Method for determining position of seepage-proofing line for seepage around dam

Abstract

The invention discloses a method for determining the position of a dam-surrounding seepage-proofing line, which comprises the following steps of: 1) drilling, and carrying out a seepage test and underground water level long-term observation in a drill hole; 2) drawing a contour line relative to the top surface of the impervious layer based on the result of the penetration test; based on the long-term observation data of the underground water level, an underground water level equal water level line is drawn; (3) based on the groundwater surface equal water level and the opposite impervious layer top surface contour line, a dam-surrounding seepage-proofing line is preliminarily planned; and (4) determining a dam-surrounding seepage prevention line. According to the method, the drilling coordinates are combined with detailed and comprehensive hydrogeological conditions such as underground water and rock-soil body permeability, and the optimal dam-surrounding seepage prevention line position is determined by comparing two schemes of the initially-planned underground water surface and the relatively-impervious layer top surface, so that the seepage prevention line position is determined on the premise that the dam-surrounding seepage safety is guaranteed. And the anti-seepage route is shortened, the engineering amount of the anti-seepage curtain is reduced, and the construction treatment cost is saved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of water conservancy and hydropower engineering investigation, and more particularly to a method for determining the position of a seepage prevention line for seepage around a dam. BACKGROUND

[0002] Seepage around a dam is a geological phenomenon in which reservoir water seeps along the dam abutment and the water-permeable rock-soil mass downstream after the reservoir is impounded. As one of the types of reservoir seepage, seepage around a dam exists in varying degrees in almost all water conservancy and hydropower engineering reservoirs. Seepage around a dam is highly dangerous. For example, the seepage loss of reservoir water directly reduces the effective storage capacity of the reservoir, affecting the functions and benefits of the reservoir, such as power generation, irrigation, and water supply. Seepage around a dam can cause the near-dam bank slope to be unstable and affect the structural safety of the dam and other hydraulic structures. Sudden seepage around a dam can even cause dam failure and threaten the safety of the lives and property of downstream residents. Therefore, for seepage around a dam, the appropriate position of the seepage prevention line must be determined and the engineering treatment must be carried out.

[0003] In current water conservancy and hydropower engineering, for the seepage prevention line for seepage around a dam, only a seepage prevention line is generally determined according to the basic topographic and geological conditions, and the original line scheme is not changed as long as the seepage prevention conditions are not very poor after the investigation. In a small number of projects, two or more schemes are initially determined according to the micro-topographic conditions, and one of the schemes is determined after the investigation and comparison.

[0004] Because the detailed and comprehensive hydrogeological conditions of the seepage section around the dam are not used as a basis, the seepage prevention line determined in the existing engineering practice is not necessarily the optimal scheme, which results in the waste of the seepage prevention engineering quantity and the construction treatment cost. SUMMARY

[0005] To overcome the above technical deficiencies, the purpose of the present application is to provide a method for determining the position of a seepage prevention line for seepage around a dam, which is based on detailed and comprehensive hydrogeological conditions such as groundwater and rock-soil permeability, and determines the optimal position of the seepage prevention line for seepage around a dam by comparing two schemes of the initial groundwater level and the top surface of the relatively impervious layer, and has the advantages of accurate and reliable results, saving of seepage prevention engineering quantity and construction treatment cost, etc.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A method for determining the position of a seepage prevention line for seepage around a dam, which is characterized by comprising the following steps:

[0008] 1) drilling is carried out, and permeability tests and long-term groundwater level observation are carried out in the drill hole;

[0009] 2) based on the result of the permeability test, obtaining the relative impervious layer top surface elevation of the location where the borehole is located and drawing a relative impervious layer top surface contour line; based on the data of the long-term observation of the groundwater level, obtaining the groundwater level information of the location where the borehole is located and drawing a groundwater surface contour line;

[0010] 3) based on the groundwater surface contour line and the relative impervious layer top surface contour line, initially determining two dam seepage anti-seepage lines;

[0011] 4) based on the length of the two dam seepage anti-seepage lines, selecting the shorter one as the dam seepage anti-seepage line.

[0012] As a preferred solution, in step 1), the boreholes are arranged on the dam abutment slope site, vertically arranged to the horizontal plane, and parallel to each other; the borehole spacing is 50-100 meters, which is related to the terrain: when the slope of the dam abutment slope is greater than 25 degrees, the borehole spacing takes the smaller value in the range, i.e. 50m≤ borehole spacing≤ 75m; when the slope of the dam abutment slope is less than or equal to 25 degrees, the gentle slope section, the borehole spacing takes the larger value in the range, i.e. 75m< borehole spacing≤ 100m. The terrain slope greater than 25 degrees is a steep slope section, and the terrain slope less than or equal to 25 degrees is a gentle slope section. The geological conditions change greatly in the steep slope section, so a smaller borehole spacing is used; the geological conditions change less in the gentle slope section, so a larger borehole spacing is used.

[0013] As a preferred solution, the permeability test is a borehole permeability test, including borehole water pressure test or borehole water injection test.

[0014] Further, the borehole permeability test is carried out in sections throughout the hole, and each test section is 4-6 meters long; for the test section of soil or fully weathered, strongly weathered rock, the borehole water injection test is carried out to obtain the permeability coefficient of the test section, with the unit of centimeter / second; for the test section of weakly weathered, slightly weathered, fresh rock, the borehole water pressure test is carried out to obtain the water permeability rate of the test section, with the unit of Lürong.

[0015] As a preferred solution, the long-term observation of the groundwater level is carried out after the completion of the borehole and permeability test, and the observation time includes at least one complete hydrological year, which includes the wet season, the normal water season and the dry season, and the water level observation interval is 6-8 days; at each observation, the observation of the groundwater level of all boreholes is carried out on the same day.

