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DESIGN STANDARDDS-10 NATURAL HAZARDS AND EARTHWORKS

TABLE OF CONTENTS

DS-10.1 General ............................................................................................................1

DS-10.2 Landform Development ....................................................................................1

DS-10.3 Performance Criteria ........................................................................................1

DS-10.4 Landform Classification System .......................................................................3

DS-10.5 Landform Professional Opinion ........................................................................3

DS-10.6 Assessment Process ........................................................................................4

DS-10.7 Peer Review ......................................................................................................4

DS-10.8 Earthworks .......................................................................................................4

DS-10.9 Regional Council Requirements ......................................................................4

DS-10.10 Design ............................................................................................................5

DS-10.11 Companies for Soils and Earthworks Testing .................................................8

DS-10 NATURAL HAZARDS AND EARTHWORKS

Updated 01/07/2014 Page 1

DS-10.1 General

Many developments will modify the pre-development landforms and drainage patterns.Potential adverse effects can include flood damage, erosion, sedimentation, water pollution,short term slope instability and ecosystem damage.

This section of the IDC sets out the requirements for undertaking the assessment of landsuitability and stability and the design of earthworks to ensure that the development providesa suitable and safe platform for the construction of buildings, infrastructure and otherstructures in order to comply with the outcome requirements of the City Plan.

DS-10.2 Landform Development

Designs shall ensure that modified landforms meet the following criteria:

a) Every parcel of land shall possess a designated safe building platform suitable for theerection thereon of buildings/structures appropriate to the zoning of that land.

b) The designated building platform is deemed safe when certification has been receivedfrom either a Geo-Professional and/or a SQE Professional that the performance criteriaDS-10.3 Performance Criteria have been met and that building consents for thedesignated safe building platform can be issued without reference to s72 of the BuildingAct being required.

c) Development works are required to ensure the construction of safe building platformsand that any modified landforms are also safe. Conditions of consent will be imposed toensure this occurs.

d) Acceptable engineering and industry methods and standards shall be used whenassessing, designing, constructing and certifying designated safe building platforms anddevelopment works.

e) When applying for Resource Consent, each application shall provide Council with aDevelopment Evaluation Report.

f) When applying for final signoff or s224 each completed development shall provideCouncil with a Development Completion Report.

g) Minimise, isolate or eliminate health and safety hazards during both its construction andits use.

h) Minimise, isolate or eliminate any adverse ecological and environmental effects.

DS-10.3 Performance Criteria

Designated safe building platforms shall meet the following criteria:

a) The performance and functional requirements of sections B1 and E1 of the New ZealandBuilding Code.

b) Works recommended in the geotechnical and other hazards sections of the DevelopmentEvaluation Report have been completed and certified.

c) Slopes deemed to be complete shall:


Page 2 Updated 01/07/2014

i) Have a minimum factor safety against slope failure of 1.5 (static fully drainedcondition).

ii) Have a minimum factor of safety against slope failure of 1.2 for extremegroundwater or other low return period temporary load conditions.

iii) Be assessed for seismic conditions by either of the following methods:

a) Achieve a factor of safety of 1.0 for an appropriate design acceleration forstructures likely to be constructed on slopes within the 2H:1V downslopefailure zone to 4H:1V downslope runout zone or on land potentially subject toliquefaction.

b) Design may be undertaken with consideration to the potential residualdisplacement of a slope with a factor of safety less than 1.0 under the peakground acceleration used for design. If this approach is to be used the designshall include a specific assessment of the potential impact of strain softeningon the predicted displacements. This is particularly important given theoccurrence of highly sensitive soils in the region.

d) Designated safe building platforms are located clear of the 2H:1V upslope failure zone orthe building restriction line determined appropriate for the slope. (The Geo-Professionalwill determine this set back and define an appropriate building restriction line that willensure the designated safe building platform is unaffected by slippage.)

e) Designated safe building platforms located within the 4H:1V downslope runout zone havebeen protected by way of a debris protection measure.

f) Residual differential settlement is no greater than 25mm over 6m lateral distance.

Consideration shall be given to potential settlement of both engineered fill and foundationsoils of building sites. This assessment should consider both total and differentialsettlement potential. Differential settlements shall be no greater than those stated above.Any estimated differential settlement exceeding this range shall be specifically identifiedwithin the geotechnical completion report along with building developmentrecommendations to manage the estimated differential settlements.

Where estimated residual total settlements for the development exceed 25mm over50years, then this shall be brought to the attention of Council in the DevelopmentCompletion Report .

These values may be varied in the event a risk assessment based on probabilisticanalysis or other methods are undertaken and a lesser factor of safety proposed by thepractitioner.

g) Where the failure of a slope may impact a high importance structure or facility (i.e.Category 3, 4 and 5 as given in NZS 1170 or Dam Structures) then the slope shall bedesigned to ensure that the factor of safety criteria referenced above are appropriate foruse with the particular high importance structure or facility.

h) Roads, service lanes or accessways vested in Council shall meet the performancecriteria designed by the Geo–Professional at the time of Development Works Approval.



DS-10.4 Landform Classification System

Tauranga City is located on land subject to various natural hazards. The natural hazardsrange from complex soils related issues, to flood prone land and coastal erosion andinundation issues.

