Improved Thermal Computations for Artificially Frozen Shaft Excavations

Artificial ground freezing (AGF) techniques are widely used by civil and mining engineers to assist in the construction of shafts, tunnels, and other structures. The ground is frozen by a coolant circulated through pipes inserted in the ground in order to create a cofferdam that will exclude ground water and provide structural support. Formulas by Sanger and Sayles are often used to estimate the growth of the freeze. The theoretical basis of these formulas are critically examined and an alternative method of computing the extent of the frozen ground is given. The alternative method is based on some of the ideas of Sanger and Sayles and requires the numerical solution of one diffusion equation over a finite interval. Numerical results are presented using typical data for granular soils with several different dry densities and water contents.