Appendix N. Engineering Design Consultants Limited Liquefaction Potential Assessment Interpretive Geotechnical Report

Transcription

1 Appendix N Engineering Design Consultants Limited Liquefaction Potential Assessment Interpretive Geotechnical Report

2 Pioneer City West Palmerston North Liquefaction Potential Assessment Interpretive Geotechnical Report Project th May

3 Liquefaction Potential Assessment EDC File: Revision No. Date Engineer Description.. GBW Updated Report prepared by: G B Williams Date: th May Snr Geotechnical Engineer, Director CP Eng, Int PE (NZ) MIPENZ MAusIMM MIoD Report checked by: I T Hendy Date: th May Civil/Geotechnical Engineer, Director CP Eng, MIPENZ // i

4 Liquefaction Potential Assessment EDC File: Contents. INTRODUCTION.... Report Outline.... Limitations of Report.... GEOLOGICAL INFORMATION SUMMARY.... MBIE ASSESSMENT CRITERIA FOR LIQUEFACTION & LATERAL SPREADING.... PREVIOUS INVESTIGATIONS.... Geological and Nuclear Science Consultancy (GNS) Report.... Tonkin & Taylor Ltd Investigation For Palmerston North City Council.... EDC GEOTECHNICAL INVESTIGATION.... Scope.... Site Description.... Site Investigation.... Soil Profile.... Summary of Soil Properties.... LIQUEFACTION AND LATERAL SPREADING POTENTIAL.... General.... Analysis Parameters.... Liquefaction Analysis Results.... Lateral Spreading Analysis Results.... Liquefaction Analysis of T&T Borehole/SPT data.... T&T Borehole Liquefaction Analysis Results.... CRUSTAL THICKNESS.... GROUND REMEDIATION.... Area A.... Area B.... Area C.... Roading.... Services.... CONCLUSIONS AND RECOMMENDATIONS... APPENDICES: Appendix A Proarch Proposed Development Plan Appendix B EDC CPT Result Interpretation & Liquefaction Analysis Appendix C T&T Borehole Liquefaction Analysis Appendix D Geoscience Ltd Review Drawings: /G Geological Map Overlay /G Exploratory Hole Location Plan /G CPT Groundwater Contours Measures Nov /GA Soil Profile Section A /GB Soil Profile Section B /GC Soil Profile Section // ii

5 Liquefaction Potential Assessment EDC File: /GD Soil Profile Section /GE Soil Profile Section /G Crustal Thickness Contours /G Ground Zone Classification /G Contoured Depth to Gravels // iii

6 Liquefaction Potential Assessment EDC File:. INTRODUCTION. Report Outline This report is provided in connection with proposed development of the Pioneer City West site (PCW), to the west of Palmerston North City. This development lies within the City West Proposed Urban Growth Area that has been recently considered for future intensive development by the Palmerston North City Council (PNCC). The PCW site is located at NZMG coordinates E, N. The site is approximately.km west of Palmerston North City Centre. The area of land to be included in the proposed development is approximately ha. The number of lots proposed at the development site is unknown at this time. The PNCC commissioned Geological and Nuclear Sciences (GNS) for a report on the geological conditions across the City West Proposed Urban Growth Area. Following concern about liquefaction in light of the recent Christchurch earthquakes, the PNCC also commissioned Tonkin & Taylor Ltd for a detailed geotechnical investigation of the subject growth area, which included some testing and liquefaction analysis for the PCW site and surrounding land. Engineering Design Consultants Ltd (EDC) was commissioned by Pioneer City West Ltd to undertake a more detailed geotechnical investigation across the PCW site. This included a significant number of additional CPT tests. Based on the results, we undertook an assessment of the potential for liquefaction and provide recommendations for land remediation options and general foundation options. The proposed development plan was provided to us by Proarch Ltd and is included as Appendix A. This report has been finalised following peer review by Matt Wiley CPEng Principal Engineering Geologist at Geoscience Ltd. A copy of the Geoscience review is attached as Appendix D.. Limitations of Report The recommendations and opinions contained in this report are based on our visual reconnaissance of the site, information from geological maps and upon data from the field investigation as well as the results of in situ testing of soil. Inferences are made about the nature and continuity of subsoils away from and beyond the exploratory holes, but cannot be guaranteed. The descriptions detailed on the exploratory hole logs are based on the field descriptions of the soils encountered. This report has been prepared for the particular project described to us and no responsibility is accepted for the use of any part of this report in any other context or for any other purposes. Our opinions and recommendations are based on our comprehension of the current regulatory standards and must not be considered legal opinions. For legal advice, please consult your solicitor. This opinion is not intended to be advice that is covered by the Financial Advisors Act. //

7 Liquefaction Potential Assessment EDC File:. GEOLOGICAL INFORMATION SUMMARY Geologic data sourced from Institute of Geological & Nuclear Sciences (Copyright Reserved). In assessing the geology of the site we have referred to the following geological maps and records: i). Geological & Nuclear Sciences Q_Map Wellington (i) ; ii). GNS Science Consultancy report on Potential Liquefaction risk in the City West Proposed Urban Growth Area (ii). The following extract is from the QMAP :, information: SITE Qa Qa Qb Alluvial Deposits Well sorted flood plain gravels Gravel with minor sand or silt Beach deposits Marine gravel with sand The site is shown on the Q-Map as being underlain by Floodplain deposits. These are described as being Holocene floodplain gravels (Qa) are particularly well sorted. Clasts are up to boulder size, but most are less than.m across. Greywacke sandstone is the predominant clast type. (i) The GNS Science report (ii) describes the general soils at the Pioneer City West site as being part of river flats. These soils are:.. thick, young and relatively poorly drained may be susceptible to liquefaction (moderate to very high liquefaction susceptibility). The Agresearch drawing Map : Soil map of Anders Road and Racecourse Growth Options (iii) shows the majority of the site to be underlain by the Kairanga Series and the Te Arakura Series, with a narrow band (approx.m wide crossing the extension that //

