A method for determining the stability of foundation pit heave in karst areas

Abstract

This invention discloses a method for determining the stability of sudden inrush in foundation pits in karst areas, comprising: obtaining geological and hydrological parameters of the foundation pit, and calculating the pressure balance stability coefficient K of the sudden inrush using the standard pressure balance analysis method. h K h If K ≥ 1.1, then the stability requirement is met; h <1.1, Calculate the overall jacking stability coefficient K for the first surge using the overall jacking analysis method. W1 K W1 When the value is less than 1.1, reinforce the soil layer and calculate the overall stability coefficient K of the second sudden surge after reinforcement. W2 K W1 ≥1.1 or reinforced K W2 When the stress is ≥1.1, the plastic failure analysis method is used to analyze whether a plastic failure zone appears. If no plastic failure zone appears, the requirements are met. If a plastic failure zone appears, reinforcement treatment is carried out and the analysis is repeated until no plastic failure zone appears. This invention constructs a multi-level judgment system, which can more accurately determine the stability of foundation pit heave in karst areas, guide foundation pit construction practices in karst areas, and provide targeted reinforcement treatment solutions.

Description

Technical Field

[0001] This application relates to the field of geotechnical engineering design and research technology, and more specifically, to a method for determining the stability of foundation pit heave in karst areas. Background Technology

[0002] Sudden water inrush, mudslide inrush (referred to as sudden inrush), and deformation of the surrounding environment are prominent problems frequently encountered in foundation pit engineering practice. Therefore, calculating and determining sudden inrush at the bottom of the foundation pit is crucial. Calculating the resistance to sudden inrush at the bottom of foundation pits in karst areas is a challenging aspect of foundation pit support design calculations in karst regions. Due to the diversity of karst geological structures, the variability in karst development levels, and the complexity of karst water occurrence conditions and activity states, the risk control difficulty in the design and construction of foundation pit engineering in karst areas is much greater than in non-karst areas. Therefore, it is necessary to conduct specialized research on the problem of sudden inrush at the bottom of foundation pits in karst areas and propose a reasonable and feasible determination method to guide foundation pit engineering practice in karst regions.

[0003] Existing technologies typically employ pressure balance analysis, a method with simple and intuitive calculations. However, this method fails to consider factors such as soil strength, pit dimensions, excavation depth, and the effect of support structures, resulting in overly conservative calculations. Practical experience has shown that the results obtained using the standard pressure balance method differ significantly from actual conditions and are excessively conservative. Clearly, for foundation pit projects with complex karst geological structures and karst water conditions, directly applying the standard-recommended pressure balance analysis method to analyze and determine the stability of confined water inrush at the pit bottom is inappropriate.

[0004] Over the past three decades, many scholars have conducted continuous theoretical research and engineering practice on methods for identifying and mitigating bottom heave in foundation pits, achieving some theoretical results and practical experience. However, these results mainly apply to foundation pit engineering in non-karst areas. Karst areas have complex geological environments, and the influencing factors and mechanisms of bottom heave are far more complex than those in non-karst areas. Therefore, directly applying research findings on bottom heave in non-karst areas without considering karst characteristics is insufficient to accurately guide foundation pit engineering practice in karst areas.

[0005] Existing technologies do not address the design and calculation of anti-surge indentation issues in foundation pits in karst areas, and there is no specific research in the industry specifically addressing this problem.

[0006] Therefore, the existing technology has defects and urgently needs improvement. Summary of the Invention

[0007] In view of the above problems, the purpose of this invention is to provide a method for determining the stability of foundation pit heave in karst areas. This method constructs a multi-level determination system by combining the standard pressure balance analysis method, the overall jacking analysis method, and the plastic failure analysis method. It can more accurately determine the stability of foundation pit heave in karst areas, guide the practice of foundation pit construction in karst areas, and provide targeted reinforcement treatment solutions.

[0008] The first aspect of this invention provides a method for determining the stability of a foundation pit heave in karst areas, comprising: Obtain geological and hydrological parameters of foundation pits in karst areas; Based on geological and hydrological parameters, the standard pressure balance analysis method is used to calculate the inrush pressure balance stability coefficient K of the overlying soil layer of soluble rock. h ; If K h When K ≥ 1.1, the inrush stability of the overlying soil layer on the soluble rock is deemed to meet the requirements; when K h When the value is less than 1.1, the overall jacking analysis method is used to calculate the overall jacking stability coefficient K of the first surge. W1 ; When K W1 When the value is less than 1.1, the soil layer overlying the soluble rock at the bottom of the pit is reinforced using the first preset method. After reinforcement, the overall stability coefficient K of the second sudden surge is calculated. W2 ; When K W2 When the value is less than 1.1, the soil layer in the plastic failure zone is reinforced using the second preset method. When K W1 ≥1.1 or K W2 When the value is ≥1.1, the plastic failure analysis method is used to analyze whether a plastic failure zone appears in the soil layer overlying the soluble rock at the bottom of the pit; When no plastic failure zone is found, the heave stability of the soil layer overlying the soluble rock is deemed to meet the requirements; when a plastic failure zone is found, the soil layer in the plastic failure zone is reinforced using the first preset method; after reinforcement, the plastic failure analysis method is used again for analysis. If no plastic failure zone is found after reanalysis, the heave stability of the soil layer overlying the soluble rock is deemed to meet the requirements; if a plastic failure zone still appears after reanalysis, the soil layer in the plastic failure zone is reinforced according to the second preset method.

