A method for treating the transition zone of cofferdam mud by drainage consolidation combined with vibrating crushed stone piles

Abstract

The present invention belongs to the field of foundation treatment, and in particular, relates to a method for treating the transition zone between cofferdam and mud by combining drainage and consolidation with vibro-compaction crushed stone piles. The method comprises: surveying the interface between the earth-rock cofferdam and the mud-containing area; construction preparation; electro-osmosis drainage and consolidation in the mud-containing area; vibro-compaction treatment of the mud-rock interface and the mud-containing area; leveling and compaction; and quality inspection. The present invention effectively solves the difficulties in the foundation treatment of the transition zone between cofferdam and mud by combining the two technologies of electro-osmosis drainage and consolidation and vibro-compaction treatment through precise geological survey and personalized construction parameter setting, improves the stability and bearing capacity of the foundation, and provides a reliable foundation treatment solution for offshore land reclamation projects. The present invention can significantly solve the problem of poor rigid transition during the foundation treatment of the transition zone, and reduce uneven settlement in the later stage.

Description

Technical Field

[0001] The invention belongs to the field of foundation treatment, and in particular relates to a method for treating a cofferdam mud-intake transition zone by combining drainage consolidation with vibro-stone piles. Background Art

[0002] With the rapid development of civil engineering, the research and development and application of various foundation treatment technologies have become particularly important. Especially in the construction of water transport and transportation infrastructure, it is often necessary to deal with various complex foundation conditions. Among them, in the process of land reclamation construction, the foundation treatment of the transition zone between the earth-rock cofferdam and the mud receiving area is a typical problem. Such areas usually have complex geological conditions, high soil water content, poor stability, and great differences in soil properties between the cofferdam and the mud receiving area, which brings great problems and challenges to foundation treatment.

[0003] The cofferdam mud filling transition zone is located between the mud filling zone and the earth-rock cofferdam. It is a slope transition section between two different backfill materials (usually upper mud and lower stone). Due to the complex geological structure, low foundation bearing capacity and poor stability in this area, it poses great challenges to engineering construction. Traditional foundation treatment methods are often difficult to adapt to this special geological condition and cannot meet the requirements of the project for foundation bearing capacity and stability.

[0004] Traditional foundation treatment methods such as replacement and compaction can improve the bearing capacity of the foundation to a certain extent, but the effect is not ideal when dealing with special foundations such as earth-rock cofferdams and silt transition zones. The replacement method requires a large amount of filler, which is not only costly but also has a long construction period; the compaction method is limited by the soil moisture content and it is difficult to achieve an ideal compaction effect.

[0005] The Chinese invention patent (CN101182709A) discloses a method and device for strengthening the foundation by composite electroosmosis, vacuum dewatering and vacuum preloading, but it is only applicable to various types of soil with a permeability coefficient of less than 10 in a large area. -5 The method of reinforcing the soft soil foundation with a flow rate of 1.5 cm / s has limitations and is not suitable for the transition zone between the cofferdam and the mud filling. It is impossible to perform foundation treatment on the hard backfill material part of the cofferdam, and it cannot solve the problem of good connection of the transition section of the cofferdam slope. Especially in the contact area between the cofferdam and the mud filling, in order to ensure that the vacuum preloading does not leak, a silt layer of at least 1m must be reserved. After the precipitation work is completed, the strong tamping treatment will leave a silt interlayer on the upper part of the cofferdam, which will pose a major quality risk and cannot meet the requirements of rigid transition, uniform settlement and high bearing capacity.

[0006] A Chinese invention patent (CN106284293A) discloses a system and method for vacuum preloading combined with electroosmosis to reinforce soft soil foundations. However, this method is only applicable to soft soil foundations and cannot reinforce the geology at the junction of the mud receiving area and the earth-rock cofferdam, and cannot meet the requirements of rigid transition.

[0007] Therefore, a more efficient and economical treatment method is urgently needed for the foundation treatment of the transition zone between earth-rock cofferdam and silt. Summary of the invention

[0008] In order to solve the common problem of complex foundation treatment of mud-rock connection structure in the transition zone of cofferdam and mud formed in the process of land reclamation, the present invention proposes a method for treating the transition zone of cofferdam and mud by drainage consolidation combined with vibro-compaction crushed stone piles. The method comprehensively reinforces the foundation through a series of steps including geological survey, construction preparation, electro-osmosis drainage consolidation, vibro-compaction, leveling and rolling, and quality inspection.

