River and lake muddy foundation pit support structure and construction method thereof

Abstract

The invention relates to the technical field of foundation pit engineering, and discloses a muddy foundation pit support structure near a river and a lake and a construction method thereof.The muddy foundation pit support structure comprises double-layer steel sheet piles serving as the outer walls of the two sides of a foundation pit, and a U-shaped support is installed at the upper ends of the double-layer steel sheet piles; the multi-layer repeated filtering structure unit comprises a pebble bed, a steel wire filter screen layer, a reinforcement cage and an HDPE waterproof film; the sludge mixture is filled below, above and among the multiple layers of repeated filtering structure units, the jack is installed at the lower end of the U-shaped support, the top of the jack abuts against the U-shaped support, the pressure transmission assembly is arranged between the jack and the sludge mixture to achieve uniform force transmission, and the drainage pipe is buried between the double-layer steel sheet piles to drain extrusion water. The U-shaped support prevents displacement and provides a platform for the jack, the multiple layers of units construct a waterproof system, the sludge mixture is recycled, the jack is matched with the assembly and the drainage pipe to improve the compactness and strength of the mixture, and the problem of a traditional cofferdam is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foundation pit engineering, and in particular to a river and lake silt foundation pit retaining structure and a construction method thereof. BACKGROUND

[0002] In the river and lake area, the soil layer is mostly silt or pebble, which has low bearing capacity and strong water permeability, bringing challenges to the foundation pit retaining construction. The retaining system adapted to the foundation pit operation in this area needs to resist water and soil pressure, prevent water seepage, and ensure safety, and also needs to efficiently handle the silt generated by excavation to reduce costs and consumption. At present, the industry mostly uses steel sheet piles to build cofferdams, which are widely used in early stage due to their simple construction, but as the requirements for stability, water resistance, and cost control of projects increase, the limitations of traditional schemes are highlighted.

[0003] The traditional steel sheet pile cofferdam has many specific defects: the single-layer steel sheet pile has weak strength and deformation resistance, and is easily deformed by external force when it is shallow in rock, which threatens the safety of the cofferdam, and the connection and sealing between the piles are poor, which easily causes water leakage and damages the construction environment; the double-layer steel sheet pile slightly improves water resistance, but the original silt is filled between the piles, which has low stiffness and strength and is difficult to support, is easily horizontally displaced, and is difficult to stabilize, and the use of concrete to improve the strength requires additional procurement of materials and an increase in the process, resulting in high cost. In addition, the silt treatment is extensive, the stacking occupies a large area, the treatment and external transportation cost is high, the efficiency is low, and resources are wasted. SUMMARY

[0004] In order to make up for the above shortcomings, the present application provides a river and lake silt foundation pit retaining structure and a construction method thereof, aiming to improve the poor stability, poor water resistance, high construction cost of the traditional steel sheet pile cofferdam, and the low efficiency and resource waste of silt treatment in the foundation pit.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme: a river and lake silt foundation pit retaining structure, comprising a double-layer steel sheet pile, a U-shaped support, a multi-layer repeated filtration structure unit, a silt mixture, a jack, a drainage pipe and a pressure transmission assembly, the double-layer steel sheet pile serving as the outer wall of the foundation pit on both sides, and the U-shaped support being installed on the upper end of the double-layer steel sheet pile; the multi-layer repeated filtration structure unit comprises a pebble layer, a steel wire mesh layer, a steel reinforcement cage and an HDPE waterproof membrane, the pebble layer being spread between the double-layer steel sheet piles, the steel wire mesh layer being laid below the pebble layer, the steel reinforcement cage being laid below the steel wire mesh layer, and the HDPE waterproof membrane being laid below the steel reinforcement cage;

[0006] The silt mixture is filled in the lower, upper and between the units of the multi-layer repeated filtering structure unit, the jack is installed at the lower end of the U-shaped support, and the top of the jack is tightly abutted with the U-shaped support to realize stable force transmission; the pressure transmission assembly is arranged between the jack and the silt mixture, for uniformly transmitting the pressure of the jack to the silt mixture; the drain pipe is embedded between the double-layer steel sheet piles, for discharging the water squeezed out of the silt mixture.

[0007] Preferably, the spacing of the double-layer steel sheet piles is 0.5-1 meters, the steel sheet piles are driven into the rock layer or the non-water permeable layer; the minimum thickness of the pebble layer is not less than 5 centimeters.

[0008] Preferably, the width of the steel reinforcement cage is consistent with the spacing of the double-layer steel sheet piles, the height is 5 centimeters, the spacing of the steel reinforcement holes of the steel reinforcement cage is not greater than 3 centimeters, the waist rib and the hoop of the steel reinforcement cage are bent inward; the spacing of the holes of the steel wire filter layer is not less than 1 centimeter.

[0009] Preferably, the silt mixture is stirred by quicklime, polyacrylamide, slag and silt, wherein the proportions of quicklime, polyacrylamide and slag in the dry weight of the silt are 10%, 0.5% and 20% respectively, and the water content of the silt is 45%-55%.

