Construction stakeout is crucial to ensure projects are built according to plan. After years on the construction side of land development, I have seen countless errors made during construction stakeout. Now that I’m leading a team of field surveyors, I make sure these mistakes don’t occur on our jobs.
So, what are the 3 areas where mistakes are most often made during construction stakeout?
Construction Stakeout for Retaining Walls
Retaining walls have a layback. Which is the horizontal distance between the bottom of the retaining wall and the top of the wall. The layback is often missed or miscalculated.
For example, you have a set of wall plans in front of you and you are typically provided with both the (T.W.) top of wall elevation and the (B.W.) bottom of wall elevation. Most surveyors, think that is enough to stake a wall. However, a pertinent piece of information that really comes into play with higher walls and/or walls in tight places or up against easements, is the degree of slope on the wall itself.
When I have my guys stake walls, we first calculate the layback and then offset the bottom of the wall. For example, we will say it’s a 10’ offset. The stake would read something along the lines of 10’ O/S (offset) bottom face of wall/11.05’ O/S top face of wall. So the 1.05’ for the layback of the wall is reflected in the stakeout.
Construction Stakeout for Inlets
Inlets are another area where you have to be careful. Generally, on the plan and profile sheet you are provided a top of grate elevation and most will use that elevation in the field along with the invert out for staking inlets. However, this can cause a problem when constructed. Think about a curb inlet or “C-top” inlet being constructed following these guidelines on a road with an 8% slope. You will quickly see this is a problem!
If a surveyor simply gives a cut or fill to top of grate elevation and the people who construct the inlets build the inlet flat, what happens later when the surveyor comes back to stake the curb? The curb is off on both the high and low side of the inlet. This is usually discovered when the curb is going in and results in the contractor having to building up inlets and/or cutting inlet boxes to compensate for the slope of the road. Oh, and generally a call to the surveyor saying you staked wrong!
Solutions to alleviate this from happening and general good practice are as follows:
- Communication. Contact the contractor or the pipe crew installing the inlets and see how they want it laid out, never assume!
- Field crews should always mark on the stake “high side” or “low side” of an inlet. If nothing else, it will get the attention of the pipe crew and illicit a question.
Generally as a rule of thumb, I suggest you stake to the low side of an inlet and then have the stakes marked something like C/F (cut or fill) and “top grate low side.”
Finally, remember it’s always easier to raise an inlet than lower one if it’s built too high!
When Sites are Raised or Lowered
First, surveyors do not like when sites are raised or lowered. However, it is happening more often in order to balance dirt on a site.
Mistakes can happen as a byproduct of the design topo being off or use of LIDAR, which is accurate to ½ a contour interval or +/- 1’. Do the math on a 30-acre site with 1’ of vertical error and all of a sudden you have a whole lot of excess or shortage of dirt!
What happens when the owner has no plans of exporting dirt offsite or importing dirt? This is where we see sites being raised and lowered. Sometimes it’s not practical for the engineer to reissue a new set of plans to reflect the adjustment and more importantly many trades already have the plans in hand and are working off of those values.
The easiest way to account for this on the survey side of things is to raise or lower the theoretical elevation of the site control. If the site is being lowered then you raise the site vertical control and if the site is being raised you lower the site vertical control. Think opposite!!!
In many of these situations, communication is key and can help avoid mistakes. Don’t assume. If you’re not sure, ask.
When you hire a land surveyor it’s important you have someone with the experience to ask the right questions because – a lot is at stake!