Factors affecting the stability of deep excavations in clay with consideration of a full elastoplastic support system


This study investigates the stability of internally braced excavations in thick, saturated clay using a finite element method with reduced shear strength. The support system was fully modeled using elastoplastic structural elements, including struts, walls, and center posts. Effects of the ratio of the wall embedded depth to the excavation depth (Hp/He), the excavation width (B), the wall thickness (tw), the strut capacity, and the normalized undrained shear strength (\(s_{\text{u}} /\sigma_{\text{v}}^{\prime }\)) of soil were studied. Results showed that when the Hp/He ratio increased, the stability of excavations first improved and then remained unchanged with increasing Hp/He. An increase in the excavation width did not influence the stability of excavations. The wall bending moment capacity had a more pronounced effect on the stability of excavations than the strut capacity. Additionally, the stability of excavations was most affected by \(s_{\text{u}} /\sigma_{\text{v}}^{\prime }\). Finally, a simplified method was proposed to estimate the factor of safety of excavations without performing numerical analysis.

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B :

Excavation width

F fem :

Factor of safety by finite element method

F sc (R) :

Factor of safety by slip circle method using the numerical failure surface

F sc (toe) :

Factor of safety by slip circle method using the failure surface passing through wall toe

F T :

Factor of safety by Terzaghi’s method

Hp/He :

Ratio of wall embedded depth to excavation depth


Strut capacity multiplier

t w :

Wall thickness


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The authors gratefully acknowledge financial support of the National Science Council, Taiwan, R.O.C., under Grant NSC 101-2221-E-011-110-MY3.

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Correspondence to Chang-Yu Ou.

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Do, T., Ou, C. Factors affecting the stability of deep excavations in clay with consideration of a full elastoplastic support system. Acta Geotech. 15, 1707–1722 (2020). https://doi.org/10.1007/s11440-019-00886-8

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  • Deep excavations
  • Finite element method
  • Stability analysis