A method for dewatering deep foundation pit support under water-rich interlayer near ground fissures

Abstract

The present invention discloses a method for supporting and dewatering a deep foundation pit under water-rich interlayers near ground fissures, and relates to the technical field of foundation pit dewatering, including setting a dewatering well inside the foundation pit, setting an external recharge well outside the foundation pit to control the overall water level around the foundation pit, and jointly assume the support and water interception function by setting local plain concrete piles between adjacent supporting pile rows, and the support pile rows and local plain concrete piles bite in the form of bite. The present invention discloses a method for supporting and dewatering a deep foundation pit under water-rich interlayers near ground fissures. Under the support-dewatering-recharge measures, on the one hand, a dry working environment inside the foundation pit can be ensured, and under the lateral bite and longitudinal embedding of local plain concrete piles, the side seepage of the foundation pit is greatly reduced, the groundwater seepage path is increased, and the influence of external water level changes on the inside of the foundation pit is effectively reduced; on the other hand, the setting of the recharge well makes the groundwater outside the foundation pit change slowly, and the occurrence of drainage and consolidation of soil is reduced, which effectively controls the deformation of the surrounding surface near the ground fissure area.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit dewatering, and in particular to a deep foundation pit support dewatering method for use under water-rich interlayers adjacent to ground fissures. Background Art

[0002] The difficulty of foundation pit dewatering under complex geological conditions is increasing day by day. The use of reasonable deep foundation pit support dewatering methods in areas near ground fissures is the premise for ensuring the overall stability of deep foundation pits. In water-rich ground fissure strata, dewatering treatment is carried out before foundation pit excavation. As the groundwater level drops, drainage consolidation and settlement of the stratum soil occur. The settlement law generally shows that as the distance from the foundation pit dewatering well increases, the settlement value gradually decreases.

[0003] However, in the ground fissure area, there are dislocations between different terraces, which makes the settlement curve abrupt at the terrace stratification, increasing the uneven settlement difference and having a huge impact on the surrounding environment. After the conventional precipitation is over, the foundation pit is excavated and constructed. Under normal working conditions, anchor pile support is used. If the side wall seepage is serious during the excavation, a row of water-stop curtains can be added to the outside of the supporting piles to control the side wall seepage of the foundation pit. The water-stop curtains cooperate with the supporting piles to effectively control the lateral deformation and internal seepage of the foundation pit.

[0004] However, this support method must control both the external water level drop and the head pressure difference inside and outside the foundation pit in the ground fissure area. If the drop is too large, the uneven settlement of the external surface will increase, which will easily cause deformation of surrounding buildings outside the pit and lateral movement of the retaining structure, making it difficult to ensure the overall stability of the entire foundation pit; if the drop is too small, water will easily flow out from the bottom of the foundation pit under the action of the water-stop curtain, which cannot ensure dry operation inside the foundation pit and affects its overall stability. At the same time, this support method is relatively expensive economically.

[0005] In summary, conventional methods for controlling groundwater in special strata are uneconomical and undesirable. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a method for supporting and dewatering deep foundation pits under water-rich interlayers near ground fissures. In the area near the ground fissures, a support method of interlocking support piles with local plain concrete piles is adopted. According to the allowable value of settlement caused by dewatering in the ground fissure area, the length of the local plain concrete piles is determined, and the location of the recharge well outside the foundation pit is calculated. Under this support-dewatering-recharge measure, during the excavation of the deep foundation pit, on the one hand, a dry working environment inside the foundation pit can be guaranteed. At the same time, under the lateral interlocking and longitudinal embedding of the local plain concrete piles, the side seepage of the foundation pit is greatly reduced, the groundwater seepage path is increased, and the influence of external water level changes on the inside of the foundation pit is effectively reduced. Compared with the method of setting plain concrete piles throughout the length, the local interlocking is more economical. On the other hand, the setting of the recharge well makes the groundwater outside the foundation pit change slowly, reduces the occurrence of drainage and consolidation of soil, and effectively controls the surrounding surface deformation in the area near the ground fissures.

