DDA Back Analysis of Large Block Test Data

ABSTRACT: The Large Block Test (LBT) is an in-situ thermal test on an exposed block of fractured rock. Because the block is a well mapped fractured rock mass, it is a good candidate for analysis using the Discontinuous Deformation Analysis (DDA). In the DDA back analysis, local deformations at anchor points of multiple point borehole extensometers (MPBXs) are used as input to obtain the global deformed configuration of the block. From the computed global deformed configuration, fracture deformations are calculated and compared with measured fracture monitor data. This paper presents the refinement of a previous back analysis and reports the results of refined back analyses, including the results of parametric studies. With respect to the only fracture deformation component that can be computed reliably, the computed and measured deformations agree well if a set of input values based on actual measurements or reasonable estimates are used. Furthermore, the agreement worsens quickly when the input values deviate from this set of values.