An assembly type caisson construction method under complex environment

Abstract

The application provides an assembled sinking well construction method in a complex environment, and relates to the technical fields of underground engineering and pipe jacking construction, and comprises the following steps: prefabricating assembled sinking well components, a temporary cover plate and a permanent cover plate; adopting a sleeve valve pipe grouting method to reinforce in the first stage before sinking well sinking; constructing a load-bearing retaining circle beam and laying the temporary cover plate; assembling the sinking well components under the limitation of the circle beam and sinking to a preset distance above the existing pipeline to form a temporary bottom sealing; reinforcing in the second stage through a reserved grouting hole; excavating and pouring in sections downward at the bottom of the temporary bottom sealing by using a top-down method, so that the lower well wall extends to the top surface of the pipeline; treating the pipeline, breaking the pipeline wall to connect the sinking well and the pipeline; pouring the bottom plate concrete and covering the permanent cover plate; and the application solves the technical problems of being unable to carry out closed construction, pipeline protection, pipeline accurate butt joint and sand layer construction safety control in a complex environment by using the prefabrication, phased grouting and top-down combined process.

Description

Technical Field

[0001] This invention relates to the field of underground engineering and pipe jacking construction technology, and in particular to a prefabricated caisson construction method in complex environments. Background Technology

[0002] At present, the construction of pipe jacking working wells in complex environments such as intersections of main urban roads mainly includes the following schemes: (1) Open excavation and cast-in-place method: after constructing the retaining structure, the foundation pit is excavated, the well wall is cast in place, the supports are removed and backfilled, and a water-stop curtain is added; (2) Overall prefabricated caisson method: the whole is prefabricated in the factory, and after being hoisted into place on site, it sinks by its own weight or pressure; (3) Steel sheet pile retaining method: Larssen steel sheet piles are used for retaining, internal excavation is carried out, and the piles are pulled out after completion; (4) Sleeve valve pipe grouting reinforcement method: as an auxiliary measure, grout is injected into the soil around the caisson in advance to improve the soil strength and water-stopping performance. However, the existing technology has the following problems: (1) Open excavation and cast-in-place method: the placement of large equipment requires a large working surface, which is difficult to implement at busy intersections; there are many procedures and the cycle is long (60~90 days), which cannot meet the requirements of night construction and daytime traffic. (2) Precast caisson method: The caisson body is an integrated rigid structure, which cannot pass through or avoid existing pipeline obstacles, making it difficult to achieve precise connection with the existing pipeline. (3) Insufficient pipeline protection: Conventional grouting is a single full-depth reinforcement, which lacks differentiated reinforcement strategies for different construction stages, which can easily lead to pipeline settlement, deformation or even breakage. (4) Prominent contradiction between traffic load and construction space: The existing caisson structure cannot take into account the dual functions of bearing vehicle passage and reserving space for caisson operation. (5) High geological risk of sand layer: Quicksand and piping are prone to occur in high water level sand layers, and the friction reduction effect of thixotropic mud may also lead to sudden settlement and over-settlement. The reasons for the above problems are as follows: the open-cut cast-in-place method relies on large-area sites, continuous operation, and multi-process flow construction, which cannot adapt to the working conditions of intermittent construction and immediate restoration of traffic at intersections; the precast caisson is a rigid whole, and the bottom cannot be locally modified when encountering obstacles, resulting in the inability to connect; full-depth one-time grouting is difficult to control precisely and cannot be dynamically adjusted, resulting in over-reinforcement or under-reinforcement; traditional interlocking ring beams only consider construction support and do not take into account the dual functions of bearing traffic and reserving working space; the sand layer has no cohesion and is prone to piping and sand flow under dynamic water pressure; thixotropic mud reduces side friction resistance, making settlement control difficult. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0004] To address this, the present invention proposes a prefabricated caisson construction method for complex environments, comprising: prefabricating prefabricated caisson components, temporary cover plates, and permanent cover plates; employing a sleeve valve grouting method to perform a first-stage reinforcement of the soil surrounding the caisson construction area; based on the first-stage reinforcement, constructing a load-bearing retaining ring beam on the soil surrounding the caisson construction area, and laying a temporary cover plate on the load-bearing retaining ring beam to allow for daytime vehicle passage during nighttime construction; under the limiting action of the load-bearing retaining ring beam, hoisting the first prefabricated caisson component to a preset position, and then assembling subsequent prefabricated caisson components section by section until it sinks to a preset distance above the top surface of the existing pipeline. A temporary concrete seal was formed at this location; then, using the sleeve valve grouting method, the soil around the lower well wall was reinforced in the second stage using the grouting holes reserved on the prefabricated caisson components; based on the second stage reinforcement and the temporary concrete seal, the bottom of the temporary concrete seal was excavated and concrete was poured section by section using the reverse construction method until the lower well wall of the caisson extended downward to the top surface of the existing pipeline; the existing pipeline was temporarily supported and the water flow was cut off and diverted, and the pipe wall of the corresponding part of the existing pipeline was broken to connect the caisson with the existing pipeline; the bottom slab concrete was poured at the bottom of the caisson to form an overall closed system of the well chamber structure, and a permanent cover plate was installed.

[0005] In some technical solutions of the present invention, optionally, a sleeve valve pipe grouting method is used to reinforce the soil around the caisson construction area in the first stage, including: arranging holes in the soil around the caisson construction area in a quincunx pattern with a hole spacing of 0.8m; the reinforcement range is 2-3m beyond the outer wall of the proposed caisson in the horizontal direction and 2m below the bottom of the caisson in the vertical direction; drilling is carried out sequentially from the outer row of holes to the inner row of holes; during drilling, rotary drilling with alloy drill bits is used for the upper soft soil layer, and pneumatic down-the-hole hammer impact drilling is used for the lower hard soil layer; after drilling to the designed depth and cleaning the hole, the casing material is pumped to the bottom of the hole through the drill rod and poured from bottom to top to the hole opening, with a solidification time of 2-5 days; after the casing material solidifies, grouting fluid is injected into the hole through the sleeve valve pipe using a skip-injection method, with the grouting pressure controlled at 0.4-0.8MPa.

