Inclusion Effects on Stress Gage Measurements in Rock and Soil.
Technical rept. 27 Apr 83-26 Apr 84,
SRI INTERNATIONAL MENLO PARK CA
Pagination or Media Count:
One of the main difficulties in measuring stress in rocks and soils is that the stress gage and installation disturb the stress field to be measured. Another difficulty is to relate the behavior of a sensing foil embedded within a stress gage package to the stress field surrounding the gage. The work reported is the first phase of a combined theoretical and experimental program to investigate problems of in-situ stress measurement. Finite element calculations were performed on a grout-filled borehole in tuff to show how the relationship between the free-field and gage plane stresses are influenced by mismatch of fill and medium properties, load level, and slip and separation along the interface. Calculations also show the formation of a residual stress field in the borehole fill. Similar calculations were performed on a typical flatpack stress gage design to relate the free-field stresses, the stresses on the package, and the stresses acting on the plane of the piezoresistive sensing foil. Finite difference calculations were performed to obtain the response to shock loading of an ytterbium sensing foil embedded in PMMA. This work is part of a coordinated research effort with other DNA contractors on piezoresistivemechanical properties of ytterbium appropriate to stress measurement environments. A triaxial static experiment was designed and constructed for future investigations on borehole fill inclusions, including comparisons with theoretical predictions.
- Geology, Geochemistry and Mineralogy
- Soil Mechanics