Study on development and utilization scheme of underground river water resources in Shangba, Daozhen County, Guizhou Province

Yang xiuzhong 2, Pei 2, Wang 1, Zhang Lin 1, 2, feng fayan 2.

(1. Guizhou Geological Survey Institute, Guiyang 550004; 2. The Second Engineering Investigation Institute of Guizhou Bureau of Geology and Mineral Resources, Zunyi 563000)

The karst pipeline of Shangba underground river is developed in the limestone of Maokou Formation of Lower Permian, and the roof and floor are all extremely thick aquicludes, which have good boundary conditions for water storage and water resistance and conditions for building underground reservoirs. Shangba underground river not only has a large flow, but also has a large underground storage capacity. The research results show that the suitable damming section of the upper dam underground river pipeline is located at the throat confluence of two tributaries of the underground river, and the success of damming in this section is very certain. At the shoulders and bottoms of the two dams near the underground reservoir, due to the large thickness of the aquifer itself, small-scale caves and cracks were found during drilling, so slight karst leakage may occur. The treatment scheme is to carry out impervious curtain grouting on the dam axis and two abutments of the proposed underground reservoir.

Keywords: underground river; Karst water; Underground reservoir; Development and utilization conditions

1 basic geological survey

The proposed Shangba underground reservoir is located on the ridge on the west side of Longgang Valley in the middle section of Shangba underground river, extending in the northeast direction. The ridge elevation on the east and west sides of the valley is 1000 ~ 1200m, and the valley bottom elevation is 600~700m. The valley is a concentrated distribution area of farmland and population, and Yuxi Town and Daozhen County in Shangba Township are located in the valley (Figure 1).

The underground river karst pipeline in Shangba is controlled by geological structure and developed in the limestone of Maokou Formation of Lower Permian. Its bottom plate is shale of Hanjiadian Formation of Upper Permian, with a thickness of 432m, and its top plate is mud shale from Wujiaping Formation of Upper Permian to Yelang Formation of Lower Triassic, with a thickness of nearly 300m, all of which are good water-resisting layers and have good water storage isolation conditions.

The underground river forms underground runoff from SSW to NNE along the valley slope of Longgang Ridge, and is discharged from the surface at the Diaojiaolou in the eastern suburb of Daozhen County. The structural part belongs to the southeast wing of Daozhen syncline. The wing of syncline forms the ridge and valley slope topography, and the core forms the trough and valley topography and low-gentle karst hill topography. From east to west, the exposed strata are Miocene Hanjiadian Formation (S2hj), Lower Permian Qixia Formation and Maokou Formation (P 1q+M), Upper Permian Wujiaping Formation (P2w) and Changxing Formation (P2c), Lower Triassic Yelang Formation (T 1y) and Lower Triassic respectively. Blocked by the relative aquifuge of the underlying Hanjiadian Formation shale, Wujiaping Formation mudstone, argillaceous siltstone and flint banded limestone in the inferior limonite coal seam, the underground river pipeline develops along the SSW—NNE direction at the top of P 1Q+M, with the distribution elevation of the underground river of 680 ~ 1280 m, and the average hydraulic gradient of the underground river is about 37.5‰, which is located in Mount Kumgang. Among them, the length of the main tributary underground river pipeline on the east side is more than 7km, and the length of the tributary pipeline on the west side is more than 5km. The hydraulic gradient of the section of the proposed underground reservoir is about 18.7‰.

Figure 1 Communication Location Map of Shangba Underground River in Daozhen County

1- county government residence; 2- Residents of regional offices; 3- Resident of township government; 4- every village is connected; The boundaries of five districts; 6- Rural borders; 7- trunk highway; 8- feeder roads; 9- Shangba underground river; 10- water system