[0016] As a preferred solution, steps 2) to 4) are operated on the dam top view design drawing; the dam top view design drawing is obtained by orthographic projection from the top of the dam to the bottom; the dam top view design drawing contains the two-dimensional plane coordinates of the borehole, the dam, and the dam foundation seepage anti-seepage line end point.

[0017] As a preferred solution, in step 2), the relative impervious layer top surface contour line comprises contour points and coordinate information of the contour points, and the relative impervious layer top surface elevation at the positions of the contour points is the same as the normal water level elevation of the reservoir; the relative impervious layer refers to a rock-soil body with a permeability coefficient or a water permeability rate less than or equal to a standard anti-seepage value.

[0018] Further, the standard anti-seepage value is determined according to relevant technical specifications.

[0019] Further, the standard anti-seepage value is any one of a water permeability rate of 1 Lü Rong, 3 Lü Rong, 5 Lü Rong, or 10 Lü Rong; or a permeability coefficient of 1×10 -5 cm / s, 3×10 -5 cm / s, 5×10 -5 cm / s, or 1×10 -4 cm / s.

[0020] Further, the drawing step of the relative impervious layer top surface contour line is as follows:

[0021] 2.1) Based on the plane coordinates of the drill holes, the positions of the drill holes are determined; adjacent high-elevation drill holes and low-elevation drill holes are connected by dashed lines to obtain first dashed line connection lines; the high-elevation drill hole refers to a drill hole with a relative impervious layer top surface elevation higher than the normal water level elevation of the reservoir at the position thereof; the low-elevation drill hole refers to a drill hole with a relative impervious layer top surface elevation lower than the normal water level elevation of the reservoir at the position thereof;

[0022] 2.2) Based on the relative impervious layer top surface elevation at the positions of the drill holes, the positions of the contour points on each first dashed line connection line are determined;

[0023] 2.3) The contour points on each first dashed line connection line are connected by smooth curves to form a relative impervious layer top surface contour line; the relative impervious layer top surface elevation at the positions of all points on the relative impervious layer top surface contour line is the same as the normal water level elevation of the reservoir.

[0024] Further, step 2.1) specifically comprises the following steps:

[0025] determining a connection mode: selecting a high-elevation drill hole, determining a low-elevation drill hole closest to the high-elevation drill hole and not connected to other high-elevation drill holes, and connecting the high-elevation drill hole and the low-elevation drill hole by a dashed line to obtain a first dashed line connection line;

[0026] Based on the connection mode, all high-elevation drill holes and their adjacent low-elevation drill holes are sequentially connected by dashed lines.

[0027] Further, the determination of the positions of the contour points on the first dashed line connection line adopts an interpolation method, and the calculation formula is as follows:

[0028] D1 = D3 ÷ H3 x (H1 - H);

[0029] D2 = D3 ÷ H3 x (H - H2);

[0030] In the formula, D1 is the planar straight-line distance from the contour point on the first dashed connecting line to the high-elevation borehole on the first dashed connecting line; D2 is the planar straight-line distance from the contour point on the first dashed connecting line to the low-elevation borehole on the first dashed connecting line; D3 is the planar straight-line distance between the high-elevation borehole and the low-elevation borehole on the first dashed connecting line; H is the normal water storage level elevation of the reservoir; H1 is the relative elevation of the high-elevation borehole to the top surface of the impervious layer on the first dashed connecting line; H2 is the relative elevation of the low-elevation borehole to the top surface of the impervious layer on the first dashed connecting line; and H3 is the elevation difference between the relative elevation of the high-elevation borehole to the top surface of the impervious layer and the relative elevation of the low-elevation borehole to the top surface of the impervious layer.

[0031] As a preferred solution, in step 2), the groundwater level contour line includes contour points and coordinate information thereof, and the groundwater level elevation at the positions of the contour points is the same as the normal water storage level elevation of the reservoir; and the contour line is drawn based on the observation data of the boreholes in the dry season. The normal water storage level elevation of the reservoir is a design index of the reservoir. The observation value in the dry season with a relatively low water level is used to draw the contour line, so as to ensure the seepage prevention effect of the seepage prevention scheme around the dam.

[0032] Further, the drawing step of the groundwater level contour line is as follows:

[0033] 2.4) Based on the planar coordinates of the boreholes, the positions of the boreholes are determined; adjacent high-water-level boreholes and low-water-level boreholes are connected by dashed lines to obtain second dashed connecting lines; the high-water-level borehole refers to a borehole at the position of which the groundwater level elevation is higher than the normal water storage level elevation of the reservoir; and the low-water-level borehole refers to a borehole at the position of which the groundwater level elevation is lower than the normal water storage level elevation of the reservoir;

[0034] 2.5) Based on the groundwater level elevation at the positions of the boreholes, the positions of contour points are determined on each second dashed connecting line;

[0035] 2.6) The contour points on each second dashed connecting line are connected by a smooth curve to form a groundwater level contour line, and the groundwater level elevations at the positions of all points on the groundwater level contour line are the same as the normal water storage level elevation of the reservoir.

[0036] Further, step 2.4) specifically includes the following steps:

[0037] determining the connection mode: selecting a high water level borehole, determining a low water level borehole with the shortest distance to the high water level borehole and not connected to other high water level boreholes, connecting the high water level borehole and the low water level borehole with a dashed line to obtain a second dashed line connection line;

[0038] based on the connection mode, sequentially connecting all high water level boreholes with their adjacent low water level boreholes with a dashed line.

