A method for preventing seepage in a karst depression catchment reservoir engineering

Abstract

This invention discloses a seepage prevention method in karst depression water collection and reservoir construction projects, employing a combination of grouting curtain and underground river sealing measures. The method includes: 1) hydraulic parameter acquisition; 2) underground river slope calculation: based on hydraulic parameters and the difference between the underground river outlet and inlet velocities, the overall underground river slope is calculated using different methods; 3) determining the location of the upper grouting tunnel; 4) determining the underground river sealing location based on the slope; 5) calculating the grouting curtain height based on the slope; 6) constructing the grouting tunnel and sealing the underground river according to the location of the upper grouting tunnel and the underground river sealing location; and 7) grouting curtain construction. This invention improves the determination of key parameters during construction in karst depression water collection and reservoir construction projects, thereby increasing the accuracy and efficiency of seepage prevention construction and saving construction costs.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering, and in particular to a method for anti-seepage curtains and underground river sealing during the process of water collection and reservoir formation in karst depressions. It provides a new approach to solving engineering-related water shortage problems in karst areas, specifically an anti-seepage method in water collection and reservoir formation projects in karst depressions. Background Technology

[0002] Karst regions, containing abundant soluble rocks such as calcium carbonate, develop dissolution fissures, caves, and underground rivers through the erosion of flowing water, resulting in a distinct dual structure of above-ground and underground water cycles. The representative karst region of southwestern my country is rich in rainwater resources; however, the large amounts of rainfall are rapidly lost through a well-developed groundwater system, leading to severe engineering-related water shortages for regional production and daily life. Therefore, engineering measures are needed to achieve the effective utilization of rainwater resources.

[0003] Enclosing rivers with dams to create lakes and reservoirs is a primary way to address water shortages. However, these mature water conservancy solutions are often ineffective in solving the problem of domestic and industrial water use in karst regions. Karst areas typically develop into mountainous regions with alternating peaks and forests, with very few plains. Water for domestic and industrial use is primarily found in karst depressions and surrounding areas. Rivers in these regions are mainly small and medium-sized tributaries. Traditional damming methods face obstacles such as high costs, poor effectiveness, high energy consumption, and low returns. The main streams within the basin, through long-term erosion, have carved deep valleys, creating steep riverbanks with significant drops. Reservoirs built in these areas face high water extraction costs and are more effective at facilitating navigation and power generation than meeting domestic and industrial water needs. Therefore, addressing the water shortage problem in karst depression areas, utilizing engineered seepage prevention measures to collect and utilize rainwater resources has become a key focus of current water conservancy projects in karst regions. In particular, the engineering sealing of geological defects in karst seepage zones on deep river valley slopes and plateaus, utilizing the natural concave topography of karst depressions to form damless reservoirs, has become a research hotspot. Appropriate site selection can not only solve the water shortage problem in depression areas but also effectively benefit surrounding areas, offering significant advantages over traditional damming reservoir construction in terms of lower cost and higher regional adaptability. However, the engineering sealing of geological defects in karst seepage zones remains a crucial technical challenge in karst depression reservoir construction.

[0004] Currently, grouting curtain, horizontal seepage prevention, and underground river sealing are the main seepage prevention technologies in karst depression water collection and reservoir construction projects. Among them, grouting curtain and underground river sealing are key technologies for solving the leakage of karst geological layers around karst depressions. Grouting curtain is achieved by vertically injecting mortar and other seepage prevention materials into the karst geological mountains around the depression to seal the dissolution fissures. Underground river sealing is achieved by using underground underground river seepage prevention cross-section engineering measures connected to the depression. These two technologies can repair the main leakage channels below the design water level of the depression. Combined with horizontal seepage prevention on the surface of the depression, the purpose of water collection and reservoir construction can be achieved. However, current grouting curtain and underground river sealing technologies still face numerous challenges. While preliminary geological exploration can identify the main distribution areas of karst geological layers, the spatial distribution and size of solution cavities, and the main construction area, the primary issue to be addressed in actual construction is determining the height of the grouting curtain, the grouting spacing, and the location of the underground river sealing points. These parameters are crucial to the success of the sealing and cost control. Although high-density geological exploration combined with construction experience can improve the accuracy and success rate of construction, this undoubtedly increases project costs and suffers from low precision. Finding a reliable method has become a key focus of current technological research and development. During construction, underground rivers are usually inaccessible by humans, and measuring underground conditions and related parameters is extremely difficult. The necessary data can only be obtained by measuring relevant parameters in the surrounding area of ​​the depression and at the entrance and exit of the underground river.