[0006] In some technical solutions of the present invention, optionally, when prefabricating the assembled caisson components, the assembled caisson components are prefabricated into rectangular or circular cross sections with a height of 1.0m / section and a wall thickness of 0.3m; a connection groove is reserved on the upper end face of the assembled caisson components for injecting high-strength early-strength mortar; a water-stop steel plate is pre-embedded on the lower end face of the assembled caisson components; a friction-reducing coating is applied to the outer surface of the assembled caisson components; grouting holes are reserved inside the assembled caisson components, and one grouting hole is arranged centered every meter along the well wall; and hoisting embedded parts are pre-embedded at the four corners of the assembled caisson components.

[0007] In some technical solutions of the present invention, optionally, based on the first-stage reinforcement, a load-bearing soil-retaining ring beam is constructed on the soil around the open caisson construction area, and temporary cover plates are laid on the load-bearing soil-retaining ring beam, so as to realize nighttime construction and daytime vehicle passage, which includes: excavating a "loop"-shaped trench on the soil around the open caisson construction area, with a trench depth of 1.4m and a width of 1.1m; the trench is constructed in two sections, and the structural construction of each section is completed on the same day of excavation; hoisting the reinforcement framework into the trench, pouring concrete into the trench, the concrete is poured in layers with each layer being 30cm, and vibrated layer by layer, until the concrete is 1cm below the road surface, that is, the load-bearing soil-retaining ring beam is formed in the trench; then temporary cover plates are added on the load-bearing soil-retaining ring beam, so as to realize nighttime construction and daytime vehicle passage.

[0008] In some technical solutions of the present invention, optionally, under the limiting effect of the load-bearing soil-retaining ring beam, the first prefabricated open caisson component is hoisted to a preset position, then subsequent prefabricated open caisson components are assembled section by section until the caisson sinks to a preset distance above the top surface of the existing pipeline, and a temporary concrete bottom seal is formed at this position, which includes: performing a trial hoisting before hoisting the first prefabricated open caisson component, adjusting the lifting ropes to make the prefabricated open caisson component in a stable horizontal state; after the trial hoisting is completed, slowly lowering the first prefabricated open caisson component into the soil layer, and using the self-weight of the prefabricated open caisson component to make the prefabricated open caisson component settle and stabilize by its own weight; slowly applying pressure to the first prefabricated open caisson component with the excavator bucket, controlling the excavation surface not to exceed 0.6m below the top surface of the prefabricated open caisson component when excavating the core soil, so that the blade foot part remains below the undisturbed soil; after the first prefabricated open caisson component is sunk in place, pouring high-strength early-strength mortar into the connecting notch until the notch is full; hoisting the second prefabricated open caisson component, making the water stop steel plate at the bottom end of the second prefabricated open caisson component accurately fall into the mortar-filled connecting notch at the top end of the first prefabricated open caisson component, and slowly lowering it in place to make the joint dense and the connection smooth; after standing for curing, applying pressure to the second prefabricated open caisson component to make it sink as a whole; repeating the above assembly and sinking processes, assembling subsequent prefabricated open caisson components section by section and continuing to sink, until the prefabricated open caisson components sink to the preset distance above the top surface of the existing pipeline; when the blade foot of the prefabricated open caisson component sinks to the preset distance above the top surface of the existing pipeline, erecting formwork at the inner bottom of the prefabricated open caisson component and pouring reinforced concrete to form a temporary concrete bottom seal.

[0009] In some technical solutions of the present invention, optionally, a sleeve valve pipe grouting method is adopted to reinforce the surrounding soil of the lower part of the caisson using the grouting holes reserved on the prefabricated caisson components. This includes: after the temporary concrete bottom seal reaches the design strength, connecting the grouting equipment to the grouting holes reserved on the prefabricated caisson components; injecting cement-water glass double grout into the grouting holes through the sleeve valve pipe to supplement the grouting reinforcement of the surrounding soil of the lower part of the caisson; controlling the grouting reinforcement range so that it reaches 1~1.5m beyond the lower wall of the caisson in the horizontal direction and 1m below the top surface of the existing pipeline in the vertical direction, with a grouting pressure of 1.0MPa; after the grouting is completed, waiting for the grout to solidify to form a reinforcement layer in the surrounding soil of the lower part of the caisson.

[0010] In some technical solutions of the present invention, optionally, based on the second-stage reinforcement and temporary concrete sealing, the bottom of the temporary concrete sealing is excavated and concrete is poured downwards section by section using a reverse construction method until the lower wall of the caisson extends downwards to the top surface of the existing pipeline. This includes: chiseling away the concrete at the cutting edge of the first section of the prefabricated caisson component and stripping out the reinforcing steel bars at the cutting edge; determining the design length of the reverse construction method and the length of the extended reinforcing steel bars based on the distance between the top surface of the existing pipeline and the bottom surface of the cutting edge of the prefabricated caisson component; and carrying out the first section of reverse excavation below the temporary concrete sealing. Control the excavation depth of each section within 0.5m and not exceed 0.8m; after the first section is excavated, immediately tie the reinforcing bars, install the formwork, and use steel pipe frames to fix the side formwork; pour early-strength concrete into the formwork to form the lower well wall of this section; check the soil stability of the current excavation face, and if the soil stability is insufficient, suspend construction and reinforce the excavation face with additional grouting; after the early-strength concrete reaches the preset strength, repeat the above excavation and pouring procedures to carry out the next cycle of operation; construct downwards section by section until the lower well wall extends to the top surface of the existing pipeline.

[0011] In some technical solutions of the present invention, optionally, temporary support and water diversion are performed on the existing pipeline, and the pipe wall of the corresponding part of the existing pipeline is broken to connect the caisson with the existing pipeline. This includes: first, water diversion is performed on the section of the existing pipeline that needs to be broken, and a load-bearing frame for the existing pipeline is constructed; then, the pipe wall of the corresponding part of the existing pipeline is broken, with the width of the broken section controlled at 70cm, and three water outlets are evenly opened within the broken section, with each water outlet spaced apart; then, annular steel liners are installed inside the retained pipe section extending 1.5m on both sides of the broken section, and steel bars are implanted into the side wall of the retained pipe section. The steel bars are anchored to the side wall of the retained pipe section using anchoring adhesive, so that the existing pipeline and the lower wall of the caisson are integrally connected through the anchoring of steel bars.

