Evaluation Case of Characteristics for Improved Soil by Elastic Wave Velocity Test

In Japan, quality inspection of ground improvement is based on strength to confirm the required performance. Since strength is the target, the testing method is limited to unconfined compression test, and there is no alternative testing method, nor is there a clearly defined method for analyzing the factors that may cause the lack of required performance. Because of this, there is a problem of economic sustainability, such as re-executing a series of work from core sampling to testing. Therefore, we decided to study a method to deal with this problem by adding criteria such as defect factors to the inspection target. The purpose of this paper is to collect basic data for analyzing the factors that cause variations in strength and defects in quality inspections, as well as for analyzing and evaluating the results of such analysis and evaluation methods. The results of elastic wave velocity and needle penetration tests, in addition to unconfined compression test, on core specimens taken from the improved ground were briefly analyzed. The results indicated that one of the factors causing the variation in unconfined compression strength was the occupancy of voids and clods on the shear surface, which could be analyzed by the elastic wave velocity test. The correlation between unconfined compression strength and elastic wave velocity was also obtained, which could be used to estimate the unconfined compression strength. These results may suggest that the elastic wave velocity test is an effective alternative method to the unconfined compression test.