Design and construction method for deep covering layer high gravelly soil core wall rock-fill dam

Abstract

The invention discloses a design and construction method for a deep covering layer high gravelly soil core wall rock-fill dam, and belongs to the technical field of design and construction of water conservancy and hydropower engineering structures. According to the design and construction method for the deep and thick covering layer high gravel soil core wall rock-fill dam, the contradiction between settlement deformation space-time evolution of upstream rock-fill materials and gravel soil core wall materials can be well solved, and the longitudinal crack risk of the dam crest is reduced. According to the design and construction method, a fissure type weathered sand slate stock ground, an alteration zone dominant granite stock ground and an engineering area excavation material are used as dam body rockfill material sources, zoning control over the fine particle content of rockfill materials is used as a main line, and humidification deformation of upstream rockfill materials is dispersed into the dam filling process; the unloading effect of humidification deformation and the loading effect of dam filling are overlapped to achieve self-adaptive adjustment of dam body stress deformation, and finally the high gravelly soil core wall rockfill dam built on the deep covering layer is obtained, wherein the upstream rockfill material adapts to settlement deformation of the gravelly soil core wall material, and the longitudinal fission trend of the dam crest meets the requirement.

Description

Technical Field

[0001] The present invention relates to a design and construction method, in particular to a design and construction method for a high gravel soil core wall rockfill dam with a deep overburden layer, belonging to the technical field of design and construction of water conservancy and hydropower engineering structures. Background Art

[0002] According to statistics, the tallest dams built or under construction worldwide are gravel-soil core rockfill dams, with the tallest reaching 310 meters. Slope stability, seepage stability, and stress-deformation are three key factors in ensuring the reliable operation of gravel-soil core rockfill dams. While the gravel-soil core plays a role in preventing seepage, the key factor determining the dam's success is the rockfill, which accounts for over 80% of the dam's total fill.

[0003] To maximize material utilization, deep-layer anti-sliding stability through the thick overburden can be addressed by using lower-quality dam materials to form ballast masses at the upstream and downstream dam toe. However, in high-seismic intensity zones, the "whiplash effect" of earthquakes at mid- and high-elevation locations is significant. Therefore, the stability of the shallow dam slope above the ballast mass requires the use of rockfill materials with higher shear strength and seismic measures. Stress-deformation analysis, based on mechanical parameters of rockfill and core materials determined using laboratory tests, indicates that due to the relatively small settlement in the rockfill area and the relatively large settlement in the core area, the core wall is at risk of being lifted by the rockfill layers, leading to hydraulic fracturing—an arching effect. This is caused by the significant difference in the deformation moduli of the two dam materials. To mitigate this difference and coordinate deformation, a certain proportion of gravel with a particle size greater than 5 mm is often incorporated into the soil material, resulting in a gravel-soil corewall material. However, in the aforementioned study, the gravel-soil corewall material was tested using consolidated drained shear tests, resulting in a nearly synchronized deformation of the corewall and rockfill materials in the calculations. However, engineering practice has shown that, due to the requirement to maintain a moisture content above the optimal value for gravel-soil corewall materials (i.e., partially wet fill), cystic excess pore water pressure often exists within the gravel-soil corewall. This results in the corewall area accounting for only approximately 50% of the total settlement upon completion, while the downstream rockfill area accounts for approximately 90% of the total settlement during the completion period. Research has shown that the wetting and creep deformation of the upstream rockfill material of a dam cannot be ignored. The temporal evolution of this deformation is closely related to the dam material zoning and water storage planning. Some projects have failed to properly coordinate the temporal and spatial evolution of settlement between the corewall and upstream and downstream rockfill areas. During certain periods of time, the significant differential settlement between the upstream rockfill and corewall areas can lead to a "nodding effect" in the upstream rockfill area, also known as a "back-arching effect" in gravel-soil core dams. This weakens the compressive slope effect of the upstream rockfill area relative to the corewall, and can even lead to a tensioning effect, resulting in longitudinal cracks at the dam crest.

[0004] There are more and more cases of using complex dam materials to build high gravel soil core wall rockfill dams on deep foundation pits: there are many fissured weathered sandstone material fields in the western region, which are characterized by severe cutting of the rock mass by the fissure surface, obvious anisotropy of the rock mass, and the weathered fissure surface is powdery after blasting. It is difficult to fundamentally remove this powder, thus forming a thicker compacted layer on the interface of the layered and compacted rockfill material, making the vertical permeability coefficient of the rockfill significantly lower than the horizontal permeability coefficient, and the wetting and rheological deformation are greater than those of conventional hard rockfill materials. However, this fissure weathering often This material yard is formed due to its favorable open-air surface, with three sides exposed to the open air, thus providing favorable mining conditions. Another notable characteristic is that, unlike conventional material yards, the quality of the dam material in the inner areas is significantly better than in the shallow exfoliation areas. Except for the strongly weathered surface areas, the spatial distribution of useful material quality within the fractured weathered sandstone material yard is essentially uniform. The dust content (particle content less than 5mm) of the rockfill after blasting exceeds 18%. Combined with its anisotropic nature, the crushing rate after compaction is high, resulting in a dust content of over 20% in the rockfill after compaction of the dam surface. Granite material yards dominated by alteration zones are characterized by high and steep slopes, extensive exfoliation and support work, and limited initial discharge strength, but the dam material quality is relatively good. Furthermore, to conserve project investment and protect the environment, it is often desirable to fully utilize excavated material from the hub area, which has a complex composition and a high fines content.

[0005] The existing high gravel earth core rockfill dam zoning principle is as follows: the upstream reservoir drawdown area, the dam top, the downstream dam shell exterior and the downstream dam shell bottom are key areas for dam body seismic resistance and dam slope stability, and should be equipped with rockfill materials with high strength index and good permeability; the strength index requirements for rockfill materials below the upstream dead water level and inside the downstream dam shell can be appropriately lowered, and sub-rockfill materials with slightly lower strength index can be used. The specific characteristics are: 1) For high gravel-soil core rockfill dams built in deep foundation pits, the excavation work in the pivot area is large. In order to reduce waste, it is necessary to study the possibility of utilizing the excavated materials in the pivot area at the lower elevation of the dam body; 2) Zoning the rockfill material based on the control of fine particle content and setting up vertical and horizontal permeable bodies in appropriate areas according to infiltration requirements is another key challenge in the coordinated utilization of fractured weathered sandstone slate material yards and alteration zone-dominated granite material yards as material sources. 3) When using rockfill materials with large wetting deformation below the upstream dead water level, it is necessary to coordinate the temporal and spatial evolution contradictions of the settlement and deformation of the upstream rockfill materials and the gravel-soil core wall materials. While paying attention to the core wall arch effect, the reverse arch effect can be weakened through reasonable core wall zoning, rockfill zoning and water storage planning, thereby reducing the risk of longitudinal cracks on the dam crest.

[0006] Existing methods have not yet solved the above three design problems of high gravel earth core rockfill dams built in deep foundation pits in an economically reasonable and technically feasible way. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a design and construction method for a rockfill dam with a deep overburden and a high gravel-soil core wall, which can better resolve the contradiction between the temporal and spatial evolution of settlement and deformation of upstream rockfill materials and gravel-soil core wall materials, and reduce the risk of longitudinal cracks on the dam top.

[0008] The technical solution adopted to solve the above technical problems is: a design and construction method for a high gravel soil core rockfill dam with a deep overburden. The design and construction method uses a fissured weathered sandstone slate material yard, an alteration zone dominant granite material yard, and excavated materials from the project area as the dam body rockfill material source. The method focuses on zoning control of the fine particle content of the rockfill material. Based on the timing of flood discharge, diversion, and staged water storage, the wetting deformation of the upstream rockfill material is discretized into the dam filling process. The unloading effect of the wetting deformation is superimposed on the loading effect of the dam filling to achieve adaptive adjustment of the dam body stress and deformation. Ultimately, a high gravel soil core rockfill dam built on a deep overburden is obtained, in which the settlement deformation of the upstream rockfill material and the gravel soil core wall material are adapted, and the longitudinal fission trend of the dam crest meets the requirements.

[0009] Furthermore, before the filling construction of a high gravel-soil core-wall rockfill dam is carried out, the permeability and deformation requirements of the rockfill dam body are first determined based on the deformation and permeability statistical data of existing rockfill dams, and the rockfill dam body is divided into a gravel-soil core-wall area, a main rockfill area, and a secondary rockfill area based on these permeability and deformation requirements. Then, based on geological exploration and material source analysis and identification data, alteration zone-dominated granite with relatively good dam material quality is used in at least the gravel-soil core-wall area and the main rockfill area, and filling is carried out while controlling the fine particle content of the rockfill material to at least ensure that the stress and deformation of the gravel-soil core-wall area fill and the main rockfill area fill meet the control requirements.

