Design and Optimization of a terrestrial prototype for deep subsoil exploration with experimental analyses of the boring performances

A terrestrial prototype for autonomous deep soil excavation has been designed as a demonstrator for potential future Subsurface Exploration systems. The Ground Mole Demonstrator (GMD) requirements are to excavate a hole down to a depth of 100 m on soils having compressive strength up to 150 MPa, advance in the drilled hole and steer to modify the trajectory. An hybrid technique has been chosen for the excavation process, involving both percussive and rotary drilling. To finalise and optimize the design, a test setup has been built to check the performances of the boring head and to optimize the parameters of the excavation. The insertion of several additional sensors allowed the measurement of the behaviour of the components of the boring head in terms of resistant torques, and motion of the impacting mass. The achieved boring performances using a percussion frequency of 2 Hz are 1.1 and 5.5 +/- 15% mm/h on a 137 +/- 5% MPa soil specimen and on a 23 MPa one respectively. With pure rotary drilling 2.5 +/- 15% mm/h have been observed on the 23 +/- 5% MPa specimen.