Depositional environment effects on observed liquefaction performance in silt swamps during the Canterbury earthquake sequence. Issue 107 (April 2018)

• Record Type: Journal Article
• Authors: Beyzaei, Christine Z.; Bray, Jonathan D.; van Ballegooy, Sjoerd; Cubrinovski, Misko; Bastin, Sarah
• Is Part Of: Soil dynamics and earthquake engineering. Issue 107(2018)
• Page Start: 303
• Page End: 321
• Publication Date: 2018-04
• Subjects: Depositional environment -- Liquefaction -- Silty soils -- Thin layers -- Stratigraphy -- Swamp -- Groundwater table fluctuation; Soil dynamics -- Periodicals; Earthquake engineering -- Periodicals; Sols -- Dynamique -- Périodiques; Génie parasismique -- Périodiques; 624.176205
• DOI: 10.1016/j.soildyn.2018.01.035
• Languages: English
• ISSNs: 0267-7261

Abstract

Abstract: Stratified silty soils deposited in back-swamp settings are shown through regional CPT-based analyses to have mitigating effects on the manifestation of liquefaction in Christchurch. Liquefaction triggering within these deposits is inadequately captured by simplified liquefaction assessment methodologies. Differing near-surface geology and depositional environments indicated in historical documents explain in part the limitations of current liquefaction evaluation procedures in southwest Christchurch. The historical swamp areas are shown through a regional CPT study to contain stratified silt/sand deposits or thick silt layers. Consideration of depositional environment distinguishes between liquefaction performances that are not able to be differentiated through the CPT-based liquefaction triggering assessment alone. CPT resolution is shown to be insufficient to capture the thin layering at these stratified sites, and the simplified liquefaction assessment methods do not take into account the effects of the stratification on pore water pressure movement within a soil profile. Instead, continuous sampling and careful logging of high-quality samples provide important insights on stratification at these silty soil swamp sites and in discerning differences in stratigraphy resulting from differences in depositional environment. Highlights: Liquefaction evaluations do not match liquefaction observations at silty soil sites. Liquefaction triggering procedures do not capture key depositional factors. Stratified silt swamp deposits mitigate surface manifestations of liquefaction. Careful logging of continuous, high-quality samples provides important insights. CPT or SPT studies should be supplemented by geologic studies at silty soil sites.