True Triaxial Testing System for Clay with Proportional-Integral-Differential (PID) Control
Mandeville, D
University of Tennessee, Knoxville, TN

Penumadu, D
University of Tennessee, Knoxville, TN

(Received 28 October 2002; accepted 17 June 2003)

Abstract
A flexible boundary electro-pneumatic true triaxial system has been developed for testing cohesive soil. The system is capable of applying principal stresses on each face of a cubical specimen using a Proportional-Integral-Differential (PID) based closed loop control algorithm. This device has the ability to measure both the internal and external pore pressures for a 102-mm cubical specimen and uses custom developed Butyl rubber membranes. Measurement of the internal pore pressure is accomplished using a needle piezometer. Appropriate software has been developed that can automatically perform saturation, isotropic or K_o consolidation, and shear testing under stress or strain control along various stress or strain paths. Using this system, results from isotropically consolidated triaxial compression and triaxial extension stress paths are presented for cubical kaolin specimens. Comparative tests using conventional cylindrical specimens using lubricated ends were also performed. Issues related to the interference of the flexible membranes, uniformity of strains and bifurcations, interpreted friction angles, and undrained shear strength are discussed.

Keywords:
Clay, PID control, pore pressure, stress-strain behavior, true triaxial testing, uniformity

Paper ID: GTJ11756
DOI: 10.1520/GTJ11756

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Author Mandeville, D Affiliation University of Tennessee, Knoxville, TN Author Penumadu, D Affiliation University of Tennessee, Knoxville, TN Author Mandeville D, Penumadu D Title True Triaxial Testing System for Clay with Proportional-Integral-Differential (PID) Control Symposium , Committee on