Mixed node double-row pile support prestressed coupling beam construction method

Abstract

The invention discloses a mixed node double-row pile supporting prestressed coupling beam construction method. The problems that in an existing double-row pile supporting construction method, a coupling beam is passively stressed, concrete is prone to cracking, and external anchoring is relied on are solved. The method comprises the steps of constructing front-row piles and rear-row piles; concrete of the front-row crown beam and the groove is poured, and a fixed end anchorage device assembly is pre-buried below the groove; concrete of the rear row crown beam is poured, and a top pressure-bearing steel plate is fixedly connected to the crown beam main reinforcements; binding a steel reinforcement framework of the prestressed coupling beam, embedding a corrugated pipe sleeve, pre-embedding an anchoring part at one end close to the rear-row crown beam, and pouring concrete of the prestressed coupling beam in a layered manner; after the strength of the concrete reaches 90% of the design strength, the steel strand penetrates into the corrugated pipe sleeve, and three-stage tensioning is conducted; an anchoring end plate of the prestressed coupling beam anchoring part is fixedly connected with a pressure-bearing steel plate of the rear-row crown beam; connecting nodes on the side of the rear row crown beam are closed; and non-shrinkage epoxy slurry is injected into the termination cavity of the corrugated pipe sleeve on the front-row crown beam side.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering foundation pit support technology, and in particular to a construction method for prestressed coupling beams supported by hybrid node double-row piles. Background Technology

[0002] Double-row pile support systems are a common support method in deep foundation pit engineering. Their structural performance mainly depends on the coordinated work of the two rows of piles, the capping beam, and the connecting beam. However, the traditional construction and construction methods of double-row pile support systems have several inherent defects that restrict the full realization of their performance.

[0003] I. Traditional coupling beams are ordinary reinforced concrete components that rely entirely on passive force-bearing mechanisms. The bending moment generated by soil deformation during the excavation of the foundation pit directly acts on the coupling beam, resulting in insufficient bending stiffness, easy generation of structural cracks, difficulty in effectively controlling the overall displacement of the support structure, and threatening the overall stability of the foundation pit.

[0004] Second, the traditional connecting beams are rigidly cast-in-place connected to the front and rear cap beams. The joint area lacks the ability to coordinate internal forces. Under differential deformation, stress concentration is prone to occur, leading to cracks and affecting the overall stability and durability of the structure.

[0005] To compensate for the shortcomings of the aforementioned double-row pile support system structure and construction methods, the following technical solutions are usually adopted: 1. Applying prestress to the pile body, which can only improve the bending resistance of a single pile, but has limited effect on improving the stress of the coupling beam itself and the joint performance with the capping beam; 2. Strengthening its bending resistance by simply increasing the cross-section and reinforcement of the coupling beam, which not only significantly increases material costs, but also easily exacerbates the risk of cracking; 3. Using prestressed anchor cables, which is a "pull-type" reinforcement that relies on the external soil. Its anchoring effect is significantly affected by geological conditions, and it often requires occupying land outside the foundation pit boundary, increasing construction complexity and affecting the project schedule.

[0006] Therefore, how to develop a construction method that can systematically integrate active prestress control and rational node construction to improve the overall performance of the double-row pile support system has become an urgent technical problem to be solved. Summary of the Invention

[0007] Existing construction methods for double-row pile support systems suffer from problems such as passive stress on the coupling beam, easy cracking of concrete, and reliance on external anchorage. The purpose of this invention is to provide a construction method for prestressed coupling beams with hybrid joint double-row pile support.

[0008] The technical solution adopted by this invention to solve its technical problem is: a construction method for prestressed coupling beams with hybrid node double-row pile support, the steps of which are as follows:

[0009] Step 1: Constructing the front and rear rows of piles;

[0010] Step 2: Pour concrete for the front cap beam and the groove, and pre-embed the fixed end anchor assembly below the groove;

[0011] Step 3: Pour the concrete for the rear cap beam, and fix the bearing steel plate at the top of the rear cap beam to the main reinforcement of the cap beam;

[0012] Step 4: Lay and tie the steel reinforcement cage of the prestressed coupling beam, and simultaneously embed and install the corrugated pipe sleeve. The corrugated pipe sleeve is arranged along the span direction of the prestressed coupling beam and in a parabolic manner according to the design bending moment envelope diagram; erect the side formwork of the coupling beam, pre-embed anchors at one end near the rear cap beam, and pour the concrete of the prestressed coupling beam in layers.

