Effectiveness of Clay Damper for Reduction in Vibration Amplitudes

Abstract

Very soft clay is considered to be a poor construction material because of high compressibility and low shear strength. Again, a deep soft clay layer amplifies the stress amplitude during seismic wave propagation. Hence, it is a common practice either to avoid a soft clay layer or to improve the properties of the clay layer for founding a structure in the soft clay. In spite of all these demerits, the high damping ratio of a soft clay layer may be effectively used as an effective damper for reduction of stress amplitudes. Care must be taken over retention of moisture content of the clay and prevention of oozing out of the soft clay under a vertical stress. In the present study the soft clay has been wrapped with two layers of geomembrane in the form of a geocell of thickness 100 mm and has been placed below the foundation of a prototype frame structure. Two layers of geocells have been used for effective reduction of stress amplitude. Horizontal vibration has been imparted to the ground and acceleration-time histories at different locations like ground, foundation, tie beam, floor beam have been recorded. Comparison of results between a structure resting over clay damper and a structure resting over ground has been made. It is observed that the stress amplitude has been reduced to 40–50% of the normal value due to installation of the clay dampers. Hence, if properly designed, the soft clay may be effectively used to reduce the vibration during earthquakes.