抄録
This paper summarizes the theoretial and experimental comparison of physical characteristics of thick and hard rock strata which lies above wall type faces in The Republic of South Africa (Sigma Colliery) and Japan (Kushiro Colliery) and its effect to restrict surface subsidence. The difference of subsidence together with goaf solidification by the nature of rock strata is analyzed. When it is compared with the Dolerite case at an elastic modulus of 70 × 103 MPa, which is known that the 200 m face length is a minimum criteria for stable long wall operation, it is found that the face operation by the face length of more than 100 m with the hard and thick rock strata at an elastic modulus of 15 × 103 MPa will be an appropriate standard for Kushiro case. This is because of the occurrence of hanging phenomenon and its periodical heavy goaf flushing, when face standards, particularly face length is inappropriate. Thus, face design considerations are largely affected by the existence of thick and hard rock strata found in Dorelite (South Africa), Pocahontas Sand Stone (USA), Coalcliff Sand Stone (Australia) and Harutori Conglomerate/Sandy Shale (Japan).The author also indicate that the existence of very hard and thick rock strata above face can be pragmatically utilized to avoid sea water penetration in shallow coal mining district by way of applying comparatively shorter face length which will not allow sea bottom subsidence. As the results of analysis, design considerations for wall type mining, particularly face length is offered to suit various mining conditions.
