A rapid field measurement method for the determination of Joint Roughness Coefficient of large rock joint surfaces

An accurate measurement of the Joint Roughness Coefficient (JRC) of large rock joints is essential for understanding the mechanical behavior and permeability characteristics of rock mass. Determining the surface roughness of rock joints in situ, however, is time-consuming and depends on sophisticated instruments. This study was carried out to develop a systematic method of measuring the JRC values of large joint roughness profiles. The roughness profiles were accurately recorded by a hand profilograph in the field and then digitized with flexibly adjusted sampling intervals by the grayscale image processing method. The digitized profiles were correlated closely with the original roughness profiles. A computerized approach for JRC quantitative evaluation was proposed based on the roughness amplitude/joint length relationship with JRC. The interval effect analysis showed that this method was effective for estimating the JRC values of different sized rock joints. This JRC measurement method has been successfully used in a case study of killas rock joints in Changshan City, P.R. China.