Abstract
Bramley Drive, Omokoroa in 1979, the Ruahihi Canal collapse in 1981, and numerous landslides in May 2005; recently the Bramley Drive scarp was reactivated in 2011. These
failures are associated with materials loosely classified as the Pahoia Tephras - a mixture of rhyolitic pyroclastic deposits of approximately 1 Ma.
The common link with extreme rainfall events suggests a pore water pressure control on the initiation of these failures. Recent research on the structure of the soils shows a dominance of
halloysite clay minerals packed loosely in arrangements with high porosity (51 – 77 %), but with almost entirely micropores. This leads us to conclude that the permeability is very low, and
the materials remain continuously wet. The formation of halloysite is encouraged by a wet environment with no episodes of drying, supporting this assumption.
A high-resolution CPT trace at Bramley Drive indicates induced pore water pressures rising steadily to a peak at approximately 25 m depth; this depth coincides with the base of the
landslide scarp. We infer that elevated pore water pressures develop within this single, thick aquifer, triggering failure through reduced effective stresses. The inactive halloysite clay
mineral results in low plasticity indices (13 – 44 %) and hence high liquidity indices (1.2 – 2.4) due to the saturated pore space; remoulding following failure is sudden and dramatic and results in large debris runout distances.
| Original language | English |
|---|---|
| Title of host publication | Proceedings of the 19th NZGS Geotechnical Symposium |
| Subtitle of host publication | Hanging by a thread? Lifelines, infrastructure and natural disasters |
| Editors | C. Y. Chin |
| Place of Publication | Wellington |
| Publisher | Institution of Professional Engineers New Zealand |
| Pages | 537-544 |
| Number of pages | 8 |
| Volume | 2 |
| Publication status | Published - 2013 |
| Externally published | Yes |
| Event | 19th New Zealand Geotechnical Society Symposium: Hanging by a thread? Lifelines, infrastructure and natural disasters - Millennium Hotel, Queenstown, New Zealand Duration: 21 Nov 2013 → 22 Nov 2013 Conference number: 19 |
Publication series
| Name | |
|---|---|
| Publisher | Institution of Professional Engineers New Zealand |
| Number | 1 |
| Volume | 38 |
| ISSN (Print) | 0111-9532 |
Other
| Other | 19th New Zealand Geotechnical Society Symposium |
|---|---|
| Abbreviated title | 19th NZGS Symposium |
| Country | New Zealand |
| City | Queenstown |
| Period | 21/11/13 → 22/11/13 |
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Landslides in sensitive soils, Tauranga, New Zealand. / Moon, V. G.; Cunningham, M. J.; Wyatt, J.; Lowe, D. J.; Mörz, T.; Jorat, M. E.
Proceedings of the 19th NZGS Geotechnical Symposium: Hanging by a thread? Lifelines, infrastructure and natural disasters. ed. / C. Y. Chin. Vol. 2 Wellington : Institution of Professional Engineers New Zealand, 2013. p. 537-544.Research output: Chapter in Book/Report/Conference proceeding › Conference contribution
TY - GEN
T1 - Landslides in sensitive soils, Tauranga, New Zealand
AU - Moon, V. G.
AU - Cunningham, M. J.
AU - Wyatt, J.
AU - Lowe, D. J.
AU - Mörz, T.
AU - Jorat, M. E.
PY - 2013
Y1 - 2013
N2 - In the Tauranga region sensitive soil failures commonly occur after heavy rainfall events, causing considerable infrastructure damage. Several notable landslides include a large failure atBramley Drive, Omokoroa in 1979, the Ruahihi Canal collapse in 1981, and numerous landslides in May 2005; recently the Bramley Drive scarp was reactivated in 2011. Thesefailures are associated with materials loosely classified as the Pahoia Tephras - a mixture of rhyolitic pyroclastic deposits of approximately 1 Ma.The common link with extreme rainfall events suggests a pore water pressure control on the initiation of these failures. Recent research on the structure of the soils shows a dominance ofhalloysite clay minerals packed loosely in arrangements with high porosity (51 – 77 %), but with almost entirely micropores. This leads us to conclude that the permeability is very low, andthe materials remain continuously wet. The formation of halloysite is encouraged by a wet environment with no episodes of drying, supporting this assumption.A high-resolution CPT trace at Bramley Drive indicates induced pore water pressures rising steadily to a peak at approximately 25 m depth; this depth coincides with the base of thelandslide scarp. We infer that elevated pore water pressures develop within this single, thick aquifer, triggering failure through reduced effective stresses. The inactive halloysite claymineral results in low plasticity indices (13 – 44 %) and hence high liquidity indices (1.2 – 2.4) due to the saturated pore space; remoulding following failure is sudden and dramatic and results in large debris runout distances.
AB - In the Tauranga region sensitive soil failures commonly occur after heavy rainfall events, causing considerable infrastructure damage. Several notable landslides include a large failure atBramley Drive, Omokoroa in 1979, the Ruahihi Canal collapse in 1981, and numerous landslides in May 2005; recently the Bramley Drive scarp was reactivated in 2011. Thesefailures are associated with materials loosely classified as the Pahoia Tephras - a mixture of rhyolitic pyroclastic deposits of approximately 1 Ma.The common link with extreme rainfall events suggests a pore water pressure control on the initiation of these failures. Recent research on the structure of the soils shows a dominance ofhalloysite clay minerals packed loosely in arrangements with high porosity (51 – 77 %), but with almost entirely micropores. This leads us to conclude that the permeability is very low, andthe materials remain continuously wet. The formation of halloysite is encouraged by a wet environment with no episodes of drying, supporting this assumption.A high-resolution CPT trace at Bramley Drive indicates induced pore water pressures rising steadily to a peak at approximately 25 m depth; this depth coincides with the base of thelandslide scarp. We infer that elevated pore water pressures develop within this single, thick aquifer, triggering failure through reduced effective stresses. The inactive halloysite claymineral results in low plasticity indices (13 – 44 %) and hence high liquidity indices (1.2 – 2.4) due to the saturated pore space; remoulding following failure is sudden and dramatic and results in large debris runout distances.
M3 - Conference contribution
VL - 2
SP - 537
EP - 544
BT - Proceedings of the 19th NZGS Geotechnical Symposium
A2 - Chin, C. Y.
PB - Institution of Professional Engineers New Zealand
CY - Wellington
ER -