Origin and Physical-Mechanical Properties Study of Haikou Ultra-Lightweight Volcanic Ash Soft Clay

A comprehensive geotechnical investigation was conducted at a construction project site on Hainan Island. Specific geotechnical parameters of volcanic ash deposits in high-order areas and volcanic rock plateaus in northern Hainan Island were summarized. The distinct engineering characteristics of this unique soil and rock type were investigated. A multi-faceted approach was employed, including on-site drilling, standard penetration tests, seismic velocity tests, laboratory soil physical-mechanical experiments, optically stimulated luminescence tests, X-ray fluorescence semi-quantitative analysis, and mineral X-ray diffraction analysis. The depositional origin and era of these deposits were examined. Furthermore, recommended values for fundamental engineering characteristic parameters were proposed, providing a solid foundation for the utilization and foundation treatment of this soil type, thereby reducing engineering risks.