[0010] A preferred embodiment of the above scheme is as follows: the gravel-soil core wall area includes the middle and lower gravel-soil core wall areas A and the upper gravel-soil core wall area B; the primary rockfill area includes the upstream rockfill area I and the downstream rockfill area I; the secondary rockfill area includes the upstream weighted area, the upstream rockfill area, the upstream transition area, the upstream filter layer II, the upstream filter layer I, the downstream filter layer I, the downstream filter layer II, the downstream transition area, the downstream rockfill area, and the downstream weighted area; the rockfill dam body is filled in sequence from upstream to downstream in the order of the upstream weighted area, the upstream rockfill area, the upstream transition area, the upstream filter layer II, the upstream filter layer I, the gravel-soil core wall area, the downstream filter layer I, the downstream filter layer II, the downstream transition area, the downstream rockfill area, and the downstream weighted area; and the difference in the comprehensive deformation modulus Es between the rockfill areas, which is beneficial to the coordinated control of dam body deformation, is controlled within the range of 10-15%.

[0011] Furthermore, the upstream rockfill area and the downstream rockfill area each include rockfill area III, rockfill area II and rockfill area I, respectively. The quality of the rockfill materials for filling rockfill area III, rockfill area II and rockfill area I is improved in sequence. The specific requirements are that the content of particles smaller than 5 mm is no more than 25%, 21% and 18% respectively, and the permeability coefficient is no less than 1×10 -2 cm / s, 5×10 -2 cm / s, 1×10 -1 cm / s, the comprehensive deformation modulus Es is not less than 180MPa, 160MPa and 140MPa respectively, and the average saturated compressive strength of the parent rock is not less than 60MPa, 50MPa and 40MPa respectively. The rockfill filling materials are all produced using weakly weathered, weakly unloaded and fresh stones. A downstream transition zone, a dam foundation filter layer and a downstream water guide belt composed of a dam foundation transition layer are provided between the dam foundation and the rockfill body on the downstream side of area A of the gravel-soil core wall. Any seepage from the gravel-soil core wall is discharged to the outside of the downstream dam through the downstream water guide belt.

[0012] The preferred embodiment of the above scheme is that the rockfill zone III includes the upstream rockfill zone III-1, the upstream rockfill zone III-2, the downstream rockfill zone III-1 and the downstream rockfill zone III-2 respectively; the upstream rockfill zone III-1 and the downstream rockfill zone III-1 located within the overburden are filled with materials excavated from the project area; the upstream rockfill zone III-2, the downstream rockfill zone III-2 and the downstream rockfill zone II are filled with fractured weathered sand and slate materials mined from a fractured weathered sand and slate material yard with a relatively high stone powder content; the upstream rockfill zone I and the downstream rockfill zone I are filled with a mixture of rockfill materials excavated from a fractured weathered sand and slate material yard and an alteration zone-dominated granite material yard; and the deformation of the upstream rockfill zone III-2 is constrained and slope protection is achieved by setting the top elevation of the water-facing surface of the upstream rockfill zone III-2 to be at least 20 m lower than the top elevation of the upstream pressure zone.

[0013] Furthermore, the upstream rockfill zone I above the top surface of the upstream weighted zone is provided with a block stone slope protection layer, an upstream rockfill filter layer and an upstream plum blossom-shaped vertical permeable water body in sequence from upstream to downstream; the horizontal thickness of the upstream rockfill filter layer is not less than 1m, and the bottom elevation of the upstream plum blossom-shaped vertical permeable water bodies inserted into the upstream rockfill zone I at intervals is not less than 10m lower than the dead water level; a downstream horizontal permeable water body is provided between the downstream rockfill zone III-1 and the downstream rockfill zone III-2, adjacent to the downstream transition zone, and penetrating the downstream rockfill zone and the downstream weighted zone, and the top and bottom surfaces of the downstream horizontal permeable water body are evenly divided. A downstream rockfill filter layer is separately provided, and downstream plum blossom-shaped vertical permeable bodies are respectively provided on the downstream rockfill area III-2 and the downstream rockfill area II; the upstream plum blossom-shaped vertical permeable body, the downstream plum blossom-shaped vertical permeable body and the downstream horizontal permeable body are all filled with alteration zone-dominated granite materials with relatively good dam material quality, and the content of particles smaller than 5mm in the filling dam material is not more than 15%. Other requirements are the same as those for the filling materials of the rockfill area I; the transition layer filling material adopts the fractured weathered sandstone slate material field with slightly inferior material properties as the filling material source, and its saturated compressive strength is not less than 40MPa.

[0014] The preferred method of the above scheme is that the gravel-soil core wall area A, whose top elevation is flush with the top elevation of the upstream rockfill area III-2 and / or the top elevation of the downstream rockfill area II, is filled with high-deformation-resistant filling materials with an average P5 content of 43-46%, and the gravel-soil core wall area B is filled with high-deformation-resistant filling materials with an average P5 content of 40-43%, so as to discretize the wetting deformation of the gravel-soil core wall of the upstream rockfill material into the dam filling process, and unload the wetting deformation of the gravel-soil core wall of the upstream rockfill material with the dam filling process. The loading effect of dam filling is superimposed to improve the adaptive adjustment ability of the dam body's stress and deformation. After the foundation surface of the gravel core wall area is excavated, a concrete cover is set on the excavation surface. A contact clay area that adapts to large shear deformation and maintains excellent anti-seepage performance is set on the concrete cover. The area below 0.45 times the dam height is set as contact clay area A, with a horizontal thickness of 3m and a compaction degree greater than 100%; the area above 0.45 times the dam height is set as contact clay area B, with a horizontal thickness of 4m and a compaction degree of 95% to 100%. Among them, the P5 content is the mass percentage of particles larger than 5mm in the core wall filling material to the total amount of the core wall filling material.

[0015] Furthermore, the upstream rockfill III-2 zone is a rockfill mold-enhancing zone that is compacted at least two times more than the other rockfill zones. After compaction, the porosity of the rockfill mold-enhancing zone is controlled within 21%, and the porosity of other rockfill zones is controlled within 22%. This allows the wetting deformation of the upstream rockfill materials to be discretized into the dam filling process. The unloading effect of the wetting deformation is superimposed on the loading effect of the dam filling to achieve adaptive adjustment of the stress and deformation of the dam body and reduce the tendency of longitudinal cracks to form on the dam crest.

[0016] A preferred embodiment of the above scheme is that an upstream cofferdam anti-seepage system is also provided in the upstream weighted area. The upstream rockfill area III-1 and upstream rockfill area III-2 below the top elevation of the upstream cofferdam anti-seepage system are temporary rockfill drying areas in a dry state. As the filling height of the high gravel-soil core wall rockfill dam increases, water is slowly injected into the temporary rockfill drying areas in a timely manner according to regulations to pre-wet the temporary rockfill drying areas and the corresponding gravel-soil core wall areas. The wetting deformation of the upstream rockfill material is discretized into the dam filling process, thereby eliminating unacceptable wetting deformation and uneven settlement caused by sudden water filling in the temporary rockfill drying areas, and avoiding irreversible seepage damage caused by excessive unsaturated ultra-high seepage pressure caused by rapid water filling in the gravel-soil core wall in a short period of time. The top elevation of the pre-injection wetting area shall not exceed the top elevation of the upstream cofferdam anti-seepage system.

[0017] Furthermore, when controlling the fine particle content of rockfill materials by zoning, a blasting bench of 7.5m to 10m is used for the granite material field in the alteration zone with better dam material quality. The spacing and diameter of the drill holes are obtained through blasting tests. After effective locking according to geological forecasts, a "drop-loading" charging structure is used for blasting and mining to obtain rockfill materials with fine particle content that meets the requirements of the filling sequence, and the slopes are supported in a timely manner. During the transfer process of mined filling materials that do not meet the dam filling sequence, the quality control of the rockfill materials that meet the material properties is carried out by prohibiting the transfer of strongly weathered and strongly unloaded mined materials that do not meet the quality requirements.

