Before a Board of Inquiry Ruakura Development Plan Change

IN THE MATTER of the Resource Management Act 1991

AND

IN THE MATTER of a Board of Inquiry appointed under section 149J of the Resource Management Act 1991 to consider a Plan Change requested by Tainui Group Holdings Limited and Chedworth Properties Limited

Statement of Rebuttal Evidence of Kenneth John Read on behalf of Tainui Group Holdings Ltd and Chedworth Properties Ltd

16th April 2014

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Introduction

1. My full name is Kenneth John Read. I am a Senior Engineering

Geologist with Opus International Consultants.

2. I have the qualifications and experience set out at paragraphs 2

and 3 of my statement of evidence in chief (EIC), dated 26th

February 2014.

3. My rebuttal evidence is given in relation to the Plan Change

requested by Tainui Group Holdings Limited and Chedworth

Properties Limited (the Plan Change).

4. I repeat the confirmation given in my EIC that I have read the

‘Code of Conduct for Expert Witnesses’ as contained in the

Environment Court Practice Note 2011 and that my evidence has

been prepared in compliance with that Code.

5. I attended expert witness conferencing held on 11 April 2014 in

relation to Geotechnical matters. I was a party to the outcomes

of that conference recorded in the joint witness statement dated

Friday 11 April 2014.

Scope of Evidence

6. In this statement of rebuttal evidence I will respond to the

evidence of:

(a) Mark Thomson Mitchell On behalf of Greame Goodwin and

himself (submitter No 106473), in particular paragraphs 12 and

13, paragraphs 15 to 19, and paragraphs 37 and 38.

(b) Mohammed Hassan on behalf of Waikato Regional Council

(submitter No 106894), in particular paragraphs 3.1(d), and 8.1 to

8.4 inclusive.

(c) William Roy Cowie on behalf of The Ruakura Residents Group

and himself (submitter number 106774), in particular paragraph

5.16.

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7. The fact that this rebuttal statement does not respond to every

matter raised in the evidence of submitter witnesses within my

area of expertise should not be taken as acceptable of the

matters raised. Rather, I rely on my EIC, Opus’ technical reports

reference G3121, G3127 and G3134 and this rebuttal statement

to set out my opinion on what I consider to be the key

geotechnical issues matters for this hearing.

Mr Mark T Mitchell on Behalf of Mr Greame Goodwin and Himself.

(Submitter No 106473)

Number of soil test locations and presentation of findings.

8. In paragraph 15 of his evidence Mr Mitchell comments that “the

density of the soil test locations is sparse in relation to the size of

the development”. The geotechnical investigation carried out to

date has been a preliminary investigation to characterise the

ground conditions beneath the Stage 1 Area. The aim of this was

to determine if there are any major geotechnical constraints that

could prevent or have serious detrimental effects on the proposed

development. I consider the level of investigation and number of

soil testing points investgiated to be sufficient to have achieved

those aims and provide an appropriate level of information.

Paragraph 4 of the Introduction to the Opus Interpretative Report

(ref G3127) clearly states “Further investigation of each zone at

the site will be necessary to form in depth geotechnical

assessments and essentially to confirm and detail the design

measures required for the various developments. These

investigations may be required to be carried out over a number of

phases.”

9. With respect to the inclusion of geological maps and plans raised

by Mr Mitchell I confirm that these were considered during

preparation of the report but considered to be of little benefit in

this case. We instead relied on the preparation of geological

cross sections as we consider that those are the best means of

graphically demonstrating strata variation within each zone of the

Stage 1 Area investigated. I consider that the absence of such

geological plans makes no difference to the results of the

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investigation and the conclusions and recommendations drawn

from them.

10. In paragraph 16 of his evidence Mr Mitchell states his opinion that

considerable emphasis has been placed on the residential areas

in contrast to a lesser emphasis on the inland port zone. Whilst

there may appear to be a greater density of test locations in the

residential zone the majority of these are scala auger bores,

which are shallow and used widely as the basis for residential

housing foundation design. Elsewhere in the Stage 1 Area

investigated greater emphasis has been placed on determining

the deeper geology and soil properties using boreholes and

CPTS which provide the more sophisticated and reliable levels of

information necessary for the level and types of development

proposed in those Areas. With respect to the interpretation and

reporting of the information obtained from the investigation I

consider that we have investigated all Areas appropriately.