[0013] Step 5: After the concrete strength of the prestressed coupling beam reaches 90% of the design strength, the steel strands are threaded into the corrugated pipe sleeve and tensioned in three stages; after tensioning is completed, the anchor end plate of the prestressed coupling beam anchor is fastened to the bearing steel plate of the rear cap beam.

[0014] Step 6: For the connection node on one side of the rear crown beam, use a U-shaped steel plate to cover the joint of the tightened bolt connection area and fully weld it to form a continuous and sealed cavity. Fill the cavity with epoxy resin mortar; after the connection node is sealed, fill it with a corrugated pipe sleeve.

[0015] Step 7: Inject non-shrink epoxy grout into the termination cavity of the corrugated pipe sleeve near the front crown beam, lay a rubber pad in the groove, pour non-shrink mortar in layers and vibrate to compact it to form a flexible deformation compensation seal.

[0016] The hybrid node double-row pile support prestressed coupling beam construction method of the present invention firstly involves constructing double-row piles, then threading and tensioning prestressed steel strands within the coupling beam to apply prestress to the double-row pile support itself; a pre-set groove and flexible buffer layer are installed in the front row cap beam, and a prestressed steel strand system is configured inside the coupling beam, forming a rigid connection with the rear row cap beam; this hybrid node double-row pile support prestressed coupling beam construction method has the following beneficial effects:

[0017] (1) By actively applying reverse loads through prestressed steel strands, the traditional passively bent connecting beam is transformed into a prestressed load-bearing body, thereby actively constraining the pile top displacement, improving the stress state of the nodes, and effectively enhancing the overall stiffness and displacement control capability of the double-row pile support system.

[0018] (2) A “flexible front and rigid rear” node stress system is constructed between the two ends of the prestressed connecting beam and the front and rear cap beams. At the same time, prestress is applied inside the prestressed connecting beam and tensioned in stages. The flexible hinge structure of the front cap beam releases the temperature deformation and differential settlement stress, and the rigid force transmission of the stud steel plate of the rear cap beam ensures the effective transmission of prestress. The “flexible front and rigid rear” hybrid node design effectively solves the stress concentration problem caused by the rigid connection between the connecting beam and the cap beam, and improves the overall stiffness, structural stability and durability of the double-row pile support system.

[0019] (3) By forming an internal force self-balancing system together with the prestressed connecting beam and the "front flexible and rear rigid" node, the front and rear piles and the prestressed connecting beam are tightly coupled into a high-strength overall frame, so that it can independently bear the lateral earth pressure of the foundation pit without relying on external anchor cables or internal supports, thus broadening the application boundary of unsupported support technology in engineering practice and achieving effective shortening of the project period and optimization of comprehensive costs.

[0020] Furthermore, in step 2, the outline of the front capping beam is marked on the top of the front piles, and the edge line of the groove opening is marked on the starting end face of the front capping beam; the side formwork of the capping beam is erected and the customized groove steel formwork is installed simultaneously, and the groove steel formwork is bolted to the side formwork of the capping beam; then the steel reinforcement skeleton is tied, and the fixed end anchor assembly is pre-embedded at the designed position below the groove, and the fixed end anchor assembly is firmly connected to the main reinforcement of the front capping beam; the concrete is poured in layers, and the side formwork of the capping beam and the groove steel formwork are removed after the concrete has initially set.

[0021] Furthermore, in step 3, the outline of the rear cap beam and the installation position of the bearing steel plate are marked on the top of the rear piles; the side formwork of the cap beam is erected and the bearing steel plate is simultaneously anchored to the pile head reinforcement through temporary support frame and bolts; then the main reinforcement and stirrups of the cap beam are tied; the bearing steel plate and the main reinforcement of the cap beam are fully welded to form a permanent connection and the temporary support frame is removed; the concrete is poured in layers; and the side formwork of the cap beam is removed after the concrete has set.

[0022] Furthermore, in step 4, the corrugated pipe sleeve terminates 200mm from the end face of the front row crown beam, and a spiral reinforcement mesh is installed in the prestressed anchorage section area near the end face of the rear row crown beam for local reinforcement.

[0023] Furthermore, in step 3, before pouring the concrete for the rear cap beam in layers, shear studs are welded to the surface of the pressure-bearing steel plate, and the cap beam stirrups are wrapped around the shear studs; closed-cell foam sealing strips are used to fill the template joints, and a PE protective film is covered on the surface of the pressure-bearing steel plate.

