Estimation of permeability for the rock mass around the shiplocks of the Three Gorges Project, China

Changes in the bulk permeability of the fractured rock mass around the ship locks of the Three Gorges Project, China, during excavation have been inves tigated using a numerical modelling technique. The numerical model took int o account both the effect of fractures on the in situ bulk permeability and the increase in permeability resulting from the stress relief and opening of the fractures caused by excavation. Fracture patterns were estimated on the basis of field exposures in three orthogonal planes. The numerical mode l was calibrated for the in situ condition by varying the fracture stiffnes s until a close match (in terms of both magnitude and direction) was obtain ed with the equivalent permeabilities estimated on the basis of field pumpi ng tests. Excavation of the shiplocks both with and without the use of temp orary supports was modelled, and the resulting changes in stress and permea bility in the surrounding rock mass calculated. In both cases, the opening of fractures subparallel to the shiplock channels resulted in an increase i n the permeability of the ground, but when the vertical sidewalls were supp orted during excavation the increase in permeability was less marked. The r esults of the analyses highlight the effects of engineering activities on t he permeability of fractured rock masses, and demonstrate that these effect s can be controlled through the judicious choice of construction techniques and procedures. (C) 1999 Elsevier Science Ltd. All rights reserved.