[0007] To achieve the above-mentioned purpose, the present invention provides a method for supporting and dewatering a deep foundation pit under a water-rich interlayer near a ground fissure, wherein a dewatering well is arranged inside the foundation pit, and an external recharging well is arranged outside the foundation pit to control the overall water level around the foundation pit, and local plain concrete piles are arranged between adjacent supporting pile rows, and the supporting pile rows and the local plain concrete piles are engaged with each other to jointly bear the function of supporting and intercepting water;

[0008] The specific steps include:

[0009] S1. Determine the allowable value of surface deformation around the ground fissures based on the surrounding environment of the ground fissures and the surface settlement requirements after precipitation. 允 ;

[0010] S2, the allowable value of surface deformation generated around the ground fissures 允 Determine the maximum groundwater level drop value s 降 , through the maximum groundwater level drop value s 降 Calculate the groundwater level drop h 降 ;

[0011] S3, based on the groundwater level drop value h determined in step S2 降 Determine the distance m from the initial water level to the top of the local plain concrete pile and the depth l of the local plain concrete pile inserted into the bottom of the foundation pit d ;

[0012] S4. Determine the water level h based on the wetting curve equation 降 The corresponding precipitation impact distance x when

[0013] S5. To ensure the settlement after precipitation 允 Set up the recharging well and determine its location;

[0014] S6. According to the setting parameters calculated in steps S1 to S5, the construction of supporting piles and local plain concrete piles in the foundation pit, the construction of drainage wells inside the foundation pit and the construction of external recharging wells are carried out in sequence.

[0015] Preferably, in step S2, the maximum groundwater level drop value s 降 and groundwater level drop h 降 The calculation process is as follows:

[0016]

[0017] Among them, ψ w - Empirical coefficient for settlement calculation, based on regional engineering experience, if there is no experience, it is advisable to use ψ w =1;

[0018] Δh i -Thickness of the i-th soil layer; the total calculated thickness of the soil layer should be determined according to the seepage analysis or the actual soil layer distribution;

[0019] E si -Compression modulus of the i-th layer of soil; the compression modulus should be taken from the pressure section from the soil's self-weight stress to the sum of the self-weight stress and the additional effective stress;

[0020] Δσ zi -The average additional effective stress of the i-th soil layer under the ground caused by precipitation; for clay soil, the additional effective stress under the consolidation degree of the soil at the end of precipitation should be taken; where, when the i-th soil layer is above the initial groundwater level, Δσ zi =0; when the i-th soil layer is between the water level after precipitation and the initial groundwater level, Δσ zi =γ w h 降 ; When the i-th soil layer is below the water level after precipitation, Δσ zi =λ i γ w s i ;

[0021] γ w - water density;

[0022] h 降 - the vertical distance between the water level after precipitation and the initial groundwater level;

[0023] λ i - The calculation coefficient should be determined according to the groundwater seepage analysis. In the absence of analytical data, the value can also be determined based on local engineering experience;

[0024] s i -The vertical distance from the water level to the aquitard after precipitation.

[0025] Preferably, in step S3, according to the groundwater level drop value h determined in step S2 降 Determine the distance m from the initial water level to the top of the local plain concrete pile and the depth l of the local plain concrete pile inserted into the bottom of the foundation pit d The calculation formula is as follows:

[0026] m=h 降 +n 水

[0027]

[0028] The converted local plain concrete pile is inserted into the bottom of the foundation pit to a depth of l d as follows:

[0029]

[0030] Determine the total length L of the local plain concrete piles buried inside the foundation pit 素 :

[0031] L 素 ≥l d +H 基坑 -m

[0032] Among them, n 水 - Initial water level depth m;

[0033] K f - Safety factor of soil flow stability, not less than 1.6, 1.5, 1.4;

[0034] Y′-buoyancy density of soil;

[0035] Δh-water head difference inside and outside the foundation pit;

[0036] γ w -The gravity of the water.

