Super-thick layer continuous layering construction method for rockfill concrete gravity dam in narrow site

Abstract

This application provides a method for the continuous, layered construction of ultra-thick rockfill concrete gravity dams in confined spaces, comprising the following steps: cleaning, roughening, washing, and seepage prevention treatment of the dam foundation; erecting prefabricated cantilever formwork in sections along the dam axis to form construction sites; layering rockfill materials onto the construction site to form rockfill layers, with several protruding stones reserved on the surface of the rockfill layers as anchoring structures for interlayer bonding; injecting self-compacting concrete into the voids of the rockfill layers to form rockfill concrete layers; and repeating the aforementioned steps after the rockfill concrete layers reach a state capable of bearing the preset construction load, i.e., successively forming the next level of rockfill layers and rockfill concrete layers, repeating this process until the construction of the gravity dam is completed. The method for the continuous, layered construction of ultra-thick rockfill concrete gravity dams in confined spaces provided by this application eliminates the need for large trestle bridges and achieves continuous construction, making it suitable for rockfill concrete gravity dam construction operations in confined spaces.

Description

Technical Field

[0001] This application belongs to the field of riprap concrete construction technology, specifically relating to a method for continuous layer-by-layer construction of ultra-thick riprap concrete gravity dams in confined spaces. Background Technology

[0002] Rockfill concrete construction is a commonly used dam-building technique in water conservancy and hydropower projects. Its core lies in filling the gaps between large-diameter rockfill materials with high self-compacting concrete after they are placed in the slab, thereby eliminating the need for traditional vibration compaction and forming a dense integral structure.

[0003] In existing technologies, riprap concrete construction typically requires the erection of large-area construction trestle bridges to meet the needs of material transportation and concrete placement. However, in confined terrain conditions such as mountainous areas and canyons, the limited space makes it difficult or impossible to arrange large-area trestle bridges and other large construction equipment, resulting in high implementation difficulty and cost. Furthermore, the traditional thin-layer lifting method is often used in the concrete pouring process, where each layer is relatively thin (usually controlled at 1m to 2m). Each layer requires roughening, washing, and settling before the next layer can be poured. This results in cumbersome procedures, long construction periods, and the potential for cold joints to form between adjacent layers, affecting the integrity and safety performance of the dam. Summary of the Invention

[0004] This application provides a method for the construction of ultra-thick continuous layer-by-layer rockfill concrete gravity dams in confined spaces, aiming to solve the technical problems in the prior art, such as the difficulty in arranging large trestle bridges in confined mountainous areas, the cumbersome process of thin-layer layer-by-layer construction, the easy formation of cold joints between layers, and the lack of an integrated solution in the construction of rockfill concrete gravity dams.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: A method for constructing an ultra-thick, continuously layered rockfill concrete gravity dam in a confined space is provided, comprising the following steps: S1. Clean, roughen, wash and prevent seepage of the foundation of the gravity dam; S2. Prefabricated cantilever formwork is erected in sections along the axis of the gravity dam. The formwork is located above the foundation to form a construction surface capable of bearing the preset construction load. S3. Stack the rubble in layers on the construction site to form a rubble layer; wherein, several protruding stones are reserved at the top of each rubble layer, the lower part of the protruding stones is buried in the rubble layer, and the upper part is exposed on the top surface of the rubble layer, forming an anchoring structure for the interlocking interface between layers. S4. Self-compacting concrete is poured into the voids of the riprap layer to form a riprap concrete layer; S5. After the riprap concrete layer is able to bear the preset construction load of the next level, repeat S3 and S4; wherein, the two adjacent riprap concrete layers are joined through the interlayer interlocking interface, and the riprap concrete interlayer is formed by the curing and bonding of the concrete flowing into the interlayer interlocking interface. S6. Repeat S5 until the height of the rockfill concrete layer reaches the construction height requirement of the gravity dam.

[0006] In one possible implementation, the prefabricated cantilever formwork is supported on the surface of the poured dam body or foundation by adjustable supports, and the adjustable supports are anchored in the poured dam body or foundation by anchor bolts. In S2, the anchor rod is anchored to the foundation; In S5, the adjustable support and the anchor rod are released, and before repeating S3 and S4, the prefabricated cantilever formwork is hoisted to the next construction height, and the prefabricated cantilever formwork is fixed to the surface of the poured dam body by the anchor rod. In S6, after the height of the riprap concrete layer reaches the construction height requirement of the gravity dam, the prefabricated cantilever formwork is removed.

