Construction method of deep foundation pit in water-rich soft stratum

Abstract

Aiming at the water-rich soft stratum, the application explores a underground continuous wall construction method and a water-rich soft stratum deep foundation pit construction method based on the underground continuous wall construction method. The TAD method is used to construct the channel type cutting assembly type underground continuous wall outside, which can play a quick water stopping role, form a quick support for the outer water-rich soft stratum, provide conditions for the cast-in-place construction of the inner cast-in-place underground continuous wall, and reduce the influence of underground water on the inner cement soil. Under the protection of the outer channel type cutting assembly type underground continuous wall, the inner cast-in-place underground continuous wall is poured in a cast-in-place manner at intervals, which can improve the construction efficiency and completely avoid the influence of water on the cast-in-place concrete. The designed precast pile can make the cast-in-place concrete enter the reserved channel, connect the channel type cutting assembly type underground continuous wall and the cast-in-place underground continuous wall as a whole, ensure the thickness and strength of the underground continuous wall as a whole, and comprehensively integrate the advantages of the precast pile and the cast-in-place continuous wall.

Description

Technical Field

[0001] This invention belongs to the field of foundation pits, specifically relating to a method for constructing a diaphragm wall and a method for constructing deep foundation pits in water-rich soft strata based on the diaphragm wall construction method. It is applicable to water-rich soft strata, especially deep foundation pit construction. Background Technology

[0002] Diaphragm walls are commonly used retaining structures in foundation pit engineering. They are mainly divided into precast diaphragm walls and cast-in-place diaphragm walls. Precast diaphragm walls are precast on the ground, and are less affected by external factors during curing, resulting in high-quality walls. Cast-in-place diaphragm walls have a fast construction speed, but poor adaptability to geological conditions.

[0003] Water-rich and soft soil strata are a common geological feature encountered in foundation pit construction. Due to the weak soil, the thickness of diaphragm walls is usually relatively wide to provide sufficient support for the weak soil, especially under deep foundation pit construction conditions. For water-rich and soft soil strata, precast diaphragm walls have certain advantages, as they can avoid the impact of water on concrete curing.

[0004] The existing TAD (Transit-Oriented) construction method, also known as the channel-cutting prefabricated diaphragm wall construction method, is a construction process that uses channel-cutting of cement-soil diaphragm walls to implant reinforced concrete precast components, forming a prefabricated diaphragm wall. It has advantages such as requiring less land, strong adaptability, and fast construction, and can be used in water-rich strata. However, the TAD construction method typically uses specific models of TRD machines, which limit the width of the diaphragm wall that can be constructed. Furthermore, when the construction width is large, wider precast sheet piles are required, which is detrimental to hoisting and controlling verticality. Additionally, the cement-soil on both sides of the precast sheet piles is still affected by ground water, leading to cement-soil loss and resulting in low strength in the cement-soil portion of the diaphragm wall. Summary of the Invention

[0005] To address the issues of low construction efficiency and insufficient strength of diaphragm walls in deep foundation pit construction in water-rich and soft strata, this invention combines the TAD (Transformation and Adsorption) method with cast-in-place diaphragm walls, exploring a construction method for diaphragm walls in water-rich and soft strata, as well as a construction method for deep foundation pits in such strata based on this diaphragm wall construction method. This method is suitable for water-rich and soft strata, especially for deep foundation pit construction, and can guarantee the construction strength of the diaphragm wall. The specific technical solution of this invention is as follows:

[0006] A method for constructing a diaphragm wall includes the following steps:

[0007] S11. Determine the construction width of the diaphragm wall to meet the requirements of deep foundation pit support; divide the diaphragm wall into an outer channel-type prefabricated diaphragm wall and an inner cast-in-place diaphragm wall in the width direction.

[0008] S12. Processing precast sheet piles, wherein the precast sheet piles include a main body that is rectangular in shape, and a through-type reserved channel is provided in the body along the height direction, and the bottommost precast sheet pile is provided with a sealing bottom plate at the bottom of the reserved channel; along the length direction of the precast sheet piles, adjacent precast sheet piles are joined together by mortise and tenon structure.

