GEOTECHNICAL INVESTIGATION WAVERLY WIND FARM

Transcription

1 GEOTECHNICAL INVESTIGATION WAVERLY WIND FARM

2 RILEY CONSULTANTS LTD New Zealand Web: AUCKLAND 4 Fred Thomas Drive, Takapuna, Auckland 0622 PO Box , North Shore, Auckland 0745 Tel: Fax: CHRISTCHURCH 395 Madras Street, Christchurch 8013 PO Box 4355, Christchurch 8140 Tel: Fax: GEOTECHNICAL INVESTIGATION WAVERLEY WIND FARM Report prepared for: Chancery Green Ltd on behalf of Trustpower Limited Prepared by: Benjamin Roy, Engineering Geologist... Reviewed by: Steven Price, Associate, Engineering Geologist... Approved for issue by: Don Tate, Director, CPEng... Report reference: 10WAV/RC-B Date: 9 February 2016 Copies to: Trustpower Limited Electronic copy Riley Consultants Ltd 1 copy Issue: Details: Date: 0.1 Draft Geotechnical Investigation 28 August Revised Draft Geotechnical Investigation 18 September Revised Draft Geotechnical Investigation 5 October Revised Draft Geotechnical Investigation 18 March Revised Draft Geotechnical Investigation 16 October Revised Draft Geotechnical Investigation 5 February Geotechnical Investigation 9 February 2016 GEOTECHNICAL CIVIL WATER RESOURCES

3 Contents 1.0 Introduction Site Description Geology and Geomorphology Site Investigation Subsurface Conditions Stability Erosion Liquefaction Analysis Foundation Recommendations Possible Founding Solutions Piled Foundations Soil Improvement and Shallow Foundations Roading Earthworks Groundwater Extraction for Foundation Construction Methodology Analysis Permeability Modelling in Slide v Single Well Discharge Discussion of Groundwater Modelling Results Construction Sequencing Potential Discharge Locations Future Testing Conclusions Limitation References Appendices Appendix A: Appendix B: Appendix C: Appendix D: Appendix E: Machine Borehole Logs (RILEY and SKM) Laboratory Analysis Results Liquefaction Analysis Results Groundwater Calculations Drawings

4 RILEY CONSULTANTS LTD New Zealand Web: AUCKLAND 4 Fred Thomas Drive, Takapuna, Auckland 0622 PO Box , North Shore, Auckland 0745 Tel: Fax: CHRISTCHURCH 395 Madras Street, Christchurch 8013 PO Box 4355, Christchurch 8140 Tel: Fax: Introduction GEOTECHNICAL INVESTIGATION PROPOSED WIND FARM, WAVERLEY The following report has been prepared by Riley Consultants Ltd (RILEY) for Chancery Green Ltd on behalf of Trustpower Limited. It presents the results of a geotechnical investigation undertaken at the above prospective wind farm site to confirm geotechnical feasibility of the project. This report should be read in conjunction with our Civil Assessment of Access Tracks and Hardstands Report, RILEY Ref: 10WAV/RC-A, dated 5 February It is proposed to construct 48 wind turbines on the South Taranaki Coastline, near the township of Waverley. Sinclair Knight Merz Ltd (SKM) has previously undertaken a geotechnical investigation of the proposed wind farm site, as part of a civil works study for Waverley Wind Farm Ltd (WWFL). The SKM July 2007 report made recommendations regarding methodology and engineering design concepts for 45 turbines split between the eastern and western sites. RILEY has recently undertaken a geotechnical assessment of the proposed site. The investigations undertaken by RILEY cover a larger turbine layout area than the previous SKM report. The primary purpose of the recent investigations is to obtain further surface and subsurface information and complimentary data to the 2007 SKM investigations, comment on foundation options, and provide sufficient parameters for preliminary foundation design. Comments on stability, road formation, groundwater extraction for foundation construction, and earthworks are also included. 2.0 Site Description The turbines are proposed to be located on an area of generally flat to gently undulating land, roughly 7km south-west of Waverley, Taranaki. The farmed pasture land is dissected through the centre by a stream channel and further altered throughout by numerous man-made drainage channels. Access to the site is available via Peat Road from State Highway 3. Turbine sites have been proposed for 48 turbines and the indicative layout is shown on RILEY Dwg: 10WAV/RC-1, appended. 3.0 Geology and Geomorphology The :250,000 Geological Map 7 of Taranaki, published by IGNS, indicates that the site is underlain by Holocene Sand Dunes (predominantly comprising sand and silt) and Pleistocene beach deposits consisting of marine terrace cover beds (conglomerate, sand, peat, and clay). Cross Section B to B of the IGNS map, and the labelling of coastal outcrops on the geological map, indicate that Whenuakura Group rock deposits underlie the marine terrace cover. GEOTECHNICAL CIVIL WATER RESOURCES