[0007] In one possible implementation, in S4, the thickness of the rockfill layer is controlled to be 2.5~3.0m.

[0008] In one possible implementation, in S3, the porosity of the rockfill layer is controlled at 25% to 35%.

[0009] In one possible implementation, in S3, the particle size of the protruding stone is controlled to be 50~100cm.

[0010] In one possible implementation, in S3, the height of the protruding stone exposed above the top surface of the riprap layer is controlled to be 10~30cm.

[0011] In one possible implementation, the step of injecting self-compacting concrete into the voids of the riprap layer to form a riprap concrete layer includes: Multi-point flexible material distribution pipes are used to simultaneously feed materials to multiple areas. The self-compacting concrete fills the internal voids of the rockfill layer with its self-flowing properties until the slurry is evenly spread on the upper surface of the rockfill layer, forming a rockfill concrete layer.

[0012] In one possible implementation, the preset construction load includes the sum of the self-weight of the next-level rockfill, the self-weight of the next-level self-compacting concrete, and the load of the construction machinery.

[0013] In one possible implementation, in S4, after the rubble concrete layer is formed, a temperature sensing element is embedded in the rubble concrete layer to monitor the internal temperature and surface temperature of the rubble concrete layer in real time.

[0014] In one possible implementation, in S4, after the riprap concrete layer is formed, an insulation layer is covered on the surface of the riprap concrete layer, and the difference between the internal temperature and the surface temperature is controlled to be less than or equal to 18°C, and both the internal temperature and the surface temperature are less than or equal to 75°C.

[0015] In this embodiment, prefabricated cantilever formwork is erected in sections along the dam axis, forming a self-supporting construction surface. Since the formwork system can independently bear construction loads without relying on external large trestle bridges, it effectively solves the site adaptability problem of limited space where large-area trestle bridges cannot be arranged. Simultaneously, by reserving protruding stones at the top of each rockfill layer as anchoring structures for interlayer bonding, adjacent rockfill concrete layers can be bonded together with the cured concrete through these anchoring structures to form a unified structure. Furthermore, by injecting self-compacting concrete into the voids of the rockfill layers and repeating the rockfill and injection process after the layers reach a state capable of bearing the preset construction load, continuous layer-by-layer operations for ultra-thick layers (thickness greater than conventional pouring thickness) are achieved.

[0016] The core of the above method lies in using a self-supporting formwork structure to replace the traditional trestle bridge, and utilizing the interlayer interlocking interface formed by protruding boulders to eliminate the roughening process in existing technologies. Simultaneously, it effectively utilizes the flow characteristics and high filling performance of self-compacting concrete. Through the synergy of these three technical means, on the one hand, the formwork system itself forms a stable load-bearing structure, directly transferring construction loads to the already poured dam body or foundation, eliminating the need for large transportation equipment. On the other hand, the protruding boulders form a mechanical interlocking interface similar to mortise and tenon joints between layers, allowing the subsequently added self-compacting concrete to encapsulate and bond these boulders, ensuring the interlayer bonding strength meets process requirements, thus eliminating the need for interlayer roughening, washing, and waiting periods. Furthermore, the rapid early strength development of self-compacting concrete allows for the continuous initiation of the next layer's construction within a short time, eliminating the intermittent waiting time in traditional thin-layer-to-layer construction methods from a process perspective.

[0017] The method for constructing ultra-thick, continuously layered rockfill concrete gravity dams in confined spaces, as provided in this embodiment, compared to existing technologies, systematically solves the core problems of traditional rockfill concrete construction in confined spaces such as mountainous areas and canyons. These problems include the inability to deploy large trestle bridges, the cumbersome thin-layer layering process, and the tendency for cold joints to form between layers. This is achieved through the synergy of self-supporting formwork structures, inter-layer anchoring of protruding boulders, and self-compacting concrete pouring. Thus, while ensuring the integrity and safety of the dam body, it significantly improves construction efficiency and site adaptability. Furthermore, the construction cycle is significantly shorter than traditional methods, and due to its uninterrupted nature, it avoids cold joints between adjacent rockfill concrete layers, ensuring that the dam's compactness and integrity meet design requirements. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic flowchart illustrating the construction method provided in the embodiments of this application; Figure 2 A schematic diagram of the structure of a rockfill concrete gravity dam formed by the construction method provided in the embodiments of this application; Figure 3 A schematic diagram of the combined structure of prefabricated cantilever formwork, adjustable support components, and anchor bolts in the construction method provided in the embodiments of this application; Explanation of reference numerals in the attached drawings: 1. Dam foundation; 2. Prefabricated cantilever formwork; 3. Rockfill material; 4. Self-compacting concrete; 5. Multi-point flexible placing pipe; 6. Adjustable support component; 7. Anchor bolt; 8. Insulation layer; 9. Interlayer interlocking interface. Detailed Implementation

