pit and the most unfavorable sliding surface intersects with the opposing side support structure, the reaction force of the opposing side support structure on the soil is calculated using the parameters of the most unfavorable sliding surface and the parameters of the opposing side support structure. Based on the reaction force, the parameters of the most unfavorable sliding surface, and the physical and mechanical parameters of the soil, the overall stability safety factor of the excavation pit is calculated using a preset formula, which is: ;

[0012] The contribution of the reaction force of the opposing lateral support structure in the formula is calculated by the following formula: ;

[0013] This completes the overall stability calculation of the foundation pit.

[0014] In one possible implementation, when calculating the reaction force, the horizontal compression of the soil reaction calculation point is deduced based on the allowable settlement of the foundation pit and geometric relationships; the distributed soil reaction force is calculated using the horizontal compression, the horizontal reaction force coefficient of the soil, and the initial soil reaction force, according to the soil reaction force calculation formula; and the reaction force of the opposite side support structure on the soil is calculated based on the distributed soil reaction force and the action zone parameters of the opposing side support structure and the soil.

[0015] In one possible implementation, when determining the initial soil reaction force, the initial soil reaction force is calculated using the method for calculating earth pressure at rest to obtain the numerical value of the initial soil reaction force; using the numerical value of the initial soil reaction force, the horizontal compression amount, and the horizontal reaction force coefficient of the soil, the distributed soil reaction force is calculated.

[0016] In one possible implementation, when it is determined that the excavation pit is a narrow excavation pit and the most unfavorable sliding surface passes under the opposing side support structure, the soil parameters of the region outside the opposing side support structure and located above the bottom of the excavation pit are obtained; using the soil parameters of the region, the parameters of the most unfavorable sliding surface, and the physical and mechanical parameters of the soil, the contribution value of the soil in the region to the anti-sliding stability is calculated using a preset formula, which is: Based on the contribution value and the conventional anti-sliding force calculation results, the overall stability safety factor of the foundation pit is calculated using the following formula, thus completing the overall stability calculation of the foundation pit. .

[0017] In one possible implementation, when obtaining the soil parameters of the area outside the opposing side support structure and located above the bottom of the foundation pit, the cohesion, internal friction angle, soil strip width, standard value of additional distributed load, and soil strip self-weight parameters of the soil in the area are collected as the soil parameters of the area.

[0018] In one possible implementation, during the overall stability calculation of the foundation pit, additional distributed load parameters on both sides of the foundation pit are obtained; based on the additional distributed load parameters, it is determined whether there is unbalanced load on both sides of the foundation pit; if there is unbalanced load, the load parameters corresponding to the unbalanced load are included in the soil physical and mechanical parameters and used in the calculation of the overall stability safety factor of the foundation pit.

[0019] In one possible implementation, when determining the type of the foundation pit and calculating the overall stability of the foundation pit, the embedment length parameters of the support structures on both sides of the foundation pit are obtained; based on the embedment length parameters, it is determined whether the embedment lengths of the support structures on both sides of the foundation pit are different; if they are different, the embedment length difference parameters are included in the parameters of the support structures on the opposite side, and participate in the determination of the most unfavorable sliding surface position and the calculation of the overall stability safety factor.

[0020] In one possible implementation, before performing an overall stability calculation on the foundation pit, the geological condition parameters and foundation treatment parameters on both sides of the foundation pit are obtained; based on the geological condition parameters and foundation treatment parameters, it is determined whether there are different geological conditions or different foundation treatment methods on both sides of the foundation pit; if so, the different geological condition parameters or different foundation treatment parameters are incorporated into the soil physical and mechanical parameters and used in the calculation of the overall stability safety factor of the foundation pit.

[0021] In one possible implementation, when performing overall stability calculations on the foundation pit, it is determined whether reinforced soil is used inside the pit; if reinforced soil is used inside the pit, the physical and mechanical parameters of the reinforced soil are obtained; the physical and mechanical parameters of the reinforced soil are incorporated into the physical and mechanical parameters of the soil and used to determine the location of the most unfavorable sliding surface and to calculate the overall stability safety factor.

