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Andersen, Paul
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- PublicationOpen AccessRemote sensing of induced liquefaction: TLS and SfM for a full scale blast test(2022)
; ; ; ; ; ; ; ; ; ; ; ; ; Terrestrial laser scanning (TLS) and drone-based structure-from-motion (SfM) photogrammetry allowed the study of soil de formations due to blast-induced liquefaction during an experiment carried out on 4 June 2018. The research aimed at both evaluating the measurement quality and estimating the rammed aggregate piers (RAPs) effectiveness in mitigating the effects of soil liquefaction. These effects mainly consist of subsidence and deposits of ejected and extruded materials. The comparison between multitemporal 3D models provided surface variation maps and volume changes. In addition, classical topographical leveling allowed the measurement of subsurface vertical displacement along a specific cross section. The results pointed out a significant reduction, higher than 50% of soil deformation in areas improved by RAPs installation; moreover, the corresponding volume variations were no more than about 37% of those occurred in the not improved area. Finally, a critical comparison between remote sensing and leveling suggested that surface variation maps could under-estimate the area lowering up to 15% in this kind of terrain.393 7 - PublicationRestrictedLiquefaction Mitigation of Silty Sands Using Rammed Aggregate Piers Based on Blast-Induced Liquefaction TestingTo investigate the liquefaction mitigation capability of rammed aggregate piers (RAP) in silty sand, blast liquefaction testing was performed at a soil profile treated with a full-scale RAP group relative to an untreated soil profile. The RAP group consisted of 16 piers in a 4 × 4 arrangement at 2 m center-to-center spacing extending to a depth of 9.5 m. Blasting around the untreated area induced liquefaction (ru ≈ 1.0) from a 3 to 11 m depth, producing several large sand boils and causing a settlement of 10 cm. In contrast, the installation of the RAP group reduced excess pore water pressure (ru ≈ 0.75), eliminated sand ejecta, and reduced the average settlement to between 2 and 5 cm when subjected to the same blast charges. Although the liquefaction-induced settlement in the untreated area could be accurately estimated using an integrated cone penetration test (CPT)-based settlement approach, settlement in theRAPtreated area was significantly overestimated with the same approach, even after considering RAP treatment-induced densification. Analyses indicate that settlement after RAP treatment could be successfully estimated from liquefaction-induced compression of the sand and RAP acting as a composite material. This test program identifies a mechanism that explains how the settlement was reduced for the RAP group despite the elevated ru values in the silty sands that are often difficult to improve with vibratory methods.
48 1 - PublicationOpen AccessBlast-induced liquefaction in silty sands for full-scale testing of ground improvement methods: Insights from a multidisciplinary study(2020)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; In the engineering geology field increased attention has been posed in recent years to potential liquefaction mitigation interventions in susceptible sand formations. In silty sands this is a major challenge because, as the fines content increases, vibratory methods for densification become progressively less effective. An alternative mitigation technique can be the installation of Rammed Aggregate Pier® (RAP) columns that can increase the resistance of the soil, accounting for its lateral stress increase and for the stiffness increase from soil and RAP composite response. To investigate the influence of these factors on liquefaction resistance, full-scale blast tests were performed at a silty sand site in Bondeno (Ferrara, Italy) where liquefaction was observed after the 2012 Emilia-Romagna earthquake. A multidisciplinary team of forty researchers carried out devoted experimental activities aimed at better understanding the liquefaction process at the field scale and the effectiveness of the treatment using inter-related methods. Both natural and improved areas were investigated by in-situ tests and later subjected to controlled blasting. The blast tests were monitored with geotechnical and geophysical instrumentation, topographical surveying and geological analyses on the sand boils. Results showed the RAP effectiveness due to the improvement of soil properties within the liquefiable layer and a consequent reduction of the blast-induced liquefaction settlements, likely due to soil densification and increased lateral stress. The applied multidisciplinary approach adopted for the study allowed better understanding of the mechanism involved in the liquefaction mitigation intervention and provided a better overall evaluation of mitigation effectiveness2131 40