[0020] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0021] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0022] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0024] Please refer to the following: Figure 1 and Figure 2 This application describes a method for the continuous uplift construction of ultra-thick layers in a rockfill concrete gravity dam on a confined space. The construction method proposed in this application includes the following steps: S1. Clean, roughen, flush, and treat the foundation 1 of the gravity dam for seepage prevention. Roughening can be done with a pneumatic pick to remove the low-strength, loose laitance or impurities from the surface of the foundation 1. Flushing is done with a high-pressure water jet. After completing the above procedures, an acceptance test is required, specifically to check whether the bearing capacity and seepage prevention indicators of the foundation 1 surface meet the standards.

[0025] S2. Prefabricated cantilever formwork 2 is erected in sections along the axis of the gravity dam. The formwork is located above the foundation to form a construction surface capable of bearing the preset construction load. In this embodiment, the prefabricated cantilever formwork 2 adopts a lightweight structure, that is, a formwork component that allows for movement by small machinery (equipment that can be used in confined spaces). During the erection process, the verticality of the prefabricated cantilever formwork 2 must be ensured to guarantee the flatness of the self-supporting construction surface and the uniformity of its upper space. And, as... Figure 2 As shown, in this embodiment, the prefabricated cantilever formwork 2 adopts a structure in which the width gradually decreases from bottom to top (i.e., the direction of the dam's outward extension); compared with the construction trestle, the prefabricated cantilever formwork 2 occupies less space and does not affect the normal operation of the construction passage.

[0026] S3. Stack the rock material 3 in layers on the construction site (this task is performed by a small tracked loader) to form a rock layer; wherein, several protruding stones are reserved at the top of each rock layer, the lower part of the protruding stones is buried in the rock layer, and the upper part is exposed on the top surface of the rock layer, forming an anchoring structure of the interlocking interface 9 between layers.

[0027] S4. Pour self-compacting concrete 4 into the voids of the riprap layer to form a riprap concrete layer. The self-compacting concrete 4 has a strength grade of C25, and during its formation, no external vibration is required. The self-compacting concrete 4 fills the internal voids of the riprap layer through its self-flowing properties until a slurry-like layer appears on the surface, and this slurry-like layer is evenly distributed across the surface of the riprap concrete layer. In actual construction, the thickness of the slurry-like layer must be controlled to prevent it from exceeding the thickness of the riprap layer.

[0028] S5. Once the riprap concrete layer can bear the preset construction load of the next level (i.e., the material can continue to be added), repeat S3 and S4 without roughening or interruption; wherein, the two adjacent riprap concrete layers are joined by the interlayer interlocking interface 9, and the concrete flowing into the interlayer interlocking interface 9 solidifies and binds to form a riprap concrete interlayer, which can ensure that the upper and lower riprap concrete layers do not move relative to each other.

[0029] S6. Repeat S5 until the height of the rockfill concrete layer reaches the construction height requirement of the gravity dam.

[0030] In this embodiment, prefabricated cantilever formwork 2 is erected in sections along the dam axis, forming a self-supporting construction surface. Since the formwork system can independently bear construction loads without relying on external large trestle bridges, it effectively solves the site adaptability problem of limited space where large-area trestle bridges cannot be arranged. Simultaneously, by reserving protruding stones at the top of each rockfill layer as anchoring structures for the interlayer bonding interface 9, adjacent rockfill concrete layers can be bonded together with the cured concrete through this anchoring structure to form a unified structure. Furthermore, by injecting self-compacting concrete 4 into the gaps of the rockfill layer, and repeating the rockfill and injection process after it reaches a state capable of bearing the preset construction load, continuous layer-by-layer operation of ultra-thick layers is achieved.

