A caisson type water carrying construction pump set foundation and a construction method thereof

Abstract

The application discloses a caisson type water construction pump set foundation and a construction method thereof, and belongs to the field of pump set construction. When the caisson type water construction pump set foundation is constructed, a double-layer supporting net is laid underwater and graded gravel is filled after the caisson box is sunk to the design elevation, self-compacting concrete is poured on the top of the gravel layer through the pipe method, the concrete penetrates into the upper gap of the gravel layer to form a sealing band to realize bottom sealing and blocking, the sealing layer reaches the strength, and water is pumped out in stages, fine particles are carried by laminar flow penetration to form a reverse filtration closed layer by natural siltation at the supporting net, the underwater poured concrete top surface is chiseled after being pumped out, and structural bearing concrete is poured in a dry environment to serve as a pump set installation bearing surface. The sealing function and the bearing function are separated to different structural levels, sealing is realized by thin-layer underwater concrete, and bearing quality is ensured by dry pouring concrete, so that the uncontrollable quality problem of the traditional integrated underwater pouring scheme is solved.

Description

Technical Field

[0001] This invention relates to the field of pump unit construction technology, specifically to a caisson-type pump unit foundation for water-supported construction and its construction method. Background Technology

[0002] Pump foundations are the core load-bearing structures in pump station construction during water conservancy projects. Their construction quality and structural integrity directly affect the long-term stability and safety of the pump unit. In water-related environments, the construction of pump foundations needs to simultaneously resolve the contradiction between underwater operating conditions and structural sealing and load-bearing capacity, which places high demands on construction technology.

[0003] In existing technologies, for pump foundation construction in aquatic environments, the tremie method is typically used to directly pour underwater concrete into the entire space at the bottom of the caisson to form an integrated foundation support. The construction process is as follows: multiple tremie pipes are arranged according to the bottom area of ​​the caisson. Each tremie pipe consists of multiple short pipe sections connected by flanges, with a funnel at the top to receive concrete. During construction, the tremie pipes are vertically placed in the water, and the water inside the pipes is separated from the concrete by a water-tight plug. A large amount of concrete is initially poured to squeeze out the water inside the pipes before continuous pouring, keeping the bottom of the pipes buried below the concrete surface throughout the process. The concrete is squeezed out and spreads outwards within the poured structure. As the concrete surface rises, the tremie pipes are dismantled and raised section by section until the pouring surface reaches above the design elevation, at which point the pipes are removed.

[0004] However, the aforementioned integrated underwater concrete pump unit foundation still has the following drawbacks: the entire bottom space of the caisson is filled with underwater concrete, and the sealing and load-bearing functions are borne by the same concrete body, making separate design impossible. Furthermore, the large volume of underwater concrete is susceptible to defects such as honeycomb, voids, and mud inclusions during the pouring process due to factors such as water flow disturbance, control of the guide pipe lifting speed, deviations in the initial pouring volume calculation, and uneven concrete diffusion at the junction of multiple pipes. Additionally, a water-soaked laitance layer forms on the top surface, making it impossible to guarantee the overall density and strength uniformity of the concrete. Using it directly as the structural load-bearing surface for precision pump equipment cannot meet the equipment's stringent requirements for foundation flatness, strength uniformity, and long-term stability. Summary of the Invention

[0005] The purpose of this invention is to provide a caisson-type underwater pump unit foundation and its construction method, in order to solve the problem that the existing integrated underwater casting scheme couples the sealing function and the load-bearing function into the same large-volume underwater concrete body, which makes it difficult to avoid internal defects in the concrete and the overall quality uncontrollable. It is also impossible to simultaneously meet the problem of reliable sealing at the bottom of the foundation and the strict requirements of uniform strength and flatness of the bearing surface of the upper precision pump unit equipment.

[0006] The technical problem to be solved by the present invention can be achieved through the following technical solution: a caisson-type pump set foundation for underwater construction, comprising: a caisson body, wherein the caisson body is a concrete box structure with an open bottom; the bottom of the caisson body is provided with an outer support net, an inner support net, a gravel layer, underwater cast concrete, and structural support concrete in sequence from bottom to top; wherein, the outer support net is fixed to the outer side of the bottom of the caisson body, the inner support net is fixed to the inner side of the bottom of the caisson body, and a preset distance is maintained between the inner support net and the inner wall of the caisson body; the gravel layer is supported above the inner support net; the underwater cast concrete is poured and covers the upper surface of the gravel layer and penetrates into the upper gaps of the gravel layer to form an interlocking band to achieve sealing and blocking; the structural support concrete is poured on the roughened surface of the underwater cast concrete and forms a mechanical anchoring connection with the underwater cast concrete; the top surface of the structural support concrete is used to install the pump set.

