No abstract

Short-wall block filling mining (SBBM) technology has become an effective way to recover coal resources beneath the aquifer, which are unsuitable, or cannot be used by long-wall mining, such as corner coal pillars, industrial square pillars, and irregular coal blocks as well as the coal beneath buildings, railways, and water bodies. The SBBM method can not only enhance the recovery ratio but also provide a solution for the environment problems associated with gangues on the surface. However, whether the height of water flowing fractures will reach to the aquifer to cause water loss during SBBM has always been a key problem. Therefore, based on the theory of elastic foundation beam and SBBM characteristics, a mechanical model for calculating the height of a water flowing fracture zone in the overlying strata of SBBM was established, and this model calculated that the height of the water flowing fracture zone was 27.0 m in the experimental working face, and the height of the water flowing fracture zone was measured as 26.8 m according to washing fluid loss in the hole, core damage analysis, and drilling TV imaging detection. The comparison results demonstrated that the calculated value almost fit well with the field-measured data, validating the accuracy of the proposed mechanical model, while the predicted value (48.7 m) in the Regulations of coal mining under building, railways and water-bodies deviates greatly from the measured results. This reveals that the prediction formula in Regulations is not effective in predicting the height of the water flowing fracture zone in SBBM. The present research results are of great significance to further enhancing the recovery ratio of coal resources and improving the water-preserved mining theory.

The genesis of Xi’ an ground fissures and the recent activity characteristics and tendency have been introduced firstly. The architectural damage caused by ground fissures and current hazard prevention methods have been described secondly. The applications of a new material used in controlling underground engineering and coal mine disaster have been introduced. The mechanical properties of the new material have been stated also. As a result, a new foundation treatment method has been envisaged to make it possible to construct architectures on ground fissures.

An in-situ water injection test across Xi’ an ground fissures has been done, in order to simulate the activity of the fissures after water seeps, from October to December, 2005. According to the settlement observed of the bottom of testing pit, it is proven that the surface water seepage speeds the movement of ground fissures. Usually, the soil on the hanging wall of the fissures is more fragmentized than that on the footwall, which is propitious to water seepage. The seepage promotes the interaction between water and soil particles and brings about the differential settlement of two sides of fissures. Therefore, surface water seepage accelerates the activity of the ground fissures.