An evaluation method for emergency treatment of water-rich sand gravel stratum cover excavation method water stop curtain failure

Abstract

The present application relates to the technical field of subway station construction, and discloses a method for evaluating emergency treatment of water stop curtain failure in cover-excavation method in water-rich sand and gravel stratum, comprising the following steps: step 1, constructing a water stop curtain failure monitoring system and collecting data, monitoring points are arranged on the side wall of the foundation pit of the subway station, the joint of the water stop curtain and the surrounding stratum, and data of groundwater seepage flow, deformation of the surrounding stratum of the curtain and pore water pressure are collected in real time. Through the process of “monitoring and collection→grade evaluation→grouting treatment→effect review→closed-loop regulation and control”, the present application quantifies the failure degree and treatment effect, adapts to two cover-excavation methods, and provides key basis for construction safety control and optimization of treatment scheme. The emergency treatment scheme for water stop curtain failure, which can quickly respond, accurately treat and scientifically evaluate, is suitable for the construction characteristics of the cover-excavation method in the water-rich sand and gravel stratum of the subway station, and improves the safety and reliability of construction.

Description

Technical Field

[0001] This invention relates to the field of subway station construction technology, and in particular to an emergency treatment evaluation method for the failure of a cutoff wall in a water-rich gravel stratum using the over-cut method. Background Technology

[0002] Currently, the cut-and-cover method (including the forward and reverse construction methods) is widely used in urban subway station construction due to its minimal impact on the surrounding environment and high construction efficiency, especially suitable for construction in busy areas and areas with dense underground pipelines. Water-rich gravelly strata are characterized by high permeability, poor particle sorting, and high porosity. When using the cut-and-cover method in such strata, the cutoff wall, as the core structure for seepage prevention in the foundation pit, must effectively block groundwater infiltration to avoid disasters such as piping and sudden surges.

[0003] However, the groundwater in water-rich gravel strata flows rapidly, easily eroding the surface of the cutoff wall and construction joints, leading to problems such as damage and leakage. At the same time, in the cut-and-cover method of construction, the excavation of the foundation pit and the pouring of the underground structure are carried out at the same time, and seepage channels are easily formed at the junction of temporary support and permanent structure, which further aggravates the risk of failure of the cutoff wall.

[0004] In existing technologies, the treatment of water-stop curtain failures mostly adopts post-event remedial methods, without designing targeted emergency plans based on the construction characteristics of the cut-and-cover method. This results in slow treatment response and poor sealing effect. Furthermore, there is a lack of failure evaluation models for water-rich sandy gravel strata, making it impossible to quantify the degree of failure and treatment effect. This leads to a lack of basis for optimizing treatment parameters, which can easily result in repeated treatments and incomplete treatments, seriously threatening the construction safety of subway stations.

[0005] Furthermore, existing treatment methods do not fully utilize the advantages of the cut-and-cover method's construction platform. Grouting, monitoring, and other operations require additional construction scaffolding, increasing construction costs and disrupting the main structure's construction sequence. Simultaneously, they fail to consider the differences between conventional and unconventional cut-and-cover construction, resulting in insufficient adaptability and difficulty in meeting the needs of different construction scenarios. Therefore, it is necessary to provide a new evaluation method for emergency treatment of cut-and-cover method water-stop curtain failure in water-rich gravel strata to address the aforementioned technical problems. Summary of the Invention

[0006] To address the technical problems mentioned in the background section, this invention provides an evaluation method for emergency treatment of the failure of the cut-off curtain method in water-rich sandy and gravelly strata.

[0007] The present invention is achieved by the following technical solution: an emergency treatment evaluation method for the failure of the cut-and-cover method water-stop curtain in water-rich sand and gravel strata, including the following steps: Step 1. Construction and data collection of the water-stop curtain failure monitoring system, setting up monitoring points on the side wall of the cut-and-cover method subway station foundation pit, the joint of the water-stop curtain and the surrounding strata, and collecting groundwater seepage flow, deformation of the surrounding strata and pore water pressure data in real time; Step 2. Failure severity assessment and level triggering: Based on monitoring data, calculate the failure severity of the water-stop curtain using the failure severity assessment formula, classify the failure level, and trigger the corresponding emergency treatment process; Step 3. High-pressure grouting and ground reinforcement: Using the cut-and-cover method, the cover plate is used as an emergency construction platform. Through the emergency grouting holes reserved in the cover plate, high-pressure grouting is carried out to seal the failed area, and the surrounding water-rich gravel strata are reinforced and strengthened at the same time. Step 4. Quantification and verification of treatment effect: After the grouting treatment is completed, the regular monitoring frequency is restored, the seepage flow rate after grouting is collected, and the treatment effect is quantified by the sealing effect verification formula. If the qualified standard is not met, return to step 3 to optimize the grouting parameters and repeat the treatment until it is qualified. Step 5. Dynamic monitoring and closed-loop control throughout the entire construction process: Dynamically update monitoring data throughout the entire construction process, repeat steps 2-4, and achieve closed-loop control for failure management and effect evaluation.

[0008] As a further improvement to the above scheme, the following are proposed: the core structure of the subway station foundation pit using the cut-and-cover method in water-rich gravel strata and the method for storing emergency supplies. The core structure of the subway station foundation pit using the cut-and-cover method in water-rich gravel strata includes a retaining structure, a water-stop curtain, and a cover plate. The specific structural effects are as follows: (1) The retaining structure is composed of bored cast-in-place piles and high-pressure jet grouting piles between the piles, and undertakes the function of retaining soil in the foundation pit; (2) The water-stop curtain adopts a high-pressure jet grouting pile interlocking structure, which is arranged on the outer perimeter of the retaining structure, away from the foundation pit, and undertakes the function of seepage prevention for the entire foundation pit; (3) The cover plate is laid directly to the ground surface. The size of the cover plate is larger than the size of the retaining structure and fully covers the outer water-stop curtain to ensure that the cover plate can completely cover the emergency treatment operation area, while providing a stable platform for monitoring and grouting operations. (4) The connection between the cover plate and the enclosure structure and the water-stop curtain must meet the requirements of sealing and load bearing, so as to avoid the formation of seepage channels at the connection between the cover plate and the structure; The emergency supplies storage method includes the following steps: (1) For different failure levels, reserve the corresponding grouting equipment, grouting materials and monitoring equipment. For severe failure levels, reserve high-pressure grouting pumps, dual-liquid grouting machines, emergency drainage pumps, as well as sufficient cement, water glass and grouting materials. For moderate and mild failure levels, reserve conventional grouting equipment and materials. (2) Simultaneously develop emergency construction plans, clarify the division of labor among construction personnel, work procedures and parameter adjustment schemes, and ensure that treatment operations can be started quickly when failure occurs.

