PC controlled stress path triaxial cell system

Abstract

This dissertation proposed a system named “PC Controlled Stress Path Triaxial Cell System”. The aim of this system is to upgrade the current triaxial equipment at the Faculty for the Built Environment at the University of Malta. This equipment is mainly operated manually and has minimal research applications. The main requirement for this project was to design a system that can monitor and control all the different test parameters such as: pressures, displacement, volume change and load. The proposed solution consists of a master-slave architecture between the PC and a designed Data Acquisition and Control Board. This board is capable of acquiring data from different sensors as well as performing the necessary control of test parameters and actuations. Additionally, this board can be used as a standalone data-logger, having its own Real Time Clock and capability of saving on a Secure Digital Card. Furthermore, this board controls a Load Frame which is a machine used to apply load to the tested specimen. The proposed system also addresses the modifications required in order to decrease the minimum speed of this Load Frame so as to broaden the range of triaxial tests that can be performed using this equipment. Microcontroller software design is also included in this dissertation. This software waits for commands being sent by the PC and hence takes the necessary. Moreover the designed system includes a LabVIEW user interface which enables the researcher to control all the operations of the test such as: closing solenoid electro-valves, switching an air compressor and controlling the switching and speed of the Load Frame. This interface is also responsible for converting the data sent by the microcontroller and saving it in a Dropbox location for online backup. Additionally this software includes fault detection such as in the case of power-cuts. In such scenarios the user interface sends specific commands to the Data Acquisition and Control Board and this board uses a GSM/GPRS module to send warning messages to the Administration. Hence, the design of a backed-up robust system is presented in this dissertation, to safeguard results of tests that could be running for weeks and even months.