Foundation pit pile wall integrated structure under complex conditions

Abstract

This invention relates to the technical field of foundation pit support, and discloses an integrated pile-wall structure for foundation pits under complex conditions. The structure includes a diaphragm wall and cast-in-place piles. Multiple cast-in-place piles are located at the bottom of the diaphragm wall and are connected to it as a whole, forming an integrated pile-wall structure. The diaphragm wall is located in a diaphragm wall trench, and the cast-in-place piles are located in pile holes extending downwards from the bottom of the trench into the slightly weathered rock layer. The pile holes are connected to the trench. Using cast-in-place piles under the wall instead of embedding the diaphragm wall into the slightly weathered rock layer significantly reduces the difficulty and workload of trenching in hard rock strata. It reduces disturbance to the upper soft soil layer, lowering the probability of borehole collapse and surrounding settlement. It also reduces the requirements for trenching equipment and processes, decreases equipment wear and tear, improves trenching efficiency, lowers construction costs, and facilitates the smooth progress of the project.

Description

Technical Field

[0001] This invention patent relates to the technical field of foundation pit support, and more specifically, to an integrated pile-wall structure for foundation pits under complex conditions. Background Technology

[0002] Diaphragm walls, with their advantages of high rigidity, good integrity, small deformation of the support structure, good impermeability, and strong applicability, are increasingly widely used in deep foundation pits in high-rise building basements, subway stations, and other fields. As deep foundation pit projects become increasingly complex, diaphragm wall retaining structures need to be embedded in deeper rock strata, posing significant challenges to trenching technology, construction quality, and construction progress. In the "Guangzhou-Dongguan-Shenzhen Intercity Railway Qianhai to Huanggang Port Section Project - Huanggang Port Station Frame Reverse Construction Main Retaining Structure" project, the main structure foundation pit of the open-cut section at the station's longest mileage end has an outer length of approximately 349.50m, a width of approximately 51.4m, and an average excavation depth of 39m, making it an ultra-large foundation pit located near buildings and within the subway operating area. The site strata, from top to bottom, consist of artificial fill, silty clay, silty clay, fine sand, medium-coarse sand, and sandy clay. The underlying bedrock comprises completely weathered, strongly weathered, moderately weathered, and slightly weathered granite. The maximum saturated compressive strength of the moderately weathered and slightly weathered rocks are 21.0 MPa and 58.6 MPa, respectively, with RQDs of 65% and 80%. The groundwater level is approximately 4.25 m deep, the moderately weathered rock surface is approximately 25 m deep, and the slightly weathered rock surface is approximately 30 m deep. The excavation depth into the rock is approximately 14 m, with the pit bottom primarily located in the slightly weathered granite strata. For foundation pit support under these complex geological and environmental conditions—including soft soil above, hard rock below, high groundwater level, deep pit, high rock penetration rate, and proximity to buildings and subway operating areas—diaphragm wall support technology offers significant advantages.

[0003] However, using diaphragm wall support requires penetrating at least 3 meters into the pit, with the wall extending up to 17 meters into the rock. (See details...) Figure 1 The deep penetration of the wall into the rock will result in a long trenching period, causing prolonged disturbance to the soft soil layer above, which can easily lead to borehole collapse and surrounding settlement. This not only hinders the smooth progress of construction but also poses serious safety hazards to nearby buildings and subway operations. Furthermore, the high saturated compressive strength of hard rock places high demands on trenching equipment and processes, resulting in significant equipment wear and tear, leading to low trenching efficiency, increased costs, and a substantial impact on project progress. Summary of the Invention

[0004] The purpose of this invention is to provide an integrated pile-wall structure for foundation pits under complex conditions, aiming to solve the problems of large disturbance to soft soil layers, low trenching efficiency, and high cost caused by using a single underground continuous wall method for foundation pit support under complex conditions in the prior art.

[0005] This invention is implemented as follows: an integrated pile-wall structure for foundation pits under complex conditions, comprising a diaphragm wall and cast-in-place piles, wherein multiple cast-in-place piles are located at the bottom of the diaphragm wall and are connected to the diaphragm wall to form an integrated pile-wall structure; the diaphragm wall is located in a diaphragm wall trench, the bottom of which extends to the surface of slightly weathered underground rock; the cast-in-place piles are located in cast-in-place pile holes, which extend downward from the bottom of the diaphragm wall trench to the slightly weathered underground rock layer, and the cast-in-place pile holes are connected to the diaphragm wall trench.

[0006] Furthermore, the cast-in-place pile has a pile reinforcement cage, the underground continuous wall has a wall reinforcement mesh, the top of the pile reinforcement cage extends into the wall reinforcement mesh to form an anchoring section, and the anchoring section is welded to the wall reinforcement mesh.

[0007] Furthermore, the top of the pile reinforcement cage is welded to the wall reinforcement mesh to form an integrated pile-wall reinforcement cage structure. The integrated pile-wall reinforcement cage structure includes the wall reinforcement mesh at the top and multiple pile reinforcement cages at the bottom. During construction, the integrated pile-wall reinforcement cage structure is first erected and then lowered into the diaphragm wall trench and the grouting pile hole. Concrete is then poured to form the integrated pile-wall structure.

