Abstract: General dynamic drainage consolidation laboratory test, as tamping impact energy is not enough, some basic mechanical responses of soft soil in the actual project are difficult to excite, and relative features of soil are difficult to find. Through the self-developed multi-directional high energy electromagnetic force impact test system which can provide high impact energy produced by electromagnetic force and therefore could simulate the tamping energy acted in practice engineering, static and dynamic drainage consolidation model test for muck, is carried out. The experimental study obtains the response characteristics of pore pressure of this ultra-soft soil as follows: the time that upper pore pressure increases sharply to the maximum, which is very short (only 6 ms) at impact instant, and after the peak it drops rapidly to a certain value; in the initial twice tamping, the curve of pore water pressure at middle deep position shows bimodal type, the time interval between the two peak increases with the increase of tamping times gradually, and finally disappeared; each tamping, instantaneous earth pressure in the middle position shows a sharp growth and rapid decrease, and growth magnitude with the increase of tamping times shows a trend of decrease, but earth pressure value after tamping several days later is still greater than the value before tamping each time; after each tamping dissipating, the final value of pore pressure is less than the initial pore pressure, which signifies that under the certain condition of drainage, such ultra-soft soil foundation can be, indeed, acted by dynamic loading; the action mechanism of residual stress produced by dynamic tamping for soil consolidation exists, and it plays a main role for settlement, but for certain static loading, corresponding mechanism is little; the disturbance effect of inserting drainage board could not be ignored, but the disturbance effect decreases with soft soil embedded depth.

Key words: model experiment, high energy impact, muck, pore water pressure, variation law