[0012] In some technical solutions of the present invention, optionally, a base slab concrete is poured at the bottom of the caisson to form an integral closed system of the caisson structure, and the permanent cover plate is installed. Specifically, the base slab reinforcement is tied at the bottom of the caisson to form an integral connection with the wall reinforcement of the lower part of the caisson wall; the base slab concrete is poured at the bottom of the caisson and compacted to form an integral closed system of the caisson structure, and the poured base slab concrete is cured; after the base slab concrete reaches the design strength, a leak test is conducted; after the leak test is passed, cement grout is prepared and injected into the pre-reserved grouting holes on the prefabricated caisson components from bottom to top, with the grouting pressure controlled at 0.3~0.6MPa. The grout flowing out from adjacent grouting holes is used as the criterion for determining the completion of grouting in a single hole. The grouting operation is completed hole by hole until the thixotropic mud is completely replaced; after the mud replacement is completed, the permanent cover plate is hoisted and placed on the caisson.

[0013] Optionally, some technical solutions of the present invention may also include: conducting underground pipeline surveys in the construction area and installing traffic safety facilities before prefabricating components.

[0014] Compared with the prior art, the present invention has the following advantages: 1. Adaptable to complex construction conditions; This invention adopts on-site assembly of prefabricated components and segmented construction technology, which does not require a large construction site and continuous operation time. It has significant advantages in conditions where it is impossible to completely close the intersection of main urban roads and where night construction is required and daytime traffic is allowed. Actual engineering applications show that the construction cycle of a single well is 42 days (including component prefabrication), which is about 30% shorter than the traditional open-cut method.

[0015] 2. Effectively protects the safety of underground pipelines; through staged sleeve valve grouting reinforcement (cement-water glass dual grout, quincunx pattern hole spacing of 0.8m), the soil around the caisson is solidified in advance, effectively preventing soil loss and pipeline settlement during the caisson sinking process; the staged reinforcement strategy makes grouting more precise and avoids excessive grouting from causing additional pressure on the pipeline; actual monitoring data: the maximum pipeline settlement is 12mm, which is far less than the alarm value of 30mm.

[0016] 3. Achieve precise connection with existing pipelines; adopting a combination of "prefabricated upper sinking + bottom reverse construction and in-situ casting", the caisson is sunk to a preset distance above the existing pipeline and then stops. The lower part is excavated and cast in small sections (0.5m / section) using the reverse construction method, which achieves flexible connection and precise docking between the caisson structure and the existing pipeline, avoiding the problem that the whole caisson cannot pass through obstacles, and eliminating the need for secondary excavation.

[0017] 4. Ensuring daytime traffic flow; Through a comprehensive approach of “precast temporary cover slabs + load-bearing ring beams + segmented construction,” the goal of “nighttime construction and daytime traffic resumption” was achieved; In practice, daytime road traffic resumed normally, and there were no traffic congestion complaints.

[0018] 5. Effectively control the risks of quicksand, sudden subsidence, and oversettlement in sandy geological layers; reinforced by "staged sleeve valve grouting" (28-day unconfined compressive strength > 0.5 MPa, permeability coefficient < 1.0 × 10⁻⁶). -6 The comprehensive technical solution of "cm / sec) + component surface friction-reducing coating / thixotropic mud controllable drag reduction + triple anti-settlement measures" effectively controls construction risks such as quicksand, sudden settlement, and oversettlement under high water level geological conditions in sandy layers; final settlement deviation: average elevation of cutting edge +15mm, center displacement 20mm, and height difference of four corners 8mm, all of which meet the acceptance standards (≤100mm, ≤1.5%H and ≤300mm, ≤1.5%L and ≤500mm).

[0019] 6. Reliable construction quality; prefabricated components are produced in factories, ensuring quality control; on-site assembly reduces common quality defects in cast-in-place structures; in practical applications, the well wall exhibits no leakage or structural cracks.

[0020] Based on the implementation methods provided in the above aspects, this application can be further combined to provide more implementation methods. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 A flowchart illustrating a prefabricated caisson construction method in a complex environment according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a load-bearing retaining ring beam and temporary cover plate structure according to an embodiment of the present invention; Figure 3 This is a schematic plan view of the first-stage reinforcement zone according to an embodiment of the present invention; Figure 4 This is a schematic elevation view of the staged soil reinforcement area according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the grouting holes of a prefabricated caisson component according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the connection of a multi-section prefabricated caisson component according to an embodiment of the present invention; Figure 7 This is a schematic diagram of an existing pipeline integrated protection and interface structure according to an embodiment of the present invention.

[0022] In the diagram: 1. Prefabricated caisson components; 2. Load-bearing retaining ring beam; 3. Temporary cover plate; 4. Permanent cover plate; 5. Water-stop steel plate; 6. Connecting groove; 7. Sleeve valve pipe; 8. First stage reinforcement zone; 9. Second stage reinforcement zone; 10. Cutting edge; 11. Connecting pipeline; 12. Inclined beam; 13. Reverse construction section; 14. Existing pipeline; 15. Drainage outlet; 16. Grouting hole; 17. Mud replacement zone; 18. Rebar installation. Detailed Implementation

[0023] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0025] The following reference Figures 1 to 3 This invention describes a method for constructing prefabricated caissons in complex environments according to some embodiments of the present invention.

[0026] In one embodiment of the present invention, such as Figure 1 As shown, a method for constructing prefabricated caissons in complex environments is provided, including: Step 102: Prefabricate the prefabricated caisson components 1, temporary cover plate 3, and permanent cover plate 4.

[0027] Step 104: The sleeve valve pipe grouting method is used to carry out the first stage of reinforcement of the soil around the caisson construction area.

[0028] Step 106: Based on the first stage of reinforcement, construct a load-bearing retaining ring beam 2 on the soil around the caisson construction area, and lay a temporary cover plate 3 on the load-bearing retaining ring beam 2 to enable daytime vehicle passage during nighttime construction.

[0029] Step 108: Under the limiting action of the load-bearing retaining ring beam 2, the first prefabricated caisson component 1 is hoisted to the preset position, and then the subsequent prefabricated caisson components 1 are assembled section by section until they sink to a preset distance above the top surface of the existing pipeline 14, and a temporary concrete seal is formed at this position.

[0030] Step 110: Then, the sleeve valve pipe grouting method is used to reinforce the soil around the lower well wall in the second stage by using the grouting holes 16 reserved on the prefabricated caisson component 1.

[0031] Step 112: Based on the second-stage reinforcement and temporary concrete sealing, the bottom of the temporary concrete sealing is excavated and concrete is poured downwards section by section using the reverse construction method until the lower wall of the caisson extends downwards to the top surface of the existing pipeline 14.

