Groove wall reinforcing and combined grooving construction method for ultra-deep underground diaphragm wall

Abstract

The invention discloses a groove wall reinforcing and combined groove forming construction method for an ultra-deep underground diaphragm wall, and aims to solve the problems that the perpendicularity is difficult to control and the section of a reinforcing body is irregular in the deep groove wall reinforcing process of a traditional three-shaft stirrer, double-wheel stirring equipment is adopted for reinforcing the groove wall, real-time monitoring and adjustment of the perpendicularity are achieved through an inclinometer of the double-wheel stirring equipment, and the perpendicularity of the double-wheel stirring equipment can be monitored and adjusted in real time. The overall stability of the groove wall is improved. In order to consider the grooving precision and the construction efficiency, a grabbing and milling combined segmented grooving process in which a groove milling machine and a grooving machine cooperatively work is provided; the grooving machine is adopted for construction within the range of 4 m below a guide wall; a slot milling machine is adopted for construction in a range from 4m below a guide wall to 2m below a base, and the main control perpendicularity is realized by utilizing the characteristics of small cutting footage and low disturbance of the slot milling machine and combining visual monitoring; and the trenching machine construction is recovered from 2m below the base to the designed groove bottom area so as to improve the trenching efficiency. According to the method, the problems that the perpendicularity of the ultra-deep underground diaphragm wall is difficult to control and the grooving quality is unstable are effectively solved, and dual optimization of construction quality and efficiency is achieved.

Description

Technical Field

[0001] This invention belongs to the field of underground foundation engineering construction technology, and relates to a method for reinforcing the trench walls of ultra-deep underground continuous walls and a method for constructing trenches in combination. Specifically, it relates to a method for reinforcing the trench walls using a double-wheel churning machine (CSM) under complex geological conditions such as water-rich and deep soft soil, and for constructing ultra-deep underground continuous walls by combining a trenching machine (hydraulic grab bucket) and a milling machine (double-wheel milling machine) in sections. Background Technology

[0002] With the development and utilization of urban underground space, diaphragm walls, as retaining structures for deep foundation pits, are becoming increasingly deeper, and the construction environment is becoming more complex (such as proximity to rivers, water-rich sand layers, and deep soft soil). In the construction of ultra-deep diaphragm walls, the stability of the trench walls and the verticality of the trench are key factors determining the success or failure of the project.

[0003] In existing technologies, triaxial mixers are commonly used for the reinforcement of diaphragm wall trenches. However, the cross-sectional shape of the piles formed by triaxial mixers is a sawtooth three-circle shape, which can easily lead to "false joints" or weak points at the overlap between piles. Furthermore, as the reinforcement depth increases, the mechanical rigidity of the triaxial mixer itself limits its verticality control capability, which can easily cause the reinforced body to tilt inward or outward, affecting the trenching accuracy and water-stopping effect of the subsequent diaphragm wall.

[0004] In terms of trenching technology, traditional construction methods typically employ either a trenching machine (wire rope grab or hydraulic grab) or a trenching machine. Trenching machines offer high excavation efficiency and large single-pass excavation volume, but suffer from poor precision control, difficulty in excavating hard strata, and significant "piston effect" disturbance to the trench walls. Trenching machines offer high trenching precision, minimal soil disturbance, and the ability to cut hard rock, but their operating costs are extremely high, single-pass excavation volume is small, and construction efficiency is relatively low. For ultra-deep (e.g., exceeding 60m), ultra-wide (e.g., 1.2m-1.5m), and geologically complex diaphragm walls, a single trenching method often struggles to simultaneously meet the requirements of verticality quality control and construction schedule.

[0005] Therefore, there is an urgent need for a new construction method that can effectively solve the problem of verticality control in deep trench wall reinforcement and combine the advantages of different trenching equipment to achieve high-quality and high-efficiency construction of ultra-deep underground continuous walls. Summary of the Invention