5 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 2 Whenuakura Group deposits consist of Bioclastic limestone, pebbly sandstone, fine, well sorted micaceous sandstone, and massive siltstone. Locally to the site, a fine, well sorted, massive, micaceous sandstone with complete shell clasts is seen to form vertical cliffs facing the Tasman Sea, along the eastern and western extents of the sites coastline (Photo 1). Such material is typically found at depth in drilled boreholes that extend through the dune sands and old beach deposits. Typical cross sections are shown on RILEY Dwg: 10WAV/RC-2, appended. Exposures of all three major geological group materials can be seen in road cuttings, and outcrops at the surface (see Photo 1). These exposures indicate that bedding is generally sub-horizontal; however, each unit is separated by erosional unconformity surfaces that see the deposits at higher relative levels progressively further inland. Minor terraced levels of these deposits indicate periods of sea-level change and historic depositional environments. Photo 1: Whenuakura Group fine sandstone deposits forming cliffs in the western most region of the investigation area (photograph taken 200m from MH4 drilling location) The Whenuakura Group sandstone and Pleistocene Beach deposits are interpreted as underlying the entire site. The younger dune sands are present across the site, except for areas of raised undulating topography between turbine sites at the northern extent of the turbine envelope, refer RILEY Dwg: 10WAV/RC-1. This undulating topography is shown on the 2008 Taranaki IGNS Geological Map as consisting of the Pleistocene Beach deposits outcropping at the surface. The relatively flat and slightly terraced land has predominantly been altered by sequences of mining operations carried out between 1971 and The historical Waipipi Iron Sands Dredging Operation, carried out on the site, targeted the titanomagnetite rich iron deposits within the dune sand faces. The mining process (as shown on Photos 2 and 3) included dredging and separation procedures to remove the ore, followed by pumping back the unwanted tailings and leveling to provide a reinstated landform surface. Such a process has obliterated the original landform, which likely comprised rolling dunes. 9 February 2016 Riley Consultants Ltd

6 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 3 Exploration drilling carried out under supervision of SKM in 2007 revealed a black sand deposit up to 9m in thickness interpreted as tailings fill up to the maximum depth of 9m. This corresponds well with an estimated approximate 7m average mining depth. Photo 2: Ironsand dredging operation on the proposed wind farm site during the mid-1980s (from IGNS: Geology of the Taranaki Area, D.L. Homer) The coastline is a dynamic environment, with erosion in some areas and accretion in others. Inspection during our investigation indicates the western and eastern coastline portions of the study area are likely undergoing retreat, whilst sand is accreting in the central portion near proposed WTG34 to WTG48. Accretion and erosion are episodic and can be significantly altered by storm events. As such, the current pattern of accretion and erosion may alter in the future. From geological mapping undertaken on-site, there is no observable surface expression of any active fault-related movement. However, the site is closely in line with the Waverley Fault Zone, made up of several active faults trending in a north-east direction. The geological map indicates an active fault is likely to run roughly adjacent to the eastern extent of the proposed site and within 1km of the eastern-most proposed turbines (WTG37 and WTG44). The map does not indicate any active fault running through the western site. 9 February 2016 Riley Consultants Ltd

7 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 4 Likely remnant dune formation prior to mining Photo 3: Ironsand dredge and floating concentration plant in operation at the proposed wind farm site (from IGNS, mineral commodity report 15 Iron) 4.0 Site Investigation A site inspection, including geomorphic mapping, was undertaken by a senior engineering geologist and engineering geologist from RILEY. This was followed by an investigation comprising four machine drilled boreholes across the site. The boreholes were drilled to a target depth of 20m using a wire-line machine drill rig. Dual piezometers were installed in boreholes MH1 and MH2 to establish a groundwater profile across a representational area of the site. The piezometers measure the water level in two targeted zones, 2m to 5m (to measure relatively shallow water levels in the loose sand), and 17m to 20m (to measure deeper water levels in the conglomerate/sand beach deposits and sandstone beneath). Regular Standard Penetration Test (SPT) strength measurements were undertaken in each borehole at regular intervals, generally, every 1.5m of depth. SPTs were carried out using a split spoon attachment to a target depth of 450mm. Borehole positions were located off identifiable features nearby and fixed by hand-held GPS measurements. Samples were taken from each borehole for later particle size distribution (PSD) laboratory analysis. Core samples of the coherent fine sandstone were taken from MH3 and MH4 for Unconfined Compressive Strength (UCS) tests. Geological mapping of coastal cliff exposures and an inland terrace cliff were undertaken by an engineering geologist to identify the structural characteristics of underlying soil and rock types. 9 February 2016 Riley Consultants Ltd

8 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page Subsurface Conditions Results from the recent subsurface investigation were generally consistent with the assumed geological model and previous SKM drilling. The boreholes encountered surficial sands overlying silt/clay/sand/conglomerate, below which is extremely weak fine sandstone. On a visual basis within the cores, there appeared to be little difference to separate mine tailings sand from natural sand. However, magnetic testing of the core recovery showed a strong magnetic response for inferred natural titano-magnetite rich sand deposits, with observably weaker response from similar sand deposits interpreted as mine tailings. This response indicated a fill depth of 6m in MH1 and 8m in MH2. There were no direct visual indicators to identify this change from fill material to un-mined dune sand deposits. This is likely due to both the reworked nature of mine tailings and observed flushing/hole collapse difficulties faced during drilling investigations. SPT testing within the fill gave an N count of 2 to 28 (very loose to medium dense) with an average of 13 (medium dense). The natural sands gave an N count range of 2 to 50+ (very loose to very dense) and an average of 24 (medium dense). For both natural and fill sands, the density was highly variable and no trends are obvious in the information collected. Pleistocene beach deposits were observed as silt with clay, sand, organic material, and sandy conglomerate layers ranging in thickness from 5m to over 8.1m. These were located at depths ranging from 7m to 20.4m and showed varied strength from loose sandy conglomerate to very stiff silt of 150kPa strength, with pocket penetrometer testing. SPTs indicate stronger material than the overlying dune sands with an average N count of 41, although N counts were variable. The Whenuakura Group fine sandstone was encountered at depth beneath all machine borehole locations with the exception of MH1. This rock unit was not encountered within the 20m depth of the MH1 borehole; however, is inferred from cross section construction to be within a few metres of the borehole base. A summary of key relevant points is provided below: Drilling investigations undertaken by SKM, reported a black sand deposit averaging 9m in thickness and resting on a mudstone formation that dips flatly towards the sea. Natural material comprising sand dunes, volcanic sands, lignite bands, and some conglomerates were reported with mudstone rock expected at significant depth below the ground surface. From our borehole investigations, topsoil was typically of 0.05m to 0.1m thickness and was encountered at all investigation locations. Very loose to medium dense sand with occasional silt horizons is present from the surface to depths of 10m to 15m. This includes both mining tailings fill and natural dune sand deposits. SPT values ranged from N = 2 to 50+. Generally dense silt, sand, and conglomerate horizons of Pleistocene Beach deposits were encountered at 7m to 13m depth and showed SPT values ranging from N=5 to 50+, typically exceeding February 2016 Riley Consultants Ltd

