CHARACTERISTICS OF PENETRATION RESISTANCE OF A RECLAIMED SANDY DEPOSIT AND THEIR CHANGE THROUGH VIBRATORY COMPACTION

Abstract

Penetration resistance of standard penetration test is examined in relation to the in-situ relative density determined from sand sampling. Tests have been carried out at the site of Ogishima Island where was lately reclaimed with pit sand. The results are compared with the one obtained by Gibbs and Holtz based on laboratory tests. An influence of lateral stress on blow counts is further studied on the basis of in-situ tests. They have been conducted on improved ground where received a vibratory compaction. Studies on virgin deposits show that a condition of deposition exerts a considerable influence on penetration resistance. Deposits below sea level show a little smaller resistance than the one estimated from the results of Gibbs-Holtz under the same relative density. An average relation expressed as N^^-=(22σ_v'+6)D_r² is found out. But this relation cannot be applied to deposits above sea level. The average blow count N^^- is smaller at any depth than the blow count of highest frequency N_p irrespective of the condition of deposition. The difference between them is about 2 or 3.From studies on improved ground, it is shown that the penetration resistance increases considerably through compaction. Its increase could never be explained by only the increase in relative density if the relation obtained above is utilized. Hence, the relative density evaluated from blow counts becomes far higher than the actual one. This misleading is considered to result from the increase in lateral stress. Results of pressuremeter tests before and after compaction reveal an actual increase in it. The penetration resistance is, hence, promised to receive an influence of the increase not only in relative density but also in lateral stress.