CN116432273A - Suspension type seepage-proof design method for foundation dam with strong water permeability and deep coverage layer - Google Patents
Suspension type seepage-proof design method for foundation dam with strong water permeability and deep coverage layer Download PDFInfo
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Abstract
The invention provides a suspension type seepage-proofing design method for a foundation dam with a strong water-permeable deep coverage layer, which refers to the established engineering experience, combines the geological conditions of the dam foundation coverage layer of the engineering, and prepares the depth of a suspension type seepage-proofing wall, considers the spreading arrangement before the dam and the setting position of the seepage-proofing wall by matching with the dam arrangement, calculates the seepage quantity and the seepage gradient of each part through two-dimensional and three-dimensional finite element seepage field analysis, requires the seepage quantity to be less than 1% of the average flow of a plurality of years, and has the risk of seepage damage when the seepage superdrop of the bottom of the seepage-proofing wall exceeds the allowable value. The design safety evaluation method and the index for the excessive permeation gradient of the bottom of the suspension type impervious wall are introduced in the impervious design, so that the risk of great adverse effect on engineering caused by permeation damage of the deep coverage layer can be well controlled.
Description
Technical Field
The invention relates to the technical field of water conservancy and hydropower, in particular to a suspension type seepage-proofing design method for a foundation dam with a strong water permeability and a deep coverage layer.
Background
The cover layer refers to the general term of loose deposit and sediment which are covered on the bedrock through various geological actions, and the deep cover layer of the river bed generally refers to loose deposit which is piled on the bottom of the river valley and has the thickness of more than 40 m. According to the different thickness, the water and electricity construction requirements are combined, and the water and electricity construction requirements can be further subdivided into a thick covering layer (40 m-100 m), an ultra-thick covering layer (100 m-300 m) and an ultra-thick covering layer (the thickness is larger than 300 m).
The cover layer is widely distributed in the river in southwest mountain area of China, and the depth is tens of meters generally. Most of these coatings are highly water permeable coatings, which present leakage and osmotic failure problems. Many dams are built in Min river and large-ferry river basins with deep coverage layers, mainly rock-fill dams with medium and high water heads and gate dams with low water heads. The dam is built by utilizing the deep-thick coverage layer, which has the great advantages of economy, environmental protection and the like, and a large number of investigation results show that the deep-thick coverage layer has the characteristics of multiple causes, diversity of distribution range, variability of output thickness, complexity of composition structure, variability of engineering characteristics and the like, and the dam foundation coverage layer seepage prevention design is a key technical problem in the deep-thick coverage layer dam building design. .
The seepage-proofing measures of the dam foundation of the deep and thick coverage layer of the dam can be divided into two main types of horizontal seepage-proofing measures and vertical seepage-proofing measures. The horizontal barrier measure is typically a wide variety of coverings. The vertical seepage-proofing measures include water interception tank, seepage-proofing wall, curtain grouting, etc. Too large a water interception tank depth is uneconomical and therefore not applicable to deep coverage. The vertical seepage-proofing measures which are suitable for the strong water-permeable covering layer are seepage-proofing wall and curtain grouting and the combination of the seepage-proofing wall and the curtain grouting. In recent years, along with the development of deep coverage dam construction and impervious wall technology, more and more high dam foundation coverage layers adopt impervious walls for impervious. The vertical seepage prevention effect of the same scale is far better than that of the horizontal seepage prevention effect, and meanwhile, the seepage prevention wall is developed to be a reliable technology of the vertical seepage prevention, so that the economy is considered, the vertical seepage prevention is usually taken as the main part of the high-water-permeability deep-thickness covering layer, and the horizontal seepage prevention is assisted when necessary. The gate dams on the built strong water-permeable deep coverage layer are mostly in the form of short-paved and suspended impermeable walls, while the rock-fill dams with medium and high water heads are mostly in the form of closed impermeable walls, impermeable walls and curtain grouting closed coverage layers, and a small amount of engineering adopts suspended impermeable. The deep coverage layers adopt suspension type seepage prevention engineering, and the deep coverage layer foundation of the individual engineering is damaged by seepage.
