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Research papers, University of Canterbury Library

Results from cyclic undrained direct simple shear tests on reconstituted specimens of two sands from Christchurch are compared against the liquefaction resistance inferred from CPT-based empirical liquefaction triggering methods. Limitations in existing empirical triggering relationships to capture important effects related to processes which originated test soils are highlighted and discussed.

Research papers, University of Canterbury Library

Gravelly soils’ liquefaction has been documented since early 19th century with however the focus being sand-silts mixture – coarse documentation of this topic, that gravels do in fact liquefy was only acknowledged as an observation. With time, we have been impacted by earthquakes, EQ causing more damage to our property: life and environment-natural and built. In this realm of EQ related-damage the ground or soils in general act as buffer between the epicentre and the structures at a concerned site. Further, in this area, upon the eventual acknowledgement of liquefaction of soils as a problem, massive efforts were undertaken to understand its mechanics, what causes and thereby how to mitigate its ill-effects. Down that lane, gravelly soils’ liquefaction was another milestone covered in early 20th century, and thus regarded as a problematic subject. This being a fairly recent acknowledgement, efforts have initiated in this direction (or area of particle size under consideration-gravels>2mm), with this research outputs intended to complement that research for the betterment of our understanding of what’s happening and how shall we best address it, given the circumstances: socio (life) - environment (structures) - economic (cost or cost-“effectiveness’) and of course political (our “willingness” to want to address the problem). Case histories from at least 29 earthquakes worldwide have indicated that liquefaction can occur in gravelly soils (both in natural deposits and manmade reclamations) inducing large ground deformation and causing severe damage to civil infrastructures. However, the evaluation of the liquefaction resistance of gravelly soils remains to be a major challenge in geotechnical earthquake engineering. To date, laboratory tests aimed at evaluating the liquefaction resistance of gravelly soils are still very limited, as compared to the large body of investigations carried out on assessing the liquefaction resistance of sandy soils. While there is a general agreement that the liquefaction resistance of gravelly soils can be as low as that of clean sands, previous studies suggested that the liquefaction behaviour of gravelly soils is significantly affected by two key factors, namely relative density (Dr) and gravel content (Gc). While it is clear that the liquefaction resistance of gravels increases with the increasing Dr, there are inconclusive and/or contradictory results regarding the effect of Gc on the liquefaction resistance of gravelly soils. Aimed at addressing this important topic, an investigation is being currently carried out by researchers at the University of Canterbury, UC. As a first step, a series of undrained cyclic triaxial tests were conducted on selected sand-gravel mixtures (SGMs), and inter-grain state framework concepts such as the equivalent and skeleton void ratios were used to describe the joint effects of Gc and Dr on the liquefaction resistance of SGMs. Following such experimental effort, this study is aimed at providing new and useful insights, by developing a critical state-based method combined with the inter-grain state framework to uniquely describe the liquefaction resistance of gravelly soils. To do so, a series of monotonic drained triaxial tests will be carried out on selected SGMs. The outcomes of this study, combined with those obtained to date by UC researchers, will greatly contribute to the expansion of a worldwide assessment database, and also towards the development of a reliable liquefaction triggering procedure for characterising the liquefaction potential of gravelly soils, which is of paramount importance not only for the New Zealand context, but worldwide. This will make it possible for practising engineers to identify liquefiable gravelly soils in advance and make sound recommendations to minimise the impact of such hazards on land, and civil infrastructures.

Images, UC QuakeStudies

A digitally manipulated image of printer's type, spelling out "Safe Dust". The photographer comments, "After the September 2010 Christchurch earthquake liquefaction poured out of the ground mostly in the East of Christchurch. This silt, which was a form of sand was declared safe and would not harm gardens if it was spread around in moderation. After the February 2011 quake as a result of even more liquefaction and the sewers being ruptured, the liquefaction was declared as toxic. People clearing it up should wear a mask, boots and gloves especially when it had dried up and become dusty. This just so happens to be the words found on an old printing press".

Images, Alexander Turnbull Library

The cartoon shows two images of cars nose-down in ditches, the first is caused by 'liquifaction' and the second by 'stupifaction'. Context: there was another large aftershock on Boxing Day in Christchurch which resulted in quite a lot of liquefaction. There is always concern over the Christmas holidays about drinking while driving. Other Titles - Liquefaction Quantity: 1 digital cartoon(s).

Images, UC QuakeStudies

A collapsed section of road in north-east Christchurch. In the background, residents have piled liquefaction from their properties on the side of the road where it will be collected by road maintenance contractors.

Images, UC QuakeStudies

A collapsed section of road in north-east Christchurch. In the background, residents have piled liquefaction from their properties on the side of the road where it will be collected by road maintenance contractors.

Images, UC QuakeStudies

Wheelbarrows being returned to Burwood Park by students from the University of Canterbury. The students have been using them to clear liquefaction from Christchurch properties as part of the Student Volunteer Army.

Images, UC QuakeStudies

A view across Armagh Street to several damaged buildings including the Croydon House Bed and Breakfast Hotel. Liquefaction has covered the footpath and the houses have been cordoned off with emergency tape.

Images, UC QuakeStudies

Wheelbarrows being returned to Burwood Park by students from the University of Canterbury. The students have been using them to clear liquefaction from Christchurch properties as part of the Student Volunteer Army.