In underground coal mines, floor heave is a major problem that is caused by groundwater, high strata stress and weak floors. Controlling the stability of the roadways is the key to maintaining the safety and efficiency of underground mining. Appropriate cement grouting is an effective and attractive floor reinforcement technique that can control excessive floor heave and closure. Cement grouting also reduces the permeability of the rock mass and consequently controls the movement of groundwater into the roadway. Injecting cement grout into roadway floors provides a more uniform reinforcement throughout the floor. It may even be possible to reinforce an extremely fractured floor. In this respect, this technique is superior to floor bolting/dowelling. This technique may be performed either as a pre- or post- development reinforcement. It is very difficult, however, to reinforce a floor that is not heavily fractured by the injection technique. Therefore, before floor injection, floor blasting is performed in order to create an adequate number of fractures in the floor. Fracturing by blasting also relieves and improves stress conditions in the floor. From this point of view, the behaviour of grouting injection as floor reinforcement material is discussed. That is to say that the results of an injection analysis, an injection experiment and a viscosity measurement to understand the injection process of cement grout into soil voids were studied. The injection analysis was performed by combining two analyses, the analysis of the clogging process, and the analysis of the transportation process. As to the analysis of the transportation process, since a cement-based grouting material can be described as a Bingham fluid, the equation of plug flow related to a Bingham fluid inside a circular pipe, instead of Darcy’s law, was expanded and analysed. The injection experiment was performed under low-pressure on a decomposed granite sample. The injection s experiment was performed using three mixtures with cement/water ratios (C/W) of 1/10, 1/5, and 1/3.5, respectively, to examine the influence of variable cement/water ratios. The viscosity model is proposed from the result measured with the aid of Brookfield viscometer. To calculate yield stress, viscosity data obtained with the Brookfield viscometer was used. However, for the determination of plastic viscosity, because some cement particles will be in the state of aggregation and so on, the viscosity measurements obtained by the use of the Brookfield viscometer are overestimated in comparison with a theoretical equation that assumed that cement particles are dispersed in the solution completely. However, it is thought that cement particles cannot form aggregates easily in the soil voids or cracks. Therefore, the plastic viscosity model of grouting material is expected to follow the proposed theoretical equation. Finally, the assumption that the grouting material was injected in the state of laminar flow was verified by data obtained from the Lugeon test. The field data which are satisfied with this condition is simulated using the plastic viscosity and the yield stress model of grouting material.

Soil water erosion is frequently reported as serious problem in soils in Southeast Asia with tropical climates, and the variations in pH affect the development of the erosion. This study investigated the effects of changes in pH on soil water erosion based on changes in the physical properties of the simulated soils with pH adjusted from 2.0 to 10.0 through artificial rainfall tests. The zeta potential was entirely shifted to positive direction at each pH condition due to Al, Ca, and Mg. In the pH range of 6.0 to 2.0, the aggregation of soil particles resulting from the release of Al³⁺ from clay minerals and/or molecular attraction between soil particles caused the plastic index (I_P) of the soil to decrease. The decrease in I_P led to the development of soil water erosion at the pH range. When the pH exceeded 6.0, the repulsive force generated by the negative charges on soil particles decreased I_P, resulting in accelerated erosion by water. The results suggest that changes in pH causes physical properties of the soil to change through changes of the zeta potential in the clayey soil rich in Al, Ca, and Mg, leading to the development of soil water erosion.

Stability of the retained goaf-side gateroad (RGSG) is influenced mainly by the movements of the roof strata near coal seam after coalface passes by. To make effective controlling technology for the stability of the RGSG, we analyze the roof structure over the RGSG to illustrate the mechanism causing the RGSG instability under different roof conditions. We then examine the dynamic evolution of the deformation and abutment stress in the rock surrounding the RGSG during coal seam mining, using the FLAC3D numerical software to reveal the instability characteristics of the RGSG under different roof conditions. Next, corresponding stability controlling technologies for the RGSGs are proposed and tested in three typical deep underground coalmines. Results show that: sink and rotation of the roof cantilever over the RGSG impose severer influence on the stability of the RGSG. The RGSG suffers disturbances three times during the coal-seam mining, and the deformation and abutment stress in the rock surrounding the RGSG increase significantly when the main roof becomes thicker and the immediate roof becomes thinner. Staged support technology involving grout cable bolts has better controlling results of the RGSG stability than that composed of conventional rock bolts, when the RGSG is beneath weak immediate roof with large thickness. Roof structure optimizing technology involving pre-split technology can improve the stability of the RGSG effectively when the RGSG is covered by hard main roof with large thickness directly.

To study the effectiveness of grouting reinforcement on a large heaving floor of the retained goaf-side gateroad (RGSG) at a 900 m depth in the Zhuji coal mine, a numerical model involving strain softening constitutive material was built. First, the simulated deformations of the RGSG were compared with field data to verify the reliability of the numerical model. Then, the dynamic distribution of the stress in the RGSG floor was examined to reveal the mechanism of floor heave. Finally, grouting reinforcement was proposed to control the RGSG floor, and the corresponding effectiveness was verified by improving the rock mechanics of the floor strata based on the results of numerical uniaxial compressive tests. The results demonstrated that a fairly good match was achieved between the field and numerical data, and the proposed FLAC3D (Fast Lagrangian Analysis of Continua) numerical model was an effective approach to study the stability of the deep RGSG. A variation of the ratio between horizontal stress to vertical stress in the floor strata was the root cause of floor heave in the deep RGSG. Ideally, the floor heave could be reduced by 41%, 62%, and 79% when the floor strata of 1 m depth were reinforced with grouting schemes I, II, and III, respectively.