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The purpose of this paper is to provide scientific basis for the stability evaluation of overburden rock of repeated mining goaf under the expressway. The objectives of the present study are to reveal the development of overburden rock fractures under repeated mining and to identify the fractal characteristics of the overburden rock fractures. The results show that (1) the separation fracture and vertical fracture fissure are developed in the overburden rock under repeated mining; (2) after the mining of the lower coal seam, the fractures developed in the overburden rock of the goaf are obviously retained in general. The number of fractures on both sides of the goaf is relatively large, while in the central part, it is relatively small and the fractures in most areas are basically closed; (3) under the same advancing length of working face in the lower coal seam, the fractal dimension in the caving zone is larger than that of the fractured zone; (4) with the increase of the advancing length of working face in the lower coal seam, the variation trend of the fractal dimension appears from small to large and then to small and stable; (5) when the repeated mining is over and the overburden rock movement is basically stable, the ratio of the fractal dimension in the caving zone and the fractured zone is 1.067:1. The results have an important reference value for ensuring the safety of the expressways above the repeated mining goaf in Shanxi region and similar areas.

To study the settlement process of high-filled embankment before and after construction, an elastic viscoplastic constitutive model of over-consolidated soil is designed based on finite element analysis. The model is used to predict the settlement of subgrade before and after construction. First, the lower load surface is used as the reference yield surface of strain rate. Based on the principle of relative over stress, two rate sensitive parameters are established through the measurement of triaxial compression test with different strain rates. Second, the relative over stress function, stress function, and dynamic yield criterion function are established. Finally, two kinds of over-consolidated soils with over-consolidation ratios of 16 and 8 are tested for triaxial shear creep, and the finite element software is used for simulation analysis. The results show that the ultimate axial strain decreases with the decrease of deviatoric stress. When the creep time exceeds 3000min, the model has good prediction effect. The finite element calculation results of different backfill layers in inversion parameters show that the maximum settlement layer of high-filled embankment may not occur at the top or bottom, so attention should be paid in the construction process of high-filled embankment. This exploration provides a reference for the study of long-term deformation and strength of high-filled embankment.

Jinci Spring is a popular karst spring in northern China and has important historical and cultural value. The spring stopped flowing since it first dried up on April 30, 1994, which has resulted in further water deficit in the area. This study aimed to further the sustainable utilization of Jinci Spring and used long-term karst groundwater monitoring data to investigate the causes of the drying up of Jinci Spring using the capture principle. The sustainable yield and the sustainability threshold of karst groundwater were quantified, and the ecological water level restrictions for early warning and water supply were determined. A simple two-dimensional (2D) numerical model of karst groundwater was used to design three restoration and protection scenarios under which the dynamics of karst groundwater level were simulated and the restoration and protection scheme was optimized. The results showed that (1) climate change and the long-term consumption of karst aquifer storage are the key factors contributing to the drying up of Jinci Spring; (2) the range of sustainable yield of karst groundwater is 0.622–2.35 m3/s; (3) the sustainability threshold of karst groundwater is (12.35 × 108 m3, 13.91 × 108 m3); (4) the ecological water level restriction for early warning and the ecological water level restriction for water supply are 803.35 meter above sea level (m asl) and 803.21 m asl, respectively; (5) Scenario 1 is the optimal restoration and protection scheme that meets the ecological criteria for Jinci Spring. The results of this study can provide an important basis for the implementation of the ecological restoration program for Jinci Spring.

In order to control the deformation of concrete face rockfill dams and improve the safety and stability of concrete face rockfill dams, this study uses the finite element analysis method, statistical analysis method, and numerical calculation to systematically study the stress and deformation characteristics of concrete face rockfill dam and its anti-seepage wall under complex geological conditions. The numerical simulation of the secondary development platform based on finite element software shows that the deformation caused by the foundation compression deformation, rheological deformation, and hydraulic coupling effect is the main cause of the large deformation of the overburden dam on the overburden layer. Among them, the foundation compression deformation is the main source of foundation deformation, and the deformation caused by rheological deformation and hydraulic coupling effect is the main source of secular deformation. Rockfill compression deformation is the main source of dam deformation, and the contribution of rheological deformation to dam deformation is greater than that caused by hydraulic coupling effect. In this study, the stress deformation and leakage characteristics of concrete face rockfill dam are analyzed, and the statistical laws of mechanical properties of concrete face rockfill dam are revealed. The sedimentation of the dam crest of most concrete rockfill dams is less than or equal to 0.40% H (H is the height of the face rockfill dam), and the sedimentation of most dams during the completion period is less than 1.0% H. After water storage, the panel deflection is close to the dam crest sedimentation value. Most of the dam’s panel deflection is less than 0.40% H, of which more than half is less than 0.2% H. Large rockfill deformation is the main cause of panel tensile stress, as well cracking and crushing damage.

Due to coal mining taking place on a large scale in northern China, it is inevitable that wide-spread dewatering occurs in the aquifers overlying the resulting goaf. The purpose of this paper is to protect the groundwater of overlying unconsolidated aquifers. Based on physical model experiment, seepage experiments, and numerical simulation, this paper determines the patterns and distribution of the overburden rocks in the goaf, establishes the correlation between the fracture ratio and the hydraulic conductivity of the rock mass, and characterizes the groundwater flow pattern. The results show that (1) the residual fracture occurring ratio within the residual fracture zone is approximately 1.82 times that of the fracture compaction zone and 1.93 times that of the coal wall support zone; (2) the hydraulic conductivity of the rock mass in different parts of the goaf increases with increasing fracture ratio, the relationship of the two follows a power curve; (3) the predicted groundwater levels from numerical simulation is good fit with the measured and indicates that the hydraulic conductivities derived from seepage experiments are rational. We demonstrate how a laboratory-scale physical model can be used effectively to verify existing conceptual models in such a way that the impact of coal mining on groundwater resources can be predicted for similar regions.