A deep foundation pit support system and its construction method

Abstract

This invention relates to a deep foundation pit support system and construction method in the technical field of building construction. The support system includes a retaining portion located on the sidewall of the foundation pit and a supporting portion located inside the foundation pit. The retaining portion includes an inner support pile, an outer support pile, and a water-stop curtain arranged in a row. The supporting portion includes an upper inner support beam and a lower inner support beam. A capping beam is provided at the top of the inner support piles. The periphery of the upper inner support beam is connected to the capping beam. A waist beam is provided in the middle of the inner support piles. The periphery of the lower inner support beam is connected to the waist beam. Several column piles are vertically connected to the upper and lower inner support beams in the direction of gravity. A trestle bridge for vehicles is provided on one side of the upper and lower inner support beams. The construction method adopts a lowering auxiliary device. Since this system eliminates the use of internal support steel pipes, and optimizes the lattice column guiding device and construction process, the cost and construction difficulty of the foundation pit project are reduced.

Description

Technical Field

[0001] This invention relates to a deep foundation pit support system and its construction method, belonging to the technical field of building construction. Background Technology

[0002] With the rapid development of my country's market, the demand for various construction projects continues to increase, leading to a surge in the number of such projects and placing higher demands on construction project management. Deep foundation pit construction is a crucial component of many construction projects, and its effectiveness directly impacts the project's long-term usability. Therefore, it is essential to establish a scientific foundation pit support system, continuously optimize key technical applications, effectively reduce construction costs, and improve support performance. As building scale continues to increase and construction technologies become increasingly sophisticated, construction companies must pay sufficient attention to various construction techniques, especially for ultra-deep foundation pit projects exceeding a certain scale. Ensuring safety is paramount to effectively promote industry development and build higher-quality buildings.

[0003] One of the most common support methods for deep foundation pits is the internal support scheme using steel pipe bracing. This scheme requires a large number of temporary steel pipe supports, which are long, consume a lot of materials, and involve a large amount of hoisting work during support construction. The installation of a large number of temporary steel pipe internal supports increases the cost of foundation pit projects, is not conducive to the conservation of social resources, and the removal of temporary supports not only affects the construction period but also has an adverse impact on the environment. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention provides a deep foundation pit support system and its construction method.

[0005] The technical solution of the present invention is as follows:

[0006] A deep foundation pit support system includes a retaining section located on the sidewall of the foundation pit and a supporting section located inside the foundation pit. The retaining section includes an inner support pile, an outer support pile, and a water-stop curtain arranged in a row. The supporting section includes an upper inner support beam and a lower inner support beam. A capping beam is provided at the top of the inner support piles. The periphery of the upper inner support beam is connected to the capping beam. A waist beam is provided in the middle of the inner support piles. The periphery of the lower inner support beam is connected to the waist beam. Several column piles are vertically connected to the upper and lower inner support beams in the direction of gravity. A trestle bridge is provided on one side of the upper and lower inner support beams. The trestle bridge leads from the ground to the bottom of the foundation pit in a sloping manner.

[0007] The inner support piles are made of concrete, the water-stop curtain is a three-axis cement-soil mixing pile, the outer support piles are high-pressure double-pipe jet grouting piles, the inner support piles are located inside the outer support piles and the two are alternately distributed to form a continuous support pile row, and the water-stop curtain is located outside the continuous support pile row.

[0008] The upper perimeter of the crown beam is sloped, and a shotcrete slope is provided on the slope. An expansion joint is opened at intervals along the direction of the pit wall for the shotcrete slope.

[0009] It also includes several dewatering wells, each consisting of a steel well pipe, a filter pipe, and a sedimentation pipe connected end to end. The filter pipe has pipe walls with holes arranged in a quincunx pattern. The filter pipe and sedimentation pipe are filled with a gravel filter layer on the outside, and the outer wall of the filter pipe is covered with a filter screen.

[0010] The pit has a drainage ditch and a water collection tank circumferentially formed around its bottom surface, with the drainage ditch flowing into the water collection tank.

[0011] The column pile is composed of a steel lattice column, a pile reinforcement cage, and pile concrete. The steel lattice column and the reinforcement cage are pre-connected and fixed, and the pile concrete is connected to the steel lattice column and the reinforcement cage through subsequent pouring.