[0009] In this scheme, based on geological and hydrological parameters, the standard pressure balance analysis method is used to calculate the inrush pressure balance stability coefficient K of the overlying soil layer of soluble rock. h ,include: Inrush pressure balance stability coefficient K h The calculation formula is expressed as: ; Where D is the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer, The pressure head height at the top surface of the confined aquifer. It is the density of water.

[0010] In this scheme, the overall jacking analysis method is used to calculate the overall jacking stability coefficient K of the first surge. W1 ,include: The stability coefficient of the first surge overall lifting is K. W1 The calculation formula is expressed as: ; in, Dimensionless size factor Let be the shear strength of the soil layer at the bottom of the pit, and D be the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer, The pressure head height at the top surface of the confined aquifer. It is the density of water.

[0011] In this scheme, the plastic failure analysis method is used to analyze whether a plastic failure zone appears in the overlying soil layer of the soluble rock at the bottom of the pit, including: Establish a finite element calculation model; Set boundary conditions: the side that is not in contact with the enclosure structure is a vertical sliding boundary, and the side that is in contact with the enclosure structure is a fixed constraint. Apply a uniformly distributed water head pressure load to the bottom plate of the impermeable layer on the model; Calculation of yield stress ratio based on the Drucker-Prager yield criterion ; When the yield stress ratio When the value is greater than 1, a plastic failure zone is generated in the soil layer overlying the soluble rock at the bottom of the pit.

[0012] This plan, after obtaining the geological and hydrological parameters of the foundation pit in the karst area, also includes: Identify karst geological structure types based on geological and hydrological parameters; If the sandy soil reinforcement sealing layer is identified as a Class I karst geological structure, the sandy soil reinforcement sealing layer is simplified to a Class II karst geological structure water-proof layer. If it is a weak soil layer with a Class III karst geological structure, the weak soil layer is simplified to a water-resistant layer with a Class II karst geological structure. Based on the geological and hydrological parameters of the aquitard, the final geological and hydrological parameters are set.

[0013] In this scheme, after reinforcement treatment, the overall jacking stability coefficient K of the second surge is calculated.W2 ,include: Calculate the overall jacking stability coefficient K of the second surge. W2 The calculation formula is expressed as: ; in, To strengthen the shear strength of the soil at the shear failure surface, γ represents the shear strength of the unreinforced soil layer, γ represents the natural unit weight of the impermeable soil layer, and D represents the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. This refers to the height of the confined water head. The density of water, The thickness of the reinforced soil layer is denoted by α, which is a calculation coefficient.

[0014] This plan also includes: Shear strength of the soil layer at the bottom of the pit The formula for calculating earth pressure at rest is expressed as follows: ; The formula for calculating passive earth pressure is expressed as follows: ; in, , Let be the cohesion and friction angle between the impermeable soil layer at the bottom of the pit and the shear failure surface, respectively; let c and φ be the cohesion and internal friction angle of the impermeable soil layer at the bottom of the pit, respectively; and let K0 be the coefficient of at-rest earth pressure of the impermeable soil layer at the bottom of the pit. p denoted as the passive earth pressure coefficient of the impermeable soil layer at the bottom of the pit, and D as the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer.

[0015] In this scheme, the yield stress ratio is calculated based on the Drucker-Prager yield criterion. ,include: Equivalent stress calculated based on the Drucker-Prager yield criterion With material yield parameter : ; ; ; ; ; in, It is the yield function. It is an influence coefficient related to stress hydrostatic pressure. It is the yield parameter of the soil material. , These represent the first invariant of the stress tensor and the second invariant of the deviatoric stress tensor, respectively, and c and φ represent the cohesion and internal friction angle of the impermeable soil layer at the bottom of the pit, respectively. It defines equivalent stress. It is the material yield parameter; According to equivalent stress With material yield parameter Calculate the yield stress ratio : .