DS-10 - Apx B.4 Table 1: Risk Classification Table outlines the various natural hazard issuesin Tauranga City, an order of risk for each hazard and the appropriate professional to utilisewhen obtaining professional opinion on the development of land subject to natural hazards.

DS-10.5 Landform Professional Opinion

Natural hazards in Tauranga City broadly fall into the following two categories:

a) Geotechnical hazards.

b) Other hazards.

Following the requirements of QA-2.4 Compilation of the Development Evaluation Report,this report is compiled by a Geo-Professional, a Suitably Qualified and ExperiencedProfessional or both in conjunction with DS-10 - Appendix B Landform Classification System.

DS-10.5.1 Geo-Professional and Geo-Professional Accreditation System

For geotechnical hazards professional opinion is provided by a Geo-Professional.

The Geo-Professional is approved to compile the portion of the Development EvaluationReport and the Development Completion Report relating to geotechnical hazards andundertake the requirements outlined in DS-10 - Appendix C - Geo-ProfessionalAccreditation System on geotechnical issues within the City.

Council maintains a geotechnical classification and accreditation system to ensure theopinion and services provided by Geo-Professionals adequately manage the risksassociated with the complex soils in the City.

Council will only accept geotechnical opinion from an accredited Category 1 or 2Geo-Professional.

DS-10 Appendix C – Geotechnical Classification and Accreditation System outlines theclassification and accreditation process and its links with the landform classificationsystem.

DS-10.5.2 Suitably Qualified and Experienced Professional

For other hazards professional opinion is provided by a SQE Professional.

The SQE Professional is approved to compile the portion of the Development EvaluationReport and the Development Completion Report relating to other hazards and undertakethe requirements outlined in DS-10 Appendix D – Suitably Qualified and ExperiencedProfessional.



Council will only accept professional opinion on land hazards from a person meeting thefollowing requirements in DS-10 Appendix D – Suitably Qualified and ExperiencedProfessional.

DS-10.6 Assessment Process

Assessments shall be undertaken as follows:

a) The assessment process for hazards undertaken is referenced in QA-2.4 Compilation ofthe Development Evaluation Report.

b) The assessment process needs to be undertaken in a manner that ensures a consistentapproach to research, investigation and analysis of the particular hazards. DS-10Appendix A – Associated Standards and DS-10 - Appendix G - Assessment andReporting (Informative Only) provide information on assessment techniques andchecklists that will provide a framework when compiling a Development EvaluationReport or Development Completion Report.

c) As a minimum, the assessment process shall address the matters raised in QA-2.4.1Geotechnical Assessment Report or QA-2.4.2 Other Hazards Assessment Report.

DS-10.7 Peer Review

Refer to QA-2.9 Peer Review.

DS-10.8 Earthworks

The following shall apply:

The Consent Holder shall appoint a Category 1 or 2 Geo-Professional.

Observation, quality assurance and review of the earthworks design during the constructionphase are covered in CS-3 Earthworks.

DS-10.9 Regional Council Requirements

Where required under the Regional Water and Land Plan the developer shall obtain anearthworks consent from the Bay of Plenty Regional Council and shall comply with allconditions specified in that consent.

A copy of the consent shall be submitted to Council as part of the application fordevelopment or, if not available at that time, before any work commences on the site.

Note: Earthworks volumes in excess of 5000m³ (made up of the total cut and fill volume) anddisturbed areas greater than 1 hectare are subject to a Bay of Plenty Regional CouncilEarthworks Consent.

Note: For earthworks volumes less than 5000m³ the City Plan shall apply.



DS-10.10 Design

Unless otherwise approved by Council, the design of the landform shall be in accordancewith the IDC and supplemented by the standards and informative section DS-10 – AppendixG: Assessment and Reporting (Informative Only).

DS-10.10.1 Minimum Requirements

All earthworks for a development shall:

a) Comply with the design criteria for completed landforms.

b) Allow for the reduction of overland flow velocity and the concentration of overlandflow for the completed landform geometry and gradients.

c) Provide for the permanent management of overland flow stormwater acrosslandforms (e.g. contour drains, cut-off drains, permanent overland flowpathsexclusive of pedestrian or vehicle accessways etc).

d) Provide for the construction of man-made structures to create safe landforms anddesigned building platforms.

e) Where necessary, provide for the installation of debris protection devices.

f) Define the earth fill and subgrade construction standards, define testing frequency,volumes and outline methods of testing to be used.

g) Allow for observation, quality assurance and review of the earthworks design duringthe construction phase as covered in CS-3 Earthworks.

Engineering appraisal and design are required:

a) Prior to detailed planning, which may involve some form of subsurface investigation.

b) During the review of and advice on design concepts.

c) During construction to ensure the adequacy of the bulk filling and the execution ofthe earthworks design.

DS-10.10.2 Groundwater

The following 2 scenarios shall be undertaken when designing for groundwater:

a) Scenario 1 - a design condition that shall reflect normal seasonal fluctuations (i.e.normal winter groundwater).

b) Scenario 2 - an extreme condition that shall reflect a credible worst casegroundwater level that might be expected to occur for a low return period.

