Partitioned combined type water power station volute embedding structure and construction method thereof

Abstract

The application discloses a partition combined type water turbine plant volute embedding structure and a construction method thereof, and the structure comprises a volute arranged in peripheral concrete and a cushion layer arranged between the volute and the peripheral concrete; the volute comprises, in sequence, an inlet direct embedding section, a controllable gap cushion layer section and a nose end pressure maintaining section according to stress characteristics along a water flow direction; and a pressure maintaining assembly is arranged on the nose end pressure maintaining section. According to the stress characteristics of different sections of the volute, the inlet direct embedding section, the controllable gap cushion layer section and the nose end pressure maintaining section are arranged in a targeted manner, the stress requirements of different regions are adapted, and stress concentration is avoided; the cushion layer is controlled through the gradient of thickness and elastic modulus, the volute and the concrete are jointly loaded according to a preset proportion, and the stress overload of a single component is reduced; meanwhile, the peripheral concrete is provided with a preset stress release groove, and the cushion layer is provided with a built-in drainage channel, so that the temperature stress and water seepage hidden danger are further relieved, the concrete cracking is effectively prevented, and the crack resistance and durability of the structure are improved.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and hydropower engineering technology, and in particular relates to a partitioned combined hydropower station spiral casing embedded structure and its construction method. Background Technology

[0002] As the core flow-through and load-bearing component of a hydro-generator unit, the method of embedding the spiral casing directly determines the safety, stability, and durability of the unit's operation, while also affecting construction efficiency and project costs. Currently, existing spiral casing embedding methods are mainly divided into three categories: direct embedment, subbase embedment, and pressure-supported casting. These three structural forms struggle to simultaneously meet the requirements of structural safety, ease of construction, and long-term operational stability. Their respective shortcomings are as follows:

[0003] 1. In the direct burial method, the outer wall of the steel volute is in direct contact with the surrounding concrete without any buffer or force transmission control structure. Its advantages are high structural rigidity and simple construction. However, due to the significant difference in elastic modulus between the steel volute and the concrete, stress concentration is easily generated under water pressure, temperature stress and unit vibration. This can lead to through cracks in the surrounding concrete. Further development of these cracks can cause problems such as water seepage and frost heave, which seriously affect the durability of the structure and even threaten the safe operation of the unit.

[0004] 2. The cushion layer embedment method involves laying an elastic cushion layer on the outer wall of the steel volute. The deformation of the cushion layer regulates the force transmission ratio between the steel volute and the concrete, alleviating stress concentration. However, existing cushion layers generally use materials with a single thickness and a single elastic modulus, which cannot be specifically adapted to the stress characteristics of different cross-sections of the volute. This leads to uncontrollable force distribution, and the cushion layer is prone to problems such as excessive local compression and aging failure. After long-term operation, there are still hidden dangers such as concrete cracking and steel shell debonding. It is especially unsuitable for pumped storage power station units with high head and large flow.

[0005] 3. The pressure-holding casting method involves filling the volute with water or air to a preset pressure after installation, then pouring the outer concrete. Once the concrete reaches its design strength, the internal pressure is released, relying on the shrinkage of the concrete and the elastic rebound of the volute to form a combined load-bearing structure. While this method can optimize stress distribution to some extent, the construction process is complex, requiring specialized pressurization equipment and sealing measures. It has a long construction period, high costs, and is difficult to control pressure during pressurization, leading to risks such as uneven pressure and seal failure. Therefore, it is not suitable for large-scale application.

[0006] In summary, existing technological improvements only address localized optimizations of a single embedding method, failing to consider the overall stress characteristics of the spiral casing. This makes it difficult to fundamentally solve core problems such as uneven stress distribution, complex construction, and poor durability. Therefore, developing a spiral casing embedding structure and construction method that can adapt to the stress characteristics of different spiral casing cross-sections, achieve controllable force transmission, simplify construction processes, and improve structural durability has become a pressing technical challenge in the field of water conservancy and hydropower engineering.

