Treatment method for weak intercalated layer under gravity dam foundation and safety dam foundation

Abstract

The invention relates to the technical field of water conservancy and hydropower engineering, in particular to a treatment method for a weak intercalated layer under a gravity dam foundation and a safety dam foundation. Comprising the steps of shear-resistant tooth wall construction, consolidation grouting construction and prestressed anchoring construction. At the dam heel position of the gravity dam, a reinforced concrete shear-resistant tooth wall which penetrates through the weak interlayer and is embedded into the stable bedrock at the lower part of the weak interlayer is constructed downwards from the foundation surface of the dam foundation of the gravity dam; consolidation grouting penetrating through the weak intercalated layer is carried out in the dam foundation area of the gravity dam containing the shear-resistant tooth wall; pre-stressed anchor cables which penetrate through the weak interlayer and are anchored to the stable bed rock are arranged at the position, on the downstream side of the shear-resistant tooth wall, of the dam foundation of the gravity dam, and tensioning is conducted. The anti-shearing strength of the slip face is directly improved through the anti-shearing tooth wall, the integrity and the deformation modulus of the foundation are improved through consolidation grouting, and normal pressure stress is actively applied through the pre-stressed anchor cable so that the anti-sliding resistance can be enhanced. And the work amount and the cost are saved, and the fundamental improvement of the deep anti-sliding stability of the dam foundation is ensured through the reliable quantitative design.

Description

Technical Field

[0001] This invention relates to the technical field of water conservancy and hydropower engineering, specifically to a method for treating weak interlayers under the foundation of a gravity dam and a safe dam foundation. Background Technology

[0002] In the field of water conservancy and hydropower engineering, gravity dams are water-retaining structures that rely primarily on their own weight to maintain stability against sliding and overturning. Due to their significant advantages such as simple cross-sectional shape, well-defined stress distribution, and high safety, they are widely used in reservoirs, hydropower stations, and other projects. However, the stability of gravity dams is highly dependent on foundation conditions, typically requiring the dam body to be situated on intact bedrock.

[0003] However, in actual engineering projects, weak interlayers often exist within the dam foundation rock mass, formed by geological tectonic activity or sedimentary discontinuities. Because the shear strength of these weak interlayers is relatively low, under loads such as upstream water pressure, if the bedrock above the weak interlayer fractures, or if the interlayer has an exposed free surface, the dam body is prone to sliding downstream along this interlayer, making it difficult to meet the specifications for deep-layer anti-sliding stability. Simultaneously, the deformation modulus of the soil in the weak interlayers is usually small; under the enormous gravity load of the dam body, the interlayer soil is prone to compressive deformation, causing dam settlement and affecting the safety of the project.

[0004] Currently, in engineering practice, the following two conventional solutions are mainly adopted for dealing with weak interlayers in dam foundations: First, changing the dam site plan. However, with the increasing scarcity of suitable dam sites in my country, relocation may not only lead to the dam site being far from the water supply area, increasing long-term operating costs, but may also force the project to halt due to the lack of other suitable dam sites in the region, affecting regional development plans. Second, completely removing the weak interlayer. At the designated dam site, a large-scale excavation project is carried out to remove all the weak interlayers and their overlying layers within the dam foundation's influence area until the underlying stable and intact bedrock is exposed. Then, concrete is used to backfill to the designed foundation surface. However, this significantly increases the workload, substantially driving up construction costs and posing considerable pressure in terms of economic efficiency and schedule control.

[0005] Therefore, there is an urgent need for a solution that can effectively ensure the stability and safety of the dam foundation without relocation or large-scale excavation, while also being economical and adaptable to construction, to address the treatment of weak interlayers under the foundation of gravity dams. Summary of the Invention

[0006] This invention addresses the problem of comprehensively managing weak interlayers without relocation or large-scale excavation, thereby ensuring the deep anti-sliding stability and safety of the dam foundation.

[0007] To address the aforementioned problems, this invention provides a method for treating weak interlayers beneath the foundation of a gravity dam and a safe dam foundation.