8 Liquefaction Potential Assessment EDC File: leads towards Pioneer Highway) of the Manawatu Series. The geological soil map is shown on Drawing /G. The Te Arakura series on this site is represented by the Te Arakura Silt Loams (plus both heavy and light phases) and in some places as a fine Sandy Loam, these soils are shown at the northern and north-eastern end of the site. These are described in the Soil of the Manawatu County, North Island, New Zealand (iv) as Gley soils are imperfectly to poorly designed soils formed on those parts of the river flats which have been free of flooding and have only had negligible accumulation in historic times. They have greyish brown A horizons overlying olive grey to olive firm B horizons with many to abundant reddish and brownish mottles. In the more poorly drained soils, iron-manganese concretions occur in a layer just below the A horizon. Slight clay accumulation occurs in the B horizon. Published grading curves show potential susceptibility to liquefaction for some samples but not for others. The Kairanga Series is identified as silt and sandy loams (similar phases to the Te Arakura soils noted above). These are described as gley soils with poor drainage and range from fine sandy loams to heavy silty loams, often grey or dark grey and clayey with very coarse blocky or prismatic structure. The A horizons are dark and overly grey or olive grey B horizons. Some of the soils have gradations that indicate a potential susceptibility for liquefaction, some do not. The Manawatu series is represented by silt loams and fine sandy loams. These are Moderately well to excessive drained recent soils. Occur on the levees and flats which are infrequently flooded and only slowly accumulating. They have deep brown to greyish brown A horizons which grade into olive brown subsoils. These soils typically have steep uniform grading curves that indicate a high to very high susceptibility for liquefaction. //

9 Liquefaction Potential Assessment EDC File:. MBIE ASSESSMENT CRITERIA FOR LIQUEFACTION & LATERAL SPREADING Following the Canterbury Earthquake events, the Department of Building and Housing (now part of the Ministry of Business Innovation and Employment - MBIE) developed a methodology for assessing the options for repair or replacement of damaged foundations (v). The documents are not mandatory and as the foreword to the December document indicates Different and improved details and methods may well be developed as the recovery proceeds. Initially, the land was split into a four zones: Green repair/rebuild process can begin Red land repair would be prolonged and uneconomic Orange hold zone, further assessment required; to be re-zoned Red or Green depending on further investigation White un-zoned parts of the Port Hills and CBD; still being mapped. Now with further investigation and understanding, most of the land has been categorised as either Green or Red. Subsequently, the Green Zone has been further split into Technical Categories, based on the potential for settlement. The following table is based on Table. included in section Part A, Section. of the MBIE guidance document dated December (v). Foundation Technical Category TC (where confirmed) TC (where confirmed) TC (where confirmed) Uncategorised Future Land Performance Expectation from Liquefaction Expected Nominal SLS land Settlement Expected Nominal ULS land Settlement Liquefaction damage is unlikely in a future large earthquake - mm - mm Liquefaction damage is possible in a future large earthquake - mm - mm Liquefaction damage is possible in a future large earthquake > mm > mm Land in the un-categorised area will contain properties that experience future land performance as per one of the above categories. It also includes urban nonresidential land, unmapped rural land, the Port Hills and Banks Peninsula. Normal consented conditions apply. This may include the need for engaging a geotechnical engineer to determine the appropriate solution for the property, based on a site-specific assessment. Nominal Lateral Stretch Generally not expected < mm > mm Note: In terms of engineering design standards, small to medium sized earthquake corresponds to a Serviceability Limit State (SLS) event with a nominal return period of years, and a moderate to large earthquake corresponds to an Ultimate Limit State (ULS) event with a nominal return period of years (refer to Part B, Section. of MBIE Guidance Document (v) ) for importance level structures. For new foundations, this methodology is based around the results of geotechnical investigations to determine the nature of the soils below a site, the liquefaction potential of those soils and if liquefaction does occur, the amount of settlement that is likely to manifest itself. The MBIE guidance document includes recommendations for foundation design that could be applied to the subject site due to the similarity of soil conditions. These MBIE recommendations provide robust and well-balanced engineering solutions that will //