[0007] Patent application CN104234912A discloses a compression gap spiral casing structure for a water turbine. It includes a metal spiral casing and a surrounding concrete layer. The inlet end of the metal spiral casing is a straight pipe section. A flexible material is fixed between the metal spiral casing and the surrounding concrete. Under pressure, the flexible material undergoes plastic deformation, forming a compression gap. The force transmission coefficient of the flexible material is no greater than 50 MPa / m, the deformation modulus of the flexible material is 0.05 MPa to 0.5 MPa, and the thickness of the flexible material is no greater than 10 mm. This structure solves the problems and their implications regarding the mechanical stability and durability of the bedding material in a bedding spiral casing structure throughout the entire lifespan of the spiral casing, improving the overall integrity of the spiral casing structure. However, this structure lacks a drainage structure for the flexible material. The flexible material has a single, uniform structure without zoning or gradient design, making the gap and force transmission uncontrollable. Furthermore, it does not monitor the concrete stress or the deformation of the flexible material.

[0008] Patent application CN109185010A discloses a method for embedding the spiral casing of a hydropower station based on the principle of thermal effect structural deformation. This device aims to optimize the stress state between the steel spiral casing and concrete, and reduce the risk of concrete cracking. However, this device relies on thermal effects to control structural deformation and depends on temperature field regulation, which limits its construction conditions.

[0009] Patent document CN223022761U discloses a monitoring and early warning device for pressure-holding pouring of a hydropower station spiral casing, including a spiral casing pressure-holding pouring assembly and monitoring and early warning components installed on the periphery of the spiral casing top cover and on the outer wall of the spiral casing body. Although this method sets up a monitoring and early warning structure for spiral casing pouring construction to ensure construction and operation safety, it only focuses on monitoring and early warning during the pressure-holding pouring process and lacks technical content on spiral casing structural zoning, soft cushion layer design between the spiral casing and concrete, and cushion layer gap control. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a partitioned combined hydropower station spiral casing embedded structure and its construction method.

[0011] The present invention is achieved through the following technical solutions.

[0012] The present invention provides a partitioned combined hydropower station spiral casing embedded structure, including a spiral casing disposed within an outer concrete enclosure, and a cushion layer disposed between the spiral casing and the outer concrete enclosure. The spiral casing includes an inlet direct-buried section, a controllable gap cushion layer section, and a nose-end pressure-maintaining section connected sequentially along the water flow direction, and a pressure-maintaining component is disposed on the nose-end pressure-maintaining section.

[0013] Preferably, the thickness of the padding layer gradually increases from top to bottom, and the elastic modulus of the padding layer gradually increases from the connection of the inlet direct-buried section to the connection of the nose pressure-holding section.

[0014] Preferably, the thickness of the bottom layer is 3 to 4 times the thickness of its top layer; the elastic modulus at the connection between the layer and the inlet direct-buried section is 0.5 to 1.0 MPa, and the elastic modulus at the connection between the layer and the nose pressure-holding section is 2.0 to 3.0 MPa.

[0015] Preferably, the pressure-holding assembly includes a pressure-holding airbag and a pressure-relief valve. The pressure-holding airbag is disposed within the pressure-holding section at the nose end, and a pressure sensor is disposed within the pressure-holding airbag. The pressure-holding airbag and the pressure-relief valve are connected through a pipe, and the pressure-relief valve is disposed outside the pressure-holding section at the nose end.

[0016] Preferably, stress relief grooves are provided on the inner wall of the outer concrete at the controllable gap cushion section and the nose pressure-holding section, and a sealing strip is provided at the junction of the volute and the outer concrete, with the sealing strip embedded in the stress relief groove.

[0017] Preferably, the stress relief groove is arranged circumferentially every 2m along the axis of the volute.

[0018] Preferably, a plurality of strain sensors are provided at the corresponding subbase within the outer concrete, and the plurality of strain sensors are arranged in a quincunx pattern.

[0019] Preferably, the volute is spiral-shaped.

[0020] Preferably, a drainage channel is provided within the cushion layer, and a first gap exists between the cushion layer and the volute.

[0021] A construction method for a partitioned combined hydropower station spiral casing embedded structure includes the following steps:

[0022] S1: Assemble the volute. Steel plates are sequentially cut, bent, and welded to form the inlet direct-buried section, controllable gap cushion section, and nose-end pressure-holding section of the volute. After non-destructive testing of the welds and confirmation of their qualification, the outer walls of each section are treated. Specifically, the outer wall of the inlet direct-buried section undergoes rust removal and roughening treatment with a roughness Ra≥50μm; the outer wall of the controllable gap cushion section is leveled to a flatness ≤2mm / m; after hoisting each section to its designed position, it is spliced ​​and fixed, with the axial deviation after splicing controlled within 5mm.