[0007] Preferably, the mesh size of the outer support mesh is larger than that of the inner support mesh, and the mesh size of the inner support mesh is smaller than that of the smallest particle size of the crushed stone in the crushed stone layer.

[0008] Preferably, the crushed stone layer adopts a gradation method in which large-diameter crushed stone forms the skeleton and small-diameter crushed stone fills the gaps between the skeleton.

[0009] Preferably, the roughening depth of the top surface of the underwater cast concrete is not less than 6mm, and the roughening area is not less than 70% of the total area of ​​the top surface of the underwater cast concrete.

[0010] Preferably, the outer and inner sides of the bottom of the caisson body 1 are respectively provided with pre-embedded anchors along the circumference. The outer support net is fixedly connected to the outer side of the bottom of the caisson body through the outer pre-embedded anchors, and the inner support net is fixedly connected to the inner side of the bottom of the caisson body through the inner pre-embedded anchors.

[0011] Preferably, the underwater concrete is self-compacting concrete with a slump spread of not less than 600 mm.

[0012] Preferably, the ratio of the maximum to the minimum particle size of the crushed stone in the crushed stone layer is in the range of 2-3:1, and the flatness deviation of the top surface of the crushed stone layer after compaction and leveling does not exceed 20mm.

[0013] Preferably, the structure is provided with a steel mesh frame inside the concrete, and the bottom of the steel mesh frame is anchored into the pit of the roughened surface of the underwater concrete.

[0014] Preferably, the construction method of the caisson-type pump set foundation with water support includes the following steps: S1: Caisson fabrication and sinking. A caisson box with an open bottom is fabricated on the ground. The caisson box is placed in the construction water area. Soil is removed from the inside of the caisson box using a grab bucket, allowing the caisson box to gradually sink to the design elevation under its own weight. S2: Lay the support net. Lay the outer support net underwater and fix it to the pre-embedded anchor on the outer side of the bottom of the caisson body. Then lay the inner support net and fix it to the pre-embedded anchor on the inner side of the bottom of the caisson body. A preset distance is maintained between the inner support net and the inner wall of the caisson body. S3: Fill with crushed stone layer. Underwater crushed stone is placed inwards above the support net and compacted to form a crushed stone layer. The gradation of the crushed stone is controlled so that the porosity of the upper part of the crushed stone layer is between 25% and 35%. S4: Underwater casting of sealing and blocking layer. Self-compacting concrete is cast underwater above the crushed stone layer through the duct method. The concrete slurry seeps into the gaps in the upper part of the crushed stone layer under its own weight to form an interlocking band. After solidification, it forms an underwater cast concrete that is integrated with the crushed stone layer, thus achieving sealing and blocking of the bottom of the caisson. S5: Staged pumping. After the underwater concrete reaches the design strength, the water level in the caisson is reduced in stages. The pumping rate at each stage is controlled so that the seepage below the underwater concrete is in a laminar flow state. The seepage carries fine particles from the surrounding soil to naturally block the bottom of the gravel layer and the outer and inner support nets to form a reverse filter sealing layer until the water in the caisson is pumped out. S6: Roughening treatment, the top surface of the underwater poured concrete is washed and roughened to remove surface laitance and loose material, forming an irregular rough surface. S7: Pour the structural support layer, tie the steel mesh on the roughened surface and pour the structural support concrete, so that the structural support concrete and the underwater concrete form a mechanical anchoring connection through the roughened surface. After the structural support concrete reaches the design strength, install the pump set.

[0015] Preferably, in step S5, the depth of each stage of precipitation is 300-500 mm. After each stage of precipitation, the pump is stopped and observed for no less than 12 hours, and the return water rate is recorded. When the return water rate of a certain stage is greater than the return water rate of the previous stage, pumping is suspended and the water level is restored to the level of the previous stage. The next stage of pumping is restarted after the self-sealing effect has fully developed.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: 1. This invention utilizes a multi-layered composite structure at the bottom of the caisson, consisting of a double-layered support mesh, a graded crushed stone layer, underwater cast-in-place concrete, and structural support concrete. This separates the sealing and load-bearing functions into different structural layers. The underwater cast-in-place concrete only needs to cover the upper surface of the crushed stone layer and penetrate into its upper gaps to form an interlocking band to achieve sealing and blocking. The casting thickness is much smaller than that of traditional integral filling schemes, significantly reducing the amount of underwater concrete used and the construction difficulty. The structural support concrete is cast in a dry environment after drainage, ensuring complete control over construction quality. Its strength uniformity and surface flatness meet the installation requirements of precision pump equipment. The sealing layer and the load-bearing layer are mechanically anchored through roughened surfaces to achieve overall collaborative work, solving the problem of uncontrollable quality caused by the coupling of sealing and load-bearing functions in traditional schemes.