[0009] S13. The TAD method is used to construct a channel-type cutting prefabricated underground continuous wall on the periphery. The channel-type cutting prefabricated underground continuous wall includes a prefabricated continuous wall formed by connecting prefabricated sheet piles, as well as outer cement soil outside the prefabricated continuous wall and inner cement soil inside the prefabricated continuous wall; dewatering wells are constructed in the foundation pit to drain the groundwater in the foundation pit.

[0010] S14. Determine the maximum single excavation length of the cast-in-place continuous wall soil. The maximum single excavation length of the cast-in-place continuous wall soil refers to the maximum excavation length of the cast-in-place continuous wall soil under the condition that the excavation width and depth of the cast-in-place continuous wall soil are determined, and the channel-type cutting prefabricated underground continuous wall can stably support the surrounding soil. A certain safety factor is taken to obtain the safe excavation length per single step.

[0011] The soil of the cast-in-place continuous wall is divided into several sections along the direction and numbered. The length of each section is the safe excavation length for a single operation. The excavation and casting work is carried out in an intermittent excavation manner from the reserved passage to the construction connection hole of the cast-in-place continuous wall soil.

[0012] Preferably, the width of the outer channel-cut prefabricated diaphragm wall is smaller than the width of the inner cast-in-place diaphragm wall.

[0013] Preferably, each precast sheet pile is provided with two independent reserved channels along its length.

[0014] Preferably, the upper and lower ends of the precast sheet pile are fixed with metal joints, and the outline of the metal joints is the same as the end outline of the precast sheet pile.

[0015] Preferably, in addition to the topmost precast sheet pile, an auxiliary joint is provided at the top of the precast sheet pile. The auxiliary joint is located directly above the reserved channel and can enter the reserved channel of the adjacent upper precast sheet pile.

[0016] Preferably, the auxiliary connector is in the shape of a truncated pyramid and has a rectangular reserved connection channel inside.

[0017] Preferably, the precast sheet pile has reinforcing bars along its height, and the ends of the reinforcing bars are connected to the metal joint.

[0018] Preferably, the precast sheet pile has a first tenon, a third tenon groove, a second tenon, a third tenon groove, and a first tenon groove arranged sequentially along the width direction on one side, and a first tenon groove, a third tenon, a second tenon groove, a third tenon groove, and a first tenon groove arranged sequentially along the width direction on the other side.

[0019] Preferably, the second tenon and the second mortise are respectively provided with corresponding first sealing grooves and second sealing grooves. The first sealing grooves and the second sealing grooves are joined together to form a circumferentially closed sealing groove, and a waterproof board is placed in the sealing groove.

[0020] Preferably, a TRD construction method machine is used to excavate a trench-shaped space with a set width and depth on the ground and simultaneously inject grout to form cement soil. Multiple precast sheet piles connected to each other in the height direction are lifted together and inserted into the cement soil. Adjacent precast sheet piles are inserted sequentially along the direction using mortise and tenon structures to form a precast continuous wall.

[0021] Preferably, adjacent precast sheet piles are connected in the height direction by auxiliary joints, and metal joints between adjacent precast sheet piles are welded until the design depth is reached. The bottom precast sheet pile is provided with a sealing bottom plate, and the top precast sheet pile is not provided with an auxiliary joint.

[0022] Preferably, the odd-numbered segments are excavated first, and concrete is poured on-site from the reserved passage to the construction connection hole of the cast-in-place continuous wall soil. The even-numbered segments are excavated first, and concrete is poured on-site from the reserved passage to the construction connection hole of the cast-in-place continuous wall soil.

