Abstract
Uncertainty in ground datasets often stems from spatial variability of soil parameters and changing groundwater regimes. In urban settings and where engineering ground interventions need to have minimum and well-anticipated ground movements, uncertainty in ground data leads to uncertain analysis, with substantial unwelcomed economical and safety implications. A probabilistic random set finite element modelling (RSFEM) approach is used to revisit the stability and serviceability of a 27 m deep submerged soil nailed excavation built into a cemented soil profile, using a variable water level and soil shear strength. Variation of a suite of index parameters, including mobilized working loads and moments in facing and soil inclusion elements, as well as stability and serviceability of facing and the integrated support system, are derived and contrasted with field monitoring data and deterministic FE modelling outputs. The validated model is then deployed to test the viability of using independent hydraulic actions as stochastic variables as an alternative to dependent hydraulic actions and soil shear strength. The achieved results suggest that utilizing cohesion as a stochastic variable alongside the water level predicts system uncertainty reasonably well for both actions and material response; substituting the hydraulic gradient produces a conservative probability range for the action response only.
Highlights
Rapid and sustained urban sprawl is expected to continue to accommodate an estimated 70% of the world population in cities by 2050 [1]
This suggests that while the conventional design practice gives a reliable estimation of the soil nail axial force, variability of the water level can yield greater orders of axial loads, which is technically unexpected
A real-world deep excavation problem incorporating soil nailing was analysed and revisited, employing the random set finite element method to test the viability of the probabilistic frameworks in solving complex geotechnical problems, where spatial variability is prevalent
Summary
Rapid and sustained urban sprawl is expected to continue to accommodate an estimated 70% of the world population in cities by 2050 [1]. In an urban context and where the subsurface is already congested (by buried utilities and underground structures), any further disturbance can lead to variations in groundwater conditions, with immediate implications on some soil engineering properties. Spatial variability of shallow disturbed ground and limited space for intrusive ground investigation, as well as extreme climates that reportedly cause a broad range of problems, including fatigue [3] and mineral dissolution [4], add to the uncertainty and cast doubt on the reliability of the estimated stability and serviceability of support systems. These systems are commonly designed through deterministic analysis of engineered grounds using ground properties that are statistically moderated, and in the context of some standards, further factored down by an arguably arbitrary partial factor
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