If you’re planning a large commercial or industrial fence installation in Phoenix or throughout Arizona, you probably need a geotechnical investigation.
Let’s take a closer look at what a geotechnical investigation is, how it relates to fences, and why it could save you money. Even though this type of testing adds time and expense up front, it can help you avoid costly surprises during construction.
What Is a Geotechnical Investigation?
A geotechnical investigation of a fence line is a process where a specialist drills a series of cores and removes the contents of those cores for analysis.
During that analysis, the position of the hole is noted, and the composition of the soil layers are recorded. The number of cores taken varies by site, but there are usually several cores taken across different areas of the property to get an accurate snapshot of subsurface conditions.
Geotechnical testing also typically indicates whether there is a high water table or any other potential subterranean challenges that can affect fence design and installation. This is especially important in regions like Phoenix, where you can encounter rocky soil or caliche that requires specialized digging methods.
The deeper your fence posts will be installed, the greater the chance of running into soil-related problems. If your fence specification calls for deep footings, such as for a tall industrial fence, this is a key reason to consider geotechnical testing.
Do You Need a Geotechnical Investigation for Your Fence?
If you’re installing a residential fence, or have been previously filled, graded, and compacted, you may not need a geotechnical investigation. These sites often have documented soil conditions, making major unknowns less likely.
If you’re planning to install a fence on a large commercial or industrial site (especially an undeveloped or remote site) there’s no telling what lies beneath the surface. Soil variability can be significant, and latent site conditions like rock layers or groundwater can derail a fence project. In these scenarios, it’s smart to get geotechnical testing results to guide the design and installation.
Contractors Exclude Unknown Adverse Subterranean Conditions
Even if you create a highly detailed specification and scope of work, contractors quoting the project can’t accurately plan for unknown subsurface conditions. Therefore, they won’t include the cost of difficult digging or special excavation methods in a typical quote.
There are several things that could be considered difficult digging, including:
- Very sandy soil that collapses back into holes during excavation
- High water tables that fill holes with groundwater
- Extremely hard ground or rock layers that require heavy-duty equipment
Potential remedies include shoring, formwork, using screw piles, or core drilling into rock layers. Each solution carries its own cost, and since those costs aren’t covered in basic quotes, you could face expensive change orders if your contractor encounters difficult conditions without warning.
Getting Rates for Difficult Excavations
If you decide not to do a geotechnical investigation but still want some cost predictability, you can request unit rates from your fence contractors for various issues related to difficult excavation. Common items might include:
- Additional charges for digging in hard soil or rock
- A rate for shoring or formwork per footing
- Hourly rates for pumps to remove groundwater
Although you won’t know the exact number of these additional services until work begins, getting these rates ahead of time helps you understand the potential financial impact before you move forward.
More Information Is Always Better
When it comes to getting quotes from fence contractors, providing as much information as possible about potential site conditions is the best way to avoid costly surprises down the road. This is why a full geotechnical investigation (when warranted) is often well worth the investment.
Also, be sure to look carefully at any terms and qualifications in bids and quotes. If one price is substantially lower than the others, there’s a chance that difficult digging conditions or other challenges were excluded. Unfortunately, they can resurface as costly change orders later.
Western Fence Co. has years of experience working on commercial and industrial fence projects in the Phoenix Metro area. Our team understands local soil conditions and project requirements. If you need guidance on complex fence installations, learn more about our Phoenix commercial fence services.