[0032] Step 114: Temporarily support and divert water flow from the existing pipeline 14, break the pipe wall at the corresponding part of the existing pipeline 14, and connect the caisson to the existing pipeline 14.

[0033] Step 116: Pour concrete for the bottom slab at the bottom of the caisson to form an integral closed system for the caisson structure, and install the permanent cover plate 4.

[0034] In step 104, as Figure 3 As shown, the sleeve valve pipe grouting method is used to carry out the first stage of soil reinforcement around the caisson construction area, including: In the first stage of the caisson construction area, the soil in the reinforcement zone 8 is arranged in a quincunx pattern with holes spaced 0.8m apart. The reinforcement range extends 2-3m beyond the outer wall of the proposed caisson in the horizontal direction and 2m below the bottom of the caisson in the vertical direction.

[0035] Drilling is carried out sequentially from the outer row of holes to the inner row of holes. During drilling, rotary drilling with alloy drill bit is used for the upper soft soil layer, and pneumatic down-the-hole hammer is used for the lower hard soil layer. The upper soft soil layer consists of soft soil such as miscellaneous fill and medium sand; the lower hard soil layer consists of coarse sand and gravel.

[0036] After drilling to the designed depth and cleaning the hole, the casing material is pumped to the bottom of the hole through the drill rod and poured from bottom to top to the hole opening. The casing material has a solidification time of 2 to 5 days. The casing material is made of cement, clay and water in a ratio of cement:clay:water = 1:1.5:1.88.

[0037] After the casing material solidifies, a staggered injection method is used to prevent grout leakage. Grouting fluid is injected into the holes through sleeve valve pipe 7, with the injection pressure controlled at 0.4~0.8MPa. The grouting fluid is either a single-component grout prepared with 42.5 grade ordinary Portland cement or a cement-water glass double-component grout. The single-component grout is a cement slurry, where water and cement are mixed in a 1:1 ratio. The cement-water glass double-component grout is a mixture of cement slurry and water glass in a 1:1 volume ratio. The reinforcement standard is a 28-day unconfined compressive strength > 0.5MPa and a permeability coefficient < 1.0×10⁻⁶. -6 cm / sec; thus completing the first stage of reinforcement of zone 8.

[0038] In step 102, as Figure 5As shown, when prefabricating the prefabricated caisson members, the prefabricated caisson member 1 is prefabricated into a rectangular or circular cross-section, with a height of 1.0m per section and a wall thickness of 0.3m; a connecting notch 6 is reserved on the upper end face of the prefabricated caisson member 1 for pouring high-strength early-strength mortar; a water stop steel plate 5 is embedded on the lower end face of the prefabricated caisson member; the outer surface of the prefabricated caisson member 1 is coated with an anti-friction coating, and grouting holes 16 are reserved in the prefabricated caisson member 1, with one grouting hole 16 arranged centrally per linear meter along the caisson wall; lifting embedded parts are embedded at the four corners of the prefabricated caisson member 1; no water stop steel plate 5 is arranged below the first section of the prefabricated caisson member 1, which is replaced by a cutting edge 10 to facilitate the penetration of the prefabricated caisson member 1 into the soil; wherein, the water stop steel plate 5 of the prefabricated caisson member 1 is embedded and fabricated during prefabrication, and achieves a water stop effect by cooperating with high-strength grouting material when two sections of the prefabricated caisson member 1 are connected.

[0039] The prefabricated temporary cover plate 3 has dimensions of 2.4m × 3.85m × 0.25m, anti-slip textures are arranged on the top surface of the temporary cover plate 3, and a limiting device corresponding to the supporting surface of the load-bearing soil-retaining ring beam 2 is arranged on the bottom surface, and 2 temporary cover plates 3 are prefabricated for each caisson position.

[0040] The permanent cover plate 4 is manufactured as a permanent inspection well cover according to design requirements, such as the need to meet long-term service performances including leak detection, sealing, and anti-theft properties.

[0041] After all prefabricated members are completed, acceptance is carried out before leaving the factory, including structural dimension deviations (length ±0.5% and ≤100mm, wall thickness ±15mm), arrangement of grouting holes 16 of the prefabricated caisson member 1, member strength (tested by a rebound hammer or tested on specimens under the same conditions), position and welding quality of the water stop steel plate 5 of the prefabricated caisson member 1.

[0042] In step 106, as Figure 2 shown, based on the first-stage reinforcement, a load-bearing soil-retaining ring beam 2 is constructed on the soil around the caisson construction area, and temporary cover plates 3 are laid on the load-bearing soil-retaining ring beam 2, so as to realize night construction and daytime vehicle passage, including: According to the coordinates of the caisson structure, the four inner and outer corners of the trench are accurately set out, and the elevations of the top surface of the back wall and the cover plate supporting surface are controlled based on the elevation of the existing road surface; the asphalt surface is cut by hanging lines before excavation (with a depth of no less than 5cm).

[0043] A small excavator is used to excavate a "loop"-shaped trench on the soil around the caisson construction area, the trench has a depth of 1.4m and a width of 1.1m, over-excavation is prohibited on the side and bottom surfaces, and the insufficient part is trimmed manually.

[0044] The trench is constructed in two sections (or multiple sections according to site conditions), and excavation of each section and structural construction are completed on the same day.

[0045] The steel reinforcement cage is prefabricated in the prefabrication yard and hoisted as a whole. During the fabrication, spot welding and additional auxiliary steel reinforcement are used to ensure the overall rigidity of the cage. After the trench is excavated and trimmed, the steel reinforcement cage is immediately hoisted into the trench and the side formwork is fixed. Concrete is poured into the trench in layers of 30cm each, and each layer is vibrated until the concrete is 1cm below the road surface, thus forming a load-bearing retaining ring beam 2 in the trench.

[0046] After the concrete in the construction section has set on the same day, it is covered with geotextile and watered for curing. After the night construction is completed, a 20mm thick steel plate (2.3m×6.0m) is used to cover the constructed section and restore traffic. The height difference between the steel plate and the road surface is controlled within ±5mm, and a gentle slope is set at the joint of the steel plate.

[0047] After the concrete strength of the load-bearing retaining ring beam 2 reaches 100%, the core soil inside the ring beam is excavated to a depth of 1.25m. Over-excavation of the core soil is prohibited to prevent the collapse of the soil under the ring beam. A temporary cover plate 3 is added to the load-bearing retaining ring beam 2. Ordinary steel plates are strictly prohibited from being used to replace the precast temporary cover plate 3. This is to enable daytime vehicle passage during nighttime construction, so that road traffic can be restored normally during the day and there are no traffic congestion complaints.

