Foundation treatment structure for gravity dam under soft rock foundation condition in strong earthquake zone

Abstract

The utility model relates to the field of water conservancy and hydropower facilities especially relates to a gravity dam foundation treatment structure for solving the gravity dam foundation bearing capacity and anti -slip stability problem under the soft rock foundation condition of strong earthquake area, including the base surface of gravity dam, consolidation grouting layer, bored pile and concrete dam body, concrete dam body sets up in the base surface top, and the consolidation grouting layer is set up below the base surface, and the bored pile sets up below concrete dam body, and the top of bored pile and concrete dam body bottom fixed connection, and the bottom of at least one bored pile sets up below three kinds of rock mass demarcation line, the utility model is especially applicable to the gravity dam foundation treatment construction under the soft rock foundation condition of strong earthquake area.

Description

Technical Field

[0001] This utility model relates to the field of water conservancy and hydropower facilities, and in particular to a gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones. Background Technology

[0002] The bearing capacity and anti-sliding stability of gravity dams have always been core issues in the design and construction of gravity dam projects. With the development of water conservancy and hydropower, dam sites with excellent geological conditions are gradually being developed and utilized, forcing the construction of new gravity dams to be carried out on sites with relatively poor geological conditions, such as soft rock foundations in earthquake-prone areas. This significantly increases the importance of research on the bearing capacity and anti-sliding stability of gravity dams.

[0003] Soft rock, due to its poor integrity, results in weak bearing capacity and deformation capacity of the foundation at the base of dams. Furthermore, the foundation rock mass exhibits well-developed fissures and weak structural planes, leading to stability issues such as sliding resistance along the foundation surface, in shallow layers, and in deep layers. Currently, in the construction of gravity dams with soft rock foundations in strong earthquake zones, foundation reinforcement is necessary to improve the bearing capacity and stability of the gravity dam. One such method is consolidation grouting. Consolidation grouting involves high-pressure injection of cement grout or other special grouting materials into the foundation rock mass, followed by the placement of the concrete dam body on the consolidation grout layer, thus systematically improving the foundation rock mass. Consolidation grouting can enhance rock mass integrity, effectively fill various primary and secondary fissures and fracture zones, improve the physical and mechanical properties of the rock mass, and structurally reinforce fault fracture zones, weak interlayers, and other adverse geological features. However, since the construction depth of consolidation grouting is generally 6-15m, its improvement on the mechanical properties of the dam foundation is limited, and therefore its effectiveness in addressing deep anti-sliding stability issues is not significant. Furthermore, the effect of consolidation grouting in reinforcing the dam foundation is closely related to the groutability of the rock mass; when the rock mass of the dam foundation has low permeability, its reinforcement effect is not obvious. Therefore, consolidation grouting alone has limited effect on improving the bearing capacity and stability of gravity dams under soft rock foundation conditions in strong earthquake zones, and it cannot effectively solve the problem of deep anti-sliding stability. The dam still faces the risk of sliding and instability along weak structural planes or rock strata deep within the foundation. Utility Model Content

[0004] The technical problem to be solved by this utility model is to provide a gravity dam foundation treatment structure that solves the problems of bearing capacity and anti-sliding stability of gravity dam foundation under soft rock foundation conditions in strong earthquake zones.

[0005] The technical solution adopted by this utility model to solve its technical problem is: a gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones, including a gravity dam foundation surface, a consolidation grouting layer, cast-in-place piles and a concrete dam body. The concrete dam body is set above the foundation surface, a consolidation grouting layer is set below the foundation surface, the cast-in-place piles are set below the concrete dam body, the top of the cast-in-place piles is fixedly connected to the bottom of the concrete dam body, and the bottom of at least one cast-in-place pile is set below the boundary line of the three types of rock masses.

[0006] Furthermore, the concrete dam body includes a dam heel and a dam toe, with cast-in-place piles installed at the bottom of the dam heel and at the bottom of the dam toe.

[0007] Furthermore, the ratio between the height of the dam heel and the length of the dam heel ranges from 1.5 to 2.

[0008] Furthermore, the ratio between the height of the dam toe and the length of the dam toe ranges from 1.5 to 2.