Both scenarios shall reflect potential transient conditions that may occur in slopes. Thisshall include allowance for water filled tension cracks or saturation of soils such as theRotoehu Ash.

Note: Groundwater is a generic term that encompasses the naturally occurring soil moisturecondition (normal and worst case), perched water tables, pore water conditions (both normaland worst case), wetting front etc.



DS-10.10.3 Protection of Trees or Other Features

All designs shall include the provision of protecting existing trees where required by theCity Plan. All site activities including clearing, storage, cutting and filling must be keptaway from the root zone of such protected trees (defined as the extent of the drip line ofthe canopy). If there is any doubt, then the advice of an arboriculturalist shall be sought.

DS-10.10.4 Preparation for Fill

The stripped ground surface prepared by the Contractor shall be inspected by theGeo-Professional before any fill is placed thereon. Confirmation of this inspection havingoccurred is required as part of QA-4.4.2 Geotechnical Completion Report.

Earth fills constructed on or against sloping ground and horizontal benches shall beundertaken in accordance with NZS 4431 The Code of Practice for Earthfill forResidential Development.

DS-10.10.5 Temporary Drainage and Erosion Control

Measures shall be taken to prevent excessive water-logging of surface materials yet tobe excavated or compacted or both and to prevent fill material from being eroded andre-deposited at lower levels.

All dust, sediment, erosion control and temporary stormwater discharge shall beundertaken in accordance with Bay of Plenty Regional Council’s Erosion and SedimentControl for Land Disturbing Activities publication.

DS-10.10.6 Subsoil Drainage

Subsoil drainage control systems shall be designed to lead groundwater away from allsprings and potential areas of ground water under or adjacent to fills in order to prevent:

a) Saturation of the fill before construction of the fill is completed.

b) Internal erosion (piping).

c) Internal ground water pressures (normal and worst case) which may reduce shearstrengths in the earthfill.

d) Effects on the adjoining land or structures from an alteration to the normal groundwater conditions. e.g. groundwater table drawdown"

Temporary subsoil drains shall discharge to an outlet such as a stable watercourse or apiped stormwater system.

The position of all subsoil drains shall be recorded on the As-Built plans. Permanentsubsoil drains shall be specifically designed taking into account their long termmaintenance and who will ultimately own and maintain them. These matters need to beaddressed at the time of Development Works Approval.



DS-10.10.7 Compaction Requirements

Unless specified otherwise by the Geo-Professional or where the criteria provided inNZS 4431 The Code of Practice for Earthfill for Residential Development are adopted,the minimum standard of compaction to be met for fill material shall be as follows:

a) Cohesive Soils

The maximum dry density of the fill material shall be established using the standardcompaction test presented in NZS 4402 Methods of Testing Soils for CivilEngineering Purposes.

For compaction tests a site specific optimum moisture content/dry density curve isrequired. Once maximum dry density has been established, the compacted fillmaterial shall meet one of the following strength measurements:

i) Minimum dry density of not less than 95% of the value of the maximum drydensity obtained in the laboratory sample.

ii) Minimum undrained shear strength of 150kPa and a maximum voids ratio of10%. The shear strength of the fill material shall be determined using a shearvane test as prescribed in NZGS Test Method for Determining the Vane ShearStrength of a Cohesive Soil using a Hand Held Shear Vane. The use of scalapenetrometer results to measure shear strength in cohesive soils will not beaccepted.

b) Cohesionless Soils

The maximum and minimum dry densities, using the most suitable method for thematerial, shall be obtained from laboratory testing as prescribed in NZS 4402Methods of Testing Soils for Civil Engineering Purposes then either:

i) The dry density of the fill material is expressed as a relative density in terms ofthe laboratory tests. This can be done by using a Scala Penetrometercalibrated adjacent to a test bed as follows:

a) Prior to commencement of earthworks establish the maximum dry densityand optimum moisture content of the cohesionless soil. After completion ofa portion of the earthworks prepare a test bed and re-measure the drydensity and establish the percentage compaction. The Scala Penetrometercan then be calibrated adjacent to the test bed.

b) This test shall not be used as a substitute for the maximum density and %compaction tests unless they are correctly calibrated. This method is foruse on cohesionless soils only. Monitoring of dry density by using a"Clegg" style hammer can also provide acceptable results if calibrated in asimilar manner.

ii) The dry density of the compacted fill material shall not be less than 95% of themaximum dry density of the fill material obtained from testing required by NZS4402 Methods of Testing Soils for Civil Engineering Purposes.

DS-10.10.8 Density Acceptance Criteria

The minimum acceptance criteria for test results shall be as follows:



a) For less than 10 tests all tests shall meet or exceed the specified minimum standard.

b) For more than 10 tests the average of 10 consecutive tests shall exceed thespecified minimum standard.

c) Only 1 test in10 test results may be less than 90% of the minimum standard.

DS-10.11 Companies for Soils and Earthworks Testing

Refer IT-1 Appendix B - Company Requirements for Soils, Earthworks, Materials andPavement Testing for requirements.



