Landslides in sensitive soils, Tauranga, New Zealand.

In the Tauranga region sensitive soil failures commonly occur after heavy rainfall events, causing considerable infrastructure damage. Several notable landslides include a large failure at 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

A new attraction-detachment model for explaining flow sliding in clay-rich tephras

Altered pyroclastic (tephra) deposits are highly susceptible to landsliding, leading to fatalities and property damage every year. Halloysite, a low-activity clay mineral, is commonly associated with landslide-prone layers within altered tephra successions, especially in deposits with high sensitivity, which describes the post-failure strength loss. However, the precise role of halloysite in the development of sensitivity, and thus in sudden and unpredictable landsliding, is unknown. Here we show that an abundance of mushroom cap–shaped (MCS) spheroidal halloysite governs the development of sensitivity, and hence proneness to landsliding, in altered rhyolitic tephras, North Island, New Zealand. We found that a highly sensitive layer, which was involved in a flow slide, has a remarkably high content of aggregated MCS spheroids with substantial openings on one side. We suggest that short-range electrostatic and van der Waals interactions enabled the MCS spheroids to form interconnected aggregates by attraction between the edges of numerous paired silanol and aluminol sheets that are exposed in the openings and the convex silanol faces on the exterior surfaces of adjacent MCS spheroids. If these weak attractions are overcome during slope failure, multiple, weakly attracted MCS spheroids can be separated from one another, and the prevailing repulsion between exterior MCS surfaces results in a low remolded shear strength, a high sensitivity, and a high propensity for flow sliding. The evidence indicates that the attraction-detachment model explains the high sensitivity and contributes to an improved understanding of the mechanisms of flow sliding in sensitive, altered tephras rich in spheroidal halloysite

Rainfall threshold for initiating effective stress decrease and failure in weathered tephra slopes

Rainfall is one of the most important triggers of slope failure. Weathered pyroclastic (tephra) deposits are especially vulnerable to slope failure because they commonly form slopes of high porosity and high clay content. Empirically derived thresholds for the triggering of landslides are commonly based on rainfall conditions and have been widely applied in volcanic soils. However, so far only few researchers utilized pore water pressure in the slope as additional variable for the threshold calibration. Here, we derived a new rainfall threshold for initiating the decrease in effective stress in the slope by analyzing a long-term record of rainfall and piezometer data from a slide-prone coastal area in northern New Zealand that consists of clayey, halloysitic tephra deposits. The level of effective stress decrease increased with rainfall intensity and duration. We observed highest effective stress decrease of up to 36% during rainfall events that triggered landslides in our study area. The effective stress threshold exhibits a satisfactory predictive capability. The probability of correctly predicting a decrease in effective stress is 53%. The effective stress threshold contributes towards the implementation of the decrease in effective stress into rainfall thresholds for the occurrence of landslides

Sub-surface stratigraphy of Stella Passage, Tauranga Harbour.

Port of Tauranga Ltd supported two initiatives designed to develop a greater understanding of the distribution of sediments below Stella Passage (Figure 1), particularly relating to areas that may require future dredging: (1) As part of INTERCOAST PhD research by Ehsan Jorat, Port of Tauranga provided logistic support for a series of high-resolution Cone Penetration Test (CPT) soundings along a transect on the western margin of Stella Passage in February – March 2012; (2) Port of Tauranga provided part-funding of a Summer Scholarship student (Amy Christophers) over the 2012/13 summer, particularly to look at pre-existing cores and core descriptions. In addition, the University of Waikato undertook a series of sub-bottom seismic profile measurements in Stella Passage as part of a Summer Scholarship funded by the University over the 2012/13 summer. This report summarises the current state of these investigations

Monitoring the landslide at Bramley Drive, Tauranga, NZ

Omokoroa Peninsula, Tauranga Harbour, is prone to landslides in sensitive pyroclastic soils, especially in coastal bluffs. The largest is the landslide at Bramley Drive that first occurred in 1979, and was reactivated in 2011 and 2012. Since 2012 the landslide has been monitored with laser scans, vibro-and static-CPT, pore water logging at 3 depths, and a borehole inclinometer. Laser scan results track degradation of the scarp and allow development of a preliminary magnitude-frequency curve for failure events on the scarp. To date the borehole inclinometer has shown no obvious shear surface development. However, deformations in phase with the solid earth tides are evident in the cumulative displacement plots. Layers of weak soils separated by sharp boundaries are believed to exaggerate the deformations of the solid earth tides to the extent that they are measurable with a simple inclinometer. Residual deformation after subtraction of the earth tide effects indicate some movement over winter of 2014 associated with sensitive soils at or near the failure surface. The depth of this movement corresponds with a zone of high induced pore water pressures under vibratory CPTu. Pore water pressures indicate two discrete aquifers: an upper aquifer in tephra layers high in the upper part of the sequence that responds to atmospheric pressures; and a second aquifer in the underlying ignimbrites. Pressures in the bottom aquifer are lower than in the overlying aquifer in summer and higher in winter. Large spikes in pore water pressure have been observed during winter of 2014; these coincide with the time of deformation noted in the inclinometer traces

Geotechnical Offshore Seabed Tool (GOST): CPTu measurements and operations in New Zealand.

