| In the construction of Expressway in China,due to the vast territory of our country,limited by the natural environment,geographical location and geological conditions,the excavation and filling project is of great scale.In the construction of highway in mountainous areas,according to the principle of adapting measures to local conditions and taking local materials,excavation waste is widely used as subgrade filling materials.However,when water-sensitive soft rock which is easy to disintegrate,soften and water-sensitive is used as subgrade filling,the study on the evolution of its engineering characteristics and long-term stability has not been paid attention to,and the design theory and construction technology problems caused by it need to be solved urgently.Based on the Dakaimen-Gasa Expressway Project in Xinping County(Daga Expressway),this paper studies the engineering performance test,long-term stability evaluation of subgrade and its control measures in dry-wet cycling conditions,using the methods of laboratory test,field test and numerical simulation to study the water-sensitive soft rocks such as Triassic,Jurassic sand-mudstone,mudstone and so on.The main research results of this paper are as follows:1.The DaGa Expressway test section belongs to the loose sediment accumulation area on the foothill slope,with a slope of 16-23 degrees.Through on-site investigation and mineral composition analysis,it is found that this kind of purple-red muddy water-sensitive soft rock is mainly composed of clay minerals and felsic grains,and the content of weakly cemented clay minerals is as high as 57.4%,so it is easy to disintegrate,soften and water-sensitive.Engineering characteristics.2.The essence of dry-wet cycling is to destroy the grain structure of water-sensitive soft rock.Compared with the initial state,dry-wet cycling enhances the cohesion of water-sensitive soft rock by 66.7%,but decreases the internal friction angle by 62.5%,and weakens the water-sensitive soft rock filler in general.At the same time,the test results show that the shear strength decreases mainly in the first six dry-wet cycles.The proportion was 86.6%,and then stabilized.3.Based on the Fredlund&Xing model,the seepage model of water-sensitive soft rock high-filled subgrade under rainfall infiltration is established.The reasonableness of the model is verified by the Seep/W numerical model.The calculation results show that the pore water pressure inside the subgrade soil changes from negative to positive,the matrix suction is gradually lost,and the stability coefficient of the subgrade decreases continuously.The depth of the generalized humidification peak is different at different positions of the subgrade.The depths of the generalized humidification peaks at the shallow,middle and deep slopes of the central part are 5m,8m,10m and 12m,respectively.4.Based on the Green-Ampt infiltration model,a seepage model of water-sensitive soft rock high-filled subgrade considering the humidification peak reduction zone was established.The research shows that the minimum stability coefficient is only 1.99 when considering rainfall infiltration.When considering the interaction of rainfall infiltration and dry-wet cycle,the minimum stability coefficient is,0.92,the subgrade is unstable;the attenuation of stability coefficient is concentrated in the first 9 phases.Dry and wet cycle,the decline rate accounted for 92.1%,and then stabilized.5.Based on the long-term stability model analysis of water-sensitive soft rock high-filled subgrade,the effects of overlying load,vertical spacing and laying length on the control effect of geogrid reinforced layer are studied.The calculation results show that the reinforcement effect of the shallow sliding surface is most significant due to the influence of the overlying load.When the vertical spacing is 2m and the laying length is 8m,the stability of the subgrade is improved significantly and the engineering cost is low. |
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