2 characteristics of underground river system

The karst basin of Shangba underground river in Daozhen County covers an area of 38.6km2, and the recharge area of the proposed Shangba underground reservoir is 18km2, which is composed of water-bearing strata such as Daozhen syncline T 1y, P2c, P2w, P 1Q+M and S2hj. The system boundary consists of P2w yellow-green, brown and black-gray shale, clayey limestone, calcareous mudstone and coal-bearing seam. The waterproof floor is composed of mottled shale, mudstone, sandstone and silty claystone such as S2hj purplish red and grayish green. The boundary of underground river karst basin system is complete, forming an independent underground river recharge, drainage and drainage system. Due to the development of high-angle tensile fracture F 1 from Nanyakou to the deep ditch of surface water rock in the southwest of the system, part of the karst cave pipeline water in the P 1m limestone aquifer is replenished to the karst cave aquifer in the middle and upper part of P2w along the side of the fault zone, forming a relatively open P2w secondary discharge boundary, and the lowest elevation of the open discharge boundary is 1030m. Below this elevation, the water-proof boundary composed of shale and sandstone with limonite layer at the bottom of P2w has good integrity and water-proof performance, and the flow through the F 1 fracture zone is 35 ~ 65L/s ... which is relatively stable dynamically. The underground river system of Shangba is controlled by lithology and geological structure, and it is distributed in the slope zone of Linggu in the southeast of Longgang trough valley. The upper and lateral boundaries of the underground river system are composed of carbonate rocks P 1q+M and clastic rocks in the southeast wing of the Daozhen syncline. Underground rivers are developed in P 1Q limestone, and pipeline runoff is formed in thick P 1m and massive limestone along the strike. The middle and upper reaches of the Shangba underground river are distributed at an altitude of 945 ~ 1280 m, and its system structure characteristics and boundary conditions are very clear (Figures 2 and 4).

Figure 2 Hydrogeological Profile of Shangba Underground River in Daozhen County

1-limestone; 2- sandstone; 3- shale; 4- Underground river pipeline; 6— Stratigraphic code; 7— Karst shaft; 8- section direction

3 development and utilization conditions of Shangba underground river

Fig. 3 schematic diagram of longitudinal section of karst main pipeline in the middle and upper reaches of Shangba underground river.

The underground river of Shangba is located between the elevation of the existing diversion tunnel of Shangba and the elevation of Meijiang exit, with a straight line distance of 8.75km, a drop of 300m and an average hydraulic gradient of 365,438 0 ‰. If an underground river pipeline is detected in a section with a length of 8.55km, and the position fluctuation of the underground river hydraulic bucket is found out, a diversion tunnel can be dug at P2c limestone on the west side of the ridge, and P2w coal measures strata can be exposed to P650 at a proper position above the bucket. Because the underground reach in the middle reaches is composed of two parallel branch pipes, which are distributed in the gallery of the water hall and the karst pool, the development length and scale are large, which is beneficial to the regulation and storage of underground reservoirs. It is estimated that the length of diversion tunnel is only about 450 ~ 500 m to achieve the goal. It can make full use of the favorable conditions that the height difference between the underground riverbed and the Shangba Valley is 240 ~ 300 m, covering Shangba Township and Yuxi Town in Daozhen County, and solving the contradiction between supply and demand of drinking water for people and livestock and industrial water. Implement centralized irrigation protection of farmland.

Fig. 4 Structural model of karst groundwater system

The underground river karst pipeline in Shangba is developed in the limestone of Qixia-Maokou Formation of Lower Permian, with the thickness of 465,438+065,438+0.2m. The mud shale at the bottom of Lower Permian and Hanjiadian Formation is 432m thick, and the mud shale at the top of Longtan Formation of Upper Permian to Yelang Formation of Lower Triassic is nearly 300m thick, all of which are good water-resisting layers. The dam site of the underground reservoir is planned to be 50m below the confluence of two underground river pipelines in Mount Kumgang (Figure 5). At the proposed dam site, the underground river space forms a long and narrow corridor with a tunnel width of 13 ~ 16m and a tunnel height of 25 ~ 27m. The cave wall is smooth, and the rock occurrence is 3 15 ~ 320. The design dam type of Shangba underground reservoir is concrete plug dam, with a dam width of 14m, a dam height of 25m, a dam thickness of 5m and a designed maximum head of 84m in front of the reservoir. The underground reservoir has good engineering geological conditions.

Fig. 5 Schematic diagram of development and utilization of underground river in Shangba.

3. 1 storage conditions and storage space

When the underground reservoir is blocked in the underground river, the underground water storage space is mainly the underground river pipeline, followed by the karst caves and cracks in the water-bearing medium. Karst is relatively developed between 950 ~1000 meters, but it is very weak at 900 meters. Therefore, we can use the geometric generalization method of underground river water storage space to evaluate and estimate the underground water storage capacity of the above section (Figure 6). The calculation formula is:

V=V 1+V2

Where: v-underground storage capacity (m3);

V 1- volume of underground river pipeline (m3);

v 1 = h B L/2；

V2—— volume of cavity of rock mass submerged by backwater (m3),

V2=h b Lμ/2

H—— water depth in front of underground reservoir dam (m);

B—— average width of underground river pipeline, in m;

L—— backwater length (m);

B—— width of recharge runoff zone of karst aquifer (m);

μ —— Water supply or karst rate of karst water body.