[0008] On the one hand, the present invention provides a method for treating weak interlayers under the foundation of a gravity dam, comprising the following steps: At the heel of the gravity dam, a reinforced concrete shear-resistant toothed wall is constructed from the foundation surface of the gravity dam foundation downwards, passing through the weak interlayer and embedded in the stable bedrock below it. In the foundation area of ​​the gravity dam containing the shear-resistant toothed wall, consolidation grouting penetrating the weak interlayer is implemented; At the gravity dam foundation downstream of the shear-resistant toothed wall, prestressed anchor cables that penetrate the weak interlayer and are anchored to the stable bedrock are laid out and tensioned.

[0009] Preferably, the shear-resistant toothed wall and the gravity dam body are integrally cast with concrete.

[0010] Preferably, the vertical cross-section of the shear-resistant toothed wall is an inverted right-angled trapezoid, the upstream face of the shear-resistant toothed wall is a vertical face and aligned with the heel of the gravity dam, and its downstream face is an inclined face.

[0011] Preferably, the depth to which the shear-resistant toothed wall is embedded in the stable bedrock below the weak interlayer is not less than 0.5 meters, and the slope of the downstream face of the shear-resistant toothed wall is 1:0.4 to 1:1.

[0012] Preferably, the cutting length L1 of the shear-resistant toothed wall along the river direction at the bottom surface of the weak interlayer is determined according to the following method: Based on the shear strength parameters of the shear-resistant toothed wall, the shear strength parameters of the weak interlayer, the cutting length L1, and the length L2 of the uncut portion of the weak interlayer, the comprehensive shear strength parameters of the slip surface are calculated by weighted average. Based on the requirements of the comprehensive shear strength parameters, the required cutting length L1 is derived and calculated; The slip surface is the interface between the weak interlayer and the stable bedrock below it.

[0013] Preferably, the grouting holes of the consolidation grouting are arranged in a quincunx pattern, and the hole spacing and row spacing are both 2.5 meters to 3.0 meters. The grouting depth of the consolidation grouting penetrates the weak interlayer and extends into the stable bedrock below it by at least 3 meters.

[0014] Preferably, the prestressed anchor cables are arranged in a quincunx pattern, and their hole spacing and row spacing are both 2.5 meters to 3.0 meters.

[0015] Preferably, the design tension of each bundle of the prestressed anchor cables is 1000t to 1500t.

[0016] Preferably, the construction of the prestressed anchor cable includes: A borehole is drilled downward from the foundation surface of the gravity dam foundation, the borehole penetrating the weak interlayer and extending into the stable bedrock below it to the designed anchoring depth; A high-strength steel strand body is installed in the borehole, and the lower end anchoring section of the strand body is located within the designed anchoring depth range of the stable bedrock. After applying the designed tension force to the cable, tensioning and locking are performed. Pressure grouting is performed on the borehole to form a grout body that grips and anchors the cable.

[0017] On the other hand, the present invention also provides a safe dam foundation for a gravity dam formed by the above-described processing method.

[0018] The beneficial effects of this invention are: This invention discloses a method for treating weak interlayers under the foundation of a gravity dam. The shear-resistant toothed wall acts as a rigid main pile, directly cutting off the most dangerous potential sliding channel downwards from the corner of the dam heel, i.e., the critical stress point. High-strength concrete replaces part of the weak medium in the interlayer, enhancing the overall shear resistance of the sliding surface—a fundamental solution to the anti-sliding stability problem. Simultaneously, consolidation grouting implemented in the shear-resistant toothed wall area, through grout penetration, compression, and cementation, improves the density and mechanical properties of the weak interlayer and surrounding soil and rock, enhancing its bearing capacity and deformation resistance, thereby effectively controlling settlement. Prestressed anchor cables arranged downstream of the shear-resistant toothed wall provide crucial active restraint. By anchoring and tensioning the deep, stable bedrock, they continuously apply normal prestress to the weak interlayer. This not only further compacts the soil but, more importantly, significantly increases the normal stress on the sliding surface, thereby significantly enhancing its shear resistance. This forms a three-dimensional anti-sliding pattern that complements the shear-resistant toothed wall. This invention achieves maximum safety benefits with minimal engineering intervention by precisely reinforcing key components, combining excellent reliability, economy, and broad site adaptability, thus opening up a completely new technical path for constructing safe dam foundations on complex ground.