[0009] To achieve the above purpose, the technical solution of the present invention is as follows:

[0010] A method for treating a cofferdam mud-intake transition zone by drainage consolidation combined with vibrating crushed stone piles, characterized in that it comprises the following steps:

[0011] S1: Survey of the interface between the earth-rock cofferdam and the mud receiving area. The survey adopts the drilling method, with drilling points arranged at a hole spacing of 10 meters, penetrating the mud-rock interface and obtaining core sample information, thereby obtaining the height of the mud-rock interface, and drawing a detailed geological profile based on these data to fully reflect the geological characteristics of the interface between the earth-rock cofferdam and the mud receiving area;

[0012] S2: Construction preparation;

[0013] S3: Electroosmotic drainage consolidation in mud receiving area. The electroosmotic drainage consolidation drainage board is arranged in a square with a spacing of 1.0m during installation. The installation depth is based on the survey results of the interface between the earth-rock cofferdam and the mud receiving area in step S1, and is installed in different lengths according to the cross-section diagram of the transition zone, so that the bottom of the drainage board is 0.5m away from the mud-rock interface to prevent air leakage, and the exposed length is not less than 0.3m;

[0014] S4: Vibration treatment of mud-rock interface and mud-receiving area. After the electro-osmosis drainage and consolidation of mud-receiving area are completed, the process of vibrating crushed stone pile construction is adopted. The vibrating crushed stone piles are arranged in an equilateral triangle at the mud-rock interface and mud-receiving area, with a pile spacing of 2.5m. The rear row of piles in the mud-receiving area is arranged in an equilateral triangle with a spacing of 4.0m. The vibrating crushed stone piles enter the earth-rock cofferdam at the mud-rock interface by no less than 1.0m.

[0015] S5: Leveling and rolling: Use a bulldozer to remove debris and obstacles on the surface of the site and perform preliminary site leveling; use a roller to perform rolling operations to compact the site;

[0016] S6: Quality inspection: after the reinforcement is completed, the bearing capacity of the foundation in the transition area is inspected.

[0017] In the step S4, the front row of vibro-stone piles in the mud receiving area refers to the first four rows of piles; the setting of the pile spacing can be adjusted according to the foundation conditions and engineering requirements, and the adjustment range of the vibro-stone pile spacing is 2.5~4.0m, which specifically includes the following steps:

[0018] S401: Level the site and measure and place the piles;

[0019] S402: Drilling at the pile position, using a vibrating hammer to assist in the burying of the steel casing. After the positioning of the steel casing is completed, the surveyor verifies the pile centerline position. If it meets the requirements, the drilling equipment is used to drill, and the steel casing follows up to protect the wall to prevent the hole from collapsing during the drilling process;

[0020] S403: The pile driver is in place and vibrates to form holes. A crane is used to lift the 180kW vibrator to a position vertically above the setting point. The crane slowly lowers the vibrator. According to the pile forming requirements, various construction parameters are controlled and the holes are vibrated according to the set parameters.

[0021] During the process of vibrating and drilling holes, the vibrator should be kept vertical, and close attention should be paid to whether the vibrator is deviated. Once the vibrator is found to be tilted, timely adjustments should be made; during the vibrating process, water should be kept flowing out of the nozzle to prevent the nozzle from being blocked by sand and soil, and the vibrator should be slowly sunk until it reaches the designed elevation. At this depth, the vibrator should keep vibrating for 30 to 60 seconds, and then slowly lifted by 0.5m;

[0022] S404: Filling gravel and vibrating to form piles. Use a loader to transport the materials to the vicinity of the pile hole, and manually add stones into the hole. The particle size of the gravel filler is 40-80mm. When the vibrator reaches the vibration current and vibration retention time specified in the design, the piles are lifted in sections and constructed section by section. Repeat this step until the entire depth is compacted.

[0023] S405: Clean the hole, lift the vibrator out of the hole mouth, and then quickly penetrate from the original hole 1-3 times to make the pile hole unblocked; turn off the vibrator and high-pressure water pump, and the pile making is completed.

[0024] In step S1, a geological survey is conducted on the cofferdam mud transition zone before construction to find out the mud thickness of each section so as to determine the depth of the drainage board and the vibro-compacted gravel pile.