[0024] Furthermore, the corrugated sleeve is a multi-channel metal corrugated pipe.

[0025] Furthermore, in step 7, the length of the termination cavity of the corrugated sleeve is 200mm. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the construction process of the front crown beam in one embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the construction process of the rear crown beam in one embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the construction process of a prestressed coupling beam in one embodiment of the present invention;

[0029] Figure 4 This is a flowchart of an embodiment of the construction method for prestressed coupling beams with hybrid node double-row pile support according to the present invention. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the purpose of illustrating the embodiments of the present invention.

[0031] Combination Figures 1 to 4 The construction method of the hybrid node double-row pile supported prestressed coupling beam of the present invention is described in detail below:

[0032] Step 1, Construction of double-row piles: Use a total station to accurately mark the location of the double-row piles, use a rotary drilling rig to form holes, lower the steel cage and pour concrete to the design elevation to form the front row piles and the rear row piles respectively.

[0033] Step 2, construct the front row of capping beams and build flexible node foundations: pour concrete for the front row of capping beams and the grooves, and pre-embed fixed end anchor components below the grooves.

[0034] Step 3: Construct the rear cap beam and build a rigid node foundation and tension end bearing surface: Pour concrete for the rear cap beam, and fix the bearing steel plate at the top of the rear cap beam to the main reinforcement of the cap beam.

[0035] Step 4, construct the prestressed coupling beam: such as Figure 3As shown, the positions of the center axis, outline, and prestressed anchorage endpoints of the prestressed coupling beam are accurately marked. The reinforcing steel cage of the coupling beam is laid and tied according to design requirements. Corrugated pipe sleeves are simultaneously installed, running along the span of the prestressed coupling beam and arranged parabolically according to the design bending moment envelope (radius of curvature ≥ 15 times the pipe diameter). The corrugated pipe sleeve terminates 200mm from the front end face (near the front row of capping beams), and spiral reinforcement mesh is installed in the prestressed anchorage section area on the rear end face (near the rear row of capping beams) for local reinforcement. After the reinforcing steel cage and corrugated pipe sleeves pass inspection, the side formwork of the coupling beam is erected, and anchorages (including anchor plates and anchorage end plates) are simultaneously pre-embedded at the rear end. Micro-expansion concrete is poured and vibrated in layers. Curing is carried out promptly after the concrete has initially set.

[0036] Step 5, Prestressing tensioning and rigid joint fastening: (e.g.) Figure 4 As shown, after the concrete strength of the prestressed coupling beam reaches 90% of the design strength, a wire threading machine is used to pull the steel strands through the corrugated pipe sleeve, and jacks are used for three-stage tensioning. First, the initial tension is about 20% of the design control stress to eliminate the friction of the duct and straighten the steel strands. Then, the second tension is applied and continuously loaded to 50% of the design control stress. Finally, the load is applied in stages to 100% and over-tensioned to 105% of the design control stress and held for 5 minutes to ensure effective establishment of prestress. After the tensioning is completed, high-strength bolts are immediately used to fasten the anchor plate of the rear anchor of the prestressed coupling beam to the bearing steel plate of the rear cap beam.

[0037] Step 6, sealing of the rear node: At the connection node on the side of the rear cap beam (i.e., the tensioning end of the prestressed steel bar), a U-shaped steel plate is used to cover the joint of the tightened bolted connection area and fully welded to form a continuous and sealed cavity. Epoxy resin mortar is poured into the cavity to achieve rigid sealing and force transmission of the rear node. After the rear node is sealed, within 48 hours after tensioning, the excess exposed steel strands are cut off, and epoxy resin anti-rust paint is applied to the surface of the anchor for temporary protection. Then, vacuum-assisted grouting is used to densely fill the corrugated pipe sleeve.

[0038] Step 7, front row node filling: inject non-shrink epoxy grout into the corrugated pipe sleeve termination cavity (cavity length 200mm) on the front row crown beam side (i.e. prestressed steel reinforcement embedded end), lay a 30mm thick rubber pad in the groove, pour 40mm thick non-shrink mortar in layers and vibrate to compact to form a flexible deformation compensation seal.

[0039] In this embodiment, the steel template wall thickness of the front crown beam groove is 6mm. The groove dimensions are as follows: the length L (along the crown beam axis) is adapted to the width of the prestressed connecting beam and a 20mm space is reserved for deformation release on both sides, i.e., length L = width of prestressed connecting beam + 40mm; the width W (along the crown beam height) is adapted to the height of the prestressed connecting beam and a 20mm embedding allowance is reserved, i.e., width W = height of prestressed connecting beam + 20mm; the depth D must include a 30mm rubber pad, a 40mm non-shrink mortar, and a 20mm error compensation, i.e., D ≥ 90mm.