[0023] S2: Maintain pressure on the volute. A pad is set on the outer wall of the controllable gap pad section and the nose pressure-maintaining section. The pad is set along the circumference of the volute. A drainage channel is pre-embedded in the pad. A pressure-maintaining airbag, pressure sensor and pressure relief valve are installed on the nose pressure-maintaining section. The pressure-maintaining airbag is inflated and the pressure of the pressure-maintaining airbag is adjusted to the required pressure.

[0024] S3: Set a sealing strip and a sensor. Embed the sealing strip into the stress relief groove at the junction of the volute and the outer concrete, and compact and fix it. Set a number of strain sensors at the corresponding pad layer in the outer concrete. The strain sensors are arranged in a quincunx pattern. The strain sensors extend to the first gap and the strain sensor signal transmission line is led out to the monitoring terminal.

[0025] S4: Pour the outer concrete. The pouring sequence of the outer concrete is from the inlet direct-buried section of the volute to the nose pressure-holding section. During the pouring process, monitor the stability of the pressure holding pressure in real time. The outer concrete is cured until it reaches 70% to 90% of the design strength.

[0026] S5: Remove the pressure and adjust the sensor. Release the pressure of the pressure-holding airbag through the pressure relief valve. After depressurization, remove the pressure-holding airbag, pressure sensor and pressure relief valve. Seal the interface for installing the pressure-holding airbag inside the volute. Apply an anti-permeability coating to the outer concrete surface. Repair the pitting defects on the outer concrete surface. Adjust the strain sensor to ensure that the monitoring terminal can accurately collect the stress of the outer concrete and the deformation data of the cushion layer.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. The structural stress distribution of the present invention is more reasonable, and the crack resistance is significantly improved: The present invention adopts a zoned combination design. According to the stress characteristics of different cross sections of the volute, the inlet direct-buried section, the controllable gap cushion layer section and the nose pressure-holding section are set in a targeted manner to adapt to the stress requirements of each area and avoid stress concentration. The controllable gap cushion layer achieves the joint bearing of the steel volute and concrete according to a preset ratio through gradient control of thickness and elastic modulus, reducing the overload of a single component. At the same time, the pre-set stress relief groove of the outer concrete and the built-in drainage channel of the cushion layer further alleviate the temperature stress and water seepage risks, effectively prevent concrete cracking, and improve the crack resistance and durability of the structure.

[0029] 2. The structural force transmission of the present invention is controllable, resulting in higher operational stability: Compared with the traditional single-layer burial method, the controllable gap layer of the present invention adopts a gradient elastic modulus and variable thickness design, and the force transmission ratio can be precisely adjusted according to design requirements, solving the problems of uncontrollable force transmission and poor durability of traditional layer. At the same time, the local pressure-holding design at the nose effectively controls local deformation, ensures uniform deformation of the entire volute, improves the structural operational stability, and is suitable for the operation requirements of high-head and high-flow pumped storage power stations.

[0030] 3. Simplified construction process, reduced costs, and shorter construction period: This invention eliminates the traditional pressure-holding and casting method of overall water filling and pressure holding, and adopts local temporary pressure holding at the nose end. It does not require special large-scale pressure filling equipment and sealing measures, making the construction process simpler and reducing the difficulty of operation. At the same time, the zoned construction and clear process can realize parallel operation. Compared with the traditional pressure-holding and casting method, the construction period using the construction method of this application can be shortened by 15% to 25%, reducing construction costs and construction risks, and facilitating large-scale promotion and application.

[0031] 4. Enhanced durability and applicability: The present invention features a built-in drainage microchannel in the subbase, an anti-seepage coating on the outer concrete, and sealing strips at the joints, which improves the structure's anti-seepage and anti-frost heave performance in multiple dimensions and extends the service life of the structure. At the same time, the structure and construction method can flexibly adjust the size of each zone, subbase parameters, and pressure holding pressure according to the head and flow requirements of different hydropower stations, making it suitable for the spiral casing installation projects of various hydropower stations and pumped storage power stations, with extremely strong applicability.

