NUMERICAL STUDY ON SAND BOILING IN EXCAVATIONS AND/OR COFFERDAMS

• Main Authors: IGNATIUS TOMMY PRATAMA, 陳福隆
• Other Authors: Chang-Yu Ou
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/k24d5u

碩士 === 國立臺灣科技大學 === 營建工程系 === 106 === The flow of water through soils in the retaining system may induce some alterations on the magnitude of the working stresses in soils, especially the effective overburden stress. Sand boiling is one of the stability issues related to the change of effective stress due to groundwater flow, but only a few researchers investigate the effect from the effective stress point of view. Accordingly, the primary objective of this study is to investigate the impact of effective stress change inside the excavation zone subject to seepage flow and to evaluate the factors affecting the safety against sand boiling. The study was carried out on 23 experimental failure cases with various excavation geometries and soil densities by utilizing PLAXIS and SEEP/W finite element programs. The results indicate that the failure progression of sand boiling is initiated from the excavation surface, then propagates to the area close to the pile. In addition to the failure propagation, the excavation geometry has a visible effect in establishing the failure mechanism and the governing the computed hydraulic gradient. Concerning the requirement of a reliable safety adequacy, the factor of safety adequacy is proposed in this study by adopting the equivalency theory between reliability and factor of safety. Eventually, two actual failure case histories are introduced to validate the applicability of the proposed factor of safety. The results indicate that the application of the proposed method can describe well the failure condition of an excavation with respect to sand boiling. Note also the application of the proposed factor of safety should obey the applied constraints in this study.