A core tube double-channel underground continuous wall deep foundation pit enclosure structure and a construction method thereof

Abstract

The application discloses a kind of core tube double lane underground continuous wall deep foundation pit enclosure structure and construction method, overall technical scheme is " constructs double lane underground continuous wall tube middle tube enclosure system, superimposed connection beam lattice formula subsection pull, second lane underground continuous wall first layer earthwork range dense anchor rod design, underground continuous wall-superimposed connection beam-anchor rod-cement soil retaining wall overall collaborative bearing, concrete slope protection surface layer covers enclosure structure body all fields". The application constructs "three sets of hoop" collaborative bearing system, forms multiple lines of defense by double lane underground continuous wall and cement soil retaining wall, is connected with dense anchor rod by superimposed connection beam lattice formula pull, substantially improves the overall stiffness and lateral displacement resistance of structure, effectively controls lateral deformation and groundwater seepage in the process of foundation pit excavation, significantly enhances the safety and stability of foundation pit under superdeep, complex working conditions.

Description

Technical Field

[0001] This invention relates to the field of deep foundation pit support technology, specifically to a core tube double-layer underground continuous wall deep foundation pit support structure and construction method. Background Technology

[0002] With the continuous acceleration of urbanization in my country, the demand for the development and utilization of underground space is becoming increasingly urgent. Deep foundation pit engineering is being used more and more widely in the construction of large-scale infrastructure such as high-rise buildings, subway stations, and underground integrated pipe corridors. As a core engineering measure to ensure the safety of foundation pit construction, control the deformation of surrounding soil, and prevent groundwater seepage, the technical rationality and reliability of the foundation pit retaining structure are directly related to the overall safety of the project, construction efficiency, and the stability of the surrounding environment.

[0003] Currently, traditional foundation pit support methods, such as single-channel diaphragm walls and pile-anchor support, are gradually revealing numerous technical bottlenecks when facing deep foundation pit projects with ultra-deep (excavation depth exceeding 15m), ultra-large spans, complex surrounding environments (adjacent to existing buildings, dense underground pipelines), or harsh geological conditions (soft soil, high dynamic water pressure, hard soil areas).

[0004] Firstly, the structural rigidity is insufficient, making it difficult to effectively control lateral deformation during the excavation process, which can easily lead to risks such as settlement of the surrounding soil and cracking of existing buildings.

[0005] Secondly, the water-stopping system is not perfect. A single water-blocking structure is prone to leakage under complex geological conditions, which affects construction safety.

[0006] Third, the cooperative bearing capacity among the various enclosure components is weak, and there is a lack of effective connection and force transmission mechanisms, resulting in unclear load transfer paths and insufficient overall resistance to instability.

[0007] Fourth, traditional construction techniques rely heavily on on-site casting, which results in long construction cycles, high resource consumption, and difficulties in disposing of waste such as slurry and construction waste, which does not conform to the industry development trend of green building and resource utilization.

[0008] Fifth, its low degree of prefabrication makes it difficult to meet the requirements of modern engineering for construction efficiency, quality control, and low-carbon environmental protection.

[0009] To address the aforementioned industry pain points and align with the development trends of prefabricated, green, and intelligent construction, there is an urgent need to develop a new deep foundation pit retaining structure system that combines high rigidity, strong integrity, precise deformation control, reliable water-stopping performance, and conforms to the concept of green construction. Summary of the Invention

[0010] The purpose of this invention is to provide a core tube double-layer underground continuous wall deep foundation pit retaining structure and construction method to solve the problems mentioned in the background art.

[0011] To achieve the above objectives, the present invention provides the following technical solution: a core-tube double-layer diaphragm wall deep foundation pit retaining structure, comprising a first diaphragm wall and a second diaphragm wall, wherein the foundation pit excavation is protected by a core-tube double-layer diaphragm wall formed by the first and second diaphragm walls, wherein the first diaphragm wall is located inside the second diaphragm wall; a composite connecting beam is provided between the first and second diaphragm walls, and the composite connecting beam is segmented and located at the top of both; a cement-soil retaining wall is also provided outside the second diaphragm wall, and anchor bolts are driven from the inside of the second diaphragm wall toward the cement-soil retaining wall within the first layer of excavation height; a concrete slope protection layer is provided on the top of the composite connecting beam and the cement-soil retaining wall.

[0012] Preferably, the outermost cement-soil retaining wall forms the first ring of reinforced soil, the second diaphragm wall in the middle of the retaining structure forms the second ring of soil retention and water stop, and the first diaphragm wall on the inner side of the retaining structure forms the third ring of soil retention and water stop; the width of the cement-soil retaining wall is not less than 3.0m, the design thickness of the first and second diaphragm walls is not less than 0.6m, and the distance between the first and second diaphragm walls is not less than 2.0m and not more than 4.5m.

[0013] Preferably, the first and second diaphragm walls are connected by a composite tie beam lattice structure in segments. The composite tie beams are prefabricated in a prefabricated PC factory with a cross-sectional dimension of not less than 250mm×250mm. The reinforcing bars of the composite tie beams are anchored into the cast-in-place joints of the first and second diaphragm walls, respectively. The cast-in-place joints are formed by pouring fine aggregate concrete of not less than C30. The spacing between two adjacent composite tie beams shall not exceed 1.8m. When the excavation depth of the foundation pit exceeds 15m or is subject to long-term vibration or high dynamic water pressure, the spacing between two adjacent composite tie beams shall not exceed 1.2m.

[0014] Preferably, the anchor bolts are densely arranged on the second diaphragm wall within the 2.0m excavation depth of the first layer of earthwork. The anchor bolts are driven obliquely into the cement-soil retaining wall from the inside of the second diaphragm wall. The length of the anchor bolts is not less than 2.5m, and the angle between the anchor bolts driven into the cement-soil retaining wall and the horizontal is 15°~30°. The anchor bolts are evenly distributed around the perimeter of the foundation pit, and the spacing between two adjacent anchor bolts in the longitudinal and transverse directions does not exceed 450mm. The ends of the anchor bolts are fixed to the inside of the second diaphragm wall with anchors. The distance between the first row of anchor bolts at the top of the second diaphragm wall and the bottom of the composite connecting beam does not exceed 300mm.

