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Because of the heterogeneous nature of soils, engineering analyses of consolidation phenomena are always approximations—sometimes close, sometimes very rough. Consolidation tests performed in accordance with accepted laboratory techniques usually require a week or more to complete, a fact that appears inconsistent with the accuracy of the data obtained. This paper describes a small, compact machine capable of performing both consolidation and shear tests, and a testing technique which will materially reduce the time required for gathering consolidation and shear strength data, with little sacrifice of the accuracy obtained by longer test methods. The process involves three distinct steps: (1) design and construction of the Consolishear (2) pilot testing of the apparatus and correlation of test results with those of consolidometers using larger specimens, and (3) devising a procedure for testing by which the results of short-time tests could be accurately extrapolated to any desired time of testing. Preliminary tests performed in the conventional manner (on a stiff clay) indicated no significant difference in results obtained with the Consolishear and with larger consolidometers. Further testing (on the same soil) to develop a more rapid technique was carried out with the Consolishear. The proposed testing technique uses a time of application for each load increment of slightly more than the time required to reach 100 per cent consolidation (as established by conventional graphical construction). Extrapolation of test data is done by extending the lower portion of each compression-square root of time curve as a straight line to any desired time of loading (within limits). The resulting void ratio-pressure curve checks closely with that obtained by usual test methods. Complete shear and consolidation data can be gathered in a day, using a bank of three Consolishears.
Karol, R. H.
Assistant Professor of Civil Engineering, Rutgers University, New Brunswick, N. J.