[0037] Preferably, in step S4, according to the seepage approximation in "Groundwater Dynamics" as a constant flow analysis, the equal water head surfaces around the dewatering well are coaxial cylindrical surfaces, and the water level drawdown depth h is inverted by the infiltration curve equation under the assumption of axisymmetry in homogeneous and isotropic formations. 降 The corresponding precipitation impact distance x is converted and calculated using the following formula:

[0038]

[0039] The water level at the bottom of the foundation pit is consistent with the water level in the drainage well. The equivalent foundation pit is a large well model, and the width of the foundation pit is the diameter of the large well model. The water level h is determined 降 The corresponding precipitation impact distance x when the value is , the deformation formula is as follows:

[0040]

[0041] Among them, h-is equivalent to the distance from the water level at the bottom of the foundation pit to the relatively weak permeable layer, l+h-is equivalent to the distance from the water level inside the precipitation well to the relatively weak permeable layer, and r represents the radius of the precipitation well;

[0042] H-the distance from the initial water level to the relatively weak permeable layer;

[0043] B-equivalent width of foundation pit;

[0044] R - influence radius, k – hydraulic conductivity of aquifer;

[0045] s w -well water level drop, s w =H 基坑 -n 水 , when the well water level drops less than 10m, take 10m.

[0046] Preferably, in step S5, to ensure that the allowable settlement s is generated after precipitation 允 Set up the recharge well and determine the location of the recharge well, and use the following formula for calculation:

[0047] x 回灌 =Rx

[0048] Among them, x 回灌 -The distance between the recharging well and the foundation pit edge (m).

[0049] Preferably, in step S6, when constructing the supporting piles and local plain concrete piles in the foundation pit, local plain concrete piles are arranged between adjacent supporting piles, and the buried depth of the top of the local plain concrete piles is m obtained in step S3. The supporting piles are determined according to the design requirements. The length of the local plain concrete piles is L. 素 The engagement between piles shall not be less than 200mm. The supporting pile construction shall be carried out first, and then the local plain concrete pile engagement shall be carried out.

[0050] Preferably, in step S6, the construction process of the internal dewatering well of the foundation pit and the external recharging well includes:

[0051] ①After determining the well location and well depth, excavate the wellhead;

[0052] ②Install the wellbore;

[0053] ③After the wellbore is installed, grouting is carried out on the well wall;

[0054] ④Installation of precipitation well equipment, which includes water pumps, piping systems, and monitoring equipment.

[0055] Preferably, after the construction of step S6 is completed, dewatering is performed before the foundation pit is excavated. The dewatering well is arranged inside the foundation pit and gradually removed as the foundation pit is excavated. After the excavation design elevation is reached, dewatering is continued during the foundation pit excavation to maintain a dry working environment inside the foundation pit.

[0056] During the dewatering process inside the foundation pit, water is recharged in the external recharge well to ensure that the groundwater level outside the foundation pit does not drop too much. The water replenishment in the external recharge well is fed back based on the dewatering efficiency in the dewatering well to stabilize the groundwater level at the designed water level, and then excavation and support of the foundation pit are carried out.

[0057] Preferably, during the foundation pit excavation and support process, the foundation pit excavation is carried out in layers strictly according to the design requirements, and anchor cable construction is carried out immediately after each layer of excavation is completed, so as to control the surface deformation caused by the foundation pit excavation through the anchor pulling effect.

[0058] The present invention provides a method for supporting and dewatering a deep foundation pit under a water-rich interlayer near a ground fissure. The method adopts a support method in which a supporting row of piles is engaged with a local plain concrete pile. The length of the local plain concrete pile is determined according to the allowable value of settlement caused by dewatering in the ground fissure area, and the location of the recharge well outside the foundation pit is calculated. Under this support-dewatering-recharge measure, on the one hand, a dry working environment inside the foundation pit can be ensured. At the same time, under the lateral engagement and longitudinal embedding of the local plain concrete piles, the water seepage on the side of the foundation pit is greatly reduced, and the groundwater seepage path is also increased, effectively reducing the impact of external water level changes on the inside of the foundation pit. On the other hand, the setting of the recharge well slows down the change of groundwater outside the foundation pit, reduces the occurrence of drainage and consolidation of soil, and effectively controls the deformation of the surrounding surface near the ground fissure area.