[0009] Furthermore, cast-in-place piles are installed at the bottom of the concrete dam in the area between the dam heel and the dam toe.

[0010] Furthermore, cast-in-place piles were installed in the area of ​​the downstream sliding surface of the concrete dam.

[0011] Furthermore, the cast-in-place pile is a reinforced concrete rotary-drilled cast-in-place pile.

[0012] Furthermore, this includes the potential deepest slip surface, which is located above the boundary line of the three types of rock masses, and the bottom of the cast-in-place pile is set at a depth of at least 2m below the potential deepest slip surface.

[0013] Furthermore, this includes the horizontal bearing capacity of a single pile at the junction of the cast-in-place pile and the potential deepest slip surface, wherein the horizontal bearing capacity of the single pile is greater than the shear force at the junction of the cast-in-place pile and the potential deepest slip surface.

[0014] Furthermore, it includes earthquake-resistant steel mesh, which is installed within the concrete dam body along and perpendicular to the direction of water flow.

[0015] The beneficial effects of this utility model are: I. Installation of cast-in-place piles and consolidation grouting layer. Specifically: cast-in-place piles enhance the bearing capacity and stability of the dam foundation; consolidation grouting strengthens the integrity and homogeneity of the dam foundation rock mass, increases the elastic modulus of the dam foundation, reduces the permeability of the dam foundation, and improves the bearing capacity of the dam foundation; the cast-in-place piles and consolidation grouting layer construct a synergistic bearing system of rigid piles and flexible grouting layer, significantly improving the foundation bearing capacity and solving the anti-sliding stability issues of the dam body along the foundation surface, shallow layer, and deep layer.

[0016] Second, the cast-in-place piles extend downwards to below the boundary line of the three types of rock masses, allowing the cast-in-place piles to cut off the weak structural surface, causing the sliding surface to move down to the hard rock layer. Combined with the grout vein network formed by the consolidation grouting layer, the anti-sliding safety factor is increased by 20% to 35%.

[0017] Third, compared with traditional foundation reinforcement techniques, rotary drilling grouting piles have advantages such as faster construction efficiency and can avoid large-scale excavation. Specifically, construction speed can be increased by 40% to 60%, and earthwork excavation volume reduced by more than 30%.

[0018] IV. Significant Economic Benefits: This solution saves more than 25% on material costs, shortens the construction period by more than 20%, and reduces the overall cost by 18% to 22%. Furthermore, it aligns with the development trend of green construction in water conservancy projects and possesses significant comprehensive technical and economic advantages.

[0019] This invention is particularly applicable to the construction of gravity dam foundations under soft rock foundation conditions in earthquake-prone areas. Attached Figure Description

[0020] Figure 1 This is a schematic diagram showing the positional relationship between the concrete dam body, the consolidated grouting layer, the cast-in-place piles, and the boundary lines of the three types of rock masses in this utility model.

[0021] Figure 2 This is a schematic diagram of the heel and toe of the concrete dam body of this utility model.

[0022] Figure 3 This is a schematic diagram showing that the cast-in-place pile of this utility model is divided into an upper pile foundation and a lower pile foundation at the junction of the potential deepest slip surface.

[0023] Figure 4 This is a schematic diagram of the structure combining the concrete dam body and the cast-in-place piles of this utility model.

