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Research papers, University of Canterbury Library

Deformational properties of soil, in terms of modulus and damping, exert a great influence on seismic response of soil sites. However, these properties for sands containing some portion of fines particles have not been systematically addressed. In addition, simultaneous modelling of the modulus and damping behaviour of soils during cyclic loading is desirable. This study presents an experimental and computational investigation into the deformational properties of sands containing fines content in the context of site response analysis. The experimental investigation is carried on sandy soils sourced from Christchurch, New Zealand using a dynamic triaxial apparatus while the computational aspect is based on the framework of total-stress one-dimensional (1D) cyclic behaviour of soil. The experimental investigation focused on a systematic study on the deformational behaviour of sand with different amounts of fines content (particle diameter ≤ 75µm) under drained conditions. The silty sands were prepared by mixing clean sand with three different percentages of fines content. A series of bender element tests at small-strain range and stress-controlled dynamic triaxial tests at medium to high-strain ranges were conducted on samples of clean sand and silty sand. This allowed measurements of linear and nonlinear deformational properties of the same specimen for a wide strain range. The testing program was designed to quantify the effects of void ratio and fines content on the low-strain stiffness of the silty sand as well as on the nonlinear stress-strain relationship and corresponding shear modulus and damping properties as a function of cyclic shear strains. Shear wave velocity, Vs, and maximum shear modulus, Gmax, of silty sand was shown to be significantly smaller than the respective values for clean sands measured at the same void ratio, e, or same relative density, Dr. However, the test results showed that the difference in the level of nonlinearity between clean sand and silty sands was small. For loose samples prepared at an identical relative density, the behaviour of clean sand was slightly less nonlinear as compared to sandy soils with higher fines content. This difference in the nonlinear behaviour of clean sand and sandy soils was negligible for dense soils. Furthermore, no systematic influence of fines content on the material damping curve was observed for sands with fines content FC = 0 to 30%. In order to normalize the effects of fines on moduli of sands, equivalent granular void ratio, e*, was employed. This was done through quantifying the participation of fines content in the force transfer chain of the sand matrix. As such, a unified framework for modelling of the variability of shear wave velocity, Vs, (or shear modulus, Gmax) with void ratio was achieved for clean sands and sands with fines, irrespective of their fines content. Furthermore, modelling of the cyclic stress-strain behaviour based on this experimental program was investigated. The modelling effort focused on developing a simple constitutive model which simultaneously models the soil modulus and damping relationships with shear strains observed in laboratory tests. The backbone curve of the cyclic model was adopted based on a modified version of Kondner and Zelasko (MKZ) hyperbolic function, with a curvature coefficient, a. In order to simulate the hysteretic cycles, the conventional Masing rules (Pyke 1979) were revised. The parameter n, in the Masing’s criteria was assumed to be a function of material damping, h, measured in the laboratory. As such the modulus and damping produced by the numerical model could match the stress-strain behaviour observed in the laboratory over the course of this study. It was shown that the Masing parameter n, is strain-dependent and generally takes values of n ≤ 2. The model was then verified through element test simulations under different cyclic loadings. It was shown that the model could accurately simulate the modulus and the damping simultaneously. The model was then incorporated within the OpenSees computational platform and was used to scrutinize the effects of damping on one-dimensional seismic site response analysis. For this purpose, several strong motion stations which recorded the Canterbury earthquake sequence were selected. The soil profiles were modelled as semi-infinite horizontally layered deposits overlying a uniform half-space subjected to vertically propagating shear waves. The advantages and limitations of the nonlinear model in terms of simulating soil nonlinearity and associated material damping were further scrutinized. It was shown that generally, the conventional Masing criteria unconservatively may underestimate some response parameters such as spectral accelerations. This was shown to be due to larger hysteretic damping modelled by using conventional Masing criteria. In addition, maximum shear strains within the soil profiles were also computed smaller in comparison to the values calculated by the proposed model. Further analyses were performed to study the simulation of backbone curve beyond the strain ranges addressed in the experimental phase of this study. A key issue that was identified was that relying only on the modulus reduction curves to simulate the stress-strain behaviour of soil may not capture the actual soil strength at larger strains. Hence, strength properties of the soil layer should also be incorporated to accurately simulate the backbone curve.

Images, UC QuakeStudies

Damage to buildings along Norwich Quay in Lyttelton. To the left is the Lyttelton Hotel with a crumbled top. Bricks have fallen on the awning and all along the footpath. To the right is a cafe that was damaged severely in the earthquake. The front wall of the top storey has crumbled onto the street, crushing a car. Wire fencing and road cones have been used to create a cordon around the buildings.

