A water-stopping enclosure system for a deep foundation pit near a river and a construction method thereof

Abstract

This invention discloses a water-stopping and retaining system for deep foundation pits near rivers and its construction method, belonging to the field of building construction technology. It includes water-stopping retaining piles, engineering piles, a capping beam, anchor cables, counterweight soil, a bracing structure, a basement structure, and a replacement support plate. The water-stopping retaining piles are formed by interlocking and bonding of mixing piles, cast-in-place piles, and high-pressure jet grouting piles. The mixing piles are arranged on the side closest to the river, and the high-pressure jet grouting piles fill the gaps between the mixing piles and the cast-in-place piles. The bottom of the entire water-stopping retaining pile extends below the impermeable or weakly permeable layer of the site. The bracing structure includes bracing columns and bracing conversion piles. The bracing conversion piles are set on the basement floor slab poured above the engineering piles. The upper end of the bracing column is detachably connected to the capping beam, and the lower end is connected to the bracing conversion pile. The bracing column does not penetrate downwards into the basement floor slab. This technical solution improves the construction effect of deep foundation pits near rivers and reduces construction costs.

Description

Technical Field

[0001] This invention belongs to the field of building construction technology, specifically relating to a water-stopping and retaining system for deep foundation pits near rivers and its construction method. Background Technology

[0002] There are multiple construction restrictions for deep foundation pits near rivers and canals: First, it is forbidden to extend anchor cables and support components within the protection red line of the river and canal, and conventional external anchor cable support schemes cannot be implemented; Second, surface water, shallow groundwater, and deep confined water continuously replenish the foundation pit laterally, and the risks of sidewall sand inrush, water seepage, and piping are much higher than those of ordinary inland foundation pits; Third, the site is generally covered with highly compressible silty soft soil, and one-time full-section excavation is very likely to cause large deformation of the retaining wall, threatening the safety of the river embankment and surrounding buildings and structures.

[0003] Existing mainstream support solutions have inherent flaws: 1. Independent lattice support system: requires a large number of separate support piles, the support is prone to conflict with the main beams and columns, and the support penetrates the bottom slab to form a permanent weak area for waterproofing. In soft soil conditions, the support has a large slenderness ratio and insufficient limiting stiffness. 2. Cast-in-place concrete internal support: The formwork has a long curing period, and its removal generates a large amount of construction waste that cannot be reused. Large-area foundation pits are also very expensive. 3. Reverse construction method: The process is complicated and complex, the underground working space is narrow, waterproofing and joint treatment are difficult, and the equipment and management costs are high.

[0004] Existing technologies cannot simultaneously address multiple requirements such as seepage prevention, compliance with red line regulations, elimination of bottom slab leakage, soft soil deformation control, and cost reduction. Therefore, this application proposes a water-stopping and retaining system for deep foundation pits near rivers and its construction method. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a water-stopping and retaining system for deep foundation pits along rivers and its construction method, so as to solve the problems of poor seepage prevention, need for independent pile foundations for support, leakage through the bottom slab, support exceeding the red line, difficulty in controlling soft soil deformation, and high construction period and cost of existing foundation pits along rivers.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A water-stopping and retaining system for deep foundation pits near rivers includes water-stopping retaining piles, engineering piles, capping beams, anchor cables, counterweight soil, inclined bracing structures, basement structures, and replacement slabs. The water-stopping retaining piles are formed by interlocking and bonding of mixing piles, cast-in-place piles, and high-pressure jet grouting piles. The mixing piles are positioned near the river, and the high-pressure jet grouting piles fill the gaps between the mixing piles and the cast-in-place piles. The bottom of the entire water-stopping retaining pile extends below the impermeable or weakly permeable layer of the site. The inclined bracing structure includes inclined bracing columns and inclined bracing conversion bearing platforms. The inclined bracing conversion bearing platforms are installed on the basement floor slab poured above the engineering piles. The upper end of the inclined bracing column is detachably connected to the capping beam, and the lower end is connected to the inclined bracing conversion bearing platform. The inclined bracing column does not penetrate the ground downwards. The lateral water and soil pressure of the lower chamber floor slab is transmitted to the engineering piles through the capping beam, the inclined bracing columns, and the inclined bracing conversion pile cap. The anchor cables are laid diagonally downward along the outer side of the capping beam, with the top of the anchor cables anchored and embedded in the concrete of the capping beam. The anchoring sections of the anchor cables are all arranged on the original soil within the river protection red line. The anchor cables and the capping beam cooperate to form a temporary limiting structure at the top of the foundation pit. The counterweight soil is the stepped soil reserved in the layered excavation of the foundation pit, which is arranged inside the water-stop retaining piles to offset the active earth pressure near the river. The replacement support plate extends outward from the basement floor slab and is cast in place, fitting against the inner side of the water-stop retaining piles. After the inclined bracing is removed, it bears the lateral constraint. A trench is formed between the basement exterior wall and the water-stop retaining piles. The trench is backfilled and compacted with plain soil in layers to form a lateral seepage prevention buffer layer.

[0007] Furthermore, the diagonal bracing column is a detachable steel pipe, and the diagonal bracing conversion bearing platform adopts a steel structure.

[0008] Furthermore, the mixing piles are selected as single-axis mixing piles or triple-axis mixing piles, and the high-pressure jet grouting piles adopt single-tube, double-tube or triple-tube technology. During the construction of the three types of piles, they are overlapped and driven together to eliminate the cold joints between the piles.