[0059] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a plan layout diagram of the internal dewatering well of the foundation pit, the external recharging well, the local plain concrete piles and the supporting pile rows in the present invention;

[0061] Figure 2 It is the layout diagram of local plain concrete piles and supporting pile rows in the present invention;

[0062] Figure 3 It is a cross-sectional arrangement diagram of the internal dewatering well of the foundation pit, the external recharging well, the local plain concrete piles and the supporting pile rows in the present invention;

[0063] Figure 4 It is a schematic diagram for calculating the location of the external recharging well and the length of the local plain concrete piles in the present invention.

[0064] Reference numerals

[0065] 1. Dewatering well; 2. Local plain concrete piles; 3. Support piles; 4. External recharge well; 5. Anchor cables. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0067] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or devices.

[0068] Like reference numerals and letters denote similar items in the following drawings, and thus, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0069] Embodiment 1

[0070] A method for dewatering deep foundation pit support under water-rich interlayers near ground fissures, such as Figures 1 to 4 As shown, a dewatering well 1 is set inside the foundation pit. The distance from the initial water level to the top of the local plain concrete pile 2 is calculated according to the allowable settlement value of the area around the ground fissure, and the location of the external recharge well 4 is determined in combination with the dewatering and recharge curves; the depth of the strong and weak water-blocking interlayer is determined according to the results of the stratum exploration, and the construction parameters of the local plain concrete pile 2 are determined in combination with the depth of the strong and weak water-blocking interlayer. The anchor support pile 3 and the local plain concrete pile 2 are engaged in the form of joint support and water interception; after the excavation of the foundation pit is completed, the external recharge well 4 controls the overall water level around the foundation pit and reduces the uneven surface settlement in the area near the ground fissure. The local plain concrete pile 3 increases the seepage path, reduces the overall water inflow inside the foundation pit, and is beneficial to the overall stability of the foundation pit.

[0071] The specific steps include:

[0072] S1. Surface deformation around foundation pits is generally caused by precipitation and excavation. The farther away from the foundation pit, the less impact the excavation has on it. Based on the Technical Code for Building Foundation Pit Support (JGJ120-2012), the Technical Code for Monitoring of Building Foundation Pit Engineering (GB50497-2009) and the Code for Measurement of Building Deformation (JGJ 8-2016), etc., and with reference to the deformation requirements of existing buildings around ground fissures and the level of foundation pit support, combined with the settlement control experience in this area, the allowable value of surface deformation around ground fissures caused by precipitation in foundation pits is determined. 允 .

[0073] S2, s in actual precipitation process 降 Should be less than the allowable value of ground deformation s determined in step S1 允 According to the allowable settlement value around the ground fissure and the Technical Code for Construction Foundation Pit Support (JGJ120-2012), the maximum groundwater level drop value s in the region is derived. 降 , and then calculate the groundwater level drop value h under the profile by reverse calculation 降 .

[0074] The calculation process is as follows:

[0075]

[0076] Among them, s 允 -Calculate the allowable deformation of the stratum in the cross section (m);

[0077] ψ w - The empirical coefficient for settlement calculation should be determined based on the regional engineering experience. If there is no experience, it is advisable to use ψ w =1;

[0078] Δh i -Thickness of the i-th soil layer (m); the total calculated thickness of the soil layer should be determined according to the seepage analysis or the actual soil layer distribution;

[0079] E si -Compression modulus of the i-th layer of soil (kPa); the compression modulus of the pressure section from the soil's self-weight stress to the sum of the self-weight stress and the additional effective stress should be taken;

[0080] Δσ′ zi -The average additional effective stress (kPa) of the ith soil layer under the ground caused by precipitation. For clay soil, the additional effective stress under the consolidation degree of the soil at the end of precipitation should be taken.

