Geotechnical proficiency testing for field-based soil plasticity and expansivity assessment: do we need it?
Author:  Gilbert, C.D., and Vaughan, S.A.
Presented/Published:  Proceedings of the 12th ANZ Young Geotechnical Professionals Conference - 12YGPC, Hobart, Tasmania, Australia, 2018

The intention of this study was to assess whether proficiency testing, as outlined in ISO/IEC 17043:2010, could be beneficial for field assessment of selected soil properties, similar to the laboratory ‘interlab’ system.
The geotechnical profession is unique amongst engineering disciplines, as project-specific specialised quantitative testing is not always used to establish material properties used for analysis and design. For the numerous smaller projects, plasticity, for example, is typically assessed on-site through experience as opposed to laboratory testing. This experience is specific to each consultant and, in conjunction with no requirements for inter-consultant comparison, presents the position where industry-wide consistency is unknown.
The study undertook a proficiency test on soil plasticity logging between various geotechnical consultants using the procedure outlined in ISO/IEC 17043:2010 section 4.4. Participating consultants received a uniform soil sample for logging by at least two staff members. The participating companies and engineers were kept anonymous throughout the study. The participants were also asked to interpret the soil class according to AS 2870:2011. Results were collated and compared to a laboratory tested control sample to assess logging and interpretation consistency.
The implications of any variance between participants and laboratory tests were also explored. Whilst plasticity was the parameter chosen for investigation, the results of the exercise provide an insight into whether proficiency testing by a regulatory body or professional organisation would benefit the industry and its customers. Processes that reduce the inconsistency and variance in the field-based assessment of soil performance characteristics could reduce the risk of excessive conservatism or the risk of underestimating plasticity and underspecifying foundations.

Geological inputs into the Waipori dams stability review
Author:  King, L.A., and Fritz, T.
Proceedings of the 20th NZGS Geotechnical Symposium. Eds. GJ Alexander & CY Chin, Napier, 2017
Waipori, concrete arch dam, geological appraisal, geological mapping, dam stability
Three concrete arch dams (Mahinerangi Dam, Waipori Nos. 2 and 4) and one gravity weir (Waipori No.3) of varying ages provide the impoundments for the Waipori Hydro-electric Scheme. Findings of a comprehensive dam safety review carried out in 2012 indicated some knowledge shortcomings when assessing the stability of the No.2 and No.4 structures. It was proposed to fill these knowledge gaps by carrying out a multi-staged assessment of the two structures comprising a comprehensive desk study and gap analysis; fieldwork comprising detailed engineering geological mapping and intrusive geological investigation; determination of analysis parameters, and assessment of kinematically feasible failure modes to inform a Finite Element Method model build and analysis.
Whilst regulatory requirements are entirely different today to when the dams were initially constructed (1914 and 1956) and given that records of construction are minimal, this project demonstrates the importance of carrying out thorough reviews of historical records where they exist, prior to launching into deep and expensive site investigation. The reviews turned up several important documents which reduced site investigation inputs later and aided in building a clearer understanding of the history of work at the sites.
mapping was a key element to understanding risk at the sites in a geologically complex setting, more so than intrusive investigation, which was carried out primarily to gain samples for strength testing. mapping and traditional geological analysis tools such as aerial photo interpretation, stereonets and assessment of rock quality from boreholes have been critical for provision of rock mass properties and determination of potential kinematically feasible failure mechanisms of these ageing assets. The first stages of work have provided valuable inputs into the forthcoming finite element analysis (FEA).

Anzac Cliffs - Geotechnical aspects of cliff stabilisation works
Author:  Orgias, S.R., Tate, D.R., and Pranjoto, S.
Proceedings of the 20th NZGS Geotechnical Symposium. Eds. GJ Alexander & CY Chin, Napier, 2017
Anzac Cliffs, slope stabilisation, fill buttress
The Anzac Cliffs project involves two main elements: reshaping of the steep cliff, and realignment of the Manawatu River away from the cliff. The realignment of the river below Anzac Cliff was the last major development of the Lower Manawatu Scheme, City Reach Project. The project included the realignment of a 460m section of the Manawatu River opposite Anzac Park. The reshaping works were undertaken to stabilise the 50m high Anzac Cliffs adjacent to the river. The remedial works addressed the ongoing erosion of the unstable cliff by the Manawatu River.
Hazards associated with the project include direct river erosion undermining the lower cliff, and ongoing instability of cliff-face materials. The construction of foundations for a fill buttress within the active river channel and below the unstable cliff provided significant challenges, particularly due to the presence of liquefiable materials in its formation.
This paper provides a review of hazards associated with the project; sets out geotechnical investigations and analysis undertaken; and describes the development of the detailed design for the cliff stabilisation works. A review of construction and monitoring techniques for both the foundation treatment and compaction of granular and earth fill materials is presented, together with an outline of the management of numerous considerable technical and safety risks.