Fig. 6 Schematic diagram of underground storage capacity estimation

According to the preliminary investigation, the total length of the two branch pipes under the upper dam and above the proposed underground dam is 16.4km. According to the change of the underground river pipeline, the underground storage capacity is the underground river pipeline section with a total drop of less than 60m on the dam, with an average tunnel width of 40-3535m and a tunnel height of 15- 120m ... According to the formula (/kloc) In addition, according to rough statistics, if the volume karst rate μ = 0.03, the average width is 2 16m, and the average head height is 2500m, the storage space of underground river is about 972,000m3. The total storage capacity of underground reservoir V 1+V2 can reach 3.8 million m3. Similarly, the flow attenuation equation (table 1) is used to calculate the consumption of groundwater storage capacity of karst pipeline in dry season of underground river, and the modulus ratio of reservoir height is made, and the underground storage capacity is estimated to be 3.8 million m3 according to V storage capacity /2.

Table 1 Calculation Table of Groundwater Flow Attenuation in Shangba Underground Reservoir

Note: Qt = Q0e-ATA = (logq0? logQt)/0.4343×(TN-t0)； The continuous attenuation time of one-time rainfall is t = 3 1 day.

3.2 Analysis of leakage conditions of underground reservoirs

The water conveyance pipeline of Shangba underground reservoir is located in limestone of Permian Qixia Formation and Maokou Formation. Qixia Formation and Maokou Formation are karst-developed, with karst fissures and caves, and groundwater flows out in the form of springs in the suburbs, with a large flow. On the west side of the water storage pipeline layer is the Permian Wujiaping Formation, which is relatively isolated from water. It should be said that the water level rose by an average of 39.5m, and after the highest rise of 79m, the leakage condition in the reservoir area did not exist. Except that the tensional and torsional fractured karst cave area of the standard water rock at the tail of the reservoir area is at 1030m, and leakage will occur above the elevation, through the preliminary exploration in the preliminary design stage, the groundwater leakage in the reservoir area is estimated to be about zero. The karst hydrodynamic conditions of underground river pipelines often play a decisive role in the leakage of underground reservoirs. Because the underground river is located in the thick limestone layer of monoclinic structure, the development direction of karst underground river pipeline is mainly along the NNE direction and along the dip angle of strata. According to the analysis of drilling data, when drilling ZK 1 exposed extremely thick limestone section with the elevation of P 1m962.5 ~ 936m, three small karst caves less than 0.7m3 were found, which were isolated and connected by stratum solution fractures. Based on this, it can be inferred that the scale and possibility of horizontal development of karst pipelines along the vertical strata except underground rivers are extremely small, and its development conditions are mainly controlled by geological structures and lithological conditions. The S2hj shale with rock dip angle of 26 ~ 35 has good waterproof conditions under the limestone aquifer P1Q+M. At the top of the P 1q+m limestone aquifer, the upper Permian Wujiaping Formation (P2w) coal measures stratum is 258m thick, and the argillaceous siltstone is 42.6m thick, with argillaceous limestone, clayey rock and limonite, which has good water blocking conditions. The strata and geological structures in the area are relatively stable, and there is no obvious transverse tensile fault distribution on the surface, so the possibility of karst pipeline and karst leakage along the aquifer roof is extremely small. In addition, because the main karst pipeline (right pipeline) of the underground river is located above the confluence of two tributaries of the underground river, there is basically no big crack point in the proposed reservoir area, and there is no large seepage low trough landform development in the vertical direction of the rock stratum. The water-resisting section of P2w sandstone mudstone is completely exposed, and the occurrence of the rock stratum is stable, and there is no double-layer or multi-layer karst pipeline development in the vertical direction. This is especially true downstream after the confluence of two tributaries. The side wall of the pipeline is smooth and upright, the riverbed is shallow, and the siltation thickness is 0.8 ~ 0.6m The siltation is mainly sand, pebbles and a small amount of silt, and the riverbed is hard and complete. According to the trace of the flood level line of the underground river pipeline in the middle and upper reaches, the perennial flood level can flood the underground river and the main karst cave pipeline, while the flood level with the return period of more than 10 years leaves a trace at the bottom of the skylight shaft, which shows that there is no large hidden karst leakage channel in the underground river section, and neither centralized karst pipeline leakage nor decentralized karst pipeline leakage will occur, so there will be no leakage problem in the adjacent valley. Therefore, the dam site and reservoir area are selected in this section, and there will be no major leakage problem. However, after the normal storage of the reservoir, there may be slight surface cracks and leakage. It is predicted that in the future, leakage may occur under the dam and the left abutment, and the leakage amount is less than 0.5% of the reservoir water. According to the comprehensive analysis of the above-mentioned underground reservoir leakage, the possible leakage areas of underground river pipelines are mainly distributed under the intersection of two tributaries of underground river and near the entrance of underground river undercurrent (presumably a large crack point). Only underground river and karst cave pipelines in this area have the conditions of large hydraulic gradient and deep pipeline development. Although there are water-resisting layers and relative water-resisting layers, the aquifer itself is very thick, with large caves and cracks in the middle. In particular, it is possible to form dispersed subsurface flow zones of interlayer corrosion cracks through the joints and interlayer cracks of rock strata, and these dispersed seepage zones are more than 60m away from the dam of the reservoir, and most of them are filled and cemented by clay and river sand at the bottom of the underground river bed. According to the analysis of simple water pressure test, the water absorption ω of accumulation layer and P2w rock stratum is small, generally the water absorption ω of sand shale is less than 0.01~ 0.03l/min m2, and the water absorption ω of marl with shale is 0.05 ~ 0.08 L/min·m2 and 0.06 ~ 0.30 L/min·m2 (Table 2), and the water permeability q is generally less than. Of course, based on the initial determination that the average depth of the grouting curtain line at the head of the reservoir is 70.0m and the area is 9 1700.0m2, it is still necessary to adopt advanced investigation methods to further carry out more detailed engineering geological exploration, verify the karst leakage with objective and scientific data, supplement and correct the grouting scheme, and determine the dam site for blocking the hole.