[0008] Furthermore, the construction of the integrated pile-wall steel cage structure includes the following steps:

[0009] S210: Fabricate the pile reinforcement cage and the wall reinforcement mesh according to the design drawings;

[0010] S220: The pile reinforcement cage is hoisted into the pile hole, then the pile reinforcement cage is vertically lifted to the opening of the diaphragm wall trench, and then the pile reinforcement cage is horizontally fixed at the opening of the trench by the horizontal support, and the center position of the pile reinforcement cage is marked on the ground at this time.

[0011] S230: Hoist the wall reinforcement mesh to the top of the slot so that the top of the pile reinforcement cage extends into the wall reinforcement mesh, and weld the anchoring section to the wall reinforcement mesh;

[0012] S240: Remove the transverse support and slowly lower the integrated pile wall steel cage structure into the diaphragm wall groove.

[0013] Furthermore, in step 230, the entire integrated structure of the pile wall reinforcement cage is lifted upwards, and then horizontally arranged fixing rods are set between adjacent pile reinforcement cages.

[0014] Furthermore, the middle of two adjacent pile reinforcement cages is provided with support members arranged opposite to each other, and the end of the fixing rod is located in the support member.

[0015] Furthermore, the support member includes a transversely arranged support groove and a longitudinally arranged fixing groove. The bottom end of the fixing groove is connected to the end of the support groove, the top end of the fixing groove is open, and the interior of the fixing groove is hollow. The fixing groove includes a fixing side for fixing the support member to the pile reinforcement cage and a notch side arranged opposite to the fixing side. The notch side is provided with a notch groove, which extends from the top end of the fixing groove to the support groove. The end of the fixing rod has a fixing head, which is movably connected in the fixing groove.

[0016] Furthermore, the size of the fixing head is greater than the width of the notch and less than the width of the hollow cavity of the fixing groove; when the fixing rod is arranged horizontally, the fixing rod is supported by the support groove, and the fixing head is located in the fixing groove.

[0017] Furthermore, the fixing groove also includes two oppositely arranged sidewalls, the two sides of which are respectively connected to the fixing side and the notch side; a baffle is also provided on the inner wall of the sidewall, the two ends of which are respectively connected to the two sidewalls, and the baffle is located above the fixing head.

[0018] Furthermore, the construction process of the diaphragm wall trench and the cast-in-place pile hole includes the following steps:

[0019] S110: The hydraulic grab bucket in the soil layer sequentially grabs the trench to the moderately weathered rock surface, forming the first trench section located in the soft soil layer;

[0020] S120: A rotary drilling rig is used to drill holes at the bottom of the first trench section to the pile bottom elevation, forming multiple grouting pile holes;

[0021] S130: At the bottom of the first trench section, the trench is milled sequentially to the wall bottom elevation, which is located above the pile bottom elevation, thereby forming a diaphragm wall trench;

[0022] S140: Clean the slag from the grouting pile holes and the diaphragm wall trench;

[0023] At the bottom of the first trench section, above the wall bottom elevation, the portion excluding the grouting pile holes forms a part to be removed; in step S130, a rotary drilling rig is used to drill a guide hole to the wall bottom elevation in the part to be removed, and then a double-wheel milling machine is used to mill the trench along the guide hole in sequence to the wall bottom elevation, thus removing the part to be removed above the wall bottom elevation.

[0024] Compared with existing technologies, the integrated pile-wall structure for foundation pits under complex conditions provided by this invention uses cast-in-place piles under the wall to replace the deep diaphragm wall construction technology embedded in slightly weathered rock layers, greatly reducing the difficulty and workload of trenching construction in hard rock strata (especially the part below slightly weathered rock layers). Since milling is not required below the slightly weathered rock surface, only the drilling of cast-in-place pile holes is needed, thus shortening the trenching time, reducing disturbance to the upper soft soil layer, lowering the probability of hole collapse and surrounding settlement, and facilitating smooth construction. At the same time, since milling is not required below the slightly weathered rock surface, the requirements for trenching equipment and processes are reduced, reducing equipment wear and tear, improving trenching efficiency, lowering construction costs, and facilitating the smooth progress of the project. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a diaphragm wall for foundation pits in existing technology;

[0026] Figure 2 This is a schematic diagram of the integrated pile-wall structure for foundation pits under complex conditions provided by the present invention;

[0027] Figure 3 This is a schematic diagram of the construction process of the integrated pile-wall structure under complex conditions provided by the present invention;

[0028] Figure 4 This is a schematic diagram of the trench excavation process for the integrated foundation pit pile wall structure under complex conditions provided by the present invention;

[0029] Figure 5 This is a schematic diagram of the initial and closing borehole drilling of the integrated foundation pit pile wall structure under complex conditions provided by the present invention.

[0030] Figure 6 This is a schematic diagram of the integrated pile-wall reinforcement cage structure of the foundation pit pile-wall integrated structure under complex conditions provided by the present invention;

[0031] Figure 7 This is a schematic diagram of the cooperation between the fixing rod and the support component of the integrated pile wall structure for foundation pits under complex conditions provided by the present invention;

[0032] Figure 8 This is a lateral schematic diagram of the cooperation between the fixing rod and the support component of the integrated pile wall structure for foundation pits under complex conditions provided by the present invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] 100-First trench section, 110-Moderately weathered rock surface, 120-Slightly weathered rock surface, 130-Poured pile hole, 140-Guide hole, 150-Diaphragm wall trench; 200-Integrated pile-wall reinforcement cage structure, 210-Pile reinforcement cage, 220-Wall reinforcement mesh, 230-Fixing rod, 231-Fixing head; 310-Poured pile, 320-Diaphragm wall, 330-Trench wall reinforcement part; 400-Supporting component, 410-Supporting trench, 420-Fixing trench, 421-Fixing side, 422-Notch side, 423-Notch trench, 424-Side wall, 425-Stop strip. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] The implementation of the present invention will be described in detail below with reference to specific embodiments.