Liquefaction of soils during a seismic event.

11. In paragraphs 12, 13, 17, 18 and 19 of his evidence Mr Mitchell

discusses the liquefaction assessment carried out to date.

12. In paragraph 12 Mr Mitchell compares the Stage 1 Area to low

lying areas of Christchurch which have been seriously adversely

affected by liquefaction following the recent series of seismic

events there. The geology, geomorphology and geography of

those parts of Christchurch to which Mr Mitchell refers are

significantly different from that at Ruakura, and I do not consider

it an approriate comparison.

13. In Paragraph 13 Mr Mitchell states that in his opinion there has

been insufficient investigation of the probability of liquefaction. In

the reports reviewed by Mr Mitchell the probability of liquefaction

has been assessed using the procedures described in

NZS1170:2004 “National Standard for Structural Design Actions,

Part 5: Earthquake Actions – New Zealand” to determine the

appropriate Peak Ground Acceleration (PGA), and current

industry standard computer software to calculate if, and to what

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degree, any liquefaction could occur. This software in turn uses

current industry standard methods and procedures to calculate

the potential for liquefaction.

14. Our assessment methodology is consistent with the New Zealand

Geotechnical Society Guidelines1. We have also used 3 methods

of assessment:

(a) using Standard Penetrations Test results in boreholes, (SPTs);

(b) data from Cone Penetrometer Tests (CPTs); and

(c) shear wave velocity measurements using seismic CPTS.

15. The results obtained from each of these methods of assessment

were cross checked as a means of verifying the results. A

number of separate assessments were carried out. We have

also used seasonally adjusted groundwater levels in the

calculations. I therefore believe that in the reports presented to

date we have adequately assessed the probability of liquefaction

occurring. Notwithstanding this we recommended in our reports

that further assessment be carried out at detailed investigation

and design stage to further refine the liquefaction hazard and to

develop mitigation strategies. I consider this approach

appropriate.

16. In our reports there is comment on the estimated total and

differential ground surface settlements that may occur as a

consequence of liquefaction. However it has come to light in

further review for this evidence that there has been an error in

transposing data into the Interpretative Report and in particular

the units of measurement for the potential liquefaction induced

settlement. Settlements reported in millimetres (mm) should read

centimetres (cm). However I consider this transposing error does

not affect the conclusions I draw from the calculations for the

reasons given in subsequent paragraphs below.

1 Geotechnical Earthquake Engineering Practice, Module 1 – Guideline for the

identification assessment and mitigation of liquefaction hazards. NZGS July 2010

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17. We also comment on the presence of a near surface crust in all

areas where there is a low risk of liquefaction in the near surface

soils. The presence of a non-liquefied crust of sufficient

thickness to prevent surface expressions of liquefaction is

important in limiting the surface effects of liquefaction.

18. The reports also recommend that TGH seek access to a site

specific seismic assessment risk assessment prepared by GNS

on behalf of the New Zealand Transport Agency for the Waikato

Expressway. This work included the Ruakura area. I have viewed

that assessment2 and the PGAs calculated in that site specific

assessment are lower than those estimated in the Opus reports

for the Ruakura Plan Change Area using the procedures in

NZS1170:5, implying that the assessment presented to date is

conservative. In terms of the local seismicity the GNS site

specific assessment for the Waikato Expressway describes the

whole area in which the expressway lies (which encompasses the

Ruakura Area) to have a ‘low general level of seismic hazard’.

19. In paragraph 17 of his evidence Mr Mitchell comments on

groundwater levels being low at the time of our soil testing. This

is recognised in the Interpretative Report (Report ref G3127,

page 16 and 3rd bullet point on Page 30) and was allowed for in

the liquefaction assessment carried out by using higher

groundwater levels than were observed at the time of the

investigation.

20. Also in paragraph 17 of his evidence Mr Mitchell states “the fact

that over a substantial period of the year, groundwater levels are

likely to be relatively close to ground level, except for the rounded

hills” and “in my opinion there is a relatively high risk of

liquefaction of some site soils under moderate seismic activity”.

