Segmented manufacturing and synchronous sinking construction method for open caisson

Abstract

The invention discloses an open caisson sectional manufacturing and synchronous sinking construction method, and relates to the technical field of open caisson construction.The open caisson sectional manufacturing and synchronous sinking construction method comprises the steps that a circular foundation pit is formed through excavation; two layers of medium-coarse sand are laid at the bottom of the circular foundation pit and tamped, and a sand cushion layer is formed; a plurality of sleepers are arranged on the sand cushion layer, and combined steel formworks are arranged on the multiple sleepers; a first section of anti-freezing and anti-seepage concrete body is formed through pouring of the combined steel formwork, and the combined steel formwork is dismantled; sinking the first section of anti-freezing and anti-seepage concrete body by adopting a dry operation method, and removing part of sleepers; a next section of anti-freezing and anti-seepage concrete body is constructed on the first section of anti-freezing and anti-seepage concrete body; and the next section of anti-freezing and anti-seepage concrete body is sunk through a dry operation method, and the other part of sleepers are removed till the open caisson structure is formed. The stability of the open caisson structure is improved, and the construction risk is reduced.

Description

Technical Field

[0001] This invention relates to the field of caisson construction technology, and in particular to a method for caisson segment fabrication and synchronous sinking. Background Technology

[0002] In the traditional construction of deep caissons, uneven soil excavation and changes in groundwater levels often lead to uneven release of soil reaction forces. This uneven release of soil reaction forces can cause construction risks such as tilting, displacement, or even sudden sinking of the caisson structure during construction. Summary of the Invention

[0003] The main objective of this invention is to propose a method for the segmented fabrication and synchronous sinking of caissons, which aims to reduce the risks of tilting, displacement, and sudden sinking caused by uneven release of local soil reaction forces during the construction of deep caissons.

[0004] To achieve the above objectives, the present invention proposes a method for segmented fabrication and simultaneous sinking of caissons, comprising: Excavation to form a circular foundation pit; Two layers of medium-coarse sand are laid at the bottom of the circular pit and compacted to form a sand cushion layer; Multiple sleepers are arranged on the sand cushion layer, and combined steel formwork is installed on the multiple sleepers; The first section of frost-resistant and impermeable concrete was poured using the combined steel formwork, and then the combined steel formwork was removed. The first section of the frost-resistant and impermeable concrete body was sunk using a dry operation method. Some of the sleepers were removed and C30 reinforced concrete was poured to seal the bottom of the first section of the frost-resistant and impermeable concrete body. The next section of frost-resistant and impermeable concrete is constructed on the first section of frost-resistant and impermeable concrete. The first section of the frost-resistant and impermeable concrete body and the next section of the frost-resistant and impermeable concrete body are sunk using the dry operation method. Another part of the sleepers are removed and the C30 reinforced concrete is poured again to seal the bottom of the next section of the frost-resistant and impermeable concrete body until the caisson structure is formed.

[0005] In one embodiment, the steps of sinking the first section of frost-resistant and impermeable concrete using a dry operation method, removing part of the sleepers, and pouring C30 reinforced concrete to seal the bottom of the first section of frost-resistant and impermeable concrete include: The dry operation method is used to cyclically excavate the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer at a preset depth until the first section of frost-resistant and impermeable concrete sinks to a preset distance; Remove the portion of the sleepers located beneath the first section of the frost-resistant and impermeable concrete structure; The bottom of the first section of frost-resistant and impermeable concrete was sealed by pouring C30 reinforced concrete.

[0006] In one embodiment, the step of using the dry excavation method to cyclically excavate the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer at a preset depth until the first section of frost-resistant and impermeable concrete sinks to a preset distance includes: Using the dry operation method, the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer are excavated at the center of the caisson to the preset depth to form a circular groove; Symmetrically excavate the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer along the periphery of the circular groove to form a flat bottom; The dry excavation method is used again to excavate the flat bottom at the center of the caisson to the preset depth, in order to form another larger circular groove; The flat bottom is excavated symmetrically along the periphery of the other circular groove until the first section of frost-resistant and impermeable concrete body sinks to a preset distance.

[0007] In one embodiment, the preset depth is h, where 0.4m ≤ h ≤ 0.6m.

[0008] In one embodiment, the steps of using the dry operation method to sink the first section of frost-resistant and impermeable concrete and the next section of frost-resistant and impermeable concrete, removing another portion of the sleepers, and re-pouring the C30 reinforced concrete to seal the bottom of the next section of frost-resistant and impermeable concrete until a caisson structure is formed include: Multiple three-section water-stop tie rods are installed on the outer periphery of the connection between the first section of the antifreeze and anti-permeability concrete body and the next section of the antifreeze and anti-permeability concrete body to form a water-stop frame. Multiple waterstop steel plates are installed on the waterstop frame, surrounding the connection between the first section of frost-resistant and impermeable concrete and the next section of frost-resistant and impermeable concrete. The first and next sections of frost-resistant and impermeable concrete are lowered, another part of the sleepers are removed, and C30 reinforced concrete is poured again to seal the bottom of the next section of frost-resistant and impermeable concrete until the caisson structure is formed.