[0009] Furthermore, the surface of the end of the diagonal brace column connected to the diagonal brace conversion bearing is provided with an external thread, and a locking nut is threaded onto the external thread. An annular pressure plate is provided on the end of the locking nut facing the diagonal brace conversion bearing. The annular pressure plate is sleeved on the diagonal brace column, and the outer surface of the annular pressure plate is fixedly connected to the end face of the locking nut. An adjustment component is provided inside the diagonal brace conversion bearing, and the adjustment component is used to adjust the support posture of the diagonal brace column.

[0010] Furthermore, the adjustment assembly includes a mounting cavity disposed on the inclined brace conversion platform. A rotating block is disposed within the mounting cavity. Rotating shafts are located at both ends of the rotating block and are rotatably connected to the side of the inclined brace conversion platform. A clearance cavity is located in the middle of the rotating block. Slide tracks are located on both sides of the clearance cavity. A slider is disposed within each slide track. One end of the slider is slidably connected within the slide track, and the other end of the slider extends from the clearance cavity to the outside of the rotating block. A limiting plate is located on the other end of the slider. The contact surfaces of the limiting plate and the rotating block are both planar. A limiting hole is located in the middle of the limiting plate, and the limiting hole matches the diameter of the inclined brace column. Locking pins are symmetrically disposed on the limiting plate and are slidably connected to it. Several locking holes are symmetrically disposed on both sides of the contact surface between the rotating block and the limiting plate. The locking nut drives an annular pressure plate to move on the inclined brace column, causing the annular pressure plate to contact the end of the locking pin, thereby pressing the locking pin against the locking hole.

[0011] Furthermore, a compression spring is sleeved on the locking pin, one end of the compression spring is fixed to the end of the locking pin facing the annular pressure plate, and an annular groove is provided on the limiting plate on the outside of the locking pin, and the other end of the compression spring is fixed in the annular groove.

[0012] A construction method for a water-stopping and retaining system for deep foundation pits near rivers includes the following construction steps: S1. Complete the parameter design by combining the river's annual water level, strata, foundation pit and red line dimensions, and level and reinforce the riverbank soil; S2. The engineering piles and triple-layered water-stop retaining piles are constructed synchronously in the zone. The bottom of the piles is embedded in the impermeable layer for no less than 1.5m. After completion, the pile body and seepage prevention are tested. S3. Destroy the integral cast-in-place continuous crown beam of the pile head, lay out and tension the anchor cables within the red line, excavate the earthwork in layers and steps, with a single excavation height of ≤2m, retain the step counter-pressure soil throughout the process, and rely on the anchor cables and counter-pressure soil to control deformation. S4. After excavating to the foundation, pour the basement floor slab. Install steel diagonal bracing conversion bearing platforms at the corresponding positions of the floor slab. After the strength meets the standard, hoist the diagonal bracing columns. The upper and lower ends of the diagonal bracing are connected to the cap beam and the diagonal bracing conversion bearing platform, respectively. After the diagonal bracing is formed, excavate the counter-pressure soil in sections to complete the stress conversion. S5. The basement is poured from bottom to top, and the floor slabs of each floor are simultaneously extended outwards and replaced with supporting slabs and closely attached to the water-stop retaining piles, so as to share the lateral load of the diagonal bracing layer by layer. S6. After the basement and the replacement slab reach the replacement strength, the diagonal bracing is removed in sections, and the connection opening is sealed with micro-expansion concrete. S7. Complete the waterproofing of the basement vertical structure and exterior walls, and backfill the trench between the enclosure and the exterior walls with plain soil in layers and compact it to form a seepage-proof buffer layer.

[0013] Furthermore, the earthwork excavation in step S3 and the removal of counter-pressure soil in step S4 are both carried out in a segmented stepped construction manner, with the height of a single excavation not exceeding 2m.

[0014] The beneficial effects of this invention are as follows: This technical solution employs a three-dimensional water-stopping retaining structure formed by triple pile casing and interlocking, effectively blocking multi-layer groundwater seepage, eliminating cold joints between piles, preventing water seepage and sand inrush on the pit sidewalls, and ensuring a dry construction environment for the pit. Relying on the existing engineering piles for force transmission, and combined with a detachable inclined bracing structure that does not penetrate the basement floor slab, it avoids the risk of permanent leakage in the floor slab, eliminating the need for additional temporary pile foundations and effectively reducing construction costs. All anchor cable anchoring sections are located within the river protection red line, meeting the compliant construction requirements for riverside pits. Through a step-by-step force conversion mechanism involving anchor cables, counter-pressure soil, steel inclined bracing, and replacement support plates, it precisely controls deformation throughout the soft soil pit construction process, resulting in excellent support stability. Finally, backfilling with fertile soil forms a lateral seepage-proof buffer closed loop, significantly improving the waterproof durability of the basement exterior walls and making it suitable for various deep soft soil pit construction scenarios near rivers.

[0015] Other advantages, objectives, and features of the invention will be set forth in the following description and will be apparent to those skilled in the art in some respects, or may be learned by practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0016] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 This is a schematic plan view of the overall water-stopping enclosure system of the present invention; Figure 2 This is a plan view of the water-stopping retaining piles in the water-stopping retaining system of the present invention; Figure 3 This is a schematic diagram of the construction of water-stopping retaining piles and engineering piles in the construction method of the present invention; Figure 4 This is a schematic diagram of the construction of the capping beam in the construction method of the present invention; Figure 5 This is a schematic diagram illustrating the retention of counterweight soil in the construction method of this invention; Figure 6 This is a schematic diagram of the construction bracing structure in the construction method of the present invention; Figure 7 This is a schematic diagram of the removal of counter-pressure soil and the construction of the basement structure in the construction method of the present invention; Figure 8 This is a schematic diagram of the removal of the diagonal bracing structure in the construction method of the present invention; Figure 9This is a schematic diagram of the layered backfilling of plain soil in the trench between the retaining wall and the outer wall in the construction method of the present invention; Figure 10 This is a schematic diagram of the overall connection of the diagonal bracing structure in the water-stopping enclosure system of the present invention; Figure 11 This is an exploded view of the diagonal bracing structure in the water-stopping enclosure system of the present invention; Figure 12 This is a three-dimensional schematic diagram of the rotating block and the diagonal bracing conversion platform in the water-stopping enclosure system of the present invention.