[0015] Preferably, the concrete slope protection surface layer contains not less than The bidirectional steel mesh is supported on the composite reinforcement of the composite connecting beam. The cast-in-place joint and the concrete slope protection surface layer are cast together with fine stone concrete of not less than C30. The thickness of the concrete slope protection surface layer is not less than 100mm, and its width exceeds the boundary of the cement soil retaining wall area by not less than 300mm.

[0016] This invention also provides a construction method for a core tube double-layer underground continuous wall deep foundation pit retaining structure. The overall construction process is as follows:

[0017] Step S1: Measure and lay out the positional relationships, then construct the guide wall;

[0018] Step S2: Construction of the double-layer diaphragm wall, chiseling the top steel reinforcement;

[0019] Step S3: Erection of the composite connecting beam and joint treatment;

[0020] Step S4: Excavation of the soil layer between the two underground continuous walls and installation of anchor bolts;

[0021] Step S5: Backfilling of earthwork between the two underground continuous walls and hoisting of steel mesh;

[0022] Step S6: Concrete slope protection surface layer pouring, and full excavation of foundation pit.

[0023] This invention also provides a construction method for a core tube double-layer underground continuous wall deep foundation pit retaining structure. The detailed construction process is as follows:

[0024] Step S1: Measure and lay out the lines to determine the positional relationship; construction of the cement-soil retaining wall:

[0025] First, a total station is used to accurately determine the specific location relationships of the foundation pit, the first diaphragm wall, the second diaphragm wall, and the cement-soil retaining wall, as well as the location of each pile. Then, construction of the cement-soil retaining wall is carried out. The first step involves positioning and straightening the pile driver. The mixing pile driver is moved to the designated pile location, and the pile frame is adjusted using a level and theodolite to ensure that the verticality deviation of the drill rod is within 1%. The mixing head is aligned with the center of the pile location. The second step involves pre-mixing and sinking. The mixer is started, and the mixing head is driven downwards along the guide frame, cutting through the soil and rotating until the designed pile bottom elevation is reached. During sinking, only mixing is performed; no grouting is applied to loosen the soil. The third step involves grouting, mixing, and lifting. After reaching the designed depth, the grout pump is turned on, and the proportioned cement grout is sprayed through the drill rod from the mixing head. After continuous grouting and mixing at the pile bottom for 60 seconds, the grout is then applied at a 1.0... The mixing head is raised at a uniform speed of m / min while spraying and mixing, ensuring thorough mixing of the grout with the soil. The fourth step involves repeated lowering and mixing. After raising the head to the pile top or the designed re-mixing depth, the grout pump is shut off again, and the mixing head is lowered back to the pile bottom for a second mixing to increase uniformity. The fifth step involves repeating the spraying, mixing, and raising process. After lowering the head to the pile bottom, the grout pump is restarted for spraying, and the mixing head is raised to the pile top at the designed speed to complete the second spraying and mixing. For important projects or complex areas with hard soil, this process is repeated. Under working conditions, a four-mixing and two-spraying process is used for treatment; the sixth step is pile top treatment and machine relocation. After the mixing head is lifted out of the ground, the machine is turned off, and the pile top elevation is checked. If there is slurry or depression, it is repaired or slurry is added. The pile driver is then moved to carry out the construction of the next pile; the construction of piles is continuous, and the construction interval between adjacent piles does not exceed 24 hours; the "one-hole-within-one" process of three-axis mixing piles is adopted to ensure that the piles are tightly interlocked to form a continuous cement-soil retaining wall of equal thickness without weak joints. Process acceptance and recording are carried out.

[0026] Step S2: Construction of the double-layer diaphragm wall, chiseling the top reinforcement of the wall:

[0027] After the construction of the cement-soil retaining walls around the foundation pit is completed, the guide walls for the first and second diaphragm walls can be constructed. The guide wall construction adopts a "double-hoop ring arrangement, with the guide walls not removed throughout the process, and poured together with the cast-in-place joints of the composite connecting beams and the concrete slope protection surface layer." The top elevation of the guide wall is designed to be 50mm lower than the concrete slope protection surface layer. The guide wall uses reinforced concrete structure with a concrete strength of not less than C30, specifically divided into inner and outer guide walls, respectively placed at the top of the first and second diaphragm walls. During on-site construction, precise layout is essential, strictly controlling the axis and elevation. The centerline must coincide with the axis of the first and second diaphragm walls, and the net distance between the inner wall surfaces should be slightly larger than the designed wall thickness by 50mm. Secondly, the guide walls are built on a solid foundation; if weak soil layers are encountered, they should be replaced and reinforced to prevent uneven settlement. The designed depth of the guide walls is 1500mm. ~2000mm, the top is higher than the ground to prevent surface water from flowing in. The concrete pouring ensures strength and integrity. The backfill on the side of the wall must be compacted. After construction, the verticality, spacing and top elevation of the inner wall surface are carefully checked to provide an accurate reference for the trenching machine. After the construction of the double underground continuous wall is completed, the curing and finished product protection are strengthened. After the concrete strength of the double underground continuous wall reaches more than 50% of the design strength, the top reinforcement of the double underground continuous wall can be excavated. The exposed length of the design reinforcement after the top of the double underground continuous wall is not less than 35d, where d is the diameter of the longitudinal reinforcement of the underground continuous wall. The top of the guide wall adopts the "elevation reduction" treatment method, that is, the top of the guide wall is 30mm lower than the bottom elevation of the design composite connecting beam. The construction of the second underground continuous wall adopts the "secondary process", that is, the first construction is to 2000mm below the design wall top elevation, and the second construction is synchronized with the anchor bolt construction, and the "post-poured concrete" method is used to complete all operations.