[0022] Compared with the prior art, the advantages of this invention are as follows:

[0023] ① This invention first calculates and determines the type of foundation pit according to the standard method. For ordinary foundation pits, the standard method is used. For narrow foundation pits, the corresponding calculation method is adopted according to the relative position of the most unfavorable sliding surface and the opposite side support structure. This makes the calculation process fit the actual conditions of different foundation pits and avoids the problem that the traditional method does not match the actual situation of narrow foundation pits because it assumes that the foundation pit is a semi-infinite body. This improves the accuracy of the calculation results in the safety evaluation of foundation pits.

[0024] ② In calculating the overall stability of narrow foundation pits, this invention considers the anti-sliding contribution of the support structure's reaction force when the most unfavorable sliding surface intersects with the opposite side support structure, and considers the anti-sliding contribution of the soil above the bottom of the pit when the sliding surface passes under the support structure. Compared with the conventional method that only considers the soil's own anti-sliding effect, this invention significantly improves the overall stability safety factor of narrow foundation pits, eliminating the need for excessive design to ensure foundation pit safety. This reduces the amount of support structure materials and construction costs while ensuring project safety, thus saving on project expenses.

[0025] ③ Furthermore, this invention can also take into account unbalanced loads on both sides of the foundation pit, different embedment lengths of the support structures on both sides, different geological conditions or different foundation treatment methods on both sides, and the use of reinforced soil in the pit. It can handle these complex working conditions without introducing other calculation methods, simplifying the operation process of calculating the overall stability of narrow foundation pits, improving calculation efficiency, and also broadening the scope of application of the calculation method to meet the needs of more practical engineering scenarios. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram illustrating the intersection of the most unfavorable sliding surface and the bottom surface of the foundation pit in an embodiment of the present invention, within the width of the foundation pit and calculated according to the standard method.

[0028] Figure 2This is a schematic diagram illustrating the calculation of overall stability when the most unfavorable sliding surface intersects with the opposing side support structure according to an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram illustrating the calculation of overall stability when the most unfavorable sliding surface passes under the opposing side support structure according to an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram with parameters for calculating the overall stability when the most unfavorable sliding surface intersects with the opposing side support structure, according to an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram with parameters for calculating the overall stability when the most unfavorable sliding surface passes under the opposing side support structure according to an embodiment of the present invention;

[0032] Figure 6 This is a flowchart illustrating the overall stability calculation method for a narrow foundation pit according to an embodiment of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0034] Example:

[0035] It should be noted that the terms "comprising" and "having" and any variations thereof in the embodiments of the present invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0036] See Figure 6 This invention provides a method for calculating the overall stability of a narrow foundation pit, comprising the following steps:

[0037] Step 101: Perform overall stability calculations on the foundation pit according to standard methods to obtain the location of the most unfavorable sliding surface;

[0038] Step 102: Based on the location of the most unfavorable sliding surface, determine whether the foundation pit is a normal foundation pit or a narrow foundation pit. If the intersection of the most unfavorable sliding surface and the bottom surface of the foundation pit is within the width of the foundation pit, then the foundation pit is determined to be a normal foundation pit. If the most unfavorable sliding surface intersects with the opposite side support structure or passes under the opposite side support structure, then the foundation pit is determined to be a narrow foundation pit.

[0039] Step 103: If the foundation pit is a normal foundation pit, the overall stability calculation of the foundation pit shall be completed according to the standard method. If the foundation pit is a narrow foundation pit, the overall stability calculation of the foundation pit shall be completed by adopting the corresponding calculation method based on the relative position of the most unfavorable sliding surface and the opposite side support structure.

[0040] Specifically, when the excavation pit is determined to be a narrow excavation pit and the most unfavorable sliding surface intersects with the opposing side support structure, the reaction force of the opposing side support structure on the soil is calculated using the parameters of the most unfavorable sliding surface and the parameters of the opposing side support structure. Using the reaction force, the parameters of the most unfavorable sliding surface, and the physical and mechanical parameters of the soil, the overall stability safety factor of the excavation pit is calculated using a preset formula, which is: ;

[0041] The contribution of the reaction force of the opposing lateral support structure in the formula is calculated by the following formula: ;

[0042] This completes the overall stability calculation of the foundation pit.

[0043] In the above embodiments, when calculating the reaction force, the horizontal compression of the soil reaction calculation point is deduced based on the allowable settlement of the foundation pit and the geometric relationship; the distributed soil reaction force is calculated using the horizontal compression, the horizontal reaction force coefficient of the soil, and the initial soil reaction force using the soil reaction force calculation formula; the reaction force of the opposite side support structure on the soil is calculated based on the distributed soil reaction force and the action section parameters of the opposite side support structure and the soil.

