Dam foundation altered rock mass reinforcement structure and its construction method

Abstract

This invention relates to a structure and construction method for reinforcing altered rock masses in dam foundations. The purpose of this invention is to provide a simple, stable, adaptable, and convenient structure and construction method for reinforcing altered rock masses in dam foundations. The technical solution of this invention is: a structure for reinforcing altered rock masses in dam foundations, used to reinforce dam foundations with fault zones and geological defects in the altered rock masses. Its characteristic is that it has grooves excavated on the foundation surface of the dam foundation corresponding to the underlying fault zones and altered rock masses. Concrete is backfilled into the grooves to form concrete plugs, and the area of ​​the backfilled concrete is reinforced with cement grouting. This invention is applicable to civil engineering projects such as water conservancy and hydropower.

Description

Technical Field

[0001] This invention relates to a structure for reinforcing altered rock masses in dam foundations and its construction method. It is applicable to civil engineering projects such as water conservancy and hydropower. Background Technology

[0002] Fault zones are areas of relatively concentrated strain within the Earth's crust and are also primary sites for the accumulation and activity of geological fluids. Under the influence of tectonic activity and fluids, rocks within fault zones often undergo varying degrees of fragmentation and deformation, resulting in significant changes in their mineral composition and microstructure.

[0003] Due to complex geological conditions, water conservancy and hydropower projects often have fault zones (or weak interlayers, fracture zones) of a certain scale in the dam foundation. If these fault zones are located in the shallow surface of the dam foundation, the treatment plan is relatively conventional and the implementation difficulty is generally not high. However, if these fault zones have a steep dip angle and extend deep into the dam foundation, or even if rock alteration occurs along the fault zone, it will greatly damage the integrity of the rock and cause the formation of new clay minerals such as chlorite and montmorillonite, leading to a rapid deterioration of the physical and mechanical properties of the dam foundation rock. This has a significant impact on the safe operation of the project and is a prominent engineering and technical challenge in dam foundation treatment in water conservancy and hydropower projects.

[0004] For example, a moderately dipping fault (55-65°) exists in the lower third of the left bank foundation of a concrete arch dam in a certain project. This fault obliquely cuts across the river, typically 10-20 cm wide, and is filled with breccia, altered rock, and rock fragments. The surface is smooth and straight. Altered rock masses are distributed along both sides of the fault plane, with a thickness of 0.2-1.5 m in the hanging wall and 0.6-2.6 m in the footwall. The alteration zone is dominated by breccia, schist, and rock fragments, with localized tectonic lenses and cleavage zones. Multiple striations are present, and compression characteristics are significant. The shallow surface of the alteration zone shows severe iron-manganese staining. The uniaxial saturated compressive strength of the altered rock mass is 20-40 MPa, classifying it as Class IV rock mass. This type of fault zone and altered rock mass negatively impacts the dam foundation's bearing capacity and deformation control, and may become a relatively concentrated seepage channel or cause localized seepage failure. Therefore, prudent foundation reinforcement measures must be taken.

[0005] Currently, the reinforcement of altered rock masses in dam foundations generally involves grouting with suitable chemical grouting materials to improve the integrity, mechanical strength, and seepage prevention performance of the dam foundation rock mass, striving to meet various design specifications. Chemical grouting not only places high demands on grouting materials (requiring indoor testing to select suitable chemical grouting materials, as well as on-site production testing for verification), but also significantly increases the amount of foundation treatment and construction period, resulting in a substantial increase in project investment. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a simple, stable, adaptable and convenient dam foundation altered rock mass reinforcement structure and its construction method, in view of the above-mentioned problems.

[0007] The technical solution adopted in this invention is: a dam foundation altered rock mass reinforcement structure, used to reinforce dam foundations with fault zones and geological defects in altered rock masses, characterized in that: it has grooves excavated on the foundation surface of the dam foundation and corresponding to the fault zones and altered rock masses below, the grooves are backfilled with concrete to form concrete plugs, and the area of ​​the backfilled concrete in the grooves is reinforced with cement grouting.

[0008] The depth of the groove is determined according to 1.0 to 1.5 times the width of the fault zone and the altered rock mass, and the upstream and downstream excavation slope ratio of the groove is determined according to the dip angle of the fault zone.

