Influence of geomechanical factors and methods of rock outcrops competence increasein horizontal drivages

The analysis of types and forms of competence loss shows the mostcharacteristic ones: parabolic, occurring in homogeneous rocks with ultimate strength of up to 30 MPa; fractured, with the distancebetween the fractures (L) of 0.01...0.1 m (over 8 fractures per 1 m); arched circular, formed in homogeneous rocks, σcontraction =25...45 MPa; multilayered fractured, with L 0.2...0.3 m; trapezoid, formed mainly due to little adhesion between the layers (m) with thecapacity of 0.2 ... 0.6 m, σcontraction = 25...40 MPa [1]. Most samples are of the arched form or close to it. The key factors influencingthe competence are fractures, moisture content and layers. Coal and carbonaceous argillites being strongly fractured and small-layered,with the capacity layer of less than 0.1 m, are prone to spontaneous desquamation during 10...15 minutes, the rest of the rocks with theultimate strength of 60 MPa at the outcrop area of 5 m2 desquamate in 35 min and more. With σcontraction = 50...60 MPa and layercapacity of over 0.8 m, rock outcrop at surface are stable for at least two hours. With m = 0.1...0.4 m and σcontraction up to 40 MParocks are stable for for an hour. With m less than 0.1 m stability time is 10...20 min [2]. Most fractures are filled with clay, carbonate,carbonaceous and other substances. The top of fractures may have a thin layer of clay and lime substances. The width of fractures is upto 8 mm, but 2 mm is a more frequent figure. Highly fractured broken rocks located mainly above the coal layers with L = 0.01...0.2 mare stable for 20 min. The study of humidity shows that sandstones on carbonate cement with the increase of moisture content loseapproximately 5% of strength properties, silts on siliceous and carbonate-siliceous cement - 14%, siltstones with clay cement -20...30%, argillites - 40 ... 60%, and carbonaceous argillites - up to 80%. The depth of drivages and the effect of their width on thedisplacement of rock outcrops are also considered. Tool and field observations were conducted, the results of which are as following [3]:a 4 to 6 m broader drivage gives a 23...28% increase in displacement. Deeper (150 to 600 m) location in layers of 1.6...2.5 m displacesthe rock surface with σcontraction < 45 Мpa by 3...3.5 times, with σcontraction = 45...80 МPa - by 2...2.4 times.

Keywords

Authors

References