[0012] The trestle bridge is a concrete trestle bridge with two stair sections. The first stair section is connected to the lower inner support beam by an upper inner support beam, and the second stair section is connected to the bottom of the pit by a lower inner support beam. An intermediate platform is set at the junction of the first and second stair sections, and a bottom platform is set at the junction of the second stair section and the bottom of the pit. The bridge deck of the trestle bridge is arranged for two lanes.

[0013] The upper inner support beam and the lower inner support beam have the same structure, each including edge truss beams arranged in a ring around the shape of the foundation pit. Several opposing truss beams are arranged between the edge truss beams, and corner truss beams are arranged at the corners of the edge truss beams and the foundation pit wall and the corners of the opposing truss beams.

[0014] A construction method for a deep foundation pit support system includes the following construction steps:

[0015] The first step is to measure and set out the ground, excavate the initial pit, and set up the edge with slope and construct shotcrete slope protection.

[0016] The first step is to construct the internal support piles and column piles;

[0017] The first step is to construct the water-stop curtain after the internal support piles have been cured to 70% of their design strength.

[0018] The first step is to construct the external support piles after the water-stop curtain has been cured to 70% of its design strength.

[0019] The first step is to construct dewatering wells and carry out pre-dewatering after the external support piles have been cured to 70% of their design strength;

[0020] The first step is to excavate the slope to the bottom elevation of the cap beam, and then construct the cap beam and the upper inner support beam;

[0021] The first step is to excavate in layers until the upper inner support beam reaches 80% of its design strength, then excavate to the bottom elevation of the lower inner support beam; and construct the first section of the trestle bridge.

[0022] The first step is to construct the wainscoting and the lower inner support beam;

[0023] First, after the strength of the waist beam and the lower inner support beam reaches 80% of the design strength, excavate in layers to the bottom of the pit; then construct the second section of the trestle bridge.

[0024] The first step is to excavate the pit within the pit and construct the base slab, drainage ditch, and water collection trough.

[0025] In the first step, the construction column pile, including the steel lattice column and the pile reinforcement cage, is lowered into the column pile hole. This step is assisted by a lowering auxiliary device.

[0026] The lowering auxiliary device includes an annular mounting plate with ear plates on its four sides. Each ear plate has adjustable feet that can be threaded. Mounting grooves are formed on both sides of the inner edge of the annular mounting plate. Guide groove plates perpendicular to the annular mounting plate are fixedly connected within these grooves. The guide groove plates have guide slots, with the spacing between the two sides wider at the top and narrower at the bottom, transitioning to a sloping middle. A guide wheel positioning mechanism is movably mounted on the guide groove plate. The guide wheel positioning mechanism includes an H-shaped guide wheel frame with an inner opening that rotates. Two right-angled grooved guide wheels are installed with vertical spacing. A sliding pin is inserted through the outer opening of the H-shaped guide wheel frame and is embedded in the guide groove. Two contact springs with vertical spacing are fixedly installed on the outer opening wall of the H-shaped guide wheel frame. The other end of the contact springs abuts against the side of the guide groove plate. A magnet that can magnetically attract the contact springs is embedded in the upper side of the guide groove plate. Contact rods are fixedly installed on both outer walls of the H-shaped guide wheel frame. Contact steel bars that can interfere with and abut against the contact rods are welded to the upper end of the steel lattice column of the column pile.

[0027] When using the lowering auxiliary device, first place the device horizontally above the column pile hole. Then, temporarily fix the guide wheel positioning mechanisms on both sides to the upper end of the guide groove plate by magnetic attraction. Next, use lifting equipment to vertically hoist the steel lattice column and pile reinforcement cage to the top of the column pile hole and slowly lower them. The pile reinforcement cage and steel lattice column pass through the guide wheel positioning mechanisms on both sides one after the other. When the upper end of the pile reinforcement cage is lowered to the vicinity of the guide wheel positioning mechanism, the contact steel bar at the upper end of the pile reinforcement cage interferes with the contact rod of the guide wheel positioning mechanism on both sides, causing the guide wheel positioning mechanism to disengage from the magnetic attraction and slide down to the lower end of the guide groove plate. As the distance between the guide grooves on both sides narrows, the guide wheel positioning mechanisms on both sides adhere to the vertical edges of the steel lattice column on both sides and constrain the verticality of the steel lattice column. At this time, continue to lower the steel lattice column and pile reinforcement cage until the contact steel bar at the upper end of the pile reinforcement cage interferes with the contact rod of the guide wheel positioning mechanism on both sides again. Finally, adjust the elevation of the steel lattice column by the four corner supports to complete the placement and positioning of the steel lattice column.