[0032] 5. This invention enables long-term online monitoring of concrete stress and subgrade deformation by deploying fiber optic strain sensors. It can monitor the structural operating status in real time, promptly detect potential hazards and issue early warnings, reduce operation and maintenance costs, and improve the safety and reliability of structural operation. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the volute structure of the present invention;

[0034] Figure 2 This is a schematic diagram of the cross-sectional structure of the present invention.

[0035] In the diagram: 1-volute, 1A-inlet direct-buried section, 1B-controllable gap cushion section, 1C-nose end pressure-holding section, 2-outer concrete, 2A-strain sensor, 3-cushion, 3A-first gap, 3B-drainage channel, 4-pressure-holding component. Detailed Implementation

[0036] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0037] Example:

[0038] This embodiment takes the spiral casing installation project of a pumped storage power station as an example. This power station is a high-head power station with a head of 300m and a turbine generator flow rate of 50m³ / h. 3 / s, the volute 1 is made of Q345R steel plate, the overall spiral diameter of the volute 1 is 8m, and the thickness of the outer concrete 2 is set to 2.5~3.5m according to the actual situation.

[0039] like Figures 1 to 2As shown, a partitioned combined hydropower station spiral casing embedded structure includes a spiral casing 1 set within an outer concrete 2, and a cushion layer 3 set between the spiral casing 1 and the outer concrete 2. The spiral casing 1, along the water flow direction and according to its stress characteristics (stress characteristics refer to the mechanical factors such as the magnitude of water pressure, stress, deformation distribution characteristics, and force transmission relationship with the outer concrete 2 at different cross-sectional positions of the spiral casing 1, are designed and treated in a partitioned manner), includes an inlet direct-buried section 1A, a controllable gap cushion layer section 1B, and a nose-end pressure-maintaining section 1C connected in sequence. A pressure-maintaining component 4 is installed in the nose-end pressure-maintaining section 1C.

[0040] The inlet direct-buried section 1A is located in the large cross-section area of ​​the inlet of the volute 1. This area bears the greatest water pressure and the strongest vibration load, and must have high overall stiffness and vibration resistance. Therefore, no cushion layer 3 structure is set outside this section. The outer wall of the volute 1 here is in direct contact with the outer concrete 2. Through the direct bonding between the volute 1 and the outer concrete 2, the stiffness is superimposed, which improves the vibration resistance and overall stability of the structure, while avoiding the problem of stiffness reduction caused by the presence of the cushion layer 3.

[0041] The controllable gap cushion section 1B is located in the middle area of ​​the volute 1. This area is the main force transmission section of the volute 1. The force is relatively uniform, but the force transmission requirements are complex. It is necessary to achieve controllable force transmission and joint bearing between the volute 1 and the surrounding concrete 2. The outer wall of this section is provided with a cushion layer 3. The cushion layer 3 is made of a gradient elastic modulus elastic material. This material is composed of multiple elastic composite layers with different elastic moduli. Its elastic modulus changes in a gradient along the thickness of the cushion layer (1.5~15mm). The gradient change rate of the cushion layer 3 is set to 0.5~2.0MPa / mm according to the force requirements of the volute.

[0042] The volute 1 is spiral-shaped.

[0043] A drainage channel 3B is provided inside the padding layer 3, and a first gap 3A exists between the padding layer 3 and the volute 1. The drainage channel 3B can extend through the first gap 3A.

[0044] The padding layer 3, which can be prepared using existing technologies with gradient elastic modulus materials, can be achieved in the following ways: 1. It is made by laminating and compounding elastic material sheets with different elastic moduli (e.g., low elastic modulus foamed rubber sheets, medium elastic modulus nitrile rubber sheets, and high elastic modulus polyurethane elastomer sheets); 2. It is prepared using a gradient formulation integrated foaming molding process. Relevant manufacturers can complete the preparation of the above-mentioned padding layer 3 according to engineering requirements. Those skilled in the art can choose any of the above methods to prepare padding materials that meet the requirements of elastic modulus gradient based on the actual engineering situation.

[0045] The performance parameters of the cushion layer 3 meet the following requirements: along the thickness direction of the cushion layer 3, from the side near the volute 1 to the side near the outer concrete 2, the elastic modulus of the cushion layer 3 increases from 0.5 to 1.0 MPa to 2.0 to 3.0 MPa, with a gradient change rate of 0.2 to 0.5 MPa / mm.

