Annexure 13 Geotech Assessment - Hurunui District · TP03 and TP04 encountered alluvial fan gravels (with a silty clay layer in TP04). The lower gravel layers had strong groundwater

Annexure 13

Geotech Assessment

REPORT

Geotechnical investigationand assessment88 Argelins Road, Hanmer Springs

Prepared forMorford Properties LtdPrepared byTonkin & Taylor LtdDateAugust 2018Job Number1004804.v1

Document Control

Title: Geotechnical investigation and assessment, 88 Argelins Road, Hanmer Springs

Date Version Description Prepared by: Reviewed by: Authorised by:

29 August2018

1 Report A Winkley B McDowell G Lovell

Distribution:

Morford Properties Ltd 1 copy (pdf)

Harley Manion 1 copy (pdf)

Aston Consultants 1 copy (pdf)

Tonkin & Taylor Ltd (FILE) 1 copy

Tonkin & Taylor LtdGeotechnical investigation and assessment - 88 Argelins Road, Hanmer SpringsMorford Properties Ltd

August 2018Job No: 1004804.v1

Table of contents

1 Introduction 12 Scope of work 13 Site description and observations from August 2016 14 Geotechnical information 2

4.1 Published geological information 24.2 Geotechnical investigations 2

4.2.1 T+T 2016 test pits 24.2.2 T+T 2018 boreholes 34.2.3 e2Environmental 2018 test pit/standpipe piezometer installations 34.2.4 Neighbouring geotechnical investigations in 2009 4

4.3 Groundwater levels 44.4 Groundwater temperature and pH 5

5 Hanmer Fault Zone 55.1 General 55.2 88 Argelins Road 5

6 Discussion of sub-surface conditions 66.1 Indicative ground model 66.2 Indicative groundwater model 6

7 General development considerations 77.1 Hanmer Fault zone setbacks 77.2 Natural hazards 77.3 Site subsoil class for seismic design of structures 97.4 Foundation and subgrade conditions 97.5 Further work at subdivision consent and design stages 10

8 Summary 109 Applicability 11

Appendix A : Figures

Appendix B : Geotechnical investigation data

1



1 IntroductionThis report presents the results of a geotechnical investigation and assessment completed by Tonkin& Taylor Ltd (T+T) for the area of land at 88 Argelins Road in Hanmer Springs (the site). The workdescribed in this document was commissioned by Morford Properties Limited (Morford), and hasbeen carried out in accordance with the terms and conditions outlined in the T+T letter ofengagement dated 18 May 2018 (T+T ref. 1004804.0000_loe3). The purpose of this geotechnicalassessment report is to accompany a plan change application by Morford to change the zoning fromrural to suburban.

2 Scope of workT+T has carried out the following scope of work for the purposes of this geotechnical assessment:

· Desk-based review of readily available existing geotechnical information, reports and aerialphotographs relevant to the site.

· Site walkover by a T+T senior engineering geologist.· Site-specific ground investigations (Figure 1, Appendix A) comprising:

- Six test pits across the site, carried out in September 2016.- Three machine-drilled boreholes in the south-western area of the site, carried out in

June 2018.· Installation of standpipe piezometers in the machine-drilled boreholes for groundwater

monitoring purposes.· Testing of groundwater samples on site for pH and temperature.· Assessment of the location of fault traces and deformed and tilted land surfaces based on the

results of a topography survey carried out by Fox and Associates (Fox).· Interpretation of the survey information and provision of recommendations regarding

exclusion zones around the fault traces in the northern portion of the site.· Assessment of the site against Section 106 of the Resource Management Act (RMA).· Preparation of this geotechnical report outlining the findings of the above work.

The investigation and assessment outlined in this report has been carried out to a level sufficient toaccompany a plan change application. Further geotechnical investigations will be required as the sitedevelopment plans progress through future consenting and design stages.

3 Site description and observations from August 2016The legal description of the 13 ha site is Section 1 SO 18574. A site walkover was undertaken on3 August 2016 to assist in the preliminary geotechnical assessment of the site. Pertinentobservations include the following:

· The site generally slopes down towards the southwest at about 1.5o (2 to 3%). The surfaceappears to be composed of the 18,000 year old alluvial fan surfaces of the Dog Stream andChattertons River catchments.

· The Barn Trace and Car Park Trace of the Hanmer Fault zone are defined on Figure 2(Appendix A) by the locations of the toe of the scarp slopes. The Barn Trace runs out just eastof the red barn, while the Car Park Trace forms a well-defined scarp slope along the north-eastern boundary of the site.

2



· The extents of the Car Park Trace on the neighbouring hospital grounds is obscured bymanmade cuts and fills across the scarp. Human ground modifications are also present to alesser extent between the fault traces in the area of the red barn.

· The slope of the Dog Stream fan surface appears to be flattened and slightly reversed into asubdued bulge (active fold) in front of the Car Park Trace, indicating possible tilting and foldingof the land surface between the fault traces and off the eastern end of the Barn Trace.

· Drains have been cut across the site to carry groundwater seepage flows from the toe of theCar Park Trace and to a lesser extent the toe of the Barn Trace.

· A large (approximately 12,000 m2) historically poorly drained area is observed in the south ofthe site (Figure 1, Appendix A). Drains have been cut around this area (Figure 2, Appendix A) inan attempt to control the seepage water.

