This paper presents an evaluation for effectiveness of pre-dewatering on dynamic compaction for the reclaimed land built at near-shore. The Single-point Impact Test (SIT) and cone penetrometer are developed to perform the dynamic compaction under different water levels and drained conditions. The relationship between effective dynamic stress and cone resistance after impacts is presented. Dissipations of pore pressures measured in laboratory and filed are compared. Both cone resistances and improvement ratio in soils with higher water level are less than those with lower water level and in dry soils. The observations reveal that by lowering down the groundwater table prior to dynamic compaction in field, the soil resistances can be increased in depths and the depth of improvement could be extended.
Dynamic Compaction is regarded as one of the major techniques to improve the liquefaction resistance or bearing capacity of reclaimed land or loose ground due to its advantage of simple and fast procedure of construction. In this method, a heavy tamper is dropped onto the ground to be densified from a height of a few of 10 m. To ensure effect of the depth of improvement, the energy is generally applied in phases on a grid pattern over the area to be improved by either single or multiple passes. Nevertheless, the limitation of applied energy and ground water table restrain the depth of improvement. From the viewpoint of economy for practical cases, reducing the degree of saturation in soil deposits may be a better alternative than by raising the applied energy. The way to draw down the ground water level, in practice, is the best choice to During the process of the dynamic compaction, the pore pressure usually is generated in the soil deposit. In practice, a waiting period for dissipation of induced pore pressures is necessary for the nextproceeding phase of dynamic compaction.