DS-10 - Appendix AAssociated Standards

DS-10 - Appendix A.1 General

The latest revision or operative version of the following standards shall be used inconjunction with the IDC:

a) Council documentation:

i) City Plan

ii) TCC Technical Library references: TL485, TL607 and TL2325

b) New Zealand/Australian/British Standards:

i) NZS 4402:1986 Methods of Testing Soils for Civil Engineering Purposes

ii) NZS 4404:2010 Land Development and Subdivision Infrastructure

iii) NZS 4431:1989 Code of Practice for Earth Fill for Residential Development

c) Other reference material:

i) Resource Management Act 1991

ii) New Zealand Building Act

iii) New Zealand Health and Safety in Employment Act 1992

iv) BRANZ Study SR4, Assessment of Slope Stability at Building Sites, BRANZand Worley Consultants Ltd (1987)

v) "Geotechnical Issues in Land Development"; proceedings from the NZGeotechnical Society Symposium, Hamilton 1996

vi) "The Design of Permanent Slopes for Residential Building Development";Crawford , S A and Millar, P J, EQC Research Project 95/183, NZGeomechanics News (June 1998)

vii) "The role of Peer Review"; Crawford, S A NZ Geomechanics News (Dec 1995)

viii) TCC OZONE Library references: TL485, TL607 and TL2325

ix) Relic Slip Verification Study – Tauranga District Council Environs compiled byLaurie Richards, David Bell and Roydon Thompson dated March 31 2001

x) Tauranga Storm Event - 18 May 2005 - Final Causation Report - Hegan,Wesley and Richards - 2005



DS-10 - Appendix BLandform Classification System

DS-10 - Appendix B.1 Landform Classification System

Tauranga City is located on land subject to various natural hazards. The natural hazardsrange from complex soils related issues to flood prone land and coastal erosion andinundation issues.

DS-10 - Appendix B.4 Table 1: Risk Classification provides a relationship betweenlandform category, the likelihood and consequence of failure, the impact on thedevelopment and the professional required to investigate, define and report on solutionsfor development associated with the most commonly experienced hazards in TaurangaCity.

DS-10 Appendix B.4 Table 1: Risk Classification represents a combination of opinionpublished by various Geo-Professionals as referenced in DS-10 Appendix A.1 Generalc).

DS-10 - Appendix B.2 Geotechnical Hazards

Geotechnical studies have been undertaken within and adjacent to the City dating backto the 1970's. These studies include Tonkin and Taylor Ltd’s work at the Minden andOmokoroa; NZ Geological Survey, Department of Scientific and Industrial Research,Relic Slips and Geological Factors 1980 and 1984; Gerard Bird Maungatapu Pennisula,The Nature and Causes of Coastal Landsliding; Robert Oliver, Thesis on theMaungatapu Peninsula; Richards, Bell and Thomson, Relic Slip Verification Study TDCEnvirons; Richards, Slope Stability Criteria Tauranga; Richards, Tonkin and Taylor Ltd,University of Auckland, Tauranga Storm Event - 18 May 2005 - Final Causation Reportetc, University of Waikato, Geology of the Tauranga Area..

These plus other studies provide valuable information on the issues associated with thegeology Tauranga City is located on. They should be used as reference documentswhen undertaking work within the City.

It is clear from the various reports that the 2H:1V upslope failure zone and the 4H:1Vdownslope runout zone be used as a minimum for slope category definition in all parts ofthe City. These failure zones correlated strongly with the slip observations during theCivil Defence emergency associated with the May 18 2005 storm event, which impactedover 300 sites.

DS-10 - Appendix B.3 Other Hazards

Tauranga City has over the years undertaken much hazard management research whichhas assisted in defining the issues associated with many other natural hazards. Thework is on-going especially in the area of catchment and flood management.



This research is clear on the need for appropriate risk definition and solution as part ofthe management of the natural hazard. The most common other hazards have beenplaced into DS-10 Appendix B.4 Table 1: Risk Classification to provide guidance onreporting and whom undertakes that reporting.



DS-10 - Appendix B.4 Table 1: Risk Classification

Risk Type/Evidence of Hazard Likelihoodof Failure

Consequenceof Failure Implications for Development

Guide toInvestigating

Hazard

PeerReview

RequiredWho

Undertakes?

VERYHIGH -GeotechnicalHazards

2H:1V & 4H:1V Failure Zones:Where a proposed structure or designatedsafe building platform is to beconstructed/located (either in part or whole)within either the 2H:1V upslope failure zone or4H:1V downslope runout zone.The zones may or may not be associated withone or more of the following features:a) Evidence of active or large scale historic

instability within the property or adjoiningthe property.

b) Hummocky debris.c) Moderate to extensive water seepage

evident.PeatWhere a proposed structure or designatedsafe building platform is to be:d) Constructed/located over peat materials

that will permanently remain in place.e) Supported on piles constructed through

peat material.

Likely toVery Likely

Probable lossof life or injury.Extensive orsignificantdamage toproperty,structures oreconomic loss.

Land requires development works to improve:a) Stabilityb) Construct protection measures,c) Improve soils bearing capacity and

properties etc.to ensure its suitability for land and/or buildingdevelopment.Development options may include avoidanceof the hazard altogether rather than mitigationor remediation through development works.The post development risk is that while risk tothe designated safe building platform orconsented structure is removed, avoided ormitigated, some parts of lots may still besubject to risks associated with the hazardspresent.Ongoing development restrictions are likely.

