A complex stratum underground continuous wall joint pre-grouting reinforcement construction method

Abstract

The present application belongs to the technical field of underground continuous wall construction, and discloses a complex stratum underground continuous wall joint pre-grouting reinforcement construction method, in order to solve the problems of long construction period, high cost and poor stratum adaptability of the existing underground continuous wall joint anti-seepage treatment method. The present application comprises positioning and setting out of guide walls, joints and grouting holes according to the survey report and design drawings; the grouting holes comprise first grouting holes, at least one group of second grouting holes and at least one group of third grouting holes, and then the first grouting holes, the second grouting holes and the third grouting holes are grouted and reinforced by using sectional grouting. The present application has the advantages of adapting to local conditions and flexible adjustment, and is suitable for super-deep underground continuous wall construction under various stratum conditions. The present application makes full use of the advantages of sleeve valve pipe grouting, and the grouting amount is accurately controllable, which can significantly improve the engineering benefit.

Description

Technical Field

[0001] This invention belongs to the field of diaphragm wall construction technology, specifically relating to a method for pre-grouting reinforcement of diaphragm wall joints in complex strata. Background Technology

[0002] Diaphragm walls are a type of retaining and waterproofing structure used for ultra-deep foundation pits (depth > 10m). They offer advantages such as good structural continuity, excellent impermeability, and high overall rigidity. Especially in deep foundation pit projects in coastal areas, where high water levels make dewatering difficult, diaphragm walls are frequently used for support. Furthermore, diaphragm wall construction results in low vibration and noise, and high space utilization, making them ideal for urban construction. As urban underground space is increasingly developed and utilized, the excavation depth of foundation pit projects is growing. As one of the commonly used retaining structures for foundation pits, diaphragm walls traverse increasingly complex and variable geological formations, leading to greater difficulty in controlling joint quality during construction and making seepage problems particularly prominent.

[0003] Regarding the issue of water seepage at the joints of diaphragm walls, existing technologies also include methods for preventing seepage at these joints. For example, application number 201310676753X discloses a waterproof structure and construction method for diaphragm wall joints, comprising a first diaphragm wall and a second diaphragm wall that intersect each other. A straight, bent section is provided at the end where the second diaphragm wall connects to the first diaphragm wall. This bent section extends outwards from the pit and is close to the first diaphragm wall. A single row of three-axis mixing piles extending continuously along the length of the second diaphragm wall is provided on the wall facing inwards from the pit. A group of three-axis mixing piles consisting of multiple rows of parallel three-axis mixing piles extending continuously along the length of the second diaphragm wall is provided on the wall facing outwards from the pit. Multiple high-pressure jet grouting piles are installed at the joint between the end of the bent section of the second diaphragm wall and the first diaphragm wall for sealing.

[0004] For example, patent application number 2019209006779 discloses a seepage prevention structure at the joint of a continuous wall, including multiple steel sheet piles and jet grouting piles; the steel sheet piles are inserted in a row and overlap each other outside the seepage point, forming an area sufficient to cover the seepage point; the jet grouting piles are installed in the gap between the steel sheet piles at both ends and the continuous wall, and the gaps between the steel sheet piles at other positions and the continuous wall are reinforced by grouting.

[0005] For example, patent application number 2020201216470 discloses a new and old diaphragm wall interface treatment structure: including an extended section of diaphragm wall, a new diaphragm wall, and an old diaphragm wall; one end of the extended section of diaphragm wall is connected to the new diaphragm wall, and the other end is in contact with the old diaphragm wall, with multiple grouting pipes installed at the contact point between the extended section of diaphragm wall and the old diaphragm wall; by grouting through the grouting pipes, the gap between the new diaphragm wall and the old diaphragm wall is filled, as is the gap between the extended section of diaphragm wall and the old diaphragm wall. The new diaphragm wall includes a first-phase trench section and a second-phase trench section, with a joint sealing device between the first-phase trench section and the second-phase trench section; the extended section of diaphragm wall is connected to the first-phase trench section.

[0006] As exemplified above, the existing technologies currently available for addressing the water seepage problem at the joints of underground continuous walls include: (1) constructing high-pressure jet grouting piles outside the trench wall on the soil-facing side; (2) high-pressure grouting outside the trench wall on the soil-facing side; and (3) grouting behind the perforated wall after excavation.

[0007] However, for the high-pressure jet grouting piles mentioned above, the seepage prevention effect is the best because the jet grouting body forms a tight envelope around the joint, and the grouting pressure is generally large, ensuring the diffusion radius of the grout. However, the construction cost is high, the site space requirement is large, and the adaptability to the strata is poor.