[0046] The nose-end pressure-maintaining section 1C is located in the small cross-sectional area at the nose end of the volute 1. This area has the smallest cross-sectional size and the most obvious stress concentration, which is prone to excessive local deformation. This section adopts a combination of thin padding and temporary pressure maintenance. The thickness of the padding 3 is 1-2 mm, which covers the entire outer wall of the nose-end pressure-maintaining section 1C to buffer local stress.

[0047] The thickness of the padding layer 3 gradually increases from top to bottom, with the bottom thickness being 3 to 4 times the top thickness. The top thickness of the padding layer 3 is 2 to 5 mm, and the bottom thickness is 8 to 15 mm, adapting to the stress differences at different positions of the volute circumferential direction. Along the water flow direction, the thickness of the padding layer 3 gradually decreases from the connection point of the inlet direct-buried section 1A to the connection point of the nose pressure-holding section 1C, decreasing from 1.5 to 2.0 mm in the inlet direct-buried section 1A to 1.0 to 1.2 mm in the nose pressure-holding section 1C (the rate of decrease in thickness depends on the distance from the end of the inlet direct-buried section 1A to the nose). The axial distance from the starting point of the pressure-holding section 1C varies uniformly. For example, in this embodiment, the axial length is 5m, and the thickness of the padding layer 3 decreases at a rate of (2.0-1.2~1.5-1.0) / 5, that is, the thickness of the padding layer 3 decreases at a rate of 0.1~0.16mm / m. The elastic modulus of the padding layer 3 gradually increases from the connection point of the inlet direct-buried section 1A to the connection point of the nose-end pressure-holding section 1C. The elastic modulus of the padding layer 3 at the connection point of the inlet direct-buried section 1A is 0.5~1.0MPa, and the elastic modulus of the padding layer 3 at the connection point of the nose-end pressure-holding section 1C is 2.0~3.0MPa. By gradient control of the thickness and elastic modulus of the cushion layer 3, a preset force transmission gap is formed, realizing the effect of joint load bearing of the volute 1 and the outer concrete 2 in a preset ratio. When the internal pressure of the volute 1 is small, the volute 1 mainly bears the load; when the internal pressure of the volute 1 increases to the design value, the cushion layer 3 is compressed to the preset thickness, causing the gap between the volute 1 and the outer concrete 2 to change. At this time, the volute 1 and the outer concrete 2 jointly bear the load, avoiding overload of a single component.

[0048] The outer wall of the volute 1 and the padding layer 3 are bonded and fixed using a two-component structural adhesive. The structural adhesive can be a commercially available adhesive; in this embodiment, the commercially available MIGAO HR20 reservoir reinforcement engineering adhesive (compressive strength ≥100MPa, shear strength ≥13MPa, containing A and B colloids, with a mixing volume ratio of A:B=3:1) is used. The adhesive coating thickness is 0.5–1.0 mm, and the bonding strength is ≥1.5MPa. This adhesive is commonly used for the installation of existing volute 1. The padding layer 3 bonding requirements are: the air bubble area of ​​a single padding layer 3 ≤5cm². 2After pasting, the padding layer 3 is not loose or wrinkled; the padding layer 3 is provided with drainage channels 3B of Φ3~5mm, and the spacing between adjacent drainage channels 3B is 200~300mm, which is used to drain the seepage water between the padding layer 3 and the volute 1 and the outer concrete 2, to prevent the padding layer 3 from debonding and aging caused by seepage, as well as the damage caused by frost heave of the outer concrete 2, and to further improve the durability of the structure.

[0049] The installation steps for pad 3 are as follows:

[0050] A1: Apply two-component structural adhesive to the edge of the outer wall of the volute 1 where it contacts the pad 3. The two-component structural adhesive only covers the bonding area around the edges of the pad 3, and does not apply two-component structural adhesive to the middle area of ​​the pad 3.

[0051] A2: Align the pad 3 with the bonding position, and gently press the edges of the pad 3 to bond and fix the two-component structural adhesive, while keeping the center of the pad 3 free. Due to the variable thickness of the pad 3, a stable first gap 3A is naturally formed between the outer wall of the volute 1 and the inner side of the thinner part of the pad 3, relying on the shape of the pad 3 itself. Since the pad 3 is only bonded and fixed by the edges, and the center is not bonded to the outer wall of the volute 1, and is supported by the casting mold of the outer concrete 2, it is ensured that the first gap 3A will not close before or during the casting of the outer concrete 2.