DS-10 Appendix GAssessment andReporting(Informative Only)

Yes Category 1Geo-Professional






Hazard

PeerReview

RequiredWho

Undertakes?

HIGH -GeotechnicalHazards

2H:1V & 3H:1V Upslope Failure Zones:Where a proposed structure or designatedsafe building platform is to beconstructed/located (either in part or whole) inthe zone between the 2H:1V and 3H:1Vupslope failure zones and one or more of thefollowing features is present:a) Clearly or poorly defined headscarpb) Evidence of historic instability (instability

may occur during and after extremeclimatic conditions and may extend beyondthe site boundaries).

c) Possible hummocky debris.d) Little to moderate evidence of water

seepage.Geological Features (Combinations)Moderately sloping land (15o<x<20o) locatedoutside of the failure zones (upslope anddownslope) that possess evidence of active orhistoric instability, landslip or face failureexhibited.Instability may occur within the propertyboundary or extend where located on anadjacent property, the effects of that instabilityare likely to affect the proposeddevelopment/proposed designated safebuilding platform.Moderate to excessive water seepage evident,hummocky debris.PeatConstructed/located on ground where theunderlying peat has been completely removedbut where this is underlain by othercompressible soils.Other

Unlikely toLikely

Possible lossof life or injury.Significant tomoderatedamage toproperty,structures oreconomic losspossible.

Land requires development works to improve:a) Stabilityb) Construct protection measures,c) Improve soils bearing capacity and

properties etc.to ensure its suitability for land and/or buildingdevelopment.Development options may include avoidanceof the hazard altogether rather than mitigationor remediation through development works.The post development risk is that while risk tothe designated safe building platform orconsented structure is removed, avoided ormitigated, some parts of lot may still be subjectto risks associated with the hazards present.Ongoing development restrictions are likely.


Discretionary

Category 1Geo-Professional






Hazard

PeerReview

RequiredWho

Undertakes?

Estuarine materials, low strength orcompressible soils are present such thatliquefaction and/or lateral spread hazards willneed to be determined.Horticultural filling

High -OtherHazards

Flood Prone Land.Coastal Erosion.Building platforms below minimum buildingplatform levels.Land possessing localised flood pronedepressions, dishes etc. with no overlandoutlet.Land subject to overland flowpaths.

Unlikely toLikely

Possible lossof life or injury.Significant tomoderatedamage toproperty,structures oreconomic losspossible.

Suitable for building development orsubdivision subject to the DevelopmentEvaluation Report defining solutions to avoid,mitigate or remedy the natural hazard.The post development risk is that while risk tothe designated safe building platform orconsented structure is removed, avoided ormitigated, some parts of lots may still besubject to risks associated with the hazardspresent.Development restrictions possibly required.

Best Practice forSpecific hazard

Discretionary

SQEProfessional

MODERATE -

2H:1V & 3H:1V Upslope Failure Zones:Where a proposed structure or designated

Unlikely Low to virtuallynil risk of loss

Suitable for building development orsubdivision. Some development works may be

DS-10 Appendix GAssessment and

Discretionary

Category 1 or2






Hazard

PeerReview

RequiredWho

Undertakes?

GeotechnicalHazards

safe building platform is to beconstructed/located (either in part or whole) inthe zone between the 2H:1V and 3H:1Vupslope failure zones with no othergeomorphic features present.PeatWhere a proposed structure or designatedsafe building platform is to beconstructed/located on ground where theunderlying peat material has been completelyremoved and the peat materials are locatedover competent soils with minimal likelihood ofsettlement occurring.OtherSpecific design of foundations where thethickness of compressible soils below thefoundation are 4m or greater. (Excludes peator materials listed in “Other” in the High Riskcategory).Little or no evidence of soil creep or instability.Instability may occur if development does nothave due regard for the site conditions.Stormwater disposal by way of soakage isproposed within areas defined as "SpecificDesign" and is located within 100m of a relicslip or 2H:1V upslope failure zone.

of life or injury.Moderatedamage toproperty andstructures oreconomic loss

required to improve stability or bearingcapacity.Engineering practices suitable to hillsideconstruction required.The post development risk is generally nohigher than normally accepted.Risk to designated building platforms orstructures removed.Development restrictions unlikely.

Reporting(Informative Only)

Geo-Professional

MODERATE –OtherHazards

Off-site effects created by urban intensification Unlikely Localisedflooding fromproperty toanother. Minordamage oreconomic loss.

Suitable for building development orsubdivision subject to the DevelopmentEvaluation Report defining solutions to avoid,mitigate or remedy the natural hazard.The post development risk is that some partsof completed lots may still be subject to risksassociated with present hazards but thatadjoining property has risks mitigated.Risk to designated building platforms or


Discretionary

SQEProfessional






Hazard

PeerReview

RequiredWho

Undertakes?

structures removed.Development restrictions unlikely.

