DESIGN STANDARD NATURAL HAZARDS AND EARTHWORKS

Transcription

1 DS-10 DESIGN STANDARD 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 Design...5 DS Companies for Soils and Earthworks Testing...8

2 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 land suitability and stability and the design of earthworks to ensure that the development provides a suitable and safe platform for the construction of buildings, infrastructure and other structures 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 the erection thereon of buildings/structures appropriate to the zoning of that land. b) The designated building platform is deemed safe when certification has been received from either a Geo-Professional and/or a SQE Professional that the performance criteria DS-10.3 Performance Criteria have been met and that building consents for the designated safe building platform can be issued without reference to s72 of the Building Act being required. c) Development works are required to ensure the construction of safe building platforms and that any modified landforms are also safe. Conditions of consent will be imposed to ensure this occurs. d) Acceptable engineering and industry methods and standards shall be used when assessing, designing, constructing and certifying designated safe building platforms and development works. e) When applying for Resource Consent, each application shall provide Council with a Development Evaluation Report. f) When applying for final signoff or s224 each completed development shall provide Council with a Development Completion Report. g) Minimise, isolate or eliminate health and safety hazards during both its construction and its 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 Zealand Building Code. b) Works recommended in the geotechnical and other hazards sections of the Development Evaluation Report have been completed and certified. c) Slopes deemed to be complete shall: Updated 01/07/2014 Page 1

3 i) Have a minimum factor safety against slope failure of 1.5 (static fully drained condition). ii) iii) Have a minimum factor of safety against slope failure of 1.2 for extreme groundwater or other low return period temporary load conditions. 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 for structures likely to be constructed on slopes within the 2H:1V downslope failure zone to 4H:1V downslope runout zone or on land potentially subject to liquefaction. b) Design may be undertaken with consideration to the potential residual displacement of a slope with a factor of safety less than 1.0 under the peak ground acceleration used for design. If this approach is to be used the design shall include a specific assessment of the potential impact of strain softening on the predicted displacements. This is particularly important given the occurrence of highly sensitive soils in the region. d) Designated safe building platforms are located clear of the 2H:1V upslope failure zone or the building restriction line determined appropriate for the slope. (The Geo-Professional will determine this set back and define an appropriate building restriction line that will ensure the designated safe building platform is unaffected by slippage.) e) Designated safe building platforms located within the 4H:1V downslope runout zone have been 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 foundation soils of building sites. This assessment should consider both total and differential settlement potential. Differential settlements shall be no greater than those stated above. Any estimated differential settlement exceeding this range shall be specifically identified within the geotechnical completion report along with building development recommendations to manage the estimated differential settlements. Where estimated residual total settlements for the development exceed 25mm over 50years, then this shall be brought to the attention of Council in the Development Completion Report. These values may be varied in the event a risk assessment based on probabilistic analysis or other methods are undertaken and a lesser factor of safety proposed by the practitioner. 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 be designed to ensure that the factor of safety criteria referenced above are appropriate for use with the particular high importance structure or facility. h) Roads, service lanes or accessways vested in Council shall meet the performance criteria designed by the Geo Professional at the time of Development Works Approval. Page 2 Updated 01/07/2014

4 DS-10.4 Landform Classification System Tauranga City is located on land subject to various natural hazards. The natural hazards range from complex soils related issues, to flood prone land and coastal erosion and inundation issues. DS-10 - Apx B.4 Table 1: Risk Classification Table outlines the various natural hazard issues in Tauranga City, an order of risk for each hazard and the appropriate professional to utilise when 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 Experienced Professional or both in conjunction with DS-10 - Appendix B Landform Classification System. DS 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 Evaluation Report and the Development Completion Report relating to geotechnical hazards and undertake the requirements outlined in DS-10 - Appendix C - Geo-Professional Accreditation System on geotechnical issues within the City. Council maintains a geotechnical classification and accreditation system to ensure the opinion and services provided by Geo-Professionals adequately manage the risks associated with the complex soils in the City. Council will only accept geotechnical opinion from an accredited Category 1 or 2 Geo-Professional. DS-10 Appendix C Geotechnical Classification and Accreditation System outlines the classification and accreditation process and its links with the landform classification system. DS 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 Evaluation Report and the Development Completion Report relating to other hazards and undertake the requirements outlined in DS-10 Appendix D Suitably Qualified and Experienced Professional. Updated 01/07/2014 Page 3