· The pitch and putt golf course, in the western portion of the site, is located in the 50 to 100 mwide flood channel of the Hospital Stream, which is incised about 1 m into the alluvial fansurface. The low flow in the stream is to groundwater seepage along the Hanmer Fault zone.Discharge of geothermal water from the hot pools into Hospital Stream is routed through twinculverts under Argelins Road and through the existing subdivision to the west of the site. Apreliminary assessment of the flood channel is provided by e2 Environmental in their report.

· Apart from the historically poorly drained area the ground surface was firm and dry at thetime of the site visit in 2016 (surface ponding was noted in a lesser area in 2018, as shown onFigure 1, Appendix A). Standing and flowing water was present in the cut drains about 1 mbelow ground level.

· The soil profile exposed in the walls of the cut drains comprised approximately 0.1 to 0.3 m ofsilt loam topsoil overlying 0.3 m of low plasticity silt, which in turn overlie about 0.5 m ofgravelly silt to the base of the cut drains (1 to 1.5 m deep).

4 Geotechnical information

4.1 Published geological information

Published geological information1 indicates that the site is generally underlain by Holocene-age rivergravel, sand with minor silt, and alluvial fan deposits.

4.2 Geotechnical investigations

4.2.1 T+T 2016 test pits

Six test pits were excavated and backfilled by a 13.5 tonne excavator using a 1.8 m wide cleaningbucket on 27 September 2016. The locations of the test pits are shown on Figure 1 (Appendix A).Engineering logs of the test pits (TP01 to TP06) are presented in Appendix B.

TP01 was excavated in the historically poorly drained area in the south-western area of the site. Thetopsoil was moist to saturated, and groundwater inflows occurred into the pit from 0.7 m depth.Strong groundwater inflows were encountered in alluvial fan gravel deposits to the end of the pit at3.9 m depth. Grey to black gravel and a sulphurous smell suggested a reducing environment,possibly due to the upwelling of geothermal water. The groundwater was not noticeably warm.

TP02 and TP06 in the central part of the site encountered silty clay soil and fibrous peat layers atdepths from 3.3 m to the base of the pits at 4.8 and 4.2 m respectively. The peat and clay layersunderlie approximately 3 m of alluvial fan gravels. These layers appear to be similar to the peat and

1 Rattenbury, M.S., Townsend, D.B., Johnston, M.R. (compilers) 2006. Geology of the Kaikoura area. Institute of Geological& Nuclear Sciences 1:250 000 geological map 13. 1 sheet + 70 p. Lower Hutt, New Zealand: GNS Science.

3



organic clay layers described on the neighbouring site (see Section 4.2.4 below). The peat is 0.7 mthick in TP02, while thinner layers (< 0.1 m) and eroded gravel contacts are present in TP06.Groundwater inflows occurred from about 1.5 m depth in these test pits.

TP03 and TP04 encountered alluvial fan gravels (with a silty clay layer in TP04). The lower gravellayers had strong groundwater inflows, were easily excavated, and slumped and flowed in thestockpile.

TP05 was excavated through brown grey alluvial fan gravels to the base of the pit at 4.1 m.Groundwater inflows occurred from 3 m depth. This profile is what might be considered typical foran alluvial fan.

Soils encountered in the test pits were described as wet below a depth of 1.3 to 1.8 m in TP02 toTP06. The soil was saturated below about 0.5 m depth in TP01, located in the historically poorlydrained area.

4.2.2 T+T 2018 boreholes

Three machine-drilled boreholes were carried out by Texco Drilling Ltd (Texco) on 6 and 7 June 2018.The boreholes were advanced to a depth of 4.0 m below ground level using a cable tool drill rig, andwere located in the south-western portion of the site within the historically poorly drained area. Thelocations of the boreholes are shown on Figure 1 (Appendix A) and bore logs are provided inAppendix B.

The boreholes were drilled to allow the installation of standpipe piezometers for groundwatermonitoring purposes. The standpipe piezometers are 50 mm internal diameter PVC pipes with abase cap, 3 m long slotted section, sand pack to 100 mm above the slots, and backfilled withbentonite. Stand up lockable tobys have been concreted in place.

BH1 encountered clayey silt to a depth of 2.3 m, which was primarily underlain by alluvial gravel fandeposits to the end of the hole at 4.0 m depth. A thin layer of clay and peat was found between 3.4and 3.7 m depth.

BH2, carried out 40 m to the north-west of BH1 encountered silty and/or sandy gravel to a depth of2.8 m. This is underlain by a layer of fibrous peat to the end of the hole at 4.0 m depth.

BH3, carried out approximately 100 m west of BH1 and 2, encountered 0.5 m of topsoil and clay,underlain by alluvial fan gravel mixtures to 3.0 m depth. Between 3.0 and 4.0 m there was a layer offibrous peat.

Standard Penetration Tests (SPTs) were carried out from 1.5m, 3m and 4m below ground level. SPTN values ranging from 4 to 38 indicate medium dense gravel and stiff to hard silt from <1.5 m to3.5 m depth, and firm to stiff silt from 3 m to 4.5 m depth

4.2.3 e2Environmental 2018 test pit/standpipe piezometer installations

e2Environmental organised the excavation of eight test pits across the site (Figure 1, Appendix A) inApril 2018, for the purposes of infiltration testing and standpipe piezometers installation. The testpits were advanced to depth from 1.5 m to 2.2 m below ground level, encountering silt and gravelsoils. Organic soils and peat were not intercepted. For further details regarding these investigationsand tests refer to the e2Environmental report2.