[0039] Further, the determination of the position of the equal water level point on the second dashed line connection line adopts an interpolation method, and the calculation formula is as follows:

[0040] D4=D÷H4×(H5-H);

[0041] D5=D÷H4×(H-H6);

[0042] In the formula, D4 is the planar straight line distance from the equal water level point on the second dashed line connection line to the high water level borehole on the second dashed line connection line; D5 is the planar straight line distance from the equal water level point on the second dashed line connection line to the low water level borehole on the second dashed line connection line; D is the planar straight line distance between the high water level borehole and the low water level borehole on the second dashed line connection line; H4 is the elevation difference between the underground water surface of the high water level borehole and the underground water surface of the low water level borehole on the second dashed line connection line; H5 is the underground water surface elevation of the high water level borehole on the second dashed line connection line; H6 is the underground water surface elevation of the low water level borehole on the second dashed line connection line; and H is the normal water storage level elevation of the reservoir.

[0043] Further, the underground water surface elevation at the position of the borehole is the average value of the underground water level observation value of the borehole in the dry season.

[0044] Further, steps 2) and 3) are performed in Autocad drawing software, and the smooth curve is drawn by the command of a spline curve in the Autocad drawing software.

[0045] As a preferred solution, in step 3), the initially proposed seepage prevention line around the dam has two lines:

[0046] One line starts from the end point S and extends to the underground water surface equal water level line; the drawing method comprises the following steps: determining the planar coordinates of the end point S, finding the point A on the underground water surface equal water level line with the closest straight line distance to the end point S, and connecting the point A and the end point S to form a line segment SA, and the line segment SA is the initially proposed seepage prevention line around the dam extending from the end point S to the underground water surface equal water level line;

[0047] Another starting from the endpoint S, extending to the relative impervious layer top surface contour; drawing method comprises: determining the plane coordinates of the endpoint S, finding the B point on the relative impervious layer top surface contour which is closest to the endpoint S in straight line distance, connecting the B point and the endpoint S into a line segment SB, the line segment SB is the preliminary anti-seepage line of the dam seepage prevention line extending from the endpoint S to the relative impervious layer top surface contour.

[0048] Wherein the endpoint S is the endpoint of the dam foundation seepage prevention line.

[0049] The dam foundation seepage prevention line is the line in the range of the dam foundation, and the dam seepage prevention line outside the dam end is the dam seepage prevention line, and the two lines are connected to form a whole, so that the effective anti-seepage effect can be achieved. The dam seepage prevention line and the dam foundation seepage prevention line are connected through the endpoint S, and a complete anti-seepage system of the dam is formed.

[0050] As a preferred scheme, in step 4), the final determination method of the dam seepage prevention line comprises: comparing the lengths of the two dam seepage prevention lines, and selecting the one with shorter length as the dam seepage prevention line.

[0051] Further, in step 4), if the lengths of the two dam seepage prevention lines are the same, the line is determined comprehensively in combination with the geological conditions, construction difficulty and economy.

[0052] Compared with the prior art, the beneficial effects of the present application are:

[0053] The method for determining the position of the dam seepage prevention line provided by the present application is a method for determining the optimal position of the dam seepage prevention line by comparing the two schemes of the preliminary underground water surface and the relative impervious layer top surface through the borehole coordinates in combination with the detailed and comprehensive hydrogeological conditions such as the underground water and the rock-soil permeability. Compared with the line determined by using the prior scheme, the anti-seepage line is shortened, the anti-seepage curtain engineering quantity is reduced, and the construction treatment cost is saved under the premise of ensuring the safety of the dam seepage. BRIEF DESCRIPTION OF DRAWINGS

[0054] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings shown.

[0055] Figure 1 The flow chart of the method for determining the position of the dam seepage prevention line of the present application;

[0056] Figure 2Fig. 1 is a contour map of water level and top surface of relatively impervious layer in an embodiment of the present application;

[0057] Figure 3 Fig. 4 is a diagram for determining the position of anti-seepage line for seepage around dam in an embodiment of the present application.

[0058] In the diagram, 1 is a contour of water level, 2 is a contour of top surface of relatively impervious layer, 3 is a borehole and number / water level elevation of underground water, and 4 is a borehole and number / top surface elevation of relatively impervious layer. DETAILED DESCRIPTION

[0059] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0060] As shown in Fig. 1, a method for determining the position of anti-seepage line for seepage around dam according to the present application comprises the following steps: Figure 1

[0061] 1) Drilling is implemented, and permeation test and long-term observation of underground water level are performed in the borehole.

[0062] The borehole is arranged at the dam abutment slope position and is arranged vertically to the horizontal plane, and the boreholes are parallel to each other and are in grid shape on the plane. The distance between the boreholes is 50-100 meters, which is related to the terrain. When the slope of the dam abutment slope is greater than 25 degrees, the distance between the boreholes is smaller in the range, i.e. 50m≤distance between boreholes≤75m. When the slope of the dam abutment slope is less than or equal to 25 degrees, the distance between the boreholes is greater in the range, i.e. 75m<distance between boreholes≤100m.

[0063] The permeation test is borehole permeation test, including borehole water pressure test or borehole water injection test. The borehole permeation test is performed in sections in the whole borehole, and the length of each test section is 4-6 meters. For the test section of soil or fully weathered and strongly weathered rock, borehole water injection test is performed to obtain the permeation coefficient of the test section, which is in centimeter / second. For the test section of weakly weathered, slightly weathered and fresh rock, borehole water pressure test is performed to obtain the water permeability of the test section, which is in Lürong.

[0064] The long-term observation of underground water level is performed after the completion of the borehole and permeation test, and the observation time includes at least one complete hydrological year, which includes wet season, normal water season and dry season. The interval of water level observation is 6-8 days, and the observation of underground water level of all boreholes should be performed on the same day.

[0065] ​2) Based on the results of the above penetration test, the relative impervious layer top elevation at the location of the borehole is obtained and a relative impervious layer top contour line is drawn; based on the data of the long-term observation of the groundwater level, the groundwater level information of the borehole is obtained and a groundwater surface contour line is drawn. Among them, the relative impervious layer top elevation is determined by the penetration test results, which is a prior art and will not be described here.

