Thesis (D.Eng.)--Chulalongkorn University, 2007

The relationship between modulus and strain of soil is extremely non-linear so the profound knowledge of this relationship is essential for standard design of construction. In this research, to elucidate this relationship, a series of laboratory tests is performed to determine the shear modulus degradation curve for reconstituted and undisturbed clay samples by using the bender elements tests. The tests are performed by using a modified triaxial apparatus and a consolidometer each of which is equipped with a pair of bender elements. The research results show that shear modulus determined from the bender elements test has relationships with shear strain and shear modulus calculated from a conventional triaxial test. The relationships are proposed. Besides, the shape of the normalised shear modulus degradation curve determined by bender elements test is not affected by the plasticity index. This research yields two novel findings. Firstly the variable-path length and continuous wave method is used to determine phase velocity of shear wave. The proposed method combined with the conventional time domain method gives the explicit picture of the relationship between phase and group velocities. The other finding is swept wave and cross-correlation technique can be used to compute the travel time based on time domain method. By also using swept signal, frequency response of soil sample can be computed and frequency response determined is used to regenerate received signal. The study also reveals that the installation of bender elements into the clay sample generates almost no disturbance and the magnitude of shear strain generated from bender elements tests is 10[superscript -4]%.