Abstract
Soil spatial variability is a common situation in marine geotechnical engineering, while most studies have primarily focused on evaluating the uniaxial vertical (V), horizontal (H), or moment (M) bearing capacity of foundations in spatially variable clay. Whereas the process of combined bearing capacity analysis by probe method is complex, resulting in low efficiency. As a result, the simplified modified swipe (SMS) method is proposed in this paper, which can represent the capacity in any direction of the load space accurately and takes just 6.5 times the duration of a single probe loading for a half-failure envelope. Based on the established three-dimensional random finite element models, the effectiveness of this method is demonstrated by analyzing the combined bearing capacity of five kinds of foundations in spatially variable clay. Furthermore, Monte Carlo simulations revealed that the spatial variability of the soil cause various failure envelopes, and the response of the combined bearing capacity is not identical in all directions. The VHM failure envelopes with different probabilities are given and could be found that the safety factors recommended by the guidelines are insufficiently conservative for structures susceptible to soil spatial variability. Finally, a strategy for applying different safety factors to both load directions is proposed, which could be helpful for the design of foundations in spatially variable clay.
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Abbreviations
- A :
-
Cross-sectional plan area of foundations
- COV:
-
Coefficient of variation
- D :
-
Foundation diameter
- E :
-
Young’s modulus
- Fs:
-
Factor of safety
- Fs_x :
-
Factor of safety in x direction
- Fs_y :
-
Factor of safety in y direction
- H :
-
Horizontal loading
- H ult :
-
The horizontal ultimate bearing capacity
- L :
-
Skirt length of caissons and tripod bucket foundations
- M :
-
Moment loading
- MCS:
-
Monte Carlo simulation
- M ult :
-
The moment ultimate bearing capacity
- N :
-
Number of Monte Carlo simulations
- N c H :
-
The horizontal bearing capacity factor
- N c H_ Det :
-
The horizontal bearing capacity factor in deterministic soil
- N c M :
-
The moment bearing capacity factor
- N c M_ Det :
-
The moment bearing capacity factor in deterministic soil
- Nc Nor_space :
-
The bearing capacity factor in normalized loading space
- N c V :
-
The vertical bearing capacity factor
- N c V_ Det :
-
The vertical bearing capacity factor in deterministic soil
- V :
-
Vertical loading
- V ult :
-
The vertical ultimate bearing capacity
- X amp1 :
-
The displacement amplitude of the first step in the first loading direction of the SMS method
- X amp2 :
-
The displacement amplitude of the second step in the first loading direction of the SMS method
- Y amp2 :
-
The displacement amplitude of the second step in the second loading direction of the SMS method
- k :
-
The gradient of the undrained strength
- lt:
-
Lid thickness of caisson; foundation thickness of surface footing and embedded foundation
- s u :
-
The undrained shear strength
- s u0 :
-
The undrained shear strength at the foundation tip level
- s um :
-
The undrained shear strength at mudline
- t :
-
Skirt thickness
- v :
-
Poisson’s ratio
- θ :
-
Rotational displacement
- δ h :
-
The horizontal scale of fluctuation
- δ v :
-
The vertical scale of fluctuation
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Acknowledgements
The work forms part of the activities of the State Key Laboratory of Hydraulic Engineering Simulation and Safety at Tianjin University. The corresponding author is supported by the National Natural Science Foundation of China (No. 51890911). The support is gratefully acknowledged.
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Fan, S., Zhang, Y. & Li, S. Fully assessing foundation failure envelopes under combined loads in spatially variable clay. Acta Geotech. (2024). https://doi.org/10.1007/s11440-023-02214-7
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DOI: https://doi.org/10.1007/s11440-023-02214-7