With respect to groundwater levels used in our liquefaction

assessment we have used elevated groundwater levels based on

measured observations over a winter period provided by Harrison

Grierson. I consider that by this action we have accounted for the

2 GNS Science Report “Seismic hazard maps and spectra for Waikato Expressway”

GNS Science Consultancy Report 2010/206

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seasonal high water levels described by Mr Mitchell in the

assessment of potential liquefaction.

21. The calculations presented in our reports have demonstrated that

some liquefaction of soils at depth will occur in the worst case

(ultimate limit state, ULS, 1 in 500 year earthquake) assessed

under the current New Zealand Standard. By so doing so we

have quantified the risk and potential effects of liquefaction rather

than relying on opinion and subjective assessment.

22. Subsequent to Mr Mitchells filing eveidence I ca nconfirm that the

liquefaction risk for the “serviceability limit state” (SLS, 1 in 25

year earthquake) has been assessed. Using the NZS1170.5

criteria we estimate a PGA of 0.045g. CPTs 103, 105 and

SCPT1 (presented in Opus Report G3127) which showed the

greatest degree of liquefaction in the ULS analyses were selected

for analyses. Near surface groundwater levels were assumed as

before, and it has been calculated that liquefaction will not occur

at the locations of these CPTs in the SLS case. I therefore

consider that this confirms and further demonstrates that there is

a low risk of liquefaction under ‘moderate’ seismic activity. A copy

of the relevant calculation for CPT 103 is attached in Appendix A.

23. In paragraph 18 Mr Mitchell questions whether or not the

liquefaction assessment undertaken is a ‘full seismic assessment’

on the basis of not including seasonal variation in groundwater

levels, groundwater level in relation to the ground surface, and

the local site geology. Each individual assessment and

calculation presented in the reports is based on an elevated

groundwater level to reflect winter conditions, took into account

the ground level at each borehole and CPT location, and was

based on the geology at the specific location of each borehole

and CPT. The software outputs presented a conservative ‘first

cut’ of the potential settlement which has been assessed

separately in more detail. The other effects such as potential loss

of bearing capacity have to be assessed separately from these

outputs. This is normal practice.

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24. I believe it worth noting that the liquefaction assessment of the

borehole and CPT data in the Inland Port Area yielded the lowest

level of liquefaction observed in those areas investigated and

assessed to date and that in the Inland Port Area ground level is

to be raised by filling by approximately 1 to 2m. This additional

weight of fill will act to reduce the potential for liquefaction of

underlying soils from that calculated and presented in the reports

to date.

25. From the results of our analyses I confirm our conclusion that

widespread liquefaction is not expected to occur in a

serviceability level seismic event (i.e. a 1 in 25 year event).

26. Whilst the revision of the units of measurement relating to the

degree of potential soil liquefaction that could arise in an ultimate

limit state seismic event (1 in 500 years) would potentially be

significant, I consider that there are a range of engineering

measures available to prevent soil liquefaction and to mitigate its

effects to appropriate levels.

27. In paragraph 19 of his evidence Mr Mitchell questions the

practicality of using detention ponds to manage stormwater as a

consequence of potential liquefaction induced ground settlement.

Liquefaction is not anticipated in the serviceability level

earthquake. In a major event I anticipate that the ponds will be

quickly and easily repaired if necessary. This philosophy has

been widely adopted in the region, and is demonstrated by the

wide use and continued construction of such ponds in Waikato

and Waipa Districts in similar ground conditions with relatively

level ground and potentially liquefiable soils.

Soil and groundwater conditions – Graeme Goodwin Site.

28. In paragraph 35 of his evidence Mr Mitchell describes soils

conditions determined by soil testing on Mr Goodwin’s property. I

have not seen the results of the testing Mr Mitchell refers to

however it is broadly consistent with the results of soil testing

done in that vicinity as part of the Stage 1Opus investigations.

