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.