134 Mahurangi West Road, Puhoi Geotechnical Completion Report
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8 August 2019 134 MAHURANGI WEST ROAD, PUHOI GEOTECHNICAL COMPLETION REPORT Traverse Limited Ref: AKL2019-0006AD Rev. 1 www.cmwgeosciences.com 134 MAHURANGI WEST ROAD, PUHOI - GEOTECHNICAL COMPLETION REPORT 8 AUGUST 2019 AKL2019-0006AD Date Revision Comments 1 August 2019 A Initial draft for internal review 1 August 2019 B Final draft for internal review 5 August 2019 0 Final issue to Client 8 August 2019 1 Updated Resource Consent References Name Signature Position Project Engineering Geologist Prepared by Tessa Galbraith Principal Geotechnical Engineer Reviewed by Andrew Linton Principal Geotechnical Engineer, Authorised by Sam Gibb CPEng CMW Geosciences ii Ref. AKL2019-0006AD Rev. 1 Geotechnical Completion Report This report is to be read in its entirety together with the appended Statement of Professional Opinion 134 MAHURANGI WEST ROAD, PUHOI - GEOTECHNICAL COMPLETION REPORT 8 AUGUST 2019 Table of Contents 1. INTRODUCTION ..................................................................................................................................... 1 2. PROJECT BACKGROUND .................................................................................................................... 1 3. DESCRIPTION OF EARTHWORKS ...................................................................................................... 1 4. GEOTECHNICAL QUALITY CONTROL ................................................................................................ 2 4.1. Site Observations ............................................................................................................................. 2 4.2. Compaction Control ......................................................................................................................... 2 5. EVALUATION OF COMPLETED EARTHWORKS ................................................................................ 2 5.1. Natural Hazards ............................................................................................................................... 2 5.2. Land Stability and Erosion Control ................................................................................................... 3 5.3. Fill Induced Settlement..................................................................................................................... 3 5.4. Road Subgrades .............................................................................................................................. 3 5.5. Design of Shallow Foundations ....................................................................................................... 3 5.5.1. Bearing Capacity...................................................................................................................... 3 5.5.2. Foundation Settlements ........................................................................................................... 4 5.5.3. Soil Expansiveness Classification ........................................................................................... 4 5.6. Topsoil Depths ................................................................................................................................. 4 6. CLOSURE ............................................................................................................................................... 4 USE OF THIS REPORT ................................................................................................................................. 5 Appendices Appendix A – Statement of Professional Opinion as to the Suitability of Land For Building Development Appendix B – Drawings Appendix C – Field Test Data CMW Geosciences iii Ref. AKL2019-0006AD Rev. 1 Geotechnical Completion Report This report is to be read in its entirety together with the appended Statement of Professional Opinion 134 MAHURANGI WEST ROAD, PUHOI - GEOTECHNICAL COMPLETION REPORT 8 AUGUST 2019 1. INTRODUCTION In accordance with our instructions, this Geotechnical Completion Report has been prepared for Traverse Limited as part of the documentation to be submitted to Auckland Council following earthworks to form the accessway and four new lots within the 134 Mahurangi West Road development. Construction of this residential subdivision has been undertaken in accordance with the Auckland Council Resource Consent numbers BUN60302422, SUB60036198-A and LUC60302409-A, dated 17 June 2019. This report contains our Suitability Statement, specific comments related to items raised in the Resource Consent, relevant test data and the Cato Bolam Consultants as-built plan set as provided in Appendix B. This report covers the construction period March 2019 to May 2019 and is intended to be used for certification purposes for new lots (listed below) created from Lot 5 DP 177495 as follows: • three new residential lots numbered Lot 1, Lot 3, Lot 4 and Lot 5, and • the accessway to these lots (excluding Lot 3). This stage of the 134 Mahurangi West Road Development is located off Mahurangi West Road, Puhoi. As can be seen from the as-built plans, two of the lots have been affected by filling as part of the earthworks operations to a maximum depth of approximately 2.0 metres. Lot 2 of the development comprises the existing house site, and is excluded from this Completion Report. 