[0018] The beneficial effects of the present invention are as follows: the technical solution provided by the present application adopts a fissured weathered sandstone slate material yard, an alteration zone-dominated granite material yard and excavated materials from the engineering area as the source of dam body rockfill materials, takes the zoning control of the fine particle content of the rockfill materials as the main line, and according to the timing arrangement of flood discharge, diversion and phased water storage, discretizes the wetting deformation of the upstream rockfill materials into the dam filling process, and superimposes the unloading effect of the wetting deformation with the loading effect of the dam filling to realize adaptive adjustment of the stress and deformation of the dam body, and finally obtains a high gravel soil core wall rockfill dam built on a deep overburden layer, in which the settlement deformation of the upstream rockfill materials and the gravel soil core wall materials are adapted, and the longitudinal fission trend of the dam top meets the requirements, thereby better solving the contradiction between the temporal and spatial evolution of the settlement deformation of the upstream rockfill materials and the gravel soil core wall materials, and effectively reducing the risk of longitudinal cracks on the dam top. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A cross-sectional view of a high gravel core wall rockfill dam along the water flow direction involved in the design and construction method for a high gravel core wall rockfill dam with a deep overburden layer according to the present invention; Figure 2 for Figure 1 lateral cross-sectional view of .

[0020] Marked in the figure are: gravel-soil core wall area A 1, upper gravel-soil core wall area B 2, upstream rockfill area I 3, downstream rockfill area I 4, upstream weighted area 5, upstream transition area 6, upstream filter layer II 7, upstream filter layer I 8, downstream filter layer I 9, downstream filter layer II 10, downstream transition zone 11, downstream weighted area 12, dam foundation filter layer 13, dam foundation transition layer 14, upstream rockfill area III-1 15, upstream rockfill area III-2 16, downstream rockfill area III-1 17, downstream rockfill area III-2 18, downstream rockfill area II 19, block rock slope protection layer 20, upstream rockfill filter layer 21, upstream plum blossom-shaped vertical permeable body 22, downstream horizontal permeable body 23, downstream rockfill filter layer 24, downstream plum blossom-shaped vertical permeable body 25, concrete cover 26, contact clay area A 27, contact clay area B 28, and upstream cofferdam anti-seepage system 29. DETAILED DESCRIPTION

[0021] like Figure 1 、 Figure 2 The present invention provides a design and construction method for a high gravel core rockfill dam with a deep overburden layer, which effectively resolves the conflict between the temporal and spatial evolution of settlement and deformation between upstream rockfill materials and gravel core materials, and reduces the risk of longitudinal cracks at the dam crest. The design and construction method utilizes a fissured weathered sandstone slate material yard, an altered zone-dominated granite material yard, and excavated material from the project area as the dam body rockfill material source. The method prioritizes zoning control of the fine particle content of the rockfill material. Based on the timing of flood discharge, diversion, and phased water storage, the wetting deformation of the upstream rockfill material is discretized into the dam filling process. The unloading effect of the wetting deformation is superimposed on the loading effect of the dam filling to achieve adaptive adjustment of the dam body stress and deformation. Ultimately, a high gravel core rockfill dam built on a deep overburden layer is achieved, in which the settlement and deformation of the upstream rockfill material and the gravel core materials are compatible, and the longitudinal cracking trend at the dam crest meets the requirements. The technical solution provided in this application adopts a fissured weathered sandstone slate material yard, an alteration zone-dominated granite material yard, and excavated materials from the engineering area as the source of dam rockfill materials. With the zoning control of the fine particle content of the rockfill materials as the main line, the wetting deformation of the upstream rockfill materials is discretized into the dam filling process according to the timing arrangement of flood discharge, diversion, and staged water storage. The unloading effect of the wetting deformation is superimposed on the loading effect of the dam filling to achieve adaptive adjustment of the stress and deformation of the dam body. Ultimately, a high gravel-soil core rockfill dam built on a deep overburden is obtained, in which the settlement deformation of the upstream rockfill materials and the gravel-soil core wall materials are adapted to each other, and the longitudinal fission trend of the dam crest meets the requirements. This effectively resolves the contradiction between the temporal and spatial evolution of the settlement deformation of the upstream rockfill materials and the gravel-soil core wall materials, and effectively reduces the risk of longitudinal cracks on the dam crest.

[0022] Accordingly, to facilitate subsequent filling, especially filling in a prescribed sequence and to maximize the realization of the present invention, the wetting deformation of the upstream rockfill material is discretized into the dam filling process, the unloading effect of the wetting deformation is superimposed on the loading effect of the dam filling to achieve adaptive adjustment of the stress and deformation of the dam body, and the mutual adaptability of the settlement deformation between the upstream rockfill material and the gravel-soil core wall material is maximized. Before filling and construction of a high gravel-soil core wall rockfill dam, the present invention first determines the permeability and deformation requirements of the rockfill dam body based on the deformation and permeability statistical data of existing rockfill dams. Based on these permeability and deformation requirements, the rockfill dam body is divided into a gravel-soil core wall area, a main rockfill area, and a secondary rockfill area. Then, based on geological exploration and material source analysis and identification data, relatively high-quality alteration zone-dominated granite material is used in at least the gravel-soil core wall area and the main rockfill area. Filling is carried out while controlling the fine particle content of the rockfill material to ensure that at least the stress and deformation of the gravel-soil core wall area and the main rockfill area meet the control requirements. In this case, the gravel-soil core wall area described in the present application includes the middle and lower gravel-soil core wall area A 1 and the upper gravel-soil core wall area B 2; the primary rockfill area includes the upstream rockfill area I 3 and the downstream rockfill area I 4; the secondary rockfill area includes the upstream weighted area 5, the upstream rockfill area, the upstream transition area 6, the upstream filter layer II 7, the upstream filter layer I 8, the downstream filter layer I 9, the downstream filter layer II 10, the downstream transition area 11, the downstream rockfill area, and the downstream weighted area 12; the rockfill dam body is constructed in the order of the upstream weighted area 5, the upstream rockfill area, the upstream transition area 6, the upstream filter layer II 7, the upstream filter layer I 8, the gravel-soil core wall area, the downstream filter layer I 9, the downstream filter layer II 10, the downstream transition area 11, the downstream rockfill area, and the downstream weighted area 12 from upstream to downstream; and the difference in the comprehensive deformation modulus Es between the rockfill areas, which facilitates coordinated control of dam body deformation, is controlled within a range of 10-15%. More specifically, the upstream rockfill area and the downstream rockfill area each include rockfill area III, rockfill area II, and rockfill area I, respectively. The quality of the rockfill materials for rockfill area III, rockfill area II, and rockfill area I is improved in sequence. The specific requirements are that the content of particles smaller than 5 mm is no more than 25%, 21%, and 18%, respectively, and the permeability coefficient is no less than 1×10 -2 cm / s, 5×10 -2 cm / s, 1×10 -1cm / s, the comprehensive deformation modulus Es is not less than 180MPa, 160MPa and 140MPa respectively, and the average saturated compressive strength of the parent rock is not less than 60MPa, 50MPa and 40MPa respectively. The rockfill filling materials are all produced using weakly weathered, weakly unloaded and fresh stones. A downstream water guide belt consisting of a downstream transition zone 11, a dam foundation filter layer 13 and a dam foundation transition layer 14 is provided between the dam foundation and the rockfill body on the downstream side of the gravel-soil core wall area A. Any seepage from the gravel-soil core wall is discharged to the outside of the downstream dam through the downstream water guide belt. Rockfill Area III includes upstream rockfill Area III-1 15, upstream rockfill Area III-2 16, downstream rockfill Area III-1 17, and downstream rockfill Area III-2 18. Upstream rockfill Area III-1 15 and downstream rockfill Area III-1 17, located within the overburden layer, are filled with materials excavated from the project area. Upstream rockfill Area III-2 16, downstream rockfill Area III-2 18, and downstream rockfill Area II 19 are filled with fractured weathered sand and slate materials mined from a fractured weathered sand and slate material yard with a high stone powder content. Upstream rockfill Area I 3 and downstream rockfill Area I 4 are filled with a mixture of rockfill materials excavated from a fractured weathered sand and slate material yard and a granite material yard dominated by the alteration zone. The top elevation of the water-facing surface of the upstream rockfill Area III-2 is set to be at least 20 m lower than the top elevation of the upstream pressure zone to constrain deformation of the upstream rockfill Area III-2 16 and achieve slope protection.