[0009] The concrete plug is provided with reinforcing bars and steel mesh corresponding to the grooved groove wall and the foundation surface of the dam.

[0010] The reinforcing bar adopts 300cm long, 200cm embedded in the rock; the steel mesh is made of

[0011] The grooved backfill concrete area is reinforced with cement grouting, which includes two parts: intensified and deepened grouting of the original foundation and grouting of the shallow surface layer affected by the grooved excavation, blasting, and unloading relaxation.

[0012] The spacing between the grouting holes in the anti-seepage curtain of the dam is increased in areas where it is close to the fault zone and altered rock mass.

[0013] The dam's drainage holes maintain a certain distance from the fault zone and altered rock mass.

[0014] A construction method for the reinforcement treatment structure of the altered rock mass of the dam foundation, characterized in that:

[0015] Excavation and grooving;

[0016] After the grooved foundation surface passes inspection, backfilling and grouting will be carried out.

[0017] Reinforce the area of ​​the grooved backfill concrete with cement grouting;

[0018] In areas where the fault zone and altered rock mass are close to the anti-seepage curtain, the spacing between the curtain grouting holes should be increased.

[0019] In areas where the fault zone and altered rock mass are close to the seepage prevention curtain, reduce the depth of the drainage holes and adjust the angle of the drainage holes to maintain a certain distance between the drainage holes and the fault zone and altered rock mass.

[0020] The excavation and grooving include:

[0021] Precision pre-splitting controlled blasting construction was carried out using industrial electronic detonators. The dam foundation pioneer slot bottom vibration isolation and horizontal pre-splitting forming technology were adopted. Small-charge, multi-zone weak-grooving excavation and blasting were carried out for local unfavorable geological areas. When the groove depth was not large, the breaker hammer was used directly for chiseling.

[0022] The reinforcement of the backfill concrete area with cement grouting includes:

[0023] ①After the backfill concrete reaches 50% of its design strength, concrete cover grouting is performed on the 0-20m section of the backfill concrete section of the trench.

[0024] ② For the 0-4m section of bedrock surface in the backfill concrete section of the trench, re-drill holes between the concrete cover consolidation grouting holes and lay the lead pipe to the corner of the dam or other locations as instructed by the supervising engineer.

[0025] ③ After the concrete pouring height of the upper dam reaches 30m and 3 days after the grouting of the transverse joints of the corresponding dam section is completed, the concrete cover and grouting pipe will be grouted.

[0026] The beneficial effects of this invention are as follows: This invention achieves foundation treatment by using a "concrete plug + reinforced cement grouting + drainage adjustment" reinforcement structure and its construction method, reducing on-site implementation difficulty, ensuring construction quality, saving project investment, and ensuring safe project operation. This invention effectively reinforces geological defects such as large-scale, long-extending fault zones and altered rock masses within the foundations of concrete structures, ensuring foundation bearing capacity, deformation control, and the effectiveness of anti-seepage curtain grouting. It minimizes foundation deformation and leakage, features a simple structure, is safe and reliable, has strong applicability, improves construction efficiency, accelerates foundation reinforcement project progress, saves project investment, and has strong promotional value. Attached Figure Description

[0027] Figures 1-3 This is a schematic diagram of the structure of an embodiment.

[0028] In the diagram: 1. Groove; 2. Concrete chamber; 3. Reinforcing bar; 4. Reinforcing mesh; 5. Pipe. Detailed Implementation

[0029] This embodiment describes a dam foundation altered rock mass reinforcement structure, used to reinforce dam foundations with geological defects such as fault zones and altered rock masses. It includes excavating grooves formed on the foundation surface of the dam foundation that correspond to the positions of the fault zones and altered rock masses below. The groove depth is determined according to 1.0 to 1.5 times the width of the fault zones and altered rock masses, and the upstream and downstream excavation slope ratio of the groove is determined according to the dip angle of the fault zones.

[0030] In this example, the groove is backfilled with concrete to form a concrete plug. The concrete plug contains reinforcing bars and a steel mesh corresponding to the groove wall and the dam foundation surface. The reinforcing bars are generally made of... 300cm long, 200cm embedded in the rock; the reinforcing mesh is generally made of...

