Device and method for treating sudden gushing of deep-width ratio foundation pit in strong-weak water permeable layer interactive stratum

Abstract

The application discloses a device and method for treating large-depth-width ratio pit gushing of strong-weak water permeable layer interactive stratum. The system comprises a normal working state conventional relief well and an emergency relief well for preventing unexpected situations, and the two kinds of relief wells have the same structure and different action areas. The relief well comprises a relief well bore, an outer well pipe and an inner well pipe. The conventional relief well is used for internal pressure reduction, the pore water pressure of the soil body is reduced, the effective vertical stress is increased, the side friction between the soil body and the foundation pit support structure is increased, and thus the anti-gushing capacity of the foundation pit is improved; the emergency relief well improves the anti-gushing capacity of the foundation pit by reducing the water pressure of the pressure-bearing water-bearing layer, and is opened when the conventional relief well fails. Compared with the conventional pressure reduction method, the application can reduce the construction depth of the foundation pit waterproof curtain, reduce the construction difficulty, save the cost, and has little influence on the surrounding environment when the internal pressure reduction is performed, and when the conventional relief well fails, the anti-gushing stability of the foundation pit can be ensured by opening the emergency relief well.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering foundation pit anti-surge technology, specifically relating to a device and method for dealing with the surge of foundation pits with large depth-to-width ratio in strata with alternating strong and weak permeability layers. Background Technology

[0002] In recent years, with the development of urban construction, water conservancy, transportation and other industries, more and more foundation pit projects have emerged that face complex hydrogeological conditions. Among them are foundation pits with a large depth-to-width ratio, such as the foundation pit of the working shaft of the shield tunneling machine. The standard method commonly used for the anti-surge calculation and analysis of such foundation pits ignores the shape characteristics of the foundation pit, especially in strata with multiple layers of strong and weak permeability. The standard method is relatively conservative because it fails to fully consider the side friction resistance between the soil layer below the bottom of the foundation pit and the foundation pit retaining structure, and cannot obtain economical and reasonable calculation and analysis results. The side friction resistance between the soil layer below the bottom of the foundation pit and the foundation pit retaining structure is not fully understood.

[0003] Currently, conventional methods for reducing pressure and preventing sudden inrush are used when the overburden above the confined aquifer at the bottom of the foundation pit is insufficient to resist the confined water head. These methods involve using a retaining structure to isolate the confined water or installing well points to extract the confined water, thereby reducing the water head pressure and minimizing its destructive effect on the foundation pit floor. However, when the foundation pit is overlain by multiple deep confined aquifers, completely isolating them with a retaining structure is difficult and costly. Installing well points to extract the confined water may cause adverse consequences such as ground subsidence around the foundation pit, building cracking, and damage to underground pipelines, posing a threat to the environment.

[0004] Conventional methods for calculating the resistance to sudden inrush in foundation pits treat the overlying soil layer of the confined aquifer as a completely impermeable whole, using its gravity to balance the pressure of the confined water. This method considers the weight of the overlying soil layer as the main resistance force, but does not account for the frictional force between the walls and soil on both sides. Therefore, this method is suitable for conventional foundation pits where the width of the pit is much larger than the thickness of the impermeable layer at the bottom. In these pits, the control effect is achieved by the bulging and cracking in the middle of the bottom slab, and the frictional force between the walls and soil on both sides has little effect. However, for foundation pits with a large depth-to-width ratio, such as shield tunnels, the width of the pit is close to or even smaller than the thickness of the impermeable layer under the bottom slab. When subjected to the water pressure of the confined aquifer, the impermeable layer under the bottom slab of the pit exhibits a rigid integral deformation state. In this case, the contribution of the frictional force between the walls and soil on both sides to resist sudden inrush cannot be ignored.

[0005] However, if the pore water pressure of the impermeable layer below the bottom of the foundation pit is very high, its effective vertical stress will be very low, which will result in very low friction between the wall and the soil.