LOW -GeotechnicalHazards

Building platforms located clear of 2H:1Vupslope failure zone, 3H:1V upslope failurezone and 4H:1V downslope runout zones.No evidence of instability observed.Instability not expected unless major sitechanges occur and development does nottake issues into account.Gently sloping land (less than 15o)Specific design of foundations where thethickness of compressible soils below thefoundation are less than 4m. (Excludes peat ormaterials listed in "Other" in the High Riskcategory).Stormwater disposal by way of soakage isproposed within the areas defined as "SpecificDesign" and is located outside of 100m of arelic slip or 2H:1V upslope failure zone.

HighlyUnlikely

No loss of lifeor injury. Minordamage,limited to siteunless majordevelopmentoccurs or loweconomic loss.

Suitable for building development orsubdivision subject to the developmentdefining solutions to avoid, mitigate or remedythe natural hazard.Risk to designated building platforms orstructures removed.No development restrictions needed.


Discretionary

Category 1, 2 or3Geo-Professional or SQEProfessional

VERYLOW -GeotechnicalHazards

Typically shallow soil cover with flat to gentlysloping topography.

Nil Virtually nil ornil


Discretionary

SQEProfessional



DS-10 - Appendix CGeo-Professional Accreditation System

DS-10 - Appendix C.1 General

Site investigation and risk assessment of geotechnical hazards in Tauranga City requireconsiderable geotechnical skills, experience and judgement. The nature of many of thesoils and landforms in Tauranga City is considered by experts as being very complexand difficult to assess how soils and landform profiles will perform in normal and extremeconditions.

To ensure the risks associated with complex geotechnical hazards are appropriatelymanaged, when undertaking building or land development, Council maintains a registerof Accredited Geo-Professionals.

This Geo-Professionals register is located on the Tauranga City Council's website.

The register provides for levels of expertise based on the complexity of the landform,refer to DS-10 Appendix B Landform Classification System, matched to an AccreditedGeo-Professional whose relevant qualifications, training and experience in the TaurangaCity environment along with appropriate peer support will ensure a robust managementof the risks associated with geotechnical hazards.

Only professionals who are accredited Geo-Professionals are approved to compile theparts of the Development Evaluation Report and Development Completion Reportrelating to geotechnical hazards or undertake the role of the Geo-Professional within theTauranga City area.

DS-10 - Appendix C.2 Geo-Professional

Refer to GEN-4 Definitions for definition of a Geo-Professional.

DS-10 - Appendix C.3 Three Tier Geo-Professional Accreditation System

The Council maintains a 3 tier register of Accredited Geo-Professionals.

a) The 3 tiers are:i) Category 1 Geo-Professional: Chartered Professional Engineer or Engineering

Geologist who is acknowledged by the Accreditation Panel as possessing theappropriate qualifications, skills and relevant experience in Tauranga City toprovide advice on all geotechnical issues found within Council’s area. Thiscategory may also include professionals of high national or internationalstanding who, despite not having extensive local experience or having beinginterviewed by the Accreditation Panel, Council considers to have sufficienttechnical ability to provide advice on specific ground conditions.



ii) Category 2 Geo-Professional: A Chartered Professional Engineer orEngineering Geologist who is acknowledged by the Accreditation Panel aspossessing the appropriate qualifications, skills and relevant experience inTauranga City to provide advice on a limited number of less complexgeotechnical issues found in the Council area.

iii) Category 3 Geo-Professional: A Chartered Professional Engineer or anEngineering Geologist with an appropriate level of supervised work experiencein a related field. (Typically those professionally qualified and practisingGeo-Professionals or Engineering Geologists not listed on Tauranga CityCouncil’s Register.)

b) Admittance to either Category 1 or Category 2 (for either a Chartered ProfessionalEngineer or an Engineering Geologist) status on the register is by way of interviewby an independent panel of specialists (Accreditation Panel) convened by TaurangaCity Council.

c) Accreditation on the Register is for a period of 5 years. At completion of the 5 yearperiod the practitioner is required to be re-interviewed by the Accreditation Panel.

d) An application fee is payable by the applicant for the accreditation process.

DS-10 - Appendix C.4 Landforms Outside of Level of Accreditation

A Geo-Professional may undertake work in a category of landform one step above theircurrent classification. To do this the Geo-Professional shall engage a Category 1Geo-Professional to mentor and peer review their investigation approach, practices,testing and Development Evaluation Report and Development Completion Report.

(This provides the Geo-Professional a mechanism to develop professionally withguidance and demonstrate that they are becoming experienced enough through theongoing mentoring and coaching to be accredited to the next level of expertise.)

The following outlines this process:

a) Prior to commencing any site investigation or research the Geo-Professionalengages a Category 1 Geo-Professional to act as mentor and peer reviewer. Thementor discusses the approach proposed to be used by the Geo-Professional for theinvestigation and comes to an agreement with the Geo-Professional on the proposedapproach for the subject site. The site investigation is then undertaken in accordancewith the agreed approach. Regular communication between the two professionals isundertaken during the investigation and while defining the geological model for thesite, to ensure professional coaching occurs about key findings, assumptions andrecommendations.

b) The completed Geotechnical Assessment Report is then peer reviewed by thementor prior to submission to Council, who shall confirm the findings of the report asbeing appropriate and able to be relied upon by Council.

c) The cost for the peer review shall be met by the Consent Holder.



d) In some circumstances the Geo-Professional may seek approval from Council toengage an appropriately qualified and experienced person who is not on the registerof Accredited Geo-Professionals to act as mentor and peer reviewer. Such anapplication shall be made in writing to the Council stating clearly the qualificationsand experience of the proposed reviewer. It should be noted that approval will begiven only in exceptional circumstances.