[0031] In this embodiment, the backfill concrete area of ​​the groove is reinforced with cement grouting, which includes two parts: denser and deeper (with cover) grouting of the original foundation and grouting of the shallow surface layer affected by the blasting and unloading relaxation of the groove excavation. The spacing and depth of the denser and deeper grouting need to be determined through calculation and analysis based on the dam foundation stress and deformation requirements. The grouting pipes generally penetrate to a rock depth of 4m, with a spacing of 1.5m and a row spacing of 3m (denserification as needed). The grouting pipes generally cover an area approximately 3m beyond the groove excavation area. The grouting pipes use a circulating method, typically combining 3-5 holes into one pipe.

[0032] In this embodiment, considering the needs of dam foundation seepage prevention and drainage, the spacing of the grouting holes in the curtain is increased in areas where the fault zone and altered rock mass are close to the seepage prevention curtain, and the grouting pressure is appropriately increased to further improve the seepage prevention curtain effect in the altered rock mass area. Simultaneously, to prevent seepage damage to the altered rock mass, the depth of the drainage holes is reduced in areas where the fault zone and altered rock mass are close to the seepage prevention curtain, and the angle of the drainage holes is adjusted so that the distance between the drainage holes and the fault zone and altered rock mass is not less than 8m (this distance is determined based on the allowable permeability gradient).

[0033] The specific construction method in this embodiment is as follows:

[0034] S01, Grooving excavation of fault zone and altered rock mass

[0035] To minimize the damage or impact of grooving excavation on the dam foundation rock mass, precise pre-splitting controlled blasting with industrial electronic detonators was employed. This involved using bottom vibration isolation and horizontal pre-splitting techniques in the dam foundation pilot slots, and small-charge, multi-zone, weak-grooving excavation blasting for targeted areas with unfavorable geological conditions. When the grooving depth was shallow, it was directly removed using a hydraulic breaker.

[0036] After the groove is excavated, reinforcing bars should be placed alternately along the groove wall in a timely manner. 300cm long, 200cm embedded in the rock, the steel mesh is generally made of...

[0037] S02, Backfill concrete

[0038] After the grooved foundation surface has passed inspection, backfill concrete pouring can be carried out on the grooved surface. The grade and mix proportion of the backfill concrete are determined as needed.

[0039] The concrete for the dam or superstructure should be poured only after the backfill concrete has cooled to the average ground temperature over many years. The contact surface between the backfill concrete and the superstructure concrete should be roughened or chiseled. The outer surface of the backfill concrete should be flush with the original foundation surface. The general pouring layer thickness is 3m (which can be adjusted appropriately according to the actual site conditions). The minimum interval between layers is 5 days, and the maximum interval between layers is 14 days. The pouring surface should be roughened or chiseled.

[0040] Several temporary construction joints can be arranged along the length of the groove, with a maximum spacing of 12m. The temporary construction joints need to be roughened and reinforced with dowel bars. L = 3m @ 1.5m × 1.5m, with 1.5m on each side of the seam.

[0041] The pouring temperature and maximum temperature of backfill concrete should be controlled as needed. Water cooling should be carried out when necessary, and the cooling process of concrete, as well as surface insulation, curing and protection requirements should be properly implemented.

[0042] Before backfilling with concrete, it is necessary to pre-embed holes for subsequent reinforcement grouting. Steel pipe.

[0043] S03, Strengthen cement grouting

[0044] The reinforced cement grouting within the grooved backfill concrete area includes two parts: grouting to densify and deepen the existing foundation (with a cover load) and grouting of the shallow surface layer affected by the grooved excavation, blasting, and unloading relaxation. Wet-ground cement is used as the grouting material. The grouting pressure is based on ensuring grouting quality and preventing harmful uplift of the concrete and rock surface. The cumulative uplift deformation value of the bedrock section is not allowed to exceed 200 μm, and the cumulative uplift deformation value of the concrete is not allowed to exceed 100 μm.

[0045] ① After the backfill concrete reaches 50% of its design strength, concrete cover grouting is performed on the 0-20m section of the backfill concrete section of the trench.

[0046] ② For the 0-4m section of bedrock surface in the backfill concrete section of the trench, re-drill holes between the concrete cover consolidation grouting holes and install lead pipes to the dam back corner or other locations as instructed by the supervising engineer.

