A theory is proposed to evaluate the loosening earth pressure (vertical earth pressure after excavation) acting on a shallow tunnel in unsaturated ground with an arbitrary groundwater level. The theory is developed based on the limit equilibrium theory, combining soil–water characteristic curves, Mohr–Coulomb failure criteria, and effective stress for unsaturated soils. The proposed theory is applied to predict the vertical distribution of loosening earth pressure in unsaturated ground, which shows a significant difference from that in saturated ground. In unsaturated ground, suction contributes to the increase in effective loosening earth pressure and shear resistance. The remarkable effects of groundwater depth, soil type, and scale of overburden height and trapdoor width on loosening earth pressure are also revealed. Based on the soil–water characteristic curve, the degree of saturation decreases, which causes wet density to decrease and the total and effective loosening earth pressures to have contrary tendencies. Moreover, effective loosening earth pressures vary with soil type as the degree of saturation varies. The total loosening earth pressures are, however, very similar regardless of soil type, because wet density and shear resistance have similar tendencies. The proposed theory provides a valid model for loosening earth pressure in unsaturated ground that will be useful for shallow tunnel excavations.

中文翻译：

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疏松地下浅埋隧道上方土压力的理论

提出了一种理论来评估作用于任意地下水位的非饱和地下浅埋隧道中的松动土压力（开挖后的垂直土压力）。该理论是在极限平衡理论的基础上发展起来的，结合了土壤-水特征曲线，Mohr-Coulomb破坏准则以及非饱和土壤的有效应力。所提出的理论被用于预测非饱和土中松动土压力的垂直分布，这与饱和土中的土压力显着不同。在非饱和地面中，吸力有助于有效地松动土压力和抗剪力。还揭示了地下水深度，土壤类型，上覆高度和活板门宽度的尺度对松动土压力的显着影响。根据土壤-水特征曲线，饱和度降低，这导致湿密度降低，总的有效地松土压力具有相反的趋势。此外，随着土壤饱和度的变化，有效的松土压力随土壤类型而变化。但是，不管土壤类型如何，总的松动土压力都非常相似，因为湿密度和抗剪强度具有相似的趋势。所提出的理论为疏松非饱和土中的土压力提供了有效的模型，这将对浅埋隧道的开挖有用。有效的松土压力随土壤类型的变化而变化，饱和度也不同。但是，不管土壤类型如何，总的松动土压力都非常相似，因为湿密度和抗剪强度具有相似的趋势。所提出的理论为疏松非饱和土中的土压力提供了有效的模型，这将对浅埋隧道的开挖有用。有效的松土压力随土壤类型的变化而变化，饱和度也不同。但是，不管土壤类型如何，总的松动土压力都非常相似，因为湿密度和抗剪强度具有相似的趋势。所提出的理论为疏松非饱和土中的土压力提供了有效的模型，这将对浅埋隧道的开挖有用。