Evolution and remediation of ground failure risk for temporary roads carrying cyclic heavy haul traffic

Increasing popularity of offsite modular construction has increased demand for transportation of very large (1000-3000 tonne) indivisible loads. Crossing poor soils presents a serious risk of ground failure, particularly as larger vehicles’ greater influence depths produce a very different soil response to conventional vehicles. Temporary haul roads designed conventionally may be excessively conservative and unaffordable as a temporary asset; cost reduction through observational risk management is sought. This thesis experimentally investigates soft silt and clay soils through cyclic triaxial testing. Particular focus is given to anisotropically normally consolidated silt, carefully manufactured through slurry consolidation to replicate liquefiable fabric. Soil samples are tested under the unusual loading conditions associated with heavy haul roads (slow, large-strain, infrequent). A new design approach for temporary heavy haul roads is demonstrated: cyclic traffic load can be used to improve soil, either by gradually rearranging fabric (medium-strain treatment) or remoulding and consolidating excess pore water pressure (large-strain treatment). Liquefiable silt benefits from both, plastic clay only from the latter. These findings, combined with a robust monitoring regime and management of heavy traffic, could be used to improve soil strength over time during operations. This could realise significant project savings and increase viability of modular construction

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. </jats:p

Degradation of soft subgrade soil from slow, large, cyclic heavy haul road loads: a review

Extraction of resources in remote locations can require temporary haul roads to transport extremely large, slow-moving, indivisible loads (e.g., plant, oil–gas production modules, and reactors, weighing in excess of 1000 t) without interruptions. Poor subgrade soils may experience larger cyclic strains and greater cyclic degradation under these conditions than under conventional roads, yet the short engineering life precludes many foundation-strengthening options due to cost. As there is little research into this unique situation, this paper synthesizes research from a broad range of applications to discuss implications on expected soil response. Reference is made to critical state theory and discrete element method (DEM) modelling to develop fundamental concepts considering particle-scale interactions. Cyclic failure is proposed to be a kinematically unstable process, triggered by shear banding on the Hvorslev surface, tensile liquefaction or fabric-governed meta-stable liquefaction; the latter is particularly influenced by stress history and anisotropy. This paper finds pore-water pressure accumulation under load and dissipation between loads are key to cyclic degradation and furthermore to be dependent upon load duration, principal stress rotation, and repetition frequency. For meta-stable, liquefiable soils in particular, inclination of principal stresses is at least as important in assessing failure risk as magnitude of stresses.</jats:p

Excess Pore-Water Pressure Generation and Mud Pumping in Railways Under Cyclic Loading

2019, Springer Nature Singapore Pte Ltd. High-speed heavy haul trains have become one of the most popular and economical modes of transportation in the modern world to cater for increased demand in freight for agricultural and mining activities. However, when these trains travel through vulnerable areas occupying soft subgrade formations, frequent maintenance is required to prevent differential settlement and localized failures of track. The poor performance of track caused by ballast fouling is also often observed where fines are fluidized and pumped into the ballast voids (mud pumping), which in turn create ballast pockets, mud holes and track instability. When saturated subgrade is subjected to short-term undrained cyclic loading, the pore-water pressure can accumulate inducing fine particles to migrate upwards into the ballast layer. Mud pumping causes millions of dollars of damage to heavy haul rail networks every year in Australia. This paper presents a critical review primarily focused on the role of excess pore-water pressure generation on mud pumping under cyclic loading. Mitigation of these issues can result in considerable savings to rail authorities on recurrent track maintenance activities