9 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 6 Whenuakura Group fine sandstone appears as a massive unit, significantly weathered at depth. The extremely weak sandstone was encountered at variable depths, between 13m and 18m depth (although it was not encountered in MH1 to 20.4m depth). UCS testing provided values of 508kPa to 745kPa and SPT values were generally N=50+, however, it was observed as low as N=39 (results from UCS laboratory testing are shown in Appendix B). Groundwater levels were measured to be 2.7m depth at MH1 within the sands, reducing to 0.7m depth at MH2 near the coastline (i.e. near ground surface). Groundwater level in the beach deposits was measured at 6m depth, whilst the Whenuakura Rock was dry. SKM had previously measured groundwater levels at 2.6m depth. It is considered likely that groundwater is perched above the sandstone within the sands and beach deposits. Key strength characteristics of the soils are presented in Table 1 below. Table 1: Key Strength Characteristics of Soils Material Fill old tailings Holocene Dune Sands Pleistocene Beach Deposits Whenuakura Sandstone 6.0 Stability SPT N Count 2 to 28 range 13 average 2 to 50+ range 24 average 5 to 50+ range 41 average 39 to 50+ range 48 average Shear Strength pocket penetrometer (kpa) 30 to 150 range Unconfined Compressive Strength (kpa) 508 to 745 range 626 average The site is generally flat to gentle lying, which is in part due to landform modification by previous mining of the 1970s and 1980s. On these gentle grades, slope movement under extreme static conditions (ground saturation) is considered unlikely. However, there are steeper slopes on the site associated with dunes near the coast and more inland remnant dunes in the central portion of the site. There are intermediate slopes of approximately 2m to 4m height, which separate successive terraces as they fall towards the coast. In general, there is very little evidence of recent or active slope instability across the site, with the exception of coastal erosion and active dune processes. This is considered a reflection of the relatively gentle nature of the site and rapid draining characteristics of the underlying sands. Stability analyses have been undertaken with respect to the inter-terrace steeper slopes. Assuming a worst case sand of Ø = 25 and groundwater level at the surface in an extreme event, we assess a Factor of Safety (FoS) of 1.2 for the steepest such inter-terrace slope (1:5) under static conditions, approximately 80m from the closest proposed turbine (WTG18). Inter-terrace slopes, which are closer to proposed turbines, are not as steep and have an assessed FoS of >1.5 under similar extreme conditions. 9 February 2016 Riley Consultants Ltd

10 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 7 The critical situation for stability will likely be immediately following a strong seismic event. Analyses, as outlined in the following section, indicate the sands below the water table can potentially liquefy under earthquake shaking. In this situation, the FoS for steeper slopes decreases to <1.0, i.e. local failure. Analyses indicate that at a setback of 30m from the crest of steeper slopes (defined as >1V:5H, 11 ), a FoS of >1.0 is calculated for this transient situation, which is typically considered acceptable. There is potential for turbine sites to be located in proximity to the coastal dunes, such as shown on the indicative layout (refer RILEY Dwg: 10WAV/RC-1). We consider these turbines have been sited sufficiently far back not to be significantly affected by active dune processes. The turbine foundations and associated construction pads can potentially be sited clear of any marginal slopes. During the drilling investigation, difficulties were faced within saturated sand material at depth. Potentially loose material frequently collapsed and jammed drilling equipment suggesting high water table saturation of the sands could potentially affect foundation excavation. Photos 2 and 3 show further evidence of mining excavations holding water (likely assisted by natural high groundwater level); however, a temporary cut to a natural dune above the water table in Photo 2 shows a relatively steep face without collapse. There is considered likely to be large variability in the density and stability of sands both within the natural and reworked sand formations. On the information available, it is difficult to ascertain safe batter angles at each site across the proposed wind farm and can be determined at the detailed design stage. The stability of steeper sand slopes, either in cut or natural ground, can be improved by either local re-grading, vegetation growth, overlay with geotextile, or possible setback from the identified hazard. We do not consider slope instability presents a significant risk to the proposed turbines. In isolated cases where it may present a risk, this can be addressed by the above techniques. 6.1 Erosion The investigation area is subject to coastal shoreline erosion, aeolian wind erosion, and stream incision reshaping the local environment over time. The shoreline varies from sea cliffs at the western and eastern extents of the area, to extensive dunes and sand beaches through the central region of the site. Wind erosion and stream flow are both likely to provide ongoing remobilisation of loose deposits. Proposed turbine locations have generally been setback from drainage channels and areas of active dune migration to limit the effect of ongoing wind and stream erosion. 7.0 Liquefaction Analysis Significant depths of sand underlie the proposed turbine platforms along with a relatively high groundwater level (within 3m of ground surface). Plotting of particle size distribution from recovered sand samples, as shown in Appendix B, indicates the sands are within limits identifying potentially liquefiable soils as defined by the Ministry of Transport, Japan, Active fault zones, which could generate strong ground motion, have been identified nearby in the Taranaki Basin and Waverley Fault Zone near Waverley Township, as indicated on IGNS maps. 9 February 2016 Riley Consultants Ltd