[0066] The drawing process can be carried out in Autocad drawing software, based on the dam top plane design drawing, to draw the relative impervious layer top contour line and the groundwater surface contour line. The dam top plane design drawing includes the two-dimensional plane coordinates of the borehole, the dam, and the dam foundation seepage anti-seepage line end point.

[0067] I. The relative impervious layer top contour line includes contour points and their coordinate information, and the relative impervious layer top elevation at the location of the contour point is the same as the normal water storage level elevation of the reservoir; the relative impervious layer refers to the rock-soil body with a permeability coefficient or permeability rate less than or equal to the anti-seepage standard value. The anti-seepage standard value is determined according to the relevant technical specification "Code for Design of Roller Compacted Earth Dam" (s1274-2020). The anti-seepage standard value is: any one of the permeability rates 1 m / h, 3 m / h, 5 m / h, 10 m / h; or, any one of the permeability coefficients 1 x 10 -5 cm / s, 3 x 10 -5 cm / s, 5 x 10 -5 cm / s, 1 x 10 -4 cm / s.

[0068] The drawing steps of the above relative impervious layer top contour line are as follows:

[0069] 2.1) Based on the plane coordinates of the borehole, the borehole position is determined; the adjacent high-elevation borehole and low-elevation borehole are connected with a dashed line to obtain a first dashed line connection line; the high-elevation borehole refers to the borehole whose relative impervious layer top elevation at the location is higher than the normal water storage level elevation of the reservoir; the low-elevation borehole refers to the borehole whose relative impervious layer top elevation at the location is lower than the normal water storage level elevation of the reservoir; which includes the following steps:

[0070] Determine the connection mode: select a high-elevation borehole, determine a low-elevation borehole that is closest to it and not connected to other high-elevation boreholes, and connect the high-elevation borehole and the low-elevation borehole with a dashed line;

[0071] Based on the connection mode, all high-elevation boreholes and their adjacent low-elevation boreholes are connected with a dashed line.

[0072] 2.2) Based on the relative impervious layer top surface elevation of the location of the borehole, the position of the contour point on each first dashed connecting line is determined. The position of the contour point on the first dashed connecting line is determined by interpolation, and the calculation formula is as follows:

[0073] D1=D3÷H3×(H1-H);

[0074] D2=D3÷H3×(H-H2);

[0075] In the formula, D1 is the straight line distance from the contour point on the first dashed connecting line to the high elevation borehole on the first dashed connecting line; D2 is the straight line distance from the contour point on the first dashed connecting line to the low elevation borehole on the first dashed connecting line; D3 is the straight line distance between the high elevation borehole and the low elevation borehole on the first dashed connecting line; H is the normal reservoir water level elevation; H1 is the relative impervious layer top surface elevation of the high elevation borehole on the first dashed connecting line; H2 is the relative impervious layer top surface elevation of the low elevation borehole on the first dashed connecting line; H3 is the elevation difference between the relative impervious layer top surface of the high elevation borehole and the relative impervious layer top surface of the low elevation borehole on the first dashed connecting line.

[0076] 2.3) The contour points on each first dashed connecting line are connected by a smooth curve to form a relative impervious layer top surface contour line; the relative impervious layer top surface elevation of all points on the relative impervious layer top surface contour line is the same as the normal reservoir water level elevation.

[0077] II. The groundwater surface contour line includes the contour points and their coordinate information, and the groundwater surface elevation of the contour points is the same as the normal reservoir water level elevation. The drawing of the contour line is based on the borehole groundwater level observation data, and the arithmetic mean of the observation values in the dry season is used. The normal reservoir water level elevation is a design index of the existing reservoir. Using the observation values in the dry season with relatively low water level to draw the contour line can ensure the anti-seepage effect of the anti-seepage scheme around the dam.

[0078] The drawing steps of the groundwater surface contour line are as follows:

[0079] 2.4) Based on the planar coordinates of the borehole in the horizontal plane, the position of the borehole is determined; the adjacent high water level borehole and low water level borehole are connected by a dashed line to obtain a second dashed connecting line; the high water level borehole refers to the borehole whose groundwater surface elevation at the location is higher than the normal reservoir water level elevation; the low water level borehole refers to the borehole whose groundwater surface elevation at the location is lower than the normal reservoir water level elevation; the specific operation is as follows:

[0080] Determine the connection method: select a high water level borehole, determine a low water level borehole that is closest to the high water level borehole and is not connected to other high water level boreholes, and connect the high water level borehole and the low water level borehole by a dashed line;

[0081] Based on the connection mode, all high water level boreholes are connected with their adjacent low water level boreholes by dashed lines in sequence;

[0082] 2.5) Based on the underground water surface elevation (groundwater level) of the position of the borehole, the position of the equal water level point on each second dashed connection line is determined respectively;

[0083] The position of the equal water level point on the second dashed connection line is determined by interpolation method, and the calculation formula is as follows:

[0084] D4=D÷H4×(H5-H6);

[0085] D5=D÷H4×(H-H6);

[0086] In the formula, D4 is the planar straight line distance from the equal water level point on the second dashed connection line to the high water level borehole on the second dashed connection line; D5 is the planar straight line distance from the equal water level point on the second dashed connection line to the low water level borehole on the second dashed connection line; D is the planar straight line distance between the high water level borehole and the low water level borehole on the second dashed connection line; H4 is the elevation difference between the underground water surface of the high water level borehole and the underground water surface of the low water level borehole on the second dashed connection line; H5 is the underground water surface elevation of the high water level borehole on the second dashed connection line; H6 is the water level elevation of the low water level borehole on the second dashed connection line; H is the normal reservoir water level elevation;

[0087] 2.6) The equal water level points on each second dashed connection line are connected by smooth curves to form the underground water surface equal water level line, and the underground water surface elevation of all points on the underground water surface equal water level line is the same as the normal reservoir water level elevation.

