Unsaturated flow through a variable aperture fracture in Topopah Spring welded tuff.

摘要

The role of fractures in unsaturated flow through welded and nonwelded tuffaceous rocks is a fundamental question being addressed in performance assessment activities for the Yucca Mountain Project. A computer simulation test case was devised to investigate fracture-matrix interactions for a meter-scale block of Topopah Spring welded tuff. A data set produced by a laser scan of an actual fracture was used to generate the fracture geometry of a three-dimensional model. Simulation results indicate that pulses of water input to the top of the fracture produce gradients of flow down the fracture and into the matrix. The rate and extent of the advance appear to be influenced by the ambient saturation in the matrix. At 90% matrix saturation, an infiltration pulse of 1 cm water in 1 h increased the pressure head by 250 cm. The wetting front penetrated approximately 3 cm vertically and less than 0.5 cm horizontally. 8 refs; 3 figs; 2 tabs