[0023] Furthermore, in order to maximize the overall permeability stability of the rockfill dam body and to control the fine particle content of the dam material, the upstream rockfill area I 3 above the top surface of the upstream weighted area of ​​the present application is further provided with a block stone slope protection layer 20, an upstream rockfill filter layer 21 and an upstream plum blossom-shaped vertical permeable body 22 from upstream to downstream; the horizontal thickness of the upstream rockfill filter layer 21 is not less than 1m, and the bottom elevation of the upstream plum blossom-shaped vertical permeable bodies 22 inserted into the upstream rockfill area I 3 at intervals is not less than 10m below the dead water level; a through-hole is provided between the downstream rockfill area III-1 area 17 and the downstream rockfill area III-2 area 18, adjacent to the downstream transition area. The downstream horizontal permeable body 23 is provided with a downstream rockfill filter layer 24 on its top and bottom surfaces respectively; the downstream rockfill zone III-2 18 and the downstream rockfill zone II 19 are provided with a downstream plum blossom-shaped vertical permeable body 25 respectively; the upstream plum blossom-shaped vertical permeable body 22, the downstream plum blossom-shaped vertical permeable body 25 and the downstream horizontal permeable body 23 are all filled with alteration zone-dominated granite material of relatively good dam material quality, with the content of particles smaller than 5 mm in the filling material not exceeding 15%. Other requirements are the same as those for the filling material of the rockfill zone I; the transition layer filling material adopts a fractured weathered sandstone slate material field with slightly inferior material properties as the filling material source, and its saturated compressive strength is not less than 40 MPa. The gravel-soil core wall area A1, whose top elevation is flush with the top elevation of the upstream rockfill area III-2 and / or the top elevation of the downstream rockfill area II, is filled with high-deformation-resistant fill materials with an average P5 content of 43-46%. The gravel-soil core wall area B2 is filled with high-deformation-resistant fill materials with an average P5 content of 40-43%. This is to discretize the wetting deformation of the gravel-soil core wall of the upstream rockfill into the dam filling process, superimpose the unloading effect of the wetting deformation of the gravel-soil core wall of the upstream rockfill with the loading effect of the dam filling, and improve the adaptive adjustment ability of the stress and deformation of the dam body. After the foundation surface of the gravel soil core wall area is excavated, a concrete cover 26 is set on the excavation surface. A contact clay area that adapts to large shear deformation and maintains excellent anti-seepage performance is set on the concrete cover 26. The area below 0.45 times the dam height is set as contact clay area A 27, with a horizontal thickness of 3m and a compaction degree greater than 100%; the area above 0.45 times the dam height is set as contact clay area B 28, with a horizontal thickness of 4m and a compaction degree of 95% to 100%. Among them, the P5 content is the mass percentage of particles larger than 5mm in the core wall filling material to the total amount of the core wall filling material. Upstream rockfill III-2 zone 16 is a rockfill augmentation zone that is compacted at least twice more than its rockfill zone. After compaction, the porosity of the rockfill augmentation zone is controlled within 21%, and the porosity of other rockfill zones is controlled within 22%. This disperses the wetting deformation of the upstream rockfill material into the dam filling process. The unloading effect of the wetting deformation is superimposed on the loading effect of the dam filling to achieve adaptive adjustment of the stress and deformation of the dam body and reduce the tendency of longitudinal cracks to form on the dam crest.An upstream cofferdam anti-seepage system 29 is also provided within the upstream weighted area 5. The upstream rockfill area III-1 15 and upstream rockfill area III-2 16 below the top elevation of the upstream cofferdam anti-seepage system serve as temporary rockfill drying areas in a dry state. As the filling height of the high gravel-soil core rockfill dam rises, water is slowly injected into the temporary rockfill drying areas in a timely manner as required to pre-wet the temporary rockfill drying areas and the corresponding gravel-soil corewall areas. The wetting deformation of the upstream rockfill materials is then discretized into the dam filling process to eliminate unacceptable wetting deformation and uneven settlement caused by sudden water filling in the temporary rockfill drying areas. Furthermore, irreversible seepage damage caused by excessive unsaturated, ultra-high seepage pressure resulting from rapid water filling of the gravel-soil corewall in a short period of time is avoided. The top elevation of the pre-watered wetting areas does not exceed the top elevation of the upstream cofferdam anti-seepage system. When controlling the fine particle content of rockfill materials by zoning, the blasting bench section used for the granite material yard dominated by the alteration zone with better dam material quality is 7.5m to 10m. The spacing and diameter between drill holes are obtained through blasting tests. After effective locking according to geological forecasts, the "drop-loading" charging structure is used for blasting mining to obtain rockfill materials with fine particle content that meets the requirements of the filling sequence, and the slopes are supported in time. During the transfer process of the mined filling materials that do not meet the dam filling sequence, the quality control of the rockfill materials that meet the material properties is carried out by prohibiting the transfer of strongly weathered and strongly unloaded mined materials that do not meet the quality requirements.

[0024] The technical solution of this application is further described below through specific embodiments: The technical problem to be solved by the present invention is to provide a design method for a high gravel soil core rockfill dam built in a deep foundation pit, which comprehensively utilizes the fissured weathered sandstone slate material yard, the alteration zone dominant granite material yard, and the excavated material in the engineering area as the rockfill material source.

[0025] To solve the above technical problems, the technical solution adopted by the present invention is: on the basis of geological survey and zoning identification, with the zoning control of fine particle content of rockfill materials as the main line, the dam body zoning design and water storage planning are based on the differentiated characteristics of the fractured weathered sandstone slate material yard, the alteration zone dominant granite material yard, and the excavated material source of the project area.

[0026] The properties of the excavated materials in the project area are relatively complex: 1) Due to the limited excavation site, the purpose of excavation is mainly to ensure the designed size and avoid blasting damage, thereby saving support costs. Therefore, the blasting parameters are quite different from those of the rockfill site, and the gradation of the blasted materials is poor. 2) The excavation sequence often does not match the dam filling sequence, making it difficult to transport the excavated materials to the dam immediately after excavation. It is often necessary to transfer the excavated materials from the project area to the dam before transporting them to the dam. 3) The transfer process can provide preliminary control over the material properties, that is, it can be required that obviously unqualified strongly weathered and strongly unloaded materials should not be stored in the transfer site. However, it is difficult to control the gradation of the dam materials in the transfer site. In addition, the transfer time is difficult to control, and the transferred materials may further weather and alter. Therefore, the high content of fine powder after rolling is a prominent feature of the excavated materials in the project area.

[0027] The mining conditions of the fissured weathered sandstone slate material field are good, but the quality of the dam material is relatively poor, which means that it is conducive to supplying materials in the early stage of the project but is not suitable for filling to the high elevation parts of the dam body.

[0028] Granite material yards dominated by alteration zones often face open space on one side, with limited space at high elevations. Consequently, initial discharge strength is low, necessitating excavation to mid- and low-elevation areas for large-scale material discharge. This results in high-quality dam materials, making them suitable for filling key areas of the dam to control stress and deformation. The rock mass strength of such yards is high, and slope stability is governed by the development of the alteration zone. This often results in a typical steep-slope-slope combination slip pattern, with a steeply dipping alteration surface serving as the trailing fracture surface and a moderately dipping alteration surface serving as the bottom sliding surface. The shear outlet formed as the underlying excavation of the yard represents the period of greatest slope stability risk. Therefore, the relatively good rock mass quality should not be misleading. The development of the alteration zone must be ascertained through exploration holes, drilling, and television monitoring in anchor pilot holes. This allows for the design of anchoring and monitoring plans, which should be dynamically updated and adjusted based on survey results during construction. The depth of anchoring and monitoring measures at the mid- and upper slope elevations is particularly important. This depth should be sufficient to control the potential shearing of the alteration surface at the final mining platform of the yard, avoiding a "boating" effect caused by insufficient anchoring and monitoring depth, which could result in failure to achieve the desired design results.

[0029] Because the granite material yard dominated by the alteration zone has high rock mass strength and well-developed alteration surfaces, using 15m deep blasting steps, as in conventional material yards, often results in slower results. First, a more complex uneven vertical charging structure is required, using an unbalanced transitional charging structure where the charge in the middle and low hole sections is less than that in the shallow section, in order to achieve the desired blasting effect. This is costly and carries significant risks. Second, due to the limited height control of the locking structure at the top of the step, the middle and lower sections of the step often collapse after blasting, posing a significant safety issue and hindering support cost control. If a conventional "drop-charge" charging structure is used, where explosives fill the entire borehole, the bottom blasting material often contains more fine powder and the shallow section contains more oversized rock. This lacks intermediate particle sizes, making it impossible to obtain qualified rockfill materials with continuous grading, and also reduces the proportion of useful material in the material yard. An effective way to balance construction safety and blasting material quality is to reduce the blasting steps to 7.5m to 10m, select appropriate borehole spacing and hole diameters through blasting tests, use a "drop-load" charging structure for blasting after effectively locking the holes according to geological forecasts, and support the slopes in a timely manner.