[0008] For high-pressure grouting, its seepage prevention effect is not as good as the first method due to the limitation of grouting pressure. In ultra-deep excavation, it is easy to cause waste because grouting cannot be done in sections.

[0009] Grouting after excavation and perforation is essentially a remedial measure, and the timeliness of the grout is difficult to guarantee. There is a high possibility of leakage recurring during later construction of the main structure. Furthermore, addressing water seepage after excavation will affect other procedures, and in cases of severe seepage, work may even be halted due to safety concerns. Summary of the Invention

[0010] In order to solve the above-mentioned technical problems, this invention provides a pre-grouting reinforcement construction method for diaphragm wall joints in complex strata, which takes into account both seepage prevention effect and economic benefits. It can be applied to seepage prevention treatment at the joints of diaphragm walls in complex strata, and has the advantages of being adaptable to local conditions and flexible in the specific construction process. It is suitable for ultra-deep diaphragm wall construction under various strata conditions.

[0011] To solve the technical problem, the technical solution adopted by this invention is as follows:

[0012] A method for pre-grouting reinforcement of joints in underground continuous walls in complex strata, characterized by comprising:

[0013] S1: Determine the highly permeable layer that needs grouting reinforcement and the grouting range based on the survey report and design drawings;

[0014] S2: Based on the coordinate reference points provided by the owner, locate and lay out the guide wall, joints, and grouting holes according to the survey report and design drawings. The grouting holes include a first grouting hole, at least one set of second grouting holes, and at least one set of third grouting holes. The first grouting hole includes back-soil side grouting holes and front-soil side grouting holes. The back-soil side grouting holes are located on the outer side of the back-soil side trench wall of the diaphragm wall, and the front-soil side grouting holes, second grouting holes, and third grouting holes are located on the outer side of the front-soil side trench wall of the diaphragm wall. The back-soil side grouting holes are evenly distributed along the length of the back-soil side trench wall of the diaphragm wall and cover the entire back-soil side trench wall. Each set of third grouting holes consists of 3 holes, and the 3 third grouting holes are in a triangular shape. Two of the third grouting holes correspond to the left and right ends of the I-beam joint of the diaphragm wall, while the other third grouting hole corresponds to the center of the I-beam joint. The third grouting hole corresponding to the center of the I-beam joint is further away from the soil-facing side wall than the two third grouting holes corresponding to the left and right ends of the I-beam joint. Each group of second grouting holes includes two second grouting holes, which are distributed outside the group of third grouting holes (that is, the three third grouting holes are distributed in the soil and rock mass between the two second grouting holes). The soil-facing side grouting holes are evenly distributed on the soil-facing side wall of the diaphragm wall, except for the positions occupied by the second and third grouting holes.

[0015] In the specific implementation process, the distance between each back-soil side grouting hole and the back-soil side trench wall is the same, meaning that the back-soil side grouting holes are arranged side-by-side along the back-soil side trench wall. Similarly, the distance between the soil-facing side grouting hole, the second grouting hole, and the third grouting hole corresponding to the central position of the I-beam joint and the soil-facing side trench wall is the same, meaning that the soil-facing side grouting hole, the second grouting hole, and the third grouting hole corresponding to the central position of the I-beam joint are arranged side-by-side along the soil-facing side trench wall.

[0016] S3: A pilot hole is drilled according to the drilling location, and the drilling depth is determined based on the grouting depth. The first grouting hole is drilled to a depth 0.5m below the bottom of the filler rock layer; the second grouting hole is drilled to a depth 0.5m below the bottom of the middle sand layer; and the third grouting hole is drilled to a depth 0.5m below the bottom of the strongly weathered bedrock. In other words, the first grouting hole must penetrate the bottom of the filler rock layer and be drilled down 0.5m; the second grouting hole must penetrate the bottom of the middle sand layer and be drilled down 0.5m; and the third grouting hole must penetrate the bottom of the strongly weathered bedrock and be drilled down 0.5m.

[0017] S4: After drilling, the prepared casing material is pressed into the bottom of the borehole using a drill rod through an extrusion grouting machine;

[0018] S5: After the casing material is replaced, immediately insert the prepared sleeve valve tubes in sequence;

[0019] S6: Deploy mobile grouting stations and pumping stations;

[0020] S7: Prepare the grouting slurry according to the type of stratum to be reinforced;

[0021] S8: After connecting the grouting pipe, conduct a water pressure test;

[0022] S9: The retreating segmented grouting process begins by using sleeve valves to reinforce the drilled grouting holes in segments. That is, grouting is carried out in segments from the bottom of the hole upwards within each grouting hole.