Images, UC QuakeStudies

Damage to buildings along Norwich Quay in Lyttelton. To the left is the Lyttelton Hotel with a crumbled top. Bricks have fallen on the awning and all along the footpath. To the right is a cafe that was damaged severely in the earthquake. The front wall of the top storey has crumbled onto the street, crushing a car. Wire fencing and road cones have been used to create a cordon around the buildings.

Images, UC QuakeStudies

Damage to Lyttelton following the 22 February 2011 earthquake. The fish and chip shop on London Street (centre) has a collapsed gable and awning. Bricks, plaster and wood are lying where they fell on the footpath, as well as the broken sign. To the left is the Lava Bar which suffered severe structural damage after the earthquake. To the right, the Coastal Living store can be seen which was open after the September earthquake but pulled down after February.

Audio, Radio New Zealand

Rural Maori children in the Gisborne region will be visited at school by Health Officials in an effort to reduce the incidence of rheumatic fever; A designers' group says the Canterbury earthquake has created an opportunity for the local iwi to put its architectural stamp on the new Christchurch; Workers who carved the pou on Northland's popular new cycle trail will meet the Prime Minister later this month; Kaitaia people will be among the first in the country to see a long-awaited film about the much-loved comedian - Billy T James.

Audio, Radio New Zealand

When the 6.3 magnitude earthquake struck Christchurch at 2:20 on Monday afternoon Barry Ross was outside his home at Godley Head on the Port Hills, where is he is the Department of Conservation caretaker. Barry's house is thought to be the closest to the epicentre that day and such was the force of the quake he was thrown to the ground and some of the cliff nearby fell away. He lost power and water for a few days but now he's back home, clearing up and determined to get on with life.

Audio, Radio New Zealand

Christchurch has a big bill to contend with, if it still wants the multi-use stadium that's been in the works since the earthquakes 11 years ago. The problem-plagued project has blown out another $150 million, meaning it's going to cost $680 million and counting. The finish date's been pushed out too - to April 2026. Christchurch City Council's punting the hefty decision making back to the ratepayers. The options - increase the budget, scale back the project, or halt work altogether. Tessa Guest reports, and Crusaders CEO Colin Mansbridge talks to Lisa Owen.

Images, UC QuakeStudies

A photograph of the earthquake damage to R&R Sport on the corner of Colombo and Tuam Streets. Most of the side wall has crumbled, the bricks spilling onto the footpath below. Plywood and plastic sheeting has been used to weather proof the building. Wire fencing and road cones have been placed around the building as a cordon. A cherry picker is parked on the footpath in between the building and the fence.

Images, UC QuakeStudies

Detail of damage to the former Princess Cinema in New Brighton. Bricks have fallen from the wall, exposing the interior. The photographer comments, "This is the back of the old Princess Cinema in New Brighton after the earthquake in Christchurch, New Zealand on 22 February. The bricks seem to be just on the edge of falling. This building has now been knocked down as it was so dangerous".

Images, UC QuakeStudies

A photograph of the earthquake damage to the Country Theme store on the corner of Manchester and St Asaph Streets. Sections of the second storey walls have crumbled, and the bricks have fallen onto the footpath below. Wire fences have been placed around the building as a cordon. Red stickers on the front door and the wire fence indicate that the building is not safe to enter.

Images, UC QuakeStudies

A photograph looking north down Gayhurst Road, taken from the side of the bridge over the Avon River. Residential properties used to line the left-hand side of the road, and St Paul's church once stood on the corner. This was before the land was red-zoned as a result of the 2010 and 2011 Canterbury earthquakes. Separated cycle ways have recently been installed on both sides of the road. The photograph was modelled off an image taken by Mark Lincoln in September 2010.

Images, UC QuakeStudies

A photograph looking north down Gayhurst Road, taken from the side of the bridge over the Avon River. Residential properties used to line the left-hand side of the road, and St Paul's church once stood on the corner. This was before the land was red-zoned as a result of the 2010 and 2011 Canterbury earthquakes. Separated cycle ways have recently been installed on both sides of the road. The photograph was modelled off an image taken by Mark Lincoln in September 2010.

Images, UC QuakeStudies

A photograph looking north down Gayhurst Road, taken from the side of the bridge over the Avon River. Residential properties used to line the left-hand side of the road, and St Paul's church once stood on the corner. This was before the land was red-zoned as a result of the 2010 and 2011 Canterbury earthquakes. Separated cycle ways have recently been installed on both sides of the road. The photograph was modelled off an image taken by Mark Lincoln in September 2010.

Images, UC QuakeStudies

A photograph of a block of earthquake-damaged rooms at Stonehurst Accommodation on Gloucester Street. The bottom storey of the block has collapsed and the remaining rooms are now resting on an incline. The front walls of these rooms have also collapsed and the rubble has spilled in to the courtyard in front. Cordon tape has been draped across the courtyard in front of the rubble. To the left there is a car parked amongst the rubble.

