DETERMINATION OF INSITU STRESSES FROM EXCAVATION-INDUCED STRESS CHANGES

The state of in situ stress described by the magnitudes and orientations of the principal stresses is an important design parameter for the construction of underground openings. Conventional methods of in situ stress determination, such as overcoring, only provide information for a small domain and are usually very costly. In this paper, a method for field stress determination in a volume of rock that is representative for an underground opening is presented. This method requires the measurement of stress changes induced by the excavation of an opening (tunnel). The best fit stress field is then determined by comparing measured and predicted stress changes. An error function is defined between the two sets of stress changes and the best-fit solution is obtained by error minimization. The methodology and its applicability are explained by an example of a circular opening for which closed form solutions are available. Application of this method to a case study has shown great potential. The back-analyzed stresses are extremely close to those determined by a large number of overcoring tests. Compared with conventional techniques of stress determination, this new method is superior in that: (1) the stress information can be updated during construction; (2) it gives the stress state in a relatively large volume of rock rather than at a point; and (3) most important, it is relatively inexpensive. © 1990 Springer-Verlag.