浅层点振源作用下饱和砂层的超孔隙水压力

地震时,由于向上传播的地震波的作用,可能在饱和松砂中产生很高的超孔隙水压力,导致砂土发生液化。但至今还缺乏地震时土中超孔降水压力发生过程的实测资料。作者利用振动水冲器在施工过程所产生的振动,记录其周围饱和松砂中超孔隙水压力的产生过程,发现在这种振动条件--浅层点振源,形成的超孔隙水压力,基本上是由两部分组成的。即脉动孔隙水压力与应变孔隙水压力。脉动孔隙水压力是振动纵波在水中直接传播的结果。振动的纵、横波还通过土骨架向外传播,传播过程使土骨架产生应变势。应变超孔隙水压力是上耦合于骨架剩余应变势的反映。这两部分的比例与震中距及砂土密度有失。超孔隙水压力场与地面加速度场相似,基本上是震中距的幂函数.

Development of Excess Pore Water Pressure in Saturated Sand Stra turn under the Action of Vibrating Source from a Shallow Point

During earthquake, a high excess pore water pressure may be occurred in saturated sand due to an upward transmitting earthquake ware,which leads to cause loose sand into liquefaction. But there is no any measured data about the developing process of excess pore water pressure during earthquake until now. The authors recorded the developing process of excess pore water pressure around the loose sand by means of vibration from vibroflot at the period of construction and found the excess pore water pressure formed on such condition, as a shallow point vibrating source, consists of two parts fundamentally, pulse pore water pressure and strain pore water pressure. The pulse pore water pressure results from the vibrating P wave transmitted in the pore water and the P wave and S wave transmit outward through the soil skeleton, which produces strain potential on the skeleton of soil. The strain excess pore water pressure is a response of the residual strain potential coupled with the skeleton of soil. The rate between the above two parts are related to the distance from the shake center and to the density of sand. In level surface the field of excess pore water pressure is quite similar to the field of acceleration of ground.They all are the power-functions of distance to the shake center.