[0005] In recent years, there has been considerable research on seepage prevention technologies related to karst depression water collection and reservoir construction projects, such as curtain grouting and river closure. For example, Chinese patent CN202210163631.X proposes a curtain grouting construction method for reservoirs in karst areas, which improves the hole forming process, curtain grouting method, and grouting pipe structure. Chinese patent CN202123449289.X proposes a grouting curtain structure for karst areas, which improves the grouting pipe setting, steel pipe pile setting, and grout injection process. Another Chinese patent CN201610434986.2 proposes a curtain grouting construction method for strongly karst strata, which improves the grouting effect and reduces unnecessary grout loss. While these technologies have addressed some aspects of the construction process for seepage prevention curtains and underground river sealing in karst depressions, and refined the construction process of grouting curtains, the problems in determining and setting key parameters for seepage prevention in grouting curtains and underground river sealing projects in karst depression water collection and reservoir construction remain unresolved. The determination of key parameters is inefficient and inaccurate, resulting in high construction costs and a significant impact on construction quality. Summary of the Invention

[0006] The purpose of this invention is to propose a seepage prevention method for water collection and reservoir construction projects in karst depressions, improving the determination of key parameters during construction to enhance construction accuracy and efficiency, and reduce construction costs. This invention achieves its purpose through the following technical solution: A seepage prevention method in a karst depression water collection and reservoir project employs a combination of grouting curtain and underground river sealing measures. A three-dimensional schematic diagram of the karst depression is shown below. Figure 1 The present invention includes the following steps: Step 1: Hydraulic parameter acquisition: The inlet and outlet of the underground river and the direction of the underground river in the depression to be constructed are investigated through field operations, and hydraulic parameters are measured and acquired. Step 2: Underground River Slope Calculation: Based on the hydraulic parameters obtained in Step 1, such as... Figure 2 As shown, when the ratio of the inlet velocity to the outlet velocity of the underground river is greater than or equal to a set threshold, the overall gradient of the underground river is calculated using formula (1); when the ratio of the inlet velocity to the outlet velocity is less than a set threshold, the overall gradient of the underground river is calculated using formula (2); the set threshold is 0.4~0.6. (1) In the formula: S It is the overall slope of the underground river; v 1 It is the inlet water flow velocity, in m / s; v 2 It is the outlet water flow velocity, in m / s; n 1 It is the inlet roughness; n 2 It is the export roughness; b 1 It is the width of the inlet river, in meters; b 2 It is the width of the river at the outlet, in meters; h 1 The depth of the river at the entrance, in meters (m); h 2 The depth of the river at the outlet, in meters (m). (2) In the formula: z1 is the inlet elevation, m; z2 is the outlet elevation, m; l It is the straight-line distance from the outlet to the inlet of the underground river, in meters (m); g is the acceleration due to gravity, in meters per second (m / s²). 2 ; Step 3: Determine the location of the upper grouting tunnel: such as... Figure 3 As shown, based on the location of the designed water level and the measured distribution range of karst geology, an upper grouting tunnel is selected above the designed water level, and the elevation of the upper grouting tunnel is determined. Step 4: Determining the location for sealing off the underground river: The location for sealing off the underground river is determined by the elevation of the sealing point. Hand the distance from the blockade point to the underground river outlet L The decision is made, and the calculation formula is as follows: (3) (4) In the formula: H It is the elevation of the underground river blockage point, in meters (m). z 3 It is the elevation of the upper grouting tunnel, in meters; S It is the overall slope of the underground river; d t It is the diameter of the upper grouting tunnel, in meters; L It is the distance from the blockade point to the outlet of the underground river, in meters (m). Step 5, Calculation of grouting curtain height: The calculation formula is as follows,

[0007] (5) In the formula: d It is the height of the grouting curtain, in meters (m). Step 6, as follows Figure 3 , 4 As shown, the grouting tunnel and the underground river closure are carried out according to the location of the upper grouting tunnel and the location of the underground river closure determined in steps three and four: the upper grouting tunnel is constructed above the designed water level; the lower grouting tunnel is constructed below the designed water level in a direction parallel to the upper grouting tunnel, and the lower grouting tunnel is perpendicular to the underground river on the horizontal plane. The intersection of the lower grouting tunnel and the underground river is the location of the underground river closure. Step 7: Based on the grouting curtain height obtained in Step 5, carry out grouting curtain construction: Drill holes from the bottom of the upper grouting tunnel and inject grout vertically into the lower karst geological layer until the top of the underground river.

