Large-strain behavior of liquefiable sandy sloped ground evaluated by undrained cyclic torsional shear tests (original) (raw)

The effects of liquefaction on sloped ground generally include failure due to abrupt flow sliding or a more progressive accumulation of residual deformation. Although such phenomena have been often observed following major earthquakes, their mechanisms are not fully understood yet. In this paper, based on results of a series of large-strain undrained cyclic torsional simple shear tests with initial static shear (i.e. sloped ground conditions) conducted on loose Toyoura sand specimens (relative density 44-48%), an attempt is made to address this issue. Three distinct failure mechanisms that sandy sloped ground may experience during earthquakes have been identified from the tests: cyclic liquefaction, rapid flow liquefaction and shear failure. Of these, rapid flow liquefaction is the most critical since it produces sudden development of large shear deformation (i.e. flow sliding). Alternatively, when the offset of liquefaction is not achieved, a more progressive accumulation of large ...

Prediction of earthquake-induced liquefaction for level and gently sloped ground

This paper presents a simplified procedure for predicting earthquake-induced level and sloped ground failure, namely liquefaction and shear failure. It consists of a framework where cyclic stress ratio (CSR), static stress ratio (SSR) and undrained shear strength (USS) are formulated considering simple shear conditions, which simulate field stress during earthquakes more realistically. The occurrence or not of ground failure is assessed by means of a plot ηmax (= [SSR+CSR]/USS) vs. ηmin (= [SSR-CSR]/USS), where a liquefaction zone, a shear failure zone and a safe zone (i.e. no-liquefaction and no-failure) are defined. Using this procedure, a soil column was examined and failure assessment was obtained for various soil elements, located at different depths beneath ground level. A total of 6 cases were generated by considering 2 slope inclination levels (i.e. i=0% and 5%) and 3 relative density states (i.e. Dr=25%, 50% and 75%). The 2012 Emilia Earthquake (Mw=5.9 and amax=0.26g), that...

Experimental investigation of the effect of relative densities and type of loading on sand liquefaction under irregular earthquake loading

2021

The cyclic triaxial test has been widely used to evaluate the liquefaction potential of soil over the past few decades. When a specimen is subjected to repeated shear loading, the sand particles tend to rearrange their stacking into a denser state. While drainage is prevented, the generation of pore pressure and loss of effective stress have resulted. This paper presents a systematic experimental investigation into liquefaction behavior of saturated sand subject to seismic loading with various relative densities such as 30, 50 and 70 percent. Dynamic triaxial tests were run on saturated firozkooh sand using irregular time history loads that recorded during the 1999 Chi-Chi earthquake in Taiwan. The records could be classified as shock and vibration type waveforms. The effect of each type of waveforms and relative densities of sand samples on liquefaction potential of sand was evaluated also in order to compare these results with previous studies, some cyclic tests have been done wit...

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

2015

Severe liquefaction was repeatedly observed during the 2010-2011 Christchurch earthquakes, 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 water bodies (i.e. lateral spreading) ranging from centimetres to several metres. 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 soils experience in the field during horizontal seismic shaking. Several hollow 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 level...

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