Construction method for reducing deformation of faceplate and foundation liquefaction risk of upper faceplate dam of deep and thick covering layer in water storage period

Abstract

The invention discloses a construction method for reducing panel deformation and foundation liquefaction risks of an upper panel dam of a deep and thick covering layer in the water storage period, and belongs to the technical field of water conservancy projects. The method comprises the steps that (1) in the construction process, the whole face plate dam and upstream outer side filling soil are synchronously filled, so that the outer side filling soil generates pre-pressure on the face plate dam and provides an early-stage stress history, it is ensured that face plate deformation in the subsequent water storage period mainly presents linear elastic response approximately within the early-stage stress range, face plate deformation after water storage is reduced, and the construction efficiency is improved; the width of the outer filling bottom is calculated and determined according to the designed water pressure and the filling density, and it is guaranteed that the prestress reaches two times of the designed water pressure; (2) outer side filling soil applies ballasting load to the covering layer foundation, and the compactness of the foundation is improved; after filling is completed, outer side filling soil is excavated step by step to form a face plate dam structure; and (3) the outer side filling soil is moved to the more outer side area of the covering layer, and a ballasting zone is formed to improve the liquefaction resistance of the foundation. Deformation of the face plate in the water storage period is remarkably reduced, the overall safety of the dam body and the liquefaction resistance of the foundation are improved, and good engineering application value and popularization prospects are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of water conservancy engineering, and relates to a construction method suitable for a panel dam on a thick covering layer, in particular to a construction method in which the panel dam is constructed as a whole and the outer backfill upstream is simultaneously constructed, so that the outer backfill generates prestress on the panel dam and provides an advance stress history for the panel dam, and at the same time generates a weighting effect on the foundation of the thick covering layer, so as to reduce the deformation of the panel during the water storage period and reduce the risk of foundation liquefaction. Background Art

[0002] At present, as an economical and efficient dam type, the concrete face dam is widely used in high dam and large reservoir projects. However, under the condition of deep overburden, due to the complex foundation conditions and water pressure during the water storage period, the concrete face dam is prone to large deformation, which affects the long-term safety of the dam body.

[0003] In existing construction technology, the deformation of the panel dam during the impoundment period is usually adjusted by thickening the panel or optimizing the joint design. These passive means fail to preload the panel dam during construction, and the ability to reduce the deformation of the panel during the impoundment period is limited. In addition, the construction of the panel dam requires the deployment of extrusion side walls, which makes the construction more complicated. In addition, under the action of earthquakes, the foundation of the thick overburden layer is prone to liquefaction due to the increase in pore pressure. Traditional reinforcement measures (such as vibro-stone piles and consolidation grouting) have limited effect on improving the liquefaction of large-area thick overburden layers. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes an innovative construction method, specifically, a construction method for reducing the deformation of the panel during the water storage period of the panel dam on the deep overburden layer and the risk of foundation liquefaction. By synchronously filling the panel dam as a whole and the upstream outer fill in the filling stage, that is, synchronously filling the panel dam as a whole and the upstream outer fill, the outer fill generates prestress on the panel dam during the filling process, simulating the effect of water pressure on the panel dam during the water storage period, and providing the prior stress history, ensuring that the panel deformation in the subsequent water storage period mainly presents an approximate elastic response within the prior stress range, reducing the deformation of the panel during the water storage period after the filling is completed. At the same time, the outer fill can also apply a weight load to the foundation of the deep overburden layer during the filling process, improve the compactness of the foundation of the deep overburden layer and reduce the risk of liquefaction. After the loading and weighting are completed, that is, after the filling is completed, the outer fill is excavated to form a panel dam structure that meets the design size, and the outer fill is moved to a more outer area to form a weight belt, and the foundation of the deep overburden layer is further weighted, thereby significantly improving the safety of the dam body and the anti-liquefaction ability of the foundation.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer, the construction method comprising:

[0007] First, during the construction process, the whole panel dam and its upstream outer fill are filled simultaneously. During the filling process, the outer fill generates prestress for the panel dam and provides the panel dam with the prior stress history, ensuring that the panel deformation in the subsequent water storage period mainly presents an approximately elastic response within the prior stress range, reducing the deformation of the panel during the water storage period. At the same time, a compressive load is applied to the deep overburden foundation to improve the compactness of the foundation and reduce the risk of liquefaction.

[0008] Secondly, after the filling is completed, the outer fill is excavated according to the design requirements, and the pressure of the outer fill is gradually unloaded to form a panel dam structure that meets the design dimensions.

[0009] Finally, the excavated outer fill is moved to the outer area of ​​the thick cover layer to form a weighted zone to further improve the foundation's ability to resist liquefaction.

[0010] Furthermore, the bottom width of the outer fill is calculated and determined according to the design water pressure and fill density, and the filling height is consistent with the filling height of the panel dam to simulate the loading effect of the design water pressure on the panel dam. The bottom width of the outer fill is defined as W, the design water pressure is P, the slope angle is θ, and the fill density is ρ, then the bottom width of the fill is W = P / ρgsinθ.