Design and construction of a commercial building on a closed municipal solid waste landfill in Takapuna, Auckland
Author:  Li, N.
Presented/Published:  Proceedings of the 11th ANZ Young Geotechnical Professionals Conference - 11YGPC, Queenstown, New Zealand, 25-28 October 2016
Keywords:  Solid waste landfill, construction, excavation, pile installation, leachate migration, landfill gas mitigation measures
Ground engineering works on closed municipal solid waste landfills provide challenges beyond those related to construction on other brownfield sites within the urban environment. Design and construction of a multi-level commercial building on the closed Barrys Point landfill site in Auckland presented challenges for foundation design, durability, and mitigation of hazards (refuse, gas, and leachate) related to landfill material. Geotechnical inputs for the new building included deep-piled foundations and landfill gas protection measures. Engineering observation of construction for the gas protection measures was required to comply with stringent consent conditions. This paper describes challenges, during detailed design and construction of the new building, posed by the complex ground conditions on-site. The challenges included the development of pile installation methods that would not contribute to leachate migration, and construction of the passive landfill gas protection system. Permanent design features of the building includes deep-driven steel piles, and landfill gas mitigation measures entailing a specifically designed gas manifold system and a subfloor slab with high-density polyethylene (HDPE) geo-membrane to prevent ingress of landfill gas into the new building.

Counterfort drain performance in the Auckland area
Author:  Torvelainen, S. M.
Presented/Published:  Proceedings of the 11th ANZ Young Geotechnical Professionals Conference - 11YGPC, Queenstown, New Zealand, 25-28 October 2016
Keywords:  Counterfort drain, buttress drain, trench drain, groundwater, slope stability, piezometers
Counterfort drains are a method of lowering groundwater levels in soils and subsequently reducing pore water pressures on possible failure planes that can induce slope instability. This paper discusses
the typical detail of counterfort drains employed and whether counterfort drains continue to be effective in reducing groundwater levels as has been demonstrated in Fitch (1990). Maintenance issues, monitoring and performance over time is outlined. Up to date costs of construction of counterfort drains are also given. The appropriateness of counterfort drain use in different types of Auckland Region Northland Allochthon geology is investigated. Counterfort drains are shown to generally have a demonstrable effect on groundwater levels. Their effectiveness is dependent on site specific geology rather than the overall geological unit present. Provided site specific factors are fully considered they can routinely be considered as a slope stability improvement option in the Auckland region.

"Seeking Relief" rising pore pressures in Earth Dams - A case study
Author:  Burrows, N. P.
Presented/Published:  Proceedings of the 11th ANZ Young Geotechnical Professionals Conference - 11YGPC, Queenstown, New Zealand, 25-28 October 2016
Patea Dam is owned by Trustpower Ltd. (Trustpower) and is a zoned earth dam. On commissioning, lake pressures were observed to be transferring into the underlying geology. This created an increased artesian pressure within the footprint of the structure, reducing the dam’s Factor of Safety (FoS) below what would be expected of a high Potential Impact Classification (PIC) dam. Remedial measures were investigated to correct long-term pressure trends at Patea Dam and ensure the longterm safety of the dam for its owner; the residents below the dam; and the recreational users of Lake Rotorangi. The approach of drilling relief wells into the underlying foundation is a method that had been historically used at Patea Dam, resulting in successful alleviation of excess artesian pressures. In April of 2015 a further two wells were commissioned to reduce the ongoing build-up of pore pressure. Numerous obstacles were overcome during the installation process, including challenging access and dangerous weather conditions to reach a satisfactory outcome for all parties involved. Initial results saw an approximate drop of 2m in the artesian pressures below the toe of the dam increasing the dams FoS and reducing artesian pressures to below identified alarm levels. This case study shows how relief wells can be successfully installed, even with numerous challenges, to safeguard an important piece of New Zealand’s infrastructure for the future.

