Modelling of track foundation behaviour at Zig Zag tunnels near Lithgow, NSW

In situ fragmentation and rock particle sorting on arid hills

“…We can estimate the depth of intense heating using the damping depth d m , the depth at which the temperature fluctuations are 1/ e of the temperature fluctuations at the surface, given by d m = (2 D f ω −1) − 0.5 , where D f is the thermal diffusivity and ω is the frequency of temperature variations [ Kirkham and Powers , ]. Given that the thermal diffusivity of rock is low, D f ∼ 4 × 10 − 7 m 2 s − 1 [e.g., Ahmed and Meehan , ], diurnal heating and cooling is expected to produce a damping depth of d m ∼ 0.1 m. The heat flux produced by solar radiation (the solar constant) is q = 1.36 W m − 2 [ Kopp and Lean , ], and with typical siltstone properties E ∼ 2 × 10 3 MPa, ε = 0.2 [e.g., Haque et al , ], α x ∼ 4 × 10 − 5 K − 1 [e.g., Hettema et al , ], and λ ∼ 4 W m − 1 K − 1 [e.g., Gallagher , ], we estimate the magnitude of the tensile stress to be σ x ∼ 0.001 MPa. The tensile strength is typically σ t ∼ 0.5 MPa [e.g., Haque et al , ]; more than 2 orders of magnitude greater than σ x .…”

“…Given that the thermal diffusivity of rock is low, D f ∼ 4 × 10 − 7 m 2 s − 1 [e.g., Ahmed and Meehan , ], diurnal heating and cooling is expected to produce a damping depth of d m ∼ 0.1 m. The heat flux produced by solar radiation (the solar constant) is q = 1.36 W m − 2 [ Kopp and Lean , ], and with typical siltstone properties E ∼ 2 × 10 3 MPa, ε = 0.2 [e.g., Haque et al , ], α x ∼ 4 × 10 − 5 K − 1 [e.g., Hettema et al , ], and λ ∼ 4 W m − 1 K − 1 [e.g., Gallagher , ], we estimate the magnitude of the tensile stress to be σ x ∼ 0.001 MPa. The tensile strength is typically σ t ∼ 0.5 MPa [e.g., Haque et al , ]; more than 2 orders of magnitude greater than σ x . This establishes that fracturing by thermal cycling occurs as fatigue failure, and that diurnal, rather than higher frequency temperature fluctuations are likely dominating breakage.…”