[0044] In the above embodiments, when determining the initial soil reaction force, the initial soil reaction force is calculated according to the static earth pressure calculation method to obtain the value of the initial soil reaction force; using the value of the initial soil reaction force, the horizontal compression amount and the horizontal reaction force coefficient of the soil, the distributed soil reaction force is calculated.

[0045] Specifically, when the excavation pit is determined to be a narrow excavation pit and the most unfavorable sliding surface passes under the opposing side support structure, soil parameters are obtained for the area outside the opposing side support structure and located above the bottom of the excavation pit. Using the soil parameters of this area, the parameters of the most unfavorable sliding surface, and the physical and mechanical parameters of the soil, a preset formula is used to calculate the contribution of the soil in this area to the anti-sliding stability. This preset formula is: Based on the contribution value and the conventional anti-sliding force calculation results, the overall stability safety factor of the foundation pit is calculated using the following formula, thus completing the overall stability calculation of the foundation pit. .

[0046] In the above embodiments, when obtaining the soil parameters of the area outside the opposing side support structure and located above the bottom of the foundation pit, the cohesion, internal friction angle, soil strip width, standard value of additional distributed load, and soil strip self-weight parameters of the soil in the area are collected as the soil parameters of the area.

[0047] Optionally, during the overall stability calculation of the foundation pit, the additional distributed load parameters on both sides of the foundation pit are obtained; based on the additional distributed load parameters, it is determined whether there is an unbalanced load on both sides of the foundation pit; if there is an unbalanced load, the load parameters corresponding to the unbalanced load are included in the soil physical and mechanical parameters and used in the calculation of the overall stability safety factor of the foundation pit.

[0048] Optionally, when determining the type of the foundation pit and calculating the overall stability of the foundation pit, the embedment length parameters of the support structures on both sides of the foundation pit are obtained; based on the embedment length parameters, it is determined whether the embedment lengths of the support structures on both sides of the foundation pit are different; if they are different, the embedment length difference parameters are included in the parameters of the support structures on the opposite side, and are used to determine the most unfavorable sliding surface position and calculate the overall stability safety factor.

[0049] Optionally, before performing overall stability calculations on the foundation pit, the geological condition parameters and foundation treatment parameters on both sides of the foundation pit are obtained; based on the geological condition parameters and foundation treatment parameters, it is determined whether there are different geological conditions or different foundation treatment methods on both sides of the foundation pit; if so, the different geological condition parameters or different foundation treatment parameters are included in the soil physical and mechanical parameters and used in the calculation of the overall stability safety factor of the foundation pit.

[0050] Optionally, when performing overall stability calculations on the foundation pit, it is determined whether reinforced soil is used in the pit; if reinforced soil is used in the pit, the physical and mechanical parameters of the reinforced soil are obtained; the physical and mechanical parameters of the reinforced soil are incorporated into the physical and mechanical parameters of the soil and used to determine the location of the most unfavorable sliding surface and to calculate the overall stability safety factor.

[0051] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0052] An embodiment of the present invention provides a method for calculating the overall stability of a narrow foundation pit, the method comprising the following steps:

[0053] Step 201: First, calculate according to the standard method. If the intersection of the most unfavorable sliding surface and the bottom of the pit is within the width of the pit, then the pit is a normal pit and can be calculated according to the standard method. Figure 1 As shown;

[0054] Step 202: If the calculation is performed according to the standard method, and the most unfavorable sliding surface intersects with the opposite side support structure or passes under the opposite side support structure, then the foundation pit is determined to be a narrow foundation pit, and the standard method is no longer applicable. It is necessary to calculate according to the narrow foundation pit method.