[0009] In one embodiment, the step of laying two layers of medium-coarse sand at the bottom of the circular pit and compacting them to form a sand cushion layer includes: A first layer of medium-coarse sand of a preset thickness is laid at the bottom of the circular pit, water is sprinkled and it is compacted to a preset compaction coefficient; A second layer of medium-coarse sand is laid on the first layer of medium-coarse sand with the preset thickness, water is sprinkled and compacted to the preset compaction coefficient to form the sand cushion layer.

[0010] In one embodiment, the preset thickness is b, where 0.15m ≤ b ≤ 0.35m.

[0011] In one embodiment, the preset compaction coefficient is a, where 0.95 ≤ a.

[0012] In one embodiment, the steps of casting the first section of frost-resistant and impermeable concrete using the combined steel formwork and then removing the combined steel formwork include: Antifreeze-resistant and impermeable concrete is poured into the combined steel formwork at a first preset height to form the first layer of concrete, and a convex-concave construction joint is set on the first layer of concrete. Antifreeze-resistant and impermeable concrete is poured again on the first layer of concrete at a second preset height to form the first section of antifreeze-resistant and impermeable concrete body. The second preset height is greater than the first preset height. Remove the combined steel formwork.

[0013] In one embodiment, when the next section of frost-resistant and impermeable concrete is at the top layer, the step of applying the next section of frost-resistant and impermeable concrete on the first section of frost-resistant and impermeable concrete includes: The top slab of the next section of the frost-resistant and impermeable concrete body is constructed on the first section of the frost-resistant and impermeable concrete body at the first pouring height; The well wall of the next section of antifreeze and antipermeable concrete is constructed on the first section of antifreeze and antipermeable concrete at a second pouring height, wherein the second pouring height is greater than the first pouring height.

[0014] The technical solution of this invention effectively controls the uniform sinking of each segment of the caisson by constructing the concrete body in sections and simultaneously sinking it using a dry construction method, combined with a sand cushion layer and sleeper support system. Furthermore, the segmented bottom sealing and water-stopping structure solves the problems of caisson tilting, displacement, and segmental leakage found in traditional methods. The segmented construction process decomposes the overall load into multiple stages, avoiding stress concentration caused by a single sinking. The gradual removal of sleepers during simultaneous sinking, combined with the pouring of bottom sealing concrete, forms a stable intermediate support system, significantly reducing the risk of sudden sinking. The combined application of the sand cushion layer and sleepers optimizes the distribution of foundation reaction forces, ensuring the caisson structure maintains a uniform stress state throughout the sinking process. This improves the stability of the caisson structure and reduces construction risks. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1 This is a flowchart illustrating an embodiment of the caisson segment fabrication and synchronous sinking construction method provided by the present invention.

[0017] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0020] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0021] In existing technologies, traditional caisson construction typically employs a single-stage sinking process after integral casting. However, as the depth of underground space development increases and the caisson structure height exceeds conventional dimensions, the contact area between the caisson wall and the soil significantly increases during the sinking process, making it difficult to effectively control the distribution of soil reaction forces. Particularly in soft soil conditions, local differences in soil bearing capacity can easily cause the caisson to tilt, and sudden events often lead to caisson displacement or even structural damage. Existing technologies attempt to reinforce the foundation through layered excavation or grouting, but these methods struggle to simultaneously address the dynamic balance between structural weight transfer and soil stress release.

[0022] To address this technical problem, this invention proposes a method for the segmented fabrication and simultaneous sinking of caissons.

[0023] Please see Figure 1 In one embodiment of the present invention, the method for segmented fabrication and simultaneous sinking of the caisson includes: Step S10: Excavate to form a circular foundation pit; Step S20: Lay two layers of medium-coarse sand at the bottom of the circular pit and compact them to form a sand cushion layer; Step S30: Arrange multiple sleepers on the sand cushion layer, and install combined steel formwork on the multiple sleepers; Step S40: The first section of frost-resistant and impermeable concrete is poured using the combined steel formwork, and then the combined steel formwork is removed. Step S50: The first section of the frost-resistant and impermeable concrete body is sunk using a dry operation method. Some of the sleepers are removed and C30 reinforced concrete is poured to seal the bottom of the first section of the frost-resistant and impermeable concrete body. Step S60: Apply the next section of frost-resistant and impermeable concrete onto the first section of frost-resistant and impermeable concrete. Step S70: The first section of the frost-resistant and impermeable concrete body and the next section of the frost-resistant and impermeable concrete body are sunk using the dry operation method. Another part of the sleepers are removed and the C30 reinforced concrete is poured again to seal the bottom of the next section of the frost-resistant and impermeable concrete body until the caisson structure is formed.

