Abstract
Methods of measuring contemporary stress are briefly reviewed with particular interest in precise measurements at depth. Stress-relief methods are widely used techniques in the engineering field. Wireless strain-cells indicate the high possibility of stress-relief methods for deep wells. Numerical calculation on the stress field within the elastically coupled materials, [rock + mortar + strain-meter], shows that the stress inside the over-cored rock is not completely relieved. More reliable results can be given by such analysis than that without considering residual stress effects. The hydraulic fracturing method has been widely used in the geophysical field. However, serious suspicions about the interpretation of reopening pressure have also been raised in the past 20 years. As possible answers to these suspicions have been proposed recently, it is necessary to check the past results again and cross-check the results of different methods. Non-hydrofracturing methods are free from problems associated with the permeation of pressure fluid into artificial fracture and borehole wall. Furthermore, some non-hydrofracturing methods do not need the assumption of principal stresses having a constant direction, which can be an advantage over hydrofracturing methods for long-term observations of stress variations. Core-based and boreholewall-fracture-based methods, unfortunately, cannot now be considered to be precise measurement methods. However, these methods have the potential to estimate stress, particularly at great depths.