[0055] ① If the most unfavorable sliding surface intersects with the opposite side support structure, the contribution of the opposite side support structure to the soil reaction force needs to be considered in the calculation. The following formula (1) is used to calculate the overall stability of the foundation pit. (1)

[0056] In equation (1), For the first The ratio of the anti-slip force to the sliding force of a circular arc sliding body; , The first The cohesion of the soil at the slip surface of the soil strip, and the angle of internal friction; For the first The width of the soil strip; No. Standard value of additional distributed load on soil strip For the first The weight of the earthen strips, For the first The radius of the circular sliding surface; For the first Water pressure on the slip surface of the soil strip; For the first The length of the slip arc of each soil strip; This refers to the reaction force of the opposing side support structure on the soil. For reaction force The anti-slip moment;

[0057] The contribution of the reaction force of the opposing lateral support piles to the sliding soil mass to the overall stability is as follows: (2)

[0058] In formula (2), the reaction force of the opposing side support piles on the sliding soil is... (kN), calculated using the following formula: (3)

[0059] In equation (4), To distribute the soil reaction force (kPa); The horizontal reaction coefficient of the soil (kN / m) 3 ); The horizontal compression (m) at the soil reaction calculation point. The initial soil reaction force (kPa) can be calculated as the at-rest earth pressure.

[0060] Calculate the horizontal compression at the point. The settlement can be estimated based on the allowable settlement of the foundation pit, as follows:

[0061] like Figure 2 As shown, the sliding surface OiAB intersects the opposing support structure at point B, and point C is the intersection of the support structure and the bottom of the pit. The BC segment represents the reaction force zone of the support structure on the soil. Assuming point A slides along the sliding arc to point A1, the AA1 segment of the sliding arc is extremely small relative to the sliding radius. Therefore, the AA1 segment can be approximated as the settlement of point A, and this settlement cannot exceed the allowable settlement of the pit. If the sliding surface OiAB is assumed to be a rigid body, without the obstruction of the support structure, points B and C will slide around the center Oi to points B1 and C1 respectively. Since the radii are the same, BB1 = AA1 = the allowable settlement of the pit. Due to the obstruction of the support structure, the compression in the arc direction can be considered as BB1, which is converted to the horizontal compression as BB2. The value of BB2 can be calculated based on the sliding arc angle and trigonometric relationships. Similarly, the value of CC2 can be calculated based on proportional relationships.

[0062] ② If the sliding surface passes through the support structure on the opposite side below its bottom elevation, such as Figure 3 As shown. At this point, it is necessary to consider the beneficial effect of the soil in the CBED area above the bottom of the excavation pit behind the opposing lateral support structure on the overall stability, calculated using the following formula:

[0063] Calculated using the following formula; (4)

[0064] The contribution of the CBED region can be determined by referring to the circular arc sliding strip method, taking into account the self-weight of the soil strip, the cohesion of the sliding arc section, and the beneficial effect of the frictional resistance between the soil strip and the sliding surface. Its contribution to the stability safety factor is reflected in the following formula: (5)

[0065] In equation (5), , These are the first (and second) units within the BCDE regions (hereinafter the same). The cohesion of the soil at the slip surface of the soil strip, and the angle of internal friction; For the first The width of the soil strip; No. Standard value of additional distributed load on soil strip For the first The weight of the earthen strips, For the first The radius of the circular sliding surface; For the first Water pressure on the slip surface of the soil strip; For the first The length of the slip arc of each soil strip;

[0066] Figure 2 and Figure 3 The attached figures are labeled as follows: For the first The width of the soil strip; No. Standard value of additional distributed load on soil strip For the first The weight of the earthen strips, For the first The radius of the circular sliding surface; This refers to the passive earth pressure exerted on the soil above the intersection of the slip arc and the opposing side support structure. For passive earth pressure The anti-slip moment; Frictional resistance The anti-slip moment.

[0067] The following will combine specific data and appendices. Figure 4 Appendix Figure 5 The technical solutions in the embodiments of the present invention will be clearly and completely described.

[0068] Assume the foundation pit depth is h=4m, the foundation pit support spacing is w=4m, the support pile length is L=7m, and the natural unit weight of the soil is... Cohesion internal friction angle The proportional coefficient of the horizontal resistance coefficient of the foundation The calculated width is bj=1m, which is simplified and is not affected by groundwater, pore water pressure, or external ground load.

[0069] (1) First, determine if the foundation pit is narrow:

[0070] (1.1) First, perform the calculation according to the standard method;

[0071] The center of the sliding arc is tentatively set at a position 3m above the ground level from the retaining pile. The sliding arc passes through the bottom of the retaining pile and intersects with the bottom of the foundation pit. The width of the sliding soil strip is bj=1m. The angle is measured using CAD software. and the area of ​​each soil strip.