Seepage prevention treatment scheme: it is suggested to carry out seepage prevention curtain grouting treatment in the dam area. The impervious curtain is arranged at the head of the reservoir, and it is arranged in an arc shape according to the topography and karst leakage. The design length of the curtain is 250m, and the curtain grouting drilling should be carried out within 5m of the dam abutment, the fluctuation zone of groundwater level under the dam and the seasonal fluctuation zone of groundwater level, and the water permeability should be below 10lu. Polymer cement mortar should be used as grouting material, and double-liquid grouting pump pipe should be used for comprehensive subsection grouting. According to preliminary estimation, the impervious grouting area is 1250m× 104m.

Table 2 Statistical Table of Rock Permeability Test Characteristics

4 engineering geological characteristics and problems worthy of attention

4. 1 engineering geological characteristics

The P 1Q+M limestone aquifer in the underground reservoir area is a gently inclined rock stratum, which is a hard engineering geological rock stratum. The roof and floor of this rock stratum (east and west sides) are mud shale and belong to soft rock stratum. At the same time, the stratum in this area is complete and there is no fault development. The combination of structure and stratum lithology and the characteristics of underground river development are extremely beneficial to the construction of underground reservoirs. According to the preliminary investigation results, the roof, floor and cave walls on both sides of the underground river pipeline are formed by natural dissolution of carbonate rocks, and the cross section of the cave is naturally balanced arch. The extremely thick layer and massive limestone of Maokou Formation have high compressive and shear strength, and the uniaxial saturated compressive strength of fresh rock is greater than the shear strength, which meets and exceeds the design requirements and is beneficial to the stability of the dam.

According to the cave survey, the cave wall of the proposed dam site at the throat junction of two underground rivers is straight and smooth, the rocks are fresh and complete, the bedding cracks and suture lines develop and extend in the same direction, only a group of vertical joints are developed, the joint occurrence is 200 ∠ 66, and the dissolution cracks in the tunnel section are not developed. However, in the two tributaries of the underground river and the tunnel section between them, joints and cracks are developed, and the rock occurrence is 365,438+00 ~ 325 ∠ 24 ~ 35, mainly 65,438+005 ~ 65,438+05 ∠ 68. These fractures control the development direction of dissolution fractures in P 1m thick massive limestone and extremely thick limestone, which makes the interweaving of structural network, dissolution fractures and suture complex, that is, there are "X" type torsional joints and tensile joints, which together with bedding fractures (suture lines) form an "M" type structural joint network. The development degree of each group of joints is different, which often makes a group of joints cut intermittently, making its direction different. Its tensile joints develop along a pair of X-shaped torsional joints, and the trend changes greatly. According to the observation and comparison of ground and underground caves in several sections, it is proved that the development of joint cracks obviously weakens or even disappears with the deepening of depth. The width of the small structural fracture zone in the area is thick and thin, the scale of interlayer dislocation is generally short, and the horizontal downward continuation is not deep.