[0028] The present invention has the following beneficial effects:

[0029] This invention discloses a deep foundation pit support system employing a cast-in-place pile row + reinforced concrete internal bracing system construction technology. This includes optimized design of the internal bracing structure, fabrication of the lattice column guiding device, improvements to the lattice column positioning construction process and measures, and measures for controlling the verticality of the lattice columns. Because this system eliminates the need for internal bracing steel pipes and optimizes the lattice column guiding device and construction process, it reduces the cost and construction difficulty of foundation pit projects. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a deep foundation pit support system structure according to the present invention;

[0031] Figure 2 This is a schematic diagram of the retaining structure of a deep foundation pit support system according to the present invention;

[0032] Figure 3 This is a schematic diagram of a trestle structure for a deep foundation pit support system according to the present invention;

[0033] Figure 4 This is a bird's-eye view structural diagram of the upper inner support beam and the lower inner support beam of a deep foundation pit support system according to the present invention.

[0034] Figure 5 This is a schematic diagram of a dewatering well structure for a deep foundation pit support system according to the present invention;

[0035] Figure 6-10 This is a schematic diagram of the construction method for a deep foundation pit support system according to the present invention;

[0036] Figure 11 This is a schematic diagram of the hoisting and lowering construction of traditional steel lattice columns;

[0037] Figure 12 This is a schematic diagram of the lowering auxiliary device structure of a deep foundation pit support system according to the present invention;

[0038] Figure 13 This is a schematic diagram of the annular mounting plate structure of the lowering auxiliary device for a deep foundation pit support system according to the present invention.

[0039] Figure 14 This is a partial structural schematic diagram of a lowering auxiliary device for a deep foundation pit support system according to the present invention;

[0040] Figure 15 This is a partial overhead view of the lowering auxiliary device of a deep foundation pit support system according to the present invention. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] See Figure 1-5 A deep foundation pit support system includes a retaining portion located on the sidewall of the foundation pit and a supporting portion located inside the foundation pit.

[0044] The retaining structure includes an inner support pile 10, an outer support pile 30, and a water-stop curtain 20 arranged in a row. The inner support pile 10 is made of concrete, the water-stop curtain 20 is a three-axis cement-soil mixing pile, and the outer support pile 30 is a high-pressure double-pipe jet grouting pile. The inner support pile 10 is located inside the outer support pile 30, and the two are alternately distributed to form a continuous support pile row. The water-stop curtain 20 is located outside the continuous support pile row.

[0045] The supporting part includes an upper inner support beam 40 and a lower inner support beam 50. The upper inner support beam 40 and the lower inner support beam 50 have the same structure. Each of them includes edge truss beams 451 that are attached to the shape of the foundation pit and arranged in a ring. Several opposing truss beams 452 are arranged between the edge truss beams 451. Corner bracing truss beams 453 are arranged at the corners of the edge truss beams 451 and the foundation pit wall and at the corners of the opposing truss beams 452.

[0046] The top of the inner support pile 10 is provided with a cap beam 60, and the periphery of the upper inner support beam 40 is connected to the cap beam 60. The middle of the inner support pile 10 is provided with a waist beam 70, and the periphery of the lower inner support beam 50 is connected to the waist beam 70. The upper inner support beam 40 and the lower inner support beam 50 are vertically connected to several column piles 80 in the direction of gravity. The column pile 80 is composed of a steel lattice column 81, a pile reinforcement cage 82, and pile concrete 83. The steel lattice column 81 and the reinforcement cage 82 are pre-connected and fixed, and the pile concrete 83 is connected to the steel lattice column 81 and the reinforcement cage 82 by later pouring.

