Selective Tests of Grouting Material for Fractured Coal and Rock Masses in a Water-borne HS Environment
Coal mining is vulnerable to multiple kinds of threat from water incursion. Many coal seams contain dissolved H2S, which may be released during mining, seriously endangering the health of workers. Orthogonal testing was used to analyze the physical and mechanical properties of composite slurries in different proportions. The results showed slurry with a water-solid ratio of 0.8:1 to have the optimal combination of properties. A uniform experimental method was used to investigate the impact of the water-cement ratio, concentration of sodium silicate, and volume of cement-sodium silicate (CS) on the setting time and consolidating strength of CS slurry. This paper provides the appropriate application scope of two grouting materials (optimized composite slurry and CS slurry), based on experimental data and the results of a large number of in situ trials. Finally, the optimized composite slurry and cement-sodium silicate slurry were used to carry out grouting of the center auxiliary transport roadway of the 3 coal seam at the Ningtiaota Coal Mine, operated by the Shaanxi Coal Industry Group. It was shown that the type and formula of the slurry could be changed in a timely manner, based on the water outlet and concentration of H2S at the site, achieving successful grouting reinforcement and seepage-proofing.
Research on the grouting diffusion mechanism and its application of grouting reinforcement in deep roadway
For the deficiencies of common grouting technology in deep soft rock roadways, three-step grouting technology is proposed to reinforce the surrounding rock to get better results. The three-step grouting diffusion mechanism is explored in this paper, and the technique is applied to field engineering. Step one is to grout with low grouting pressure to fill the gravel pack interval and blocked the channels which relieves the grouting pressure in the shallow surrounding rock. Step two is mainly for the filling of the fractures space in the surrounding fractured rock to improve the bearing capacity of the surrounding rock through the effect of grout cementation and filling with grout solidifying. In step three grouting is prepared to further reinforce the strong deformation sections of the roadway. Although increasing the working procedures of grouting, the three-step grouting technology ensures the radius of grouting diffusion. The inspection holes monitoring shows that grouting diffusion depth is generally more than 3 m, and that the three-step grouting technology has achieved the expected effective range of grouting reinforcement. The roadway deformation monitoring datum of grouting before and after indicates that three-step grouting technology has greatly improved the effect of grouting reinforcement of surrounding rock and effectively improved the bearing capacity of rock mass,and thus the overall stability of surrounding rock of roadway is effectively controlled.
EXPLOITATION OF POOR GREEK KAOLINS: STRENGTH DEVELOPMENT OF METAKAOLIN CONCRETE AND EVALUATION BY MEANS OF K-VALUE
In this paper, the effect of metakaolin on concrete properties is investigated. A poor Greek kaolin was thermally treated at defined conditions, and the produced metakaolin was superfine ground. In addition, a commercial metakaolin of high purity was used. Eight mixture proportions were used to produce high-performance concrete, where metakaolin replaced either cement or sand in percentages of 10% or 20% by weight of the control cement content. The strength development of metakaolin concrete was evaluated using the efficiency factor (k-value). The produced metakaolin as well as the commercial one imparts a similar behavior with respect to the concrete strength. Both metakaolins exhibit very high k-values (close to 3.0 at 28 days) and are characterised as highly reactive pozzolanic materials that can lead to concrete production with an excellent performance.