[0016] This invention discloses a method for determining the stability of sudden inrush in foundation pits in karst areas, comprising: obtaining geological and hydrological parameters of the foundation pit, and calculating the pressure balance stability coefficient K of the sudden inrush using the standard pressure balance analysis method. h K h If K ≥ 1.1, then the stability requirement is met; h <1.1, Calculate the overall jacking stability coefficient K for the first surge using the overall jacking analysis method. W1 K W1 When the value is less than 1.1, reinforce the soil layer and calculate the overall stability coefficient K of the second sudden surge after reinforcement. W2 K W1 ≥1.1 or reinforced K W2 When the stress is ≥1.1, the plastic failure analysis method is used to analyze whether a plastic failure zone appears. If no plastic failure zone appears, the requirements are met. If a plastic failure zone appears, reinforcement treatment is carried out and the analysis is repeated until no plastic failure zone appears. This invention constructs a multi-level judgment system, which can more accurately determine the stability of foundation pit heave in karst areas, guide foundation pit construction practices in karst areas, and provide targeted reinforcement treatment solutions. Attached Figure Description

[0017] Figure 1 A flowchart of a method for determining the stability of a foundation pit inrush in a karst area, according to the present invention, is shown. Detailed Implementation

[0018] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0019] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0020] Figure 1A flowchart of a method for determining the stability of a foundation pit inrush in a karst area, according to the present invention, is shown.

[0021] like Figure 1 As shown, this invention discloses a method for determining the stability of a foundation pit heave in karst areas, comprising: S101, to obtain the geological and hydrological parameters of the foundation pit in the karst area; S102, based on geological and hydrological parameters, the standard pressure balance analysis method is used to calculate the inrush pressure balance stability coefficient K of the overlying soil layer of soluble rock. h ; S103, if K h When K ≥ 1.1, the inrush stability of the overlying soil layer on the soluble rock is deemed to meet the requirements. h When the value is less than 1.1, the overall jacking analysis method is used to calculate the overall jacking stability coefficient K of the first surge. W1 ; S104, when K W1 When the value is less than 1.1, the soil layer overlying the soluble rock at the bottom of the pit is reinforced using the first preset method. After reinforcement, the overall stability coefficient K of the second sudden surge is calculated. W2 ; S105, when K W2 When the value is less than 1.1, the soil layer in the plastic failure zone is reinforced using the second preset method. S106, when K W1 ≥1.1 or K W2 When the value is ≥1.1, the plastic failure analysis method is used to analyze whether a plastic failure zone appears in the soil layer overlying the soluble rock at the bottom of the pit; S107. When no plastic failure zone appears, the heave stability of the soil layer overlying the soluble rock is determined to meet the requirements. When a plastic failure zone appears, the soil layer in the plastic failure zone is reinforced by the first preset method. After reinforcement, the plastic failure analysis method is re-analyzed. S108. If no plastic failure zone is found after reanalysis, the heave stability of the soil layer overlying the soluble rock is deemed to meet the requirements. If a plastic failure zone still appears after reanalysis, the soil layer in the plastic failure zone is reinforced according to the second preset method.

[0022] According to embodiments of the present invention, geological and hydrological parameters of the site of the foundation pit are obtained through on-site investigation, borehole sampling and indoor testing. By adopting the standard pressure balance analysis method, the overall jacking analysis method and the plastic failure analysis method, calculations and analyses are performed to construct a multi-level inrush stability judgment system, which can more accurately guide the work practice in karst areas and propose targeted reinforcement treatment schemes.

[0023] The definition of sudden inrush is sudden water or mud inrush in the foundation pit, which is a prominent problem frequently encountered in foundation pit engineering practice.

[0024] The geological parameters obtained should include at least: the thickness D of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit, and the natural unit weight of the impermeable soil layer. (When the impermeable soil layer contains multiple layers of different soil types,) (The following values ​​are taken: unit weight of each soil layer weighted by its thickness), cohesion c of the impermeable soil layer at the bottom of the pit, internal friction angle φ of the impermeable soil layer at the bottom of the pit, and yield parameters of the soil material. 1. Static earth pressure coefficient K0 of the impermeable soil layer at the bottom of the pit; 2. Passive earth pressure coefficient K of the impermeable soil layer at the bottom of the pit. p Hydrological parameters include at least the pressure head height h at the top surface of the confined aquifer. w The density of water w Influence coefficient related to stress hydrostatic pressure .

[0025] Then, based on geological parameters, the karst geological structure type is identified, and the model is simplified.