[0028] Step S3: Erection of composite connecting beams, joint treatment:

[0029] After the double-layer diaphragm wall construction is completed and the top reinforcement bars have been excavated according to the design elevation, the wall top reinforcement bars that have been excavated in the double-layer diaphragm wall are straightened and secondary processed. If the exposed length of the wall top reinforcement bars is less than 35d due to the diaphragm wall construction in the aforementioned process, the method of "adding anchor plates" is adopted to deal with it. The number of anchor plates is not less than 50% of the total number of exposed reinforcement bars, and the anchor plates are staggered and arranged in a wave pattern to strengthen the length of the exposed reinforcement bars at the top of the double-layer diaphragm wall into the cast-in-place joints at both ends of the composite connecting beam in the subsequent process. After all the above procedures are completed, the top of the cement-soil retaining wall within 800mm of the location of each composite connecting beam is excavated or chiseled down to the bottom elevation of the composite connecting beam. Then, the top of the cement-soil retaining wall is fully utilized as a base. The support system for the composite connecting beams involves hoisting each composite connecting beam one by one. During on-site construction, the composite connecting beams are prefabricated in a prefabricated PC factory and then transported, stacked, and hoisted into place. All the reinforcing bars at both ends of the composite connecting beams are anchored into the exposed reinforcing bars at the top of the double-layer diaphragm wall. Since the diaphragm wall is relatively thick, the reinforcing bars at the ends of the composite connecting beams can be directly set with a 90-degree bend straight section, without the need for anchor plates, provided that the anchorage length meets the specifications. After the composite connecting beams are hoisted, the planar position and elevation of the composite connecting beams are checked and confirmed to be correct. Aluminum formwork is then used to quickly support the cast-in-place joints of the composite connecting beams and the diaphragm wall. Fine aggregate concrete of not less than C30 is used for one-time casting and curing. The relevant concealed works are inspected and recorded.

[0030] Step S4: Excavation of the soil layer between the two diaphragm walls and installation of anchor bolts:

[0031] After the composite connecting beams are in place, the first layer of earthwork between the first and second diaphragm walls is excavated. During on-site construction, the excavation depth between the first and second diaphragm walls is 1600mm~2000mm. During excavation, machinery must not touch the two diaphragm walls. After excavation, the inner walls of the diaphragm walls are cleaned manually, focusing on removing debris and residual laitance from the second diaphragm wall construction within 2000mm below the top. The internal reinforcement of the second diaphragm wall within the secondary post-cast area is also addressed, especially the exposed reinforcement at the top. Then, formwork and support systems are erected on the inner wall of the second diaphragm wall. While supporting the wall formwork system, anchor sleeves are installed inside the cement-soil retaining wall. The outer wall of the anchor sleeve is roughened to enhance the bond strength between the anchor sleeve and the concrete of the second diaphragm wall. The anchor sleeve is fixed inside the reinforcement cage of the second diaphragm wall. Finally, fine aggregate concrete with a strength one grade higher than that of the second diaphragm wall concrete is poured in one go. The construction is carried out in sections. Except for the construction joint left in the first process of the second diaphragm wall, no construction joints should be left in the entire process of pouring the secondary post-cast concrete within 2000mm below the top of the second diaphragm wall. The curing should be strengthened. After the second diaphragm wall is completed, the anchors can be driven into the cement-soil retaining wall one by one through the anchor sleeves pre-embedded inside the second diaphragm wall within the secondary post-cast process range. The relevant hidden works acceptance and recording work should be done throughout the process.

[0032] Step S5: Backfilling of earthwork between the two diaphragm walls and installation of steel mesh:

[0033] After all anchor bolts within 2000mm below the top of the second diaphragm wall have been installed, the soil between the two diaphragm walls will be backfilled immediately. Modified soil formed from dehydrated and solidified engineering waste mud will be used as the main aggregate, mixed with an appropriate amount of recycled building powder as a mineral admixture, and supplemented with a small amount of polymer soil stabilizer and water. During construction, a combination of layered paving and small vibratory equipment will be used, strictly controlling the loose thickness of each layer and the number of compaction passes to ensure a filling density of over 95%, and monitoring compaction and deformation will be conducted. The soil between the two diaphragm walls will be backfilled to 30mm below the bottom of the composite connecting beam. After the backfilling is completed, the steel mesh at the top of the composite connecting beam will be installed. The steel mesh will be made of materials no less than [amount missing]. The double-layer steel mesh, with a cutting width that can fully cover the entire area from the first underground continuous wall to the edge of the cement-soil retaining wall, ensures proper acceptance and recording of related concealed works.

[0034] Step S6: Concrete slope protection layer pouring, full excavation of foundation pit:

[0035] After the steel mesh at the top of the composite connecting beam is installed, the concrete slope protection surface layer can be poured. Before construction, remove loose soil and other debris from the slope surface due to the aforementioned process, and check and correct the steel reinforcement of the composite connecting beam and the steel mesh above it. Use fine aggregate concrete with a strength grade of not less than C30, and the surface layer thickness is 150mm~200mm. During the pouring process, adopt the method of "segmented pouring, first pouring the fine aggregate concrete in the left and right ranges of the corner of the foundation pit, and then pouring the fine aggregate concrete in other parts", vibrate and compact it, and smooth and polish the surface. After the concrete has initially set, cover and water it for curing for no less than 7 days to prevent cracking.

[0036] Compared with the prior art, the beneficial effects of this invention are as follows:

[0037] 1. This invention constructs a "three-hoop" collaborative bearing system, which forms multiple defense lines through double underground continuous walls and cement-soil retaining walls, and is combined with overlapping tie beams in a grid-like structure and dense anchor rods to significantly improve the overall structural stiffness and resistance to lateral displacement, effectively control lateral deformation and groundwater infiltration during the excavation process, and significantly enhance the safety and stability of the foundation pit under ultra-deep and complex working conditions.

[0038] 2. During construction, modified soil from engineering waste mud and recycled building powder are used as backfill materials to realize the resource utilization of waste. The prefabrication of composite connecting beams reduces on-site casting operations, reduces dust and noise pollution, and conforms to the concept of green and low-carbon construction, reducing environmental burden and resource consumption.

[0039] 3. The rapid on-site hoisting of precast components, combined with aluminum formwork erection and integrated casting of guide walls, shortens the construction cycle. The technical parameters and acceptance standards for each key process are clearly defined, improving construction efficiency and quality control. It can be adapted to deep foundation pit projects with different geological conditions, excavation depths and surrounding environments.

