Volume 12, Issue 4 (December 1989)
Measurements of Normal Deformations in Joints During Shear Using Inductance Devices
The use of inductance coils for measuring normal deformations involving dilation or compression across a discontinuity is described. Discontinuities may be in the form of interfaces between dissimilar materials or rock joints. In contrast to the conventional schemes for measuring normal deformation that involve installation of measuring devices (linear variable differential transformers, LVDTs) away from the discontinuity, the proposed procedure allows measurements close to the discontinuity. Application is discussed with respect to a test program performed on idealized (rock) joints; the test program consists of slow and fast cyclic, large-scale direct shear tests.
The installation of the coils within specimens and special calibration procedures unique to the direct shear test configuration are described. Measurements obtained with inductance coils are verified by comparison with measurements taken by using other instruments, and by comparison with anticipated experimental results.
This study has shown that inductance coils are useful for improved and reliable measurements of normal deformations across a discontinuity.