[0081] When the i-th soil layer is above the initial groundwater level, Δσ′ zi =0; when the i-th soil layer is between the water level after precipitation and the initial groundwater level, Δσ′ zi =γ w h 降; When the i-th soil layer is below the water level after precipitation, Δσ′ zi =λ i γ w s i ;

[0082] γ w - Weight of water (kN / m 3 );

[0083] h 降 -Vertical distance between the water level after precipitation and the initial groundwater level (m);

[0084] λ i - The calculation coefficient should be determined according to the groundwater seepage analysis. In the absence of analytical data, the value can also be determined based on local engineering experience;

[0085] s i -Vertical distance from the water level to the aquitard after precipitation (m).

[0086] S3, based on the groundwater level drop value h determined in step S2 降 , determine the distance m(m) from the initial water level to the top of the local plain concrete pile 2, and at the same time back-calculate the depth l of the local plain concrete pile 2 inserted into the bottom of the foundation pit d ; The calculation formula is as follows:

[0087] m=h 降 +n 水

[0088]

[0089] The converted local plain concrete pile 2 is inserted into the bottom of the foundation pit to a depth of l d as follows:

[0090]

[0091] Determine the total length L of the local plain concrete pile 2 buried inside the foundation pit 素 :

[0092] L 素 ≥l d +H 基坑 -m

[0093] Among them, n 水 - Initial water level depth (m);

[0094] K f - The safety factor of soil flow stability should not be less than 1.6, 1.5, or 1.4;

[0095] γ′-buoyancy density of soil (kN / m 3 );

[0096] Δh-water head difference inside and outside the foundation pit (m);

[0097] γ w - Weight of water (kN / m 3 ).

[0098] S4. According to the seepage approximation in "Groundwater Dynamics" as a constant flow analysis, the equal water head surfaces around the dewatering well 1 are coaxial cylindrical surfaces. Under the assumption of axisymmetry in homogeneous and isotropic formations, the water level drop depth h is inferred by the infiltration curve equation. 降 The corresponding precipitation impact distance x is converted and calculated using the following formula:

[0099]

[0100] Considering that the water level at the bottom of the foundation pit is consistent with the water level in the precipitation well, the equivalent foundation pit is a large well model, and the width of the foundation pit is the diameter of the large well model. The water level h is determined 降 The corresponding precipitation impact distance x when the value is , the deformation formula is as follows:

[0101]

[0102] In the formula, h- is equivalent to the distance from the water level at the bottom of the foundation pit to the relatively weak permeable layer (m), l+h- is equivalent to the distance from the internal water level of the precipitation well 1 to the relatively weak permeable layer (m), and r represents the radius of the precipitation well 1 (m);

[0103] H-the distance from the initial water level to the relatively weak permeable layer (m);

[0104] B-equivalent width of foundation pit (m), considering that the water level at the bottom of the foundation pit is consistent with the water level in the dewatering well, the equivalent foundation pit is a large well model, and the width of the foundation pit is the diameter of the large well model;

[0105] R-influence radius (m), k-permeability of the aquifer (m / d);

[0106] s w -well water level drop, s w =H 基坑 -n 水 , when the well water level drops less than 10m, take 10m.

[0107] S5. To ensure the allowable settlement after precipitation 允 , set up reinjection well 1 and determine the position x of reinjection well 1 回灌 The calculation is performed using the following formula:

[0108] x 回灌 =Rx

[0109] In the formula, x 回灌-The distance between the recharging well and the foundation pit edge (m).

[0110] S6. After the positions of the dewatering wells 1 and the external recharging wells 4 are determined, the support piles 3 and the local plain concrete piles 2 are constructed in the foundation pit, that is, the local plain concrete piles 2 are set between the adjacent support piles 3, and the top burial depth of the local plain concrete piles 2 is the depth obtained in step S3. m (m). Among them, the support length of the support pile 3 is determined according to the design requirements, and the length of the local plain concrete pile 2 is L 素 The bite part between the piles is not less than 200mm. The supporting pile row 3 is constructed first, and then the local plain concrete pile 2 is bitten. The supporting pile row 3 bears the lateral soil pressure, and the local plain concrete pile 2 is water-proof. The combination of the two has a good support and water-stopping effect.

[0111] S7, Construction of dewatering well 1 inside foundation pit and construction of external recharging well 2:

[0112] ① After determining the well location and depth, excavate the wellhead. During the excavation process, attention must be paid to ensuring the stability and safety of the wellhead to avoid collapse and accidents.

