BASIC MATERIAL COMPOSITION OF CARBONACEOUS ROCKS IN GUANGXI PROVINCE AND ITS INFLUENCE ON ENGINEERING GEOLOGICAL CHARACTERISTICS

Carbonaceous rock formation frequently appears as the main rock layer or interlayer in the stratigraphic units of different ages in Guangxi Province. Due to its easy weathering, cracking, disintegrating, softening, and the environmental sensitivity of engineering properties, it has brought many complex problems to the highway construction in Guangxi Province. Multiple research methods were adopted to investigate the geochemical characteristics and influence factors of disintegration for carbonaceous rocks. They include existing geological survey data collection, field geological survey and sampling tests. Researches on the distribution and assemblage characteristics of carbonaceous rocks, mineral composition and geochemical characteristics of organic matter were carried out. Meanwhile, influence factors of disintegration for carbonaceous rock and corresponding engineering measures were discussed. The research showes that carbonaceous rocks are distributed from Neoproterozoic to Paleogene in Guangxi Province. 24 major stratigraphic units containing carbonaceous rocks were identified. Its basic material composition is mainly composed of clay minerals, quartz and carbonate minerals. And the organic matter content of carbonaceous rocks in Guangxi Province is high, which belongs to the carbonaceous rocks of middle-high level source rocks. The illite and illite-smectite mixed-layer mineral in clay minerals, high content of organic matter and sulfide are the main material factors for the disintegration of carbonaceous rocks under natural exposure. Tectonic activity, water swelling and thermal dehydration of clay minerals, oxidation and decomposition reactions of organic matter and reducing minerals, and natural factors are the four main reasons for the disintegration of carbonaceous rock slopes. Related research findings can provide important references for the design, construction, prevention and treatment of slope engineering, tunnel engineering and subgrade engineering in carbonaceous rock areas.