title: Sensitive rhyolitic pyroclastic deposits in the Tauranga region:  mineralogy, geomechanics and microstructure of peak and remoulded states

authors: Cunningham, Michael J.

abstract: Soil sensitivity has previously been recognised as a significant contributor to soil failures both internationally and within New Zealand, particularly in the Tauranga region. Sensitive soils are characterised by initial high peak shear strength, yet very low remoulded shear strength. While international sensitive soils have been well characterised, the nature of sensitivity in rhyolitic deposits in New Zealand is poorly understood. This study characterises both sensitive and non-sensitive rhyolitic tephra derived soil samples from the Tauranga region in order to identify the fundamental differences in the materials between states of peak and remoulded strength.

Field and laboratory investigations were undertaken to analyse sensitivity. Field investigations included shear vane testing for the quantification of sensitivity, and stratigraphic profiling. Laboratory testing comprised geotechnical testing (particularly shear strength and Atterberg limits), petrographic observations through scanning electron microscopy (SEM) and X-ray diffraction (XRD), and measurement of the rheology of remoulded sensitive materials. 

Five localities were used in this study. Three sites were considered sensitive (Omokoroa, Te Puna and Pahoia Peninsula), while the remaining two (Rangataua Bay and Tauriko) were considered non-sensitive on the basis of the Milne et al. (Milne, J.D.G.; Clayden, B.; Singleton, P.L.; Wilson, A.D. 1995: Soil description handbook. Manaaki Whenua Press, Lincoln, Canterbury) sensitivity test. Field observations showed sensitive material is of tephric origin, likely associated with the Te Puna Ignimbrite (~ 0.93 Ma). The deposits considered generally classify as sensitive to extra sensitive (7-15) with no samples being identified as quick. The non-sensitive material has characteristically different field behaviour where the material does not release moisture, or flow, upon remoulding. The non-sensitive material is associated with the Te Ranga Ignimbrite (~ 0.27 Ma).

Moisture contents are typically high for the sensitive materials, always exceeding their respective liquid limits (liquidity indices > 1), while the opposite is true for the non-sensitive samples. Porosity is also high for the sensitive materials (> 61 %), whereas non-sensitive materials return lower porosity values of < 60 %. Characterising the peak strength state of the sensitive materials, triaxial testing show consistent effective cohesion and friction angles ranging between 8–16 kPa and 28–41 ⁰, respectively. Viscometric flow characteristics indicate that pH adjustment has a critical impact on remoulded sensitive material: typically as the pH becomes more alkaline, clay particle association is reduced and the soil weakens further, while with increased acidity there is a small increase in yield stress.

XRD indicates that all materials are dominated by halloysite. The wet to saturated rhyolitic materials promote a silica-rich environment that is slow draining, leading to favourable conditions for halloysite formation over other clay minerals. Most commonly, halloysite was observed in sphere, tube and to a lesser extent, plate morphologies. SEM, XRD and EDX analyses revealed previously undocumented, large (~ 60 µm–~ 1.5 mm) halloysite books in selected sensitive materials. The books are hypothesised to have formed from the incorporation of iron into the halloysite unit cell to form plate morphologies, followed by Ostwald ripening under conditions of low iron in the soil solution, and coalescence during a relatively dry period to form the large books.

The soil microstructure of the sensitive materials in comparison with the non-sensitive soils appears to provide the critical distinction in determining the variation between the peak to remoulded strength characteristics for the sensitive material. The sensitive material is comprised of similar sized small spheres and short, stubby tubular halloysite morphologies. These pack inefficiently, producing a low density of packing. Such an arrangement produces many small micropores which facilitate the development of high moisture contents, producing liquidity indices > 1. The primary microstructure is matrix-skeletal for sensitive samples. The non-sensitive samples are comprised of large spheres and long, thin tubular halloysite morphologies. These particles pack much more efficiently, where the tubes fill the voids produced between large spherical formations. The result is a much tighter structural arrangement in the clay fraction, with reduced potential for high moisture contents to build up, leading to liquidity indices < 1. The non-sensitive material typically displays a matrix microstructure. 