[0011] Furthermore, the outer filling is formed by multi-layer filling, the thickness of a single layer is 0.5-1.0m, and the compaction degree of each layer after vibration rolling treatment is not less than 95%.

[0012] Furthermore, the prestress applied to the outer fill is twice the design water pressure. The deadweight of the outer fill during the filling process is used to generate prestress on the panel dam to provide a stress history. This loading history provides a large initial stress for the panel, ensuring that the water pressure during subsequent water storage is within the initial stress range, so that the deformation of the panel presents an approximately elastic response, effectively reducing the overall deformation of the panel during the water storage period.

[0013] Furthermore, the outer filling applies a weight load to the foundation of the deep covering layer, and the weight load time is 30 to 60 days after the completion of the panel dam filling, so as to improve the compactness of the deep covering layer and reduce the risk of liquefaction.

[0014] Furthermore, the outer fill excavation is carried out in a zoned and layer-by-layer manner, and the excavation sequence is to gradually expand outward from the center area of ​​the panel dam. The excavation depth is consistent with the dam body filling height, and the excavation depth of each layer is 0.5 to 1.0 m to ensure uniform stress release of the dam body and foundation and avoid uneven settlement or deformation.

[0015] Furthermore, the outer filling after excavation is moved to the outer area of ​​the thick covering layer to form a weighted belt with a width of 1.5 to 2 times that of the liquefied area of ​​the thick covering layer, so as to further improve the anti-liquefaction ability of the outer foundation.

[0016] Furthermore, after the excavation is completed, an anti-seepage geomembrane is laid in the panel dam area, and the concrete panel is cast-in-place in different areas. At the same time, the construction of the panel joints and water stop joints is completed to ensure the anti-seepage and panel stability during the water storage period.

[0017] Furthermore, the outer filling is constructed with well-graded soil and stone materials with a particle size range of 10 to 50 mm to ensure that the filling has good compaction performance and drainage performance.

[0018] Furthermore, the construction method is suitable for areas with deep overburden layers with an overburden thickness of more than 30m. Through the synergistic effect of fill weight and prestress, the deformation of the panel dam during the water storage period is reduced to ≤5cm, and the liquefaction shear strength of the overburden foundation is increased by ≥30%, that is, the maximum horizontal deformation of the panel dam after unloading of the outer fill is controlled within 5cm, and the liquefaction shear strength of the foundation is increased by no less than 30%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The construction method proposed in the present invention for reducing the deformation of the panel during the water storage period of the panel dam on the deep overburden layer and the risk of foundation liquefaction can reduce the deformation of the panel during the water storage period and improve the anti-liquefaction ability of the deep overburden layer foundation. It is mainly reflected in the synchronous filling of the panel dam as a whole and the upstream outer fill during the construction phase, so that the outer fill generates prestress on the panel dam and provides a large prior stress history for the panel dam, ensuring that the water pressure during subsequent water storage is within the prior stress range, so that the deformation of the panel presents an approximately elastic response, significantly reducing the deformation of the panel during the water storage period; during the filling process, the outer fill applies a compressive load to the deep overburden layer foundation, effectively improving the compactness of the foundation and reducing the risk of liquefaction;

[0021] (2) The construction method proposed by the present invention does not require the deployment of extruded side walls, thereby reducing construction complexity, and compared with conventional construction methods, the amount of earthwork required for construction does not increase.

[0022] (3) The construction method proposed in the present invention is suitable for the construction of panel dams in areas with deep overburden. It can effectively reduce the panel deformation of the panel dam during the water storage period under complex geological conditions and improve the anti-liquefaction ability of the foundation. It has good engineering application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the overall structure of the face dam after construction of the present invention;

[0024] Figure 2 It is a schematic diagram of the overall structure of the present invention after the upstream fill is moved outward.

[0025] In the figure: 1 panel dam body; 2 panel; 3 outer fill; 4 weight belt; 5 thick cover layer. DETAILED DESCRIPTION

[0026] The implementation of the method of the present invention is described in detail below in conjunction with the accompanying drawings, but they do not constitute a limitation of the present invention and are only used as examples. At the same time, the advantages of the method of the present invention will become clearer and easier to understand through the description.

[0027] like Figure 1 , 2 As shown, the present invention proposes a construction method for reducing the deformation of the panel during the water storage period of a panel dam on a deep overburden layer and the risk of foundation liquefaction. The core structure includes a panel dam body 1, a panel 2, a synchronously constructed outer fill 3, a weight belt 4, and a deep overburden layer foundation 5. By synchronously filling the panel dam 1 and the upstream outer fill 3, the loading and unloading effect of the outer fill 3 on the panel dam 1 is utilized to provide a stress history, which significantly reduces the deformation of the panel 2 during the water storage period, and improves the anti-liquefaction ability of the deep overburden layer foundation 5 through the weight effect of the outer fill 3. The specific operation process is as follows:

[0028] 1) This embodiment is for a panel dam with a dam body height of 80m and a dam crest width of 10m on a deep overburden layer with a thickness of 30m. According to engineering geological conditions and design requirements, the panel dam and the upstream outer fill are built simultaneously, and the bottom width of the outer fill is 87m, and the height is consistent with the dam body.

