Milford Centre Ltd. Private Plan Change GEOTECHNICAL ASSESSMENT

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3 Milford Centre Ltd. Private Plan Change GEOTECHNICAL ASSESSMENT Final 15 April 2008

4 Milford Centre Ltd. Private Plan Change GEOTECHNICAL ASSESSMENT Final 15 April 2008 Sinclair Knight Merz 25 Teed Street PO Box 9806 Newmarket, Auckland New Zealand Tel: Fax: Web: COPYRIGHT: The concepts and information contained in this document are the property of Sinclair Knight Merz Limited. Use or copying of this document in whole or in part without the written permission of Sinclair Knight Merz constitutes an infringement of copyright. LIMITATION: This report has been prepared on behalf of and for the exclusive use of Sinclair Knight Merz Limited s Client, and is subject to and issued in connection with the provisions of the agreement between Sinclair Knight Merz and its Client. Sinclair Knight Merz accepts no liability or responsibility whatsoever for or in respect of any use of or reliance upon this report by any third party.

5 Table of Contents 1. Executive Summary 1 2. Introduction General Background Scope 2 3. Site Setting Site Description High Density Residential Proposal Geology Hydrogeology 4 4. Geotechnical Appraisal Previous Investigations September 1993 Foundation Investigation May 2006 Subsoil Investigation for Carpark Areas January 2007 Rotary Percussion Drilling Geotechnical Considerations 7 5. Recommendations 8 6. References 9 Appendix A - Figures 10 Geotech final PAGE i

6 1. Executive Summary A geotechnical assessment has been undertaken for a proposed plan change application for the Milford Shopping Centre ( MSC ) site. The plan change is intended to provide for high density residential development. The basis for this report is development of approximately 250 residential units, by way of several new buildings. The scope for this report is to: - identify geotechnical conditions, - discuss hydrogeological issues, - provide commentary on geotechnical issues, and - provide geotechnical recommendations for the development in respect of the proposed plan change. The geology beneath the site is not uniformly consistent. Previous investigations indicated the following profile: heterogeneous fill deposits, underlain by alluvial/colluvial deposits which are in turn, in places, underlain by solid strata belonging to the East Coast Bays Formation. This is incised by basaltic lava belonging to the Kerikeri Volcanic Group to the east of the site. From the information known about the site it is anticipated that groundwater flow will be in a northwest/northerly direction toward the Wairau Estuary. Groundwater is likely to be encountered in excavations and will need to be/can be adequately controlled during construction. Based on current geotechnical information, the underlying ground conditions are considered suitable for the development planned. In our opinion, there are no geotechnical nor hydrogeological reasons for refusing the proposed plan change. We recommend that further site investigations are carried out, at the resource consent phase, to provide design parameters for foundations and retaining walls, and the safe management of excavations and groundwater during construction. Geotech final PAGE 1

7 2. Introduction 2.1 General Sinclair Knight Merz (SKM) has been commissioned by Milford Centre Ltd ( MCL ) to prepare a geotechnical assessment for a proposed plan change application for the Milford Shopping Centre ( MSC ) site. Site location and layout plans are presented on drawings 001 and 002 in Appendix A. 2.2 Background The proposed plan change seeks to achieve an amendment of relevant existing provisions within the operative North Shore City Council district plan as well as the insertion of new provisions into the district plan. The proposed amendments to the district plan will provide for high density residential development. It is noted that the provisions will themselves provide for resource consent approval for the development to be sought at a later date. Building consent approval will of course also be required. These processes subsequent to the plan change will provide an opportunity for Council to adequately control, by way of design assessment and through consent conditions, any specific requirements that arise from the recommendations of this report. The basis for analysis within this report is approximately 250 residential units, to be provided for within the existing site by way of several new buildings which could be built to the following Reduced Levels (RL): - Building 1 63 metres - Building metres - Building metres 2.3 Scope The scope of this geotechnical assessment is to: - identify geotechnical conditions, - discuss hydrogeological issues, - provide commentary on geotechnical issues, and - provide geotechnical recommendations for the development to be provided for via the plan change. Geotech final PAGE 2