Upon remoulding, the structure of the sensitive material was broken down and appeared continuous. Connectors were typically destroyed, while tubes, plates and books were broken into smaller remnants. The similar sized spherical and tubular particles appeared to be easily mobilised following disturbance where they would fail in a fluidised manner from the high moisture held within the sample. The non-sensitive material, however, indicated very little change upon remoulding. The clay particle interactions were still arranged in a tight structure, which did not breakdown sufficiently to become entrained within the available moisture.

The sensitivity of rhyolitic tephra, therefore, is primarily attributed to the relative size and packing of the halloysite particle morphologies. The low density of packing produced an open structure, allowing for high moisture contents to develop, which following remoulding, leads to irreversible structural breakdown and release of stored water, promoting flow characteristics of the soil and thus high sensitivity.

text: Sensitive rhyolitic pyroclastic deposits in the Tauranga region:  mineralogy, geomechanics and microstructure of peak and remoulded states Soil sensitivity has previously been recognised as a significant contributor to soil failures both internationally and within New Zealand, particularly in the Tauranga region. Sensitive soils are characterised by initial high peak shear strength, yet very low remoulded shear strength. While international sensitive soils have been well characterised, the nature of sensitivity in rhyolitic deposits in New Zealand is poorly understood. This study characterises both sensitive and non-sensitive rhyolitic tephra derived soil samples from the Tauranga region in order to identify the fundamental differences in the materials between states of peak and remoulded strength.

Field and laboratory investigations were undertaken to analyse sensitivity. Field investigations included shear vane testing for the quantification of sensitivity, and stratigraphic profiling. Laboratory testing comprised geotechnical testing (particularly shear strength and Atterberg limits), petrographic observations through scanning electron microscopy (SEM) and X-ray diffraction (XRD), and measurement of the rheology of remoulded sensitive materials. 

Five localities were used in this study. Three sites were considered sensitive (Omokoroa, Te Puna and Pahoia Peninsula), while the remaining two (Rangataua Bay and Tauriko) were considered non-sensitive on the basis of the Milne et al. (Milne, J.D.G.; Clayden, B.; Singleton, P.L.; Wilson, A.D. 1995: Soil description handbook. Manaaki Whenua Press, Lincoln, Canterbury) sensitivity test. Field observations showed sensitive material is of tephric origin, likely associated with the Te Puna Ignimbrite (~ 0.93 Ma). The deposits considered generally classify as sensitive to extra sensitive (7-15) with no samples being identified as quick. The non-sensitive material has characteristically different field behaviour where the material does not release moisture, or flow, upon remoulding. The non-sensitive material is associated with the Te Ranga Ignimbrite (~ 0.27 Ma).

Moisture contents are typically high for the sensitive materials, always exceeding their respective liquid limits (liquidity indices > 1), while the opposite is true for the non-sensitive samples. Porosity is also high for the sensitive materials (> 61 %), whereas non-sensitive materials return lower porosity values of < 60 %. Characterising the peak strength state of the sensitive materials, triaxial testing show consistent effective cohesion and friction angles ranging between 8–16 kPa and 28–41 ⁰, respectively. Viscometric flow characteristics indicate that pH adjustment has a critical impact on remoulded sensitive material: typically as the pH becomes more alkaline, clay particle association is reduced and the soil weakens further, while with increased acidity there is a small increase in yield stress.

XRD indicates that all materials are dominated by halloysite. The wet to saturated rhyolitic materials promote a silica-rich environment that is slow draining, leading to favourable conditions for halloysite formation over other clay minerals. Most commonly, halloysite was observed in sphere, tube and to a lesser extent, plate morphologies. SEM, XRD and EDX analyses revealed previously undocumented, large (~ 60 µm–~ 1.5 mm) halloysite books in selected sensitive materials. The books are hypothesised to have formed from the incorporation of iron into the halloysite unit cell to form plate morphologies, followed by Ostwald ripening under conditions of low iron in the soil solution, and coalescence during a relatively dry period to form the large books.