[0010] Preferably, the pressure transmission assembly comprises a square wood board and a force transmission column, the square wood board and the HDPE waterproof film are sequentially placed above the uppermost layer of silt mixture, and the force transmission column is arranged between the jack and the square wood board.

[0011] Preferably, the drain pipe is a PVC pipe, drainage holes are arranged at intervals on the drain pipe, a drain pipe filter screen is wrapped outside the drainage holes, the joint position of the drain pipe is wrapped with waterproof coiled material and wrapped with waterproof adhesive tape; the height of the drainage hole is consistent with the total height of the pebble layer and the steel reinforcement cage, and the drainage hole and the wrapped drain pipe filter screen part are flush with the pebble layer and the steel reinforcement cage part.

[0012] A construction method of a river and lake silt foundation pit enclosure structure, comprising the following steps:

[0013] S1: double-layer steel sheet piles are applied as the outer walls of the two sides of the foundation pit, and U-shaped supports are installed at the upper ends of the double-layer steel sheet piles;

[0014] S2: the double-layer steel sheet pile grooves are cleaned and the mud is discharged, and the leakage parts between the steel sheet piles that are not tightly connected are plugged;

[0015] S3: Laying multiple layers of repeated filtering structure units: laying a minimum thickness of 5 cm of pebble layer between the double-layer steel sheet piles; laying a steel wire filter layer with a hole spacing of not less than 1 cm below the pebble layer; laying a steel reinforcement cage below the steel wire filter layer, the steel reinforcement cage having a width consistent with the double-layer steel sheet pile spacing, a height of 5 cm, and an anchor bending of the waist and hoop inward, and a steel reinforcement hole spacing of not more than 3 cm; laying an HDPE waterproof membrane below the steel reinforcement cage to complete the laying of the first layer of filtering structure unit;

[0016] S4: Filling silt mixture and repeated construction: filling the silt mixture above the first layer of filtering structure unit, the silt mixture being made of quicklime, polyacrylamide, and slag in proportions of 10%, 0.5%, and 20% of the dry weight of the silt, respectively, and mixed with silt having a water content of 45%-55%; repeating step S3 to lay the previous layer of filtering structure unit, and then filling the silt mixture above the layer of filtering structure unit, and so on until the double-layer steel sheet piles are filled to the designed height;

[0017] S5: Installing pressure transmission components and jacks: sequentially placing an HDPE waterproof membrane and a square wood board above the uppermost layer of silt mixture; installing a jack at the lower end of the U-shaped support, and setting a force transmission column between the jack and the square wood board;

[0018] S6: Burying drainage pipes and draining water: simultaneously performing steps S3-S5, burying PVC drainage pipes, setting drainage holes at intervals on the drainage pipes, wrapping the drainage holes with drainage pipe filters, wrapping the joint positions of the drainage pipes with waterproof coiled material and sealing them with waterproof adhesive tape; ensuring that the height of the drainage holes is consistent with the total height of the pebble layer and the steel reinforcement cage of each layer, and is flush with the pebble layer and the steel reinforcement cage of the corresponding layer; draining the water squeezed out of the silt mixture through the drainage pipes;

[0019] S7: Pressurizing and shaping: starting the jack to push the square wood board to compress the silt mixture through the force transmission column.

[0020] Preferably, in S1, the spacing of the double-layer steel sheet piles is 0.5-1 m, and the steel sheet piles are driven into the rock layer or non-porous layer; in S2, a micro single-shaft mixer and a high-pressure jet mixing device are used to clean the trench, and the soil and silt in the trench are flushed out as cement slurry; the water leakage part is plugged by pasting a waterproof coiled material.

[0021] Preferably, in S7, the compression and shaping height of each layer of silt mixture is 2 m, and a silt mixture compression test is performed before construction to determine the compression ratio, and the amount of silt mixture to be mixed and placed each time is calculated according to the compression ratio.

[0022] Preferably, the method further comprises the following steps: if the supporting period is within 3 months, periodically checking the jack reading during the construction process to monitor the stress state of the structure in real time and ensure the stability of the enclosure system; if the supporting period is greater than 3 months, in addition to periodically checking the jack reading during the construction process, an HDPE waterproof membrane is laid on the uppermost layer of the silt mixture, and a 5-10 cm thick concrete top is poured, and the distance between the upper layer of the silt mixture and the top of the steel sheet pile is not less than 10 cm; after the cofferdam construction is completed, the jacks and U-shaped supports are removed, and the steel sheet piles are pulled out.

[0023] The present application has the following advantages:

[0024] 1、In the present application, the double-layer steel sheet piles serve as the outer walls on both sides of the foundation pit, providing a stable foundation support for the entire enclosure system and effectively resisting the water and soil pressure in the river or lake area; the U-shaped supports are installed on the upper end of the double-layer steel sheet piles, which not only prevents the double-layer steel sheet piles from being displaced due to external forces during subsequent construction and ensures the overall consistency of the structure, but also provides a stable installation platform for the jacks, laying a foundation for subsequent pressure transmission.