DS-10 - Appendix DSuitably Qualified and Experienced Professional

DS-10 - Appendix D.1 General

Where a development is proposed for a site that is subject to other hazards a SQEProfessional shall be engaged to investigate, define the hazards/risk and formulatesolutions to ensure the risks associated with the hazard are avoided, remedied ormitigated and the designated safe building platform certified as meeting the performancecriteria above.

DS-10 - Appendix D.2 Suitably Qualified and Experienced Professional (SQEProfessional)

Refer to GEN-4 Definitions for definition of a suitably qualified and experiencedprofessional.

DS-10 - Appendix D.3 Role and Responsibilities of SQE Professional

See GEN-4 Definitions for the role and responsibilities of a suitably qualified andexperienced professional.



DS-10 - Appendix EAccredited Geo-Professionals

DS-10 - Appendix E.1 Listing

Category 1 Geo-Professionals

Please refer to the Accredited Geo-Professionals List on the Tauranga CityCouncil's web-site.



DS-10 - Appendix FPeer Review Requirements

DS-10 - Appendix F.1 General

Refer to:

a) QA-2 Appendix A.1 Requirement.

b) QA-2 Appendix A.2 Peer Review Procedures.c) QA-2 Appendix A.3 External Expert Advice.d) QA-2 Appendix A.4 Peer Review Guidelines (Informative).



DS-10 - Appendix GAssessment and Reporting (Informative Only)

DS-10 - Appendix G.1 General

The assessment of landforms shall utilise the following principals and may besupplemented by the expert opinion stated in the documents noted in DS-10 APX AAssociated Standards:

a) All earthworks for a development shall:

i) Comply with the design criteria for completed landforms.

ii) Take the reduction of overland flow velocity and the concentration of overlandflow into account for the completed landform geometry and gradients.

iii) Provide for the permanent management of overland flow across landforms(contour drains, cut-off drains, formalised overland flowpaths not formingaccessways etc).

iv) Provide for the construction of man-made structures to create safe landformsand designed building platforms.

v) Where necessary provide for the installation of debris protection devices.

vi) Define the earth fill and subgrade construction standards, define testingfrequency, volumes and outline methods of testing to be used.

b) Observation, quality assurance and review of the earthworks design during theconstruction phase are covered in CS-3 Earthworks.

Engineering appraisal and design are required:

i) Prior to detailed planning, which may involve some form of subsurfaceinvestigation.

ii) During the review of and advice on design concepts.

iii) During construction to ensure the adequacy of the bulk filling and theexecution of the earthworks design.

c) Development Evaluation Reports and Geotechnical Completion Reports relating toCategory 1 and 2 landforms shall:

i) Be subject to a level of quality control appropriate to the complexity of theproject. This extends to an independent review within the company preparingthe report of the technical areas, key assumptions of the report, investigationfindings, adopted soils model, parameters and final conclusions opinions.

ii) Presence of and influence on the development from existing geomorphicfeatures.

iii) Assessment of historic landform stability and landform processes.

iv) Other engineering issues influencing the proposed development such as butnot restricted to, seismic stability, liquefaction, shrink/swell effects, foundationrequirements, limitations on surface water flow etc.



v) In undertaking the assessment, the expertise of both a Geo-Professional andengineering geologist may be required to ensure a full understanding of thesite is gained.

DS-10 - Appendix G.2 Balancing Landform Choices

The final choice of landform is dependent on many factors, which may be specific to thedevelopment. These include the:

a) Relationship with surrounding landscapes.

b) Natural drainage patterns.

c) Size of the development.

d) Proposed and existing roading patterns.

e) Preservation of natural features.

f) Enhancement of natural features where compromised by fragmentation or reductiondue to the development.

g) Stability of the land.

h) Function and purpose of the development.

i) Potential for flooding, erosion and other natural events.

The order of importance of these factors will vary from project to project.

The final choice of landform must represent the most desirable compromise between thedevelopment requirements, the preservation of natural features including the existing soilprofile, and the natural quality of the landscape. Preservation aspects include retainingnatural watercourses, and excluding any development from natural gullies (refer to theDistrict Plan).

DS-10 - Appendix G.3 Reducing Waste

When designing the development, consider ways in which waste can be reduced.

a) Design to reduce waste during construction e.g. minimise earthworks, reuseexcavated material elsewhere.

b) Use materials with a high recycled content e.g. recycled concrete subbase.Proposed recycled materials will need approval from the Council to ensure thatenvironmental contamination does not occur.

Refer to the Resource Efficiency in the Building and Related Industries (REBRI) websitefor guidelines on incorporating waste reduction in your project www.rebri.org.nz.

