The Study Of Weathering Characteristics Of Emeishan Basalt Of Rock Block

Emeishan basalt is widely distributed in the southwest of China, and the geological environment of hot and rainy in the region is especially conducive to the chemical weathering of rock. the weathered rock and parent rock have big differences in integrity, mineral composition, mechanical properties etc. weathering of rock is one of the most important material source or carrier for geological disasters such as landslide, debris flow, rock desertification etc, that occurred frequently and caused huge loss to human life, At the same time, geotechnical engineers and designers have concerned the problem for a long time, which the constructed foundation surface of weathered rock mass and its optimal value. In this paper, the low penetrated rock block of the emeishan basalt slope in unsaturated zone as the research object, through field investigation and laboratory tests such as SEM, thin section identification, rock chemical analysis, etc, and the paper made a systematic and in-depth analysis of the change laws of the macro or micro features, composition of mineralogy, the mobility low of chemical elements etc.Rock block obviously show the layer structure that the outer layer is saprolite and the interior is stone core. from inside to out the weathering degree of rock block express more higher, and the mutation is particularly obvious in dimensional boundary region of between stone core and saprolite. we find surface erosion of core stones is not obvious, what’s more, the fracture is undeveloped. However, surface erosion of saprolite is obvious and rock-forming minerals such as feldspar show significant clayzation phenomenon, at the same time, we can be observed mineral show irregular flake, and the fracture is extremely developed. In the early stage of weathering that the alteration is low degree, in addition to the trivalent iron presents agglomerating and ferrous iron shows losing behavior, other elements have no evidently movement behavior or the changes unsensitive to the weathering degree. with the weathering development, when the weathering degree is more higher, the activity relatively weak of major elements such as Al, migration better of Na, Ca,and different valence state of Fe, all behaviors are significant sensitivity to the the weathering degree, the relationship between both of them is simple and clear. and the rock physical mechanics characteristic parameters such as density, porosity, and compressive strength etc have significant change, even the slightly weathered basalt, the integrity, macro characteristics have no significant difference compare to parent rock, however, rock Strength have a sharp decrease. according to the microscopic observation, the microfracture is developing and rendering material of iron in the structure surface,it may be account for cause of reduced intensity.Based on the above research, according to the migrated characteristics of major elements, the paper puts forward a new index:the A-FM index of weathering (A-FM), and compareing to the weathering index such as CIW, CIA, R, Whether the weathering early of the alteration is lower or late of the alteration is higher, A-FM index always have significant sensitive to the weathering degree, the relationship between A-FM index and the weathering degree is simple and clear, therefore, we can use A-FM index as importance reference when evaluate the weathering degree of basalt.