Determination of Field Stress Ratio and Young’s Modulus using the under excavation technique

The under-excavation technique (UET) is a simple method of assessing the Field Stress Ratio (k) and Young’s Modulus (E) of a rock mass from its response to an advancing excavation. The key to this method is that a hole in an elastic medium under stress will have a unique convergence signature which can be measured. The advantages of this method are its simplicity, low cost, utility, applicability to excavations of irregular dimensions, is non-invasive and views the rock mass at a suitably large scale. Further, it can be applied to any excavation in relatively homogeneous material, being particularly suited to tunnels and shafts.

This paper (1) outlines the theoretical background for the UET, (2) explains a practical and simple way to apply it, and (3) offers the case study of the Eastern Distributor Tunnel where it has been successfully applied.