7.a Geotechnical Engineering
Soil liquefaction and slope failures during the 2011 Tohoku, Japan Earthquake
R.P. Orense
A devastating earthquake hit the Tohoku and Kanto regions of Japan on 11 March 2011, causing extensive damage to life and property as a result of large-scale tsunami and damage to nuclear power plants. Many slope failures occurred in hilly areas, such as in residential lands on valley fills in Miyagi Prefecture close to the epicentre.
Moreover, although located about 380 km away from the epicentre, many residential and commercial buildings and lifeline facilities in Tokyo Bay area suffered extensive damage due to soil liquefaction and associated ground deformations. This paper discusses the results of the damage investigation conducted in the area after the earthquake, with emphasis on slope failures in valley fills and liquefaction-induced damage to buildings, roads, lifelines and other infrastructure. In addition, the performance of ground improved by various remediation techniques is discussed. Finally, lessons learned from the event are summarised.
Application of new Gel-push sampling procedure to obtain high quality laboratory test data for advanced geotechnical analyses
M.L. Taylor, M. Cubrinovski & I. Haycock
In Mid 2011, during the 2010-2012 Canterbury earthquake sequence, a site investigation programme was undertaken within the Christchurch CBD to characterise the engineering behaviour of the soils responsible for the observed ground performance. This paper presents the trialling of new Gel-push sampler technology recently acquired by the University of Canterbury for obtaining high quality undisturbed samples of cohesionless materials from liquefaction prone sites. The sampler technology and methodology are discussed followed by presentation of initial results of shear wave velocity testing on samples with comparison to field measurements, providing indicative quality of the samples and the ability of the sampler to achieve high quality samples suitable for liquefaction strength testing.
Full Scale Testing of Ground Remediation Options for Residential Property Repair following the Canterbury Earthquakes
H.J. Bowen, P.J. Millar & N.J. Traylen
A series of full scale tests have been undertaken to assess the performance of ground strengthening methods to improve seismic performance of liquefiable soils in the Christchurch area. The tests used sequences of explosive charges to simulate seismic shaking at levels representative of SLS and ULS events and induced liquefaction and expulsion of sand. Monitoring included measurement of ground motion, pore pressure development and settlements. The results have determined that the treatment of the upper crust by densification or cement stabilisation is an effective method of reducing settlements and preventing surface expulsion of liquefiable soil. Other options including deep soil mixing and a perimeter curtain wall were less effective but achieved the proposed design objectives and also have application.
Earthquake geotechnical engineering issues associated with design of Waikato Expressway.
A. Murashev, C. Keepa & G. Hayes
The Waikato Expressway is being constructed in a number of sections. Opus has been involved in the scheme assessment and specimen design stages for the Hamilton and Cambridge Bypass sections and is currently part of the alliance team constructing the Te Rapa Bypass section. These sections of the Waikato Expressway are constructed on the thick alluvial sands and silts. The deep sediments and complex ground water conditions in the Waikato basin provide challenges for seismic design.
Geotechnical assessment of the gully soils is complicated by the steep gully slopes, interbedded nature of the soils, perched and artesian water tables. The geotechnical earthquake engineering challenges involved management of liquefaction hazards and performance based design of slopes and bridge foundations. This paper discusses the liquefaction susceptibility of the Hinuera deposits, foundation concepts for bridges including discussion on soil structure interaction and managing liquefaction risks at bridges. Bridge foundation performance was analysed using finite element time history analysis.
Progressive mainshock-aftershock damage in Christchurch, New Zealand
H.B. Mason & Z. Chen
Aftershocks following an earthquake can be damaging to the built environment, as observed in New Zealand during 2010 and 2011. In this paper, the aftershock sequence is discussed and a soil-foundation-structure numerical model is introduced. The numerical model represents a 9-story, inelastic, steel, eccentrically-braced frame structure founded on a shallowly-embedded mat foundation. Soil-foundation-structure interaction effects were explicitly considered by employing nonlinear Winkler springs. The model was subjected to the 22 February 2011 Christchurch Earthquake and two larger aftershocks, and the progressive seismic damage was tracked. Results show that for this type of structure, the seismic damage caused by the aftershocks is negligible compared to the mainshock. More modelling effort is needed to examine the progressive damage of other soil-foundation-structure models.
Pre and post-earthquake dynamic analysis of an RC building including soil-structure interaction
F. Butt & P. Omenzetter
This paper presents a study of the dynamic analysis of a building before and after devastating earthquakes using system identification. The eight storey reinforced concrete building is instrumented with 10 accelerometers. The time domain N4SID system identification technique was used to obtain the frequencies, damping ratios and mode shapes considering fixed and pseudo flexible base models taking into account the soil-structure-interaction. The response of the building before and after the Darfield (04/09/2010) and Christchurch (22/02/2011) earthquakes was ascertained to evaluate the significant changes in the behaviour. It was concluded from the investigation that monitoring the seismic response of the building is useful for a better understanding of its behaviour during earthquakes, and also that the participation of soil is significant towards the seismic response of the building and it should be considered in models to simulate the real behaviour.
Detailed Seismic Assessment and Seismic Improvements of Market Road Underpass
D. Novakov, D. Ashby, T. Chin, A. George & G. Gregg
A seismic improvement works were completed on Market Road Underpass (MRU) in Auckland. The bridge consists of three structures: The Underpass, the Motorway Off-ramp and the Rail Overbridge. In the NZTA's "Seismic Screening" of all state highway bridges MRU ranked 4th in its programme for further investigation and retrofitting. Assessment of seismic capacity of the bridge was completed by Opus in 2004 and 2008. The adopted benchmark event against which the performance of the bridge has been assessed is seismic shaking with a return period of 1000 years together with collapse avoidance under the 2500 year return period shaking. Seismic performance of the bridge under the above levels of shaking was determined to be inadequate, limited predominantly by the shear capacity of the beam-column joints and the abutment columns and stability of the unreinforced masonry pier common to the Underpass and the Rail Overbridge. Seismic improvement of the bridge was successfully completed in mid 2011 and included installation of new piles at one of the abutments, new auxiliary support at the critical pier common to the Underpass and the Rail Overbridge, strengthening of the pier beam-column joints, and installation of new shear keys at the Off-ramp. Works completed will improve the expected seismic performance of the bridge to the level required. Overall cost of the improvements was about NZ$1.5 million.