[0017] 2. This invention addresses the deficiency in traditional integrated underwater casting schemes where sealing and load-bearing functions cannot be separated. It proposes a layered and sequential construction strategy: first sealing with water, then draining, and finally pouring the load-bearing layer in dry conditions. The core of this strategy is to use only a thin layer of underwater-cast concrete to penetrate the crushed stone layer and form an interlocking band to complete the sealing and blocking. The pouring of the load-bearing layer, which has strict quality requirements, is moved to a dry environment after drainage. By reconstructing the construction sequence, the sealing and load-bearing functions are completely decoupled, taking into account both the reliability of underwater sealing and the precise controllability of the load-bearing structure.

[0018] 3. The construction method of the present invention uses staged pumping after the sealing layer is formed to control the seepage to a laminar flow state. The seepage carries fine soil particles from the surrounding soil to naturally block the bottom of the gravel layer and the double-layer support net to form a reverse filter sealing layer. This transforms the harmful seepage carrying sand phenomenon in traditional engineering into a favorable self-sealing mechanism, further enhancing the long-term seepage resistance below the sealing layer and ensuring the long-term service safety of the pump foundation. Attached Figure Description

[0019] Figure 1 This is a three-dimensional structural diagram of the caisson body provided by the present invention; Figure 2 A three-dimensional structural diagram of the outer and inner support nets provided by the present invention; Figure 3 A schematic diagram of the three-dimensional structure of the crushed stone layer provided by the present invention; Figure 4 A schematic diagram of a three-dimensional structure for underwater concrete casting provided by the present invention; Figure 5 A schematic diagram of the underwater concrete casting structure provided by the present invention; Figure 6 A schematic diagram of an underwater concrete casting steel mesh structure provided by the present invention; Figure 7 This is a schematic diagram of the pump unit installation structure provided by the present invention.

[0020] Explanation of reference numerals in the attached figures: 1. Caisson body; 11. External support net; 12. Internal support net; 13. Crushed stone layer; 14. Underwater concrete pouring; 15. Structural support concrete; 16. Pump set. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0022] Example 1 In existing technologies, for pump foundation construction in aquatic environments, the duct method is usually used to directly pour underwater concrete into the entire space at the bottom of the caisson to form an integrated foundation support.

[0023] However, this method has the following prominent problems: First, the amount of underwater concrete pouring is large, and the entire bottom space of the caisson needs to be filled with concrete, resulting in high material consumption and high cost.

[0024] Secondly, large-volume underwater concrete is easily affected by factors such as water flow disturbance and improper control of the guide pipe lifting speed during the pouring process, resulting in defects such as honeycomb, voids and mud inclusions inside, and the overall density of the concrete cannot be guaranteed.

[0025] Third, the concrete poured in the underwater environment has large strength dispersion and a thick surface laitance layer. Directly using it as the structural bearing surface of precision pump equipment makes it difficult to meet the equipment's requirements for foundation flatness, strength uniformity, and long-term stability.

[0026] Fourth, the integrated underwater casting scheme cannot achieve a design that separates the sealing function from the load-bearing function. Once leakage occurs at the bottom, underwater grouting must be carried out again for repair, which is costly and the effect is uncertain.

[0027] like Figures 1 to 3 As shown in this embodiment, a caisson-type water-supported construction pump set foundation is provided, including a caisson body 1. The caisson body 1 is a concrete box structure with an open bottom. An outer support net 11 and an inner support net 12 are arranged sequentially from the outside to the inside at the bottom of the caisson body 1. The outer support net 11 is fixed to the outer side of the bottom of the caisson body 1, and the inner support net 12 is fixed to the inner side of the bottom of the caisson body 1. A preset distance is maintained between the inner support net 12 and the inner wall of the caisson body 1.

[0028] The bottom of the caisson 1 is provided with a gravel layer 13, underwater cast concrete 14 and structural support concrete 15 in sequence from bottom to top. The gravel layer 13 is supported above the inner support net 12 and formed by underwater filling and leveling. The underwater cast concrete 14 is a self-compacting concrete layer that is underwater cast above the gravel layer 13 by means of a tremie pipe. The grout at the bottom of the concrete layer 14 seeps into the upper gaps of the gravel layer 13 and fuses with the gravel layer 13 to form a rigid whole, thereby permanently fixing and locking the gravel layer 13 and achieving a seal. The structural support concrete 15 is a reinforced concrete slab that is dry-cast on the roughened surface of the underwater cast concrete 14 after being dewatered and dried. A pump unit 16 is installed on the top surface of the structural support concrete 15.