[0024] The circular foundation pit refers to a circular trench excavated around the projected area of ​​the caisson. This can be achieved through mechanical excavation combined with manual finishing, and its function is to provide a uniform bearing surface for the sand cushion layer. The medium-coarse sand layer refers to sand material of suitable particle size, which can be laid in layers and compacted using a plate vibratory compaction process to form a flexible buffer layer that disperses the structural load. The sleepers are wooden load-bearing components arranged at intervals along the circular axis, specifically pine timber arranged radially, used to establish a multi-point support system between the sand cushion layer and the concrete body. The combined steel formwork refers to a mold assembled from standard modules, specifically using bolted, detachable steel plates to ensure uniform lateral pressure transmission during concrete pouring. Segmented bottom sealing refers to filling the bottom gaps after each section has sunk, specifically using the tremie method to continuously pour reinforced concrete, forming a progressively expanding base support surface.

[0025] Specifically, at the bottom of the excavated circular foundation pit, a sand cushion layer is formed by laying medium-coarse sand in layers and compacting each layer to ensure uniform load distribution. Sleepers are arranged in a ring on the surface of the sand cushion layer, forming discrete support points to reduce localized pressure. Combined steel formwork is erected above the sleepers, and after the first section of concrete is poured, the soil below is removed using a dry-work method to achieve controlled sinking. During the sinking of the first section, the sleepers are removed in stages, and sealing concrete is poured into the resulting gaps to form a staged stable base. Subsequent concrete sections are poured on top of the sunken structure, and a synchronous sinking process allows the upper and lower sections to work together, gradually removing the remaining sleepers and completing the final sealing, thus achieving the progressive forming of the caisson structure.

[0026] This method reduces the depth of single-stage settlement by constructing sections, achieving a dynamic balance between soil stress release and structural stiffness enhancement. Existing technologies using continuous excavation are prone to sudden settlement, while staged removal of sleepers combined with bottom sealing creates a stepped bearing capacity compensation mechanism. Conventional single-layer sand cushions are insufficient to withstand large loads, while double-layer compaction enhances the stress diffusion capacity of the foundation.

[0027] The technical solution provided by this invention utilizes segmented concrete construction and synchronous dry-laying methods, combined with a sand cushion layer and sleeper support system, to effectively control the uniform sinking of each segment of the caisson. Furthermore, the segmented bottom sealing and water-stopping structures solve the problems of caisson tilting, displacement, and segmental leakage found in traditional methods. The segmented construction process decomposes the overall load into multi-stage transmission, avoiding stress concentration caused by a single sinking. The gradual removal of sleepers during synchronous sinking, combined with the pouring of bottom sealing concrete, forms a stable intermediate support system, significantly reducing the risk of sudden sinking. The combined application of the sand cushion layer and sleepers optimizes the distribution of foundation reaction forces, ensuring the caisson structure maintains a uniform stress state throughout the sinking process. This improves the stability of the caisson structure and reduces construction risks.

[0028] In an embodiment of the present invention, the steps of sinking the first section of frost-resistant and impermeable concrete using a dry operation method, removing part of the sleepers, and pouring C30 reinforced concrete to seal the bottom of the first section of frost-resistant and impermeable concrete include: Step S51: Using the dry operation method, the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer are excavated in a cyclic manner at a preset depth until the first section of frost-resistant and impermeable concrete sinks to a preset distance. Step S52: Remove part of the sleepers below the first section of frost-resistant and impermeable concrete; Step S53: Pour C30 reinforced concrete to seal the bottom of the first section of frost-resistant and impermeable concrete body.

[0029] The dry-operation sinking method described in this application refers to a construction process in which the caisson is kept dry, either without water or with minimal water, during the sinking process. Soil below and around the cutting edge of the caisson is removed manually or mechanically, allowing the caisson to gradually sink to the design elevation under its own weight, overcoming the frictional resistance of the caisson wall. This method is suitable for geological conditions with low groundwater levels or after dewatering treatment. Its advantages include clear visibility inside the caisson, easy control of the sinking direction and speed, and ease of observation and handling of problems encountered during construction. Furthermore, in this application, the dry-operation sinking method allows for accurate positioning and phased removal of pre-placed sleepers, ensuring that reinforced concrete is poured at the appropriate time for bottom sealing, thereby guaranteeing the construction quality and overall stability of the caisson structure. Furthermore, the specific implementation method of the dry operation method in this application includes the following steps: First, before the caisson is lowered, it must be ensured that the groundwater level in the construction area is lower than the excavation surface. If the groundwater level is high, dewatering measures such as wellpoint dewatering, deep well dewatering, or curtain grouting must be adopted to lower the groundwater level to at least 0.5 to 1.0 meters below the excavation surface, keeping the well dry. Second, in the well, manual labor combined with small excavating machinery is used to symmetrically and evenly remove the soil below the cutting edge. The excavation sequence follows the principle of "first the middle, then the perimeter, layered and block-based, uniform and symmetrical". The thickness of each excavation is controlled at 0.3 to 0.5 meters to avoid caisson collapse. The excavated soil should be promptly removed from the caisson using buckets, conveyor belts, or vertical lifting equipment to maintain unobstructed working space inside. Simultaneously, during the sinking process, continuous monitoring should be conducted for any water seepage or gushing. If minor seepage occurs, a sump and pump should be used to drain the water promptly, ensuring the caisson remains dry. Finally, once the caisson reaches the predetermined depth, the pre-laid sleepers should be removed in batches according to design requirements, and C30 reinforced concrete should be poured immediately to seal the bottom, completing the construction of this section of the caisson. Throughout the entire process, dry working conditions should be maintained inside the caisson to ensure construction safety and quality control. Cyclic excavation refers to the repeated excavation of soil in stages, which can be achieved using mechanical excavation equipment combined with manual trimming. Step-by-step excavation ensures the continuity of the sinking process. Removing some sleepers refers to gradually removing the supporting structure after the concrete body sinks. This can be achieved through segmented dismantling, avoiding sudden changes in stress during sinking by removing the supports in batches. C30 reinforced concrete refers to concrete with a strength grade of 30MPa and without steel reinforcement. This can be achieved by adjusting the cement and aggregate ratio. Its fluidity and hardening characteristics can meet the requirements of bottom sealing operations.