[0019] The safe dam foundation of the present invention has the same beneficial effects as the above-mentioned method for treating weak interlayers under a gravity dam foundation compared to the prior art, and will not be repeated here. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for treating weak interlayers under the foundation of a gravity dam according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a safe dam foundation according to one embodiment of the present invention.

[0021] Explanation of reference numerals in the attached drawings: 11-Heel of gravity dam; 12-Foundation of gravity dam; 13-Main body of gravity dam; 2-Weak interlayer; 3-Stable bedrock; 4-Shear-resistant toothed wall; 41-Upstream face; 42-Downstream face; 5-Prestressed anchor cable; 6-Slip surface. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0023] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the following description. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used only to distinguish different devices, modules, or components, and are not intended to limit the order of functions performed by these devices, modules, or components or their interdependencies.

[0024] It should be noted that the terms "a" and "a plurality of" used in this invention are illustrative rather than restrictive. Those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0025] In related technologies, under the gravity dam foundation 12, the potential failure surface most likely to undergo shear slippage under the load of the gravity dam body 13, formed by the top or bottom surface of the weak interlayer 2, is the slip surface 6. This slip surface 6 is an objectively existing geological weak interface, and its material composition and mechanical properties (i.e., shear strength parameters) are significantly inferior to those of the hanging and footwall rock masses. This slip surface 6 is also the calculation benchmark surface for deep anti-slip stability analysis and the core target of all reinforcement measures.

[0026] To address the problems existing in the aforementioned related technologies, this invention provides a method for treating weak interlayers under the foundation of a gravity dam and a safe dam foundation.

[0027] See Figure 1 This invention provides a method for treating weak interlayers under the foundation of a gravity dam, specifically including the following steps: S1. Construction of shear-resistant toothed wall 4: At the heel of the gravity dam 11, a reinforced concrete shear-resistant toothed wall 4 is constructed from the foundation surface of the gravity dam foundation 12, passing through the weak interlayer 2 and embedded in the stable bedrock 3 below it. S2. Consolidation grouting construction: In the area of ​​the gravity dam foundation 12 containing the shear-resistant toothed wall 4, consolidation grouting is carried out to penetrate the weak interlayer 2. S3. Prestressed anchorage construction: At the gravity dam foundation 12 downstream of the shear-resistant toothed wall 4, prestressed anchor cables 5 that penetrate the weak interlayer 2 and are anchored to the stable bedrock 3 are installed and tensioned.

[0028] It should be noted that, in this embodiment of the invention, the slip surface 6 refers to the interface between the weak interlayer 2 and the stable bedrock 3 below it.

[0029] The shear-resistant toothed wall 4 of this invention, acting as a rigid main pile, directly cuts off the most dangerous potential sliding channel downwards from the corner of the heel 11 of the gravity dam, which is also the key stress point. It replaces part of the weak medium of the weak interlayer 2 with high-strength concrete, thereby improving the comprehensive shear resistance of the sliding surface 6. This is the fundamental solution to the anti-sliding stability problem. Simultaneously, the consolidation grouting implemented in the area of ​​the shear-resistant toothed wall 4, through grout penetration, compression, and cementation, improves the density and mechanical properties of the weak interlayer 2 and the surrounding soil and rock, enhancing its own bearing capacity and deformation resistance, thus effectively controlling settlement. The prestressed anchor cables 5 arranged downstream of the shear-resistant toothed wall 4 provide crucial active restraint. By anchoring and tensioning the deep stable bedrock 3, they continuously apply normal prestress to the weak interlayer 2. This not only further compacts the soil but, more importantly, significantly increases the normal stress on the sliding surface, thereby significantly enhancing its shear resistance. Together with the shear-resistant toothed wall 4, they form a three-dimensional anti-sliding pattern that complements each other. This invention achieves maximum safety benefits with minimal engineering intervention by precisely reinforcing key components, combining excellent reliability, economy, and broad site adaptability, thus opening up a completely new technical path for constructing safe gravity dams on complex foundations.

[0030] In one embodiment of the present invention, the shear-resistant toothed wall 4 and the gravity dam body 1 are integrally cast with concrete.