[0031] The core of the above method lies in using a self-supporting formwork structure to replace the traditional trestle bridge, and utilizing the interlayer interlocking interface 9 formed by protruding boulders to eliminate the roughening process in existing technologies; at the same time, it also effectively utilizes the flow characteristics and high filling performance of self-compacting concrete 4. Through the synergy of these three technical means, on the one hand, the formwork system itself forms a stable load-bearing structure, directly transferring the construction load to the already poured dam body or foundation, without occupying the site to arrange large transportation equipment; on the other hand, the protruding boulders form a mechanical interlocking interface similar to "mortise and tenon" between layers, allowing the subsequently added self-compacting concrete 4 to wrap and bond these boulders, ensuring that the interlayer bonding strength meets the process requirements, thereby eliminating the interlayer roughening, washing, and static waiting processes; at the same time, the rapid early strength development of self-compacting concrete 4 allows the construction of the next layer to start continuously in a short time, eliminating the intermittent waiting time in the traditional thin-layer-to-layer method from the process level.

[0032] The method for constructing ultra-thick, continuously layered rockfill concrete gravity dams in confined spaces, as provided in this embodiment, compared to existing technologies, systematically solves the core problems of traditional rockfill concrete construction in mountainous and canyon areas. These problems stem from the inability to deploy large trestle bridges, the cumbersome thin-layer layering process, and the tendency for cold joints to form between layers. This is achieved through the synergy of self-supporting formwork structures, inter-layer anchoring of protruding boulders, and the pouring of self-compacting concrete. This significantly improves construction efficiency and site adaptability while ensuring the integrity and safety of the dam body. Furthermore, the construction cycle is significantly shorter than traditional methods, and the uninterrupted nature of the method prevents cold joints between adjacent rockfill concrete layers, ensuring that the dam's compactness and integrity meet design requirements.

[0033] It should be further noted that the microstructure and strength characteristics of the concrete bond at the nine interlayer bonding interfaces have been experimentally verified. Specifically: According to the analysis of scanning electron microscopy, the thickness of the interface transition zone between the protruding stone surface and the self-compacting concrete 4 is about 40~60μm, which is thinner than the interface transition zone of traditional vibrated concrete. Moreover, the ettringite crystals are fully developed and form a tight interlock with the stone surface.

[0034] According to the mercury intrusion porosimetry test at the interface, the porosity at this point is only 12.5%, which is lower than the 15%~18% of the traditional concrete interface, indicating that the interface has good compactness.

[0035] The interlaminar shear strength comparison test data are as follows: the specimen with interlaminar interlocking interface 9 has an interlaminar shear strength of 2.8 MPa, while the interlaminar shear strength of the specimen with traditional roughening treatment is 2.1 MPa; the strength is increased by about 33% in comparison.

[0036] According to the interlaminar tensile strength test results, the interlaminar tensile strength of the specimen with interlaminar interlocking interface 9 is 1.6 MPa, while that of the specimen with traditional roughening treatment is 1.2 MPa; the improvement is about 33%.

[0037] The above data confirms that the mechanical interlocking interface formed by protruding stones not only eliminates the need for roughening but also significantly enhances the interlayer bonding performance.

[0038] In some embodiments, such as Figure 2 and Figure 3 As shown, the aforementioned prefabricated cantilever formwork 2 is supported on the surface of the poured dam body or foundation by adjustable support members 6, and the adjustable support members 6 are anchored in the poured dam body or foundation by anchor rods 7. Based on this, the following supplements are made to the process steps: In S2, the prefabricated cantilever formwork 2 is supported on the foundation by adjustable support 6 (or the prefabricated cantilever formwork 2 forms the inner bottom surface of the construction site), and the corresponding anchor rod 7 is anchored on the foundation. In S5, the adjustable support 6 and anchor rod 7 are released, and before repeating S3 and S4, the prefabricated cantilever formwork 2 is hoisted to the next construction height, and the prefabricated cantilever formwork 2 is fixed to the surface of the poured dam body through the anchor rod 7. In S6, after the height of the rockfill concrete layer reaches the construction height requirement of the gravity dam, the prefabricated cantilever formwork 2 is removed.

[0039] In other words, when erecting the prefabricated cantilever formwork 2, the prefabricated cantilever formwork 2 is arranged in sections along the axis of the dam body, and the prefabricated cantilever formwork 2 is supported on the poured dam body or foundation by adjustable support members 6, and anchored by anchor rods 7.