8 3. Site Setting 3.1 Site Description The MSC site is located at 143 Kitchener Road, Milford and is located within a block defined by Milford Road to the east, Ihumata Road to the north, Omana Road to the west and the shops fronting Kitchener Road to the south. The site is utilised by the existing MSC. The shopping centre comprises a mixed occupancy, primarily a retail mall. Well known retailers operating from the MSC include The Warehouse, Woolworths and Whitcoulls. Associated asphalt carparking as well as landscaping are also located on site. Prior to development of the MSC in , the Milford Mariana Hotel, shops and a motel with associated private residences were located on the site. At its widest point (Milford Road to Omana Road) the site is approximately 205m across. Topographically, the site generally falls in a northwest direction towards the Wairau creek, with levels ranging from approximately RL 13m nearest the Milford Road / Kitchener Road intersection, to approximately RL 2.5m in the lower area of the site fronting Omana Road / the Wairau Creek. 3.2 High Density Residential Proposal The basis for analysis within this report is approximately 250 residential units, to be developed on the site by way of several new buildings which range from RL 34 metres to RL 63 metres. The main buildings will be located: - Building 1 fronting Omana Road to the northwest of the site - Building 2 fronting Omana Road, near the existing roundabout, to the north of the site - Building 3 set back from Milford Road, to the north east of the site The areas of development are shown on drawing 002 in Appendix A. 3.3 Geology Information regarding the site geology has been obtained principally from the Geology of the Auckland Urban Area Map (Sheet 2, 1:50:000), as well as from previous investigations carried out in 1993, 2006 and The geology beneath the site is not uniformly consistent. Generally, the site is indicated to be underlain by alluvial/colluvial deposits which are in turn, in certain places, underlain by solid strata belonging to the East Coast Bays Formation comprising residually weathered, alternating sandstone and mudstone with variable volcanic content and interbedded volcaniclastic grit beds. Geotech final PAGE 3

9 Incising the alluvium toward the east of the site is basalt lava belonging to the Kerikeri Volcanic Group. Previous intrusive investigations have identified heterogeneous fill deposits directly beneath hardstanding across the site. These deposits have been generally described as firm to stiff, orange/brown/grey, dry to moist clay or silt containing organic matter, gravel (basaltic/scoriaeous) and occasional glass, wood and shell fragments. Fill has also been described as loose to stiff, slightly plastic, dark brown/grey moist silty gravel/silt. This was identified at the centre and south of the site. We have not reviewed any information regarding the potential for contamination within the fill. Volcanic ash and lapilli generally described as stiff, moist, moderately plastic, reddish brown, sandy silt with minor clay and gravel was recorded to the northeast of the site beneath the current carpark area. A cross-section (taken NW-SE through the site) identifying the geology beneath the site and a borehole location plan are presented on drawings 003 and 004 respectively in Appendix A. 3.4 Hydrogeology Local water resources which affect groundwater flow are: - the Wairau estuary adjacent to the site to the north west - Lake Pupuke located approx 400m from the site to the south - Milford Beach / Hauraki Gulf Coastline located approx 600 m from the site, to the north east Based on the available information, which includes levels pre and post development (in reference to the existing MSC); groundwater exists at relatively shallow depths beneath the site. Groundwater levels, recorded in boreholes toward the east of the site, show that depths to groundwater have varied, since 1993, between 1.5 and 5.9 m). There is limited information regarding groundwater for this site. However, recent monitoring was initiated by SKM, including; re-drilling of borehole P8 (now renamed BH08) and installing two standpipe piezometers at deep and shallow depths. Recent monitoring visits (July to August 2007) have identified groundwater at depths of between 1.4m and 1.78m. Monitoring will continue until December It is anticipated that groundwater flow will be in a northwest/northerly direction toward the Wairau Estuary. Geotech final PAGE 4