[0023] This invention also provides a method for constructing deep foundation pits in water-rich, soft strata, comprising the following steps:

[0024] S1. Construct the underground continuous wall retaining structure of the foundation pit using one of the underground continuous wall construction methods described above;

[0025] S2. Excavate the earthwork layer by layer, and construct the capping beam, concrete retaining wall, anchor cables and waist beam. Set up drainage ditches and sump pits around the foundation pit.

[0026] Beneficial Technical Effects: 1. For deep foundation pits in water-rich and soft strata, this invention combines the TAD (Transmission-Adjustable Diaphragm) method with cast-in-place diaphragm walls. The TAD method utilizes a channel-cut prefabricated diaphragm wall constructed on the outer perimeter, which provides rapid water-stopping and creates rapid support for the surrounding water-rich and soft strata, facilitating the cast-in-place construction of the inner diaphragm wall. It also reduces the impact of groundwater on the inner cement-soil. Under the protection of the outer channel-cut prefabricated diaphragm wall, the inner cast-in-place diaphragm wall is intermittently poured using a cast-in-place method, improving construction efficiency while completely avoiding the impact of water on the cast-in-place concrete, thus ensuring the strength of the cast-in-place diaphragm wall.

[0027] 2. A special precast sheet pile structure was designed, especially in the reserved connection channel and the sealing of the bottom plate. Later, the cast-in-place concrete can be entered into the reserved channel through the construction connection hole, connecting the outer channel-type cut prefabricated underground continuous wall with the inner cast-in-place underground continuous wall as a whole, ensuring the thickness and strength of the underground continuous wall, and combining the advantages of precast sheet piles and cast-in-place continuous walls. Attached Figure Description

[0028] Figure 1 This is a partial schematic diagram of the foundation pit retaining structure of the present invention;

[0029] Figure 2 These are top views of various forms of precast sheet piles according to the present invention;

[0030] Figure 3 This is a partial schematic diagram of the precast sheet pile splicing in the foundation pit retaining structure of the present invention;

[0031] In the figure, there are: outer cement soil 11, inner cement soil 12, precast sheet pile 2, main body 20, first tenon 21, third tenon groove 22, second tenon 23, first sealing groove 24, steel bar 25, reserved channel 26, reserved connection channel 27, auxiliary joint 28, metal joint 29, connecting hole 30, first tenon groove 31, third tenon 32, second tenon groove 33, second sealing groove 34, sealing base plate 4, cast-in-place underground continuous wall 5, and precast continuous wall 6. Detailed Implementation

[0032] The following is in conjunction with the appendix Figure 1-3 The present invention will be further described below.

[0033] This invention explores a method for constructing diaphragm walls in water-rich and soft strata, as well as a method for constructing deep foundation pits in water-rich and soft strata based on this method. It is applicable to water-rich and soft strata, especially for deep foundation pit construction, and can ensure the construction strength of the diaphragm wall.

[0034] like Figure 1 As shown, a method for constructing a diaphragm wall according to the present invention includes the following steps:

[0035] S11. Level the site; determine the construction width of the diaphragm wall to meet the requirements of deep foundation pit support; divide the diaphragm wall into an outer channel-type cutting and assembly diaphragm wall and an inner cast-in-place diaphragm wall 5 in the width direction; preferably, the width of the outer channel-type cutting and assembly diaphragm wall is smaller than that of the inner cast-in-place diaphragm wall 5; the width of the channel-type cutting and assembly diaphragm wall is preferably the width of the cement-soil diaphragm wall that can be constructed by the existing TRD method machine, or preferably the width of the channel-type cutting and assembly diaphragm wall that can be constructed by the existing TAD method, that is, there is no need to specially customize the TRD method machine and the matching cutting box, and mature equipment models can be directly selected;