2 Draft Infrastructure Servicing Report, June 2018, e2 ref 18012

4



4.2.4 Neighbouring geotechnical investigations in 2009

Harley Manion of Harcourts has provided a copy of plan change information for Hanmer Farm, theapproximately 25 ha property bounded by Hanmer Springs Road, Argelins Road and the southernboundary of 88 Argelins Road. A geotechnical investigation and assessment by Aurecon (2009) wasincluded in the information.

Aurecon excavated 4 trenches (5 to 7 m long and 2.5 to 4.1 m deep) situated about 200 to 300 mapart across the Hanmer Farm site. Ten dynamic cone penetration (DCP) tests were carried outacross the site, with the probe refusing in gravels at depths ranging from 0.5 to 2.1 m.

The trenches exposed near surface silt and gravel similar to that observed by T+T in the test pits on88 Argelins Road. A significant finding of the investigation was the presence of organic clay and/orfibrous peat in all the trenches at depths ranging from 1.5 to 3.3 m below the ground surface. Theorganic horizons ranged from 0.5 to 1 m thick. Trenches were stopped approximately 0.3 m into siltygravel beneath the organic horizon.

The DCP results suggest stiff near surface silts, medium dense to dense gravels and firm to softorganic clay.

4.3 Groundwater levels

Since the installation of the standpipe piezometers in the three T+T boreholes and six of thee2Environmental test pits, groundwater level monitoring has been carried out on a fortnightly basis.Table 4.1 (below) provides the depths to groundwater that have been recorded to date. The depthof groundwater below ground level and contours of groundwater reduced level for July 2018 areshown on Figure 3.

The readings indicate that, over the period of May to July 2018, the depth to groundwater is greatestin the northern portion of the site (e2 TP01, 04, 07a), between approximately 1.1 and 1.8 m. In thesouth-eastern portion of the site (e2 TP06, 08) the depth to groundwater is approximately 0.3 to1.6 m. In the south-western portion of the site (i.e. the historically poorly drained area) T+T BH1 and3, and e2 TP03 indicate that the depth to groundwater is approximately 0.2 to 0.6 m. Several of thereadings from T+T BH2 indicate that groundwater pressures are sub-artesian at the piezometerfounding depth of 4.0 m.

5



Table 4.1: Measured depth to groundwater (relative to surrounding ground) in metres

Date ofreading e2 TP01 e2 TP03 e2 TP04 e2 TP06 e2

TP07a e2 TP08 T+T BH1 T+T BH2 T+T BH3

28/5/18 1.18 0.15 1.74 0.92

> 1.79(dry at

pipebase)

1.01 - - -

14/6/18 - - - - - - 0.15 0.50 0.30

16/6/18 1.14 0.21 1.55 0.56 1.32 0.23 0.22- 0.21

(aboveground)

0.39

28/6/18 - - - - - - 0.36- 0.60

(aboveground)

0.52

12/7/18 1.23 0.34 1.64 0.85

> 1.79(dry at

pipebase)

0.85 0.41- 0.04

(aboveground)

0.44

30/7/18 1.31 0.35 1.74

> 1.55(dry at

pipebase)

> 1.79(dry at

pipebase)

1.37 0.59 0.18 0.52

4.4 Groundwater temperature and pH

T+T carried out on-site pH and temperature testing of groundwater samples from BH1 and BH2 usinga hand-held YSI meter on 7 June 2018. The recorded groundwater temperature was between 9.5and 10.2°C (ambient air temperature was 4°C). The recorded groundwater pH was between 3.7 and5.0.

5 Hanmer Fault Zone

5.1 General

The Hanmer Fault zone, which crosses the north of the site and the hospital grounds immediately tothe north is a fault duplex. The west section of the Hanmer Fault cuts through the golf course as asingle high scarp, while the east section forms a single high scarp south of Leamington Street. Theeast and west sections are approximately parallel, but misaligned by about 100 m. The fault duplex isa group of discontinuous fault traces that form a 150 m wide ‘tear’ across the land surface betweenthe misaligned west and east fault sections. Strike slip, dip slip and thrust faulting, tilting and foldingoccurs across the fault duplex.

Past academic studies of the fault, which included mapping, trenching and radio carbon dating oforganic samples indicate that the return period for movement (rupture) on the fault zones isapproximately 300 to 600 years, with movement probably occurring at similar times to activity onthe Hope Fault. Ground displacement in future earthquake events is likely to be in the order of 0.3 to1.9 m, both lateral (strike slip) and vertical (dip slip) movement.

5.2 88 Argelins Road

Surface features related to the Hanmer Fault zone have been visually assessed, both on site andutilising a 0.25 m contour plan developed from an aerial survey conducted by Fox Associates. The

6



base, or toe of scarp slopes for the Barn Trace and Car Park Trace are shown in red on Figure 2(Appendix A). The toe of the Barn Trace is obscured in places by manmade cut and fill activities, asshown on Figure 2. A zone of tilt and active folding is inferred between the Car Park and Barn Traces.

In addition to the fault scarps and active folding there may be areas of tectonic tilt to the south ofthe fault traces where the ground slope is notably flatter than that of the undisturbed, south slopingfan surfaces. There are other possible explanations for the flatter slopes observed, but assumingthey are the result of earthquake events, the tilt from a sloping fan surface to ‘flat’ surface is anapproximately 1.5o change that will have occurred over several earthquake events. If we considerthat the fault traces may be ‘growing’ from west to east with successive earthquake events,evidenced by the decreasing heights and ‘termination’ of the Barn Trace and Car Park Trace towardsthe east. Then the possible tilt may have occurred relatively recently, say over the past 10earthquakes (about 5,000 years). This would equate to 0.15o of tilt, or approximately 10 mm ofsurface level change over 40 m distance per earthquake event.