[0025] The multi-layer repeated filtration structure unit constructs a perfect waterproof and water seepage treatment system: the gravel layer is laid between the double-layer steel sheet piles, which not only can bear the weight of the upper structure, but also can preliminarily filter the seepage water and intercept larger particles; the steel wire mesh layer is located below the gravel layer, which can further intercept small particles in the silt mixture and prevent the subsequent water storage structure from being blocked; the steel reinforcement cage is laid below the steel wire mesh layer, which can efficiently collect the seepage water after two layers of filtration, and the inwardly bent anchor design of the waist rib and hoop rib can also prevent the HDPE waterproof membrane below from being pierced, ensuring the waterproof integrity; the HDPE waterproof membrane directly separates the water source at the bottom, reducing the external water seepage into the foundation pit from the root.

[0026] The silt mixture is filled below, above and between the multi-layer repeated filtration structure unit, successfully converting the silt generated by the foundation pit excavation into part of the supporting structure, completely solving the problems of occupying space for silt storage and incurring additional costs for external transportation, and realizing the non-polluting resource utilization of silt; the jacks apply pressure to the silt mixture through the pressure transmission assembly, promoting its compression and dehydration, and cooperating with the drainage pipe to timely discharge the extrusion water, greatly improving the compactness and structural strength of the silt mixture, and finally improving the stability and waterproof performance of the entire double-layer steel sheet pile supporting structure, effectively solving the core problems of poor waterproof effect and easy instability of traditional steel sheet pile cofferdams.

[0027] 2. In this invention, the 0.5-1 meter spacing design of the double-layer steel sheet piles takes into account both structural rigidity and material economy. It avoids insufficient support due to excessive spacing and prevents material loss due to excessively small spacing. The requirement that the steel sheet piles be driven into rock strata or impermeable layers strengthens the pull-out and displacement resistance of the foundation support. The minimum thickness of the pebble layer of not less than 5 cm ensures the stable performance of its support and filtration functions and avoids structural deformation or filtration failure due to insufficient thickness.

[0028] The precise design of the rebar cage parameters ensures that its width matches the spacing of the double-layer sheet piles and its height is adapted to the water storage requirements. The spacing between the rebar holes is no more than 3 cm to ensure smooth water seepage. The inward bending and anchoring of the waist bars and stirrups completely prevents damage to the HDPE waterproof membrane. The spacing between the holes in the steel wire mesh layer is no less than 1 cm, which intercepts impurities while ensuring smooth water seepage and avoiding filter blockage that affects drainage efficiency.

[0029] The optimization of the proportions of the sludge mixture (quicklime, polyacrylamide, and slag accounting for 10%, 0.5%, and 20% of the dry weight of the sludge, respectively) and the moisture content of the sludge (45%~55%) allows the sludge mixture to have good mixing properties and, through the hydration of quicklime, the flocculation of polyacrylamide, and the reinforcing effect of slag, to form a structural strength of 5-10 MPa after compression. This significantly reduces the amount of concrete used in traditional construction and substantially lowers material costs.

[0030] Square wooden boards can evenly distribute the pressure of the jacks to the top layer of silt mixture, avoiding structural defects caused by uneven local stress. The force transmission columns can compensate for insufficient jacking length, ensuring that the pressure can still be effectively transmitted when the height of the structural layer increases.

[0031] In the design of drainage pipes, PVC material combines corrosion resistance and economy. Waterproof membrane wrapping and waterproof tape wrapping at pipe joints completely prevent water leakage at the joints. The drain pipe filter screen on the outside of the drain hole prevents silt blockage. The height of the drain hole is consistent with the overall height of the pebble layer and the steel cage, and the corresponding parts are flush, ensuring that seepage water flows into the drain pipe for discharge efficiently.

[0032] The construction methods ensure quality through a process-oriented approach: a miniature single-shaft mixer and a high-pressure jet mixing device thoroughly remove impurities from the trench, and the application of waterproof membrane further enhances waterproofing; layered construction and control of the 2-meter compression molding height for each layer, combined with pre-constructed compression tests, allow for precise calculation of the amount of silt mixture to ensure the density of each layer; differentiated treatment for support cycles (regularly checking jack readings within 3 months, and waterproofing and concrete sealing at the top after 3 months) adapts to different project needs and ensures long-term support stability. Attached Figure Description

[0033] Fig. 1 This is a three-dimensional structural diagram of a retaining structure for silty foundation pits near rivers and lakes proposed in this invention.

[0034] Fig. 2 A top view structural schematic diagram of a river and lake silt foundation pit retaining structure according to the present application;

[0035] Fig. 3 A front view structural schematic diagram of a river and lake silt foundation pit retaining structure according to the present application;

[0036] Fig. 4 A cross-sectional structural schematic diagram of a river and lake silt foundation pit retaining structure according to the present application;

[0037] Fig. 5 A partial structural schematic diagram of a drainage pipe of a river and lake silt foundation pit retaining structure according to the present application.