[0036] S12. Process precast sheet piles 2, such as Figure 2-3 As shown, the precast sheet pile 2 includes a rectangular body 20. A reserved channel 26 is provided within the rectangular body 20 along its height direction. In this embodiment, two independent reserved channels 26 are provided, but one or more independent reserved channels 26 can also be provided. Except for the precast sheet pile 2 constructed at the bottom, the reserved channel 26 penetrates the entire rectangular body 20. A sealing base plate 4 is provided at the bottom of the reserved channel 26 for the precast sheet pile 2 constructed at the bottom. In the height direction, a metal joint 29 is fixed to the end of the precast sheet pile 2. The outline of the metal joint is the same as the end outline of the precast sheet pile 20. Adjacent precast sheet piles 20 can be connected by welding the metal joint 29 to ensure connection strength. To facilitate the docking of the precast sheet piles 20 in the height direction, a reserved channel 26 is provided within the precast sheet pile 20. An auxiliary joint 28 is provided at the top (except for the precast sheet piles at the very top). The auxiliary joint 28 is located directly above the reserved channel 26. The auxiliary joint 28 is in the shape of a truncated pyramid. The auxiliary joint 28 of the lower precast sheet pile 20 can enter the reserved channel 26 of the adjacent upper precast sheet pile 20. The auxiliary joint 28 is provided with a rectangular reserved connection channel 27 inside. That is, the auxiliary joint 28 is hollow to ensure that the reserved channels 26 of adjacent precast sheet piles 20 are connected in the height direction. Since the bottom precast sheet pile 20 is provided with a sealing bottom plate 4, the reserved channel in the vertical direction is connected from top to bottom, and the lower part is sealed by the sealing bottom plate 4. The main body 20 of the precast sheet pile is also provided with steel bars 25 along the height direction. The ends of the steel bars 25 are connected to the metal joint 29.

[0037] Along the direction of the diaphragm wall, i.e., along the length of the precast sheet piles 2, adjacent precast sheet piles 2 are joined by a mortise and tenon structure, and a sealing structure is provided within the mortise and tenon structure to seal in the width direction. Specifically, one side of the precast sheet pile 2 is provided with a first tenon 21, a third tenon 22, a second tenon 23, a third tenon 22, and a first tenon 21 in sequence along the width direction, and the corresponding other side is provided with a first tenon 31, a third tenon 32, a second tenon 33, a third tenon 32, and a first tenon 31 in sequence along the width direction. The first tenon 21, the third tenon 22, and the second tenon 23 are respectively matched with the first tenon 31, the third tenon 32, and the second tenon 33 for mortise and tenon connection. In order to improve the sealing in the width direction, the second tenon 23 and the second tenon 33 are respectively provided with corresponding first sealing grooves 24 and second sealing grooves 34. When adjacent precast sheet piles 2 are connected in the direction, the first sealing grooves 24 and the second sealing grooves 34 are joined to form a circumferentially closed sealing groove.

[0038] S13. The TAD method is used to construct a channel-type cutting prefabricated underground continuous wall on the periphery. The channel-type cutting prefabricated underground continuous wall includes a prefabricated continuous wall 6 formed by connecting prefabricated sheet piles 2, as well as an outer cement-soil 11 outside the prefabricated continuous wall 6 and an inner cement-soil 12 inside the prefabricated continuous wall 6. The channel-type cutting prefabricated underground continuous wall, especially the prefabricated continuous wall 6, can play a water-stopping role.

[0039] Specifically, the TRD method machine is used to excavate a trench-shaped space of a set width and depth on the ground (corresponding to the outer channel-type prefabricated underground continuous wall range) and simultaneously grouting to form cement-soil within the trench-shaped space; adjacent precast sheet piles 2 are connected in the height direction through auxiliary joints 28, and metal joints 29 between adjacent precast sheet piles 2 are welded until the design depth is reached, wherein the bottom precast sheet pile 2 is equipped with a sealing bottom plate 4, and the top precast sheet pile 2 does not have auxiliary joints 28; then, multiple precast sheet piles 2 connected vertically are lifted vertically together using specialized crane equipment, and then workers grasp the side wall mortise and tenon structure to simultaneously perform vertical insertion work, inserting multiple precast sheet piles 2 connected vertically into the cement-soil, verifying and calibrating the vertical accuracy, and fixing them with fixing clamps to complete the erection work; adjacent precast sheet piles are inserted sequentially along the direction through mortise and tenon structure to form precast continuous wall 6, and a waterproof board is placed in the sealing groove to prevent groundwater outside the outer cement-soil 11 from entering the inner cement-soil 12 from the width direction of the precast sheet pile (mortise and tenon connection);