[0072] The calculation table is as follows:

[0073] Fs=4.03>1.30, which meets the specification requirements.

[0074] In practice, it is also necessary to search for the most unfavorable sliding surface with the smallest safety factor according to the method of the present invention with a certain step size. Since the manual calculation process is cumbersome, this embodiment does not perform the search calculation, and it is recommended to develop a computer program to perform the calculation.

[0075] (2) Calculation based on a narrow foundation pit:

[0076] (2.1) If the most unfavorable sliding surface intersects with the opposite side support structure, the overall stability of the foundation pit shall be calculated using formula (1);

[0077] The center of the sliding arc is temporarily taken as the position of the top of the support pile. The sliding arc passes through the bottom of the support pile and intersects with the support pile on the opposite side. The width of the sliding soil strip is bj=1m and Ri=7m. The angle is measured using CAD software. and the area of ​​each soil strip.

[0078] The calculation table is as follows:

[0079] In practice, it is also necessary to search for the most unfavorable sliding surface with the smallest safety factor according to the method of the present invention with a certain step size. Since the manual calculation process is cumbersome, this embodiment does not perform the search calculation, and it is recommended to develop a computer program to perform the calculation.

[0080] Assuming point A slides along the arc to point A1, the arc segment AA1 is extremely small relative to the sliding radius. Therefore, it can be approximated that segment AA1 represents the settlement of point A. This settlement cannot exceed the allowable settlement of the foundation pit, which is set at 50mm. If the sliding surface OiAB is assumed to be a rigid body, without the obstruction of a supporting structure, points B and C will slide around the center Oi to points B1 and C1 respectively. Since the radii are the same, BB1 = AA1 = 50mm. Due to the obstruction of the supporting structure, the compression in the arc direction can be considered as BB1, which is converted to BB2 in the horizontal direction. Based on the arc angle and trigonometric relationships, BB2 = 40.93mm. Similarly, CC2 = 28.47mm can be calculated using proportional relationships.

[0081] coefficient of earth pressure at rest

[0082] Earth pressure at rest at point B

[0083] Earth pressure at rest at point C

[0084] Soil reaction strength at point B

[0085] Soil reaction strength at point C

[0086] The reaction force of the opposing side support piles on the sliding soil mass

[0087] Anti-slip torque of reaction force

[0088] The resultant force of sliding forces

[0089] Safety factor of soil reaction force contribution

[0090] The safety factor of this slip arc is:

[0091] (2.2) If the most unfavorable sliding surface passes under the opposite side support structure, the overall stability of the foundation pit is calculated using formula (5).

[0092] The center of the sliding arc is temporarily taken as the position of the top of the support pile. The sliding arc passes through the bottom of the support piles on both sides. The width of the sliding soil strip is bj = 1m, R k =R j =8.06m, angle measured using CAD software and the area of ​​each soil strip.

[0093] The calculation table is as follows:

[0094] The calculation table is as follows:

[0095]

[0096] In practice, it is also necessary to search for the most unfavorable sliding surface with the smallest safety factor according to the method of the present invention with a certain step size. Since the manual calculation process is cumbersome, this embodiment does not perform the search calculation, and it is recommended to develop a computer program to perform the calculation.

[0097] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0098] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for calculating the overall stability of a narrow foundation pit, characterized in that, Includes the following steps: The overall stability of the foundation pit was calculated according to the standard method to obtain the location of the most unfavorable sliding surface. Based on the location of the most unfavorable sliding surface, the foundation pit is determined to be a normal foundation pit or a narrow foundation pit. If the intersection of the most unfavorable sliding surface and the bottom surface of the foundation pit is within the width of the foundation pit, the foundation pit is determined to be a normal foundation pit. If the most unfavorable sliding surface intersects with the opposite side support structure or passes under the opposite side support structure, the foundation pit is determined to be a narrow foundation pit. If the foundation pit is a regular foundation pit, the overall stability calculation of the foundation pit shall be completed according to the standard method. If the foundation pit is a narrow foundation pit, the overall stability calculation of the foundation pit shall be completed by adopting the corresponding calculation method based on the relative position of the most unfavorable sliding surface and the opposite side support structure.

