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Articles, Christchurch uncovered

For some of us, that title may have conjured up childhood memories of making ‘sand-saucer’ gardens for the local flower show or ‘pet and garden’ day at school. But I’ve actually something different in mind. We have found quite a … Continue reading →

Articles, Christchurch uncovered

The chilly weather in Christchurch of late has many of us dreaming of glistening seas, white sand beaches and pina coladas. A while ago, “winter is coming” gags were being fired about among the many Game of Thrones fans, and … Continue reading →

Images, UC QuakeStudies

A pile of liquefaction silt in Parklands has been decorated with a Santa hat, Christmas decorations and a pair of jandals to form a silt 'snowman'. The photographer comments, "Not the most welcome Santa to find on your doorstep on Xmas Eve. This was made out of damp liquefaction in Parklands".

Images, UC QuakeStudies

Dried liquefaction in North New Brighton. The photographer comments, "This shape formed as the liquefaction after the 23 December earthquake in Christchurch started to dry out".

Research papers, University of Canterbury Library

Well-validated liquefaction constitutive models are increasingly important as non-linear time history analyses become relatively more common in industry for key projects. Previous validation efforts of PM4Sand, a plasticity model specifically for liquefaction, have generally focused on centrifuge tests; however, pore pressure transducers installed at several free-field sites during the Canterbury Earthquake Sequence (CES) in Christchurch, New Zealand provide a relatively unique dataset to validate against. This study presents effective stress site response analyses performed in the finite difference software FLAC to examine the capability of PM4Sand to capture the generation of excess pore pressures during earthquakes. The characterization of the subsurface is primarily based on extensive cone penetration tests (CPT) carried out in Christchurch. Correlations based on penetration resistances are used to estimate soil parameters, such as relative density and shear wave velocity, which affect liquefaction behaviour. The resulting free-field FLAC model is used to estimate time histories of excess pore pressure, which are compared with records during several earthquakes in the CES to assess the suitability of PM4Sand.

Images, UC QuakeStudies

People walking amongst silt in Hagley Park shortly after the 22 February 2011 earthquake. These silt deposits were caused by the soil liquefying during the 22 February 2011 earthquake. The water flowed out, bringing sand with it.

Images, UC QuakeStudies

A pile of liquefaction silt on Medway Street is cordoned off with road cones. The photographer comments, "Piles of sand and subsiding roads at the intersection of Medway St with Woodchester Ave and Flesher Ave, 10 days after the February quake".

Images, UC QuakeStudies

People walking amongst silt in Hagley Park shortly after the 22 February 2011 earthquake. These silt deposits were caused by the soil liquefying during the 22 February 2011 earthquake. The water flowed out, bringing sand with it.

Images, UC QuakeStudies

Dried liquefaction silt in North New Brighton. The photographer comments, "The day before this was liquefaction pouring out of the ground, but within a day it has dried up and will soon turn into a gritty dust".

Images, UC QuakeStudies

A photograph of contractor Tony Fisher of Fisher Agricultural Ltd. inspecting a dug-out soil pit on a farm near River Road in Lincoln. There is a thick layer of saturated sand between the topsoil and the subsoil where the grass roots end.

Videos, UC QuakeStudies

A video of a tractor on a farm near River Road in Lincoln. The tractor is making a several passes over a sand volcano with a rotary hoe. This was one of several soil-remediation techniques tested on farms affected by the 4 September 2010 earthquake.

Videos, UC QuakeStudies

A video of a tractor on a farm near River Road in Lincoln. The tractor is passing over a large sand volcano with a power harrow. This was one of several soil-remediation techniques tested on farms affected by the 4 September 2010 earthquake.

Images, UC QuakeStudies

A van partially submerged in liquefaction. The photographer comments, "A van that unluckily drove into a hole caused by the terrible liquefaction on Beach Road, North New Brighton during the Christchurch earthquake".

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

Liquefaction silt and sand cover the lawn of a residential property. The photographer comments, "This is a garden inundated with liquefaction. Though most liquefaction is grey in Christchurch there must have been golden sandy beaches before the volcanoes erupted millions of years ago".

Images, UC QuakeStudies

Dried liquefaction silt in North New Brighton. The photographer comments, "The liquefaction after the 23 December earthquake in Christchurch started to dry out and the thicker deposits started to curl up like broken drain pipe".

Videos, UC QuakeStudies

A video about the Student Volunteer Army delivering chemical toilets and building sandbag walls in Avondale after the 22 February 2011 earthquake. The sandbag walls are being built along the banks of the Avon River to prevent flooding caused by land subsidence.

Images, UC QuakeStudies

A small wooden cross is inserted between stones laid out in the shape of a large cross. The photographer comments, "This is an Earthquake Memorial on Manchester Street, Christchurch, New Zealand. This message is on the tree next to the memorial: 'Earthquake Memorial. 185 people died as a result of the 22 February 2011 earthquake. 185 precious lives are remembered here, with 185 pieces of Halswell stone recovered from St Luke's Church, damaged beyond repair on that day. May they rest in peace. St Luke's in the City'".

