Loosening earth pressure above shallow trapdoor in unsaturated soil with different groundwater level

Abstract

The consideration of unsaturated conditions is infrequently addressed in current Terzaghi’s soil arching research. A modified analytical method for calculation of unsaturated loosening earth pressure above shallow trapdoor is proposed in this paper. By assuming the existence of a vertical slip surface above the trapdoor, the stress state of the soil in the loosening area are delineated in the extended Mohr–Coulomb circle. To account for the non-uniform distribution of vertical stress at arbitrary points along the horizontal differential soil trip, a virtual rotation circle trajectory of major principal stress is employed. Subsequently, the average vertical stress acting on the soil trip is determined through integral approach. Taking into account the influence of matric suction on soil weight and apparent cohesion, the differential equation governing the soil trip is solved analytically for cases of uniform matric suction distribution and alternatively using the finite difference method for scenarios involving non-uniform matric suction distribution. The proposed method’s validity is confirmed through comparison with published results. The parameter analysis indicates that the loosening earth pressure initially decreases and subsequently increases with the increase of the soil saturation. With the rise of groundwater level, the normalized effective loosening earth pressure shows a decreasing trend.

Graphical abstract

Keywords

soil arching effect / unsaturated soil / trapdoor test / loosening earth pressure / groundwater level variation

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Acknowledgements

This research was supported by the National Natural Science Foundation of China (Grant No. 41874067), the Innovative Funds Plan of Henan University of Technology (No. 2022ZKCJ07), and the Commonweal Technology Project of Jinhua City (No. 2023-4-037).

Competing interests

The authors declare that they have no competing interests.

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