[0047] ③ After the concrete pouring height of the upper dam reaches 30m and 3 days after the grouting of the transverse joints of the corresponding dam section is completed, the concrete cover and grouting pipe will be grouted.

[0048] S04. In addition, in accordance with the seepage prevention requirements of the dam foundation, the spacing of the grouting holes in the curtain should be increased in areas where the fault zone and altered rock mass are close to the seepage prevention curtain, and the grouting pressure should be appropriately increased to further improve the seepage prevention curtain effect in the altered rock mass area.

[0049] To prevent seepage damage to the altered rock mass, the depth of the drainage holes is reduced and the angle of the drainage holes is adjusted in areas where the fault zone and altered rock mass are close to the seepage barrier, so that the distance between the drainage holes and the fault zone and altered rock mass is generally not less than 8m (the appropriate distance for this location is determined based on the allowable permeability gradient).

Claims

1. A construction method for reinforcing altered rock mass in dam foundation, characterized in that: The dam foundation altered rock mass reinforcement structure is used to reinforce the dam foundation with fault zones and geological defects of altered rock mass. It has grooves excavated on the foundation surface of the dam foundation and corresponding to the fault zones and altered rock mass below. Concrete is backfilled into the grooves to form concrete plugs. The area of ​​the backfilled concrete in the grooves is reinforced with cement grouting. The grooved backfill concrete area is reinforced with cement grouting, which includes two parts: intensified and deepened grouting of the original foundation and grouting of the shallow surface layer affected by grooved excavation blasting and unloading relaxation. The construction method includes: Excavation and grooving; After the grooved foundation surface passes inspection, backfilling and grouting will be carried out. Reinforce the area of ​​the grooved backfill concrete with cement grouting; In areas where the fault zone and altered rock mass are close to the anti-seepage curtain, the spacing between the curtain grouting holes should be increased. In areas where the fault zone and altered rock mass are close to the anti-seepage curtain, reduce the depth of the drainage holes and adjust the angle of the drainage holes to maintain a certain distance between the drainage holes and the fault zone and altered rock mass. The reinforcement of the backfill concrete area with cement grouting includes: ①After the backfill concrete reaches 50% of its design strength, concrete cover grouting is performed on the 0-20m section of the backfill concrete section of the trench. ② For the 0-4m section of bedrock surface in the backfill concrete section of the trench, re-drill holes between the concrete cover consolidation grouting holes and lay the lead pipe to the corner of the dam or other locations as instructed by the supervising engineer. ③ After the concrete pouring height of the upper dam reaches 30m and 3 days after the grouting of the transverse joints of the corresponding dam section is completed, the concrete cover grouting pipe is carried out. The groove depth is determined according to 1.0 to 1.5 times the width of the fault zone and altered rock mass, and the upstream and downstream excavation slope ratio of the groove is determined according to the dip angle of the fault zone.

2. The construction method for the reinforcement structure of the altered rock mass of the dam foundation according to claim 1, characterized in that: The concrete plug is provided with reinforcing bars and steel mesh corresponding to the grooved groove wall and the foundation surface of the dam.

3. The construction method for the reinforcement structure of the altered rock mass of the dam foundation according to claim 2 is characterized in that: The reinforcing bars are Φ28@150×150cm, 300cm long, and 200cm embedded in the rock; the steel mesh is Φ28@25×25cm.

4. The construction method for the reinforcement structure of the altered rock mass of the dam foundation according to claim 1, characterized in that: The spacing between the grouting holes in the anti-seepage curtain of the dam is increased in areas where it is close to the fault zone and altered rock mass.

5. The construction method for the reinforcement structure of the altered rock mass of the dam foundation according to claim 1, characterized in that: The dam's drainage holes maintain a certain distance from the fault zone and altered rock mass.

6. The construction method for the reinforcement structure of the altered rock mass of the dam foundation according to claim 1, characterized in that, The excavation and grooving process includes: using industrial electronic detonators for precise pre-splitting controlled blasting construction; employing dam foundation pilot trench bottom vibration isolation and horizontal pre-splitting forming technology; and carrying out small-charge, multi-zone weak grooving excavation and blasting for local unfavorable geological areas. When the grooving depth is not large, it is directly removed by using a hydraulic breaker.

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