[0025] The step S3 specifically includes the following steps:

[0026] S301: Survey and lay out the transition area, lay out the construction area, set up the boundary stakes, and make sure the location of the conductive plastic drainage board is set;

[0027] S302: Lay geotextile. According to the actual situation on site, lay a layer of 200g / m2 on the original mud surface. 2 woven cloth;

[0028] S303: Make drainage boards and filter pipes. Conductive plastic drainage boards are existing products pre-produced by manufacturers. They are cut into the required length at the processing site as vertical drainage channels. The lower end is wrapped with non-woven fabric or filter cloth to prevent mud contamination. Filter pipes are soft permeable pipes, which are centrally produced in factories. After the pipe body is punched and wrapped with permeable filter cloth, it is rolled and transported to the construction site.

[0029] S304. Install vertical plastic drain boards. The vertical conductive plastic drain boards are laid in a square arrangement with a spacing of 1m. The depth of penetration into the mud is divided into different lengths according to the transition zone cross-section diagram, so that the bottom of the drain board is 0.5m away from the mud-stone interface and the exposed length is not less than 0.3m. The installation is done manually, and the conductive plastic drain boards are installed to the design required depth with the help of casing equipment;

[0030] S305: Lay and connect the filter pipe. The upper end of the conductive plastic drain board is connected to the filter pipe by winding and wrapping it with non-woven fabric. After the connection is completed, a layer of 150g / ㎡ geotextile is wrapped at the connection between the drain board and the filter pipe to prevent soil particles from entering the silt. Then the other end of the filter pipe is connected to the main pipe.

[0031] S306: Lay geotextile and sealing membrane. The sealing membrane is pre-customized by the manufacturer according to the size of the vacuum preloading area to be carried out in the next step. The size of the whole sealing membrane is guaranteed to cover the entire vacuum preloading area at one time. During processing, the size of the membrane should be considered to be buried in the sealing groove, leaving enough surplus. The seams of the sealing membrane are firmly bonded, and the width of the double heat-sealed flat lap seam shall not be less than 15mm.

[0032] S307: Test vacuuming. After all vacuuming equipment is in place, test vacuuming is started to form a vacuum pre-pressing area. In the initial stage, the rate of vacuum pressurization is controlled. As the air under the membrane is discharged and the drainage and consolidation degree of the soil layer increases, the vacuum degree inside the membrane gradually increases and stabilizes above 60kPa. At the beginning of the vacuuming stage, as the air and water are discharged, the sealing state of the sealing membrane and the sealing groove is fully checked. If there is any leakage, the leaking part is repaired and sealed in time to prevent affecting the vacuum effect.

[0033] S308: Preloading by vacuum combined with electroosmosis, start the vacuum pump, and pass current through the drainage board to drain and consolidate; first start the vacuum pump to draw a vacuum, and at the same time start the power supply to start electroosmosis, vacuum preloading and electroosmosis are carried out simultaneously, the vacuum is transmitted from the horizontal drainage main pipe to the horizontal drainage branch pipe, and then to the drainage electrode and the cavity of the plastic drainage board, and diffuses into the foundation, the current is conducted through the wire, the drainage electrode and the soil between the electrodes, forming an electric potential difference between the anode and the cathode, on the one hand, the free water in the soft foundation flows into the plastic drainage board and the drainage electrode under the action of the vacuum negative pressure. The water molecules are gathered through the filter cloth and the small holes on the electrode steel pipe into the drainage electrode cavity, and are discharged under the vacuum negative pressure in the drainage pipe. On the other hand, water molecules are polar and are gathered from the anode to the cathode under the action of the potential difference. The electroosmosis increases the activity of water molecules and accelerates the penetration rate. At the same time, the electroosmosis also acts on the bound water in the soil, prompting the bound water to break away from the constraints of the soil particles and be discharged, further reducing the water content of the soil. Under the combined action of vacuum and electroosmosis, the soil is quickly drained and consolidated, and the foundation produces consolidation settlement. When the settlement reaches the unloading standard, the construction is stopped.

[0034] In step S304, the drainage boards are arranged in a square with a spacing of 1m. Each 3×3 electrodes form a group. The eight electrodes around are anodes and the central electrode is cathode, which are connected to the positive and negative electrodes of the power supply respectively. The depth is 5m. The filter tube uses a UPVC plastic tube with a diameter of 50mm. A small hole with a diameter of 8mm is drilled every 5cm on the tube wall to make a flower tube, which is covered with a layer of 90g / m 2 Non-woven geotextile.

