Secondary trenching construction method for ground-connected walls suitable for water-rich sand and gravel layers

Abstract

The invention discloses a secondary trenching construction method for a ground-connected wall in a water-rich sand and gravel layer, comprising the following steps: 1. arranging a dewatering well (16) within the construction range of a newly built ground-connected wall (3), and dewatering the water to below the excavation working surface of an outer guide wall (1); 2. excavating the outer guide wall by sloping, wherein the outer guide wall is located between an existing ground-connected wall (2) and a newly built ground-connected wall; 3. constructing the outer guide wall, and promptly backfilling the excavated earthwork of the outer guide wall; 4. constructing jet grouting piles (5) on the inner side of the newly built ground-connected wall; 5. excavating the soil between the jet grouting piles and the outer guide wall, and constructing the inner guide wall (6); 6. excavating the soil, forming a secondary trenching for the newly built ground-connected wall, and casting the newly built ground-connected wall; 7. arranging a capping beam (8) on the outer guide wall and the newly built ground-connected wall, and constructing an inner support (9) in a foundation pit through the capping beam. The invention can avoid hole collapse during the secondary trenching of the ground-connected wall in the water-rich sand and gravel layer, thereby improving the quality of the secondary trenching of the newly built ground-connected wall.

Description

Technical Field

[0001] The invention relates to a ground-connected wall construction method, in particular to a ground-connected wall secondary trenching construction method suitable for water-rich sand and gravel layers. Background Art

[0002] At present, with the increasingly tight construction land area, in order to maximize the economic benefits of construction projects, the underground depth of building structures has gradually deepened, the distance between underground exterior walls and the land red line has become smaller and smaller, and the construction difficulty has become greater and greater.

[0003] In some projects where foundation pit support has been completed, if secondary support is required later to further deepen the underground structure, such projects often employ a ground-diaphragm wall deepening process. However, during the construction of the secondary trenching of the new ground-diaphragm wall, the soil layer is disturbed by the previous trenching of the existing ground-diaphragm wall, which is prone to the risk of collapse. This risk is particularly increased when constructing in a sandy and gravel layer with a low internal friction angle and high groundwater levels. Furthermore, due to land use restrictions, the newly deepened ground-diaphragm wall is generally combined with the basement exterior wall, meaning the new ground-diaphragm wall also serves as the basement exterior wall. This approach places high demands on the quality of the secondary trenching of the new ground-diaphragm wall, and traditional methods of construction do not meet these requirements.

[0004] The traditional method for secondary trenching of diaphragm walls involves excavating the guide wall and then performing secondary trenching. This traditional method carries a significant risk of hole collapse during construction, especially in areas with poor soil conditions such as water-rich gravel and sandy gravel. Therefore, a construction method is needed to mitigate the risk of hole collapse during secondary trenching of diaphragm walls in water-rich gravel and sandy gravel layers. Summary of the Invention

[0005] The purpose of the present invention is to provide a secondary trenching construction method for ground-anchored walls suitable for water-rich sand and gravel layers, which can avoid hole collapse during the secondary trenching of ground-anchored walls constructed in water-rich sand and gravel layers and improve the quality of the secondary trenching of newly built ground-anchored walls.

[0006] The present invention is achieved in that:

[0007] A secondary trenching construction method for a ground-connected wall in a water-rich sand and gravel layer comprises the following steps:

[0008] Step 1: Arrange dewatering wells within the construction scope of the new ground-connected wall and lower the water level to below the excavation working surface of the outer guide wall;

[0009] Step 2: Slope and excavate the outer guide wall, which is located between the existing ground-connected wall and the new ground-connected wall;

[0010] Step 3: Construct the outer guide wall and promptly backfill the excavated earthwork of the outer guide wall;

[0011] Step 4: Construct jet grouting piles on the inner side of the newly built ground-connected wall;

[0012] Step 5: Excavate the soil between the jet grouting piles and the outer guide wall and construct the inner guide wall;

[0013] Step 6: Excavate the soil, create a secondary trench for the new ground-connected wall, and cast the new ground-connected wall;

[0014] Step 7: Set up top beams on the outer guide wall and the newly built ground connection wall, and use the top beams to construct internal supports in the foundation pit.

[0015] In step 1, the water level is lowered to at least 500 mm below the excavation working surface of the outer guide wall.