[0029] The entire foundation system deconstructs the traditional integrated underwater casting scheme into a multi-layered structure with separate functions. The crushed stone layer 13 serves as a transition medium layer, and its upper gaps provide a seepage channel for the grout of the underwater cast concrete 14. After solidification, the two fuse to form a rigid whole to achieve a reliable physical seal. The lower part of the crushed stone layer 13, together with the outer support net 11 and the inner support net 12, constitutes a reverse filtration drainage system.

[0030] The underwater concrete 14 serves only to seal, block, and fix the crushed stone layer 13. Its thickness is much smaller than that of the traditional monolithic pouring scheme, and the pouring quality is controllable. The structural bearing concrete 15 is poured in a dry environment, and its strength grade, flatness, and density can all be controlled according to conventional land construction standards, truly bearing the working load of the pump unit 16.

[0031] It should be emphasized that the core improvement of this embodiment lies in addressing the problem of coupling sealing and load-bearing functions and difficulty in balancing quality in the existing underwater integral casting scheme. This solution proposes to decompose the caisson foundation into a three-layer functional separation structure consisting of a crushed stone transition layer, an underwater sealing layer, and a dry load-bearing layer.

[0032] The underwater concrete 14 only needs to meet the sealing performance requirements. Its small volume and thin thickness significantly reduce the risk of quality defects. The structural bearing concrete 15 is constructed using conventional processes after the water is drained, and its strength and flatness are completely controllable. Thus, the adverse effects of the underwater environment on concrete quality are solved, while the stringent requirements of the precision pump equipment for the foundation bearing capacity are met, realizing the design concept of functional separation and each performing its own function.

[0033] It should be noted that the caisson body 1 is a precast concrete structure, and its wall thickness is determined by calculation based on the sinking depth and lateral earth pressure. The bottom cutting edge of the caisson body is wedge-shaped to facilitate sinking and cutting the soil.

[0034] During the sinking construction, the soil in the caisson body 1 is removed from the inside of the caisson by an excavator, and the caisson body gradually sinks to the design elevation by its own weight.

[0035] Due to the characteristics of excavation by excavators, after the caisson body 1 is lowered into place, the soil surface at its bottom is uneven and undulating, making it impossible to directly serve as the supporting base for the crushed stone layer 13, nor can the soil surface be leveled in an underwater environment.

[0036] This is precisely why the outer support net 11 and the inner support net 12 are set up in this scheme, so that the support of the crushed stone layer 13 is not dependent on the uneven excavated soil surface.

[0037] It should be noted that the crushed stone layer 13 is not a simple crushed stone pile, but a designed graded crushed stone structure.

[0038] The crushed stone layer 13 adopts a gradation method with large-diameter crushed stone as the skeleton and small-diameter crushed stone filling the gaps between the skeleton, so that the upper part maintains a porosity of 25%-35%.

[0039] The design intent of this gap ratio is that if the gap ratio is too small, the grout of the underwater-cast concrete 14 cannot effectively penetrate to form an interlocking band, resulting in poor sealing; if the gap ratio is too large, the overall strength and stability of the crushed stone layer 13 will be insufficient, and it will be unable to provide reliable support for the overlying concrete layer.

[0040] In this embodiment, the outer support net 11 is fixed to the outer side of the bottom of the caisson body 1, and the inner support net 12 is fixed to the inner side of the bottom of the caisson body 1. The outer support net 11 and the inner support net 12 form a double-layer clamping structure from the outside to the inside, which constrains the gravel layer 13 above the inner support net 12.

[0041] The mesh size of the outer support net 11 is larger than that of the inner support net 12. The outer support net 11 serves as a structural load-bearing layer, supporting the weight of the crushed stone layer 13 and the overlying load from the outside, preventing the crushed stone from leaking out from the bottom opening of the caisson. The inner support net 12 serves as a filter barrier layer, with a mesh size smaller than the minimum particle size of the crushed stone layer 13, preventing crushed stone particles from passing through the mesh and falling downwards.

[0042] A preset distance is maintained between the inner support net 12 and the inner wall of the caisson body 1. The design motivation for this distance is that during the underwater filling process of the crushed stone layer 13, the water flow disturbance will inevitably cause the crushed stone particles to be washed and disturbed.

[0043] If the inner support net 12 is installed tightly against the inner wall of the box without any gaps, the gravel may be squeezed to the angle between the net and the wall under the action of water flow, resulting in stress concentration, which may cause local deformation or damage to the inner support net 12.

[0044] After maintaining the spacing, the inner supporting net 12 has a certain elastic deformation buffer space when bearing the gravel load and water flow impact. The net can produce slight deflection within the spacing range without being rigidly squeezed and destroyed.

[0045] More importantly, before the crushed stone layer 13 is fixed by the underwater concrete 14, the crushed stone is in a loose state underwater, and the repeated scouring of the water flow may cause the crushed stone to loosen and fall. The double-layered clamping structure of the inner support net 12 and the outer support net 11 constrains the crushed stone layer 13 between them. Even if the water flow scours, the crushed stone can only be partially rearranged in the space between the nets, and will not be completely washed away, thus ensuring the integrity and stability of the crushed stone layer 13 before the underwater concrete 14 is poured.