[0035] The vacuum pumping equipment in step S307: a jet vacuum pump is used, the power of the single machine is not less than 7.5kW, the vacuum pressure of the single machine is not less than 96kPa, the potential gradient of the power output is generally not more than 0.5V / cm, the voltage is less than 60V, and the current density is not more than 50A / m 2 , the electrode conversion cycle is once a week.

[0036] The drainage board length setting, vibro-stone pile length setting, and pile spacing setting are all individually adjusted according to geological survey results and engineering requirements. The vibro-stone pile spacing adjustment range is 2.5~4.0m to meet the foundation treatment needs in different areas and under different conditions.

[0037] The geological structure of the cofferdam mud-intake transition zone is: during the offshore land reclamation process, the transition zone where the mud-intake zone connects with the earth-rock cofferdam. This area is a slope transition section of two different backfill materials, with an upper mud and lower rock structure.

[0038] The innovative points of the present invention are:

[0039] (1) The present invention adopts a triangularly arranged drainage board. By accurately controlling the installation depth and spacing of the drainage board, it is ensured that the drainage board can effectively drain the moisture in the foundation under special geological conditions, improve the density and stability of the foundation, and provide good construction conditions for subsequent vibroflotation treatment.

[0040] (2) The present invention makes personalized adjustments to the length of the drainage board according to geological survey results and engineering requirements to meet the foundation treatment requirements in different areas and under different conditions, ensuring the drainage effect while avoiding leakage that affects the quality effect.

[0041] (3) The present invention adopts a construction process of following up with casing after drilling a hole, and reinforces the foundation through vibro-stone piles. The front row of vibro-stone piles in the mud-rock interface area and the mud receiving area are arranged in an equilateral triangle, and the rear row of piles are arranged in an equilateral triangle. The pile spacing is optimized and adjusted according to the foundation conditions and engineering requirements. This arrangement can give full play to the reinforcement effect of vibro-stone piles, improve the bearing capacity and stability of the foundation, ensure rigid transition conditions, and improve construction efficiency.

[0042] (4) Close integration of geological survey and construction preparation: The present invention takes the geological survey results as an important basis for construction preparation, and ensures the optimization of foundation treatment effect through precise geological survey and scientific construction preparation.

[0043] (5) Strong adaptability: The present invention is suitable for foundation treatment in the cofferdam-mud transition zone under different geological conditions and engineering requirements, and has strong adaptability and promotion value.

[0044] The present invention effectively solves the problems of uneven settlement and rigid transition after foundation treatment in the transition zone, combines two different foundation treatment processes, complements their advantages, and solves the problem of special geological conditions that conventional foundation treatment processes cannot solve. It is a new type of composite foundation treatment process, and has the characteristics of high construction efficiency, uniform settlement, and fast construction speed, and can significantly improve the bearing capacity of the foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a typical cross-section of the transition zone;

[0046] Figure 2 This is a typical cross-section diagram of drainage consolidation construction:

[0047] Figure 3 This is a typical cross-section diagram of vibro-stone pile construction;

[0048] Figure 4 This is a schematic diagram of the layout of the conductive plastic drainage board;

[0049] Figure 5 This is a schematic diagram of vibro-compacted stone pile layout in the Nani area;

[0050] In the figure: 1 earth-rock cofferdam area, 2 mud receiving area, 3 in-situ silt area, 4 anode drainage board, 5 cathode drainage board. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited to the specific embodiments. Example 1

[0052] See attached Figure 1 to Figure 5 The construction method shown comprises the following steps:

[0053] A method for treating a cofferdam mud-intake transition zone by drainage consolidation combined with vibrating crushed stone piles comprises the following steps:

[0054] S1: Survey of the interface between the earth-rock cofferdam and the mud receiving area. The survey adopts the drilling method, with drilling points arranged at a hole spacing of 10 meters, penetrating the mud-rock interface and obtaining core sample information, thereby obtaining the height of the mud-rock interface, and drawing a detailed geological profile based on these data to fully reflect the geological characteristics of the interface between the earth-rock cofferdam and the mud receiving area;

[0055] S2: Construction preparation;

[0056] S3: Electroosmotic drainage consolidation in mud receiving area. The electroosmotic drainage consolidation drainage board is arranged in a square with a spacing of 1.0m during installation. The installation depth is based on the survey results of the interface between the earth-rock cofferdam and the mud receiving area in step S1, and is installed in different lengths according to the cross-section diagram of the transition zone, so that the bottom of the drainage board is 0.5m away from the mud-rock interface to prevent air leakage, and the exposed length is not less than 0.3m;