[0113] ②The installation of the wellbore can ensure the stability of the wellbore wall and prevent collapse. During the installation of the wellbore, attention should be paid to the verticality and sealing of the wellbore to ensure the quality and stability of the wellbore.

[0114] ③ After the wellbore is installed, grouting is performed on the well wall to prevent groundwater leakage and damage to the well wall. Appropriate grouting materials and construction methods are selected to ensure the grouting effect and the stability of the well wall.

[0115] ④ Installation of precipitation well equipment. Install water pumps, piping systems, monitoring equipment, etc. to ensure the normal operation and use of precipitation wells. Through the implementation of the above process flow, the smooth construction of precipitation wells and recharging wells is guaranteed.

[0116] S8. The interior of the foundation pit is dewatered steadily, and the recharge well 4 outside the foundation pit is recharged to the designed dewatering depth.

[0117] After the construction of the support structure and the dewatering well 1 is completed, dewatering is carried out before the foundation pit is excavated. Among them, the dewatering well 1 is arranged inside the foundation pit and is gradually removed as the foundation pit is excavated. After the excavation design elevation is reached, continuous dewatering is carried out to maintain a dry working environment inside the foundation pit. As the dewatering inside the foundation pit is carried out, the external recharge well 4 also recharges the water level to ensure that the groundwater level outside the foundation pit does not drop too much. The water supply in the external recharge well 4 is fed back based on the dewatering efficiency in the dewatering well 1. As each well works stably, the working efficiency of each well is adjusted to stabilize the groundwater level at the designed water level, and then the foundation pit is excavated and supported.

[0118] S9. Foundation pit excavation and anchor cable construction.