10 4. Geotechnical Appraisal 4.1 Previous Investigations To date, three geotechnical investigation assessment reports/letters have been produced regarding the site. This section of the report briefly reviews the key findings from the following investigations: Foundation Investigation for Proposed Milford Shopping Centre dated September 1993, Soil & Rock Consultants (Ref: 93123); Subsoil Investigation for Carpark Areas at Milford Shopping Centre, Milford, North Shore City, dated May 2006, Soil & Rock Consultants (Ref: 06114); and Rotary Percussion Drilling Carpark area at Milford Shopping Centre, Milford dated January 2007, Soil & Rock Consultants (Ref: 06114). A summary borehole location plan is presented on drawing 004 in Appendix A. 4.2 September 1993 Foundation Investigation The 1993 Soil & Rock Consultants report was produced prior to construction of the existing MSC. The intrusive investigation comprised 11 boreholes (to a maximum depth of 19.5m), 6 hand auger holes (to a maximum depth of 3.3m) and 6 Scala Penetrometer tests. The subsoil conditions were recorded with respect to the two terraces or ground levels which formed the topography of the site in Generally ground conditions across the site comprised asphalt underlain by varying units of clay and silt overlying basalt. Basalt was recorded at depths of between 1 and 5.2m with a maximum thickness of 3.5m. Recommendations were provided for development of the MSC. 4.3 May 2006 Subsoil Investigation for Carpark Areas The 2006 Soil & Rock Consultants report was produced after development of the MSC. The investigation was carried out to assess subsurface ground conditions related to expanding the existing car parking space. Following intrusive investigation comprising 21 hand augerholes (AH1 to AH21) and Scala penetrometer testing, subsoil conditions were found to be consistent with those identified in the previous site investigation report. The report states the site comprised volcanic deposits overlain by hardfill and earthfill. Geotech final PAGE 5

11 The main findings included a basalt mound beneath the old Marina hotel building and across the MSC carpark. 4.4 January 2007 Rotary Percussion Drilling Rotary drilling was carried out in January 2007 to further quantify the depth and thickness of basalt rock beneath the shopping centre carpark. The supplementary investigation comprised 13 boreholes. The depth to basalt was proved between 2.2 and 4.3m. The maximum thickness of basalt was recorded as approximately 6.8m, located at the north-western corner of the carpark. It should be noted that thicknesses determined by this intrusive investigation are based solely on the base of the borehole. The actual thickness of the basalt is likely to exceed this. Generally the basalt was fractured at the top of the unit. The material lying straigraphically above the basalt was described as Volcanic Ash, generally described as reddish brown, sandy SILT, minor gravel, very stiff, moist, and moderately plastic. Groundwater was recorded in one location at the centre of the carpark, within the fractured basalt at depths of 5.5 and 5.9m. Geotech final PAGE 6

12 4.5 Geotechnical Considerations Foundation Design Based on current geotechnical information, the underlying ground conditions are considered suitable for the proposed development. This position is based on the results of earlier reporting and our site investigations. Foundations for the main buildings are likely to be piled, however there is the potential for pad or raft foundations in the areas underlain by basalt. Further investigation is required to develop foundation design parameters. Excavations and Groundwater Excavations at the site should be feasible using an appropriate type of hydraulic plant. However, any significant excavations into the basalt may require controlled blasting to minimise the duration of adverse effects from noise and vibration. All excavations at the site will require adequate lateral support, or battering back to a safe angle, to ensure their stability. The potential for contamination of the fill identified at the centre and south of the site will need to be assessed at resource consent stage, so that appropriate plans can be developed for safe management and disposal of the material. Groundwater is likely to be encountered in excavations and will need to be adequately controlled during construction. Geotech final PAGE 7

13 5. Recommendations In our opinion, there are no geotechnical nor hydrogeological reasons for refusing the proposed plan change. We recommend that further site investigations be carried out at the resource consent phase to provide design parameters for foundations and retaining walls, and the safe management of excavations and groundwater during construction. The further detailed geotechnical investigation should include shallow and deep boreholes. This should also include the installation of groundwater monitoring wells and geotechnical laboratory testing. These assessments will provide the basis for Council to institute the necessary conditions through the further consent processes to ensure adequate foundations, retaining structures and groundwater controls are in place. Geotech final PAGE 8

14 6. References The Geology of the Auckland Area (1:250,000 Map extract 3), Institute of Geological and Nuclear Sciences, Foundation Investigation for Proposed Milford Shopping Centre dated September 1993, Soil & Rock Consultants (Ref: 93123). Subsoil Investigation for Carpark Areas at Milford Shopping Centre, Milford, North Shore City, dated May 2006, Soil & Rock Consultants (Ref: 06114). Rotary Percussion Drilling Carpark area at Milford Shopping Centre, Milford dated January 2007, Soil & Rock Consultants (Ref: 06114). Geotech final PAGE 9

15 Appendix A - Figures Geotech final PAGE 10

Lake Rotoiti Wastewater Scheme - Stage 1 Investigations. Rotorua Lakes Council

Lake Rotoiti Wastewater Scheme - Stage 1 Investigations Rotorua Lakes Council i Contents 1 Introduction...1 2 Site Description...1 3 Geological Setting...1 4 Geotechnical Investigation...1 4.1 Borehole