[0009] As a further improvement to the above solution, monitoring holes and emergency grouting holes are reserved on the cover plate. These monitoring holes and emergency grouting holes are both reserved simultaneously during the construction of the cover plate and penetrate the full thickness of the cover plate. The specific details are as follows: (1) The monitoring holes are arranged on the cover plate in the area corresponding to the outer high-pressure jet grouting pile interlocking water-stop curtain, the gap between the retaining structure and the water-stop curtain, and the stratum outside the water-stop curtain; (2) The monitoring hole drilling depth L is designed in different areas: the monitoring hole depth L in the outer high-pressure jet grouting pile interlocking water-stop curtain body area and the gap area between the retaining structure and the water-stop curtain covers the full excavation depth H of the foundation pit + 2~5m below the excavation surface to capture curtain leakage within the entire excavation range; in the stratum area outside the water-stop curtain, it covers the entire water-rich sand and gravel layer + 3~5m below the excavation surface to monitor deep stratum deformation and pore water pressure; seepage flow monitoring instruments are installed in layers with burial depths of L / 3, 2*L / 3, and L, corresponding to shallow, middle, and deep water-rich layers; (3) The emergency grouting holes are arranged on the cover plate in the area corresponding to the outer high-pressure jet grouting pile interlocking water-stop curtain, the gap between the retaining structure and the water-stop curtain, and are vertically aligned with the center of the corresponding structure. (4) The emergency grouting holes are divided into two categories: the grouting holes of the water-stop curtain body are used to repair the damage, cracks and interlocking gaps of the curtain itself; the grouting holes of the structural gaps are used to seal the seepage channels at the junction of the retaining structure and the water-stop curtain, and simultaneously reinforce the loose soil in the gaps. (5) The drilling depth h of the emergency grouting hole is consistent with the full length of the outer high-pressure jet grouting pile interlocking water-stopping curtain, extending 5m below the permeable layer and covering the full depth of the curtain. The segmented grouting process is adopted, and grouting is only performed on the failure depth section. The segment length is 1.0~1.5m, and the hole depth penetrates the failure area by no less than 1.5m. (6) The monitoring holes and the emergency grouting holes are arranged in staggered sections. A section is divided at a certain interval along the edge of the foundation pit. One set of monitoring holes is arranged on the odd-numbered sections. There are 3 monitoring holes in one set, which correspond to the water-stop curtain body, the structural gap and the outer stratum respectively. One set of emergency grouting holes is arranged on the even-numbered sections. There are 2 emergency grouting holes in one set, which correspond to the water-stop curtain body and the structural gap respectively. The distance between any two holes is not less than 500mm. (7) The cables inside the cover plate are laid out through horizontal pipelines that are pre-buried during construction. The pipelines are vertically connected to each monitoring hole and the ends are uniformly led to a special equipment box in the non-passage area at the edge of the cover plate, so as to realize the cable laying in a completely hidden manner and completely avoid interference with ground traffic.

[0010] As a further improvement to the above solution, the failure degree evaluation formula in step S2 is as follows: ; In the formula, The degree of failure of the water curtain is indicated by a value ranging from 0 to 1. ≥0.7 indicates severe failure, 0.4≤ <0.7 indicates moderate failure. <0.4 indicates a minor failure. Actual seepage flow (m) 3 / d), Critical allowable seepage flow rate (m 3 / d), determined by the permeability coefficient of water-rich gravel strata and the size of the foundation pit. This is a weighting coefficient, ranging from 0.6 to 0.8, prioritizing the impact of seepage flow on the degree of failure. The value represents the deformation of the strata surrounding the curtain (mm). The maximum allowable deformation (mm) is determined based on the stability requirements of surrounding buildings and the foundation pit; The actual seepage flow The measured maximum value of the monitoring hole in the main body area of ​​the cutoff wall corresponding to the failure point is taken as the formation deformation amount. The measured maximum value of the monitoring wells in the surrounding strata corresponding to the failure point is taken. The monitoring well data in the structural gap area is only used to assist in verifying the seepage source, and the pore water pressure data is only used for early warning. Neither of them is directly substituted into the formula. according to The calculation results classify the failure levels of the water-stop curtain into three levels: A value ≥0.7 indicates a severe failure, requiring immediate initiation of emergency remediation procedures; a value ≤0.4 indicates a failure. A value less than 0.7 indicates a moderate failure; initiate standard emergency response procedures. A value less than 0.4 indicates a minor failure, requiring targeted reinforcement and treatment.

[0011] As a further improvement to the above solution, in step S3, corresponding high-pressure grouting parameters and processes are adopted for different failure levels of the water-stop curtain. The pressure is adjusted to ensure that the grouting fluid can penetrate into the pores of the sand and gravel and fill the failure channels. The grouting pressure of the high-pressure grouting is calculated by the following formula: ; In the formula, The grouting pressure is measured in MPa. The density of the grout (kg / m³) 3 When using cement-water glass dual-liquid grouting fluid, The value is taken as 1800~2200 kg / m 3 ,g g is the acceleration due to gravity (m / s 2 ), which is taken as 9.8 m / s 2 , H h1 is the buried depth of groundwater table (m); h L is the depth of grouting hole (m), k is the pressure correction coefficient, adjusted according to the failure grade of the water-stop curtain; when the failure is severe k=1.4~1.5, when the failure is moderate k=1.2~1.3, when the failure is mild k=1.1~1.2.

[0012] As a further improvement of the above solution, in step S4, the plugging effect verification formula is as follows: ; wherein, η is the plugging effect evaluation index, η≥0.9 indicates qualification; Q1 is the seepage flow after grouting (m 3 / d), Q0 is the seepage flow before grouting (m 3 / d), α is the failure degree of the water-stop curtain before grouting; when η≥0.9, the treatment is judged as qualified, and the emergency treatment process is ended; when η<0.9, the treatment is judged as unqualified, the causes of unqualified treatment (such as unreasonable grouting parameters, insufficient layout density of grouting holes) are analyzed, the grouting pressure and hole spacing parameters are optimized, and the process returns to step 3 for repeated treatment until qualification; monitoring data is dynamically updated throughout the construction process, and the failure degree α and the treatment effect η are calculated in real time, and steps 2 to 4 are repeated to realize closed-loop regulation of water-stop curtain failure treatment and effect evaluation, and continuously guarantee the safety of foundation pit construction.

[0013] As a further improvement of the above solution, the monitoring system in step S1 includes a seepage flow monitor, a displacement sensor and a pore water pressure gauge, and the monitoring frequency is once every 1~2h; when the monitoring data has abnormal fluctuations such as sudden increase of seepage flow and accelerated stratum deformation, after a failure warning is triggered, the monitoring frequency is increased to once every 15~30min to track the development trend of failure in real time; the monitoring points shall be arranged to cover the whole range of the water-stop curtain, and be arranged in key positions such as construction joints, foundation pit corners and failure-prone areas.

[0014] As a further improvement to the above scheme, in step S3, the layout density of the emergency grouting holes is adjusted according to the failure level: the hole spacing is 0.8~1.2m in severely failed areas, 1.2~1.5m in moderately failed areas, and 1.5~2.0m in slightly failed areas. The emergency grouting holes are arranged perpendicular to the water-stop curtain, and the hole depth penetrates the failed area by no less than 1.5m to ensure that the grouting fluid can fully fill the failed channels and reinforce the surrounding strata. The grouting reinforcement adopts a segmented grouting process, with segment lengths... The grouting depth is 1.0~1.5m. The grouting sequence is from the periphery to the core, and from the deep layer to the shallow layer. After grouting, a pressure maintenance process is adopted, with the maintenance pressure being 0.8~0.9 times the grouting pressure and the maintenance time being no less than 30 minutes, to ensure that the grouting liquid fully solidifies and forms a stable anti-seepage reinforcement layer. The grouting adopts a combination of permeation grouting and fracturing grouting processes, and the grouting pressure is controlled at 0.1~0.3MPa. It only fills the original curtain pores and damaged channels, without damaging the integrity of the original water-stop curtain and enclosure structure.

[0015] As a further improvement to the above scheme, in the cut-and-cover construction method, emergency grouting holes are reserved simultaneously after the cover plate construction is completed. The grouting operation is carried out in coordination with the layered excavation process of the foundation pit, and priority is given to treating the failure areas around the excavation surface of the foundation pit to avoid seepage disasters during the excavation process. When adapted to the cut-and-cover reverse construction method, the top plate is used as a construction platform, and the grouting operation is carried out in an overlapping manner with the underground structure pouring process. Priority is given to sealing the failure areas that affect the structural construction, taking into account both the treatment effect and the construction progress.

