Study On Construction Technique Of Railway Expansive Soil (Rock) Cutting

Purpose: The characteristics of strength attenuation caused by the clutter distribution of cracks and repeat expansion and contraction deformation of expansive soil (rock) in the soil, often bring serious damages to the human engineering constructions, resulting in many geological disasters. The new Yunnan-Guangxi railway and the existing Nanning-kunming High-speed Railway have the same geological conditions. The route takes the principle "try to avoid" of line selection, and try to pull the slope as high as possible through by bridge. There are still many sections in the new Yunnan-Guangxi railway that have to pass through the expansive soil (rock) sections, due to the curve radius,line slope, station and many other factors. It is required to adopt reasonable treatment measures and construction technology programs to achieve good engineering results in these special areas.Method: The research emphasis of this paper is the construction technology of new modified cement-based waterproof structure layer in expansive soil (rock)cutting section and construction technology of flexible ecological expansion and slope protection for expansive soil (rock) cutting slope.The new modified cement-based waterproof structure layer is an important part of waterproofing and drainage system of fully closed bed structure of expansive soil (rock) cutting, pre-mixing is needed before the formal paving of the waterproof structural layer, and then the prepared modified cement-based composite materials will be put into the mixing equipment according to the match ratio to determine the reasonable mixing time, moisture and other parameters. The rough pavement of waterproof structural layer is conducted using graders or bulldozers firstly, and then the fine pavement is conducted artificially, and slow rolling is needed using double-cylinder roller. The number of rolling time is appropriate to be five, which can be adjusted appropriately according to the field rolling results. After the construction of the new modified cement-based waterproof structure layer, the composite geo-membrane is covered on its surface, and it will be cured with sprayed water and curing time of not less than 3 days. After the end of curing the core of the waterproof structural layer is drilled out to check the thickness, distribution uniformity of material composition, strength, impermeability and other parameters.The main technical indexes of the ecological bag, joint buckle, geotechnical grille and composite geo-membrane used in the flexible ecological slope should meet the corresponding standard requirements. The inner soil of the ecological bag is mixture of medium coarse sand and silty clay, which ensures the long-term fertilizer effect of the planting soil in the bag. The pinning of the joint buckle should ensure the connection of the two adjacent bag bodies, in order to ensure the firm connection of the joint buckle , strike with a rubber hammer lightly and thrust the pawl into the bag. The soil in the bag should be compacted in layers, and the bag body should be angular in the compaction process so thenreach the result of internal reality and external beauty. The function of the roots of the plants in the flexible ecological protection slope is equivalent to the roleof anchor arm, the afforest of the slope can implemented by grass planting,inarching, hydraulic spray seeding and external-soil spray seeding.Results and conclusions: After adopting new cement base waterproof anddrainage structure layer, the engineering quantity of excavation of roadbed and slope protection is reduced, and the temporary land used for dumping abandoned soil also decreased accordingly, it is economical, environmental, conducive to the land conservation; the material of the structure layer is easy to buy, the construction companies may use the existing cement mixing station to mix on site, it is convenient to compact with the equipment of embankment filling project, and better to control the quality; the deformation of the structure layer is small in long-term train load, the water sacs will not appear below the track under long-term load like the flexible materials, the long-term waterproof effect is good, the new cement based waterproof and drainage structure can be continuously constructed and the construction joint is less and the surface water infiltration channel is reduced.The flexible ecological slope has a strong integrity. The swelling energy of slope which is behind the wall can be absorbed by the deformation of flexible body. That is benefit to slope body drainage and slope surface drainage as well as cutting off leakage of surface water and cyclic drying-wetting effect. Using the excavation and tunnel waste as fillers to reduce subgrade and tunnel discarding soil and land is benefit to slope protection greening and environmental protection. The vegetation can absorb harmful gas and emit oxygen through photosynthesis, absorb noises, reduce strong light reflection,reduce dust, regulate temperature and humidity around. All the advantages above make the traffic environment more comfortable.