A method for constructing underground continuous walls in coastal fill boulders strata

Abstract

This invention discloses a method for constructing diaphragm walls in coastal fill-rock strata, belonging to the field of building construction technology. The method includes: S1, trench wall reinforcement with interlocking piles, using concrete interlocking piles to reinforce the trench walls, followed by guide wall construction; S2, rotary drilling and milling of the trench, using a rotary drilling rig to mill the trench section; S3, trench trimming with a dual-wheel milling drill bit; S4, trenching with a trenching machine, first using a rotary drilling rig to construct three guide holes at both ends and in the middle according to the trench section's layout position; the trenching machine's grab bucket uses the already formed guide hole walls as natural guides to sequentially grab the soil and fill rock between the guide holes; real-time dynamic correction: during trenching, the grab bucket's built-in real-time verticality monitoring system and hydraulic correction push plate achieve dynamic control of construction quality; S5, circulating mud management; S6, ultrasonic testing of the trench section; S7, rebar cage fabrication and horizontal transportation; S8, rebar cage hoisting and docking. This invention can significantly improve the construction quality, efficiency, and safety of diaphragm walls under these geological conditions.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, specifically to a method for constructing a diaphragm wall in coastal fill strata. Background Technology

[0002] In the construction of diaphragm walls in coastal fill-rock strata, existing technologies typically employ a conventional process using hydraulic grab trenching machines combined with impact drilling to treat the fill-rock strata, supplemented by bentonite slurry for wall protection. However, given the complexity of fill-rock strata and the unique coastal environment, this traditional approach has revealed a series of significant drawbacks and shortcomings.

[0003] 1. Existing technologies are not sufficiently adaptable in the trenching process.

[0004] Current trenching construction for diaphragm walls in coastal fill-rock strata presents several challenges. During trenching, large-diameter fill stones and boulders, anchor cables left over from previous construction, and unexplored reinforced concrete structures are frequently encountered. Hydraulic grab buckets are highly susceptible to damage to the grab teeth, jamming, and even equipment malfunction when handling large-diameter, high-strength boulders, resulting in extremely low trenching efficiency and irregular trench shapes. Furthermore, due to the loose structure and well-developed porosity of the fill-rock strata, coupled with the connection between groundwater and seawater and the influence of tides, the trench walls are highly prone to instability during construction, leading to localized collapses or severe mud loss. This negatively impacts trenching accuracy and construction safety, posing significant safety hazards.

[0005] 2. Existing technologies have poor control over mud wall protection and slag removal.

[0006] Conventional bentonite slurry systems experience a significant decrease in colloidal stability and wall-protecting performance under the chemical erosion and salinity of seawater. Furthermore, the intense disturbance during trenching introduces fine sand and debris from the formation, leading to a rapid increase in the sand content of the slurry. This not only further weakens the wall-protecting effect but also results in a thick accumulation of sediment at the bottom of the trench. Traditional methods of cleaning, relying on grab buckets to remove sediment and simple circulation, are insufficient to completely remove the sediment, severely impacting the end-bearing capacity and joint quality of the diaphragm wall.

[0007] 3. In the steel cage construction phase, existing technologies face severe site constraints.

[0008] Coastal sites often have narrow working areas, lacking the conditions for the overall fabrication and stacking of large steel cages, and also making it difficult to provide sufficient working space for large hoisting equipment. Therefore, traditional overall hoisting solutions are difficult to implement, and forcing their adoption would bring extremely high organizational and safety risks.

[0009] 4. In terms of process quality control, existing technologies lack initiative and real-time capability.

[0010] During construction, the assessment of trench wall verticality and hole collapse relies heavily on experience or periodic spot checks, making precise monitoring throughout the entire process impossible. For problems that have already occurred, such as deviation or collapse, reactive measures are often necessary, resulting in high costs and limited effectiveness in correcting the situation.

[0011] Existing technologies in this unique geological and environmental context exhibit systemic defects such as equipment incompatibility, low process reliability, passive quality control, high safety risks, and low overall efficiency. These shortcomings constrain the safety, quality, and schedule of the project, necessitating a systematic construction method for diaphragm walls in coastal fill boulders strata that can address the trenching, wall protection, slag removal, rebar cage hoisting, and real-time monitoring stages. Summary of the Invention

[0012] The main objective of this invention is to provide a method for constructing underground continuous walls in coastal fill boulders strata, in order to solve the problems existing in the prior art.