[0029] 2) The filling is carried out in layers, with each layer of 0.8m thick. The filler is well-graded soil and stone with a particle size of 30mm. The compaction density reaches 95% after the filling is compacted. During the filling process, the outer filling provides a prestress of twice the water pressure during the water storage period, and the weight is continuously pressed until the completion of the panel dam for 30 days.

[0030] 3) After the filling is completed, the outer fill is excavated according to the design requirements to form a panel dam structure that meets the design dimensions. The excavation process is carried out layer by layer, with an excavation depth of 0.8m for each layer and a total excavation depth of 80m. The excavation sequence expands from the middle of the panel dam to the outside to ensure uniform stress release and avoid uneven settlement or local deformation of the dam body.

[0031] 4) The excavated outer fill is moved to the outer area of ​​the cover layer to form a 60m wide weight belt. After the outer fill is excavated, an anti-seepage geomembrane is laid in the panel dam area, and the concrete panel is cast in place in sections. The concrete panel adopts the slipform process, with a width of 4m in each section. After completion, the water stop and joint treatment are carried out.

[0032] Adaptive changes made according to actual needs are all within the protection scope of the present invention.

[0033] The present invention is not limited to the specific details of the above embodiments, and any improvements or equivalent variations within the scope of the claims belong to the protection scope of the present invention. The reference numerals are only for ease of understanding and should not be regarded as limiting the scope of the claims.

Claims

1. A construction method for reducing the deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer, characterized in that: The construction method is: First, during the construction process, the whole face-filled dam and its upstream outer fill are filled simultaneously. During the filling process, the outer fill generates pre-stress on the face-filled dam and provides the pre-stress history of the face-filled dam. At the same time, a compressive load is applied to the foundation of the overburden layer to improve the compactness of the foundation and reduce the risk of liquefaction. Secondly, after the filling is completed, the outer fill is excavated according to the design requirements, and the pressure of the outer fill is gradually unloaded to form a panel dam structure that meets the design dimensions; Finally, the excavated outer fill is moved to the outer area of ​​the cover layer to form a weighted zone to further improve the foundation's ability to resist liquefaction.

2. A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer according to claim 1, characterized in that: The bottom width of the outer fill is determined by calculation based on the design water pressure and fill density, and the filling height is consistent with the filling height of the panel dam.

3. A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer according to claim 1, characterized in that: The outer filling is formed by multi-layer filling, the thickness of a single layer is 0.5-1.0m, and the compaction degree of each layer after vibration rolling treatment is not less than 95%.

4. A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer according to claim 1, characterized in that: The pre-pressure applied by the outer fill is twice the design water pressure. The deadweight of the outer fill during the filling process is used to generate pre-pressure on the panel dam to provide stress history and reduce the overall deformation of the panel during the water storage period.

5. A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer according to claim 1, characterized in that: The outer fill excavation is carried out in a zoned and layer-by-layer manner, and the excavation sequence is to gradually expand from the central area of ​​the panel dam to the outside. The excavation depth is consistent with the dam body filling height, and the excavation depth of each layer is 0.5 to 1.0 m.

6. A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer according to claim 1, characterized in that: Move the outer backfill after excavation to the outer area of ​​the thick cover layer to form a weight-bearing belt with a width 1.5 to 2 times that of the liquefied area of ​​the thick cover layer, so as to improve the anti-liquefaction ability of the outer foundation.

7. A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer according to claim 1, characterized in that: After the excavation is completed, the anti-seepage geomembrane is laid in the panel dam area, and the concrete panel is cast in situ in different areas. At the same time, the construction of the panel joints and water stop joints is completed to ensure the anti-seepage and panel stability during the water storage period.

8. A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer according to claim 1, characterized in that: The outer filling is made of well-graded soil and stone materials with a particle size range of 10 to 50 mm.

9. A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer according to claim 1, characterized in that: The outer filling applies a weight load to the foundation of the covering layer, and the weight load time is 30 to 60 days after the completion of the panel dam filling, so as to improve the compactness of the deep covering layer and reduce the risk of liquefaction.

10. A construction method for reducing deformation of the face plate and the risk of foundation liquefaction during the impoundment period of a face plate dam on a thick overburden layer according to claim 1, characterized in that: The construction method is suitable for areas with thick overburden layers with a thickness of more than 30m. The maximum horizontal deformation of the panel dam after unloading of the outer fill is controlled within 5cm, and the liquefied shear strength of the foundation is increased by no less than 30%.

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