In this study, four failure excavations were investigated using the finite element method (FEM) with reduced shear strength. Center posts were considered in the finite element model. For comparison, both the elastic and elastoplastic support system were employed. Results showed that as using the elastoplastic support system, the FEM gave more reasonable estimates of stability of the excavations than as using the elastic support system. Effects of the ratio between wall embedded depth to excavation depth (Hp/He), excavation width (B), wall thickness (tw), strut capacity, and normalized undrained shear strength (su/sv’) of soil on stability of excavations in clay were studied. Results showed that when the Hp/He ratio increases, stability of excavations was firstly improved and then remained unchanged with Hp/He. An increase in the excavation width did not influence stability of excavations. The wall bending moment capacity had a more pronounced effect on stability of excavations than the strut capacity. And stability of excavations was clearly affected by su/v’. Finally, a simplified method to estimate the factor of safety and failure mechanisms were proposed for excavations in clay.

ACI (2011). "Building code requirements for structural concrete (ACI 318-11) and Commentary (ACI 318R-11)." American Concrete Institute, Detroit.
AISC (2005). "Specification for structural steel buildings (AISC 360-05)." American Institute of Steel Construction, Illinois.
Arup (2005). "Report for the Ministry of Manpower Committee of Inquiry - Circle Line, Singapore Contract 824 - Supplemental Expert Report (Volume 1 & 2)." Ove Arup & Partners.
Aswin, L. (2010). "Analyses of basal heave for excavations in soft clay using the finite element method." Master, National taiwan university of science and technology, Taipei.
Bjerrum, L., and Eide, O. (1956). "Stability of strutted excavations in clay." Geotechnique, 6(1), 16.
Brinkgreve, R. B. J., and Bakker, H. L. (1991). "Non-linear finite element analysis of safety factors." Conference on computer methods and advances in geomechanics, Balkema, Cairns.
Broms, B. B., Wong, I. H., and Wong, K. S. (1986). "Experience with finite element analysis of braced excavation in Singapore." International symposium on numerical models in geomechanicsBelgium, 16.
Cai, F. E. I., and Ugai, K. (2000). "Numerical analysis of the stability of a slope reinforced with piles." Soils and Foundations, 40(1), 73-84.
Caquot, A. I., and Kérisel, J. L. (1948). Tables for the calculation of passive pressure, active pressure and bearing capacity of foundations, Gautier-Villars.
Chen, R., Li, Z., Chen, Y., Ou, C., Hu, Q., and Rao, M. (2013). "Failure Investigation at a Collapsed Deep Excavation in Very Sensitive Organic Soft Clay." Journal of Performance of Constructed Facilities, 0(0), 04014078.
Cheng, Y. M., Lansivaara, T., and Wei, W. B. (2007). "Two-dimensional slope stability analysis by limit equilibrium and strength reduction methods." Computers and Geotechnics, 34(3), 137-150.
COI (2005). "Report of the Committee of Inquiry into the incident at the MRT circle line worksite that led to the collapse of Nicoll highway 20 April 2004." Ministry of Manpower, Singapore.
Dawson, E. M., Roth, W. H., and Drescher, A. (1999). "Slope stability analysis by strength reduction." Geotechnique, 49(6), 6.
Do, T., Ou, C., and Lim, A. (2013). "Evaluation of Factors of Safety against Basal Heave for Deep Excavations in Soft Clay Using the Finite-Element Method." Journal of Geotechnical and Geoenvironmental Engineering, 139(12), 2125-2135.
Do, T. N. (2011). "Factor of safety against basal heave for deep excavations in soft clay using the finite element method." master, National taiwan university of science and technology, Taipei.
Donald, I. B., and Giam, S. K. (1988). "Application of the nodal displacement method to slope stability analysis." Conference on geomechanicsSydney, 5.
Donald, I. B., Tan, C. P., and Goh, A. T. C. (1985). "Stability of geomechanical structures assessed by finite element method." 2nd international conference of computing in civl engineering, Science press, Beijing, Hangzhou.