[0038] Legend:

[0039] 1 steel sheet pile, 2 jack, 3 U-shaped support, 4 drainage pipe, 5 force transmission column, 6 square wood board, 7 HDPE waterproof membrane, 8 silt mixture, 9 pebble layer, 10 steel wire filter screen layer, 11 steel reinforcement cage, 4-1 drainage pipe filter screen, 4-2 drainage hole. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0041] Embodiment one, with reference to Figs. 1~5 A river and lake silt foundation pit retaining structure, comprising a double-layer steel sheet pile 1, a U-shaped support 3, a multi-layer repeated filtering structure unit, a silt mixture 8, a jack 2, a drainage pipe 4 and a pressure transmission assembly, the double-layer steel sheet pile 1 serving as an outer wall on both sides of the foundation pit, and the U-shaped support 3 being installed on the upper end of the double-layer steel sheet pile 1; the multi-layer repeated filtering structure unit comprises a pebble layer 9, a steel wire filter screen layer 10, a steel reinforcement cage 11 and an HDPE waterproof membrane 7, the pebble layer 9 being spread between the double-layer steel sheet pile 1, the steel wire filter screen layer 10 being laid below the pebble layer 9, the steel reinforcement cage 11 being laid below the steel wire filter screen layer 10, and the HDPE waterproof membrane 7 being laid below the steel reinforcement cage 11; the silt mixture 8 being filled below, above and between the multi-layer repeated filtering structure unit, the jack 2 being installed at the lower end of the U-shaped support 3, and the top of the jack 2 being tightly abutted against the U-shaped support 3 to realize stable force transmission; the pressure transmission assembly being arranged between the jack 2 and the silt mixture 8, for uniformly transmitting the pressure of the jack 2 to the silt mixture 8; and the drainage pipe 4 being buried between the double-layer steel sheet pile 1, for discharging water squeezed out of the silt mixture 8.

[0042] Double-layer steel sheet pile 1 provides foundation support as the outer wall of both sides of the foundation pit, U-shaped support 3 is installed at the upper end to prevent relative displacement and provide a platform for jack 2, pebble layer 9 in the multi-layer repeated filter structure unit supports filtration, steel wire filter screen layer 10 intercepts impurities, steel reinforcement cage 11 stores water, HDPE waterproof membrane 7 separates the bottom water source, and silt mixture 8 is filled around the filter unit to realize resource utilization. Jack 2 transmits pressure to silt mixture 8 through a pressure transmission assembly, and drainage pipe 4 discharges extrusion water, thereby improving support stability and waterproofness and efficiently utilizing silt. This is because the functions of each component are complementary to form a complete support system, and each link cooperates to ensure structural performance and resource utilization.

[0043] Example two, refer to Figs. 1~5On the basis of embodiment one, the spacing of the double-layer steel sheet pile 1 is 0.5-1 meters, the steel sheet pile 1 is driven into the rock layer or non-pervious layer; the minimum thickness of the pebble layer 9 is not less than 5 centimeters; the structural rigidity and material economy are considered, the uplift resistance and displacement resistance of the foundation are strengthened, and the stable function of the pebble layer 9 is ensured, the reasonable spacing and driving depth are adapted to the river and lake water soil pressure, and the sufficient thickness meets the support and filtration requirements of the pebble layer 9. The width of the steel reinforcement cage 11 is consistent with the spacing of the double-layer steel sheet pile 1, and the height is 5 centimeters, the steel reinforcement hole spacing of the steel reinforcement cage 11 is not greater than 3 centimeters, the waist and hoop of the steel reinforcement cage 11 are bent and anchored inward; the steel wire mesh layer 10 has a hole spacing of not less than 1 centimeter; the steel reinforcement cage 11 avoids piercing the HDPE waterproof membrane 7 and ensures smooth water seepage and prevents filter screen blockage, the bent anchor design of the steel reinforcement cage 11 protects the waterproof membrane, and the size of the filter screen hole considers impurity interception and water seepage efficiency. The sludge mixture 8 is stirred by quicklime, polyacrylamide, slag and sludge, wherein the proportions of quicklime, polyacrylamide and slag in the dry weight of sludge are 10%, 0.5% and 20% respectively, and the water content of the sludge is 45%-55%; it has good mixing properties and the structural strength after compression reaches 5-10 MP, reducing the amount of concrete and cost, the hydration of quicklime, flocculation of polyacrylamide and strengthening of slag synergistically improve the strength, and the reasonable water content adapts to the mixing and compression process. The pressure transmission assembly includes a square wood board 6 and a force transmission column 5, the square wood board 6 and the HDPE waterproof membrane 7 are placed on the uppermost layer of the sludge mixture 8 in turn, and the force transmission column 5 is arranged between the jack 2 and the square wood board 6; the pressure of the jack 2 is uniformly transmitted and the insufficient jacking length is compensated, the square wood board 6 can disperse the pressure to avoid uneven local stress, and the force transmission column 5 can adjust the height of the structure layer to ensure effective pressure transmission. The drain pipe 4 is made of PVC material, drainage holes 4-2 are arranged on the drain pipe 4 at intervals, the outer side of the drainage hole 4-2 is wrapped with a drain pipe filter screen 4-1, and the joint position of the drain pipe 4 is wrapped with waterproof material and wound with waterproof tape; the height of the drainage hole 4-2 is consistent with the overall height of the pebble layer 9 and the steel reinforcement cage 11, and the position of the drainage hole 4-2 and the outer wrapped drain pipe filter screen 4-1 is flush with the position of the pebble layer 9 and the steel reinforcement cage 11; it prevents interface leakage, blockage of the drainage hole 4-2 and efficient discharge of seepage water, PVC material is corrosion-resistant, the interface is sealed after waterproof treatment, the drain pipe filter screen 4-1 prevents silt blockage, and the hole height is adapted to the water storage layer to ensure that the seepage water flows into it.