[0037] In the accompanying drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components. In the description of this invention, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the accompanying drawings are only for illustrative purposes and should not be construed as limiting this patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0038] Reference Figure 2-8 The image shown is a preferred embodiment of the present invention.

[0039] The integrated pile-wall structure for foundation pits under complex conditions includes a diaphragm wall 320 and cast-in-place piles 310. Multiple cast-in-place piles 310 are located at the bottom of the diaphragm wall 320 and are connected to the diaphragm wall 320 to form an integrated pile-wall structure. The diaphragm wall 320 is located in a diaphragm wall trench 150, and the bottom of the diaphragm wall trench 150 extends to the underground slightly weathered rock surface 120. The cast-in-place piles 310 are located in cast-in-place pile holes 130, which extend downward from the bottom of the diaphragm wall trench 150 into the underground slightly weathered rock layer, and the cast-in-place pile holes 130 are connected to the diaphragm wall trench 150.

[0040] The integrated pile-wall structure for foundation pits under complex conditions provided in this embodiment utilizes cast-in-place piles to replace the deep diaphragm wall embedded in slightly weathered rock layers, significantly reducing the difficulty and workload of trenching in hard rock strata (especially the portion below slightly weathered rock layers). Since milling is not required below 120mm of the slightly weathered rock surface, only 130mm of cast-in-place pile holes need to be drilled, thus shortening the trenching time, reducing disturbance to the upper soft soil layer, lowering the probability of borehole collapse and surrounding settlement, and facilitating smooth construction. Simultaneously, the elimination of milling below 120mm of the slightly weathered rock surface reduces the requirements for trenching equipment and processes, decreasing equipment wear and tear, improving trenching efficiency, lowering construction costs, and promoting the smooth progress of the project.

[0041] Specifically, the diameter of the lower cast-in-place pile 310 is the same as the thickness of the upper diaphragm wall 320, so that the integrated pile-wall structure is more in line with the mechanical principles and is more robust.

[0042] Specifically, the cast-in-place pile 310 contains a pile reinforcement cage 210, and the diaphragm wall 320 contains a wall reinforcement mesh 220. The top of the pile reinforcement cage 210 extends into the wall reinforcement mesh 220, forming an anchoring section, which is welded to the wall reinforcement mesh 220. The anchoring section of the pile reinforcement cage 210 extends to a certain depth into the wall reinforcement mesh 220, ensuring a stable connection between the cast-in-place pile 310 and the diaphragm wall 320.

[0043] The top of the pile reinforcement cage 210 is welded to the wall reinforcement mesh 220 to form an integrated pile-wall reinforcement cage structure 200. The integrated pile-wall reinforcement cage structure 200 includes the wall reinforcement mesh 220 at the top and multiple pile reinforcement cages 210 at the bottom. During construction, the integrated pile-wall reinforcement cage structure 200 is first erected and then lowered into the diaphragm wall trench 150 and the grouting pile hole 130. Concrete is then poured to form the integrated pile-wall structure.

[0044] Furthermore, the construction of the integrated pile-wall steel cage structure 200 includes the following steps:

[0045] S210: Fabricate the pile reinforcement cage 210 and wall reinforcement mesh 220 according to the design drawings;

[0046] S220: The pile reinforcement cage 210 is hoisted into the grouting pile hole 130, and then the pile reinforcement cage 210 is vertically lifted to the opening of the diaphragm wall groove 150. The pile reinforcement cage 210 is then horizontally fixed in the groove opening by the horizontal support members, and the center position of the pile reinforcement cage at this time is marked on the ground, corresponding to the center of the pile hole; so that the pile reinforcement cage 210 can always be aligned with the grouting pile hole 130 below, which facilitates the subsequent hoisting and placement operation.

[0047] S230: Hoist the wall steel mesh 220 to the top of the slot so that the top of the pile steel cage 210 extends into the wall steel mesh 220, and weld the anchor section to the wall steel mesh 220.

[0048] S240: Remove the transverse support and slowly lower the integrated pile wall steel cage structure 200 into the diaphragm wall groove 150.

[0049] The above operations can be well applied to deep foundation pit support structures, which not only facilitates the overall construction of the integrated pile-wall steel cage structure 200, but also ensures that the constructed integrated pile-wall steel cage structure 200 can be accurately lowered into the diaphragm wall trench 150 and the cast-in-place pile hole 130.

[0050] Furthermore, in step 230, the integrated pile wall steel cage structure 200 is lifted as a whole, and then horizontally arranged fixing rods 230 are set between adjacent pile steel cages 210.

[0051] By setting horizontally arranged fixing rods 230 between two adjacent pile reinforcement cages 210, the adjacent pile reinforcement cages 210 can be kept in the vertical direction, preventing the adjacent pile reinforcement cages 210 from splitting into an "eight" shape during the hoisting and lowering process, which would prevent them from being inserted into the grouting pile hole 130.