[0040] After the precast sheet piles 2 are spliced ​​to form the precast continuous wall 6, dewatering wells are constructed in the foundation pit to drain the groundwater in the foundation pit and to cure the cement soil. The specific construction method of the dewatering wells is as follows: dewatering wells are drilled in an array within the designed foundation pit area. The diameter of the dewatering wells is 450mm. Well pipes with a diameter of 219*6mm are hoisted and placed. Fine gravel filter material is backfilled, the wells are washed, water pumps are placed, and dewatering is carried out.

[0041] S14. After the outer channel-cut prefabricated diaphragm wall has been cured and reached the set strength, determine the maximum single excavation length of the cast-in-place diaphragm wall soil. The maximum single excavation length of the cast-in-place diaphragm wall soil refers to the state in which the channel-cut prefabricated diaphragm wall can maintain stability and support the outer soil under the excavation length and the designed excavation width and depth. Take a certain safety factor to obtain the safe single excavation length.

[0042] The soil for the cast-in-place continuous wall is divided into several sections along the direction of the wall. Each section is the safe length for a single excavation and is numbered. Excavation and casting are carried out using an intermittent excavation method. First, the odd-numbered sections (e.g., ...) are excavated. Figure 1 Sections 1# and 3# in the middle), and simultaneously, from the reserved passage 26 to the construction connection hole 30 of the cast-in-place continuous wall soil, connecting the reserved passage 26 and the space after the excavation of the cast-in-place underground continuous wall 5 soil, to carry out on-site concrete pouring, the concrete can enter the reserved passage through the connection hole; excavate even-numbered sections (such as... Figure 1 (Sections 2# and 4# in the middle), and at the same time, from the reserved passage 26 to the construction connection hole 30 of the cast-in-place continuous wall soil, the reserved passage 26 and the space after the excavation of the soil of the cast-in-place underground continuous wall 5 are connected to the space after the excavation of the soil, and the concrete is poured on site; the construction of the cast-in-place underground continuous wall 5 is completed.

[0043] The present invention further provides a method for constructing deep foundation pits in water-rich, soft strata, comprising the following steps:

[0044] S1. Construct the underground continuous wall retaining structure of the foundation pit using one of the underground continuous wall construction methods described above;

[0045] S2. Earthwork excavation: Earthwork excavation is divided into several zones and carried out in an overlapping manner;

[0046] The first layer of earthwork is excavated, and the capping beam and concrete retaining wall are constructed. The second layer of earthwork is excavated, and the anchor cables and waist beams are constructed. This process is repeated for subsequent layers of earthwork excavation, and the anchor cables and waist beams are constructed until the design depth is reached. The specific construction method for the anchor cables and waist beams is as follows: first, boreholes are drilled using a drilling rig, then anchor rods are lowered, grouting is performed, the waist beams are constructed, the anchor cables are tensioned, and the boreholes are drilled downwards and outwards towards the underground continuous wall. Drainage ditches and sump pits are set up around the foundation pit.

