Claudio Cappellaro

This work stems from the curiosity stimulated by a paper by Yttrup and Abramsson, which appeared in the journal Australian Geomechanics in 2003. Their work proposes a kinematic limit analysis method to compute the ultimate strength of steel screw piles in sand when first the bending and then the plastic collapse of the pile helix occurs. It is accompanied by insightful comments drawn from geotechnical design experience. The paper has both academic and professional impact as it is cited in scientific journals and used in engineering practice in Australia and New Zealand. However, the original paper is quite brief in its exposition. Here, Yttrup and Abramsson’s model is critically reconstructed, providing guidance that can help avoid potential pitfalls in its application. A variation of the model is proposed. Then, the calculated results are discussed and compared with experimental results, starting with those of the original paper. This work hopes to contribute to enhancing the appraisal, adoption, and utility of Yttrup and Abramsson’s model in design practice and in subsequent studies.

The aim of this paper is to provide new insight into the catastrophic mobility of the earthquake-induced flow-type Takanodai landslide that occurred on 16 April 2016, which had fatal consequences. A geological and geotechnical interpretation of the site conditions and experimental investigations of the mechanical behavior of weathered Kusasenrigahama (Kpfa) pumice are used to characterize the landslide failure mechanism. The results of large-strain undrained torsional shear tests indicate that Kpfa pumice has the potential to rapidly develop very large shear strains upon mobilization of its cyclic resistance. To evaluate the actual field performance, a series of new liquefaction triggering analyses are carried out. The liquefaction triggering analyses indicate that Kpfa pumice did not liquefy during the M_w6.2 foreshock event, and the hillslope remained stable. Instead, it liquefied during the M_w7.0 mainshock event, when the exceedance of the cyclic resistance of the Kpfa pumice deposit and subsequent flow-failure type of response can be considered the main cause of the landslide. Moreover, the combination of large cyclic stress ratios (CSR = 0.21–0.35)—significantly exceeding the cyclic resistance ratio CRR = 0.09–0.13)—and static shear stress ratios (α = 0.15–0.25) were critical factors responsible for the observed flow-type landslide that traveled more than 0.6 km over a gentle sloping surface (6°–10°).