[0023] In some embodiments, when drilling a pilot hole in step S3, a third grouting hole should be drilled first, then a second grouting hole should be drilled, and finally a first grouting hole should be drilled.

[0024] In some embodiments, the drilling of the first grouting hole should employ a skip-drilling method. Specifically, a "skip-drill-one" skip-drilling method is used. That is, the first grouting holes (the grouting hole on the soil-facing side and the grouting hole on the soil-reverse side) are both formed by drilling one hole and skipping one hole. Those skilled in the art will understand and appreciate the skip-drilling method.

[0025] In some embodiments, when performing segmented grouting reinforcement using the sleeve valve pipe in step S9, the first grouting hole should be filled completely; the second grouting hole should be grouted for a distance of more than 0.5m below the bottom of the filler stone layer, and grouting should be performed within a range from 0.5m above the top of the middle sand layer to 0.5m below the bottom of the middle sand layer, while the remaining section in the second grouting hole should not be grouted; the third grouting hole should be grouted for a distance of more than 0.5m below the bottom of the filler stone layer, grouting should be performed within a range from 0.5m above the top of the middle sand layer to 0.5m below the bottom of the middle sand layer, and grouting should be performed within a range from 0.5m above the top of the strongly weathered bedrock to 0.5m below the bottom of the strongly weathered bedrock, while the remaining section in the third grouting hole should not be grouted.

[0026] In some embodiments, after the positions of the guide wall and joints in step S2 are determined, permanent and temporary markings should be made before the positioning and layout of each grouting hole position are carried out.

[0027] In some embodiments, when performing segmented grouting in step S9, the length of each grouting segment is 0.3-0.4m. After completing one segment of grouting, the grouting core tube of the sleeve valve pipe is lifted upwards to perform the next segment of grouting.

[0028] In some embodiments, when processing the steel cage of the underground continuous wall, a wall toe grouting pipe is arranged at each of the left and right ends of the steel cage.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention relates to a pre-grouting reinforcement method for diaphragm wall joints in complex geological formations, utilizing sleeve valve pipe grouting technology for seepage prevention and reinforcement of diaphragm wall joints. Compared to high-pressure jet grouting piles, it offers better geological adaptability and lower costs; compared to ordinary steel pipe grouting, it allows for segmented and repeated grouting. Compared to high-pressure grouting, it enables segmented grouting, allowing for flexible application based on geological conditions, achieving both waterproofing and economic benefits for the diaphragm wall.

[0031] The design of the sleeve valve tube cutting length and grouting volume of this invention can be estimated based on the geological profile of the continuous wall structure in the geotechnical engineering investigation report and design documents, which is more targeted and economically efficient.

[0032] This invention proposes a novel arrangement for the first, second, and third grouting holes, employing a combination of long and short holes with appropriate densification. This arrangement is unique in the field of diaphragm wall construction. While ensuring waterproofing, it minimizes the amount of grouting and the construction period, maximizing both safety and economy. Furthermore, the segmented reinforcement of the first, second, and third grouting holes can also serve as reinforcement for the trench walls. In subsequent construction, this reduces or eliminates the need for further reinforcement of the trench walls (the back side and the front side), further shortening the overall construction period and reducing costs.

[0033] If the joint position is misaligned with the grouting hole due to construction reasons in the later stages of this invention, measures such as additional drilling and extension can be taken to adjust it.

[0034] The pre-grouting reinforcement method proposed in this invention has the advantages of adaptability and flexibility, making it suitable for ultra-deep diaphragm wall construction under various geological conditions. Furthermore, this method fully utilizes the advantages of sleeve valve grouting, ensuring precise control of the grouting volume and significantly improving project efficiency. Attached Figure Description

[0035] Figure 1 This is a flowchart of an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the planar arrangement of the first grouting hole, the second grouting hole, and the third grouting hole of the present invention;

[0037] Figure 3 This is a schematic cross-sectional view of the diaphragm wall after grouting reinforcement at the center of the I-beam joint; where... Figure 3The diagram on the left shows a cross-sectional view of the first grouting hole on the backfill side trench wall. Figure 3 The diagram on the right shows a cross-sectional view of the third grouting hole on the soil-facing side of the trench. After grouting and reinforcement of the first grouting hole, a grouting body 11 is formed by filling with rubble. After grouting and reinforcement of the middle sand layer in the second and third grouting holes, a middle sand layer grouting body 12 is formed. After grouting and reinforcement of the strongly weathered bedrock in the second and third grouting holes, a weathered bedrock grouting body 13 is formed.

