Pipe jacking working well construction method for soft clay geology

Abstract

The invention provides a pipe jacking working well construction method for soft clay geology. The pipe jacking working well construction method comprises the steps that S1, replacement filling and cushion layer construction are conducted in a construction area corresponding to a working well; s2, a formwork is erected for blade foot pouring, S3, excavation is conducted from the middle of the open caisson to the periphery in a layered mode, the open caisson is filled with backfill sand for back pressure after final sinking, and well wall heightening is conducted after backfill; s4, after the backfill sand is cleaned, sinking and heightening are carried out for multiple times until excavation is carried out to a preset elevation; s5, riprapping and leveling the well bottom, and then moving from the well edge to the middle for layered pouring to form a back cover; and S6, after water pumping is completed, reinforcing steel bars are bound, concrete is poured, and a bottom plate is formed. The mode that symmetrical excavation is conducted and soil bodies are reserved along the periphery of a blade foot to form a soil embankment is adopted, the well wall evenly sinks under the action of self weight, and the problems that the well wall inclines and cracks are caused by uneven sinking are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of pipe jacking construction, and in particular relates to a pipe jacking working well construction method for soft clay geology. Background Art

[0002] Constructing a pipe jacking shaft in soft clay soil presents numerous challenges. Soft clay soils, characterized by low strength, high compressibility, and poor permeability, can easily lead to problems such as shaft wall instability, uneven subsidence, and poor bottom sealing during construction. Traditional construction methods struggle to effectively address these geological challenges, often resulting in extended construction periods, increased costs, and even compromised overall shaft quality and safety.

[0003] Therefore, it is necessary to provide an improved technical solution to the above-mentioned deficiencies in the prior art. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art. The present invention provides a method for constructing a pipe jacking working well in soft clay geology.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: A method for constructing a pipe jacking working well in soft clay soil, comprising: Step S1: staking out according to the design drawings, and performing replacement filling and cushion construction in the construction area corresponding to the working pit; Step S2: Setting up formwork to cast the blade foot. After the concrete strength of the blade foot reaches the designed strength, the cushion layer under the blade foot is chiseled off. Step S3: Excavating the caisson in layers from the center to the surrounding areas using excavation equipment, and retaining soil around the blade foot to form an earth bank. The soil layer is cut towards the blade foot in a symmetrical manner to cause the caisson wall to sink under its own weight. After the caisson is finally sunk, backfill sand is filled to provide counter pressure, and the caisson wall is raised after backfilling. Step S4: After cleaning the backfill sand, sinking and raising the excavation repeatedly until the excavation reaches the preset elevation; Step S5: After the caisson is completed, the floating mud and blade feet are cleaned underwater, the bottom of the well is ripped and leveled, and a concrete pipe is inserted into the bottom of the well. Concrete is first poured from the middle to the surrounding areas, and then poured in layers from the side of the well to the middle to form a bottom seal. Step S6: After the bottom seal concrete is poured, underwater reinforcement is laid, and the underwater reinforcement is extended into the bottom seal concrete. After the bottom seal concrete reaches a preset strength, water is pumped out; After the water is pumped out, the steel bars are tied and concrete is poured to form the base plate.

[0006] Preferably, in step S2, mixing piles are constructed synchronously on the periphery of the working well to form a cylindrical curtain corresponding to the caisson, and a deviation correction device is provided on the inner side of the mixing piles to correct the deviation of the well wall.

[0007] Preferably, the correction device comprises: The ring beam is annular and matches the mixing pile, and is cast into one piece with the upper end of the mixing pile by tying with steel bars; A base, wherein the base is anchored to the inner wall of the ring beam by anchor bolts, and a plurality of the bases are evenly distributed around the circumference of the ring beam; A push rod is fixed on the base to compress the well wall radially along the ring beam to correct the well wall.

[0008] Preferably, a mounting tube with an opening pointing toward the ring beam is provided on the base, two sliders distributed in the longitudinal direction are provided in the mounting tube, and the two push rods drive the sliders respectively; One end of the slider is provided with a guide roller corresponding to the well wall, and the other end of the slider is provided with a friction pad corresponding to the well wall.

[0009] Preferably, a brick formwork corresponding to the blade foot is built on the inner side of the blade foot, and a beveled edge is built on the outer side of the brick formwork to form the blade portion of the blade foot. The cushion layer below the blade foot is divided into multiple blocks, and the cushion layer is removed simultaneously on both sides of the blade foot.