5 Council will only accept professional opinion on land hazards from a person meeting the following requirements in DS-10 Appendix D Suitably Qualified and Experienced Professional. 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 of the Development Evaluation Report. b) The assessment process needs to be undertaken in a manner that ensures a consistent approach to research, investigation and analysis of the particular hazards. DS-10 Appendix A Associated Standards and DS-10 - Appendix G - Assessment and Reporting (Informative Only) provide information on assessment techniques and checklists that will provide a framework when compiling a Development Evaluation Report or Development Completion Report. c) As a minimum, the assessment process shall address the matters raised in QA Geotechnical Assessment Report or QA 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 construction phase 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 an earthworks consent from the Bay of Plenty Regional Council and shall comply with all conditions specified in that consent. A copy of the consent shall be submitted to Council as part of the application for development 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) and disturbed areas greater than 1 hectare are subject to a Bay of Plenty Regional Council Earthworks Consent. Note: For earthworks volumes less than 5000m³ the City Plan shall apply. Page 4 Updated 01/07/2014

6 DS Design Unless otherwise approved by Council, the design of the landform shall be in accordance with the IDC and supplemented by the standards and informative section DS-10 Appendix G: Assessment and Reporting (Informative Only). DS 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 overland flow for the completed landform geometry and gradients. c) Provide for the permanent management of overland flow stormwater across landforms (e.g. contour drains, cut-off drains, permanent overland flowpaths exclusive of pedestrian or vehicle accessways etc). d) Provide for the construction of man-made structures to create safe landforms and designed 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 during the 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 of the earthworks design. DS 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 case groundwater level that might be expected to occur for a low return period. Both scenarios shall reflect potential transient conditions that may occur in slopes. This shall include allowance for water filled tension cracks or saturation of soils such as the Rotoehu Ash. Note: Groundwater is a generic term that encompasses the naturally occurring soil moisture condition (normal and worst case), perched water tables, pore water conditions (both normal and worst case), wetting front etc. Updated 01/07/2014 Page 5

7 DS Protection of Trees or Other Features All designs shall include the provision of protecting existing trees where required by the City Plan. All site activities including clearing, storage, cutting and filling must be kept away from the root zone of such protected trees (defined as the extent of the drip line of the canopy). If there is any doubt, then the advice of an arboriculturalist shall be sought. DS Preparation for Fill The stripped ground surface prepared by the Contractor shall be inspected by the Geo-Professional before any fill is placed thereon. Confirmation of this inspection having occurred is required as part of QA Geotechnical Completion Report. Earth fills constructed on or against sloping ground and horizontal benches shall be undertaken in accordance with NZS 4431 The Code of Practice for Earthfill for Residential Development. DS Temporary Drainage and Erosion Control Measures shall be taken to prevent excessive water-logging of surface materials yet to be excavated or compacted or both and to prevent fill material from being eroded and re-deposited at lower levels. All dust, sediment, erosion control and temporary stormwater discharge shall be undertaken in accordance with Bay of Plenty Regional Council s Erosion and Sediment Control for Land Disturbing Activities publication. DS Subsoil Drainage Subsoil drainage control systems shall be designed to lead groundwater away from all springs 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 shear strengths in the earthfill. d) Effects on the adjoining land or structures from an alteration to the normal ground water conditions. e.g. groundwater table drawdown" Temporary subsoil drains shall discharge to an outlet such as a stable watercourse or a piped stormwater system. The position of all subsoil drains shall be recorded on the As-Built plans. Permanent subsoil drains shall be specifically designed taking into account their long term maintenance and who will ultimately own and maintain them. These matters need to be addressed at the time of Development Works Approval. Page 6 Updated 01/07/2014