[0031] It should be noted that the key process of integrally casting the shear-resistant toothed wall 4 and the gravity dam body 1 with concrete is to ensure that the two form a structural whole and achieve coordinated stress distribution. In actual construction, the following construction sequence is usually adopted: First, at the critical part of the gravity dam heel 11, the shear-resistant toothed wall 4 and its adjacent gravity dam body 1 foundation are constructed together and cast as a whole in one go, thereby forming a continuous rigid resistance body at the structural root. After the concrete of this part reaches the predetermined strength, the already cast shear-resistant toothed wall 4 and the foundation surface of the gravity dam foundation 12 in this area are used as the working surface to sequentially carry out consolidation grouting construction and prestressed anchor cable construction through the weak interlayer 2. After these foundation reinforcement measures are completed, the remaining part of the gravity dam body 1 is cast upwards and to both sides in layers and sections. This ensures that there are no weak joints between the shear-resistant toothed wall 4 and the gravity dam body 1, allowing for direct force transmission. It also provides a solid and stable working surface for subsequent grouting and anchoring, ensuring that all treatment measures can fully play their intended role.

[0032] Furthermore, the key structural detail of integrally casting the shear-resistant toothed wall 4 and the gravity dam body 1 with concrete enables synergistic stress distribution and ensures effective reinforcement. Eliminating construction joints or weak contact surfaces between the shear-resistant toothed wall 4 and the gravity dam body 1 allows the enormous horizontal load and self-weight borne by the gravity dam body 1 to be directly and without loss transferred to the shear-resistant toothed wall 4, which penetrates deep into the stable bedrock 3, through this completely continuous rigid structure. This not only enhances the rooting effect and overturning resistance of the shear-resistant toothed wall 4, but more importantly, it ensures that the high shear strength provided by the concrete of the shear-resistant toothed wall 4 can be fully utilized to resist the deep sliding of the gravity dam foundation 12 along the slip surface 6. This, together with subsequent consolidation grouting and prestressed anchor cable 5 measures, forms a three-dimensional anti-slip system that combines rigidity and flexibility, from localized blockage to overall improvement, effectively addressing the problem of the weak interlayer 2 with minimal engineering work.

[0033] In one embodiment of the present invention, the vertical cross section of the shear-resistant toothed wall 4 is an inverted right-angled trapezoid, the upstream surface 41 of the shear-resistant toothed wall 4 is a vertical surface and aligned with the heel of the gravity dam 11, and its downstream surface 42 is an inclined surface.

[0034] It should be noted that, firstly, the upstream face 41 is perfectly aligned with the heel 11 of the gravity dam, ensuring that the enormous horizontal thrust transmitted from the gravity dam body 13 acts vertically and without eccentricity directly on the shear-resistant toothed wall 4, avoiding stress concentration and additional bending moments. Secondly, the design of the downstream face 42 as an inclined surface is crucial. On the one hand, the inclined surface provides a gradually widening cross-section along the river, continuously enhancing the shear and bending resistance of the shear-resistant toothed wall 4 from bottom to top, effectively resisting the shear force generated by deep sliding; on the other hand, the inclined surface has a larger contact area with the stable bedrock 3 above and below the weak interlayer 2, providing stronger interfacial bonding and frictional resistance when combined with grouting measures. Furthermore, the trapezoidal cross-section of the shear-resistant toothed wall 4, while achieving the same structural performance, significantly reduces the amount of concrete compared to a rectangular cross-section, lowering engineering costs; its downstream face 42 also better conforms to the natural stability angle of the excavated slope, which is beneficial to the stability of the foundation pit and construction safety. Therefore, this specific cross-sectional shape is not only a rational choice in mechanics but also a concrete structural embodiment of the economical and efficient core concept of this invention.

[0035] In one embodiment of the present invention, the shear-resistant toothed wall 4 is embedded in the stable bedrock 3 below the weak interlayer 2 to a depth of not less than 0.5 meters, and the slope of the downstream face 42 of the shear-resistant toothed wall 4 is 1:0.4 to 1:1.

[0036] It should be noted that the slope of the downstream face 42 is 1:0.4 to 1:1, which is a standardized expression for the steepness of the slope in engineering. Specifically, it means that for every 1 meter the downstream face 42 descends vertically (in the depth direction), its horizontal (along the river direction) projection length increases by 0.4 to 1 meter. Here, 1:0.4 represents a steeper slope, and 1:1 represents a gentler slope. A steeper slope (such as 1:0.4) is beneficial for arranging shear-resistant toothed walls 4 within a limited space, minimizing the volume of concrete pouring, and is suitable for foundations with good rock integrity and strong lateral bearing capacity. A gentler slope (such as 1:1) provides a larger base bearing area and anti-sliding stability, helping to distribute stress more evenly, and is suitable for situations with stricter deformation control requirements or relatively weaker foundation conditions.