[0088] The smooth curve in step 2) can be drawn by the spline curve command in Autocad or other drawing software.

[0089] 3) Based on the above underground water surface equal water level line and the relative impervious layer top surface contour line, the preliminary dam seepage prevention line is proposed;

[0090] The preliminary dam seepage prevention line has two lines: one starts from the end point S and extends to the underground water surface equal water level line; the other starts from the end point S and extends to the relative impervious layer top surface contour line; wherein the end point S is the end point of the dam foundation seepage prevention line.

[0091] The line extending from the end point S to the underground water surface equal water level line is: obtaining the planar coordinates of the end point S, determining the position of the end point S on the plan view based on the planar coordinates of the end point S, finding the point A on the underground water surface equal water level line which has the closest straight line distance to the end point S on the plan, connecting the point A and the end point S to form a line segment SA, and the line segment SA is the preliminary dam seepage prevention line extending from the end point S to the underground water surface equal water level line.

[0092] The line extending from the endpoint S to the contour of the top surface of the relatively impervious layer is: obtaining the plane coordinates of the endpoint S, determining the position of the endpoint S on the plan based on the plane coordinates of the endpoint S, finding the point B on the contour of the top surface of the relatively impervious layer which is closest to the endpoint S on the plan, connecting the point B and the endpoint S to form a line segment SB, and the line segment SB is the preliminary anti-seepage line extending from the endpoint S to the contour of the top surface of the relatively impervious layer around the dam.

[0093] 4) determining the anti-seepage line around the dam.

[0094] The final determination method of the anti-seepage line around the dam includes: comparing the lengths of the line segment SA and the line segment SB, selecting the line segment with shorter length as the anti-seepage line around the dam, and if the lengths of the two line segments are equal, one of the line segments or a combination of geological conditions, construction difficulty and economy is selected to determine the line.

[0095] The content of the application is further described below through specific examples.

[0096] The preliminary geological survey of a large-scale hydropower project needs to determine the position of the anti-seepage line around the dam. The normal storage level of the reservoir of the large-scale hydropower project is an existing design index of the reservoir, which is 386 meters. Except step 1), Autocad drawing software is used in the whole determination process, and the operation is performed on the left bank abutment plan of the reservoir. The determination of the position of the anti-seepage line around the dam of the large-scale hydropower project by using the method of the application includes the following steps:

[0097] Step 1): drilling, and performing permeability test and long-term observation of underground water level in the drill hole;

[0098] The drill holes are arranged on the slope of the left bank abutment of the proposed reservoir in a grid shape. The slope gradient is 35-45 degrees, the drill hole spacing is 51.2-75 meters, a total of 6 drill holes are implemented, and the drill holes are parallel to each other and perpendicular to the horizontal plane.

[0099] The drill hole permeability test is performed during the drilling process. The outcropped bedrock on the slope is generally weakly weathered, and the whole or strongly weathered rock mass is locally seen. The drill hole permeability test is performed by drill hole water pressure test, and the test section length is generally 5 meters. The test operation and test data arrangement are performed according to the relevant existing technical standards, and the test result is the permeability rate with the unit of Lürong.

[0100] The long-term observation of underground water level is performed after the completion of the drill hole. The observation time is from April 21, 2023 to September 28, 2024, which is 1 year and 5 months, including 1 complete hydrological year of the wet season, the normal water season and the dry season. The water level observation interval is 1 week, and the underground water level of each drill hole is observed on the same day.

[0101] Step 2): Based on the results of the above penetration test, the relative impervious layer top surface elevation of the location of the borehole is obtained and a relative impervious layer top surface contour line is drawn; based on the data of the long-term observation of the groundwater level, the groundwater level information of the borehole is obtained and a groundwater surface contour line is drawn.

[0102] In the two-dimensional drawing software, based on the left bank abutment plan view, the coordinate position of each borehole in the plan view is determined, and the following operations are performed:

[0103] I. Draw a relative impervious layer top surface contour line

[0104] The relative impervious layer top surface contour line is a line that passes through all points with the same elevation as the normal water level of the reservoir, which is a design index of 386 meters for the reservoir. The elevation of the relative impervious layer top surface at the location of the borehole is determined by the results of the penetration test. The relative impervious layer refers to rock-soil with a permeability coefficient or permeability rate less than or equal to the standard value of imperviousness, which is determined according to relevant technical specifications and regulations. The standard value of imperviousness for this reservoir project is a permeability rate of 5 m / d. The relative impervious layer top surface contour line is drawn based on the borehole penetration test data, as shown in FIG. b, and the specific drawing steps are as follows: Figure 2 b

[0105] 2.1) Based on the borehole plan coordinates, the borehole positions are determined on the plan view; the adjacent high-elevation boreholes and low-elevation boreholes are connected by dashed lines to obtain three first dashed connection lines. High-elevation boreholes refer to boreholes with a relative impervious layer top surface elevation higher than the normal water level of the reservoir, such as boreholes ZK1, ZK3, and ZK5 in FIG. b, with corresponding relative impervious layer top surface elevations of q1=391.4 m, q3=412.6 m, and q5=410.7 m, respectively. Low-elevation boreholes refer to boreholes with a relative impervious layer top surface elevation lower than the normal water level of the reservoir, such as boreholes ZK2, ZK4, and ZK6 in FIG. b, with corresponding relative impervious layer top surface elevations of q2=376.1 m, q4=375.2 m, and q6=382.3 m, respectively. The three first dashed connection lines are ZK1-ZK2, ZK3-ZK4, and ZK5-ZK6. Figure 2 b Figure 2 b

[0106] 2.2) On the three first dashed connection lines ZK1-ZK2, ZK3-ZK4, and ZK5-ZK6, the positions of the contour points are determined, such as points P, Q, and R in FIG. b. Figure 2 b

[0107] The position of the contour point is determined by interpolation, and the following formula is used for calculation: the straight-line distance from the contour point to the high-elevation borehole = the straight-line distance between the high-elevation borehole and the low-elevation borehole ÷ the difference in the elevation of the top surface of the relatively impervious layer at the positions of the high-elevation borehole and the low-elevation borehole × (the elevation of the top surface of the relatively impervious layer at the position of the high-elevation borehole - the normal water level of the reservoir).

