Experimental Study On The Engineering Properties Of Loess-like Silty Loam

Loess-like silty loam is a lithologic soil on the quaternary upper pleistocene alluvium (alQ3), its formation characteristics is the gray, give priority to with silt, clay content is low, belongs to bad gradation soil. The main show of the saturation silty loam is low strength, big deformation, the poor stability of surrounding soil and difficult precipitation. The dissertation combined the recession flow tunnel construction of Yellow River-Crossing Project in the South-to-North Water Projection. According to these phenomena, focuses on Experimental research of the loess-like silty loam, through the field trenclu laboratory soil test and model test, some conclusions are drawn as follows:(l)With the increment of consolidation pressure, the consolidation coefficient based on the consolidation test initially increases, then decreases. And when the consolidation pressure is200kPa, the largest coefficient of consolidation could be engaged. Therefore the influence of consolidation pressure on the coefficient should be fully considered in the project.(2)Direct shear test study on the relationship between the different moisture content and the shear strength. As the moisture content is more than20%, of silty loam is very low, below20%, the shear strength has sharply increase, show that the moisture content was reduced to20%can effectively improve the soil shear strength, Strength experiment also show that moisture content reduced to20%, With the increase of the vertical pressure, moisture content is almost no loss, so it deserves attention greatly to choice the reasonable Precipitation Scheme.(3)In order to study the mechanical property under the tunnel excavation stress state, design the tri-unload test. The test show that the damage principal stress of Loess-like silty loam declines exponentially with the increase of the moisture content, the axial train increase greatly.(4)Creep test to select moisture content15%of the silty loam, the damage principal stress is only about2/5of the three-axis fast shear, the construction of the effect of time have not to be ignored. The stress-strain isochrones relation be similar to Duncan-zhang model, it is inadvisable to choose linear rheological model(5)For simulating the tunnel precipitation, excavation, get the model test of1:150, due to the moisture content at or near saturation, the bottom of tunnel face appear drainage after excavation, with seepage phenomenon, the static liquefaction occur under the effect of both permeability and stress release of the soil, at the same time, the soil presents the Plastic-flow, soon produce collapse destroyed. It is verified that the water content locally accumulate after excavation in Silty loam, the instantaneously losing strength, showing the Plastic-flow destruction mechanism.