Monitoring the landslide at Bramley Drive, Tauranga, NZ

V. G. Moon, W. P. de Lange, C. P. Garae, T. Mörz, M. E. Jorat, S. Kreiter

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

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.
Original languageEnglish
Title of host publicationProceedings of the 12th ANZ Conference on Geomechanics
PublisherNew Zealand Geotechnical Society (NZGS)
Pages737-744
Number of pages8
Volume2
Publication statusPublished - 25 Feb 2015
Externally publishedYes
Event12th Australia New Zealand Conference on Geomechanics: The Changing Face of the Earth – Geomechanics & Human Influence - Wellington, New Zealand
Duration: 22 Feb 201525 Feb 2015
Conference number: 12

Conference

Conference12th Australia New Zealand Conference on Geomechanics
Abbreviated titleANZ 2015
CountryNew Zealand
CityWellington
Period22/02/1525/02/15

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    Moon, V. G., de Lange, W. P., Garae, C. P., Mörz, T., Jorat, M. E., & Kreiter, S. (2015). Monitoring the landslide at Bramley Drive, Tauranga, NZ. In Proceedings of the 12th ANZ Conference on Geomechanics (Vol. 2, pp. 737-744). New Zealand Geotechnical Society (NZGS). https://fl-nzgs-media.s3.amazonaws.com/uploads/2016/06/2015-ANZ-12-Wellington-Vol-2.pdf