Experimental study on bearing characteristics of filled piers in coal mine goaf

The high concentration slurry is poured into the goaf to form filled piers. The bearing capacity of the piers to the superstructure are affected by the overlap size. In order to grasp the influence of the overlap size on the bearing capacity of the overlying rock layer, high concentration slurry was prepared which selected cement as the cementing material, standard sand as the aggregate. 3D printing technology was used to make the mold to produce the overlapped round table samples. The uniaxial compression test was carried out. Test results show that, when the top area and height of each single pier are the same, the smaller the accumulation angle is, the greater the ultimate bearing capacity is. The ultimate bearing capacity of overlapped two round table specimens with a stacking angle of 30 ° and a stacking angle of 45 ° is in the range of 2.0 to 3.5 times of the corresponding single round table specimen. After the specimen is hardened, the ultimate bearing capacity of the overlapped pier specimen increases first and then decreases as the overlap size increases. When piers filling are used to control the mined-out area, the spacing between the grouting holes should be reasonably set so that the injected slurry forms overlapping piers in large hollow goaf. The bearing capacity of overlapping pier group is better than that of evenly distributed single piers. When filling the goaf with an accumulation angle of 30° to overlap the piers and the distance between the grouting holes is the value corresponding to the limit overlap size of 38.5%, the overall bearing capacity in the treatment site is the largest. The results of this research will provide a basis for the actual use of high concentration slurry for partial filling and treatment of goaf.