Routes for exceptional loads: a new soil mechanics perspective

Off-site prefabrication can bring cost, quality and programme benefits to construction projects but often requires the transportation of large, indivisible loads (in the order of 1000–10 000 t) on temporary routes that can cross soft soils. Through simple numerical modelling, this paper demonstrates that the fundamental behaviour of the ground supporting these large loads can differ significantly from that expected in conventional road design practice; the interaction between many closely spaced wheels means the vehicle's influence depth and failure mechanism are significantly deeper. Surface soils are less influential. Deeper soil was found to be more prone to local yield, developing large localised strains at low proportions (10–30%) of the ultimate capacity. Instead of designing temporary roads to avoid yield and degradation under cyclic loads, significant savings may be possible if limited degradation is permitted, with recovery through consolidation between loads. Investigation and monitoring of deep subsoils during operations is recommended for real-time evaluation of geotechnical risk.