[0040] 4. Multi-component collaborative stress optimization of load transfer path reduces material usage per component, resource utilization and prefabricated construction reduce overall costs, and composite modified soil backfill and integral concrete slope protection layer ensure long-term structural stability, achieving a balance between engineering safety, economy and reliability. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the deep foundation pit retaining structure of the present invention;

[0042] Figure 2 This is a diagram showing the positional relationship between the composite connecting beam and the concrete slope protection surface layer in this invention;

[0043] Figure 3 This is a flowchart of the overall process of the construction method of the present invention. Detailed Implementation

[0044] This invention discloses a deep foundation pit retaining structure with a core tube and double-layer diaphragm wall. The overall structure mainly consists of a first diaphragm wall 1, a second diaphragm wall 2, a composite connecting beam 3, anchor bolts 4, a cement-soil retaining wall, and a concrete slope protection layer 5. The specific structure is as follows (see reference). Figure 1 and Figure 2 :

[0045] The excavation of the foundation pit is protected by a double-layer diaphragm wall, consisting of a first diaphragm wall 1 and a second diaphragm wall 2. The first diaphragm wall 1 is located inside the second diaphragm wall 2, and a composite connecting beam 3 is provided between the first diaphragm wall 1 and the second diaphragm wall 2. The composite connecting beam 3 is segmented and located at the top of the first diaphragm wall 1 and the second diaphragm wall 2. Anchor bolt holes are provided on the second diaphragm wall 2 within the first layer of excavation height. A cement-soil retaining wall is also provided on the outside of the second diaphragm wall 2 away from the foundation pit. Anchor bolts 4 are driven through the anchor bolt holes on the second diaphragm wall 2 and installed inside the cement-soil retaining wall. A concrete slope protection layer 5 is provided on the top of the composite connecting beam 3 and the cement-soil retaining wall, thus forming a core tube double-layer diaphragm wall deep foundation pit protection structure.

[0046] The overall technology follows the design concept of "constructing a double-layer underground continuous wall tube-in-tube retaining system, 3-layer composite connecting beams in a grid-structured segmented connection, 4-layer dense anchor rods within the first-layer earthwork area of ​​the second underground continuous wall, 3-layer composite connecting beams, 4-anchor rods, and 5-cement-soil retaining wall for overall coordinated load bearing, and 5-concrete slope protection layer covering the entire area of ​​the retaining structure".

[0047] To enhance the safety bearing capacity of the deep foundation pit retaining structure, the first diaphragm wall 1, the second diaphragm wall 2, and the cement-soil retaining wall form a "three-ring" bearing system within a cylinder. The outermost cement-soil retaining wall forms the first ring of reinforced soil; the second diaphragm wall 2 in the middle of the retaining structure forms the second ring of soil retention and water stoppage; and the cement-soil retaining wall and the second diaphragm wall 2 are reinforced with dense anchor bolts 4. The first diaphragm wall 1 on the inner side of the retaining structure forms the third ring of soil retention and water stoppage. Furthermore, the first diaphragm wall 1 and the second diaphragm wall 2 are connected by a lattice-type composite connecting beam 3, forming a three-ring retaining effect during foundation pit excavation. The width of the cement-soil retaining wall is not less than 3.0m, the design thickness of the first diaphragm wall 1 and the second diaphragm wall 2 is not less than 0.6m, and the distance between the first diaphragm wall 1 and the second diaphragm wall 2 is not less than 2.0m and not more than 4.5m.

[0048] To further enhance the collaborative bearing capacity between the first diaphragm wall 1 and the second diaphragm wall 2, from the perspective of the force transfer path of the retaining structure, a composite connecting beam 3 is provided at the top of the first diaphragm wall 1 and the second diaphragm wall 2. The composite connecting beam 3 is prefabricated in a prefabricated PC factory, with a cross-sectional dimension of not less than 250mm × 250mm. The two ends of the composite connecting beam 3 form cast-in-place nodes 6 with the top of the first diaphragm wall 1 and the second diaphragm wall 2. The reinforcing bars of the composite connecting beam 3 are anchored into the cast-in-place nodes 6 at the top of the first diaphragm wall 1 and the second diaphragm wall 2, respectively. The cast-in-place nodes 6 are cast using fine aggregate concrete of not less than C30. The spacing between two adjacent composite connecting beams 3 shall not exceed 1.8m. When the excavation depth of the foundation pit exceeds 15m, or when subjected to long-term vibration or high dynamic water pressure, or other complex working conditions, the spacing between two adjacent composite connecting beams 3 shall not exceed 1.2m.

[0049] To further enhance the collaborative bearing capacity between the second diaphragm wall 2 and the cement-soil retaining wall, densely packed anchor bolts 4 are installed on the second diaphragm wall 2 within the 2.0m excavation depth of the first layer of earthwork. Anchor bolt sleeves 7 are inserted into the anchor bolt holes of the second diaphragm wall 2, and the anchor bolts 4 are placed in the anchor bolt sleeves 7. The anchor bolts 4 are driven obliquely into the cement-soil retaining wall from the inside of the second diaphragm wall 2. The designed length of the anchor bolts 4 is not less than 2.5m. The angle between the anchor bolts 4 and the horizontal is preferably 15°~30°. They are evenly distributed around the perimeter of the excavation pit. The spacing between two adjacent anchor bolts 4 in both the longitudinal and transverse directions does not exceed 450mm. The ends of the anchor bolts 4 are fixed to the inside of the second diaphragm wall 2 with anchors. The distance between the first row of anchor bolts 4 at the top of the second diaphragm wall 2 and the bottom of the composite connecting beam 3 does not exceed 300mm.

[0050] In view of the need for coordinated load-bearing of the overall retaining structure and the needs of the working surface around the top of the foundation pit, a concrete slope protection layer 5 is provided on top of the composite connecting beam 3 and the cement-soil retaining wall. The concrete slope protection layer 5 contains a minimum of The bidirectional steel mesh is supported on the composite reinforcement of the composite connecting beam 3. The cast-in-place node 6 and the concrete slope protection layer 5 are cast together with fine stone concrete of not less than C30. The thickness of the concrete slope protection layer 5 is not less than 100mm, and its width exceeds the boundary of the cement soil retaining wall area by not less than 300mm.

[0051] Based on the aforementioned core tube double-layer diaphragm wall deep foundation pit retaining structure, its corresponding construction method is provided for reference. Figure 3 The overall construction process is as follows:

[0052] Step S1: Measure and lay out the positional relationships, then construct the guide wall;

[0053] Step S2: Construction of the double-layer diaphragm wall, chiseling the top steel reinforcement;

[0054] Step S3: Erection of the composite connecting beam and joint treatment;

[0055] Step S4: Excavation of the soil layer between the two underground continuous walls and installation of anchor bolts;

[0056] Step S5: Backfilling of earthwork between the two underground continuous walls and hoisting of steel mesh;

[0057] Step S6: Concrete slope protection surface layer pouring, and full excavation of foundation pit.

[0058] The key technical solutions for the above construction process are as follows:

[0059] Step S1: Measure and lay out the lines to determine the positional relationship, then construct the cement-soil retaining wall.

