Abstract: This paper presents the geotechnical investigation results of the collapsible loess soil underneath the proposed Second Elementary School site of Irrigation District in Town of Tianyangshan, Wuzhong City of Ningxia Autonomous District. The effect of the groundwater fluctuation on the strength of the collapsible loess throughout the standard penetration test (SPT) and laboratory tests. The moisture content in the loess soil was closely monitored. The results indicate that, when the groundwater raise, the SPT blow count in the soil decreases and the soil strength significantly reduces. The compressibility coefficient of saturated loess is higher than that of nonsaturated sample. When the degree of saturated increases, the surface tension among soil particles, matric suction and cementation among soil particles reduce accordingly. In the practical design, not only the collapsibility of the loess should be aware but also the soften of loess soil when it is wetted.

Key words: Loess, Collapsibility, Moisture Contents, Standard Penetration Tests, Consolidation