[0026] According to an embodiment of the present invention, based on geological and hydrological parameters, the standard pressure balance analysis method is used to calculate the inrush pressure balance stability coefficient K of the overlying soil layer of soluble rock. h ,include: Inrush pressure balance stability coefficient K h The calculation formula is expressed as: ; Where D is the thickness (m) of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural unit weight (kN / m³) of the impermeable soil layer (when the impermeable soil layer contains multiple layers of different soil types). (The unit weight of each soil layer is taken as a weighted average of its thickness), h w The pressure head height (m) of the top surface of the confined aquifer is the height of the water level in the confined aquifer measuring pipe above the bottom of the pit. The specific weight of water (kN / m³).

[0027] It should be noted that, in the next step of determining stability, the calculated K needs to be used... h Compared with the safety factor threshold, which is set at 1.1, the current "Technical Specification for Foundation Pit Support" stipulates that when there is a confined aquifer with a water head higher than the bottom of the pit, and no cutoff curtain is used to isolate the hydraulic connection between the inside and outside of the foundation pit, the inrush pressure balance stability coefficient K is... h It should not be less than 1.1.

[0028] If K h≥1.1, at this point, the self-weight of the impermeable soil layer is sufficient to resist the head pressure of the confined water, and it is determined that the inrush stability of the soil layer overlying the soluble rock meets the requirements. No further complex calculations or analyses are required, and the process ends.

[0029] If K h When the value is less than 1.1, the soil's own weight alone is insufficient to meet the stability requirements for sudden inrush, potentially posing a risk of such inrush. However, because the standard pressure balance method does not consider the soil's shear strength (cohesion and internal friction angle) and the effect of the foundation pit's planar dimensions, the calculation results are usually conservative. Therefore, to more accurately assess the project's safety and avoid unnecessary over-reinforcement, the overall jacking analysis method should be used for further analysis.

[0030] According to an embodiment of the present invention, the overall jacking analysis method is used to calculate the overall jacking stability coefficient K of the first surge. W1 ,include: The stability coefficient of the first surge overall lifting is K. W1 The calculation formula is expressed as: ; Where D is the thickness (m) of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural unit weight (kN / m³) of the impermeable soil layer (when the impermeable soil layer contains multiple layers of different soil types). (The unit weight of each soil layer is taken as a weighted average of its thickness), h w The pressure head height (m) at the top surface of the confined aquifer. The specific weight of water (kN / m³) This is a dimensionless size factor, calculated as the perimeter of the excavation pit (m) multiplied by the soil layer thickness (m) divided by the area of ​​the excavation pit (m²). For a rectangular excavation pit, it is... , , These are the length (m) and width (m) of the foundation pit, respectively. 0 represents the shear strength (kPa) of the soil layer at the bottom of the pit, which is a key parameter in this step and reflects the soil's ability to resist vertical shear failure.

[0031] It should be noted that the overall jacking analysis method is similar to the pressure balance analysis method. However, in addition to considering the weight of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit, this method also considers factors such as the lateral pressure of the soil layer and the shear strength of the foundation pit, making it more reasonable than the pressure balance analysis method.

[0032] Next, the stability coefficient K of the first surge overall jacking will be determined. W1 The determination will be based on the calculated K. W1 The value is compared with a safety factor threshold. In this embodiment, the safety factor threshold is set to 1.1. If KW1 A value ≥1.1 indicates that, considering the soil shear strength, the overall foundation pit meets the requirements for resistance to sudden inrush stability. At this point, the process is not terminated directly; instead, a plastic failure analysis is performed to further analyze whether localized plastic failure zones exist.

[0033] If K W1 A value less than 1.1 indicates insufficient overall stability of the foundation pit, posing a risk of sudden jacking and heaving. In this case, reinforcement measures must be implemented, specifically using the first pre-set method to improve the shear strength of the soil at the bottom of the pit.

[0034] The first pre-set method is to reinforce the soil layer of a certain thickness at the bottom of the pit with high-pressure jet grouting or high-pressure grouting.

[0035] According to an embodiment of the present invention, the plastic failure analysis method is used to analyze whether a plastic failure zone appears in the overlying soil layer of soluble rock at the bottom of the pit, including: Establish a finite element calculation model; Set boundary conditions: the side that is not in contact with the enclosure structure is a vertical sliding boundary, and the side that is in contact with the enclosure structure is a fixed constraint. Apply a uniformly distributed water head pressure load to the bottom plate of the impermeable layer on the model; Calculation of yield stress ratio based on the Drucker-Prager yield criterion ; When the yield stress ratio When the value is greater than 1, a plastic failure zone is generated in the soil layer overlying the soluble rock at the bottom of the pit.

