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

PPT Presentation

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The presentation examines rate-aware pile design in glaciogenic silts, where soil fabric and installation method strongly influence settlement and pile performance.<br /><br />The deposit consists of late-Pleistocene rock-flour silts with an open, anisotropic, weakly bonded, metastable fabric. Intact soil has high small-strain stiffness, but disturbance can cause contractive collapse and strain softening. Baseline predictions estimated 50–70 mm of free-field settlement under serviceability-level shaking and 310–465 mm under more severe events, assuming liquefaction susceptibility to 16 m depth.<br /><br />In-situ tests showed a rate effect: standard-rate CPTu penetration generated high excess pore pressure, while slower CPT penetration recorded greater resistance. This highlights the importance of accounting for penetration rate and soil state when interpreting test results.<br /><br />The reported case involved about 160 mm of settlement. The authors attribute this response to high-energy, closed-ended pile driving, which remoulded the silt near the pile toe toward its critical state. This reduced stiffness, resulted in toe-dominated pile behaviour, and prevented shaft setup. By contrast, lower-energy vibratory installation preserved more of the soil structure, enabled shaft setup, and was associated with millimetre-level movements.<br /><br />The key design message is that performance in fabric-sensitive silts and soft clays depends not only on a nominal strength value, but also on whether installation preserves or remoulds the soil fabric.

Keywords

rate-aware pile design

glaciogenic silts

soil fabric

pile installation method

settlement

CPTu penetration rate

excess pore pressure

soil remoulding

pile performance

liquefaction susceptibility