[0013] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for constructing a diaphragm wall in coastal fill boulders strata includes the following steps: S1. Construction of interlocking piles for trench wall reinforcement The soil on both sides of the underground continuous wall is reinforced by concrete interlocking piles, with a reinforcement depth of not less than 1m penetrating the rock-filled strata or the easily permeable strata. After the interlocking piles are completed, the guide wall is constructed, using a C30 reinforced concrete structure, with the top of the wall flush with the ground. S2, Rotary drilling and milling trench Rotary drilling rigs are used to mill trenches within the rock-fill depth range; S3, Dual-wheel milling drill bit grooving Remove any interlocking concrete turbulence that could not be completely eliminated from the edge of the rotary drilling rig, locally intruded pile body, and clamped boulders; S4, Trenching machine forms trenches In the first stage, rotary drilling is used to establish the benchmark: First, a rotary drilling rig is used to construct three guide holes at both ends and in the middle in strict accordance with the layout position of the trench section. The hole depth is consistent with the design depth of the diaphragm wall. The second stage is trenching by grab bucket: the grab bucket of the trenching machine relies on the wall of the already formed guide hole as a natural guide to grab the soil and fill stones between the guide holes in sequence. The third stage is real-time dynamic correction: During the trenching process, the construction quality is dynamically controlled by relying on the real-time verticality monitoring system built into the grab bucket and the hydraulic correction push plate. S5, Circulating Mud Control Integrate daily tidal forecasts with real-time monitoring of mud levels in the tank; Active adjustment mechanism: During low tide, the drop in sea level leads to an increase in the pressure difference between the inside and outside of the tank. High-quality mud is added in time to strictly maintain the liquid level at the set elevation of 50cm below the top surface of the guide wall to prevent the tank wall from collapsing due to lateral pressure imbalance. During high tide, some mud is pre-pumped out to prevent overflow. Every 2-4 hours or after each certain advance, the specific gravity, viscosity and sand content of the mud are tested on site. Based on the test data, new mud, thickeners or weighting materials are dynamically added to ensure that the mud always maintains a specific gravity sufficient to balance the ground pressure and a viscosity sufficient to form a dense mud cake. S6, Tank Section Inspection After the hole cleaning is completed and the mud parameters are qualified, ultrasonic testing should be carried out immediately. S7. Reinforcing cage fabrication and horizontal transportation The steel cage is fabricated and transported in sections; S8, Reinforcing cage hoisting and docking A main and auxiliary crane coordinated operation scheme was adopted; Main crane: Bears the main load throughout the process, and is responsible for the vertical lifting of the steel cage, the adjustment of its attitude in the air, and the final lowering into the trench; Auxiliary hoist: In the initial stage of lifting, assist the main hoist in lifting the horizontal steel cage to a vertical position. Then, release the lifting point and switch to stabilizing the upper section of the steel cage that has been placed in the trench during the docking process to prevent it from swinging, and provide precise alignment assistance for the lower section of the cage. The auxiliary hoist needs to move flexibly. The steel cage connection adopts a rigid connection method of inserting and welding pre-embedded connecting steel plates; S9, Concrete Pouring First, configure the concrete pouring equipment; Then, the concrete pouring process is controlled.

[0014] Furthermore, in step S2, a "closed-row drilling" process is adopted, in which overlapping boreholes are drilled along the axis of the trench section with a predetermined pile diameter and spacing.

[0015] Furthermore, during the S3 step of the grooving process, measuring instruments are used to monitor and ensure that the flatness and verticality of the grooving wall after grinding meet the requirements.

[0016] Furthermore, in step S5, for situations where the stratum within the diaphragm wall trench area has a high sand content, a deep purification and control method is adopted to treat the mud regeneration and recycling of high sand content strata: Once the tank reaches the designed depth, the purification system consisting of a sand washing pump and a screening machine is immediately started. This system continuously pumps out the high-sand-content mud from the bottom of the tank. First, large particles of drilling slag are separated by a vibrating screen. Then, the mud enters a hydrocyclone desander, where fine sand particles are efficiently separated under centrifugal force. After purification, the mud with the required sand content is returned to the tank, forming a closed-loop circulation.

[0017] Furthermore, in step S6, the inspection needs to be scanned at least once along the long side and the short side of the groove segment to fully evaluate the groove shape; Data analysis and decision-making: Compare the test data with the verticality standards required by the design; If the requirements are met: the trench section shape is qualified, the steel cage hoisting process can proceed after the documents are signed; If the requirements are not met: the system will automatically trigger a repair procedure, and the detection report will accurately indicate the depth, range, location, and severity of the deviation.

[0018] Furthermore, in step S6, the repair process involves repairing the groove again based on the "diagnostic report" and taking targeted repair measures. ① Localized trench repair For localized protrusions at a specific depth, the square-headed twin-wheel milling drill bit or a grab bucket with a correction plate can be lowered again to perform precise milling or scraping in the designated area until the obstacle is eliminated. ② Comprehensive trench repair If the deviation range is large or shows a trend of skewness, it may be necessary to perform full-depth correction grooving on the deviation side. ③ Retesting closed loop After the repair is completed, ultrasonic testing must be carried out again until the data fully meets the design requirements, forming a strict closed loop of "testing-repairing-retesting".

[0019] Furthermore, in step S8, the method of connecting the reinforcing cage is as follows: ① At the end of each section of the reinforcing cage, several Q235B connecting steel plates with a thickness of 20mm and a width of 200mm are pre-welded vertically; the length of the steel plates is determined according to the lap splicing requirements of the main reinforcement, and holes for the main reinforcement to pass through are accurately opened on them or butt grooves are processed. ② Precise matching After the first cage section is lowered to the design elevation and temporarily fixed, the main crane slowly and precisely lowers the second cage section, so that the connecting steel plate at the bottom of the second cage section is fully aligned with and inserted into the corresponding steel bar at the top of the first cage section that is already in place. ③ Rigid connection formation After the connection is in place and inspected to ensure it is correct, the welder immediately performs double-sided full welding of the main reinforcing bars on both sides to the connecting steel plate.

[0020] Furthermore, in step S8, the final step is to install and protect the testing pipelines to ensure that ultrasonic testing of the wall quality can be performed later. The acoustic logging pipes and inclinometer pipes must be installed simultaneously with the reinforcing cage.

[0021] Furthermore, in step S9, the concrete pouring equipment configuration includes: ① Catheter selection: Select a circular spiral quick-connect catheter with a diameter of 250mm; ②Lowering and positioning: Use a special concrete pouring frame to hoist and fix the guide pipe; ③ Grouting port setting: A square funnel is installed at the top of the guide pipe. Its capacity needs to be calculated to ensure that it can meet the amount of concrete needed to form a sufficient buried pipe depth during the initial grouting.