[0008] Further optimization steps, including step seven, also include: calculating the curtain spacing based on the grouting pump pressure measured during the previous grouting curtain construction. P 1 Formation pressure P 2 Grouting time t Mud viscosity µ The distance between the next curtain and the previous curtain is calculated using the following formula; (6) In the formula: L’ It is the distance between the two curtains, in meters (m). k It is the equivalent penetration rate, m 2 ; P 1 It is the injection pump pressure, in Pa; P 2 It is the formation pressure, in Pa; tIt is the grouting time, in seconds; µ It is the viscosity of the slurry, Pa∙s; Ø It is the effective porosity.

[0009] Based on the calculated curtain spacing, the construction of each grouting curtain is carried out sequentially.

[0010] Further optimization involves setting the threshold value to 0.5 in step two.

[0011] Further optimization, the specific operations in step one include: measuring the water flow velocity at the inlet and outlet of the underground river. v Roughness n River width b , water depth h Elevation z The latitude and longitude coordinates were used to determine the karst geological distribution range at the outlet of the underground river in the depression through geological exploration. Simultaneously, rock cores were collected within the karst geological distribution range to determine the equivalent permeability of rock fractures. k and effective porosity Ø The spatial straight-line distance between the underground river's outlet and inlet was obtained using latitude and longitude coordinates and orthophotos from unmanned aerial vehicles. l .

[0012] The following is the derivation process of the main formulas of this invention: 1. The derivation process of the slope calculation formula (1) in this invention: Formula (1) is based on Manning's formula and is derived by solving the slope in reverse. The derivation process is as follows.

[0013] (7) In the formula V For the river speed, R For hydraulic radius, S For the slope, n This is the roughness coefficient.

[0014] In the above formula, wetted perimeter R It can be further calculated using the following formula (8): (8) In the formula R For hydraulic radius, A The cross-sectional area of ​​the river. P For wet period, b For the river width, h The water is deep.

[0015] Substituting formula (8) into formula (7), we obtain the following Manning formula: (9) The slope in the above formula (9) S When used as the term to be solved, the formula further transforms into the following form: (10) The flow velocity at the inlet and outlet of the underground river v 1 、v 2 Roughness n 1 、n 2 River width b 1 、b 2 and water depth h 1 、h 2 Substituting into formula (10), the final slope calculation formula is as follows: (1) 2. The gradient calculation formula (2) takes into account the possibility of a steep drop during the gradient process of the underground river. Therefore, the gradient of the underground river ( S It consists of two parts: energy gradient and friction gradient (11), of which friction gradient ( S f The energy gradient is calculated using formula (1), while the energy gradient is calculated using formula (1). S e The value is obtained by calculating the energy gradient formula.

[0016] (11) Among them, energy gradient ( S e ) is obtained by formula (12).

[0017] (12) In the formula, S e ∆E is the energy gradient, ∆E is the change in energy of the water flow (m), and l is the spatial distance from the inlet to the outlet of the underground river (m).

[0018] ∆E is further calculated using the following formula (13). (13) In the formula, z1 and z2 are the elevations (m) of the underground river inlet and outlet, respectively; v1 and v2 are the flow velocities (m / s) of the underground river inlet and outlet, respectively; h1 and h2 are the water depths (m) of the underground river inlet and outlet, respectively; and g is the acceleration due to gravity (m / s²). 2 ).

[0019] Substituting formula (13) into (12) yields the energy gradient ( S e ) Calculation formula (14).

[0020] (14) Substituting formulas (14) and (1) into formula (11) yields the gradient ( S The calculation formula (2) is as follows.

