Laboratory Tests On The Mechanism Of Slope Instability Induced By Acid Rain

Chemical weathering is widely spread in the southwestern China because of its humid subtropical climate.At the same time,the rapid industrial development has brought serious air pollution to China.As a result,the southwest of China has become one of the regions that are seriously affected by acid rain.Chemical weathering results in the formation of clay minerals in mafic rocks.Consequently,the structure of rocks can be altered because clay minerals decompose in acidic conditions,due to which the shear strength of joints in the rock mass decreases considerably and slope failures can occur.Gabbro is one of the most extensively found mafic rocks on the surface of the Earth,and slope failure along joints in this kind of rock is common in areas that experience acid rain.However,only a few experiments have been conducted on the effects of chemical decomposition on gabbro slope stability despite the occurrence of slope failures.In this study,lab tests were designed using hydrochloric acid of a reasonable concentration to model chemical decomposition along rock joints of an actual gabbro slope in southwestern China.Optical polarization microscopy was performed to analyse the mineral composition of the rock slope,and X-ray powder diffraction(XRD)was conducted to quantify the mineral phases of rock samples before and after decomposition in acidic conditions,the results of XRD proved that the main clay minerals in the weathered rock samples are illite,chlorite,and kaolinite.These clay minerals are more likely to be decomposed in acidic conditions than plagioclase and pyroxene,this can explain the change of the rock structure based on the alteration of rock mineral content.A scanning electron microscope(SEM)was used to observe microcrack development in the rock samples due to the action of the acid on them,the micrographs of the rock samples after applying hydrochloric acid showed that the cracks developed considerably after applying hydrochloric acid,this can illustrate the reduction of shear strength from the microscopic perspective.Furthermore,a direct shear test was performed to illustrate the reduction in shear strength caused by the decomposition of clay minerals.Finally,slope stability was calculated using the shear strength parameters before and after decomposition,and the significance of acidic chemical decomposition on the stability of the slope was demonstrated.