[0022] Furthermore, in step S9, the concrete pouring process control includes: ① The concrete surface rises evenly During the pouring process, the two guide pipes must be used synchronously and alternately to pour concrete, and the amount of concrete poured at each point must be strictly controlled to ensure that the concrete level in the entire trench section is horizontal and rises synchronously. ② Liquid level difference control The difference in concrete surface height at each guide pipe location should not exceed 0.5m; ③ The pouring was completed before final setting.

[0023] Compared with the prior art, the present invention has the following beneficial effects: This construction method, through systematic technological innovation, has created significant and multi-layered economic benefits in coastal fill rock strata. Its core value lies in directly transforming technological advantages into cost and time advantages, specifically reflected in the following four aspects: (1) Equipment maintenance and downtime costs are significantly reduced: Through the active pretreatment of rotary drilling and milling and double wheel milling, the main risk sources that cause equipment damage (large stones, concrete protrusions) are eliminated, allowing the core equipment (trenching machine) to operate under ideal working conditions, which greatly reduces the maintenance costs and unexpected downtime caused by hydraulic system damage, bucket tooth wear and bucket jamming failure.

[0024] (2) Consumption of major materials has been effectively controlled: ① Slurry materials: The closed-loop circulation purification system of slurry, consisting of a "sand washing pump + screening machine", significantly improves the reuse rate of slurry materials such as bentonite, while reducing the amount of waste slurry transported and disposed of, directly saving on material purchase and environmental disposal costs.

[0025] ② Concrete materials: Refined pouring control and improved trench wall stability reduced non-design waste of concrete caused by hole collapse and overfilling, ensuring the accuracy of material usage.

[0026] (3) Increased efficiency: The "rotary grab combined" process concentrates the most time-consuming hard rock treatment in the guide hole, making the trenching efficiency much higher than the conventional method of trenching by grab bucket.

[0027] The quality closed loop formed by ultrasonic testing and real-time correction solves problems such as verticality before pouring, avoiding the disastrous loss of time and cost due to rework and reconstruction caused by substandard walls.

[0028] (4) Reduced risk costs and post-maintenance costs: High-quality walls (good verticality, no mud inclusions, and thin sediment) fundamentally improve the safety and stability of the foundation pit and reduce the support risks and potential accident costs during the excavation stage. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the steps of a method for constructing a diaphragm wall in a coastal fill boulders stratum according to the present invention.

[0030] Figure 2 This is a schematic diagram of the plan layout for the reinforcement of the diaphragm wall trench in a diaphragm wall construction method for coastal fill strata according to the present invention.

[0031] Figure 3 This is a schematic diagram of the "three-turn two-grab" method for trenching the diaphragm wall in a diaphragm wall construction method for coastal fill boulders in this invention.

[0032] Figure 4 This is a schematic diagram of the segmented reinforcement cage of the diaphragm wall in a construction method for diaphragm walls in coastal fill strata according to the present invention.

[0033] Figure 5 This is a schematic diagram of the steel plate connecting the steel cage of the diaphragm wall in a construction method for diaphragm walls in coastal fill strata according to the present invention. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] Example 1

[0036] Combination Figures 1-5 This invention provides a method for constructing a diaphragm wall in coastal fill strata, comprising the following steps: S1. Construction of interlocking piles for trench wall reinforcement To avoid grout leakage or instability and collapse of the borehole during the construction of diaphragm wall filling with rock, silt, and sand layers, the following measures are adopted: The 800@600 C20 plain concrete interlocking pile reinforcement method is used to reinforce the soil on both sides of the diaphragm wall by trench wall reinforcement, with a reinforcement depth of not less than 1m penetrating the rockfill stratum (or the easily permeable stratum). After the interlocking piles are completed, the guide wall is constructed, using a "╗╔" shaped C30 reinforced concrete structure, with the top of the wall flush with the ground.

[0037] S2, Rotary drilling and milling trench

[0038] When constructing diaphragm walls in coastal fill-rock strata, the first step is to use a rotary drilling rig to mill the trenches within the fill-rock depth range. This is a crucial pretreatment process.

[0039] The core purpose of this process is to proactively remove complex and hard obstacles in the shallow strata before conventional trenching equipment enters the site, thus clearing obstacles for subsequent operations.

[0040] Specifically, the "close-drilling" technique is adopted, in which overlapping boreholes are drilled along the axis of the trench section with a predetermined pile diameter and spacing, to achieve the following technical effects: ① Significantly improves the efficiency of subsequent tank formation by pre-processing the most difficult part.

[0041] ② Effectively control trench wall stability: Form a relatively regular initial hole wall, reducing the disturbance to the loose rock-filled strata during subsequent trenching.

[0042] ③ Significantly reduces the risk of equipment failure: avoids the grab bucket directly facing unknown obstacles.

[0043] The specific objects processed in step S2 are as follows: ① Large-diameter fill stones and strip stones The artificially placed boulders and slabs in the strata vary in size, are irregularly distributed, and have high strength. The rotary drilling rig, equipped with a tubular drill and a spiral drill bit, can break, loosen, and remove these large obstacles through "close-packed drilling" to form relatively continuous preliminary slots, preventing the grab bucket from getting stuck, deviating, or being damaged when it comes into direct contact with the subsequent grab bucket.

[0044] ② Remaining anchor cables

[0045] Metal components such as prestressed anchor cables that may remain on the site are "hidden killers" for trenching equipment. The drill teeth of a rotary drilling rig can cut or entangle these metal objects and pull them out, preventing them from getting tangled in the grab bucket or damaging the hydraulic system, thus eliminating safety hazards.

[0046] ③ Unexplored reinforced concrete structures

[0047] For old foundations, pile foundations and other reinforced concrete structures that have not been fully explored by geological surveys, the carbide drill bits of rotary drilling rigs have strong milling capabilities, which can gradually break them up and remove them, solving problems that conventional equipment cannot handle at all.