2. PROJECT BACKGROUND The geotechnical investigations and design were undertaken by Engineering Geology Limited and CMW Geosciences as presented in the following reports: • Geotechnical Investigation Report for Proposed Subdivision – RL George, 134 Mahurangi West Road, Puhoi carried out by Engineering Geology Limited, referenced 5814b, dated 14 October 2016; • Geotechnical Investigation Report for 134 Mahurangi West Road, Puhoi carried out by CMW Geosciences, referenced AKL2019-0006AB Rev.0, dated 6 March 2019; • Building Platform Review Letter for 134 Mahurangi West Road, Puhoi carried out by CMW Geosciences, referenced AKL2019-0006AC Rev.0, dated 23 April 2019. 3. DESCRIPTION OF EARTHWORKS Earthworks to form the accessway commenced in early March 2019 with sediment controls and erosion protection including a temporary sediment retention pond constructed by Traverse Limited. This was followed immediately by topsoil stripping across the site. Once topsoil stripping had been inspected, cut and fill operations began with the benching of the cut/fill areas to form the accessway. Earthworks operations then began on the platform for Lot 5, including the formation of cut and fill batters to the west and east of the platform respectively. Fills of up to 1.0m were placed in Lot 3, alongside the accessway here. Earthworks were mostly complete by late April. Only minor cuts of up to 0.5m were undertaken to form Lot 1 and Lot 4. The main items of plant used by the contractor, Traverse Limited, included: • 3x 30 Tonne Excavators • Sheepsfoot Compactor/roller • 6 Tonne Loader/Dumper CMW Geosciences 1 Ref. AKL2019-0006AD Rev. 1 Geotechnical Completion Report This report is to be read in its entirety together with the appended Statement of Professional Opinion 134 MAHURANGI WEST ROAD, PUHOI - GEOTECHNICAL COMPLETION REPORT 8 AUGUST 2019 4. GEOTECHNICAL QUALITY CONTROL 4.1. Site Observations During the earthworks site visits were typically undertaken a few times each week to assess compliance with NZS 4431 and specific design recommendations and specifications. Site visits were carried out to observe and confirm compliance relating to: • Adequate topsoil stripping; • Fill areas prior to the placement of fill materials to ascertain that all mullock and soft inorganic subsoils had been removed; • Placement and compaction of engineered fills. 4.2. Compaction Control Compaction of engineered earth fills was controlled by undrained shear strength measured by hand held shear vane calibrated using the NZGS 2001 method and by air voids as defined by NZS4402. The criteria for undrained shear strength were a minimum single value of 110 kPa and minimum average of any 10 consecutive tests of 140 kPa. The criteria for air voids were a maximum single value of 12% and maximum average of any 10 consecutive tests of 10%. Vane shear strength, water content and in situ density tests were carried out on all areas of the engineered filling to at least the frequency recommended by NZS 4431. These tests showed on two occasions that the required compaction standards were not being achieved and to the best of our knowledge the failing areas of fill were re-worked as necessary. Subsequent testing confirmed compliance with the specification. 5. EVALUATION OF COMPLETED EARTHWORKS 5.1. Natural Hazards The appended as-built drawings depict the extents of a series of zones that contain limitations intended to ensure that future building and/ or earthworks on the lots is undertaken in a manner that does not lead to buildings being subject to any of the natural hazards described in Section 71(3) of the Building Act, i.e. erosion, falling debris, subsidence, slippage, and inundation. Consideration of the inundation hazard was outside the scope of CMW’s brief and has been assessed by others. The applied zones include: • Specific Design Zones (slope) – applied to building platforms within Lot 1, Lot 4 and Lot 5. Intended to protect building development from long term creep effects on or adjacent to steep slopes and to protect the slopes from inappropriate loading or undermining. Any cuts and fills or foundations that extend beyond the proposed building platform or are located on slopes that are over 1V:3H will require specific investigation and