[0057] S4: Vibration treatment of mud-rock interface and mud-receiving area. After the electro-osmosis drainage and consolidation of mud-receiving area are completed, the process of vibrating crushed stone pile construction is adopted. The vibrating crushed stone piles are arranged in an equilateral triangle at the mud-rock interface and mud-receiving area, with a pile spacing of 2.5m. The rear row of piles in the mud-receiving area is arranged in an equilateral triangle with a spacing of 4.0m. The vibrating crushed stone piles enter the earth-rock cofferdam at the mud-rock interface by no less than 1.0m.

[0058] S5: Leveling and rolling: Use a bulldozer to remove debris and obstacles on the surface of the site and perform preliminary site leveling; use a roller to perform rolling operations to compact the site;

[0059] S6: Quality inspection: after the reinforcement is completed, the bearing capacity of the foundation in the transition area is inspected.

[0060] In step S4, the front row of vibro-stone piles in the mud-rock interface area and the mud receiving area refers to the first four rows of piles; the setting of the pile spacing is further optimized and adjusted according to the foundation conditions and engineering requirements, specifically including the following steps:

[0061] S401: Level the site and measure and place the piles;

[0062] S402: Drilling at the pile position, using a vibrating hammer to assist in the burying of the steel casing. After the positioning of the steel casing is completed, the surveyor verifies the pile centerline position. If it meets the requirements, the drilling equipment is used to drill, and the steel casing follows up to protect the wall to prevent the hole from collapsing during the drilling process;

[0063] S403: The pile driver is in place and vibrates to form holes. A crane is used to lift the 180kW vibrator to a position vertically above the setting point. The crane slowly lowers the vibrator. According to the pile forming requirements, various construction parameters are controlled and the holes are vibrated according to the set parameters.

[0064] During the process of vibrating and drilling holes, the vibrator should be kept vertical, and close attention should be paid to whether the vibrator is deviated. Once the vibrator is found to be tilted, timely adjustments should be made; during the vibrating process, water should be kept flowing out of the nozzle to prevent the nozzle from being blocked by sand and soil, and the vibrator should be slowly sunk until it reaches the designed elevation. At this depth, the vibrator should keep vibrating for 30 to 60 seconds, and then slowly rise 0.5m;

[0065] S404: Filling gravel and vibrating to form piles. Use a loader to transport the materials to the vicinity of the pile hole, and manually add stones into the hole. The particle size of the gravel filler is 40-80mm. When the vibrator reaches the vibration current and vibration retention time specified in the design, the piles are lifted in sections and constructed section by section. Repeat this step until the entire depth is compacted.

[0066] S405: Clean the hole, lift the vibrator out of the hole mouth, and then quickly penetrate from the original hole 1-3 times to make the pile hole unblocked; turn off the vibrator and high-pressure water pump, and the pile making is completed.

[0067] In step S1, a geological survey is conducted on the cofferdam mud transition zone before construction to find out the mud thickness of each section so as to determine the depth of the drainage board and the vibro-compacted gravel pile.

[0068] The step S3 specifically includes the following steps:

[0069] S301: Survey and lay out the transition area, lay out the construction area, set up the boundary stakes, and make sure the location of the conductive plastic drainage board is set;

[0070] S302: Lay geotextile. According to the actual situation on site, lay a layer of 200g / m2 on the original mud surface. 2 woven cloth;

[0071] S303: Make drainage boards and filter pipes. Conductive plastic drainage boards are existing products pre-produced by manufacturers. They are cut into the required length at the processing site as vertical drainage channels. The lower end is wrapped with non-woven fabric or filter cloth to prevent mud contamination. Filter pipes are soft permeable pipes, which are centrally produced in factories. After the pipe body is punched and wrapped with permeable filter cloth, it is rolled and transported to the construction site.

[0072] S304. Install vertical plastic drain boards. The vertical conductive plastic drain boards are laid in a square arrangement with a spacing of 1m. The depth of penetration into the mud is divided into different lengths according to the transition zone cross-section diagram, so that the bottom of the drain board is 0.5m away from the mud-stone interface and the exposed length is not less than 0.3m. The installation is done manually, and the conductive plastic drain boards are installed to the design required depth with the help of casing equipment;

[0073] S305: Lay and connect the filter pipe. The upper end of the conductive plastic drain board is connected to the filter pipe by winding and wrapping it with non-woven fabric. After the connection is completed, a layer of 150g / ㎡ geotextile is wrapped at the connection between the drain board and the filter pipe to prevent soil particles from entering the silt. Then the other end of the filter pipe is connected to the main pipe.