[0016] As a further improvement to the above scheme, in step 2, the critical allowable seepage flow rate... Permeability coefficient of water-rich gravel strata K Cross-sectional area of ​​foundation pit seepage A Differential head of seepage H w The calculation is as follows: ; In the formula, K The formation permeability coefficient (m / d) is determined by field pumping tests; A is the seepage cross-sectional area (m²). 2 The calculation is based on the dimensions of the excavation pit and the height of the cut-and-cover method.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By constructing a closed-loop system of "monitoring-treatment-evaluation", this invention can achieve rapid response and precise treatment of water-stop curtain failure, solve the problems of post-event remediation and untimely treatment in existing technologies, and significantly improve the safety of cut-and-cover subway station construction in water-rich sand and gravel strata.

[0018] 2. This invention quantifies the failure level and treatment effect by establishing a failure degree evaluation formula and a sealing effect verification formula, providing a scientific basis for parameter optimization, avoiding repeated treatment, reducing construction costs, and solving the pain point that existing technologies cannot accurately evaluate.

[0019] 3. This invention makes full use of the cut-and-cover cover plate as a construction platform, eliminating the need for additional scaffolding. It is compatible with both conventional and reverse cut-and-cover construction methods, reducing construction interference, balancing treatment effectiveness and construction progress, and improving the adaptability and practicality of the solution.

[0020] 4. This invention adopts a graded treatment strategy, which optimizes grouting parameters and hole spacing according to the failure level. It is highly targeted and can ensure the treatment effect of severely failed areas while avoiding over-treatment of moderate and mildly failed areas, thus improving the economic efficiency of construction. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the semi-cut-and-cover maintenance structure and water-stop curtain of the present invention; Figure 2 This is a diagram showing the layout of the monitoring holes and emergency grouting holes of the present invention. Detailed Implementation

[0022] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0023] The emergency treatment evaluation method for the failure of the cut-off wall in the cover-and-cut method for water-rich sandy and gravelly strata in this embodiment includes the following steps: Step 1. Construction and data acquisition of the water-stop curtain failure monitoring system: Monitoring points are set up on the side wall of the excavation pit of the cut-and-cover subway station, the joint of the water-stop curtain and the surrounding strata to collect groundwater seepage flow, deformation of the surrounding strata and pore water pressure data in real time. Step 2. Failure severity assessment and level triggering: Based on monitoring data, calculate the failure severity of the water-stop curtain using the failure severity assessment formula, classify the failure level, and trigger the corresponding emergency treatment process; The following are the reference standards for quantifying time nodes: 1. Abnormal response and failure evaluation: Data verification (excluding false anomalies) shall be completed within 5 minutes after the monitoring data is triggered abnormally, and the failure degree calculation and level determination shall be completed within 15 minutes.

[0024] 2. Grouting start time limit: Start the grouting equipment and begin operation within 30 minutes for severe failure; within 1 hour for moderate failure; and within 2 hours for minor failure.

[0025] 3. Time limits for graded treatment: Complete the sealing of the core area within 24 hours for severe failure; within 48 hours for moderate failure; and within 72 hours for minor failure.

[0026] 4. Effectiveness verification time limit: The first sealing effect verification shall be completed within 2 hours after the grouting is completed, and the regular monitoring frequency shall be gradually restored within 24 hours after passing the verification.

[0027] Step 3. High-pressure grouting and ground reinforcement: Using the cut-and-cover method, the cover plate is used as an emergency construction platform. Through the emergency grouting holes reserved in the cover plate, high-pressure grouting is carried out to seal the failed area, and the surrounding water-rich gravel strata are reinforced and strengthened at the same time. Step 4. Quantification and verification of treatment effect: After the grouting treatment is completed, the regular monitoring frequency is restored, the seepage flow rate after grouting is collected, and the treatment effect is quantified by the sealing effect verification formula. If the qualified standard is not met, return to step 3 to optimize the grouting parameters and repeat the treatment until it is qualified. Step 5. Dynamic monitoring and closed-loop control throughout the entire construction process: Dynamically update monitoring data throughout the entire construction process, repeat steps 2-4, and achieve closed-loop control for failure management and effect evaluation.

[0028] The trigger thresholds for each stage of the closed-loop control are as follows: 1. Abnormal monitoring data → Failure assessment: Activated upon meeting any of the following conditions: ① Sudden increase in infiltration flow rate ≥20% within 1 hour and absolute value ≥5m³ 3 / d; ② Daily formation deformation ≥2mm or hourly deformation ≥0.5mm; ③ Pore water pressure reaches 1.2 times the hydrostatic pressure.

[0029] 2. Failure assessment → Grouting treatment: ω≥0.7 (severe failure) immediately initiate emergency treatment; 0.4≤ω<0.7 (moderate failure) initiate routine treatment; ω<0.4 (minor failure) initiate targeted reinforcement treatment.

[0030] 3. Grouting treatment → Effect verification: After grouting is completed and pressure is stabilized for 30 minutes, collect stable seepage flow data 2 hours after grouting and start the calculation of sealing effect.

[0031] 4. Effect verification → Parameter optimization / closed-loop termination: ζ≥0.9 is considered qualified and the closed-loop is terminated; ζ<0.9 is considered unqualified and the parameters are optimized according to priority: ① First adjust the grout ratio and setting time; ② Then adjust the grouting pressure; ③ Then increase the spacing of the grouting holes; ④ Finally, drill additional grouting holes.

[0032] The core structure of a subway station foundation pit constructed using the cut-and-cover method in water-rich gravelly strata includes a retaining structure, a water-stop curtain, and a cover plate. The specific structural effects are as follows: (1) The retaining structure is composed of bored cast-in-place piles and high-pressure jet grouting piles between the piles, and undertakes the function of retaining soil in the foundation pit; (2) The water-stop curtain adopts a high-pressure jet grouting pile interlocking structure, which is arranged on the outer perimeter of the retaining structure, away from the foundation pit, and undertakes the function of seepage prevention for the entire foundation pit; (3) The cover plate is laid directly to the ground surface. The size of the cover plate is larger than the size of the retaining structure and fully covers the outer water-stop curtain to ensure that the cover plate can completely cover the emergency treatment operation area, while providing a stable platform for monitoring and grouting operations. (4) The connection between the cover plate and the enclosure structure and the water-stop curtain must meet the requirements of sealing and load bearing, so as to avoid the formation of seepage channels at the connection between the cover plate and the structure; The emergency supplies storage method includes the following steps: (1) For different failure levels, reserve the corresponding grouting equipment, grouting materials and monitoring equipment. For severe failure levels, reserve high-pressure grouting pumps, dual-liquid grouting machines, emergency drainage pumps, as well as sufficient cement, water glass and grouting materials. For moderate and mild failure levels, reserve conventional grouting equipment and materials. (2) Simultaneously develop emergency construction plans, clarify the division of labor among construction personnel, work procedures and parameter adjustment schemes, and ensure that treatment operations can be started quickly when failure occurs.