[0006] Tong Liyuan et al., in their Chinese invention patent CN106337426A, proposed a "dewatering method to increase the stability of foundation pits resisting sudden inrush in confined aquifers." This method involves deepening and extending dewatering wells into the semi-permeable layer overlying the confined aquifer to release water pressure. After dewatering, the well acts as an impermeable layer, increasing the weight of the impermeable layer and thus enhancing the foundation pit's resistance to sudden inrush. However, this technology lacks detailed design for the dewatering well, failing to address potential issues such as wellbore collapse and well casing deformation during operation, and thus cannot guarantee the long-term stability of the dewatering well. Furthermore, this technology only considers the weight of the impermeable layer overlying the confined aquifer as resistance to sudden inrush, neglecting the lateral frictional resistance between the overlying soil layer and the foundation pit's retaining structure. This makes the technology theoretically conservative and not economically viable. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a system and method for treating large depth-to-width ratio foundation pits that utilizes side friction resistance, which is particularly suitable for strata with multiple layers of strong and weak permeability.

[0008] To achieve the above objectives, the present invention provides a device for handling sudden inrushes in foundation pits with large depth-to-width ratios in formations with alternating strong and weak permeability layers, including conventional pressure relief wells and emergency pressure relief wells. The two types of pressure relief wells have the same structure but different locations of operation.

[0009] Conventional pressure relief wells operate within the confined aquifer and soil layer within the perimeter of the foundation pit retaining structure, while emergency pressure relief wells operate within the confined aquifer and soil layer outside the perimeter of the foundation pit retaining structure.

[0010] The system includes conventional decompression wells and emergency decompression wells installed inside the foundation pit retaining structure. The conventional decompression wells are used to decompress the confined water and soil layer within the scope of the foundation pit retaining structure, while the emergency decompression wells are used to decompress the confined water and soil layer outside the scope of the foundation pit retaining structure.

[0011] Both the conventional decompression well and the emergency decompression well include a decompression well borehole, an outer well casing located inside the decompression well borehole, and an inner well casing located inside the outer well casing. The space between the borehole and the outer well casing is filled with concrete, and a support layer is provided on top of the concrete.

[0012] The inner well casing includes the inner well casing filter section and the inner well casing blind section located above the inner well casing filter section. The inner well casing filter section of the conventional decompression well is located in the area of ​​the highly permeable layer inside the foundation pit retaining structure and the area of ​​the weakly permeable layer between the highly permeable layers. The inner well casing filter section of the emergency decompression well is located in the area of ​​the highly permeable layer outside the foundation pit retaining structure. Both the inner well casing filter sections of the conventional decompression well and the emergency decompression well are equipped with a reverse filter layer, and the inner well casing blind section is equipped with an anti-seepage layer.

[0013] This invention provides a device for handling sudden inrush in foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability. It utilizes conventional pressure-reducing wells for internal pressure reduction, effectively controlling the pore water pressure in the impermeable layer, increasing its effective vertical stress, and significantly enhancing the friction between the soil layer and the foundation pit retaining structure, thereby improving the foundation pit's resistance to sudden inrush. This method leverages the characteristic of the impermeable layer beneath the foundation pit's bottom slab undergoing rigid overall deformation under confined water pressure, fully utilizing the friction between the soil layer and the foundation pit retaining structure to improve the foundation pit's resistance to sudden inrush. To prevent the conventional pressure-reducing wells from failing, an emergency pressure-reducing well is installed. When the conventional pressure-reducing wells fail, the emergency pressure-reducing well is activated to lower the water pressure in the confined soil layer, preventing sudden inrush damage to the foundation pit.

[0014] In a further improvement to the present invention, the diameter of the outer well pipe should not be less than 200 mm.

[0015] In a further improvement to the present invention, the borehole diameter should be at least 300 mm larger than the outer well pipe diameter.

[0016] In a further improvement to the present invention, the inner well pipe filter section is made of steel pipe with a wall thickness of 4 mm or more and a length of not less than 4.5 m.

[0017] A further improvement to the present invention is that the porosity of the inner well casing filter section is greater than or equal to 15%.