[0040] This erection method creates a load transfer path of "formwork-anchor bolt-cast dam body," meaning that the loads from the riprap, concrete, and construction machinery borne by the prefabricated cantilever formwork 2 are transferred to the anchor bolts 7 via adjustable supports 6, and then the anchoring force of the anchor bolts 7 is transferred to the cast dam body or foundation, thus realizing the self-supporting function of the formwork system. Therefore, even without the construction of a large trestle bridge, construction requirements can be met, completely solving the constraint of difficult equipment layout in confined spaces.

[0041] It should be added that the adjustable support 6 can be finely adjusted for verticality according to the slope of the dam body, ensuring that the verticality and other installation accuracy of the prefabricated cantilever formwork 2 meet the requirements.

[0042] Based on the combined structure of prefabricated cantilever formwork 2, adjustable support 6, and anchor bolts 7, the prefabricated cantilever formwork 2 adopts a cyclical reuse method during the continuous layer-by-layer construction process. Specifically: after the lower layer of riprap concrete reaches a load-bearing state, the anchor bolts 7 and adjustable support 6 of the prefabricated cantilever formwork 2 are removed, and the entire formwork is hoisted to the height of the next layer to be poured. The adjustable support 6 is then reinstalled and fixed using the pre-embedded anchor points on the already poured dam body.

[0043] The turnover speed of the prefabricated cantilever formwork 2 is highly coordinated with the construction progress: during the development of the concrete strength of the next layer, the preparation, transfer, and preliminary stacking of the upper layer of riprap 3 are carried out simultaneously. Once the concrete reaches a load-bearing state, the formwork is immediately disassembled and the upper layer of riprap is constructed, achieving a seamless connection between formwork turnover and riprap operation. In actual operation, for a single work surface, 2 to 3 sets of prefabricated cantilever formwork 2 are typically configured for cyclical use. Each set of formwork completes a layer-up every 2.5 days on average, which is about 60% more efficient than traditional thin-layer layer-up methods.

[0044] In some embodiments, such as Figure 2 As shown, in S4, the thickness of the rockfill layer is controlled between 2.5 and 3.0 m.

[0045] Compared to the traditional 1.0~1.5m thin-layer rockfill, this ultra-thick-layer rockfill scheme nearly doubles the single-layer construction height, effectively reducing the number of layers and the frequency of formwork turnover, thus significantly accelerating the construction progress.

[0046] In some embodiments, such as Figure 2 As shown, in S3, the porosity of the rockfill layer is controlled at 25%~35%.

[0047] This porosity range ensures that the filling channels of the self-compacting concrete 4 are unobstructed, preventing the concrete from not being able to fill completely due to excessively small voids, while also preventing the increase in concrete usage and cost caused by excessively large voids, thus achieving the optimal economic match between the riprap skeleton and the concrete filling.

[0048] In some embodiments, such as Figure 2 As shown, in S3, the particle size of the protruding stones is controlled between 50 and 100 cm.

[0049] The protruding stones within this size range have sufficient self-weight and embedment depth to prevent them from being easily washed away or floated up during subsequent concrete pouring, thus ensuring the anchoring effect.

[0050] In some embodiments, such as Figure 2 As shown, in S3, the height of the protruding stones exposed above the top surface of the rockfill layer is controlled between 10 and 30 cm.

[0051] This exposure height ensures that the protruding parts form a reliable mechanical interlocking height between layers, allowing the bottom of the next layer of riprap 3 and the self-compacting concrete 4 to completely enclose these protruding stones, forming an anchoring effect similar to rebar installation, and significantly enhancing the interlayer shear strength.

[0052] In addition, it should be noted that in terms of spacing, the protruding stones should be evenly spaced along the top surface of the riprap layer, with the spacing controlled within the range of 1.5 to 2.0 times the stone particle size, to ensure a continuous and uniform interlocking interface between the upper and lower layers, and to avoid weak zones in some areas due to lack of anchorage.

[0053] Among them, such as Figure 2 As shown, the relative positional relationship between the protruding boulders and the upper and lower layers of riprap is as follows: the lower part of the protruding boulders is embedded in the riprap layer and interlocks with the lower riprap material 3, while the upper part serves as the support point and anchor point of the upper riprap material 3, so that the upper and lower riprap layers form a mechanical interlock through these protruding boulders, thereby enhancing the interlayer shear strength.