6 Discussion of sub-surface conditions

6.1 Indicative ground model

Based on the test pit and borehole investigation, information from the neighbouring site andobservations across the Hanmer basin in general we interpret the site as being formed by a series ofoverlapping alluvial fan surfaces which have been modified by uplift on the Hanmer Fault zone andthe incision of drainage channels on the surface. The alluvial fan gravels were likely deposited morethan 18,000 years ago forming the surface that slopes gently to the south. The surface silt andtopsoil has built up since that time. Figure 2 (appendix A) shows an interpretation of the distal limitsof the 18,000 year surfaces of the Dog Stream and Chattertons River fans intersecting in the middleof the site.

The peat and clay soil horizons located between about 2m and 4 m depth in BH1, 2 and 3, and TP2, 4and 6 are interpreted as being representative of several separate sub horizontal lenses that haveformed in swamp depressions or areas of restricted drainage on, or between fan surfaces. Similarmodern day swamps are observed across the Hanmer basin. The peat deposits may be partly erodedaway during the deposition of younger fan gravel layers. We consider that the peat found in theinvestigations is unlikely to form continuous sloping layers beneath the ground surface, howeverlenses of peat may be locally significant from a development perspective. Figure 3 (Appendix A)shows the peat depth below ground surface and the thickness encountered in the investigations.

Layers of fan gravel with lenses of peat and clay soils are likely to be repeated at depth below thesite (below the depth of the test pit and borehole investigation). Denser river gravel deposits mayoccur at depths of tens to hundreds of metres below the site, with bedrock several hundred metresbelow the site.

6.2 Indicative groundwater model

Significant groundwater flow is occurring from north-east to south-west in the permeable fangravels, largely sub parallel to, and about 1.2 to 2 m below the ground surface. Figure 3 (Appendix A)shows groundwater depths and contours of groundwater level across the site.

The historically poorly drained area shows groundwater approximately 0.5 m below the surface,with indications of sub-artesian pressures in the shallow gravel. These elevated groundwater levelsmay be fed by a distributed groundwater flow of geothermal origin similar to the spring flows thatoccur along the fault traces in the north of the site. The combination of slight topographic changes,interbedding of different alluvial fan deposits and organic soil horizons may be responsible for thedistributed nature of the seepage

7



Seepage and spring flows along the base of the fault traces are currently intercepted in open drainsand run through small ponds and drains as indicated on Figure 1 (Appendix A). Depending on thelevel of development proposed, graded open drainage and/or subsoil drains will be required tointercept and route the seepage flows. We understand that e2Environmental are carrying outconceptual drainage plans for the proposed development.

7 General development considerations

7.1 Hanmer Fault zone setbacks

Based on observation of recent fault ruptures and studies of past ruptures on the Hanmer Fault,future fault ruptures are considered unlikely to occur beyond the visible extent of the fault scarpslopes. A fault rupture avoidance zone, or setback of 10 m is recommended for future developmentof the site, as shown on Figure 2 (Appendix A). The setback is a recognition of the uncertainty in thelocation of a future fault rupture relative to the observed scarp slope. Where the inferred toe of theBarn trace is obscured by human modifications the fault setback is 20 m, or 10 m from the toe of thetopographic slope.

The existing guidance on fault rupture3 recommends avoidance of the development of buildingimportance category 2 (BIC2), lightweight residential, or higher importance structures within thesetback zone due to the risk of catastrophic damage and potential loss of life from future groundrupture. While recent observations may suggest that the likelihood of building collapse leading torisk to life in timber framed residential structures affected by fault rupture is relatively low,expectations of future owners around the likelihood of damage beyond repair, including obtaininginsurance cover is also a major consideration when assessing setbacks or avoidance zones aroundfault hazards.

Development of residential or light commercial structures is considered feasible in the possible tiltzones that extend about 40 m south of the fault traces. The scenario discussed in Section 5.2 resultsin a nominal change in ground level of 10 mm over 40 m distance in a future earthquake event.Allowing for a local ground change of 2 to 4 times this amount the expected settlement/uplift acrossa future building platform could be considered as < 50 mm for a ULS design event. This level ofsettlement is analogous to the ‘TC2’ liquefaction zoning developed during the ChristchurchEarthquake Sequence (CES). Structures constructed using ‘TC2’ type foundation systems, with theoption for improving resilience further by building in ease of releveling, are considered a feasibleoption for development in the tilt zone.

7.2 Natural hazards

Slope and soil stability, and earthquake (seismic) hazards have been considered in this geotechnicalassessment and are summarised in Table 7.1 below.

Climate related hazards are not considered. These could include hazards from severe storm eventsand climate change, such as flooding, high winds, tornados, intense rainfall, hail and/or snow, sealevel rise, droughts, bush fires and dust storms. Appropriate design of structures following therelevant codes and standards is expected to provide adequate mitigation to climate hazards such aswind, snow and fire.

Flooding hazards are potentially present on the site, including flood flow along Hospital Stream,upslope overland flow from the Hanmer Fault scarps, and the effects of conveyance of surface water

3 Ministry for the Environment, July 2003. Planning for development of land on or near to active faults. (GNS client report2202/124)

8



through the site and onto the neighbouring downslope site. Flood hazards are addressed in thee2Environmental report (refer footnote 2).

