Materiały konferencyjne SEP 1993 - tom 2

Underground Exploitation School '93 quantitatively evaluated was the increase of the strains concentration compared to the State of rocks without the floating mass. The load coefficient was K b (7) where K - maximal coefficient of the strains concentration in the roof max suffering no floating mass; the problem (fiat resilient-elastic axis-symmetrical) of a single heading deformation was soIved (according to the programme "Shtrek", elaborated at VNIMI). The floating mass was accounted for via introduction of a conventional depth of heading increased by the load coefficient as compared with the reality H = H K P n The solution resulted in determination of the zones of roof rocsklimit deformation RL(M) under various values of the compression strenght limit R(Mna) for the protective layer and its thickness m(M) . The analytical dependence betwen these values has been established: / RL = ( 0 , 2 - 0 , 12 m ) I H R V / (8) m e [ 0 , 5 . . . 2 , 0 ]M ; 7 6 [ 1,5 . . . 2,2 ] ^Ai^ H < 1 6 0M ; R e [0,5 . .. 2,5] MHa i5 i.O as o as 1.0 t.5 2,0 2 .5 3.0\ Fig. 1. Dependence of the non-elastic defomiations zones on the protective layer compaction strenght limit. Fig. 1 shows that when the protec- tive layer thickness is m3 = 1.0 m and the heading depth H = 96-i- lOOm the criterical strength limit is R = 0.5 ... 0.6 mPa, because at this value the protective layer exceeded the deforma- tion limit over the whole thickness. The strength being brought up to 1.0 mPa, the Im thick layef possesses suf- ficient carrying capacity, 0.5 m thick- ness sufficient to preclude the outburst oniy under condition that the srength would equal 1.5...2.0 mPa. The minima] recommended thickness of the protective layer with the compres- sion strength limit value know is oblained from RL = m. Then the thickness is determined by 156 Tom II