[0030] Specifically, during the sinking of the first section of the frost-resistant and impermeable concrete, the soil was first excavated using a dry method, with each excavation depth controlled within a preset range. This cyclical operation allowed the concrete to gradually sink to the target position. Once the preset sinking distance was reached, the sleepers supporting the structure were removed in batches, with the number removed dynamically adjusted based on sinking monitoring data. Finally, C30 reinforced concrete was continuously poured in the cleared work space to form a complete sealing layer. This process ensured the uniform release of soil reaction forces during sinking by controlling the amount of soil excavation, the amount of support removal, and the rhythm of the sealing construction in stages.

[0031] This scheme employs a gradual settlement process through cyclical excavation at a predetermined depth, combined with phased removal of sleepers, to progressively adjust soil stress and effectively prevent sudden settlement. Simultaneously, a reinforced concrete bottom sealing technique is used to reduce construction complexity while ensuring structural stability.

[0032] This application enables precise control of the sinking rate and attitude of the caisson structure, preventing tilting accidents caused by localized soil stress concentration. The phased removal of supports and layered sealing operations work synergistically to ensure uniform distribution of foundation reaction forces during sinking, significantly reducing construction risks. The continuous pouring of the reinforced concrete sealing layer further enhances the bearing capacity of the structure's bottom, providing a stable foundation for subsequent segmental construction.

[0033] In an embodiment of the present invention, the step of using the dry excavation method to cyclically excavate the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer at a preset depth until the first section of frost-resistant and impermeable concrete sinks to a preset distance includes: Step S511: Using the dry operation method, excavate the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer at the center of the caisson to the preset depth to form a circular groove. Step S512: Symmetrically excavate the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer along the periphery of the circular groove to form a flat bottom; Step S513: The dry operation method is used again to excavate the flat bottom at the center of the caisson to the preset depth to form another larger circular groove; Step S514: symmetrically excavate the flat bottom along the periphery of the other circular groove until the first section of frost-resistant and impermeable concrete body sinks to a preset distance.

[0034] The preset depth refers to the vertical height of a single excavation operation, for example, it can be set to 0.5 meters, and the sinking speed can be controlled by excavating in stages.

[0035] Specifically, after initially excavating to form a circular groove at the center of the caisson, symmetrical excavation is carried out along the edge of the groove to form a flat bottom support surface. After the first layer of sinking is completed, a second excavation is carried out at the center of the flat bottom to form a new groove, and the symmetrical expansion operation is repeated. This step-by-step cyclical excavation method allows the soil support force to be released gradually and evenly. Through the alternating formation of the central groove and the surrounding flat bottom, the stress concentration area at the bottom of the caisson is effectively dispersed. The excavation depth is controlled within a preset range, for example, a depth of 0.4 to 0.6 meters, which ensures that the sinking amount in a single step is controllable and avoids the risk of sudden sinking due to over-excavation.

[0036] This method utilizes a centrally symmetrical, layered, cyclical excavation process to release soil stress in stages, overcoming the tilting problem caused by excessive removal of soil on one side in existing technologies. Compared to direct, full-scale excavation to form a large working surface, the step-by-step formation of a circular groove and a flat bottom combined structure is more conducive to maintaining the dynamic balance of forces in all directions on the caisson.

[0037] This application effectively controls the release rate of soil support force during the sinking process of the caisson. Through a centrally symmetrical step-by-step excavation process, the caisson obtains uniform sinking force in the vertical direction. The initial excavation of the circular groove defines the stress release core area, and the symmetrical expansion of the flat bottom structure ensures the balanced distribution of the surrounding support force. The dual effects work together to suppress the occurrence of caisson displacement and sudden sinking.