[0018] In a further improvement to the present invention, the bottom of the inner well casing is sealed by welding with a perforated steel plate.

[0019] In a further improvement to the present invention, the filter media of the reverse filter layer should be selected as hard gravel or pebbles with good roundness and uniform particle size.

[0020] A further improvement to the present invention is that a filter screen is provided on the outside of the inner well pipe filter section, and the pipe wall has holes.

[0021] A further improvement to the present invention is that the seepage-proof layer is formed by sealing the blind pipe section of the inner well pipe with high-quality clay balls with a diameter of φ50 within a height of at least 5m.

[0022] A further improvement to the present invention is that plain concrete is poured on the outside of the outer well pipe, and the supporting layer is a layer of crushed stone backfilled into the upper empty groove after the plain concrete has hardened.

[0023] If the pore water pressure of the impermeable layer below the bottom of the foundation pit is very high, for this type of foundation pit, the pore water pressure of the impermeable layer can be effectively controlled by reducing pressure, thereby increasing its effective vertical stress and making full use of the friction between the wall and the soil. This way, the requirements for the foundation pit to resist sudden surge can be met without large-scale pressure reduction, which is more economical and reasonable.

[0024] A method for handling sudden inrush of foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability, employing the aforementioned system, the method comprising the following steps:

[0025] Drill a well hole on the ground and hoist an outer well casing into the well hole;

[0026] Insert the bottom of the outer well pipe into the soil, pour concrete on the outside of the outer well pipe to the designated elevation, and backfill and install the support layer after the concrete has hardened.

[0027] Drill a hole inside the outer well casing and lower the inner well casing in;

[0028] The inner well casing is divided into a blind pipe section and a filter pipe section. The filter pipe section of the inner well casing has holes in its pipe wall and a reverse filter layer is installed. The blind pipe section of the inner well casing has an anti-seepage layer installed.

[0029] Compared with the prior art, the beneficial effects that the present invention can achieve are at least as follows:

[0030] 1. This invention can effectively reduce the construction depth of the foundation pit retaining structure (water-stop curtain), greatly reducing construction difficulty and cost.

[0031] 2. When the present invention uses a pressure relief well for drainage and pressure reduction, it is not necessary to carry out complete dewatering. Only the soil layer within the water interception range of the retaining structure (water-stop curtain) needs to be dewatered, which greatly reduces the impact on the surrounding environment.

[0032] 3. The foundation pit anti-surge treatment method provided by the present invention is particularly suitable for foundation pits with a large depth-to-width ratio and geological environments with multiple layers of strong and weak permeability.

[0033] 4. The emergency pressure relief well provided by this invention can be used as a supplement to the conventional pressure relief well. When the conventional pressure relief well fails to relieve pressure, activating the emergency pressure relief well can still ensure the safety of the foundation pit against sudden inrush.

[0034] 5. Based on the self-weight of the soil at the bottom of the pit, this invention makes full use of the friction between the underlying soil layer and the retaining structure to improve the pit's resistance to sudden inrush. It improves upon the overly conservative and insufficient conventional calculations for pit inrush resistance. Compared with conventional calculation methods, the theoretical model of this invention is more realistic and consistent with the results of actual engineering projects. It not only provides a reasonable theoretical supplement but also significantly reduces the cost of pit inrush resistance measures and improves the progress of project implementation.

[0035] 6. This invention provides a detailed design for the pressure relief well, dividing it into inner and outer layers. Concrete is poured between the outer well pipe and the wellbore, and crushed stone is backfilled to form a supporting force, solving the problems of well wall collapse and well pipe deformation that may occur during the use of the pressure relief well. Clay balls and gravel are filled between the inner and outer well pipes. The gravel acts as a filter layer to prevent water flow from carrying out fine sand and to prevent pipe wall blockage. The clay balls can effectively prevent surface water or water in the upper soil layer from seeping into the well along the well wall or filling material, while keeping the well dry and preventing moisture from damaging the well structure. Attached Figure Description

