engleski

Another Way to Compute the Underground Room Support

There is an obvious need in engineering practice for researching the complex problem of interaction between rock and primary support in making safe an underground opening driving. As probably for no other construction, the static computation for the primary support is burdened with so many difficult definable factors, as the changes of geological conditions, unknown impacts of discontinuity system, insufficient knowledge of physical-mechanical characteristics, unknown relation between horizontal and vertical stresses, complexity of constitutive laws and failure criteria, development of shotcrete strengths in process of binding and hardening and other. Intensity of the support loading with rock depends on realized deformations of the statically indefinite rock-support system. Rock deformations are increasing so long, until the stress condition in rock does not harmonize with reactive compression of the support and with equalizing of the deformations on the contact. Since it is difficult to determine the impact of the rock on the primary support, as well as the relation between support deformation (e.g. from shotcrete) and its carrying capacity, which would result from these deformations, because young, relaxed concrete is in question. Instead of computing the support condition resulting from an assumed deformation of the rock-support system, carrying capacity of the support is introduced into computation and the influence of the support on the rock is analysed. The rock loading on the opening boundary is therewith determined and it becomes the input information to analyse the stress condition and rock deformation. It is more reliable to assume the impact of boundary condition of the support on rock without regarding deformations. Beside limit carrying capacity– support reaction, it is also controlled if the rock satisfies the failure criteria conditions. The loading with support reactive compression and with anchors must be balanced. On the case of road tunnel driving, the method of boundary elements with the Hoek-Brown’ s failure criteria was used in computations. Computations have to be performed by choosing the mechanical rock characteristics in accordance with the categories of rocks and the assumed limit bearing capacities of appropriate support types. When the support is well chosen, the rock near opening is strained under the failure limit, and such a computation proves the construction stability.

Tunnel; Suport systems; Ultimate limit states; Failure criterion; Boundary elements

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