[0024] The markings in the diagram are as follows: 1. Concrete dam body; 2. Original ground line; 3. Boundary line between three types of rock mass; 4. Potential deepest slip surface; 5. Slip surface with minimum safety factor; 6. Cast-in-place pile; 61. Upper pile foundation; 62. Lower pile foundation; 63. Interface between pile foundation and potential deepest slip surface; 64. Reinforcing steel of cast-in-place pile; 7. Water flow direction; 11. Dam heel; 12. Dam heel height H1; 13. Dam heel length B1; 14. Dam toe; 8. Dam toe height H2; 15. Dam toe length B2; 9. Seismic reinforcement mesh; 16. Foundation surface; 17. Consolidation grouting layer. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] like Figures 1 to 4The diagram shows a gravity dam foundation treatment structure for soft rock foundation conditions in a strong earthquake zone. A strong earthquake zone generally refers to an area with frequent and intense seismic activity. Based on historical earthquake records, it is an area likely to experience destructive earthquakes of intensity ≥ VII (7 degrees) or higher. Soft rock refers to rock with low strength, easy weathering, and easy softening or plastic deformation upon contact with water; its engineering mechanical properties are between those of hard rock and soil. It generally refers to rock strata with a uniaxial compressive strength of less than 30 MPa, characterized by easy deformation, softening upon contact with water, easy weathering, and low self-stability. Common soft rock types include mudstone, shale, weathered sandstone, tuff, and coal-bearing strata. A gravity dam is a large-volume water-retaining structure constructed of concrete or stone. Its basic cross-section is a right-angled triangle, and the entire structure consists of several dam sections. Under water pressure and other loads, the gravity dam mainly relies on the anti-sliding force generated by the self-weight of the concrete dam body 1 to meet stability requirements, while simultaneously relying on the pressure generated by the self-weight of the dam body to offset the tensile stress caused by water pressure to meet strength requirements. Cast-in-place piles (6) are piles made by rotary drilling followed by pouring reinforced concrete into the hole. They are a commonly used foundation treatment method, primarily used to reinforce soil or rock layers to improve the bearing capacity and stability of the foundation. These piles can be used individually or arranged in rows or grids to form a stronger foundation support system. According to the "Engineering Rock Mass Classification Standard" (GB 50218-94), rock masses are classified into five categories based primarily on rock strength, rock mass integrity, and structural characteristics. In this scheme, rock masses below the three-category boundary line (3) include Class I, Class II, and Class III rock masses.

[0027] like Figure 1 As shown, after excavation downwards from the original ground line 2, a concrete dam 1 is constructed, located below the original ground line 2. Water flows to the right as indicated by flow direction 7. Several cast-in-place piles 6 are installed at the bottom of the concrete dam 1. Figure 2 As shown, the concrete dam body 1 has a dam heel 11 facing upstream of the water flow and a dam toe 12 facing downstream of the water flow. Generally, the length of the dam heel B1 is about 3 to 8 m, and the length of the dam toe B2 is about 3 to 8 m. The ratio between the dam heel height H1 and the dam heel length B1 of the dam heel 11 is preferably in the range of 1.5 to 2, and the ratio between the dam toe height H2 and the dam toe length B2 of the dam toe 12 is preferably in the range of 1.5 to 2, thereby preventing stress concentration at the dam toe 12 and the dam heel 11.

[0028] Cast-in-place piles 6 are installed at the bottom of the dam heel 11, the bottom of the dam toe 12, the bottom of the middle section of the concrete dam body 1, and in the downstream potential slip surface area. The piles are densely arranged at the bottom of the dam toe 12 and the bottom of the dam heel 11, with a spacing of 2m to 4m between piles. At the bottom of the middle section of the concrete dam body 1 and in the downstream potential slip surface area, the piles can be evenly distributed, with a spacing of 6m to 10m between piles.

[0029] Cast-in-place piles 6 extend vertically downwards. These piles are C30 reinforced concrete rotary-dug piles. By distributing the load from the superstructure across multiple piles 6, the vertical stress on the dam foundation surface is evenly distributed, reducing the stress level at any single point and effectively improving the stress distribution at the foundation. Simultaneously, extending the piles 6 into the rock mass and through weak zones, their anchoring and shearing properties can cut off potential sliding surfaces within the foundation, effectively solving the deep sliding problem of the dam. Figure 1 As shown, the cast-in-place pile 6 extends downwards, passing through the deepest potential sliding surface 4 and the sliding surface with the minimum safety factor 5, reaching the boundary line 3 of the three types of rock mass. That is, the bottom of the cast-in-place pile 6 is directly fixed in the area of ​​the three types of rock mass, achieving stable fixation. The layout of the cast-in-place pile 6 can be analyzed based on the finite element deep anti-sliding numerical calculation, analyzing the area in the rock mass where the shear stress exceeds the shear strength, calculating the equivalent plastic strain when the foundation of the concrete dam body 1 reaches the ultimate failure, in order to analyze its potential sliding surface trend.