[0052] In one embodiment, a horizontally arranged fixing rod 230, such as a thin steel bar, can be welded to the middle of two adjacent pile reinforcement cages 210 to maintain the vertical arrangement of the pile reinforcement cages 210 and prevent swaying and misalignment. In subsequent operations, during the lowering of the integrated pile wall reinforcement cage structure 200, the pile reinforcement cage 210 will gradually be lowered into the grouting pile hole 130. When it is lowered to a certain depth, the fixing rod 230 will encounter the slightly weathered rock layer between two adjacent grouting pile holes 130. After applying a certain force, the welded part of the fixing rod 230 will be detached under stress, so that the integrated pile wall reinforcement cage structure 200 can continue to be lowered.

[0053] In another embodiment, a support member 400 is provided in the middle of two adjacent pile reinforcement cages 210, and the end of the fixing rod 230 is located in the support member 400. By connecting the support member 400 and the fixing rod 230, the connection stability between the fixing rod 230 and the pile reinforcement cage 210 can be optimized, and it can be avoided that the pile reinforcement cage 210 will detach due to its tendency to shake during the lowering process of the integrated pile wall reinforcement cage structure 200 before it is lowered into the grouting pile hole 130.

[0054] Furthermore, the support member 400 includes a transversely arranged support groove 410 and a longitudinally arranged fixing groove 420. The bottom end of the fixing groove 420 connects to the end of the support groove 410, the top end of the fixing groove 420 is open, and the interior of the fixing groove 420 is hollow. The fixing groove 420 includes a fixing side 421 for fixing the support member 400 to the pile reinforcement cage 210 and a notch side 422 opposite to the fixing side 421. The notch side 422 is provided with a notch groove 423, which extends from the top end of the fixing groove 420 to the support groove 410. The end of the fixing rod 230 has a fixing head 231, which is movably connected in the fixing groove 420. The transversely arranged support groove 410 supports the end of the fixing rod 230, allowing the fixing rod 230 to maintain a relatively horizontal arrangement. The fixing head 231 at the end of the fixing rod 230 is movably connected to the fixing groove 420 arranged longitudinally and open at the top, which restricts the horizontal freedom of the fixing rod 230 and keeps the pile reinforcement cage 210 vertical during the lowering process. In addition, when the integrated pile wall reinforcement cage structure 200 is lowered to a certain depth, the fixing rod 230 is supported by the slightly weathered rock layer between the adjacent grouting pile holes 130, which can be easily detached and pushed out of the support member 400, thereby facilitating the continued lowering of the integrated pile wall reinforcement cage structure 200.

[0055] The size of the fixing head 231 is larger than the width of the notch 423 but smaller than the width of the hollow cavity of the fixing groove 420. The diameter of the fixing rod 230 is smaller than the width of the notch 423. When the fixing rod 230 is horizontally arranged, it is supported by the support groove 410, passes through the notch 423, and the fixing head 231 is located in the fixing groove 420. The size of the fixing head 231 is larger than the width of the notch 423, which restricts the fixing head 231 from moving horizontally out of the fixing groove 420. The size of the fixing head 231 is smaller than the width of the hollow cavity of the fixing groove 420, which allows the fixing head 231 to move up and down within the fixing groove 420.

[0056] Furthermore, the fixing groove 420 also includes two oppositely arranged side walls 424, with their two sides respectively connecting to the fixing side 421 and the notch side 422; the inner wall of the side wall 424 is also provided with a stop strip 425, with both ends of the stop strip 425 connected to the two side walls 424 respectively, and the stop strip 425 is located above the fixing head 231. The stop strip 425 can prevent the fixing head 231 from detaching from the support member 400 when the pile reinforcement cage 210 shakes slightly; when the integrated pile wall reinforcement cage structure 200 is lowered to a certain depth, the fixing rod 230 is supported by the slightly weathered rock layer between the adjacent grouting pile holes 130, and this supporting force corresponds to the gravity of the integrated pile wall reinforcement cage structure 200. The stop strip 425 is disengaged from the side wall 424 by the upward force of the fixing head 231, thereby the fixing head 231 is disengaged from the support member 400, which facilitates the continued lowering of the integrated pile wall reinforcement cage structure 200. The stress on welded connections is difficult to control, while the load-bearing capacity of the retainer 425 is easier to control. Moreover, the stress at the weld position is multi-directional, and the weld may detach due to the horizontal force. However, the support 400 restricts the horizontal force, and it is very convenient to control the upward force on the fixing head 231.

[0057] Specifically, the construction process of the diaphragm wall trench 150 and the cast-in-place pile hole 130 includes the following steps:

[0058] S110: The hydraulic grab bucket of the soil layer sequentially grabs the groove to the moderately weathered rock surface 110, forming the first groove section 100 located in the soft soil layer; the soft soil layer is above the moderately weathered rock surface 110, and the moderately weathered rock layer and slightly weathered rock layer are below it.

[0059] S120: A rotary drilling rig is used to drill holes to the bottom elevation of the pile bottom at the bottom of the first trench section 100, forming multiple grouting pile holes 130;

[0060] S130: At the bottom of the first trench section 100, the trench is milled sequentially to the bottom elevation of the wall, which is above the bottom elevation of the pile, thus forming the diaphragm wall trench 150; the bottom elevation of the wall is near the slightly weathered rock surface 120.