[0048] In step 108, as Figure 4 and Figure 6 As shown, under the limiting action of the load-bearing retaining ring beam 2, the first prefabricated caisson component 1 is hoisted to the preset position, and then subsequent prefabricated caisson components 1 are assembled section by section until they sink to a preset distance above the top surface of the existing pipeline 14, and a temporary concrete seal is formed at this position, including: Each prefabricated caisson component inspected on site must have concrete strength reaching 100% of its design strength before it can be used.

[0049] Before hoisting the first prefabricated caisson component 1, a trial hoisting is conducted to adjust the hoisting ropes so that the prefabricated caisson component 1 is in a stable horizontal state. Specifically, when hoisting the first prefabricated caisson component 1, a limiting wooden block is added to the inside of the load-bearing retaining ring beam 2 to ensure that the component is centered and vertical. Before hoisting, a trial hoisting is conducted to adjust the hoisting ropes so that the component is in a stable horizontal state.

[0050] After the trial lifting is completed, the first prefabricated caisson component 1 is slowly lowered into the soil layer, and its own weight is used to stabilize it by self-sinking. The bucket of an excavator is used to slowly pressurize the first prefabricated caisson component 1, with the pressurization point set at the center of the component. The pressure is transmitted using sleepers. The core soil is excavated according to the actual sinking depth. When excavating the core soil, the excavation surface is controlled to not exceed 0.6m below the top surface of the prefabricated caisson component 1, so that the cutting edge 10 is kept below the original soil to prevent twisting. During the core soil excavation, personnel are required to direct the process to avoid mechanical collisions with the prefabricated caisson component.

[0051] After the first prefabricated caisson component 1 is sunk into place, high-strength early-strength mortar is poured into the connecting slot 6 until the slot is full. Specifically, after the first section is sunk into place and passes the inspection, the debris and water in the connecting slot 6 at the top of the first section are cleaned; C50 high-strength early-strength mortar is poured into the connecting slot until it is full. The mortar is mixed with special grouting material.

[0052] The second prefabricated caisson component 1 is hoisted so that the water-stop steel plate 5 at the bottom of the second prefabricated caisson component is accurately placed into the mortar-filled connection groove 6 at the top of the first prefabricated caisson component 1. The water-stop steel plate 5 is ≥3mm thick and ≥300mm wide, and is embedded in the center, with half of it embedded at the top and bottom. Then it is slowly lowered into place to make the joint tight and the interface smooth.

[0053] After static curing, once the mortar strength reaches 60%, pressure is applied to the second prefabricated caisson component 1 to allow it to sink as a whole.

[0054] Repeat the above assembly and sinking process, assemble the subsequent prefabricated caisson components 1 section by section and continue to sink until the prefabricated caisson components 1 sink to a preset distance above the top surface of the existing pipe 14, the preset distance being 30cm.

[0055] During the aforementioned sinking process, monitoring and corrective measures are required. Therefore, the sinking process is divided into three stages: the normal sinking stage, the final sinking stage, and the sinking cessation and bottom sealing stage.

[0056] During the normal sinking phase, the sinking begins from the first section of the caisson component and continues until the cutting edge of the caisson is approximately 2 meters from the design elevation. Monitoring measures include setting up observation points at the four corners and center of the caisson, with clear and secure markings; setting up no fewer than three benchmark points in the surrounding stable area; setting elevation control points every 2 meters on both the inner and outer sides of the caisson wall; conducting comprehensive observations no fewer than twice every 8 hours; and sinking with normal soil removal, controlling the soil removal range and amount based on the actual sinking depth to ensure that the cutting edge 10 is below the original soil.

[0057] Correction actions should follow the principle of "correcting as you excavate, correcting while in motion," with each correction not being too large to prevent structural cracking. When tilting is detected, more soil is excavated on the higher side of the caisson (eccentric excavation method), while a soil embankment is retained or backfilled with sand and gravel on the lower side to increase resistance. When displacement is detected, more soil is excavated on the opposite side of the displacement direction to tilt the caisson in that direction, maintaining the tilted posture and continuing to excavate and sink until the centerline approaches the design position, at which point it is straightened. When torsion is detected, soil is excavated diagonally on one side of the caisson and backfilled diagonally on the other, using the difference in earth pressure torque to reset the caisson. If sinking is difficult, thixotropic mud is injected through the pre-set grouting holes 16 on the outside of the caisson wall to reduce drag, with the grouting pressure controlled at 0.2~0.5MPa.

[0058] During the final sinking stage, when the cutting edge 10 of the caisson is approximately 2 meters from the design elevation, the final sinking stage begins. The monitoring points used during the normal sinking stage are used, with observations every 2 hours. The correction measures during the final sinking stage follow the same methods as during the normal sinking stage, but the deviation standards must be controlled as follows: the height difference between the four corners of the caisson must not exceed 1.5%L (L is the distance between two corners of the rectangular caisson, and the unit is the same as L), and the absolute value must not exceed 500 mm; the displacement of the caisson center must not exceed 1.5%H (H is the sinking depth of the caisson), and the absolute value must not exceed 300 mm. When any deviation value approaches or exceeds the above control standards, correction measures should be initiated. The correction measures are the same as during the normal sinking stage, but the amount of correction should be further reduced each time to prevent over-sinking.

[0059] During the cessation of settlement and sealing of the bottom, when the cutting edge 10 of the caisson sinks to about 30cm above the outer surface of the existing pipeline, the cessation of settlement and sealing of the bottom begins. The monitoring measures are to observe once every time soil is taken during the correction construction and once every 24 hours during the sinking cessation period. The cessation of settlement is controlled by the "micro-differential excavation" method. The thickness of each soil taken is ≤10cm. When the cumulative self-sinking of the caisson is no more than 10mm within 8 hours, it is judged as stable and temporary bottom sealing concrete construction is immediately carried out. The temporary bottom sealing concrete is C20 reinforced concrete with a thickness of 15cm and is equipped with φ10@150 steel mesh. It is poured under waterless conditions to prevent the caisson from sinking further. Thixotropic mud is no longer injected during the cessation of settlement to avoid further friction reduction leading to over-sinking.