[0021] (2) 3. Formula for calculating the location of the underground river blockage point The derivation process of calculating the elevation of the underground river blocking point: as follows Figure 5 As shown, the origin of the underground river is set as (0,0,0), and the coordinates of the inlet are set as (0,y1,z1), where y1 is the Y coordinate of the inlet, z1 is the inlet elevation, and the river slope is S. The upper grouting tunnel is in the XZ plane (i.e., y=0), and the tunnel elevation is a fixed value z3, whose coordinates are represented as (x,0,z3). The underground river is in the YZ plane, connecting the inlet (0,y1,z1) and the outlet (0,0,0), and its parametric equation is (15): (15) Calculate the shortest distance between the two straight lines. A point on the underground river is (0, y, Sy), and a point on the tunnel line is (x, 0, z3). The square of the distance between the two points is (16): (16) Find the extreme values ​​by differentiating x and y, we get: x = 0 (minimum point). Substitute this into formula (16), and consider the diameter of the upper grouting tunnel ( d t The error caused by this leads to the formula for calculating the distance between the sealing point and the upper grouting tunnel (5): (5) The elevation of the sealing point is obtained by subtracting the straight-line distance between the grouting tunnel elevation and the sealing point (3).

[0022] (3) In the formula, H It is the elevation (m) of the underground river blockage point. z 3 It is the elevation (m) of the upper grouting tunnel. S It is an underground river slope. d t It is the diameter (m) of the upper grouting tunnel.

[0023] The derivation process of calculating the distance to the underground river blockade point: The distance to the underground river blockade point refers to the projected straight-line distance from the blockade point to the underground river outlet, which is calculated based on the slope and the elevation of the blockade point (4).

[0024] (4) In the formula, L It is the projected straight-line distance (m) from the blockage point to the outlet of the underground river. H S is the elevation of the closure point (m), and S is the river slope.

[0025] 4. Derivation of Grouting Curtain Height The height of the grouting curtain refers to the vertical distance from the upper grouting tunnel to the underground river. The derivation process is shown in the derivation process of the underground river closure point elevation calculation, which is the same as the distance between the underground river closure point and the upper grouting tunnel. d )equal: (5) In the formula, d It is the height of the grouting curtain (m). z 3 It is the elevation (m) of the upper grouting tunnel. S It is an underground river slope. d t It is the diameter (m) of the upper grouting tunnel.

[0026] 5. Derivation of Calculation for Spacing of Grouting Holes The spacing between grouting cavities refers to the distance between multiple downward grouting cavities in the upper grouting tunnel. These cavities are distributed in the XZ plane and are mainly used to inject grout to seal fissures in the strata and form a grouting curtain. The distance between grouting cavities is closely related to the lateral movement distance of the grout in a single grouting cavity. Assuming the lateral movement distance of the grout in a single grouting cavity is l', the spacing L' between two adjacent grouting cavities should be calculated according to the following formula (17): (17) The lateral movement distance (l') of mortar in a single grouting hole can be derived based on Darcy's law (18): (18) In the formula, v For Darcy velocity (m / s), Δ P The difference between the injection pressure and the formation pressure (Pa) is the pressure difference between the injection pressure and the formation pressure. l ' represents the flow path length (m). k Equivalent permeability (m 2 ), µ The viscosity is slurry (Pa·s).

[0027] However, in actual flow velocities, the pore occupancy needs to be considered, and formula (18) is further modified to (19): (19) Build movement distance ( l ') and time ( t The differential equation of ) and the distance moved ( l ') Over time (t The change satisfies: (20) Further simplification into differential equations: (twenty one) Solving equation (21) by integration over both sides, with the initial condition t=0, l'=0: (twenty two) get: (twenty three) The final solution is: (twenty four) However, according to the law of conservation of mass, the injected volume is equal to the filling volume. Therefore, the coefficient is corrected to 1, resulting in: (25) Substituting formula (25) into (17) yields the formula (26) for calculating the distance L' between two adjacent irrigation holes.

[0028] (26) In the formula, Δ P The difference between injection pressure and formation pressure ( Pa ), l ' represents the flow path length (m). k Equivalent permeability (m 2 ), µ The viscosity of the slurry is expressed in Pa·s. Ø t is the effective porosity, and t is the injection time (s). Thus, formula (6) is obtained: The advantages and beneficial effects of this invention are: This invention presents a new method for determining key parameters in karst depression water collection and reservoir construction projects. This method addresses the need for high-density geological exploration and extensive empirical estimation data; instead, it calculates the required data based solely on measurements of relevant parameters in the depression's surrounding area and at the underground river's inlet and outlet. Practical verification has shown that this seepage prevention method improves construction efficiency and reduces project costs while ensuring construction quality. Attached Figure Description

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] Figure 1 This is a three-dimensional schematic diagram of a karst depression according to the method of the present invention.

