EXPERIMENTAL STUDY ON DYNAMIC ELASTIC MODULUS OF REINFORCED SOFT CLAY AROUND SUBWAY TUNNEL UNDER VIBRATION LOADING

Although reinforcing soft clay around subway,as a technique,has been used in settlement treatment,some issues on dynamic characteristics of reinforced soft clay remain unaddressed.Based on a series of dynamic triaxial tests of reinforced soft clay around Helen Subway station of Shanghai metro line No.4 with laboratory GDS test apparatus,the effects of cyclic loading frequency,stress amplitude,initial deviator stress and confining pressure on dynamic elastic modulus were studied.The results show that(i) the degradation process of dynamic elastic modulus can be divided into rapid stage and slow stage with the increase of cycle vibration number,and the period of the slow stage is longer than that of the rapid stage(ii) cyclic loading frequency has a significant effect on dynamic elastic modulus;(iii) with the increase of cyclic stress amplitude,initial deviator stress and confining pressure,the dynamic elastic modulus increases greatly,however,its velocity is not notably influenced by the change of the three factors.Finally,a degradation model of dynamic-elastic modulus was built with the logarithmic function and the model parameters being determined by regression analysis method.