Disclosure of Invention
The invention mainly aims to provide a suspension type seepage-proofing design method for a foundation dam with a strong water permeability and a deep coverage layer, which solves the problems in the background technology.
In order to solve the technical problems, the invention adopts the following technical scheme: the method comprises the following specific steps:
s1, referring to established engineering experience, combining geological conditions of a dam foundation covering layer, drawing up the depth of a suspension type impervious wall, and calculating the spreading arrangement and the impervious wall setting position in front of a dam by matching with dam arrangement;
s2, analyzing and calculating leakage quantity and the permeation gradient of each part through a two-dimensional and three-dimensional finite element seepage field, wherein the leakage quantity is required to be less than 1% of the average flow for many years;
s3, ensuring that the escape gradient of the surface of the downstream covering layer is smaller than the allowable permeation gradient of the covering layer, wherein the permeation gradient of the covering layer at other parts except the part of the bottom of the suspension type impervious wall in the covering layer is not more than the allowable permeation gradient;
s4, when the permeation gradient of the covering layer can not meet the requirements, the requirements are met by enlarging the suspension type seepage-proofing depth and horizontally paving the upper stream;
and S5, calculating the excessive limit of the permeation slope of the covering layer at the bottom of the impervious wall, and considering the safety when the maximum value is smaller than the critical permeation slope of the covering layer, and further researching the safety influence possibly caused by whether the internal corrosion of the covering layer occurs or not when the maximum value is larger than the critical permeation slope of the covering layer.
In the preferred scheme, the characteristics of the dam foundation river bed covering layer are analyzed, and a plurality of calculation and comparison schemes of seepage prevention depths are determined.
In the preferred scheme, the seepage flow of each seepage prevention scheme is calculated under the normal water storage level in the operation period of the dam by analyzing the three-dimensional seepage flow of the dam area.
In the preferred scheme, the permeability gradient distribution characteristics are calculated according to three-dimensional seepage, the distribution rule of the permeability gradient of the covering layer in each scheme is analyzed, and the permeability gradient of the covering layer at the lower part of the dam body is calculated.
In a preferred embodiment, in step S5, the step of analyzing the corrosion inside the cover layer is as follows:
a1, judging the soil gushing of the inner tube;
a2, soil erosion analysis;
a3, analyzing the corrosion range and the deformation caused by the corrosion range;
and A4, analyzing the influence of the corrosion on the seepage field and the stress deformation.
In the preferred scheme, in the step A2, through a seepage corrosion test, the loss amount of fine particles of a soil layer under different hydraulic gradients and the osmotic coefficient change and skeleton deformation process caused by the loss amount are calculated, and the osmotic stability discrimination parameters are obtained, so that the osmotic safety of the bottom of the impervious wall is quantitatively analyzed.
The invention provides a design method for the suspension type seepage prevention of a foundation dam with a strong water-permeable deep coverage layer, wherein the seepage exceeding drop of the bottom of the seepage prevention wall is at risk of seepage damage, the prior design method has no method and standard for risk control and safety evaluation, and individual engineering is subjected to seepage damage, so that great seepage prevention reinforcement difficulty and investment are brought. The design safety evaluation method and the index for the excessive permeation gradient of the bottom of the suspension type impervious wall are introduced in the impervious design, so that the risk of great adverse effect on engineering caused by permeation damage of the deep coverage layer can be well controlled.
