Slope Stabilisation using Stone Column Ground Improvement DOWNLOAD

REEVES, S | NZ GEOMECHANICS NEWS | JUNE, 2017

Ground remediation methods have been used for many years to improve ground conditions to enable development. Ground remediation has become increasingly common as industrialisation has caused rapid development of cities. Areas within cities, previously undeveloped due to adverse ground conditions, can now be remediated to enable development. Adverse ground conditions can include, but are not limited to, organic, loose, soft, liquefiable and compressible soils. Remediation methods can be used on flat and sloping sites. Sloping sites may be prone to slope instability and can require stabilisation. Ground remediation methods have also been used in areas where the soils are susceptible to liquefaction induced ground deformation. Christchurch, New Zealand, is a city where such remediation methods are being used for this and other purposes.

Stone columns have been used in Christchurch as a ground improvement method and have numerous applications for improving ground conditions, including slope stabilisation. Factors that can cause slope instability include cyclic loading (associated with earthquake loading) that can result in the generation of excess pore water pressures within the soils, which can adversely affect the shear strength of the soil. Stone columns are capable of mitigating the triggering of liquefaction by providing drainage (which helps prevent the build up of excess pore water pressures) and by increasing the stiffness of the soils, which mitigates the amount of shear strain occurring in the soils during cyclic loading. Stone columns are also capable of addressing slope stability issues such as landslide mitigation or stabilisation (Aboshi et al., 1979; Goughnour et al., 1991). Goughnour et al. (1991) state that slope instability can be improved by increasing the shear resistance of the soil along a potential slip surface by replacing or displacing the insitu soil. Improved drainage of pore water pressures can also be achieved by providing a more permeable gravel column within the slope, increasing the strength of the insitu soils and improving stability (Abramson, 2002; Deb et al., 2012). Mechanically the shear resistance of stone columns is dependent on the applied load, or normal stress, and the shear displacement at the location of the failure plane (Alfaro et al., 2009).

An initial geotechnical assessment of the site was undertaken by Fraser Thomas Ltd to characterise the subsurface conditions of the site, determine the suitability of the existing foundation systems and provide information for preliminary ground remediation design details. Stone columns were selected to remediate the soils underlying the eastern part of the site which were considered to be prone to liquefaction and slope instability (under seismic loading conditions).

Managing Risk For Workers On Slopes Following The 2016 Kaikōura Earthquakes DOWNLOAD

MUSGRAVE, R.; GERRARD, L. | 2019 PACIFIC CONFERENCE ON EARTHQUAKE ENGINEERING, AUCKLAND, NEW ZEALAND | APRIL, 2019

Disaster recovery takes place in an abnormal environment. A defining tension exists between the need to rebuild quickly, but with careful deliberation. This tension poses risks for the health and safety of workers involved, at a time when risk levels are higher than normally encountered in the workplace. A key question is how to implement “best practice” health and safety procedures to protect workers in condensed timeframes that are distinctive post-disaster. This case study on the Kaikōura Earthquake will specifically address the demands placed on rope access workers involved in the reconstruction of the distributed transport network, the hazards encountered and how risk was managed.
Key findings are that the transition from disaster response to recovery is a crucial phase of reconstruction, during which clarification of expectations and information sharing benefit workers. Quantification of risk, including a consideration of societal risk, should be a process that is both transparent and inclusive of workers, according to the law and to “best practice”. Preparation activities, such as pre-disaster training, planning and testing of emergency procedures can reduce risk.
Future research is recommended into reconstruction following the Kaikōura Earthquake to evaluate emergent safety culture and develop a model to improve risk communication through a multi-level organization to workers at field level. Improvements in the management of safety for reconstruction workers will allow for more effective and efficient recovery in future natural hazard events affecting critical lifelines and infrastructure, improving the resilience of transportation networks and communities in New Zealand.

 Low Temperature Recrystallisation Of Alluvial Gold In Paleoplacer Deposits DOWNLOAD

STEWART, J; KERR, G; PRIOR, D; HALFPENNY, A; PEARCE, M; HOUGH, R; CRAW. D | ORE GEOLOGY REVIEWS | APRIL, 2017

Detrital gold particles in paleoplacer deposits develop recrystallised rims, with associated expulsion of Ag, leading to the formation of Ag-poor rims which have been recognised in most placer gold particles around the world. Recrystallisation is facilitated by accumulation of strain energy as the gold particles are deformed, particularly on particle margins, during transportation in a fluvial system. The recrystalli- sation process ensues after sedimentary deposition and can occur at low temperatures (<40 C) over long geological time scales (millions of years). In the Otago placer goldfield of southern New Zealand, paleo- placers of varying ages contain gold with varying transport distances and these display differing degrees of rim formation. Narrow (1–10 mm) recrystallised rims with 0–3 wt% Ag formed on gold particles that had been transported <10 km from their source and preserved in Eocene sediments. Relict, coarse grained ( 100 mm) gold particle cores have 3–10 wt% Ag, which is representative of the source gold in nearby basement rocks. Gold in the Miocene paleoplacers was recycled from the Eocene deposits and transported >20 km from their source. The gold particles now have wider recrystallised rims (up to 100 mm), so that some particles have essentially no relict cores preserved. Gold in Cretaceous paleoplac- ers have wide ( 100 mm) recrystallised low-Ag rims, even in locally-derived particles, partly as a result of diagenetic effects not seen in the younger placers. Gold particles in all the paleoplacers have delicate gold overgrowths that are readily removed during recycling, but are replaced by groundwater dissolution and reprecipitation on a time scale of <1 Ma. The recrystallisation that leads to Ag-poor rim formation is primarily related to the amount of deformation imposed on particles during sedimentary transport, and is therefore broadly linked to transport distance, but is also partly controlled by the age of the paleoplacer on time scales of tens of millions of years. Gold particles that have been derived directly from basement sources can retain their original composition for long distances (tens to hundreds of kilometres) in a river system, with only minor recrystallised rim development. Gold particles that have been recycled through paleoplacer deposits can lose this link to source composition after relatively short transport distances because of extensive recrystallisation.