[0038] Markings in the diagram: 1. First grouting hole; 2. Second grouting hole; 3. Third grouting hole; 4. Toe grouting hole; 5. I-beam joint; 6. Back soil side trench wall; 7. Reinforcing cage; 8. Front soil side trench wall; 9. Sealing bar; 10. Pouring guide pipe; 11. Grouting body for the fill stone layer; 12. Grouting body for the middle sand layer; 13. Grouting body for the weathered bedrock; 14. Sleeve; 15. Sleeve valve pipe. Detailed Implementation

[0039] The present invention will be further described below with reference to embodiments. These embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the protection scope of the present invention.

[0040] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description; they do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "joined" should be interpreted broadly, for example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0041] Combined with appendix Figure 1 To be continued Figure 3 The present invention provides a method for pre-grouting reinforcement of joints in complex strata underground continuous wall construction, comprising:

[0042] S1: Based on the survey report and design drawings, determine the highly permeable layers requiring grouting reinforcement and the grouting area. The survey report should list the permeability coefficients of each soil layer to facilitate the later determination of the reinforcement area for segmented grouting. The design drawings should describe the segmentation of the continuous wall, specifying the trench number and width for later verification and layout.

[0043] S2: Based on the coordinate reference points provided by the owner, the positioning and layout of the guide wall, joints, and grouting holes are carried out according to the survey report and design drawings. The grouting holes include a first grouting hole 1, at least one set of second grouting holes 2, and at least one set of third grouting holes 3. The first grouting hole 1 includes back-soil side grouting holes and front-soil side grouting holes. The back-soil side grouting holes are located on the outer side of the back-soil side trench wall of the diaphragm wall. The front-soil side grouting holes, second grouting holes 2, and third grouting holes 3 are located on the outer side of the front-soil side trench wall 8 of the diaphragm wall. The back-soil side grouting holes are evenly arranged along the length of the back-soil side trench wall 6 of the diaphragm wall and cover the entire back-soil side trench wall 6. Each set of third grouting holes consists of 3 holes, and the 3 third grouting holes are in a triangular shape. Two third grouting holes 3 correspond to the left and right ends of the I-beam joint 5 of the diaphragm wall, and another third grouting hole 3 corresponds to the center of the I-beam joint 5. The position of the third grouting hole 3 corresponding to the center of the I-beam joint 5 is further away from the soil-facing side wall 8 than the two third grouting holes corresponding to the left and right ends of the I-beam joint 5. Each group of second grouting holes includes two second grouting holes, which are distributed on the outside of a group of third grouting holes (that is, three third grouting holes are distributed in the rock and soil mass between the two second grouting holes). The soil-facing side grouting holes are evenly distributed on the soil-facing side wall 8 of the diaphragm wall, except for the positions occupied by the second grouting holes 2 and the third grouting holes 3.

[0044] In the specific implementation process, the distance between each back-soil side grouting hole arranged on the outer side of the back-soil side trench wall 6 of the diaphragm wall and the back-soil side trench wall is the same, that is to say, the back-soil side grouting holes are arranged side by side along the back-soil side trench wall. The distance between the soil-facing side grouting hole, the second grouting hole, and the third grouting hole corresponding to the central position of the I-beam joint and the soil-facing side trench wall is the same, that is to say, the distance between each soil-facing side grouting hole, the second grouting hole, and the third grouting hole corresponding to the central position of the I-beam joint is the same, that is to say, the distance between each soil-facing side grouting hole, the second grouting hole, and the third grouting hole corresponding to the central position of the I-beam joint is the same, along the soil-facing side trench wall.

[0045] The first grouting hole is a grouting reinforcement hole for the fill stone layer. Since the fill stone layer is generally loose and uneven, the pores between it are easy to form water seepage channels, and the difference in density can also form water-stagnant zones. Therefore, the permeability coefficient and water content are generally large, and grouting reinforcement is necessary.

[0046] The second grouting hole is for the middle sand layer. Sand layers generally have complex pore structures and relatively uniform pore sizes. When the site is located in a coastal area or near a river or lake, it has a large permeability coefficient and must be reinforced by grouting.

[0047] The third grouting hole is for strongly weathered bedrock. Strongly weathered bedrock generally has a broken rock mass structure and well-developed weathering fissures. Strongly weathered bedrock below the groundwater level often contains bedrock fissure water and generally has a large permeability coefficient. Therefore, it is still necessary to reinforce strongly weathered bedrock with grouting.