[0006] To address the aforementioned issues, this invention discloses a method for reinforcing trench walls and constructing trenches for ultra-deep underground continuous walls. By optimizing the trench wall reinforcement process and constructing a "grab-milling-grab" combined trenching mode, both construction quality and efficiency are improved.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for reinforcing the trench walls and constructing an ultra-deep underground diaphragm wall includes the following steps: S1: Site preparation and guide wall construction: Level the site, use software to simulate groundwater and implement dewatering, and construct a “┓┏” shaped guide wall; S2: Double-wheel mixing tank wall reinforcement: Double-wheel mixing equipment is used to reinforce the soil on both sides of the tank wall to 2m below the foundation, forming a high-precision reinforced water-stop curtain with verticality controlled within 1 / 300. S3: Combined trenching excavation: Based on the soil characteristics and reinforcement range, the underground continuous wall trench section is divided into three working areas in the depth direction, and trenching machines and milling machines are used in a relay excavation manner; trenching is carried out in the order of "trenching machine - milling machine - trenching machine"; S4: Tank cleaning, slurry replacement and wall brushing: The tank is cleaned using the air-lift reverse circulation method, the thickness of the sediment at the bottom of the tank is controlled to be <10cm, and the side wall joints are brushed no less than 20 times. S5: Reinforcing cage hoisting and concrete pouring: The reinforcing cage is hoisted into the trench in sections or as a whole, and underwater concrete is poured using the tremie pipe method.

[0008] As a supplement to the present invention, step S1 describes the pre-construction process of simulating groundwater using software and implementing dewatering: A: A three-dimensional seepage numerical model was established using Visual ModFlow software, based on the permeability coefficient in the geological survey report (…). K xx , K yy , K zz Perform simulation calculations; B: Based on the simulation results, dewatering wells are arranged to control the groundwater level around the trench section at a specific depth below the ground surface (such as 5-10m) to ensure the stability of the trench wall during the trenching process.

[0009] As a supplement to the present invention, the double-wheel stirring tank wall reinforcement construction in step S2 adopts a "positioning control and overlapping process", which specifically includes: A: Set control lines in the direction parallel to the trench, and use the double plumb bobs under the operating platform (the spacing is the same as the width of the double wheel mixer, such as 2800mm) to align with the control lines for rough positioning; B: Use the inclination meter installed on the double-wheel agitator to display the drill pipe inclination in real time and control the verticality deviation within 1 / 300; C: Interlocking joints are implemented between adjacent mixing piles, with an overlap width of 200mm. The position of the pendulum is adjusted so that the edge of the next gear penetrates into the pile body of the previous pile, ensuring the continuity of the water-stop curtain.

[0010] As a supplement to the present invention, the specific operation process of the trench excavation construction described in step S3 is as follows: A: First section (surface guide zone): From the top of the guide wall to a depth of 4m below the guide wall, excavation will be carried out using a trenching machine (hydraulic grab bucket); B: Second section (reinforced soil layer fine excavation area): From 4m below the guide wall to 2m below the foundation pit (i.e., the area of ​​the trench wall reinforcement zone), a trench milling machine is used for cutting and excavation; taking advantage of the trench milling machine's characteristics of minimal soil disturbance and reverse circulation slag removal, the verticality is actively controlled and corrected in this section. C: Third section (high-efficiency zone of deep original soil layer): From 2m below the foundation pit to the bottom of the diaphragm wall design trench, trenching machine (hydraulic grab bucket) will be used again for excavation, taking advantage of its large single excavation volume to improve the construction efficiency of deep soil layer.

[0011] As a supplement to the present invention, ultrasonic testing technology is used for quality traceability during the trenching construction process in step S3: A: Use an ultrasonic testing instrument to scan the verticality and aperture of the excavated trench wall, generate digital records, and make the construction quality of each grab and each milling traceable. B: Based on the actual measured depth of the trench section using a measuring hammer, assess the quality grade of the trench section.

[0012] As a supplement to the present invention, the reverse circulation slag discharge process is adopted in the construction stage of the trenching machine in step S3. The mud index is controlled as follows: funnel viscosity 25-30s, relative density 1.03-1.10, pH value 8-9. When the trenching machine cuts the soil, the cut soil is discharged through the reverse circulation system to reduce the lateral squeezing disturbance to the soil in the reinforced area.

[0013] As a supplement to the present invention, the diaphragm wall is constructed using a phased skip-excavation method: A: Divide the trench into Phase I and Phase II. Construct Phase I first, and then construct Phase II after the concrete reaches the design strength. B: For "L" or "Z" shaped corner trough sections, when the length of the trough section is less than the opening size of the grab bucket of the troughing machine (e.g., 2.8m), the method of lengthening the guide wall is adopted to make the length of the working surface meet the mechanical operation requirements.

[0014] As a supplement to the present invention, the qualified standard for cleaning the tank and changing the mud in step S4 is: after cleaning the bottom and changing the mud for 1 hour, the mud specific gravity within 200mm of the bottom of the tank is not greater than 1.3, and the thickness of the sediment at the bottom of the tank is not greater than 100mm.

