The problem with increasing metal-content of a development working’s combined support

Directly in the roof of mine working the zone of unloading occurs, similar to the shape of Protod’yakonov’s arch of natural balance (Figure 1a). The zone size of rock ultimate state is usually evaluated by the condition of appearing tensile stresses ( 0y ). Every mine rocks can badly resist to this stresses, especially layered and weak rocks. Following mentioned condition the sizes of ultimate state area of roof rocks are practically even: 2.02 m width and 0.43 m height for SVP-27; 2.09 m width and 0.44 m height for SVP-19. So, if to change from SVP-27 frame to SVP-19 frame zone’s width will be increased only in 3.5%, and height – 2.3%. In both versions quite limited areas are observed (till 0.2…0.3 m), actions of tensile y reach up to 1 MPa in places between neighboring bolts. Enumerated facts can prove almost similar diagram of vertical y stress distribution in the roof, both as qualitative and quantitative meanings.