10 Liquefaction Potential Assessment EDC File: reduce the risk of injury to people and damage to homes in future earthquakes. These foundation options include the following: Technical Category Notes: This table is based on information from Tables.,. and. of the MBIE Guidance document. Foundation types A, B and C are defined in Part A, Section. the MBIE Guidance document (v). These designs have been developed without anticipating an adequate crust is in place and therefore do not take into account any crustal thickness. *SED = Specific Engineering Design Required. The MBIE guidance document includes the following statement: Objectives Geotechnical ULS bearing capacity>kpa Geotechnical ULS bearing capacity to kpa The principal objective of this document is to provide building repair and reconstruction solutions and options that:. are appropriate to the level of land and building damage experienced. take account of the likely future performance of the ground. meet Building Act and Building Code requirements. are acceptable to insurers and property owners. Geotechnical ULS bearing capacity<kpa Foundation Types A&B Type C Types A&B Type C Types A&B Type C TC NZS NZS SED* SED SED SED type Piles Slab-on-grade foundation TC NZS shallow pile/ foundations TC SED NZS shallow pile/foundations Stiffened Raft Options - SED typically Deep Piles, Ground Improvement or Surface Structures/shallow foundations as outlined in the MBIE document Although this document was specifically written for Christchurch and does include the comment The information on reducing the effects of liquefaction on residential properties should not necessarily be taken as a best practice guide for addressing liquefaction in other parts of Canterbury or New Zealand, given the similarity of geotechnical conditions, it is considered that these documents are appropriate for assessing risk and making recommendations for developments on the Pioneer City West site. Part C of the MBIE document (v) includes in section., the following general principles:. The guidance provides design solutions and methods that aim to substantially improve the performance of house foundations in future seismic events, recognising that the land performance may still induce deformations and loads that could cause some damage.. It aims to improve the robustness of foundations to comply with life safety requirements in ultimate limit state (ULS) seismic events (and also provide a level of potential repairability in that design event) and to minimise damage and repair costs in serviceability limit state (SLS) events. Some damage may result in either damage event.. Following the methods and solutions provided in the document provides reasonable grounds for designers and Building Consent Authorities that the resulting repairs or rebuild will meet the requirements of the Building Code. SED SED //

11 Liquefaction Potential Assessment EDC File:. PREVIOUS INVESTIGATIONS. Geological and Nuclear Science Consultancy (GNS) Report The GNS Science report (ii) gives an in depth assessment of the potential for liquefaction in the Palmerston North Region based on a developed database of geotechnical data, LIDAR (LIght Detection And Ranging) aerial mapping to assess the thickness of the potentially liquefiable soils and also the potential sources of earthquakes that could trigger liquefaction. Much of the report covers the detail of how this information was collected and analysed, including definitions of the terms used and limitations due to the methodology and lack of detailed information (e.g. lack of detailed borehole/cone Penetration Test (CPT) data). Part of the project objectives included an assessment of the liquefaction potential of the Anders Road area, which lies relatively close to the proposed Pioneer City West site. The report states: The assessment of liquefaction potential involves two general steps (Table ): () Evaluation of liquefaction susceptibility. This involves the identification of those areas or layers which have the characteristics of liquefiable materials and subsoil materials. () Evaluation of liquefaction opportunity. This involves determination of the occurrence of earthquake shaking strong enough to generate liquefaction in susceptible materials. Liquefaction potential is site dependent. Certain soils and subsurface materials are more prone to liquefaction than others. Saturated, unconsolidated, relatively uniform fine sands or coarse silts at depths less than m are most prone to liquefaction.. Liquefaction susceptibility is a function of soil properties and water saturation, whereas opportunity is a function of the number of seismogenic sources in the region and the periodicity of earthquake generation. Table Table illustrating the liquefaction hazard assessment process Liquefaction Susceptibility Liquefaction Opportunity A function of the soil s ability to resist liquefaction. This depends on: Soil Composition (grain size & composition) Relative density Water table depth Depth of soil layer + A function of the intensity of seismic shaking. This depends on: magnitude and proximity of earthquake frequency of events MM VII duration of shaking = Liquefaction Potential Note: LIQUEFACTION HAZARD = LIQUEFACTION POTENTIAL + GROUND FAILURE POTENTIAL //

12 Liquefaction Potential Assessment EDC File: The GNS Science report describes the general soils in the Palmerston North vicinity. The report identifies two major groups, The soils of the river flats and Soils of the terrace land The soils at the Pioneer City West site are part of those included in the river flats description: are thick, young and relatively poorly drained may be susceptible to liquefaction (moderate to very high liquefaction susceptibility).. The Manawatu sandy loam has very high liquefaction potential. The Kairanga fine sandy loam has negligible to moderate liquefaction potential. The soils map (included on Drawing /G) shows the majority of the site to be underlain by the Kairanga Silt Loam, with a narrow band (approx. m wide crossing the extension that leads towards Pioneer Highway) of the Manawatu Silt Loam. This suggests therefore that the majority of the Pioneer City West s site is potentially underlain by negligible to moderate liquefaction potential soils with a narrow band of potentially very high liquefaction potential soils. The GNS Science report identifies a number of faults that could trigger liquefaction based on historical evidence. It is noted that in the M. Wairarapa earthquake (although more than km away) led to significant shaking in what is now Palmerston North city. This was estimated at a Modified Mercali (MM) Scale (heavily damaging to some buildings) to MM (Destructive some buildings damaged and many weak buildings destroyed). For comparative purposes, the Feb event in Christchurch was rated at a MM to MM ). MM shaking could be anticipated (according to the GNS report) every years and MM level shaking every years. Further detail on the liquefaction susceptibility is given, indicating: Soils close to former stream channels (the Mangaone, Kawau, Little Kawau, Terrace, Awatea and unnamed streams swampy depressions and lagoons (former channels and cut-off oxbows) close to the Manawatu River. Are likely to contain soils susceptible to liquefaction. The GNS Science report adopts a similar scale of Liquefaction Ground Damage Potential to that used in Canterbury: Zone Description of Liquefaction Ground Damage Potential Very High: Significant ground subsidence (likely to be > mm) plus lateral spreading High: Probably no lateral spreading, but ground subsidence > mm Moderate: Ground subsidence probably in the range of to mm Low: Probably up to mm of ground subsidence Negligible: No liquefaction anticipated Part of the western area of Palmerston North city is underlain by soils provisionally identified by the GNS report as being either Zone or as defined in the table above. The report comments that there is relatively little geotechnical information available but it does contain a moderate to good distribution of CPT testing. The report also indicates that In light of the soils map information, this assessment may be conservative and with additional data it may be possible to lower the susceptibility assessment. Based on the database that is available, GNS Science has developed anticipated groundwater levels. Based on their information, static groundwater levels could be //