11 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 8 Due to the potential risks of liquefaction, a computer based assessment was performed using Liquefy Pro, a package capable of assessing earthquake induced liquefaction and settlement. The analyses were based on the following parameters; material descriptions from machine borehole logs, SPT strength values, and an assumed average groundwater level of 2.6m. Two earthquake scenarios were assessed for the 500- and 1,000-year return period earthquakes of 7.5 Magnitude, normalised to 0.27g and 0.35g acceleration. The analyses identified liquefiable materials in each RILEY investigation borehole location (MH1 to MH4), for both scenarios of earthquake induced shaking. The results are shown in Appendix C. Typical liquefiable material is identified from 3m to 8m depth in both the natural and reworked sands. Liquefaction in the material encountered is considered possible to depths of 12.5m in the seismic events modelled, and induced settlement across the four sites is modelled as ranging from 20cm to 47cm (500-year return period) and 22cm to 47cm (1,000-year return period). The main hazard to a near surface turbine foundation is differential settlement leading to tilting of the structure. For 400mm total settlement, and assuming differential settlement is 50%, the tilt is 1:75 for a 15m diameter foundation. This tilt far exceeds typical limits for a conventional building of 1:250, and it is noted a wind turbine is far more sensitive to tilting than a conventional building. To limit potential differential settlement to acceptable limits, any ground improvement works will need to essentially render the entire ground beneath the turbine non-liquefiable. Lateral spreading is considered to be a possible risk across the site. The proposed turbines are situated on gentle slopes, typically of 3% or less, empirical calculation methods of Youd 2002 indicate lateral spreading of the ground could potentially occur at between approximately 400mm to 700mm displacement downslope in a significant (ULS 500-year) seismic event across much of the site. In the situation of lateral spreading, ground improvement is preferable to piles (although piles can potentially be used). Suitably designed and constructed ground improvement beneath and immediately surrounding turbines (i.e. extending out from the foundation edge half the depth of liquefiable soils) could provide adequate protection to the structure against such movement, subject to specific assessment. Specific assessment of the extent and likely magnitude of lateral spreading displacement will need to be undertaken at detailed design stage. This will likely require testing at the turbine sites by CPT or dynamic probe testing; both relatively rapid methods of testing and obtaining soil data without sample recovery. 8.0 Foundation Recommendations There is a range of differing foundation options for wind turbines from shallow pads to deeper piles. Shallow foundations for wind turbines typically comprise a mass concrete pad, suitable to spread the turbine weight, minimise rocking, and resist overturning forces. Such pads typically need to be supported on material of uniform high stiffness. Shallow foundations are not considered suitable to support the proposed wind turbines at the site without soil improvement, as analysis identifies liquefiable subsoils typically from 3m to 8m depth, and in some cases, greater. Under assessed return period earthquake events, shallow foundations without soil improvement would likely be subject to excessive tilting and settlement as foundation soils are subject to liquefaction. Similarly, a pad tied down with anchors is not recommended as this does not adequately support the turbine during seismic events, which may lead to liquefaction. 9 February 2016 Riley Consultants Ltd

12 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page Possible Founding Solutions Several founding solutions are considered potentially feasible to support the proposed turbines. Piles could comprise either driven or cast in-situ bored piles. Alternatively, where predicted liquefaction does not extend to significant depth, soil improvement to reduce liquefaction potential could be undertaken to allow the use of a shallow pad. For this stage of the project, it is assumed the estimated total settlement would need to be reduced to a maximum of 40mm (compared with current estimated 220mm to 470mm). This equates to a tilt of 1:750 over a 15m diameter foundation, which is the typical limit for a foundation sensitive to settlement effects. The actual tolerable settlement limits would require further specific assessment at detailed design stage. Design optimisation may lead to differing foundation solutions across the site at different turbine locations, dependant on the depth of predicted liquefaction. It is expected that subsurface investigation will be required at each of the proposed turbine positions at detailed design stage. Outlined in the following sections are discussion, general recommendations, and proposed design parameters for each of the possible suitable foundation solutions for the site Piled Foundations Piled foundations are considered an option and should be subject to further geotechnical investigation and design input specific for each turbine location at detailed design stage. An issue for piles would be the risk of lateral spreading and subsequent pile loading. This can potentially be accommodated through piles able to withstand heavy lateral loading and be adequately socketed into non-liquefiable material by approximately 10m. The economics of accommodating such lateral loading may potentially lead to ground improvement being the preferred foundation solution. Either driven or bored cast in-situ piles are considered feasible. Recent investigations indicate bored piles will likely encounter collapsing sands where density is low and below the water table (which is typically within 3m of ground surface). The occurrence of these collapsing sands will likely be variable and full casing through the Holocene Sands and upper Pleistocene Beach Deposits may be required. The advantage with bored piles is the potential for extended embedment into the founding strata to achieve significant skin friction and the ability to verify the founding material. Driven piles avoid the issue of hole collapse and potentially could be the most suitable piling option to the site conditions. The weak rock at typically 13m to 20m depth (although likely between 20m and 25m at some locations) will provide a suitable founding strata. The overlying Pleistocene Beach Deposits may provide suitable founding material. Although the strength of these Pleistocene Beach Deposits is more variable than the underlying rock, SPT N counts for this material are typically 40 to 50+. Founding in these materials could potentially shorten piles by some 5m compared with founding on rock. In addition, conglomerate horizons within the Pleistocene Beach Deposits may present difficulties extending piles to greater depth whether driven or bored. For either bored or driven piles, allowance will need to be made for potential down drag effects of non-liquefiable material during a seismic event. Where lateral spreading is identified as an issue, piles would need to be designed to withstand lateral spreading forces and piles may extend 10m below the base of the liquefied soils (in these situations the economics of piled foundations may be questionable and ground improvement could be the preferred foundation system). 9 February 2016 Riley Consultants Ltd