[0108] On the ZK1-ZK2 dotted line, the straight-line distance between the high-elevation borehole and the low-elevation borehole is 67.7 meters, the elevations of the top surface of the relatively impervious layer at the positions of the high-elevation borehole and the low-elevation borehole are 391.4 meters and 376.1 meters respectively, and the normal water level of the reservoir is 386 meters, so the straight-line distance from the point P to the high-elevation borehole ZK1 is 23.9 meters, and the position of the point P is determined accordingly.

[0109] On the ZK3-ZK4 dotted line, the straight-line distance between the high-elevation borehole and the low-elevation borehole is 70.5 meters, the elevations of the top surface of the relatively impervious layer at the positions of the high-elevation borehole and the low-elevation borehole are 412.6 meters and 375.2 meters respectively, and the normal water level of the reservoir is 386 meters, so the straight-line distance from the point Q to the high-elevation borehole ZK3 is 50.1 meters, and the position of the point Q is determined accordingly.

[0110] On the ZK5-ZK6 dotted line, the straight-line distance between the high-elevation borehole and the low-elevation borehole is 80.0 meters, the elevations of the top surface of the relatively impervious layer at the positions of the high-elevation borehole and the low-elevation borehole are 410.7 meters and 382.3 meters respectively, and the normal water level of the reservoir is 386 meters, so the straight-line distance from the point R to the high-elevation borehole ZK5 is 69.6 meters, and the position of the point R is determined accordingly.

[0111] 2.3) The points P, Q, and R on the three first dotted lines are connected by a smooth curve to form a contour line of the top surface of the relatively impervious layer, as shown by the solid line 2 in b, and the elevations of the top surface of the relatively impervious layer at the positions of all points on this line are the same as the normal water level of the reservoir. Figure 2

[0112] II. Drawing a groundwater level contour line

[0113] The elevations of the groundwater level at the positions of all points on this groundwater level contour line are the same as the normal water level of the reservoir, and the normal water level of the reservoir is the existing design index of 386 meters. The drawing of the contour line is based on the observation data of the groundwater level in the boreholes, and the average value of the observation data of the groundwater level in the dry season when the water level is relatively low is used, as shown in a. The specific drawing steps are as follows: Figure 2

[0114] ​​2.4) Based on the drilling plane coordinates, the drilling positions are determined on the plan; adjacent high water level drillings, low water level drillings are connected with dotted lines, and three second dotted line connecting lines are obtained. The high water level drilling refers to the drilling whose position is higher than the normal water level of the reservoir, such as Figure 2 the drillings ZK1, ZK3, ZK5 in a correspond to the underground water level of the drillings respectively W1=410.2m, W3=407.8m, W5=406.6m; the low water level drilling refers to the drilling whose position is lower than the normal water level of the reservoir, such as Figure 2 the drillings ZK2, ZK4, ZK6 in a correspond to the underground water level of the drillings respectively W2=369.5m, W4=368.0m, W6=359.5m. The three second dotted line connecting lines are ZK1-ZK2, ZK3-ZK4, ZK5-ZK6 respectively. The underground water level of the drilling position is the arithmetic mean of the underground water level observation value of the drilling in the dry season.

[0115] One high water level drilling can be connected with other multiple low water level drillings, such as ZK1 can be connected with ZK2, or can be connected with ZK4, ZK6 respectively, but because the distance between ZK1 and ZK2 is small, the interpolation accuracy is relatively high; the distance between ZK1 and ZK4, ZK6 is large, and the interpolation accuracy is relatively small, so the nearest ZK2 to ZK1 is selected for connection.

[0116] If the underground water level of the positions of the two adjacent drillings such as ZK1 and ZK2 is higher than the normal water level of the reservoir, then the drillings below ZK1 and ZK2 are constructed respectively until the underground water level of the drilling position is lower than the normal water level of the reservoir. If the underground water level of the positions of the two adjacent drillings such as ZK1 and ZK2 is lower than the normal water level of the reservoir, then the drillings above ZK1 and ZK2 are constructed respectively until the underground water level of the drilling position is higher than the normal water level of the reservoir. Generally, the drilling positions are uniformly distributed during the construction, and the above situation does not exist.

[0117] 2.5) On the three second dotted line connecting lines ZK1-ZK2, ZK3-ZK4, ZK5-ZK6, the positions of the equal water level points are determined respectively, such as Figure 2 the points E, F, G in a.

[0118] The position of the equal water level point on the second dotted line connecting line is determined by interpolation, and the following formula is used for calculation: the straight line distance of the equal water level point to the high water level drilling = the straight line distance of the high, low water level drilling ÷ the difference of the underground water level of the high, low water level drilling × (the underground water level of the high water level drilling - the normal water level of the reservoir).

[0119] On the dotted line ZK1-ZK2, the straight-line distance between the high-water-level boreholes and the low-water-level boreholes is 67.7 meters. The groundwater surface elevations of the high-water-level boreholes and the low-water-level boreholes are 410.2 meters and 369.5 meters, respectively. The normal water level elevation of the reservoir is 386 meters. Therefore, the straight-line distance from point E to the high-water-level borehole ZK1 is 67.7 ÷ (410.2 - 369.5) × (410.2 - 386) = 40.3 meters. Thus, the location of point E is determined.

