A rigid milling joint for diaphragm wall in the retaining structure of a large circular foundation pit and its construction method

Abstract

The present invention discloses a rigid milling joint for a diaphragm wall of a large circular foundation pit and a construction method. The rigid milling joint includes a first-phase groove wall, a first-phase groove steel reinforcement cage, a combined square pipe, a grouting pipe, a rubber bladder, a T-shaped steel plate, a second-phase groove steel reinforcement cage, and second-phase groove concrete. The grouting pipe and the rubber bladder are adhered to the inner side of the combined square pipe with glue. The combined square pipe is fixed to the first-phase groove steel reinforcement cage by welding. The cross-sectional area of the T-shaped steel plate is determined by a calculation formula according to the design value of the bending moment in the joint area. When the second-phase groove is trenched, the milling machine mills the concrete to break the square polyvinyl chloride pipe in the combined square pipe, forming a groove. The T-shaped steel plate is inserted into the groove formed after the combined square pipe is broken. After the second-phase groove concrete has finally set, the grouting pipe is used to grout the joint seam. The present invention forms an overlap between the first-phase groove steel reinforcement cage and the second-phase groove steel reinforcement cage, enabling the milling joint to have bending resistance. The flexural bearing capacity can be determined by a calculation formula. The design is scientific, the construction is simple, the construction cost is effectively reduced, the project quality is improved, and it has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering, and more specifically, to a rigid milling joint of a large circular foundation pit retaining underground continuous wall and a construction method thereof. Background Art

[0002] An underground continuous wall refers to a continuous reinforced concrete wall formed by using a special trenching machine to dig narrow trench sections underground under the condition of mud wall protection, placing steel cages, pouring concrete and connecting them together. It has the advantages of good water-stopping effect, high overall rigidity and little impact on the environment, and has been widely used in the field of civil engineering.

[0003] The underground continuous wall is connected by multiple unit slots, and the quality of the joints is directly related to the integrity and impermeability of the wall structure. The milling joint is a common joint form of the underground continuous wall. It can withstand greater pressure, but cannot withstand bending moment. It is often used as a joint form for circular foundation pit enclosure ground-connected walls. As the plane size of the circular foundation pit continues to increase, the arch effect weakens, and there will be a certain bending moment in the joint area. The traditional milling joint is no longer suitable as a joint form for large circular foundation pit enclosure ground-connected walls. It is urgent to invent a rigid milling joint that can withstand a certain bending moment. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a rigid milling joint and a construction method for a large circular foundation pit retaining underground continuous wall. By forming an overlap between the first-phase trough section steel cage and the second-phase trough section steel cage, the milling joint has bending resistance, and the bending bearing capacity is determined by a calculation formula. The design is scientific and the construction is simple, which effectively reduces the construction cost and improves the project quality.

[0005] The technical solution adopted by the present invention to solve this technical problem is:

[0006] A large-scale circular foundation pit enclosure underground continuous wall rigid milling joint, the first-stage trough section wall and the second-stage trough section wall are adjacent to each other through mutually engaged concave-convex milling joints, the groove of the milling joint is defined by setting a pipe body, the pipe body is arranged along the longitudinal length of the first-stage trough section wall, when the second-stage trough is formed, the pipe body is milled when the milling machine mills the concrete, and the groove is formed at the position of the pipe body, the pipe body is a combined square pipe, including a square steel pipe and a square polypropylene pipe, wherein one side of the square steel pipe is welded to the trough section steel cage in the first-stage trough section wall, and the other side opening is butted against the open side of the square polypropylene pipe, the inner side of the pipe wall of the square steel pipe is pre-buried with a grouting pipe along the length direction of the square steel pipe, and the inner sides of the square steel pipe and the square polypropylene pipe are pre-set with a rubber bag;

[0007] A T-shaped steel plate is fixedly connected to the groove section steel cage of the second phase groove section wall, and the T-shaped steel plate is inserted into the groove formed after the pipe body is broken;

[0008] After the concrete of the second-phase groove section reaches final setting, grouting is carried out on the joint seam through the grouting pipe.

