Study on earth pressures in expansive soil roadbed under weather influence

By eight simulated test of expansive soil roadbed, the filled soils coming from Ningming section of Nanning-Youyiguan Highway in Guangxi and Cili section of Changde-Zhangjiajie Highway in Hunan were used to simulate the influences of the drainage boundary, the density of soil, water accumulation on the top of roadbed, sunshine and precipitation. It is obtained that: ① Soil pressures in the expansive soil roadbed are related to degree of compaction, drainage boundary condition and moisture content of filled soils; ② Soil pressures increase from 0.006 MPa to 0.073 MPa, while water is accumulated on the top of roadbed and the moisture content of soil increases from optimum value to saturated; ③ In the case of the overcast sky, or under the sunshine and the precipitation, the soil pressures in the expansive soil roadbed generally rise and fall by 0.001 MPa, with the maximum rise and maximum fall of 0.002 MPa; ④ The depth of the expansive soil roadbed influenced weather is about 2.5 m to 3.0 m, the nearer to the surface of roadbed is the greater the soil pressure varies; ⑤ The variation of soil pressure equals to the sum of variation of self-weight of soil and variation of its expansive pressure, and both of the latter are induced by change of moisture content. These results are very important for design and construction of expansive soil roadbed.