[0038] In an embodiment of the present invention, the preset depth is h, where 0.4m ≤ h ≤ 0.6m.

[0039] The preset depth h refers to the vertical distance of a single downward excavation in each excavation operation. This depth can be controlled using a laser rangefinder or a mechanical limiting device. The depth range is determined by balancing the soil stress release rate and the structural settlement stability. This range is chosen because excessively shallow excavation depths increase the number of cycles, leading to reduced construction efficiency, while excessively deep excavation depths may cause sudden changes in local soil bearing capacity.

[0040] Specifically, during the initial excavation at the center of the caisson, controlling the excavation depth to no more than 0.6 meters per layer allows for the phased release of soil stress. Once a circular groove is formed, maintaining the same excavation depth during symmetrical excavation of the surrounding soil prevents stress concentration on one side. This depth range ensures a controllable settlement of the caisson structure after each layer of soil excavation; for example, each settlement can be controlled within the range of 50-80 millimeters, achieving stable settlement through multiple cycles. During the secondary excavation in the flat-bottom area, this depth parameter is maintained to ensure uniform reduction of soil support force in all areas.

[0041] Through the above technical solutions, this application effectively controls the stress release gradient during soil excavation, ensuring that the verticality deviation of the caisson structure remains within allowable limits during phased sinking; for example, the inclination rate can be controlled within 0.5%. By standardizing excavation parameters, the number of correction operations caused by improper depth selection is reduced, ensuring that the structural posture meets design requirements before the bottom sealing concrete is poured.

[0042] In an embodiment of the present invention, the steps of using the dry operation method to sink the first section of frost-resistant and impermeable concrete and the next section of frost-resistant and impermeable concrete, removing another part of the sleepers, and re-pouring the C30 reinforced concrete to seal the bottom of the next section of frost-resistant and impermeable concrete until a caisson structure is formed include: Step S71: Multiple three-section water-stop tie rods are installed on the outer periphery of the connection between the first section of the antifreeze and anti-permeability concrete body and the next section of the antifreeze and anti-permeability concrete body to form a water-stop frame. Step S72: Install multiple waterstop steel plates on the waterstop frame, which surround the connection between the first section of frost-resistant and impermeable concrete and the next section of frost-resistant and impermeable concrete. Step S73: Sink the first section of frost-resistant and impermeable concrete and the next section of frost-resistant and impermeable concrete, remove another part of the sleepers and pour the C30 reinforced concrete again to seal the bottom of the next section of frost-resistant and impermeable concrete until the caisson structure is formed.

[0043] The three-section water-stop tie rod refers to a connecting rod consisting of a middle water-stop section and two fixed sections at both ends. Specifically, it can be implemented with a middle section made of rubber sealing material and both ends made of threaded steel rods. The water-stopping effect at the connection is achieved by pre-embedding the fixed sections and pressing the sealing sections together. The water-stop steel plate refers to a metal plate with a folded edge structure. Specifically, it can be made of 3mm thick galvanized steel plate bent into an L-shape or U-shape, and fixed to the water-stop frame by welding or bolting to cover the gaps at the concrete connection.

[0044] Specifically, in the outer area of ​​the joint between the upper and lower concrete sections, the fixed sections at both ends of the three-section water-stop tie rod are first pre-embedded into the adjacent concrete sections, with the middle sealing section exposed outside the joint to form a continuous water-stop zone. Next, L-shaped water-stop steel plates are continuously laid along the circumference of the joint and welded to the fixed sections of the water-stop tie rod to form a double sealing barrier. During the sinking process, the water-stop frame and steel plates work together to effectively prevent external water from seeping into the joint. Simultaneously, by evenly removing the sleepers and pouring the bottom sealing concrete in stages, the overall uniform sinking of the caisson structure is ensured.

[0045] This solution uses a combination of three-section tie rods and folded steel plates to achieve active sealing at the joints and maintain the geometric stability of the caisson structure through rigid support, significantly reducing the risk of sudden changes in local soil bearing capacity caused by water seepage.

[0046] In an embodiment of the present invention, the step of laying two layers of medium-coarse sand at the bottom of the circular foundation pit and compacting them to form a sand cushion layer includes: Step S21: Lay the first layer of medium-coarse sand at the bottom of the circular pit with a preset thickness, sprinkle water and compact it to a preset compaction coefficient; Step S22: Lay a second layer of medium-coarse sand on the first layer of medium-coarse sand with the preset thickness, sprinkle water and compact it to the preset compaction coefficient to form the sand cushion layer.

[0047] Medium-coarse sand refers to sand with a fineness modulus between 2.3 and 3.7, specifically made from natural river sand or manufactured sand. It features continuous particle size distribution and a mud content below 3%, effectively transferring loads and reducing compressive deformation. The preset thickness refers to the thickness of a single layer of medium-coarse sand, for example, between 0.15 meters and 0.35 meters. This thickness range ensures sufficient load-bearing capacity after compaction and facilitates construction. Watering and compaction involves wetting the sand layer in layers and then compacting it using a plate vibrator or roller. Specifically, the amount of water sprayed can be controlled to achieve the optimal moisture content for compaction, thereby improving the overall density of the sand cushion layer. The preset compaction coefficient is the ratio of the dry density of the compacted sand layer to its maximum dry density, for example, set to no less than 0.95. This indicator quantifies the density of the sand cushion layer, ensuring its stability as a foundation bearing layer.