Table 7.1: Assessment of slope & seismic hazards and qualitative risk

Hazard Comment Likelihood ofoccurrence

Consequence tobuilding

QualitativeRisk1

Soil erosion(including sub-surface erosion)

Very gently sloping site with plasticsilt soils

Unlikely Minor Very Low toLow

Large scalelandslides

Very gently sloping alluvial fansurfaces across the site

Not Credible Major Very Low

Small scale,shallow landslip

Fault scarp slopes may be subject toslope instability within the faultsetback limits. Risk assessed or thearea south of the fault setback

Possible Insignificant Very Low toLow

Rock fall/boulder roll

There are no rock source areas on,or up slope of the site

Not Credible Medium Very Low

Debris flow andDebris Flood

The site is on old, inactive fansurfaces, isolated from debris flowsources. Secondary flood routing insubdivision mitigates consequence

Unlikely Minor Very Low toLow

Fault surfacerupture

See discussion in Section 7.1 above.Risk assessed for the area south ofthe fault setback

Possible Minor toInsignificant

Very Low toLow

Earthquakeinduced slopecracking andrenting.

The site is on inactive alluvial fansurfaces with very gentle slopes

Unlikely Medium tominor

Low

Strongearthquakeshaking

Near fault earthquake shakingapplies at this location

Likely Medium tominor

Low toModerate

Liquefactioninduced damage

Silt, gravel and peat soils in upper4m of the soil profile. No surfacesigns of liquefaction across the sitefrom the Kaikoura Earthquake,which generated shaking equivalentto a 250 year return period designevent

Possible Minor Low

Tsunami No Not Credible No for furtherdiscussion

Very Low

9



1. The qualitative risk terms used in Table 1 are based on risk matrices presented in Appendix 3 of “Draft Guidelinesfor Assessing Planning, Policy and Consent Requirements for Landslide Prone Land”, GNS Science Misc Series7,February 2007.

Based on the assessments summarised above and in the context of Section 106 of the RMA there isno significant risk from slope, soil and seismic hazards to an appropriately engineered developmenton the site. The engineering of hazard mitigation measures, subdivision infrastructure, andlightweight buildings to avoid and mitigate significant risk is considered to be technically feasible.Further discussion is provided in Sections 7.3 and 7.4 below.

7.3 Site subsoil class for seismic design of structures

In terms of NZS 1170.54 the site subsoil class is assessed to be Class D (deep or soft soil). Thisrecommendation is also based on published geological information that indicates the depth tobedrock is greater than 100 m beneath the site.

7.4 Foundation and subgrade conditions

The following discussion is based on limited investigations for the purpose of a plan change levelassessment. Further investigation, characterisation and design will be required for any futuresubdivision consent, and subsequent building consents.

Based on the indicative ground model described in Section 6.1, we expect that foundation conditionswill be suitable for the development of lightweight, 1 to 2 storey structures such as residential andlight commercial buildings with shallow foundations located in the medium dense gravel and stiff tohard silt soils that occur approximately 2 to 2.5m below current ground level. The extent ofgroundworks, sub soil drainage, and the foundation types employed will differ in scale andcomplexity across the site, subject to the need to mitigate settlement from underlying peat deposits,and control drainage of shallow groundwater.

The construction of lightweight residential and commercial structures over areas of fibrous peat islikely to result in unacceptable levels of consolidation settlement. For example a 1 m thick layer offibrous peat located 3.5 m below foundation level could experience approximately 100 to 200 mm ofconsolidation settlement over several years to decades of time.

The potential for consolidation settlement can be mitigated by preloading the areas underlain bypeat. Preloading involves the placement of approximately 1 to 2 m of fill over the existing landsurface and monitoring the settlement that occurs. The preload may need to be in place for 1 to 2years, after which it can be removed and structures can be built.

Based on the current investigations and interpretation of site conditions we expect peat layers to beof variable extent and thickness. The eastern part of the site located on the 18,000 year Dog Streamfan surface (Figure 2, Appendix A) may have little shallow peat. Thicker fibrous peat layers areobserved in the middle and southwest parts of the site.

If dense to very dense alluvial (river) gravel layers occur at depth they may be suitable for thefounding of piles to support larger structures (and possibly for residential development), howeverthe alluvial fan type gravels as observed in test pits may not be suitable for the founding of piles.Further investigation would be required to assess deeper gravel horizons below the site if pilefoundations were being considered for a specific development.

Subgrade conditions on the site for roads and pavements are likely to comprise silt and silty gravelmaterials within about 1 m of the existing ground surface. An assumption of low CBR values (CBR <3)is considered appropriate for these materials at this stage.

4 Standards New Zealand (2004) – NZS 1170.5:2004 – Structural Design Actions Part 5: Earthquake Actions – New Zealand.

10



Sub-soil drainage of shallow groundwater may be required, and is feasible along the fault setbackzone and in the historically poorly drained area depending on the proposed development in thoseareas.

7.5 Further work at subdivision consent and design stages

Ground investigations for subdivision design and consent will be required at a greater density acrossthe site, and to assess the deeper soil profiles and groundwater conditions to at least 15m belowground level. Cored boreholes to retrieve samples for the assessment of peat soil settlement andCPTs to allow the assessment for liquefaction potential should form part of an appropriateinvestigation. Geophysical methods may be employed to assess the lateral extent of peat soil lensesbeneath the site. The number, depth and type of investigations will be developed for the site basedon the geological environment of the Hanmer Basin as discussed in Section 6 of this report.