[0060] In step 110, as Figure 4 As shown, the sleeve valve grouting method is then used to reinforce the surrounding soil at the bottom of the caisson in a second stage, utilizing the grouting holes pre-drilled on the prefabricated caisson components. This includes: After the temporary concrete seal reaches the design strength, the grouting equipment is connected to the grouting holes reserved on the prefabricated caisson components; cement-water glass grout is injected into the grouting hole 16 through the sleeve valve pipe 7 to supplement the second-stage reinforcement zone at the bottom of the caisson with grouting reinforcement; the grouting reinforcement range is controlled so that it reaches 1~1.5m beyond the bottom wall of the caisson in the horizontal direction and 1m below the top surface of the existing pipeline in the vertical direction, and the grouting pressure is 1.0MPa; after the grouting is completed, the grout solidifies to form a reinforcement layer in the second-stage reinforcement zone 9 at the bottom of the caisson.

[0061] In step 112, as Figure 4 As shown, based on the second-stage reinforcement and temporary concrete sealing, the bottom of the temporary concrete sealing is excavated and concrete is poured section by section downwards using the reverse construction method until the lower part of the caisson wall extends downwards to the top surface of the existing pipeline 14, including: Remove the concrete from the cutting edge 10 section of the first prefabricated caisson component and peel off the reinforcing steel bars from the cutting edge 10 section.

[0062] Based on the distance between the top surface of the existing pipeline 14 and the bottom surface of the cutting edge 10 of the prefabricated caisson component, the design length and the length of the extension steel bars for the reverse construction method are determined; HRB400φ16 steel bars are used for the caisson wall and bottom slab, HRB400φ20 steel bars are used at the corners, and HRB400φ25, HRB400φ20, and HRB400φ10 steel bars are used for pipeline reinforcement. The steel bars are welded by single-sided lap welding, and the lap length is not less than 10d.

[0063] The first section of reverse excavation is carried out below the temporary concrete seal (construction area 13 of the reverse section). The excavation depth of each section is controlled within 0.5m. It can be adjusted appropriately according to the actual soil conditions after excavation, but shall not exceed 0.8m.

[0064] After the first section of excavation was completed, the reinforcing bars were immediately tied, the formwork was installed, and the side formwork was fixed using a steel pipe frame.

[0065] Early-strength concrete is poured into the template to form the lower part of the well wall.

[0066] Check the soil stability at the current excavation face. If the soil stability is insufficient, suspend construction and reinforce the excavation face with additional grouting. After the early-strength concrete reaches the preset strength (70% of the concrete strength), repeat the above excavation and pouring procedures to start the next cycle.

[0067] Construction proceeded downwards section by section until the lower well wall extended to the top surface of the existing pipeline 14.

[0068] In step 114, as Figure 7 As shown, temporary support and water diversion are performed on the existing pipeline 14, and the pipe wall of the corresponding part of the existing pipeline 14 is broken to connect the caisson to the existing pipeline 14, including: First, the section of existing pipeline 14 that needs to be breached will be cut off from water flow and a load-bearing frame for the existing pipeline 14 will be constructed. Specifically, the water cut-off and diversion will involve installing an airbag (diameter adapted to the pipeline diameter, working pressure 0.2~0.3MPa) to seal the upstream inspection well of the breached section, laying a DN600 steel pipe as a temporary diversion pipe along the outside of the breached section, and installing a high-flow submersible pump (≥200m) downstream. 3 / h, head ≥15m) as emergency drainage, dual-circuit power supply; the temporary support of the existing pipeline is to set HW200×200 steel vertical support columns on both sides of the broken section and below the adjacent pipe section, one column every 1.0m along the longitudinal direction of the pipeline, and the top is set with an arc-shaped support plate that fits tightly against the pipe wall (a rubber pad is embedded between the support plate and the pipe wall). The adjacent support columns are connected by channel steel horizontal connecting beams to form an overall load-bearing frame.

[0069] Then, the pipe wall of the existing pipe 14 at the corresponding part is broken, and the width of the broken section is controlled to be 70cm. Three drainage outlets 15 (i.e., water outlets) are evenly opened within the broken section, and the drainage outlets 15 are arranged at intervals. Inclined beams 12 are set at the positions of the drainage outlets 15 on both sides of the broken section. One end of the inclined beam 12 is connected to the pipe wall of the existing pipe 14, and the other end is connected to the vertical support column of the steel section, which is used to reinforce and support the pipe wall of the existing pipe 14 after the drainage outlets 15 are opened.

[0070] Next, annular steel liners are installed inside the retained pipe sections extending 1.5m on each side of the demolition section, and rebars 18 are installed on the side walls of the retained pipe sections. The rebars are anchored to the side walls of the retained pipe sections using anchoring adhesive, so that the existing pipe 14 and the lower wall of the caisson are integrally connected by the anchoring rebars 18. Specifically, annular steel liners (made of 10mm thick Q235 steel plate, assembled in 2-3 pieces circumferentially and bolted) are installed inside the pipes extending 1.5m on each side of the demolition section, and anchored to the pipe walls using expansion bolts (arranged in a staggered pattern with a spacing of 300mm×300mm). The gaps are filled with high-strength non-shrink grout. HRB400φ16 rebars are implanted through the side walls of the retained pipe sections to a depth of 16cm and anchored with anchoring adhesive to form a reliable connection with the subsequent reinforcement structure.

[0071] After the existing pipe 14 is connected to the caisson, the access pipe 11 is hoisted into place, so that one end of the access pipe 11 is connected to the corresponding part of the lower part of the caisson wall, and the other end extends to the outside of the caisson, forming a through structure of access pipe 11 → caisson → existing pipe 14.

[0072] Then, temporary brick sealing walls are set up on both sides of the broken section to retain the pipe ports. MU10 bricks and M10 cement mortar are used, with a thickness of 240mm. A 300mm×300mm overflow port is reserved at the top. Anti-siltation curtain is set up 3m downstream of the broken section. The anti-siltation curtain is made of geotextile and wire mesh.