[0036] It should be noted that when using the plastic failure analysis method, the overall jacking stability coefficient must meet the requirements (i.e., K). W1 ≥1.1 or reinforced K W2 When the stress concentration is ≥1.1), although the foundation pit is generally stable, local areas at the bottom of the pit may still experience plastic deformation due to stress concentration, which could lead to sudden surge. Therefore, this embodiment further employs a finite element-based plastic failure analysis method for refined verification.

[0037] To further study the stress distribution in the plastic failure zone, this example uses the general-purpose finite element software Midas GTS for simulation analysis. Based on the acquired geological and hydrological parameters, a finite element model of the soil layer at the bottom of the pit is constructed.

[0038] The plastic failure analysis method assumes that the soil layer at the bottom of the pit is an ideal elastic-plastic material. When the material does not yield, it only undergoes elastic deformation. Once it yields, it undergoes plastic deformation. As the plastic deformation develops, the material fails. The failure condition is the yield condition, and the failure surface coincides with the initial yield surface. The plastic yield of the soil layer conforms to the Drucker-Prager criterion.

[0039] According to an embodiment of the present invention, after obtaining the geological and hydrological parameters of the foundation pit in the karst area, the method further includes: Identify karst geological structure types based on geological and hydrological parameters; If the sandy soil reinforcement sealing layer is identified as a Class I karst geological structure, the sandy soil reinforcement sealing layer is simplified to a Class II karst geological structure water-proof layer. If it is a weak soil layer with a Class III karst geological structure, the weak soil layer is simplified to a water-resistant layer with a Class II karst geological structure. Based on the geological and hydrological parameters of the aquitard, the final geological and hydrological parameters are set.

[0040] It should be noted that, considering the diversity of geological structures in karst areas, the geological model in this embodiment is standardized according to the "Technical Specification for Exploration, Design and Construction in Karst Areas". This specification classifies karst geological structures into four categories (I, II, III, and IV), corresponding to overlying strata of sandy soil, clayey soil, soft to fluid plastic clay, and clastic rock, respectively.

[0041] For different types of karst geological structures, this embodiment adopts the following analysis and judgment strategy: If identified as a Class I karst geological structure (overlying sandy soil): Since the bottom of the foundation pit is a sandy soil layer, and the karst water is well connected with the pore water in the sandy soil layer, it is usually necessary to reinforce and seal the bottom of the sandy soil layer with jet grouting piles and grouting before the foundation pit is excavated. After reinforcement, the sandy soil layer is subjected to sudden surge stability analysis and judgment as a water-proof layer of Class II karst geological structure, and then enters the subsequent calculation process.

[0042] If identified as a Class II karst geological structure (overlying clay): The calculations are performed directly using the obtained geological parameters.

[0043] If identified as a Class III karst geological structure (overlying soft to fluid-plastic clay): Although there is a layer of weak soil of varying thickness between the soluble rock and the overlying soil, its resistance to sudden inrush is not fundamentally different from that of the cohesive soil layer in Type II structures. Therefore, the inrush stability analysis and assessment of Type III karst geological structures are also conducted in accordance with those of Type II karst geological structures.

[0044] If identified as a Class IV karst geological structure (overlying clastic rock): In such cases, the bottom of the foundation pit is usually exposed rock strata. When groundwater suddenly surges into the pit, the problem can generally be solved by grouting the cracks that cause the water inflow. This method is not applicable to this situation.

[0045] Explanation of the mechanical mechanisms of Type II and Type III structures: Although karst water in Type II structures is mainly found in caves, under the influence of water head pressure, it can migrate along fissures to the bottom of the overlying soil layer or seep into it, exerting a supporting effect on the overlying soil layer. This mechanism is not fundamentally different from the supporting effect on the overlying soil layer produced by Type III structures, so a unified model can be used for calculation.

[0046] Through the above simplification, the complex karst geological problem is transformed into a stability analysis problem for Class II karst geological structures.

[0047] According to an embodiment of the present invention, after reinforcement treatment, the overall jacking stability coefficient K of the second surge is calculated. W2 ,include: Calculate the overall jacking stability coefficient K of the second surge. W2 The calculation formula is expressed as: ; in, The shear strength (kPa) of the soil reinforced at the shear failure surface. γ is the shear strength (kPa) of the unreinforced soil layer (original soil layer), γ is the natural unit weight (kN / m³) of the impermeable soil layer, and D is the thickness (m) of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The height of the confined water head (m) The specific weight of water (kN / m³) Let α be the thickness of the reinforced soil layer (m), and α be a dimensionless size factor, which is the perimeter of the foundation pit (m) multiplied by the soil layer thickness (m) divided by the area of ​​the foundation pit (m2). For a rectangular foundation pit, it is: , , These represent the length (m) and width (m) of the foundation pit, respectively.