The Geotechnical Offshore Seabed Tool (GOST) was used in three field campaigns in on-and offshore areas in Tauranga, Bay of Plenty, New Zealand. Offshore measurements were performed along the main shipping channel in the Tauranga Harbor and onshore measurements were conducted at the locations of two landslides at Pyes Pa and Omokoroa. From each of these sites a sample static CPTu profile is described and reviewed. Additionally, a vibratory CPTu from the Pyes Pa landslide is presented. The CPTu results were used for subsurface sediments investigations at the tested locations

A magneto-optical method for viscosimetric measurements

International audienc

Impédancemètre automatique 100 Ω−1\mathsf{\Omega{-}1} TΩ\mathsf{\Omega}

This work presents a wholly automated high impedance system working in the frequency range 1 mHz–10 kHz and conceived to measure complex impedances ($R_{\rm p}$//$C_{\rm p}$) UP to $10^{12}\Omega$. Therefore we have built, surrounding a gain phase analyser, a high impedance programmable electrometer working on shunt mode. This apparatus using high resistances and low leakage capacitors, resorts to the high impedance electronics, the components are selected by the way of very high insulating Reed switches drived by a VXI bus.Dans ce travail nous présentons un système haute impédance totalement automatique fonctionnant dans la gamme de fréquence 1 mHz–10 kHz et conçu pour la mesure des impédances complexes ($R_{\rm p}$//$C_{\rm p}$) jusqu'à 10$^{12}\Omega$. Pour cela nous avons construit, autour d'un analyseur vectoriel, un électromètre haute impédance programmable fonctionnant en mode shunt. Ce dispositif utilisant des résistances de hautes valeurs et des condensateurs à faibles fuites, fait appel à l'électronique haute impédance ; les composants sont sélectionnés au moyen de relais Reed de très haute isolation commandés par un bus VXI

Dielectric study of primary amines from room temperature down to −180 °C and from 10 kHz up to 35 GHz

The aim of this paper is to present the NH2 dielectric behaviour in the primary amines for the importance it bears in the interaction of aminoacids and proteins and their influence in the electric conduction processes. For that, the dielectric properties of 1-propylamine, 1-butylamine and 1-pentylamine have been studied. Measurements were performed between room temperature and −180 °C in the low frequency range and micro-waves measurements were done between −40 °C and 25 °C. The isofrequency recordings of dispersion ε′ and absorption ε′′, for these three primary amines, show clearly the relaxations and the effect of the aliphatic chain length

Investigation of Erythema, Radiation Dose, and Radiation-Induced Apoptosis in the Peripheral Blood Lymphocytes of Patients Treated with Radiofrequency Catheter Ablation

Introduction: The long-term use of fluoroscopy in cardiac interventional procedures increases the patient dose and causes severe skin reactions, which lead to growing concern. The aim of the present study was to evaluate the risk and the effect of X-ray irradiation on apoptosis in the peripheral blood lymphocytes of patients treated with ablation in electrophysiological studies. Material and Methods: A total of 30 patients who underwent ablation therapy participated in this study. The absorbed dose in the given area was measured by a thermos luminescent dosimeter (TLD). The duration of dose delivery, absorbed dose by the apparatus, and dose area product (DAP) factor were measured for each patient. The skin changes were observed within the 1st day to 5th week after the operation. Blood sampling was conducted (before and 24 h after the treatment), and then, flow cytometry was performed to investigate the apoptotic changes in the blood lymphocytes. Results: The statistical analysis showed that there was a significant difference in the apoptosis of patient blood lymphocytes before irradiation and following that (P<0.05). There was a correlation between the amount of DAP and TLD dose (P<0.001). Furthermore, a correlation was observed between the total apoptosis and fluoroscopic time. The patient radiation dose in the ablation test was not in the threshold level required to create skin erythema. Conclusion: The results of the present study revealed that the use of long-time fluoroscopy in electrophysiological studies may cause a significant increase of apoptosis in the peripheral blood lymphocyte of patients treated using this procedure. © 202