[0048] S3: A pilot hole is drilled according to the drilling location, and the drilling depth is determined based on the grouting depth. The first grouting hole is drilled to a depth 0.5m below the bottom of the filler rock layer; the second grouting hole is drilled to a depth 0.5m below the bottom of the middle sand layer; and the third grouting hole is drilled to a depth 0.5m below the bottom of the strongly weathered bedrock. In other words, the first grouting hole must penetrate the bottom of the filler rock layer and be drilled down 0.5m; the second grouting hole must penetrate the bottom of the middle sand layer and be drilled down 0.5m; and the third grouting hole must penetrate the bottom of the strongly weathered bedrock and be drilled down 0.5m.

[0049] S4: After drilling, the prepared casing material is pressed into the bottom of the borehole using a squeeze grouting machine and a drill rod; in the specific implementation process, the casing material is made of cement, bentonite and water.

[0050] The mass ratio of the three materials in the casing material is: cement: bentonite: water = 1:1.5:2, and the viscosity of the prepared casing material is 27s.

[0051] S5: After the casing material is replaced, immediately insert the prepared sleeve valve tubes in sequence.

[0052] S6: Deploy mobile grouting stations and pumping stations.

[0053] S7: Prepare the grout according to the type of stratum to be reinforced. The specific grout ratio should be adjusted according to the actual site conditions and recorded to ensure the quality of subsequent diaphragm wall construction; water glass must be diluted before use. Ordinary Portland cement with a strength grade of 42.5 and diluted water glass are used as the main preparation materials, with a water-cement ratio of 0.8:1-1:1, a cement grout to water glass grout volume ratio of 0.6-1, a water glass modulus of 2.6-3.0, and a water glass concentration of 30-40 Be°, gradually increasing the grout concentration.

[0054] S8: After connecting the grouting pipe, conduct a water pressure test; use the grouting pump at 1.5-2 times the grouting pressure to check whether the grouting pipe is leaking and to determine whether the equipment is in normal condition.

[0055] S9: The retreating segmented grouting process begins by using sleeve valves to reinforce the drilled grouting holes in segments. That is, grouting is carried out in segments from the bottom of the hole upwards within each grouting hole.

[0056] In the specific implementation process, sleeve valve pipes and grouting systems can be directly procured as needed. The sleeve valve pipes are used for backward grouting to achieve a three-stage reinforcement system consisting of a rock fill layer, a sand layer, and a strongly weathered bedrock. For example, 4m standard PVC sleeve valve pipe segments with a diameter of 48mm can be procured and assembled and lowered on-site as needed.

[0057] In the specific implementation process, the opening of the sleeve valve pipe 15 is tightly fitted with a rubber sleeve and the grouting hole is covered; the bottom end of the sleeve valve pipe is tightly wrapped with geotextile or other materials to prevent the casing material from entering the sleeve valve pipe. Each section of the sleeve valve pipe 15 is connected to each other through the sleeve 14, and the connection between the sleeve 14 and the sleeve valve pipe 15 is bonded firmly to the sleeve valve pipe and the connecting sleeve with U-PVC adhesive.

[0058] When lowering the sleeve valve tube, its verticality should be ensured, with a deviation of no more than 0.3%, and the upper part of the sleeve valve tube should be above the ground.

[0059] The pre-grouting reinforcement method proposed in this invention has the advantages of adaptability and flexibility, making it suitable for ultra-deep diaphragm wall construction under various geological conditions. Furthermore, this method fully utilizes the advantages of sleeve valve grouting, ensuring precise control of the grouting volume and significantly improving project efficiency.

[0060] In some embodiments, when drilling a pilot hole in step S3, a third grouting hole should be drilled first, then a second grouting hole should be drilled, and finally a first grouting hole should be drilled.

[0061] In some embodiments, the drilling of the first grouting hole should employ a skip-drilling method. Specifically, a "skip-drill-one" skip-drilling method is used. That is, the first grouting holes (the grouting hole on the soil-facing side and the grouting hole on the soil-reverse side) are both formed by drilling one hole and skipping one hole. Those skilled in the art will understand and appreciate the skip-drilling method.