The soil microstructure of the sensitive materials in comparison with the non-sensitive soils appears to provide the critical distinction in determining the variation between the peak to remoulded strength characteristics for the sensitive material. The sensitive material is comprised of similar sized small spheres and short, stubby tubular halloysite morphologies. These pack inefficiently, producing a low density of packing. Such an arrangement produces many small micropores which facilitate the development of high moisture contents, producing liquidity indices > 1. The primary microstructure is matrix-skeletal for sensitive samples. The non-sensitive samples are comprised of large spheres and long, thin tubular halloysite morphologies. These particles pack much more efficiently, where the tubes fill the voids produced between large spherical formations. The result is a much tighter structural arrangement in the clay fraction, with reduced potential for high moisture contents to build up, leading to liquidity indices < 1. The non-sensitive material typically displays a matrix microstructure. 

Upon remoulding, the structure of the sensitive material was broken down and appeared continuous. Connectors were typically destroyed, while tubes, plates and books were broken into smaller remnants. The similar sized spherical and tubular particles appeared to be easily mobilised following disturbance where they would fail in a fluidised manner from the high moisture held within the sample. The non-sensitive material, however, indicated very little change upon remoulding. The clay particle interactions were still arranged in a tight structure, which did not breakdown sufficiently to become entrained within the available moisture.

The sensitivity of rhyolitic tephra, therefore, is primarily attributed to the relative size and packing of the halloysite particle morphologies. The low density of packing produced an open structure, allowing for high moisture contents to develop, which following remoulding, leads to irreversible structural breakdown and release of stored water, promoting flow characteristics of the soil and thus high sensitivity.

year: 2012

title: Exploring connections of children and counselling within education contexts

authors: Flanagan, Paul G.

abstract: This presentation will report on two studies related to children in Aotearoa New Zealand. First, a study that examined the effects for children of the language about sexuality and childhood used by their parents, teachers and counsellors. Second, a current study that scopes the practice of counselling in primary schools. These two studies invite analysis of the intersection of childhood, counselling and education. The presentation will examine ideas of counselling as a location for supporting children’s identity development within primary schools. Such support will be viewed through critical lenses of political, historical and cultural contexts of childhood in Aotearoa New Zealand.

text: Exploring connections of children and counselling within education contexts This presentation will report on two studies related to children in Aotearoa New Zealand. First, a study that examined the effects for children of the language about sexuality and childhood used by their parents, teachers and counsellors. Second, a current study that scopes the practice of counselling in primary schools. These two studies invite analysis of the intersection of childhood, counselling and education. The presentation will examine ideas of counselling as a location for supporting children’s identity development within primary schools. Such support will be viewed through critical lenses of political, historical and cultural contexts of childhood in Aotearoa New Zealand.