[0048] Specifically, during construction, the first layer of medium-coarse sand is evenly spread at the bottom of the foundation pit, with the thickness controlled mechanically or manually. Water is then sprayed to bring the sand layer to its optimal moisture content. Next, compaction equipment is used to repeatedly roll the first layer of sand until the preset compaction coefficient is achieved. After completing the first layer, the same steps are repeated on the compacted surface to lay and compact the second layer of sand, ultimately forming a composite sand cushion layer with uniform load-bearing capacity. This layered construction method, through two independent compaction processes, eliminates the internal density differences caused by a single thick layer.

[0049] This scheme controls the thickness and compaction coefficient in layers to form a stable layered structure in the sand cushion layer, significantly reducing the risk of stress concentration caused by local loose areas.

[0050] In an embodiment of the present invention, the preset thickness is b, where 0.15m ≤ b ≤ 0.35m.

[0051] The preset thickness refers to the thickness of each layer of medium-coarse sand, which can be precisely controlled using layered paving equipment, for example, between 0.15 meters and 0.35 meters. This thickness range ensures that each layer of sand is fully compacted during the compaction process, while preventing the compaction energy from being ineffectively transferred to the bottom layer due to excessive thickness.

[0052] Specifically, when constructing the sand cushion layer at the bottom of the foundation pit, medium-coarse sand is first evenly laid on the base to a predetermined thickness using paving equipment, for example, a laser leveling instrument is used to control the laying thickness to 0.25 meters. Then, a water truck is used to evenly moisten the sand, ensuring the sand reaches its optimal moisture content for compaction. Next, a plate vibratory compactor is used, with the number of compaction passes determined by on-site testing, until the predetermined compaction coefficient is achieved. After completing the first layer, the same procedure is repeated for the second layer, ultimately forming a double-layer sand cushion layer. This construction method, by precisely controlling the thickness of each layer, ensures that the sand layer achieves a uniform and dense compaction effect during the compaction process.

[0053] This method, by limiting the layer thickness and combining it with a layered compaction process, makes the overall density of the sand layer more uniform, effectively improving the bearing stability of the sand cushion layer, thereby providing reliable foundation support for the subsequent caisson structure.

[0054] In an embodiment of the present invention, the preset compaction coefficient is a, where 0.95 ≤ a.

[0055] The preset compaction coefficient refers to the ratio of the compacted density of the sand layer to its maximum density after compaction. This can be achieved through layered watering, mechanical rolling, or vibratory compaction. This parameter is used to quantify the density control standard of the sand cushion layer. A compaction coefficient ≥0.95 indicates that the sand layer needs to achieve a high degree of compaction after compaction. This can be achieved by comparing the dry density of the sand layer in layers with the maximum dry density measured in the laboratory. This requirement ensures that the sand cushion layer has uniform bearing capacity and resistance to deformation.

[0056] Specifically, during construction at the bottom of the circular foundation pit, the first layer of medium-coarse sand is laid. After moistening with water, it is compacted in layers using a road roller or plate compactor. After each layer is completed, the compaction coefficient is tested using the ring cutter method or sand cone method until it reaches 0.95 or higher. Then, the second layer of medium-coarse sand is laid, and the above compaction and testing process is repeated to finally form a sand cushion layer with the required density and uniform distribution. By strictly controlling the compaction coefficient of each layer, the sand cushion layer can provide a stable support base for the upper sleepers and concrete structure, avoiding uneven stress during the sinking of the caisson due to local loose sand layers.

[0057] This solution significantly improves the overall density and uniformity of the sand cushion layer by setting a lower limit for the compaction coefficient and conducting layered testing, thereby reducing the risk of displacement of the caisson caused by differences in the base support force from the root.

[0058] In an embodiment of the present invention, the steps of casting the first section of frost-resistant and impermeable concrete using the combined steel formwork and then removing the combined steel formwork include: Step S41: Pour antifreeze and impermeable concrete into the combined steel formwork at a first preset height to form a first layer of concrete, and set a convex and concave construction joint on the first layer of concrete. Step S42: Pour antifreeze and impermeable concrete again on the first layer of concrete at a second preset height to form the first section of antifreeze and impermeable concrete body. The second preset height is greater than the first preset height. Step S43: Remove the combined steel formwork.

