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Cost Effective Settlement Monitoring

With the cost of human intervention rising, what is the value of focusing your team on the work that matters?

Whatever the objective for your instrumentation and monitoring program, whether quality assurance, risk management, construction control or data driven design, the intention (as with any aspect of project management) is a maximised return on investment. This post takes a look at where the bulk of that investment cost lies, some of the risks that threaten to undermine your investment, and how complementary activities are not only supplemental, but often necessary to a successful program. The intended value of the instrumentation has been established – that’s why it was designed and specified on your project in the first place – so how do we maximise that value and minimise the risk?

It’s not an uncommon experience for I&M managers to feel like the Instrumentation & Monitoring budget is being pried from a begrudging Project Manager’s hands. It’s understandable. Besides the all too frequent absence of any budget for instrumentation (much less a sufficient one) not all construction PMs are overly familiar with I&M and for those that are, past negative experiences can taint their perspective for a long time. True or not, it can often be seen as a cost that doesn’t directly correlate to construction progress, and rarely aligns with KPIs. It’s always nice to prove them wrong. When the monitoring information serves to progress production, validate design, or even (not infrequently) save lives, the value for money is crystal clear. However, in a situation where the data is incomplete, late, or incorrect, not only is significant time and money wasted, but the missed opportunity of a reliable data set can also have dire consequences for the project.

The goal of improved quality, timeliness and reliability of data has driven the move toward automation, and while this approach is becoming more of a standard than an exception, there are still some instances where designers opt for manual monitoring. Their reasoning is still founded on the objective of a maximised return on investment. Below are some of the rationales I’ve come across, and some thoughts on why these reasons may be losing their validity in the context of true cost, and ultimate intended value.

Cost

When looking at the installed materials alone it may seem the cost of installing in-place measurement devices is significant compared to a manual approach. The napkin analysis seems easy:

(L * N) + RO – A

Where L is cost of labour per reading, N the number of readings over the duration of the project, RO is the cost of readout equipment and A is the cost of automation.

A diligent engineer will dig deeper and add on the cost of calibration of the manual equipment, perhaps replacement equipment to use during calibration or back up equipment for contingency in case of damage (not uncommon when inexperienced workers are handed the task of caring for it – more on that later). What is harder to quantify is the impact of unforeseen changes. Project delays? N goes up. Extended consolidation period? N goes up. Unexpected readings demand increased monitoring frequency? N goes up – and potentially more readout equipment is needed to allow further monitoring teams to be mobilised.

The true lifetime cost of an instrument goes well beyond the equipment and monitoring itself: Designing, planning and approving each installation; establishing access; undertaking drilling and installation work; slowing or moving production to accommodate installation; ongoing monitoring and maintenance costs, data processing and management; and finally reviewing and evaluating the reports. Is the money saved on a low cost system worth the risk of underperformance?

In-place instruments, while not flawless, are factory calibrated, produced in quality managed, repeatable processes and tested ad nauseam. Once installed, the only variable experienced should be the site conditions that they are monitoring. Manual instruments introduce variability with every survey. Operator error could render the data unusable or worse – lead to misinformed decisions. The cost of the former may be as low as sending someone out to repeat the reading or lead to delays to construction. The cost of the latter is almost limitless.

Adaptability

Geotechnical instrumentation is, by its very nature placed in dynamic environments, whether that is the epicentre of construction activity or the precarious edge of an unpredictable slope. The ability to adapt to conditions is essential both during installation and where applicable, during construction.

Sadly, geotechnical investigations tend to be on the leaner side of optimum. The information available when designing an I&M program can often be reliant on the results of an investigation some hundred metres away (or worse). The most accurate information we get about the site we are installing our instruments on becomes available right there during installation as the drillers retrieve the cuttings or core. It is only then that we can establish the optimum configuration of our instruments -the configuration that will deliver the most value. Locating the stratigraphic boundaries lets us know where to socket our inclinometers and which zones are of particular interest, where to install our piezometers and the depths to target with our extensometers. In many cases, pre-built automated systems can be difficult to adapt to accommodate the variation between expectations, and what is observed on site.

When earthworks begin and embankments are being raised or excavation is starting, instruments then need to adapt to their changing environment. Manual systems simply require a well-managed and documented change in height of their access tube or extension rods. Until recently, even if an automated system could be extended or shortened, the process has been laborious and disruptive at best. Adding or removing sections of tube or rod is a far more attractive option than pulling lengths of cable and dozens of expensive sensors out, adapting the installation, reinstalling, re-baselining, only to go back out and do it again in a few weeks’ time, right in the thick of construction activity.

What we are seeing now, is that as the industry adopts new technologies, instrumentation is becoming more and more adaptable. The rise of battery powered wireless data loggers means aggregating all of the instruments via cable to a single point through kilometres of trenches is no longer necessary. Digital sensors mean instruments can be added or removed from a system without the need for more cable, more ducting and more data logger channels. In-Place instruments, even within boreholes, can be extended or adapted on-site as required with minimum impact on the existing instrumentation, or on the construction process.

Physical Inspection

No one will question the importance of an engineer’s boots on the ground, at the coalface, observing site conditions and monitoring visual cues that might indicate something that is not represented in the instrument data. While qualitative, a brief visual inspection can provide more information than hours of data mining ever could and to the end that a manual monitoring schedule prompts engineers or operators out onto the field, this is a plus. However, you need to know what to look for. The inspection needs to be carried out by someone with the appropriate training and experience. The value of the monitoring visit is proportional to the degree of expertise held by the person being sent to site. Sadly, that task can often be allocated based on cost rather than capacity. Manual monitoring of a construction site is a task that is often underestimated. The work is slow, repetitive and time consuming and can often be overlooked as “simple”; work you might otherwise give to a graduate or (seen all too often) a labourer. But when left to inexperienced or untrained personnel, the difference between good quality data and poor quality data quickly becomes apparent, and the qualitative aspect of the survey is lost entirely. 

An automated monitoring system allows knowledgeable, experienced engineers to prioritise visual assessment when conducting an inspection. The time not spent conducting manual surveys can be spent reviewing the data and supplementing it with their qualified contextual analysis, allowing them to issue tangible, actionable reports. This is the basis of a value added, risk managed monitoring system.

Summary

A thorough cost-benefit analysis demands that we account for all costs, direct or indirect, and that the risks and opportunities presented by each of our options are considered. The lifetime cost of a geotechnical instrument extends far beyond the materials installed. It extends back to the planning and enabling works, disruption to production, the installation, ongoing monitoring, maintenance, reporting, analysis and so on and so forth. Selecting the right equipment to automate your monitoring may seem like an additional expense, but when considered in its broader cost context, and accounting for reduction of risk, increased quality and frequency of reporting, along with the recovered opportunity cost of your engineer’s time, the balance quickly shifts in favour of in-place measurement equipment.

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