The “constant rate of strain” consolidation test has been widely used for several decades to provide a continuous load–displacement response. An exact theoretical solution can be obtained for this consolidation problem. Two other solution techniques have pedagogic advantage in their simplicity, and in their ability to (i) clarify the phases of response of the consolidating sample and (ii) be extended to incorporate additional details of material response or testing configuration. The parabolic isochrone technique imposes a particular mode shape on the isochrones at all times. Treating the sample as a single system, and applying the boundary conditions at the system level, the governing equation becomes an ordinary differential equation. For more elaborate soil properties or experimental procedures a finite difference description of the problem is readily programmed and solved. These solution techniques are used to illustrate the importance of distinguishing between the observed response of the system — the soil specimen under test — and the behaviour of the soil elements that make up this system. Examples are given of erroneous conclusions that might be drawn if this distinction is not recognised.
- Constant rate of strain