[0073] In step 116, concrete is poured at the bottom of the caisson to form a closed system for the caisson structure, and a permanent cover plate 4 is installed. Specifically, the bottom slab reinforcement is tied at the bottom of the caisson to form an integral connection with the wall reinforcement of the lower part of the caisson. After the reverse construction is completed and the existing pipeline 14 is connected to the caisson, the loose soil and silt at the base are cleaned, and the geological conditions of the base are checked to see if they match the design. The bottom slab of the caisson is tied to the wall reinforcement to form an integral connection, and C30 concrete is poured for the bottom slab of the caisson. The concrete is compacted to form a closed, integral load-bearing system for the well chamber structure. After the concrete of the caisson bottom slab has set, it is cured and a leak test is conducted after it reaches the design strength. After the leak test is passed, cement grout is prepared and injected into the pre-reserved grouting holes 16 on the prefabricated caisson component 1 from bottom to top. The grouting pressure is controlled at 0.3~0.6MPa. The completion of grouting in a single hole is determined by the flow of grout from adjacent grouting holes. The grouting operation is completed hole by hole until the thixotropic mud is completely replaced, forming the mud replacement zone 17.

[0074] After the mud replacement is completed, the temporary support, annular steel lining, temporary sealing wall and temporary diversion pipe of the existing pipeline 14 are removed to restore the normal water flow of the pipeline; the permanent cover plate 4 is hoisted and placed on the caisson to complete the construction of the inspection well structure; the soil around the caisson is backfilled in a symmetrical layered manner with a compaction degree of ≥90%~95% to restore the original appearance of the road, and manhole covers are installed at the corresponding positions on the road surface and the caisson for later inspection and use.

[0075] While prefabricating the precast assembly caisson components 1, temporary cover 3, and permanent cover 4 in step 102, the following steps are also included: before prefabricating the components, conducting underground pipeline exploration in the construction area and setting up traffic safety facilities; specifically, after roughly outlining the caisson location, manually digging a cross-shaped trench within the caisson area to detect underground pipelines, with a trench depth of not less than 3m; the detection range should cover a distance of twice the caisson depth beyond the outer edge; after discovering pipelines, promptly notify the relevant pipeline units for on-site confirmation, coordinate the relocation of relocated pipelines, and adjust the caisson location or take special protection measures for pipelines that cannot be relocated according to their spatial location; at the same time, prepare a traffic diversion plan and submit it to the traffic management department for approval; according to the approved plan, set up construction warning and speed reduction signs at 300m, 200m, and 50m in the direction of oncoming traffic; determine the nighttime construction period (21:00 to 6:00 the next day) and the daytime road restoration plan; and configure traffic safety facilities such as traffic cones, LED warning light strips, and reflective road barriers.

[0076] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for constructing prefabricated caissons in complex environments, characterized in that, include: Precast assembled caisson components, temporary cover plates, and permanent cover plates; The sleeve valve pipe grouting method was used to reinforce the soil around the caisson construction area in the first stage. Based on the first stage of reinforcement, a load-bearing retaining ring beam is constructed on the soil around the caisson construction area, and a temporary cover plate is laid on the load-bearing retaining ring beam to enable daytime vehicle passage during nighttime construction. Under the limiting action of the load-bearing retaining ring beam, the first section of the prefabricated caisson component is hoisted to the preset position, and then the subsequent prefabricated caisson components are assembled section by section until they sink to a preset distance above the top surface of the existing pipeline, and a temporary concrete seal is formed at this position. Then, the sleeve valve pipe grouting method is adopted to reinforce the soil around the lower well wall in the second stage by using the grouting holes reserved on the prefabricated caisson components. Based on the second stage reinforcement and the temporary concrete sealing, the bottom of the temporary concrete sealing is excavated and concrete is poured in sections downwards using the reverse construction method until the lower wall of the caisson extends downwards to the top surface of the existing pipeline. The existing pipeline is temporarily supported and the water flow is cut off and diverted. The pipe wall of the corresponding part of the existing pipeline is broken to connect the caisson to the existing pipeline. A base slab of concrete is poured at the bottom of the caisson to form an integral closed system of the caisson structure, and the permanent cover plate is installed.

2. The prefabricated caisson construction method in complex environments according to claim 1, characterized in that, The method of using sleeve valve pipe grouting is used to carry out the first stage of reinforcement of the soil around the caisson construction area, including: The soil around the caisson construction area is arranged in a quincunx pattern with holes spaced 0.8m apart. The reinforcement range extends 2-3m beyond the outer wall of the proposed caisson in the horizontal direction and 2m below the bottom of the caisson in the vertical direction. Drilling is carried out sequentially from the outer row of holes to the inner row of holes. When drilling, rotary drilling with alloy drill bit is used for the upper soft soil layer, and pneumatic down-the-hole hammer is used for the lower hard soil layer. After drilling to the designed depth and cleaning the hole, the casing material is pumped to the bottom of the hole through the drill pipe and poured from bottom to top to the hole opening. The solidification time is 2 to 5 days. After the casing material solidifies, grout is injected into the hole through the sleeve valve pipe using a skip injection method, with the grouting pressure controlled at 0.4~0.8MPa.

3. The prefabricated caisson construction method in complex environments according to claim 1, characterized in that, When prefabricating the assembled caisson components, the assembled caisson components are prefabricated into rectangular or circular cross-sections, with a height of 1.0m / section and a wall thickness of 0.3m; a connecting groove is reserved on the upper end face of the assembled caisson component for injecting high-strength early-strength mortar; a cutting edge is provided on the lower end face of the first section of the assembled caisson component, and water-stop steel plates are pre-embedded on the lower end faces of the remaining assembled caisson components; a friction-reducing coating is applied to the outer surface of the assembled caisson component, and grouting holes are reserved in the assembled caisson component, with one grouting hole arranged centered every meter along the caisson wall; hoisting embedded parts are pre-embedded at the four corners of the assembled caisson component.

4. The prefabricated caisson construction method in complex environments according to claim 1, characterized in that, Based on the first stage of reinforcement, a load-bearing retaining ring beam is constructed on the soil surrounding the caisson construction area, and a temporary cover plate is laid on the load-bearing retaining ring beam to allow for daytime vehicle passage during nighttime construction, including: Excavate a "hui"-shaped trench on the soil around the open caisson construction area, wherein the trench has a depth of 1.4m and a width of 1.1m; the trench is constructed in two sections, and the structural construction of each section is completed on the same day of excavation; Hoist the reinforcement skeleton into the trench, and pour concrete into the trench, wherein the concrete is poured in layers of 30cm each and vibrated layer by layer until the concrete is 1cm below the road surface, so as to form the load-bearing soil-retaining ring beam in the trench; Then cover the load-bearing soil-retaining ring beam with the temporary cover plate, so as to realize night-time construction and daytime vehicle passage.

