Northern Ireland has approximately 25,000 km of road network, which encompass a substantial number of large cuttings in Till. A slope failure of a deep cutting in Till at Dromore, along the A1 Belfast – Newry dual carriageway in Northern Ireland was reported by Hughes et al. (2007).
The factor postulated for instigating the slope failures was a reduction in long-term shear strength due to a combination of progressive deformations, strain-softening and dissipation of excess pore water pressure generated during the initial excavation, together with pore water pressure dynamics triggered by weather patterns; such progressive deformation is generally referred to as creep and fatigue.
A reliable estimation of geotechnical parameters is therefore necessary in order to accurately predict the performance of such structures.
This presentation therefore reports the investigations carried out to understand this time-dependent behaviour of overconsolidated Till using three strands of investigation: site characterisation, laboratory investigation and numerical modelling.
More specifically, a review of the pore pressure data is presented, as well as two methods of deducing in situ small strain stiffness, and stress path testing of reconstituted Till samples was carried out under static and dynamic pore water pressure conditions. The results of these laboratory and field stiffness investigations were used to calibrate field-scale hydrogeological and mechanical numerical models of the cutting in Lodgement Till at Loughbrickland.
This research was aimed at aiding asset owners, such as the Department of Infrastructure and Translink, in managing geotechnical risks, allowing them to develop assessment and adaption strategies to ensure the future safety and resilience of geotechnical transport assets.
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