This was a large slip that occurred along SH4 that was part of an older, larger, landslip. This unfortunately reactivated due to an ongoing increase in pore water pressure within the landslip mass and on the basal shear surface.
Pressures rose to a point where the material in the slip became buoyant and began to slide along a shallow preferential shear plane up to 40m below ground level.
A temporary road had been implemented and Cirro were asked to assist with the Instrumentation and Monitoring requirements.
Delivering an instrumentation solution on this particular site meant that we had to overcome a number of challenges:
This photo shows the gateway that we deployed on the hilltop.
The client wanted all instrument data, both new and existing, to be hosted in one online location so everyone would have access to the information they needed.
A custom site overview was implemented, so that users could see the latest drone imagery of the site, with the location of each instrument showing it’s icon in green, orange or red to indicate the alarm status.
The users had set up multiple alarms to be notified of any exceedances which was key for successful management of the TARP.
The graph also illustrates the alarm and alert thresholds that had been established (the horizontal lines at the top of the graph). When these are triggered, SMS and emails are issued to subscribed users.
The Geotechnical Lead on this project would log in to check the data coming in every day, keeping an eye on the groundwater and pumping activity. As the water pressures continued to decline, the factor of safety gradually increased.
Nick Peters – Senior Engineering Geologist:
“I still log into check the data coming in every other day, keeping an eye on the groundwater and pumping activity. As the water pressures continue to decline, the factor of safety gradually increases. There’s a masters thesis written all over this project, in particular around the relationship between groundwater level response to rainfall, the effectiveness of the pumping wells installed, or looking more closely at the hydrogeological and geological models."