Element tests on the hydraulic/mechanical behaviour of unsaturated decomposed granite soil under various conditions.

Masado is a completely decomposed granite soil widely distributed in western Japan. One of the major causes of the failure of a slope, either made of natural Masado (cut slope) or manmade Masado (reclaimed slope), is heavy rainfall. It is therefore essential to investigate the hydraulic/mechanical behaviour of saturated/unsaturated Masado and provide a fundamental database for constitutive modelling. In this paper, a series of water retention, oedometer and triaxial tests on unsaturated Masado were conducted. The water retention properties of Masado were clarified first, and then, oedometer and triaxial compression tests were conducted under various hydraulic/mechanical conditions. Different from normal loading patterns, i.e., constant suction or constant net confining stress under different drainage/ventilation condition in triaxial tests, a very special loading pattern named as constant degree of saturation was designed and conducted for the triaxial tests, in order to determine if it could be a suitable state variable for a constitutive model. From the tests, it is found that the strength and deformation of Masado are greatly dependent on the interaction among the suction, the degree of saturation and the hydraulic/mechanical loading conditions. Based on the test results, it is possible for us to propose a constitutive model based on the rational state variables obtained in the tests conducted in the research. [ABSTRACT FROM AUTHOR]