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Research papers, University of Canterbury Library

The Canterbury Earthquake Sequence 2010-2011 (CES) induced widespread liquefaction in many parts of Christchurch city. Liquefaction was more commonly observed in the eastern suburbs and along the Avon River where the soils were characterised by thick sandy deposits with a shallow water table. On the other hand, suburbs to the north, west and south of the CBD (e.g. Riccarton, Papanui) exhibited less severe to no liquefaction. These soils were more commonly characterised by inter-layered liquefiable and non-liquefiable deposits. As part of a related large-scale study of the performance of Christchurch soils during the CES, detailed borehole data including CPT, Vs and Vp have been collected for 55 sites in Christchurch. For this subset of Christchurch sites, predictions of liquefaction triggering using the simplified method (Boulanger & Idriss, 2014) indicated that liquefaction was over-predicted for 94% of sites that did not manifest liquefaction during the CES, and under-predicted for 50% of sites that did manifest liquefaction. The focus of this study was to investigate these discrepancies between prediction and observation. To assess if these discrepancies were due to soil-layer interaction and to determine the effect that soil stratification has on the develop-ment of liquefaction and the system response of soil deposits.

Images, UC QuakeStudies

Damage to River Road in Richmond. The road surface is badly cracked and slumped, and liquefaction silt covers part of the road. The photographer comments, "Liquefaction in River Rd. This is minor compared to many streets in town".

Images, UC QuakeStudies

Part of the forecourt at the Shell Shirley petrol station has lifted above the rest, after the underground petrol tanks were pushed upwards by liquefaction. Liquefaction silt covers the lower part of the forecourt. The photographer comments, "Tanks at Shell Shirley floated out of the ground".

Research papers, University of Canterbury Library

Background Liquefaction induced land damage has been identified in more than 13 notable New Zealand earthquakes within the past 150 years, as presented on the timeline below. Following the 2010-2011 Canterbury Earthquake Sequence (CES), the consequences of liquefaction were witnessed first-hand in the city of Christchurch and as a result the demand for understanding this phenomenon was heightened. Government, local councils, insurers and many other stakeholders are now looking to research and understand their exposure to this natural hazard.

Research papers, University of Canterbury Library

Earthquake-triggered soil liquefaction caused extensive damage and heavy economic losses in Christchurch during the 2010-2011 Canterbury earthquakes. The most severe manifestations of liquefaction were associated with the presence of natural deposits of clean sands and silty sands of fluvial origin. However, liquefaction resistance of fines-containing sands is commonly inferred from empirical relationships based on clean sands (i.e. sands with less than 5% fines). Hence, existing evaluation methods have poor accuracy when applied to silty sands. Also, existing methods do not quantify appropriately the influence on liquefaction resistance of soil fabric and structure, which are unique to a specific depositional environment. This study looks at the influence of fines content, soil fabric (i.e. arrangement of soil particles) and structure (e.g. layering, segregation) on the undrained cyclic behaviour and liquefaction resistance of fines-containing sandy soils from Christchurch using Direct Simple Shear (DSS) tests on soil specimens reconstituted in the laboratory with the water sedimentation technique. The poster describes experimental procedures and presents early test results on two sands retrieved at two different sites in Christchurch.

Images, UC QuakeStudies

The sewage treatment ponds in Bromley. In the distance trucks and diggers can be seen piling up liquefaction silt. The photographer comments, "Looking NW from the causeway through the sewage wetlands. Mountains of liquefaction silt are being piled up near the corner of Breezes Rd and SH74-Anzac Drive".

Images, UC QuakeStudies

Trucks and diggers build large piles of liquefaction silt. In the foreground can be seen the Bromley sewage treatment ponds. The photographer comments, "Looking NW from the causeway through the sewage wetlands. Mountains of liquefaction silt are being piled up near the corner of Breezes Rd and SH74-Anzac Drive".

Research papers, University of Canterbury Library

Earthquake-triggered soil liquefaction caused extensive damage and heavy economic losses in Christchurch during the 2010-2011 Canterbury earthquakes. The most severe manifestations of liquefaction were associated with the presence of natural deposits of clean sands and silty sands of fluvial origin. However, liquefaction resistance of fines-containing sands is commonly inferred from empirical relationships based on clean sands (i.e. sands with less than 5% fines). Hence, existing evaluation methods have poor accuracy when applied to silty sands. The liquefaction behaviour of Christchurch fines-containing (silty) sands is investigated through a series of Direct Simple Shear (DSS) tests. This type of test better resembles earthquake loading conditions in soil deposits compared to cyclic triaxial tests. Soil specimens are reconstituted in the laboratory with the water sedimentation technique. This preparation method yields soil fabrics similar to those encountered in fluvial soil deposits, which are common in the Christchurch area. Test results provide preliminary indications on how void ratio, relative density, preparation method and fines content influence the cyclic liquefaction behaviour of sand-silt mixtures depending on the properties of host sand and silt.

Images, UC QuakeStudies

Trucks and diggers build large piles of liquefaction silt. One pile has been covered with plastic sheeting, weighted down with tyres. In the foreground can be seen the Bromley sewage treatment ponds. The photographer comments, "Looking NW from the causeway through the sewage wetlands. Mountains of liquefaction silt are being piled up near the corner of Breezes Rd and SH74-Anzac Drive".

Images, UC QuakeStudies

Trucks and diggers build large piles of liquefaction silt. One pile has been covered with plastic sheeting, weighted down with tyres. In the foreground can be seen the Bromley sewage treatment ponds. The photographer comments, "Looking NW from the causeway through the sewage wetlands. Mountains of liquefaction silt are being piled up near the corner of Breezes Rd and SH74-Anzac Drive".