[0010] Preferably, in step S5, the elevation of each point on the bottom of the pit is measured, and pouring is started from the lowest point when sealing the bottom.

[0011] Preferably, the mixing piles are constructed by a three-axis mixer, using a skip-type double-hole full-set remixing connection method. After the cement slurry on the pile top has initially set, the loose soil at the pile head is manually cleaned.

[0012] Preferably, the heightening of the well wall is carried out in the form of cast-in-place, the well wall formwork is assembled with wooden formwork, and some parts are cut and made according to the structural dimensions. Scaffolding is set up on the outside of the well wall, and cantilever scaffolding is installed on the inside according to the construction progress.

[0013] Preferably, during the sinking process of the well wall, the water level in the well is monitored, and water is replenished or drained according to the changes in the water level.

[0014] Beneficial Effects: Symmetrical excavation and retaining soil around the cutting edge to form an earth bank allow the shaft wall to sink evenly under its own weight, avoiding problems such as tilting and cracking caused by uneven sinking. A cylindrical curtain formed by mixing piles around the working shaft effectively prevents lateral flow of the surrounding soft clay, improving shaft wall stability. Furthermore, the presence of a correction device allows for timely correction of the shaft wall, ensuring verticality during sinking and further ensuring its stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them: Figure 1 This is a construction flow chart of a working well in a specific embodiment provided by the present invention; Figure 2 A schematic diagram of the distribution of the deviation-correcting device in a specific embodiment provided by the present invention; Figure 3 A simplified structural diagram of the deviation-correcting device in a specific embodiment of the present invention; Figure 4 This is a schematic diagram of the blade foot sinking in a specific embodiment provided by the present invention; Figure 5 This is a schematic diagram of the well wall height connection in the specific embodiment provided by the present invention.

[0016] In the figure: 1. Working pit; 2. Correction device; 3. Ring beam; 101. Blade foot; 102. Height connection; 103. Backfill sand; 201. Base; 202. Mounting pipe; 203. Guide roller; 204. Friction pad; 205. Push rod. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0018] In the description of the present invention, the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention. The terms "connected" and "connected" used in the present invention should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate component. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0019] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0020] like Figure 1-5As shown, in the area dominated by silty clay, the characteristic value of the foundation bearing capacity is only 50kPa, and the unit friction resistance of the outer wall is only 10kPa. When the caisson is connected to a height of 102, the overall stability is poor. In view of this, the present application designs a construction method for a jacking working well 1 for soft clay geology, comprising: step S1, laying out according to the design drawings, and performing replacement and cushion construction in the construction area corresponding to the working well 1; the replacement area is a ring with a width of 2.7m and a thickness of 1m, and the concrete cushion layer is a ring with a width of 1.6m and a thickness of 0.25m, and the replacement and cushion areas are adapted to the well wall.

[0021] Step S2, set up the formwork to cast the blade foot 101. After the concrete strength of the blade foot 101 reaches the design strength, the cushion layer under the blade foot 101 is chiseled off; after each group of construction workers symmetrically demolishes each section, the blade foot 101 should be immediately filled with original soil, and small soil piles of appropriate height should be built inside and outside the blade foot 101, and compacted layer by layer to transfer the sinking weight to the cushion layer. Strengthen observation during demolition.

[0022] Step S3: Excavation is carried out in layers from the middle of the caisson to the surrounding areas using excavation equipment, and soil is retained around the blade foot 101 to form an earth embankment. The soil layer is cut towards the blade foot 101 in a symmetrical manner, so that the well wall sinks under the action of its own weight. After the well wall of each segment sinks, backfill sand 103 is filled to perform counterpressure. After backfilling, the well wall is raised 102. The backfill sand 103 counterpressure is applied by means of the internal frictional resistance of the caisson, thereby increasing the total frictional resistance during the caisson production and sinking process. Step S4, after cleaning the backfill sand 103, multiple sinking and raising 102 are carried out until the excavation reaches the preset elevation; the construction is carried out in a manner of 6 productions and 6 sinkings, and each production time is about 8 days. After the first section is completed, it needs to be strengthened to 100% according to the design requirements for about 20 days before the caisson sinking construction can be carried out.