[0016] In step 2, the excavation depth of the outer guide wall shall not exceed the elevation of the floor beam slab located below and adjacent to the top of the existing ground-connected wall, and the thickness of the outer guide wall shall be the distance between the inner skin of the existing ground-connected wall and the outer skin of the newly built ground-connected wall; the slope of the outer guide wall excavation shall be 45°.

[0017] Described step 3 comprises the following sub-steps:

[0018] Step 3.1: Carry out steel bar binding construction of the outer guide wall;

[0019] Step 3.2: Pre-embed steel pipes in the outer guide wall at the joints between two adjacent sections of newly built ground-connected walls;

[0020] Step 3.3: Concrete pouring and construction of outer guide wall;

[0021] Step 3.4: After the outer guide wall reaches the designed strength, backfill the soil excavated in the early stage.

[0022] In the step 3.1, embedded reinforcement is preset in the existing ground-connected wall, and the stirrups of the outer guide wall are fixedly connected to the existing ground-connected wall through the embedded reinforcement.

[0023] In step 3.2, the outer guide wall located at the joint of the two adjacent sections of the newly built ground-connected wall is L-shaped, so that a gap is formed between the outer guide wall and the existing ground-connected wall, and the gap is backfilled with concrete. The steel pipe is pre-buried in the vertical section of the L-shaped structure and extends downward to the bottom of the outer guide wall.

[0024] In step 4, the bottom of the jet grouting pile extends to the bottom of the valve plate of the foundation pit.

[0025] In step 5, a plurality of wooden supports are arranged at intervals between the inner guide wall and the outer guide wall.

[0026] In step 6, the new ground-connected wall is excavated and constructed in sections, and I-beam joints are set at the joints of two adjacent sections of the new ground-connected wall; before the secondary trenching of the new ground-connected wall, grouting pipes are arranged according to the actual geological construction conditions, and grouting reinforcement is performed on the soil disturbed during the construction of the existing ground-connected wall.

[0027] In the step 7, the reinforcement of the newly constructed ground-connected wall is anchored into the top beam, the existing ground-connected wall and the top beam are anchored by planting reinforcement, and the top beam is arranged along the existing ground-connected wall.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention adopts the method of first lowering the water level and then laying the slope to excavate the outer guide wall of the ground diaphragm wall, backfilling the excavation area of ​​the outer guide wall, constructing rotary jet grouting piles, excavating and constructing the inner guide wall, and finally carrying out the secondary trenching construction of the new ground diaphragm wall. Before the secondary trenching construction of the new ground diaphragm wall, it is determined whether soil grouting reinforcement is needed according to soil conditions. This optimizes the construction process, ensures the construction safety of the secondary trenching of the new ground diaphragm wall in the water-rich sand and gravel layer area, and effectively solves the problem of easy hole collapse during the secondary trenching construction of the new ground diaphragm wall.

[0030] 2. In the present invention, since the top beam and the internal support are constructed, the top beam is anchored to the newly built ground-connected wall and the existing ground-connected wall. The top beam and the internal support effectively offset the soil pressure transmitted to the newly built ground-connected wall and the existing ground-connected wall, thereby ensuring the safety of the newly built ground-connected wall and the existing ground-connected wall, making the newly built ground-connected wall have sufficient stability and can also serve as the outer wall of the basement, and also solving the problem of insufficient embedding depth of the existing ground-connected wall after the excavation depth is increased.

[0031] 3. The present invention provides an I-beam joint at the joint of two adjacent sections of newly built ground-connected walls, thereby increasing the seepage path. At the same time, a steel pipe is embedded in the outer guide wall at the joint of the two adjacent sections of newly built ground-connected walls for later grouting, so that the joint of the two adjacent sections of newly built ground-connected walls is densely filled, effectively solving the hidden danger of water leakage at the joint of the two adjacent sections of newly built ground-connected walls. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of the secondary trenching construction method of the ground-connected wall applicable to water-rich sand and gravel layers of the present invention;

[0033] Figure 2 This is a construction plan of the secondary trenching construction method for ground-connected walls applicable to water-rich sand and gravel layers according to the present invention;

[0034] Figure 3 This is a construction elevation diagram of steps 2 and 3 in the secondary trenching construction method for ground-connected walls in a water-rich sand and gravel layer according to the present invention;

[0035] Figure 4This is a construction elevation view of step 4 of the secondary trenching construction method for ground-connected walls in a water-rich sand and gravel layer according to the present invention;