[0031] Figure 2This is a schematic diagram of the vertical cross-section of the underground river in the karst depression according to the method of the present invention.

[0032] Figure 3 This is a schematic diagram of the vertical profile construction of the underground river in the karst depression using the method of the present invention.

[0033] Figure 4 This is a schematic diagram of the vertical cross-section construction of the seepage-proof curtain according to the method of the present invention.

[0034] Figure 5 A schematic diagram illustrating the derivation process of the key formulas.

[0035] Figure 6 The image shows a comparison of the reservoir before and after its construction, as illustrated in the example. Figure 6 a represents the period before construction. Figure 6 b represents the state after construction.

[0036] Figure 7 Schematic diagram of the longitudinal section of the middle channel. Detailed Implementation

[0037] Example 1: A seepage prevention method in a karst depression water collection and reservoir construction project is described in this embodiment. The project involves the construction of the Lujiaoba karst depression in Kaiyang County, Guizhou Province, to achieve water collection and reservoir construction. Figure 6 This is a before-and-after comparison of the reservoir's construction.

[0038] This invention includes the following steps: Step 1: Hydraulic parameter acquisition: Through field operations, investigate the entrance and exit of the underground river in the depression to be constructed and the direction of the underground river, and measure the water flow velocity at the entrance and exit of the underground river. v Roughness n River width b , water depth h The latitude and longitude coordinates were used; geological exploration was conducted to determine the distribution range of karst geology at the outlet of the underground river in the depression, and rock cores were collected within the karst geology distribution range to determine the equivalent permeability of rock fractures. k and effective porosity Ø The spatial straight-line distance between the underground river's outlet and inlet was obtained using latitude and longitude coordinates and orthophotos from unmanned aerial vehicles. l and elevation z .

[0039] In this embodiment, before the project construction, an investigation was conducted within the planned reservoir area to identify one underground river, the Lianchun River. The upstream entrance of the underground river is located in Lujiaoba Village, Kaiyang County, and the downstream exit is located in Lacaitang Group, Kaiyang County. The river flows into the Yujing River downstream. The depression reservoir is located in the Lujiaoba area. Since the downstream rivers are all underground, it is necessary to carry out sealing operations in the downstream mountains. Through on-site monitoring, the river width, water depth, flow velocity, and other information are shown in the table below: Step 2: Underground River Slope Calculation: Based on the hydraulic parameters obtained in Step 1, when the ratio of the inlet velocity to the outlet velocity of the underground river is greater than or equal to a set threshold, the overall slope of the underground river is calculated using formula (1); when the ratio of the inlet velocity to the outlet velocity is less than a set threshold, the overall slope of the underground river is calculated using formula (2); the set threshold is 0.5. (1) In the formula: S It is the overall slope of the underground river; v 1 It is the inlet water flow velocity, in m / s; v 2 It is the outlet water flow velocity, in m / s; n 1 It is the inlet roughness; n 2 It is the export roughness; b 1 It is the width of the inlet river, in meters; b 2 It is the width of the river at the outlet, in meters; h 1 The depth of the river at the entrance, in meters (m); h 2 The depth of the river at the outlet, in meters (m). (2) In the formula: z1 is the inlet elevation, m; z2 is the outlet elevation, m; l It is the projected distance from the outlet to the inlet of the underground river, in meters (m); g is the acceleration due to gravity, in meters per second (m / s²). 2 ; Since the inlet and outlet velocities are approximately the same, the slope formula (1) in this technology is used to calculate the slope. By substituting the measured parameters into the formula, the slope of the Lianchun River from the downstream inlet of Lujiaoba to the outlet of Lacaitang is calculated to be 13 / 1000. This section is the main construction area for the grouting curtain during the construction of the underground river, and also the main area for the underground river sealing point. A schematic diagram of the longitudinal profile of the Qijiaojing-Lianchun River channel is shown below. Figure 7 As shown.

