Comparison of Borehole Dilatometer Tests with Radial and Uniaxial Jacking Tests in Rock

ABSTRACT: Over the years there has been a trend away from large scale, proven and time-tested rock deformation field tests in rock, like uniaxial (UJT) and radial (RJT) jacking tests to rock dilatometer tests (RDT). The reasoning ranged from RDT being cheaper, better, and more, but without providing research and Quality & Assurance (Q&A) data that supported those conclusions. The amount and type of data collected from the larger volume of rock evaluated by the RJT (~552 m3) and UJT (~9.9 m3), as compared to the RDT (~0.145 m3 for NQ), the UJT and RJT can provide more and better data, which in comparison makes those tests less expensive than the RDT. Furthermore, the RDT is like a hydraulic fracturing technique and can create a longitudinal borehole fracture when the dilatometer pressure exceeds the tensile strength and in-situ stresses around the borehole wall. As a result, the RDT typically provides different and even lower values than the larger UJT and RJT field tests. This presentation compares the UJT and RJT methods with the RDT method and the reasons RDT results are often lower and different than laboratory, empirical, and larger field-testing results. This presentation primarily discusses the volumetric RDT but is applicable to the other rock RDT methods.