RESPONSE OF SANDY SOILS WITH RUBBER-SAND MIXTURE LAYER USED AT DIFFERENT DEPTHS TO SINGLE PERIOD SINUSOIDAL INPUT GROUND MOTION

Abstract

Novel protection methods have been proposed by various researchers that recommended placingrecycled rubber and rubber/sand mixtures (RSM) as lightweight material below buildingfoundations, for vibration absorption. This paper presents comparable analyses between a baselinecase of pure sand soil profile and others in presence of a rubber-sand mixture (RSM) layer atdifferent depths from the foundation level. This study is focusing on the effect of increasing thedepth of the utilized layer of RSM, on the ground response during certain input ground motion. Siteresponse analyses were performed by applying simple constant amplitude sinusoidal wave withsingle predominant period (Tp). Input ground motions were classified according to predominantperiod (Tp) into two categories. The first category is the low period (high frequency) range whichcovers 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 groundmotion was classified into weak and strong amplitude where, if acceleration amplitude is less thanor equal to 0.2g, it was classified as weak amplitude and if acceleration amplitude is more than 0.2git was classified as strong amplitude. Depth of RSM layer is classified also into shallow for depthsless than 4.0 m and deep for depths more than or equal 4.0m. It was noted that placing a 2mthickness layer of RSM caused shifting of the maximum spectral acceleration at the top surfacetowards high periods (low frequencies) zone relative to baseline model of pure sand soil. Increasingthe depth of RSM layer or/and acceleration amplitude of input ground motion (G.M.) caused moreshifting for the maximum spectral acceleration of the top surface towards high periods (lowfrequencies). Shifting was accompanied with decreasing in the values of spectral accelerations thatled to more reduction in the spectral ratio. In addition, the existence of soft RSM layer between twostiff layers resulted in that the top and bottom layers move out of phase and consequently acceleratedamping of top layer movement.