[0062] In some embodiments, when performing segmented grouting reinforcement using the sleeve valve pipe in step S9, the first grouting hole should be filled completely; the second grouting hole should be grouted for a distance of more than 0.5m below the bottom of the filler stone layer, and grouting should be performed within a range from 0.5m above the top of the middle sand layer to 0.5m below the bottom of the middle sand layer, while the remaining section in the second grouting hole should not be grouted; the third grouting hole should be grouted for a distance of more than 0.5m below the bottom of the filler stone layer, grouting should be performed within a range from 0.5m above the top of the middle sand layer to 0.5m below the bottom of the middle sand layer, and grouting should be performed within a range from 0.5m above the top of the strongly weathered bedrock to 0.5m below the bottom of the strongly weathered bedrock, while the remaining section in the third grouting hole should not be grouted.

[0063] In some embodiments, after the positions of the guide wall and joints in step S2 are determined, permanent and temporary markings should be made before the positioning and layout of each grouting hole position are carried out.

[0064] In some embodiments, when performing segmented grouting in step S9, the length of each grouting segment is 0.3-0.4m. After completing one segment of grouting, the grouting core tube of the sleeve valve pipe is lifted upwards to perform the next segment of grouting.

[0065] When using a sleeve valve pipe for grouting, the grouting can be stopped when the grouting pressure reaches the design final pressure and the duration is not less than 2 minutes. After the sleeve valve pipe grouting is finished, the sleeve valve pipe should be cleaned with clean water in preparation for secondary grouting.

[0066] As a preferred embodiment in this case, to further ensure the quality of joint construction, two wall toe grouting pipes 4 should be arranged when processing the continuous wall reinforcement cage 7; the wall toe grouting pipes 4 should be tied away from the concrete pouring guide pipe 10; wall toe grouting should be carried out after the concrete strength reaches 80%. The underground continuous wall is equipped with a reinforcement cage 7, and the reinforcement cage 7 is equipped with sealing bars 9, which will be understood by those skilled in the art and will not be elaborated further here.

[0067] This invention relates to a pre-grouting reinforcement method for diaphragm wall joints in complex geological formations, utilizing sleeve valve pipe grouting technology for seepage prevention and reinforcement of diaphragm wall joints. Compared to high-pressure jet grouting piles, it offers better geological adaptability and lower costs; compared to ordinary steel pipe grouting, it allows for segmented and repeated grouting. Compared to high-pressure grouting, it enables segmented grouting, allowing for flexible application based on geological conditions, achieving both waterproofing and economic benefits for the diaphragm wall.

[0068] The design of the sleeve valve tube cutting length and grouting volume of this invention can be estimated based on the geological profile of the continuous wall structure in the geotechnical engineering investigation report and design documents, which is more targeted and economically efficient.

[0069] This invention proposes a novel arrangement for the first, second, and third grouting holes, employing a combination of long and short holes with appropriate densification. This arrangement is unique in the field of diaphragm wall construction. While ensuring waterproofing, it minimizes the amount of grouting and the construction period, maximizing both safety and economy. Furthermore, the segmented reinforcement of the first, second, and third grouting holes can also serve as reinforcement for the trench walls. In subsequent construction, this reduces or eliminates the need for further reinforcement of the trench walls (the back side and the front side), further shortening the overall construction period and reducing costs.

[0070] If the joint position is misaligned with the grouting hole due to construction reasons in the later stages of this invention, measures such as additional drilling and extension can be taken to adjust it.

[0071] As a preferred implementation method in this case, the construction of the foundation pit support for a subway station in Shenzhen is taken as an example. According to the geotechnical investigation report and design documents, taking the III-9 diaphragm wall as an example, the strata traversed by the diaphragm wall construction are mainly three-phase strata in a typical coastal area, consisting of artificial fill, marine sediments, and lower granite.

[0072] Furthermore, based on the criteria for determining highly permeable layers, namely, a permeability coefficient greater than 1m / d, the highly permeable layers that the continuous wall construction traverses are determined to be, in order, the filler stone layer, the middle sand layer, and the highly weathered granite layer (i.e., the highly weathered bedrock layer).

[0073] Furthermore, the depth and extent of segmented reinforcement for the fill stone layer, sand layer, and blocky strongly weathered granite layer were determined, and the top and bottom elevations of each layer were extended outward by 0.5m for reinforcement.

[0074] The top elevation of the reinforced area = the top elevation of the stratum + 0.5m, and the depth is the top elevation of the guide wall - the top elevation of the stratum - 0.5m;

[0075] The bottom elevation of the reinforced stratum is equal to the bottom elevation of the stratum - 0.5m, and the depth is equal to the top elevation of the guide wall - the bottom elevation of the stratum + 0.5m.