[0074] S306: Lay geotextile and sealing membrane. The sealing membrane is pre-customized by the manufacturer according to the size of the vacuum preloading area to be carried out in the next step. The size of the whole sealing membrane is guaranteed to cover the entire vacuum preloading area at one time. During processing, the size of the membrane should be considered to be buried in the sealing groove, leaving enough surplus. The seams of the sealing membrane are firmly bonded, and the width of the double heat-sealed flat lap seam shall not be less than 15mm.

[0075] S307: Test vacuuming. After all vacuuming equipment is in place, test vacuuming is started to form a vacuum pre-pressing area. In the initial stage, the rate of vacuum pressurization is controlled. As the air under the membrane is discharged and the drainage and consolidation degree of the soil layer increases, the vacuum degree inside the membrane gradually increases and stabilizes above 60kPa. At the beginning of the vacuuming stage, as the air and water are discharged, the sealing state of the sealing membrane and the sealing groove is fully checked. If there is any leakage, the leaking part is repaired and sealed in time to prevent affecting the vacuum effect.

[0076] S308: Preloading by vacuum combined with electroosmosis, start the vacuum pump, and pass current through the drainage board to drain and consolidate; first start the vacuum pump to draw a vacuum, and at the same time start the power supply to start electroosmosis, vacuum preloading and electroosmosis are carried out simultaneously, the vacuum is transmitted from the horizontal drainage main pipe to the horizontal drainage branch pipe, and then to the drainage electrode and the cavity of the plastic drainage board, and diffuses into the foundation, the current is conducted through the wire, the drainage electrode and the soil between the electrodes, forming an electric potential difference between the anode and the cathode, on the one hand, the free water in the soft foundation flows into the plastic drainage board and the drainage electrode under the action of the vacuum negative pressure. The water molecules are gathered through the filter cloth and the small holes on the electrode steel pipe into the drainage electrode cavity, and are discharged under the vacuum negative pressure in the drainage pipe. On the other hand, water molecules are polar and are gathered from the anode to the cathode under the action of the potential difference. The electroosmosis increases the activity of water molecules and accelerates the penetration rate. At the same time, the electroosmosis also acts on the bound water in the soil, prompting the bound water to break away from the constraints of the soil particles and be discharged, further reducing the water content of the soil. Under the combined action of vacuum and electroosmosis, the soil is quickly drained and consolidated, and the foundation produces consolidation settlement. When the settlement reaches the unloading standard, the construction is stopped.

[0077] In step S304, the drainage boards are arranged in a square with a spacing of 1m. Each 3×3 electrodes form a group. The eight electrodes around are anodes and the central electrode is cathode, which are connected to the positive and negative electrodes of the power supply respectively. The depth is 5m. The filter tube uses a UPVC plastic tube with a diameter of 50mm. A small hole with a diameter of 8mm is drilled every 5cm on the tube wall to make a flower tube, which is covered with a layer of 90g / m 2 Non-woven geotextile.

[0078] The vacuum pumping equipment in step S307: a jet vacuum pump is used, the power of the single machine is not less than 7.5kW, the vacuum pressure of the single machine is not less than 96kPa, the potential gradient of the power output is generally not more than 0.5V / cm, the voltage is less than 60V, and the current density is not more than 50A / m 2 , the electrode conversion cycle is once a week.

[0079] The drainage board length setting, vibro-stone pile length setting, and pile spacing setting are all individually adjusted according to geological survey results and engineering requirements. The vibro-stone pile spacing adjustment range is 2.5~4.0m to meet the foundation treatment needs in different areas and under different conditions.

[0080] The geological structure of the cofferdam mud-intake transition zone is: during the offshore land reclamation process, the transition zone where the mud-intake zone connects with the earth-rock cofferdam. This area is a slope transition section of two different backfill materials, with an upper mud and lower rock structure.

[0081] The comparison of the foundation treatment after construction is shown in Table 1. According to the static load test results, the characteristic value of the foundation bearing capacity in the reinforcement area is 180 kPa. The combined dynamic penetration and Rayleigh wave test results show that the present invention has a significant effect in treating the complex geological structure in the transition area. The foundation bearing capacity meets the design requirements, and the transition is stable. The maximum settlement difference per 10m is only 1.85m, which is much lower than other construction methods.