[0030] In order to resolve the temporal and spatial contradiction between the dam filling demand and the material supply from the material yard, the fissured weathered sandstone material yard and the alteration zone dominant granite material yard should be located on the upstream and downstream sides of the dam respectively during project planning. This will help the project to still use the alteration zone dominant granite material yard with better quality as the material source after the water is stored in stages.

[0031] From upstream to downstream, the dam body is divided into the upstream weighted area, upstream rockfill area, upstream transition area, upstream filter layer II, upstream filter layer I, gravel-soil core wall area, downstream filter layer I, downstream filter layer II, downstream transition area, downstream rockfill area, and downstream weighted area. The gravel-soil core wall area is further divided into gravel-soil core wall area A and gravel-soil core wall area B; the upstream rockfill area is further divided into upstream rockfill area III-1, upstream rockfill area III-2, and upstream rockfill area I; and the downstream rockfill area is further divided into downstream rockfill area III-1, downstream rockfill area III-2, downstream rockfill area II, and downstream rockfill area I. Upstream rockfill area I and downstream rockfill area I are referred to as primary rockfill areas, while the remaining rockfill areas are referred to as secondary rockfill areas.

[0032] The upstream cofferdam and downstream cofferdam that create dry land construction conditions for deep foundation pit excavation serve as part of the upstream weight-bearing area and downstream weight-bearing area respectively.

[0033] In order to lower the infiltration line in the downstream dam body and avoid seepage damage to the dam foundation cover layer, a downstream water guide belt is set up, which consists of the downstream transition zone, the dam foundation filter layer and the dam foundation transition layer. Under normal circumstances, the possible seepage of the core wall will be drained to the downstream of the dam.

[0034] The rockfill area is divided into rockfill area III, rockfill area II, and rockfill area I, with the quality getting better in descending order. The content of particles smaller than 5 mm is no more than 25%, 21%, and 18%, respectively, and the permeability coefficient is no less than 1×10 -2 cm / s, 5×10 -2 cm / s, 1×10 -1 cm / s, the comprehensive deformation modulus Es shall not be less than 180MPa, 160MPa, and 140MPa respectively, and the average saturated compressive strength of the parent rock shall not be less than 60MPa, 50MPa, and 40MPa respectively. It is required to use weakly weathered, weakly unloaded, and fresh stones for production, and it is prohibited to use strongly weathered, strongly unloaded, and weak interlayer stones for production.

[0035] The comprehensive deformation modulus (Es) of a dam material is a modulus that comprehensively reflects the material's ability to resist deformation, obtained through compression testing using pressures ranging from 0 to the maximum pressure corresponding to the proposed dam. Compared to the standard deformation modulus determined using pressures of 0.1 to 0.2 MPa, the comprehensive deformation modulus better reflects the true characteristics of each dam material zone as it performs its function. Research has shown that controlling the difference in comprehensive deformation modulus (Es) between rockfill zones within a range of 10% to 15% is beneficial for coordinated deformation control of the dam body.

[0036] The area below the original riverbed elevation is called the backfill area, which has good constraint conditions and is beneficial to controlling the deformation of the dam body. The upstream rockfill area III-1 and the downstream rockfill area III-1 are set up respectively, and the excavated materials from the project area are used for filling; the upstream rockfill area III-2, the downstream rockfill area III-2 and the downstream rockfill area II mainly use the fractured weathered sandstone slate material yard with a high stone powder content as the material source; the upstream rockfill area I and the downstream rockfill area I use the mixed rockfill materials excavated from the fractured weathered sandstone slate material yard and the alteration zone dominant granite material yard.

[0037] The top elevation of the water surface of the upstream rockfill III-2 area is at least 20m lower than the top elevation of the upstream weighted area, so that the upstream weighted area can play a good role in deformation constraint and slope protection for the upstream rockfill III-2 area.

[0038] After layered compaction of the rockfill materials mined from the fractured weathered sandstone slate field, a thick compacted layer forms on the rockfill interface, making the vertical permeability of the rockfill significantly lower than the horizontal permeability. Therefore, increasing the vertical permeability of the rockfill is the key.

[0039] The area between the upstream normal water level and the dead water level is known as the reservoir drawdown zone. Water levels fluctuate frequently. To ensure dam slope stability and prevent the loss of fine particles, which could lead to seepage damage and localized dam collapse, upstream rockfill zone I, located above the top of the upstream weighted zone, is equipped with stone slope protection, upstream rockfill filtration, and an upstream plum blossom-shaped vertical headwater body, sequentially from upstream to downstream. The horizontal thickness of the upstream rockfill filtration is no less than 1 meter, and the bottom elevation of the upstream plum blossom-shaped vertical headwater body is no less than 10 meters below the dead water level.

[0040] A downstream horizontal permeable body is set up between the downstream rockfill area III-1 and the downstream rockfill area III-2, adjacent to the downstream transition zone, and runs through the downstream rockfill area and the downstream heavy pressure area. Downstream rockfill filtration layers are set up on the top and bottom surfaces of the downstream horizontal permeable body to timely lower the dam infiltration line and prevent the rockfill materials with a high fine powder content from seepage damage when local defects occur in the anti-seepage system.

[0041] Downstream plum blossom-shaped vertical head water bodies are set up in the downstream rockfill area III-2 and the downstream rockfill area II to promptly drain possible seepage water in the corresponding rockfill areas to low elevations, avoid the horizontal flow of fine powder in the compacted layer, and ensure the stability of the dam slope and seepage.

[0042] The upstream plum blossom-shaped vertical head water body, the downstream plum blossom-shaped vertical head water body and the downstream horizontal permeable body are filled with high-quality rockfill area I materials, with the content of particles smaller than 5mm not exceeding 15%. The rest requirements are the same as those of rockfill area I.

[0043] Since the grading requirements of transition material are higher than those of rockfill material and it is easier to compact, while the rolling layer thickness is thinner than that of rockfill material, and the rolling function is equivalent, if stones with the same material properties are used to produce rockfill material and transition material, the comprehensive mechanical properties of transition material are often better than those of rockfill material, forming a hard support layer between the core wall and the rockfill material, which is not conducive to the deformation coordination of the dam body. Therefore, the transition material uses fractured weathered sandstone with slightly inferior material properties as the source material, and the saturated compressive strength is not less than 40MPa.

[0044] Based on the results of calculations and analysis, the deformation zone of the gravel-soil core wall primarily occurs in the lower two-thirds. Therefore, this area is designated as Gravel Core Wall Area A, balancing both anti-seepage performance and deformation resistance. The upper one-third is designated as Gravel Core Wall Area B, balancing both anti-seepage performance and deformation adaptability. Based on the functional positioning of these two core wall areas, the average P5 content of Gravel Core Wall Area A is controlled to be 43-46%, while the average P5 content of Gravel Core Wall Area B is controlled to be 40-43%. The P5 content refers to the mass percentage of particles larger than 5 mm in the core wall material. A higher P5 content improves deformation resistance but weakens anti-seepage performance.

[0045] After the gravel core wall foundation surface is excavated, a concrete cover is often installed to prevent contact scouring and provide auxiliary anti-seepage protection. A contact clay zone is set on the concrete cover to accommodate large shear deformations and maintain excellent anti-seepage performance. According to calculation and analysis results, the maximum deformation of the dam core wall occurs near 0.5 times the dam height. Therefore, the area below 0.45 times the dam height is designated as contact clay zone A, with a horizontal thickness of 3m and a compaction greater than 100%. The area above 0.45 times the dam height is designated as contact clay zone B, with a horizontal thickness of 4m and a compaction of 95% to 100% to better accommodate core wall deformation.

[0046] In the aforementioned dam material zoning, the top elevation of gravel-soil corewall zone A is aligned with the top elevations of upstream rockfill zone III-2 and downstream rockfill zone II. This means that the gravel-soil corewall zone, with its relatively strong deformation resistance, is matched with the rockfill zone, with its weaker deformation resistance. This is beneficial for coordinated dam deformation and thus reduces the core wall arching effect. However, to avoid a "nodding effect" in the upstream rockfill zone, or a "reverse arching effect" in the gravel-soil corewall dam, where the upstream rockfill zone experiences significant wetting deformation within a short period of time when the reservoir reaches its top, while the gravel-soil corewall zone experiences relatively lagging deformation due to excess pore water pressure, weakening the compression slope effect of the upstream rockfill zone relative to the corewall and even inducing a tensioning effect, thereby risking longitudinal cracks at the dam crest, it is necessary to reconcile the temporal and spatial evolution of the settlement and deformation of the upstream rockfill and gravel-soil corewall materials. The wetting deformation of the upstream rockfill material should be discretized into the dam filling process. The unloading effect of this wetting deformation should be superimposed on the loading effect of the dam filling to achieve adaptive adjustment of the dam body's stress and deformation, thereby reducing the risk of longitudinal cracks at the dam crest.