[0033] The cover plate has pre-reserved monitoring holes and emergency grouting holes. These holes are pre-reserved simultaneously during the cover plate construction and penetrate the full thickness of the cover plate. The specific details are as follows: 1) The cross-sectional spacing is determined according to the permeability coefficient of the strata: 800~1000mm for highly permeable gravel (K≥8m / d), 1200~1500mm for moderately permeable (4≤K<8m / d), and 1800~2000mm for poorly permeable (K<4m / d); the spacing in areas prone to failure, such as construction joints and corners of foundation pits, should be increased to 1 / 2 of the standard spacing. 2) The monitoring holes are all φ100mm: compatible with conventional seepage flow meters, displacement sensors, etc. (outer diameter φ70~90mm), with a 10~30mm installation gap reserved to ensure smooth equipment lowering and hole wall stability; the grouting holes are all φ110mm: compatible with high-pressure grouting pipes (outer diameter φ60~80mm), meeting the flow rate requirements of 1.2~2.0m / s for cement-water glass double liquid grout, avoiding pipe blockage and grouting pressure loss.

[0034] (1) The monitoring holes are arranged on the cover plate in the areas corresponding to the outer high-pressure jet grouting pile interlocking water-stop curtain, the gap between the retaining structure and the water-stop curtain, and the stratum outside the water-stop curtain, as follows: Standard section: One set of monitoring holes is set up every 15~20m along the long side of the foundation pit, and each set contains 3 holes (corresponding to the above three areas respectively); one set is set up every 10~15m along the short side.

[0035] Key areas for enhanced detection: construction joints of the water-stop curtain, corners of the foundation pit, and areas with changes in cross-section. The density of the deployment is doubled (1 set every 5-10m) to ensure accurate detection of anomalies in high-risk areas.

[0036] Relationship with grouting holes: All monitoring holes and emergency grouting holes are staggered and spaced at least 500mm apart to avoid mutual interference.

[0037] Each monitoring hole has a pre-embedded PVC sleeve (100mm in diameter). The bottom of the sleeve is flush with the bottom surface of the cover plate, and the top is flush with the top surface of the cover plate. The sleeve is sealed with sealant between itself and the concrete.

[0038] The monitoring equipment (seepage flow monitor, displacement sensor, pore water pressure gauge) is lowered to the corresponding depth through the casing, and the cables are connected to the horizontal pipelines pre-embedded inside the cover plate, and uniformly led to a special equipment box in the non-passage area at the edge of the cover plate, which is completely hidden without any external exposure.

[0039] After the monitoring holes are installed, they should be sealed with special sealing covers when no equipment is installed to prevent rainwater and debris from entering.

[0040] (2) The monitoring hole drilling depth L is designed in different areas: the monitoring hole depth L in the outer high-pressure jet grouting pile interlocking water-stop curtain body area and the gap area between the retaining structure and the water-stop curtain covers the full excavation depth H of the foundation pit + 2~5m below the excavation surface to capture curtain leakage within the entire excavation range; in the stratum area outside the water-stop curtain, it covers the entire water-rich sand and gravel layer + 3~5m below the excavation surface to monitor deep stratum deformation and pore water pressure; seepage flow monitoring instruments are installed in layers with burial depths of L / 3, 2*L / 3, and L, corresponding to shallow, middle, and deep water-rich layers; (3) The emergency grouting holes are arranged on the cover plate in the area corresponding to the outer high-pressure jet grouting pile interlocking water-stop curtain, the gap between the retaining structure and the water-stop curtain, and are vertically aligned with the center of the corresponding structure. By vertically aligning the center of the outer high-pressure jet grouting piles with the center of the water-stop curtain (i.e., the projected position of the center of each jet grouting pile), the failure points such as damage, cracks, and interlocking gaps of the water-stop curtain itself can be directly repaired. The grouting liquid is directly injected into the interior of the curtain body to fill the pores and damaged channels.

[0041] By aligning the vertically aligned 300mm operating gap between the retaining structure and the water-stop curtain, the seepage channel at the junction of the two can be sealed off, while the loose soil in the gap is reinforced to prevent groundwater from seeping around the junction.

[0042] The grouting process combines penetrating grouting and fracturing grouting. The grouting pressure is controlled at 0.1~0.3MPa according to the failure level (far lower than the pressure that would damage the original jet grouting pile). The grouting liquid will only fill the pores and damaged areas of the original curtain, and can instead strengthen the strength and impermeability of the original water-stop curtain.

[0043] Under normal conditions, holes are evenly spaced at 1.8m intervals to cover the entire area. If a few local failure points occur that are not in the reserved hole positions, they can be quickly drilled on the cover plate (drilling a φ110mm hole on a reinforced concrete cover plate only takes 10~15 minutes). When drilling, the hole should be aligned with the center of the corresponding structure, which will not affect the timeliness of emergency treatment.

[0044] (4) The emergency grouting holes are divided into two categories: the grouting holes of the water-stop curtain body are used to repair the damage, cracks and interlocking gaps of the curtain itself; the grouting holes of the structural gaps are used to seal the seepage channels at the junction of the retaining structure and the water-stop curtain, and simultaneously reinforce the loose soil in the gaps. (5) The drilling depth h of the emergency grouting hole is consistent with the full length of the outer high-pressure jet grouting pile interlocking water-stopping curtain, extending 5m below the permeable layer and covering the full depth of the curtain. The segmented grouting process is adopted, and grouting is only performed on the failure depth section. The segment length is 1.0~1.5m, and the hole depth penetrates the failure area by no less than 1.5m. (6) The monitoring holes and the emergency grouting holes are arranged in staggered sections. A section is divided at a certain interval along the edge of the foundation pit. One set of monitoring holes is arranged on the odd-numbered sections. There are 3 monitoring holes in one set, which correspond to the water-stop curtain body, the structural gap and the outer stratum respectively. One set of emergency grouting holes is arranged on the even-numbered sections. There are 2 emergency grouting holes in one set, which correspond to the water-stop curtain body and the structural gap respectively. The distance between any two holes is not less than 500mm. (7) The cables inside the cover plate are laid out through horizontal pipelines that are pre-buried during construction. The pipelines are vertically connected to each monitoring hole and the ends are uniformly led to a special equipment box in the non-passage area at the edge of the cover plate, so as to realize the cable laying in a completely hidden manner and completely avoid interference with ground traffic.

[0045] In step S2, the failure severity evaluation formula is as follows: ; In the formula, The degree of failure of the water curtain is indicated by a value ranging from 0 to 1. ≥0.7 indicates severe failure, 0.4≤ <0.7 indicates moderate failure. <0.4 indicates a minor failure. Actual seepage flow (m) 3 / d), Critical allowable seepage flow rate (m 3 / d), determined by the permeability coefficient of water-rich gravel strata and the size of the foundation pit. This is a weighting coefficient, ranging from 0.6 to 0.8, prioritizing the impact of seepage flow on the degree of failure. The value represents the deformation of the strata surrounding the curtain (mm). The maximum allowable deformation (mm) is determined based on the stability requirements of surrounding buildings and the foundation pit; Each monitoring well includes 3 wells. In this calculation, the "measured maximum value of the monitoring well corresponding to the failure area" was substituted into the formula. The two core parameters come from monitoring wells in different areas. The pore water pressure data is only used for auxiliary early warning and is not directly substituted into the formula.

[0046] The actual seepage flow was substituted into the data from the monitoring boreholes in the main body area of ​​the first zone of the water-stop curtain; the formation deformation was substituted into the monitoring data from the monitoring boreholes in the surrounding formation area of ​​the third zone.

[0047] The function of the monitoring holes in the second zone (structural gap zone) is only to assist in verifying the source of seepage. They are not directly substituted into the formula. When abnormal seepage is detected in the main body zone, the seepage data of the monitoring holes in the gap zone are checked simultaneously. If seepage also occurs in the gap zone, it indicates that the failure of the water-stop curtain has developed to the structural connection point, and the weight of the failure level judgment needs to be appropriately increased.