[0054] In some embodiments, such as Figure 2 As shown, the aforementioned process of "injecting self-compacting concrete 4 into the voids of the riprap layer to form a riprap concrete layer" includes: using a multi-point flexible material distribution pipe 5 to simultaneously feed material into multiple areas, and filling the internal voids of the riprap layer with the self-flowing property of the self-compacting concrete 4 until the surface is uniformly covered with slurry.

[0055] In other words, when self-compacting concrete 4 is poured into the voids of the rockfill layer to form a rockfill concrete layer, a multi-point flexible material distribution pipe 5 is used to simultaneously feed material into multiple areas. The self-flowing nature of the self-compacting concrete 1 fills the internal voids of the rockfill layer until the upper surface of the rockfill layer is uniformly covered with slurry.

[0056] During this process, multi-point synchronous material placement shortens the path of single-point material placement, reduces the flow resistance of concrete, makes the filling more uniform and sufficient, avoids local accumulation or segregation, and ensures the overall compactness of the rubble concrete.

[0057] The mix design of self-compacting concrete 4 is as follows: water-cement ratio 0.32~0.35, sand ratio 48%~52%, appropriate amount of fly ash and high-efficiency water-reducing agent added, and expansion controlled at 650~700mm; and the passage time of the V-shaped funnel is controlled at 8~12 seconds.

[0058] By adopting the above technical solution, the mix design enables the self-compacting concrete 4 to have high fluidity and good gap-filling capacity, allowing it to flow and self-fill over long distances in the riprap voids, achieving a compacted state without vibration. Field filling test data shows that the self-compacting concrete 4 using this mix design can achieve a filling rate of over 98.5% in a riprap layer of 2.5~3.0m thickness. Furthermore, the interface between the riprap and concrete is well-bonded, with no visible voids or honeycombs. The 28-day compressive strength of the concrete specimens meets the C25 design grade requirements, and the strength dispersion coefficient is less than 0.12, indicating uniform and stable filling effect.

[0059] In some embodiments, the aforementioned preset construction load includes the sum of the self-weight of the next-level rockfill 3, the self-weight of the next-level self-compacting concrete 4, and the load of the construction machinery (such as a small tracked loader).

[0060] Using the above three load components as the basis for judgment ensures the safety and stability of the riprap concrete layer when bearing subsequent construction loads. Specifically, the criterion for determining whether the layer can bear the preset construction load is a combination of strength age and rebound testing. Based on the early strength development curve of self-compacting concrete 4, the initial criterion is that the compressive strength of concrete test blocks cured under the same conditions for 24 hours after pouring is not less than 8 MPa. Simultaneously, a rebound hammer is used on-site to test the surface of the riprap concrete layer. When the rebound value converted to strength is not less than 10 MPa, it is determined to have reached the load-bearing state.

[0061] The basis for this criterion is that a strength of 8-10 MPa is sufficient to withstand the static and dynamic loads of small machinery, and can ensure the interfacial bond strength between the concrete and the riprap, preventing interfacial peeling or interlayer displacement during subsequent riprap construction. According to actual engineering monitoring data, self-compacting concrete 4 can reach this strength within 18-24 hours after pouring, which is more than half the waiting time of 48-72 hours for traditional concrete.

[0062] In some embodiments, in S4, after the riprap concrete layer is formed, a temperature sensing element is embedded in the riprap concrete layer to monitor the internal temperature and surface temperature of the riprap concrete layer in real time.

[0063] By monitoring temperature changes in real time, temperature control measures can be taken in a timely manner to prevent temperature cracks caused by the concentrated release of heat of hydration.

[0064] In some embodiments, in S4, after the riprap concrete layer is formed, an insulation layer 8 is covered on the surface of the riprap concrete layer to control the difference between the internal temperature and the surface temperature to be less than or equal to 18°C, and the internal temperature and the surface temperature to be less than or equal to 75°C.

[0065] The temperature control standard is determined based on the hydration heat characteristics of riprap concrete and the temperature stress analysis of the dam body: controlling the internal and external temperature difference within 18℃ can effectively reduce the tensile stress generated by the temperature gradient and avoid surface cracks. Meanwhile, keeping the maximum temperature below 75℃ can prevent the risk of reduced concrete strength and delayed formation of ettringite caused by high temperatures.

[0066] According to on-site monitoring data, no temperature cracks appeared in the dam body after the adoption of this temperature control measure, which verified the scientific nature and effectiveness of the temperature control index.