Evidence Of A Post-Glacial Rock Avalanche Impact On Lake Wanaka, New Zealand DOWNLOAD

HALLIDAY, G.S. | LANDSLIDES AND ENGINEERED SLOPES. EXPERIENCE, THEORY AND PRACTICE – AVERSA ET AL. (EDS)  | JUNE,2016

The Lake Wanaka Rock Avalanche is a large translational rockslide (est. volume 5–10 × 106 m) near the head of Lake Wanaka in the Southern Alps. Failure occurred in the early post-glacial era, on steep schist slopes weakened by toppling. The rock avalanche impacted the lake and a large tsunami is inferred. The trigger was likely a seismic event or extreme rainfall. There is a high probability of an
Mw 8 earthquake on the nearby Alpine Fault (Australian-Pacific plate boundary) in the next 50 years. The quake is likely to trigger rapid “first-time” rockslides around the steep lakeshore, and the lakeside town of Wanaka is potentially at risk from any earthquake generated tsunami. The public needs to be informed of the risk, and advised to immediately move from shoreline areas to higher ground after a strong earthquake,

Evidence For Coseismic Rock Avalanches And Debris Flows In Fractured Mylonites of The Alpine Fault, Paringa, New Zealand DOWNLOAD

HALLIDAY, G.S; CAMARA, A. | LANDSLIDES AND ENGINEERED SLOPES, EDS EBERHARDT ET AL. 2012 | JUNE, 2012

A 400m wide bowl-shaped depression with a volume of 3 million m3 lies at the head of a valley below Ward Hill in the Southern Alps,and intersects a similar depression to the west. The features lie 1km from the active trace of the Alpine Fault (Australian-Pacific plate boundary) in fault cataclasite and fractured mylonites of an abandoned thrust nappe. They are inferred to be source area depressions of rock avalanches, probably triggered by earthquakes (Mw 8) on the fault. The Ward Hill feature has retrogressed by rockslide- debris flows, probably triggered by both earthquakes and rainfall events. Measurements of the largest specimens of trees on the debris fan have found none likely to be older than 300 years. This may be explained by debris flows associated with the last Alpine Fault earthquake in 1717. The high probability of a new Alpine Fault earthquake presents potential debris flow hazards to buildings and an important highway.

A Small Rock Avalanche In Toppled Schist, Lake Wanaka, New Zealand DOWNLOAD

HALLIDAY, G. | LANDSLIDES AND ENGINEERED SLOPES – CHEN ET AL. (EDS) © | JUNE, 2008

A rock avalanche of 100,000 m3 occurred in a glacial valley in the Southern Alps of New Zealand in 2002. It originated on a 35◦ slope and released debris over a steep bluff. The resulting rock avalanche travelled 300 m, coming to rest on a gently sloping glacial bench. Individual boulders continued downslope and a number hit the Haast Pass Highway 600 m below. The bedrock in the region is mica schist, dipping at 50◦ into the slope. Large scale toppling is evident in the source area, with dips reduced to 20–35◦ in fractured, dilated rock. Aerial photos taken several years before the rock avalanche show a fresh scarp around the head, indicating significant slope deformation prior to failure. It is inferred that the scarp was the result of incipient sliding that eventually led to a catastrophic failure through loss of strength by strain weakening. The residual friction angle on the sliding surface is believed to be significantly less than the 35◦ slope inclination, providing conditions for rapid sliding.

Alarm Criteria and Monitoring for Hazardous Landslides , 1993 DOWNLOAD

SALT, G.S. | Opening address to ISL Landslide Workshop 1988 | 1993

Where hazardous landslides have been identified, case histories show that prediction of the onset of any rapid movement has not always been successful. Studies have been made of the precursory movements for a number of notable landslides and relevant geotechnical characteristics examined. Guidelines are provided for effective monitoring and improved evaluation of the potential for rapid landsliding of a hazardous slope.

Investigation and Remediation of Existing Landslides, 2020 DOWNLOAD

GRIMSHAW, L.G & HALLIDAY G.S

Slope Analysis for Reservoir Engineering, 1991 DOWNLOAD

SALT G.A

Landslide Mobility and Remedial Measures - DOWNLOAD

SALT G.A, Geotechnical Group, New Zealand Geological Survey, New Zealand

Jackson Creek Landslide Stabilisation - DOWNLOAD

GILLON M.D, ANDERSON C.K, HALLIDAY G.S, WATTS C.R