[0048] It should be noted that the stability coefficient K for the second surge overall jacking will be used next. W2 The determination will be based on the calculated K. W2 It is compared with a safety factor threshold. In this embodiment, the safety factor threshold is set to 1.1.

[0049] If K W2 A value ≥1.1 indicates that the overall foundation pit meets the requirements for resistance to sudden inrush stability after reinforcement. At this point, the process is not terminated directly, but rather a plastic failure analysis is performed to further analyze whether localized plastic failure zones exist.

[0050] If K W2 A value less than 1.1 indicates that the overall stability of the reinforced foundation pit is still insufficient, posing a risk of sudden jacking and heave. In this case, a reinforcement process must be implemented, namely, using the second pre-set method to ensure the foundation pit meets the requirements for heave stability and the absence of a plastic failure zone.

[0051] The second pre-set method is a treatment method that uses one or a combination of two of the following methods: reducing the karst water head, strengthening the strata, reducing the confined water head, or adding a vertical retaining structure.

[0052] According to an embodiment of the present invention, it further includes: Shear strength of the soil layer at the bottom of the pit The formula for calculating earth pressure at rest is expressed as follows: ; in, , Here, K0 represents the cohesion (kPa) and friction angle (°) between the impermeable soil layer at the bottom of the pit and the shear failure surface, respectively; K0 is the static earth pressure coefficient of the impermeable soil layer at the bottom of the pit; and D is the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer.

[0053] The formula for calculating passive earth pressure is expressed as follows: ; in, , K represents the cohesion (kPa) and friction angle (°) between the impermeable soil layer at the bottom of the pit and the shear failure surface, respectively. c represents the cohesion (kPa) of the impermeable soil layer at the bottom of the pit. p denoted as the passive earth pressure coefficient of the impermeable soil layer at the bottom of the pit, and D as the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer.

[0054] It should be noted that, in order to accurately obtain This embodiment provides two calculation modes, which can be selected according to the engineering safety level: The first calculation method is a conservative one, which uses at-rest earth pressure for calculation. The formula for calculating 0 is: ; in, , Here, K0 represents the cohesion (kPa) and friction angle (°) between the impermeable soil layer at the bottom of the pit and the shear failure surface, respectively; K0 is the static earth pressure coefficient of the impermeable soil layer at the bottom of the pit; and D is the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer.

[0055] The formula for calculating K0 is: ; Where φ′ is the internal friction angle of the soil.

[0056] The second calculation method conforms to Rankine's earth pressure theory, which uses passive earth pressure calculation. The formula for calculating 0 is: ; in, , K represents the cohesion (kPa) and friction angle (°) between the impermeable soil layer at the bottom of the pit and the shear failure surface, respectively. c represents the cohesion (kPa) of the impermeable soil layer at the bottom of the pit. p denoted as the passive earth pressure coefficient of the impermeable soil layer at the bottom of the pit, and D as the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer.

[0057] K p The calculation formula is: ; Where φ represents the internal friction angle (°) of the impermeable soil layer at the bottom of the pit.

[0058] According to an embodiment of the present invention, the yield stress ratio is calculated based on the Drucker-Prager yield criterion. ,include: Equivalent stress calculated based on the Drucker-Prager yield criterion With material yield parameter : ; ; ; ; ; Where f is the yield function, It is an influence coefficient related to stress hydrostatic pressure. These are the yield parameters of the soil material, where I1 and J2 are the first invariant of the stress tensor and the second invariant of the deviatoric stress tensor, respectively, and c and φ are the cohesion and internal friction angle of the impermeable soil layer at the bottom of the pit, respectively. σ e It is the definition of equivalent stress, σ y It is the material yield parameter; According to the equivalent stress σ e With the material yield parameter σ y Calculate the yield stress ratio : ; It should be noted that, in order to determine the degree of plastic failure of the soil at the bottom of the pit due to sudden inrush, for an ideal elastoplastic material that obeys the Drucker-Prager criterion, the equivalent stress is defined according to the yield equation. Material yield parameters Equivalent stress With material yield parameter The ratio is called the yield stress ratio. When the yield stress of the impermeable soil layer at the bottom of the pit is greater than... When the value is greater than 1, the soil at the bottom of the pit undergoes plastic yielding failure. The larger the size, the larger the distribution area of ​​plastic failure. The magnitude of the value directly reflects the degree of plastic failure caused by the sudden inrush of soil at the bottom of the pit. This method is generally applicable to the stability analysis of the impermeable layer at the bottom of foundation pits in soft soil areas.

[0059] when When ≤1: it indicates that the soil element is in an elastic state or has just reached the yield state, and no plastic failure has occurred.