[0015] As a supplement to the present invention, in step S5, for super-heavy steel cages weighing more than 500t, a dual-crane lifting process (such as an 800t main crane and a 400t auxiliary crane) is adopted. The lifting is completed by lifting horizontally, tilting, straightening in the air, unhooking the auxiliary crane, and the main crane entering the trench by a single crane. "U"-shaped lifting bars, longitudinal truss reinforcing bars and "7"-shaped bars are set on the steel cage to ensure lifting rigidity.

[0016] The present invention has the following beneficial effects:

[0017] (1) This invention employs a double-wheel agitator to deeply reinforce the soil on both sides of the trench wall, and combines this with a segmented trenching construction process of "grab-milling-grab" to construct an integrated construction method for trench wall reinforcement and trenching suitable for ultra-deep diaphragm walls. Under water-rich and complex reinforcement soil conditions, this integrated process achieves a synergistic improvement in trench wall stability, trenching verticality, and construction efficiency, fundamentally solving the problems of difficult verticality control, unstable trenching quality, and high construction risk in the construction of ultra-deep diaphragm walls.

[0018] (2) Improve the quality of trench wall reinforcement: The use of a double-wheel mixer instead of a three-axis mixer solves the joint hazards caused by the sawtooth cross section. The digital verticality control system effectively overcomes the problem of difficult verticality control in deep reinforcement, providing good geological conditions for subsequent excavation.

[0019] (3) Balancing accuracy and efficiency: An innovative "grab-mill-grab" segmented construction method was adopted. A milling machine was used to ensure accuracy in the upper and middle parts (reinforcement zone), where verticality control is most critical; a trenching machine was used to increase speed in the deep parts where accuracy was already guided and the volume was huge. This scheme not only ensured the verticality of the wall (better than 1 / 300), but also avoided the high cost and construction delays caused by using a milling machine throughout the entire process.

[0020] (4) Reduce construction risks: The trench wall reinforcement extends to 2m below the foundation. Combined with auxiliary dewatering measures, the lateral pressure of groundwater on the trench wall is effectively isolated. Combined with the low-disturbance excavation of the trenching machine, the risk of hole collapse in the deep foundation pit construction of water-rich strata is greatly reduced.

[0021] (5) Digital quality traceability: By combining ultrasonic testing with the mechanical self-monitoring system, the construction process of concealed works is visualized and traceable. Attached Figure Description

[0022] Figure 1 This is a flowchart of the construction process of the present invention; Figure 2 This is a schematic diagram of the construction of a groove formed by grabbing, milling, and grabbing. Detailed Implementation

[0023] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Example

[0024] This embodiment relies on the retaining structure of a working shaft of a cross-river tunnel. The underground continuous wall is 1.5m thick and 69m deep. The geological conditions are mainly silt and silty clay, and the groundwater level is relatively high.

[0025] A method for reinforcing the trench walls of ultra-deep underground diaphragm walls and constructing them as a combined trench, including... Step 1: Precipitation Simulation and Precipitation Forecast The original farmland underwent "three connections and one leveling" (water, electricity, road access, and land leveling), and a ring road was constructed for the soft foundation. A three-dimensional seepage model was created using VisualModFlow software. By inputting the stratum permeability coefficient (e.g., silt layer Kxx=9 m / d), the calculation showed that the groundwater level needed to be lowered to 5-10m below the ground surface. Based on this, dewatering wells were placed at 30m intervals outside the pit and 40m intervals inside the pit for pre-dewatering.

[0026] Step 2: Guide Wall Construction Measurement and layout: extend the guide wall edge line 5cm outward, adopt "┓┏" shaped reinforced concrete guide wall with concrete strength C25, set supports between guide walls, and set positioning marks on the top surface of the guide wall.

[0027] Step 3: Double-Wheel Mixer (CSM) Trench Wall Reinforcement. Addressing the poor verticality control of the original three-axis mixer, a double-wheel mixer was selected. Control lines were set parallel to the trench direction, and two plumb bobs spaced 2800mm apart were suspended below the double-wheel mixer operating platform. Using the inclinometer readings displayed on the operator's cab screen, the drill rods were adjusted in real time, requiring the verticality error to be controlled within 1 / 300 (e.g., deviation <0.12m at a depth of 36m). The reinforcement depth was set from the top of the guide wall to 2m below the foundation pit elevation. The pile center distance was 2600mm, with an overlap of 200mm between adjacent piles. By adjusting the plumb bob positions, the next milling wheel was inserted 200mm into the previous one, ensuring the continuity of the cutoff wall.