[0052] During normal operation of the spiral casing embedded structure of this combined hydropower station, the water pressure is entirely borne by the spiral casing 1, and the first gap 3A is used to house the strain sensor 2A. During flood and water discharge checks, the water pressure increases sharply, and the spiral casing 1 undergoes slight deformation. At this time, the deformation of the spiral casing 1 completely fills the first gap 3A, thereby achieving the effect of the spiral casing 1 and the surrounding concrete 2 jointly bearing the pressure.

[0053] The pressure-holding assembly 4 includes a pressure-holding airbag and a pressure-relief valve. The pressure-holding airbag is located inside the nose-end pressure-holding section 1C, and a pressure sensor with an accuracy of ±0.01 MPa is installed inside the airbag. The pressure-holding airbag and the pressure-relief valve are connected by a pipeline, and the pressure-relief valve is located outside the nose-end pressure-holding section 1C. The pressure-holding airbag is installed within a range of 300-500 mm from the inner wall of the nose-end pressure-holding section 1C. The pressure sensor is used to monitor the pressure holding pressure in real time. The pressure-relief valve is linked with the pressure sensor to achieve automatic pressure regulation. By temporarily holding the pressure, the deformation of the nose-end pressure-holding section 1C is controlled to prevent local cracking during the pouring and curing of the surrounding concrete 2.

[0054] Stress relief grooves are provided on the inner wall of the outer concrete 2 at the locations corresponding to the controllable gap cushion section 1B and the nose-end pressure-holding section 1C. A sealing strip is provided at the junction of the volute 1 and the outer concrete 2. The sealing strip is embedded in the stress relief groove to prevent water accumulation in the groove and cracking of the outer concrete 2. The sealing strip is a butyl sealing strip.

[0055] Several strain sensors 2A are installed within the outer concrete 2 corresponding to the cushion layer 3, extending to the first gap 3A. These strain sensors 2A are arranged in a quincunx pattern and are distributed fiber optic strain sensors. The strain sensors 2A are buried at a depth of 200–250 mm, with signal transmission lines leading to an external monitoring terminal. This allows for long-term monitoring of stress changes in the outer concrete 2 and compression deformation of the cushion layer 3, enabling real-time monitoring and early warning of the structural operating status. The data acquisition frequency is ≥1 time / hour.

[0056] The outer concrete 2 is poured on the outside of the spiral shell 1, using C25 to C40 concrete. The appropriate type of concrete is selected according to the dam's low head (<100m), medium head (100m to 300m), and high head (>300m) conditions. The preset stress relief groove has a width of 50 to 80mm and a depth of 100 to 150mm. The stress relief groove is arranged circumferentially every 2m along the axis of the spiral shell 1 to further alleviate the effects of temperature stress and local stress concentration, and prevent concrete cracking. The surface of the outer concrete 2 is coated with a polyurea anti-seepage coating. This polyurea anti-seepage coating can be a commercially available coating for water conservancy projects. In this embodiment, commercially available Xiupo SP-7818 polyurea anti-seepage coating for water conservancy and hydropower is used to enhance the overall anti-seepage performance.

[0057] The sealing performance is enhanced by setting a sealing strip to prevent water seepage; a polyurea anti-seepage coating is applied to the outer concrete surface 2 to further improve the anti-seepage performance. The coating is applied twice with a total thickness of 0.8 to 1.2 mm.

[0058] A construction method for a partitioned combined hydropower station spiral casing embedded structure includes the following steps:

[0059] S1: Assemble the volute 1. According to the design drawings, Q345R steel plates are sequentially cut, bent, and welded to form the inlet direct-buried section 1A, the controllable gap cushion section 1B, and the nose-end pressure-holding section 1C of the volute 1. After the welds are non-destructively tested and confirmed to be qualified, the outer walls of each section are treated. Specifically, the outer wall of the inlet direct-buried section 1A is sequentially subjected to rust removal and roughening treatment with a roughness Ra≥50μm to enhance its adhesion to concrete. The outer wall of the controllable gap cushion section 1B is leveled to achieve a flatness ≤2. mm / m, facilitating the bonding and fixing of the padding layer 3; an installation interface for the pressure-holding component 4 is reserved on the outer wall of the nose-end pressure-holding section 1C; after the segment components are hoisted to the design position by a tower crane, they are spliced ​​and fixed. The axial deviation after splicing is: inlet direct-buried section 1A≤3mm, controllable gap padding layer section 1B≤5mm, nose-end pressure-holding section 1C≤2mm; after splicing, each segment component can be firmly fixed with supporting objects. The inlet direct-buried section 1A, controllable gap padding layer section 1B and nose-end pressure-holding section 1C are seamlessly connected, working together to achieve overall load-bearing and deformation control;

