Following the Mw 6.2 Christchurch Earthquake on 22 February 2011, extensive ground cracking in loessial soils was reported in some areas of the Port Hills, southeast of central Christchurch. This study was undertaken to investigate the mechanisms of earthquake-induced ground damage on the eastern side of the Hillsborough Valley. A zone of extensional cracking up to 40m wide and 600m long was identified along the eastern foot-slope, accompanied by compression features and spring formation at the toe of the slope. An engineering geological and geomorphological model was developed for the eastern Hillsborough Valley that incorporates geotechnical investigation data sourced from the Canterbury Geotechnical Database (CGD), the findings of trenching and seismic refraction surveying carried out for this research, and interpretation of historical aerial photographs. The thickness and extent of a buried peat swamp at the base of the slope was mapped, and found to coincide with significant compression features. Ground cracking was found to have occurred entirely within loess-colluvium and to follow the apices of pre-1920s tunnel-gully fan debris at the southern end of the valley. The ground-cracking on the eastern side of the Hillsborough Valley is interpreted to have formed through tensile failure of the loess-colluvium. Testing was carried out to determine the tensile strength of Port Hills loess colluvium as a function of water content and density, in order to better understand the occurrence and distribution of the observed ground cracking. A comprehensive review of the soil tensile strength testing literature was undertaken, from which a test methodology was developed. Results show remoulded loess-colluvium to possess tensile strength of 7 - 28 kPa across the range of tested moisture contents (10-15%) and dry densities (1650-1900kg/m3). A positive linear relationship was observed between tensile strength and dry density, and a negative linear relationship between moisture content and tensile strength. The observed ground damage and available geotechnical information (inclinometer and piezometer records provided by the Earthquake Commission) were together used to interpret the mechanism(s) of slope movement that occurred in the eastern Hillsborough Valley. The observed ground damage is characteristic of translational movement, but without the development of lateral release scarps, or a basal sliding surface - which was not located during drilling. It is hypothesised that shear displacement has been accommodated by multiple slip surfaces of limited extent within the upper 10m of the slope. Movement has likely occurred within near-saturated colluvial units that have lost strength during earthquake shaking. The eastern Hillsborough Valley is considered to be an ‘incipient translational slide’, as both the patterns of damage and shearing are consistent with the early stages of such slide development. Sliding block analysis was utilised to understand how the eastern Hillsborough Valley may perform in a future large magnitude earthquake. Known cumulative displacements of ~0.3m for eastern Hillsborough Valley during the 2010-2011 Canterbury Earthquake Sequence were compared with modelled slope displacements to back-analyse a lower-bound yield acceleration of 0.2 - 0.25g. Synthetic broadband modelling for future Alpine and Hope Fault earthquakes indicates PGAs of approximately 0.08g for soil sites in the Christchurch area, as such, slope movement is unlikely to be reactivated by an Alpine Fault or Hope Fault earthquake. This does not take into account the possible role of strength loss due to excess pore pressure that may occur during these future events.
The State Services Commission is investigating Canterbury earthquake insurer Southern Response. A new pharmacy council ethics code has upset doctors.
Photograph captioned by Fairfax, "Nick Rogers, geotechnical specialist, explains the EQC plan to remediate land damaged in the Canterbury earthquake".
Photograph captioned by Fairfax, "Nick Rogers, geotechnical specialist, explains the EQC plan to remediate land damaged in the Canterbury earthquake".
Photograph captioned by Fairfax, "Removal of 4 September earthquake-damaged chimney of the 145 year old Canterbury Provincial Council Building".
Photograph captioned by Fairfax, "Nick Rogers, geotechnical specialist, explains the EQC plan to remediate land damaged in the Canterbury earthquake".
Photograph captioned by Fairfax, "Nick Rogers, geotechnical specialist, explains the EQC plan to remediate land damaged in the Canterbury earthquake".
Photograph captioned by Fairfax, "Removal of 4 September earthquake-damaged chimney of the 145 year old Canterbury Provincial Council Building".
Photograph captioned by Fairfax, "Removal of 4 September earthquake-damaged chimney of the 145 year old Canterbury Provincial Council Building".
Photograph captioned by Fairfax, "Removal of 4 September earthquake-damaged chimney of the 145 year old Canterbury Provincial Council Building".
Photograph captioned by Fairfax, "Removal of 4 September earthquake-damaged chimney of the 145 year old Canterbury Provincial Council Building".
Photograph captioned by Fairfax, "Removal of 4 September earthquake-damaged chimney of the 145 year old Canterbury Provincial Council Building".
It all started two years ago today at 4:36 in the morning, a magnitude 7.1 earthquake shook Canterbury.
In the wake of the February disaster, the Canterbury Earthquake Recovery Authority was set up to coordinate the overall recovery.
An economic recovery programme for Christchurch - including multi-billion dollar investments - has been announced by the Canterbury Earthquake Recovery Minister.
Parliament is debating under urgency the Canterbury Earthquake Recovery Bill, but the Greens plan to vote against the first reading.
The head of the Canterbury Earthquake Recovery Authority, Roger Sutton, flew over the quake-hit city after today's first shake.
The Government is welcoming a report from the Canterbury Earthquake Royal Commission that calls for urgent changes to building standards.
While buildings and businesses bore the brunt of the Canterbury earthquake, some popular outdoor recreation places have also been hit.
One of the two victims from Monday's earthquake lived in the remote alpine settlement of Mount Lyford in north Canterbury.
An overseas expert has defended the structural engineer who declared the Canterbury Television building sound after the September 2010 earthquake.
The Royal Commission into the Canterbury earthquakes has been told of new deficiencies in the structure of the CTV Building.
Sumner residents whose properties have been condemned have vented their frustrations at a meeting with the Canterbury Earthquake Recovery Authority.
Photograph captioned by Fairfax, "Nick Rogers, geotechnical specialist, explains the EQC plan to remediate land damaged in the Canterbury earthquake".
Photograph captioned by Fairfax, "Removal of 4 September earthquake-damaged chimney of the 145 year old Canterbury Provincial Council Building".
Photograph captioned by Fairfax, "Mary heading to Timaru to sub after the closure of The Press building following Canterbury's earthquakes".
Photograph captioned by Fairfax, "Steve McCarthy, assistant rescue manager with Civil Defence during a press conference following Canterbury's earthquake".
Canterbury homeowners are questioning the validity of a survey which was supposed to independently test the quality of earthquake repairs.
Kaikōura's struggling business community wants a container mall similar to Christchurch's re-start mall set up after the Canterbury earthquakes.
Haydon Wilson of Kensington Swan discusses the ongoing legal ramifactions of the Canterbury Earthquakes, in particular the Quake Outcasts case.