5. The prefabricated caisson construction method in complex environments according to claim 3, characterized in that, Under the limiting effect of the load-bearing soil-retaining ring beam, hoist the first section of the prefabricated open caisson member to a preset position, then assemble subsequent prefabricated open caisson members section by section until the caisson sinks to a preset distance above the top surface of the existing pipeline, and form a temporary concrete bottom seal at this position, which includes: Carry out trial hoisting before hoisting the first section of the prefabricated open caisson member, and adjust the sling to make the prefabricated open caisson member in a stable horizontal state; After the trial hoisting is completed, slowly lower the first section of the prefabricated open caisson member into the soil layer, and use the self-weight of the prefabricated open caisson member to make the prefabricated open caisson member settle and stabilize by itself; Use the excavator bucket to slowly apply pressure to the first section of the prefabricated open caisson member, and control the excavation surface not to exceed 0.6m below the top surface of the prefabricated open caisson member when excavating the core soil, so that the cutting edge part is kept below the undisturbed soil; After the first section of the prefabricated open caisson member is sunk in place, pour high-strength early-strength mortar into the connecting notch until the notch is full; Hoist the second section of the prefabricated open caisson member, make the water-stop steel plate at the bottom end of the second section of the prefabricated open caisson member accurately fall into the connecting notch filled with mortar at the top of the first section of the prefabricated open caisson member, and slowly lower it into place to make the joint dense and the connection smooth; After standing for curing, apply pressure to the second section of the prefabricated open caisson member for overall sinking; Repeat the above assembly and sinking procedures, assemble subsequent prefabricated open caisson members section by section and continue to sink until the prefabricated open caisson members sink to a preset distance above the top surface of the existing pipeline; When the cutting edge of the prefabricated open caisson member sinks to the preset distance above the top surface of the existing pipeline, set up formwork at the inner bottom of the prefabricated open caisson member and pour reinforced concrete to form a temporary concrete bottom seal.

6. The prefabricated caisson construction method in complex environments according to claim 1, characterized in that, Then adopt the sleeve valve pipe grouting method, and use the pre-reserved grouting holes on the prefabricated open caisson member to perform the second-stage reinforcement on the surrounding soil at the lower part of the open caisson, which includes: After the temporary concrete bottom seal reaches the design strength, connect the grouting equipment to the pre-reserved grouting holes on the prefabricated open caisson member; Inject cement-water glass double slurry into the grouting holes through the sleeve valve pipe to perform supplementary grouting reinforcement on the surrounding soil at the lower part of the open caisson; Control the grouting reinforcement range, so that the horizontal direction reaches 1~1.5m outside the lower well wall of the open caisson, the vertical direction reaches 1m below the top surface of the existing pipeline, and the grouting pressure is 1.0MPa; After the grouting is completed, wait for the slurry to solidify, and a reinforcement layer is formed in the surrounding soil at the lower part of the open caisson.

7. The prefabricated caisson construction method in complex environments according to claim 1, characterized in that, Based on the second-stage reinforcement and the temporary concrete sealing, the bottom of the temporary concrete sealing is excavated and concrete is poured downwards section by section using a reverse construction method until the lower part of the caisson wall extends downwards to the top surface of the existing pipeline, including: Remove the concrete from the cutting edge portion of the prefabricated caisson component described in the first section and peel off the reinforcing steel bars from the cutting edge portion; Based on the distance between the top surface of the existing pipeline and the bottom surface of the cutting edge of the prefabricated caisson component, determine the design length and the length of the extension steel bars for the reverse construction method; carry out the first section of reverse excavation below the temporary concrete seal, controlling the excavation depth of each section within 0.5m and not exceeding 0.8m; After the first section of excavation was completed, the reinforcing bars were immediately tied, the formwork was installed, and the side formwork was fixed using steel pipe frames. Early-strength concrete was poured into the template to form the lower part of the well wall in this section; Check the soil stability at the current excavation face. If the soil stability is insufficient, suspend construction and reinforce the excavation face with additional grouting. After the early-strength concrete reaches the preset strength, repeat the above excavation and pouring procedures to start the next cycle. Construction proceeds downwards segment by segment until the lower well wall extends to the top surface of the existing pipeline.

8. The prefabricated caisson construction method in complex environments according to claim 1, characterized in that, The temporary support and water diversion of the existing pipeline, and the breaking of the pipe wall at the corresponding part of the existing pipeline to connect the caisson to the existing pipeline, include: First, the water flow in the section of the existing pipeline that needs to be broken is cut off and diverted, and then the stress-bearing frame of the existing pipeline is constructed. Then, the pipe wall of the corresponding part of the existing pipe is broken, the width of the broken section is controlled to be 70cm, and three drainage outlets are evenly opened within the broken section, with each outlet spaced apart. Then, annular steel liners are installed inside the retained pipe sections extending 1.5m on both sides of the demolition section, and steel bars are implanted into the side walls of the retained pipe sections. The steel bars are anchored to the side walls of the retained pipe sections using anchoring adhesive, so that the existing pipe and the lower wall of the caisson are connected as a whole through the anchoring of steel bars.

9. The prefabricated caisson construction method in complex environments according to claim 1, characterized in that, The process involves pouring concrete for the bottom slab at the bottom of the caisson to form a fully enclosed structure, and then installing the permanent cover plate. The bottom plate reinforcement is tied to the bottom of the caisson, so that the bottom plate reinforcement is integrally connected with the wall reinforcement of the lower part of the caisson wall; The bottom slab concrete is poured at the bottom of the caisson and vibrated to compact it, so that the caisson structure forms an integral closed system. The poured bottom slab concrete is then cured. After the base slab concrete reaches the design strength, a leak detection test will be conducted. After the leak test is passed, cement grout is prepared and injected into the pre-reserved grouting holes on the prefabricated caisson component from bottom to top. The grouting pressure is controlled at 0.3~0.6MPa. The grout flowing out from the adjacent grouting hole is used as the criterion for judging the completion of grouting in a single hole. The grouting operation is completed hole by hole until the thixotropic mud is completely replaced. After the mud replacement is completed, the permanent cover plate is hoisted and placed on the caisson.

10. The prefabricated caisson construction method in complex environments according to claim 1, characterized in that, Also includes: Before prefabricating components, underground pipelines in the construction area are investigated, and traffic safety facilities are installed.

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