Dewatering and excavation are fundamental processes influencing soil deformation in deep foundation pit construction. Excavation causes stress redistribution through unloading, while dewatering lowers the groundwater level, increases effective stress, and generates seepage forces and compressive deformation in the surrounding soil. To systematically investigate their combined influence, this study conducted a scaled physical model test under staged excavation and dewatering conditions within a layered multi-aquifer-aquitard system. Throughout the experiment, soil settlement, groundwater head, and pore water pressure were continuously monitored. Two dimensionless parameters were introduced to quantify the contributions of dewatering and excavation: the total dewatering settlement rate eta dw and the cyclic dewatering settlement rate eta dw,i. Under different experimental conditions, eta dw ranges from 0.35 to 0.63, while eta dw,i varies between 0.32 and 0.82. Both settlement rates decrease with increasing diaphragm wall insertion depth and increase with greater dewatering depth inside the pit and higher soil permeability. An analytical formula for dewatering-induced soil settlement was developed using a modified layered summation method that accounts for deformation coordination between soil layers and includes correction factors for unsaturated zones. Although this approach is limited by scale effects and simplified boundary conditions, the findings offer valuable insights into soil deformation mechanisms under the combined influence of excavation and dewatering. These results provide practical guidance for improving deformation control strategies in complex hydrogeological environments.

Dynamic loading-seepage causes the migration of railway subgrade filling particles, leading to frequent engineering problems such as ballast fouling, mud pumping, settlement, and erosion. However, few studies have focused on the permeation features and internal erosion characteristics of subgrade materials, making it difficult to uncover the evolution mechanism of service performance of subgrade under complex geo-environmental conditions. Therefore, the seepage characteristics and permeability stability of subgrade materials were investigated using self-developed equipment to reveal the seepage failure mechanism under dynamic loading. The main conclusions are as follows: (1) The internal stability of the soil is affected by fluctuations in pore water pressure and hydraulic gradients in graded aggregate and gravel-sand-silt mixtures caused by dynamic loading. (2) Critical hydraulic gradients leading to the migration of fine particles (J(cr)) and seepage failure (J(F)) in graded aggregate and gravel-sand-silt mixtures are determined as follows: J(cr) =1.30 and J(F) =6.88 for graded aggregate, and J(cr) =1.23 and J(F) =2.71 for gravel-sand-silt mixtures. (3) The seepage failure process of subgrade materials can be divided into three stages under coupled action of train loading and seepage: stable seepage, dominant flow development, and seepage failure. The relationship between flow velocity and hydraulic gradient follows the Darcy's law under the low hydraulic gradient. (4) The evolution process of subgrade performance was analyzed, and the mechanisms and types of railway flood hazard were summarized. The research provides theoretical support for the design and maintenance of railway disaster prevention, and has significant engineering implications.

Broken coal and rock (BCR) are an important component medium of the caving zone in the goaf (or gob), as well as the main filling material of fault fracture zone and collapse column. The compaction seepage characteristics of BCR directly affect the safe and efficient mining of coal mines. Thus, numerous laboratory studies have focused on the compaction seepage characteristics of BCR. This paper first outlines the engineering problems involved in the BCR during coal mining including the air leakage, the spontaneous combustion, the gas drainage, and the underground reservoirs in the goaf. Water inrush related to tectonics such as faults and collapse columns and surface subsidence related to coal gangue filling and mining also involve the compaction seepage characteristics of BCR. Based on the field problems of BCR, many attempts have been made to mimic field environments in laboratory tests. The experimental equipment (cavity size and shape, acoustic emission, CT, etc.) and experimental design for the BCR were firstly reviewed. The main objects of laboratory analysis can be divided into compression tests and seepage test. During the compaction test, the main research focuses on the bearing deformation characteristics (stress-strain curve), pore evolution characteristics, and re-crushing characteristics of BCR. The seepage test mainly uses gas or water as the main medium to study the evolution characteristics of permeability under different compaction stress conditions. In the laboratory tests, factors such as the type of coal and rock mass, particle size, particle shape, water pressure, temperature, and stress path are usually considered. The lateral compression test of BCR can be divided into three stages, including the self-adjustment stage, the broken stage, and the elastic stage or stable stage. At each stage, stress, deformation, porosity, energy, particle size and breakage rate all have their own characteristics. Seepage test regarding the water permeability experiment of BCR is actually belong to variable mass seepage. While the experimental test still focuses on the influence of stress on the pore structure of BCR in terms of gas permeability. Finally, future laboratory tests focus on the BCR related coal mining including scaling up, long term loading and water immersion, mining stress path matching were discussed.