[0047] To achieve the above goals, the first step is to set up a rockfill mold-enhancing area; the second step is to combine the layout of the reservoir diversion and discharge structures and carry out reservoir water storage in three stages.

[0048] The so-called mold-increasing area refers to the upstream rockfill III-2 area, which is compacted twice more than other rockfill areas. The pore slope after compaction is controlled to be no more than 21%, and the porosity of other rockfill areas after compaction is controlled to be no more than 22%. The other compaction parameters remain unchanged.

[0049] The dam's spillway structures are located within the mountains on both sides of the dam, and are, from high to low, comprised of a tunnel-type spillway, a swirling shaft spillway, a deep-hole spillway, and a discharge tunnel. Diversion structures are also located within the mountains on both sides, and from high to low, comprised of a terminal diversion tunnel, a mid-stage diversion tunnel, and an initial diversion tunnel. The swirling shaft spillway is integrated with the second half of the terminal diversion tunnel, while the discharge tunnel is integrated with the second half of the mid-stage diversion tunnel. This reduces project costs while achieving the goal of stratified diversion, storage, and flood discharge within the high dam and large reservoir.

[0050] A smaller-scale ecological water supply tunnel for the construction period is arranged at a position slightly higher than the elevation of the bottom plate of the initial diversion tunnel: first, it can ensure the continuous discharge of ecological flow during the first stage of water storage in the reservoir to meet environmental protection requirements; second, it can be arranged as far as possible before the flood season, and the initial diversion tunnel is first sluiced and blocked, and the flow passes through the ecological water supply tunnel for the construction period. The ecological water supply tunnel for the construction period is sluiced and blocked before the flood season. Since the cross-section of the ecological water supply tunnel for the construction period is smaller than that of the initial diversion tunnel and the blocking period is short, the construction period before water storage is extended as much as possible while the risk of blocking construction during the flood season is greatly reduced; third, the ecological water supply tunnel for the construction period can be used to temporarily continue the diversion during the dry season, so as to inspect and repair the initial diversion tunnel.

[0051] During the early stages of dam construction, the upstream cofferdam retained water, and the initial diversion tunnel channeled the flow. The upstream rockfill areas III-1 and III-2, below the top elevation of the upstream cofferdam's anti-seepage system, remained dry, referred to as the temporary rockfill dry zone. For deep foundation pit projects, the elevation difference in the temporary rockfill dry zone could exceed 110 meters. To prevent unacceptable wetting deformation and uneven settlement from sudden water filling in the temporary rockfill dry zone after the water level exceeded the top elevation of the upstream cofferdam's anti-seepage system during the first phase of impoundment, and to prevent irreversible seepage damage caused by excessive unsaturated hyperinfiltration pressure in the core wall due to rapid water filling in a short period of time, water was slowly injected into the temporary dry zone as the dam body rose during construction. This allowed the temporary rockfill dry zone and the corresponding core wall areas sufficient time for deformation and seepage adjustment. The top elevation of the pre-injected wet zone was controlled to not exceed the top elevation of the upstream cofferdam's anti-seepage system.

[0052] The first-phase water storage level is the level at which the mid-term diversion tunnel meets the ecological flow discharge requirements, and is no higher than the level at which the gates of the construction-phase ecological water supply tunnel can be normally closed. To ensure that the dam filling progress meets the requirements for the upcoming flood season, the gates of the initial diversion tunnel will be closed before the flood season, allowing sufficient time for plugging. The construction-phase ecological water supply tunnel will then be used for flow. The gate opening of the construction-phase ecological water supply tunnel will be used to control the discharge flow to meet the ecological flow requirements while raising the water level. When the reservoir water level reaches the first-phase water storage level, the gates of the construction-phase ecological water supply tunnel will be closed, completing the first-phase water storage. The mid-term and final diversion tunnels will then be used for diversion and flood control.

[0053] Since most of the areas below the first phase water storage level have been filled with water and humidified in advance, the first phase water storage speed can be left uncontrolled, greatly compressing the water storage process and thus extending the construction time before water storage.

[0054] The top elevation of the upstream weighted area is the same as the 20-year flood level during the flood season after the first phase of water storage, which can ensure that the top of the upstream weighted area will not be submerged in most years. It can be used as a mixing and storage platform for gravel-soil core wall materials, thereby solving the problem of tight production sites for gravel-soil core wall materials and saving transportation costs.

[0055] During the flood season, the final diversion tunnel gate is used to control discharge and raise the average water level as much as possible, so that the rockfill area and core wall area below the average water level will undergo wetting deformation and seepage adjustment as early as possible. During the second phase of water storage, the water storage speed of this part of the early wetted area does not need to be controlled.

[0056] The second phase of water storage occurs at the end of the flood season in the same year as the first phase. The top elevation of the second phase of water storage is the dead water level of the reservoir, which is also the power generation level required for the first batch of units to be put into operation. The water level is raised to the average flood season level using the mid-term diversion tunnel, with no requirement for water storage rate. At this point, the flow rate of the final diversion tunnel has met the ecological flow requirement, and the gates of the mid-term diversion tunnel are closed. Then, the mid-term diversion tunnel plugging and structural reconstruction of the junction with the venting tunnel are carried out. Simultaneously, by adjusting the gate opening of the final diversion tunnel, the water level is raised to the dead water level according to project requirements. The second phase of water storage is completed, and the final diversion tunnel, venting tunnel, and deep-hole spillway are used for diversion and the second flood season.

[0057] At the end of the flood season in the second year, the diversion tunnel gates were closed, and plugging construction and structural reconstruction of the section connected to the vertical shaft spillway were carried out. Then, the water level rise rate was controlled according to project requirements by using the gate openings of the venting tunnel and deep hole spillway until the water level reached the normal storage level, and the project was completed.

[0058] Example 1 The upstream quarry of a certain project is mainly composed of metamorphic sandstone, with developed fissure weathering, three sides facing the open air, and good mining conditions; the downstream quarry is mainly composed of granite, with developed alteration zones, a long strip quarry, one side facing the open air, and low initial discharge strength; the excavated materials in the project area are complex and have a high stone powder content.

[0059] The retaining dam is a gravel-soil core rockfill dam with a foundation elevation of 2,195 meters, a crest elevation of 2,510 meters, and a maximum height of 315 meters. The overburden depth exceeded 45 meters, so the core wall was excavated and rebuilt on bedrock.

[0060] From upstream to downstream, the dam body is divided into the upstream weighted area, upstream rockfill area, upstream transition area, upstream filter layer II, upstream filter layer I, gravel-soil core wall area, downstream filter layer I, downstream filter layer II, downstream transition area, downstream rockfill area, and downstream weighted area. The gravel-soil core wall area is further divided into gravel-soil core wall area A and gravel-soil core wall area B; the upstream rockfill area is further divided into upstream rockfill area III-1, upstream rockfill area III-2, and upstream rockfill area I; and the downstream rockfill area is further divided into downstream rockfill area III-1, downstream rockfill area III-2, downstream rockfill area II, and downstream rockfill area I. Upstream rockfill area I and downstream rockfill area I are referred to as primary rockfill areas, while the remaining rockfill areas are referred to as secondary rockfill areas.

[0061] The upstream and downstream cofferdams are fully integrated with the upstream and downstream ballasts, with top elevations of 2308m and 2265m respectively. The foundation surface is constructed from the downstream transition zone to the top of the downstream cofferdam, with a dam foundation filter layer and a dam foundation transition layer installed in sequence.

[0062] The rockfill area is divided into rockfill area III, rockfill area II, and rockfill area I, with the quality getting better in descending order. The content of particles smaller than 5 mm is no more than 25%, 21%, and 18%, respectively, and the permeability coefficient is no less than 1×10 -2 cm / s, 5×10 -2 cm / s, 1×10 -1 cm / s, the comprehensive deformation modulus Es shall not be less than 180MPa, 160MPa, and 140MPa respectively, and the average saturated compressive strength of the parent rock shall not be less than 60MPa, 50MPa, and 40MPa respectively. It is required to use weakly weathered, weakly unloaded, and fresh stones for production, and it is prohibited to use strongly weathered, strongly unloaded, and weak interlayer stones for production.

