ULTIMATE BEARING CAPACITY ANALYSIS OF CAISSON FOUNDATION IN SEEPAGE FIELD

Abstract

In 2011 off the Pacific coast of Tohoku Earthquake, lots of seawalls were destroyed by Tsunami. By the survey of destroyed seawalls, not only the wave pressure to dyke but also seepage force in ground have been reported to contribute to the instability of seawalls. However, it has been difficult to consider the effect of seepage force in the stability analysis of seawalls. This paper presents the hybrid stability analysis of rigid plastic finite element method and seepage finite element method in order to evaluate the total stability of seawall against tsunami. To simplify the problem, ultimate bearing capacity of caisson is investigated under the specific seepage condition by setting the sea water levels of upstream and downstream of caisson. Through case studies, the effect of seepage force on the instability of seawall is examined by handling the magnitude of seepage force. The effect of embedment of caisson on ultimate bearing capacity is also investigated. The depth of embedment works to the stabilization of seawall from the two aspects. One is the mechanical stabilization of caisson by overburden pressure and the assistance in shear strength of overburden ground. The other is the decrease in seepage force by embedment. The obtained ultimate bearing capacity shows the proposed analysis method well simulated the stability of caisson under the seepage force condition.