[0048] S3, Dual-wheel milling drill bit grooving

[0049] The main task is to remove the interlocking concrete turbulence that could not be completely eliminated from the edge of the rotary drilling rig, locally intruded pile bodies, and clamped boulders.

[0050] During the grooving process, measuring instruments are used to monitor and ensure that the flatness and verticality of the grooving wall meet the requirements after grinding, ultimately forming a grooving hole that allows the grab bucket to move up and down smoothly without interference from local hard objects.

[0051] While the rotary drilling and milling process in step S2 can remove large-volume obstacles within the trench, its circular drill bit and impact-type operation method often leave behind high-strength concrete protrusions or irregularities on both sides of the trench wall, especially at the junction with the plain concrete interlocking piles on both sides. If these protrusions are not addressed, they will directly lead to the following problems during the grab bucket trenching process: ① Jammed grab: The grab's toothed plates cannot close or open, causing the equipment to stop.

[0052] ② Scratching of the tank wall: This leads to abnormal wear on the grab bucket body and guide plate.

[0053] ③ Groove deviation: The grab bucket loses control of its trajectory under the interference of hard objects, affecting its verticality.

[0054] Therefore, the core purpose of trench repair is to adjust the trench wall to within the designed clearance dimensions, forming a continuous, flat, and vertical guide surface to create an unobstructed working environment for the grab bucket.

[0055] Step S3 employs a method of replacing the square-headed twin-wheel milling drill bit on the rotary drilling rig's power head. Its technical advantages are: ① High-efficiency cutting: The two milling wheels equipped with carbide teeth on the twin-wheel milling drill head rotate in opposite directions, enabling precise and efficient grinding and cutting of hard materials such as concrete and rock strata, with significant effect on handling local protrusions.

[0056] ② Flexible adaptation: Utilizing the powerful torque and downforce of existing rotary drilling rigs as a power source, and changing drill bits through quick-change couplings, the equipment achieves "one machine for multiple uses," eliminating the need to introduce additional large-scale dedicated trenching machines, making it economical and efficient.

[0057] ③ High controllability: Operators can precisely control the feed of the milling wheel in depth and lateral direction, so as to achieve targeted grinding of specific areas of the groove wall and avoid excessive disturbance to the already formed groove wall.

[0058] S4, Trenching machine forms trenches

[0059] The first stage involves establishing a benchmark using rotary drilling: First, a rotary drilling rig is used to construct three guide holes at both ends and in the middle, strictly following the trench section layout. The hole depth is consistent with the design depth of the diaphragm wall. Utilizing the high mobility and easy correction capabilities of the rotary drilling rig, the verticality of the guide holes is ensured, and any obstacles such as boulders and concrete within the holes are simultaneously removed, creating a trenching spatial benchmark with accurate positioning and high verticality.

[0060] The second stage involves the grab bucket forming the trench: the grab bucket of the trenching machine uses the walls of the pre-formed guide holes as a natural guide to sequentially grab the soil and fill stones between the guide holes. The construction follows the principle of "first the sides, then the center," completing the trench sections between adjacent guide holes first, and then processing the remaining middle section, so that the trenches are gradually connected, effectively utilizing the spatial constraint of the guide holes and reducing grab bucket swaying and deviation.

[0061] The third stage involves real-time dynamic correction: During the trenching process, dynamic control of construction quality is achieved by relying on the real-time verticality monitoring system built into the grab bucket and the hydraulic correction push plate. Operators continuously monitor the verticality data, and once a deviation is found to exceed the allowable range, the correction push plate is immediately activated to apply horizontal thrust to the hole wall on the deviated side. The trench wall posture is gradually adjusted during the movement of the grab bucket, forming a real-time closed-loop control of "monitoring-feedback-correction" to ensure that the verticality of the trench meets the design requirements.

[0062] When trenching for diaphragm walls in coastal fill-rock strata, the direct use of traditional hydraulic grab trenching machines is not only inefficient but also carries risks such as grab jamming, damage, and trench hole misalignment. Therefore, a composite trenching process combining rotary drilling and grab trenching (three rotary and two grab trenching steps) is adopted in step S4. The core of this process is the coordinated operation of rotary drilling and the trenching machine to decompose and process complex strata, achieving both efficiency and precision.

[0063] S5, Circulating Mud Control

[0064] To address the dual challenges of coastal fill strata and fully weathered granite with high sand content, the mud management during the trenching process of diaphragm walls has been transformed from traditional static maintenance into a "dual-layer dynamic circulation control" system. This system aims to proactively respond to tidal disturbances and endogenous formation degradation, ensuring the continuous and reliable wall protection effect.

[0065] (1) Surface dynamic control: Real-time adjustment of liquid level and performance in response to tides, aiming to offset the direct impact of tidal circulation on the stability of the tank wall. The core is "using dynamic control" to maintain the constant advantage of mud hydrostatic pressure.

[0066] ① Tidal-linked liquid level control: Dedicated personnel for monitoring: Dedicated positions are set up to integrate daily tidal forecasts with real-time monitoring of mud levels in the tank.

[0067] Active adjustment mechanism: During low tide, the drop in sea level increases the pressure difference between the inside and outside of the tank, requiring timely replenishment of high-quality mud to strictly maintain the liquid level at the set elevation of "50cm below the top surface of the guide wall" to prevent the tank wall from collapsing due to lateral pressure imbalance. During high tide, some mud is pre-pumped to prevent overflow and ensure civilized construction.

[0068] ② Real-time performance monitoring and adjustment: Under tidal and excavation disturbances, mud properties change rapidly. The mud's specific gravity, viscosity, and sand content need to be tested on-site every 2-4 hours or after each certain advance. Based on the test data, new mud, thickeners (such as CMC), or weighting materials (such as barite powder) are dynamically added to ensure the mud maintains a specific gravity sufficient to balance ground pressure (typically above 1.15) and a viscosity capable of forming a dense mud cake.

