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Soil, unlike many other materials, is history dependent and path dependent, meaning that its behavior is governed by the recent stress and strain history and by the current stress and strain state. The stress history and stress path imposed in a conventional laboratory test may or may not be the same as those relevant to soil in the field under structures, with the result that the soil properties measured in laboratory tests may not apply to soil behavior in the ground. Testing systems capable of controlling stress and strain paths available today are expensive and complicated to operate. Because these advanced testing systems have been mostly adapted from generic materials testing apparatus, performing realistic testing programs for soils is difficult if not impossible to achieve.
Recent advances in computer technology make it possible to program an inexpensive micro computer to perform all the necessary tasks to automatically accomplish very accurate control for a wide variety of geotechnical laboratory tests.
This work describes the design and implementation of a computer-aided geotechnical testing system. It includes the development of a digital closed-loop servo controller and multi-testing environment shell with an easy to use graphical user interface. The program was designed in a modular fashion to allow an easy implementation of application test modules to perform different tests. Each test module can be programmed to handle specific test requirements that are otherwise difficult to perform. These specific requirements may include, for example, the transfer of control from stress to strain at a particular test stage. Applications modules developed in this work include: a triaxial test module for performing conventional triaxial tests as well as advanced procedures such as stress or strain path control, a permeability module for performing constant and falling head tests using the triaxial apparatus, and a universal module to perform cyclic loading for a triaxial specimen with the capability of synchronized dynamic control of axial and confining stresses. The testing system has been successfully used to perform triaxial, static and dynamic, as well as permeability tests, resulting in an excellent tool for education, research, and practical purposes.