[0047] The perimeter above the cap beam 60 is sloped, and a shotcrete slope protection 100 is installed on the slope. The shotcrete slope protection 100 uses an 80mm thick C20 fine stone surface and is reinforced with φ6@200x200 steel mesh. An expansion joint is opened at intervals along the pit wall direction of the shotcrete slope protection 100. Asphalt hemp rope or asphalt-coated wood board is filled along the three sides of the joint to a depth of not less than 200mm.

[0048] A trestle bridge 90 is installed on one side of the upper inner support beam 40 and the lower inner support beam 50. The trestle bridge 90 leads from the ground to the bottom of the foundation pit in a sloping manner. The trestle bridge 90 is a concrete trestle bridge with two stair sections. The first stair section 91 connects the upper inner support beam 40 to the lower inner support beam 50, and the second stair section 92 connects the lower inner support beam 50 to the bottom of the foundation pit. An intermediate platform 93 is set at the junction of the first stair section 91 and the second stair section 92, and a bottom platform 94 is set at the junction of the second stair section 92 and the bottom of the foundation pit. The bridge deck of the trestle bridge 90 is arranged for two lanes.

[0049] It also includes several dewatering wells 120. Each dewatering well 120 includes a steel well pipe 121 connected end to end, a filter pipe 122 and a sedimentation pipe 123. The filter pipe 122 has pipe holes 124 arranged in a quincunx pattern on its pipe wall. The filter pipe 122 and the sedimentation pipe 123 are filled with a sand and gravel filter layer 125 on their outer side. The outer wall of the filter pipe 122 is covered with a filter screen 126.

[0050] A drainage ditch 130 and a water collection trough 140 are circumferentially formed around the bottom surface of the foundation pit, with the drainage ditch 130 flowing into the water collection trough 140.

[0051] like Figure 6-10 As shown, based on the support system of Embodiment 1 above, the present invention also discloses a construction method for a deep foundation pit support system, including the following construction steps:

[0052] Step 1: Surveying and setting out, excavating the initial pit on the ground, setting the edge with slope and constructing a 100mm shotcrete slope protection;

[0053] Step 2: Construct internal support piles 10 and column piles 80;

[0054] Step 3: After the internal support piles 10 have been cured to 70% of their design strength, construct the water-stop curtain 20.

[0055] Step 4: After the water-stop curtain 20 has been cured to 70% of its design strength, construct the external support piles 30.

[0056] Step 5: After the external support piles have been cured to 70% of their design strength, construct the dewatering wells and carry out pre-dewatering.

[0057] Step 6: Then excavate the slope to the bottom elevation of the cap beam 60, and construct the cap beam 60 and the upper inner support beam 40;

[0058] Step 7: After the upper inner support beam 40 reaches 80% of its design strength, excavate in layers to the bottom elevation of the lower inner support beam 50; construct the first section 91 of the trestle bridge 90.

[0059] Step 8: Construct the wainscoting 70 and the lower inner support beam 50;

[0060] Step 9: After the strength of the waist beam 70 and the lower inner support beam 50 reaches 80% of the design strength, excavate in layers to the bottom of the pit; construct the second section of the trestle bridge 90.

[0061] Step 10: Excavate the pit within the pit and construct the bottom slab cushion layer 110, drainage ditch 130 and water collection trough 140.

[0062] Example 2

[0063] In actual construction applications, in step 2 of embodiment 1 above, the construction column pile 80, including the steel lattice column 81 and the pile reinforcement cage 82, is lowered into the column pile hole. For example... Figure 11 The diagram illustrates the traditional construction method for hoisting and lowering steel lattice columns. When the steel lattice column 81 and the pile reinforcement cage 82 are hoisted and lowered using hoisting equipment, the verticality of the steel lattice column 81 is monitored using a theodolite and manually controlled during the lowering process. Even after lowering, the steel lattice column 81 cannot be completely lowered because its weight is significant and the hole depth far exceeds its length. Lowering it would cause it to sink continuously, ultimately leading to the failure of the vertical support system. The traditional method involves placing the lower end of the steel lattice column 81 into the pile according to design requirements and using pre-drilled hoisting holes on the column to suspend it at the designed height using steel beams. The beams are removed only after the concrete has reached its final set. This method involves separate steps for vertical positioning and elevation determination of the steel lattice column 81, which is not only difficult to operate but also inefficient.

