Peculiarities of Rock Massif Behavior in a Zone of Transition From Subzero to Above Zero Temperatures

Abstract

ABSTRACT This paper reveals the results of the studies relating to a rock massif behaviour in a zone of transition from subzero to above - zero temperatures. Distribution of rock areas having above - and sub - zero temperatures and various aggregate moisture condition had been established within one horizon. For the first time underpermafrost waters had been found in the areas with tectonic disturbances and high rock jointing. While opening water - bearing areas a water inflow totalled 3-8 m3ph (up to 25m3ph), and in 4-5 months of flowing by itself it lowered to 0.6 - 1 m3 ph. Maximum rock temperature ( +0.6 °C ) was fixed during opening driving with its temperature further lowering by total the negative temperature balance of the air fed to a mine. Rock strength characteristics considerably changed for the worse comparing to the upper horizons. At was established that by rizing the temperatures from −2.2 °C to above - zero ones rock strength lowered by 18 - 20%, and by water - soaking compressive rock strength decreased by 9-55%, tensile strength by 7 - 40%, cohesion by 19 - 49%, an angle of internal friction by 6-15%, Poisson's ratio by 18-25%. The rocks of a transition temperature zone tend to freezing and partially to packing, the compressive strength of frozen together samples reaching 0.6 MPa. As a result of a pressure waters inpact washing - out of binding material from cracks takes place, what lowers the stability of mine workings. Frequent roof and wall caving at a horizon of transition temperatures made it necessary to provide a metal arch support with tight wall and roof lagging (with a support lagging behind the face not more than 2.5 m) for mine workings. The instability of mining workings made it necessary to change from one method of rock pressure control (pillars) to another (caving). The conducted investigations allow to predict the behaviour of rock massif of metamorphic rocks when reaching a zone of transition from subzero to above - zero rock temperatures.