[0009] Further preferably, the cross-sectional length of the combined square pipe includes two specifications of 25 cm and 30 cm. The width of the square steel pipe is 10 cm, and the width of the square polypropylene pipe includes two specifications of 15 cm and 20 cm, which are selected according to the groove section depth H and the groove section verticality control standard X. The specific selection methods include the following three cases:

[0010] Case 1: When H*X + 3 cm ≤ 7.5 cm, both the combined square pipes with cross-sectional lengths of 25 cm and 30 cm meet the requirements;

[0011] Case 2: When 7.5 cm < H*X + 3 cm ≤ 10 cm, select the combined square pipe with a cross-sectional length of 30 cm;

[0012] Case 3: When H*X + 3 cm > 10 cm, increase the groove section verticality control standard to 1 / 1000 and select the combined square pipe with a cross-sectional length of 30 cm.

[0013] Further preferably, two grouting pipes are arranged in each square steel pipe, respectively located on the upper and lower sides of the inner wall of the square steel pipe.

[0014] Further preferably, a rubber bladder is preset inside the square steel pipe and the square polypropylene pipe, which can expand after inflation. The cross-section of the rubber bladder after inflation is rectangular, and the size is the same as the cross-sectional size of the square steel pipe and the square polypropylene pipe.

[0015] Further preferably, the equivalent thickness d of the T-shaped steel plate satisfies the following formula:

[0016]

[0017] Among them, M is the design value of the bending moment in the joint area; d p is the protective layer thickness of the T-shaped steel plate, D is the thickness of the joint area, f cd is the design value of the axial compressive strength of concrete, the design value of the compressive strength of ordinary steel, x is the thickness of the compression zone in the joint area; is the correction coefficient for resisting bending moment.

[0018] Further preferably, the calculation formula for the thickness x of the compression zone in the joint area is:

[0019]

[0020] Among them, f sd is the design value of the tensile strength of ordinary steel.

[0021] Further preferably, the thickness x of the compression zone in the joint area should also meet the structural construction requirements, that is: , otherwise, the equivalent thickness d of the T-shaped steel plate per unit height in the joint area is calculated according to the following formula:

[0022] .

[0023] Further preferably, the T-shaped steel plates are arranged discontinuously.

[0024] T-shaped

[0025] Among them, is the height of a single T-shaped steel plate, and h is the vertical spacing distance;

[0026] Among them, the height of a single T-shaped steel plate and the value of the vertical spacing distance h of the T-shaped steel plates are both related to the diaphragm wall groove section verticality control standard X. According to the statistics of the on-site groove section implementation situation, the height of a single T-shaped steel plate , the value of the vertical spacing distance h of the T-shaped steel plates includes the following three types:

[0027] The first type: when the groove section verticality control standard does not exceed 1 / 400, the height of a single T-shaped steel plate is not greater than 100 mm, and the vertical spacing distance h of the T-shaped steel plates is greater than 10*H / 400, where H is the groove section depth;

[0028] The second type: when the groove section verticality control standard exceeds 1 / 800, the height of a single T-shaped steel plate is not greater than 200 mm, and the vertical spacing distance h of the T-shaped steel plates is greater than 3*H / 800;

[0029] The third type: when the groove section verticality control standard X is between 1 / 400 and 1 / 800, the height of a single T-shaped steel plate and the vertical spacing distance h of the T-shaped steel plates are determined by the linear interpolation method.

[0030] The present invention further discloses a construction method for a rigid milling joint of a diaphragm wall for the enclosure of a large circular foundation pit, including the following steps:

[0031] S1. Use a grooving machine to perform grooving operations on the first-phase groove section;

[0032] S2. Glue the grouting pipe to the inner side of the square steel pipe in the combined square pipe, and glue the rubber bladder to the inner sides of the square steel pipe and the square polypropylene pipe. One side of the square steel pipe is fixed to the first-phase groove section steel cage by welding, and then lower the first-phase groove section steel cage;

[0033] S3. Use an air compressor to fill the rubber bladder inside the square steel pipe and the square polypropylene pipe with gas until the air pressure inside the rubber bladder is the concrete unit weight * H, with the unit of kPa, and then stop inflating. The concrete unit weight is taken as 24 kN / m³.

[0034] S4. Pour the concrete for the first-stage trench segment.

[0035] S5. Extract the gas from the rubber bladder inside the square steel pipe and the square polypropylene pipe, and pull out the rubber bladder from the square steel pipe and the square polypropylene pipe for reuse in the next cycle.