[0048] The function of the pore water pressure gauge is to provide early warning only and not to directly substitute it into the formula. When the pore water pressure changes by ≥10kPa, the monitoring frequency should be increased immediately, and the seepage flow and deformation data of the corresponding area should be closely monitored to predict the risk of failure.

[0049] Data timeliness: The data substituted into the formula are all real-time data from the latest monitoring. After the failure warning is triggered (the monitoring frequency is increased to 15~30 minutes / time), the failure level is recalculated every 30 minutes, and the treatment plan is dynamically adjusted.

[0050] Weighting coefficients are typically calculated using empirical values ​​or multi-factor weighted quantification. In water-rich sandy and gravelly strata, seepage failure is the direct cause of piping and sudden inrush, which develops rapidly and is highly destructive. Formation deformation is mostly a secondary effect after seepage development, with a delayed response. Seepage flow data can directly and sensitively reflect the seepage prevention integrity of the cutoff curtain, and therefore it is given higher weight in failure evaluation.

[0051] The baseline value is determined according to the protection level of surrounding buildings: 3mm for Level 1 protection (important buildings in bustling areas), 4mm for Level 2 protection (general buildings), and 5mm for Level 3 and below (no important buildings in suburban areas). Correction based on the overturning safety factor of the foundation pit support: when the safety factor is ≥1.3, take the benchmark value; when 1.2≤safety factor<1.3, multiply by 0.9. The final value is limited to the range of 3~5mm.

[0052] The actual seepage flow The measured maximum value of the monitoring hole in the main body area of ​​the cutoff wall corresponding to the failure point is taken as the formation deformation amount. The measured maximum value of the monitoring wells in the surrounding strata corresponding to the failure point is taken. The monitoring well data in the structural gap area is only used to assist in verifying the seepage source, and the pore water pressure data is only used for early warning. Neither of them is directly substituted into the formula. according to The calculation results classify the failure levels of the water-stop curtain into three levels: A value ≥0.7 indicates a severe failure, requiring immediate initiation of emergency remediation procedures; a value ≤0.4 indicates a failure. A value less than 0.7 indicates a moderate failure; initiate standard emergency response procedures. A value less than 0.4 indicates a minor failure, requiring targeted reinforcement and treatment.

[0053] In step S3, corresponding high-pressure grouting parameters and processes are adopted for different failure levels of the water-stop curtain. The pressure is adjusted to ensure that the grouting fluid can penetrate into the pores of the sand and gravel and fill the failure channels. The grouting pressure of the high-pressure grouting is calculated by the following formula: ; In the formula, The grouting pressure is measured in MPa. The density of the grout (kg / m³) 3 When using cement-water glass dual-liquid grouting fluid, The value is taken as 1800~2200 kg / m 3 , g Acceleration due to gravity (m / s²) 2 (), take 9.8 m / s 2 , H 1 represents the depth of the groundwater level (m); h The depth of the grouting hole is (m). This is a pressure correction factor, adjusted according to the failure level of the waterstop curtain; in case of severe failure... =1.4~1.5, moderate failure =1.2~1.3, for minor failures =1.1~1.2.

[0054] The core safeguards are twofold: ① A real-time monitoring system is established in advance (monitoring frequency 1-2 hours / time, 15-30 minutes / time after warning) to detect early minor failures (ω<0.4). At this point, only targeted reinforcement grouting is required, without emergency treatment; ② Grouting holes are pre-reserved synchronously with the cover plate. The cover plate serves as an existing construction platform, eliminating the need for additional support structures. Grouting can be quickly initiated after failure is triggered. Combined with cement-water glass dual-liquid grouting fluid (fast setting speed), it can quickly seal the seepage channels and prevent the failure from worsening.

[0055] In step S4, the formula for verifying the blocking effect is as follows: ; In the formula, is the plugging effect evaluation index, ≥ 0.9 indicates qualification; is the seepage流量 after grouting (m 3 / d), is the seepage流量 before grouting (m 3 / d), is the failure degree of the water-stop curtain before grouting; when ≥ 0.9, the treatment is judged as qualified, and the emergency treatment process is ended; when < 0.9, the treatment is judged as unqualified. Analyze the causes of unqualification (such as unreasonable grouting parameters and insufficient arrangement density of grouting holes), optimize grouting pressure and hole spacing parameters, and return to step 3 to repeat the treatment until qualification; Dynamically update monitoring data during the whole construction process, and calculate the failure degree in real time and treatment effect , repeat steps 2-4 to realize closed-loop control of water-stop curtain failure treatment and effect evaluation, and continuously guarantee the safety of foundation pit construction.

[0056] The monitoring system in step S1 includes a seepage flow monitor, a displacement sensor and a pore water pressure gauge, with a monitoring frequency of once every 1 to 2 hours. When abnormal fluctuations occur in the monitoring data, such as sudden increase in seepage flow and accelerated formation deformation, after a failure warning is triggered, the monitoring frequency is increased to once every 15 to 30 minutes to track the development trend of the failure in real time. The monitoring points shall be arranged to cover the entire range of the water-stop curtain, and be arranged emphatically at construction joints, foundation pit corners and failure-prone areas.

[0057] 1. Judgment criteria for abnormal fluctuation of monitoring data: 1. Abnormal seepage flow: sudden increase of seepage flow ≥ 20% within 1 hour and the absolute value ≥ 5m³ / d; 2. Abnormal formation deformation: daily deformation ≥ 2mm or hourly deformation ≥ 0.5mm; II. Emergency disposal process after warning: 1. Rapid positioning: determine the failure area according to the position of the monitoring hole corresponding to the abnormal data, and verify the seepage source combined with the data of the monitoring hole in the gap area; 2. Temporary control: start the emergency drainage system, and apply temporary surcharge on the cover plate corresponding to the failure area to suppress the expansion of deformation; 3. Grade determination: immediately calculate the failure degree ω, and start the corresponding grade grouting treatment plan.

[0058] III. Early warning threshold and application of pore water pressure: 1. Early warning threshold: when the pore water pressure reaches 1.2 times of hydrostatic pressure, start the warning; when it reaches 1.3 times of hydrostatic pressure, start the alarm; 2. Application method: When an early warning is issued, the monitoring frequency should be increased to once every 30 minutes; when an alarm is triggered, grouting equipment and materials should be prepared in advance, and emergency treatment should be prepared.

[0059] I. The process for analyzing the causes of abnormal monitoring data is as follows: 1. Data verification: Eliminate false anomalies such as sensor malfunction, cable damage, and human interference; 2. Area location: By cross-validating data from adjacent monitoring wells, the area of ​​the anomaly can be pinpointed; 3. Cause determination: Based on the correlation analysis of multiple parameters such as seepage flow, deformation, and pore water pressure, the causes are distinguished into three categories: leakage of the water-stop curtain, ground disturbance, and construction impact.

[0060] II. Dynamic Control Logic: Monitoring frequency adjustment: 1-2 hours / time under normal operating conditions; 30 minutes / time after warning; 15 minutes / time during failure treatment; gradually restore the normal frequency after treatment is qualified.

[0061] Grouting parameter adjustments: Adjust the grout setting time according to the real-time seepage flow (the setting time is shortened by 5 seconds for every 20 m³ / d increase in seepage flow); adjust the grouting pressure according to the formation deformation (the pressure is reduced by 0.05 MPa for every 0.5 mm increase in deformation); dynamically adjust the grouting hole spacing and grouting volume according to the sealing effect.