13 Liquefaction Potential Assessment EDC File: in the range of about to m depth across the site, but there could also be some perched groundwater, (i.e. localised areas where soil conditions have led to underground ponding of groundwater that are not contiguous across large areas). The digital modelling based on the LIDAR data and the geotechnical information indicates that in the Longburn, Cloverlea and Anders Racecourse development areas (includes the Pioneer City West site), some thickness of potentially liquefiable soils exist. Figure a indicates somewhere between to m of potentially liquefiable soils with the deepest potentially liquefiable soils at the Pioneer Highway end of the site (south east). The report states raise caution regarding the (further) development of areas where thick, saturated coverbeds are modelled. A suitable response and strong recommendation to this note of caution would be to require careful geotechnical investigation of all new development sites in these suspect areas. The report states in relation to the Anders Road, Racecourse residential growth areas:..there may well be areas possibly susceptible to liquefaction near Pioneer Highway. We recommend that comprehensive site investigations with good geotechnical advice precede development. A major lesson from the Canterbury earthquakes damage is that provided house and buildings are constructed on foundations that take account of local site subsoil conditions and continue to provide support when foundation soils yield, deform inelastically, and/or liquefy, then the houses and buildings can survive undamaged. Measures can also be taken to minimise damage to infrastructure, such as buried pipelines. Note: This report was issued before the MBIE documents which do not require design to protect from all earthquakes.. Tonkin & Taylor Ltd Investigation For Palmerston North City Council A preliminary geotechnical investigation (vi) was undertaken by Tonkin & Taylor Ltd. (T&T) on behalf of Palmerston North City Council that included this site. Four machine drilled boreholes were located on the Pioneer City West site (BH s,, and plus BH located just outside of the southern boundary). T&T also undertook CPT testing that included sixteen CPT s on this site (CPT s,,,,,,,,,,,,,, and with CPT also located just outside of the site boundary). The T&T report also included a desk study, a walkover of the site, some laboratory testing of samples from the boreholes and a MASW geophysical investigation (one transect on the Pioneer City West site). The CPT s were pushed to refusal, but the depth to refusal varied between. to.m. The report states: The investigations indicate that the site is underlain by typically to m of interbedded silts and sands overlying sandy fine to coarse gravels. The thickness of the individual silt and sand beds is in the order of.m. Rock is expected to underlie the gravels at greater than m depth. The sands and silts vary from very loose to medium dense. The underlying gravels are typically dense. The aerial photographs and lidar data show that the site is crossed by old courses of the Mangaone stream. These old courses have been infilled with silts and sands. BH was drilled through an infilled channel and recorded silts and sands to.m depth. //

14 Liquefaction Potential Assessment EDC File: Localised areas of the stream channels have been infilled with fill (i.e. soils, rubble, ballast etc). Section. of the T&T report is titled Implications for Private Building Development. The report indicates for the whole of the City West site (that includes the PCW site): a) Settlement. Assessed settlements as a consequence of liquefaction are: SLS: to mm [if only using the data for the PCW site, settlements range from to m, with the majority being in the range of to mm]. ULS: to mm [if only using the data for the PCW site, settlements range from to m with the majority being in the range of to mm]. With reference to the table from DBH [now MBIE] guidelines.. this indicates that TC (enhanced foundations) and TC (piles or ground improvement) would be required if no ground improvements are undertaken. b) Crust Thickness.. in addition to settlement crust thickness must also be considered in selecting a foundation system (Technical Category). the non-liquefied crust expected for the ULS event in City West is likely to be thin (typically less than m). This thin crust is unlikely to provide reliable support to shallow foundations and dictate the need for TC rather than TC foundations in most instances. All foundations will require specific investigations and design. Because of the variable ground conditions across City West it is not possible to delineate the area between TC and TC. This variability is demonstrated by variations in settlement estimates and crust and liquefied thickness.. //

15 Liquefaction Potential Assessment EDC File:. EDC GEOTECHNICAL INVESTIGATION. Scope As requested, we undertook a geotechnical investigation using Cone Penetration Testing (CPT), to determine the likely subsoil conditions and provide data for the analysis of the potential for liquefaction across the site. The fieldwork was undertaken by Geotech Drilling Ltd, between Wednesday th November to Friday th November. As part of our supervision, we visited the site on Friday th November. Drawing /G shows the location of the EDC CPT s plus those exploratory CPT s and Machine Boreholes of T&T and from the PNCC s database. Section. of the MBIE Guidance document (v), includes the following table with respect to the Site investigation density for overall ground characterisation. Investigation Stage Plan Change Subdivision Consent Site over hectare Total Number of Test/Investigation Locations (cumulative) Site m or more but less than hectare. to. per hectare to total total (minimum of ). per lot (minimum of total per lot ) (urban) per house site (rural) Site less than m The current site is approx. ha in area. For a Plan Change, from the above table between and exploratory holes would be needed. CPT s were undertaken as part of this investigation, in addition to the CPT s and Machine Boreholes that T&T had previously completed. The investigation conducted at this site therefore complies with the above requirements.. Site Description The site is located to the west of Palmerston North City. It is a pan-handle shaped block of land, with the long axis oriented approximately north-west to south-east and the main area of the site is located in the north-western section of the site. It is bounded to the north by No. Line (Tremaine Avenue Extension), to the west by Longburn Rongotea Rd and to the south by Pioneer Highway. East of the site are some large residential blocks with (in the south) some paddocks. //