[0076] The reinforcement range for the fill stone layer is 4.8-9.8m; the reinforcement range for the middle sand layer is -13.1-21.2m; and the reinforcement range for the strongly weathered granite layer is -42.5-50.6m.

[0077] Furthermore, based on the design documents and survey report, determine the positions of the soil-facing trench wall 8, the soil-repellent trench wall 6, the I-beam joint 5, the first grouting hole 1, the second grouting hole 2, and the third grouting hole 3; and mark them with conspicuous red markers according to the layout results.

[0078] Furthermore, the cutting length of the sleeve valve pipe is determined according to the grouting range; the cutting length of the first grouting hole 1 is 16m, using 4 standard sections; the cutting length of the second grouting hole 2 is 28m; and the cutting length of the third grouting hole 3 is 56m.

[0079] Furthermore, a drilling rig is used for pilot drilling; the drilling rig model selected is XY-100, and the drilling sequence should be type 3 → type 2 → type 1, expanding the hole from the center position of the I-beam joint 5 to both sides; when drilling the first grouting hole 1, the principle of "skipping 1 and drilling 1" should be followed.

[0080] Furthermore, the casing material is prepared according to the ratio of cement: bentonite: water = 1:1.5:2, with a viscosity of 27s. After drilling, the prepared casing material is pressed into the bottom of the drilled holes (i.e., into the first grouting hole 1, the second grouting hole 2, and the third grouting hole 3) using a squeeze grouting machine with a drill rod. The pressing order is the same as the drilling order.

[0081] Furthermore, immediately after the casing material is replaced, sleeve valve pipes are sequentially inserted into boreholes 1, 2 and 3 (i.e., first grouting hole 1, second grouting hole 2 and third grouting hole 3), with the pipe insertion sequence being the same as the drilling sequence.

[0082] Then, mobile grouting stations and pumping stations are deployed.

[0083] Furthermore, when preparing the grout, the water glass must be diluted before use. The main materials are ordinary Portland cement with a strength grade of 42.5 and diluted water glass. The water-cement ratio is 0.8:1-1:1, the volume ratio of cement grout to water glass grout is preferably 0.6-1, the water glass modulus is 2.6-3.0, and the water glass concentration is preferably 30-40 Be°. The grout concentration should be increased from thin to thick.

[0084] Furthermore, after connecting the grouting pipe, use a grouting pump at 1.5-2 times the grouting pressure to check whether the grouting pipe is leaking and to determine whether the equipment is in normal condition.

[0085] Further, the backward segmented grouting process is initiated, with grouting proceeding from bottom to top in grouting holes 1, 2, and 3 (i.e., first grouting hole 1, second grouting hole 2, and third grouting hole 3), with each lifting distance being 0.3-0.4m; the grouting sequence is the same as the drilling sequence, and the grouting pressure is 0.2-1.5MPa; when the grouting pressure reaches the designed final pressure and the duration is not less than 2 minutes, the grouting can be terminated; after the sleeve valve pipe grouting is completed, the sleeve valve pipe is cleaned with clean water in preparation for secondary grouting.

[0086] As a preferred embodiment in this case, the grouting holes 1, 2 and 3 are covered by a tight rubber sleeve outside the opening; the bottom and head of the sleeve valve pipe 15 are tightly wrapped with geotextile or other materials to prevent the casing material from entering the sleeve valve pipe; a 20cm long sleeve pipe 14 is used to connect adjacent sleeve valve pipes, and U-PVC adhesive is used to firmly bond the sleeve valve pipe 15 and the connecting sleeve pipe 14.

[0087] As the preferred implementation method in this case, the verticality of the grouting holes 1, 2, and 3 should be ensured, and the deviation should not exceed 0.3%; the sleeve valve pipe 15 should be lowered to the bottom of the hole, and the upper part should be 20cm above the ground.

[0088] As a preferred embodiment in this case, the sleeve valve pipe 15 is sealed at the pipe opening after it is lowered to prevent debris from entering the grouting pipe and affecting the grouting quality.

[0089] As a preferred embodiment in this case, the first sleeve valve tube 15 is fitted with a plug, and then clean water is injected into the tube to prevent the sleeve valve tube 15 from bending too much.

[0090] As a preferred implementation method in this case, after the grouting pipe is installed, quick-setting cement mortar is used to fill the area 3-5m below the ground surface and at the orifice to prevent grout return during grouting.