[0044] Embodiment three, referring to Figs. 1~5 A construction method of a river and lake sludge foundation pit enclosure structure, comprising the following steps:

[0045] S1: driving a double-layer steel sheet pile 1 as the outer wall of the foundation pit on both sides, and installing a U-shaped support 3 on the upper end of the double-layer steel sheet pile 1;

[0046] S2: cleaning the groove of the double-layer steel sheet pile 1 and discharging the slurry, and plugging the leakage part between the steel sheet piles 1 which is not tightly connected;

[0047] S3: Laying multiple layers of repeated filtering structure units: laying a minimum thickness of 5 cm of pebble layer 9 between the double-layer steel sheet piles 1; laying a steel wire filter screen layer 10 with a hole spacing of not less than 1 cm below the pebble layer 9; laying a steel reinforcement cage 11 below the steel wire filter screen layer 10, the steel reinforcement cage 11 having a width consistent with the spacing of the double-layer steel sheet piles 1 and a height of 5 cm, the waist rib and hoop of the steel reinforcement cage 11 being bent inward, and the steel reinforcement hole spacing being not greater than 3 cm; laying an HDPE waterproof membrane 7 below the steel reinforcement cage 11 to complete the laying of the first layer of filtering structure units;

[0048] S4: Filling with silt mixture 8 and repeated construction: filling the silt mixture 8 above the first layer of filtering structure units, the silt mixture 8 being prepared by mixing quicklime, polyacrylamide, and slag at a ratio of 10%, 0.5%, and 20% respectively of the dry weight of the silt, and a water content of 45%-55% with the silt; repeating step S3 to lay the next layer of filtering structure units, and then filling the silt mixture 8 above the layer of filtering structure units, and so on until the double-layer steel sheet piles 1 are filled to the designed height.

[0049] S5: Installing the pressure transmission assembly and jack 2: placing the HDPE waterproof membrane 7 and square wood board 6 successively above the uppermost layer of silt mixture 8; installing the jack 2 at the lower end of the U-shaped support 3 and setting the force transmission column 5 between the jack 2 and the square wood board 6.

[0050] S6: Burying the drain pipe 4 and draining: simultaneously with the construction of steps S3-S5, burying the PVC drain pipe 4, setting the drain holes 4-2 at intervals on the drain pipe 4, wrapping the drain holes 4-2 with the drain pipe filter screen 4-1, wrapping the joint positions of the drain pipe 4 with waterproof coiled material and winding and sealing with waterproof tape; ensuring that the setting height of the drain holes 4-2 is consistent with the overall height of each layer of pebble layer 9 and steel reinforcement cage 11, and is flush with the corresponding layer of pebble layer 9 and steel reinforcement cage 11; draining the water squeezed out of the silt mixture 8 through the drain pipe 4.

[0051] S7: Pressurizing and shaping: starting the jack 2 to push the square wood board 6 to compress the silt mixture 8 through the force transmission column 5.

[0052] During construction, the steel sheet piles are applied according to the process, the trench is cleaned and plugged, multiple layers of repeated filtering structure units are laid, the silt mixture 8 is filled, the pressure transmission assembly and jack 2 are installed, the drain pipe 4 is buried simultaneously, and the pressurizing and shaping is performed, which can ensure the construction quality and improve the supporting effect, the cleaning and plugging reduces impurities and water leakage hazards, the layered construction and simultaneous pipe burying ensure the structure to be compact and the drainage to be smooth, and the pressurizing and shaping improves the strength of the silt mixture 8.