[0119] With the stabilization of precipitation and recharge, the subsequent foundation pit excavation operation is carried out. The foundation pit excavation is strictly carried out in layers according to the design requirements. Anchor cable construction is carried out immediately after each layer of excavation is completed. The anchor pulling effect can better control the surface deformation caused by the foundation pit excavation. While the foundation pit is excavated, the exposed precipitation well 1 structure inside the foundation pit is removed, and the precipitation power is adjusted to maintain the dry working environment inside the foundation pit. The precipitation well 1 and the external recharge well 4 adjust the precipitation-recharge well 4 with each other, so that the groundwater inside and around the foundation pit forms a stable seepage field, which ensures the overall stability of the foundation pit while reducing the impact of large precipitation on the surrounding environment and improving the local stability in the entire ground fissure area.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for supporting and dewatering deep foundation pits near water-rich interlayers near ground fissures, characterized in that: A dewatering well is set inside the foundation pit, and an external recharging well is set outside the foundation pit to control the overall water level around the foundation pit. Local plain concrete piles are set between adjacent supporting piles, and the supporting piles and local plain concrete piles are engaged with each other to jointly bear the function of supporting and intercepting water. The specific steps include: S1. Determine the allowable value of surface deformation around the ground fissures based on the surrounding environment of the ground fissures and the surface settlement requirements after precipitation. 允 ; S2, the allowable value of surface deformation generated around the ground fissures 允 Determine the maximum groundwater level drop value s 降 , through the maximum groundwater level drop value s 降 Calculate the groundwater level drop h 降 ; S3, based on the groundwater level drop value h determined in step S2 降 Determine the distance m from the ground to the top of the local plain concrete pile and the depth l of the local plain concrete pile inserted into the bottom of the foundation pit d ; S4. According to the infiltration curve equation, the water level drop is inferred to be the groundwater level drop value h. 降 The corresponding precipitation impact distance x when S5, to ensure that the settlement after precipitation is the allowable value of surface deformation s 允 Set up the recharging well and determine its location; S6, according to the setting parameters calculated in steps S1 to S5, the construction of supporting piles and local plain concrete piles in the foundation pit, the construction of drainage wells inside the foundation pit and the construction of external recharging wells are carried out in sequence; In step S3, according to the groundwater level drop value h determined in step S2, 降 Determine the distance m from the ground to the top of the local plain concrete pile and the depth l of the local plain concrete pile inserted into the bottom of the foundation pit d The calculation formula is as follows: m=h 降 +n 水 The converted local plain concrete pile is inserted into the bottom of the foundation pit to a depth of l d as follows: Determine the total length L of the local plain concrete piles inside the foundation pit 素 : L 素 ≥l d +H 基坑 -m Among them, n 水 - Initial water level depth (m); K f - Safety factor of soil flow stability, not less than 1.6, 1.5, 1.4; γ'-floating density of soil; Δh-water head difference inside and outside the foundation pit; γ w - water density; In step S4, according to the seepage approximation in "Groundwater Dynamics" as a constant flow analysis, the equal water head surfaces around the dewatering well are coaxial cylindrical surfaces. Under the assumption of axisymmetry in homogeneous and isotropic formations, the water level drop is inverted through the infiltration curve equation to obtain the groundwater level drop value h 降 The corresponding precipitation impact distance x is converted and calculated using the following formula: The water level at the bottom of the foundation pit is consistent with the water level in the dewatering well. The equivalent foundation pit is a large well model, the width of the foundation pit is the diameter of the large well model, and the water level drop is determined as the groundwater level drop value h 降 The corresponding precipitation impact distance x, the deformation formula is as follows: Among them, h-is equivalent to the distance from the water level at the bottom of the foundation pit to the relatively weak permeable layer, l+h-is equivalent to the distance from the water level inside the precipitation well to the relatively weak permeable layer, and r represents the radius of the precipitation well; H-the distance from the initial water level to the relatively weak permeable layer; B-equivalent width of foundation pit; R - influence radius, k – permeability coefficient of aquifer; s w -well water level drop, s w =H 基坑 -n 水 , when the well water level drops less than 10m, take 10m; In step S5, to ensure that the settlement after precipitation is within the allowable value of surface deformation s 允 Set up the recharge well and determine the location of the recharge well, and use the following formula for calculation: x 回灌 =R-x Among them, x 回灌 -The distance between the recharging well and the foundation pit edge (m); In step S6, when constructing the supporting piles and local plain concrete piles in the foundation pit, local plain concrete piles are set between adjacent supporting piles. The buried depth of the local plain concrete pile top is the distance m from the ground to the top of the local plain concrete pile obtained in step S3. The supporting pile length is determined according to the design requirements. The length of the local plain concrete pile is L. 素 The engagement between piles shall not be less than 200mm. The supporting pile construction shall be carried out first, and then the local plain concrete pile engagement shall be carried out.

2. A method for dewatering deep foundation pit support under water-rich interlayers near ground fissures according to claim 1, characterized in that: In step S6, the construction process of the internal dewatering well and the external recharging well of the foundation pit includes: ①After determining the well location and well depth, excavate the wellhead; ②Install the wellbore; ③After the wellbore is installed, grouting is carried out on the well wall; ④Installation of precipitation well equipment, which includes water pumps, piping systems, and monitoring equipment.

3. A method for dewatering deep foundation pit support in water-rich interlayers near ground fissures according to claim 1, characterized in that: Step S6: After the construction is completed, dewatering is performed before the foundation pit is excavated. The dewatering well is arranged inside the foundation pit and gradually removed as the foundation pit is excavated. After the excavation design elevation is reached, dewatering is continued during the foundation pit excavation to maintain a dry working environment inside the foundation pit; During the dewatering process inside the foundation pit, water is recharged in the external recharge well to ensure that the groundwater level outside the foundation pit does not drop too much. The water replenishment in the external recharge well is fed back based on the dewatering efficiency in the dewatering well to stabilize the groundwater level at the designed water level, and then excavation and support of the foundation pit are carried out.

4. A method for dewatering deep foundation pit support in water-rich interlayers near ground fissures according to claim 3, characterized in that: During the foundation pit excavation and support process, the foundation pit excavation is carried out in layers strictly according to the design requirements. Anchor cable construction is carried out immediately after each layer of excavation is completed, and the surface deformation caused by the foundation pit excavation is controlled by the anchor pulling effect.

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