SYMPOSIA PAPER Published: 01 January 1966

Foundation Testing Techniques for Arch Dams and Underground Powerplants


To ensure that foundation tests are performed on representative specimens and field sites, geologists take advantage of regional surveys, vicinity surface mapping, and subsurface conditions at the site as revealed from borings and borehole camera studies. Following this, the physical properties of the rock are determined from drill cores. Deformation of the rock, for computation of arch reactions and deflections, is determined by numerous laboratory tests of sound rock specimens and by jacking and seismic tests in the field that show the influence of cracks and other inherent weaknesses. The shear strength of the rock is determined triaxially in the laboratory with specimens from holes oriented at various angles to the foliation plane. In the field, large blocks of rock are tested to obtain the influence of joint systems on shear strength and resistance to sliding under various normal loads. Strain relief techniques are used to obtain in situ stresses on the walls and roof of an exploratory tunnel and within the rock mass by means of deep drill holes. Rock deformation caused by excavation of a machine hall chamber is measured by the use of multiple borehole extensometers and convergence gage points. When jointed rock is bolted together and used as a structural material, tests are made to determine the torque-tension relationship for bolts to be sure that the anchors will hold and not relax their grip with time. As a safety measure and to check design assumptions, deformation meters are installed between the base of the dam and the foundation rock at various depths below the structure.

Author Information

Wallace, G., B.
Division of Research, Bureau of Reclamation, Denver, Colo.
Olsen, O., J.
Division of Research, Bureau of Reclamation, Denver, Colo.
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Developed by Committee: D18
Pages: 272–297
DOI: 10.1520/STP45145S
ISBN-EB: 978-0-8031-6016-3
ISBN-13: 978-0-8031-6170-2