[0037] The shear-resistant toothed wall 4 must be embedded at a depth of no less than 0.5 meters into the stable bedrock 3. This is a mandatory requirement to ensure that the shear-resistant toothed wall 4 achieves the minimum necessary anchorage length in the stable bedrock 3. This depth ensures sufficient adhesion and friction between the bottom of the shear-resistant toothed wall 4 and the bedrock, resisting possible pull-out or deep shearing of the shear-resistant toothed wall 4, and ensuring that its anti-slip function as a deep pile is fundamentally realized. Therefore, the combination of slope range and embedment depth ensures that the shear-resistant toothed wall 4 can achieve maximum anti-slip benefits with minimal engineering work, while also flexibly adapting to different site geological conditions.

[0038] In one embodiment of the present invention, the cutting length L1 of the shear-resistant toothed wall 4 along the river direction at the bottom surface of the weak interlayer 2 is determined according to the following method: Based on the shear strength parameters of the shear-resistant toothed wall 4, the shear strength parameters of the weak interlayer 2, the cutting length L1, and the length L2 of the uncut portion of the weak interlayer 2, the comprehensive shear strength parameters of the slip surface 6 formed by the bottom surface of the weak interlayer 2 are calculated by weighted average. Based on the requirements of the comprehensive shear strength parameters, the required cutting length L1 is derived and calculated. Among them, the slip surface 6 is the interface between the weak interlayer 2 and the stable bedrock 3 below it.

[0039] Furthermore, the shear strength parameters of the shear-resistant toothed wall 4 include the friction coefficient f2 and cohesion c2; the shear strength parameters of the weak interlayer 2 include the friction coefficient f1 and cohesion c1; and the comprehensive shear strength parameters of the slip surface 6 include the friction coefficient f3 and cohesion c3.

[0040] The calculation formula is as follows: ; .

[0041] Wherein, f1 and c1 are the shear strength parameters of the weak interlayer 2 when it remains intact without being cut off, determined through geological exploration and indoor / field tests, representing given geological conditions. f2 and c2 are the shear strength parameters of the concrete of the shear-resistant toothed wall 4, determined by the concrete design grade according to design specifications, representing selected material properties. The slip surface 6 formed by the bottom surface of the weak interlayer 2 specifically refers to the interface between the weak interlayer 2 and the stable bedrock 3 beneath it.

[0042] We can assume a value for L1 and obtain L2. Calculate f3 and c3 using the two formulas mentioned above. Simultaneously check whether f3 and c3 meet the deep anti-sliding stability requirements of the dam body as specified in the "Gravity Dam Design Code". If not, recalculate L1 and perform a trial calculation; if it does, the current L1 is a feasible solution, and the minimum value that meets the requirements is usually taken as the economically reasonable design value.

[0043] In one embodiment of the present invention, the grouting holes of the consolidation grouting are arranged in a quincunx pattern, and the hole spacing and row spacing are both 2.5 meters to 3.0 meters. The grouting depth of the consolidation grouting penetrates the weak interlayer 2 and extends into the stable bedrock 3 below it by at least 3 meters.

[0044] It should be noted that the spacing between grouting holes is limited to 2.5 to 3.0 meters. This is a balanced choice based on the grout diffusion radius and the groutability of the foundation. This ensures effective overlap of grout between adjacent holes to form a complete reinforcement network, while avoiding the waste of engineering work and construction interference caused by excessively dense hole spacing. The requirement that the grouting depth must penetrate the weak interlayer 2 and extend at least 3 meters into the stable bedrock 3 below it ensures that the grout can be fully injected and improve the entire weak interlayer 2, enhancing its shear strength and compression modulus. At the same time, a rigid anchoring and transition zone is formed in and below the interface (i.e., slip surface 6) between the weak interlayer 2 and the stable bedrock 3 below it. This not only enhances the anti-sliding capacity of this key interface but also improves the path of load transfer from the gravity dam body 13 to the deep stable rock mass, reducing uneven settlement.