[0028] Step 4: Groove construction using a combination of grabbing, milling, and grabbing. like Figure 2As shown, a three-stage operation combining a milling machine and a trenching machine is employed: 0m to -4m (guide wall section): The trenching machine (hydraulic grab bucket) is used for excavation, quickly clearing the surface soil and avoiding direct contact between the milling machine's cutter and the guide wall. -4m to 2m below the foundation (reinforcement section): The operation switches to the milling machine. This section is crucial for verticality control. The milling machine uses its cutter to cut the soil and performs reverse circulation for slag removal. The operator uses a display to perform "on-the-fly milling and correction," adjusting the machine's posture to ensure the verticality of the trench wall in this section is better than 1 / 500. Due to the minimal disturbance caused by the milling machine, the newly completed trench wall reinforcement layer is effectively protected. 2m below the foundation to -69m (deep section): The operation switches back to the trenching machine. Utilizing the high-precision trenches already excavated by the milling machine as "guide tubes," the trenching machine's grab bucket descends smoothly, leveraging its advantages of large grabbing capacity and high speed to complete the excavation of the remaining deep soil.

[0029] Step 5: Quality Inspection and Mud Circulation Throughout the trenching process, technicians monitored the entire operation. After trenching was completed, a new type of ultrasonic testing instrument was used to scan the entire trench section to check its width and verticality. The mud was prepared using bentonite and circulated during construction using a "cyclone + solidification" and filter press system to ensure that the mud specific gravity at the bottom 200mm of the trench after cleaning was not greater than 1.15.

[0030] Step Six: Hoist the steel reinforcement cage and pour concrete. The diaphragm wall was cleaned using an air-lift reverse circulation method, with the sediment thickness controlled to be less than 10cm. A specialized wall brush was used to brush the I-beam joints at least 20 times from top to bottom. Finally, an 800t and a 400t crawler crane were used to lift and safely lower the steel cage, weighing over 800 tons, into the trench. Underwater C40 concrete was then poured using a tremie pipe method to complete the diaphragm wall construction.

[0031] Actual construction verification has shown that the trench wall reinforcement and "grab-milling-grab" combined trenching construction method of this invention significantly improves both construction efficiency and trenching quality compared to the originally planned "triaxial mixer + single trenching machine" scheme. In this embodiment of the project, the average trenching time for a single diaphragm wall is approximately 48-52 hours, with the milling machine accounting for about 35% of the operation time and the trenching machine accounting for about 65%, shortening the construction period by approximately 25%-30% compared to the scheme using a milling machine throughout the entire process. Furthermore, compared to the traditional method of using a trenching machine alone, the efficiency of deep trenching is increased by more than 20%.

[0032] Regarding the quality of trenching, through the synergistic effect of double-wheel stirring wall reinforcement and the main verticality control of the milling machine, the measured overall verticality of the diaphragm wall was controlled within 1 / 400, and the key control section was better than 1 / 500, which is significantly better than the 1 / 250 to 1 / 300 level generally achieved by conventional processes; the trench width deviation was controlled within ±30mm, the trench wall stability was good, and no quality accidents such as hole collapse or necking occurred during the trenching process.

[0033] Furthermore, the trench wall reinforcement depth extends to 2m below the foundation. Combined with pre-dewatering and low-disturbance milling construction methods, this effectively reduces the lateral impact of groundwater on the trench wall. During trenching, the mud parameters remained stable, and no adverse phenomena such as sudden inrush or leakage occurred. The above construction data demonstrate that this invention has significant engineering applicability and promotional value in ultra-deep, water-rich strata.

[0034] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A method for reinforcing the trench walls and constructing an ultra-deep underground continuous wall, characterized in that: Includes the following steps: S1: Site preparation and guide wall construction: Level the site, simulate groundwater using software and implement dewatering, and construct a "┓┏" shaped guide wall; S2: Double-wheel mixing tank wall reinforcement: Double-wheel mixing equipment is used to reinforce the soil on both sides of the tank wall to 2m below the foundation, forming a high-precision reinforced water-stop curtain with verticality controlled within 1 / 300. S3: Combined trenching excavation: Based on the soil characteristics and reinforcement range, the underground continuous wall trench section is divided into three working areas in the depth direction, and trenching machines and milling machines are used in a relay excavation manner; trenching is carried out in the order of "trenching machine - milling machine - trenching machine"; S4: Tank cleaning, slurry replacement and wall brushing: The tank is cleaned using the air-lift reverse circulation method, the thickness of the sediment at the bottom of the tank is controlled to be <10cm, and the side wall joints are brushed no less than 20 times. S5: Reinforcing cage hoisting and concrete pouring: The reinforcing cage is hoisted into the trench in sections or as a whole, and underwater concrete is poured using the tremie pipe method.