[0067] The above content is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for continuous layer-by-layer construction of ultra-thick rockfill concrete gravity dams in confined spaces, characterized in that: Includes the following steps: S1. Clean, roughen, wash and prevent seepage of the foundation of the gravity dam; S2. Prefabricated cantilever formwork is erected in sections along the axis of the gravity dam. The formwork is located above the foundation to form a construction surface capable of bearing the preset construction load. S3. Stack the rubble in layers on the construction site to form a rubble layer; wherein, several protruding stones are reserved at the top of each rubble layer, the lower part of the protruding stones is buried in the rubble layer, and the upper part is exposed on the top surface of the rubble layer, forming an anchoring structure for the interlocking interface between layers. S4. Self-compacting concrete is poured into the voids of the riprap layer to form a riprap concrete layer; S5. After the riprap concrete layer is able to bear the preset construction load of the next level, repeat S3 and S4; wherein, the two adjacent riprap concrete layers are joined through the interlayer interlocking interface, and the riprap concrete interlayer is formed by the curing and bonding of the concrete flowing into the interlayer interlocking interface. S6. Repeat S5 until the height of the rockfill concrete layer reaches the construction height requirement of the gravity dam.

2. The method for continuous layer-by-layer construction of ultra-thick rockfill concrete gravity dams in confined spaces as described in claim 1, characterized in that, The prefabricated cantilever formwork is supported on the surface of the poured dam body or foundation by adjustable support members, and the adjustable support members are anchored in the poured dam body or foundation by anchor rods. In S2, the anchor rod is anchored to the foundation; In S5, the adjustable support and the anchor rod are released, and before repeating S3 and S4, the prefabricated cantilever formwork is hoisted to the next construction height, and the prefabricated cantilever formwork is fixed to the surface of the poured dam body by the anchor rod. In S6, after the height of the riprap concrete layer reaches the construction height requirement of the gravity dam, the prefabricated cantilever formwork is removed.

3. The method for continuous layer-by-layer construction of ultra-thick layers in a rockfill concrete gravity dam in a confined space as described in claim 1, characterized in that... In S4, the thickness of the rockfill layer is controlled at 2.5~3.0m.

4. The method for continuous layer-by-layer construction of ultra-thick rockfill concrete gravity dams in confined spaces as described in claim 1, characterized in that... In S3, the porosity of the rockfill layer is controlled at 25%~35%.

5. The method for continuous layer-by-layer construction of ultra-thick layers in a rockfill concrete gravity dam in a confined space as described in claim 1, characterized in that... In S3, the particle size of the protruding stones is controlled between 50 and 100 cm.

6. The method for continuous layer-by-layer construction of ultra-thick rockfill concrete gravity dams in confined spaces as described in claim 1 or 5, characterized in that, In S3, the height of the protruding stone exposed above the top surface of the rock pile is controlled to be 10~30cm.

7. The method for continuous layer-by-layer construction of ultra-thick rockfill concrete gravity dams in confined spaces as described in claim 1, characterized in that, The step of injecting self-compacting concrete into the voids of the riprap layer to form a riprap concrete layer includes: Multi-point flexible material distribution pipes are used to simultaneously feed materials to multiple areas. The self-compacting concrete fills the internal voids of the rockfill layer with its self-flowing properties until the slurry is evenly spread on the upper surface of the rockfill layer, forming a rockfill concrete layer.

8. The method for continuous layer-by-layer construction of ultra-thick layers in a rockfill concrete gravity dam in a confined space as described in claim 1, characterized in that, The preset construction load includes the self-weight of the next-level rockfill, the self-weight of the next-level self-compacting concrete, and the sum of the loads on the construction machinery.

9. The method for continuous layer-by-layer construction of ultra-thick layers in a rockfill concrete gravity dam in a confined space as described in claim 1, characterized in that, In S4, after the riprap concrete layer is formed, a temperature measuring element is embedded in the riprap concrete layer to monitor the internal temperature and surface temperature of the riprap concrete layer in real time.

10. The method for continuous layer-by-layer construction of ultra-thick layers in a rockfill concrete gravity dam in a confined space as described in claim 9, characterized in that, In S4, after the riprap concrete layer is formed, an insulation layer is covered on the surface of the riprap concrete layer to control the difference between the internal temperature and the surface temperature to be less than or equal to 18°C, and the internal temperature and the surface temperature to be less than or equal to 75°C.

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