Since preparation of my EIC we have also carried out seven

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auger boreholes around the enclave formed by Ryburn and

Percival Roads which included Mr Goodwin’s property. A copy of

our letter report on the findings of those auger boreholes is

presented in Appendix B, together with a plan showing the

location of Mr Goodwin’s property. The findings of these auger

holes are in general agreement with Mr Mitchell’s statement. No

buried peat horizons were observed in the new auger holes.

29. In paragraph 37 of his evidence Mr Mitchel states that “it will first

be necessary to excavate and remove the upper 1.8m of soft soil”

and to replace them with imported granular fill. This method of

ground improvement is one of a number of means of dealing with

potential settlement issues associated with the relatively poor

near surface soils in this area. Surcharging these with additional

fill and allowing settlements to occur prior to construction on the

fill is an accepted and widely used alternative. This method of

overcoming settlement risks associated with near surface poorer

soils is currently being employed on the Waikato Expressway

Tamahere to Cambridge Section which is under construction over

very similar soils. I have been heavily involved with the peer

review of that work. I can confirm TGH have already been in

discussions regarding a site trial to determine the efficiency of

this method for development in the Inland Port Area.

30. There are also other alternative ground improvement techniques

that could be employed such as installing vibro-stone columns to

support the new fill. I expect that final decision will be made on a

balance of cost, efficiency, risk, ground improvement

effectiveness, and sustainability considerations. I have not

attempted to verify the figures quoted by Mr Mitchell in paragraph

38 of his evidence however it is clear that the excavation and

replacement method described is likely to be high cost, have low

geotechnical risk and to be questionable with respect to

sustainability. I therefore expect alternatives to be thoroughly

explored before a decision is made.

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Mohammed Hassan on behalf of Waikato Regional Council

(submitter No 106894)

31. In paragraphs 3(d) 8.3 and 8.4 of his evidence Mr Hassan

comments on settlement of peat and refers to a plan (Annexure 5

of his evidence) showing the indicative locations of peat in the

vicinity of the Plan Change Area. I am in general agreement with

his comments regarding on going peat settlement but cannot

comment on the figures he has quoted. I note however that the

area of peat shown on the plan that encroaches onto the Plan

Stage Area we have investigated has only thin surface organic

soils.

William Roy Cowie on behalf of The Ruakura Residents Group and himself

(submitter No. 106774)

32. In paragraph 5.16 of his evidence Mr Cowie comments that “the

Residents Land is consolidated peat and other soft soils in depth

from 0.5m to 1.5m”. This is broadly consistant with the findings

of the Stage 1 investigations and investigations carried out

around the Percival and Ryburn Road properties since

preparation of my EIC. A copy of the findings of that work

including a plan showing where the additional investigations were

located is presented in Appendix B, together with plan showing

the location of Mr Cowies property.

33. I note however that the organic soils proved in these holes were

generally less than 200mm thick and limited to surface deposits.

If this is typical of the soils within the boundaries set by Ryburn

and Percival Roads then I expect the housing to be founded

beneath these surface organic soils. Based on our investigations

elsewhere in this area there is a possibility of thin buried organic

soils below the depths investigated by these additional augers.

On the assumption that these thin burried organic soils are

localised and discontinous, as I believe to be the case, I

anticipate that potential surface settlement caused by further

consolidation of these soils, brough on by changes in

groundwater level or additional surface loading with be both

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localised and marginal. These can be fully assessed at the

detailed design stage.

34. I cannot comment on the ground vibration issue raised by Mr

Cowie as that is outside my area of expertise. I understand that

this issue has been addressed in the rebuttal evidence of Mr

Carpenter.

Conclusion

1. Having read all the statements of evidence provided by the submitters in

relation to potential liquefaction, the level of investigation carried out in

the preparation of the Opus technical reports, and the presence of peat

and soft soils in the Ryburn Road and Percival Road area, I have no

reason to alter my overall conclusions expressed in my EIC that in my

expert opinion and based on the evidence available to me, there are no

major geotechnical constraints that could preclude development of the

Plan Change Area for the proposed land uses.

Kenneth John Read

16 April 2014

Appendix A

Calculation of liquefaction potential at CPT103,

Serviceability Limit State, PGA 0.045G

Appendix B

Submitters Properties and Auger location plan.

Additional Auger investigation at Rydale and Percival Roads.