STATEMENT OF EVIDENCE OF SHANE LANDER (GEOTECHNICAL - QD2) ON BEHALF OF MURPHYS DEVELOPMENTS LIMITED

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1 IN THE MATTER of the Housing Accords and Special Housing Areas Act 2013 ("HASHAA") AND IN THE MATTER of Proposed Qualifying Development Application ("QD2") for 125 Murphys Road, Flat Bush BETWEEN Murphys Developments Limited ("the applicant") AND Auckland Council STATEMENT OF EVIDENCE OF SHANE LANDER (GEOTECHNICAL - QD2) ON BEHALF OF MURPHYS DEVELOPMENTS LIMITED 11 NOVEMBER 2015

2 1. Introduction, Qualifications and Experience 1.1 My full name is Shane Gareth Lander. I hold a Bachelor of Engineering from Auckland University (1998) and a New Zealand Certificate of Engineering (Civil) from Carrington Polytechnic (1995). I am a member of the Institute of Profession Engineers New Zealand (MIPENZ), a Chartered Professional Engineer (CPEng) and am on the register of International Professional Engineers New Zealand (Int.PE(NZ)). I have practised as a professional geotechnical engineer in the following capacities: 1.2 I have 20 years experience undertaking professional geotechnical engineering assessments, construction observations and compliance documentation for clients in both the public and private sectors on a wide variety of minor to major projects within a range of geological settings. This has included hundreds of lots in the in the Southern Landslide Zone geology of Tuscany Estates residential development to the east of the study area, and similarly many substantial subdivisions and building developments to the north within the alluvial lowlands of Flat Bush, including the proposed Ormiston Town Centre, and associated infrastructure and stormwater treatment / attenuation ponds. 2. Code of Conduct 2.1 I confirm that I have read the Code of Conduct for Expert Witnesses contained in the Environment Court Practice Note 2014 and that I agree to comply with it. I confirm that, unless I state otherwise, I have considered all material facts that I am aware of that might alter or detract from the opinion that I express, and that the evidence is within my area of expertise. Geotechnical Evidence QD2 Page 2

3 3. Scope of Evidence 3.1 I have prepared three geotechnical reports for the study area, the first being a desktop study on some properties south of 125 Murphys Road (Ref J00039) dated 25 February 2015, the second being supplementary geotechnical advice dated 14 March 2015 (Ref J00039) pertaining to the Plan Variation, and the last being a comprehensive geotechnical investigation report (GIR) on 6 May 2015 (Ref J00016) addressing the first stage Qualifying Development at 125 Murphys Road. I have also provided an addendum memorandum to the latter report dated 4 August My evidence outlines the key findings of those reports, and then provides focus on the proposed road embankment. 3.2 My evidence is structured as follows: 4. Summary of Key Conclusions 4.1 Two different geological units exist in the study area, these being Tauranga Group alluvium and East Coast Bays Formation sedimentary lithology. 4.2 The study area comprises topography and ground conditions that are typical of other regions of the Flat Bush area. There are existing geotechnical reports relating to the study area and as such, ground conditions and geotechnical issues are reasonably well understood by me. 4.3 The proposed road embankment crossing will comprise engineer compacted GAP65 hardfill, with box culvert beneath and be supported by an engineer designed gabion retaining walls. There is an existing Vector gas line approximately 4m from the toe of the northern retaining wall. 4.4 It is apparent from my 6 March 2015 report that transition to bedrock deposits will be present within approximately 1.5m of the existing ground surface. 4.5 I have concluded that the road embankment can be safely constructed as proposed, provided the base of the retaining walls found upon the transition to bedrock materials at or below the invert level of the gas main. In doing so, I consider that the structure will not have adverse geotechnical effects to prevailing site conditions and loads will not be adversely transferred onto the gas main to the north. Geotechnical Evidence QD2 Page 3

4 5. Summary of Geological Setting 5.1 The study area is bounded by Murphys Road to the west and farmland to the north and east. The study area is mostly in pasture and is characterised by a branched tributary gully systems which becomes single as it approaches the northern boundary. The land either side of the gully systems is broadly undulating. Numerous service lines / utilities traverse the land in the vicinity of the qualifying development. 5.2 Two different geological units exist in the study area. The lower (northern) reaches of the site contains Tauranga Group alluvium, while the more elevated (central and southern) portions contain East Coast Bays Formation of the Waitemata Group sedimentary lithology. The elevated southwestern portion of the site falls within a large and significant area known as the Southern Landslide Zone, which generally defines the steeper ground of the Manukau Heights, Brookby and Whitford regions. 5.3 The site geomorphology is typical of this portion of the Flat Bush area and is characterised by moderately steep slopes that fall to the north, north-west and north-east. The flanks encompassing the gullies typically contain steep slopes (exceeding 1(v):4(h)), and these show signs of active soil creep and relic shallow seated slope failure. The general topography of the landform either side (remote from) the gully systems appears smooth with no obvious signs of past or recent slope movement. 6. Summary of Geotechnical Reports Desktop Study on Some Properties South of 125 Murphys Road dated 25 February My desktop report provided a summary of geological ground conditions with regard to the properties numbered 51, 57, 53, 67, 71, 75 and 79 Murphys Road; all located south of number 125 Murphys Road. 6.2 I recommended that comprehensive geotechnical investigations conducted by a Chartered Geotechnical Engineer would need to be undertaken on the aforementioned properties to identify the mechanisms of slope failure on the gully margins, and to confirm the existing ground conditions are congruent with accepted geotechnical ground models. 6.3 I concluded that such geotechnical risks can be eliminated or mitigated during earthworks design and in doing so, the land may be considered suitable for re-zoning to future urban use. Geotechnical Evidence QD2 Page 4