[0036] Figure 1 A schematic diagram illustrating a method for handling sudden inrush of foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers, provided by an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the filter pipe section inside the decompression well according to an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram showing the distribution of pressure relief wells within the foundation pit according to an embodiment of the present invention;

[0039] In the diagram: 1. Retaining structure of the foundation pit; 2-1, 2-2, 2-3 weakly permeable layers; 3-1, 3-2, 3-3 strongly permeable layers; 4. Crushed stone; 5. Concrete; 6. Clay ball; 7. Gravel or gravel; 8. Filter screen; 9. Well hole; 10. Outer well pipe; 11. Inner well pipe; 12. Blind pipe section of the inner well pipe of a conventional decompression well; 13. Filter pipe section of the inner well pipe of a conventional decompression well; 14. Blind pipe section of the inner well pipe of an emergency decompression well; 15. Filter pipe section of the inner well pipe of an emergency decompression well; 16. Well wall opening; 17. Reinforcing steel bars evenly distributed around the pipe; 18. Conventional decompression well; 19. Emergency decompression well. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Conventional methods for reducing pressure and preventing sudden inrushes involve isolating the confined aquifer through the foundation pit retaining structure or using well points to extract the confined aquifer, thereby reducing the destructive effect of the confined aquifer on the foundation pit floor. However, when the foundation pit is overlain by multiple deep confined aquifers, completely isolating them with a retaining structure is difficult and costly. Using well points to extract the confined aquifer may cause adverse consequences such as ground subsidence around the foundation pit, building cracking, and damage to underground pipelines, posing environmental hazards. To address these issues, this invention provides a method for handling sudden inrushes in foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers.

[0042] Please see Figure 1 This invention provides a method for handling large depth-to-width ratio foundation pits in strata with alternating strong and weak permeability layers. It is suitable for foundation pits with alternating weak permeability layers (2-1, 2-2, 2-3) and strong permeability layers (3-1, 3-2, 3-3). The method includes conventional pressure relief wells 18 under normal operating conditions and emergency pressure relief wells 19 to prevent unexpected situations. The two types of pressure relief wells have the same structure but different operating areas. A large depth-to-width ratio foundation pit refers to a foundation pit with a large ratio of depth to width; in layman's terms, it refers to a deep foundation pit with a relatively small width.

[0043] The conventional decompression well 18 is used to decompress the confined aquifer (highly permeable layer) 3-1 and 3-2 within the scope of the foundation pit retaining structure 1 (a highly permeable layer is not entirely a confined aquifer; a confined aquifer refers to a highly permeable layer below a weakly permeable layer, and 3-1 and 3-2 here are both below the weakly permeable layer, so they can be called confined aquifers). The emergency decompression well 19 is used to decompress the confined aquifer 3-3 outside the scope of the foundation pit retaining structure 1. When the conventional decompression well 18 fails to decompress the aquifer, the emergency decompression well 19 is opened. This provides the decompression strategy and suitable formations for the aforementioned decompression well, suitable for deep-to-wide foundation pits with multiple layers of alternating strong and weak permeability. The alternation of weak permeability layers 2-1, 2-2, and 2-3 with strong permeability layers 3-1, 3-2, and 3-3 results in a deep strong permeability layer and multiple impermeable layers (weak permeability layers, where the impermeable layer is a weak permeable layer above the confined aquifer (strong permeability layer), which bears water pressure due to its weak permeability and is called an impermeable layer) all pose a risk of sudden water inrush. This approach utilizes the pressure exerted by the confined aquifer on the deep-to-wide foundation pit... The impermeable layer beneath the base plate exhibits rigid, integral deformation characteristics. Decompression is achieved through conventional pressure-reducing wells 18, which depressurize the soil layers (3-1, 2-2, 3-2) within their effective range. After decompression, the wells effectively control the pore water pressure within their range, thereby increasing the effective vertical stress. The friction between the soil layer and the foundation pit retaining structure is proportional to the effective vertical stress of the soil layer. Therefore, conventional pressure-reducing wells 18 can significantly increase the friction between the soil layer and the foundation pit retaining structure, enhancing the foundation pit's resistance to sudden inrush. To prevent pressure-reducing failure of conventional pressure-reducing wells 18, emergency pressure-reducing wells 19 are installed. When conventional pressure-reducing wells 18 fail, emergency pressure-reducing wells 19 are activated to lower the water pressure in the confined soil layer, preventing sudden inrush damage to the foundation pit.

