The soft soil can generate excess pore water pressure under dynamic load,which causes the decrease of effective stress and the attenuation of undrained strength of soft soil.In order to research the strength softening law of soft soil varying with vibration times under dynamic loading,a calculation formula for dynamic pore pressure-vibration times relation considering vibration frequency is established to test and analyze which is introduced into the calculation formula for undrained shear strength under dynamic load based on critical soil mechanics theory to analyze the development rules of the relation curve of undrained shear strength varying with vibration times in mechanism and compare with the test results.The results show that the modified pore pressure-vibration times relation calculation formula could consider the influence of vibration frequency.Under 10000 vibration times,u/σ'3 is 0.45 ～0.65.The semi-empirical undrained shear strength-vibration times calculation formula could predict the undrained strength at any vibration times under different vibration frequencies.The undrained shear strength attenuates to 25 ％ ～ 80 ％ under 10 000 vibration times.%动荷载加载时软土会产生超静孔隙水压力,使有效应力逐渐降低,引起软土不排水强度衰减.为了研究软土在动荷载作用下随振动次数变化的强度软化规律,建立一个考虑振动频率因素的动孔压-振动次数关系计算公式,进行试验验证分析,并将该公式引入基于临界土力学理论的动荷载作用下不排水抗剪强度计算公式中,从机理上分析不排水抗剪强度随振动次数变化关系曲线的发展规律,与试验结果进行对比验证.结果表明:改进的孔压-振动次数关系计算公式能考虑振动频率的影响,在10000振动次数下u/σ'3为0.45～0.65.建立的半经验不排水抗剪强度-振动次数关系计算公式能预测不同振动频率下,任意振动次数的不排水强度值,振动次数为10000时不排水抗剪强度衰减到25％～80％.
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