[0045] In one embodiment of the present invention, the prestressed anchor cables 5 are arranged in a quincunx pattern, with a hole spacing and row spacing of 2.5 meters to 3.0 meters. The design tension of each bundle of prestressed anchor cables 5 is 1000t to 1500t.

[0046] It should be noted that the prestressed anchor cables 5 are arranged in a quincunx pattern to ensure that the anchor cable group forms a uniform and continuous active restraint network within a specific gravity dam foundation 12 area downstream of the shear-resistant toothed wall 4. The selection of its arrangement has a clear engineering intent, including that the anchor cable group is not uniformly distributed throughout the entire gravity dam foundation 12 area, but is focused on the key slip zone behind the shear-resistant toothed wall 4, so that the normal prestress applied to the weak interlayer 2 can effectively act on the remaining slip surface 6 (L2 segment) that the shear-resistant toothed wall 4 cannot completely cut off, thereby forming a synergistic anti-slip mechanism with the rigid anti-slip of the upstream shear-resistant toothed wall 4, which is a pincer attack and a closed force system.

[0047] Limiting the hole spacing and row spacing of the prestressed anchor cables 5 to 2.5 meters to 3.0 meters ensures the superposition and diffusion of prestress from adjacent anchor cables, forming a continuous compressive stress zone and improving the overall density and shear resistance of the weak interlayer 2. It also avoids the weakening effect of excessively dense prestressed anchor cables 5, construction interference, and cost waste. The design tension of a single bundle of prestressed anchor cables 5 is specified as 1000 to 1500 tons (approximately 9800 kN to 14700 kN). This enormous prestress ensures a significant increase in normal stress on the slip surface 6 of the weak interlayer 2, thereby directly and substantially improving its anti-slip friction resistance.

[0048] In one embodiment of the present invention, the construction of the prestressed anchor cable 5 includes: S31: Drill a hole downward from the foundation surface of the gravity dam foundation 12, the hole penetrates the weak interlayer 2 and extends into the stable bedrock 3 below it to the designed anchoring depth; S32: A high-strength steel strand body is installed in the borehole, and the lower end of the strand body is anchored within the design anchoring depth range of the stable bedrock 3; S33: After applying the designed tension force to the cable, perform tension locking; S34: Pressure grouting is performed on the borehole to form a grout body that grips and anchors the cable.

[0049] It should be noted that step S31 (drilling to the designed anchorage depth) is fundamental. It ensures that the force transmission path avoids the weak interlayer 2 and embeds the anchorage foundation deep into the stable bedrock 3 with stable properties and high bearing capacity. This solves the problem of not being able to establish reliable anchorage in weak media. Step S32 (precise cable placement) is key to achieving directional force application. By strictly setting the cable anchorage section within a stable design depth range, it provides a clearly defined point of application for subsequent tension force in space. Step S33 (tensioning and locking) is not a simple installation, but rather an active injection of a predetermined and enormous normal pressure into the foundation system. This force is transmitted in reverse through the cable, directly and significantly increasing the normal stress on the potential slip surface 6, thereby instantly improving its anti-slip frictional resistance and achieving a fundamental shift in the mechanical state from passively resisting slippage to actively suppressing slippage. The final step, S34 (pressure grouting and anchor sealing), bears the dual responsibility of preserving the stress system and ensuring its long-term durability. The grouting ensures that the prestress can be maintained without loss over a long period. At the same time, it seals and protects the high-strength cable body, isolating it from the external corrosive environment and guaranteeing the reliability of this active reinforcement system throughout its entire lifespan. Together with the rigid interception of the upstream shear-resistant toothed wall 4 and the media strengthening function of the consolidation grouting of the gravity dam foundation 12, it forms a front-plugging and rear-pressure reinforcement network, ensuring that this invention achieves greater safety benefits with a smaller amount of engineering work.

[0050] On the other hand, the present invention also provides a safe dam foundation for a gravity dam formed by the above-described processing method.