[0082] Table 1 Comparison of foundation treatment after construction .

Claims

1. A method for treating the transition zone of cofferdam mud by drainage consolidation combined with vibrating crushed stone piles, characterized in that: The following steps are involved: S1: Survey the interface between the earth-rock cofferdam and the mud receiving area; survey the height of the mud-rock interface and form a geological profile; S2: Construction preparation; S3: Electroosmotic drainage consolidation in muddy areas. The electroosmotic drainage consolidation drainage board is arranged in a square with a spacing of 1.0m during the installation process. The installation depth is based on the survey results of the interface between the earth-rock cofferdam and the muddy area in step S1, and is installed in different lengths according to the cross-sectional diagram of the transition zone, so that the bottom of the drainage board is 0.5m away from the mud-rock interface to prevent air leakage, and the exposed length is not less than 0.3m; the drainage board length setting, vibro-stone pile length setting, and pile spacing setting are all individually adjusted according to geological survey results and engineering requirements. The vibro-stone pile spacing adjustment range is 2.5~4.0m to meet the foundation treatment needs in different areas and under different conditions. Specifically, the following steps are included: S301: measuring and setting out; S302: laying geotextile; S303: making drainage boards and filter pipes; S304, install vertical plastic drain boards; the distance between drain boards is 1m, arranged in a square, each 3×3 electrodes form a group, the surrounding eight electrodes are anodes, the center one is cathode, connected to the positive and negative poles of the power supply respectively, the installation depth is 5m, the filter tube uses UPVC plastic pipe with a diameter of 50mm, drill a small hole with a diameter of 8mm on the pipe wall every 5cm, make a flower pipe, and cover it with a layer of 90g / m 2 Non-woven geotextiles; S305: Laying and connecting filter tubes; S306: Laying geotextile and sealing membrane; S307: Try to evacuate the air; S308: vacuum combined with electroosmotic preloading; S4: Vibration treatment of mud-rock interface and mud-receiving area. After the electro-osmosis drainage and consolidation of mud-receiving area are completed, the process of vibrating crushed stone pile construction is adopted. The vibrating crushed stone piles are arranged in an equilateral triangle at the mud-rock interface and mud-receiving area, with a pile spacing of 2.5m. The rear row of piles in the mud-receiving area is arranged in an equilateral triangle with a spacing of 4.0m. The vibrating crushed stone piles enter the earth-rock cofferdam at the mud-rock interface by no less than 1.0m. The front row of vibro-stone piles in the mud receiving area refers to the first four rows of piles; the spacing adjustment range of the vibro-stone piles is 2.5~4.0m, which specifically includes the following steps: S401: Level the site and measure and place the piles; S402: Pile position hole; S403: The pile driver is in place and the hole is vibrated; S404: Filling gravel and vibrating to form piles; S405: Clear hole; S5: Leveling and rolling: Use a bulldozer to remove debris and obstacles on the surface of the site and perform preliminary site leveling; use a roller to perform rolling operations to compact the site; S6: Quality inspection: after the reinforcement is completed, the bearing capacity of the foundation in the transition area is inspected.

2. The method of treating the cofferdam mud-intake transition zone by drainage consolidation combined with vibrating crushed stone piles according to claim 1 is characterized in that: In step S1, a geological survey is conducted on the cofferdam mud transition zone before construction to find out the mud thickness of each section so as to determine the depth of the drainage board and the vibro-compacted gravel pile.

3. The method for treating the transition zone of cofferdam mud by using drainage consolidation combined with vibro-stone piles according to claim 1 is characterized in that: The vacuum pumping equipment in step S307: a jet vacuum pump is used, the power of the single machine is not less than 7.5kW, the vacuum pressure of the single machine is not less than 96kPa, the potential gradient of the power output is generally not more than 0.5V / cm, the voltage is less than 60V, and the current density is not more than 50A / m 2 , the electrode conversion cycle is once a week.

4. A method for treating the transition zone of cofferdam mud by drainage consolidation combined with vibro-stone piles according to any one of claims 1 to 3, characterized in that: The geological structure of the cofferdam mud-intake transition zone is: during the offshore land reclamation process, the transition zone where the mud-intake zone connects with the earth-rock cofferdam. This area is a slope transition section of two different backfill materials, with an upper mud and lower rock structure.

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