Claims

1. A method for pre-grouting reinforcement of joints in underground continuous wall systems in complex strata, characterized in that, include: S1: Determine the highly permeable layer that needs grouting reinforcement and the grouting range based on the survey report and design drawings; S2: Based on the coordinate reference points provided by the owner, locate and lay out the guide wall, joints, and grouting holes according to the survey report and design drawings; the grouting holes include a first grouting hole, at least one set of second grouting holes, and at least one set of third grouting holes, wherein the first grouting hole includes back-soil side grouting holes and front-soil side grouting holes, the back-soil side grouting holes are located on the outer side of the back-soil side trench wall of the diaphragm wall, and the front-soil side grouting holes, second grouting holes, and third grouting holes are located on the outer side of the front-soil side trench wall of the diaphragm wall; the back-soil side grouting holes are evenly arranged along the length of the back-soil side trench wall of the diaphragm wall and... The entire backfill sidewall is covered; each group of third grouting holes consists of 3 holes, which are triangular in shape. Two of the third grouting holes correspond to the left and right ends of the I-beam joint of the diaphragm wall, while the other third grouting hole corresponds to the center of the I-beam joint. The third grouting hole corresponding to the center of the I-beam joint is further away from the frontfill sidewall than the two third grouting holes corresponding to the left and right ends of the I-beam joint. Each group of second grouting holes includes 2 second grouting holes, which are distributed on the outside of the group of third grouting holes. S3: Drilling rigs are used to drill pilot holes according to the drilling location, and the drilling depth is determined according to the grouting depth; the first grouting hole is drilled to a depth 0.5m below the bottom of the filler stone layer, the second grouting hole is drilled to a depth 0.5m below the bottom of the middle sand layer, and the third grouting hole is drilled to a depth 0.5m below the bottom of the strongly weathered bedrock; S4: After drilling, the prepared casing material is pressed into the bottom of the borehole using a drill rod through an extrusion grouting machine; S5: After the casing material is replaced, immediately insert the prepared sleeve valve tubes in sequence; S6: Deploy mobile grouting stations and pumping stations; S7: Prepare the grouting slurry according to the type of stratum to be reinforced; S8: After connecting the grouting pipe, conduct a water pressure test; S9: The retreating segmented grouting process is initiated by using sleeve valve pipes to reinforce the drilled grouting holes in segments. During segmented grouting reinforcement with sleeve valve pipes, the first grouting hole should be completely filled. For the second grouting hole, grouting should be carried out from 0.5m below the bottom of the filler layer, and from 0.5m above the top of the middle sand layer to 0.5m below the bottom of the middle sand layer. The remaining sections in the second grouting hole should not be grouted. For the third grouting hole, grouting should be carried out from 0.5m below the bottom of the filler layer, from 0.5m above the top of the middle sand layer to 0.5m below the bottom of the middle sand layer, and from 0.5m above the top of the strongly weathered bedrock to 0.5m below the bottom of the strongly weathered bedrock. The remaining sections in the third grouting hole should not be grouted.

2. The method for pre-grouting reinforcement of joints in underground continuous walls in complex strata according to claim 1, characterized in that, In step S3, when drilling to form a grouting hole, the third grouting hole should be drilled first, then the second grouting hole should be drilled, and finally the first grouting hole should be drilled.

3. The method for pre-grouting reinforcement of joints in underground continuous walls in complex strata according to claim 2, characterized in that, The distances between the back soil side grouting holes and the back soil side trench wall of the diaphragm wall are the same; the distances between the soil-facing side grouting holes, the second grouting hole, and the third grouting hole corresponding to the central position of the I-beam joint and the soil-facing side trench wall are the same.

4. The method for pre-grouting reinforcement of joints in underground continuous walls in complex strata according to claim 3, characterized in that, In step S3, when drilling the first grouting hole in the grouting hole, the drilling method should be used to form the hole.

5. The method for pre-grouting reinforcement of joints in complex strata underground continuous wall construction according to claim 1, characterized in that, After the positions of the guide wall and joints in step S2 are determined, permanent and temporary markings should be made before positioning and laying out the positions of each grouting hole.

6. The construction method for pre-grouting reinforcement of joints in complex strata diaphragm walls according to any one of claims 1-5, characterized in that, When performing segmented grouting in step S9, each grouting segment is 0.3-0.4m long. After completing one segment of grouting, the grouting core pipe of the sleeve valve pipe is lifted upward to perform the next segment of grouting.

7. The method for pre-grouting reinforcement of joints in underground continuous walls in complex strata according to claim 1, characterized in that, When processing the steel reinforcement cage of the underground continuous wall, a wall toe grouting pipe is arranged at each of the left and right ends of the steel reinforcement cage.

Images