[0046] After the crushed stone layer 13 is stabilized under the constraint of the inner and outer support nets, underwater concrete 14 is poured through the tremie pipe method. The self-compacting concrete grout seeps into the upper gap of the crushed stone layer 13 under its own weight. After solidification, the concrete and the upper part of the crushed stone layer 13 are fused into a rigid whole, and the crushed stone layer 13 is permanently fixed and locked.

[0047] Subsequently, the stability of the crushed stone layer 13 no longer depends on the constraint of the supporting net, but on the rigid consolidation of the concrete. Thus, the outer supporting net 11 and the inner supporting net 12 play a temporary constraint role during construction, ensuring that the crushed stone layer 13 is not washed away by the water flow before the underwater concrete 14 is poured and solidified. The underwater concrete 14 plays a permanent fixing role, achieving the dual goals of sealing and structural stability by integrating with the crushed stone layer 13.

[0048] Meanwhile, the redundant design of the double-layer mesh structure ensures that even if a single layer of mesh is partially damaged, the crushed stone layer 13 will not collapse as a whole, thus improving the structural safety and reliability.

[0049] Example 2 It is understandable that in Example 1, after the underwater concrete 14 is poured on top of the crushed stone layer 13, a sealing and blocking layer is formed. Subsequently, the water in the caisson 1 needs to be pumped out for dry construction.

[0050] However, although the underwater concrete 14 is sealed by interlocking bands and the crushed stone layer 13, the seal is not absolutely leak-free. The lower part of the crushed stone layer 13 is still connected to the outside water. The pressure difference will inevitably drive the water to seep into the caisson through the gaps in the lower part of the crushed stone layer 13.

[0051] If water is pumped out quickly at once, a large head difference will be formed instantly inside and outside the caisson. The water will flow through the lower part of the gravel layer 13 and the areas of the outer support net 11 and the inner support net 12 at a high velocity. At this time, the seepage is in a turbulent state: on the one hand, the high velocity seepage may wash away the fine particles at the bottom of the gravel layer 13, forming a dominant seepage channel or even piping, which will cause the sealing system to fail.

[0052] On the other hand, rapid pumping causes the bottom of the underwater concrete 14 to bear a large upward water pressure. If the concrete strength has not been fully developed or there are weak points in the interlocking band, it may cause the bottom plate to bulge or be partially penetrated. Therefore, how to safely and reliably complete the pumping operation inside the caisson is a key technical obstacle to the implementation of the first embodiment.

[0053] like Figures 4 to 5 As shown, in order to solve the above problems, this embodiment provides a method for staged pumping and using the seepage self-sealing effect to achieve gradual water stoppage.

[0054] Specifically, after the underwater concrete 14 reaches the design strength, the water level inside the caisson 1 is gradually lowered in stages, with each stage lowering the water depth by 300-500mm. After each stage of lowering, the pump is stopped and the water level is observed for no less than 12 hours, and the return water rate is recorded.

[0055] Control the pumping rate at each stage to ensure that the seepage Reynolds number in the crushed stone layer 13 below the underwater concrete 14 does not exceed 5, thus ensuring that the seepage is always in a laminar flow state.

[0056] Under laminar flow conditions, fine particles in the external soil migrate slowly with the seepage water, gradually accumulating and clogging at the bottom of the gravel layer 13 and at the mesh openings of the inner and outer support nets 12 and 11, naturally forming a reverse filter sealing layer. This causes the seepage volume to decrease step by step as the pumping stage increases, ultimately achieving complete drainage of the water in the caisson.

[0057] When the water level inside the caisson drops by one level, the difference in water head between the inside and outside drives external water to seep into the caisson through the bottom of the gravel layer 13.

[0058] Because the pumping rate is controlled and the seepage velocity is low, it is in a laminar flow state. The drag force of the water flow on the fine particles in the medium is consistent and stable. The fine particles migrate along the seepage direction and gradually accumulate at the abrupt change in the flow channel section, namely at the gaps between the gravel at the bottom of the gravel layer 13, the mesh of the inner support net 12, and the mesh of the outer support net 11.

[0059] As sedimentation increases, the cross-sectional area of ​​the seepage channel shrinks, the permeability coefficient decreases, and under the same head difference, the seepage volume automatically decreases, manifested as a gradual decrease in the return water rate. This is a positive feedback process: the smaller the seepage volume, the more stable the fine particle sedimentation; the more stable the sedimentation, the further the seepage volume decreases until seepage essentially stops.

