Sandia National Laboratories

AAI was contracted to Sandia National Laboratories to provide geotechnical, analytical, and field services to the Yucca Mountain site characterization studies in the early- to mid-1990s.  AAI established an office in Las Vegas, Nevada, to support the project with up to ten engineers, scientists, and geologists.  Modeling studies ranged from drift stability under thermal and seismic loads to regional stress changes and fault activation studies.  A drift design methodology using both analytical and empirical methods was developed.  Two three-dimensional stress analysis tasks are detailed below.

The three-dimensional boundary-element program, BEST3D, was used to understand the stress distribution along the intersection of the main tunnel and waste emplacement drift.  The stress results were used to predict the rock mass failure over the drift wall using Mohr-Coulomb strength parameters.

Analysis of the thermally induced stress changes along the shaft axis were required for input to the shaft liner design.  AAI completed this task at QA Level 1 using the STRES3D code.  Each panel was modeled as rectangular and horizontal, each with differing elevations and time of waste emplacement.  The thermally induced strain and stress changes along the axis of the shaft at the breakout rooms and Exploratory Studies Facility were evaluated.  This model was again used to evaluate stress changes at specific drift locations using the same emplacement geometry and emplacement scheme.

AAI participated in the preparation of a shaft liner design guide for the proposed exploratory shafts at Yucca Mountain.  A computer program (SHAFT), developed by AAI based on an original solution for stresses and displacements around a circular shaft, was employed to consider in-situ, thermal, and seismically-induced stresses in the shaft liner.  Fiber-reinforced concrete and various forms of reinforcing were investigated to minimize problems with liner cracking.

Other projects included tunnel mapping and installation of rock instrumentation during construction of the Exploratory Studies Facilities.

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