Images, UC QuakeStudies

A view of the ICTS building at the University of Canterbury, seen from level 7 of the James Hight building. The photographer comments, "First looks at our new temporary (maybe) office space. Our group will stay here until April or May 2011, then will move to another floor in the Central Library. We look down on the IT Building, which is doomed. The ugly draughty IT building is going to be demolished in the next campus revamp. The 'Butterfly Building' behind, originally the mainframe computer centre, will remain, as it's architecturally significant, apparently".

Images, UC QuakeStudies

A photograph of the earthquake damage to the Montgomery's Building on the corner of Colombo and Tuam Streets. Large sections of the façade have collapsed, exposing the inside of the building. The bricks and other rubble have mostly been cleared from the footpath and street in front. Wire fences have been placed around the building as a cordon. In the distance there is a large pile of bricks on a property where another building has collapsed.

Images, UC QuakeStudies

A sewage pumping station on Avonside Drive has been lifted out of the ground by liquefaction. In the background, the damaged Snell Place footbridge over the Avon River is closed off with cordon fencing. The photographer comments, "A Sunday afternoon ride to New Brighton, then back via Aranui, Wainoni, Dallington, and Richmond. Not a cheerful experience. Dallington footbridge. The two pieces of this foot bridge have moved towards each other, so the bridge has developed quite a peak. The sewage pumping station has been heaved out of the ground by hydraulic pressure during quakes".

Audio, Radio New Zealand

Little is known about The Wizard of New Zealand who took centre stage in Christchurch's Cathedral Square from the 70s until the Christchurch earthquakes in 2011, which saw the city in a state of disrepair. A man who challenged political, social and cultural ideology, The Wizard posed provocative questions in this public space, much to the delight, and sometimes dismay, of passersby. But the background to why The Wizard was there in the first place has been something of a mystery... until now. Sonia Yee finds out more in this episode of Eyewitness.

Audio, Radio New Zealand

DAVID SHEARER to the Prime Minister: Does he stand by his statement: “I’m not going to go and relitigate every comment I’ve made prior to this point because I don’t think that would actually be helpful”? TODD McCLAY to the Minister of Finance: How has the Government balanced the need for responsible fiscal management with its continued support for New Zealand families? METIRIA TUREI to the Prime Minister: Ka whakatau a ia i te kōrero i whakaputaina māna, arā, “I do not accept the view that we are a deeply unequal country. I do not think the evidence suggests that, and people drawing that conclusion are wrong”? Translation: Does he stand by the statement made on his behalf, “I do not accept the view that we are a deeply unequal country. I do not think the evidence suggests that, and people drawing that conclusion are wrong”? JACQUI DEAN to the Minister for Canterbury Earthquake Recovery: What recent announcements has the Government made around the rebuild of the Christchurch city centre? Hon PAREKURA HOROMIA to the Minister of Māori Affairs: Does he stand by all his statements? MAGGIE BARRY to the Minister of Health: Has any progress been made on the Zero Fees for Under Sixes scheme taking coverage over and above the 70 percent of children covered in 2008 achieved by the previous Government? Hon TREVOR MALLARD to the Associate Minister of Education: What progress has been made on the charter schools policy? ALFRED NGARO to the Minister for Social Development: What announcements has she made on the release of the White Paper for Vulnerable Children? CLARE CURRAN to the Minister of Transport: Does he stand by his statement in his press release of 24 May 2012 that “KiwiRail has successfully undertaken a significant investment programme over the previous two years, including: New locomotives and wagons, and refurbishment of the current locomotive fleet”? Rt Hon WINSTON PETERS to the Minister of Finance: Does he stand by the statement made on his behalf that there are no plans to sell KiwiRail? MELISSA LEE to the Minister for Ethnic Affairs: What reports has she received about the Office of Ethnic Affairs working with the Red Cross? JULIE ANNE GENTER to the Minister of Transport: What alternatives did the Government investigate before committing itself to the Road of National Significance between Puhoi and Wellsford, which is now projected to cost $1.76 billion up from $1.69 billion two years ago?

Images, UC QuakeStudies

A photograph of the partially-deconstructed NewstalkZB Building on Worcester Street. The windows on the south side of the building have been removed, exposing the inside. A crane can be seen in the background.

Images, UC QuakeStudies

A photograph of the partially-deconstructed NewstalkZB Building on Worcester Street. The windows on the south side of the building have been removed, exposing the inside. A crane can be seen in the background.

Images, UC QuakeStudies

A photograph of earthquake damage to the Crown Masonic Lodge on Wordsworth Street, also known as the Freemasons Centre. Sections of the brick wall at the front of the building have collapsed. The entranceway is supported with wooden bracing.