[0061] S140: Clean the slag and holes of the grouting pile hole 130 and the diaphragm wall trench 150;

[0062] At the bottom of the first trench section 100, above the wall bottom elevation, the portion excluding the grouting pile hole 130 forms a part to be removed; in step S130, a rotary drilling rig is used to drill a guide hole 140 to the wall bottom elevation in the part to be removed, and then a double-wheel milling machine is used to mill the trench along the guide hole 140 in sequence to the wall bottom elevation, thus removing the part to be removed above the wall bottom elevation.

[0063] During the sequential milling process, ensure that the milling wheel of the twin-wheel milling machine is within the guide hole 140. The milling wheel will mill and break the hard rock. The hydraulic system drives the mud pump to pump the mud into the trench wall. The sand suction port in the middle of the milling wheel will discharge the drilled rock debris and mud to the ground for centralized treatment. The treated mud will continue to be pumped into the trench. While the mud is circulating to remove debris, the rock is being drilled to the bottom elevation of the wall.

[0064] In another embodiment, when the lateral length of the first groove segment 100 is relatively short, the grouting pile hole above the bottom elevation of the wall is used as the guide hole, that is, the grouting pile hole above the depth of the slightly weathered rock surface is used as the guide hole for the auxiliary double wheel milling groove. The guide hole and the grouting pile hole are combined into one. At this time, in step S130, the double wheel milling machine is used to sequentially mill the groove along the grouting pile hole 130 to the bottom elevation of the wall, and the part to be removed above the bottom elevation of the wall is removed.

[0065] The construction technique of using cast-in-place piles under the wall to replace the deep diaphragm wall embedded in the slightly weathered rock layer is adopted. After the hydraulic grab bucket grabs the soil layer above the trench, the rotary drilling rig drills multiple cast-in-place pile holes 130 on the moderately weathered rock surface 110 to a distance below the bottom of the foundation pit. Among them, the holes below the depth of the slightly weathered rock surface 120 are used as cast-in-place pile holes 130. The trench is milled to the bottom elevation of the wall at the slightly weathered rock surface 120 using a double wheel milling method to complete the trenching of the wall. Then, the integrated pile and wall reinforcement cage is lowered into the trench, and finally the pile and wall concrete is poured to form an integrated pile and wall reinforced concrete support structure, which greatly reduces the difficulty and workload of trenching construction in hard rock strata.

[0066] Since the portion of the slightly weathered rock surface below 120 mm does not require milling, only 130 mm bored pile holes need to be drilled. This shortens the trenching time, reduces disturbance to the upper soft soil layer, lowers the probability of borehole collapse and surrounding settlement, and facilitates smooth construction. Furthermore, the elimination of milling below 120 mm of the slightly weathered rock surface reduces the requirements for trenching equipment and processes, decreases equipment wear and tear, improves trenching efficiency, lowers construction costs, and promotes the smooth progress of the project.

[0067] During the sequential milling process, ensure that the milling wheel of the twin-wheel milling machine is within the guide hole 140. The milling wheel will mill and break the hard rock. The hydraulic system drives the mud pump to pump the mud into the trench wall. The sand suction port in the middle of the milling wheel will discharge the drilled rock debris and mud to the ground for centralized treatment. The treated mud will continue to be pumped into the trench. While the mud is circulating to remove debris, the rock is being drilled to the bottom elevation of the wall.

[0068] In the following specific embodiment, the integrated pile-wall structure for foundation pits under complex conditions is constructed as follows:

[0069] (1) Measurement and positioning, construction of guide wall

[0070] The site was leveled and compacted using an excavator. Based on the coordinates of the plan and the elevation of the control points, the 320 axis of the diaphragm wall and the pile positions were measured, laid out, and marked.

[0071] The upper part of the trench section contains layers of poorly cohesive soil such as artificial stone filling, silty clay, and sand, which are prone to collapse under hydrodynamic conditions, making it unfavorable for the construction of the diaphragm wall trench. Therefore, the trench wall can be reinforced by driving triaxial mixing piles in advance.

[0072] After reinforcing the trench wall at the location of the slot to form the trench wall reinforcement section 330, the trench is excavated to expand the earthwork. During the trench excavation, pay attention to the alignment of the center line of the guide wall with the axis of the underground continuous wall 320. The guide wall is 20cm thick and 1m wide, and its top surface is 10cm above the ground. After the guide wall is poured with concrete and the formwork is removed, two wooden supports are added every 1m along its longitudinal direction to prevent deformation.

[0073] (2) Excavate trenches and use a soil hydraulic grab bucket to sequentially grab the trenches to the rock surface.

[0074] The standard trench section is 5.5m long and 1.2m thick. The soil trenching uses Bauer GB80S hydraulic grab buckets with a power of 280kW, a maximum lifting force of 550kN, and a maximum lifting weight (including soil) of 32t. A standard hydraulic grab bucket with a width of 2.8m and a thickness of 1.2m is selected.

[0075] To ensure the quality of the trenching and the smooth installation of the steel mesh, the first section was over-excavated by 0.7m at both ends, and then the trenching was carried out in three stages: first the two sides, then the middle, with a trenching width of 6.9m; the closed section was carried out in two stages, with a trenching width of 4.1m.

[0076] During the trench excavation, mud is pumped into the guide wall while excavating to maintain the liquid level in the trench section. At the same time, the measured value of the verticality detector on the hydraulic grab bucket is observed and the grab bucket is adjusted in time to ensure that the verticality of the trench wall meets the requirements.

[0077] (3) Move the grab bucket and drill the grouting pile hole 130 mm to the bottom elevation of the pile.