8 DS Compaction Requirements Unless specified otherwise by the Geo-Professional or where the criteria provided in NZS 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 standard compaction test presented in NZS 4402 Methods of Testing Soils for Civil Engineering Purposes. For compaction tests a site specific optimum moisture content/dry density curve is required. Once maximum dry density has been established, the compacted fill material shall meet one of the following strength measurements: i) Minimum dry density of not less than 95% of the value of the maximum dry density obtained in the laboratory sample. ii) Minimum undrained shear strength of 150kPa and a maximum voids ratio of 10%. The shear strength of the fill material shall be determined using a shear vane test as prescribed in NZGS Test Method for Determining the Vane Shear Strength of a Cohesive Soil using a Hand Held Shear Vane. The use of scala penetrometer results to measure shear strength in cohesive soils will not be accepted. b) Cohesionless Soils The maximum and minimum dry densities, using the most suitable method for the material, shall be obtained from laboratory testing as prescribed in NZS 4402 Methods 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 of the laboratory tests. This can be done by using a Scala Penetrometer calibrated adjacent to a test bed as follows: ii) a) Prior to commencement of earthworks establish the maximum dry density and optimum moisture content of the cohesionless soil. After completion of a portion of the earthworks prepare a test bed and re-measure the dry density and establish the percentage compaction. The Scala Penetrometer can 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 for use on cohesionless soils only. Monitoring of dry density by using a "Clegg" style hammer can also provide acceptable results if calibrated in a similar manner. The dry density of the compacted fill material shall not be less than 95% of the maximum dry density of the fill material obtained from testing required by NZS 4402 Methods of Testing Soils for Civil Engineering Purposes. DS Density Acceptance Criteria The minimum acceptance criteria for test results shall be as follows: Updated 01/07/2014 Page 7

9 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 the specified minimum standard. c) Only 1 test in10 test results may be less than 90% of the minimum standard. DS Companies for Soils and Earthworks Testing Refer IT-1 Appendix B - Company Requirements for Soils, Earthworks, Materials and Pavement Testing for requirements. Page 8 Updated 01/07/2014

10 DS-10 - Appendix A Associated Standards DS-10 - Appendix A.1 General The latest revision or operative version of the following standards shall be used in conjunction 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) iii) NZS 4404:2010 Land Development and Subdivision Infrastructure 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, BRANZ and Worley Consultants Ltd (1987) v) "Geotechnical Issues in Land Development"; proceedings from the NZ Geotechnical 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, NZ Geomechanics News (June 1998) vii) "The role of Peer Review"; Crawford, S A NZ Geomechanics News (Dec 1995) viii) ix) TCC OZONE Library references: TL485, TL607 and TL2325 Relic Slip Verification Study Tauranga District Council Environs compiled by Laurie Richards, David Bell and Roydon Thompson dated March x) Tauranga Storm Event - 18 May Final Causation Report - Hegan, Wesley and Richards Updated 01/07/2014 Page 9

11 DS-10 - Appendix B Landform Classification System DS-10 - Appendix B.1 Landform Classification System Tauranga City is located on land subject to various natural hazards. The natural hazards range from complex soils related issues to flood prone land and coastal erosion and inundation issues. DS-10 - Appendix B.4 Table 1: Risk Classification provides a relationship between landform category, the likelihood and consequence of failure, the impact on the development and the professional required to investigate, define and report on solutions for development associated with the most commonly experienced hazards in Tauranga City. DS-10 Appendix B.4 Table 1: Risk Classification represents a combination of opinion published by various Geo-Professionals as referenced in DS-10 Appendix A.1 General c). DS-10 - Appendix B.2 Geotechnical Hazards Geotechnical studies have been undertaken within and adjacent to the City dating back to the 1970's. These studies include Tonkin and Taylor Ltd s work at the Minden and Omokoroa; 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 the Maungatapu Peninsula; Richards, Bell and Thomson, Relic Slip Verification Study TDC Environs; Richards, Slope Stability Criteria Tauranga; Richards, Tonkin and Taylor Ltd, University of Auckland, Tauranga Storm Event - 18 May Final Causation Report etc, University of Waikato, Geology of the Tauranga Area.. These plus other studies provide valuable information on the issues associated with the geology Tauranga City is located on. They should be used as reference documents when undertaking work within the City. It is clear from the various reports that the 2H:1V upslope failure zone and the 4H:1V downslope runout zone be used as a minimum for slope category definition in all parts of the City. These failure zones correlated strongly with the slip observations during the Civil Defence emergency associated with the May storm event, which impacted over 300 sites. DS-10 - Appendix B.3 Other Hazards Tauranga City has over the years undertaken much hazard management research which has assisted in defining the issues associated with many other natural hazards. The work is on-going especially in the area of catchment and flood management. Page 10 Updated 01/07/2014

