One-dimensional compression theoretical model for shield foam-conditioned coarse-grained soil considering influences of gradation

Under the state of chamber pressure, the pore pressure of conditioned soil will be generated, and it can balance the water pressure in front of the excavation to reduce the level of groundwater infiltration. Therefore, one-dimensional compression calculation of conditioned soil is of great significance for guiding the safe excavation of shield. Therefore, based on the Boyer' s law and the discontinuous particle accumulation theory, the model for calculating the undrained pore pressure considering gradation parameters and soil-conditioning parameters is established. According to the deformation characteristics of foam-conditioned soil, the method for the initial compression modulus E_s is proposed, and the compression model for the foam-conditioned soil is established. Furthermore, the compression model is introduced into the pore pressure model, and a simple model for the pore pressure is proposed. In order to verify the reliability of the proposed model for the pore pressure and compression, the undrained one-dimensional compression tests on the foam-conditioned coarse-grained soil with different gradations are carried out by using the self-designed large-scale compression devices, and the measured values of pore pressure and compression are obtained. The comparison between the measured and calculated values shows that the pore pressure model and compression model can describe the variation of the pore pressure and compression of foam-conditioned soil under different gradations. The foam injection ratio and gradation have a significant impact on the pore pressure of the foam-conditioned soil.