[0078] After the grab bucket reaches 110mm from the moderately weathered rock surface, the grab bucket is moved away from the construction trench section, and the rotary drilling rig is positioned to construct the grouting pile hole 130mm. This project uses a Sany SR365R rotary drilling rig with a power of 300kW and a maximum output torque of 365kN·m.

[0079] In the trench section, two 1.2m diameter grouting pile holes 130 are drilled successively on the weathered rock surface 110 to the pile bottom elevation. Two more 1.2m diameter guide holes 140 are led to the bottom elevation of the wall at both ends of the first trench section to assist in the double wheel milling of the trench.

[0080] When using a rotary drilling rig, first use the cutting tooth bucket to level the rock surface, then lower the 1.2m diameter rotary drill bit. When it is about 1m from the rock surface, lower it slowly and gently, and rotate the drill bit at a low speed (5rpm) to approach the rock surface. After contacting the rock surface, use the hoisting mode to gradually form a complete cutting groove, and then apply normal pressure to drill. Core taking and drilling are carried out alternately.

[0081] During the drilling process of the rotary drilling rig, every 2-3 meters of advance of the rotary drill bit, observe the changes of the inclinometer in the control room and check the verticality of the borehole. If any deviation is found, correct it in time. At the same time, pay attention to controlling the quality of the mud in the trench and the mud level to keep the trench wall stable.

[0082] (4) The rotary drilling rig is moved, and the twin-wheel trenching machine mills the trenches in sequence to the bottom elevation of the wall.

[0083] After drilling is completed, the rotary drilling rig is moved away from the construction trench section, and the twin-wheel trench cutter is positioned. This project uses a Bauer BCS40 twin-wheel trench cutter, with a power of 354kW, a maximum rock breaking hardness of 150MPa, and a maximum lifting force of 500kN.

[0084] The first open-width groove section is formed in three stages: first the two sides are milled, then the middle is milled, with an actual milled groove width of 6.9m; the closed-width groove section is formed in two stages, with an actual milled groove width of 4.1m.

[0085] During construction, ensure that the milling wheel is within the guide hole 140. The milling wheel will mill and break the hard rock. The hydraulic system drives the mud pump to pump the mud into the trench to protect the wall. The sand suction port in the middle of the milling wheel will discharge the drilled rock debris and mud to the ground for centralized treatment. The treated mud will continue to be pumped into the trench. While the mud is circulating to remove debris, the rock is drilled to the bottom elevation of the wall.

[0086] During construction, the verticality of the slot is effectively controlled by extending or retracting the guide plate and correction plate of the hydraulic jack system, adjusting the posture of the milling head and slowing down the descent speed of the milling head; after a period of operation, the milling wheel is removed from the slot section for washing and the wear of the gears is checked to ensure rock breaking efficiency.

[0087] After the twin-wheel milling machine completes the construction, it is moved and a hydraulic grab bucket is used to repair the trench to ensure the verticality of the trench wall. Then, the hydraulic grab bucket is lowered to the bottom of the trench section to remove the sediment at the bottom of the trench to ensure that the sediment at the bottom of the trench meets the design requirements.

[0088] (5) Cleaning the slag in the 130mm slag scoop bucket of the cast-in-place pile hole.

[0089] After the diaphragm wall trench 150 is completed, the rotary drilling rig is positioned and the rotary drilling bucket is used to remove the rock blocks and drill cuttings that accumulated in the pile hole during the trenching process.

[0090] After the rotary drilling bucket removes the slag, a rotary drilling cleaning bucket is used to clean the bottom of the hole. After cleaning, the sediment at the bottom of the pile hole is measured to ensure that the drilling depth is consistent with the final hole depth and that the sediment thickness meets the design requirements.

[0091] (6) Ultrasonic wall tester inspection slot

[0092] After excavating trenches and pile holes, use an ultrasonic wall gauge to check whether the depth, thickness, width, and verticality of the trench sections meet the requirements.

[0093] If the inspection is passed, the trenching and hole-forming construction is completed, and the next step is carried out; if the inspection fails, the trench and hole are repaired until they meet the design requirements.

[0094] (7) The pile reinforcement cage 210 is hoisted into the pile hole 130 and then lifted to the groove opening of the diaphragm wall groove 150 for positioning.

[0095] Fabricate the cast-in-place pile reinforcement cage 210 according to the design drawings, and check whether its length, diameter, weld points, etc. are qualified.

[0096] The pile reinforcement cage 210 is lifted using a double hook multi-point lifting method, and the operation is slow to avoid twisting or bending, and to prevent the pile reinforcement cage 210 from deforming due to improper lifting operation.

[0097] The pile reinforcement cage 210 is hoisted into the opening of the diaphragm wall trench 150, and the center point of the pile reinforcement cage 210 is aligned with the center point mark of the reinforcement cage on the trench wall, and then slowly lowered.

[0098] First, lower two pile reinforcement cages 210 into the grouting pile hole 130, then lift them vertically to the groove opening. Then, use two horizontal support members (e.g., steel spreader poles) to horizontally fix the pile reinforcement cages 210 at the groove opening. Mark the center line position of the pile reinforcement cages 210 on the ground to facilitate subsequent hoisting into the hole.

[0099] (8) The wall reinforcement mesh 220 is lifted to the groove and connected to the pile reinforcement cage 210.

