Using a limit states approach for ice road design

ABSTRACT: Natural resource development in northern Canada has often relied on winter roads and ice roads to provide economical site access and resupply routes. These winter roads provide significant socio-economic benefits to the industrial sites and communities they connect. The state of practice for determining allowable loads has largely been based on empirical ice capacity equations developed in the 1970s that are found in most of the ice bearing capacity guides being used in Canada. Industrial ice roads that have sufficient construction quality assurance and operational controls in place can take advantage of higher allowable flexural stresses without compromising ice road safety. This paper explores the application of limit states design (LSD) to the Tibbitt to Contwoyto Winter Road (TCWR). This road is over 300 km long and about 80% of it is built over ice each winter. A Ground Penetrating Radar (GPR) system collects thousands of ice thickness measurements. By exploiting the ice data generated by GPR profiling and the dispatch system for tracking vehicle loads, we can generate probability distribution curves for ice resistance and vehicle load effects for a typical winter road season. An analysis of ice flexural strength data sets found in the literature provided two ice resistance scenarios: A. 1422 kPa ±396 kPa and B. 1730 kPa ±250 kPa. We determined that in levels II and III reliability analyses, the probability of initiating ice cracks is 1 to 2% for scenario A and much lower for scenario B. Further work is necessary to calibrate the load and resistance factors.