[0017] The following labels are shown in the attached diagram: 1. Water-stop retaining piles; 110. Mixing piles; 111. Cast-in-place piles; 112. High-pressure jet grouting piles; 2. Engineering piles; 3. Crown beams; 4. Anchor cables; 5. Counterbalance soil; 6. Diagonal bracing structure; 610. Diagonal bracing column; 611. External thread; 612. Locking nut; 613. Annular pressure plate; 614. Limiting plate; 615. Locking pin; 616. Compression spring; 617. Sliding block; 618. Rotating block; 619. Slide rail; 620. Clearance cavity; 621. Locking hole; 622. Rotating shaft; 623. Diagonal bracing conversion pile cap; 7. Basement structure; 8. Replacement support plate; 9. Plain soil. Detailed Implementation

[0018] like Figure 1 and Figure 2As shown, a water-stopping and retaining system for a deep foundation pit near a river includes water-stopping retaining piles 1, engineering piles 2, capping beams 3, anchor cables 4, counterweight soil 5, inclined bracing structure 6, basement structure 7, and replacement support plate 8. The water-stopping retaining piles 1 are formed by interlocking and driving together three types of piles: mixing piles 110, cast-in-place piles 111, and high-pressure jet grouting piles 112. The mixing piles 110 are arranged on the side closest to the river, and the high-pressure jet grouting piles 112 fill the gaps between the mixing piles 110 and the cast-in-place piles 111. The bottom of the water-stopping retaining piles 1 extends to below the impermeable or weakly permeable layer of the site. The inclined bracing structure 6 includes inclined bracing columns 610 and inclined bracing conversion bearing platforms 623. The inclined bracing conversion bearing platforms 623 are set on the basement floor slab poured above the engineering piles 2. The upper end of the inclined bracing column 610 is detachably connected to the capping beam 3, and the lower end is connected to the inclined bracing conversion bearing platform 623. On platform 623, the diagonal bracing column 610 does not penetrate the basement floor slab downwards. Lateral water and soil pressure is transmitted to the engineering pile 2 through the capping beam 3, the diagonal bracing column 610, and the diagonal bracing conversion platform 623. The anchor cable 4 is laid diagonally downwards along the outside of the capping beam 3. The top of the anchor cable 4 is anchored and embedded in the concrete of the capping beam 3. The entire anchoring section of the anchor cable 4 is arranged on the original soil within the river protection red line. The anchor cable 4 and the capping beam 3 cooperate to form a temporary limiting structure at the top of the foundation pit. The counterweight soil 5 is the stepped soil reserved for the layered excavation of the foundation pit. It is arranged inside the water-stop retaining pile to offset the active earth pressure near the river. The replacement support plate 8 extends outward from the basement floor slab and is cast in place, fitting the inside of the water-stop retaining pile 1. After the diagonal bracing is removed, it bears the lateral constraint. A trench is formed between the basement outer wall and the water-stop retaining pile 1. The trench is backfilled and compacted with plain soil in layers to form a lateral seepage prevention buffer layer.

[0019] This system employs a coupled working mechanism of multi-component collaborative support, phased stress distribution, and three-dimensional water-stopping. It utilizes triple-layered interlocking water-stopping retaining piles 1 to construct a continuous, closed, three-dimensional anti-seepage curtain. The piles penetrate deep into the impermeable layer to block the flow of deep groundwater. Simultaneously, the structural characteristics of different piles are used to achieve seepage buffering, stress support, and gap sealing respectively. The existing engineering piles 2 serve as the permanent load-bearing foundation. The inclined bracing conversion pile cap 623 receives the lateral water and soil pressure transmitted by the inclined bracing column 610, forming a closed force transmission path that does not penetrate the foundation slab, completely avoiding the impact of the foundation slab. Leakage defects; during the excavation stage of the foundation pit, the anchor cables 4 installed inside the red line provide active restraint tension, which, together with the passive earth pressure of the stepped counterweight soil 5 reserved inside, suppresses the deformation of the retaining piles during the excavation period; during the basement construction stage, the inclined bracing structure 6 is gradually replaced by the extended cast-in-place replacement support plate 8 to bear the lateral load, so as to achieve a stable force conversion of the support system; during the construction completion stage, the plain soil 9 is backfilled in layers in the trench to form a lateral seepage prevention buffer layer, which seals the residual seepage channels, and finally forms a full-cycle riverside foundation pit retaining system that integrates water stopping, shape control, force bearing and seepage prevention.