[0036] S6. Use a grooving machine to carry out grooving operations for the second-stage trench segment. The grooving machine grooves downward from the middle part of the square polypropylene pipe, mill a certain width of the concrete of the first-stage trench segment in the joint area to form a concrete biting surface, and break a part of the square polypropylene pipe of the combined square pipe to form the groove.

[0037] S7. Use a square pipe shape detector to detect the shape of the square steel pipe, determine whether the square steel pipe is intact, and fit the attitude of the square steel pipe.

[0038] S8. According to the attitude of the square steel pipe, adjust the lap length between the T-shaped steel plate and the second-stage steel cage, weld the T-shaped steel plate on the second-stage steel cage, and lower the second-stage steel cage along the groove formed after the combined square pipe is broken, so that the T-shaped steel plate is inserted into the groove.

[0039] S9. Pour the concrete for the second-stage trench segment.

[0040] S10. After the concrete of the second-stage trench segment has finally set, use the grouting pipe to grout the joint seam.

[0041] As a further optimization of the above construction method, the square pipe shape detector includes an inclinometer, a detection probe, and a steel wire rope. Among them, the inclinometer is vertically suspended inside the detection probe through the steel wire rope, and the other end of the steel wire rope is fixed on a winch arranged on the ground. The winch controls the recovery and lowering of the steel wire rope.

[0042] The detection probe is a cubic steel bar framework with an outer contour consistent with the inner contour of the square steel pipe. The plane size of the outer contour of the detection probe is smaller than the plane size of the inner contour of the square steel pipe.

[0043] The present invention has at least the following beneficial effects:

[0044] (1) The present invention increases the seepage path at the joint and is equipped with a grouting pipe to grout the joint seam, improving the anti-seepage performance of the joint.

[0045] (2) The present invention forms a lap joint between the steel cage of the first-stage groove section and the steel cage of the second-stage groove section, enabling the milling joint to have bending resistance, and proposes a calculation method for the bending bearing capacity of a T-shaped steel plate.

[0046] (3) Since it is necessary to place the concrete for pouring the first-stage groove, and the concrete enters the combined square pipe, and it is required that the concrete side pressure does not damage the combined square pipe during the pouring of the first-stage groove concrete. Therefore, the present invention temporarily sets a rubber bladder inside the combined square pipe, which can be inflated before the concrete pouring, ensuring that the concrete will not enter the pipe from the bottom of the combined square pipe. At the same time, it can also balance the outside concrete side pressure and prevent the structural damage caused by the excessive pressure difference between the inside and outside of the combined square pipe.

[0047] (4) The present invention is scientifically designed and simple to construct, effectively improving the anti-seepage performance and bending resistance of the milling joint, reducing the construction cost, and having broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a top view of a rigid milling joint of a diaphragm wall according to the present invention;

[0049] Figure 2 It is a top view of the first-stage steel cage after completing the welding of the combined square pipe according to the present invention;

[0050] Figure 3 It is a top view of the first-stage steel cage after the rubber bladder inside the combined square pipe is inflated according to the present invention;

[0051] Figure 4 It is a top view of the completed wall of the first-stage groove section according to the present invention;

[0052] Figure 5 It is a top view of the concrete bite surface and the groove of the combined square pipe formed by milling a certain width of the concrete at the joint of the first-stage groove section and breaking part of the square polypropylene pipe according to the present invention;

[0053] Figure 6 It is a top view of the second-stage steel cage according to the present invention;

[0054] Figure 7 It is a top view of the pin inserted into the groove of the combined square pipe when the second-stage steel cage is lowered according to the present invention;

[0055] Figure 8 It is a cross-sectional view of the combined square pipe according to the present invention;

[0056] Figure 9 It is a three-dimensional view of the combined square pipe according to the present invention;

[0057] Figure 10 It is a three-dimensional schematic diagram of the square polypropylene pipe in the combined square pipe after being milled according to the present invention;

[0058] Figure 11 Schematic diagram for the design calculation of the T-shaped steel plate of the present invention;

[0059] Figure 12 Three-dimensional schematic diagram of the square pipe shape detector of the present invention.