2. The method for reinforcing the trench walls and constructing an assembled trench for an ultra-deep underground continuous wall according to claim 1, characterized in that: Step S1 describes the pre-construction process of simulating groundwater using software and implementing dewatering: A: Use Visual ModFlow software to build a three-dimensional seepage numerical model and perform simulation calculations based on the permeability coefficient in the geological survey report; B: Based on the simulation results, dewatering wells are arranged to control the groundwater level around the trench section at a specific depth below the ground surface to ensure the stability of the trench wall during the trenching process.

3. The method for reinforcing the trench walls and constructing an assembled trench for an ultra-deep underground continuous wall according to claim 1, characterized in that: Step S2 describes the double-wheel mixing tank wall reinforcement construction using a "positioning control and overlapping process," which specifically includes: A: Set control lines in the direction parallel to the trench, and use the double plumb bobs under the operating platform to align with the control lines for coarse positioning; B: Use the inclination meter installed on the double-wheel agitator to display the drill pipe inclination in real time and control the verticality deviation within 1 / 300; C: Interlocking joints are implemented between adjacent mixing piles, with an overlap width of 200mm. The position of the pendulum is adjusted so that the edge of the next gear penetrates into the pile body of the previous pile, ensuring the continuity of the water-stop curtain.

4. The method for reinforcing the trench walls and constructing an assembled trench for an ultra-deep underground continuous wall according to claim 1, characterized in that: The specific work process for the combined trench excavation construction described in step S3 is as follows: A: First section: From the top of the guide wall to a depth of 4m below the guide wall, excavation will be carried out using a trenching machine; B: Second section: From 4m below the guide wall to 2m below the foundation pit, a trenching machine will be used for cutting and excavation; taking advantage of the trenching machine's characteristics of minimal soil disturbance and reverse circulation slag removal, the verticality will be actively controlled and corrected in this section. C: Third section: From 2m below the foundation pit to the bottom of the diaphragm wall design trench, trenching machine will be used again for excavation, taking advantage of its large single excavation volume to improve the construction efficiency of deep soil layers.

5. The method for reinforcing the trench walls and constructing an assembled trench for an ultra-deep underground continuous wall according to claim 1, characterized in that: Ultrasonic testing technology is used for quality traceability during the trenching process in step S3. A: Use an ultrasonic testing instrument to scan the verticality and aperture of the excavated trench wall, generate digital records, and make the construction quality of each grab and each milling traceable. B: Based on the actual measured depth of the trench section using a measuring hammer, assess the quality grade of the trench section.

6. The method for reinforcing the trench walls and constructing a combined trench for ultra-deep underground continuous wall according to claim 1, characterized in that: In step S3, the trenching machine construction stage adopts a reverse circulation slag removal process, and the mud index is controlled as follows: funnel viscosity 25-30s, relative density 1.03-1.10, pH value 8-9; when the trenching machine cuts the soil, the cut soil is discharged through the reverse circulation system to reduce the lateral squeezing disturbance to the soil in the reinforced area.

7. The method for reinforcing the trench walls and constructing a combined trench for ultra-deep underground continuous wall according to claim 1, characterized in that: The underground diaphragm wall was constructed using a phased, skip-excavation method. A: Divide the trench into Phase I and Phase II. Construct Phase I first, and then construct Phase II after the concrete reaches the design strength. B: For "L" or "Z" shaped corner trough sections, when the length of the trough section is less than the opening size of the grab bucket of the troughing machine, the method of lengthening the guide wall is adopted to make the length of the working surface meet the mechanical operation requirements.

8. The method for reinforcing the trench walls and constructing a combined trench for ultra-deep underground continuous wall according to claim 1, characterized in that: The qualified standard for cleaning and replacing mud in step S4 is: one hour after cleaning and replacing mud, the mud specific gravity within 200mm of the bottom of the tank is not greater than 1.3, and the thickness of sediment at the bottom of the tank is not greater than 100mm.

9. The method for reinforcing the trench walls and constructing a combined trench for ultra-deep underground continuous wall according to claim 1, characterized in that: In step S5, for super-heavy steel cages weighing over 500t, a dual-crane lifting process is adopted, which involves lifting horizontally, tilting, straightening in mid-air, unhooking the auxiliary crane, and placing the main crane into the trench. "U"-shaped lifting bars, longitudinal truss reinforcing bars, and "7"-shaped bars are installed on the steel cage to ensure lifting rigidity.

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