12 This research is clear on the need for appropriate risk definition and solution as part of the management of the natural hazard. The most common other hazards have been placed into DS-10 Appendix B.4 Table 1: Risk Classification to provide guidance on reporting and whom undertakes that reporting. Updated 01/07/2014 Page 11

13 DS-10 - Appendix B.4 Table 1: Risk Classification Risk VERY HIGH - Geotechn ical Hazards Type/Evidence of Hazard 2H:1V & 4H:1V Failure Zones: Where a proposed structure or designated safe building platform is to be constructed/located (either in part or whole) within either the 2H:1V upslope failure zone or 4H:1V downslope runout zone. The zones may or may not be associated with one or more of the following features: a) Evidence of active or large scale historic instability within the property or adjoining the property. b) Hummocky debris. c) Moderate to extensive water seepage evident. Peat Where a proposed structure or designated safe 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. Likelihood of Failure Likely to Very Likely Consequence of Failure Probable loss of life or injury. Extensive or significant damage to property, structures or economic loss. Implications for Development Land requires development works to improve: a) Stability b) Construct protection measures, c) Improve soils bearing capacity and properties etc. to ensure its suitability for land and/or building development. Development options may include avoidance of the hazard altogether rather than mitigation or remediation through development works. The post development risk is that while risk to the designated safe building platform or consented structure is removed, avoided or mitigated, some parts of lots may still be subject to risks associated with the hazards present. Ongoing development restrictions are likely. Guide to Investigating Hazard DS-10 Appendix G Assessment and Reporting (Informative Only) Peer Review Required Who Undertakes? Yes Category 1 Geo-Professio nal Page 12 Updated 01/07/2014

14 Risk HIGH - Geotechn ical Hazards Type/Evidence of Hazard 2H:1V & 3H:1V Upslope Failure Zones: Where a proposed structure or designated safe building platform is to be constructed/located (either in part or whole) in the zone between the 2H:1V and 3H:1V upslope failure zones and one or more of the following features is present: a) Clearly or poorly defined headscarp b) Evidence of historic instability (instability may occur during and after extreme climatic conditions and may extend beyond the site boundaries). c) Possible hummocky debris. d) Little to moderate evidence of water seepage. Geological Features (Combinations) Moderately sloping land (15o<x<20o) located outside of the failure zones (upslope and downslope) that possess evidence of active or historic instability, landslip or face failure exhibited. Instability may occur within the property boundary or extend where located on an adjacent property, the effects of that instability are likely to affect the proposed development/proposed designated safe building platform. Moderate to excessive water seepage evident, hummocky debris. Peat Constructed/located on ground where the underlying peat has been completely removed but where this is underlain by other compressible soils. Other Likelihood of Failure Unlikely Likely Consequence of Failure to Possible loss of life or injury. Significant to moderate damage to property, structures or economic loss possible. Implications for Development Land requires development works to improve: a) Stability b) Construct protection measures, c) Improve soils bearing capacity and properties etc. to ensure its suitability for land and/or building development. Development options may include avoidance of the hazard altogether rather than mitigation or remediation through development works. The post development risk is that while risk to the designated safe building platform or consented structure is removed, avoided or mitigated, some parts of lot may still be subject to risks associated with the hazards present. Ongoing development restrictions are likely. Guide to Investigating Hazard DS-10 Appendix G Assessment and Reporting (Informative Only) Peer Review Required Discretion ary Page 13 Updated 01/07/2014 Who Undertakes? Category 1 Geo-Professio nal

15 Risk Type/Evidence of Hazard Estuarine materials, low strength or compressible soils are present such that liquefaction and/or lateral spread hazards will need to be determined. Horticultural filling Likelihood of Failure Consequence of Failure Implications for Development Guide to Investigating Hazard Peer Review Required Who Undertakes? High - Other Hazards Flood Prone Land. Coastal Erosion. Building platforms below minimum building platform levels. Land possessing localised flood prone depressions, dishes etc. with no overland outlet. Land subject to overland flowpaths. Unlikely Likely to Possible loss of life or injury. Significant to moderate damage to property, the structures or economic loss possible. Suitable for building development or subdivision subject to the Development Evaluation Report defining solutions to avoid, mitigate or remedy the natural hazard. The post development risk is that while risk to designated safe building platform or consented structure is removed, avoided or mitigated, some parts of lots may still be subject to risks associated with the hazards present. Development restrictions possibly required. Best Practice for Specific hazard Discretion ary SQE Professional MODERA TE - 2H:1V & 3H:1V Upslope Failure Zones: Where a proposed structure or designated Unlikely Low to virtually nil risk of loss Suitable for building development or subdivision. Some development works may be DS-10 Appendix G Assessment and Discretion ary Page 14 Updated 01/07/2014 Category 1 or 2