[0069] (2) Deep purification and control: mud recycling for treating high sand content strata

[0070] This layer addresses the internal problems of high sand content in the strata within the diaphragm wall trench area, which easily leads to the formation of thick sediment. The core is "purification and regeneration," ensuring the quality of the trench from the root.

[0071] ① Once the trench reaches the designed depth, immediately start the dedicated purification system of "sand washing pump + screening machine". This system continuously pumps out the high sand content mud from the bottom of the trench. First, large particles of drilling cuttings are separated by a vibrating screen. Then, the mud enters a hydrocyclone desander, where fine sand particles are efficiently separated under centrifugal force.

[0072] ② After purification, the slurry with the required sand content is returned to the tank, forming a closed-loop circulation. This process effectively inhibits the regeneration rate of sediment and significantly reduces its final thickness.

[0073] S6, Tank Section Inspection

[0074] Inspection Implementation: After the hole cleaning is completed and the mud index is qualified, ultrasonic testing should be carried out immediately. The test should scan at least once along the long side (X direction) and short side (Y direction) of the trench section to comprehensively evaluate the trench shape.

[0075] Data analysis and decision-making: Compare the test data with the verticality standard required by the design (e.g., ≤1 / 300).

[0076] ① If the requirements are met: the trench section shape is qualified, the steel cage hoisting process can proceed after the documents are signed.

[0077] ② If the requirements are not met: The system will automatically trigger a repair procedure. The inspection report will accurately indicate the depth, range, location, and severity of the deviation.

[0078] Repair treatment (re-repairing the groove): Based on the "diagnostic report", take targeted repair measures: ① Localized trench repair For localized protrusions at a specific depth, the square-headed twin-wheel milling drill bit or a grab bucket with a correction plate can be lowered again to perform precise milling or scraping in the designated area until the obstacle is eliminated.

[0079] ② Comprehensive trench repair

[0080] If the deviation range is large or shows a trend of skewness, it may be necessary to perform full-depth correction grooving on the deviation side.

[0081] ③ Retesting closed loop

[0082] After the repair is completed, ultrasonic testing must be carried out again until the data fully meets the design requirements, forming a strict closed loop of "testing-repairing-retesting".

[0083] S7. Reinforcing cage fabrication and horizontal transportation

[0084] Given the inherent limitations of coastal construction sites, such as narrow working areas and difficulties in the passage of large equipment, traditional methods of fabricating and hoisting steel cages as a whole are not feasible. Therefore, a comprehensive solution involving "factory fabrication, modular segmentation, and adaptive transportation" is needed. The core of this solution lies in minimizing the impact of space constraints through meticulous pre-planning and innovative on-site logistics.

[0085] (1) Fabrication of steel cage

[0086] ① Decisive factors in segmented production: The primary reason for segmentation is not technology, but the physical space of the site.

[0087] The narrow coastal site could not provide the jig space required for the overall fabrication of steel cages (over 40 meters long), nor did it have enough space for large crawler cranes (e.g., over 250 tons) to lift, rotate, and move the entire cage. After being divided into sections, the length (e.g., 9m, 12m) and weight of each section were significantly reduced, making it suitable for small and medium-sized cranes to operate in confined spaces.

[0088] ② Refined design with staggered joints: In order to ensure the integrity of the structure and avoid all joints forming a weak surface at the same elevation, a staggered joint design is required.

[0089] When preparing the reinforcement cage fabrication drawings, it's not simply a matter of dividing the reinforcement cage for each wall into equal sections. Instead, like allocating puzzle pieces, the sectioning scheme for adjacent sections (walls) is considered holistically. For example, for two adjacent diaphragm walls, if the first wall's section length is designed as "9m + 12m + 12m + 7.1m," then the adjacent walls can be adjusted to "7.1m + 12m + 12m + 9m." This way, when the two walls are constructed adjacent to each other, their horizontal joints are naturally staggered. This ensures the overall rigidity and seepage prevention continuity of the diaphragm wall, avoiding the formation of continuous weak points.

[0090] ③ Finished Product Management and Labeling: Each completed steel cage must be clearly labeled with its corresponding trench number (e.g., "J8-3") and segment number (e.g., "Section 1 of 4"), and stacked in a reasonable manner according to the hoisting sequence to lay the foundation for efficient transportation and hoisting in the future.

[0091] (2) Horizontal transport of steel cage

[0092] ① The flatbed truck used for transporting steel cages is made of H-beams and channel steel welded together, with a sturdy structure, low center of gravity, and strong load-bearing capacity. Sleepers are laid on top to distribute the load. Its dimensions are specially customized to the width of temporary roads and turning radius at the construction site.

[0093] ②Towing power: Towed by excavators commonly found on site. Excavators have the advantages of good off-road capability, flexibility, and the ability to use local materials, making them a perfect replacement for heavy trucks that require wide roads.

[0094] ③ Efficient transfer process: Inside the processing plant, a truck crane smoothly lifts the segmented rebar cages onto pre-positioned flatbed trucks. An excavator then pulls the flatbed trucks, transporting the rebar cages horizontally along a predetermined route to the designated lifting position next to the target trench section. The entire transportation process is smooth and efficient, and does not rely on on-site main crane equipment resources, achieving separation of logistics and lifting operations.