[0060] Description of the reference numerals in the drawings: 1 is the concrete of the first-stage groove section, 2 is the steel reinforcement cage of the first-stage groove section, 3 is the grouting pipe, 4 is the combined square pipe, 4-1 is the square steel pipe, 4-2 is the square polypropylene pipe, 4-3 is the steel plate, 5 is the steel reinforcement cage of the second-stage groove section, 6 is the T-shaped steel plate, 7 is the concrete of the second-stage groove section, 8 is the rubber bladder, 9 is the square pipe shape detector, 9-1 is the inclinometer, 9-2 is the detection probe, and 9-3 is the steel wire rope. Detailed implementation manners

[0061] The present invention will be described in detail and completely below with reference to the drawings. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the drawings, it should be particularly noted that: the technical solutions and technical features provided in each part including the following description of the present invention can be combined with each other without conflict.

[0062] In addition, the embodiments of the present invention described below are generally only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0063] The following further describes the present invention in detail with reference to the drawings and embodiments, and the specific implementation process is as follows:

[0064] The technical solution adopted by the present invention to solve this technical problem is: a design method for a rigid milling joint of a diaphragm wall, including the first-phase groove-section concrete 1, the first-phase groove-section steel reinforcement cage 2, the grouting pipe 3, the combined square pipe 4, the square steel pipe 4-1, the square polyvinyl chloride pipe 4-2, the steel plate 4-3, the second-phase groove-section steel reinforcement cage 5, the T-shaped steel plate 6, the second-phase groove-section concrete 7, the rubber bladder 8, the square-pipe shape detector 9, the inclinometer 9-1, the detection probe 9-2, and the steel wire rope 9-3. The combined square pipe 4 is composed of the square steel pipe 4-1, the square polyvinyl chloride pipe 4-2, and the steel plate 4-3. The combined square pipe 4 is 300 mm long and 200 mm wide, where the square steel pipe 4-1 part is 100 mm long and the square polyvinyl chloride pipe 4-2 part is 200 mm long. The square steel pipe 4-1 is welded and fixed to the first-phase groove-section steel reinforcement cage 2. The grouting pipe 3 is glued to the inner side of the square steel pipe 4-1. There are two rubber bladders 8, which are respectively fixed to the inner sides of the square steel pipe 4-1 and the square polyvinyl chloride pipe 4-2. When the second-phase groove is being excavated, the grooving machine mills the first-phase groove-section concrete 1 and breaks the square polyvinyl chloride pipe 4-2 part to form a groove. Subsequently, the square-pipe shape detector 9 is used to detect the attitude of the square steel pipe 4-1. After determining that the square pipe 4-1 is intact and its attitude, the T-shaped steel plate 6 is inserted into the groove formed after the combined square pipe 4 is broken. After the second-phase groove-section concrete 7 has finally set, the grouting pipe 3 is used to grout the joint seam.

[0065] In the technical solution of the present invention, the grouting pipe 3, the combined square pipe 4, and the rubber bladder 8 are all arranged in a full-length manner; the width of the steel plate in the combined square pipe 4 is 50 mm; the grouting pipe 3 is a reusable grouting pipe. When grouting, the slurry outlet opens outward under pressure. When grouting stops, the slurry outlet automatically closes. After each grouting is completed, a certain amount of clear water is injected to wash the grouting pipe and the slurry outlet to prevent the cement slurry from solidifying and blocking the grouting pipeline, so as to achieve repeated use and multiple groutings. The rubber bladder 8 can expand after being inflated, and the cross-sectional dimension after expansion is the same as the cross-sectional dimensions of the square steel pipe 4-1 and the square polyvinyl chloride pipe 4-2.

[0066] In the technical solution of the present invention, the square-pipe shape detector 9 includes an inclinometer 9-1, a detection probe 9-2, and a steel wire rope 9-3. The usage method of the square-pipe shape detector 9 is as follows:

[0067] S1: Before lowering the second-phase groove-section steel reinforcement cage 5, put the square-pipe detector 9 into the square steel pipe 4-1, slowly lower the detection probe 9-2 by using the steel wire rope 9-3, and collect the data of the inclinometer 9-1 every 5 m, and record the current inclinometer data and the depth where the current detection probe is located;

[0068] S2: If the detection probe 9-2 can be lowered to the bottom elevation of the groove, it indicates that the square steel pipe 4-1 is not damaged. According to the data of the inclinometer 9-1 at different depths, the attitude of the square steel pipe can be fitted;

[0069] S3: If the detection probe 9-2 fails to be lowered to the elevation of the bottom of the groove, it indicates that the square steel pipe 4-1 is damaged by the grooving machine during the grooving of the second-phase groove. In this case, the rigid milling joint proposed in this solution cannot be used.