13 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 10 Bored Piles Piles should be socketed into the underlying weak sandstone rock or very dense Pleistocene Beach deposits to provide end bearing capacity, and skin friction resistance in material below liquefiable soils. Possible founding solutions include pile groups beneath a pad or a single large caisson-type pile. The following parameters are recommended for preliminary structural design of end bearing piles embedded more than five times diameter into extremely weak rock or very dense Pleistocene Beach deposits: Geotechnical Ultimate bearing capacity 2,500kPa. Dependable bearing capacity 1,250kPa (ultimate limit state design). Allowable bearing pressure 850kPa (working stress design). Skin friction beneath liquefiable deposits and within very dense Pleistocene Beach or rock deposits can be assumed as follows (any skin friction within the overlying sand deposits should be ignored): Geotechnical Ultimate skin friction 100kPa. Liquefaction induced settlement can potentially produce down drag on the pile from the upper non-liquefied material. This will impart additional load on the pile, which can be assessed assuming a negative skin friction of 50kPa Geotechnical Ultimate from the upper soils. Driven Piles Given the variable ground conditions encountered during investigations and the need to resist uplift forces, a suitable driven pile will likely be at hollow steel tubular section. For preliminary design purposes, we have assumed a 500mm Ø to 600mm Ø section. It is expected the driven piles will extend a minimum of two times the diameter into the founding stratum. The following parameters are recommended for preliminary structural design of end bearing piles: Geotechnical Ultimate bearing capacity 3,000kPa to 3,500kPa. Dependable bearing capacity 1,500kPa to 1,750kPa. Allowable bearing pressure 1,000kPa to 1,200kPa. It is envisaged the piles will found on weak rock or, if possible, on the overlying very dense beach deposits. For skin friction beneath liquefiable deposits and within either very dense beach or weak rock deposits the following can be assumed: Geotechnical Ultimate skin friction 100kPa. For liquefaction induced down drag of the upper non-liquefied soils, the following can be assumed: Down drag ultimate skin friction 50kPa. 9 February 2016 Riley Consultants Ltd

14 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page Soil Improvement and Shallow Foundations If assessed liquefaction induced settlements can be reduced to an estimated 40mm or less, then supporting the turbine on shallow foundation would potentially be feasible (subject to confirmation of settlement limits). The risk of liquefaction and subsequent ground settlement can be reduced by the following types of work; densification, solidification, drainage, dewatering, and reinforcement of the susceptible soils. Densification and solidification are highly reliable techniques, with numerous successful examples. Drainage is considered to be reliable along with reinforcement; however, there are fewer examples to date. Dewatering is considered impractical for the site, primarily due to the vast size. Suitable soil improvement methods for the encountered site conditions are discussed below. It is recommended that CPT testing be performed prior and following any densification or solidification ground improvement works to evaluate the degree of improvement in liquefaction resistance and suitability to support the proposed turbine. An advantage to the Waverley Wind Farm is its distance from townships or sensitive structures. As such, vibration-type methods are likely feasible, subject to specific review. For any ground improvement programme, on-site review should be undertaken during the works and adjustments to the programme should be made as required. Specific assessment will be required to determine bearing capacity and rocking stiffness for a shallow-type foundation, depending on the ground improvement method adopted. However, for design purposes and assuming successful ground improvement, the following can be assumed: Assumed SPT N count 25 and foundation minimum 1m depth. Geotechnical Ultimate bearing capacity 720kPa. Dependable bearing capacity 360kPa. Allowable bearing pressure 240kPa. Possible improvement techniques include: Dynamic Compaction The use of a tamper that is repeatedly raised and dropped on a cable from height to impact the ground is an available option. Heavy tampers and greater drop heights can improve the ground down to approximately 9m depth, considered likely to be suitable for many of the proposed Waverley turbine sites (although, sites with deeper potential liquefaction will likely require an alternative method or piles). Groundwater level ideally needs to be 2m depth or greater. For some lower elevation sites, local dewatering may be required during works. The availability of suitable equipment at the time of construction is likely limited. Overseas experience indicates this method would likely be one of the most cost-effective. Additional sand would be required for backfilling of resultant surface depression. Vibrocompaction The use of a vibrating probe, or flot, to densify in-situ soils by vibration along with water jets. Particle size distribution tests indicate the sand on-site is within the acceptable range for densification by vibrocompaction. This process will leave a conical depression in the ground, which can be filled by compacted sand or hardfill, which could be sourced locally. Whilst this method is likely well suited to the site conditions and is relatively quick, the availability of suitable equipment in New Zealand at the current time is limited. 9 February 2016 Riley Consultants Ltd