[0095] S8, Reinforcing cage hoisting and docking

[0096] Within the narrow construction site by the sea, the hoisting and docking of ultra-long steel reinforcement cages for diaphragm walls is a critical operation that demands extremely high levels of equipment coordination, operational precision, and process integration. This project employs a "dual-machine hoisting and precise aerial docking" technique, the core of which lies in transforming prefabricated segmented steel reinforcement cages from factory sections into a complete, integral structure above the trench opening through meticulous organization and specialized tooling.

[0097] (1) Reinforcing cage hoisting

[0098] Considering the weight and dimensions of each section of the reinforcing cage after segmentation, and the limited space, a main and auxiliary hoisting collaborative operation scheme is adopted: ① Main crane: Bears the main load throughout the process, responsible for the vertical lifting of the steel cage, aerial attitude adjustment, and final lowering into the trench. Crawler cranes, with their low ground pressure and stable lifting capacity, are suitable for heavy-duty lifting operations on soft coastal soil.

[0099] ② Auxiliary hoist: In the initial stage of hoisting, assist the main hoist in lifting the horizontal steel cage to a vertical position. Then, release the hoisting point and switch to stabilizing the upper section of the steel cage that has been placed in the trench during the docking process to prevent it from swinging, and provide precise alignment assistance for the lower section of the cage. The auxiliary hoist needs to move flexibly and it is advisable to use a truck crane.

[0100] (2) Connection of steel cage

[0101] The vertical connection of the segmented steel cage is the core to ensure the integrity of the wall structure. This project adopts a rigid connection method of inserting and welding pre-embedded connecting steel plates. ① Tooling Design At the end of each section of the reinforcing cage, several Q235B connecting steel plates, each 20mm thick and 200mm wide, are pre-welded vertically. The length of the steel plates is determined according to the lap splicing requirements of the main reinforcement bars, and holes for the main reinforcement bars to pass through are accurately drilled on them or mating grooves are machined on them.

[0102] ② Precise matching

[0103] After the first cage section is lowered to the design elevation and temporarily secured, the main crane slowly and precisely lowers the second cage section. The key to this operation is ensuring that the connecting steel plate at the bottom of the second cage section is perfectly aligned with and inserted into the corresponding reinforcing bar at the top of the already positioned first cage section. The lap length between the reinforcing bar and the steel plate must strictly comply with design requirements to ensure sufficient load-bearing area.

[0104] ③ Rigid connection formation

[0105] After the connection is in place and inspected to ensure it is correct, the welder immediately performs double-sided full welding on the main reinforcing bars and connecting steel plates. The quality requirements for this weld are extremely high, and it must be ensured that it can transmit all the tensile and shear forces of the reinforcing bars, so that the segmented reinforcing cage is equivalent to a whole in terms of stress performance.

[0106] (3) Inspection pipeline installation and protection

[0107] To ensure the quality of the wall is tested using ultrasonic testing later, the sonic logging tubes and inclinometer tubes must be installed simultaneously with the reinforcing cage. Their fixing method fully considers protection during hoisting and concrete pouring: the tubes are fixed inside the reinforcing cage using a "flexible top, rigid bottom" strategy. The bottom end of the tube uses an "S"-shaped hook made of Φ6mm steel bars to firmly lock it to the main reinforcing bars of the cage, preventing concrete from flowing in during pouring. The upper and middle parts of the tube are mainly flexibly bound with wire, especially at segment joints, leaving approximately 20cm of vertical space for movement.

[0108] S9, Concrete Pouring

[0109] In coastal reclaimed rock strata, the concrete pouring of diaphragm walls is the ultimate critical process that determines the final quality, impermeability, and structural integrity of the walls. Given the depth of the trench, the complexity of the strata, and the operation in a muddy environment, the mature underwater grouting process using tremie pipes is strictly adopted, and a series of refined control parameters are used to ensure that the concrete forms a uniform, dense, and continuous wall within the trench.

[0110] (1) Configuration of concrete pouring equipment

[0111] ① Conduit Selection: A circular spiral quick-connect conduit with an inner diameter of 250mm was selected. This specification strikes a balance between ensuring smooth concrete descent and adequate diffusion. The spiral quick-connect conduit offers advantages such as rapid connection, reliable sealing, and strong torsional resistance, effectively preventing joint loosening and mud seepage caused by conduit rotation or shaking during deep trench grouting. It is a key component ensuring the continuity of underwater grouting.

[0112] ②Lowering and Positioning: A specialized concrete pouring frame is used to hoist and secure the guide pipes. The pouring frame can accurately position the lowering position of each guide pipe and firmly suspend its upper end, ensuring that the guide pipes remain vertical and stable throughout the pouring process and avoiding collisions with the reinforcing cage.

[0113] ③ Grouting port setting: A square funnel is installed at the top of the guide pipe. Its capacity needs to be calculated to ensure that it can meet the amount of concrete required to form a sufficient burial depth during the initial grouting, so as to bury the bottom of the guide pipe in one go and prevent mud backflow.

[0114] (2) Control of concrete pouring process

[0115] ① The concrete surface rises evenly

[0116] During the pouring process, the two guide pipes must be used synchronously and alternately to pour concrete, and the amount of concrete poured at each point must be strictly controlled to ensure that the concrete level in the entire trench section is horizontal and rises synchronously.

[0117] ② Liquid level difference control

[0118] The height difference of the concrete surface at each guide pipe should not exceed 0.5m. This is to prevent uneven pressure caused by excessive liquid level difference, which could push the poured but not yet set concrete to one side, carrying mud and forming a sloping weak interlayer or quality defect zone.

[0119] ③ The pouring was completed before final setting.

[0120] This is a rigid requirement regarding the continuity of the pouring process and the total time required. The concrete for the entire trench section must be poured continuously within a single construction shift to ensure that the later-poured concrete can fully bond with the earlier-poured sections before initial setting, forming a unified whole. For ultra-deep and ultra-long diaphragm walls, this is the lifeline for avoiding horizontal construction cold joints and ensuring the integrity of the wall structure.

