Tensile resistance of rock anchors

Using the Euler's variational method and assuming a rock mass failure criterion of Hoek and Brown type (Hoek E, Brown ET. Empirical strength criterion for rock masses. J Geotech Eng Division, American Society of Civil Engineers 1980:106(GT9)1013-35. Hoek E, Wood D, Shah S. A modified Hoek-Brown criterion for jointed rock masses. In: Hudson JA, editor. Proc.. Rock Characterization Symp. of ISRM: Eurock 92. London: British Geotechnical Society, 1992. p. 209-14), the tensile resistance of rock anchors is obtained. The rupture surface shape through the rock mass is also obtained and checked against some published data. Depending on the slenderness ratio (L/D; L = anchor length, D = anchor diameter) two types of failure surfaces are obtained; short and long ones. This second type of surface is a complex one and it is composed by a cylinder and a surface of revolution with an hyperbolic type shape. The values of the ultimate pullout strength, depending on the rock type and its Bieniawski indexes, are obtained and compared with the values published in technical literature. A reasonable agreement is obtained. (C) 1999 Elsevier Science Ltd. All rights reserved.