[0062] In step S3, the density of the emergency grouting holes is adjusted according to the failure level: the hole spacing is 0.8~1.2m in severely failed areas, 1.2~1.5m in moderately failed areas, and 1.5~2.0m in lightly failed areas. The emergency grouting holes are arranged perpendicular to the water-stop curtain, and the hole depth penetrates the failed area by no less than 1.5m to ensure that the grouting fluid can fully fill the failed channels and reinforce the surrounding strata. The grouting reinforcement adopts a segmented grouting process, with a segment length of 1.0~1.5m. The grouting sequence is from the periphery to the core, and from the deepest part to the core. After the initial shallow layer is grouted, a pressure maintenance process is adopted, with the maintenance pressure being 0.8 to 0.9 times the grouting pressure and the maintenance time not less than 30 minutes, to ensure that the grout fully solidifies and forms a stable anti-seepage reinforcement layer. The grouting adopts a combination of permeation grouting and fracturing grouting processes, with the grouting pressure controlled at 0.1 to 0.3 MPa. It only fills the original curtain pores and damaged channels, without damaging the integrity of the original water-stop curtain and retaining structure. To avoid damaging the original structure, a graded pressure increase method can be adopted, with each stage increasing the pressure by 0.05 MPa and stabilizing the pressure for 5 minutes. The pressure at the grouting orifice is monitored in real time. When the pressure exceeds 0.3 MPa or the curtain / retaining structure deformation is detected to be ≥0.5 mm, the pressure is immediately reduced to 0.1 MPa. When grouting in sections, the next section is constructed only after the grouting strength of the upper section reaches 70% of the design value.

[0063] When using the cut-and-cover construction method, emergency grouting holes are reserved simultaneously after the cover plate construction is completed. The grouting operation is carried out in coordination with the layered excavation process of the foundation pit, prioritizing the treatment of the failure areas around the excavation surface of the foundation pit to avoid seepage disasters during the excavation process. When adapting to the cut-and-cover reverse construction method, the top plate is used as a construction platform, and the grouting operation is carried out in an overlapping manner with the underground structure pouring process. Priority is given to sealing the failure areas that affect the structural construction, taking into account both the treatment effect and the construction progress.

[0064] In step 2, the critical allowable seepage flow rate Permeability coefficient of water-rich gravel strata K Cross-sectional area of ​​foundation pit seepage A Differential head of seepage H w The calculation is as follows: ; In the formula, K The formation permeability coefficient (m / d) is determined by field pumping tests; A is the seepage cross-sectional area (m²). 2 The seepage cross-sectional area is calculated as follows: effective seepage height of the cutoff wall * seepage failure perimeter, combined with the dimensions of the excavation pit and the height of the cutoff wall in the cut-and-cover method.

[0065] This invention addresses the challenges of high permeability in water-rich gravelly strata, the susceptibility of water-stop curtains to leakage and failure, and the complexities of cut-and-cover construction. It constructs an integrated emergency management system encompassing monitoring, evaluation, grouting, verification, and closed-loop operation. This system achieves real-time monitoring of multiple parameters, including seepage flow, stratum deformation, and pore water pressure, by simultaneously pre-reserving monitoring holes and emergency grouting holes on the cut-and-cover cover plate. Based on an original failure assessment formula, the failure level of the water-stop curtain is quantitatively determined, and high-pressure grouting is used for sealing and reinforcement at different levels. The cover plate serves as a construction platform, eliminating the need for additional supports and adapting to both conventional and reverse cut-and-cover construction methods. The sealing effect verifies the quantitative management effect of the formula, enabling dynamic control throughout the entire process.

[0066] I. The hole position adjustment and avoidance plan is as follows: 1. Reverse construction method for avoiding top slab hole locations: During the structural design phase, grouting holes are planned simultaneously to avoid beam-column joints and areas with dense reinforcement; where avoidance is not possible, φ110mm inclined grouting holes (inclination angle 15°~30°) are used to cover the target area, and the bottom deviation of the holes is controlled within ±100mm.

[0067] 2. Temporary hole replacement: For failure points found after the main structure is poured, water drills are used to fill holes on the structural slab. The hole diameter is the same as the reserved hole, and the replacement hole is located ≥300mm from the edge of the structure.

[0068] II. Coordination process between grouting and main construction: 1. Continuous construction method: After every 3-5m of excavation, suspend excavation for 24 hours, and prioritize the treatment of the failure area within 2m above and 1m below the excavation surface; after the treatment is qualified, proceed with the next layer of excavation.

[0069] 2. Reverse construction method: The "zoned pouring-zoned grouting" mode is adopted, dividing the foundation pit into 4 to 6 construction sections. After each section of the structure is poured and reaches 70% strength, the grouting operation of that section is carried out immediately. The grouting is carried out in an alternating manner with the pouring of adjacent sections of the structure, without interfering with each other.

[0070] III. Adaptation Scheme for Partial Cut-and-Cut Construction Method: 1. Cut-and-cover section: The monitoring and grouting system of the cut-and-cover method is used, and holes are reserved on the cover plate.

[0071] 2. Open-cut section: Grouting holes are reserved at the top of the cap beam, with the hole depth consistent with the entire length of the cutoff wall; monitoring holes are set on the ground outside the cap beam and cutoff wall, using the same staggered arrangement as the cut-and-cover section.

[0072] Joint treatment: At the junction of the cut-and-cover section and the open-cut section, the number of monitoring holes and grouting holes is increased, and the hole spacing is reduced to 2 / 3 of the standard spacing to ensure that there are no blind spots in monitoring and treatment in the joint area.

[0073] This invention can quickly and accurately address the failure of water-stop curtains, achieving integrated quantitative control of "water blocking - reinforcement - stabilization," effectively reducing the risk of sudden inrush and piping, and significantly improving the safety and reliability of cut-and-cover subway station construction in water-rich sand and gravel strata. It is applicable to emergency treatment scenarios for the failure of water-stop curtains in complex water-rich strata such as urban subway foundation pits and underground integrated pipe corridors.

[0074] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation of the invention and not by way of limitation. In fact, those skilled in the art will understand that modifications and variations may be made to the invention without departing from the scope or spirit of the invention. For example, features shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desired that the present invention include such modifications and variations that fall within the scope of the appended claims and their equivalents. Example

[0075] Please combine Figures 1 to 2This embodiment describes an emergency treatment evaluation method for the failure of a cut-and-cover water-stop curtain in a water-rich gravel stratum. The example uses a subway station's cut-and-cover excavation pit, with a total length of 120m, a standard section width of 20m, and an excavation depth of 18m. The surface layer is 2m thick plain fill, and the lower layer is a 26m thick water-rich gravel layer. The stratum permeability coefficient K=9.2m / d, the groundwater level is 3.2m deep, and the soil cover thickness from the station structure's top slab to the ground surface is 4m. The core structure adopts a system of "drilled cast-in-place piles + high-pressure jet grouting piles between piles + external high-pressure jet grouting piles for water-stopping + a fully covered reinforced concrete capping plate." The retaining structure consists of φ800mm bored cast-in-place piles with a center-to-center distance of 1200mm and a pile length of 25m. The spaces between the piles are filled with φ500mm high-pressure jet grouting piles, which overlap with the cast-in-place piles on both sides by 100mm. The water-stop curtain is a φ800mm high-pressure jet grouting pile interlocking structure located 300mm outside the retaining structure, with adjacent piles overlapping by 300mm and a pile length of 28m (embedded 5m below the permeable layer). The cover plate is made of C35 reinforced concrete with a thickness of 0.8m and a plan dimension of 121.2m × 21.2m, which fully covers the outer water-stop curtain and is laid directly to the ground surface.