[0044] In some embodiments of the present invention, the pressure relief well includes a pressure relief well borehole 9, an outer well casing 10 located within the pressure relief well borehole 9, and an inner well casing 11 located within the outer well casing 10. Concrete 5 is filled between the pressure relief well borehole 9 and the outer well casing 10 to a specified elevation. After the concrete 5 hardens, the upper empty space is backfilled with crushed stone 4. To prevent soil particles from entering the gap between the pressure relief well borehole 9 and the outer well casing 10 under water pressure, a certain height of concrete 5 is filled between the gaps. After the concrete 5 hardens, the upper empty space is backfilled with crushed stone 4. This increases the stability around the well casing and prevents well wall collapse and well casing deformation.

[0045] In some embodiments of the present invention, a reverse filter layer is provided between the outer well casing 10 and the inner well casing 11, in the inner well casing filter section 13 of the conventional decompression well and the inner well casing filter section 15 of the emergency decompression well, and is wrapped with a steel wire mesh 8. Through holes 16 are opened in the pipe wall. Clay balls 6 are filled in the inner well casing blind section 12 of the conventional decompression well and the inner well casing blind section 14 of the emergency decompression well. The inner well casing filter section 13 is the area of ​​the inner well casing used for water seepage. The inner well casing filter section 13 of the conventional decompression well is located in the area of ​​the highly permeable layer within the foundation pit retaining structure and the area of ​​the weakly permeable layer between the highly permeable layers (e.g.,...). Figure 1 Soil layers 3-1, 2-2, and 3-2 (in the soil layer), the filter pipe section 15 of the emergency pressure relief well is located in a highly permeable layer outside the foundation pit retaining structure (such as soil layer 3-1, soil layer 2-2, and soil layer 3-2). Figure 1 Middle soil layer 3-3); the blind pipe section of the inner well pipe is the area of ​​the inner well pipe excluding the filter pipe section.

[0046] For conventional decompression wells, the inner well casing is required for pumping water when the well casing is driven to 3-1 or below, and the outer well casing is not required. For emergency decompression wells, the inner well casing is required for pumping water when the well casing is driven to 3-3 or below, and the outer well casing is driven to the bottom of the soil layer 2-3.

[0047] In some embodiments of the present invention, gravel or gravel 7 is filled in the inner well pipe filter section 13 to form a reverse filter layer. The reverse filter layer can guide seepage into the well, prevent water flow from carrying out fine sand, prevent pipe wall blockage, and at the same time, it can serve as a filter medium to help remove impurities in the water, keep the water quality clean, and also increase the stability around the well pipe, prevent well wall collapse, and ensure the long-term effective operation of the pressure relief well.

[0048] The steel wire mesh 8 wrapped around the inner well pipe filter sections 13 and 15 not only serves a filtering function but also provides additional protection for the filter pipe, enhancing its overall stability. Blocking large particles also improves the drainage efficiency of the pressure relief well. The through holes 16 in the well wall provide multiple water inlet channels, allowing groundwater to enter the pressure relief well through the filter pipe.

[0049] In some embodiments of the present invention, the blind pipe sections 12 and 14 of the inner well pipe are located at the upper part of the well, without openings, and do not participate in drainage. Clay balls 6 are filled within a height of at least 5m in the blind pipe sections 12 and 14 of the inner well pipe. The clay balls, with a specification of φ50, effectively prevent surface water or water from the upper soil layer from seeping into the well along the well wall or filling material. Filling with clay balls also keeps the well dry, preventing moisture from damaging the well structure. Simultaneously, the clay ball filling increases the structural stability of the well, preventing well wall collapse or well pipe deformation.

