IMPROVEMENT OF LASER MEASUREMENT SYSTEM FOR RADIAL DEFORMATION OF TRIAXIAL SPECIMENS
(1. Department of Architectural Engineering，Logistical Engineering University of PLA，Chongqing 401331，China；
2. Institute 8358，China Aerospace Science and Industry Corporation，Tianjin 300192，China)
Abstract：Taking advantages of laser photoelectricity measurement technique and position sensing detector(PSD) with high precision，the laser measurement system for measuring radial deformation of triaxial specimens is improved. Three aspects of improvement have been done as follows：(1) In order to avoid the deflection of vertical incident light，the square pressure chamber is adopted instead of the circular one. (2) Two PSDs are used to measure radial deformation in left and right sides of specimen instead of one PSD in original system，which couldn′t take into account the specimen eccentricity in triaxial shear tests. So the measuring precision would be enhanced. (3) A stepper motor of controlling transducer lift and down is used instead of common motor. It can ensure the transducer goes back to the same initial position. This system is used to measure standard specimen，standard specimen in the pressure chamber and standard specimen in the pressure chamber full of water. The function relationship between change in electrical signal and change in diameter is obtained. The consolidation tests on saturated sand containing clay are carried out. The comparison of measured and calculated results indicates that the volumetric changing results obtained by the improved triaxial measurement system are reliable. This system can be applied to study the problem of triaxial specimens，such as local deformation and end restraint；it also has great prospect to study deformation localization，formation of shear zone and volumetric changing measurement of unsaturated soils.
2011, Vol. 30 