[0064] Based on this, this embodiment discloses a lowering assistance device 200, such as... Figure 12-15As shown, the lowering auxiliary device 200 includes an annular mounting plate 210. Ear plates 211 are provided around the annular mounting plate 210, and each ear plate 211 has a support foot 212 that can be adjusted in height via threads. Mounting grooves 213 are formed on both sides of the inner edge of the annular mounting plate 210. A guide groove plate 220 perpendicular to the annular mounting plate 210 is fixedly connected within the mounting groove 213. The guide groove plate 220 has guide grooves 221, with the spacing between the two guide grooves 221 being wider at the top and narrower at the bottom, transitioning to a sloping middle. A guide wheel positioning mechanism 230 is movably mounted on the guide groove plate 220. Because the radial dimension of the pile reinforcement cage 82 is larger than the radial dimension of the steel lattice column 81, and the pile reinforcement cage 82 needs to pass through the guide wheel positioning mechanism 230 first, the guide groove 221 is designed with an irregular shape to allow for clearance when the pile reinforcement cage 82 passes underneath. The function is to avoid interference with the guide wheel positioning mechanism 230 on both sides; the guide wheel positioning mechanism 230 includes an H-shaped guide wheel frame 231, with two right-angle groove guide wheels 232 rotatably mounted on the inner opening of the H-shaped guide wheel frame 231, and a sliding pin 234 passing through the outer opening of the H-shaped guide wheel frame 231. The sliding pin 234 is embedded in the guide groove 221. Two contact springs 235 are fixedly installed on the outer opening wall of the H-shaped guide wheel frame 231, with the other end of the contact spring 235 abutting against the side of the guide groove plate 220. A magnet 240 that can magnetically attract the contact spring 235 is embedded in the upper side of the guide groove plate 220. Contact rods 233 are fixedly installed on the outer walls of both sides of the H-shaped guide wheel frame 231. A contact steel bar 84 that can interfere with and abut against the contact rod 233 is welded to the upper end of the steel lattice column 81 of the column pile 80.

[0065] A lowering auxiliary device 200 is used to assist in the lowering of the steel lattice column 81 and the pile reinforcement cage 82. The specific operation method is as follows:

[0066] When using the lowering auxiliary device 200, first place the device horizontally above the column pile hole. Then, temporarily fix the guide wheel positioning mechanisms 230 on both sides to the upper end of the guide groove plate 220 by magnets 240. Next, use lifting equipment to vertically hoist the steel lattice column 81 and the pile reinforcement cage 82 above the column pile hole and slowly lower them into the pile hole. The pile reinforcement cage 82 and the steel lattice column 81 pass through the guide wheel positioning mechanisms 230 on both sides. When the upper end of the pile reinforcement cage 82 is lowered to the vicinity of the guide wheel positioning mechanism 230, the contact steel bar 84 at the upper end of the pile reinforcement cage 82 contacts the guide wheel positioning mechanisms 230 on both sides. The contact rod 233 interferes and abuts, causing the guide wheel positioning mechanism 230 to disengage from the magnetic attraction and slide down to the lower end of the guide groove plate 220. As the distance between the guide grooves 221 on both sides narrows, the guide wheel positioning mechanisms 230 on both sides attach to the vertical edges on both sides of the steel lattice column 81 and constrain the verticality of the steel lattice column 81. At this time, the steel lattice column 81 and the pile reinforcement cage 82 are lowered until the contact reinforcement 84 at the upper end of the pile reinforcement cage 82 interferes and abuts with the contact rod 233 of the guide wheel positioning mechanism 230 on both sides again. Finally, the elevation of the steel lattice column 81 is adjusted by the support feet 212 at the four corners to complete the placement and positioning of the steel lattice column 81.

