Experiment Research On Rupture Mechanism Of Loess By Triaxial Tension Test

Recently, the distribution and activity character of ground fissure have been mastered basically, but its genetic mechanism is immature being many different points of view and disputes on it because there are some key basic problems being unresolved. This paper researched the mechanism of ground fissures in Fen-Wei basin by experiment studying loess samples with fracture fillings and without fracture fillings excavated from the trench in Xi'an and Jing-yang ground fissures field. Based on a series of triaxial tensile test of loess, the rupture characteristics and behavior related to loess ground fissures were analyzed and the genesis and expansion mechanism of ground fissures developed in loess were discussed.The triaxial tensile test of intact loess indicates that the tensile strength and strain of loess are very small. And with the increase of confining pressure, the tensile stress would become compressive stress. When the tensile stress in loess is bigger than tensile strength, the tensile cracks would come into being to release the tensile stress, with the buried depth increases, the crack would become closed. The triaxial tensile test of loess with fracture fillings indicates that the stress state and the initial structural plane controlled the rupture development and cracks are easier to be formed near initial cracks under low confining pressure. The triaxial tensile test of remolded loess indicates that the tensile strength of loess is related to the confining pressure and water content. Under uniaxial tension, with increasing of water content, the tensile strength increases firstly and then decreases, Under triaxial tension, with increasing of water content, tensile strength decreases At the same time, the author carried out theoretical analysis from microscopic view to predict the uniaxial tensile strength of remolded loess. The predicted value is 7.4kPa and the measured value is 7.9kPa when w=10%; The predicted value is 10.25kPa and the measured value is 12.1kPa when w=15%;which indicates theoretical analysis agree with the test result well。The broken test of loess showed that the tectonic stress field of Fen-Wei basin was the controlling factor to ground fissures, and other factors were additional factors.