Method of designing large cross-section tunnels linings in rocks massif whose deformation modulus decrease near the opening following a definite law due to cracks arised under drilling and blasting operations is given. Method is based upon the analytic solution of corresponding elasticity theory plane contact problem for a multi-layer ring of an arbitrary form supporting the hole in a linearly deformable medium. Examples of the design are given.
The importance of registration the rock deformation modulus decrease near the opening surface being the result of blasting operations for tunnel linings design is shown in (1968) and Backlashov, Kartosia (1977).
The solution of the problem of determining the lining stressed state with the registration of the described rock technological heterogeneity has at present been obtained only for round cross-section linings. The technique generalising the approach mentioned for arbitrary (with one axis symmetry) cross section linings is offered in the paper presented. The design method offered allows to determine the stressed state of the lining undergoing actions of the internal water head, own weight of rocks surrounding the tunnel, underground water external pressure including the cases where water filtration through the lining is possible. The method is based upon a substitution of a rock deformation modulus continious change by a discrete change upon the solutions of corresponding elasticity theory problems for a multi-layer ring of an arbitrary shape in a linearly deformable medium. Solution of the elasticity theory contact problem has been obtained with the application of complex variable analytic functions theory, apparatus of conformal transversations and complex series. The complete stresses are represented as sums of initial stresses and additional stresses appearing due to the presence of the working. As to the displacements only the additional once are taken into account. The method developed has been programmed for the computers. The method described may be used for designing the linings fastened to the rocks by anchors.
The examples of designing the arch form lining of the hydrotechnic tunnel with a 13.4 metres span and 16.5 metres height (the average working radius R= 8.4 m) are given below. Deformation rock modulus change according law (1) with parametres K = 0.8; m = 2. For comparison the dash lines show the distributions of the same forces (numerical values are given in brackets) in case the technological heterogeneity is not taken into account, i.e. Ej IE1 = 1 (i=2, 3,•••,10).
logical rock heterogeneity exerts considerable influence on the lining stressed state. We can mark that the method described may be used for designing the tunnels linings at any rock deformation modulus change.