8 SummaryFuture residential and/or commercial development of 88 Argelins Road is considered feasible from ageotechnical perspective, with potential limitations on the land area available for development dueto the geotechnical hazards and issues identified and discussed in this report and summarisedbelow.

The Car Park and Barn traces of the Hanmer Fault cut across the north-east corner of the site. Werecommend that the fault traces, plus a 10 m wide setback zone (Figure 2, Appendix A) beconsidered as a fault avoidance zone for future development.

An area of potential ground tilt in a future fault rupture is identified south of the fault. Developmentis considered possible in this area with adoption of appropriate foundation systems (‘TC2’ type) tomitigate possible future land deformation in an earthquake event.

The upper approximately 3 to 4 m of the soil profile generally comprises stiff silt and medium densegravel soils, which are generally suitable for residential and/or commercial development. Areasunderlain by fibrous peat deposits will require mitigation, such as pre loading to allow development.This mitigation may involve the placement of 1 m of fill for 1 to 2 years before development, orsimilar.

Sub-soil drainage of shallow groundwater may be required, and is feasible along the fault setbackzone and in the historically poorly drained area depending on the proposed development in thoseareas.

In the context of Section 106 of the RMA there is considered to be no significant risk from slope, soiland seismic hazards to an appropriately engineered development on the site.

11



9 ApplicabilityThis report has been prepared for the exclusive use of our client Morford Properties Ltd, withrespect to the particular brief given to us and it may not be relied upon in other contexts or for anyother purpose, or by any person other than our client, without our prior written agreement.

Report prepared by: Reviewed by:

.......................................................... ...........................….......…...............

Anna Winkley Barry McDowellGeotechnical Engineer Senior Engineering Geologist

Authorised for Tonkin & Taylor Ltd by:

..........................................................

Grant LovellProject Director

ammw\\ttgroup.local\corporate\christchurch\tt projects\1004804\workingmaterial\2018-08-29.bmcd_ammw.report.docx

Appendix A: Figures

TP1

TP2

TP3

TP4

TP5

TP6

BH1

BH2

BH3

TP04

TP05

TP06

TP08

TP07A

TP07

TP01

TP02

TP03

HISTORICALLY POORLY DRAINED AREA

SURFACE WATER JUNE-JULY 2018

SPRI

NG F

LOW

S

HOSP

ITAL

STR

EAM

ARGE

LINS

ROAD

MORFORD PROPERTIES

88 ARGELINS ROAD, HANMER

SITE LAYOUT AND INVESTIGATION LOCATIONS

1:2000 FIGURE 1 1

BM Aug.18RDB Aug.18

1004804

L:\1004804\WorkingMaterial\CAD\FIG\1004804-F01.dwg 2018-Aug-29 12:04:42 PM Plotted By: RACHEAL BROOKES

CHECKED

DESIGNED

COPYRIGHT ON THIS FIGURE IS RESERVED DO NOT SCALE FROM THIS FIGURE - IF IN DOUBT, ASK.

SCALE (A3) REVFIG No.

TITLE

PROJECT

CLIENTPROJECT No.

DRAWN

APPROVED DATE

LEGENDEXISTING CONTOUR 2.0mEXISTING CONTOUR 0.25m

PARCELS

TP4

TEST PITS (T+T 2016)

BH1

BOREHOLES (T+T 2018)

DRAINS WITH PERENNIALSPRINGS FLOW

E SOAKAGE PITS (E 2018)TP04

2

ORIGINAL IN COLOUR

A3 SCALE 1:20000 20 40 60 80 100 (m)

NOTES:1. CONTOURS SUPPLIED BY FOX ASSOCIATES ON 08/04/2018. FILE REF: 3821M 20180424

SURFACE EXPORT.2. AERIAL PHOTOGRAPHY SUPPLIED BY FOX ASSOCIATES, PHOTOGRAPHY DATED 21/03/2018.3. COORDINATE DATUM: NZGD2000, AMURI CIRCUIT COORDINATES. LEVEL DATUM: LINZ (MSL)

LYTTELTON VERTICAL DATUM 1937.4. CONCEPT SUBDIVISION LAYOUT INDICATIVE FOR PLAN CHANGE ONLY.

2

29/8/2018

?

?

HANMER FAULT ZONE

TOE BARN TRACE

EXIS

TING

SUBD

IVIS

ION

ARGE

LINS

ROAD

HOSP

ITAL

STR

EAM

FOLD

CHA

NNEL

LIMIT OF 18,000 YEAR

DOG STREAM FAN

EXIS

TING

SUBD

IVIS

ION

ACTIVEFOLD

TOE CAR PARK TRACE

LIMIT

OF 18,0

00 YEAR CHATT

ERTON RIVER FA

N

HISTORICALLY POORLYDRAINED AREA

PRELIMINARY DRAFT

MORFORD PROPERTIES


GEOMORPHOLOGY FEATURES

1:2000 FIGURE 2 1

RDB Jul18BM Jul.18

1004804


CHECKED

DESIGNED



TITLE

PROJECT

CLIENTPROJECT No.

DRAWN

APPROVED DATE

ORIGINAL IN COLOUR

A3 SCALE 1:20000 20 40 60 80 100 (m)

LEGENDEXISTING CONTOUR 2.0m

EXISTING CONTOUR 0.25m

PARCELS

NOTES:1. CONTOURS SUPPLIED BY FOX ASSOCIATES ON 08/04/18. FILE REF:

3821M 20180424 SURFACE EXPORT.2. COORDINATE DATUM: NZGD2000, AMURI CIRCUIT COORDINATES.