[0121] This method, tailored to the characteristics of coastal fill strata, has developed a systematic implementation plan. Its core process and specific implementation methods are as follows: 1. Slot pretreatment (1) Milling: Before the trench is formed, a rotary drilling rig equipped with a tubular drill and a spiral drill bit is used to drill closely in the trench section (the depth is generally up to the bottom of the fill layer, such as 0-18m), actively breaking and removing obstacles such as dumped boulders, anchor cables, and leftover concrete.

[0122] (2) Groove repair: Replace with a square-headed double-wheel milling drill bit to precisely grind the concrete protrusions on both sides of the groove wall, especially at the junction with the interlocking pile, to ensure that the groove wall is flat and to create an unobstructed working environment for the subsequent trenching machine.

[0123] 2. Trenching and Mud Dynamic Management

[0124] (1) Composite trenching: The process of "rotary-grab combination, three-rotary-two-grab" is adopted. That is, three guide holes are first drilled at both ends and the middle of the trench section to the design depth using a rotary drilling rig. Then, the remaining part of the trench is completed using a hydraulic grab bucket with the guide holes as a reference. During the process, the verticality is corrected in real time using the grab bucket machine with a correction push plate.

[0125] (2) Active mud management

[0126] Tidal response: Dedicated personnel monitor the tides and dynamically adjust the mud level in the tank (keeping it 50cm below the top of the guide wall) to maintain stable hydrostatic pressure.

[0127] Mud purification: After the tank is formed, a "sand washing pump + screening machine" is immediately used to carry out closed-loop circulation of mud, which significantly reduces the sand content and controls sedimentation from the source.

[0128] 3. Construction compatibility of reinforcing cage

[0129] (1) Sectional manufacturing and transportation

[0130] Depending on site conditions, the steel cage is divided into reasonable sections (e.g., 4 sections) and prefabricated in the factory. A self-made heavy-duty flatbed truck, towed by an excavator, is used to complete the "last mile" horizontal transport in the narrow site.

[0131] (2) Precision hoisting and connection

[0132] A main and auxiliary crane (such as a 130t crawler crane + an 85t truck crane) are used in conjunction for precise aerial docking. The sections are inserted into place using pre-embedded 20mm thick connecting steel plates, and the main reinforcing bars are fully welded to both sides of the steel plates to form a rigid whole. Sonic logging pipes and other components are flexibly fixed, with allowable movement to prevent damage.

[0133] 4. Terminal pouring and quality closed loop

[0134] (1) Refined grouting: The tremie pipe method is used for pouring, and the principle of "tremie pipe spacing ≤ 3m, distance from joint ≤ 1.5m, concrete surface height difference ≤ 0.5m" is strictly controlled to ensure that the concrete rises evenly and continuously and is formed in one go.

[0135] (2) Quality inspection closed loop: Before the cage is lowered, the verticality of the tank section is checked at full depth using an ultrasonic sidewall tester. If it fails to meet the requirements, it is returned to the "tank repair" process for repair and retesting, forming a strict quality control closed loop.

[0136] In summary, this implementation method, through the systematic coupling of four major aspects—pretreatment to eliminate risks, dynamic process control, innovative construction organization, and closed-loop final quality—forms a complete, reliable, and efficient proprietary construction method system, successfully overcoming a series of global challenges in the construction of diaphragm walls in coastal rockfill strata.

[0137] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for constructing a diaphragm wall in a coastal fill riprap stratum, characterized in that, The following steps are included: S1. Construction of interlocking piles for trench wall reinforcement The soil on both sides of the underground continuous wall is reinforced by concrete interlocking piles, with a reinforcement depth of not less than 1m penetrating the rock-filled strata or the easily permeable strata. After the interlocking piles are completed, the guide wall is constructed, using a C30 reinforced concrete structure, with the top of the wall flush with the ground. S2, Rotary drilling and milling trench Rotary drilling rigs are used to mill trenches within the rock-fill depth range; S3, Dual-wheel milling drill bit grooving Remove any interlocking concrete turbulence that could not be completely eliminated from the edge of the rotary drilling rig, locally intruded pile body, and clamped boulders; S4, Trenching machine forms trenches. In the first stage, rotary drilling is used to establish the benchmark: First, a rotary drilling rig is used to construct three guide holes at both ends and in the middle in strict accordance with the layout position of the trench section. The hole depth is consistent with the design depth of the diaphragm wall. The second stage is trenching by grab bucket: the grab bucket of the trenching machine relies on the wall of the already formed guide hole as a natural guide to grab the soil and fill stones between the guide holes in sequence. The third stage is real-time dynamic correction: During the trenching process, the construction quality is dynamically controlled by relying on the real-time verticality monitoring system built into the grab bucket and the hydraulic correction push plate. S5, Circulating Mud Control Integrate daily tidal forecasts with real-time monitoring of mud levels in the tank; Active adjustment mechanism: During low tide, the drop in sea level leads to an increase in the pressure difference between the inside and outside of the tank. High-quality mud is added in time to strictly maintain the liquid level at the set elevation of 50cm below the top surface of the guide wall to prevent the tank wall from collapsing due to lateral pressure imbalance. During high tide, some mud is pre-pumped out to prevent overflow. Every 2-4 hours or after each certain advance, the specific gravity, viscosity and sand content of the mud are tested on site. Based on the test data, new mud, thickeners or weighting materials are dynamically added to ensure that the mud always maintains a specific gravity sufficient to balance the ground pressure and a viscosity sufficient to form a dense mud cake. S6, Tank Section Inspection After the hole cleaning is completed and the mud parameters are qualified, ultrasonic testing should be carried out immediately. S7. Reinforcing cage fabrication and horizontal transportation The steel cage is fabricated and transported in sections; S8, Reinforcing cage hoisting and docking A main and auxiliary crane coordinated operation scheme was adopted; Main crane: Bears the main load throughout the process, and is responsible for the vertical lifting of the steel cage, the adjustment of its attitude in the air, and the final lowering into the trench; Auxiliary hoist: In the initial stage of lifting, assist the main hoist in lifting the horizontal steel cage to a vertical position. Then, release the lifting point and switch to stabilizing the upper section of the steel cage that has been placed in the trench during the docking process to prevent it from swinging, and provide precise alignment assistance for the lower section of the cage. The auxiliary hoist needs to move flexibly. The steel cage connection adopts a rigid connection method of inserting and welding pre-embedded connecting steel plates; S9, Concrete Pouring First, configure the concrete pouring equipment; Then, the concrete pouring process is controlled.