[0050] In some embodiments of the present invention, the diameter of the outer well pipe 10 is not less than 200 mm; if the diameter is too small, it will affect the drainage effect. The diameter of the well hole 9 is more than 300 mm larger than the diameter of the outer well pipe 10. The larger diameter can reduce the positional offset during well pipe installation, provide more operating space for lowering the well pipe and filling, and improve the stability of the pressure relief well.

[0051] In some embodiments of the present invention, the inner well pipe filter sections 13 and 15 are made of steel pipes with a wall thickness of 4 mm or more to ensure the strength and durability of the filter pipes, and the length of the steel filter pipes is not less than 4.5 m to ensure that the filter pipes have sufficient effective filtration area.

[0052] In some embodiments of the present invention, the porosity of the inner well casing filter sections 13 and 15 is greater than or equal to 15%, ensuring that the filter has sufficient water intake performance and filtration effect. The bottom of the inner well casing is sealed with a perforated steel plate welded to prevent impurities from entering the well casing.

[0053] In some embodiments of the present invention, the filter material of the reverse filter layer in the inner well casing 11 is selected as hard gravel or gravel with good roundness and uniform particle size. While preventing fine particles from entering the well casing, it can also improve the permeability of the filter layer and enhance the stability of the filter layer. Better filter layer material can ensure the effective operation and long-term stability of the decompression well.

[0054] Please see Figure 3 In some embodiments of the present invention, the conventional pressure relief wells 18 and emergency pressure relief wells 19 should be evenly distributed inside the foundation pit, with the two types of pressure relief wells distributed alternately and crosswise to ensure that the two types of pressure relief wells can play a role in most areas inside the foundation pit and prevent the risk of sudden surge in local areas of the foundation pit.

[0055] In some embodiments of the present invention, a method for handling sudden inrush of foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability is also provided. The specific steps are as follows:

[0056] Step 1: Drill a hole on the ground and hoist in the outer well casing 10. For conventional pressure relief wells, the outer well casing is driven to the boundary between soil layer 2-1 and soil layer 3-1. For emergency pressure relief wells, the outer well casing is driven to the boundary between soil layer 3-3 and soil layer 2-3.

[0057] Step 2: Insert the bottom of the outer well pipe 10 into the soil, pour concrete 5 on the outside of the outer well pipe 10 to the specified elevation, and after the concrete 5 hardens, backfill the upper empty trench with crushed stone 4.

[0058] Step 3: Drill a hole inside the outer well casing 10 and hoist in the inner well casing 11;

[0059] Step 4: The inner well pipe 11 is divided into a blind pipe section and a filter pipe section. The filter pipe section 13 of the conventional decompression well is located in the area of ​​the strong permeable layer and the weak permeable layer between the strong permeable layers within the foundation pit retaining structure (soil layer 3-1, soil layer 2-2, soil layer 3-2). For the filter pipe section 15 of the emergency decompression well, it is located in the strong permeable layer outside the foundation pit retaining structure (soil layer 3-3). The filter pipe section has small holes in the pipe wall, is wrapped with a steel wire mesh, and is backfilled with gravel or gravel. Some blind pipe sections are backfilled with clay balls.

[0060] This invention provides a method for handling sudden inrush in foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability. It utilizes the characteristic that the impermeable layer beneath the foundation pit deforms rigidly when subjected to confined water pressure. By installing conventional pressure-reducing wells for internal pressure reduction, the friction between the soil layer and the foundation pit retaining structure is increased, enhancing the foundation pit's resistance to sudden inrush. This solves the problems of high construction difficulty and significant environmental impact associated with conventional pressure-reducing methods in such strata. Furthermore, by installing emergency pressure-reducing wells, when conventional wells fail, the water pressure in the confined soil layer is reduced, preventing sudden inrush damage and addressing the issue of inrush failure when conventional wells fail. Filling the space between the pressure-reducing well borehole 9 and the outer well pipe 10 with concrete solves the problem of soil particles entering the gap between the borehole 9 and the outer well pipe 10 under water pressure. This invention can adapt to different underground environments and usage requirements by controlling the particle size and gradation of gravel or gravelly sand 7.