Faheem, H., Cai, F., Ugai, K., and Hagiwara, T. (2003). "Two-dimensional base stability of excavations in soft soils using FEM." Computers and Geotechnics, 30(2), 141-163.
Goh, A. T. C. (1990). "Assessment of basal stability for braced excavation systems using the finite element method." Computers and Geotechnics, 10(4), 325-338.
Goh, A. T. C. (1994). "Estimating Basal‐Heave Stability for Braced Excavations in Soft Clay." Journal of Geotechnical Engineering, 120(8), 1430-1436.
Griffiths D. V., and A., L. P. (1999). "Slope stability analysis by finite elements." Geotechnique, 49(3), 17.
Hsieh, P.-G., Ou, C.-Y., and Liu, H.-T. (2008). "Basal heave analysis of excavations with consideration of anisotropic undrained strength of clay." Canadian Geotechnical Journal, 45(6), 788-799.
JSA (1988). "Guidelines of design and construction of deep excavations." Japan society architecture, Tokyo.
Kullhawy, F. H., and Mayne, P. W. (1990). "Manual on stimating soil properties for foundation design." Electric Power Research.
Ladd, C. C., and Foott, R. (1974). "New design procedure for stability of soft clays." journalf of the geotechnical engineering division, 100(7), 24.
Liu, C. C., Hsieh, H. S., and Huang, C. S. (1997). "A study of the stability analysis for deep excavations in clay." Geotechnical conferenceTaipei, 9.
Matsui T., and C., S. K. (1992). "Finite element slope stability analysis by shear strength reduction technique." Soils and Foundations, 32(1), 12.
NAVFAC (1982). "Foundations and earth structures." Design manual 7.2, Naval facilities engineering command, Virginia, 279.
Ou, C.-Y., and Lai, C.-H. (1994). "Finite-element analysis of deep excavation in layered sandy and clayey soil deposits." Canadian Geotechnical Journal, 31(2), 204-214.
Ou, C. Y. (2006). Deep excavation: theory and practice, Taylor & Francis, Singapore.
Padfield, C., J., and Mair, R., J. (1984). "Design of retaining walls embedded in stiff clay." CIRIA Report, CIRIA, London, England, 146.
Peck, R. B. (1969). "Deep excavation and tunneling in soft ground." Conference on soil mechanics and foundation engineeringMexico, 66.
Rankine, W. M. J. (1857). "On stability on loose earth." Philosophical transactions of Royal Society of London, 19.
Reddy, A. S., and Srinivasan, R. J. (1967). "Bearing capacity of footing on layered clay." journal of the soil mechanics and foundations division, 93(2), 17.
Skempton, A. W. (1951). "The bearing capacity of clays." Building research congressLondon, 10.
Sloan, S. W., and Randolph, M. F. (1982). "Numerical prediction of collapse loads using finite element methods." International journal for numerical and analytical methods in geomechanics, 6, 10.
Tan, C. P., and Donald, I. B. (1985). "Finite element calculation of dam stability." 11th international conference on soil mechanics and foundation engineeringSan Francisco.
Terzaghi, K. (1943). Theoretical soil mechanics, John Wiley & Sons, New York.
TGS (2001). "Design specifications for the foundation of the building." Taiwan geotechnical society, Taipei.
Ugai, K. (1989). "A method of calculation of global safety factor of slopes by elasto-plastic FEM." Soils and Foundations, 29(2), 6.
Ugai, K., and Leshchinsky, D. (1995). "Three-dimensional limit equilibrium and finite element analyses: a comparison of results." Soils and Foundations, 35(4), 7.
Whittle, A. J., and Davies, R. V. (2006). "Nicoll highway collapse: evaluation of geotechnical factors affecting design of excavation support system." International conference on deep excavationsSingapore.
Yong, R. N., and Mckyes, E. (1971). "Yield and failure of a clay under triaxial stresses." journal of the soil mechanics and foundations division, 97(1), 18.
Zienkiewicz, O. C., Humpheson, C., and Lewis, R. W. (1975). "Associated and non-associated visco-plasticity and plasticity in soil mechanics." Géotechnique, 671-689.