Proposed Kotuku flood detention dam - geology and geotechnical design features
Author:  Scott, D.
Presented/Published:  Proceedings of the 10th ANZ Young Geotechnical Engineering Conference 10YGPC, 2015
In the North Island of New Zealand, volcanic soil and rock pose seepage issues for water retaining structures, and very careful investigation and design is necessary. The proposed Kotuku Flood Detention Dam has been designed to reduce flooding within Whangarei City, and is expected to commence construction in the 2014/2015 earthworks season. The proposed dam is classified a high potential impact classification (PIC) dam, and hence the geotechnical issues have been rigorously analysed. The proposed dam and catchment are located within a complex geological environment, where a basalt flow and flow margin, firm alluvial soils, and massive sandstone rock are present in the proposed dam foundation. This paper describes the geotechnical issues posed by site geology in preparing a detailed design of the 18m earth embankment dam. Investigation and testing has been undertaken to assess the site geology, including founding conditions, seepage potential and materials for dam construction. Permeability testing, including packer, falling and constant head tests, provided input to forming a geological model of the subsurface conditions. Transient groundwater analysis on the geological model was undertaken for a 36 hour, 1% annual exceedance probability (AEP) flood event. This analysis led to the development of a detailed design for the proposed dam, which comprises a clay liner, undercuts of alluvial and selected residual and flow margin materials, toe drains and internal drainage.

Use of the dynamic cone penetrometer to assess the liquefaction susceptibility of Christchurch alluvial soils
Author:  Ashfield, D., Ashby, G., Fitch, N., Ladley, E., Power, P., & Smith, T.
Presented/Published:  Proceedings of the 19th NZGS Geotechnical Symposium. Ed. CY Chin, Queenstown, 2013
Keywords:  Dynamic probe heavy, dynamic probe super heavy, standard penetration test (SPT), Christchurch, alluvium, alluvial
Thorough geotechnical investigation and in-situ testing of alluvial soils is often fraught with difficulties. Unfavourable and/or dramatic changes in material characteristics in locations where inter-bedded layers of alluvial gravel, sand, silt and/or organic materials are present, often means that a combination of Cone Penetrometer Tests (CPTs) with “pre-drilling” and rotary mud and/or sonic drilling needs to be undertaken so that adequate minimum investigation data and depth is achieved.
In Christchurch alluvial soils, sample disturbance, artesian ground water pressures, and/or base heave, often result in incomplete data and some doubt as to the reliability of the investigation results. Two configurations of the dynamic probe (DP) have been identified by the authors as a reliable and cost-effective method to obtain geotechnical data for liquefaction hazard assessment purposes: dynamic probe heavy (DPH) and super heavy (DPSH-B). Collectively DPH and DPSH-B are referred to as DP.
This paper describes the logistical, technical and financial advantages of using the above dynamic probe tests and presents comparisons between test results obtained at numerous control locations using DPH/DPSH-B, and CPT and Standard Penetration Test (SPT) apparatus. Recommendations for normalising factors to correct DPH/DPSH-B test results and calculate an equivalent SPT N60 value are discussed, and comparisons between the results of liquefaction hazard assessment based on DP to SPT and CPT data is also presented.

Slope failure and modelling uncertainty in complex volcanic terrain, Opito Bay, New Zealand
Author:  Steven Price
Presented/Published:  Proceedings of the 11th international symposium on landslides and engineered slopes, Banff, 2012
The Ohinau Drive ground movement affected multiple lots adjacent to a volcanic hill and was a complex variable depth failure. Following disturbance to infrastructure in 1996, localised artesian pressures were encountered under the slide mass. Groundwater drainage was undertaken by an inclined large diameter bored drain, later complemented by a second drain. Inclinometers, and multi-level piezometers, have provided over 10 years of data. Geotechnical models have been subject to stability analyses for measured and assumed worst case groundwater levels, and seismic shaking. Uncertainties were present in the geotechnical model due to geological and hydrological complexity. These were addressed in sensitivity analyses, land monitoring and engineering measures. Model robustness and stability measures were disputed by Council, leading to an independent hearing process. The geotechnical expert for the hearing controllers agreed the monitoring of observed ground performance since 1996 proved the site was likely to remain stable provided drainage remained operational.

Practical aspects of construction decisions for large wind turbine foundations
Author:  Don Tate and Steven Price
Presented/Published:  Proceedings 18th NZGS Geotechnical Symposium on Soil-Structure Interaction. Ed. CY Chin, Auckland, 2008
Keywords:  Wind turbine, greywacke, foundation stiffness, Clegg hammer
The Stage 3 expansion of the Tararua wind farm involved construction of 31 new turbines. Cyclical rocking under wind loading requires a strong foundation material and particularly high stiffness. Greywacke rock was the preferred founding material. This paper concentrates on the practical aspects of construction decisions which must be made by the supervising engineer. This aspect does not figure highly relative to other aspects in geotechnical engineering literature, but is an important part of engineering practice.