4.2 Noteworthy issues

Small compression-torsion faults and interlayer dislocation are occasionally seen in the middle of Wujiaping coal measures stratum on the surface, but the fault distance is only 15 ~ 35m. According to the profile observation of diversion tunnel, the structural planes of small cracks are dense, which become gentle and undulating near the surface, and often produce secondary small folds, which make thick weathered layers appear in the weak engineering geological rock groups on the surface and complicate the engineering geological conditions of rock masses. Although there are thick water-resisting strata on both sides of P 1Q+M water-bearing strata in the reservoir area, which have good water-resisting boundary conditions, the water-bearing strata themselves are thick, with the thickness of 297.0 ~ 486.0 m, and the underground reservoir area has strong karst water-bearing strata, dense vertical and horizontal pipelines and caves, especially the axis of 1 # groundwater diversion tunnel. The surface fissures with the development direction of 3 15, cutting depth of 30 ~ 50m and slope angle of 25 ~ 35 develop dense zones, which make the thickness of the mountain thinner, and may become a way to slightly disperse karst leakage to the limestone section at the bottom of Wujiaping Formation after water storage in the underground reservoir area in the future. Should be particularly noteworthy.

5 Conclusions and suggestions

5. 1 conclusion

(1) In Daozhen County, the ridge of the valley of the Xiaba River extends in the northeast direction, with the ridge elevation on the east and west sides of the valley 1000 ~ 1200m and the valley bottom elevation of 600~700m. Yuxi Town and Daozhen County in Shangba Township are located in this valley, with relatively concentrated farmland and population distribution. The underground river karst pipeline in Shangba is developed in the limestone of Maokou Formation of Lower Permian, and its bottom plate is shale of Hanjiadian Formation of Upper Permian, with a thickness of 432m, and its top plate is shale of Wujiaping Formation of Upper Permian to Yelang Formation of Lower Triassic, with a thickness of nearly 300m, all of which are good water-resisting layers and have good conditions for water storage isolation and underground reservoir construction.

(2) The recharge area of Shangba underground river is 38.6km2, and the catchment area of Shangba underground reservoir is 18km2. The underground river is composed of two branch pipes, with a total length of 25.2km. In dry season, the minimum discharge at the outlet of the underground river is 0. 1 1m3/s, and the multi-year average discharge is 0.3321m3/s. The multi-year average groundwater runoff modulus of the proposed underground reservoir basin of Shangba Underground River is m =18.45l. The width of the cave in the underground section of the Upper Dam is 10~80m ~ 80m, and the height is 20 ~ 65438. According to the karst rate of 3%, the space of karst pipes, shafts, sinkholes, skylights and secondary fractured pipes in the water-bearing rock mass of underground river system is estimated. When the average backwater head height of karst pipelines and cracks is 60m, the storage capacity of underground reservoirs can reach 3.8 million m3. Therefore, the Shangba underground river not only has a large flow, but also has a large underground storage capacity. The annual average natural recharge of the proposed Shangba underground reservoir basin is1047.120×104m3/a, and the annual average natural runoff is1047.3105×104m3/a.

(3) The conclusion of comprehensive evaluation of the environmental engineering geological conditions of Shangba underground reservoir is that Shangba reservoir has the conditions for building dams and reservoirs, and the topographic geological conditions of the dam site are good, so it is appropriate to build cork concrete plug dams. Tensile fault structures are developed in the gully at the left end of the upstream of the reservoir area. When the groundwater level rises to 1030m, the reservoir water will leak from it, so the normal water level is set as 1030m. After the elevation control, it is preliminarily estimated that the storage capacity can reach 3.8 million m3 and the elevation of the dam bottom is 946.0m, so the maximum water pressure at the dam bottom is 0.84MPa.