16 Liquefaction Potential Assessment EDC File: Site Figure : Site location (Aerial Photo courtesy of Google) The following photographs show views of the site: Photograph : Showing view looking south west from rail overbridge on Rongatea-Longburn Road //

17 Liquefaction Potential Assessment EDC File: Photograph : Showing typical view of paddocks Photograph : Showing view from No line (Tremaine Extension) looking South west //

18 Liquefaction Potential Assessment EDC File: Photograph : Showing view from No line (Tremaine Extension) looking South east past existing farm buildings Photograph : Showing typical view of paddocks //

19 Liquefaction Potential Assessment EDC File: Photograph : Showing typical view of paddocks Photograph : Showing typical view of paddocks //

20 Liquefaction Potential Assessment EDC File: Photograph : Showing one of the drainage ditches crossing the site Photograph : Showing typical view of paddocks //

21 Liquefaction Potential Assessment EDC File: Photograph : Showing typical view of paddocks Photograph : Showing view down race on east side of panhandle //

22 Liquefaction Potential Assessment EDC File:. Site Investigation We supervised Cone Penetration Tests at the approximate locations indicated on Drawing /G: The layout of the holes was designed to determine the likely nature and distribution of subsoils for assessment of liquefaction and lateral spreading, and to provide information for future design of foundations and infrastructure. Porewater pressures were recorded during the CPT testing and at the end of the test, the groundwater level was dipped using a hand held dip-meter. Drawing /G shows the dipped groundwater and approximate groundwater depth contours based on the dipped levels. The logs are contained in Appendix B. BH Cone Penetration Tests (CPT s to inclusive) were undertaken by Geotech Drilling Ltd with a tractor mounted CPT rig. The probe is pushed into the ground with a constant rate of penetration. The cone end resistance, pore pressure and the side resistance of the soil on the cone are measured electronically and the results computed to provide the cone end resistance. Based on the ratio between the cone resistance and the sleeve resistance plus the pore pressure readings, an assessment of the soil s behaviour type is made. This assessment is based on tests carried out elsewhere and in some instances may not correctly identify the soil s behaviour. The CPT s were sunk to depths ranging from.m to.m, with the majority being in excess of m depth (mostly between.m and.m). In all cases, the probes were terminated at refusal on or in a relatively strong layer that is assumed to be dense sands or gravels.. Soil Profile The investigation identified the following: ---Ground Level--- Interbedded layers of Sand, silty Sand, sandy Silt, clayey Silt and Clay with some fine grained sensitive strata --- Base varies from. to.m --- Dense Gravels (CPT refusal and strata in which T&T s boreholes were terminated) ---Maximum extent of investigation--- Groundwater was encountered in most of the exploratory holes at depths of about.m to.m. This is above the anticipated levels in the GNS report. Drawings /GA to E show simplified geological cross sections through the site based on the results of the CPT s. These clearly indicate the interbedded, discontinuous nature of the sediments. Drawing /GB also clearly shows the deeper channel of sediments that are assumed to be part of the Manawatu series. //

23 Liquefaction Potential Assessment EDC File:. Summary of Soil Properties Soil Type* Description Depth Range to top of Stratum (m) Range of Thickness (m) Typical Range of CPT End Bearing (MPa) Topsoil Topsoil fine sandy silt/silty sand. Alluvium Interbedded silty sands,.. to - sandy silts, silty clay, clays, including some sensitive fine grained soils Gravels Dense granular material... - (proven) Soil Type* - based on the descriptions included in the T&T Factual Report to allow easy comparison //

24 Liquefaction Potential Assessment EDC File:. LIQUEFACTION AND LATERAL SPREADING POTENTIAL. General Liquefaction case history indicates the majority of liquefaction occurs in young (Holocene or less than, years old) sediments. Liquefaction is also possible in older sediments (Late Pleistocene Era >,yo) but less liquefaction in sediments of this type has been observed. There is potential for liquefaction (or cyclic softening, if cohesive) to occur following an earthquake event of sufficient magnitude under the following preconditions: If the soils are fine-grained and non-cohesive (silts and sands), fine grained cohesive silts and clays with low plasticity or soils with a loose sand-gravel matrix; If the soils are saturated (below the water table); The soils at the site consist of shallow (~. to m thick) Holocene subsoil, silt, clay and sand overlying deep gravels of the (Pleistocene Era, >,yo) with some minor sand/clay constituents. The Mangaone Stream is located some m to the east of the site. This stream has significant stopbanks on either side to protect the surrounding land against flooding. Part C of the MBIE guidance document for TC soils in Canterbury suggests (in section.) that the risk of lateral spreading of TC land would only be minor to moderate beyond m from a free face unless there is any evidence on or in the vicinity of the site of such movement. In this case, as there has been no recent earthquake event there is no sign of any movement. There are a number of drainage channels surrounding and crossing the site. These range from swales alongside roads to channels up to approx..m deep. The channels crossing the site will be culverted and therefore the distance to drainage channels around the perimeter of the site has been used. Given the location of the drainage chanels that surround the site (mostly within the road curtilages), these chanels are unlikely to be culverted. It is proposed to construct drainage lakes/ponds as part of the stormwater control for the development. Although these will be on the site, mitigation should be undertaken to ensure that lateral spreading as a result of the free-face formed by these lakes/ponds will not occur. Analysis of predicted liquefaction related ground settlement and lateral spreading was undertaken on the results of the CPT testing, using the Geologismiki Software CLiq v... The methods of calculation are in accordance with those currently recommended by the MBIE.. Analysis Parameters We have undertaken the liquefaction analyses of the EDC CPT s using the Idriss & Boulanger (I&B) () calculation method. The fines correction for cyclic liquefaction has been determined according to Robertson & Wride (), I&B claylike behaviour () has been assumed and settlement has been calculated according to the Zhang et al. method (). //