[0100] After the pile reinforcement cage 210 is fixed in the trench and its position is marked, the wall reinforcement mesh 220 of the underground continuous wall 320 is slowly lifted by a crawler crane. When it is lifted to 0.5m above the ground, it is paused to check whether there is any disassembly, deformation or other abnormalities in the wall reinforcement mesh 220. If there are no abnormalities, it is lifted vertically to the top of the trench by the main crane.

[0101] Along the centerline of the I-beam and aligned with the center of the trench section, the wall reinforcement mesh 220 is lowered into the pile reinforcement cage 210 with an anchoring length of 1.5m (i.e., the top of the pile reinforcement cage 210 extends 1.5m into the wall reinforcement mesh 220). Then, the pile reinforcement cage 210 and the wall reinforcement mesh 220 are welded together to form an integrated pile-wall reinforcement cage structure 200. The welding length is 1.5m to ensure the rigidity of the integrated pile-wall reinforcement cage structure 200.

[0102] (9) The integrated structure of the pile wall reinforcement cage is hoisted into the slot by 200mm.

[0103] After the pile wall reinforcement cage is welded into a whole, it is lifted up as a whole. Then, a fixing rod 230 (for example, a thin steel bar) is welded in the middle of the two pile reinforcement cages 210. The fixing rod 230 is arranged horizontally, and the two ends of the fixing rod 230 are respectively connected to the middle of the two pile reinforcement cages 210, so that the pile reinforcement is corrected to a vertical state, preventing the pile reinforcement cage 210 from splitting into an "eight" shape during the hoisting and lowering process and thus failing to enter the pile hole.

[0104] Using a crawler crane, the modified integrated pile wall reinforcement cage structure 200 is aligned with the center of the pile reinforcement cage 210, while keeping the center line of the I-beam and the edge line of the groove coincide, and is slowly lowered; when it is lowered to the opening of the lower grouting pile hole 130, the fixing rod 230 collides with the rock and falls off, and the pile wall reinforcement cage continues to be lowered smoothly to the design elevation.

[0105] (10) Placement of a double-port double-infusion catheter

[0106] After the 200mm integrated pile wall steel cage structure is hoisted into the trench, the underwater concrete pouring method with double guide pipes is used for the 130mm cast-in-place pile hole. Before placing the pouring guide pipe, a water tightness test and a pressure test are conducted on the pouring guide pipe to ensure that the pouring guide pipe does not leak.

[0107] A crawler crane is used to set up a grouting platform at the slot, and grouting pipes are placed into the two grouting pile holes 130, controlling the distance between the bottom of the grouting pipe and the bottom of the pile hole to be 30-50cm.

[0108] (11) Secondary hole cleaning

[0109] Before pouring concrete for the pile wall, the thickness of the sediment at the bottom of the pile hole (130mm) is measured. If it exceeds the design requirements, a second cleaning is performed. The cleaning method uses air-lift reverse circulation, which replaces and removes the sediment at the bottom of the hole through high-quality mud circulation.

[0110] (12) Pile-wall integrated double-diaphragm grouting

[0111] After the secondary cleaning of the hole meets the requirements, underwater concrete pouring is carried out, using two sets of pouring pipes for simultaneous pouring.

[0112] First, the concrete of the lower cast-in-place pile 310 is poured, and at the same time, the cover plate of the pouring bucket is lifted to start the initial pouring. During the pouring process, the height difference of the concrete liquid level in the two adjacent pouring pipes is controlled within 50cm, and the depth of the pouring pipe embedded in the concrete is controlled between 2 and 4m.

[0113] When the grouting guide pipe is raised to the hole of the grouting pile, the concrete grouting volume of the two holes is increased simultaneously and the concrete is continuously poured in, so that the bottom of the 320mm underground continuous wall is successfully sealed and the concrete liquid level of the wall rises evenly to form an integrated pile-wall support structure.

[0114] After pouring to the designed elevation of the top of the wall, maintain an over-pouring height of no less than 80cm to ensure that the top elevation of the wall meets the design requirements after removing the laitance.

[0115] Compared with the prior art, the integrated pile wall structure for foundation pits under complex conditions provided by the present invention has the following beneficial effects.

[0116] (1) The support is safe and reliable.

[0117] In this invention, compared with the single diaphragm wall support technology, the integrated pile-wall foundation pit support technology reduces the trench depth of the diaphragm wall, thus reducing disturbance to the upper soft soil layer. This can prevent deformation of the surrounding strata of the adjacent subway tunnel and reduce the impact on subway operation. At the same time, the diaphragm wall at the top of the integrated pile-wall support structure is located in soft soil and strongly weathered strata, providing good seepage prevention. The lower cast-in-place piles 310 can be embedded in slightly weathered hard rock. Through cooperation with the support structure inside the foundation pit, the pile wall provides more stable support and the support structure is safe and reliable.

[0118] (2) Improved construction efficiency

[0119] In this invention, the wall-supported cast-in-place pile structure utilizes a rotary drilling rig to drill two combined guide (pile) holes at a depth of 110 on the moderately weathered rock surface to the pile bottom elevation. Holes at a depth above 120 on the slightly weathered rock surface serve as guide holes for auxiliary double-wheel milling of the groove, while holes below 120 on the slightly weathered rock surface serve as cast-in-place pile holes 130. The combined drilling of the guide holes and pile holes effectively improves construction efficiency. Simultaneously, in this invention, the portion above 120 on the slightly weathered rock surface utilizes a diaphragm wall, while the portion below 120 on the slightly weathered rock surface utilizes cast-in-place piles 310, forming an integrated pile-wall support structure. This reduces the difficulty and workload of trenching into the rock, accelerating the project progress.