[0076] A total of 52 monitoring holes (28 in the main body area of ​​the water-stop curtain, 16 in the structural gap area, and 8 in the surrounding stratum area) and 134 reserved grouting holes are installed. They are arranged in a 900mm longitudinal staggered cross section. Odd-numbered cross sections are equipped with 3 monitoring hole groups (20m deep in the main body / gap area and 29m deep in the stratum area), and even-numbered cross sections are equipped with 2 grouting hole groups (28m deep and 1.8m spacing). The distance between monitoring holes and grouting holes is ≥500mm. A φ50mm PVC horizontal pipeline is pre-embedded in the cover plate to connect all monitoring holes, and the end is led to a special equipment box in the non-passage area in the northwest corner of the station.

[0077] When the foundation pit was excavated to a depth of 15m, seepage flow was monitored in the cutoff wall section at section K1+620. Q act= 128m 3 / d, corresponding to a deformation of Δs=3.6mm monitored in the surrounding strata, with no important buildings nearby, Δs max =5mm, calculated =0.2163<0.4, indicating a slight failure.

[0078] Use the grouting holes reserved at the failed section and adjacent sections, with a hole spacing of 1.8m; use grouting material with a density of 2000 kg / m³. 3 The cement-water glass double-liquid grout was designed with κ=1.15 for mild failure and a grouting hole depth of 16.5m (penetrating the failure zone by 1.5m). The calculated grouting pressure was approximately 0.44MPa. A segmented grouting process was adopted, with each segment being 1.2m long, first the deep layer and then the shallow layer. After the grouting was completed, the pressure was maintained at 0.38MPa for 30min.

[0079] After grouting, the seepage flow rate dropped to 4.2 m³ / d. The calculated sealing effect evaluation index ζ≈0.9929 met the qualified standard of ζ≥0.9, and the regular monitoring frequency was restored. Subsequent monitoring continued until the foundation pit construction was completed, and no seepage abnormalities were found again, which verified the effectiveness of this method in the cut-and-cover construction condition of water-rich sandy gravel strata.

[0080] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. An evaluation method for emergency treatment of the failure of a cutoff wall in a water-rich gravel stratum using the over-cut method, characterized in that, Includes the following steps: Step 1. Construction and data acquisition of the water-stop curtain failure monitoring system: Monitoring points are set up on the side wall of the excavation pit of the cut-and-cover subway station, the joint of the water-stop curtain and the surrounding strata to collect groundwater seepage flow, deformation of the surrounding strata and pore water pressure data in real time. Step 2. Failure severity assessment and level triggering: Based on monitoring data, calculate the failure severity of the water-stop curtain using the failure severity assessment formula, classify the failure level, and trigger the corresponding emergency treatment process; Step 3. High-pressure grouting and ground reinforcement: Using the cut-and-cover method, the cover plate is used as an emergency construction platform. Through the emergency grouting holes reserved in the cover plate, high-pressure grouting is carried out to seal the failed area, and the surrounding water-rich gravel strata are reinforced and strengthened at the same time. Step 4. Quantification and verification of treatment effect: After the grouting treatment is completed, the regular monitoring frequency is restored, the seepage flow rate after grouting is collected, and the treatment effect is quantified by the sealing effect verification formula. If the qualified standard is not met, return to step 3 to optimize the grouting parameters and repeat the treatment until it is qualified. Step 5. Dynamic monitoring and closed-loop control throughout the entire process: Dynamically update monitoring data throughout the construction process, repeat steps 2-4, and achieve closed-loop control for failure management and effect evaluation.

2. The emergency treatment evaluation method for the failure of the cut-off wall in the cut-off method for water-rich sand and gravel strata as described in claim 1, including the core structure of the subway station foundation pit and the emergency material reserve method in the cut-off method for water-rich sand and gravel strata, is characterized in that, The core structure of the subway station foundation pit constructed using the cut-and-cover method in water-rich gravel strata includes a retaining structure, a water-stop curtain, and a cover plate. The specific structural effects are as follows: (1) The retaining structure is composed of bored cast-in-place piles and high-pressure jet grouting piles between the piles, and undertakes the function of retaining soil in the foundation pit; (2) The water-stop curtain adopts a high-pressure jet grouting pile interlocking structure, which is arranged on the outer perimeter of the retaining structure, away from the foundation pit, and undertakes the function of seepage prevention for the entire foundation pit; (3) The cover plate is laid directly to the ground surface. The size of the cover plate is larger than the size of the retaining structure and fully covers the outer water-stop curtain to ensure that the cover plate can completely cover the emergency treatment operation area, while providing a stable platform for monitoring and grouting operations. (4) The connection between the cover plate and the enclosure structure and the water-stop curtain must meet the requirements of sealing and load bearing, so as to avoid the formation of seepage channels at the connection between the cover plate and the structure; The emergency supplies storage method includes the following steps: (1) For different failure levels, reserve the corresponding grouting equipment, grouting materials and monitoring equipment. For severe failure levels, reserve high-pressure grouting pumps, dual-liquid grouting machines, emergency drainage pumps, as well as sufficient cement, water glass and grouting materials. For moderate and mild failure levels, reserve conventional grouting equipment and materials. (2) Simultaneously develop emergency construction plans, clarify the division of labor among construction personnel, work procedures and parameter adjustment schemes, and ensure that treatment operations can be started quickly when failure occurs.

3. The emergency treatment evaluation method for the failure of the cut-off wall in the over-cut method for water-rich gravel strata as described in claim 2, characterized in that, The cover plate has pre-reserved monitoring holes and emergency grouting holes. These holes are pre-reserved simultaneously during the cover plate construction and penetrate the full thickness of the cover plate. The specific details are as follows: (1) The monitoring holes are arranged on the cover plate in the area corresponding to the outer high-pressure jet grouting pile interlocking water-stop curtain, the gap between the retaining structure and the water-stop curtain, and the stratum outside the water-stop curtain; (2) The monitoring hole drilling depth L is designed in different areas: the monitoring hole depth L in the outer high-pressure jet grouting pile interlocking water-stop curtain body area and the gap area between the retaining structure and the water-stop curtain covers the full excavation depth H of the foundation pit + 2~5m below the excavation surface to capture curtain leakage within the entire excavation range; in the stratum area outside the water-stop curtain, it covers the entire water-rich sand and gravel layer + 3~5m below the excavation surface to monitor deep stratum deformation and pore water pressure; seepage flow monitoring instruments are installed in layers with burial depths of L / 3, 2*L / 3, and L, corresponding to shallow, middle, and deep water-rich layers; (3) The emergency grouting holes are arranged on the cover plate in the area corresponding to the outer high-pressure jet grouting pile interlocking water-stop curtain, the gap between the retaining structure and the water-stop curtain, and are vertically aligned with the center of the corresponding structure. (4) The emergency grouting holes are divided into two categories: the grouting holes of the water-stop curtain body are used to repair the damage, cracks and interlocking gaps of the curtain itself; the grouting holes of the structural gaps are used to seal the seepage channels at the junction of the retaining structure and the water-stop curtain, and simultaneously reinforce the loose soil in the gaps. (5) The drilling depth h of the emergency grouting hole is consistent with the full length of the outer high-pressure jet grouting pile interlocking water-stopping curtain, extending 5m below the permeable layer and covering the full depth of the curtain. The segmented grouting process is adopted, and grouting is only performed on the failure depth section. The segment length is 1.0~1.5m, and the hole depth penetrates the failure area by no less than 1.5m. (6) The monitoring holes and the emergency grouting holes are arranged in staggered sections. A section is divided at a certain interval along the edge of the foundation pit. One set of monitoring holes is arranged on the odd-numbered sections. There are 3 monitoring holes in one set, which correspond to the water-stop curtain body, the structural gap and the outer stratum respectively. One set of emergency grouting holes is arranged on the even-numbered sections. There are 2 emergency grouting holes in one set, which correspond to the water-stop curtain body and the structural gap respectively. The distance between any two holes is not less than 500mm. (7) The cables inside the cover plate are laid out through horizontal pipelines that are pre-buried during construction. The pipelines are vertically connected to each monitoring hole and the ends are uniformly led to a special equipment box in the non-passage area at the edge of the cover plate, so as to realize the cable laying in a completely hidden manner and completely avoid interference with ground traffic.