[0047] This invention is not limited to the preferred embodiments described above. Anyone can derive other methods in various forms under the guidance of this invention. Any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A method for constructing a diaphragm wall, characterized in that, Includes the following steps: S11. Determine the construction width of the diaphragm wall to meet the requirements of deep foundation pit support; divide the diaphragm wall into an outer channel-type prefabricated diaphragm wall and an inner cast-in-place diaphragm wall in the width direction. S12. Processing precast sheet piles, wherein the precast sheet piles include a main body that is generally rectangular in shape, and a through-type reserved channel is provided in the body along the height direction, and the bottommost precast sheet pile is provided with a sealing bottom plate at the bottom of the reserved channel; along the length direction of the precast sheet piles, adjacent precast sheet piles are joined together by a mortise and tenon structure; an auxiliary joint is provided at the top of the precast sheet piles, the auxiliary joint is located directly above the reserved channel, and can enter the reserved channel of the adjacent upper precast sheet piles; a reserved connection channel is provided inside the auxiliary joint; S13. The TAD method is used to construct a channel-type cutting prefabricated underground continuous wall on the periphery. The channel-type cutting prefabricated underground continuous wall includes a prefabricated continuous wall formed by connecting prefabricated sheet piles, as well as outer cement soil outside the prefabricated continuous wall and inner cement soil inside the prefabricated continuous wall; dewatering wells are constructed in the foundation pit to drain the groundwater in the foundation pit. S14. Determine the maximum single excavation length of the cast-in-place continuous wall soil. The maximum single excavation length of the cast-in-place continuous wall soil refers to the maximum excavation length of the cast-in-place continuous wall soil under the condition that the excavation width and depth of the cast-in-place continuous wall soil are determined, and the channel-type cutting prefabricated underground continuous wall can stably support the surrounding soil. A certain safety factor is taken to obtain the safe excavation length per single step. The soil of the cast-in-place continuous wall is divided into several sections along the direction and numbered. The length of each section is the safe excavation length for a single operation. The excavation and casting work is carried out in an intermittent excavation manner from the reserved passage to the construction connection hole of the cast-in-place continuous wall soil.

2. The method for constructing a diaphragm wall according to claim 1, characterized in that, The width of the outer channel-type prefabricated diaphragm wall is smaller than the width of the inner cast-in-place diaphragm wall.

3. The method for constructing a diaphragm wall according to claim 1, characterized in that, The precast sheet pile is fixed to the upper and lower ends with metal joints, the outline of which is the same as the end outline of the precast sheet pile; the precast sheet pile body is also provided with reinforcing bars along the height direction, and the ends of the reinforcing bars are connected to the metal joints.

4. The method for constructing a diaphragm wall according to claim 1 or 3, characterized in that, The precast sheet pile has a first tenon, a third tenon groove, a second tenon, a third tenon groove, and a first tenon groove arranged sequentially along the width direction on one side, and a first tenon groove, a third tenon, a second tenon groove, a third tenon groove, and a first tenon groove arranged sequentially along the width direction on the other side.

5. The method for constructing a diaphragm wall according to claim 4, characterized in that, The second tenon and the second mortise are respectively provided with corresponding first sealing grooves and second sealing grooves. The first sealing grooves and the second sealing grooves are joined together to form a circumferentially closed sealing groove, and a waterproof board is placed in the sealing groove.

6. The method for constructing a diaphragm wall according to claim 1 or 3, characterized in that, The TRD method machine is used to excavate a trench-shaped space with a set width and depth on the ground and simultaneously grout to form cement soil. Multiple precast sheet piles connected to each other in the vertical direction are lifted together and inserted into the cement soil. Adjacent precast sheet piles are inserted sequentially along the direction using mortise and tenon joints to form a precast continuous wall.

7. The method for constructing a diaphragm wall according to claim 1 or 3, characterized in that, First, excavate the odd-numbered sections, and simultaneously pour concrete on-site from the reserved passage to the construction connection hole of the cast-in-place continuous wall soil. Then, excavate the even-numbered sections, and simultaneously pour concrete on-site from the reserved passage to the construction connection hole of the cast-in-place continuous wall soil.

8. A method for constructing deep foundation pits in water-rich, soft strata, comprising the following steps: S1. Constructing a diaphragm wall retaining structure using the diaphragm wall construction method described in any one of claims 1-7; S2. Excavate the earthwork layer by layer, and construct the capping beam, concrete retaining wall, anchor cables and waist beam. Set up drainage ditches and sump pits around the foundation pit.

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