[0060] If the analysis results show that no plastic failure zone was found (i.e., no failure zone was found throughout the entire area) If the area is ≤1, then the inrush stability of the overlying soil layer of the soluble rock is determined to meet the requirements, and the process ends.

[0061] If the analysis results show the presence of a plastic failure zone (i.e., the existence of...) The area >1 refers to the area where a certain thickness of soil at the bottom of the pit is reinforced by high-pressure jet grouting or high-pressure grouting through a first preset method (such as high-pressure jet grouting or grouting reinforcement).

[0062] After reinforcement, the soil parameters of the area were updated, and the plastic failure analysis method described above was used again for analysis.

[0063] If a plastic failure zone still appears after reanalysis, a second pre-set method is required to ensure that the foundation pit meets the requirements of surge stability and does not exhibit a plastic failure zone.

[0064] The second pre-set method is a treatment method that uses one or a combination of two of the following methods: reducing the karst water head, strengthening the strata, reducing the confined water head, or adding a vertical retaining structure.

[0065] Those skilled in the art can adjust the first preset method and the second preset method according to actual needs.

[0066] All information (including but not limited to user device information, user personal information, etc.), data (including but not limited to data used for analysis, stored data, displayed data, etc.), and signals (including but not limited to signals transmitted between user terminals and other devices) involved in this application have been authorized by the user or fully authorized by all parties, and the collection, use, and processing of related data must comply with the relevant laws, regulations, and standards of the relevant countries and regions. For example, the "geological parameters and hydrological parameters of foundation pits in karst areas" involved in this disclosure were obtained with full authorization.

[0067] This invention discloses a method for determining the stability of sudden inrush in foundation pits in karst areas, comprising: obtaining geological and hydrological parameters of the foundation pit, and calculating the pressure balance stability coefficient K of the sudden inrush using the standard pressure balance analysis method. h K h If K ≥ 1.1, then the stability requirement is met; h <1.1, Calculate the overall jacking stability coefficient K for the first surge using the overall jacking analysis method. W1 K W1 When the value is less than 1.1, reinforce the soil layer and calculate the overall stability coefficient K of the second sudden surge after reinforcement. W2 K W1 ≥1.1 or reinforced K W2 When the stress is ≥1.1, the plastic failure analysis method is used to analyze whether a plastic failure zone appears. If no plastic failure zone appears, the requirements are met. If a plastic failure zone appears, reinforcement treatment is carried out and the analysis is repeated until no plastic failure zone appears. This invention constructs a multi-level judgment system, which can more accurately determine the stability of foundation pit heave in karst areas, guide foundation pit construction practices in karst areas, and provide targeted reinforcement treatment solutions.

[0068] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0069] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units. They may be located in one place or distributed across multiple network units. Some or all of the units may be selected to achieve the purpose of this embodiment according to actual needs.

[0070] In addition, in the various embodiments of the present invention, each functional unit can be integrated into one processing unit, or each unit can be a separate unit, or two or more units can be integrated into one unit; the integrated unit can be implemented in hardware or in the form of hardware plus software functional units.

[0071] Those skilled in the art will understand that all or part of the steps of the above method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps of the above method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0072] Alternatively, if the integrated units of this invention are implemented as software functional modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the embodiments of this invention, or the parts that contribute to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the methods of the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, ROM, RAM, magnetic disks, or optical disks.

Claims

1. A method for determining the stability of a foundation pit heave in karst areas, characterized in that, include: Obtain geological and hydrological parameters of foundation pits in karst areas; Based on the aforementioned geological and hydrological parameters, the standard pressure balance analysis method is used to calculate the inrush pressure balance stability coefficient K of the overlying soil layer of soluble rock. h ; If K h When K ≥ 1.1, the inrush stability of the overlying soil layer on the soluble rock is deemed to meet the requirements; when K h When the value is less than 1.1, the overall jacking analysis method is used to calculate the overall jacking stability coefficient K of the first surge. W1 ; When K W1 When the value is less than 1.1, the soil layer overlying the soluble rock at the bottom of the pit is reinforced using the first preset method. After reinforcement, the overall stability coefficient K of the second sudden surge is calculated. W2 ; When K W2 When the value is less than 1.1, the soil layer in the plastic failure zone is reinforced using the second preset method. When K W1 ≥1.1 or K W2 When the value is ≥1.1, the plastic failure analysis method is used to analyze whether a plastic failure zone appears in the soil layer overlying the soluble rock at the bottom of the pit; When no plastic failure zone is found, the heave stability of the overlying soil layer of soluble rock is deemed to meet the requirements. When a plastic failure zone appears, the soil layer in the plastic failure zone is reinforced using the first preset method; After reinforcement, the plastic failure analysis method was used again for analysis; If no plastic failure zone is found after reanalysis, the heave stability of the overlying soil layer of soluble rock is deemed to meet the requirements. If a plastic failure zone still appears after reanalysis, the soil layer in the plastic failure zone shall be reinforced according to the second preset method.