LEVEL DATUM: LINZ (MSL) LYTTELTON VERTICAL DATUM 19373. CONCEPT SUBDIVISION LAYOUT. INDICATIVE FOR PLAN CHANGE ONLY.

CUT & FILL (HUMAN MODIFICATION)

DEVELOPMENT SETBACK FROMHANMER FAULT ZONE (10m)

EAST MARGIN OF HOSPITALSTREAM FLOOD CHANNEL

29/8/18

0.52

0.35

0.70 0.59

0.18

0.80

1.20 1.30

1.70

1.30

<2.0

1.70

1.70

1.30

1.801.30

1.40

TP1

TP2

TP3

TP4

TP5

TP6

BH1

BH2

BH3

TP04

TP05

TP06

TP08

TP07A

TP07

TP01

TP02

TP03

SPRI

NG F

LOW

S

HOSP

ITAL S

TREA

M

3.0m1.0m

NONE>3.9m

2.8m1.1m

3.4m0.3m

2.2m0.6m

NONE>4.1m

NONE>4.1m

2.0m1.7m

3.7m0.7m

TP1

TP2

TP3

TP4

TP5

TP6

BH1

BH2

BH3

TP04

TP05

TP06

TP08

TP07A

TP07

TP01

TP02

TP03

SPRI

NG F

LOW

S

HOSP

ITAL S

TREA

M349

348

347346

345

344.3

344.9

345.8

343.7

346.9

348.8

349.2

349.3

368.7346.3

346.1

346.7

TP1

TP2

TP3

TP4

TP5

TP6

BH1

BH2

BH3

TP04

TP05

TP06

TP08

TP07A

TP07

TP01

TP02

TP03

SPRI

NG F

LOW

S

HOSP

ITAL S

TREA

M

MORFORD PROPERTIES


GROUNDWATER AND ORGANIC HORIZON

1:4000 FIGURE 3 1

BM Aug.18RDB Aug.18

1004804


CHECKED

DESIGNED



TITLE

PROJECT

CLIENTPROJECT No.

DRAWN

APPROVED DATE

LEGENDPARCELS

TP4

TEST PITS (T+T 2016)

BH1

BOREHOLES (T+T 2018)

DRAINS WITH PERENNIALSPRINGS FLOW

E SOAKAGE PITSTP4

2

ORIGINAL IN COLOUR

A3 SCALE 1:40000 40 80 120 160 200 (m)

NOTES:1. CONTOURS SUPPLIED BY FOX ASSOCIATES ON 08/04/18. File Ref: 3821M 20180424 SURFACE

EXPORT.2. AERIAL PHOTOGRAPHY SUPPLIED BY FOX ASSOCIATES, PHOTOGRAPHY DATED 21/03/2018.3. COORDINATE DATUM: NZGD2000, AMURI CIRCUIT COORDINATES. LEVEL DATUM: LINZ (MSL)

LYTTELTON VERTICAL DATUM 1937.4. CONCEPT SUBDIVISION LAYOUT INDICATIVE FOR PLAN CHANGE ONLY.

GROUNDWATER, DEPTH BELOW GROUND LEVEL (m) (JULY 2018)

DEPTH TO ORGANIC HORIZON AND PEAT THICKNESS

GROUNDWATER REDUCED LEVEL (M) AND CONTOURS (JULY 2018)

PEAT 3.0m - DEPTH bgl1.0m - THICKNESS

OR NONE - PEAT ABSENT>4.1m - TO BASE OF TEST PIT

GROUNDWATER CONTOURS346

DEPTH bgl FROM PIEZOMETER READING, OROBSERVED SATURATION AT TIME OF TP EXCAVATION.

29/8/18

Appendix B: Geotechnical investigation data

Bore

Log -

27/0

7/2

018 2

:00:2

9 P

M -

Pro

duce

d w

ith C

ore

-GS

by

GeR

oc

v3.2

a

SHEET: 1 OF 1

BOREHOLE No.: BH1

PROJECT: 88 Argelins Rd, Hanmer LOCATION: CHCH JOB No.: 1004804.0000_1

GEOLOGICAL

WA

TE

R

DE

FE

CT

SP

AC

ING

(cm

)

BOREHOLE LOG

GEOLOGICAL UNIT,

GENERIC NAME,

ORIGIN,

MATERIAL COMPOSITION.

SA

MP

LE

S

ENGINEERING DESCRIPTION

20

60

200

600

2000F

LU

ID L

OS

S (

%)

25

50

75

DE

PT

H (

m)

GR

AP

HIC

LO

G

RL

(m

)

ME

TH

OD

CO

RE

RE

CO

VE

RY

(%

)

TESTS

CA

SIN

G

WE

AT

HE

RIN

GM

OIS

TU

RE

CO

ND

ITIO

N

ST

RE

NG

TH

/DE

NS

ITY

CL

AS

SIF

ICA

TIO

N

SH

EA

R S

TR

EN

GT

H(k

Pa

)

CO

MP

RE

SS

IVE

ST

RE

NG

TH

(MP

a)

1 5 20

50

100

250

10

25

50

100

200

CO-ORDINATES: 5291554.00 mN1585642.00 mE(NZTM2000)

R.L.: 345.00m

DATUM: DRILL FLUID:

DRILL METHOD: CP

DRILL TYPE:

DRILLED BY: Texco

CHECKED: BMCDLOGGED BY: ABOT

HOLE FINISHED: 07/06/2018

HOLE STARTED: 06/06/2018

Description andAdditional Observations

344

343

342

341

Silty Sand with some rootlets, TOPSOIL

Clayey SILT; light orange tan. Firm to stiff; lowplasticity; moist to wet.