[0060] First, a total station is used to accurately determine the specific location relationships of the foundation pit, the first diaphragm wall, the second diaphragm wall, and the cement-soil retaining wall, as well as the location of each pile. Then, the cement-soil retaining wall is constructed.

[0061] The first step is to position and straighten the pile driver. Move the mixing pile driver to the designated pile position, use a level and theodolite to adjust the pile frame, and ensure that the verticality deviation of the drill rod is within 1%. Align the mixing head with the center of the pile position.

[0062] The second step is pre-mixing and sinking (first mixing). Start the mixer and make the mixing head cut and rotate downward along the guide frame until the designed pile bottom elevation. During the sinking process, only mixing is performed and no grout is sprayed to loosen the soil.

[0063] The third step is grouting, mixing, and lifting (first grouting). After reaching the designed depth, the grout pump is turned on, and the cement grout prepared in proportion is sprayed out from the mixing head through the drill rod. After continuously spraying and mixing at the bottom of the pile for 60 seconds, the mixing head is lifted at a uniform speed of 1.0 m / min, while maintaining grouting and mixing to ensure that the grout is fully mixed with the soil.

[0064] The fourth step is to repeat the sinking and mixing (second mixing). After raising the pile to the top or the designed re-mixing depth, turn off the grout pump again and sink the mixing head to the bottom of the pile for a second mixing to increase uniformity.

[0065] The fifth step involves repeating the spraying, mixing, and lifting process (second spraying). After the pile sinks to the bottom, the grout pump is restarted for spraying, and the mixing head is lifted to the top of the pile at the designed speed to complete the second spraying and mixing. For important projects or complex conditions such as hard soil areas, a four-mixing and two-spraying process is used.

[0066] Step 6: Pile top treatment and machine relocation. After the mixing head is lifted out of the ground, the machine is turned off. The elevation of the pile top is checked. If there is slurry or depression, it needs to be repaired or slurryed. The pile driver is then moved to carry out the construction of the next pile.

[0067] Construction of piles should be continuous, and the interval between adjacent piles should not exceed 24 hours. The "one-hole-within-one" process of three-axis mixing piles should be adopted to ensure that the piles are tightly interlocked to form a continuous cement-soil retaining wall of uniform thickness without weak joints. Process acceptance and recording should be carried out.

[0068] Step S2: Construction of the double-layer diaphragm wall, chiseling the top reinforcement bars.

[0069] After the construction of the cement-soil retaining wall around the foundation pit is completed, the guide walls for the first and second diaphragm walls can be constructed. The guide wall construction adopts the technical scheme of "double hoop ring arrangement, the guide wall is not removed throughout the process, and it is poured together with the cast-in-place joint of the composite connecting beam and the concrete slope protection surface layer". The top surface elevation of the guide wall is designed to be 50mm lower than the concrete slope protection surface layer. The guide wall adopts a reinforced concrete structure with a concrete strength of not less than C30. Specifically, it is divided into two guide walls: an inner guide wall and an outer guide wall, which are respectively arranged on the top of the first and second diaphragm walls.

[0070] During on-site construction, precise layout is essential, with strict control over the axis and elevation. The centerline should coincide with the axes of the first and second diaphragm walls, and the net distance between the inner wall surfaces should be slightly larger than the designed wall thickness by 50mm. Secondly, the guide wall should be built on a solid foundation. If soft soil layers are encountered, replacement and reinforcement are necessary to prevent uneven settlement. The guide wall is designed to be 1500mm-2000mm deep, with its top extending above ground level to prevent surface water inflow. Concrete pouring must ensure strength and integrity, and the backfill on the wall sides must be compacted. After construction, the verticality, spacing, and top elevation of the inner wall surface must be carefully checked to provide an accurate reference for the trenching machine.

[0071] After the construction of the double-layer diaphragm wall is completed, strengthen the curing and protection of finished products. Once the concrete strength of the double-layer diaphragm wall reaches more than 50% of the design strength, the top reinforcement of the double-layer diaphragm wall can be excavated. The exposed length of the design reinforcement after the top of the double-layer diaphragm wall is excavated shall not be less than 35d (d is the diameter of the longitudinal reinforcement of the diaphragm wall).

[0072] To facilitate the subsequent hoisting of the composite connecting beams and the construction of cast-in-place joints, the top of the guide wall is treated with a "lower elevation" method, meaning the top of the guide wall is 30mm lower than the designed bottom elevation of the composite connecting beams. For the construction of the second diaphragm wall, a "two-stage process" is adopted: the first stage is constructed to a point 2000mm below the designed top wall elevation, and the second stage is carried out simultaneously with the anchor bolt construction, using a "post-cast concrete" method to complete all operations.

[0073] Step S3: Erection of composite connecting beams and joint treatment

[0074] After the construction of the double-layer diaphragm wall is completed and the top reinforcement of the wall has been chiseled according to the design elevation, the wall top reinforcement of the double-layer diaphragm wall that has been chiseled out is straightened and processed a second time. When the exposed length of the wall top reinforcement is less than 35d due to the construction of the diaphragm wall in the aforementioned process, the method of "adding anchor plates" is adopted to deal with it. The number of anchor plates is not less than 50% of the total number of exposed reinforcements. The anchor plates are staggered and arranged in a wave pattern to strengthen the length of the exposed reinforcement at the top of the double-layer diaphragm wall into the cast-in-place joints at both ends of the composite connecting beam in the subsequent process.

[0075] After all the aforementioned procedures are completed, the top of the cement-soil retaining wall within 800mm of each composite connecting beam location is excavated or chiseled down to the bottom elevation of the composite connecting beam. Then, the top of the cement-soil retaining wall is fully utilized as the support system for the composite connecting beam, and each composite connecting beam is hoisted one by one.

[0076] During on-site construction, the composite connection is prefabricated in the prefabricated PC factory and then transported, stacked, and hoisted into place. All the reinforcing bars at both ends of the composite connection beam are anchored into the exposed reinforcing bars at the top of the double-layer underground continuous wall. Since the underground continuous wall is relatively thick, the reinforcing bars at the ends of the composite connection beam can be directly set with a 90-degree bend straight section on the basis of meeting the standard anchorage length, without the need to set anchor plates.

[0077] After the composite connecting beams are hoisted, the planar position and elevation of the composite connecting beams are checked and confirmed to be correct. Aluminum formwork is then used to quickly support the cast-in-place joints of the composite connecting beams and the underground continuous wall. Fine aggregate concrete of not less than C30 is used for one-time casting and curing. The relevant concealed works are then inspected and recorded.

