A large-strain model was developed to study the consolidation behavior of soil deposits improved with prefabricated vertical drains and subjected to surcharge and vacuum preloading. The smear effect resulting from the installation of drains was incorporated in the model by taking the average values of permeability and compressibility in the smear zone. The dependence of permeability and compressibility on void ratio and the effects of non-Darcian flow at low hydraulic gradients were also incorporated in the model. The creep effect was also taken into account for secondary consolidation of soft soil deposits. The model was applied to two different embankments located at Suvarnabhumi International Airport, Thailand, and Leneghan, Australia. It was observed that the creep effect led to an additional settlement of 12%-17% after the primary consolidation phase. The study further demonstrated that creep settlements increased with the non-Darcian effect. The difference between surface settlement results with and without the creep effect increased from about 12% to 15% when the non-Darcian parameter (n) increased from 1 to 1.6. However, beyond a threshold value of n >= 1.6, the influence of non-Darcian flow on creep settlement diminished. The value of average and actual effective stresses increased by about 13% and 17%, respectively, when the value of n increased from 1 to 2. However, the impact of n on effective stresses became negligible for values of n >= 2.5. The rate of consolidation decreased approximately by about four times when the permeability ratio ((k) over tilde (u)/(k) over tilde (s)) increased from 1 to 5.

The Discrete Element Method (DEM) has been widely used to study the macro-micro behaviour of granular materials at large strains (>1%). However, investigations over a wider strain range are lacking. This study conducts DEM triaxial tests on specimens with different particle physical properties to examine their influence on macro-micro behaviour from small strains (below 1 %) to large strains. Small-strain behaviour is characterised by the maximum shear modulus, elastic range and stiffness degradation rate. Large-strain behaviour is analysed through the peak stress ratio, critical state stress ratio and void ratio. Then, the micro-mechanisms underlying these results are examined using the Stress-Force-Fabric (SFF) relationship, which links the (macro) stress ratio and (micro) anisotropy source. This study is the first to apply the SFF relationship to small strain behaviour. Results reveal the qualitative relationship between particle physical properties and macro-behaviour at different strains: increasing particle Young's modulus enhances the maximum shear modulus but accelerates stiffness degradation; increasing shearing and rolling friction significantly reduces the stiffness degradation at small strains and enhances strength and dilation at large strains. This study also highlights the limitation of the Hertz contact model in capturing both small-strain and large-strain behaviour quantitatively using a single set of parameters. Hence, modellers should calibrate model parameters based on whether their focus is on large-strain or small-strain behaviour. For micro-behaviour, the relative importance of anisotropy sources depends on strain level rather than particle physical properties. At small strains, the mechanical anisotropy source (both normal and tangential forces) primarily controls stiffness and its degradation. At large strains, material strength is influenced by both mechanical and geometrical anisotropy sources, with anisotropy from the normal force being the most significant, followed by contact normal, tangential forces, and branch vector.

Prefabricated horizontal drains and vacuum preloading have advantages in the consolidation of ultra-soft dredged sludge and soils for maintenance dredging, reclamation, and ground improvement in coastal regions. While laboratory tests and field trial projects have been reported, a convenient analysis and design method is still unavailable. This study proposes a new simple method for the settlement analysis of soft soils considering horizontal drains, vacuum preloading, creep, and large-strain effects. A unified equation is constructed to account for various layouts of horizontal drains in consolidation. A new explicit method is developed to consider the large-strain deformation with the nonlinear evolution of permeability and compressibility of ultra-soft soils under vacuum preloading. The viscous compression is taken into account using a simplified Hypothesis B method. The proposed solution also facilitates convenient consideration of multiple layers of soils and drains subjected to staged loading. The proposed method is examined by a series of physical model tests with different horizontal drain dimensions. Finally, the method is applied in the analysis of two well-documented field cases in Hong Kong and Japan, which confirms its effectiveness and accuracy.

This study analyzes the stability of surrounding rock for a circular opening based on the energy and cavity expansion theory, and regards the surrounding rock failure of circular opening as an unstable state driven by energy. Firstly, based on the large-strain cylindrical cavity contraction and energy dissipation method, the deformation caused by the excavation of surrounding rock is regarded as the cylindrical cavity contraction process. By introducing the energy dissipation mechanism, the energy dissipation solution of cylindrical cavity contraction is obtained. The energy dissipation process of surrounding rock is characterized by the strain energy changes in the elastic and elasto-plastic regions of this cavity contraction analysis. Secondly, the deformation control effect of support and surrounding rock parameters on the energy dissipation of surrounding rock is studied based on the energy dissipation solution of surrounding rock under support conditions. Finally, the effectiveness and reliability of the analytical approach was demonstrated by comparing the support design results with those in the literature. The research results indicate that the three-dimensional mechanical properties and dilatancy angle of rock and soil mass have a significant impact on the energy support design of surrounding rock. This study provides a general analysis method for the stability analysis of surrounding rock of deep buried tunnels and roadway.

In this study, a single-layer SPH approach that takes into account full soil-water interactions is proposed. The approach updates the propagation of pore pressure through combination of volumetric strain and Darcy's law, accounting for the momentum equation, soil constitutive behavior, and the development of pore pressure at each timestep of the simulation. The proposed method is validated by analytical solutions of consolidation problems. To showcase its capability in simulating large-deformation problems with hydro-mechanical interactions, a physical test of a seepage-induced sinkhole was simulated using the proposed SPH method. The good agreements suggest that the proposed method can capture the key features of sinkhole developments and serve as a promising tool to explore the associated failure mechanism. A series of parametric studies are then conducted to reveal the influences of material properties and hydraulic conditions on the failure behavior of sinkholes, including failure patterns, influence zone, and surface settlement.