External Measurement of Axial Strain in the Triaxial Test
The errors involved in measuring axial strains in the triaxial test are reviewed based on previously published results. A technique is described to allow more reliable external measurements to be obtained and used for strain calculations. The technique is simple, inexpensive, and can be implemented in any soils laboratory. Comparisons are made between the strains obtained by this method and those using local transducers (connected to the specimen); satisfactory results are obtained. Triaxial tests were made on specimens of an artificially bonded soil, Corinth marl, and remolded London clay. Errors involved in previous tests are explained, and the “bedding error” is defined in a more precise way. In some tests, this error was eliminated due to a combination of factors such as soil grading, the finishing quality of the specimen surfaces, and the ratio of confining pressure to soil strength.