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Soil testing in wet weather

April 29, 2021
Industry Insights

It’s not just your weekend BBQ or the kids’ footy that becomes doubtful when the “big wet” sets in. Lengthy, intense rain events can delay or derail any building project, even at the very first step — soil testing.

There’s a whole host of solid reasons why soil testing can go slow in a wet week. We’ve compiled them in this special report, and also explained our processes and communication strategies to keep you informed about your project, and what to expect when nature dictates a different course for our best laid plans.

The importance of soil testing

As we noted in a previous post, the nature of the land you build on is perhaps the biggest variable of a building project and is critical to get right before starting construction. Soil testing determines the site classification, which influences several aspects of the design, including the foundation.

A lot of contracts are also subject to soil testing, since the outcome can affect the design of the foundations and/or structure, in turn affecting the contract pricing.

If you have a contract that is subject to soil testing and the soil test is delayed due to wet weather, you may need to request an extension on the contract. 

Why would rain delay my soil tests?

A “bit of rain” might not be a big deal for experienced engineers with a common-sense approach to their work, but sustained wet weather often means the best course is to postpone soil testing. The reasons for this come under three main categories:

1. Quality issues

A.   Lack of site access — Vehicle with drill rig (totalling 2.5 tonnes) can’t get onto boggy sites.

B.   Limitations of Manual Push Tubes (PTs) or Hand Augers (HAs) — Can be used by field technicians as an alternative, but they can’t go as deep as the drill rig, nor cut through subsurface stones. They’re not as precise as the rig and sometimes samples can get stuck in the PTs, or are too slushy to be of any use.

C.   Compromised test results — In abnormal moisture conditions, there is risk that some test results are compromised.

This is the bottom of a manual push tube. A tool sometimes used to collect soil samples when we can’t access a site with drill rigs. But when soil testing in wet weather, these tools can become clogged with the soil sample, rendering them ineffective.

2. Costs and Compliance

  1. Councils and Developers — Both restrict vehicles with drill rigs to drive onto wet boggy sites, under threat of heavy fines (up to $10,000) for soil tracked onto roads.
  2. Extra design and building costs  – Compromised test results (see above) may lead to unnecessary extra design and build costs. STA generally considers these abnormal conditions at time of design.
  3. Retrieval of bogged vehicles, damage to property — costly damage to vehicles and/or property from accidents in slippery conditions, eg hitting a tree. 
  4. Damage to turf lawns and grass verges —Soft ground can lead to destruction of lawns, leading to compensation costs. 
  5. Carefully working in the wet takes more time —Extra time is generally needed due to site conditions and cleaning of equipment.
  6. Deceptive ground conditions — It can be difficult to assess ground conditions, even after inspection, potentially leading to a bogged vehicle.

3. Human Safety risks

  1. Increased risk of equipment accidents — Drilling on slopes can be very dangerous even when mildly wet. The vehicle could slide down a slippery hill or embankment and end up in a fence or gully. 
  2. Slip hazard increased —more potential for injury due to wet conditions.
  3. Lightning hazard – the drill rigs cannot be used when there is a chance of lighting strikes

How long will my project be delayed?

Every site is different (even next to each other), every project is different and every rain event is different. So this is difficult to answer, but the main factors are:

  1. Developer or council decision when to allow technicians back on site.
  2. Onsite inspections — field technicians will be checking client sites for access and suitability to drill. Some days ground conditions on site can be surprisingly dry, but other times the opposite is true. It’s important to note that a site may remain boggy and inaccessible for days after the rain stops.

How does STA keep customers updated?

At STA, we’re committed to continuously improving our processes and client communication. We make it easy for you to get answers from the right people by providing direct access to our technical teams, enabling faster response. Our systems utilise email notifications to alert clients to updates as they happen.

In wet weather, we do the following to keep you updated and ensure we can get back on site as soon as possible:

  • We revisit sites to check conditions ourselves where possible (and send clients a Site Delay update, with photo).
  • We keep tabs on weather and site conditions so we can respond rapidly once conditions are suitable.
  • We are in daily communication with developers for changes to site access.
  • For customers subscribed to the STA Daily Progress Report, they receive an updated status of their job whenever new information is received (such as Site Delay update, info from Developers, etc)

Get in touch

While rain events may cause delays beyond our immediate control, you can rest assured we’ll be ready to go at the first opportunity. To discuss wet weather or any other issues, simply call us on (07) 3071 7444 or use our online contact form.

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