[0078] Step S4: Excavation of the soil layer between the two diaphragm walls and installation of anchor bolts.

[0079] After the composite connecting beams are in place, the first layer of earthwork between the first and second diaphragm walls can be excavated to provide working space and a working surface for anchor bolt construction. During on-site construction, the excavation depth between the first and second diaphragm walls should be 1600mm~2000mm, and machinery and equipment must not touch the two diaphragm walls during the excavation process.

[0080] After the excavation is completed, the inner walls of the double diaphragm walls will be cleaned manually. Special attention will be paid to cleaning the soil and debris such as laitance left over from the construction of the second diaphragm wall within 2000mm below the top of the second diaphragm wall. The internal steel bars of the second diaphragm wall within the secondary post-cast area will be properly treated, especially the length of the exposed steel bars at the top.

[0081] Then, the formwork and support system are set up on the inner wall of the second diaphragm wall. At the same time as setting up the formwork support system of the second diaphragm wall, the anchor sleeves are installed inside the cement-soil retaining wall. The outer wall of the anchor sleeve is roughened to enhance the bond strength between the anchor sleeve and the concrete of the second diaphragm wall. The anchor sleeve is fixed inside the steel cage of the second diaphragm wall.

[0082] Finally, fine aggregate concrete with a strength one grade higher than that of the second diaphragm wall was poured in one go. The construction was carried out in sections. Except for the construction joint left in the first process of the second diaphragm wall, no construction joints were left in the entire process of pouring the secondary post-concrete within 2000mm below the top of the second diaphragm wall. Curing was strengthened.

[0083] After the second diaphragm wall is completed, the anchor bolts can be driven one by one into the cement-soil retaining wall through the anchor bolt sleeves pre-embedded inside the second diaphragm wall within the secondary post-casting process range. The relevant concealed works acceptance and recording work should be done throughout the process.

[0084] Step S5: Backfilling the earthwork between the two diaphragm walls and installing the steel mesh.

[0085] After all anchor bolts within 2000mm below the top of the second diaphragm wall have been installed, the soil between the two diaphragm walls should be backfilled immediately. Backfilling the soil between the two diaphragm walls is a key step in controlling the coordinated stress and long-term deformation performance of the walls. Traditional plain soil backfilling often affects the coordinated load-bearing capacity of the structure due to insufficient compaction.

[0086] To achieve the goals of energy conservation, low carbon emissions, and resource utilization, a systematic treatment using composite soil materials is designed. Modified soil, formed from dehydrated and solidified engineering waste mud, serves as the main aggregate (resource utilization rate exceeding 60%), mixed with an appropriate amount of recycled building powder (such as waste concrete powder and brick powder) as mineral admixtures, and supplemented with a trace amount of polymer soil stabilizer mixed with water. This composite ratio not only achieves the co-processing of waste mud and construction waste, significantly reducing the environmental burden and cost of off-site landfilling, but also results in backfill with low compressibility, self-hardening, and micro-expansion characteristics, effectively filling wall gaps and maintaining long-term compaction, reducing active earth pressure on side walls.

[0087] During construction, a combination of layered paving and small-scale vibratory compaction equipment should be used to strictly control the loose thickness of each layer and the number of compaction passes, ensuring that the filling density reaches more than 95%, and to monitor the compaction degree and deformation. This method transforms traditional passive backfilling into proactive performance-based construction based on a circular economy, significantly improving the overall structural integrity and environmental benefits.

[0088] The backfill between the two diaphragm walls is carried out to 30mm below the bottom of the composite connecting beam. After the backfilling between the two diaphragm walls is completed, the steel mesh at the top of the composite connecting beam is installed. The steel mesh uses materials no less than... The double-layer steel mesh should be cut to a width that can fully cover the entire area from the first diaphragm wall to the edge of the cement-soil retaining wall. The relevant concealed works acceptance and recording work should be done well.

[0089] Step S6: Concrete slope protection layer pouring, and full excavation of the foundation pit.

[0090] After the steel mesh at the top of the composite connecting beam is installed, the concrete slope protection surface layer can be poured. To ensure that the first diaphragm wall, the second diaphragm wall, and the cement-soil retaining wall work together to bear the load, the concrete slope protection surface layer pouring process around the top of the foundation pit needs to focus on achieving structural integrity and load transfer.

[0091] Before construction, loose soil and other debris from the aforementioned treatment process should be removed from the slope surface. The reinforcing bars of the composite connecting beam and the reinforcing mesh above them should be checked and corrected. Fine aggregate concrete with a strength grade of not less than C30 should be used, and the surface layer thickness should be 150mm~200mm. During the pouring process, a "segmented pouring" technique should be adopted, first pouring the fine aggregate concrete within a 2000mm range on both sides of the corner of the foundation pit, and then pouring the fine aggregate concrete for other parts. The concrete should be vibrated to ensure compaction, and the surface should be smoothed and polished.

[0092] After the concrete has initially set, it needs to be covered and watered for at least 7 days to prevent cracking. This rigid surface layer acts like a "ring-shaped retaining beam," which can transfer local loads to the entire retaining system, effectively restraining top deformation and enhancing the overall stability of the foundation pit retaining structure.

[0093] In summary, this invention constructs a "three-hoop" collaborative load-bearing system, forming multiple lines of defense through double underground continuous walls and cement-soil retaining walls, combined with overlapping connecting beams in a grid-like structure and dense anchor bolt connections, which significantly improves the overall structural stiffness and resistance to lateral displacement, effectively controls lateral deformation and groundwater infiltration during the excavation process, and significantly enhances the safety and stability of the foundation pit under ultra-deep and complex working conditions.