Sandy GRAVEL; dark grey. Gravel, fine to medium;sand, medium to coarse.

GRAVEL, with some sand; dark grey. Gravel, fine tomedium; sand, fine to coarse.

CLAY; blue grey. Low plasticity; moist.

PEAT (FIBROUS); dark brown. Moist.

Sandy GRAVEL; dark grey. Gravel, fine to medium;sand fine to medium. Saturated

W

M-W

W

4m: Target depth

3/58/9

10/10N=37Solid

4/87/73/1

N=18Solid

1/44/22/2

N=10Solid

14

/06

/20

18

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Log is representative of soil profile as large amounts of core loss was experienced. SPT values may be incorrect as operator didnt always drop weight fromsame height

Hole Depth4m

COMMENTS:

Scale 1:25 Rev.: B

Bore

Log -

27/0

7/2

018 2

:01:2

8 P

M -

Pro

duce

d w

ith C

ore

-GS

by

GeR

oc

v3.2

a

SHEET: 1 OF 1

BOREHOLE No.: BH2


GEOLOGICAL

WA

TE

R

DE

FE

CT

SP

AC

ING

(cm

)

BOREHOLE LOG

GEOLOGICAL UNIT,

GENERIC NAME,

ORIGIN,


SA

MP

LE

S


20

60

200

600

2000F

LU

ID L

OS

S (

%)

25

50

75

DE

PT

H (

m)

GR

AP

HIC

LO

G

RL

(m

)

ME

TH

OD

CO

RE

RE

CO

VE

RY

(%

)

TESTS

CA

SIN

G

WE

AT

HE

RIN

GM

OIS

TU

RE

CO

ND

ITIO

N

ST

RE

NG

TH

/DE

NS

ITY

CL

AS

SIF

ICA

TIO

N

SH

EA

R S

TR

EN

GT

H(k

Pa

)

CO

MP

RE

SS

IVE

ST

RE

NG

TH

(MP

a)

1 5 20

50

100

250

10

25

50

100

200


R.L.: 345.00m

DATUM: NA DRILL FLUID:

DRILL METHOD: CP

DRILL TYPE:

DRILLED BY: Texco





344

343

342

341


Clayey SILT; light orange tan. Firm to stiff; lowplasticity; moist to wet.

GRAVEL, with some silt and sand. Wet to saturated;gravel, fine to coarse, subrounded to rounded; sand,medium to coarse.

Sandy GRAVEL; dark grey. Gravel, medium to coarse,subrounded to rounded; sand, fine to medium.

Clayey GRAVEL; dark grey. Gravel, fine to coarse,rounded to subrounded.

PEAT (FIBROUS); dark brown.

Clayey; dark grey. Low plasticity; moist to wet.

W

M

W

4m: Target depth

6/88/87/5

N=28Solid

1/12/44/3

N=13Solid

2/21/12/2N=6Solid

07

/06

/20

18

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5


Hole Depth4m

COMMENTS:

Scale 1:25 Rev.: B

Bore

Log -

27/0

7/2

018 2

:01:4

7 P

M -

Pro

duce

d w

ith C

ore

-GS

by

GeR

oc

v3.2

a

SHEET: 1 OF 1

BOREHOLE No.: BH3


GEOLOGICAL

WA

TE

R

DE

FE

CT

SP

AC

ING

(cm

)

BOREHOLE LOG

GEOLOGICAL UNIT,

GENERIC NAME,

ORIGIN,


SA

MP

LE

S


20

60

200

600

2000F

LU

ID L

OS

S (

%)

25

50

75

DE

PT

H (

m)

GR

AP

HIC

LO

G

RL

(m

)

ME

TH

OD

CO

RE

RE

CO

VE

RY

(%

)

TESTS

CA

SIN

G

WE

AT

HE

RIN

GM

OIS

TU

RE

CO

ND

ITIO

N

ST

RE

NG

TH

/DE

NS

ITY

CL

AS

SIF

ICA

TIO

N

SH

EA

R S

TR

EN

GT

H(k

Pa

)

CO

MP

RE

SS

IVE

ST

RE

NG

TH

(MP

a)

1 5 20

50

100

250

10

25

50

100

200


R.L.: 345.50m

DATUM: NA DRILL FLUID:

DRILL METHOD: CP

DRILL TYPE:

DRILLED BY: Texco





345

344

343

342

341


CLAY. Firm to stiff; low plasticity; moist to wet.

Silty GRAVEL; dark grey. Moist to wet; gravel, fine tomedium.

Sandy GRAVEL; dark grey. Moist to saturated; gravel,fine to medium; sand, medium to coarse.

PEAT (FIBROUS); dark brown. Saturated.

CLAY; dark bluish grey. Low plasticity; moist to wet.

W

M-W

W

4m: Target depth

2/33/44/4

N=15Solid

1/11/11/1N=4Solid

2/13/69/7

N=25Solid

14

/06

/20

18

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5


Hole Depth4m

COMMENTS:

Scale 1:25 Rev.: B

Documents

Annexure 13 Geotech Assessment - Hurunui District · TP03 and TP04 encountered alluvial fan gravels (with a silty clay layer in TP04). The lower gravel layers had strong groundwater