15 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 12 Stone Columns Similar to vibrocompaction, a probe is fed into the ground along with aggregates, which are compacted into vertical columns. These stone columns improve the bearing capacity, and reduce settlement and liquefaction susceptibility. This technique is potentially suitable to the site, provided sufficient quantity of suitable aggregate is available. As with vibrocompaction, the availability of suitable machinery in New Zealand at this time is limited. Compaction Grouting A very stiff low mobility grout is injected to form concrete bulbs in the ground, pushing the surrounding ground outward, thereby causing compaction. These bulbs can be stacked upon one another to form columns. Compaction grouting has been used in Japan and the U.S. in recent times, and is considered suitable for the sands encountered on-site. This technique struggles to densify near surface deposits due to less overburden pressure. Deep Soil Mixing Typically, mechanical mixing of soil and stabiliser (often cement) using rotating auger and mixing bar arrangement, creates high strength or low permeability columns, or panels, thus minimising liquefaction induced ground displacement. This method has been employed widely for the past 30 years and is used in New Zealand. The soils on-site should be suitable for this method. For all ground improvement options, specific assessment is required and review of available specialist equipment in New Zealand to assess which method is most appropriate, expedient, and economic. As outlined in Section 7.0, to achieve likely acceptable differential settlement tolerances, any ground improvement works will need to reduce significantly or eliminate completely the potential for liquefaction. 9.0 Roading The design and construction of the access tracks will be required to accommodate the traffic volumes anticipated for construction, any over-sized turbine components and the self-tracking of the heavy lift construction crane. The site access tracks will have unbound metal pavements and will be designed in accordance with accepted industry design standards suitable for the intended purpose of the tracks (e.g. AUSTROADS Design Manual for Unbound Metal Pavements). The AUSTROAD design method provides pavement thicknesses from tables based on the input of the following main parameters: Design life traffic volumes, which will vary depending on the number of turbines being serviced by a particular track. The desired performance level of the track. Rigidity of subgrade which is quantified as the empirical Californian Bearing Ratio (%) (CBR). 9 February 2016 Riley Consultants Ltd

16 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 13 Our assessment shows the tracks will be primarily founded on loose sands with high variability and likely some areas underlain by very loose sands. High groundwater levels and areas prone to ponded surface water are likely to be encountered variably across the proposed roading tracks. The site tracks will be established along existing farm access tracks where possible, and will require minor cut and fill earthworks to minimise the fall of tracks across inter-terrace slopes. The subgrade and preliminary CBR values from limited testing on-site, indicate a CBR of 3 below topsoil. Due to the highly variable nature of the surface soils encountered on-site, some areas may require compaction and/or stability treatment. Further site specific testing to provide more accurate CBR values will be required during the detailed design phase Earthworks Due to the relatively flat nature of the surface topography, the volume of earthworks is likely to be relatively small, approximately 270,000m 3 (by comparison, a 31 turbine development in the Tararua ranges had an earthworks volume of 450,000m 3 +). It is generally expected that cut materials will be used as bulk fill on-site and surplus materials placed at designated fill disposal sites. Included within surplus cut materials will be any unsuitable material or that containing topsoil/organics. Proposed cut and fill slopes will need to be investigated during detailed design phases; however, given the gentle landform, significant cuts and fills exceeding 2m in height will be extremely limited. The indicative cuts and fills for the site are typically in the order of 1.5m or less in height. Track arrangements are detailed in our separate aforementioned Civil Assessment of Access Tracks and Hardstands Report Groundwater Extraction for Foundation Construction A desktop study has been performed to calculate the anticipated volumes of water to be pumped and the extent of the drawdown of the groundwater after the required period of pumping. This was undertaken to provide an assessment of the likely effects of dewatering the excavations required for the construction of the turbine foundations. This study is empirical in nature and no field testing has been completed to verify the assumptions made as a basis of the study Methodology During previous geotechnical investigations on-site, RILEY has collected four samples representative of the sands forming the superficial deposits across the site. Particle size analyses have been carried out on these samples. Particle size distribution has a correlation to the permeability of the material, and has been used to provide estimates of the permeability of these materials. 9 February 2016 Riley Consultants Ltd

