The behavior of deep excavations in weathered rock.

摘要

The objective of this research was to contribute to the understanding of the behavior of deep open excavations in weathered rock. Case histories of open excavations are reviewed to provide information on measured displacements, general behavior and the design approach for the support system. A detailed description of the Doe/Moffitt Library excavation is presented, including: a summary of the important design and construction aspects of the project; a description of the instrumentation used to monitor the performance of the excavation; a summary of the measured behavior; and an assessment of the observed behavior. The data from the case histories and the Doe/Moffitt library excavation is compiled to develop an empirical method for predicting the displacement adjacent to an open excavation in weathered rock. The data indicate that the ratio of horizontal displacement to the depth of excavation is generally less than 0.4 percent. General guidelines for the design of support systems are also presented. The application of numerical methods for modelling open excavations in weathered rock are summarized. The Doe/Moffitt Library excavation was modelled using a two-dimensional explicit finite difference program (FLAC). The results of the analyses indicate that a continuum model with ubiquitous joints can accurately simulate the behavior of an excavation in a jointed rock mass provided the ubiquitous joints allow the dominant deformational mode of the rock mass to occur. If complex deformational modes, defined by multiple discontinuity sets, are to be modelled, a distinct element method allows a more accurate representation of the deformational mechanics.