25 Liquefaction Potential Assessment EDC File: The following parameters have been used for the analysis: A groundwater Level of.m bgl has been assumed for analysis, based on the CPT information, rather than the GNS report estimate. Peak Ground Acceleration (PGA)for residential structures at deep soil sites (Class D): ULS a h =.g SLS a h =.g NB Serviceability limit state design assesses the deformations that occur under working conditions, while Ultimate Limit State assesses the situation that would lead to the collapse of a structure. The magnitude of the design earthquake is.. The above PGA s have been determined from Section of NZGS Module and have also been used in previous analysis by T&T (vi). It should be noted that any future seismic design of buildings must take into consideration the distance of the proposed building from the Wellington Fault (approximately km east from the proposed development site). It is likely that the inclusion of a near-fault factor (refer NZS. Section ) in seismic design will result in the building design having to incorporate features to mitigate a greater horizontal acceleration than that of the PGA s above. From visiting the proposed development site, it is essentially flat. Lateral spreading analysis was undertaken assuming the most likely method of lateral spreading during liquefaction would be due to ground movement towards drainage channels (free faces) surrounding the site (as mention in section. above). In order for the Cliq software to estimate the amount of lateral ground displacement, the following information was required: The distance of the CPT location from the nearest free-face (L) The height of the nearest free-face (H) Note: L/H was required to be greater than but less than (.<L/H<) The height of the drainage ditches surrounding the site was assumed to be.m. Following the above limit for L/H, the maximum distance to a free face that is likely to cause significant lateral displacement was m. This is a generalised rule based on Canterbury conditions. Whilst there are significant similarities between the soils in both areas, we consider that this m limit for significant lateral displacement should be viewed with caution. The majority of the EDC CPT s drilled at the site were greater than a distance of m from the nearest perimeter drainage ditch, with the exception of the following EDC CPT s: EDC CPT s Distance from Drainage ditches EDC m EDC m EDC m EDC m EDC m The remainder of the EDC CPT s were assumed (conservatively) to be a distance of m away from the nearest drainage ditch for the purpose of the analysis. It is therefore probable that for the most part the following estimates of lateral spreading are over estimates (apart from those related to the CPT s mentioned in the table above). Some calculation methodologies include the ground below the base of the free face (in this case the free face is the side of the drainage ditches), when calculating the lateral spreading. We consider that such calculation is too conservative and //

26 Liquefaction Potential Assessment EDC File: therefore lateral displacement has been ignored for depths below H (x height of the drainage ditch). The methodology used in our calculations only allows for movement over the height of the drainage ditch and for upto x the height of the drainage ditch. Summary Parameter Serviceability Limit State (SLS) Ultimate Limit State (ULS) Return Period Factor R.. Magnitude.. PGA.g.g. Liquefaction Analysis Results The results sheets for each of the analyses are included in Appendix B. The following graphs summarise the results for the SLS and ULS scenarios. Based on the potential settlements calculated due to liquefaction, the site can be split into three areas. Area A (refer Drawing /G) includes most of the northern section of the site, including CPT s to and has settlements that are essentially TC. Area B includes a mixture of TC and TC potential settlements including CPT s to. Area C is the main part of the panhandle and is mainly TC, with CPT s to. The following land deformation vertical settlement limits are applicable for the Technical Zones determined by MBIE (v) : SLS The results of the CPT tests indicate: ULS TC -mm -mm TC -mm -mm TC >mm >mm Area Total Estimated Settlement SLS Case (mm) Area A CPT s to From to, with the majority < Area B CPT s to From to, with the majority < Area C CPT s to From to, with the majority < Total Estimated Settlement ULS Case (mm) From to, with the majority < From to, with the majority <. From to, with the majority < It should be noted that the majority of CPT tests undertaken by EDC were terminated before a depth of m bgl (due to refusal on gravels assumption based on T&T borehole / CPT information). The EDC CPT s that reached a depth of >m bgl were EDC to EDC. These were located in the pan-handle section of the site (refer to EDC Drawing G) where the Manawatu series soils were encountered. The remainder of the EDC CPT s undertaken at the site varied in depth from.m to.m bgl. //

27 Liquefaction Potential Assessment EDC File: OVERALL ULS VERTICAL SETTLEMENT BASED ON EDC CPT TESTING Area C Area B Area A Settlement Calculation Method - Zhang et al. () TC Type Foundations EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC VERTICAL SETTLEMENT (MM) TC DBH Enhanced Foundation Solution's TC Type Foundations //

28 Liquefaction Potential Assessment EDC File: OVERALL SLS VERTICAL SETTLEMENT BASED ON EDC CPT TESTING Area C Area B Area A Settlement Calculation Method - Zhang et al. () EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC VERTICAL SETTLEMENT (MM) TC Type Foundations TC DBH Enhanced Foundation Solution's TC Type Foundations //