[0070] In the technical solution of the present invention, the bending resistance of the rigid milling joint is mainly determined by the T-shaped steel plate 6. The design method of the T-shaped steel plate 6 mainly includes the following steps:

[0071] S1. Assume that the specifications and layout forms of the T-shaped steel plates are the same on the soil-facing side and the soil-backing side of the joint. The design value of the bending moment in the joint area is M, the equivalent thickness per unit height of the T-shaped steel plate is d, and the protective layer thickness of the T-shaped steel plate is d p , the thickness of the joint area is D, and the design value of the axial compressive strength of the concrete is f cd , the design value of the tensile strength of ordinary steel is f sd , the design value of the compressive strength of ordinary steel is , and the thickness of the compression zone in the joint area is x;

[0072] S2. To calculate the resisting bending moment of the flexural interface using the plane assumption, the resisting bending moment needs to be corrected. The concrete strength grade of the diaphragm wall is C35 or C30. According to the results of the rigid joint simulation experiment, when the sectional reinforcement ratio is less than 0.55%, the correction coefficient takes 0.75. When the sectional reinforcement ratio is greater than 0.8%, the correction coefficient takes 0.4;

[0073] S3. The equivalent thickness d of the T-shaped steel plate per unit height in the joint area needs to satisfy the following formula:

[0074]

[0075] S4. The calculation formula for the thickness x of the compression zone in the joint area is:

[0076]

[0077] S5. The thickness x of the compression zone in the joint area should also meet the structural construction requirements, that is: , otherwise, the equivalent thickness d of the T-shaped steel plate per unit height in the joint area is calculated according to the following formula:

[0078]

[0079] S6. The T-shaped steel plates are arranged discontinuously. Assume that the height of a single T-shaped steel plate is , and the vertical spacing distance is h. Then the thickness of the T-shaped steel plate: .

[0080] Among them, is the height of a single T-shaped steel plate, and h is the vertical spacing distance.

[0081] Among them, the height of a single T-shaped steel plate and the value of the vertical spacing distance h of the T-shaped steel plates are both related to the control standard of the verticality of the diaphragm wall trench section. According to the statistics of the on-site trench section implementation situation, the height of a single T-shaped steel plate and the value of the vertical spacing distance h of the T-shaped steel plates are specified as follows:

[0082] (1) When the control standard of the trench section verticality does not exceed 1 / 400, the height of a single T-shaped steel plate is not greater than 100 mm, and the vertical spacing distance h of the T-shaped steel plates should be greater than 10*H / 400, where H is the maximum depth of the trench section;

[0083] (2) When the control standard of the trench section verticality exceeds 1 / 800, the height of a single T-shaped steel plate is not greater than 200 mm, and the vertical spacing distance h of the T-shaped steel plates should be greater than 3*H / 800;

[0084] When the control standard of the trench section verticality is between 1 / 400 and 1 / 800, the height of a single T-shaped steel plate and the vertical spacing distance h of the T-shaped steel plates are determined by the linear interpolation method.

[0085] The present invention also provides a construction method for the rigid milling joint of the diaphragm wall, which mainly includes the following steps:

[0086] S1. Use a grooving machine to perform grooving operations on the first-phase trench section;

[0087] S2. Glue the grouting pipe 3 to the inner side of the combined square pipe 4, and glue the rubber bladder 8 to the inner sides of the square steel pipe 4-1 and the square polypropylene pipe 4-2. The combined square pipe 4 is fixedly welded to the first-phase trench section steel cage 2 on one side of the square steel pipe 4-1 part, and lower the first-phase trench section steel cage 2;

[0088] S3. Use an air compressor to fill the rubber bladder 8 in the square steel pipe 4-1 and the square polypropylene pipe 4-2 with gas until the air pressure in the rubber bladder 8 is the concrete unit weight * H, in kPa, and stop inflating. The concrete unit weight is taken as 24 kN / m³;

[0089] S4. Pour the concrete 1 of the first-phase trench section;

[0090] S5. Extract the gas in the rubber bladder 8 in the square steel pipe 4-1 and the square polypropylene pipe 4-2, and pull out the rubber bladder 8 from the square steel pipe 4-1 and the square polypropylene pipe 4-2 for reuse in the next cycle;

