ESTIMATION OF UNDRAINED STRENGTH FROM SOIL STRENGTH PROBE

Abstract

Undrained strength (Su) of fine-grained soils plays an important role in the geotechnical stability of infrastructure. In the absence of direct measurement of Su, correlation with in-situ cone penetration test can be useful. This study attempts to estimate undrained vane strength in select Indonesian soils from soil strength probe (SSP) cone resistance. The study is located in Riau Province, Indonesia. Fieldwork, consisting of a vane test, SSP test, and hand boring test, was performed close to each other (in a 1.5m radius) and at a depth of up to three meters at 90 locations. The physical properties of the soils were determined in the laboratory. Soils can be classified as high and low plasticity silt and clay with insensitive to moderate sensitivity. Field tests show SSP can assess soils from very soft to medium consistency. Based on the well-known Terzaghi equation, a very strong correlation, i.e. coefficient of correlation greater equal than 0.96, between uncorrected and corrected (by index plasticity) undrained shear strength from the vane shear test and SSP cone penetration test was found. The range of cone factor (N_k) values from SSP were between 27.9-42 for uncorrected Su and 37.5-69.8 for corrected Su. SSP cone factor does not correlate with plasticity index or sensitivity. The empirical correlation could be useful practically in soft to medium silty soils when direct Su measurements are unavailable.