QUALITY ASSURANCE OF CEMENT TREATED SOIL BY WET GRAB SAMPLER

The quality assurance (QA) of cement treated soil in Japan normally involves unconfined compression tests on in-situ treated soil sampled by core boring. In some other countries, treated soil excavated by wet grab sampling instead of core sampling is often used for QA. Lack of systematic research comparing the treated soil's strength obtained in these two different methods has restricted evaluation of their merits. The authors started a research project in which a series of field and laboratory tests was carried out to compare the treated soil strength and discuss the applicability of wet grab sampling to QA in wet- and dry-type deep mixing techniques. Deep-mixed soil was sampled with two types of wet grab sampler to prepare specimens soon after the field DM execution, and was subjected to unconfined compression tests after four weeks' curing in laboratory to compare the strength with that of laboratory-mixed and core sampled specimens. The wet grab specimens exhibited less variability in strength than the core specimens, but the strength itself was significantly lower than that of the core and laboratory-mixed specimens. The difference observed in the strength was particularly stark for the dry deep mixing method, necessitating further research into the causes of the difference.