[0036] Figure 5 This is a construction elevation view of step 5 of the secondary trenching construction method for ground-connected walls in a water-rich sand and gravel layer according to the present invention;

[0037] Figure 6 This is a construction elevation view of step 6 of the secondary trenching construction method for ground-connected walls in a water-rich sand and gravel layer according to the present invention;

[0038] Figure 7 This is a construction elevation view of step 7 in the secondary trenching construction method for ground-connected walls in a water-rich sand and gravel layer according to the present invention;

[0039] Figure 8 This is a schematic diagram of the reinforcement arrangement of the outer guide wall in the secondary trenching construction method of the ground-connected wall applicable to a water-rich sand and gravel layer according to the present invention;

[0040] Figure 9 This is a vertical view of the arrangement of wooden supports in the secondary trenching construction method of the ground-connected wall in the water-rich sand and gravel layer according to the present invention.

[0041] In the figure, 1 is the outer guide wall, 2 is the existing ground-connected wall, 3 is the new ground-connected wall, 4 is the floor beam and slab, 5 is the jet grouting pile, 6 is the inner guide wall, 7 is the valve plate, 8 is the top beam, 9 is the inner support, 10 is the grouting pipe, 11 is the notch, 12 is the stirrup, 13 is the steel pipe, 14 is the I-beam joint, 15 is the wooden support, and 16 is the dewatering well. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0043] Please see the attached Figure 1 A secondary trenching construction method for a ground-connected wall in a water-rich sand and gravel layer comprises the following steps:

[0044] Please see the attached Figure 2 , Step 1: Arrange a dewatering well 16 within the construction range of the new ground-connected wall 3 and dewater it to below the excavation working surface of the outer guide wall 1.

[0045] Preferably, in order to ensure safe excavation of the outer guide wall 1 , in step 1 , the water level is lowered to at least 500 mm below the excavation working surface of the outer guide wall 1 .

[0046] If the groundwater level is low and is located less than 500 mm below the excavation working surface of the outer guide wall 1, there is no need to arrange dewatering points; if the groundwater is far away from the construction area of ​​the ground-connected wall and will not affect the secondary trenching construction of the ground-connected wall, there is no need to arrange dewatering points.

[0047] The layout location and number of the dewatering wells 16 can be determined according to the actual construction environment. The layout location of the dewatering wells 16 is usually inside and around the construction area of ​​the newly built ground-connected wall 3. The process of dewatering through the dewatering wells 16 can adopt existing processes and will not be repeated here.

[0048] Please see the attached Figure 3 , Step 2: Slope and excavate the outer guide wall 1, the outer guide wall 1 is located between the existing ground-connected wall 2 and the newly built ground-connected wall 3.

[0049] Please see the attached Figure 7 The excavation depth of the outer guide wall 1 does not exceed the elevation of the floor beam 4 located below the top of the existing ground-connected wall 2 and adjacent to the top of the existing ground-connected wall 2. The thickness of the outer guide wall 1 is the distance between the inner skin of the existing ground-connected wall 2 and the outer skin of the newly built ground-connected wall 3.

[0050] The excavation depth of the outer guide wall 1 ensures that after the concrete supports within the foundation pit are removed, the floor beams 4 can support the existing ground diaphragm wall 2, thus resolving the problem of insufficient embedment depth of the existing ground diaphragm wall 2 caused by secondary excavation. The excavation depth and thickness of the outer guide wall 1 can be adjusted according to actual construction conditions.

[0051] Preferably, in step 2, the slope of the excavation of the outer guide wall 1 is 45°.

[0052] Step 3: Construct the outer guide wall 1 and backfill the excavated earth of the outer guide wall 1 in a timely manner.

[0053] Described step 3 comprises the following sub-steps:

[0054] Step 3.1: Carry out steel bar binding construction of outer guide wall 1.

[0055] Please see the attached Figure 8 If the stirrups 12 of the outer guide wall 1 are large, embedded reinforcement can be pre-installed in the existing ground-connected wall 2. The stirrups 12 of the outer guide wall 1 are fixedly connected to the existing ground-connected wall 2 by embedded reinforcement, and then the horizontal and vertical reinforcement of the outer guide wall 1 are tied, which facilitates the reinforcement engineering operation of the outer guide wall 1 and ensures the safety of the outer guide wall 1.

