Cyclic and post-cyclic behavior of Qom marl, Iran

A series of strain-controlled cyclic simple shear tests followed by monotonic ones were carried out on Qom marl to evaluate its pre- and post-cyclic behavior under different moisture contents and overburden pressures. A series of resonant column and bender element tests were also conducted to measure the dynamic properties of this type of marl. The results showed that the experience of a cyclic loading improved the marl shear strength in all moisture contents and overburden pressures, while the post-cyclic shear modulus of marl increased only when its moisture content was close to saturation. It was concluded that the possibility of subsidence in marl deposits after an earthquake is very likely due to the high potential of reducing the volume of the lower layers after cyclic loading, especially when the moisture content of the lower layers is high. The dependence of shear modulus degradation and damping ratio on shear strain level was found to decrease and increase, respectively, with increasing the marl moisture content. Moreover, it was observed that a cyclic load experience only had an effect on the compression index (Cc) and the swelling index (Cs) was independent of the seismic load.