[0059] Among them, combined steel formwork refers to a ring-shaped support structure assembled from multiple standardized steel formwork panels. Specifically, it can be achieved using arc-shaped steel plates with bolted connections. Its function is to provide rigid support for concrete pouring and control structural dimensions. Freeze-thaw resistant and impermeable concrete refers to concrete materials with freeze-thaw cycle resistance and impermeability. Specifically, it can be achieved using C30 concrete with added air-entraining agents and water-reducing agents. Its function is to maintain structural durability in groundwater environments. Concave-convex construction joints refer to the interlocking interface formed by formwork molding. Specifically, it can be achieved using precast formwork components with trapezoidal or wavy cross-sections. Its function is to increase the bond strength between upper and lower concrete layers by increasing the contact area. The first preset height refers to the thickness of the first poured concrete layer, for example, it can be controlled within the range of 0.8~1.2 meters. Its function is to control the temperature stress generated by the heat of hydration of concrete through layered pouring. The second preset height refers to the thickness of the second poured concrete layer, for example, it can be controlled within the range of 1.5~2.0 meters and must be greater than the height of the first layer. Its function is to avoid shrinkage cracks caused by continuous pouring through differentiated layering.

[0060] Specifically, after laying sleepers and erecting combined steel formwork on the sand cushion layer surface, frost-resistant and impermeable concrete is first poured into the formwork to the first preset height. Before the concrete initially sets, a trapezoidal cross-section molded template is inserted to form an interlocking structure on the surface. After the first layer of concrete reaches its design strength, the second layer of concrete is poured to the second preset height, allowing the upper layer of concrete to fully fill the lower interlocking structure and form a mechanical interlock. Once the overall structural strength meets the requirements, the formwork connecting bolts are removed sequentially, and the steel formwork is taken out, forming a complete well structure with continuous construction joints.

[0061] In some specific implementations, the first preset height can be set to 1.0 meter, at which point a trapezoidal cross-section plate with a depth of 15 cm is inserted to form a construction joint during the initial setting stage of the concrete. The second preset height can be set to 1.8 meters, during pouring, a vibrator is used to fully fill the lower uneven structure with concrete, forming an effective bonding interface. The combined steel formwork can use 5 mm thick arc-shaped steel plates, connected by M20 bolts to form a ring formwork with a diameter of 12 meters.

[0062] This solution controls structural stress through layered casting, and the concave-convex interface design creates a three-dimensional interlocking structure between the upper and lower layers, significantly improving the shear resistance of the joints. Differential height settings effectively avoid cold joint defects caused by continuous construction, ensuring the integrity and waterproof performance of the well structure.

[0063] In an embodiment of the present invention, when the next section of frost-resistant and impermeable concrete is at the top layer, the step of applying the next section of frost-resistant and impermeable concrete on the first section of frost-resistant and impermeable concrete includes: Step S701: Construct the top slab of the next section of the frost-resistant and impermeable concrete body on the first section of the frost-resistant and impermeable concrete body at the first pouring height; Step S702: The well wall of the next section of antifreeze and antipermeable concrete is constructed on the first section of antifreeze and antipermeable concrete at a second pouring height, wherein the second pouring height is greater than the first pouring height.

[0064] The first pouring height refers to the vertical dimension of a single pour of the top slab, which can be achieved using a layered pouring process, such as dividing the top slab into single or multiple layers and pouring them sequentially to the target thickness. The second pouring height refers to the vertical dimension of a single pour of the well wall, which can be achieved using a continuous pouring process, such as controlling the pouring range of the well wall by adjusting the formwork height. By setting differentiated pouring heights, a gradient is created in the concrete setting time of the top slab and the well wall, avoiding cold joints caused by synchronous setting shrinkage.

[0065] Specifically, during the construction of the top slab, the concrete is poured in layers to the first pouring height, for example, using a layered vibration compaction process to ensure density. Subsequently, the formwork for the well wall is installed to the second pouring height, and the concrete is continuously poured to this height, for example, using pumping equipment to achieve efficient filling. Because the second pouring height is greater than the first pouring height, the initial setting time of the concrete in the top slab is earlier than that of the well wall, and the interface between the two forms an interlocking joint during the solidification process, avoiding cold joints caused by temperature shrinkage or stress concentration.

[0066] This solution uses differentiated height control to create a time difference in the solidification process between the top plate and the well wall, thereby dispersing the shrinkage stress of the concrete at the interface and eliminating the conditions for cold joint formation.

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

Claims

1. A method for segmented fabrication and simultaneous sinking of a caisson, characterized in that, include: Excavation to form a circular foundation pit; Two layers of medium-coarse sand are laid at the bottom of the circular pit and compacted to form a sand cushion layer; Multiple sleepers are arranged on the sand cushion layer, and combined steel formwork is installed on the multiple sleepers; The first section of frost-resistant and impermeable concrete was poured using the combined steel formwork, and then the combined steel formwork was removed. The first section of frost-resistant and impermeable concrete was sunk using a dry operation method, and some of the sleepers were removed and C30 reinforced concrete was poured. The next section of frost-resistant and impermeable concrete is constructed on the first section of frost-resistant and impermeable concrete. The first section of the frost-resistant and impermeable concrete body and the next section of the frost-resistant and impermeable concrete body are sunk using the dry operation method. Another part of the sleepers are removed and the C30 reinforced concrete is poured again to seal the bottom of the next section of the frost-resistant and impermeable concrete body until the caisson structure is formed.