Images, UC QuakeStudies

Dried liquefaction silt in North New Brighton. The photographer comments, "This is the the top layer of liquefaction that has dried up in the hot sun. A broken eggshell is around 5 times stronger than these, but a fallen leaf is just not enough to break one. You can see underneath that the heavier sandy layer of liquefaction has dried and has cracked as well".

Research papers, University of Canterbury Library

A series of undrained cyclic direct simple shear (DSS) tests on specimens of sandy silty soils are used to evaluate the effects of fines content, fabric and layered structure on the liquefaction response of sandy soils containing non-plastic fines. Test soils originate from shallow deposits in Christchurch, New Zealand, where severe and damaging manifestations of liquefaction occurred during the 2010-2011 Canterbury earthquakes. A procedure for reconstituting specimens by water sedimentation is employed. This specimen preparation technique involves first pluviation of soil through a water column, and then application of gentle vibrations to the mould (tapping) to prepare specimens with different initial densities. This procedure is applied to prepare uniform specimens, and layered specimens with a silt layer atop a sand layer. Cyclic DSS tests are performed on water-sedimented specimens of two sands, a silt, and sand-silt mixtures with different fines contents. Through this testing program, effects of density, time of vibration during preparation, fines content, and layered structure on cyclic behaviour and liquefaction resistance are investigated. Additional information necessary to characterise soil behaviour is provided by particle size distribution analyses, index void ratio testing, and Scanning Electronic Microscope imaging. The results of cyclic DSS tests show that, for all tested soils, specimens vibrated for longer period of time have lower void ratios, higher relative density, and greater liquefaction resistance. One of the tested sands undergoes significant increase in relative density and liquefaction resistance following prolonged vibration. The other sand exhibits lower increase in relative density and in liquefaction resistance when vibrated for the same period of time. Liquefaction resistance of sand-silt mixtures prepared using this latter sand shows a correlation with relative density irrespective of fines content. In general, however, magnitudes of changes in liquefaction resistance for given variations in vibration time, relative density, or void ratio vary depending on soils under consideration. Characterization based on maximum and minimum void ratios indicates that tested soils develop different structures as fines are added to their respective host sands. These structures influence initial specimen density, strains during consolidation, cyclic liquefaction resistance, and undrained cyclic response of each soil. The different structures are the outcome of differences in particle size distributions, average particle sizes, and particle shapes of the two host sands and of the different relationships between these properties and those of the silt. Fines content alone does not provide an effective characterization of the effects of these factors. Monotonic DSS tests are also performed on specimens prepared by water sedimentation, and on specimens prepared by moist tamping, to identify the critical state lines of tested soils. These critical state lines provide the basis for an alternative interpretation of cyclic DSS tests results within the critical state framework. It is shown that test results imply general consistency between observed cyclic and monotonic DSS soil response. The effects of specimen layering are scrutinised by comparing DSS test results for uniform and layered specimens of the same soils. In this case, only a limited number of tests is performed, and the range of densities considered for the layered specimens is also limited. Caution is therefore required in interpretation of their results. The liquefaction resistance of layered specimens appears to be influenced by the bottom sand layer, irrespective of the global fines content of the specimen. The presence of a layered structure does not result in significant differences in terms of liquefaction response with respect to uniform sand specimens. Cyclic triaxial data for Christchurch sandy silty soils available from previous studies are used to comparatively examine the behaviour observed in the tests of this study. The cyclic DSS liquefaction resistance of water-sedimented specimens is consistent with cyclic triaxial tests on undisturbed specimens performed by other investigators. The two data sets result in similar liquefaction triggering relationships for these soils. However, stress-strain response characteristics for the two types of specimens are different, and undisturbed triaxial specimen exhibit a slower rate of increase in shear strains compared to water-sedimented DSS specimens. This could be due to the greater influence of fabric of the undisturbed specimens.

Videos, UC QuakeStudies

A video of a dug-out soil pit on a farm near River Road in Lincoln. There is a thick layer of saturated sand between the topsoil and the subsoil where the grass roots end. The saturated soil is collapsing as a result of contractor Tony Fisher, of Fisher Agriculture Ltd, jumping lightly up and down on the edge of the pit.

Videos, UC QuakeStudies

A video of a dug-out soil pit on a farm near River Road in Lincoln. There is a thick layer of saturated sand between the topsoil and the subsoil where the grass roots end. The saturated soil is collapsing as a result of contractor Tony Fisher, of Fisher Agriculture Ltd, having jumped lightly up and down on the edge of the pit.

Videos, UC QuakeStudies

A video of contractor Tony Fisher, of Fisher Agricultural Ltd, jumping lightly up and down on the edge of a dug-out soil pit on a farm near River Road in Lincoln. There is a thick layer of saturated sand between the topsoil and the subsoil where the grass roots end. The saturated soil starts to collapse as a result of the movement.

Images, eqnz.chch.2010

Our Street - Liquefaction Sand (23.02.2011) Woolston Christchurch Canterbury New Zealand © 2011 Phil Le Cren Photo Taken With: Canon EOS 1000D + Canon EF/EF-S lenses + 10.1 effective megapixels + 2.5-inch TFT color LCD monitor + Eye-level pentamirror SLR + Live View shooting. + EOS Built-in Sensor cleaning system + ...