[0040] Step 3: Determine the location of the upper grouting tunnel: Based on the location of the designed water level and the karst geological distribution range obtained in Step 1, select the upper grouting tunnel above the designed water level and determine the elevation of the upper grouting tunnel. Step 4: Determining the location for sealing off the underground river: The location for sealing off the underground river is determined by the elevation of the sealing point. H Distance between the blockade point and the underground river outlet L The decision is made, and the calculation formula is as follows: (3) (4) In the formula: H It is the elevation of the underground river blockage point, in meters (m). z 3 It is the elevation of the upper grouting tunnel, in meters; S It is the overall slope of the underground river; d t It is the diameter of the upper grouting tunnel, in meters; L It is the distance from the blockade point to the outlet of the underground river, in meters (m). Step 5: Calculation of Grouting Curtain Height: The formula for calculating the grouting curtain height is as follows: (5) In the formula: d It is the height of the grouting curtain, in meters (m). Step 6: Construct the grouting tunnel and seal the underground river according to the location of the upper grouting tunnel and the location of the underground river closure determined in Steps 3 and 4: Construct the upper grouting tunnel above the designed water level; construct the lower grouting tunnel below the designed water level in the same direction as the upper grouting tunnel, with the lower grouting tunnel perpendicular to the underground river on the horizontal plane, and the intersection with the underground river is the location of the underground river closure.

[0041] During construction: The upper grouting tunnel will be constructed above the designed water level. In principle, the upper grouting tunnel should be at least 10 meters above the designed water level. The upper grouting tunnel will be excavated parallel to the plane of the underground river at the point where it intersects the river perpendicularly. The lower grouting tunnel is the underground river sealing tunnel, which will be excavated parallel to the upper grouting tunnel in the vertical plane. The front end of the lower tunnel will be excavated downwards with a certain slope. When the tunnel height reaches the calculated elevation of the sealing point, horizontal excavation will continue. During excavation, the horizontal projection distance between the excavation point and the underground river outlet will be calculated at any time to ensure that the excavation direction is correct.

[0042] Step 7: Construct the grouting curtain based on the height obtained in Step 5: Drill holes vertically downwards from the bottom of the upper grouting tunnel to inject grout into the lower karst geological layer until reaching the top of the underground river. Use a geological drilling rig to drill vertically downwards from the bottom of the upper grouting tunnel, with a borehole diameter between 56mm and 76mm. The borehole height should match the grouting curtain height. Monitor the injection pump pressure during the first borehole construction. P 1 Formation pressure P 2 Grouting time t Mud viscosity µ This provides data for calculating curtain spacing during subsequent construction. Curtain spacing calculation: based on the grouting pump pressure measured during the previous grouting curtain construction. P 1 Formation pressure P 2 Grouting time tMud viscosity µ The distance between the next curtain and the previous curtain is calculated using the following formula; (6) In the formula: L’ It is the distance between the two curtains, in meters (m). k It is the equivalent penetration rate, m 2 ; P 1 It is the injection pump pressure, in Pa; P 2 It is the geostress, in Pa; t It is the grouting time, in seconds; µ It is the viscosity of the slurry, Pa∙s; Ø It is the effective porosity; Based on the calculated curtain spacing, the construction of each grouting curtain is carried out sequentially.

[0043] In this embodiment, after obtaining the gradient of the underground river, the elevation of the upper grouting tunnel is designed to be 1302.96 meters, the elevation of the underground river outlet is 1243.36 meters, and the diameter of the upper grouting tunnel is 4 meters. Substituting the elevation data into formula (3), the elevation of the underground river closure point is calculated to be 1265.08 meters, and the distance from the upper grouting tunnel is 37.88 meters, which is also the height of the grouting curtain. Through formula (4), the distance from the underground river closure point to the outlet is calculated to be 163.08 meters. Further, through field experiments, the rock core was used to determine the equivalent permeability (k) and effective porosity (Ø) of rock fractures, which were 0.0001 and 0.9, respectively. The grout viscosity was 20, the injection pressure difference was 780.4 Pa, and the injection time was 16200 s. Substituting these values ​​into the formula, the spacing between the multiple grouting curtains was calculated to be 16.76 meters.

[0044] Finally, it should be noted that the above description is only used to illustrate the technical solutions of the present invention and is not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention.