4. The emergency treatment evaluation method for the failure of the cut-off wall in the over-cut method for water-rich sandy and gravelly strata as described in claim 1, characterized in that, In step S2, the failure severity evaluation formula is as follows: ； In the formula, The degree of failure of the water curtain is indicated by a value ranging from 0 to 1. ≥0.7 indicates severe failure, 0.4≤ <0.7 indicates moderate failure. <0.4 indicates a minor failure. Actual seepage flow (m) 3 / d), Critical allowable seepage flow rate (m 3 / d), determined by the permeability coefficient of water-rich gravel strata and the size of the foundation pit. This is a weighting coefficient, ranging from 0.6 to 0.8, prioritizing the impact of seepage flow on the degree of failure. The value represents the deformation of the strata surrounding the curtain (mm). The maximum allowable deformation (mm) is determined based on the stability requirements of surrounding buildings and the foundation pit; The actual seepage flow The measured maximum value of the monitoring hole in the main body area of ​​the cutoff wall corresponding to the failure point is taken as the formation deformation amount. The measured maximum value of the monitoring wells in the surrounding strata corresponding to the failure point is taken. The monitoring well data in the structural gap area is only used to assist in verifying the seepage source, and the pore water pressure data is only used for early warning. Neither of them is directly substituted into the formula. according to The calculation results classify the failure levels of the water-stop curtain into three levels: A value ≥0.7 indicates a severe failure, requiring immediate initiation of emergency remediation procedures; a value ≤0.4 indicates a failure. A value less than 0.7 indicates a moderate failure; initiate standard emergency response procedures. A value less than 0.4 indicates a minor failure, requiring targeted reinforcement and treatment.

5. The emergency treatment evaluation method for the failure of the cut-off wall in the over-cut method for water-rich sandy and gravelly strata as described in claim 1, characterized in that, In step S3, corresponding high-pressure grouting parameters and processes are adopted for different failure levels of the water-stop curtain. The pressure is adjusted to ensure that the grouting fluid can penetrate into the pores of the sand and gravel and fill the failure channels. The grouting pressure of the high-pressure grouting is calculated by the following formula: ； In the formula, The grouting pressure is measured in MPa. The density of the grout (kg / m³) 3 When using cement-water glass dual-liquid grouting fluid, The value is taken as 1800~2200 kg / m 3 , g Acceleration due to gravity (m / s²) 2 (), take 9.8 m / s 2 , H 1 represents the depth of the groundwater level (m); h The depth of the grouting hole is (m). This is a pressure correction factor, adjusted according to the failure level of the waterstop curtain; in case of severe failure... =1.4~1.5, moderate failure =1.2~1.3, for minor failures =1.1~1.

2.

6. The emergency treatment evaluation method for the failure of the cut-off wall in the over-cut method for water-rich sandy and gravelly strata as described in claim 1, characterized in that, In step S4, the formula for verifying the blocking effect is as follows: ； In the formula, is the plugging effect evaluation index, ≥ 0.9 means qualified; is the seepage discharge after grouting (m 3 / d), is the seepage discharge before grouting (m 3 / d), is the failure degree of the water-stop curtain before grouting; when When the concentration is ≥0.9, the treatment is deemed satisfactory, and the emergency treatment process ends; when... If the value is less than 0.9, the treatment is deemed unqualified. The reasons for the unqualified treatment are analyzed (such as unreasonable grouting parameters or insufficient grouting hole density). The grouting pressure and hole spacing parameters are optimized, and the treatment is repeated in step 3 until it is qualified. Dynamically update monitoring data throughout the construction process and calculate the degree of failure in real time. With governance effectiveness Repeat steps 2-4 to achieve closed-loop control of the treatment and effect evaluation of the water-stop curtain failure, and continuously ensure the safety of foundation pit construction.

7. The emergency treatment evaluation method for the failure of the cut-off wall in the over-cut method for water-rich sandy and gravelly strata as described in claim 1, characterized in that, The monitoring system in step S1 includes a seepage flow monitor, a displacement sensor, and a pore water pressure gauge. The monitoring frequency is once every 1 to 2 hours. When abnormal fluctuations occur in the monitoring data, such as a sudden increase in seepage flow or accelerated formation deformation, a failure warning is triggered, and the monitoring frequency is increased to once every 15 to 30 minutes to track the failure development trend in real time. The monitoring points need to cover the entire area of ​​the water-stop curtain, with a focus on construction joints, foundation pit corners, and areas prone to failure.

8. The emergency treatment evaluation method for the failure of the cut-off wall in the over-cut method for water-rich sandy and gravelly strata as described in claim 1, characterized in that, In step S3, the density of the emergency grouting holes is adjusted according to the failure level: the hole spacing is 0.8~1.2m in severely failed areas, 1.2~1.5m in moderately failed areas, and 1.5~2.0m in lightly failed areas. The emergency grouting holes are arranged perpendicular to the water-stop curtain, and the hole depth penetrates the failed area by no less than 1.5m to ensure that the grouting fluid can fully fill the failed channels and reinforce the surrounding strata. The grouting reinforcement adopts a segmented grouting process, with a segment length of 1.0~1m. The grouting sequence is from the periphery to the core, and from the deep layer to the shallow layer. After grouting, a pressure maintenance process is adopted, with the maintenance pressure being 0.8 to 0.9 times the grouting pressure and the maintenance time being no less than 30 minutes, to ensure that the grout fully solidifies and forms a stable anti-seepage reinforcement layer. The grouting adopts a combination of permeation grouting and fracturing grouting processes, with the grouting pressure controlled at 0.1 to 0.3 MPa. It only fills the original curtain pores and damaged channels, without damaging the integrity of the original water-stop curtain and enclosure structure.

9. The emergency treatment evaluation method for the failure of the cut-off wall in the over-cut method for water-rich sandy and gravelly strata as described in claim 1, characterized in that, When using the cut-and-cover construction method, emergency grouting holes are reserved simultaneously after the cover plate construction is completed. The grouting operation is carried out in coordination with the layered excavation process of the foundation pit, prioritizing the treatment of the failure areas around the excavation surface of the foundation pit to avoid seepage disasters during the excavation process. When adapting to the cut-and-cover reverse construction method, the top plate is used as a construction platform, and the grouting operation is carried out in an overlapping manner with the underground structure pouring process. Priority is given to sealing the failure areas that affect the structural construction, taking into account both the treatment effect and the construction progress.

10. The emergency treatment evaluation method for the failure of the cut-off wall in the over-cut method for water-rich sandy and gravelly strata as described in claim 1, characterized in that, In step 2, the critical allowable seepage flow rate Permeability coefficient of water-rich gravel strata K Cross-sectional area of ​​foundation pit seepage A Differential head of seepage H w The calculation is as follows: ； In the formula, K The formation permeability coefficient (m / d) is determined by field pumping tests; A is the seepage cross-sectional area (m²). 2 The calculation is based on the dimensions of the excavation pit and the height of the cut-and-cover method.

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