Case Study
Our customer required installation of Vibrating Wire Piezometers (VWPs) to monitor groundwater pore pressure to determine slope stability.
The Problem
Historically, instrument installation and grouting had been carried out by drill crews using equipment that was more suited to drilling and pumping of water with little or no quality assurance or control.
Batches were inaccurate and there was no base knowledge of the properties of bentonite and ratios of cement to water. This produced unreliable results as the surrounding ground conditions were not replicated, and there were instances where the grout mix had not set correctly in the VWP installation holes.
Monitoring data was unreliable, and confidence in the monitoring of slope stability and water pressure in pit walls were poor.
The Solution
We saw an opportunity to improve the quality of the data through controlled installations using purpose built equipment and relevant professional skills. We researched the required outcomes to derive a solution for our customer.
This involved research and discussion with manufacturers of the instruments, consulting hydrogeologists, and equipment suppliers.
Through detailed research, we were able to identify reliable and efficient equipment to deliver measured quantities of consumables, and suitable mixing and pumping equipment to effectively hydrate the bentonite. Continuous pumping was a requirement of our customer in order to provide surety that holes were efficiently and fully grouted. Dedicated installation equipment was designed for the accurate depth placement of instruments.
The Outcome
A successful outcome was designed and built to meet our customer’s needs.
A colloidal grout mixer, coupled to accurate weigh bins – for the cement and bentonite ratios – were custom made to fit to a single work platform. This truck, supported by a light truck carrying the installation reels and water, were put to work.
Processes were determined to ensure installation and grouting was successfully delivered and recorded to ensure specifications and designs were met.
Close monitoring of the instruments throughout the complete grouting process was carried out by our in-house hydrogeologist.
This involves monitoring the instruments for accurate readings (to factory calibration) prior to installation, at water submersion, at grout submersion ,and on completion. Grout viscosity readings were taken using a marsh funnel for each batch prior to pumping down the hole.
These processes, alongside weigh bin checks and comprehensive reporting, allowed surety in the completions of the work and confidence that the data outcomes were accurate and useable.