5 Supplementary Advice for the Plan Variation dated 14 March I was asked to review the Coffey Geotechnics (NZ) Limited Preliminary Appraisal Report dated 4 December 2014 which encompasses the study area, and the Auckland Council Plan Variation Application dated 9 February Specifically, Council stated The proposed plan variation seeks to provide zoning for urban development across the entire SHA area with relatively intense forms of development possible. The [Coffey] geotechnical appraisal for 125 Murphys Road identified that some areas of land, identified as Area C has significant geotechnical constraints and page 28 under sub heading Risks from natural hazard state, Area C is likely to be vested as green corridor zone the zoning as applied needs to be updated to reflect this 6.6 My 14 March 2015 response expressed that substantial portions of Area C may be modified and refined by geotechnical and engineering input that will allow development alongside green corridors, as is consistent with other developments in Flat Bush to date. In my experience this is addressed during subsequent subdivision design phases. 6.7 I have attached a site plan (annotated by me as Figure A) in Attachment 1 to this evidence, depicting the extent of Area C. Geotechnical Investigation Report (GIR) the First Stage Qualifying Development dated 6 May This report presented the results of a comprehensive site investigation across the northern extent of the study area, involving the drilling of 23 boreholes, cross sectional measurements and slope stability analyses. 6.9 I concluded in this report that provided specific recommendations I made were heeded, then the land was in my view geotechnically suitable for the proposed first stage Qualifying Development I have attached a site plan (annotated as Figure B) depicting the extent of the investigations made here. Addendum Memorandum to GIR dated 4 August I prepared a technical memorandum on 4 August 2015 relating to the proposed embankment comprising a gravity retaining wall system at Park Edge Road chainage 280m, with respect to its proximity to a gas main located approximately 4m to the north. I intended that this memo was to be read in conjunction with the overarching GIR I have just described. Geotechnical Evidence QD2 Page 5

6 6.12 Based on the GIR data, I inferred that hard transition to bedrock materials would be near to the surface (within 1.5m in places) and concluded that provided the foundations for the retaining wall system founded into the those materials, and that the invert of the gravity wall system was embedded at or below the invert level of the gas main, then vertical foundation loads associated with the embankment should not be transmitted onto the gas main. 7. The Proposed Road Embankment Key Geotechnical Considerations 7.1 The proposed road embankment across the stream requires the construction of a road retained on either side by gabion basket retaining walls up to a height of approximately 9.7m on the northern side and 7.1m on the southern side. 7.2 The gabion baskets will support geogrid reinforced GAP65 hardfill forming the road embankment. Three (2m wide) box culverts will transmit waterflows through the embankment in a south to north fashion. 7.3 I have annotated onto attached Figures A and B (refer to Attachment 1) the approximate location of the culvert, which is the site of the road embankment. 7.4 You will note on Figure B that boreholes 4 to 8 and cross section A-A from the GIR are relevant to this road embankment. Accordingly, I have attached (Figure C) geotechnical cross section A-A through this area to illustrate the ground model and location of the transition to bedrock materials I have mentioned above. 7.5 As noted in my summary of the Addendum Memorandum of 4 August 2015, I am satisfied that if the foundations for the engineer designed gabion walls are located within the transition to bedrock materials and found below the invert level of the gas main where it is located 4m to the north, then the embankment will be geotechnically fit for purpose and mitigate risk to the gas main. 8. Council Officers Section 42A Report 8.1 I have reviewed the Council planner's section 42A report prepared for the Council hearing. 8.2 I note on page 84 that consent notices may be required for geotechnical matters, and that a geotechnical completion report is required for 224C application, however there is nothing unusual about this in my experience. 8.3 I note on page 85 that Auckland Transport recommends conditions in terms of the detailed design and construction methodology for the culvert crossing and road embankment. I consider my evidence addresses some fundamental geotechnical foundation aspects for the embankment, culvert and retaining walls in this regard. Geotechnical Evidence QD2 Page 6

7 8.4 To the best of my knowledge there is nothing else raised in the planner s report that requires my further comment. 9. Conclusions 9.1 I have concluded that if the foundations for the engineer designed gabion walls are located within the transition to bedrock materials and found below the invert level of the gas main, where it is located 4m to the north, then the embankment (that is adequately designed, expertly constructed and documented by appropriate engineering observations and testing) will be geotechnically fit for purpose and mitigate risk to the gas main to the north. Shane Lander 11 November 2015 Geotechnical Evidence QD2 Page 7

8 ATTACHMENT 1 Figures A, B and C

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