(4) It is preliminarily found that the areas where the underground river pipeline in Shangba may leak are mainly distributed below the confluence of the two tributaries of the underground river and near the entrance of the underground river (presumably a large crack point). Only the underground river and karst cave pipelines in this section have the conditions of large hydraulic gradient and deep pipeline development. Although there are water-resisting layers and relative water-resisting layers, the aquifer itself is very thick, with large caves and cracks in the middle. In particular, it is possible to form dispersed subsurface flow zones of interlayer corrosion cracks through the joints and interlayer cracks of rock strata, and these dispersed seepage zones are more than 60m away from the dam of the reservoir, and most of them are filled and cemented by clay and river sand at the bottom of the underground river bed. According to the analysis of simple water pressure test, the unit water absorption of accumulation layer and P2w rock stratum is small, and the ω of sand shale is generally less than 0.01~ 0.03l/min m2, and the ω of marl with shale is 0.05 ~ 0.08 L/min·m2, 0.06 ~ 0.30 L/min·m2 (Table 2), and the water permeability Q is average.

(5) The underground storage capacity of the upper dam in Daozhen County can be increased by 3.6 million m3 by blocking the dam. According to the annual runoff of underground river, the average allowable exploitation resources of Shangba underground river for many years are1047.3105×104m3/a. This project takes advantage of the characteristics of high riverbed position, large natural flow and strong underground storage capacity of Shangba underground river. A dam fence is built at the throat joint of two pipelines in the underground river pipeline to store groundwater, and a large underground reservoir is formed by using underground space to store groundwater output. Tunnel water diversion is adopted, and the height difference of 240 ~ 300 m is fully utilized, and gravity water diversion covers the valley of Daozhen County and its surrounding water-deficient areas. After the completion of this project, the farmland in Shangba and Yuxi areas can be irrigated 1.067 hm2, including paddy field of 596hm2, dry land irrigation and partial farmland conversion of 47 1 hm2, and returning farmland to forest and grassland, grassland and grassland, grassland and grassland, grassland and grassland, grassland and grassland. Returning grass to grass, returning grass to grass, returning grass to grass, returning grass to grass to grass, returning grass to grass to grass to grass to grass, returning grass to grass to grass to grass, returning grass to grass to grass to grass to grass, returning grass to grass to grass, and returning grass to grass, through the implementation of the project, on the one hand, the poor and backward economic situation in this area has been thoroughly improved, on the other hand, it has set a model for the development of karst groundwater in karst mountainous areas of ridges, hills and valleys and provided experience for the comprehensive improvement demonstration of karst ecological and geological environment.

5.2 Suggestions

(1) According to the determined dam axis, find out the detailed development, distribution, extension length and crack filling of weathering and dissolution of bedrock in dam foundation, and accurately find out the location and quantity of karst leakage in dam area. Further find out the possible leakage problems under the dam, around the dam abutment and in the reservoir area, use the groundwater dynamics method and the principle of water balance to calculate the flow of the upper and lower reaches of the underground river, and carry out tracing verification, apply advanced scientific and technological methods and means to carry out comprehensive exploration and test analysis, and combine the indoor flume simulation test and numerical calculation of seepage model to accurately find out the leakage location, leakage path, leakage characteristics and leakage water quantity, and determine the leakage range and anti-seepage principles and methods.

(2) As soon as possible, we will continue to comprehensively investigate the multi-stage karst seepage channel on the right bank of the underground reservoir dam area, especially the y006 branch tunnel system, implement the Quaternary loose sediment mountain project and the light drilling and exploration project in the cave, and submit the technically feasible and economically feasible seepage prevention scheme before the dry season.

(3) Carry out in-situ testing of dam foundation rock mass, accurately obtain the mechanical parameters of rock/rock, rock/concrete joint fracture structural plane, analyze the unfavorable factors of stability and deformation of concrete dam, and quantitatively calculate and evaluate the engineering geological stability of rock mass.

(4) Further compare and select the impervious curtain line, reasonably determine the end point of the impervious curtain, and formulate detailed impervious curtain grouting scheme and measures. In strict accordance with the relevant rules and regulations of water conservancy and hydropower, geological engineering construction treatment such as anti-seepage curtain grouting and plugging is carried out to effectively prevent seepage and plugging. Ensure that the clay and concrete block fillers in the caves and cracks near the dam foundation and abutment are not washed away and the uplift pressure is not allowed to increase during the operation of the underground dam, so as to ensure the safe operation of the underground dam and the normal water storage of the underground reservoir.