[0030] Taking rotary-dug cast-in-place piles of reinforced concrete as an example, the effects of rotary-dug cast-in-place piles on the stress distribution of the foundation of the concrete dam body 1 are as follows: 1. Relief of stress concentration: Rotary-dug cast-in-place piles can effectively disperse and transfer the load transmitted from the gravity dam. By setting multiple rows of rotary-dug cast-in-place piles in the foundation, the foundation stress originally concentrated in a certain area can be evenly distributed across multiple pile foundations, thereby reducing the local stress level of the foundation and avoiding dam foundation failure caused by excessive local stress. 2. Control of settlement: By rationally arranging rotary-dug cast-in-place piles and allowing the piles to penetrate deep into the ground, the underlying hard rock layer can be used as support, thereby effectively controlling the amount of foundation settlement and maintaining the balanced deformation of the dam body in all directions. 3. Improvement of foundation bearing capacity: Rotary-dug cast-in-place piles have a high single pile bearing capacity, which can significantly enhance the overall bearing capacity of the foundation, helping to ensure the stability of the gravity dam under various loads and preventing dam instability due to insufficient foundation bearing capacity.

[0031] Taking rotary-dug reinforced concrete piles as an example, the impact of pile 6 on the anti-sliding stability of the dam is as follows: 1. Increased friction: Rotary-dug piles enhance the connection between the concrete dam body and the foundation, increasing the shear strength parameters of the concrete dam body 1's base. Simultaneously, the pile 6 exhibits significant friction with the surrounding soil and rock, providing sufficient anti-sliding resistance. Furthermore, the pile 6 itself possesses strong shear strength, effectively resisting the sliding tendency of the concrete dam body 1 under horizontal thrust. 2. Enhanced anchoring effect: Rotary-dug piles can penetrate into a relatively intact bearing layer, forming an effective anchoring effect, thereby resisting external horizontal forces and reducing the risk of sliding. 3. Improved sliding surface conditions: Rotary-dug piles can cut off existing weak structural surfaces or any sliding surface along soft rock, altering its sliding path. Under the shear resistance of the pile foundation, the new sliding surface will move down to the hard rock layer. Since the hard rock layer has higher shear strength parameters and a longer sliding path, it can effectively resist the sliding tendency of the dam body.

[0032] Taking rotary-dug reinforced concrete piles as an example, the impact of cast-in-place piles 6 on the seismic resistance of the dam is as follows: 1. Enhanced foundation stability: The pile group formed by several cast-in-place piles 6 can improve the integrity of the concrete dam body 1 and the foundation, suppressing lateral slippage during earthquakes. 2. Improved dynamic response: The pile foundation of cast-in-place piles 6 can regulate the natural frequency of the dam-foundation system, avoiding resonance with the dominant seismic frequency and reducing the dynamic amplification effect. Simultaneously, the interaction between the piles and the soil surrounding the cast-in-place piles 6 can dissipate some seismic energy, mitigating dam vibration.

[0033] In summary, the synergistic reinforcement mechanism of cast-in-place pile 6 and consolidation grouting layer 91 in this scheme enhances the overall stability of the dam foundation through the dual effects of the bearing capacity of cast-in-place pile 6 and the grouting reinforcement of consolidation grouting layer 91, thus realizing a three-in-one bearing system of "pile-grouting-rock".

[0034] Figure 1 and Figure 3 The diagram shows the junction where the cast-in-place pile 6 intersects with the deepest potential slip surface 4. The cast-in-place pile 6 is divided into an upper pile foundation 61 and a lower pile foundation 62. The stress analysis is performed at the interface 63 between the pile foundation and the deepest potential slip surface. The horizontal bearing capacity of a single pile at this interface is greater than the shear force it bears. In other words, when the horizontal bearing capacity of a single pile at the interface 63 is greater than the shear force, it indicates that the penetration depth of the cast-in-place pile 6 through the deepest potential slip surface meets the requirements. The deepest potential slip surface 4 is located above the boundary line 3 of the three rock mass types, and the bottom of the cast-in-place pile 6 is located at least 2 meters below the deepest potential slip surface 4.