[0063] The area below the original riverbed elevation of 2245m is called the backfill area, where upstream rockfill area III-1 and downstream rockfill area III-1 are set up respectively, and the excavated materials from the project area are used for filling; upstream rockfill area III-2, downstream rockfill area III-2 and downstream rockfill area II mainly use the upstream fractured weathered sandstone slate material yard with a high stone powder content as the material source; upstream rockfill area I and downstream rockfill area I use the mixed rockfill materials excavated from the upstream fractured weathered sandstone slate material yard and the downstream alteration zone dominant granite material yard for filling.

[0064] The top elevation of the upstream rockfill III-2 area facing the water is 2,360m, a 20m difference from the top elevation of the upstream weighted area, which is 2,385m. This allows the upstream weighted area to effectively constrain deformation and protect the upstream rockfill III-2 area. The top elevation of the core wall of the upstream rockfill III-2 area is 2,380m.

[0065] The upstream rockfill III-2 area is compacted twice more than other rockfill areas. The pore slope after compaction is controlled to be no more than 21%. The porosity of other rockfill areas after compaction is controlled to be no more than 22%. The other compaction parameters remain unchanged.

[0066] The reservoir's normal water level is 2500m, its dead water level is 2420m, and its drawdown depth is 80m. In the upstream rockfill zone I, above the top of the upstream weighted area, a rock slope protection, upstream rockfill filtration, and upstream plum blossom-shaped vertical headwater body are constructed, from upstream to downstream. The upstream rockfill filtration has a horizontal thickness of 1m, and the bottom elevation of the upstream plum blossom-shaped vertical headwater body is 2410m, 10m below the dead water level.

[0067] A downstream horizontal permeable body, running through the downstream rockfill area and the downstream heavy-weight area, was constructed between downstream rockfill areas III-1 and III-2, adjacent to the downstream transition zone. A downstream rockfill filter layer, 0.5 m thick, was installed on both the top and bottom surfaces of the downstream horizontal permeable body. The bottom and top elevations of the downstream rockfill filter layer were 2245 m and 2280 m, respectively. The top elevations of downstream rockfill areas III-2 and II were 2440 m and 2380 m, respectively.

[0068] The diameter of the upstream and downstream plum blossom-shaped vertical permeable bodies is 5m, with spacing of 30m and 40m, respectively. The upstream and downstream plum blossom-shaped vertical headwater bodies, as well as the downstream horizontal permeable bodies, are constructed using high-quality rockfill Zone I materials, with a particle content of no more than 15% particles smaller than 5mm. Other requirements are the same as those for Rockfill Zone I. The transition material is the upstream fractured weathered sandstone slate, a slightly inferior material source, with a saturated compressive strength of no less than 40MPa.

[0069] The boundary between gravel core wall area A and gravel core wall area B is at an elevation of 2380m. The average P5 content is controlled at 43-46% and 40-43%, respectively. At an elevation of 2330m, the upper and lower contact clay thicknesses are 4m and 3m, respectively, and the compaction levels are controlled at 95%-100% and greater than 100%, respectively.

[0070] The flood discharge structures, from highest to lowest, consist of a tunnel spillway, a vortex shaft spillway, a deep-hole spillway, and a drain hole, with inlet elevations of 2478m, 2475m, 2443m, and 2380m, respectively. The diversion structures, from highest to lowest, consist of the final diversion tunnel, the mid-stage diversion tunnel, and the initial diversion tunnel, with inlet elevations of 2360m, 2340m, and 2261m, respectively. The vortex shaft spillway is integrated with the second half of the final diversion tunnel, while the drain hole is integrated with the second half of the mid-stage diversion tunnel. The initial diversion tunnel has cross-sectional dimensions of 15 x 19m (width x height). The ecological water supply tunnel, which will be used during the construction period, has a floor elevation of 2262.5m and cross-sectional dimensions of 6 x 6m (width x height).

[0071] During the construction process, as the dam body is filled and raised, the upstream rockfill area below the elevation of 2308m and the corresponding core wall area are pre-injected with water for wetting.

[0072] On March 12th of the first year of water storage, the gates of the initial diversion tunnel will be closed. Thereafter, the construction period ecological water supply tunnel will be used for flow. The water level will be raised while controlling the outflow rate by adjusting the gate opening during the construction period to meet the ecological flow rate requirements. On April 18th, when the water level rises to an elevation of 2344.3m and the flow rate in the intermediate diversion tunnel meets the ecological flow rate requirements, the gates of the construction period ecological water supply tunnel will be closed, completing the first phase of water storage. Thereafter, the intermediate and final diversion tunnels will be used for diversion during the flood season. There is no requirement for the initial water storage rate.

[0073] The top elevation of the upstream weighted area is 2385m, which is the same as the flood level once in 20 years during the flood season. According to the flood situation in previous years, it is highly likely that the top of the upstream weighted area will not be submerged. It can be used as a mixing and storage platform for gravel-soil core wall materials, thereby solving the problem of tight production sites for gravel-soil core wall materials and saving transportation costs.

[0074] During the flood season, the gates of the final diversion tunnel will be used to control discharge, raising the average flood season water level to 2,370 meters. The second phase of water storage will begin in early October of the first year of impoundment, using the mid-stage diversion tunnel to raise the water level to the flood season average level of 2,370 meters. There is no requirement for the impoundment rate. At this point, the flow rate of the final diversion tunnel has met the ecological flow requirements, and the gates of the mid-stage diversion tunnel are closed. Then, the mid-stage diversion tunnel plugging and structural reconstruction of the junction with the venting tunnel will be carried out. Simultaneously, by adjusting the gate opening of the final diversion tunnel, the water level will be controlled to rise to the dead water level of 2,420 meters according to project requirements. The second phase of water storage will be completed, and the final diversion tunnel, venting tunnel, and deep-hole spillway will be used for diversion and the second flood season.

[0075] At the end of the flood season in the second year, the diversion tunnel gates were closed, and plugging construction and structural reconstruction of the section connected to the vertical shaft spillway were carried out. Then, the water level rise rate was controlled according to project requirements by using the gate openings of the venting tunnel and deep hole spillway until the water level reached the normal storage level of 2500m, and the project was completed.

[0076] Computational analysis shows that, with other boundary conditions remaining the same, deformation is reduced by over 27 cm when considering staged impoundment compared to when not considering staged impoundment. Furthermore, deformation is reduced by over 80 cm when considering staged impoundment with wetting deformation compared to when considering wetting deformation after impoundment is complete. This indicates that staged impoundment can effectively reduce overall dam deformation. Staged impoundment discretizes the wetting deformation of the upstream rockfill into the dam filling process, superimposing the unloading effect of wetting deformation on the loading effect of dam filling. This enables adaptive adjustment of the dam body's stress and deformation, effectively resolving the conflicting temporal and spatial evolution of the settlement and deformation between the upstream rockfill and the gravel-soil core material, and reducing the risk of longitudinal cracks at the dam crest.

Claims

1. A design and construction method for a high gravel core rockfill dam with a deep overburden layer, characterized by: The design and construction method adopts a fissured weathered sandstone slate material yard, an alteration zone-dominated granite material yard, and excavated materials from the engineering area as the source of dam body rockfill materials. Taking the zoning control of the fine particle content of the rockfill materials as the main line, the wetting deformation of the upstream rockfill materials is discretized into the dam filling process according to the timing arrangement of flood discharge, diversion, and staged water storage. The unloading effect of the wetting deformation is superimposed on the loading effect of the dam filling to achieve adaptive adjustment of the stress and deformation of the dam body. Ultimately, a high gravel-soil core rockfill dam built on a thick overburden is obtained, in which the upstream rockfill materials are adapted to the settlement deformation of the gravel-soil core wall materials, and the longitudinal fission trend of the dam crest meets the requirements.

2. The design and construction method for a high gravel core rockfill dam with a thick overburden layer according to claim 1 is characterized by: Before filling construction of a high gravel-soil core-wall rockfill dam, the permeability and deformation requirements of the rockfill dam body are first determined based on the deformation and permeability statistical data of existing rockfill dams. Based on these permeability and deformation requirements, the rockfill dam body is divided into a gravel-soil core-wall area, a main rockfill area, and a secondary rockfill area. Then, based on geological exploration and material source analysis and identification data, relatively high-quality alteration zone-dominated granite materials are used in at least the gravel-soil core-wall area and the main rockfill area. Filling is carried out while controlling the fine particle content of the rockfill material to ensure that at least the stress and deformation of the gravel-soil core-wall area fill and the main rockfill area fill meet the control requirements.

