The existing earth pressure theories, such as Rankine's theory and Coulomb's theory, adopt planar slip surfaces to establish force equilibrium equations. For retaining walls, especially for those with narrow backfill, the shape of slip surfaces may not be straight, and the earth pressure distribution behind the retaining wall may be nonlinear due to the influence of friction and soil arching effects. To investigate the shape of slip surfaces and the earth pressure distribution behind the retaining wall under a narrow backfill condition and a translational mode, six model tests with different boundary conditions were carried out using a self-developed experimental setup, in which an analogical soil was used as a backfill to stimulate the behavior of the soil. The model tests show that the shape of slip surfaces was highly dependent on the aspect ratio (i.e., the ratio of the backfill width to the fill height). When the aspect ratio was larger than one, the shape of slip surfaces tended to become arc-shaped. The aspect ratio of 1 was determined as the threshold value for the narrow backfill condition for the material investigated. An analytical model for the active pressure distribution under a narrow backfill condition and translational mode was proposed considering nonlinear slip surfaces and the soil arching effect. The accuracy of the proposed method was verified with the experimental data obtained in this study and those reported in the literature.

An extensive suite of three-dimensional finite-element simulations was carried out to examine the response of pile-raft-soil systems under seismic excitation representative of far-field events. The numerical procedure was first validated by a series of seismic centrifuge tests performed mainly on $4\times 3$ pile-raft systems embedded in soft clays and was subsequently extended to study the influence of various factors on the computed raft acceleration and maximum bending moment near the pile head. The factors considered were pile length, pile flexural stiffness, peak base acceleration, superstructural mass, soil stiffness, soil frictional angle, pile density, and soil-layer thickness. With the help of dimensional analysis, the results of the parametric studies were processed and interpreted using regression analysis to derive correlations for predicting the maximum pile-group bending moment and peak raft acceleration. Such correlations are highly useful in the practical seismic design of pile-raft systems embedded in soft soils, because they provide quick first-order predictions for making initial engineering judgments prior to performing more-detailed and rigorous numerical simulations.

Thermal hydrolysis (TH) has been used to improve anaerobic digestion performance as well as the stability of heavy metals in sludge. Because the toxicity of heavy metals is closely related to both the concentration and the chemical speciation, more exhaustive studies on speciation distribution are urgently needed. This research aimed to investigate the effects of TH treatment (especially the time and temperature) on the concentration and stability of heavy metals in sludge, and to define the optimal TH conditions. The TH experiment indicated that the content of the stable form of Cu and Zn reached 83% and 47.4%, respectively, with TH at 210°C and 30 min. Compared with the raw sludge, the proportion of Cu and Zn increased by 11.88% and 7.3%, respectively. Results indicated that the heavy metals were combined with sludge in a more stable form with the pretreatment of TH, which improved the stability of heavy metals.

Breakage of particles has a great influence on the particle size distribution (PSD) and the associated mechanical behavior of ballast under train loads. A discrete element method (DEM) simulation of triaxial testing under monotonic loading was carried out using FRM (fragment replacement method) breakable particles as ballast and a flexible shell model as membrane. The coupled model was validated by comparing the load-deformation responses with those measured in previous experiments and was then used to analyze the contact orientations and the distribution of particle breakage from a micromechanical perspective. The simulation results show that higher confining pressure and larger axial strain may increase the grain breakage (B_g) and the fractal dimension (D) of ballast. It was observed that most breakage was first-generation breakage, and that the proportions of the second- to fifth-generation breakage decreased successively. Moreover, as the axial strain or confining pressure increased, the percentage of small particle fragments increased in correspondence with the PSD curves that remained concave upwards, as the fractal dimension D of PSD increased. In addition, the evolution of D exhibited a linear correlation with grain breakage B_g. Contrarily, a quadratic curve relation between D and volumetric strain was exhibited under different axial strain stages. Therefore, D has the potential to be a key indicator to evaluate the degree of ballast crushing and PSD degradation, which may contribute to better decision making concerning track bed maintenance.