[0056] Please see the attached Figure 8 , Step 3.2: Pre-embed a steel pipe 13 in the outer guide wall 1 , and the steel pipe 13 is located at the joint of the two adjacent sections of the newly built ground connecting wall 3 .

[0057] The steel pipe 13 can be used for later drilling and grouting. Grouting is performed after the two adjacent sections of the newly built ground-connected wall 3 are poured, so that the joints of the two adjacent sections of the newly built ground-connected wall 3 are filled densely to avoid water leakage in the later stage.

[0058] The outer guide wall 1 located at the joint of the newly built ground-connected walls 3 of the two adjacent sections has an L-shaped structure, so that a gap 11 is formed between the outer guide wall 1 and the existing ground-connected wall 2, and the gap 11 is backfilled with concrete. The steel pipe 13 is pre-buried in the vertical section of the L-shaped structure and extends downward to the bottom of the outer guide wall 1.

[0059] Preferably, when backfilling the gap 11 with concrete, C15 concrete may be used, and isolation measures may be provided on both sides and the top of the concrete to facilitate chiseling in the later stage.

[0060] Step 3.3: Concrete pouring construction of outer guide wall 1.

[0061] Step 3.4: After the outer guide wall 1 reaches the designed strength, backfill the soil excavated in the early stage.

[0062] Please see the attached Figure 4 , Step 4: Construct rotary jet grouting piles 5 on the inner side of the newly built ground-connected wall 3.

[0063] The rotary jet piles 5 are used to prevent the newly built ground-connected wall 3 from collapsing during the secondary trenching, ensuring that the newly built ground-connected wall 3 can also serve as the outer wall of the basement with good construction quality. At the same time, the construction accuracy of the newly built ground-connected wall 3 is ensured, avoiding problems such as oversizing and later chiseling.

[0064] Preferably, the bottom of the jet-jet pile 5 extends to the bottom of the valve plate 7 of the foundation pit to ensure that the secondary trenching quality of the newly-built ground-connected wall 3 meets the requirements.

[0065] Please see the attached Figure 5 , Step 5: Excavate the soil between the rotary jet grouting pile 5 and the outer guide wall 1 and construct the inner guide wall 6.

[0066] Please see the attached Figure 9 Preferably, a plurality of wooden supports 15 are arranged at intervals between the inner guide wall 6 and the outer guide wall 1 to reinforce the inner guide wall 6 and facilitate the construction of the inner guide wall 6, such as the formwork support and concrete pouring.

[0067] Please see the attached Figure 6 , Step 6: Excavate the soil, dig a trench for the new ground-connected wall 3 for the second time, and cast the new ground-connected wall 3.

[0068] Please see the attached Figure 2 The newly built ground-connecting wall 3 is excavated and constructed in sections, and an I-steel joint 14 is set at the joint of the two adjacent sections of the newly built ground-connecting wall 3 to increase the seepage path and avoid the hidden danger of water leakage at the joint of the two adjacent sections of the newly built ground-connecting wall 3.

[0069] Before the secondary trenching of the newly built ground-anchor wall 3, grouting pipes 10 can be arranged according to the actual geological construction conditions to reinforce the soil disturbed during the construction of the existing ground-anchor wall 2 by grouting to prevent the disturbed soil from collapsing during the secondary trenching of the newly built ground-anchor wall 3. The position and number of the grouting pipes 10 can be determined according to the actual situation of the soil.

[0070] Please see the attached Figure 7 Step 7: Install capping beams 8 on the outer guide wall 1 and the newly built ground diaphragm wall 3. The capping beams 8 are installed along the existing ground diaphragm wall 2. Internal supports 9 are constructed within the foundation pit using the capping beams 8. The construction of the support system within the foundation pit can be carried out using existing processes and will not be further described here.

[0071] Preferably, the steel bars of the newly built ground-connected wall 3 are anchored in the top pressure beam 8, and the existing ground-connected wall 2 and the top pressure beam 8 are anchored by embedded steel bars. The top pressure beam 8 and the internal support 9 effectively offset the soil pressure transmitted to the newly built ground-connected wall 3 and the existing ground-connected wall 2, thereby ensuring the safety of the newly built ground-connected wall 3 and the existing ground-connected wall 2.

[0072] In order to ensure the construction of the top beam 8 , the vertical section of the L-shaped structure of the outer guide wall 1 needs to be removed before the construction of the top beam 8 .

