Development of advanced control strategies for a dynamic triaxial soil testing machine

• Main Author: Milthorpe, Thomas Edward
• Published: University of Reading 2013
• Subjects: 624.1517
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590131

As civil engineering projects become increasingly ambitious, the earthworks that form a significant part of these projects become increasingly critical. Geotechnical engineering is concerned with the measurement , modelling and simulation of soil under various conditions for the application within civil engineering. In triaxial testing, an actuator applies a force or displacement to a soil sample. Dynamic triaxial testing is concerned with applying forces conforming to a rapidly changing pattern. The simplest case is concerned with applying a force in a sinusoidal pattern. The accuracy of models produced during triaxial testing depends largely on the accuracy of the equipment used for testing. As such, the control of the applied force is of great importance. The response of the soil sample directly influences the closed loop behaviour of the system. The soil sample response is unknown at the start of the test , can vary throughout a test and depends on various parameters, many of which are unobservable. This research investigates the issues faced in developing accurate control of dynamic triaxial testing equipment. Models of the load frame and various nonlinear soil sample responses are built for the purpose of simulation and controller design. Various control strategies are developed, implemented and tested, including the use of PID control, adaptive repetitive control and sliding mode control techniques. The recursive least squares algorithm is investigated and used for online identification in order to compensate for unknown and time varying plant parameters. Simulation and testing methods are investigated and several control methods are tested in simulation, on the target triaxial load frame using and finally using embedded processing hardware. Development and implementation techniques are also used including rapid prototyping and hardware-in-the-loop testing.