Foundations of cable car towers upon alpine glaciers

Abstract

This paper presents a design approach for strip footings upon glacier ice. Safety against ultimate limit state is proved by the geotechnical slip-line field solution by Prandtl. Glacier ice at 0°C can be modelled as purely cohesive material. Statistical evaluation of uniaxial compression tests with high strain rate revealed a mean value of the cohesion of 600 kPa and a characteristic value c k = 355 kPa (5% fractile). With a coefficient of variation V c = 0.3, the partial safety factor turns out to be γ c = 1.9. An approximate solution for estimating the creep settlement rate $${\dot{u}}$$ is presented to check the serviceability limit state: $${\dot{u}}=\beta_1 b^{\beta_2}p^{\beta_3},$$ with the width b of the strip foundation, p the foundation pressure and $$\beta_1=8.6 \times 10^{{-5}}\,\hbox{m\, kPa}^{-\beta_3} \hbox{a}^{-1}\,\hbox{m}^{1-\beta_2}, \beta_2=0.92, \beta_3=1.74$$ for ice at 0°C. Experiences on Stubai glacier with grate shaped footings showed that creep settlements occurring per year due to maximum foundation pressures 250 kPa did not influence the operation and the maintenance of the cable cars.