Pitoone Land Instability Monitoring

This project is now complete.

We have engaged AECOM New Zealand Ltd to implement routine monitoring of geotechnical instrumentation installed at the Pito-one landslide, Kuaotunu, for the landslide ground deformation surveillance programme.

Latest Newsletter - March 2010

This is the eleventh newsletter to you advising of progress on the ground movement monitoring programme.

1. The inclinometers, piezometers and survey marks were read again in November 2009 as part of the scheduled monitoring programme. This was the final monitoring step recommended in the independent technical expert’s report (2004).

2. The monitoring results are presented in a report called “Pitoone Landslide – November 2009 Monitoring Results”. Copies of the report have been given to us and the report may be viewed in our related information box.

3. The report does not re-assess the risk to properties.

4. To date five of the seven inclinometers have recorded ground movements. The tube in Inclinometer I1, which is located in a private driveway off Bluff Road on the eastern side of Cuvier Crescent, sheared off between 2006 and 2009 and thus it cannot be read. This is common for inclinometers that detect large amounts of ground shearing. The inclinometer does not need to be replaced.

5. In the last 36-month period of monitoring, the movements measured by the four inclinometers ranged between 8 and 30mm. The direction and location of the movements are consistent with previous movements. Three of those inclinometers are located on the eastern side of Cuvier Crescent, and the fourth is near the intersection of Seavill Park Road and Bluff Road (in the area known as the amphitheatre).

6. The four inclinometers have recorded movements of between 11 and 43mm over the 79-month period since monitoring began.

7. Inclinometer I9 and the piezometers in DH9 (located in a property off Gray Ave) are no longer required and were removed by the landowner.

8. The movement recorded by the other inclinometer is within its error range. 

9.The general direction and magnitude of movements measured by the survey marks are consistent with the results of previous survey monitoring in 2004.

10. Comparison of the ground surface movements at several inclinometer tubes measured both by inclinometer and survey indicates that the survey measurements are giving comparable, although less accurate, results. This provides overall confidence in the survey results.

11. Groundwater levels measured from piezometers in the area in November 2009 are generally found to be consistent with previous results, coming within the range of seasonal variation established by earlier records.

12. It is recommended that further monitoring should not be scheduled at present given that the latest monitoring has shown ground movements consistent with previous monitoring, and that the overall rates of movement are very low.

13. However, the monitoring network should be retained in the event that monitoring is required in the future. The need for further monitoring might be prompted, for example, by damage to structures, signs of excessive ground movement, damage to underground services, excessive deformation of the road surface or significant coastal erosion at the end of Cuvier Crescent.

14. It is recommended that Council periodically (say at five yearly intervals) review the need for further monitoring and/or reassessment of the landslide.

15. Several monitoring instruments require maintenance in order to be protected for further monitoring.