3D Geo-modelling using geophysical tools to aid injection grouting

Geophysical tools are increasingly utilised within the tunnelling and underground construction industry; investigating the extent and properties of physical domains where traditional direct investigation methods encounter restrictions. This paper describes the development and subsequent advanced processing method used by a unique robotic ground penetrating radar (GPR) tool, that is used to survey beyond a pipe-liner installed within an in-ground horizontal direction drilling (HDD) bore. The GPR device assists in the construction of underground structures by hyperTunnel Ltd, who employ adapted grout injection methods to controllably place cementitious and non-cementitious chemistry into porous ground (from installed and lined horizontal bores). The device is shown to use 900 mHz and 2.6 GHz frequency antennas to discern the coincidence of objects both beyond and on the pipe's surface, both in terms of their spatial extent and probable material type. This capacity is utilised by hyperTunnel in two complimenting elements of their construction process; to assess the ground conditions pre- and post-injection of chemistry, and to assess the spatial extent of injections for the purpose of validating construction objectives and identifying ground which requires further injections to meet said objectives. This novel use of GPR provides a key visualisation and verification tool to hyperTunnel's construction method, and its full application continues to be realised in further scenarios.