[0060] If the return water rate of a certain stage increases abnormally, it indicates that local scouring damage has occurred. At this time, pumping should be stopped and water should be reinjected to restore the water level, so that the scouring channel can be re-filled and repaired by the surrounding fine particles under still water conditions, and then the next stage of pumping should be restarted.

[0061] It should be emphasized that the core improvement of this embodiment lies in the following: In response to the technical obstacles in Embodiment 1, where the sealing system is not absolutely leak-free and rapid pumping may lead to seal failure, this solution proposes a self-sealing strategy of graded slow pumping, laminar flow control, and natural siltation.

[0062] The concept is to intentionally preserve the seepage channels under the crushed stone layer 13 instead of pursuing absolute sealing with zero leakage during the pouring stage. During the pumping stage, the seepage state is controlled to allow fine particles of the external soil to spontaneously migrate and block these channels, turning the defect into a self-healing mechanism. By utilizing the self-sealing and filtering properties of the natural soil, the key water-stopping problem in water-bearing construction is solved with extremely low construction costs and extremely high reliability.

[0063] It should be noted that the depth of each precipitation level is set at 300-500mm rather than a larger range. The design motivation is that a smaller change in the single-level head difference corresponds to a smaller increase in the seepage driving force, and the increase in the seepage velocity within the gravel layer 13 is controllable, avoiding the sudden formation of large flow velocities that could dissipate existing silt.

[0064] The design motivation for stopping the pump for 12 hours is that the migration and deposition of fine particles is a time process, and sufficient time should be given for the self-enclosure effect to develop to a stable state before the next stage of precipitation can be carried out.

[0065] It should be noted that the critical value of controlling the seepage Reynolds number below 5 is selected based on the basic principle of seepage mechanics in porous media: In granular media, when the Reynolds number exceeds about 1-10, the seepage changes from laminar flow to turbulent flow, Darcy's law fails, the flow velocity and head gradient are no longer linearly related, the direction of the force of the water flow on the particles becomes randomized, and fine particles no longer migrate and accumulate in a directional manner but are randomly dispersed.

[0066] Keeping the Reynolds number below 5 ensures that the seepage flow is always in the laminar flow zone, the migration direction of fine particles is predictable and stable, and the clogging process is reliable.

[0067] In this embodiment, when the return water rate after a certain stage of pumping is greater than the return water rate of the previous stage, it is determined that local seepage damage has occurred. The reinjection and restoration measures taken at this time have the following technical effects: after the water level is restored by reinjection, the difference between the internal and external water head disappears or reverses, the high-speed seepage in the flushing channel stops immediately, and the surrounding suspended fine particles settle naturally in still water and refill the flushed channel.

[0068] This closed-loop control strategy of anomaly detection, reinjection repair, and re-pumping ensures that even if a local accident occurs, the entire self-closed process can still self-repair and self-recover, greatly improving the fault tolerance and safety of the construction process.

[0069] Example 3 It is understandable that, in Example 2, after the water in the caisson 1 is successfully pumped out through the staged pumping self-sealing strategy, the top surface of the underwater concrete 14 needs to be filled with structural support concrete 15 as the bearing foundation of the pump unit 16.

[0070] However, the underwater concrete 14 is poured in an underwater environment, and its surface inevitably has the following problems: First, the top surface is covered with a layer of laitance formed by the floating of cement slurry. This laitance layer has extremely low strength and loose structure. If the structural bearing concrete 15 is poured directly on it, the bond strength between the two layers of concrete is far lower than the design requirements.

[0071] Secondly, the surface of the underwater-cast concrete 14 is relatively smooth after solidification in water, and there is a lack of mechanical interlocking force between the concrete interfaces. Under the long-term action of the vibration load of the pump unit 16, the interface may gradually debond and delaminate, resulting in a void between the structural support concrete 15 and the underwater-cast concrete 14, which reduces the rigidity of the pump unit 16 foundation and affects the normal operation of the equipment.

[0072] Therefore, ensuring that the interfacial bond strength between the two layers of concrete meets the long-term operation requirements of the pump unit is another key technical problem that this solution needs to address.

[0073] like Figures 6 to 7 As shown, in order to solve the above problems, in this embodiment, after the water in the caisson is drained and before the concrete 15 supporting the structure is poured, the top surface of the underwater concrete 14 is systematically roughened.

[0074] Specifically, the process involves: first, using a high-pressure water gun to rinse the top surface of the underwater-cast concrete 14 to remove the laitance layer and loose material; then, using manual or mechanical chiseling tools to roughen the top surface, with a chiseling depth of not less than 6mm and a chiseling area of ​​not less than 70% of the total area of ​​the top surface of the underwater-cast concrete 14, forming an irregular rough surface with uneven surfaces.