[0023] The initial sinking depth is 4.85m. When excavating soil, begin in the center of the caisson and gradually excavate in layers outwards, with each layer 0.4-0.5m thick. A 1.5-2m wide earth bank is maintained around blade foot 101. Then, along the caisson wall, the soil is thinned symmetrically (with the plane's geometric center of gravity as the axis of symmetry) and evenly, layer by layer, every 2-3m toward blade foot 101. Each time, 5-10cm is removed. When the soil layer breaks under the pressure of blade foot 101, the caisson sinks evenly and vertically under its own weight, without excessive tilt. If there is little or no sinking, excavate an additional 0.4-0.5m from the center and continue excavating evenly outwards in layers to ensure a steady sinking of the caisson. Do not excavate below blade foot 101 during the excavation process. Slow down the sinking speed when the caisson is 1.0m from the design elevation. When the caisson is finally sunk, the top is left 0.5m above the ground without taking soil and sinking; when backfilling, backfill evenly from the center to the surrounding layers. After backfilling, the first height connection 102 is carried out, and the height is 4.5m respectively.

[0024] During the sinking process, the water level in the well is monitored, and water is added or drained based on changes in the water level. Subsequent sinking is similar to the initial support method, except for the height difference. After each sinking, the top is left 0.5m above the ground without further sinking. Sinking is done without drainage, and the water level is controlled at -6m. If the groundwater level is insufficient, water replenishment is required.

[0025] Step S5: After the caisson is completed, divers are arranged to go into the water to remove the floating mud at the bottom of the well, clean the floating mud and the blade feet 101 underwater, throw stones to level the bottom of the well, extend the concrete pipe into the bottom of the well, first pour from the middle to the surrounding area, and then move from the side of the well to the middle to cast in layers to form a bottom seal; Step S6: After the bottom concrete is poured, underwater reinforcement is laid and inserted into the bottom concrete. After the bottom concrete reaches the preset strength, water is pumped out. After the water is pumped out, the loose layer on the concrete surface is removed, and the concrete is leveled according to the designed elevation. Then, the steel bars are tied and concrete is poured to form the bottom plate.

[0026] In step S2, mixing piles are simultaneously constructed around the working shaft 1 to form a cylindrical curtain corresponding to the caisson. The bottom of the mixing piles is higher than the pipeline elevation to ensure normal pipe jacking. A correction device 2 is installed inside the mixing piles to correct the deviation of the shaft wall. If the caisson axis does not coincide with the designed axis and a certain degree of displacement occurs, the caisson is controlled to stop tilting in the direction of the deviation and intentionally tilt the caisson in the opposite direction of the deviation.

[0027] In one embodiment, after entering the site, the caisson mixing pile construction is carried out first, and then the caisson main structure construction and sinking construction are carried out, which can improve the bearing capacity of the soft soil.

[0028] In an optional embodiment, the correction device 2 includes a ring beam 3, a base 201 and a top rod 205, wherein the ring beam 3 is a ring that is compatible with the mixing pile, and the width of the ring beam 3 is greater than the diameter of the mixing pile. First, the pile head of the mixing pile is chiseled flat, and then the formwork is excavated and supported on both sides of the curtain formed by the mixing pile, and is cast into one with the upper end of the mixing pile through steel bar binding, so as to ensure the stability of the ring beam 3 and provide stable support force for correction. A base 201 is provided on the inner wall of the ring beam 3, and the base 201 is anchored to the inner wall of the ring beam 3 by anchor bolts. Multiple bases 201 are evenly distributed about the circumference of the ring beam 3. Generally, the number of bases 201 is not less than 4, preferably 8. The top rod 205 is fixed on the base 201. When a certain deviation occurs in the well wall, the well wall is squeezed radially along the ring beam 3 to tilt in the opposite direction of the deviation of the caisson to correct the deviation of the well wall.

[0029] In this embodiment, the base 201 is provided with an arc-shaped surface corresponding to the ring beam 3, and a mounting tube 202 with an opening pointing to the ring beam 3 is provided on the side of the base 201 corresponding to the well wall. The lower surface of the mounting tube 202 contacts the ground to provide support force. Two guide grooves extending radially from the ring beam 3 are provided in the mounting tube 202. The two guide grooves are distributed longitudinally, and sliders sliding along the guide grooves are provided in the guide grooves. Two push rods 205 are provided inside the mounting tube 202 to drive the two sliders respectively; one end of one of the sliders corresponding to the well wall is provided with a guide roller 203 adapted to the well wall, and the other end of the slider corresponding to the well wall is provided with a friction pad 204 corresponding to the well wall.

