Response of sandy soils with rubber-sand mixture layer used at different depths to single period sinusoidal input ground motion

Abstract EN

Novel protection methods have been proposed by various researchers that recommended placing recycled rubber and rubber/sand mixtures (RSM) as lightweight material below building foundations, for vibration absorption.

This paper presents comparable analyses between a baseline case of pure sand soil profile and others in presence of a rubber-sand mixture (RSM) layer at different depths from the foundation level.

This study is focusing on the effect of increasing the depth of the utilized layer of RSM, on the ground response during certain input ground motion.

Site response analyses were performed by applying simple constant amplitude sinusoidal wave with single predominant period (Tp).

Input ground motions were classified according to predominant period (Tp) into two categories.

The first category is the low period (high frequency) range which covers periods less than or equal to 0.50 sec.

The second category is the high period (low frequency) range which covers periods more than 0.50 sec.

In addition, acceleration amplitude of input ground motion was classified into weak and strong amplitude where, if acceleration amplitude is less than or equal to 0.2g, it was classified as weak amplitude and if acceleration amplitude is more than 0.2g it was classified as strong amplitude.

Depth of RSM layer is classified also into shallow for depths less than 4.0 m and deep for depths more than or equal 4.0m.

It was noted that placing a 2m thickness layer of RSM caused shifting of the maximum spectral acceleration at the top surface towards high periods (low frequencies) zone relative to baseline model of pure sand soil.

Increasing the depth of RSM layer or/and acceleration amplitude of input ground motion (G.M.) caused more shifting for the maximum spectral acceleration of the top surface towards high periods (low frequencies).

Shifting was accompanied with decreasing in the values of spectral accelerations that led to more reduction in the spectral ratio.

In addition, the existence of soft RSM layer between two stiff layers resulted in that the top and bottom layers move out of phase and consequently accelerate damping of top layer movement.