[0051] It should be noted that, along the critical force transmission path of the gravity dam heel 11, a reinforced concrete shear-resistant toothed wall 4 is formed, extending downwards from and integrated with the gravity dam body 13. This shear-resistant toothed wall 4, acting as a rigid core, penetrates the weak interlayer 2 and is deeply anchored in the stable bedrock 3, fundamentally physically blocking the continuous sliding channel. In the shear-resistant toothed wall 4 and its surrounding area, the weak interlayer 2 and the fractured rock mass are strengthened by a network of grout veins formed by high-pressure consolidation grouting, improving their integrity and mechanical properties. In the critical anti-slip zone downstream of the shear-resistant toothed wall 4, the prestressed anchor cables 5, deeply embedded in the stable bedrock 3, provide a continuous compressive effect for the potential sliding surface 6 through the large normal stress actively applied to the system. Therefore, the safe dam foundation of this invention is a composite foundation with controllable performance, integrating rigid embedding, medium improvement, and active restraint. By combining the strength of the artificial structure with the reliability of the stable rock mass, multiple anti-slip defense lines are actively constructed, achieving a qualitative leap in bearing capacity. It not only meets the safety requirements of the regulations, but also provides an optimized and replicable paradigm for dam foundation construction, improving the project's economy, safety margin and long-term durability.

[0052] In one embodiment of the present invention, a reservoir dam is a concrete gravity dam with a maximum height of 37.5m and a crest length of 349m. The dam foundation is situated on basalt. Exploration revealed that within a depth range of 10.00m to 17.90m below the foundation surface of the dam section in the river valley, there is a weak interlayer 2 formed by intermittent volcanic eruptions, mainly composed of clay, constituting a weak controlling surface for the deep anti-sliding stability of the dam foundation.

[0053] In one embodiment of the present invention, the method for treating the weak interlayer under the foundation of a gravity dam, as described above, specifically includes the following steps: Construction of S1, shear-resistant toothed wall 4: At the heel 11 of the gravity dam in the riverbed section (chainage 0+072.00~0+313.50), a reinforced concrete shear wall 4 is constructed. The upstream face 41 of the shear wall 4 is flush with the upstream face of the gravity dam body, and the downstream face has a slope ratio of 1:0.4. Differentiated designs are implemented based on the differences in dam height and geological conditions in each dam section. The section from chainage 0+072.00 to 0+156.00 has a shear-resistant toothed wall with a depth of 8.3m, a bottom width of 2.7m, and a cutting length L1=2.7m.

[0054] The section from chainage 0+156.00 to 0+246.00 has a shear-resistant toothed wall with a depth of 8.3m, a bottom width of 8.0m, and a cutting length L1=8.0m.

[0055] The section from chainage 0+246.00 to 0+313.50 has a shear-resistant toothed wall with a depth of 12.6m, a bottom width of 8.0m, and a cutting length L1=8.0m.

[0056] All shear-resistant toothed walls 4 are embedded for no less than 0.5m into the dense basalt below the weak interlayer 2, i.e., the stable bedrock 3, and are integrally cast with the gravity dam body 13.

[0057] S2. Consolidation grouting construction: To improve the overall integrity of the bedrock, specifically the integrity of the stable bedrock 3 above and below the weak interlayer 2, consolidation grouting was performed on the gravity dam foundation 12. The grouting holes were arranged in a quincunx pattern, with a hole and row spacing of 3.0m and an average hole depth of 15.0m, ensuring that the grout penetrated the weak interlayer 2 and reached the stable bedrock 3 below it.

[0058] S2. Construction of prestressed anchor cables: Prestressed anchor cables 5 are installed on the gravity dam foundation 12 downstream of the shear-resistant toothed wall 4. The anchor cable row spacing is 3.0m, the hole spacing is 2.5m, and the arrangement is quincunx. The anchor cable design length is 20m, and it is anchored to the dense basalt, i.e., stable bedrock 3 below the weak interlayer 2. The single bundle of prestressed anchor cable 5 uses 4 bundles of 7Φ5 (Φ15.2) steel strands, and the design tension is 1000kN.

[0059] The table below shows the comparative calculation results of the deep anti-sliding stability safety factor of three selected typical dam sections before and after adopting the treatment method of this invention, which uses shear-resistant toothed walls 4 as the core. The calculations strictly follow the "Code for Design of Concrete Gravity Dams" and use the shear resistance formula.

[0060] Table 1. Comparison of safety factors for deep anti-sliding stability of dam foundation before and after implementation of the treatment scheme of the present invention.