[0030] Since the soil quality underground is not exactly the same, the friction force received by different parts of the well wall is different, which will lead to frequent well wall deviation problems. In this application, a friction pad 204 is provided. The friction pad 204 is a rubber pad that can generate friction at different positions around the well wall through squeezing, thereby avoiding the occurrence of deviation movement problems.

[0031] In this embodiment, the jacking pipe can be a hydraulic cylinder, and the outer wall of the guide roller 203 is provided with an arc-shaped surface, which is mainly used to straighten the well wall; the friction force distribution of the circumferential direction of the well wall is determined according to the settlement rate of the well wall, and the friction pad 204 is a rubber pad, and the surface is a curved surface corresponding to the well wall. Under the action of extrusion, the friction force of the circumferential direction of the well wall is kept balanced through the friction pad 204, thereby improving the construction efficiency and quality.

[0032] The inner side of blade foot 101 is built with a corresponding brick formwork, and the outer side of the brick formwork is built with a beveled edge to form the blade portion of blade foot 101. During construction, a 25mm thick layer of plaster should be reserved on the inner side. Mu15 sintered ordinary bricks are used for the masonry. The masonry is staggered at the top and bottom, with interlocking joints inside and outside. The "three-in-one" bricklaying method (one shovel of mortar, one brick, one squeeze and kneading) is used. Vertical joints are left at the starting point and in the middle of the masonry.

[0033] The cushion layer under the blade foot 101 is divided into multiple blocks, and the cushion layers are removed simultaneously on both sides of the blade foot 101 symmetrically, and the size and number of each block are marked on the concrete cushion layer; when chiseling, proceed in the specified chiseling order.

[0034] In an optional embodiment, in step S5, the elevation of each point on the pit floor is measured. A diver, working with the top of the wellhead, uses a measuring rope to measure and record the depth at each point at 0.5m intervals, marking the location of each measurement point. The measurement results are compiled and analyzed, and an elevation map of the pit floor is drawn. When sealing the bottom, concrete is poured starting from the bottom, gradually moving toward the perimeter of the well, and then moving from the well edge toward the center, layer by layer. Concrete pouring must be continuous and uninterrupted until completion. During the pouring process, a diver is deployed to provide timely monitoring of the underwater concrete pouring depth and the catheter insertion depth.

[0035] In an optional embodiment, the mixing piles are constructed by a three-axis mixer, using a skip-type double-hole full-set remixing connection method. The mixer drill bit is lifted according to the selected lifting speed. The pile bottom is sprayed for more than 30 seconds to fully mix the cement slurry and the pile end soil. The mixing head is then lifted and rotated while spraying. After it is lifted to the designed elevation of the pile top, it is rotated in situ and sprayed for 30 seconds. The mortar pump is then turned off to ensure that the pile head is uniform and dense. After the cement slurry at the pile top has initially set, the loose soil at the pile head is manually cleaned to ensure the integrity of the pile body and the cleanliness of the site.

[0036] In an optional embodiment, the shaft wall joint 102 is cast in situ. Pre-buried casings of φ3060 and φ2600 are installed in the working shaft 1 and receiving shaft, respectively. After the caisson formwork is removed, the reserved hole is sealed, and the masonry is maintained together with the main caisson structure. The reserved hole is sealed with 50-mm brick masonry, and both the inner and outer walls are finished with waterproof mortar. During construction, 12# channel steel is welded horizontally at 10cm intervals on the outer and inner sides of the masonry within the hole. Pre-buried steel pipes are welded to the channel steel to ensure masonry stability.

[0037] The shaft wall formwork is assembled from wooden formwork, with sections cut to size. Scaffolding is erected on the outside of the shaft wall, while cantilevered scaffolding is installed on the inside according to the construction schedule. The inside operating frame is a floor-standing type during the construction of the first section of the caisson. The cantilevered scaffolding is arranged in the same manner as the floor-standing scaffolding, with a maximum height of 5.5m and a 1.5m guardrail installed on the top.

