Study on Tensile Strength and Tensile-Shear Coupling Mechanism of Loess around Lanzhou and Yanan City in China by Unconfined Penetration Test

摘要

Tensile strength is an important but seldom noticed parameter that reveals the constitutive relations of soil. For the loess, the tensile strength can be used to explain earthwork-induced damages such as tension cracks in cut slopes and corresponding slope failures, or natural disasters such as ground fissures. The present study chose an indirect method, particularly the unconfined penetration (UP) test, to measure the tensile strength of remolded loess and undisturbed Q2 and Q3 loess obtained from different districts in China. The results indicated that the tensile strength of the undisturbed loess was primary determined by the void ratio. In addition, multiple correlations were observed between the void ratio and the degree of saturation. The tensile linear stiffness exhibited an exponential increase following an increase in the tensile strength. The mechanism of the tensile-shear coupling strength criterion was proposed. Linear relations between the mechanical parameters were deduced under the tensile-shear coupling condition and were verified by the remolded and undisturbed loess, respectively. Both the unconfined compressive strength and cohesion decreased under the tensile-shear coupling condition. Comparisons with other strength models validated the suitability of the tensile-shear coupling strength criterion for the loess. This study aims to present a more comprehensive understanding on the tensile strength of loess and offer parameter guidance for stability calculations in practical engineering.