Evaluation of Strength and Deformability of Soft Sedimentary Rocks in Dry and Saturated Conditions Through Needle Penetration and Point Load Tests: A Comparative Study

摘要

The preparation of standardized soft rock specimens to perform unconfined compressive strength (UCS) tests is typically difficult, expensive and time-consuming. Needle penetration test (NPT) was originally developed in Japan as an alternative for the indirect estimation of UCS of soft rocks. The needle penetrometer is a simple, portable and non-destructive testing device that measures applied load and penetration depth for the rock to calculate the needle penetration index (NPI). A complimentary, portable and widely used destructive test is the point load test (PLT), which measures regular and irregular specimens by the application of a concentrated load using two coaxial conical platens that yield the point load strength index (I-S(50)). We investigated and compared the NPT and PLT in terms of measuring changes induced by water saturation and obtaining UCS and the static Young's modulus (E-st) for dry and saturated soft sedimentary rocks. The results point to significant correlation functions from which to infer UCS and E-st in terms of NPI and I-S(50) in dry and saturated soft rocks. Furthermore, both NPT and PLT are suitable tests for evaluating changes in strength and deformability induced by water saturation. We also found a good correlation between the NPI and I-s(50).