[0120] On the dotted line ZK3-ZK4, the straight-line distance between the high-water-level boreholes and the low-water-level boreholes is 70.5 meters. The groundwater surface elevations of the high-water-level boreholes and the low-water-level boreholes are 407.8 meters and 368.0 meters, respectively. The normal water level elevation of the reservoir is 386 meters. Therefore, the straight-line distance from point F to the high-water-level borehole ZK3 is 70.5 ÷ (407.8 - 368.0) × (407.8 - 386) = 38.6 meters. Thus, the location of point F is determined.

[0121] On the dotted line ZK5-ZK6, the straight-line distance between the high-water-level boreholes and the low-water-level boreholes is 80.0 meters. The groundwater surface elevations of the high-water-level boreholes and the low-water-level boreholes are 406.6 meters and 359.5 meters, respectively. The normal water level elevation of the reservoir is 386 meters. Therefore, the straight-line distance from point G to the high-water-level borehole ZK5 is 80.0 ÷ (406.6 - 359.5) × (406.6 - 386) = 35.0 meters. Thus, the location of point G is determined.

[0122] 2.6) Connect points E, F, and G on the three second dashed lines with a smooth curve to form groundwater level contour lines, such as... Figure 2 The solid line 1 in a represents the groundwater level at all points on the line, which is the same as the normal water level of the reservoir.

[0123] Step 3): Based on the above groundwater level contour lines and the top contour lines of the relatively impermeable layer, a preliminary seepage prevention route around the dam is proposed.

[0124] like Figure 3 As shown, the seepage prevention lines around the dam have two directions, both starting from the endpoint S of the seepage prevention line at the dam foundation, extending to the groundwater level and the contour line of the top surface of the relatively impermeable layer, respectively. Therefore, two preliminary seepage prevention line schemes are proposed as follows:

[0125] 1) Based on the coordinates of endpoint S, determine the position of endpoint S on the plan; there is a moving point A on the groundwater level line, find the point A that is closest to the line segment between endpoint S, then the line segment SA is a seepage prevention line scheme (groundwater level scheme);

[0126] 2) Based on the plane coordinates of endpoint S, determine the position of endpoint S on the plan; there is a moving point B on the contour line of the top surface of the relatively impermeable layer. Find the point B that is closest to the line segment between endpoint S and the point B. Then the line segment SB is another seepage prevention line scheme (the top surface of the relatively impermeable layer scheme).

[0127] Through the end point S, the seepage prevention line around the dam is connected with the seepage prevention line of the dam foundation, and a complete seepage prevention system of the dam is formed.

[0128] Step 4): determining the seepage prevention line around the dam

[0129] As shown in the figure, by comparing the lengths of the line segment SA and the line segment SB, the line segment with the smaller length is selected as the position of the seepage prevention line around the dam. Because the length of the line segment SA is 114 meters, the length of the line segment SB is 92 meters, SA>SB, and the line segment SB with the smaller length is selected as the position of the seepage prevention line. Figure 3

[0130] Compared with the line segment SA, the length of the seepage prevention line SB is reduced by 22 meters, and the seepage prevention length is saved by 19.3%.

[0131] For the seepage problem around the left bank of the dam in the embodiment, a seepage prevention line is determined by using a traditional method in the feasibility study stage, and the optimal seepage prevention line is determined by using the method provided by the application after investigation and research in the preliminary design and construction drawing design stage. The seepage prevention line is shortened by 41 meters, the seepage curtain engineering quantity is reduced by 760 square meters, and the construction processing cost is saved by 1.14 million yuan. At the same time, the follow-up monitoring data shows that the seepage around the dam of the large-scale water conservancy project is safe.

[0132] In summary, the method for determining the position of the seepage prevention line around the dam provided by the application adjusts the interval dynamically (steep slope 50-75 meters / slow slope 75-100 meters) by grid drilling combined with the terrain slope, which ensures the data coverage density and optimizes the exploration cost. The full-hole segmented permeation test (water injection test for soil layer / pressure test for rock layer) is used, and the water level observation (including three seasons of dry / flat / dry) of a complete hydrological year is used, to ensure the multi-dimensional accuracy of the geological parameters and dynamic hydrological data, and to provide a reliable basis for positioning the seepage prevention line.

[0133] The application innovatively determines the seepage prevention boundary in two dimensions through the underground water level contour line reflecting the characteristics of the seepage field and the contour line of the top surface of the relatively impermeable layer revealing the geological structure. The contour line is drawn by using the water level data in the dry season and the strict seepage prevention standard value, and a high-safety-degree design is formed, which effectively avoids the seepage risk in the wet season.

[0134] The application realizes accurate fitting of the contour line based on the AutoCAD spline curve, calculates the coordinates of the key connection points by combining the interpolation method mathematical model, determines the shortest seepage prevention path by comparing and selecting the lengths of the line segments SA and SB, and realizes the optimal balance between engineering economy and seepage prevention reliability.

[0135] ​The application realizes seamless connection of the dam-circumventing line with the existing dam foundation anti-seepage system through the endpoint S, forming a closed anti-seepage system. The determined line can effectively intercept the dam-circumventing seepage channel and can maximize the reduction of anti-seepage structure engineering quantity and construction cost.

[0136] The long-term water level observation data of the application reflect seasonal hydrological changes, and the anti-seepage line design meets the requirements of reference safety in dry season and extreme working condition in wet season at the same time. The dynamic contour drawing method can adapt to different anti-seepage standards and is suitable for seepage control design of various dam types such as earth-rock dam and concrete dam.

[0137] The method deeply integrates engineering geological survey, hydrological dynamic monitoring and digital design technology, and solves the problems of positioning anti-seepage line by experience, excessive or insufficient protection in the traditional method.

