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Title: Study of feasibility of using Wissa-type piezometer probe to identify liquefaction potential of saturated fine sands
Authors: University of Florida. Department of Civil Engineering
Schmertmann, John H.
Keywords: Cone penetrometers
Relative density
Fine-grained soils
Soil liquefaction
Saturated soils
Pore pressure measurement
Wissa-type piezometer probe
Publisher: Soils and Pavements Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: A two-phase study was performed to investigate the feasibility of using the pore pressure response from a penetrating Wissa piezometer probe to indicate the potential for liquefaction in saturated fine sand. The Wissa probe is a cone penetrometer, similar to the Dutch cone penetrometer, with a sensing element at the tip for measurement of pore pressures. Phase I was a field study consisting of three piezometer probe tests to a depth of about four and one-half meters in each of two areas; Area 1 containing deposits of loose, easily liquefiable mine tailings sand, and Area 2 containing similar deposits compacted by a vibratory roller to a condition of stable relative density. Tests in Area 1 produced generally positive excess pore pressures, while tests in Area 2 produced generally small negative pore pressure response. Phase II was a laboratory study.consisting of four tests, each on a freshly prepared specimen of Reid-Bedford Model sand, in the 4 ft diameter by 4 ft high University of Florida triaxial chamber. Relative densities in these tests were between 30 and 81 percent, the mid-height vertical effective stress was approximately 17.5 psi, K𝗈 was approximately 0.46, and the degree of saturation approximately 97 percent. The pore pressure response in these tests was qualitatively similar to that in the field tests, but of a magnitude about one-tenth as great. The reduced response was attributed to imperfect saturation of the test specimens. Comparison of pore pressure data with relative density, as estimated from approximate correlations with penetrometer resistance, suggest that this type of probe sounding can detect very unstable, saturated, clean, fine sands with relative densities below about 20 percent. However, there may be a broad range of relative density in which the piezometer probe response is insensitive to relative density. Additionally, the magnitude of pore pressure generated at the tip of a Wissa-type probe depends not only on the effective stresses and dilatancy behavior of the in situ sand but also on its permeability and the rate of penetration used. This study was done with only one rate of penetration, 2 cm/sec. In applying this method for field estimation of liquefaction potential, associated measurements of permeability will be required. Possibly these can be obtained from the rate of pore pressure decay when penetration is stopped.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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