[0091] S6. Use a grooving machine to perform grooving operations on the second-phase groove section. The grooving machine grooves downward from the middle part of the square polypropylene pipe 4-2, milling off a certain width of the concrete 1 in the first-phase groove section in the joint area to form a concrete biting surface and breaking a part of the square polypropylene pipe 4-2 in the combined square pipe 4 to form a groove;

[0092] S7. Use a square pipe shape detector 9 to detect the shape of the square steel pipe 4-1, determine whether the square steel pipe 4-1 is intact, and fit the attitude of the square steel pipe 4-1;

[0093] S8. According to the attitude of the square steel pipe 4-1, appropriately adjust the overlapping length between the T-shaped steel plate 6 and the second-phase steel reinforcement cage 5, weld the T-shaped steel plate 6 on the second-phase steel reinforcement cage 5, and lower the second-phase steel reinforcement cage 5 along the groove formed after the combined square pipe 4 is broken, so that the T-shaped steel plate 6 is inserted into the groove;

[0094] S9. Pour the concrete 7 of the second-phase groove section;

[0095] S10. After the concrete 7 of the second-phase groove section has finally set, use a grouting pipe 3 to grout the joint seam.

[0096] Although the embodiments of the present invention have been disclosed as above, they are not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the embodiments shown and described here.

Claims

1. A rigid milling joint for the diaphragm wall of a large circular foundation pit retaining structure. The wall of the first-stage trench section and the wall of the second-stage trench section are adjacent to each other through an engaging concave-convex milling joint. The groove of the milling joint is defined by arranging a pipe body. The pipe body is longitudinally arranged along the entire length of the wall of the first-stage trench section. When the grooving machine mills the concrete during the trench forming of the second-stage trench, the pipe body is milled and broken, and the position of the pipe body forms the groove. It is characterized in that, The pipe body is a combined square pipe, including a square steel pipe and a square polypropylene pipe, wherein one side of the square steel pipe is welded to the trough section steel cage in the first phase trough section wall, and the other side opening is butted against the opening side of the square polypropylene pipe, a grouting pipe is pre-buried along the length direction of the square steel pipe on the inner side of the pipe wall, and a rubber bag is pre-set along the length of the square steel pipe and the square polypropylene pipe; A T-shaped steel plate is fixedly connected to the groove section steel cage of the second phase groove section wall, and the T-shaped steel plate is inserted into the groove formed after the pipe body is broken; After the second phase trough section concrete has finally set, grouting is performed on the joint seams through the grouting pipe; The rubber sacs preset inside the square steel tube and the square polypropylene tube can expand after being inflated, and the cross-section of the rubber sacs after expansion is rectangular, and the size is consistent with the cross-section size of the square steel tube and the square polypropylene tube; The equivalent thickness d of the T-shaped steel plate satisfies the following formula: ， Among them, M is the design value of the bending moment in the joint area; d p is the cover thickness of the T-shaped steel plate, D is the thickness of the joint area, f cd is the design value of the axial compressive strength of concrete, the design value of the compressive strength of ordinary steel, x is the thickness of the compression zone in the joint area; is the correction coefficient for the resisting bending moment.

2. The rigid milling joint of the diaphragm wall for the enclosure of a large circular foundation pit as claimed in claim 1, wherein, The cross-sectional length of the combined square tube includes two specifications of 25 cm and 30 cm, wherein the width of the square steel tube is 10 cm, and the width of the square polypropylene tube includes two specifications of 15 cm and 20 cm, which are selected according to the trough section depth H and the trough section verticality control standard X. The specific selection method includes the following three cases: Case 1: When H*X+3cm≤7.5cm, the combined square tubes with cross-sectional lengths of 25cm and 30cm both meet the requirements; Case 2: When 7.5cm<H*X+3cm≤10cm, select a modular square tube with a cross-sectional length of 30cm; Case 3: When H*X+3cm>10cm, increase the verticality control standard of the slot section to 1 / 1000, and select a combined square tube with a cross-sectional length of 30cm.

3. The rigid milling joint of the diaphragm wall for the enclosure of a large circular foundation pit according to claim 1, characterized in that, Two grouting pipes are arranged in each square steel pipe, and are respectively located on the upper and lower sides of the inner wall of the square steel pipe.