[0020] The triple-pile casing structure completely eliminates cold joints between piles, effectively blocking multi-layer groundwater seepage in riverside sites, preventing sand inrush, water seepage, and piping defects on the pit sidewalls, and ensuring a dry construction environment for the pit. Relying on the original engineering piles 2 for force transmission, there is no need to add temporary support piles. Combined with the detachable inclined bracing structure 6, the support construction cost is reduced. At the same time, the inclined bracing does not penetrate the bottom slab, eliminating the potential for permanent leakage of the basement floor slab from the root. All anchor cable 4 anchoring sections are located within the river protection red line, with no components encroaching on the control area, meeting the compliant construction requirements for riverside pits. Through the step-by-step force conversion of anchor cables 4, counter-pressure soil 5, steel inclined bracing, and replacement support plate 8, the deformation of the retaining structure is precisely controlled throughout the entire process of soft soil pit excavation and structural construction, resulting in strong support stability. The subsequent backfilling of the trench forms a seepage-proof buffer closed loop, significantly improving the overall waterproof durability of the basement exterior wall, and is suitable for various deep foundation pit construction scenarios in soft soil near rivers.

[0021] In one feasible embodiment, the diagonal bracing column 610 is a detachable steel pipe, and the diagonal bracing conversion bearing 623 is made of steel, which is simple to manufacture and easy to recycle.

[0022] In one feasible approach, the mixing pile 110 is selected as a single-axis mixing pile 110 or a three-axis mixing pile 110, and the high-pressure jet grouting pile 112 adopts a single-tube, double-tube or triple-tube process. During the construction of the three types of piles, they are overlapped and driven together to eliminate the cold joints between the piles.

[0023] Based on the soil hardness, groundwater pressure, and seepage conditions of the riverside foundation pit site, the appropriate pile type and construction technology are flexibly matched. For soft soil and uniform soil layers, single-axis mixing piles (110) can be used for rapid construction. For deep silty soft soil and areas with high requirements for pile compaction, triple-axis mixing piles (110) are used to improve soil mixing uniformity and pile integrity. For shallow seepage and conventional water pressure conditions, single-pipe and double-pipe high-pressure jet grouting processes are selected. For complex conditions with high water pressure, strong seepage, and large gaps between piles, triple-pipe high-pressure jet grouting processes are used to increase grout injection pressure and filling range. By interlocking and driving the three types of piles together, the complementary characteristics of different pile shapes are utilized to fill the gaps and cold joints at the pile joints, so that the dispersed and independent single piles interlock to form an overall sealed water-stop curtain, blocking the micro and macro seepage channels between piles.

[0024] The pile type and construction technology are highly adaptable, covering complex construction scenarios with different riverside strata and groundwater pressures. It solves the problems of poor adaptability of single pile type technology and poor quality of local pile formation. By overlapping and driving the piles together, it completely eliminates cold joints between piles, preventing sidewall seepage, sand inrush, and piping hazards caused by local pile breaks and leaks in the water-stop curtain. It significantly improves the overall continuity, density, and seepage prevention level of the water-stop curtain. It effectively avoids local leakage defects caused by stratum differences and water pressure fluctuations, eliminating the need for secondary grouting and sealing. It simplifies the construction process, ensures long-term dry operation conditions for the foundation pit, and significantly improves the stability and reliability of the foundation pit water-stop system.

[0025] like Figures 10-12 As shown, in one feasible embodiment, the end of the diagonal brace column 610 connected to the diagonal brace conversion bearing 623 is provided with an external thread 611. A locking nut 612 is threaded onto the external thread 611. An annular pressure plate 613 is fixed to the end of the locking nut 612 facing the bearing. The annular pressure plate 613 is coaxially sleeved on the outside of the diagonal brace column 610. An installation cavity is opened inside the diagonal brace conversion bearing 623. A rotatable rotating block 618 is installed in the installation cavity. The two ends of the rotating block 618 are rotatably connected to the side wall of the bearing through a rotating shaft 622, so that the rotating block 618 can freely deflect at an angle. An avoidance cavity 620 is opened in the middle of the rotating block 618. Slide rails 619 are provided on both sides of the avoidance cavity 620. A slider 617 is slidably installed in the slide rails 619. A rotating block 618 extends from the outer end of 617 and fixes a limiting plate 614. A limiting hole matching the outer diameter of the diagonal brace 610 is opened in the center of the limiting plate 614 for positioning the end of the diagonal brace 610. Locking pins 615 are symmetrically slidably arranged on the limiting plate 614. Multiple sets of locking holes 621 are symmetrically arranged on the mating plane of the rotating block 618 and the limiting plate 614. The locking pins 615 can be correspondingly inserted into the locking holes 621. By rotating and moving the locking nut 612 downward, the annular pressure plate 613 can be driven to press the end of the locking pin 615, so that the locking pin 615 is locked, realizing the rigid fixation of the limiting plate 614 and the rotating block 618. The overall structure can simultaneously realize the angle rotation of the diagonal brace 610, the fine adjustment of the diagonal displacement, and the subsequent mechanical locking and positioning.

[0026] This structure utilizes the rotation function of the built-in rotating block 618 in the bearing platform, combined with the sliding fine-tuning functions of the slider 617 and the limiting plate 614, to achieve multi-angle rotation and oblique displacement adjustment of the diagonal brace column 610. This adapts to the working conditions of deviations in the support points and inconsistent support inclination angles of the capping beam 3 on the construction site. At the same time, the diagonal brace column 610 can extend and retract within the controllable range of the avoidance cavity 620, enabling precise length compensation for on-site construction and installation errors, further eliminating assembly misalignment, and ensuring precise correspondence between the upper and lower support points. In the specific adjustment process, the rotating block 618 freely deflects based on the rotating shaft 622, which can precisely match the designed support angle of the capping beam 3. Simultaneously, the slider 617 slides along the slide rail 619, causing the limiting plate 614 and the end of the diagonal brace column 610 to move horizontally and obliquely by a small amount, achieving precise centering of the upper and lower end points of the diagonal brace column 610, so that the top of the diagonal brace column 610 is completely in contact with the preset support position of the capping beam 3 and is tightened against the capping beam 3 with a standard force inclination angle. After the length compensation, angle, and position adjustment of the diagonal brace 610 are in place and fully adapt to the support requirements of the crown beam 3, the locking nut 612 at the end of the diagonal brace 610 is tightened, which drives the annular pressure plate 613 to press axially downward, squeezing the symmetrically arranged locking pins 615. The locking pins 615 are then inserted into the locking holes 621 of the rotating block 618. The dual mechanical locking method of end face pressing and pin locking is used to fix the relative position of the limiting plate 614 and the rotating block 618, locking the final adjusted posture of the diagonal brace 610. At the same time, after the locking nut 612 is threaded and locked, it can form a rigid limiting constraint, effectively preventing the diagonal brace 610 from slipping or moving during the process of the diagonal brace system bearing water and soil loads, completely locking the support state, eliminating adjustment gaps and looseness, and ensuring that the diagonal brace support state remains stable.