[0061] Many specific details have been set forth in the foregoing description to provide a thorough understanding of the present invention. However, the above description is merely a preferred embodiment of the present invention, and the present invention can be implemented in many other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed above. Furthermore, any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, using the methods and techniques disclosed above, without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A device for handling sudden inrush in foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers, characterized in that, For foundation pits with a large depth-to-width ratio used in strata with multiple layers of weakly permeable and strongly permeable layers; The device includes a conventional decompression well (18) and an emergency decompression well (19) installed inside the foundation pit retaining structure (1). The conventional decompression well (18) is used to decompress the confined water and soil layer within the scope of the foundation pit retaining structure (1), and the emergency decompression well (19) is used to decompress the confined water and soil layer outside the scope of the foundation pit retaining structure (1). The conventional decompression well (18) and the emergency decompression well (19) both include a decompression well borehole (9), an outer well pipe (10) located in the decompression well borehole (9), and an inner well pipe (11) located in the outer well pipe (10). The well borehole (9) and the outer well pipe (10) are filled with concrete (5) and a support layer is provided above the concrete (5). The inner well pipe (11) includes an inner well pipe filter section and an inner well pipe blind pipe section located above the inner well pipe filter section. The inner well pipe filter section of the conventional decompression well (18) is located in the area of ​​the strong permeable layer inside the foundation pit retaining structure and the area of ​​the weak permeable layer between the strong permeable layers. The inner well pipe filter section of the emergency decompression well (19) is located in the area of ​​the strong permeable layer outside the foundation pit retaining structure. The inner well pipe filter sections of both the conventional decompression well (18) and the emergency decompression well (19) are equipped with a reverse filter layer. The inner well pipe blind pipe section is equipped with an anti-seepage layer. The anti-seepage layer is a clay ball (6) filled in the inner well pipe blind pipe section. The support layer is crushed stone (4) backfilled in the empty groove above the concrete (5) after the concrete (5) has hardened.

2. The device for handling sudden inrush of foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers according to claim 1, characterized in that: The diameter of the external well pipe (10) shall not be less than 200 mm.

3. The device for handling sudden inrush of foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers according to claim 1, characterized in that: The diameter of the well hole (9) is more than 300 mm larger than the diameter of the outer well pipe (10).

4. The device for handling sudden inrush of foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers according to claim 1, characterized in that: The filter pipe section of the inner well uses steel pipe with a wall thickness of 4mm or more and a length of not less than 4.5m.

5. The device for handling sudden inrush of foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers according to claim 1, characterized in that: The porosity of the internal wellbore filter section is greater than or equal to 15%.

6. The method for handling sudden inrush of foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers according to claim 1, characterized in that: The filter media of the reverse filter layer is hard gravel or gravel.

7. The device for handling sudden inrush of foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers according to claim 1, characterized in that: A filter screen (8) is installed on the outside of the inner well pipe filter section, and the pipe wall has holes.

8. A method for handling sudden inrush in foundation pits with large depth-to-width ratios in strata with alternating strong and weak permeability layers, characterized in that, Using the apparatus according to any one of claims 1-7, the method comprises the following steps: Drill a well hole (9) on the ground and hoist an outer well pipe (10) into the well hole (9); Insert the bottom of the outer well pipe (10) into the soil, pour concrete (5) on the outside of the outer well pipe (10) to the specified elevation, and backfill and set up a support layer after the concrete hardens; Drill a hole inside the outer well casing (10) and hoist in the inner well casing (11); The inner well pipe (11) is divided into a blind pipe section and a filter pipe section. A hole is opened in the pipe wall of the filter pipe section of the inner well pipe and a reverse filter layer is set. An anti-seepage layer is set in the blind pipe section of the inner well pipe.

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