Drawings
The invention is further illustrated by the following examples in conjunction with the accompanying drawings:
FIG. 1 is a map of the permeability of a formation in a maximum profile with the barrier scheme of the present invention;
FIG. 2 is a map of the reduced permeability of the formation in maximum section for the second embodiment of the present invention;
FIG. 3 is a map of the formation permeability degradation of the largest cross-section under the anti-seepage scheme of the present invention;
FIG. 4 is a map of the formation permeability degradation of the fourth largest cross-section of the permeation protection scheme of the present invention;
FIG. 5 is a map of the reduced permeability of the formation in the fifth largest section of the permeation protection scheme of the present invention;
FIG. 6 is a map of the reduced permeability of the formation in maximum section for the barrier of the present invention;
FIG. 7 is a map of the reduced formation permeability for the seventh largest section of the permeation protection scheme of the present invention;
FIG. 8 is a map of the formation permeability degradation of the largest cross section under the barrier scheme eight of the present invention;
FIG. 9 is a graph of permeability degradation of the lower overburden of a dam in accordance with the present invention;
FIG. 10 is a graph of permeability degradation of the lower overburden of a secondary dam in an anti-seepage scheme according to the present invention;
FIG. 11 is a graph of permeability degradation of the lower overburden of a three-dam in an anti-seepage scheme of the present invention;
FIG. 12 is a graph of permeability degradation of the lower overburden of a four-dam in an anti-seepage scheme of the present invention;
FIG. 13 is a graph of the permeability degradation of the lower overburden of a five-dam in an anti-seepage scheme of the present invention;
FIG. 14 is a graph of permeability degradation of the lower overburden of a six-dam in an anti-seepage scheme in accordance with the present invention;
FIG. 15 is a graph of the permeability degradation of the lower overburden of a seven-dam in the anti-seepage scheme of the present invention;
FIG. 16 is a graph of permeability degradation of the lower overburden of an eight dam in an anti-seepage scheme of the present invention;
FIG. 17 is a schematic view of the erosion scope of the curtain localized defect scheme 1 of the present invention;
FIG. 18 is a schematic view of the erosion scope of the curtain localized defect scheme 2 of the present invention;
FIG. 19 is a distribution of the latent etch deformation for the curtain localized defect scheme 1 of the present invention;
FIG. 20 is a distribution of the latent etch deformation for the curtain localized defect scheme 2 of the present invention;
FIG. 21 is a graph showing the comparison of the percolation fields before and after the erosion according to scheme 1 of the present invention;
FIG. 22 is a graph showing the comparison of the percolation fields before and after the erosion according to scheme 2 of the present invention;
FIG. 23 is a graph showing the flow rate and hydraulic ramp down of the defective zone of scheme 1 of the present invention over time;
FIG. 24 is a graph showing the flow rate and hydraulic ramp down of the defective zone of scheme 2 of the present invention over time.
Detailed Description
Example 1
As shown in fig. 1 to 24, the design method for the suspension type seepage prevention of the foundation dam with the strong water permeability and the deep coverage layer comprises the following steps of:
the river bed covering layer of a dam site area of a certain hydropower station is deep, the maximum thickness of the river bed covering layer reaches 174.57m through exploration and disclosure, the river bed covering layer is limited by the evolution process of a river valley, and the layer of the river bed covering layer is complex. Wherein the layer (1) is a mixed accumulation of alluvial and collapse accumulation (Q3al+col), and the layer thickness is 80-100 m, and the crushed gravel soil containing blocks is the main material; the layer (2) is mainly from two shoreside collapse and slope accumulation, the thickness of the upper layer is about 10 m-40 m, and the thickness of the layer is about 45 m-65 m, and the layer is mainly composed of a layer containing solitary gravel; the (3) th layer river and lake phase is piled up (Q4al+l) and divided into six sublayers, wherein the (3) -1, (3) -3, (3) -5 layers mainly comprise lake sediment fine sand and silt layers, (3) -2, (3) -4 and (3) -6 layers mainly comprise drift sand and gravel layers; the layer (4) is a collapse slope (Q4 col+dl) which is mainly distributed on the left bank slope of the dam site area and mainly comprises loose structure of the broken gravel soil containing the isolated blocks.