[0040] The hybrid node double-row pile-supported prestressed coupling beam construction method of the present invention firstly involves constructing double-row piles, then threading and tensioning prestressed steel strands within the coupling beam to apply prestress to the double-row pile retaining structure itself, without relying on external soil. A pre-set groove and flexible buffer layer are installed in the front row cap beam, while a prestressed steel strand system is configured inside the coupling beam, forming a rigid connection with the rear row cap beam. This effectively controls pile top displacement and improves the stress state of the node. This hybrid node double-row pile-supported prestressed coupling beam construction method has the following beneficial effects:

[0041] (1) By actively applying reverse loads through prestressed steel strands, the traditional passively bent connecting beam is transformed into a prestressed load-bearing body, thereby actively constraining the pile top displacement and effectively improving the overall stiffness and displacement control capability of the double-row pile support system.

[0042] (2) A “flexible front and rigid rear” node stress system is constructed between the two ends of the prestressed connecting beam and the front and rear cap beams. At the same time, prestress is applied inside the prestressed connecting beam and tensioned in stages. The flexible hinge structure of the front cap beam releases the temperature deformation and differential settlement stress, and the rigid force transmission of the stud steel plate of the rear cap beam ensures the effective transmission of prestress. The “flexible front and rigid rear” hybrid node design effectively solves the stress concentration problem caused by the rigid connection between the connecting beam and the cap beam, and improves the overall stiffness, structural stability and durability of the double-row pile support system.

[0043] (3) By forming an internal force self-balancing system together with the prestressed connecting beam and the "front flexible and rear rigid" node, the front and rear piles and the prestressed connecting beam are tightly coupled into a high-strength overall frame, so that it can independently bear the lateral earth pressure of the foundation pit without relying on external anchor cables or internal supports, thus broadening the application boundary of unsupported support technology in engineering practice and achieving effective shortening of the project period and optimization of comprehensive costs.

[0044] The above-mentioned construction method for prestressed coupling beams with double-row pile support at mixed nodes is suitable for deep foundation pit projects with strict deformation control requirements.

[0045] The construction steps for the front-row crown beam in step 2 are as follows: Figure 1As shown, the outline of the front capping beam is precisely marked on the top of the front piles, and the edge line of the groove opening is marked on the starting end face of the front capping beam (i.e., the side connected to the connecting beam). The side formwork of the capping beam is erected and the customized groove steel formwork is installed simultaneously. The groove steel formwork is bolted to the side formwork of the capping beam. Then the steel reinforcement cage is tied, and the fixed end anchor assembly (including anchor plate and matching spiral reinforcing steel) is pre-embedded at the designed position below the groove. The fixed end anchor assembly is firmly connected to the main reinforcement of the front capping beam. Concrete is poured in layers, and the groove area and the area around the fixed end anchor assembly are vibrated with a small vibrator to assist in compaction. After the concrete has initially set, the side formwork of the capping beam and the groove steel formwork are removed, and the concrete inside the groove and around the fixed end anchor assembly is mechanically roughened to form a uniform and rough reliable stress interface.

[0046] The construction steps for the rear crown beam in step 3 are as follows: Figure 2 As shown, the outline of the rear capping beam and the installation position of the bearing steel plate are accurately marked on the top of the rear piles; the side formwork of the capping beam is erected and the bearing steel plate is simultaneously anchored to the pile head reinforcement through temporary support frames and bolts. The bearing steel plate has through holes reserved for the later installation of high-strength bolts; then the main reinforcement and stirrups of the capping beam are tied, and the bearing steel plate is fully welded to the main reinforcement of the capping beam to form a permanent connection and the temporary support frame is removed; the concrete is poured in layers; after the concrete has set, the side formwork of the capping beam is removed, the protective film and laitance are removed, and the bearing surface of the clean bearing steel plate is exposed.

[0047] In step 3, before pouring the concrete for the rear cap beam in layers, the following steps are also included: welding shear studs to the surface of the pressure-bearing steel plate, with the cap beam stirrups running around the shear studs; filling the template joints with closed-cell foam sealing strips; and covering the surface of the pressure-bearing steel plate with a PE protective film.