2. The method for segmented fabrication and synchronous sinking of a caisson as described in claim 1, characterized in that, The steps of sinking the first section of frost-resistant and impermeable concrete using the dry operation method, removing part of the sleepers, and pouring C30 reinforced concrete include: The dry operation method is used to cyclically excavate the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer at a preset depth until the first section of frost-resistant and impermeable concrete sinks to a preset distance; Remove the portion of the sleepers located beneath the first section of the frost-resistant and impermeable concrete structure; The bottom of the first section of frost-resistant and impermeable concrete was sealed by pouring C30 reinforced concrete.

3. The method for segmented fabrication and synchronous sinking of caissons as described in claim 2, characterized in that, The steps of using the dry excavation method to cyclically excavate the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer at a preset depth until the first section of frost-resistant and impermeable concrete sinks to a preset distance include: Using the dry operation method, the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer are excavated at the center of the caisson to the preset depth to form a circular groove; Symmetrically excavate the first section of frost-resistant and impermeable concrete and the soil below the sand cushion layer along the periphery of the circular groove to form a flat bottom; The dry excavation method is used again to excavate the flat bottom at the center of the caisson to the preset depth, in order to form another larger circular groove; The flat bottom is excavated symmetrically along the periphery of the other circular groove until the first section of frost-resistant and impermeable concrete body sinks to a preset distance.

4. The method for segmented fabrication and synchronous sinking of caissons as described in claim 3, characterized in that, The preset depth is h, where 0.4m ≤ h ≤ 0.6m.

5. The method for caisson segment fabrication and synchronous sinking as described in any one of claims 1 to 4, characterized in that, The steps of using the dry operation method to sink the first section of frost-resistant and impermeable concrete and the next section of frost-resistant and impermeable concrete, removing another part of the sleepers, and re-pouring the C30 reinforced concrete to seal the bottom of the next section of frost-resistant and impermeable concrete until the caisson structure is formed include: Multiple three-section water-stop tie rods are installed on the outer periphery of the connection between the first section of the antifreeze and anti-permeability concrete body and the next section of the antifreeze and anti-permeability concrete body to form a water-stop frame. Multiple waterstop steel plates are installed on the waterstop frame, surrounding the connection between the first section of frost-resistant and impermeable concrete and the next section of frost-resistant and impermeable concrete. The first and next sections of frost-resistant and impermeable concrete are lowered, another part of the sleepers are removed, and C30 reinforced concrete is poured again to seal the bottom of the next section of frost-resistant and impermeable concrete until the caisson structure is formed.

6. The method for caisson segment fabrication and synchronous sinking as described in any one of claims 1 to 4, characterized in that, The steps of laying two layers of medium-coarse sand at the bottom of the circular foundation pit and compacting them to form a sand cushion layer include: A first layer of medium-coarse sand of a preset thickness is laid at the bottom of the circular pit, water is sprinkled and it is compacted to a preset compaction coefficient; A second layer of medium-coarse sand is laid on the first layer of medium-coarse sand with the preset thickness, water is sprinkled and compacted to the preset compaction coefficient to form the sand cushion layer.

7. The method for segmented fabrication and synchronous sinking of a caisson as described in claim 6, characterized in that, The preset thickness is b, where 0.15m ≤ b ≤ 0.35m.

8. The method for segmented fabrication and synchronous sinking of a caisson as described in claim 6, characterized in that, The preset compaction coefficient is a, and 0.95≤a.

9. The method for caisson segment fabrication and synchronous sinking as described in any one of claims 1 to 4, characterized in that, The steps of pouring the first section of frost-resistant and impermeable concrete using the combined steel formwork and then removing the combined steel formwork include: Antifreeze-resistant and impermeable concrete is poured into the combined steel formwork at a first preset height to form the first layer of concrete, and a convex-concave construction joint is set on the first layer of concrete. Antifreeze-resistant and impermeable concrete is poured again on the first layer of concrete at a second preset height to form the first section of antifreeze-resistant and impermeable concrete body. The second preset height is greater than the first preset height. Remove the combined steel formwork.

10. The method for caisson segment fabrication and synchronous sinking as described in any one of claims 1 to 4, characterized in that, When the next section of frost-resistant and impermeable concrete is at the top layer, the steps of applying the next section of frost-resistant and impermeable concrete on the first section of frost-resistant and impermeable concrete include: The top slab of the next section of the frost-resistant and impermeable concrete body is constructed on the first section of the frost-resistant and impermeable concrete body at the first pouring height; The well wall of the next section of antifreeze and antipermeable concrete is constructed on the first section of antifreeze and antipermeable concrete at a second pouring height, wherein the second pouring height is greater than the first pouring height.

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