[0053] Example Four, with reference to Figs. 1~5On the basis of Embodiment Three, in S1, the spacing of the double-layer steel sheet piles 1 is 0.5-1 meter, and the steel sheet piles 1 are driven into the rock layer or the non-pervious layer; in S2, a micro single-shaft mixer and a high-pressure jet mixing device are used to clean the trench, and the soil and sludge in the trench are flushed into cement slurry and discharged; a water-blocking coiled material is pasted to block the water leakage position; the stability of the foundation support is strengthened, the impurities in the trench are completely removed, and the waterproof property is improved, the reasonable spacing and the driving depth are adapted to the water and soil pressure, the professional trench cleaning is complete, and the water-blocking coiled material can effectively block the gaps between the steel sheet piles 1. In S7, the compression molding height of each layer of sludge mixture 8 is 2 meters, and a sludge mixture 8 compression test is performed before construction to determine the compression ratio, and the amount of sludge mixture 8 to be mixed and placed each time is calculated according to the compression ratio; the density of each layer is ensured, and the material is accurately used to avoid waste, the fixed compression height facilitates unified quality control, and the compression ratio obtained by the test in advance can accurately calculate the amount of material to adapt to the molding requirements. Further comprising the following steps: if the support period is within 3 months, periodically check the reading of the jack 2 during construction, monitor the stress state of the structure in real time, and ensure the stability of the enclosure system; if the support period is greater than 3 months, in addition to periodically checking the reading of the jack 2 during construction, an HDPE waterproof membrane 7 is also laid on the uppermost layer of sludge mixture 8, and 5-10 centimeters thick concrete is poured to seal the top, and the distance between the upper layer of the uppermost layer of sludge mixture 8 and the top of the steel sheet pile 1 is not less than 10 centimeters; after the cofferdam construction is completed, the jack 2, the U-shaped support 3, and the steel sheet pile 1 are removed; adapt to different support period requirements and ensure long-term stability, realize core material recycling, regularly read the structure stress, top sealing treatment enhances the waterproof property and structural stability of the top, and the removal operation realizes the reuse of the steel sheet pile 1 and other materials.

[0054] Working principle: Double-layer steel sheet pile 1 serves as the outer wall of the two sides of the foundation pit, the spacing is controlled at 0.5-1 meter and is punched into the rock layer or non-pervious layer, providing foundation support for the entire enclosure structure, the U-shaped support 3 is installed on the upper end of the double-layer steel sheet pile 1, playing a role in connecting and fixing the double-layer steel sheet pile 1 and preventing relative displacement, and at the same time providing a stable installation platform for the jack 2. The multi-layer repeated filtration structure unit is the core of realizing waterproofing and seepage water collection, among which the pebble layer 9 is spread between the double-layer steel sheet pile 1, with a minimum thickness of not less than 5 centimeters, which can not only support the weight of the upper structure, but also preliminarily filter seepage water; the steel wire mesh layer 10 is laid below the pebble layer 9, with a hollow spacing of not less than 1 centimeter, which can intercept fine particles in the silt mixture 8 to avoid subsequent structure blockage; the steel reinforcement cage 11 is laid below the steel wire mesh layer 10, with a width consistent with the spacing of the double-layer steel sheet pile 1 and a height of 5 centimeters, and the steel reinforcement hole spacing is not more than 3 centimeters with the waist and hoop bending anchors inward, which not only will not pierce the HDPE waterproof membrane 7 below, but also can collect seepage water filtered by the pebble layer 9 and the steel wire mesh layer 10 as a water storage layer; the HDPE waterproof membrane 7 is laid below the steel reinforcement cage 11, which can effectively cut off the bottom water source and prevent external water from seeping into the foundation pit. The silt mixture 8 is filled below, above and between the multi-layer repeated filtration structure unit, which is made of lime, polyacrylamide and slag in a proportion of 10%, 0.5% and 20% of the dry weight of silt respectively, and mixed with silt with a water content of 45%-55%, which not only realizes the resource utilization of silt, but also provides a certain structural strength for the enclosure structure. The PVC drainage pipe 4 is buried between the double-layer steel sheet pile 1, the splicing position is wrapped with waterproof coiled material and wrapped with waterproof tape to ensure sealing, drainage holes 4-2 are arranged on the drainage pipe 4, the outer side of the drainage hole 4-2 is wrapped with a drainage pipe filter screen 4-1 to prevent silt from blocking, and the drainage hole 4-2 is set at a height consistent with the total height of the pebble layer 9 and the steel reinforcement cage 11, and the corresponding parts are flush, so that the water squeezed out of the silt mixture 8 can be sequentially filtered by the pebble layer 9, intercepted by the steel wire mesh layer 10, and then enter the steel reinforcement cage 11, and then filtered again by the drainage hole 4-2 and the drainage pipe filter screen 4-1 into the drainage pipe 4, and finally discharged outside the enclosure structure, forming a complete seepage water collection and discharge process.

