Abstract
A rigorous solution aimed at accounting for the superposition and flow rule assumptions in the assessment of the bearing capacity of shallow strip footings under plane strain conditions has been developed using the method of characteristics and the finite element method. With reference to the Hill and Prandtl failure mechanisms, a bearing capacity factor Nγq and a superposition corrective coefficient μ that allow to directly obtain the actual bearing capacity of shallow strip foundations have been proposed. The geometry of the plastic volume involved in the failure mechanism has been also investigated, highlighting the influence of the superposition and flow rule assumptions. Starting from the numerical results obtained using the method of characteristics, several empirical relationships have been proposed for an accurate estimate of Nγq and μ as well as for the lateral extension and depth of the plastic volume. The accuracy of the numerical results has been checked through finite element analyses under the assumption of associated and non-associated flow rule showing that the proposed superposition corrective coefficient μ is not influenced by the flow rule assumption. Thus, a general bearing capacity equation for shallow strip footings has been provided which accounts for superposition approximation and non-associated flow rule.
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Abbreviations
- Δε s :
-
Incremental deviatoric strain
- γ :
-
Soil unit weight
- λ :
-
Surcharge ratio
- μ :
-
Superposition corrective coefficient
- σ′1, σ′3 :
-
Maximum and minimum principal effective stresses
- φ′:
-
Soil friction angle
- ψ :
-
Dilatancy angle
- ω :
-
Angle formed by the maximum principal effective stress with the horizontal axis
- B :
-
Foundation width
- C′:
-
Soil cohesion
- d :
-
Depth of the plastic volume
- N c, N q, N γ :
-
Bearing capacity factors
- N q N - A, N γ N - A :
-
Bearing capacity factors accounting for non-associated flow rule
- N γ q :
-
Generalized bearing capacity factor for the general case c′ ≠ 0, φ′ ≠ 0, q ≠ 0
- q :
-
Surface surcharge
- q ult :
-
Ultimate load according to the superposition assumption
- \(\overline{q}_{{{\text{ult}}}}\) :
-
Actual ultimate load
- s′:
-
Effective stress invariant
- S α, S β :
-
Curvilinear coordinates
- x :
-
Width of the plastic volume
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Acknowledgements
This work is part of the research activities carried out by the Messina Research Unit in the framework of the work package WP16—Contributi normativi—Geotecnica (Task 16.3) of a Research Project funded by the ReLuis (Network of Seismic Engineering University Laboratories) consortium (Accordo Quadro DPC/ReLUIS 2022-2024).
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Casablanca, O., Cascone, E. & Biondi, G. Influence of the superposition and flow rule assumptions on the bearing capacity of shallow strip footings. Acta Geotech. (2024). https://doi.org/10.1007/s11440-024-02284-1
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DOI: https://doi.org/10.1007/s11440-024-02284-1