[0094] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction method of a core tube double-row diaphragm wall deep foundation pit enclosure, characterized by, The deep foundation pit retaining structure includes a first diaphragm wall and a second diaphragm wall. The excavation of the foundation pit is protected by a double-layered diaphragm wall, forming a tube-within-a-tube structure, with the first diaphragm wall located inside the second diaphragm wall. A composite connecting beam is provided between the first and second diaphragm walls, with segments positioned at the top of both. A cement-soil retaining wall is also provided outside the second diaphragm wall, constructed from the inside of the second diaphragm wall within the first-level excavation height. It has anchor bolts; the top of the composite connecting beam and the cement-soil retaining wall is provided with a concrete slope protection layer; the outermost cement-soil retaining wall forms the first ring of reinforced soil, the second underground continuous wall in the middle of the retaining structure forms the second ring of soil retention and water stop, and the first underground continuous wall on the inner side of the retaining structure forms the third ring of soil retention and water stop; the width of the cement-soil retaining wall is not less than 3.0m, the design thickness of the first underground continuous wall and the second underground continuous wall is not less than 0.6m, and the distance between the first underground continuous wall and the second underground continuous wall is not less than 2.0m and not more than 4.5m; The overall steps of the construction method for the deep foundation pit retaining structure are as follows: Step S1: Measure and lay out the positional relationships, then construct the guide wall; Step S2: Construction of the double-layer diaphragm wall, chiseling the top steel reinforcement; Step S3: Erection of the composite connecting beam and joint treatment; Step S4: Excavation of the soil layer between the two underground continuous walls and installation of anchor bolts; Step S5: Backfilling of earthwork between the two underground continuous walls and hoisting of steel mesh; Step S6: Concrete slope protection surface layer pouring, and full excavation of foundation pit.

2. The construction method according to claim 1, characterized in that: The first and second diaphragm walls are connected by a composite tie beam lattice structure in segments. The composite tie beams are prefabricated in a precast PC factory with a cross-sectional dimension of not less than 250mm×250mm. The reinforcing bars of the composite tie beams are anchored into the cast-in-place joints of the first and second diaphragm walls, respectively. The cast-in-place joints are formed by pouring fine aggregate concrete of not less than C30. The spacing between two adjacent composite tie beams shall not exceed 1.8m. When the excavation depth of the foundation pit exceeds 15m or when the pit is subjected to long-term vibration or complex working conditions with high dynamic water pressure, the spacing between two adjacent composite tie beams shall not exceed 1.2m.

3. The construction method according to claim 1, characterized in that: The anchor bolts are densely arranged on the second diaphragm wall within the first layer of earth excavation depth of 2.0m. The anchor bolts are driven obliquely into the cement-soil retaining wall from the inside of the second diaphragm wall. The length of the anchor bolts is not less than 2.5m. The angle between the anchor bolts driven into the cement-soil retaining wall and the horizontal is 15°~30°. The anchor bolts are evenly distributed around the perimeter of the foundation pit. The distance between two adjacent anchor bolts in the longitudinal and transverse directions does not exceed 450mm. The ends of the anchor bolts are fixed to the inside of the second diaphragm wall with anchors. The distance between the first row of anchor bolts at the top of the second diaphragm wall and the bottom of the composite connecting beam does not exceed 300mm.

4. The construction method according to claim 1, characterized in that: The concrete slope protection surface layer is equipped with a two-way steel mesh with a diameter of not less than Φ8@150. The steel mesh is supported on the steel reinforcement of the composite connecting beam. Fine stone concrete with a grade of not less than C30 is used to cast the cast-in-place joint and the concrete slope protection surface layer together. The thickness of the concrete slope protection surface layer is not less than 100mm, and its width exceeds the boundary of the cement soil retaining wall area by not less than 300mm.