[0048] The corrugated pipe body is a multi-channel metal corrugated pipe, through which 1860MPa grade low-relaxation steel strands are inserted.

[0049] The bearing steel plate is ≥20mm thick and has a cross-sectional dimension that is 1.2 times that of the connecting beam cross-section; the shear studs on the surface of the steel plate are Φ16@150mm and arranged in double rows in an alternating pattern.

[0050] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the scope of the claims.

Claims

1. A construction method for a prestressed coupling beam supported by double-row piles at hybrid nodes, characterized in that, The steps are as follows: Step 1: Constructing the front and rear rows of piles; Step 2: Pour concrete for the front cap beam and the groove, and pre-embed the fixed end anchor assembly below the groove; Step 3: Pour the concrete for the rear cap beam, and fix the bearing steel plate at the top of the rear cap beam to the main reinforcement of the cap beam; Step 4: Lay and tie the steel reinforcement cage of the prestressed coupling beam, and simultaneously embed and install the corrugated pipe sleeve. The corrugated pipe sleeve is arranged along the span direction of the prestressed coupling beam and in a parabolic manner according to the design bending moment envelope diagram; erect the side formwork of the coupling beam, pre-embed anchors at one end near the rear cap beam, and pour the concrete of the prestressed coupling beam in layers. Step 5: After the concrete strength of the prestressed coupling beam reaches 90% of the design strength, the steel strands are threaded into the corrugated pipe sleeve and tensioned in three stages; after tensioning is completed, the anchor end plate of the prestressed coupling beam anchor is fastened to the bearing steel plate of the rear cap beam. Step 6: For the connection node on one side of the rear crown beam, use a U-shaped steel plate to cover the joint of the tightened bolt connection area and fully weld it to form a continuous and sealed cavity. Fill the cavity with epoxy resin mortar; after the connection node is sealed, fill it with a corrugated pipe sleeve. Step 7: Inject non-shrink epoxy grout into the termination cavity of the corrugated pipe sleeve near the front crown beam, lay a rubber pad in the groove, pour non-shrink mortar in layers and vibrate to compact it to form a flexible deformation compensation seal.

2. The construction method for prestressed coupling beams with hybrid node double-row pile support according to claim 1, characterized in that: In step 2, the outline of the front cap beam is marked on the top of the front piles, and the groove opening edge line is marked on the starting end face of the front cap beam; the cap beam side template is erected and the customized groove steel template is installed simultaneously, and the groove steel template is bolted to the cap beam side template; then the steel reinforcement skeleton is tied, and the fixed end anchor assembly is pre-embedded at the designed position below the groove, and the fixed end anchor assembly is firmly connected to the main reinforcement of the front cap beam; The concrete was poured in layers, and the side formwork of the cap beam and the grooved steel formwork were removed after the concrete had initially set.

3. The construction method for prestressed coupling beams with hybrid node double-row pile support according to claim 1, characterized in that: In step 3, the outline of the rear crown beam and the installation position of the pressure-bearing steel plate are marked on the top of the rear piles; Erect the side formwork of the capping beam and simultaneously anchor the bearing steel plate to the pile head reinforcement through temporary support frame and bolts. Then tie the main reinforcement and stirrups of the capping beam, fully weld the bearing steel plate to the main reinforcement of the capping beam to form a permanent connection and remove the temporary support frame; pour concrete in layers; remove the side formwork of the capping beam after the concrete has set.

4. The construction method for prestressed coupling beams with hybrid node double-row pile support according to claim 1, characterized in that: In step 4, the corrugated pipe sleeve terminates 200mm from the end face of the front row crown beam, and a spiral reinforcement mesh is installed in the prestressed anchorage section area near the end face of the rear row crown beam for local reinforcement.

5. The construction method for prestressed coupling beams with hybrid node double-row pile support according to claim 1, characterized in that: In step 3, before pouring the concrete for the rear cap beam in layers, the following steps are also included: welding shear studs to the surface of the pressure-bearing steel plate, with the cap beam stirrups running around the shear studs; filling the template joints with closed-cell foam sealing strips; and covering the surface of the pressure-bearing steel plate with a PE protective film.

6. The construction method for prestressed coupling beams with hybrid node double-row pile support according to claim 1, characterized in that: The corrugated sleeve is a multi-channel metal corrugated pipe.

7. The construction method for prestressed coupling beams with hybrid node double-row pile support according to claim 1, characterized in that: In step 7, the length of the termination cavity of the corrugated sleeve is 200mm.

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