[0120] (3) Comprehensive cost economy

[0121] In this invention, when drilling the bottom cast-in-place piles of the integrated pile-wall support structure, the guide hole 140 drilled and milled during the single diaphragm wall entry into the rock is utilized, serving two purposes in one hole, simplifying the construction process and saving drilling costs. At the same time, compared with the single integral diaphragm wall support that trenches into slightly weathered rock layers and has a large rock penetration depth, this invention uses cast-in-place piles under the wall to replace the diaphragm wall embedded in the slightly weathered rock layer at a certain depth, reducing the difficulty and workload of trenching in hard rock, thereby saving the time of trenching construction and the cost of machinery, steel bars, wall protection mud, concrete, etc.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An integrated pile-wall structure for foundation pits under complex conditions, characterized in that, The system includes a diaphragm wall and cast-in-place piles. Multiple cast-in-place piles are located at the bottom of the diaphragm wall and are connected to the diaphragm wall to form an integrated pile-wall structure. The diaphragm wall is located in a diaphragm wall trench, the bottom of which extends to the surface of the slightly weathered rock underground. The cast-in-place piles are located in pile holes, which extend downward from the bottom of the diaphragm wall trench into the slightly weathered rock layer underground, and are connected to the diaphragm wall trench. The cast-in-place pile has a pile reinforcement cage, and the underground continuous wall has a wall reinforcement mesh. The top of the pile reinforcement cage extends into the wall reinforcement mesh to form an anchoring section, and the anchoring section is welded to the wall reinforcement mesh. The top of the pile reinforcement cage is welded to the wall reinforcement mesh to form an integrated pile-wall reinforcement cage structure. The integrated pile-wall reinforcement cage structure includes the wall reinforcement mesh located at the top and multiple pile reinforcement cages located at the bottom. During construction, the integrated pile-wall steel cage structure is first erected and then lowered into the diaphragm wall trench and the grouting pile hole. Concrete is then poured to form the integrated pile-wall structure. The construction of the integrated pile wall steel cage structure includes the following steps: S210: Fabricate the pile reinforcement cage and the wall reinforcement mesh according to the design drawings; S220: The pile reinforcement cage is hoisted into the pile hole, then the pile reinforcement cage is vertically lifted to the opening of the diaphragm wall trench, and then the pile reinforcement cage is horizontally fixed at the opening of the trench by the horizontal support, and the center position of the pile reinforcement cage is marked on the ground at this time. S230: Hoist the wall reinforcement mesh to the top of the slot so that the top of the pile reinforcement cage extends into the wall reinforcement mesh, and weld the anchoring section to the wall reinforcement mesh; S240: Remove the transverse support and slowly lower the integrated pile wall steel cage structure into the diaphragm wall groove; In step 230, the integral structure of the pile wall reinforcement cage is lifted up as a whole, and then horizontally arranged fixing rods are set between adjacent pile reinforcement cages; The middle of two adjacent pile reinforcement cages is provided with support members arranged opposite to each other, and the end of the fixing rod is located in the support member; The support member includes a transversely arranged support groove and a longitudinally arranged fixing groove. The bottom end of the fixing groove is connected to the end of the support groove, the top end of the fixing groove is open, and the interior of the fixing groove is hollow. The fixing groove includes a fixing side for fixing the support member to the pile reinforcement cage and a notch side arranged opposite to the fixing side. The notch side is provided with a notch groove, which extends from the top end of the fixing groove to the support groove. The end of the fixing rod has a fixing head, which is movably connected in the fixing groove.

2. The integrated pile-wall structure for foundation pits under complex conditions as described in claim 1, characterized in that, The size of the fixing head is greater than the width of the notch and less than the width of the hollow cavity of the fixing groove; when the fixing rod is arranged horizontally, the fixing rod is supported by the support groove, and the fixing head is located in the fixing groove.

3. The integrated pile-wall structure for foundation pits under complex conditions as described in claim 2, characterized in that, The fixing groove also includes two oppositely arranged sidewalls, the two sides of which are respectively connected to the fixing side and the notch side; the inner wall of the sidewall is also provided with a baffle, the two ends of which are respectively connected to the two sidewalls, and the baffle is located above the fixing head.

4. The integrated pile-wall structure for foundation pits under complex conditions as described in any one of claims 1-3, characterized in that, The construction process of the diaphragm wall trench and the cast-in-place pile hole includes the following steps: S110: The hydraulic grab bucket in the soil layer sequentially grabs the trench to the moderately weathered rock surface, forming the first trench section located in the soft soil layer; S120: A rotary drilling rig is used to drill holes at the bottom of the first trench section to the pile bottom elevation, forming multiple grouting pile holes; S130: At the bottom of the first trench section, the trench is milled sequentially to the wall bottom elevation, which is located above the pile bottom elevation, thereby forming a diaphragm wall trench; S140: Clean the slag from the grouting pile holes and the diaphragm wall trench; At the bottom of the first trench section, above the wall bottom elevation, the portion other than the grouting pile holes forms a part to be removed; in step S130, a rotary drilling rig is used to drill a guide hole to the wall bottom elevation in the part to be removed, and then a double-wheel milling machine is used to mill the trench along the guide hole to the wall bottom elevation in sequence, thus removing the part to be removed above the wall bottom elevation.

Images