16 Risk Geotechn ical Hazards MODERA TE Other Hazards Type/Evidence of Hazard safe building platform is to be constructed/located (either in part or whole) in the zone between the 2H:1V and 3H:1V upslope failure zones with no other geomorphic features present. Peat Where a proposed structure or designated safe building platform is to be constructed/located on ground where the underlying peat material has been completely removed and the peat materials are located over competent soils with minimal likelihood of settlement occurring. Other Specific design of foundations where the thickness of compressible soils below the foundation are 4m or greater. (Excludes peat or materials listed in Other in the High Risk category). Little or no evidence of soil creep or instability. Instability may occur if development does not have due regard for the site conditions. Stormwater disposal by way of soakage is proposed within areas defined as "Specific Design" and is located within 100m of a relic slip or 2H:1V upslope failure zone. Likelihood of Failure Off-site effects created by urban intensification Unlikely Consequence of Failure of life or injury. Moderate damage to property and structures or economic loss Localised flooding from property to another. Minor damage or economic loss. Implications for Development required to improve stability or bearing capacity. Engineering practices suitable to hillside construction required. The post development risk is generally no higher than normally accepted. Risk to designated building platforms or structures removed. Development restrictions unlikely. Suitable for building development or subdivision subject to the Development Evaluation Report defining solutions to avoid, mitigate or remedy the natural hazard. The post development risk is that some parts of completed lots may still be subject to risks associated with present hazards but that adjoining property has risks mitigated. Risk to designated building platforms or Guide to Investigating Hazard Reporting (Informative Only) Best Practice for Specific hazard Peer Review Required Discretion ary Page 15 Updated 01/07/2014 Who Undertakes? Geo-Professio nal SQE Professional

17 Risk LOW - Geotechn ical Hazards VERY LOW - Geotechn ical Hazards Type/Evidence of Hazard Building platforms located clear of 2H:1V upslope failure zone, 3H:1V upslope failure zone and 4H:1V downslope runout zones. No evidence of instability observed. Instability not expected unless major site changes occur and development does not take issues into account. Gently sloping land (less than 15o) Specific design of foundations where the thickness of compressible soils below the foundation are less than 4m. (Excludes peat or materials listed in "Other" in the High Risk category). Stormwater disposal by way of soakage is proposed within the areas defined as "Specific Design" and is located outside of 100m of a relic slip or 2H:1V upslope failure zone. Typically shallow soil cover with flat to gently sloping topography. Likelihood of Failure Highly Unlikely Nil Consequence of Failure No loss of life or injury. Minor damage, limited to site unless major development occurs or low economic loss. Virtually nil or nil Implications for Development structures removed. Development restrictions unlikely. Suitable for building development or subdivision subject to the development defining solutions to avoid, mitigate or remedy the natural hazard. Risk to structures removed. No development restrictions needed. designated building platforms or Guide to Investigating Hazard DS-10 Appendix G Assessment and Reporting (Informative Only) Best Practice for Specific hazard Peer Review Required Discretion ary Discretion ary Who Undertakes? Category 1, 2 or 3 Geo-Profession al or SQE Professional SQE Professional Page 16 Updated 01/07/2014