2. The method for determining the stability of foundation pit heave in karst areas according to claim 1, characterized in that, Based on the geological and hydrological parameters, the standard pressure balance analysis method is used to calculate the inrush pressure balance stability coefficient K of the overlying soil layer of soluble rock. h ,include: The surge pressure balance stability coefficient K h The calculation formula is expressed as: ； Where D is the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer, The pressure head height at the top surface of the confined aquifer. It is the density of water.

3. The method for determining the stability of foundation pit heave in karst areas according to claim 1, characterized in that, The overall jacking analysis method is used to calculate the overall jacking stability coefficient K of the first surge. W1 ,include: The first surge overall lifting stability coefficient K W1 The calculation formula is expressed as: ； in, Dimensionless size factor Let be the shear strength of the soil layer at the bottom of the pit, and D be the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer, The pressure head height at the top surface of the confined aquifer. It is the density of water.

4. The method for determining the stability of foundation pit heave in karst areas according to claim 1, characterized in that, The analysis of whether a plastic failure zone appears in the overlying soil layer of the soluble rock at the bottom of the pit using the plastic failure analysis method includes: Establish a finite element calculation model; Set boundary conditions: the side that is not in contact with the enclosure structure is a vertical sliding boundary, and the side that is in contact with the enclosure structure is a fixed constraint. Apply a uniformly distributed water head pressure load to the bottom plate of the impermeable layer on the model; Calculation of yield stress ratio based on the Drucker-Prager yield criterion ; When the yield stress ratio When the value is greater than 1, a plastic failure zone is generated in the soil layer overlying the soluble rock at the bottom of the pit.

5. The method for determining the stability of foundation pit heave in karst areas according to claim 1, characterized in that, After obtaining the geological and hydrological parameters of the foundation pit in the karst area, the process also includes: Based on the geological and hydrological parameters, the karst geological structure type is identified; If the sandy soil reinforcement sealing layer is identified as a Class I karst geological structure, the sandy soil reinforcement sealing layer is simplified to a Class II karst geological structure water-proof layer. If it is a weak soil layer with a Class III karst geological structure, the weak soil layer is simplified to a water-resistant layer with a Class II karst geological structure. Based on the geological and hydrological parameters of the impermeable layer, the final geological and hydrological parameters are set.

6. The method for determining the stability of foundation pit heave in karst areas according to claim 1, characterized in that, After the reinforcement treatment, the overall jacking stability coefficient K of the second surge is calculated. W2 ,include: The calculation of the overall jacking stability coefficient K of the second surge is as follows. W2 The calculation formula is expressed as: ； in, To strengthen the shear strength of the soil at the shear failure surface, γ represents the shear strength of the unreinforced soil layer, γ represents the natural unit weight of the impermeable soil layer, and D represents the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. This refers to the height of the confined water head. The density of water, The thickness of the reinforced soil layer is denoted by α, which is a calculation coefficient.

7. The method for determining the stability of foundation pit heave in karst areas according to claim 3, characterized in that, Also includes: Shear strength of the soil layer at the bottom of the pit The formula for calculating earth pressure at rest is expressed as follows: ； The formula for calculating passive earth pressure is expressed as follows: ； in, , Let be the cohesion and friction angle between the impermeable soil layer at the bottom of the pit and the shear failure surface, respectively; let c and φ be the cohesion and internal friction angle of the impermeable soil layer at the bottom of the pit, respectively; and let K0 be the coefficient of at-rest earth pressure of the impermeable soil layer at the bottom of the pit. p denoted as the passive earth pressure coefficient of the impermeable soil layer at the bottom of the pit, and D as the thickness of the impermeable soil layer from the top of the confined aquifer to the bottom of the pit. The natural density of the impermeable soil layer.

8. The method for determining the stability of foundation pit heave in karst areas according to claim 4, characterized in that, The yield stress ratio was calculated based on the Drucker-Prager yield criterion. ,include: Equivalent stress calculated based on the Drucker-Prager yield criterion With material yield parameter : ； ； ； ； ； in, It is the yield function. It is an influence coefficient related to stress hydrostatic pressure. It is the yield parameter of the soil material. , These represent the first invariant of the stress tensor and the second invariant of the deviatoric stress tensor, respectively, and c and φ represent the cohesion and internal friction angle of the impermeable soil layer at the bottom of the pit, respectively. It defines equivalent stress. It is the material yield parameter; According to equivalent stress With material yield parameter Calculate the yield stress ratio : 。

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