[0038] The formwork is assembled from wooden formwork, partially cut to the structural dimensions. The formwork is reinforced with φ48*2.7mm steel pipes and 50mm*70mm square timbers, ensuring vertical alignment during installation. Horizontal reinforcement of the caisson utilizes steel pipes spaced 0.6m apart, with two steel pipes combined for reinforcement. Vertical reinforcement utilizes square timbers spaced 0.2m apart. The inner and outer formwork is secured with waterstop tie rods.

[0039] 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, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for constructing a pipe jacking pit in soft clay soil, characterized in that: include: Step S1: staking out according to the design drawings, and performing replacement filling and cushion construction in the construction area corresponding to the working pit; Step S2: Setting up formwork to cast the blade foot. After the concrete strength of the blade foot reaches the designed strength, the cushion layer under the blade foot is chiseled off. Step S3: Excavating the caisson in layers from the center to the surrounding areas using excavation equipment, and retaining soil around the blade foot to form an earth bank. The soil layer is cut towards the blade foot in a symmetrical manner to cause the caisson wall to sink under its own weight. After the caisson is finally sunk, backfill sand is filled to provide counter pressure, and the caisson wall is raised after backfilling. Step S4: After cleaning the backfill sand, sinking and raising the excavation repeatedly until the excavation reaches the preset elevation; Step S5: After the caisson is completed, the floating mud and blade feet are cleaned underwater, the bottom of the well is ripped and leveled, and a concrete pipe is inserted into the bottom of the well. Concrete is first poured from the middle to the surrounding areas, and then poured in layers from the side of the well to the middle to form a bottom seal. Step S6: After the bottom seal concrete is poured, underwater reinforcement is laid, and the underwater reinforcement is extended into the bottom seal concrete. After the bottom seal concrete reaches a preset strength, water is pumped out; After the water is pumped out, the steel bars are tied and concrete is poured to form the base plate.

2. The method for constructing a pipe jacking well in soft clay soil according to claim 1, wherein: In step S2, mixing piles are constructed synchronously on the periphery of the working well to form a cylindrical curtain corresponding to the caisson, and a deviation correction device is provided on the inner side of the mixing piles to correct the deviation of the well wall.

3. The method for constructing a pipe jacking well in soft clay soil according to claim 2, wherein: The deviation correcting device comprises: The ring beam is annular and matches the mixing pile, and is cast into one piece with the upper end of the mixing pile by tying with steel bars; A base, wherein the base is anchored to the inner wall of the ring beam by anchor bolts, and a plurality of the bases are evenly distributed around the circumference of the ring beam; A push rod is fixed on the base to compress the well wall radially along the ring beam to correct the well wall.

4. The method for constructing a pipe jacking well in soft clay soil according to claim 3, wherein: The base is provided with a mounting tube with an opening pointing to the ring beam, and two sliders distributed along the longitudinal direction are provided in the mounting tube, and the two push rods drive the sliders respectively; One end of the slider is provided with a guide roller corresponding to the well wall, and the other end of the slider is provided with a friction pad corresponding to the well wall.

5. The method for constructing a pipe jacking well in soft clay soil according to claim 1, wherein: The inner side of the blade foot is built with a brick formwork corresponding to the blade foot, and the outer side of the brick formwork is built with a beveled edge to form the blade part of the blade foot. The cushion layer under the blade foot is divided into multiple blocks, and the cushion layer is removed simultaneously on both sides of the symmetrical blade foot.

6. The method for constructing a pipe jacking well in soft clay soil according to claim 1, wherein: In step S5, the elevation of each point on the pit bottom is measured, and pouring is started from the lowest point when sealing the bottom.

7. The method for constructing a pipe jacking well in soft clay soil according to claim 2, wherein: The mixing piles are constructed using a three-axis mixer and a skip-type double-hole full-set remixing connection method. After the cement slurry on the pile top has initially set, the loose soil at the pile head is cleaned manually.

8. The method for constructing a pipe jacking well in soft clay soil according to claim 1, wherein: The height connection of the well wall is carried out in the form of cast-in-place. The well wall formwork is assembled with wooden formwork, and some parts are cut and made according to the structural dimensions. Scaffolding is set up on the outside of the well wall, and cantilever scaffolding is installed on the inside according to the construction progress.

9. The method for constructing a pipe jacking well in soft clay soil according to claim 1, wherein: During the sinking process of the well wall, the water level in the well is monitored, and water is added or drained according to the changes in the water level.

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