| As an important water conservancy project,plain reservoir plays an important role in water supply,irrigation,shipping,power generation and other fields.During the initial impoundment of the plain reservoir with geomembrane,the pore gas in the unsaturated soil layer under the geomembrane is very easy to accumulate and the groundwater level rises,which leads to the local or large area floating and even bursting of the geomembrane,and eventually leads to a series of engineering safety problems.After consulting relevant patents,data and field investigation,the check valve with one-way drainage function can effectively reduce the uplift pressure outside the reservoir.On the premise of summarizing the previous research results,the author proposed a new type of drainage exhaust decompression check valve,and tested its drainage and water sealing,durability and anti-silting performance.At the same time,taking Dongsanli Reservoir in Pingyin County as an example,the influence of the check valve on geomembrane displacement and pore water pressure outside the reservoir was studied.The research results can provide a reference for the structure design of geomembrane impervious body of the reservoir in the future.The main research results and conclusions are as follows:(1)A new type of drainage,exhaust and decompression check valve for reservoir basin was developed.The valve body structure is mainly composed of an upper hemisphere,a lower hemisphere and a rubber valve tongue;The upper and lower hemispheres are connected by bolts,and the lower hemisphere is evenly arranged with drainage and exhaust holes.The outer parts of the lower hemispheres are wrapped with a layer of geotextiles and filled with composite geotextiles in the ball to play a filtrating role to prevent the blockage of the check valve;A protective cover is provided at the top of the upper hemisphere,and the rubber valve tongue is drawn out from the outlet at the top of the upper hemisphere.The check valve is installed at the junction of the blind ditch at the bottom of the reservoir,and is closely caulked with the geomembrane to form a complete impervious body,which can effectively play a role in the impervious body at the bottom of the reservoir.(2)Based on the model test,the drainage,water sealing,durability and anti-siltation performance of two new types of drainage exhaust decompression check valves(type A with small holes and type B with large holes)were studied with different opening rate of the valve tongue(50%,30%,5%).The results show that the two types of check valves performed well in the test of water drainage and sealing and did not appear the phenomenon of delayed closure or water leakage after closing;In the test of durability and anti-sedimentation performance,type B check valve,which has an increased effective water flow area,performed significantly better than type A check valve and is more suitable for use in the bottom of the reservoir.The test results can provide reference for the mass production and application of the check valve in the future.(3)Based on Dongsanli Reservoir project in Pingyin County,the numerical simulation of the operation effect of the check valve in the actual reservoir bottom was carried out,and the influence of the check valve on geomembrane displacement and pore water pressure outside the reservoir was studied.The results show that the check valve has a good drainage and decompression effect,and it plays a good role in protecting the impervious water body of the geomembrane in the reservoir basin.With the increase of the water head difference between the inside and outside,the displacement of the geomembrane at the bottom of the reservoir with the check valve decreased significantly compared with that without the check valve.The pore water pressure at the bottom of the reservoir with the check valve decreased by 85.4%,29.1%,58.1% and 66.1% respectively compared with that without check valve. |
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