[0138] Obviously, those skilled in the art can make various modifications and variations to the application without departing from the spirit and scope of the application. Thus, if these modifications and variations of the application belong to the scope of the claims of the application and equivalent technologies thereof, the application also intends to include these modifications and variations.

[0139] The contents not described in detail in the specification belong to the prior art known to those skilled in the art.

[0140] The above is only the preferred embodiment of the application, and does not limit the patent scope of the application. Any equivalent structural transformation made under the inventive concept of the application, using the content of the specification and drawings, or directly / indirectly applied in other related technical fields is included in the patent protection scope of the application.

Claims

1. A method for determining the location of a seepage prevention line around a dam, characterized in that: Includes the following steps: 1) Conduct drilling and perform permeability tests and long-term groundwater level monitoring within the boreholes; 2) Based on the results of the permeability test, obtain the elevation of the top surface of the relatively impermeable layer at the location of the borehole and draw a contour line of the top surface of the relatively impermeable layer; based on the long-term groundwater level observation data, obtain the groundwater level information at the location of the borehole and draw a groundwater level contour line. 3) Based on the groundwater level contour lines and the top contour lines of the relatively impermeable layer, two seepage prevention routes around the dam are initially proposed. 4) Based on the lengths of the two seepage prevention lines around the dam, select the shorter one as the seepage prevention line around the dam.

2. The method for determining the location of the seepage prevention line around the dam according to claim 1, characterized in that: In step 1), the boreholes are arranged on the slope of the dam abutment, perpendicular to the horizontal plane and downward, and the boreholes are parallel to each other; the distance between the boreholes is 50 to 100 meters.

3. The method for determining the location of the seepage prevention line around the dam according to claim 1, characterized in that: The permeation test is a borehole permeation test, including a borehole water pressure test or a borehole water injection test.

4. The method for determining the location of the seepage prevention line around the dam according to claim 1, characterized in that: The long-term groundwater level observation is carried out after the borehole and seepage test are completed. The observation period includes at least one complete hydrological year, which includes the wet season, normal season and dry season. The water level observation interval is 6 to 8 days. During each observation, the groundwater level of all boreholes is observed on the same day.

5. The method for determining the location of the seepage prevention line around the dam according to claim 1, characterized in that: In step 2), the contour lines of the top surface of the relatively impermeable layer include contour points and their coordinate information. The elevation of the top surface of the relatively impermeable layer at the location of the contour points is the same as the normal water level of the reservoir.

6. The method for determining the location of the seepage prevention line around the dam according to claim 5, characterized in that: The steps for drawing the contour lines of the top surface of the relatively impermeable layer are as follows: 2.1) Based on the coordinates of the borehole, determine the borehole location; connect adjacent high-elevation and low-elevation boreholes with dashed lines to obtain a first dashed connection line; the high-elevation borehole refers to a borehole whose elevation relative to the top surface of the impermeable layer is higher than the normal water level of the reservoir; the low-elevation borehole refers to a borehole whose elevation relative to the top surface of the impermeable layer is lower than the normal water level of the reservoir. 2.2) Based on the relative elevation of the top surface of the impermeable layer at the location of the borehole, determine the positions of the contour points on the first dashed line connecting each point; 2.3) Connect the contour points on each of the first dashed lines with a smooth curve to form a contour line of the top surface of the relatively impermeable layer; the elevation of the top surface of the relatively impermeable layer at the location of all points on the contour line of the top surface of the relatively impermeable layer is the same as the normal water level of the reservoir.

7. The method for determining the location of the seepage prevention line around the dam according to claim 1, characterized in that: In step 2), the groundwater level contour lines include isostatic points and their coordinate information. The groundwater level elevation at the location of the isostatic points is the same as the normal water level elevation of the reservoir. The contour lines are drawn based on groundwater level observation data from boreholes during the dry season.

8. The method for determining the location of the seepage prevention line around the dam according to claim 7, characterized in that: The steps for drawing the groundwater level contour lines are as follows: 2.4) Based on the coordinates of the borehole, determine the borehole location; connect adjacent high-water-level and low-water-level boreholes with dashed lines to obtain a second dashed connection line; the high-water-level borehole is a borehole whose groundwater level is higher than the normal water level of the reservoir; the low-water-level borehole is a borehole whose groundwater level is lower than the normal water level of the reservoir. 2.5) Based on the groundwater surface elevation at the location of the borehole, determine the positions of the equal water points on each of the second dashed lines; 2.6) Connect the isostatic points on each of the second dashed lines with a smooth curve to form the groundwater surface isostatic line. The groundwater surface elevation at all points on the groundwater surface isostatic line is the same as the normal water level elevation of the reservoir.

9. The method for determining the location of the seepage prevention line around the dam according to claim 1, characterized in that: In step 3), the initially proposed seepage prevention and control lines around the dam include two: One of them starts from endpoint S and extends to the groundwater level line; the drawing method includes: determining the coordinates of endpoint S, finding point A on the groundwater level line that is closest to endpoint S in a straight line, and connecting point A and endpoint S to form line segment SA. The line segment SA is the initially proposed seepage prevention line around the dam that extends from endpoint S to the groundwater level line. Another line starts from endpoint S and extends to the contour line of the top surface of the relatively impermeable layer. The drawing method includes: determining the coordinates of endpoint S, finding point B on the contour line of the top surface of the relatively impermeable layer that is closest to endpoint S in a straight line, and connecting point B and endpoint S to form line segment SB. The line segment SB is the initially proposed seepage prevention line around the dam that extends from endpoint S to the contour line of the top surface of the relatively impermeable layer. Endpoint S is the endpoint of the seepage prevention line for the dam foundation.

10. The method for determining the location of the seepage prevention line around the dam according to claim 1, characterized in that: In step 4), if the two seepage prevention lines around the dam are the same length, the line shall be determined by combining geological conditions, construction difficulty and economic efficiency.

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