3. The design and construction method for a high gravel core rockfill dam with a thick overburden layer according to claim 2 is characterized by: The gravel-soil core wall area includes the middle and lower gravel-soil core wall area A (1) and the upper gravel-soil core wall area B (2). The main rockfill area includes the upstream rockfill area I (3) and the downstream rockfill area I (4). The secondary rockfill area includes the upstream weighted area (5), the upstream rockfill area, the upstream transition area (6), the upstream filter layer II (7), the upstream filter layer I (8), the downstream filter layer I (9), the downstream filter layer II (10), the downstream transition area (11), the downstream rockfill area and the downstream weighted area (12). The rockfill dam body is filled in the order of upstream weighted area (5), upstream rockfill area, upstream transition area (6), upstream filter layer II (7), upstream filter layer I (8), gravel core area, downstream filter layer I (9), downstream filter layer II (10), downstream transition area (11), downstream rockfill area and downstream weighted area (12) from upstream to downstream; the difference in comprehensive deformation modulus Es between the rockfill areas is controlled within the range of 10-15% to facilitate the coordinated control of dam body deformation.

4. The design and construction method for a high gravel core rockfill dam with a thick overburden layer according to claim 3 is characterized by: The upstream rockfill area and the downstream rockfill area include rockfill area III, rockfill area II and rockfill area I respectively. The quality of the rockfill materials for rockfill area III, rockfill area II and rockfill area I is improved in sequence. The specific requirements are that the content of particles smaller than 5 mm should not exceed 25%, 21% and 18% respectively, and the permeability coefficient should not be less than 1×10 -2 cm / s, 5×10 -2 cm / s, 1×10 -1 cm / s, the comprehensive deformation modulus Es is not less than 180MPa, 160MPa and 140MPa respectively, and the average saturated compressive strength of the parent rock is not less than 60MPa, 50MPa and 40MPa respectively. The rockfill filling materials are all produced by weakly weathered, weakly unloaded and fresh stones. A downstream water guide belt consisting of a downstream transition zone (11), a dam foundation filter layer (13) and a dam foundation transition layer (14) is also set between the dam foundation and the rockfill body on the downstream side of the gravel soil core wall area A. The possible seepage water in the gravel soil core wall is discharged to the outside of the downstream dam through the downstream water guide belt.

5. The design and construction method for a high gravel core rockfill dam with a thick overburden layer according to claim 4 is characterized by: The rockfill area III includes upstream rockfill area III-1 (15), upstream rockfill area III-2 (16), downstream rockfill area III-1 (17) and downstream rockfill area III-2 (18). The upstream rockfill area III-1 (15) and downstream rockfill area III-1 (17) located within the overburden layer are filled with excavated materials from the project area, while the upstream rockfill area III-2 (16), downstream rockfill area III-2 (18) and downstream rockfill area II (19) are filled with stone powder containing The upstream rockfill area I (3) and the downstream rockfill area I (4) are both filled with a mixture of rockfill materials excavated from the fractured weathered sand and slate material field and the alteration zone dominant granite material field. The top elevation of the water surface of the upstream rockfill area III-2 is set to be no less than 20m lower than the top elevation of the upstream pressure zone to constrain the deformation of the upstream rockfill area III-2 (16) and achieve slope protection.

6. The design and construction method for a high gravel core rockfill dam with a thick overburden layer according to claim 4 or 5, characterized in that: The upstream rockfill zone I (3) above the top surface of the upstream weighted zone is further provided with a rock slope protection layer (20), an upstream rockfill filter layer (21), and an upstream plum blossom-shaped vertical permeable water body (22) in sequence from upstream to downstream; the horizontal thickness of the upstream rockfill filter layer (21) is not less than 1m, and the bottom elevation of the upstream plum blossom-shaped vertical permeable water bodies (22) inserted into the upstream rockfill zone I (3) at intervals is not less than 10m below the dead water level; A downstream horizontal permeable water body (23) is set up between the downstream rockfill area III-1 (17) and the downstream rockfill area III-2 (18), adjacent to the downstream transition area, and passes through the downstream rockfill area and the downstream heavy pressure area (12). The top and bottom surfaces of the downstream horizontal permeable water body are respectively provided with downstream rockfill filter layers (24). Downstream plum blossom-shaped vertical permeable water bodies (25) are respectively provided on the downstream rockfill area III-2 (18) and the downstream rockfill area II (19). The upstream plum blossom-shaped vertical permeable water body (22), the downstream plum blossom-shaped vertical permeable water body (25) and the downstream horizontal permeable water body (23) are all filled with granite materials with relatively good quality in the alteration zone. The content of particles smaller than 5 mm in the filling material is not more than 15%. Other requirements are the same as those for the filling material of the rockfill area I. The transition layer filling material adopts a fractured weathered sandstone slate material field with slightly poor material properties as the filling material source, and its saturated compressive strength is not less than 40 MPa.

7. The design and construction method for a high gravel core rockfill dam with a thick overburden layer according to claim 3, 4 or 5, characterized in that: The gravel-soil core wall area A (1) whose top elevation is flush with the top elevation of the upstream rockfill area III-2 and / or the top elevation of the downstream rockfill area II is filled with high-deformation-resistant filling materials with an average P5 content of 43-46%, and the gravel-soil core wall area B (2) is filled with high-deformation-resistant filling materials with an average P5 content of 40-43%, so as to discretize the wetting deformation of the gravel-soil core wall of the upstream rockfill into the dam filling process, and superimpose the unloading effect of the wetting deformation of the gravel-soil core wall of the upstream rockfill with the loading effect of the dam filling. , improve the adaptive adjustment ability of the dam body stress and deformation; after the gravel soil core wall area is excavated, a concrete cover plate (26) is set on the excavation surface, and a contact clay area that adapts to large shear deformation and maintains excellent anti-seepage performance is set on the concrete cover plate (26). The area below 0.45 times the dam height is set as the contact clay area A (27), with a horizontal thickness of 3m and a compaction degree greater than 100%; the area above 0.45 times the dam height is set as the contact clay area B (28), with a horizontal thickness of 4m and a compaction degree of 95% to 100%. Among them, the P5 content is the mass percentage of particles larger than 5mm in the core wall filling material to the total amount of the core wall filling material.

8. The design and construction method for a high gravel core rockfill dam with a thick overburden layer according to claim 7, characterized in that: The upstream rockfill III-2 zone (16) is a rockfill mold-enhancing zone that is compacted at least twice more than the rockfill zone. After compaction, the porosity of the rockfill mold-enhancing zone is controlled within 21%, and the porosity of other rockfill zones is controlled within 22% to discretize the wetting deformation of the upstream rockfill material into the dam filling process. The unloading effect of the wetting deformation is superimposed on the loading effect of the dam filling to achieve adaptive adjustment of the stress and deformation of the dam body and reduce the tendency of longitudinal cracks to form on the dam top.

9. The design and construction method for a high gravel core rockfill dam with a thick overburden layer according to claim 8, characterized in that: An upstream cofferdam anti-seepage system (29) is also provided in the upstream weighted area (5). The upstream rockfill III-1 area (15) and the upstream rockfill III-2 area (16) below the top elevation of the upstream cofferdam anti-seepage system are temporary rockfill drying areas in a dry state. As the filling height of the high gravel-soil core wall rockfill dam increases, water is slowly injected into the temporary rockfill drying area in a timely manner according to regulations to pre-wet the temporary rockfill drying area and the corresponding gravel-soil core wall area, and the wetting deformation of the upstream rockfill material is discretized into the dam filling process to eliminate the unacceptable wetting deformation and uneven settlement caused by the sudden filling of the temporary rockfill drying area with water, and to avoid irreversible seepage damage caused by excessive unsaturated ultra-high seepage pressure formed by the rapid filling of the gravel-soil core wall with water in a short period of time. The top elevation of the pre-injection wetting area shall not exceed the top elevation of the upstream cofferdam anti-seepage system.

10. The design and construction method for a high gravel core rockfill dam with a thick overburden layer according to claim 9, characterized in that: When controlling the fine particle content of rockfill materials by zoning, the blasting steps used for the granite material field in the altered zone with better dam material quality are 7.5m to 10m. The spacing and diameter of the drill holes are determined through blasting tests. After effective locking based on geological forecasts, a "drop-and-load" charging structure is used for blasting and mining to obtain rockfill materials with a fine particle content that meets the filling sequence requirements. Slope support is also provided in a timely manner. During the transfer process of mined filling materials that do not meet the dam filling sequence, the quality control of the rockfill materials that meet the material properties is carried out by prohibiting the transfer of strongly weathered and strongly unloaded mined materials that do not meet the quality requirements.

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