Composite Foundation of Deep Mixing Piles for Large Steel Oil Tanks on Soft Ground

Abstract

The technique of deep mixing method is often used to reinforce soft cohesive ground, in which cement is applied as a consolidating agent, and a special deep mixing machine is utilized. This method is suitable for improving the soft cohesive ground, particularly the very soft clayey soil. The methods for estimating the settlement of composite foundation include the layer-wise summation method, the standard-recommended method, and the composite pile foundation method. The composite pile foundation method is deduced from Mindlin Solution by using Geddes integral on the principle of pile-soil interaction, sometimes named as modified Geddes integral method. It is possible that the general or local failure will come into existence in the foundation under tanks because the loaded area and the value of loading are both very large. It is necessary to perform stability analysis by using the Skempton method and simplified Bishop method of slices. The value of the factor of safety for composite foundation is required up to 1.20 to 1.25. The reasonable admixing quantity of cement should lessen gradually along the depth of cement pile shaft. That makes the whole pile shaft get the utmost out of strength. For a certain admixing quantity of cement, the time and the uniformity of agitating are key factors that influence the quality of pile shaft and the strength of improved soil.