29 Liquefaction Potential Assessment EDC File:. Lateral Spreading Analysis Results The following table has been developed by MBIE and is included in the guidance (v) for foundation design in Christchurch. The table contains the global lateral movement categories for TC properties under ULS loading conditions. Minor to Moderate Major Severe to mm Global Lateral Movement to mm Global Lateral Movement >mm Global Lateral Movement The estimated lateral displacements for each EDC CPT location are included within Appendix B. The graph on the following page summarises the results for the ULS scenario. The overall lateral displacements graph indicates the majority of CPT locations are expected to undergo global lateral movement within the Minor to Moderate category with the exception of the CPT EDC which has estimated global lateral movement in the Major category. //

30 Liquefaction Potential Assessment EDC File: OVERALL ULS LATERAL DISPLACEMENTS BASED ON EDC CPT TESTING Area C Area B Area A Major Global Lateral Movement Minor to Moderate Global Lateral Movement Lateral Spreading Calculation Method - Zhang et al. () EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC EDC LATERAL SETTLEMENT (MM) //

31 Liquefaction Potential Assessment EDC File:. Liquefaction Analysis of T&T Borehole/SPT data T&T boreholes BH, BH, BH, BH and BH are within (or nearby to) the PCW development site. These boreholes were also analysed by EDC to determine whether or not there were any significant liquefiable layers below the depth of refusal of the EDC CPT s. The boreholes were drilled to the depths shown in the following table. The EDC CPT s in the vicinity of the T&T boreholes is also included in the table. Borehole Borehole Depth bgl (m) EDC CPT s near to BH Termination depth of EDC CPT bgl (m) BH.. BH.. BH.. BH.. BH.. Note: Refer to /G for location plan of T&T boreholes We have undertaken the liquefaction settlement analyses of the T&T Borehole data using Liquefy Pro Version.. The following parameters have been used for the analysis: PGA for residential structures at deep soil sites (as above in section.): Magnitude of design earthquake =.; Soil susceptibility to liquefaction = Based on SPT N-values; Settlement analysis = Ishihara/Yoshimine; Fines correction (liquefaction) = Stark/Olsen. The SPT N-value correction factors used in analysis were as follows: Hammer energy ratio (C n ) =. Borehole diameter factor (C b ) =. Sampling method factor (C s ) =.. T&T Borehole Liquefaction Analysis Results The results sheets for each of the analyses are included in Appendix C. The following tables compare the extent of liquefiable material in the T&T boreholes with the depth of EDC CPT s undertaken nearby: Borehole Name Extent of liquefiable material bgl in borehole (m) Extent of liquefiable material bgl in nearby CPT (m) BH.. (EDC CPT ) BH.. (EDC CPT ) BH.. (EDC CPT ) BH.. (EDC CPT ) BH.. (EDC CPT ) The above table suggests that there are no significant liquefiable layers below the depths at which the EDC CPT s met refusal, with the exception of BH. The T&T BH was terminated after extending up to m into very dense gravelly sand/sandy gravel. As the boreholes were terminated in very dense material, we do not consider liquefaction to be likely beyond the depth of termination at BH (.m bgl). //

32 Liquefaction Potential Assessment EDC File: The following tables summarise the results of liquefaction settlement analysis under ULS and SLS conditions, respectively: Borehole Estimated Settlement under ULS conditions (mm) Depth of Borehole bgl (m) Estimated Settlement under ULS of Nearby EDC CPTs* (mm) Depth of CPT bgl (m) BH... (EDC CPT ). BH... (EDC CPT ). BH... (EDC CPT ). BH... (EDC CPT ). BH... (EDC CPT ). Borehole Estimated Settlement under SLS conditions (mm) Depth of Borehole bgl (m) Estimated Settlement under SLS of Nearby EDC CPTs* (mm) Depth of CPT bgl (m) BH... (EDC CPT ). BH... (EDC CPT ). BH... (EDC CPT ). BH... (EDC CPT ). BH... (EDC CPT ). * EDC CPT settlements estimated from Cliq analysis (see section.). //

33 Liquefaction Potential Assessment EDC File:. CRUSTAL THICKNESS In the event of a significant earthquake, if there is a sufficiently thick or stiff crust, it will help to span over any areas of settlement induced in the loose granular or soft cohesive alluvial soils following liquefaction. This spanning over the localised areas of settlement will help to minimise any potential damage to foundations and infrastructure constructed on the crust. The following graph shows the results of Ishihara s research. By using the thickness of the potentially liquefiable soils found at a location, (i.e. the y-axis), and reading across to intercept the line on the graph, it is possible to estimate the thickness of crust that may be required. Relationship between Crust Thickness and Ground Damage Thickness of liquified sand layer, (m) Ground damage Thickness of Surface Layer, (m) No ground damage Based on Ishihara.-.g H Using the potential liquefiable layer thickness identified from the CPT results, the above graph indicates a requirement for a crustal thickness (i.e. that zone not likely to liquefy even if groundwater is at about m bgl), that ranges from about.m to >m. Drawing /G shows the crustal thicknesses across the site (with the crustal thickness estimated from the depth of material below ground level to the top of the zone that has potential to liquefy). Crustal thicknesses range from m to >m. //