17 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 14 Using these figures, the permeability for the deposits was estimated. This figure, together with a maximum pumping rate of 4m 3 /day/well point, was used in the modelling programme Slide v.6 to provide the basic assumption for modelling the drawdown and discharge from a well point dewatering on the circumference of the anticipated excavation, as described on Cross Sections 1, 2, and 3, presented in Appendix D. The extent of drawdown for different periods of dewatering was calculated. For this calculation it is assumed that a drawdown of up to 100mm would not be significant. As a check on this analysis, the discharge and radius of drawdown was calculated for a single point discharge at the centre of the excavation. The calculations for this analysis are presented in Appendix D Analysis Permeability The grading curves for the four samples previously tested, have been inspected and found to be remarkably similar. On this basis, the test result from MH2 was chosen as being located in the area of most concern close to the wetland ponds present on-site. The D 10 for this sample is 0.125mm. Using the formula k = 10-2 x D 2 10, being 0.01 x a permeability of 1.56 x 10-4 m/sec has been calculated. This figure was cross checked against published values for similar types of material. This value would be anticipated for clean, fine to medium sand. This is the description provided for material sampled from the site, therefore, the permeability value determined is considered suitable to the soils sampled Modelling in Slide v.6 The configuration proposed for the well pointing is as shown on Cross Sections 1, 2, and 3 (Appendix D). The excavation was designed to be 21m in diameter and 2.7m deep or 2.2m deep (for either piled or shallow pad excavations, respectively) with side batters at 1:1. The well points were placed a further 1.5m from the crest of the excavation to give a diameter for the dewatering of 30m. The well points were placed at 1m centres around the circumference, initially at depths of 4.5m (see Cross Section 1) and, subsequently, at 3.5m (see Cross Sections 2 and 3). The total number of well points required for this configuration will be 94. The measured worst case groundwater depth of 0.7m was assumed (note: this is the shallowest depth measured, with groundwater of up to 2.5m depth recorded inland). Three results have been obtained and are presented in Appendix D. They are discussed below. 4.5m Deep Well Points This configuration is shown on Cross Section 1. This shows that to achieve drawdown to the base of the 2.7m deep excavation in ten days, a pumping rate of 5.3m 3 /day/well point was required. For this configuration the radius of influence would be approximately 180m. The required pumping volume for ten days will be approximately 5,000m 3. We understand the rate of 5.3m³/day/well point is beyond the capacity of available well point systems, thus, shallower wells will be required. 3.5m Deep Well Points This configuration is shown on Cross Section 2. This shows that to achieve drawdown to the base of the 2.7m deep excavation at a pumping rate of 4m 3 /day/well point, 20 days of pumping would be required. After this period, the radius of influence would be approximately 225m. The required pumping volume for the 20 days will be approximately 7,000m 3. 9 February 2016 Riley Consultants Ltd

18 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 15 To achieve a drawdown of 2.2m at the same rate of 4m 3 /day/well point (see Cross Section 3), 15 days of pumping would be required. At this time, the radius of influence would be approximately 190m. The required pumping volume to achieve this will be approximately 5,400m 3. Once the required drawdown is achieved, the pumping rate required to maintain the drawdown will decrease to 2.5m 3 /day/well point Single Well Discharge To compare the results of the modelling for well point dewatering by Slide v.6, an analysis of the requirements to meet the same conditions as delivered by the computer model, was carried out assuming a single well, fully penetrating the aquifer, and located at the centre of the excavation. The calculations in Appendix D show that to achieve 2m drawdown at 10.5m from the well after ten days and 20 days, discharge rates of 630m 3 /day and 550m 3 /day, respectively, would be required. These rates could be achieved with a 150mm diameter submersible pump. After 20 days, the radius of discernible influence (assumed to be 100mm drawdown) would be approximately 200m, and after 30 days approximately 250m. These results were in close agreement with the computer based analyses Discussion of Groundwater Modelling Results The results show that to achieve the required drawdown in ten days, a pumping rate of about 5.3m 3 /day/well point would be required. We understand that this is beyond the capacity of available well point systems, which have an upper capacity of about 4m 3 /day/well point. To accommodate this, the dewatering period was extended to enable the lower pumping rate to be used. Based on the lower pumping rate of 4m 3 /day/well point, the required dewatering can be achieved, however, a lead time before excavation starts will be required. This lead time will, to some degree, depend on the rate of excavation and whether excavation is carried out entirely in the dry or partly in the wet. To provide a construction period of ten days, a dewatering period of up to 30 days might be required. Once the required drawdown in the excavation is achieved, the pumping rate required to maintain this drawdown will decrease to an estimated 2.5m 3 /day/well point. Comparison between the two methods of analysis is reasonably good. The higher pumping rates predicted by the single point dewatering well are not unexpected as this method requires the dewatering of a considerably greater volume of surrounding soil. The slightly lower radius of influence from the single point dewatering well is also anticipated as the shape of the dewatering cone will be different Construction Sequencing Depending on the depth of the excavation and the depth of the water table at each individual site, a lead time for dewatering prior to excavation will be required. This will be 20 days in the anticipated worst case scenario, where the water table is highest and the excavation deepest. 9 February 2016 Riley Consultants Ltd

