Abstract
Severe collapse settlements in fill of stiff clays or weak rocks can occur several times due to inundation. This paper shows a method used for controlling the placement of stiff clays to reduce collapse settlement in a residential development. An in-situ compression test developed by the authors was used to observe the settlement of trial fills compacted by three types of rollers. The results of the in-situ tests were compared with those of the laboratory compression tests conducted on undisturbed samples taken from the test site, and it was shown that the vertical strains in the both cases coincided. Guide indices for the control of the placement of fill previously presented, such as the density, air void ratio or strength of the fill, have been re-evaluated following the results of the in-situ compression tests according to a current code for the maximum incremental inclination of houses by Architectural Institute of Japan. It was found that the following procedures should be adopted at the site as guidelines for placement of the stiff clays : (1) The soil should be spread in layers less than 30 cm thick and compacted by two passes of a vibrating roller of 9.8 tons at least, (2) The relative density of the fill should be greater than 98%, (3) The strength as measured by a dynamic cone test should be greater than 5 blows per 30 cm, (4) The air void ratio should be less than 12%, and (5) Water should be spread before compaction when fill-materials lose more than 1.5% of water content due to drying.