5. A construction method for a deep foundation pit retaining structure with a core tube and a double-layer underground continuous wall, characterized in that, The specific steps are as follows: Step S1: Measure and lay out the lines to determine the positional relationship; construction of the cement-soil retaining wall: First, a total station is used to accurately determine the specific location relationships of the foundation pit, the first diaphragm wall, the second diaphragm wall, and the cement-soil retaining wall, as well as the location of each pile. Then, construction of the cement-soil retaining wall is carried out. The first step involves positioning and straightening the pile driver. The mixing pile driver is moved to the designated pile location, and the pile frame is adjusted using a level and theodolite to ensure that the verticality deviation of the drill rod is within 1%. The mixing head is aligned with the center of the pile location. The second step involves pre-mixing and sinking. The mixer is started, and the mixing head is driven downwards along the guide frame, cutting through the soil and rotating until the designed pile bottom elevation is reached. During sinking, only mixing is performed; no grouting is applied to loosen the soil. The third step involves grouting, mixing, and lifting. After reaching the designed depth, the grout pump is turned on, and the proportioned cement grout is sprayed through the drill rod from the mixing head. After continuous grouting and mixing at the pile bottom for 60 seconds, the grout is then applied at a 1.0... The mixing head is raised at a uniform speed of m / min while spraying and mixing, ensuring thorough mixing of the grout with the soil. The fourth step involves repeated lowering and mixing. After raising the head to the pile top or the designed re-mixing depth, the grout pump is shut off again, and the mixing head is lowered back to the pile bottom for a second mixing to increase uniformity. The fifth step involves repeating the spraying, mixing, and raising process. After lowering the head to the pile bottom, the grout pump is restarted for spraying, and the mixing head is raised to the pile top at the designed speed to complete the second spraying and mixing. For complex conditions in important projects... The process involves four mixing and two spraying steps. The sixth step involves pile top treatment and machine relocation. After the mixing head is lifted out of the ground, the machinery is shut down, and the pile top elevation is checked. If there is slurry or depression, it is repaired or slurry is added. The pile driver is then moved to begin construction of the next pile. Construction of piles is continuous, with an interval of no more than 24 hours between adjacent piles. The "one-hole-within-one-hole" process for three-axis mixing piles is used to ensure tight interlocking between piles, forming a continuous, seamless, and uniformly thick cement-soil retaining wall. Process acceptance and recording are conducted. Step S2: Construction of the double-layer diaphragm wall, chiseling the top reinforcement of the wall: After the cement-soil retaining walls around the foundation pit are completed, the guide walls for the first and second diaphragm walls can be constructed. The guide wall construction adopts a "double-hoop ring arrangement, with the guide walls remaining in place throughout the process, and poured together with the cast-in-place joints of the composite connecting beams and the concrete slope protection surface layer." The top elevation of the guide wall is designed to be 50mm lower than the concrete slope protection surface layer. The guide wall uses reinforced concrete with a concrete strength of not less than C30, and is specifically divided into two layers: an inner guide wall and an outer guide wall, respectively positioned at the top of the first and second diaphragm walls. During on-site construction, precise layout is essential, strictly controlling the axis and elevation. The centerline must coincide with the axis of the first and second diaphragm walls, and the net distance between the inner wall surfaces should be slightly larger than the designed wall thickness by 50mm. Secondly, the guide walls are built on a solid foundation; if soft soil layers are encountered, they should be replaced and reinforced to prevent uneven settlement. The designed depth of the guide wall is 1500mm. ~2000mm, the top is higher than the ground to prevent surface water from flowing in. The concrete pouring ensures strength and integrity. The backfill on the wall side must be compacted. After construction, carefully check the verticality, spacing and top elevation of the inner wall surface to provide an accurate benchmark for the trenching machine. After the construction of the double underground continuous wall is completed, strengthen curing and protection of finished products. After the concrete strength of the double underground continuous wall reaches more than 50% of the design strength, the top reinforcement of the double underground continuous wall can be excavated. The exposed length of the design reinforcement after the top of the double underground continuous wall is not less than 35d, where d is the diameter of the longitudinal reinforcement of the underground continuous wall. The top of the guide wall adopts the "elevation reduction" treatment method, that is, the top of the guide wall is 30mm lower than the bottom elevation of the design composite connecting beam. The construction of the second underground continuous wall adopts the "secondary process", that is, the first construction is to 2000mm below the design wall top elevation, and the second construction is synchronized with the anchor bolt construction, and the "post-poured concrete" method is used to complete all operations. Step S3: Erection of composite connecting beams, joint treatment: After the double-layer diaphragm wall construction is completed and the top reinforcement bars have been excavated according to the design elevation, the wall top reinforcement bars that have been excavated in the double-layer diaphragm wall are straightened and secondary processed. If the exposed length of the wall top reinforcement bars is less than 35d due to the diaphragm wall construction in the aforementioned process, the method of "adding anchor plates" is adopted to deal with it. The number of anchor plates is not less than 50% of the total number of exposed reinforcement bars, and the anchor plates are staggered and arranged in a wave pattern to strengthen the length of the exposed reinforcement bars at the top of the double-layer diaphragm wall into the cast-in-place joints at both ends of the composite connecting beam in the subsequent process. After all the above procedures are completed, the top of the cement-soil retaining wall within 800mm of the location of each composite connecting beam is excavated or chiseled down to the bottom elevation of the composite connecting beam. Then, the top of the cement-soil retaining wall is fully utilized as a base. The support system for the composite connecting beams involves hoisting each composite connecting beam one by one. During on-site construction, the composite connecting beams are prefabricated in a prefabricated PC factory and then transported, stacked, and hoisted into place. All the reinforcing bars at both ends of the composite connecting beams are anchored into the exposed reinforcing bars at the top of the double-layer diaphragm wall. Since the diaphragm wall is relatively thick, the reinforcing bars at the ends of the composite connecting beams can be directly set with a 90-degree bend straight section, without the need for anchor plates, provided that the anchorage length meets the specifications. After the composite connecting beams are hoisted, the planar position and elevation of the composite connecting beams are checked and confirmed to be correct. Aluminum formwork is then used to quickly support the cast-in-place joints of the composite connecting beams and the diaphragm wall. Fine aggregate concrete of not less than C30 is used for one-time casting and curing. The relevant concealed works are inspected and recorded. Step S4: Excavation of the soil layer between the two diaphragm walls and installation of anchor bolts: After the composite connecting beams are in place, the first layer of earthwork between the first and second diaphragm walls is excavated. During on-site construction, the excavation depth between the first and second diaphragm walls is 1600mm~2000mm. During excavation, machinery must not touch the two diaphragm walls. After excavation, the inner walls of the diaphragm walls are cleaned manually, focusing on removing debris and residual laitance from the second diaphragm wall construction within 2000mm below the top. The internal reinforcement of the second diaphragm wall within the secondary post-cast area and the length of its exposed top reinforcement are also addressed. Then, formwork and support systems are erected on the inner wall of the second diaphragm wall. While supporting the system, anchor sleeves are installed inside the cement-soil retaining wall. The outer wall of the anchor sleeve is roughened to enhance the bond strength between the anchor sleeve and the concrete of the second diaphragm wall. The anchor sleeve is fixed inside the reinforcement cage of the second diaphragm wall. Finally, fine aggregate concrete with a strength one grade higher than that of the second diaphragm wall concrete is poured in one go. The construction is carried out in sections. Except for the construction joint left in the first process of the second diaphragm wall, no construction joints should be left in the entire process of pouring the secondary post-cast concrete within 2000mm below the top of the second diaphragm wall. The curing should be strengthened. After the second diaphragm wall is completed, the anchors can be driven into the cement-soil retaining wall one by one through the anchor sleeves pre-embedded inside the second diaphragm wall within the secondary post-cast process range. The relevant hidden works acceptance and recording work should be done throughout the process. Step S5: Backfilling of earthwork between the two diaphragm walls and installation of steel mesh: After all anchor bolts within 2000mm below the top of the second diaphragm wall have been installed, the soil between the two diaphragm walls will be backfilled immediately. Modified soil formed by dehydrating and solidifying engineering waste mud will be used as the main aggregate, with an appropriate amount of recycled building micro powder added as a mineral admixture, and a small amount of polymer soil stabilizer mixed with water. During construction, a combination of layered paving and small vibrating equipment will be used to strictly control the thickness of each layer and the number of compaction passes to ensure that the filling density reaches more than 95%, and to monitor the compaction degree and deformation. The soil between the two diaphragm walls will be backfilled to 30mm from the bottom of the composite connecting beam. After the soil between the two diaphragm walls is backfilled, the steel mesh at the top of the composite connecting beam will be installed. The steel mesh will be a double-layer steel mesh with a diameter of not less than Φ8@150. The width of the steel mesh will be able to fully cover all areas from the first diaphragm wall to the edge of the cement-soil retaining wall. The relevant concealed works will be inspected and recorded. Step S6: Concrete slope protection layer pouring, full excavation of foundation pit: After the steel mesh at the top of the composite connecting beam is installed, the concrete slope protection surface layer can be poured. Before construction, remove the loose soil from the slope surface due to the aforementioned process, and check and correct the steel reinforcement of the composite connecting beam and the steel mesh above it. Use fine aggregate concrete with a strength grade of not less than C30, and the surface layer thickness is 150mm~200mm. During the pouring process, adopt the scheme of "segmented pouring, first pouring the fine aggregate concrete in the left and right ranges of the corner of the foundation pit, and then pouring the fine aggregate concrete in other parts", vibrate and compact it, and smooth and polish the surface. After the concrete has initially set, cover and water it for curing for no less than 7 days to prevent cracking.

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