Characteristics of Ground Expanded by Pulsed Power for Anchorage

Anchor capacity is influenced by ground condition such as shear strength. In general, it has been known that the capacity in soft soil is several times lower that in rock. In addition, it also influenced by the configuration and size of the anchor zone as well. Four types of anchors have been introduced generally according to mechanism of stress transfer and how to be installed. Among them is a bell or under reamed anchor, which can increase resistance. However, the effect of enlargement of fixed zone is controversial. Since such an enlargement is formed by cut mechanically, there always exists so-called smear zone of ground which gives rise to the reduction of shear strength. This paper introduces PDT(Pulse Discharge Technology) anchoring method. The PDT anchoring method is to install an anchor using electrical power so called Pulse power. Since this technique can make not only a bore hole to be expanded but also the ground to be improved by compaction, the anchor installed by PDT is expected to develop shaft and end bearing capacity efficiently. In this study, as preliminary study, we introduce characteristics of ground expansion as well as improvement. In order for quantitative evaluation of the relation between pulse power and ground expansion a series of laboratory tests are conducted. The tests are carried out on sand with different relative densities and various number of pulse discharge. As a result, it is concluded that the expansion and soil improvement appeared to increase with an increase of the number of discharge and with a decrease of relative density.