[0027] This design completely solves the problems of traditional fixed steel diagonal braces, where the angle, position, and length are all non-adjustable, making them unsuitable for on-site construction deviations, support point offsets of the capping beam 3, mismatched stress angles, and assembly lengths. Through multiple adaptive adjustment functions including angle rotation, diagonal displacement, and telescopic length compensation, it can precisely offset construction and assembly errors, adapting to the support position, angle, and spacing requirements of the capping beam 3 under different working conditions. This ensures a tight fit between the top of the diagonal brace column 610 and the capping beam 3, with axial stress distribution, eliminating defects such as eccentric support, false support, and localized stress concentration. The system utilizes a double-locking structure consisting of a threaded pressure plate and a locking pin 615 for alignment, along with the anti-slip and limiting function of the locking nut 612. This allows for precise locking of the installation posture and effectively resists dynamic soil and water loads, preventing the diagonal brace 610 from sliding or shifting during stress. This ensures that the adjusted diagonal brace posture is permanently fixed without rebound or offset, significantly improving the installation accuracy, assembly compatibility, and stress stability of the diagonal brace. It effectively guarantees uniform stress and stable support of the foundation pit retaining structure, and significantly enhances the safety redundancy and reliability of the foundation pit construction support system.

[0028] In one feasible embodiment, a compression spring 616 is sleeved on the locking pin 615, one end of the compression spring 616 is fixed to the end of the locking pin 615 facing the annular pressure plate 613, and an annular groove is provided on the limiting plate 614 on the outer side of the locking pin 615, and the other end of the compression spring 616 is fixed in the annular groove.

[0029] By using an annular groove to isolate the annular pressure plate 613 from the compression spring 616, the spring will not be squeezed by the pressure plate under pressure conditions, effectively protecting the compression spring 616 and preventing the spring from being damaged by pressure; the compression spring 616 enables the locking pin 615 to automatically retract and unlock, simplifying the process of adjusting the angle of the diagonal brace; during the locking stage, the spring does not bear continuous compression load, further reducing the probability of fatigue failure, improving the load-bearing capacity and long-term working reliability of the mechanism, and adapting to the working conditions where the diagonal brace is subjected to large lateral water and soil pressure.

[0030] In one feasible embodiment, the inclined brace conversion bearing 623 is provided with rotation limiting components on both sides to control the rotation state of the shaft 622.

[0031] Rotation limiting components are provided on both sides of the inclined brace conversion bearing 623 to control the rotation state of the rotating shaft 622. Existing technologies generally use a single-sided bolt tightening and limiting structure at the shaft end. This solution uses symmetrically arranged rotation limiting components on both sides, with symmetrical limiting and locking structures corresponding to the two ends of the rotating shaft 622. This allows for simultaneous clamping and limiting of both ends of the rotating shaft 622, precisely controlling its rotation state. After the inclined brace column 610 completes its oblique displacement and angle rotation adjustment, precisely matching the support position and angle of the cap beam 3, the symmetrically arranged rotation limiting components on both sides of the bearing 623 simultaneously lock and limit the rotational freedom of the rotating shaft 622 from both ends. This completely fixes the adjustment angle of the rotating block 618, preventing unilateral force deviation, micro-rotation, and springback loosening of the rotating shaft 622. This ensures that the optimal support posture of the inclined brace column 610 after adjustment is permanently fixed, avoiding angle and position deviations caused by construction processes and subsequent water and soil loads and soil creep.

[0032] like Figures 3-9 As shown, a construction method for a water-stopping and retaining system for deep foundation pits near rivers includes the following construction steps: S1. Preliminary Survey and Design and Riverbank Pretreatment: Based on the annual highest water level of the river at the project site, the water level variation during the dry season, the soil layer distribution, soft soil thickness, groundwater pressure head, excavation depth of the foundation pit, the plan dimensions of the foundation pit, and the boundary of the river protection red line, complete a set of specialized designs for support parameters, water-stopping parameters, and component layout parameters; clean and level the loose surface soil and miscellaneous fill of the original riverbank on the riverside, and use replacement, compaction, or shallow grouting reinforcement methods to reinforce the riverbank soil as a whole, eliminate the risk of riverbank slippage and collapse, ensure the overall stability of the riverbank during the subsequent pile foundation construction and foundation pit excavation stages, and meet the pre-construction safety conditions for the water-adjacent foundation pit.