The main bearing layer of the river bed dam foundation covering layer foundation consists of a layer (2) and a layer (3). Wherein the (2) th layer, (3) -2 layer and (3) -4 layer have good bearing conditions; (3) the embedded depth of the two sand layers (1, 3) and (3) is larger, so that the dam foundation bearing requirement is basically met; (3) 5 layers of layers with the thickness of 10 m-13 m, 2.5 m-8.5 m below the dam foundation, shallow burial depth and larger layer thickness, and the dam foundation can have the problems of bearing and uneven deformation, stable sliding resistance and sand liquefaction. The main body of the riverbed dam foundation consists of a sand gravel layer and a broken (ovum) layer containing isolated blocks, the whole dam foundation has medium-strong water permeability, and the local silt, silt and fine sand layers are weak water permeability layers, so that the dam foundation leakage and permeation stability problems are more remarkable.
And (3) calculating and comparing the seepage prevention depth:
1) Seepage prevention scheme one: 100m deep suspension impervious wall +3 rows of covering layer grouting curtains +1 row of bedrock grouting curtains;
2) And a second seepage prevention scheme: 120m deep suspension impervious wall +3 rows of covering layer grouting curtains +1 row of bedrock grouting curtains;
3) And (3) an anti-seepage scheme III: 150m deep suspension impervious wall +3 rows of covering layer grouting curtains +1 row of bedrock grouting curtains;
4) And a seepage prevention scheme IV: 176m deep suspension impervious wall and 1 row of bedrock grouting curtain;
5) And a seepage prevention scheme V: 100m deep suspension impervious wall;
6) And a seepage prevention scheme six: 120m deep suspension impervious wall;
7) Seepage prevention scheme seven: 150m deep suspension impervious wall;
8) Seepage prevention scheme eight: 176m deep sealing impervious wall;
dam area three-dimensional seepage flow analysis:
the seepage flow calculation results of the section of the model seepage wall under each seepage prevention scheme under the flood level design in the dam operation period are shown in table 1.
Table 1: seepage control volume (m) of seepage control section of dam area of each seepage control scheme 3 /d)
As is known from Table 1, the total seepage amount of each seepage prevention scheme is less than 1% of the average flow rate of years, wherein the seepage amount of the 100m deep suspension type seepage prevention wall is 18930m 3 And/d, which is about 0.22% of the average annual flow, so that leakage does not limit the choice of dam foundation anti-seepage scheme.
The figure 1-8 shows the maximum section cover layer permeability ratio drop cloud chart under each seepage prevention scheme, the figure shows that the total permeability ratio drop of the cover layer shows a distribution rule gradually decreasing from the bottom of the seepage prevention wall to the periphery, and the cover layer permeability ratio drop at the bottom of the seepage prevention wall exceeds the cover layer allowable permeability ratio drop recommended value by 0.2-0.25 and exceeds the range of 25-100m in other schemes except the seepage prevention wall rock-entering scheme.
The permeability ratio of the lower covering layer of the dam body is reduced: as can be seen from fig. 9 to 16, the permeability ratio drop extremum of the downstream side coating decreases with increasing depth of the impermeable wall, and comparing with the under-wall impermeable curtain scheme, the under-wall impermeable curtain can effectively reduce the permeability ratio drop of the overflow point of the downstream side coating. Referring to the proposed (4) th layer of the covering layer of the current geology, the allowable permeability ratio drop recommended value is 0.15-0.18, and the overflow points of the covering layers of scheme I, two, five, six and seven have the possibility of exceeding the limit of the permeability ratio drop.
Research on the inner penetration damage standard of the soil layer at the end part of the impervious wall:
judging the inner piping soil: the layer (1) soil is named as crushed stone mixed soil, the uniform coefficient is 92.0, and the average curvature coefficient is 4.3. Although the internal instability soil was initially judged according to the internal instability discriminant criteria of Liu Jie and Kenney et al.
Soil erosion analysis: and (3) a seepage corrosion test is adopted to quantitatively give out the loss amount of fine particles of the layer (1) under different hydraulic gradients, and a seepage coefficient change and a skeleton deformation process caused by the loss amount, so as to give out reasonable seepage stability discrimination parameters.
