Vol14 No.6: 1174-1184
【Title】Formation and evolution of Emeishan basalt saprolite in vadose zones of Touzhai landslide source rockmass
【Author】YANG Ji-qing1, 2; XU Ze-min1*; ZHANG Rui2; CHEN Ji-pu1; REN Zhe1; LUO Rong-zhang1; ZHANG Xiu-shuo1
【Addresses】1 Faculty of Civil Engineering and Mechanics, Kunming University of Science and Technology, Kunming 650500, China; 2 College of Architectural Engineering, Yunnan Agricultural University, Kunming 650201, China
【Citation】Yang JQ, Xu ZM, Zhang R, et al. (2017) Formation and evolution of Emeishan basalt saprolite in vadose zones of Touzhai landslide source rockmass. Journal of Mountain Science 14(6). DOI: 10.1007/s11629-016-4169-y
【Abstract】In order to explain the formation process of slope hazards, and to identify the key factors leading to instability of a slope,Emeishanbasalt saprolite in vadose zones of the Touzhai landslide in Zhaotong, Yunnan, was studied. The formation and evolution of Emeishan basalt saprolite was examined using, amongst other techniques, field investigations, thin section analysis, scanning electron microscopy (SEM) observations, chemical analysis, physical and water-physical property tests of rock masses.Fieldobservations revealed that the majority of the weathered rock blocks were presented as a concentric layer structure in which an internal corestone was enveloped with several layers of external saprolized crust. Chemical and mineralogical analysis identified that iron was the most sensitive element and that the weathering progress usually started with the oxidation of Fe2+ to Fe3+ in rock blocks. Alkaline elements such as Si, Ca, Mg, Na and K were also dissolved and Fe and Al were concentrated in saprolized crusts. Results indicated that loss on ignition (LOI) also increased significantly. SEM results showed that the weathering intensity of the basalt blocks decreased gradually from the outside to the inside, and the mineral morphology significantly differed on both sides of the weathering front. The saprolized crusts presented cellular microstructure features due to the generation of micropore and clay minerals. Thin section analysis showed that plagioclase was relatively more stable than pyroxene and chlorite during weathering. With a centripetal propagation of the weathering front, saprolized crusts became thicker and corestones became smaller; fresh Emeishan basalt blocks gradually turned into saprolized blocks. Due to the loose structure and low strength of saprolite, the quality of the Emeishan basalt mass significantly deteriorated, this being a potentially important factor which caused the Touzhai landslide to occur.
【Keywords】Vadose zone; Emeishan basalt; Scanning electron microscopy; Saprolite; Corestone; Touzhai landslide