Basal heave stability of circular shafts
Date of Issue2016
School of Civil and Environmental Engineering
Basal heave stability is one of the major concern for engineers in Singapore due to presence of soft marine clay in most area of island. Conventional methods such as Terzaghi(1943), Bjerrum & Eide remain the commonly used methods to evaluate basal heave factor of safety but these methods disregard the stiffness of wall (EI) and depth of wall penetration (D). These methods are also only applicable for rectangular excavations. In this study, Plaxis 2d finite element method software is used to examine the parameters which affect basal heave stability for circular shafts. The examined parameters are width of excavation(B), thickness of soft clay below base of excavation(T),depth of wall penetration below base of excavation(D) , undrained shear strength (Cu) and clay wall interface strength(Rinter). A total of 30 cases are examined in this report and the computed factor of safety were compared with Cai’s method ( Cai etal 2002) . The result shows both method gives a similar trend. The basal heave factor of safety increases with decrease in B and T and increases with increase in D and Cu. The comparison between the result from this study and Cai indicate that Cai’s method always give a more conservative value. The relationship between these 2 approaches is proposed but the relationship still have to be verified with more data.
Final Year Project (FYP)
Nanyang Technological University