[0033] S2. Phased and Synchronous Construction of Engineering Piles 2 and Triple-Layer Water-Stop Retaining Piles 1, and Inspection and Acceptance: The construction of the main engineering piles 2 and triple-layer water-stop retaining piles 1 is carried out simultaneously in a phased, segmented, and continuous manner. The construction process of mixing piles 110, cast-in-place piles 111, and high-pressure jet grouting piles 112 is strictly followed to ensure effective overlap between piles and eliminate seepage cold joints. The bottom of all retaining piles is uniformly embedded in the impermeable or weakly permeable layer of the site to a depth of not less than 1.5m to completely cut off the flow channel of deep confined water. After the completion of all pile construction, low-strain tests on pile integrity, pile density tests, and seepage prevention water injection and pressure tests on the sidewalls of the foundation pit are carried out in sequence. For local gaps and weak points, high-pressure jet grouting piles 112 are used to reinforce and seal them to ensure that the water-stop curtain is continuous, sealed, and free of leakage defects.

[0034] S3, construction of the capping beam 3, tensioning of anchor cables 4, and control of layered and stepped earthwork excavation: After the strength of the retaining piles reaches the standard, the laitance and excess pile body at the pile heads will be uniformly removed, and the continuous reinforced concrete capping beam 3 will be cast in place to ensure that the tops of all retaining piles are rigidly fixed to the capping beam 3, forming an integral retaining top constraint structure; during the construction of the capping beam 3, the anchor cable 4 holes will be precisely laid out simultaneously. The anchor cables 4 will be arranged obliquely throughout the entire length in the original soil inside the river protection red line, and the anchoring section will be completely contained within the red line area. The anchor cables were tensioned, locked, and anchored for testing. The excavation of the foundation pit was carried out using a layered, segmented, and stepped excavation process, with the single excavation depth strictly controlled to ≤2m, and over-excavation and scouring were strictly prohibited. Throughout the excavation process, stepped counterweight soil 5 bodies were reserved inside the water-stop retaining piles. Through the active prestressing constraint of the anchor cables 4 and the passive earth pressure of the counterweight soil 5, the active water and soil pressure on the side of the river was effectively offset. The displacement of the top of the retaining piles and the overall deformation of the foundation pit were controlled throughout the process, ensuring the stability of the soft soil foundation pit during the excavation stage.

[0035] S4. Foundation Structure Construction, Bracing Installation, and System Stress Transfer: After the foundation pit is excavated in layers to the design foundation elevation and the foundation inspection is passed, the basement floor slab structure is cast in place as a whole in one go. Simultaneously, the precast steel bracing conversion pile cap 623 is installed at the corresponding position of engineering pile 2 to ensure that the pile cap, the floor slab, and engineering pile 2 are subjected to overall stress. After the floor slab strength reaches the design requirements, the adjustable bracing column 610 is hoisted into place. Utilizing the bracing's own angle adjustment, displacement fine-tuning, and length compensation functions, the support points and inclination angle of the capping beam 3 are precisely matched. The upper end of the diagonal brace column 610 is rigidly connected and fixed to the cap beam 3, and the lower end is fixed to the diagonal brace conversion bearing 623. The attitude is locked by locking nuts 612, locking pins 615 and rotation limiting components. After the diagonal brace support system is formed and accepted, the pre-reserved counterweight soil 5 is gradually removed by segmented, symmetrical and stepped excavation method. This allows the lateral water and soil pressure of the foundation pit to be smoothly converted from the "anchor cable 4 + counterweight soil 5 temporary support system" to the "steel diagonal brace rigid support system", achieving a smooth force conversion without stress mutation and deformation deviation.

[0036] S5. Basement structure 7 is constructed layer by layer and the replacement support plate 8 is cast in place simultaneously: The basement floor slab, each floor slab and vertical structure are constructed sequentially from bottom to top; when each floor slab is constructed, the replacement support plate 8 structure is cast outward simultaneously, so that the inner side of the replacement support plate 8 is tightly attached to the inner side wall of the water-stop retaining pile 1. The lateral water and soil load borne by the original diagonal bracing is distributed and borne by the main floor slab structure layer by layer, so as to realize the gradual transition and dispersion of support stress, avoid long-term concentrated stress on a single diagonal bracing, provide reliable structural support conditions for subsequent diagonal bracing removal, and ensure that there are no support gaps throughout the entire foundation pit construction process.

[0037] S6. Segmented Removal of Diagonal Bracing and Sealing of Openings: After the concrete strength of each floor slab of the basement and the extended replacement support plate 8 reaches the design replacement strength, and the overall structural stiffness meets the requirements of the foundation pit lateral support, the steel diagonal bracing components shall be gradually removed in accordance with the principle of "segmentation, symmetry, layering, and unloading". It is strictly forbidden to remove them all at once. After the diagonal bracing is removed, the reserved openings at the connection of the cap beam 3 and the foundation shall be sealed and compacted with micro-expansion fine stone concrete to eliminate structural holes, ensure that the joints are dense and leak-proof, and prevent the potential for water seepage at the joints in the later stage.

[0038] S7. Waterproofing construction of the exterior wall and closed-loop backfilling of the trench for seepage prevention: After the vertical structure construction of the basement is completed, the waterproof layer and protective layer of the exterior wall of the basement are laid as a whole to ensure the integrity and continuity of the exterior wall waterproofing system; for the trench area between the exterior wall of the basement and the water-stop retaining pile 1, plain soil is backfilled in layers and compacted in layers, and the thickness of each backfill layer is controlled within the specification range to form a continuous and dense lateral seepage prevention buffer soil layer, balance the lateral soil pressure of the foundation pit, block the capillary seepage channels, and complete the closed-loop construction of the overall water-stop, support and seepage prevention system of the foundation pit.