2. The method for calculating the overall stability of a narrow foundation pit according to claim 1, characterized in that, When it is determined that the foundation pit is a narrow foundation pit and the most unfavorable sliding surface intersects with the opposing side support structure, the reaction force of the opposing side support structure on the soil is calculated using the parameters of the most unfavorable sliding surface and the parameters of the opposing side support structure. The overall stability safety factor of the foundation pit is calculated using a preset formula based on the reaction force, the parameters of the most unfavorable sliding surface and the physical and mechanical parameters of the soil, thus completing the overall stability calculation of the foundation pit.

3. The method for calculating the overall stability of a narrow foundation pit according to claim 2, characterized in that, When calculating the reaction force, the horizontal compression of the soil reaction calculation point is deduced based on the allowable settlement of the foundation pit and the geometric relationship; the distributed soil reaction force is calculated using the soil reaction force calculation formula by using the horizontal compression, the horizontal reaction force coefficient of the soil and the initial soil reaction force; and the reaction force of the opposite side support structure on the soil is calculated based on the distributed soil reaction force and the action section parameters of the opposite side support structure and the soil.

4. The method for calculating the overall stability of a narrow foundation pit according to claim 3, characterized in that, When determining the initial soil reaction force, the initial soil reaction force is calculated according to the method of calculating static earth pressure to obtain the value of the initial soil reaction force; using the value of the initial soil reaction force, the horizontal compression amount and the horizontal reaction force coefficient of the soil, the distributed soil reaction force is calculated.

5. The method for calculating the overall stability of a narrow foundation pit according to claim 1, characterized in that, When it is determined that the excavation pit is a narrow excavation pit and the most unfavorable sliding surface passes under the opposite side support structure, the soil parameters of the area outside the opposite side support structure and located above the bottom of the excavation pit are obtained; using the soil parameters of the area, the parameters of the most unfavorable sliding surface, and the physical and mechanical parameters of the soil, the contribution value of the soil in the area to the anti-sliding stability is calculated using a preset formula; combining the contribution value and the conventional anti-sliding force calculation results, the overall stability safety factor of the excavation pit is calculated, and the overall stability calculation of the excavation pit is completed.

6. The method for calculating the overall stability of a narrow foundation pit according to claim 5, characterized in that, When obtaining the soil parameters of the area outside the opposing side support structure and located above the bottom of the foundation pit, the cohesion, internal friction angle, soil strip width, standard value of additional distributed load, and soil strip self-weight parameters of the soil in the area are collected as the soil parameters of the area.

7. The method for calculating the overall stability of a narrow foundation pit according to claim 2, characterized in that, During the overall stability calculation of the foundation pit, the additional distributed load parameters on both sides of the foundation pit are obtained; based on the additional distributed load parameters, it is determined whether there is unbalanced load on both sides of the foundation pit; if there is unbalanced load, the load parameters corresponding to the unbalanced load are included in the soil physical and mechanical parameters and used in the calculation of the overall stability safety factor of the foundation pit.

8. The method for calculating the overall stability of a narrow foundation pit according to claim 1, characterized in that, When determining the type of the foundation pit and calculating the overall stability of the foundation pit, the embedment length parameters of the support structures on both sides of the foundation pit are obtained; based on the embedment length parameters, it is determined whether the embedment lengths of the support structures on both sides of the foundation pit are different; if they are different, the embedment length difference parameters are included in the parameters of the support structures on the opposite side, and are used to determine the most unfavorable sliding surface position and calculate the overall stability safety factor.

9. The method for calculating the overall stability of a narrow foundation pit according to claim 1, characterized in that, Before performing overall stability calculations on the foundation pit, the geological condition parameters and foundation treatment parameters on both sides of the foundation pit are obtained. Based on the geological condition parameters and foundation treatment parameters, it is determined whether there are different geological conditions or different foundation treatment methods on both sides of the foundation pit. If so, the different geological condition parameters or different foundation treatment parameters are included in the soil physical and mechanical parameters and used in the calculation of the overall stability safety factor of the foundation pit.

10. The method for calculating the overall stability of a narrow foundation pit according to claim 1, characterized in that, When performing overall stability calculations on the foundation pit, it is determined whether reinforced soil is used inside the pit; if reinforced soil is used inside the pit, the physical and mechanical parameters of the reinforced soil are obtained; the physical and mechanical parameters of the reinforced soil are incorporated into the physical and mechanical parameters of the soil and used to determine the location of the most unfavorable sliding surface and to calculate the overall stability safety factor.

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