[0060] S2: Pressurize the volute 1. Set a pad 3 on the outer wall of the controllable gap pad section 1B and the nose pressure-holding section 1C. The pad 3 is set circumferentially along the volute 1. A drainage channel 3B is pre-embedded in the pad 3. Install a pressure-holding airbag, a pressure sensor and a pressure relief valve on the nose pressure-holding section 1C. Inflate the pressure-holding airbag and adjust the pressure holding pressure of the pressure-holding airbag to 0.4MPa. Ensure that the pressure-holding airbag is well sealed and the pressure is stable.

[0061] S3: Set up sealing strips and sensors. Embed the sealing strip into the stress relief groove at the junction of the volute 1 and the outer concrete 2. Press and fix the sealing strip. Set up a number of strain sensors 2A in the outer concrete 2 at the corresponding pad layer 3. The strain sensors 2A are arranged in a quincunx pattern. The distance between adjacent strain sensors 2A is 600mm. The strain sensors 2A extend to the first gap 3A. Lead out the signal transmission line of the strain sensor 2A to the monitoring terminal and debug it to pass the test.

[0062] S4: Pour the outer concrete 2 using C40 grade concrete, poured in layers by pumping, with each layer being 250mm thick. After pouring, compact the concrete thoroughly. The pouring sequence for outer concrete 2 is from the inlet direct-buried section 1A of the spiral casing 1 towards the nose-end pressure-holding section 1C. During pouring, monitor the stability of the pressure holding pressure in real time, ensuring it remains stable at 0.4MPa. Control the concrete temperature upon entry into the formwork at 28℃, and maintain the temperature difference between the interior and surface of the concrete at 22℃. After pouring, promptly cure the concrete for at least 28 days (≥30 days for high-head power stations). During curing, keep the concrete surface moist, using existing methods such as water spraying or covering with a moisturizing film. The curing is considered successful once the concrete test blocks confirm that the strength has reached 80% of the design strength.

[0063] S5: Remove the pressure and adjust the sensor. Release the pressure of the pressure-holding airbag through the pressure relief valve at a rate of 0.05MPa / h. After the pressure is released, remove the pressure-holding airbag, pressure sensor and pressure relief valve. Use Q345R steel plate to weld and seal the interface where the pressure-holding airbag is installed inside the volute 1. Apply a 1.0mm thick polyurea anti-permeability coating to the surface of the outer concrete 2. Repair the surface defects of the outer concrete 2. Adjust the strain sensor 2A to ensure that the monitoring terminal can accurately collect the stress of the outer concrete 2 and the deformation data of the cushion layer 3.

[0064] S6: Conduct welding quality and installation accuracy tests on the volute 1, concrete strength and impermeability tests on the outer concrete 2, bonding quality tests on the bedding layer 3, and quality tests on the operating status of the strain sensor 2A. After acceptance, the construction is completed. All tests are conducted in accordance with the corresponding engineering standards.

Claims

1. A partitioned combined hydropower station spiral casing embedded structure, characterized in that: It includes a volute (1) set inside the outer concrete (2) and a cushion layer (3) set between the volute (1) and the outer concrete (2). The volute (1) includes an inlet direct buried section (1A), a controllable gap cushion layer section (1B) and a nose pressure-holding section (1C) connected in sequence along the water flow direction. A pressure-holding component (4) is provided on the nose pressure-holding section (1C). The thickness of the pad (3) gradually increases from top to bottom; the elastic modulus of the pad (3) gradually increases from the connection of the inlet direct buried section (1A) to the connection of the nose pressure-holding section (1C).

2. The partitioned combined hydropower station spiral casing embedded structure as described in claim 1, characterized in that: The thickness of the bottom layer (3) is 3 to 4 times the thickness of its top layer; the elastic modulus of the connection between the padding layer (3) and the inlet direct buried section (1A) is 0.5 to 1.0 MPa, and the elastic modulus of the connection between the padding layer (3) and the nose end pressure-holding section (1C) is 2.0 to 3.0 MPa.