[0073] Please see the attached Figure 1 To the attached Figure 9 , Example 1:

[0074] Step 1: Arrange a dewatering well 16 within the construction range of the new ground-connected wall 3 and dewater to 500 mm below the excavation working surface of the outer guide wall 1.

[0075] Step 2: Excavate the outer guide wall 1 at a 45° slope. The outer guide wall 1 is located between the existing ground diaphragm wall 2 and the new ground diaphragm wall 3. The excavation depth of the outer guide wall 1 is to the elevation of the floor beam 4 below and adjacent to the top of the existing ground diaphragm wall 2. The thickness of the outer guide wall 1 is the distance between the inner skin of the existing ground diaphragm wall 2 and the outer skin of the new ground diaphragm wall 3.

[0076] Step 3: Construct the outer guide wall 1 and backfill the excavated earth of the outer guide wall 1 in a timely manner.

[0077] Step 3.1: Carry out steel bar binding construction of outer guide wall 1.

[0078] The outer guide wall 1 of the L-shaped structure has a height of 2800 mm and a width of 675 mm, and the size of the notch 11 is 1100*475 mm.

[0079] The stirrups of the outer guide wall 1 are made of 8mm diameter steel bars, with an anchor depth of 500mm and a spacing of 200mm. The main reinforcement on one side of the lower part of the outer guide wall 1 (close to the steel pipe 13) is made of 9mm diameter steel bars, the main reinforcement on the other side of the lower part of the outer guide wall 1 (away from the steel pipe 13) and the main reinforcement of the L-shaped horizontal section are made of 5mm diameter steel bars, and the upper main reinforcement of the outer guide wall 1 is made of 14mm diameter steel bars arranged at intervals of 200mm. The bottom main reinforcement of the outer guide wall 1 is made of 8mm diameter steel bars. Reinforcing bars are set between the main bars on both sides of the lower part of the outer guide wall 1. The reinforcing bars are made of 16mm diameter steel bars and are set at a spacing of 800mm.

[0080] Step 3.2: Pre-embed a steel pipe 13 in the outer guide wall 1 . The steel pipe 13 is located at the joint between two adjacent sections of the newly constructed ground connection wall 3 .

[0081] Step 3.3: Concrete pouring and construction of the outer guide wall 1. Backfill the gap 11 formed between the outer guide wall 1 and the existing ground connection wall 2 with C15 concrete. Isolation measures can be set on both sides and the top of the C15 concrete to facilitate later chiseling.

[0082] Step 3.4: After the outer guide wall 1 reaches the designed strength, backfill the excavated soil in the early stage in a timely manner.

[0083] Step 4: Construct jet grouting piles 5 on the inner side of the newly built ground-connected wall 3, extending to the bottom of the valve plate 7 of the foundation pit. The diameter of the jet grouting piles 5 is 650 mm, and the spacing is 450 mm.

[0084] Step 5: Excavate the soil between the jet grouting piles 5 and the outer guide wall 1 and construct the inner guide wall 6. The inner guide wall 6 is 200 mm thick, 2000 mm high, and 1000 mm wide. The distance between the inner guide wall 6 and the outer guide wall 1 is 650 mm. The existing trench bottom elevation (i.e., the top elevation of the new ground diaphragm wall 3) is -27.5 m. The distance from the inner guide wall 6 to the bottom of the valve plate is 9 m, which means the height of the new ground diaphragm wall 3 is 9 m. The crawler crane in the hardened ground area for the new ground diaphragm wall 3 construction is 15 m wide to facilitate operation.

[0085] A plurality of wooden supports 15 are arranged between the inner guide wall 6 and the outer guide wall 1. The wooden supports 15 are made of wooden rods with a size of 100*100*650mm and are arranged at a spacing of 1000mm.

[0086] Step 6: Excavate the soil, construct the secondary trench for the new ground-connected wall 3, and cast the new ground-connected wall 3 with a width of 600mm. The new ground-connected wall 3 also serves as the outer wall of the basement.

[0087] The new ground diaphragm wall 3 was excavated and constructed in sections. I-beam joints 14 were installed at the joints between adjacent sections of the new ground diaphragm wall 3. Grouting pipes were installed through steel pipes 13. The length of the grouting pipes was 9 meters. No fewer than five grouting pipes were installed at each joint, with the pipes spaced 500 mm apart. Grouting was carried out after the construction of the two adjacent sections of the new ground diaphragm wall 3 was completed.