DS-10 - Appendix G.4 Existing Landforms

Study the general nature and shape of the ground and take particular note of:

a) The geological nature and distribution of soils and rock.



b) Existing and proposed drainage conditions and the likely effects on groundwater.

c) The previous history of ground movements in similar soils in the area.

d) Where earthworks are involved, the performance of comparable cuts and fills (if any)in adjacent areas.

Air photography and other sources of information that should be reviewed andincorporated into any slope stability assessment.

DS-10 - Appendix G.5 Suitability

The choice of a suitable landform is dependent on many factors that may be specific to aparticular site. Avoid unnecessary earthworks, aim to protect original soils and drainagepatterns and to minimise disturbance, compaction, earthworks and importation of topsoil,although earthworks may be justified in the following circumstances to:

a) Minimise the risk of property damage through ground movement in the form of rockfall, slips, subsidence, creep, erosion or settlement.

b) Minimise the risk of property damage through flooding, or surface water run-off.

c) Lessen tunnel gully erosion within hillside developments.

d) Develop a more desirable roading pattern with improved accessibility to and withinthe site, and to create a better sense of orientation and identity for the area as awhole.

e) Increase the efficiency of overall land use, including the quality of individual sites andamenity areas around buildings, the economics of providing engineering servicesand the standard of roading and on-site vehicular access.

f) Create, where needed, suitably graded areas for playing fields and other communityfacilities.

g) Enhance the general environmental character of the area by softening the landscapeor by artificially creating or emphasizing landforms of visual significance, particularlyon flat sites or on areas devoid of landscape features.

DS-10 - Appendix G.6 Seismic Considerations

Consider the seismic effects on earthfills, slopes and liquefiable ground, and take theseinto account in the design and construction of any development.

DS-10 - Appendix G.7 Peat

Ensure the geotechnical design in peat areas will achieve the infrastructure design liferequired by all other parts of the IDC. Preserve the flow of groundwater through the peatat pre-development levels.



DS-10 - Appendix G.8 Table 2: Description of Geomorphological Zones and Assessment Guidelines

Risk Category Assessment Guidelines

Very High and High RiskRequires extensive and detailedengineering geological and geotechnicalassessment. Intensive investigation maybe required and development may not beeconomically feasible. Boreholes todetermine geology present will berequired.Assessment of site required by bothengineering geologist andGeo-Professionals.

a) Initial assessment to be carried out by Category 1 Geo-Professional (Engineering Geologist and Geo-Professional)b) Examination, on foot, of the surface of the site and the surrounding ground, with the assistance of existing topographical mapsc) Examination of available aerial photographs of the area (include selection from early to present time)d) Assessment of available geological data (IGNS and other maps, publications, university theses and any other published or

unpublished data)e) Review of relevant files and other historical recordsf) Check with local residence and other sources for evidence of past instability, particularly during periods of heavy rainfallg) Prepare preliminary report including geomorphological map of site, detailed cross sections showing site stratigraphy, preliminary

conclusions on site characteristics and recommendations for additional investigation, mapping and monitoring. Report to includespecific reference to all aerial photographs and other sources of information used for the study

h) Geomorphological assessment to provide conclusion on characteristics of any landslide present and the history of movement(historical or current)

i) If landslide with recent movement effects the site, further topographical surveys, ground investigations and stability analysis will berequired to demonstrate that the site can be made adequately safe by remedial works

j) Undertake investigation to determine the nature and distribution of the soils that may be prone to slip and develop engineeringgeology site model

k) Measure groundwater pressures in the soils strata and evaluate the transient pressures that may develop ender extreme rainfallconditions

l) Produce engineering geological report with details of mass movement features and other ground failure hazardsm) Carry out geotechnical evaluation, using Category 1 Engineer and including further sampling, laboratory testing, assessment of

ground properties, groundwater monitoring, etc. If strength assessment has been made by reference to test data from the othersites, provide detailed rationale for the use of such data

n) Undertake slope stability evaluation using approved methodso) Make recommendations for use of site and provide design for remedial measures if appropriate

Moderate RiskSome sites may require detailedengineering geological and geotechnicalassessmentVisual assessment. Hand and possibledrill investigation methods.

a) Assessment to be carried out by Category 1 or 2 Geo-Professional (Geologist/geomorphologist or Geo-Professional)b) Examination, on foot, of the surface of the site and the surrounding ground, with the assistance of existing topographical mapsc) Examination of available aerial photographs of the area (include selection from early to present time)d) Assessment of available geological data (IGNS and other maps, publications, university theses and any other published or

unpublished data)e) Review of council files and other historical recordsf) Check with local residence and other sources for evidence of past instability, particularly during periods of heavy rainfallg) If absence of recent or current landslide activity is confirmed, prepare report confirming this with appropriate documentation (map



and representative sections)h) If ground hazard identified, follow Steps 7 to 15 of Zone 1 procedures

Low RiskDoes not require engineering geologicaland geotechnical assessment

a) Site to be inspected by competent Category 2 person (Registered Engineer or Geologist with equivalent experience)b) Provide written confirmation of inspection and judgement that there is no landslide hazard at the site

Very Low RiskNo requirement for Engineering Geologyor Geo-Professional expertise

a) Site to be inspected by competent category 3 person

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