[0035] Figure 1 and Figure 4The diagram shows the structural layout at the junction of the concrete dam body 1 and the cast-in-place piles 6. The top surface of the consolidation grouting layer 91 is the foundation surface 9, which is tightly attached to the bottom of the concrete dam body 1. The reinforcing bars 64 of the cast-in-place piles 6 pass through the consolidation grouting layer 91 from bottom to top and extend into the interior of the concrete dam body 1, making the connection between the cast-in-place piles 6 and the concrete dam body 1 more stable. To better achieve the combined action of the dam body 1 and the cast-in-place piles 6, the concrete at the top of the cast-in-place piles 6 is embedded approximately 0.5m into the interior of the concrete dam body 1, and the reinforcing bars 64 of the cast-in-place piles 6 extend approximately 1.5m into the interior of the concrete dam body 1. The reinforcing bars 64 are distributed radially, and the construction process is strictly controlled to ensure sufficient vibration and compaction of the concrete, improving the uniformity and density of the dam body concrete. The consolidation grouting layer 91 is located below the concrete dam body 1, and its depth is generally 5-10m. An anti-seismic steel mesh 8 is installed above the top of the cast-in-place pile 6. The anti-seismic steel mesh 8 is installed along the direction of water flow and perpendicular to the water flow protection line. The height of the anti-seismic steel mesh 8 is about 50cm above the foundation surface 9. The anti-seismic steel mesh 8 can improve the integrity and stability of the concrete dam body 1 and the cast-in-place pile 6, and prevent the concrete dam body 1 from separating from the cast-in-place pile 6 during an earthquake.

Claims

1. A gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones, comprising a foundation surface (9), a consolidation grouting layer (91), cast-in-place piles (6), and a concrete dam body (1), wherein the concrete dam body (1) is located above the foundation surface (9), the consolidation grouting layer (91) is located below the foundation surface (9), and the cast-in-place piles (6) are located below the concrete dam body (1), characterized in that: The top of the cast-in-place pile (6) is fixedly connected to the bottom of the concrete dam body (1), and the bottom of at least one cast-in-place pile (6) is located below the boundary line (3) of the three types of rock mass.

2. The gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones as described in claim 1, characterized in that: The concrete dam body (1) includes the dam heel (11) and the dam toe (12). The bottom of the dam heel (11) is provided with cast-in-place piles (6), and the bottom of the dam toe (12) is provided with cast-in-place piles (6).

3. The gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones as described in claim 2, characterized in that: The ratio between the height (H1) of the dam heel (11) and the length (B1) of the dam heel (11) ranges from 1.5 to 2.

4. The gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones as described in claim 2, characterized in that: The ratio between the height (H2) of the dam toe (12) and the length (B2) of the dam toe (12) ranges from 1.5 to 2.

5. The gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones as described in claim 2, characterized in that: Cast-in-place piles (6) are installed at the bottom of the concrete dam body (1) in the area between the dam heel (11) and the dam toe (12).

6. The gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones as described in claim 2, characterized in that: Cast-in-place piles (6) are installed in the area of ​​the downstream sliding surface of the concrete dam body (1).

7. The gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones as described in any one of claims 1 to 6, characterized in that: The cast-in-place pile (6) is a reinforced concrete rotary cast-in-place pile.

8. The gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones as described in any one of claims 1 to 6, characterized in that: Including the deepest potential slip surface (4), which is located above the boundary line (3) of the three types of rock mass, the bottom of the cast-in-place pile (6) is located at a depth of at least 2m below the deepest potential slip surface (4).

9. The gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones as described in claim 8, characterized in that: The horizontal bearing capacity of a single pile at the junction of the cast-in-place pile (6) and the potential deepest slip surface (4) is greater than the shear force at the junction of the cast-in-place pile (6) and the potential deepest slip surface (4).

10. The gravity dam foundation treatment structure for soft rock foundation conditions in strong earthquake zones as described in any one of claims 1 to 6, characterized in that: It includes a seismic steel mesh (8), which is set above the foundation surface (9) along the direction of water flow and perpendicular to the direction of water flow.

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