[0055] The pressure transmission assembly is responsible for uniformly transmitting the pressure of the jack 2 to the sludge mixture 8, which comprises the square wood plate 6 and the force transmission column 5, wherein the square wood plate 6 and the HDPE waterproof film 7 are sequentially placed above the uppermost layer of the sludge mixture 8, the HDPE waterproof film 7 can prevent the moisture in the sludge mixture 8 from penetrating upwards to the square wood plate 6, and the force transmission column 5 is arranged between the jack 2 and the square wood plate 6, which is used to make up for the insufficient length of the jack 2 and ensure that the pressure can be effectively transmitted. The jack 2 is installed at the lower end of the U-shaped support 3 and abuts against the U-shaped support 3 at the top, after the jack 2 is started, the pressure generated by the jack 2 is transmitted to the square wood plate 6 through the force transmission column 5, and then the square wood plate 6 uniformly disperses the pressure to the uppermost layer of the sludge mixture 8, so that the sludge mixture 8 is compressed, and the compression forming height of each layer of the sludge mixture 8 is 2 meters. Before construction, a sludge mixture 8 compression test is performed to determine the compression ratio, and then the amount of sludge mixture 8 to be mixed and placed each time is calculated according to the compression ratio, so as to ensure that the thickness of the sludge mixture 8 after compression meets the design requirements. In the compression process, the moisture in the sludge mixture 8 is further discharged, and the structure strength can be gradually improved to the enclosure requirement standard by the reinforcing effect of quicklime, polyacrylamide and slag. Differentiated treatment is adopted for different support periods: if the support period is within 3 months, only the reading of the jack 2 needs to be checked regularly to monitor the stress state of the structure in real time to ensure the stability of the enclosure system; if the support period is greater than 3 months, the HDPE waterproof film 7 needs to be laid on the uppermost layer of the sludge mixture 8, and 5-10 centimeters thick concrete needs to be poured to seal the top, and the distance between the upper layer of the uppermost layer of the sludge mixture 8 and the top of the steel sheet pile 1 is not less than 10 centimeters, so as to enhance the waterproofness and structural stability of the top, after the cofferdam construction is completed, the jack 2 and the U-shaped support 3 are removed, and finally the steel sheet pile 1 is pulled out, and the finishing work of the whole foundation pit enclosure is completed.

[0056] Finally, it should be noted that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features, as long as they are within the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the scope of the present application shall be included in the protection scope of the present application.

Claims

1. A river and lake silt foundation retaining structure, comprising a double-layer steel sheet pile (1), a U-shaped support (3), a multi-layer repeated filter structure unit, a silt mixture (8), a jack (2), a drain pipe (4) and a pressure transmission assembly, characterized in that: The double-layer steel sheet pile (1) is used as the outer wall of both sides of the foundation pit, and the U-shaped support (3) is installed on the upper end of the double-layer steel sheet pile (1); the multi-layer repeated filtering structure unit comprises a pebble layer (9), a steel wire filter screen layer (10), a steel reinforcement cage (11) and an HDPE waterproof film (7), the pebble layer (9) is paved between the double-layer steel sheet piles (1), the steel wire filter screen layer (10) is laid below the pebble layer (9), the steel reinforcement cage (11) is laid below the steel wire filter screen layer (10), and the HDPE waterproof film (7) is laid below the steel reinforcement cage (11); The silt mixture (8) is filled below, above and between the multi-layer repeated filtering structure unit, the jack (2) is installed at the lower end of the U-shaped support (3), and the top of the jack (2) is tightly abutted against the U-shaped support (3) to realize stable force transmission; the pressure transmission assembly is arranged between the jack (2) and the silt mixture (8) and is used for uniformly transmitting the pressure of the jack (2) to the silt mixture (8); and the drain pipe (4) is buried between the double-layer steel sheet piles (1) and is used for draining water squeezed out of the silt mixture (8).

2. The retaining structure for a river or lake silt foundation according to claim 1, wherein: The spacing of the double-layer steel sheet pile (1) is 0.5-1 m, and the steel sheet pile (1) is driven into a rock layer or a non-pervious layer; and the minimum thickness of the pebble layer (9) is not less than 5 cm.

3. The retaining structure for a river or lake silt foundation according to claim 1, wherein: The width of the steel reinforcement cage (11) is consistent with the spacing of the double-layer steel sheet pile (1), the height of the steel reinforcement cage (11) is 5 cm, the spacing of the steel reinforcement holes of the steel reinforcement cage (11) is not greater than 3 cm, and the waist rib and the hoop of the steel reinforcement cage (11) are bent inward; and the spacing of the holes of the steel wire filter screen layer (10) is not less than 1 cm.

4. The retaining structure for a river or lake silt foundation according to claim 1, wherein: The silt mixture (8) is prepared by stirring quicklime, polyacrylamide, slag and silt, wherein the proportions of the quicklime, the polyacrylamide and the slag in the dry weight of the silt are 10%, 0.5% and 20% respectively, and the water content of the silt is 45%-55%.

5. The retaining structure for a river and lake silt foundation according to claim 1, wherein: The pressure transmission assembly comprises a square wood board (6) and a force transmission column (5), the square wood board (6) and the HDPE waterproof film (7) are sequentially arranged above the uppermost layer of the silt mixture (8), and the force transmission column (5) is arranged between the jack (2) and the square wood board (6).