year: 2021

title: Ngā niho tēte o Pekehāua: An indigenous articulation of governance

authors: Mahuika, Rangimarie

subjects: Indigenous Governance

abstract: This thesis originally set out to examine the structures and models available within New Zealand for a post-settlement tribal governance framework that would meet the Office of Treaty Settlements requirements while empowering the needs and aspirations of Ngāti Rangiwewehi. During the course of the study, as a result of the fast-tracking of our tribal settlement this emphasis changed. With Ngāti Rangiwewehi electing to utilise the government recommended templates for the post-settlement entity, the research shifted to consider the evolution of governance within the tribe, looking at the ways tribal governance had developed from traditional practices to our current governance frameworks. It was anticipated that gaining a deeper understanding of the factors that have shaped and influenced our governance would also give us the necessary insights to adapt the Crown model the tribe had adopted to ensure it was able to meet Ngāti Rangiwewehi’s future aspirations. This belief was grounded in an understanding that prior to the arrival of Pākehā to Aotearoa/New Zealand Ngāti Rangiwewehi, along with all other iwi Māori, had their own systems of Governance. Our governance frameworks, encapsulated within our tikanga and kawa, operated to produce a strong, vibrant, and self-determining society. Through colonisation, and its imposed Western frameworks for governance within Aotearoa New Zealand, traditional Māori frameworks for law and governance were undermined, deconstructed, or marginalised to make way for the civilizing discourses and structures of the Settler, as enforced by the British Crown. Although the dominant system of law and frameworks for governance may have changed, Ngāti Rangiwewehi and Māori desires for self-determination have not.
Against this background the central question of this study has itself evolved, initially contemplating to what extent Ngāti Rangiwewehi might be able to remain self-determining in and through their post-settlement governance arrangements. The overwhelming conclusion the study could not avoid was that any governance approach drawn from the settler-colonial Eurocentric system currently dominant in New Zealand would be incapable of supporting tribal aspirations for self-determination. What was equally evident was the continued determination that the tribe, collectively and individually, maintained to mediate the imposed governance frameworks that interfere in our ability to fully exercise our tino rangatiratanga, or in our iwi-specific context, our tino Rangiwewehitanga. This observation led to the final iteration of the thesis question which asks what frameworks for governance would best empower Ngāti Rangiwewehi to be self-determining in and beyond this post-settlement governance era? Throughout the research what became apparent was the potential to utilise our traditional frameworks for governance, described and encapsulated within this study as Rangiwewehitanga, a decolonial paradigm for tribal governance. Viewed in this way, Rangiwewehitanga expands our understanding of governance beyond the limited perspectives imposed through colonization and requires our people to recognise and return to the wisdom of our ancestral teachings to craft the most appropriate pathways forward.

text: Ngā niho tēte o Pekehāua: An indigenous articulation of governance This thesis originally set out to examine the structures and models available within New Zealand for a post-settlement tribal governance framework that would meet the Office of Treaty Settlements requirements while empowering the needs and aspirations of Ngāti Rangiwewehi. During the course of the study, as a result of the fast-tracking of our tribal settlement this emphasis changed. With Ngāti Rangiwewehi electing to utilise the government recommended templates for the post-settlement entity, the research shifted to consider the evolution of governance within the tribe, looking at the ways tribal governance had developed from traditional practices to our current governance frameworks. It was anticipated that gaining a deeper understanding of the factors that have shaped and influenced our governance would also give us the necessary insights to adapt the Crown model the tribe had adopted to ensure it was able to meet Ngāti Rangiwewehi’s future aspirations. This belief was grounded in an understanding that prior to the arrival of Pākehā to Aotearoa/New Zealand Ngāti Rangiwewehi, along with all other iwi Māori, had their own systems of Governance. Our governance frameworks, encapsulated within our tikanga and kawa, operated to produce a strong, vibrant, and self-determining society. Through colonisation, and its imposed Western frameworks for governance within Aotearoa New Zealand, traditional Māori frameworks for law and governance were undermined, deconstructed, or marginalised to make way for the civilizing discourses and structures of the Settler, as enforced by the British Crown. Although the dominant system of law and frameworks for governance may have changed, Ngāti Rangiwewehi and Māori desires for self-determination have not.
Against this background the central question of this study has itself evolved, initially contemplating to what extent Ngāti Rangiwewehi might be able to remain self-determining in and through their post-settlement governance arrangements. The overwhelming conclusion the study could not avoid was that any governance approach drawn from the settler-colonial Eurocentric system currently dominant in New Zealand would be incapable of supporting tribal aspirations for self-determination. What was equally evident was the continued determination that the tribe, collectively and individually, maintained to mediate the imposed governance frameworks that interfere in our ability to fully exercise our tino rangatiratanga, or in our iwi-specific context, our tino Rangiwewehitanga. This observation led to the final iteration of the thesis question which asks what frameworks for governance would best empower Ngāti Rangiwewehi to be self-determining in and beyond this post-settlement governance era? Throughout the research what became apparent was the potential to utilise our traditional frameworks for governance, described and encapsulated within this study as Rangiwewehitanga, a decolonial paradigm for tribal governance. Viewed in this way, Rangiwewehitanga expands our understanding of governance beyond the limited perspectives imposed through colonization and requires our people to recognise and return to the wisdom of our ancestral teachings to craft the most appropriate pathways forward.

year: 2019