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I Session 1626

True Triaxial Testing System for Geotechnical Engineering Education

Dayakar Penumadu Department of Civil and Environmental Engineering Clarkson University, Potsdam, NY 13699-5710

Abstract

The influence of stress path and drainage conditions on the strength of soils can be effectively conveyed to the undergraduate students in a laboratory environment. The objective of the present project is to demonstrate the above concepts using an automated electro-pneumatic controlled true triaxial testing device with flexible boundaries. The paper indicates the salient features of the components of that testing system to date. Two types of laboratory experiments are developed using the above device. The first experiment familiarizes the undergraduate with concepts related to static transducer calibration, analog to digital conversion, signal conditioning, software and hardware gain, and the problems of aliasing. The second experiment deals with the isotropic and anisotropic consolidation and testing of soil samples using predefined stress path. Stress and strain controlled static shear tests can be performed using the above device and essentially any stress path can be simulated through the data acquisition and control software. The primary objective of the laboratory exercises is to show the relevance of the various laboratory strength tests with actual field conditions using the same testing device and in the process explain the concepts related to electronic data acquisition and control. The significant advantage is that the same device can be used to illustrate the drained and undrained stress-strain characteristics of both isotropic and ~ consolidated soil samples. The samples can be sheared under a predefined stress path and the observed pore pressure behavior (for undrained testing) can be compared. In line with the ongoing research trends, the plan is to device soil testing programs that examine the issues related to type of consolidation, stress path and the rate of loading. The information related to the design and fabrication of a flexible boundary true triaxial testing (TTT) device for use in Civil and Environmental Engineering undergraduate education is presented in this paper. The author from his own experience firmly believes that the concept of stress path effects and aspects related to the use of computers in acquiring and controlling the physical data can be effectively taught to the undergraduate students in a laboratory testing course. These concepts can then be implemented in a foundation design course and is the incentive for developing the automated TTT setup. The portfolios and the role of two undergraduate students who were involved in the fabrication of this device is also presented. These two students were supported through an NSF-REU grant. The TTT device will be used for instructional purposes at Clarkson University, Potsdam, NY in Fall, 1996. The test setup will be used initially for performing two experiments: 1 )Transducer Calibration Experiment, 2) Soil Stress Path Testing. The details of the proposed experiments are included in the paper.

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{fig~~ 1996 ASEE Annual Conference Proceedings ‘.@llRL:: .

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Penumadu, D. (1996, June), True Triaxial Testing System For Geotechnical Engineering Education Paper presented at 1996 Annual Conference, Washington, District of Columbia. 10.18260/1-2--6353