. College of Civil Engineering and Architecture, Henan University of Technology, Zhengzhou 450001, China . MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering, Zhejiang University, Hangzhou 310058, China . State Key Laboratory of Hydro-Science and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China
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.
Fig.1 Trapdoor model considering the groundwater level.
Fig.2 Maximum principal stresses arch.
Fig.3 Comparison results with trapdoor tests and theory solution: (a) test of Liang et al. [42]; (b) test of Iglesia et al. [7].
Fig.4 Numerical model.
Soil type
Specific gravity
Effective friction angle (° )
Saturated permeability coefficient (m·s?1)
Dry density (g·cm?3)
Effective cohesion (kPa)
Irreducible saturation
m
d
Silty fine sand
2.70
34.3
3.32E?05
1.5
/
0.12
2.98 E?05
0.664
2.974
Sandy silt
2.69
34.6
7.27E?06
1.5
/
0.20
2.01 E?09
0.844
6.420
Silty clay
2.71
25.5
1.67E?07
1.6
8.1
0.60
1.00 E?02
0.709
3.434
Tab.1 Parameters of unsaturated soil [45]
Fig.5 Comparison results with numerical results.
Fig.6 Comparison results with numerical results and theory solution: (a) sand; (b) silt; (c) clay.
Fig.7 Normalized average loosening earth pressure varying with soil saturation for different soil types.
Fig.8 Average effective loosening earth pressure varying along the depth direction with different groundwater level.
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