And a seepage-deformation coupling analysis method considering the particle loss process is adopted to quantitatively analyze the seepage safety of the bottom of the impervious wall.
The extent of erosion and the resulting deformation: it can be seen that even with a small fines loss rate of 1% as a limit, the range of potential erosion is limited to the region 50m upstream of the curtain to 100m downstream of the barrier. If 5% loss is used as a limit, the erosion is limited to a range of 10m upstream and downstream of the curtain.
Fig. 19 and 20 show deformation profiles resulting from the erosion of the two solutions, respectively. Because the earth skeleton is not substantially deformed at small loss of fines, the deformation is concentrated mainly in the units around the curtain defect, with a small extent. The maximum deformation value of scheme 1 is about 1-2 cm, and the maximum deformation value of scheme 2 is 2-3 cm, which is slightly larger than that of scheme 1. Because the range of the erosion is small, and (1) the soil body of the layer has good skeleton stability after the fine particles are lost, the erosion cannot cause local large deformation under the two schemes.
Effects of corrosion on seepage field: the water head difference between the upper and lower streams of the curtain before the submergence in the scheme 1 is about 15m, and the water head difference is reduced to 5m after the submergence; scheme 2 the head difference between the upstream and downstream of the curtain before submergence is about 10m, and the drop after submergence is less than 5m. It can be seen that the main consequence of the diving is a significant increase in the head assumed by the entire downstream river.
FIGS. 23 and 24 show the time course of the flow rate and hydraulic ramp down in the defective area of the curtain for scheme 1 and scheme 2, respectively, revealing the mechanism by which the dam will terminate after a small range of underetching has occurred. The river channel at the downstream of the hydropower station is blocked by a deep coating layer, and the downstream of the curtain is a limited drainage condition. In the process of submergence, as the seepage quantity increases, the downstream water head of the curtain can be rapidly increased, the water head difference between the upstream water head and the downstream water head is reduced, so that the concentrated hydraulic gradient of the defect area is reduced, the seepage coefficient of the submergence soil body is increased, the flow speed gradually tends to be stable, the hydraulic condition is not deteriorated, and the submergence range is not developed. In the curtain reinforcement grouting process of the covering layer, the water head reduction time process of the observation hole shows that the downstream water head is very high as long as the curtain has larger leakage, and the restriction of the downstream covering layer on the leakage amount of the dam foundation is proved.
It should be noted that the above-described phenomenon of limited extent of erosion is related to the flow limiting effect of the coating downstream of the hydropower station. For the condition of open drainage with unlimited downstream or very weak flow restriction, the increase of seepage flow of the seepage-proofing system does not bring about obvious increase of downstream water head, the decrease of hydraulic gradient is not obvious, and the flow can be always increased due to the increase of seepage coefficient of the submergence soil body, thereby causing large scale submergence and bringing about disastrous results. For a hydropower station, when large gushing water appears on a downstream covering layer, the hydraulic gradient at the curtain can be increased, and the corrosion at the local defect can be restarted; therefore, the method should be treated in time, the flow limiting effect of the downstream covering layer is restored, and the pressure of the dam axis seepage prevention system is relieved.
The comparison of the concentrated hydraulic gradient and flow rates in the curtain zone of the two schemes of fig. 23 and 24 explains why the expansion of the defect zone range does not lead to a greater extent of erosion. The range of the defect area in the scheme 2 is larger, the leakage flow rate is increased to enable the water head difference between the upstream and the downstream to be smaller than that in the scheme 1, so that the hydraulic gradient and the flow rate of the defect area in the scheme 2 are both greatly reduced compared with those in the scheme 1, and the influence range of the erosion in the upstream and the downstream is smaller than that in the scheme 1.
The above embodiments are only preferred embodiments of the present invention, and should not be construed as limiting the present invention, and the scope of the present invention should be defined by the claims, including the equivalents of the technical features in the claims. I.e., equivalent replacement modifications within the scope of this invention are also within the scope of the invention.
