Hydrostatic Pressure Loading due to Ice Formation in Manholes

The magnitude of the hydrostatic pressure that results from the growth of an ice layer at the top of a water‐filled manhole is determined using both analytical (for a thin ice layer) and finite‐element methods (for a thick ice layer). The ice‐layer freeze/fracture cycle during the growth of the ice layer is predicted analytically and subsequently verified experimentally. A general expression for the hydrostatic pressure as a function of ice thickness and cross‐sectional area $({l^2}_i/a^2)$ for a square cross section is developed. Experimental results for an ice layer of a circular cross section show that up to ${l^2}_i/r^2\simeq 0.5$ the trend in pressure versus ice thickness results is predicted by the finite‐element method although in some cases the actual experimental values are approximately twice the predicted values, probably due to thickening of the ice disk around the periphery. For the ${l^2}_i/r^2\simeq 0.5$ case, hydrostatic pressures resulting from ice formation at the top of the manhole can be two orders of magnitude greater than the pressure due to the static head in a water‐filled manhole.