A nonlinear attachment-detachment model with adsorption hysteresis for suspension-colloidal transport in porous media

A set of thermo-hydro-mechanical coupling control equations was established, and the healing process of the joints between Gaomiaozi bentonite (GMZ01) buffer material blocks and the influence of the joint parameters were numerically simulated. The calculations consider the effect of joints on solute migration, the permeability and thermal conductivity of the buffer material, and the evolution of the healing effect. The effects of the joint design parameters, including the type, number, width, splicing form, and average dry density of the joint, are investigated. Studies show that, under an external water head, the joints will become hydraulic priority channels due to their higher permeability, which will shorten the saturation time of the blocks. As the bentonite gradually saturates, the swelling force compresses the joint material. This action improves the overall uniformity of the buffer material and reduces the priority channel effect. Meanwhile, the final average permeability and diffusion coefficient of the buffer material are found to mainly depend on the average dry density of the buffer material. The higher the average dry density of the buffer material is, the lower the final average permeability and diffusion coefficient are, whereas the distribution of joints and the block splicing are less affected by the average dry density of the buffer material. The findings of this study can provide a reference for the design of bentonite buffer material blocks in the repository.

“…e model parameters a and b are obtained by fitting the test results of a soil-water characteristic curve for a compacted bentonite block at 20°C obtained by Bai et al [38].…”

Section: Appendixmentioning

confidence: 99%

The Healing Process of the Joints between Buffer Material Blocks and the Influence on Solute Migration

Zhou

Liu

et al. 2021

“…Actually, the theory of displacement earth pressure means that there is a close association between the earth pressure (i.e., the stress in soil) and the induced displacement during the movement of the retaining structure, which also involves the coupling process of external force, seepage action [27,28], soil microstructure damage [7,29], and even thermal loading [23,30]. In the existing theory, the relationship between displacement and earth pressure is generally described from three aspects: (a) the displacement earth pressure curve is fitted according to the experimental data to obtain a certain functional relationship between earth pressure and displacement [31]; (b) the association between the internal friction angle and the displacement is obtained from the backfilling of retaining structure, to obtain the variation of earth pressure with the corresponding displacement; (c) in view of the stress-strain constitutive law of the soil behind the retaining structure, the calculation model of the relationship between displacement and earth pressure is established.…”

Section: Displacement Earth Pressure Theorymentioning

confidence: 99%

“…Many theories have been made on the support force of the shield excavation surface, which have formed a variety of analysis methods such as the limit analysis method, and plastic balance theory, even considering the grouting reinforcement effect [3], drainage condition [4][5][6], migration of soil particles caused by infiltration [7,8], and consolidation deformation caused by temperature disturbance during excavation [9][10][11]. e upper limit value of the active limit earth pressure of the shield excavation surface was usually used to analyze the double logarithm spiral model.…”

Section: Introductionmentioning

confidence: 99%

A Displacement‐Based Theory for Predicting the Support Force on the Shield Tunneling Surface in Sandy Soil Layers

Guang

Han

Zhang

et al. 2021

Due to the poor stability of the loose sandy soil layer, if the support force is not properly controlled during the construction process of the shield tunnel using the earth pressure balance method, it is easy to cause the ground to collapse or uplift. Therefore, understanding the support force of the excavation surface of shield tunneling in sandy soil layer is very vital to ensure the stability of the excavation surface. Firstly, it is assumed that the damaged soil is a three-dimensional wedge and a modified three-dimensional wedge in the active and passive failure modes, respectively. The shallow soil pressure theory and the soil plastic limit equilibrium theory are derived by analyzing the stress distribution on the damaged soil. The equation for revealing the inner essence between the support force of the shield excavation surface and excavation surface displacement under the condition of sand-covered soil is used. Secondly, the numerical simulation method analyzes the displacement of the excavation surface when the support force changes under different working conditions, and the relationship curve between the excavation surface support force and the shield tunneling displacement is obtained. The comparison and analysis between the numerical simulation calculation and the theoretical analysis indicate that the deduced calculation equation for the excavation surface support force based on the displacement earth pressure is reasonable.

“…Steel sleeve can form a confined space by injecting cement mortar to provide water and soil pressure on the face of the tunnel to prevent the risk of water leakage, sand leakage, and ground collapse, thereby reducing the end reinforcement range or even eliminating reinforcement requirement [1][2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Numerical Analysis on Reinforcement Range of a Closed Steel Sleeve against Collapse

Yin

2021

Before the shield machine begins to excavate, the end of the station structure often requires extensive soil reinforcement to ensure construction safety. Closed steel sleeve can prevent water leakage, sand leakage, and cave door collapse by balancing the water and soil pressure on the tunnel surface, thereby reducing the reinforcement range. In this study, a launching project of a closed steel sleeve is investigated; the Madis GTS finite element analysis software is used to simulate the triple-tube high-pressure jet-grouting pile to reinforce the water-rich sand layer. Soil displacement and stress after opening of the tunnel door are studied in detail at different longitudinal reinforcement lengths and transverse reinforcement scopes. The results show that, as the longitudinal reinforcement length increases, the displacement of the soil shows a decreasing trend, and the greater the length of the reinforced soil, the smaller the reduction in displacement. Furthermore, with the decrease of the lateral reinforcement range, though the soil settlement area has increased, the displacement remains unchanged. However, changing the end reinforcement range has no effect on the soil stress. In general, based on the strength and stability of the soil after the gate is cut out, the reinforcement range of the closed steel sleeve can be appropriately reduced compared to traditional reinforcement methods.