Insights from Coffey principal engineering geologist, Nick Clendon

Nick Clendon is the principal engineering geologist and team leader for the Wellington office at Coffey, a Tetra Tech company, specialising in geotechnical engineering, environmental services and project management services.

Last year Mainmark collaborated with Nick on a large project to deliver a seismic strengthening solution for the Seaview Wastewater Treatment Plant. The facility treats up to 53 million litres of water daily and services approximately 146,000 residents and local industries in the Upper Hutt and Lower Hutt region of New Zealand’s North Island.

We caught up with Nick to find out more about his role at Coffey and the different types of projects he manages, which can vary from site investigations to designing building foundation systems and conducting technical peer reviews.

Can you share some details about the recent ground strengthening project you completed with Mainmark?

We first started working with Mainmark when they won a competitive tender for early contractor engagement at Wellington’s Seaview Wastewater Treatment Plant. The project was a seismic ground strengthening initiative by Wellington Water to ensure the essential infrastructure could withstand the impact of a large earthquake.

The limited site access was identified early on as a significant project risk and it was essential to have the contractor on board from the start; through the design and review process.  Mainmark was able to present clear evidence of how to achieve the design targets within the project’s limitations.

We successfully completed the ground improvement works using Terefirm®, Mainmark’s resin injection technique that can be applied under existing structures, helping to mitigate the risk of damage from liquefaction.

We have since consulted on several other projects using Mainmark’s Terefil® lightweight engineered fill product and will wait to see if the option is selected.

What was your experience working with Mainmark?  Is there anything different about how they operate?

In short, our experience with Mainmark has been excellent. Like all complex jobs, there are always challenges but Mainmark didn’t shy away from addressing the issues and provided additional support to the wider team when required. Mike Baker and Theo Hnat were particularly good, providing project management and technical input respectively.  They notably have a very good understanding of the product/solutions they provide and are clear on any limitations.

The Seaview project is a good example of Mainmark’s expertise as the job was extensive and technically challenging due to the limited access of the existing pump station and milliscreen buildings.  The site’s continued operation, tight limits on acceptable displacements (uplift) during injection and the design remediation target of meeting a serviceability limit state condition for a 1:500 year earthquake event were additional challenges that needed to be addressed.

Is there anything you can share about the work you do for the Earthquake Commission and government authorities in response to earthquake remediation?

Like all things in earthquake design, the goal posts are shifting and our understanding is increasing on a daily basis. What we need in the industry is a range of options or tools to help design, repair and remediate structures. This will help address the issues and support both local and regional authorities to minimise the risk in the event of future earthquakes.

Having innovative solutions from companies like Mainmark allows us to achieve these goals. Before the Terefirm resin injection technology was introduced, there were limited cost-effective, non-invasive solutions available.

Since the Christchurch earthquakes, have you noticed any changes in the way engineers (or other professionals) are doing things?

It’s hard to believe that it has been nearly ten years since the Christchurch events and there has been a lot more forward thinking.  As geotechs, we are now engaged earlier in the design process to help minimise geotechnical risks to projects. There is also a lot more consideration around ground improvement and mitigating damage.

While life safety is still the primary goal, we are also putting more consideration into managing society tolerance for building damage which can help minimise further social impacts that earthquake damage can have.

What do you think are some of the challenges facing your industry at the moment?

A lot has improved since the Christchurch events, notably the New Zealand Geotechnical Database, which is a great outcome, and the New Zealand Geotechnical Society Modules. However, as the earthquakes fade into memory, it’s easy to relax and assume we have unlimited time. As a professional industry, we need to keep working together to keep the momentum going. There is still a lot to do to make sure the next big earthquake has a smaller impact.

Are there any exciting developments or innovations that you’re watching closely at the moment?

With the likely increase in seismic hazard factors in the near future, at least for Wellington, there will likely be an increase in assessment using non-linear soil properties and time histories to get a better understanding of building/structure performance. This will also increase the importance of good site data and verification testing, such as pile testing, to ensure the models are well calibrated and aligned.


By Claire Hartley

Claire is a strategic senior marketing and communications professional who joined Mainmark in 2015. She has extensive experience gained in a range of organisations across the APAC region and the UK; from large multinationals and start-ups to industrial B2B, IT and online businesses.