Abstract:
This paper introduces an example of a reservoir laying a layer of geotextile before the drainage prism of the dam in danger removal and reinforcement. After several years of operation, the water level at the downstream of the dam rises year by year and the overflow point is higher than the top of the prism. The seepage stability of the earth dam before and after the geotextile silting is calculated and analyzed by using the GEOS tudio software. The results show that the silting of the geotextile has a negative effect on the seepage stability of the earth dam On this basis, the selection principle of geotextile is put forward, which provides theoretical basis for engineering reinforcement.
1.What is geotextile filter fabric:
Geotextile filter fabric is a kind of artificial synthetic material, light weight, high tensile strength, convenient and durable, low cost. Because of its good hydraulic characteristics, it is widely used in water conservancy project drainage and filter facilities. The ideal filter fabric roll can prevent excessive loss of soil particles, resulting in piping or soil flow under the premise of ensuring water permeability.
At present, geotextile soil filter fabric has played an active role in dam seepage control, drainage and anti filtration, flood prevention and emergency rescue, slope water and soil conservation of many projects.
woven geotextile filter fabric is seldom used in soil filter project.4.5 oz. 8oz nonwoven geotextile filter fabric is widley used.
2.Disadvantages of Inverted Filter Geotextile:
Geotextile has different abilities of soil conservation, water permeability and anti silting. If the permeability characteristics and particle size distribution characteristics of the protected soil are not considered comprehensively in the engineering examples, the silting and blocking of geotextile may occur after use, resulting in the decline of the effect of reverse filtration and drainage and the adverse impact on the seepage stability of the earth dam.
3.Application examples of geotextile filter cloth material in dam construction:
A reservoir is located in the water system around the lake of Poyang Lake. Due to the poor filling quality of the dam body and the serious leakage of the dam foundation, the anti sliding stability of the downstream slope does not meet the specification requirements, 2006 The dam body and foundation are impervious by using plastic concrete cut-off wall and curtain grouting when the reinforcement is carried out in, the downstream drainage prism is renovated, and a layer of geotextile filter cloth material is laid at the junction of the drainage prism and the dam body soil in front of the drainage prism. After several years of operation, the area with the height of 4m above the downstream prism top of the dam is wet in large area The phenomenon of loose leaching, which was broken through by drilling, disappeared at that time, but repeated several years later.
4.What is the problem caused by non woven geotextile filter fabric :
4.1. During the operation of the reservoir, the seepage was conducted by drilling through the geotextile after the phenomenon of loose seepage appeared on the downstream slope of the dam. The seepage water flowed through the borehole to the prism, the phenomenon of loose seepage disappeared, the water level in the dam decreased, and the escape point decreased; Several years later, the soil transport and deposition in the dam blocked the borehole, raised the water level at the dam foot again, raised the escape point of seepage water, and the downstream dam slope again appeared the phenomenon of scattered infiltration.
4.2. The characteristics of water filtration fabric geotextile are mainly soil conservation, water permeability and anti silting. There are more fine particles and clay in the fill of the dam body of the reservoir, and the water filtration cloth is used as the filter structure. Under the action of seepage water pressure, the water can flow freely in the gap of the geotextile at the beginning stage, and the fine-grained soil can also reach the geotextile under the influence of seepage water, but it is dense The structure makes the fine soil particles of a certain level deposit slowly on the surface and inside of the geo filter fabric, the porosity of the geotextile decreases gradually, and the water permeability decreases accordingly; when the fine particles reach a certain degree, the siltation occurs, and the structure loses the drainage and anti filtration effect, that is to say, the phenomenon described in the paper that the water level at the dam toe rises, and the escape point is higher than the top surface of the prism appears.
5.Conclusion :
Geotextile filter fabric non woven has been widely used in the drainage and filter design of water conservancy projects such as flood control and emergency rescue, slope protection, etc. However, as a part of permanent buildings for a long time, the composition and particle size of the soil to be protected should be comprehensively analyzed. A reasonable sand pebble transition layer should be designed before and after the geotextile, and the geotextile with suitable aperture and strong anti silting and blocking property should be selected.
There are many fine particles in the fill of the dam body of the project, so the adaptability analysis of geotextile and soil material has not been carried out before the design, which can not play the role of transitional inverted filtration. The inverted filtration geotextile shall be removed and the sand pebble with good grading shall be filled for transition.
The geotextile non woven filter fabric can let the seepage of the dam body escape from the inside of the prism to ensure the safe operation of the earth dam.
For the adaptability between geotextile and different soil materials, it needs to be verified and further studied by test methods.