18 DS-10 - Appendix C Geo-Professional Accreditation System DS-10 - Appendix C.1 General Site investigation and risk assessment of geotechnical hazards in Tauranga City require considerable geotechnical skills, experience and judgement. The nature of many of the soils and landforms in Tauranga City is considered by experts as being very complex and difficult to assess how soils and landform profiles will perform in normal and extreme conditions. To ensure the risks associated with complex geotechnical hazards are appropriately managed, when undertaking building or land development, Council maintains a register of 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 Accredited Geo-Professional whose relevant qualifications, training and experience in the Tauranga City environment along with appropriate peer support will ensure a robust management of the risks associated with geotechnical hazards. Only professionals who are accredited Geo-Professionals are approved to compile the parts of the Development Evaluation Report and Development Completion Report relating to geotechnical hazards or undertake the role of the Geo-Professional within the Tauranga 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 the appropriate qualifications, skills and relevant experience in Tauranga City to provide advice on all geotechnical issues found within Council s area. This category may also include professionals of high national or international standing who, despite not having extensive local experience or having being interviewed by the Accreditation Panel, Council considers to have sufficient technical ability to provide advice on specific ground conditions. Updated 01/07/2014 Page 17

19 ii) Category 2 Geo-Professional: A Chartered Professional Engineer or Engineering Geologist who is acknowledged by the Accreditation Panel as possessing the appropriate qualifications, skills and relevant experience in Tauranga City to provide advice on a limited number of less complex geotechnical issues found in the Council area. iii) Category 3 Geo-Professional: A Chartered Professional Engineer or an Engineering Geologist with an appropriate level of supervised work experience in a related field. (Typically those professionally qualified and practising Geo-Professionals or Engineering Geologists not listed on Tauranga City Council s Register.) b) Admittance to either Category 1 or Category 2 (for either a Chartered Professional Engineer or an Engineering Geologist) status on the register is by way of interview by an independent panel of specialists (Accreditation Panel) convened by Tauranga City Council. c) Accreditation on the Register is for a period of 5 years. At completion of the 5 year period 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 their current classification. To do this the Geo-Professional shall engage a Category 1 Geo-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 with guidance and demonstrate that they are becoming experienced enough through the ongoing 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-Professional engages a Category 1 Geo-Professional to act as mentor and peer reviewer. The mentor discusses the approach proposed to be used by the Geo-Professional for the investigation and comes to an agreement with the Geo-Professional on the proposed approach for the subject site. The site investigation is then undertaken in accordance with the agreed approach. Regular communication between the two professionals is undertaken during the investigation and while defining the geological model for the site, to ensure professional coaching occurs about key findings, assumptions and recommendations. b) The completed Geotechnical Assessment Report is then peer reviewed by the mentor prior to submission to Council, who shall confirm the findings of the report as being appropriate and able to be relied upon by Council. c) The cost for the peer review shall be met by the Consent Holder. Page 18 Updated 01/07/2014

20 d) In some circumstances the Geo-Professional may seek approval from Council to engage an appropriately qualified and experienced person who is not on the register of Accredited Geo-Professionals to act as mentor and peer reviewer. Such an application shall be made in writing to the Council stating clearly the qualifications and experience of the proposed reviewer. It should be noted that approval will be given only in exceptional circumstances. Updated 01/07/2014 Page 19

21 DS-10 - Appendix D Suitably 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 SQE Professional shall be engaged to investigate, define the hazards/risk and formulate solutions to ensure the risks associated with the hazard are avoided, remedied or mitigated and the designated safe building platform certified as meeting the performance criteria above. DS-10 - Appendix D.2 Professional) Suitably Qualified and Experienced Professional (SQE Refer to GEN-4 Definitions for definition of a suitably qualified and experienced professional. DS-10 - Appendix D.3 Role and Responsibilities of SQE Professional See GEN-4 Definitions for the role and responsibilities of a suitably qualified and experienced professional. Page 20 Updated 01/07/2014

22 DS-10 - Appendix E Accredited Geo-Professionals DS-10 - Appendix E.1 Listing Category 1 Geo-Professionals Please refer to the Accredited Geo-Professionals List on the Tauranga City Council's web-site. Updated 01/07/2014 Page 21