[0061] It is evident that by adjusting the dimensions (depth, bottom width, L1) of the shear-resistant toothed wall 4 to adapt to the needs of different dam sections, and by combining quantitative calculations to determine L1, the present invention demonstrates that it combines principle and flexibility, and possesses broad engineering applicability. All sections and working conditions that originally did not meet the specifications have significantly exceeded the minimum requirements of the specifications after treatment, fundamentally ensuring the deep anti-sliding stability of the dam foundation.

[0062] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for treating weak interlayers under the foundation of a gravity dam, characterized in that, Includes the following steps: At the heel (11) of the gravity dam, a reinforced concrete shear-resistant toothed wall (4) is constructed from the foundation surface of the gravity dam foundation (12) downwards, passing through the weak interlayer (2) and embedded in the stable bedrock (3) below it. In the region of the gravity dam foundation (12) containing the shear-resistant toothed wall (4), consolidation grouting penetrating the weak interlayer (2) is carried out; At the gravity dam foundation (12) downstream of the shear-resistant toothed wall (4), prestressed anchor cables (5) that penetrate the weak interlayer (2) and are anchored to the stable bedrock (3) are laid out and tensioned.

2. The method for treating weak interlayers under the foundation of a gravity dam according to claim 1, characterized in that, The shear-resistant toothed wall (4) and the gravity dam body (1) are integrally cast with concrete.

3. The method for treating weak interlayers under the foundation of a gravity dam according to claim 1, characterized in that, The vertical cross section of the shear-resistant toothed wall (4) is an inverted right trapezoid. The upstream face (41) of the shear-resistant toothed wall (4) is a vertical face and is aligned with the heel (11) of the gravity dam. Its downstream face (42) is an inclined face.

4. The method for treating weak interlayers under the foundation of a gravity dam according to claim 2, characterized in that, The shear-resistant toothed wall (4) is embedded in the stable bedrock (3) below the weak interlayer (2) to a depth of not less than 0.5 meters, and the slope of the downstream face (42) of the shear-resistant toothed wall (4) is 1:0.4 to 1:

1.

5. The method for treating weak interlayers under the foundation of a gravity dam according to claim 1, characterized in that, The cutting length L1 of the shear-resistant toothed wall (4) along the river direction at the bottom surface of the weak interlayer (2) is determined according to the following method: Based on the shear strength parameters of the shear-resistant toothed wall (4), the shear strength parameters of the weak interlayer (2), the cutting length L1 and the length L2 of the uncut portion of the weak interlayer (2), the comprehensive shear strength parameters of the slip surface (6) are calculated by weighted average. Based on the requirements of the comprehensive shear strength parameters, the required cutting length L1 is derived and calculated; The slip surface (6) is the interface between the weak interlayer (2) and the stable bedrock (3) below it.

6. The method for treating weak interlayers under the foundation of a gravity dam according to claim 1, characterized in that, The grouting holes of the consolidation grouting are arranged in a quincunx pattern, and the hole spacing and row spacing are both 2.5 meters to 3.0 meters. The grouting depth of the consolidation grouting penetrates the weak interlayer (2) and extends into the stable bedrock (3) below it by at least 3 meters.

7. The method for treating weak interlayers under the foundation of a gravity dam according to claim 1, characterized in that, The prestressed anchor cables (5) are arranged in a quincunx pattern, and their hole spacing and row spacing are both 2.5 meters to 3.0 meters.

8. The method for treating weak interlayers under the foundation of a gravity dam according to claim 7, characterized in that, The design tension of each prestressed anchor cable (5) is 1000t to 1500t.

9. The method for treating weak interlayers under the foundation of a gravity dam according to claim 7 or 8, characterized in that, The construction of the prestressed anchor cable (5) includes: A borehole is drilled downward from the foundation surface of the gravity dam foundation (12), the borehole penetrating the weak interlayer (2) and extending into the stable bedrock (3) below it to the designed anchoring depth; A high-strength steel strand body is installed in the borehole, and the lower end anchoring section of the strand body is located within the designed anchoring depth range of the stable bedrock (3); After applying the designed tension force to the cable, tensioning and locking are performed. Pressure grouting is performed on the borehole to form a grout body that grips and anchors the cable.

10. A gravity dam foundation formed by the processing method described in any one of claims 1 to 9.

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