[0039] Additional information on the preferred implementation method: The earthwork excavation operation in step S3 and the removal of the counterweight soil 5 in step S4 are both carried out in strict accordance with the segmented and stepped flow construction process. The height of each excavation and soil removal is strictly controlled within 2m. By limiting the unloading and releasing the pressure in stages, the stress release law of the soft soil foundation near the river is adapted to effectively avoid the construction risks such as deformation of the retaining piles, heave of the pit bottom, and soil slippage caused by instantaneous large-area unloading.

[0040] The advantages of this technical solution compared to existing technologies are as follows: 1. Constructing a triple three-dimensional water-stop curtain significantly improves seepage prevention performance: This application adopts a triple-layer composite water-stop retaining pile structure consisting of mixing piles 110, cast-in-place piles 111, and high-pressure jet grouting piles 112. The pile type and construction process can be flexibly matched according to different ground water pressure conditions, completely eliminating the defects of cold joints and local leakage between piles that exist in traditional single and double water-stop piles. The pile bottom is embedded deep into the impermeable layer, vertically cutting off the groundwater bypass channel, forming a three-dimensional seepage prevention system of shallow buffer, middle layer retaining soil, and deep layer sealing water. This effectively prevents sand inrush, water seepage, and piping problems on the side wall of the foundation pit, and ensures dry construction conditions for the foundation pit throughout the process, eliminating the need for secondary leak sealing construction in the later stage.

[0041] 2. Achieve full compliance of the support structure and adapt to the river protection red line control requirements: This application arranges the entire anchoring section of anchor cable 4 in the original soil inside the river protection red line, without any support components encroaching on the river protection red line control area. This completely solves the problem of traditional outer anchor cable 4 support encroaching on the red line and failing to pass the approval. It adapts to the construction requirements of the restricted site near the river, with strong construction compliance and high feasibility.

[0042] 3. Unique adaptive adjustable diagonal bracing structure 6 solves the problem of poor adaptability to on-site construction: Compared with the shortcomings of traditional fixed steel diagonal bracing where the angle, length, and position are not adjustable, this application features an adjustable diagonal bracing structure 6 with threaded locking, sliding alignment, angle rotation, and double-sided anti-rotation limit. This allows for multi-angle rotation of the diagonal bracing column 610, fine adjustment of oblique displacement, and compensation for telescopic length, accurately offsetting errors caused by pile foundation construction and component installation, and precisely matching the support point position and support inclination angle of the cap beam 3 to ensure the axial force of the diagonal bracing. At the same time, relying on the double locking structure of locking nut 612 and locking pin 615, it effectively prevents the diagonal bracing from slipping and moving during the stress process, greatly improving the support accuracy and structural stability, and also facilitating repeated disassembly and reuse after construction.

[0043] 4. The non-penetrating slab support force transmission system eliminates the risk of leakage in the basement slab from the root: This application relies on the original engineering pile 2 for load bearing, without the need to add temporary support pile foundations. The inclined bracing column 610 is arranged as a whole above the basement floor slab without penetrating the floor slab. The force is transmitted through the steel inclined bracing conversion pile cap 623 (pre-embedded on the engineering pile 2 before the basement floor slab is poured), which completely eliminates the permanent waterproof weak point formed by the traditional support penetrating the slab, greatly improves the overall waterproof durability of the basement. At the same time, the steel inclined bracing and the pile cap can be disassembled and reused, effectively reducing the construction cost of the foundation pit support, reducing construction waste, and having good green and energy-saving performance.

[0044] 5. Three-level step-by-step stress conversion for precise control of soft soil foundation pit deformation: This application forms a three-level stress system of "anchor cable 4 + counter-pressure soil 5 temporary support → steel diagonal brace rigid support → replacement support plate 8 permanent support". Combined with the layered step-by-step excavation construction process with limited unloading, the soil stress is released step by step to avoid large deformation, pit bottom heave and soil slippage caused by instantaneous unloading of soft soil. The displacement of retaining piles is effectively constrained throughout the process, so that the foundation pit deformation meets the first-level foundation pit specification control standard and is suitable for construction scenarios of high compressibility soft soil near rivers.

[0045] 6. Forming a complete seepage prevention support closed loop and improving the overall construction quality of the project: The support system is replaced smoothly and without damage by extending the support plate 8 on the outside of the basement floor slab, ensuring that there are no gaps in the support throughout the construction process; in the later stage, the lateral seepage prevention buffer layer is formed by backfilling and compacting the soil in the trench layer, blocking the capillary seepage channels, balancing the lateral soil pressure, and improving the integrated closed loop system of foundation pit water stop, support and seepage prevention, which greatly improves the safety of foundation pit construction and the long-term waterproof stability of the basement exterior wall.