2. The method for constructing a diaphragm wall in coastal fill boulders strata as described in claim 1, characterized in that, In step S2, the "closed-row drilling" process is adopted, and overlapping drilling is carried out along the axis of the trench section with a predetermined pile diameter and spacing.

3. The method for constructing a diaphragm wall in coastal fill boulders strata as described in claim 2, characterized in that, During the S3 step of the grooving process, measuring instruments are used to monitor and ensure that the flatness and verticality of the grooving wall after grinding meet the requirements.

4. The method for constructing a diaphragm wall in coastal fill boulders strata as described in claim 3, characterized in that, In step S5, for situations where the stratum within the diaphragm wall trench area has a high sand content, a deep purification and control method is adopted to treat the mud regeneration and recycling of high sand content strata: Once the tank reaches the designed depth, the purification system consisting of a sand washing pump and a screening machine is immediately started. This system continuously pumps out the high-sand-content mud from the bottom of the tank. First, large particles of drilling slag are separated by a vibrating screen. Then, the mud enters a hydrocyclone desander, where fine sand particles are efficiently separated under centrifugal force. After purification, the mud with the required sand content is returned to the tank, forming a closed-loop circulation.

5. The method for constructing a diaphragm wall in coastal fill boulders strata as described in claim 1, characterized in that, In step S6, the inspection needs to be scanned at least once along the long side and the short side of the groove segment to fully evaluate the groove shape; Data analysis and decision-making: Compare the test data with the verticality standards required by the design; If the requirements are met: the trench section shape is qualified, the steel cage hoisting process can proceed after the documents are signed; If the requirements are not met: the system will automatically trigger a repair procedure, and the detection report will accurately indicate the depth, range, location, and severity of the deviation.

6. The method for constructing a diaphragm wall in coastal fill boulders strata as described in claim 5, characterized in that, In step S6, repair treatment: Based on the "diagnostic report," repair the groove again and take targeted repair measures: ① Localized trench repair For localized protrusions at a specific depth, the square-headed twin-wheel milling drill bit or a grab bucket with a correction plate can be lowered again to perform precise milling or scraping in the designated area until the obstacle is eliminated. ② Comprehensive trench repair If the deviation range is large or shows a trend of skewness, it may be necessary to perform full-depth correction grooving on the deviation side. ③ Retesting closed loop After the repair is completed, ultrasonic testing must be carried out again until the data fully meets the design requirements, forming a strict closed loop of "testing-repairing-retesting".

7. The method for constructing a diaphragm wall in coastal fill boulders strata as described in claim 1, characterized in that, In step S8, the steel cage is connected as follows: ① At the end of each section of the reinforcing cage, several Q235B connecting steel plates with a thickness of 20mm and a width of 200mm are pre-welded vertically; the length of the steel plates is determined according to the lap splicing requirements of the main reinforcement, and holes for the main reinforcement to pass through are accurately opened on them or butt grooves are processed. ② Precise matching After the first cage section is lowered to the design elevation and temporarily fixed, the main crane slowly and precisely lowers the second cage section, so that the connecting steel plate at the bottom of the second cage section is fully aligned with and inserted into the corresponding steel bar at the top of the first cage section that is already in place. ③ Rigid connection formation After the connection is in place and inspected to ensure it is correct, the welder immediately performs double-sided full welding of the main reinforcing bars on both sides to the connecting steel plate.

8. The method for constructing a diaphragm wall in coastal fill boulders strata as described in claim 1, characterized in that, In step S8, the final step is to install and protect the testing pipelines to ensure that ultrasonic testing of the wall quality can be performed later. The acoustic logging pipes and inclinometer pipes must be installed simultaneously with the reinforcing cage.

9. A method for constructing a diaphragm wall in coastal fill boulders strata as described in claim 1, characterized in that, In step S9, the concrete pouring equipment configuration includes: ① Catheter selection: Select a circular spiral quick-connect catheter with a diameter of 250mm; ②Lowering and positioning: Use a special concrete pouring frame to hoist and fix the guide pipe; ③ Grouting port setting: A square funnel is installed at the top of the guide pipe. Its capacity needs to be calculated to ensure that it can meet the amount of concrete needed to form a sufficient buried depth during the initial grouting.

10. A method for constructing a diaphragm wall in coastal fill boulders strata as described in claim 1, characterized in that, In step S9, the concrete pouring process control includes: ① The concrete surface rises evenly During the pouring process, the two guide pipes must be used synchronously and alternately to pour the concrete, and the amount of concrete poured at each point must be strictly controlled to ensure that the concrete level in the entire trench section is horizontal and rises synchronously. ② Liquid level difference control The difference in concrete surface height at each guide pipe location should not exceed 0.5m; ③ The pouring was completed before final setting.

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