00668939

Component

http://onlinepubs.trb.org...trr/1994/1432/1432-001.pdf

https://scholar.google.co...Vaid&publication_year=1994

The deformation response of sands, which are often anisotropic because of their alluvial mode of deposition, under generalized field stress paths that involve principal stress rotation can be assessed systematically in a hollow cylinder torsional test. In this test, the specimen is subjected to four independently controlled surface tractions that allow loading under a prescribed stress or strain path. Pursuit of such stress or strain paths requires the use of simultaneous increments to more than one stress or strain component. A computer feedback control system for carrying out complex stress path tests in a hollow cylinder torsional device is described. As opposed to the generally adopted sequential loading and transducer signal readout methods, simultaneous control of all four external surface tractions and the synchronous digital readout of all transducers is carried out. This is accomplished by using four stepper motor-driven pneumatic regulators and a system of parallel analog-to-digital converters in which the number of converters equals the number of transducer signals monitored. The system allows the performance of totally stress-controlled or strain-controlled tests. In strain-controlled tests, more than one strain component can be positively controlled. The strain-controlling option permits the accurate capture of the postpeak strain softening characteristics of loose saturated sands by overcoming undesirable runaway strains inevitable in stress-controlled tests. Thus the behavior of soil can be assessed not only under controlled stress paths but also under controlled strain paths. The details of the control system are described, and its capabilities are illustrated by using experimental data from complex stress path tests.

This paper appears in Transportation Research Record No. 1432, Innovations in Instrumentation and Data Acquisition Systems. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved

01401243

English

p. 1-8

1994-10

Transportation Research Record

0309055148

Figures (6) ; References (13)

Control systems; Deformation; Sand; Softening point; Soil mechanics; Strain (Mechanics); Stresses

Strain softening

Geotechnology; Highways; I42: Soil Mechanics

TRIS, TRB

Nov 8 1994 12:00AM

• CONCURRENT TUTORIALS AND APPLICATIONS
• DATA ACQUISITION SYSTEM AND COMPUTER CONTROL OF CALIBRATION CHAMBER TESTS ON SAND
• DESIGN AND DATA ACQUISITION FOR THERMAL CONDUCTIVITY MATRIC SUCTION SENSORS
• DEVELOPMENT OF MINIATURE EQUIPMENT FOR A SMALL GEOTECHNICAL CENTRIFUGE
• FIBER OPTIC PORE PRESSURE SENSOR DEVELOPMENT
• INSTRUMENTATION AND DATA ACQUISITION FOR FIELD SUCTION MEASUREMENT
• INSTRUMENTATION FOR REMOTE AND CONTINUOUS MONITORING OF STRUCTURE CONDITIONS
• INSTRUMENTATION OF A LANDFILL COVER TO MEASURE DEPTH OF FROST PENETRATION
• LONG-TERM PAVEMENT PERFORMANCE SEASONAL MONITORING PROGRAM: INSTRUMENTATION SELECTION AND INSTALLATION
• STATIC AND DYNAMIC MEASUREMENTS USING EMBEDDED EARTH PRESSURE CELLS
• USE OF AIR-REGULATING VALVES IN GEOTECHNICAL LABORATORY TESTING
• USING DEVICE-SPECIFIC DATA ACQUISITION FOR AUTOMATED LABORATORY TESTING