[0067] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A construction method for a deep foundation pit support system, characterized in that, The construction steps include the following: Step 1: Survey and layout, excavate the initial pit on the ground, set up the edge with slope and construct sprayed concrete slope protection (100). Step 2: Construct internal support piles (10) and column piles (80). Step 3: After the internal support piles (10) have been cured to 70% of their design strength, construct the water-stop curtain (20). Step 4: After the water-stop curtain (20) has been cured to 70% of its design strength, construct the external support piles (30). Step 5: After the external support piles (30) have been cured to 70% of their design strength, construct the dewatering wells (120) and carry out pre-dewatering. Step 6: Then excavate the slope to the bottom elevation of the cap beam (60) and construct the cap beam (60) and the upper inner support beam (40). Step 7: After the strength of the upper inner support beam (40) reaches 80% of the design strength, excavate in layers to the bottom elevation of the lower inner support beam (50); construct the first section (91) of the trestle bridge (90). Step 8: Construct the wainscoting (70) and the lower inner support beam (50); Step 9: After the strength of the waist beam (70) and the lower inner support beam (50) reaches 80% of the design strength, excavate in layers to the bottom of the pit; construct the second section of the trestle bridge (90); Step 10: Excavate the pit within the pit and construct the bottom slab cushion layer (110), drainage ditch (130) and water collection trough (140). In step 2, the construction column pile (80) including the steel lattice column (81) and the pile reinforcement cage (82) is lowered into the column pile hole. This step is assisted by a lowering auxiliary device (200). The lowering auxiliary device (200) includes an annular mounting plate (210), with ear plates (211) arranged around its perimeter. Each ear plate (211) has a support foot (212) that can be adjusted in height via a thread. Mounting grooves (213) are provided on both sides of the inner edge of the annular mounting plate (210). A guide groove plate (220) perpendicular to the annular mounting plate (210) is fixedly connected within the mounting groove (213). The guide groove plate (220) has guide grooves (221) with the spacing between the two guide grooves (221) being wider at the top and narrower at the bottom, transitioning to a sloping middle. A guide wheel positioning mechanism (230) is movably mounted on the guide groove plate (220). The guide wheel positioning mechanism (230) includes an H-shaped guide wheel frame (231). Two right-angle groove guide wheels (232) with vertical spacing are rotatably installed on the inner opening. A sliding pin (234) is provided through the outer opening of the H-shaped guide wheel frame (231). The sliding pin (234) is embedded in the guide groove (221). Two contact springs (235) with vertical spacing are fixedly provided on the outer opening wall of the H-shaped guide wheel frame (231). The other end of the contact spring (235) abuts against the side of the guide groove plate (220). A magnet (240) that can magnetically attract the contact spring (235) is embedded in the upper side of the guide groove plate (220). Contact rods (233) are fixedly provided on the outer walls of both sides of the H-shaped guide wheel frame (231). A contact steel bar (84) that can interfere with and abut against the contact rod (233) is welded to the upper end of the steel lattice column (81) of the column pile (80). When the lowering auxiliary device (200) is used during construction, it is first horizontally placed above the column pile hole. Then, the guide wheel positioning mechanisms (230) on both sides are temporarily fixed to the upper end of the guide groove plate (220) by magnets (240). Then, the steel lattice column (81) and the pile reinforcement cage (82) are vertically hoisted to the upper end of the column pile hole by the hoisting equipment and slowly lowered into the pile hole. The pile reinforcement cage (82) and the steel lattice column (81) pass through the guide wheel positioning mechanisms (230) on both sides one after the other. When the upper end of the pile reinforcement cage (82) is lowered to the vicinity of the guide wheel positioning mechanism (230), the contact steel bar (84) at the upper end of the steel lattice column (81) contacts the guide wheel positioning mechanisms (230) on both sides. The contact rod (233) interferes and abuts, causing the guide wheel positioning mechanism (230) to disengage from the magnetic attraction and slide down to the lower end of the guide groove plate (220). As the distance between the two guide grooves (221) narrows, the two guide wheel positioning mechanisms (230) attach to the vertical edges of the steel lattice column (81) and constrain the verticality of the steel lattice column (81). At this time, the steel lattice column (81) and the pile reinforcement cage (82) are continuously lowered until the contact reinforcement (84) at the upper end of the steel lattice column (81) interferes and abuts with the contact rod (233) of the two guide wheel positioning mechanisms (230) again. Finally, the elevation of the steel lattice column (81) is adjusted by the support feet (212) at the four corners to complete the placement and positioning of the steel lattice column (81).

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