A novel technique for the objective assessment of particle shape is presented. The technique uses Fourier shape descriptors and image analysis of scanning electron microscope photographs of sand grains to provide an accurate quantification of particle morphology and texture. Three lower order Fourier descriptors, denoted ‘signature descriptors’, provide measures of elongation, triangularity and squareness, while an additional descriptor, denoted ‘asymmetry’, provides a measure of particle irregularity. Together, these four descriptors quantify the overall shape of soil particles (defined as ‘morphology’). A summary of higher-order descriptors provides textural information that is related to local roughness features (defined as ‘texture’). The results of studies on three silica sands (two standard, laboratory-use and one natural, unprocessed) and one carbonate sand are presented. Breakage of particles by crushing is shown to affect the morphological signature differently depending on the type of sand, though it does not significantly alter texture. The study highlights the value of microscopy, combined with image analysis, in revealing sand grain shape and texture, and shows that simple statistical tools may be used to translate the information provided by relatively few grains to that of a larger body of soil.
The presence of a pore fluid is recognized to significantly increase the mobility of saturated over dry granular flows. However, the mechanisms through which pore fluid increases mobility may not be captured in experimental flows of small volume typical of laboratory conditions. Here we present the results of dry and initially fluid saturated or “wet” experimental flows of near‐monodisperse coarse‐grained ceramic particles in a large laboratory flume for five source volumes of 0.2–1.0 m3. Measurements include flow height, velocity profile, pore pressure, and evolving solid volume fraction, as well as the final deposit shape. The dry experiments constrain the frictional properties of the common granular material and comparison with wet flows permits an independent evaluation of the interstitial fluid effects. These results demonstrate that flow dilation and strong variation in the velocity profile are directly linked to a greatly increased mobility for wet granular flows compared to dry, and a significant influence of scale as controlled by source volume on flow behavior. Excess pore pressure need not be present for these effects to occur.
On 4 September 2010, a magnitude Mw 7.1 earthquake struck the Canterbury region on the South Island of New Zealand. The epicentre of the earthquake was located in the Darfield area about 40 km west of the city of Christchurch. Extensive damage was inflicted to lifelines and residential houses due to widespread liquefaction and lateral spreading in areas close to major streams, rivers and wetlands throughout Christchurch and Kaiapoi. Unreinforced masonry buildings also suffered extensive damage throughout the region. Despite the severe damage to infrastructure and residential houses, fortunately, no deaths occurred and only two injuries were reported in this earthquake. From an engineering viewpoint, one may argue that the most significant aspects of the 2010 Darfield Earthquake were geotechnical in nature, with liquefaction and lateral spreading being the principal culprits for the inflicted damage. Following the earthquake, an intensive geotechnical reconnaissance was conducted to capture evidence and perishable data from this event. The surveys were performed on foot, by car and from a helicopter over a period of six days. A broad-brush field reconnaissance was conducted in the first two days, followed by pin-point investigations at specific locations including detailed site inspections and field testing using: Dynamic Cone Penetration Test (DCPT), Swedish Weight Sounding (SWS), and Spectral Analysis of Surface Waves (SASW). This paper summarizes the observations and preliminary findings from this early reconnaissance work.
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