Large deformation properties of reconstituted Christchurch sand subjected to undrained cyclic torsional simple shear loading

摘要

Severe liquefaction was repeatedlyobserved during the 2010-2011Christchurchearthquakes, particularly affecting deposits of fine sands and silty sands of recent fluvial or estuarine origin. The effects of liquefaction included major sliding of soil toward waterbodies (i.e. lateral spreading)rangingfrom centimetres to severalmetres. In this paper, a series of undrained cyclic torsional shear tests were conducted to evaluate the liquefaction and extremely large deformation properties of Christchurch boiled sand.In these tests, the simple shear conditions were reproduced in order to apply realistic stress conditions that soilsexperience in the field during horizontal seismic shaking. Severalhollow cylindrical medium dense specimens (Dr = 50%) were prepared by pluviation method, isotropically consolidated at an effective stress of 100 kPa and then cyclically sheared under undrained conditions up to 100% double amplitude shear strain (γDA). The cyclic strength at different levels of γDAof 7.5%, 15%, 30% and 60%, development of extremely large post-liquefaction deformation and shear strain localisation properties were assessed from the analysis of the effective stress paths and stress-strain responses. To revealpossible distinctiveness, the cyclic undrained behaviour of CHCH boiled sand was compared with that of Toyoura sandpreviously examined under similar testing conditions