Claims

1. A seepage prevention method in karst depression water collection and reservoir construction projects, characterized in that: The method of using grouting curtain combined with underground river sealing includes the following steps: Step 1: Hydraulic parameter acquisition: The inlet and outlet of the underground river and the direction of the underground river in the depression to be constructed are investigated through field operations, and hydraulic parameters are measured and acquired. Step 2: Underground River Slope Calculation: Based on the hydraulic parameters obtained in Step 1, when the ratio of the inlet velocity to the outlet velocity of the underground river is greater than or equal to a set threshold, the overall slope of the underground river is calculated using formula (1); when the ratio of the inlet velocity to the outlet velocity is less than a set threshold, the overall slope of the underground river is calculated using formula (2); the set threshold is 0.4~0.

6. （1） In the formula: S It is the overall slope of the underground river; v 1 It is the inlet water flow velocity, in m / s; v 2 It is the outlet water flow velocity, in m / s; n 1 It is the inlet roughness; n 2 It is the export roughness; b 1 It is the width of the inlet river, in meters; b 2 It is the width of the river at the outlet, in meters; h 1 The depth of the river at the entrance, in meters (m); h 2 The depth of the river at the outlet, in meters (m). （2） In the formula: z1 is the inlet elevation, m; z2 is the outlet elevation, m; l It is the straight-line distance from the outlet to the inlet of the underground river, in meters (m); g is the acceleration due to gravity, in meters per second (m / s²). 2 ; Step 3: Determine the location of the upper grouting tunnel: Based on the design water level and the measured karst geological distribution range, select the upper grouting tunnel above the design water level and determine the elevation of the upper grouting tunnel. Step 4: Determining the location for sealing off the underground river: The location for sealing off the underground river is determined by the elevation of the sealing point. H and the distance from the blockade point to the underground river outlet L The decision is made, and the calculation formula is as follows: （3） （4） In the formula: H It is the elevation of the underground river blockage point, in meters (m). z 3 It is the elevation of the upper grouting tunnel, in meters; S It is the overall slope of the underground river; d t It is the diameter of the upper grouting tunnel, in meters; L It is the distance from the blockade point to the outlet of the underground river, in meters (m). Step 5: Calculation of Grouting Curtain Height: The calculation formula is as follows: （5） In the formula: d It is the height of the grouting curtain, in meters (m). Step 6: Based on the locations of the upper grouting tunnel and the underground river closure determined in Steps 3 and 4, construct the grouting tunnel and close the underground river: construct the upper grouting tunnel above the designed water level; construct the lower grouting tunnel below the designed water level in a direction parallel to the upper grouting tunnel, with the lower grouting tunnel perpendicular to the underground river on the horizontal plane, and the intersection with the underground river is the location of the underground river closure; Step 7: Construct the grouting curtain according to the height of the grouting curtain obtained in Step 5: Drill holes from the bottom of the upper grouting tunnel and inject mortar vertically into the lower karst geological layer until the top of the underground river is reached.

2. The seepage prevention method in karst depression water collection and reservoir construction projects according to claim 1, characterized in that: Step seven also includes: calculating the curtain spacing: based on the grouting pump pressure measured during the previous grouting curtain construction. P 1 Formation pressure P 2 Grouting time t Mud viscosity µ The distance between the next curtain and the previous curtain is calculated using the following formula; （6） In the formula: L’ It is the distance between the two curtains, in meters (m). k It is the equivalent penetration rate, m 2 ; P 1 It is the injection pump pressure, in Pa; P 2 It is the formation pressure, in Pa; t It is the grouting time, in seconds; µ It is the viscosity of the slurry, Pa∙s; Ø It is the effective porosity; Based on the calculated curtain spacing, the construction of each grouting curtain is carried out sequentially.

3. The seepage prevention method in karst depression water collection and reservoir construction projects according to claim 1, characterized in that: In step two, the set threshold is 0.

5.

4. The seepage prevention method in karst depression water collection and reservoir construction projects according to claim 1, characterized in that: The specific operations of step one include: measuring the water flow velocity at the inlet and outlet of the underground river. v Roughness n River width b , water depth h Elevation z The latitude and longitude coordinates were used to determine the karst geological distribution range at the outlet of the underground river in the depression through geological exploration. Simultaneously, rock cores were collected within the karst geological distribution range to determine the equivalent permeability of rock fractures. k and effective porosity Ø The spatial straight-line distance between the underground river's outlet and inlet was obtained using latitude and longitude coordinates and orthophotos from unmanned aerial vehicles. l .

Images