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  Assessment of Tunnelling Rock Spoils from Highly Weathered Lithology Using Rolling Friction Contact Models in Discrete Element Modelling

  The assessment of jacking forces in highly weathered lithologies (or ‘soft rocks’) typically presents challenges relating to the measure of salient mechanical parameters of such lithologies, particularly the strength and deformation properties. This is mainly due to challenges in extracting intact rock cores for conventional laboratory-based rock tests, such as uniaxial compressive strength (UCS) tests, point load tests (PLTs), and Hoek triaxial cell (HTC) tests. An innovation in addressing these challenges was through the development of equivalent rock strength parameters using direct shear tests performed on tunnelling rock spoils collected from decantation chambers during pipe-jacking. These generalised tangential peak strength parameters (ct,p and ϕt,p) were successfully used to assess arching for pipe-jacking works traversing ‘soft rocks’. Through the use of particle image velocimetry (PIV), past studies showed qualitatively that these strength parameters were attributed to interactions at the particulate level. The current study attempts to provide quantitative insight into the particulate interactions through discrete element modelling of the sheared tunnelling rock spoils. A technique comprising the use of a rolling friction contact model was applied to the spherical discrete elements in order to simulate the interactions of the angular / sub-angular tunnelling rock spoils. These numerical analyses were compared against actual direct shear tests, and demonstrated potential in being applied to high-strain analysis of frictional jacking forces in pipe-jacking drives.

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