19 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page Potential Discharge Locations The site is drained by a network of farm drains. It is estimated that across the site these will be located never more than approximately 200m from a pad site. Although, to avoid recharge of the water into the dewatered zone, it is recommended that discharge should be made a distance of greater than about 50m from the well points. It is, therefore, anticipated that discharge from the dewatering could be made at distances of between 50m and 200m from each site into an existing drain. For extraction zones in close proximity to areas sensitive to groundwater, extracted water can be discharged at the lesser setback distance to minimise effects. The anticipated flows for a 0.5m wide drain with a gradient of 1 in 200, which appears to be about the flattest gradient across the site, would increase the depth of water in the drain by about 50mm. For steeper gradients, the increase in water depth will be less than the above figure. Flows, particularly where the gradients in the drains are steeper, could be sufficient to cause scour in some places. It may, therefore, be necessary to line sections of the drains with an anti-scour fabric. Such fabric could be recovered and re-laid as required Future Testing As this study is based on empirically derived data and no site visit has been made to assess the conditions on the excavation sites, it is recommended that before detailed design of the dewatering system is drawn up, further testing be carried out. This would entail an on-site assessment, additional sampling of the sands under a selection of proposed sites, and at least one trial dewatering test. This may entail an eight hour constant discharge and recovery test on a representative bore or bores to be used for dewatering, to confirm the design and pumping rates for the dewatering systems. Before the full scope of this testing is decided, it will be necessary to liaise with Council to determine precisely their requirements so that these can be addressed in the investigation Conclusions Based on the investigations undertaken for this assessment, we consider the construction and installation of wind turbines at the proposed Waverly Wind Farm is feasible from a geotechnical perspective. We make the following specific comments: Liquefaction analysis of the subsoils identified on-site show typical liquefiable material from 3m to 8m depth in both natural and reworked sands. Liquefaction is possible to depths of 12.5m, and induced settlement across the four borehole investigation sites is modelled as ranging from 20cm to 47cm (500-year return period earthquake) and 22cm to 47cm (1,000-year return period earthquake). Liquefaction during strong seismic shaking can also lead to lateral spreading across the site, with potential movement in the order of 400mm to 700mm. Due to variable density sand deposits and potential for liquefaction, it is recommended turbines be supported on either pile foundations or on shallow foundations following suitable ground improvement. Generally, deep foundations should be piled and socketed into weak sandstone rock or the overlying very dense Pleistocene deposits. This will likely require pile depths between 12m and greater than 20m, based on current investigation results. Alternatively, a number of ground improvement techniques are potentially suitable to the encountered site conditions. Further specific geotechnical investigation (such as CPT) should be carried out at each turbine location to confirm these recommendations. 9 February 2016 Riley Consultants Ltd

20 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 17 During specific foundation design stages, consideration should be given to potential lateral spreading. Pile foundations will require further adequate socketing embedment, and bending capacity to resist loss of lateral loading from the liquefiable soils. As such, ground improvement coupled with shallow foundations may be preferred. Stability analysis has been undertaken with respect to inter-terraced steeper slopes (modelled as typically 1V:5H). Post-seismic liquefaction is the critical case, with a setback of 30m from the slope crest required for an acceptable FoS of >1.0 for the transient situation. We assess a FoS of 1.5 or greater to inter-terrace slopes near turbine locations (i.e. WTG13) under extreme static conditions. These turbines, and others located in close proximity to coastal dunes, have been sited sufficiently far back not to be significantly affected by active processes. The turbine foundations and associated construction pads can be sited clear of any marginal slopes. Steeper sand slopes, either cut or natural, that are identified during further site specific investigations, as being marginal or of concern, can be addressed and stability improved by either local regarding, vegetation growth, overlay with geotextile, or possible setback. The subgrade and preliminary CBR values from limited testing on-site indicate a CBR of three below topsoil for the site access tracks. Due to the highly variable nature of the surface soils, this value is expected to vary, and site specific testing to provide more accurate CBR values will be required during the detailed design phase. To achieve a drawdown of 2.2m at the rate of 4m 3 /day/well point, 15 days of pumping would be required. At this time, the radius of influence would be approximately 190m. The required pumping volume to achieve this will be approximately 5,400m 3. Once the required drawdown is achieved the pumping rate required to maintain the drawdown will decrease to 2.5m 3 /day/well point. Pumping rates and volumes are given in the report for alternative foundation and well depth configurations. A dewatering period of 30 days may be required, which includes a 20 day lead time, prior to excavation in the worst case assessment. It is expected extracted water can be discharged back to the ground within 50m to 200m of the extraction point Limitation This report has been prepared solely for the benefit of Chancery Green Ltd on behalf of Trustpower Limited as our client with respect to the brief and South Taranaki District Council in processing the consent(s). The reliance by other parties on the information or opinions contained in the report shall, without our prior review and agreement in writing, be at such parties sole risk. Recommendations and opinions in this report are based on data from limited test positions. The nature and continuity of subsoil conditions away from the test positions are inferred, and it must be appreciated that actual conditions could vary considerably from the assumed model. During excavation and construction the site should be examined by an engineer or engineering geologist competent to judge whether the exposed subsoils are compatible with the inferred conditions on which the report has been based. It is possible that the nature of the exposed subsoils may require further investigation and the modification of the design based upon this report. 9 February 2016 Riley Consultants Ltd

21 Geotechnical Investigation Waverley Wind Farm RILEY Ref: 10WAV/RC-B (Issue 0.6) Page 18 It is essential Riley Consultants Ltd is contacted if there is any variation in subsoil conditions from those described in the report as it may affect the design parameters recommended in the report References SKM, 2007, Civil Engineering Works stability (Rev D) for Allco Wind Energy Ltd Taranaki Regional Council, 2009, Coastal Erosion Information Inventory and recommendations for state of environment monitoring, (Pg 62-65) Institute of Geological and Nuclear Sciences Ltd, Mineral Commodity Report 15 Iron, (Pg 12) Institute of Geological and Nuclear Sciences Ltd, 2008, Geology of the Taranaki Area, (Pg 56) 9 February 2016 Riley Consultants Ltd

22 APPENDIX A Machine Borehole Logs (RILEY and SKM)

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48 APPENDIX B Laboratory Analysis Results

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55 APPENDIX C Liquefaction Analysis Results

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60 APPENDIX D Groundwater Calculations

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69 APPENDIX E Drawings

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