Routes for exceptional loads: a new soil mechanics perspective

Abstract

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. Notation

Controlled heavy-haul traffic loading as a method to remediate liquefiable soft silts

“…It was demonstrated by Krechowiecki-Shaw et al (2017) that a heavy haul vehicle can apply transient stresses to soil at depth, in a normally consolidated state (e.g. at 6.5m depth for the very soft soil considered), with sufficient magnitude to induce localised plastic yield.…”

“…In order to simulate the 'deep' stress state considered of critical importance in Krechowiecki-Shaw et al 2017, anisotropically consolidated triaxial samples were subject to undrained cyclic deviator stress pulses of varying magnitude (except when close to failure, Krechowiecki-Shaw et al, (2017), found that these large vehicles did not induce significant principal stress rotation at depth).…”

“…The influence depth of the heaviest vehicles needs to be considered in the surcharging or cyclic preloading programme and associated monitoring; interaction between wheelsets can stress the ground to a much greater depth than usual (Krechowiecki-Shaw et al, 2017). Ideally a vehicle of the same (or larger) dimensions as those used to carry the largest load, but applying smaller stresses, should be used in cyclic pre-loading.…”

“…alluvium) present the additional unusual risk of metastable liquefaction at depth to this heavy haul traffic. This is a result of interaction between adjacent wheel stress bulbs stressing much deeper soil than conventional traffic (Krechowiecki-Shaw et al, 2017), which can be normally consolidated and prone to liquefaction under relatively small disturbances. This rapid and catastrophic failure mode could suddenly topple or strand a heavy haul vehicle, with risk of casualties, irreparable damage to these multimillion-dollar payloads and ultimately significant production delays.…”

Editorial

“…The fifth paper is by Krechowiecki-Shaw et al (2018) on 'Routes for exceptional loads: a new soil mechanics perspective'. It presents a numerical model for studying the impact on soft soils in temporary routes during the transportation of large prefabricated sections with indivisible loads in the order of 1000-10 000 t. The results are presented in terms of a failure mechanism, and impact of load on surface and deeper soil.…”