Face falls of longwall are the most complex ground control problem in mining thick coal seams in China. In this study, the mechanism of face failure is assessed from the perspective of shield–strata interaction. The paper develops a better understanding of fundamental mechanism of face failure and shield–strata interaction through a theoretical coal-support deflection model and a physical modelling study, with a consideration of shield stiffness and basic operating principles of longwall shields. The theoretical model is adapted based on the Winkler model of an elastic foundation beam, and the physical model simulates the actual performance of the shield in the field by including both the initial and cyclic loading stages. The vertical displacement of the roof and the real-time horizontal displacement of the face are recorded by a Vernier caliper and a wireless displacement monitoring system, respectively. The results show that: (i) shield stiffness has a positive relationship with the load capacity. Increasing shield stiffness/capacity enhances the ground control in the open face area, but this effect becomes negligible at higher stiffness. (ii) The physical face maintains its stability and only shows slight structural failure during the shield initial loading stage. Roof deflection and face displacement increase slowly with the progressive roof loading. (iii) During the cyclic loadings, roof vertical displacement increases in a step function upon each shield yielding; face horizontal displacement increases rapidly and face fall occurs at the final yielding event of the shield. (iv) Most face failures and ground movement are observed during shield-yielding events.

Slope failure triggered by soil erosion under rainfall remains one of the most difficult problems in geotechnical engineering. Slope protection with planting vegetation can be used to reinforce the soil and stabilize the slope, but the early collapse of the planting soil before the complete growth of plants becomes a major issue for this method. This paper has proposed a composite soil treatment and slope protection method using the geocell structures and the wheat straw reinforcement. The geocell structures improve the stability of the planting soil and provide a stable and fixed environment for the vegetation, while the wheat straw reinforces the soil and also increases the fertility. The authors have performed a total of 9 experiments in this work that are classified into three groups, i.e., the unsupported slopes, the geocell reinforced, and the geocell and wheat straw composite reinforced with a consideration of three different rainfall intensities. The progressive slope failure development during the rainfall was assessed, as well as the soil erosion, the slope displacement, and the water content. The results show that the slope failure increases as the rainfall continues, and the soil degradation increases with the intensity of rainfall. The soil treatment using geocell improves the slope stability, but the geocell and wheat straw composite reinforcement has the best erosion control and slope protection.

Soil reinforcement using geocells and vegetation is one of the best forms of soil protection for shallow slope failure control. The geocell supports the vegetation growth and the vegetation cover provides protection against the surface erosion. This work proposed a soil treatment method using geocells for supporting the vegetation growth and stabilizing the shallow slope. A step-by-step installation of the geocells in the field and the development of vegetation growth were also described. The authors developed nine physical models that were reinforced with different sized geocell structures (no reinforcement and small and large geocell reinforcement). The models were placed under three rainfall intensities (50, 75, and 100 mm/h). The stability of the slope under the rainfall and the performance of the geocell reinforcement were assessed from the the development of slope failures, the soil erosion and the slope displacement. The results showed that the stability of geocell reinforced slopes were better off than the unsupported slope. The small geocell-reinforced slopes showed less measured soil erosion and also smaller slope displacement. In general, small geocells outperformed large geocells in terms of the erosion control and slope stabilization. The rainfall intensity dramatically increased the soil erosion on slopes. The geocell- and vegetation-treated slope in the field showed good resistance against the surface erosion.

Longwall face fall in the open face area is one of the most difficult ground control problems in mining thick coal seams in China especially under difficult geological conditions. This paper has proposed a new flexible bolting and grouting technology for face support. The flexible support method includes face support using flexible coir ropes and face grouting with cement and accelerator mixtures. Numerical and laboratory studies of pullout tests are performed to further improve the flexible support performance including optimization of boreholes and flexible bolts diameters, and selection of grouting materials. The results show that (a) The optimized rope‐borehole diameter ratio is around 0.5 to ensure the best face reinforcement; (b) The grouting material (a mixture of ultrafine cement, mineral powder and sodium silicate) shows advantages of low cost, effective waste disposal, reduced setting time, and good pullout limit force and is recommended for industrial application with sodium silicate at a proportion of 10% by weight and mineral powder at 30%. The application of the new flexible bolting and grouting method in Chenmanzhuang mine shows improved face stability and reduced capital cost.