[0075] A steel mesh is tied to the roughened surface, and the bottom of the steel mesh is anchored into the pit of the roughened surface. Then, structural support concrete 15 is poured, so that the bottom concrete slurry of the structural support concrete 15 fills the pit and texture of the roughened surface, and forms a mechanical anchoring connection after solidification.

[0076] The roughening process creates numerous irregular pits and protrusions on the surface of the underwater concrete 14. When the structure receives the concrete 15, the new concrete slurry fills all the pits and textured spaces. After solidification, the old and new concrete form an interlocking tooth-like structure at the interface.

[0077] When the pump unit 16 generates vertical vibration loads or horizontal shear loads during operation, the toothed structure at the interface generates a mechanical interlocking effect, preventing the two layers of concrete from sliding or separating relative to each other.

[0078] The mechanical anchoring force, combined with the chemical bond force of the concrete itself, makes the shear strength and tensile strength of the interface significantly higher than those of an unroughened smooth interface, thus meeting the durability requirements of the pump unit under long-term vibration environment.

[0079] It should be emphasized that the core improvement of this embodiment is: in response to the problem of poor bonding between the old and new concrete interfaces caused by the laitance layer and smooth surface of the underwater poured concrete 14, this solution transforms the smooth interface into a high-roughness irregular rough surface by roughening the surface, and uses the new concrete to fill the pits to form a mechanical interlock, thereby changing the stress mechanism of the interface from adhesive bonding that relies on chemical bonding to riveting that relies on geometric interlock.

[0080] Meanwhile, the design of anchoring the bottom of the steel mesh into the recess further provides cross-interface tie constraints. Even if local chemical bonding deteriorates, mechanical interlocking and steel reinforcement tie can still ensure the integrity of the interface, forming a triple protection system.

[0081] It should be noted that the requirement of a roughening depth of not less than 6 mm is based on the following considerations: If the roughening is too shallow, such as 2-3 mm, it will only remove the laitance layer but will not form a pit of effective depth. After the new concrete is filled, the height of the teeth formed will be insufficient, and the shear interlocking force will be limited.

[0082] When the chiseling depth reaches 6mm or more, the depth of the resulting pit can ensure that the aspect ratio of the teeth meets the requirements for shear force transmission.

[0083] The requirement that at least 70% of the area be roughened ensures sufficient effective anchorage area, while the unroughened area should not exceed 30%. This is allowed because some areas may be inaccessible due to obstruction by reinforcing bars or embedded parts.

[0084] It should be noted that the specific method for anchoring the bottom of the steel mesh into the roughened surface pit is as follows: after bending some of the vertical short bars of the steel mesh, insert them into the relatively deep pit formed by the roughening. When the structural bearing concrete is poured for 15 minutes, the concrete will wrap the short bars and the pit together.

[0085] The technical effect of this design is that the vertical short bars cross the interface between the old and new concrete, providing a pin-like effect when the interface is subjected to tensile or shear forces, preventing the interface from opening or slipping, and effectively preventing interface fatigue failure, especially under the impact load generated at the moment of start-up and shutdown of pump unit 16.

[0086] In this embodiment, the top surface of the structural support concrete 15 is designed as a horizontal reference surface with a flatness deviation of no more than 5mm, and the surface is pre-embedded with anchor bolts for the installation of the pump unit 16.

[0087] Since the structural bearing concrete 15 was poured in a dry environment, its vibration, finishing and curing were carried out according to conventional onshore processes, and the strength grade can reach C40 and above, which fully meets the bearing capacity and rigidity requirements of the pump equipment foundation.

[0088] Compared to the traditional approach of using underwater concrete directly as the equipment foundation, this solution offers reliable structural bearing concrete quality, controllable performance, and precise surface leveling, thus resolving the adverse effects of the underwater construction environment on the quality of the pump foundation.

[0089] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed application.

Claims

1. A caisson-type foundation for a pump unit under construction with water, characterized in that, include: The caisson box (1) is a concrete box structure with an open bottom; the bottom of the caisson box (1) is provided with an outer support net (11), an inner support net (12), a crushed stone layer (13), underwater cast concrete (14) and structural support concrete (15) in sequence from bottom to top. The outer support net (11) is fixed to the outer side of the bottom of the caisson body (1), the inner support net (12) is fixed to the inner side of the bottom of the caisson body (1), and a preset distance is maintained between the inner support net (12) and the inner wall of the caisson body (1). The crushed stone layer (13) is supported above the inner support net (12). The underwater cast concrete (14) is poured and covers the upper surface of the crushed stone layer (13) and penetrates into the upper gap of the crushed stone layer (13) to form an interlocking band to achieve sealing and blocking. The structural support concrete (15) is poured on the rough surface of the underwater cast concrete (14) and forms a mechanical anchoring connection with the underwater cast concrete (14). The top surface of the structural support concrete (15) is used to install the pump set (16).