23 DS-10 - Appendix F Peer 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). Page 22 Updated 01/07/2014

24 DS-10 - Appendix G Assessment and Reporting (Informative Only) DS-10 - Appendix G.1 General The assessment of landforms shall utilise the following principals and may be supplemented by the expert opinion stated in the documents noted in DS-10 APX A Associated Standards: a) All earthworks for a development shall: i) Comply with the design criteria for completed landforms. ii) iii) iv) Take the reduction of overland flow velocity and the concentration of overland flow into account for the completed landform geometry and gradients. Provide for the permanent management of overland flow across landforms (contour drains, cut-off drains, formalised overland flowpaths not forming accessways etc). Provide for the construction of man-made structures to create safe landforms and designed building platforms. v) Where necessary provide for the installation of debris protection devices. vi) Define the earth fill and subgrade construction standards, define testing frequency, volumes and outline methods of testing to be used. b) Observation, quality assurance and review of the earthworks design during the construction phase are covered in CS-3 Earthworks. Engineering appraisal and design are required: i) Prior to detailed planning, which may involve some form of subsurface investigation. ii) iii) During the review of and advice on design concepts. During construction to ensure the adequacy of the bulk filling and the execution of the earthworks design. c) Development Evaluation Reports and Geotechnical Completion Reports relating to Category 1 and 2 landforms shall: i) Be subject to a level of quality control appropriate to the complexity of the project. This extends to an independent review within the company preparing the report of the technical areas, key assumptions of the report, investigation findings, adopted soils model, parameters and final conclusions opinions. ii) iii) iv) Presence of and influence on the development from existing geomorphic features. Assessment of historic landform stability and landform processes. Other engineering issues influencing the proposed development such as but not restricted to, seismic stability, liquefaction, shrink/swell effects, foundation requirements, limitations on surface water flow etc. Updated 01/07/2014 Page 23

25 v) In undertaking the assessment, the expertise of both a Geo-Professional and engineering geologist may be required to ensure a full understanding of the site 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 the development. 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 reduction due 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 the development requirements, the preservation of natural features including the existing soil profile, and the natural quality of the landscape. Preservation aspects include retaining natural watercourses, and excluding any development from natural gullies (refer to the District 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, reuse excavated 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 that environmental contamination does not occur. Refer to the Resource Efficiency in the Building and Related Industries (REBRI) website for guidelines on incorporating waste reduction in your project 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. Page 24 Updated 01/07/2014

26 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 and incorporated 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 a particular site. Avoid unnecessary earthworks, aim to protect original soils and drainage patterns 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 rock fall, 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 within the site, and to create a better sense of orientation and identity for the area as a whole. e) Increase the efficiency of overall land use, including the quality of individual sites and amenity areas around buildings, the economics of providing engineering services and the standard of roading and on-site vehicular access. f) Create, where needed, suitably graded areas for playing fields and other community facilities. g) Enhance the general environmental character of the area by softening the landscape or by artificially creating or emphasizing landforms of visual significance, particularly on 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 these into 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 life required by all other parts of the IDC. Preserve the flow of groundwater through the peat at pre-development levels. Updated 01/07/2014 Page 25

27 DS-10 - Appendix G.8 Table 2: Description of Geomorphological Zones and Assessment Guidelines Risk Category Very High and High Risk Requires extensive and detailed engineering geological and geotechnical assessment. Intensive investigation may be required and development may not be economically feasible. Boreholes to determine geology present will be required. Assessment of site required by both engineering geologist and Geo-Professionals. Moderate Risk Some sites may require detailed engineering geological and geotechnical assessment Visual assessment. Hand and possible drill investigation methods. Assessment Guidelines 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 maps c) 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 records f) Check with local residence and other sources for evidence of past instability, particularly during periods of heavy rainfall g) 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 include specific 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 be required 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 engineering geology site model k) Measure groundwater pressures in the soils strata and evaluate the transient pressures that may develop ender extreme rainfall conditions l) Produce engineering geological report with details of mass movement features and other ground failure hazards m) 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 other sites, provide detailed rationale for the use of such data n) Undertake slope stability evaluation using approved methods o) Make recommendations for use of site and provide design for remedial measures if appropriate 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 maps c) 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 records f) Check with local residence and other sources for evidence of past instability, particularly during periods of heavy rainfall g) If absence of recent or current landslide activity is confirmed, prepare report confirming this with appropriate documentation (map Page 26 Updated 01/07/2014

28 Low Risk Does not require engineering geological and geotechnical assessment Very Low Risk No requirement for Engineering Geology or Geo-Professional expertise and representative sections) h) If ground hazard identified, follow Steps 7 to 15 of Zone 1 procedures 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 a) Site to be inspected by competent category 3 person Page 27 Updated 01/07/2014