Borehole Investigation of the Effectiveness of Grout Injection Technology on Coal Mine Subsidence Control

Investigation of fill distribution in post-injected longwall overburden with implications for grout take estimation

“…In this regard, Xuan et al (2015) found that the injected fill gathered mainly in a main injection section (with a height of 4.8-18.4 m) of the overburden, which included more than 90% of the total fill; vertically, the main injection section was found to be located between the bottom of the injection borehole and the strong rock layer (i.e., the key stratum, defined by Qian et al (1996)) immediately above. Considering the characteristics of the main injection section, it is reasonable to assume that the fill occupies a single horizon-the main injection horizon.…”

“…Although the fly ash grout that contains water spreads in the overburden voids during injection, the water drains gradually, leaving the grout as compacted fill, which may sometimes be wet (Ilgner, 2000;Ward et al, 2006). This was demonstrated by a field borehole investigation conducted by Xuan et al (2015). In view of this, the scope of this study was limited to the distribution of the final compacted fill rather than that of the initial flowing grout, and the grout take refers to the actual dry fly ash injected.…”

“…Similarly, using the geophysical technique of ground penetrating radar and borehole image scanning, Zhou et al (2006) and Guo et al (2007) located some of the grout fill in a longwall overburden. Recently, Xuan et al (2015) drilled two test boreholes to determine the fill distribution in a post-injected longwall mining area, and the characteristics of the main injection section were found, indicating that more than 90% of the total fill was concentrated in the studied section. Although these studies promote the understanding of injected fill distribution, they did not propose a general theoretical or empirical method to determine the overall fill distribution in longwall overburden.…”

“…put forward a hypothetical fill distribution model but did not verify it. Studies on the actual distribution of injected fill were carried out using numerical modeling (Saeidi et al, 2013) and in-situ tests (Chen et al, 2000;Xuan et al, 2015;Zhou et al, 2006). For example, Chen et al (2000) developed a fluorescent approach to visualize grouting horizons; this method was successfully tested in cement grouting into jointed rock mass.…”

A shared borehole approach for coal-bed methane drainage and ground stabilization with grouting

“…2 Because of the high injection pressure and large injection volume (generally up to 40% of the mined-out space), the main injection horizon (i.e., the horizon containing 90% of the total fill) will occur between the bottom of the injection borehole and the overlying key stratum. 3 However, if the target horizon of the injection is the gob area, the grouting is generally implemented by drilling boreholes into the mined-out areas following the extraction. 17 It is clear from the above process that to achieve borehole sharing, the timing and the targeted vertical horizons for the drainage and injection must be coordinated.…”