34 Liquefaction Potential Assessment EDC File: The following graph shows the individual CPT results for the site: Pioneer City West Crustal Thickness vs Potentially Liquefiable thickness Thickness of Liqueifiable Layer "T" Ground Damage No Ground Damage.-.g H Area A CPT's Area B CPT's Area C CPT's Thickness of Crust (m) By plotting the thickness of the liquefiable materials (based on a groundwater depth of m) from the locations of the exploratory holes and the thickness of the crust on the graph (i.e. that material that the analyses indicate is not likely to liquefy), those positions that plot to the left of the line indicate the positions where ground damage is likely in a M. event. If the positions plot to the right of the line, then no ground damage is likely (i.e. there is adequate crustal thickness). As most of the results lie to the left of the line some mitigation is needed and the MBIE approach of splitting the land into Technical Categories (TC s), is warranted. As noted above, the TC s have been designed for land that is likely to suffer some damage should an earthquake of sufficient magnitude occur. The mitigation measures will depend on the amount of damage the land is likely to suffer. In some cases, (TC ), the mitigation is more related to the type of foundations, while in TC zone some land remediation is needed. //

35 Liquefaction Potential Assessment EDC File:. GROUND REMEDIATION Given the results of the investigations, it is evident that Area A would require minimal if any ground remediation dependant on what development is being proposed. For Area B, some ground remediation will probably be required that will develop a stabilised or suitably thickened crust. In Area C a deeper band of soils will need to be treated. The MBIE has developed guidance on the types of foundations suitable for different land Technical Categories for Christchurch. As the soils at the PCW site are similar to those of Canterbury, we consider that the MBIE recommendations are appropriate for developing this site. Given the nature of the soils as identified so far, three options for developing the site are available: Option : Apply the MBIE Guidance recommendations for foundations specific to whichever Technical Category the lot lies within; or Option : Remediate the ground to improve the Technical Category so as to reduce the level of design necessary for specific foundations for any particular building; Option : A mixture of the two options noted above. The MBIE Guidance Document (v) includes recommendations for options for foundations in TC areas. The MBIE document states: In TC, new foundations will need to be capable of resisting tension effects from nominal lateral spreading. They must also be capable of accommodating settlement of the ground beneath the house. [Foundation] Options to. are considered suitable for TC. The deep pile option will require deep geotechnical investigation and specific design. Options to are designed for single or double storey dwellings with lightweight construction and lightweight roofing. Heavyweight cladding on both storeys and heavy roofing would require specific design. Options to are variations on a stiffened raft theme: Option : Enhanced foundation Slab, reinforced slab above mm of compacted wellgraded gravel fill on a suitable geogrid; Option : Enhanced foundation slab, slab on grade (ground must have a minimum geotechnical ultimate bearing capacity of kpa); Option : Enhanced foundation slab, generic beam and slab foundation, with mm deep edge beam (ground must have a minimum geotechnical ultimate bearing capacity of kpa); Option Enhanced foundation slab, waffle-slab constructed on existing ground (ground must have a minimum geotechnical ultimate bearing capacity of kpa). The MBIE document (v) also includes guidance for the design of new foundations on TC land. This included recommendations for remediation of the ground to provide adequate support for residential foundations. Ground remediation options include: Densification of either crust layer and/or the deeper liquefiable soils. This includes methods such as compaction, excavation and replacement/recompaction, vibroflotation, preloading, dynamic compaction (DC), and rapid impact compaction crust strengthening/stabilisation by permeation grouting, stabilisation mixing or replacement //

36 Liquefaction Potential Assessment EDC File: deep strengthening using deep soil-cement mix piles, jet grouting, stone columns, close spaced timber or pre-cast piles containment by ground reinforcement or curtain walls drainage using stone columns or earthquake drains Some of these methods were trialled in Canterbury. The MBIE Document indicates: The methods used in the Department s trial were representative of the densification, crust strengthening and containment groups of methods. All but the containment method provided significant improvement to the ground performance. The containment method is expected to require further development before any specific guidance can be provided. The following methods are currently included in these guidelines: Type Densified raft (i.e. re-compacted soil or replacement fill; also dynamic compaction or rapid impact compaction). Type Stabilised crust (i.e. cement mixed soils, either by excavate and replace or in situ mixing). Type Deep soil mixing (i.e. soil mixed or jet grouted columns). Type Stone columns Type Low mobility grout columns As the PCW site is currently open farmland, the remediation option is made easier in comparison the Christchurch where remediation has to fit around existing structures and infrastructure. At this site, it will be possible to undertake bulk earthworks to densify the soils using larger plant to more efficiently improve the soils to reduce the chance of liquefaction occurring.. Area A If the Canterbury guidelines are applied, then the northern part of the site (Area A) would be considered TC. Suitable foundation types (subject to specific design) include shallow foundations and piles or waffle-slabs that could be re-levelled were an earthquake event to occur that led to differential settlement and tilting.. Area B The area at the junction of the panhandle and the main area (Area B) would be classified as TC based on potential settlement, but we recommend assessing it as TC unless mitigation is undertaken. In this area, mitigation would be undertaken by way of densification of the top m of subsoil. If densification is undertaken, TC foundation types are recommended. Suitable TC foundation types include: Shallow pile/foundation wall systems (NZS: compliant); Stiffened raft slab; A deep piled raft.. Area C The thinner strip (or pan handle ) of the site that protrudes southwards towards the Pioneer Highway i.e. Area C would mostly be classified as TC based on potential settlements. The current advice for remediation in Christchurch of TC land (i.e. land where Moderate land deformations possible in a future small to medium sized //