[0088] Step 7: Install capping beams 8 on the outer guide wall 1 and the newly constructed ground diaphragm wall 3. The capping beams 8 are placed along the existing ground diaphragm wall 2. Internal supports 9 are constructed within the foundation pit through the capping beams 8. The rebar in the newly constructed ground diaphragm wall 3 is anchored into the capping beams 8. The existing ground diaphragm wall 2 and the capping beams 8 are anchored with rebar. The existing ground diaphragm wall 2 is 800 mm thick. The center elevation of the capping beam 8 is -28.10 m. The cross-sectional dimensions of the capping beam 8 are 1300 x 1000 mm. The internal supports 9 are concrete.

[0089] The above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A secondary trenching construction method for ground-connected walls in water-rich sand and gravel layers, characterized by: The following steps are involved: Step 1: Arrange a dewatering well (16) within the construction range of the new ground-connected wall (3) and dewater it to below the excavation working surface of the outer guide wall (1); Step 2: Slope excavation of the outer guide wall (1), where the outer guide wall (1) is located between the existing ground diaphragm wall (2) and the newly built ground diaphragm wall (3); Step 3: construct the outer guide wall (1) and promptly backfill the excavated earthwork of the outer guide wall (1); Step 4: Constructing jet grouting piles (5) on the inner side of the newly constructed ground-connected wall (3); Step 5: Excavate the soil between the jet grouting pile (5) and the outer guide wall (1) and construct the inner guide wall (6); Step 6: excavate the soil, build a new ground-connected wall (3), form a trench for the second time, and cast the new ground-connected wall (3); Step 7: Install a top beam (8) on the outer guide wall (1) and the newly constructed ground connection wall (3), and construct an internal support (9) in the foundation pit through the top beam (8); In the step 1, the water level is lowered to at least 500 mm below the excavation working surface of the outer guide wall (1); In the step 2, the excavation depth of the outer guide wall (1) does not exceed the elevation of the floor beam (4) located below and adjacent to the top of the existing ground-connected wall (2), and the thickness of the outer guide wall (1) is the distance between the inner skin of the existing ground-connected wall (2) and the outer skin of the newly-built ground-connected wall (3); the slope of the outer guide wall (1) during the slope excavation is 45°; Described step 3 comprises the following sub-steps: Step 3.1: Carry out steel bar binding construction of the outer guide wall (1); Step 3.2: Pre-embed a steel pipe (13) in the outer guide wall (1), wherein the steel pipe (13) is located at the joint between two adjacent sections of the newly constructed ground connection wall (3); Step 3.3: Concrete pouring and construction of outer guide wall (1); Step 3.4: After the outer guide wall (1) reaches the designed strength, backfill the soil excavated in the early stage; In the step 3.1, embedded reinforcement is pre-installed in the existing ground-connected wall (2), and the stirrups (12) of the outer guide wall (1) are fixedly connected to the existing ground-connected wall (2) through the embedded reinforcement; In the step 3.2, the outer guide wall (1) located at the joint of the two adjacent sections of the newly built ground-connected wall (3) is formed into an L-shaped structure, so that a gap (11) is formed between the outer guide wall (1) and the existing ground-connected wall (2), and concrete is backfilled in the gap (11). The steel pipe (13) is pre-buried in the vertical section of the L-shaped structure and extends downward to the bottom of the outer guide wall (1); In the step 4, the bottom of the jet grouting pile (5) extends to the bottom of the raft (7) of the foundation pit; In the step 5, a plurality of wooden supports (15) are arranged at intervals between the inner guide wall (6) and the outer guide wall (1); In the step 6, the new ground-connecting wall (3) is excavated and constructed in sections, and an I-steel joint (14) is provided at the joint of two adjacent sections of the new ground-connecting wall (3); before the secondary trenching excavation of the new ground-connecting wall (3), a grouting pipe (10) is arranged according to the actual geological construction conditions, and the soil disturbed during the construction of the existing ground-connecting wall (2) is grout-reinforced; In the step 7, the steel bars of the newly built ground-connected wall (3) are anchored into the top beam (8), the existing ground-connected wall (2) and the top beam (8) are anchored by planting steel bars, and the top beam (8) is arranged along the existing ground-connected wall (2).

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