4. The rigid milling joint of the diaphragm wall for the enclosure of a large circular foundation pit according to claim 2, wherein The calculation formula for the thickness x of the compression zone in the joint area is: ， Among them, f sd is the design value of the tensile strength of ordinary steel.

5. The large circular foundation pit retaining underground continuous wall rigid milling joint according to claim 2 is characterized in that: The compression zone thickness x of the joint area should also meet the structural configuration requirements, i.e.: , otherwise, the equivalent thickness d of the T-shaped steel plate per unit height in the joint area is calculated by the following formula: 。 6. The large circular foundation pit retaining underground continuous wall rigid milling joint according to claim 2 is characterized in that: The T-shaped steel plates are arranged intermittently. T-shaped Among them, is the height of a single T-shaped steel plate, and h is the vertical spacing distance; Among them, the height of a single T-shaped steel plate and the value of the vertical spacing distance h of the T-shaped steel plates are both related to the diaphragm wall groove section perpendicularity control standard X. According to the statistics of the on-site groove section implementation situation, the height of a single T-shaped steel plate , and the value of the vertical spacing distance h of the T-shaped steel plates include the following three types: The first type: When the verticality control standard of the groove section does not exceed 1 / 400, the height of a single T-shaped steel plate shall not be greater than 100 mm, and the vertical interval distance h of the T-shaped steel plates is greater than 10*H / 400, where H is the depth of the groove section; The second type: When the verticality control standard of the groove section exceeds 1 / 800, the height of a single T-shaped steel plate shall not be greater than 200 mm, and the vertical interval distance h of the T-shaped steel plates is greater than 3*H / 800; The third type: When the groove section verticality control standard X is between 1 / 400 and 1 / 800, the height of a single T-shaped steel plate and the vertical spacing distance h of the T-shaped steel plates are determined by the linear interpolation method.

7. The construction method of a rigid milling joint for a diaphragm wall for retaining a large circular foundation pit as described in any one of claims 1 to 6, characterized in that, The following steps are involved: S1. Use a troughing machine to carry out the first phase of troughing operation; S2, glue the grouting pipe to the inner side of the square steel pipe in the combined square pipe, glue the rubber bag to the inner side of the square steel pipe and the square polypropylene pipe, fix one side of the square steel pipe to the first-stage trough section steel cage by welding, and lower the first-stage trough section steel cage; S3. Use an air compressor to fill the rubber bags in the square steel pipe and the square polypropylene pipe with gas until the air pressure in the rubber bags is equal to the concrete bulk density*H, in KPa, and then stop filling. The concrete bulk density is 24KN / m³; H is the depth of the trench section. S4, pouring the first phase trough section concrete; S5, extracting the gas in the rubber bag in the square steel pipe and the square polypropylene pipe, and pulling the rubber bag out of the square steel pipe and the square polypropylene pipe, waiting for the next recycling; S6. Use a grooving machine to perform grooving operations on the second-phase groove section. The grooving machine grooves downward from the middle part of the square polypropylene tube, milling off a certain width of the concrete in the first-phase groove section in the joint area to form a concrete biting surface and breaking a part of the square polypropylene tube of the combined square tube to form the groove. S7. Use a square tube shape detector to detect the shape of the square steel tube, determine whether the square steel tube is intact, and fit the attitude of the square steel tube. S8. According to the attitude of the square steel tube, adjust the overlapping length between the T-shaped steel plate and the second-phase steel cage, weld the T-shaped steel plate on the second-phase steel cage, lower the second-phase steel cage along the groove formed after the combined square tube is broken, and insert the T-shaped steel plate into the groove. S9. Pour the concrete for the second-phase groove section. S10. After the concrete of the second-phase groove section has finally set, use a grouting pipe to grout the joint seam.

8. The construction method of the rigid milling joint of the diaphragm wall for the large circular foundation pit retaining wall according to claim 7, characterized in that, The square tube shape detector includes an inclinometer, a detection probe, and a steel wire rope. Among them, the inclinometer is vertically suspended in the detection probe through the steel wire rope, and the other end of the steel wire rope is fixed on a winch arranged on the ground, and the winch controls the recovery and lowering of the steel wire rope. The detection probe is a cubic steel bar framework with an outer contour consistent with the inner contour of the square steel tube, and the plane size of the outer contour of the detection probe is smaller than the plane size of the inner contour of the square steel tube.

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