Engineering Geological Characteristics of Xigeda Formation Claystone in Luding County, Western Sichuan

The Xigeda Formation is a special semi-diagenetic, which has the characteristics of "wind-induced powder, water-induced mud", and is a good carrier for engineering geological problems and geological hazards. In this study, the yellow and gray claystone of the Xigeda Formation in Haiziping Village, Luding County, western Sichuan was investigated. Its material composition, microstructure, and mechanical properties were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), field and laboratory geotechnical tests. The variation law of its physical and mechanical properties under the action of water is emphasized, and the engineering geological characteristics of the Xigeda Formation are compared and analyzed with those in other regions. Based on the above research, some conclusions are as follows. ①The Xigeda Formation claystone in Haiziping Village is mainly composed of fine sand, clay, and additional fine-grained materials. It is produced by yellow and gray thin layers interbedding and has a horizontal lamination structure. ②Yellow and gray claystone have the same material composition, but material proportions are different. The clay content of yellow claystone is 12% higher than that of gray claystone, and the calcite content is 10% inferior. The microstructure of yellow claystone is denser and cemented with clay particles more strongly. ③The permeability coefficient measured on the site of Xigeda Formation claystone in Haiziping Village is 3.62～7.34×10⁻⁴ cm/s, which is between claystones and sandstones in Xigeda Formation in other regions. The characteristic of its permeability is closely related to the development of natural joints and the characteristic of cracks that is susceptible to disturbance. ④The cohesion of yellow and gray claystone decreased with the increase of moisture content, and the higher the moisture content, the greater the decline, but the relationship between internal friction angle and moisture content was different.⑤ The mechanical properties of the Xigeda Formation in different regions and lithology have obvious differences in sensitivity to moisture content changes, among which the mechanical property weakening by the water of the Xigeda Formation claystone in Haiziping Village, Luding County is the most significant.