An unusual contact - Whitford Quarry
Author:  Steven Price
Presented/Published:  NZ Geomechanics News, ISSN 0111-6851, Issue 76, December 2008
Keywords:  Quarry, greywacke, Te Kuiti Waitemata group, fault, stability assessment
The Whitford Quarry, located some 6km south of the Beachlands settlement in East Auckland, is operated by Fulton Hogan Ltd.  Resource primarily in the form of greywacke rock, is actively being extracted from the quarry, crushed and sold as aggregate.  The quarry is located in close proximity to a large fault (Waikopua) and has overlying younger sediments that mantle the resource rock.

Geotechnical assessment of founding conditions for large wind turbines
Author:  Steven Price
Presented/Published:  Young Geotechnical Engineers Conference, Adelaide 2006
Keywords:  Tararua, Geotechnical, Geology, Wind, Turbine, Founding Conditions
The Tararua wind farm is one of the world’s top three wind farm sites. Its owner has committed to a stage 3 extension involving construction of 35 large wind turbines standing 65m, producing 3MW each.  The Tararua Ranges are located immediately adjacent to an active fault zone and have recently been up-thrusted. The ranges consist of shattered greywacke sandstone with a complex capping of Tertiary and Quaternary marine deposits, along with re-worked loess.  Proposed sites for the turbines are generally challenging as ‘easier’ sites are already occupied by in excess of 100 smaller turbines.  Though theoretically relatively low strength material is required to support the turbine weight resting on 15m diameter octagonal pads, cyclical rocking under wind and possibly seismic load, requires strong material of high stiffness. Thus, greywacke rock is the preferred founding material.  In January 2006 construction of the stage 3 extension commenced. Large earthworks are required to form foundations and adjacent crane platforms. Excavations to date have generally been consistent with conditions inferred from the geotechnical investigation, however, some sites have revealed geology more complex than envisaged, such as localised low strength gully fills on ridge crests. Thus, foundation designs have been adapted to the subsurface conditions encountered.

Slope failure in a complex volcanic terrain - Opito Bay, Kuaotunu, Coromandel Peninsula
Author:  Steven Price
Presented/Published:  Proceedings of the 5th Australia-New Zealand Young Geotechnical Professionals Conference, Rotorua, 2002
Keywords: Slope failure, headscarp, deep seated failure, hydro-thermally altered andesite, basalt
The Ohinau Drive slope failure has occurred at the northern base of the volcanic Tahanga Hill, Opito Bay. The failure has affected a recent subdivision on Ohinau Drive situated immediately adjacent to the hill.  The slide is a complex, variable depth failure encompassing several differing geological units. It extends a distance of 170m from headscarp to toe with an estimated maximum width of 130m. It comprises both shallow seated and deep seated failure mechanisms to a maximum depth of approximately 20m.  In the winter of 1996 slope instability was recognised following development of a headscarp and ongoing disturbance to kerbing and manholes.Investigations undertaken revealed complex geological conditions generally comprising hydro-thermally altered andesite partially overlain by basaltic debris and weathered basalt lava. Artesian water pressures were encountered within the andesite. The investigation results indicate that both a deep seated failure through the underlying andesite and a shallow seated movement involving the basalt debris were recently active.  A geotechnical model was constructed along two cross sections with computer aided stability analyses undertaken. Target groundwater levels were determined to achieve a satisfactory Factor of Safety to allow future subdivision development. Drainage installation and monitoring is yet to be established following liaison with Council.

Experimentally derived relationship between undrained shear strength and driven pile sets
Author:  Nigel Fitch
Presented/Published:  Master of Engineering Project, University of Auckland, February 1996
Keywords:  Piles, driven piles, undrained shear strength, experiment, NZS 3604, field testing
This report presents the results of field testing relating to the driving of foundation piles using a variety of standard commercially available plant under normal operating conditions.  Piles were driven into cohesive soils in which shear strength testing was undertaken. The driving energy used and the base area of each pile were normalised on the basis of the energy input per unit area of pile base relative to the standard conditions of NZS:3604 Appendix D.  A relationship between shear strength and normalised pile set has been derived. A practical application of the relationship is presented as an aid to foundation design practitioners.  Ultimate pile capacities were evaluated on a theoretical basis and compared with pile testing undertaken for the preparation of NZS:3604 Appendix D. Recommendations are made regarding the use of static and dynamic pile capacity formulae.

Ground stabilisation with counterfort drains design, installation, and monitoring of drawdown performance
Author:  Nigel Fitch
Presented/Published:  Proceedings NZ Geotechnical Society, Vol 16, Issue 1(G) (May 1990)
Keywords:  Ground stabilisation, counterfort drains, drawdown, performance monitoring
This paper describes the use of counterfort drainage as a method of providing ground stabilisation. Theoretical design methods are presented together with drawdown tables derived by the author for Auckland soil conditions.  Typical drainage details are given and installation techniques and costs discussed. Monitoring of performance and drawdown results from a case study are presented.

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