6. The retaining structure for a river and lake silt foundation according to claim 1, wherein: The drain pipe (4) is a PVC pipe, drainage holes (4-2) are arranged at intervals on the drain pipe (4), a drain pipe filter screen (4-1) is wrapped outside the drainage holes (4-2), the joint positions of the drain pipe (4) are wrapped with waterproof coiled material and are wound with waterproof adhesive tape; the height of the drainage holes (4-2) is consistent with the total height of the pebble layer (9) and the steel reinforcement cage (11), and the drainage holes (4-2) and the wrapped drain pipe filter screen (4-1) are flush with the pebble layer (9) and the steel reinforcement cage (11).

7. A construction method of a retaining structure for a river and lake sludge foundation pit, characterized by, The method comprises the following steps: S1: double-layer steel sheet piles (1) are used as the outer wall of both sides of the foundation pit, and U-shaped supports (3) are installed on the upper ends of the double-layer steel sheet piles (1); S2: the grooves of the double-layer steel sheet piles (1) are cleaned and the mud slurry is discharged, and the leaking parts between the steel sheet piles (1) which are not tightly connected are plugged. S3: Laying multiple layers of repeated filtering structure units: spreading a minimum thickness of not less than 5 cm of gravel layer (9) between the double-layer steel sheet piles (1); laying a steel wire filter screen layer (10) with a hole spacing of not less than 1 cm below the gravel layer (9); laying a steel reinforcement cage (11) below the steel wire filter screen layer (10), the steel reinforcement cage (11) has a width consistent with the spacing of the double-layer steel sheet piles (1) and a height of 5 cm, the waist rib and hoop of the steel reinforcement cage (11) are bent inward, and the steel reinforcement hole spacing is not greater than 3 cm; laying an HDPE waterproof membrane (7) below the steel reinforcement cage (11) to complete the laying of the first layer of filtering structure unit; S4: Filling silt mixture (8) and repeated construction: filling the silt mixture (8) above the first layer of filtering structure unit, the silt mixture (8) is made by mixing quicklime, polyacrylamide, and slag at a ratio of 10%, 0.5%, and 20% of the dry weight of the silt respectively, and silt with a water content of 45%-55%; repeating step S3 to lay the next layer of filtering structure unit, and filling the silt mixture (8) above the layer of filtering structure unit, and repeating the cycle until the double-layer steel sheet piles (1) are filled to the designed height; S5: Installing pressure transmission assembly and jack (2): placing the HDPE waterproof membrane (7) and square wood board (6) successively above the uppermost layer of silt mixture (8); installing the jack (2) at the lower end of the U-shaped support (3) and setting the force transmission column (5) between the jack (2) and the square wood board (6); S6: Burying drainage pipe (4) and draining water: synchronizing the construction of steps S3-S5, burying the PVC drainage pipe (4), setting the drainage holes (4-2) on the drainage pipe (4) at intervals, wrapping the drainage holes (4-2) with the drainage pipe filter screen (4-1) on the outside, wrapping the joint position of the drainage pipe (4) with waterproof roll material and winding it with waterproof tape for sealing; ensuring that the setting height of the drainage holes (4-2) is consistent with the total height of each layer of gravel layer (9) and steel reinforcement cage (11), and is flush with the corresponding parts of the gravel layer (9) and steel reinforcement cage (11) of the layer; draining the water squeezed out of the silt mixture (8) through the drainage pipe (4); S7: Pressurizing and shaping: starting the jack (2) to push the square wood board (6) to compress the silt mixture (8) through the force transmission column (5).

8. The construction method of a river and lake silt foundation pit enclosure structure according to claim 7, characterized in that: In S1, the spacing of the double-layer steel sheet piles (1) is 0.5-1 m, and the steel sheet piles (1) are driven into the rock layer or non-porous layer; In S2, a mini single-shaft mixer and a high-pressure jet mixing device are used to clean the trench, and the soil and silt in the trench are washed into cement slurry and discharged; the leakage part is plugged by pasting waterproof roll material.

9. The construction method of a river and lake silt foundation pit enclosure structure according to claim 7, characterized in that: In S7, the compression and shaping height of each layer of silt mixture (8) is 2 m, and a silt mixture (8) compression test is conducted before construction to determine the compression ratio, and the amount of silt mixture (8) to be mixed and placed each time is calculated according to the compression ratio.

10. The method according to claim 7, wherein the method is characterized by: Further comprising the following steps: If the supporting period is within 3 months, the jack (2) reading is checked regularly during construction, the structural stress state is monitored in real time, and the stability of the enclosure system is ensured. If the supporting period is greater than 3 months, in addition to regularly checking the reading of the jack (2) during construction, an HDPE waterproof membrane (7) is also laid on the top of the uppermost layer of silt mixture (8), and a 5-10 cm thick concrete top is poured, and the distance between the upper layer of the uppermost layer of silt mixture (8) and the top of the steel sheet pile (1) is not less than 10 cm; after the cofferdam construction is completed, the jack (2), U-shaped support (3) are removed, and the steel sheet pile (1) is pulled out.

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