Claims (6)
1. The design method for the suspension type seepage prevention of the foundation dam with the strong water permeability and the deep coverage layer is characterized by comprising the following steps: the method comprises the following specific steps:
s1, referring to established engineering experience, combining geological conditions of a dam foundation covering layer, drawing up the depth of a suspension type impervious wall, and calculating the spreading arrangement and the impervious wall setting position in front of a dam by matching with dam arrangement;
s2, analyzing and calculating leakage quantity and the permeation gradient of each part through a two-dimensional and three-dimensional finite element seepage field, wherein the leakage quantity is required to be less than 1% of the average flow for many years;
s3, ensuring that the escape gradient of the surface of the downstream covering layer is smaller than the allowable permeation gradient of the covering layer, wherein the permeation gradient of the covering layer at other parts except the part of the bottom of the suspension type impervious wall in the covering layer is not more than the allowable permeation gradient;
s4, when the permeation gradient of the covering layer can not meet the requirements, the requirements are met by enlarging the suspension type seepage-proofing depth and horizontally paving the upper stream;
and S5, calculating the excessive limit of the permeation slope of the covering layer at the bottom of the impervious wall, and considering the safety when the maximum value is smaller than the critical permeation slope of the covering layer, and further researching the safety influence possibly caused by whether the internal corrosion of the covering layer occurs or not when the maximum value is larger than the critical permeation slope of the covering layer.
2. The method for designing the suspension type seepage prevention of the foundation dam with the strong water permeability and the deep coverage layer, which is characterized in that: and analyzing the characteristics of the dam foundation riverbed covering layer, and determining a plurality of calculation and comparison schemes of the seepage prevention depths.
3. The method for designing the suspension type seepage prevention of the foundation dam with the strong water permeability and the deep coverage layer, which is characterized in that: and calculating the seepage flow of each seepage prevention scheme under the normal water storage level of the dam in the operation period through the analysis of the three-dimensional seepage flow of the dam area.
4. The method for designing the suspension type seepage prevention of the foundation dam with the strong water permeability and the deep coverage layer, which is characterized in that: and calculating the permeability gradient distribution characteristics according to the three-dimensional seepage, analyzing the distribution rule of the permeability gradient of the covering layer of each scheme, and calculating the permeability gradient of the covering layer at the lower part of the dam body.
5. The method for designing the suspension type seepage prevention of the foundation dam with the strong water permeability and the deep coverage layer, which is characterized in that: in step S5, the overlay internal erosion analysis steps are as follows:
a1, judging the soil gushing of the inner tube;
a2, soil erosion analysis;
a3, analyzing the corrosion range and the deformation caused by the corrosion range;
and A4, analyzing the influence of the corrosion on the seepage field and the stress deformation.
6. The method for designing the suspension type seepage prevention of the foundation dam with the strong water permeability and the deep coverage layer, which is characterized in that: in the step A2, through a seepage corrosion test, the loss amount of fine particles of the soil layer under different hydraulic gradients and the osmotic coefficient change and skeleton deformation process caused by the loss amount are calculated, and the osmotic stability discrimination parameters are obtained, so that the osmotic safety of the bottom of the impervious wall is quantitatively analyzed.
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| CN113987656A (en) * | 2021-11-01 | 2022-01-28 | 中国电建集团贵阳勘测设计研究院有限公司 | Method for determining engineering parameters of seepage-proofing system of gate dam with deep covering layer |
| WO2022160713A1 (en) * | 2021-01-27 | 2022-08-04 | 中钢集团马鞍山矿山研究总院股份有限公司 | Method for constructing novel starter dam suitable for upstream tailings pond |
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| CN113987656A (en) * | 2021-11-01 | 2022-01-28 | 中国电建集团贵阳勘测设计研究院有限公司 | Method for determining engineering parameters of seepage-proofing system of gate dam with deep covering layer |
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