Abstract: The deformation and stability of gentle anti-dip red sandstone slope in Hubei section of Shanghai-Chongqing Expressway is investigated. The high-steep slope in gentle anti-dip red sandstone is easy to soften and collapse. The unloading deformation of high-steep slope resulted from natural erosion can be dozens of millimetres to nearly 100 millimetres. The direction of unloading deformation overlaps with structural joints, which widen the joint fissure and increase the connectivity and finally provide a steep downslope failure surface for the high-steep slope. The unloading and softening deformations of highway cutting slope further increase the slope deformation and decrease slope stability; and the deformation modulus can decrease by 80%. Groundwater flows into unloading fissures and causes a certain height of hydrostatic pressure. Rock mass strength is significantly decreased by the softening effect of groundwater and the softening coefficient of rock block generally is about 0.3-0.7. Under 30-40 m hydrostatic pressure, the stability coefficient of slope decreases from 5.56 to 1.96 before excavation and from 2.77 to 1.07 after excavation. All of these adverse effects decrease the stability of anti-dip slope and even cause failure. It is concluded that reinforcements should be installed immediately after the slope cutting and measures should be taken to prevent the accumulation of groundwater in the unloading fissures, so as to reduce softening of slope.

Key words: red sandstone, gentle anti-dip bedded rock, high-steep cutting slope, softening, unloading deformation, stability