Rate Aware Pile Design in Glaciogenic Silts: From Fabric to Serviceability

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Abstract:

Sensitive glaciogenic silts often exhibit high smallâ€‘strain stiffness

in the intact state yet contractive, strainâ€‘softening behaviour once fabric is disturbed or loading rates are high. This paper synthesises investigation, monitoring and testing from instrumented railway bridge foundations to propose a practiceâ€‘ready workflow. Coâ€‘located dualâ€‘rate CPT (

≈ â€¯20â€¯mm/s;

≈ â€¯3â€¯mm/s) reconciled with seismic DMT (sDMT) provides a rateâ€‘aware, effectiveâ€‘stress interpretation to infer the state parameter

and to map installationâ€‘induced destructuration via

(“ damage meter” ). Field verification demonstrates critical installation effects: controlled vibratory penetration mobilized significantly higher, more uniform unit shaft resistance

compared to impact driving

and achieved superior set-up rates (~1.1 vs ~0.27 kPa/day). Post-installation sDMT data confirmed a 20– 30%

reduction adjacent to impact-driven piles, while vibratory installation left the surrounding silt fabric largely intact. Transient settlements of adjacent foundations during vibratory works were bounded

and stabilized rapidly. The resulting design guidance advocates for a shaft-dominated resistance model at the Serviceability Limit State (SLS), with toe resistance reserved for Ultimate Limit State (ULS) reserve. This approach is verified via segmental, multi-energy PDA/CAPWAP interpretation and supported by state- and structure-aware constitutive models— including PM4Silt, NorSand, and structured hypoplasticity— to rigorously assess cyclic and seismic performance. This integrated methodology bridges the discrepancy between conventional analytical predictions and observed performance, enhancing foundation reliability in sensitive, metastable glaciogenic silts.

Mr. Ri Hong (Cyrus) Kee; Mr. Sergei Terzaghi

International Conference Proceedings