This study presents the engineering geological and
geophysical assessment of the June 5, 2009 Jiwei Shan rockslide, Wulong, China.
Jiwei Shan is a part of Wulong karst terrain lithologically, it’s composed of
Quaternary Deposits, Jialingjiang Formation, Maokou, Qixia, Liangshan and
Hanjiadian Groups (chronologically from younger to older). The surface is
highly irregular (pinnached), the rocks contain two sets of fractures, networks
of convoluted solution channels and caves and there are large voids filled by
soil mantle. It’s a south-north dipping limb of an anticline fold composed of
sedimentary rocks, mainly of limestone of variable composition, mudstone and
shale and series of limestone deposited with interbedded mudstone and shale.
There are two sets of steeply dipping fractures developed in the Maokou and
upper strata of Qixia Groups; set one
trending EW and set two trending
nearly SN directions. The study has been conducted by geological
fieldwork, geophysical investigation (Vertical Electrical Sounding), petrographical
and scanning electron microscope (SEM) studies and laboratory testing on rock samples
collected from Jialingjiang Formation and Maokou and Qixia Groups. The study of
the SEM photomicrographs showed that the microcrack propagations in limestone
indicated that the increases in crack length and micropores of limestone are
indication to the weathering grade increase from II (slightly weathered rock)
to grade III and IV (moderately and highly weathered, respectively). The Qixia
Group; Middle Layer is highly weathered shale and bituminous interlayer with
clear fissility, high porosity, and gently dipping strata, it represents the
sliding surface of the rockslide. It’s comparatively weak and strongly
weathered compared to the overlain EW and SN fractured stratum. Generally, the
tectonic of the study area imposes controls on the rockslide in many ways:
created favourable terrain, provided sufficient rockslide prone materials such
as highly weathered limestone and shale, weak rocks, created very steep beds which
reduced the stability of the highly fractured bedrock of the slope.