[0046] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A water-stopping and retaining system for deep foundation pits near rivers, characterized in that: The structure includes retaining piles, engineering piles, capping beams, anchor cables, counterweight soil, diagonal bracing structures, basement structures, and replacement slabs. The retaining piles are formed by interlocking and bonding of mixing piles, cast-in-place piles, and high-pressure jet grouting piles. The mixing piles are positioned near the river channel, and the high-pressure jet grouting piles fill the gaps between the mixing and cast-in-place piles. The bottom of the retaining pile extends to below the impermeable or weakly permeable layer of the site. The diagonal bracing structure includes diagonal bracing columns and diagonal bracing conversion platforms. The diagonal bracing conversion platforms are installed on the basement floor slab poured above the engineering piles. The upper end of the diagonal bracing column is detachably connected to the capping beam, and the lower end is connected to the diagonal bracing conversion platform. The diagonal bracing column does not penetrate the basement floor slab downwards and extends laterally. Water and soil pressure is transmitted to the engineering piles through the capping beam, diagonal bracing columns, and diagonal bracing conversion pile caps. The anchor cables are laid diagonally downward along the outer side of the capping beam, with the top of the anchor cables anchored and embedded in the concrete of the capping beam. The anchoring sections of the anchor cables are all arranged on the original soil within the river protection red line. The anchor cables and the capping beam cooperate to form a temporary limiting structure at the top of the foundation pit. The counterweight soil is the stepped soil reserved in the layered excavation of the foundation pit, which is arranged inside the water-stop retaining piles to offset the active earth pressure near the river. The replacement support plate extends outward from the basement floor slab and is cast in place, fitting against the inner side of the water-stop retaining piles. After the diagonal bracing is removed, it bears the lateral constraint. A trench is formed between the basement exterior wall and the water-stop retaining piles. The trench is backfilled and compacted with plain soil in layers to form a lateral seepage prevention buffer layer.

2. The water-stopping and retaining system for deep foundation pits along rivers according to claim 1, characterized in that: The diagonal bracing column is a detachable steel pipe, and the diagonal bracing conversion bearing platform adopts a steel structure.

3. The water-stopping and retaining system for deep foundation pits along rivers according to claim 1, characterized in that: The mixing piles are selected as single-axis mixing piles or triple-axis mixing piles, and the high-pressure jet grouting piles adopt single-pipe, double-pipe or triple-pipe technology. During the construction of the three types of piles, they are overlapped and driven together to eliminate the cold joints between the piles.

4. The water-stopping and retaining system for deep foundation pits along rivers according to claim 1, characterized in that: The inclined brace column is provided with an external thread on one end surface where it connects to the inclined brace conversion bearing. A locking nut is threaded onto the external thread. An annular pressure plate is provided on the end of the locking nut facing the inclined brace conversion bearing. The annular pressure plate is sleeved on the inclined brace column, and the outer surface of the annular pressure plate is fixedly connected to the end face of the locking nut. An adjustment component is provided inside the inclined brace conversion bearing to adjust the support posture of the inclined brace column.

5. The water-stopping and retaining system for deep foundation pits along rivers according to claim 4, characterized in that: The adjustment assembly includes a mounting cavity disposed on the inclined brace conversion platform. A rotating block is disposed within the mounting cavity. Rotating shafts are located at both ends of the rotating block and are rotatably connected to the side of the inclined brace conversion platform. A clearance cavity is located in the middle of the rotating block. Slide tracks are located on both sides of the clearance cavity. A slider is disposed within each slide track. One end of the slider is slidably connected within the slide track, and the other end of the slider extends from the clearance cavity to the outside of the rotating block. A limiting plate is located on the other end of the slider. The contact surfaces of the limiting plate and the rotating block are both planar. A limiting hole is located in the middle of the limiting plate, and the limiting hole matches the diameter of the inclined brace column. Locking pins are symmetrically disposed on the limiting plate and are slidably connected to it. Several locking holes are symmetrically disposed on both sides of the contact surface between the rotating block and the limiting plate. A locking nut drives an annular pressure plate to move on the inclined brace column, causing the annular pressure plate to contact the end of the locking pin, thereby pressing the locking pin against the locking hole.

6. The water-stopping and retaining system for deep foundation pits along rivers according to claim 5, characterized in that: A compression spring is sleeved on the locking pin. One end of the compression spring is fixed to the end of the locking pin facing the annular pressure plate. An annular groove is provided on the limiting plate outside the locking pin. The other end of the compression spring is fixed in the annular groove.

7. A construction method for a water-stopping and retaining system for deep foundation pits along rivers according to any one of claims 1-6, characterized in that: The construction steps include the following: S1. Complete the parameter design by combining the river's annual water level, strata, foundation pit and red line dimensions, and level and reinforce the riverbank soil; S2. The engineering piles and triple-layered water-stop retaining piles are constructed synchronously in the zone. The bottom of the piles is embedded in the impermeable layer for no less than 1.5m. After completion, the pile body and seepage prevention are tested. S3. Destroy the integral cast-in-place continuous crown beam of the pile head, lay out and tension the anchor cables within the red line, excavate the earthwork in layers and steps, with a single excavation height of ≤2m, retain the step counter-pressure soil throughout the process, and rely on the anchor cables and counter-pressure soil to control deformation. S4. After excavating to the foundation, pour the basement floor slab. Install steel diagonal bracing conversion bearing platforms at the corresponding positions of the floor slab. After the strength meets the standard, hoist the diagonal bracing columns. The upper and lower ends of the diagonal bracing are connected to the cap beam and the diagonal bracing conversion bearing platform, respectively. After the diagonal bracing is formed, excavate the counter-pressure soil in sections to complete the stress conversion. S5. The basement is poured from bottom to top, and the floor slabs of each floor are simultaneously extended outwards and replaced with supporting slabs and closely attached to the water-stop retaining piles, so as to share the lateral load of the diagonal bracing layer by layer. S6. After the basement and the replacement slab reach the replacement strength, the diagonal bracing is removed in sections, and the connection opening is sealed with micro-expansion concrete. S7. Complete the waterproofing of the basement vertical structure and exterior walls, and backfill the trench between the enclosure and the exterior walls with plain soil in layers and compact it to form a seepage-proof buffer layer.

8. The construction method of a water-stopping and retaining system for a deep foundation pit near a river as described in claim 7, characterized in that: In step S3, the earthwork excavation and in step S4, the back pressure soil removal are both carried out in a segmented stepped construction manner, with the single excavation height not exceeding 2m.

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