2. The caisson-type pump set foundation for water-supported construction as described in claim 1, characterized in that, The mesh size of the outer support net (11) is larger than that of the inner support net (12), and the mesh size of the inner support net (12) is smaller than that of the smallest particle size of the crushed stone in the crushed stone layer (13).

3. The caisson-type pump set foundation for water-supported construction as described in claim 1, characterized in that, The crushed stone layer (13) adopts a gradation method in which large-diameter crushed stone forms the skeleton and small-diameter crushed stone fills the gaps between the skeleton.

4. The caisson-type pump set foundation for water-supported construction as described in claim 1, characterized in that, The roughening depth of the top surface of the underwater cast concrete (14) shall not be less than 6 mm, and the roughening area shall not be less than 70% of the total area of ​​the top surface of the underwater cast concrete (14).

5. The caisson-type pump set foundation for water-supported construction as described in claim 1, characterized in that, The bottom outer and inner sides of the caisson body (1) are respectively provided with pre-embedded anchors along the circumference. The outer support net (11) is fixedly connected to the bottom outer side of the caisson body (1) through the outer pre-embedded anchors, and the inner support net (12) is fixedly connected to the bottom inner side of the caisson body (1) through the inner pre-embedded anchors.

6. The caisson-type pump set foundation for water-supported construction as described in claim 1, characterized in that, The underwater concrete (14) is self-compacting concrete with a slump spread of not less than 600 mm.

7. The caisson-type pump set foundation for water-supported construction as described in claim 1, characterized in that, The ratio of the maximum to the minimum particle size of the crushed stone in the crushed stone layer (13) is 2-3:1, and the flatness deviation of the top surface of the crushed stone layer (13) after compaction and leveling does not exceed 20mm.

8. The caisson-type pump set foundation for water-supported construction as described in claim 1, characterized in that, The structure is supported by a steel mesh frame inside the concrete (15), and the bottom of the steel mesh frame is anchored into the pit of the roughened surface of the underwater concrete (14).

9. A construction method for a caisson-type pump set foundation with water supply, characterized in that, The construction method of the caisson-type pump unit foundation for underwater construction as described in any one of claims 1-8 includes the following steps: S1: Caisson fabrication and sinking. A caisson box (1) with an open bottom is fabricated on the ground. The caisson box (1) is placed in the construction water area. Soil is removed from the inside of the caisson box (1) by grab bucket, so that the caisson box (1) sinks to the design elevation under its own weight. S2: Lay the support net. Lay the outer support net (11) underwater and fix it to the pre-embedded anchor on the bottom outer side of the caisson body (1). Then lay the inner support net (12) and fix it to the pre-embedded anchor on the bottom inner side of the caisson body (1). A preset distance is maintained between the inner support net (12) and the inner wall of the caisson body (1). S3: Fill the crushed stone layer, and fill the crushed stone underwater above the inner supporting net (12) and compact and level it to form a crushed stone layer (13). Control the crushed stone gradation so that the porosity of the upper part of the crushed stone layer (13) is 25%-35%; S4: Underwater casting of sealing and blocking layer. Self-compacting concrete is cast underwater above the crushed stone layer (13) through the guide pipe method. The concrete slurry seeps into the upper gap of the crushed stone layer (13) under its own weight to form an interlocking band. After solidification, it forms underwater cast concrete (14) that is integrated with the crushed stone layer (13), thus achieving sealing and blocking of the bottom of the caisson body (1). S5: Staged pumping. After the underwater concrete (14) reaches the design strength, the water level in the caisson box (1) is reduced in stages. The pumping rate of each stage is controlled so that the seepage below the underwater concrete (14) is in a laminar flow state. The seepage carries fine particles from the surrounding soil to naturally block the bottom of the gravel layer (13) and the outer support net (11) and inner support net (12) to form a reverse filter sealing layer until the water in the caisson box (1) is pumped out. S6: Roughening treatment, the top surface of the underwater concrete (14) is washed and roughened to remove surface laitance and loose material, forming an irregular rough surface. S7: Pour the structural support layer, tie the steel mesh on the roughened surface and pour the structural support concrete (15), so that the structural support concrete (15) and the underwater poured concrete (14) form a mechanical anchoring connection through the roughened surface. After the structural support concrete (15) reaches the design strength, install the pump set (16).

10. The construction method of a caisson-type pump set foundation with water supply as described in claim 9, characterized in that, In S5, the depth of each precipitation stage is 300-500mm. After each precipitation stage, the pump is stopped and observed for no less than 12 hours, and the return water rate is recorded. When the return water rate of a certain stage is greater than the return water rate of the previous stage, pumping is suspended and the water level is restored to the level of the previous stage. The next stage of pumping is restarted after the self-sealing effect has fully developed.

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