3. The partitioned combined hydropower station spiral casing embedded structure as described in claim 1, characterized in that: The pressure-holding assembly (4) includes a pressure-holding airbag and a pressure-relief valve. The pressure-holding airbag is located inside the nose-end pressure-holding section (1C). A pressure sensor is installed inside the pressure-holding airbag. The pressure-holding airbag and the pressure-relief valve are connected through a pipe. The pressure-relief valve is located outside the nose-end pressure-holding section (1C).

4. The partitioned combined hydropower station spiral casing embedded structure as described in claim 1, characterized in that: Stress relief grooves are provided on the inner wall of the outer concrete (2) at the controllable gap cushion section (1B) and the nose pressure-holding section (1C); a sealing strip is provided at the junction of the volute (1) and the outer concrete (2), and the sealing strip is embedded in the stress relief groove.

5. The partitioned combined hydropower station spiral casing embedded structure as described in claim 4, characterized in that: The stress relief groove is arranged circumferentially every 2m along the axis of the volute (1).

6. The partitioned combined hydropower station spiral casing embedded structure as described in claim 1, characterized in that: Several strain sensors (2A) are installed at the corresponding cushion layer (3) inside the outer concrete (2), and the strain sensors (2A) are arranged in a quincunx pattern.

7. The partitioned combined hydropower station spiral casing embedded structure as described in claim 1, characterized in that: The volute (1) is spiral-shaped.

8. The partitioned combined hydropower station spiral casing embedded structure as described in claim 1, characterized in that: A drainage channel (3B) is provided in the cushion layer (3), and a first gap (3A) exists between the cushion layer (3) and the volute (1).

9. A construction method for the partitioned combined hydropower station spiral casing embedded structure as described in claim 8, characterized in that, Includes the following steps: S1: Assemble the volute (1). The steel plates are cut, bent and welded in sequence to make the volute (1) into the inlet direct buried section (1A), the controllable gap cushion layer section (1B) and the nose pressure holding section (1C) segment components. After the welds are non-destructively tested and confirmed to be qualified, the outer walls of each segment component are treated. Among them, the outer wall of the inlet direct buried section (1A) is subjected to rust removal and roughening treatment with a roughness Ra≥50μm in sequence. The outer wall of the controllable gap cushion layer section (1B) is flattened to make its flatness ≤2mm / m. After each segment component is hoisted to the design position, it is spliced ​​and fixed. The axial deviation after splicing is controlled within 5mm. S2: Pressurize the volute (1), and install a pad (3) on the outer wall of the controllable gap pad section (1B) and the nose end pressure-maintaining section (1C). The pad (3) is arranged circumferentially along the volute (1), and a drainage channel (3B) is pre-embedded in the pad (3). Install a pressure-maintaining airbag, a pressure sensor and a pressure relief valve on the nose end pressure-maintaining section (1C), inflate the pressure-maintaining airbag and adjust the pressure of the pressure-maintaining airbag to the required pressure. S3: Set a sealing strip and a sensor. At the junction of the volute (1) and the outer concrete (2), embed the sealing strip into the stress relief groove and compact it. Set a number of strain sensors (2A) in the outer concrete (2) corresponding to the pad layer (3). The strain sensors (2A) are arranged in a plum blossom shape. The strain sensors (2A) extend to the first gap (3A). Lead out the signal transmission line of the strain sensor (2A) to the monitoring terminal. S4: Pour the outer concrete (2). The pouring sequence of the outer concrete (2) is from the inlet direct buried section (1A) of the volute (1) to the nose pressure holding section (1C). During the pouring process, the stability of the pressure holding pressure is monitored in real time. The outer concrete (2) is cured until it reaches 70% to 90% of the design strength. S5: Remove the pressure and adjust the sensor. Release the pressure of the pressure-holding airbag through the pressure relief valve. After the pressure is released, remove the pressure-holding airbag, pressure sensor and pressure relief valve. Seal the interface for installing the pressure-holding airbag inside the volute (1). Apply an anti-permeability coating to the outer concrete surface and repair the surface defects of the concrete. Adjust the strain sensor (2A) to ensure that the monitoring terminal can accurately collect the stress of the outer concrete (2) and the deformation data of the cushion layer (3).

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