Article Scope
In this article, we discuss the problem of insufficient control for proper construction surveying. This problem usually happens at the start of construction. I base this article on a typical heavy civil infrastructure project. In this type of project, civil engineers prepare design plans after design surveys but before construction.
The Phone Call (Identifying The Problem)
If you perform surveys to support engineering design, you’ve gotten the call. It comes several months after you have completed the design surveys for a project. The call goes like this:
Contractor: “I’m from Get Er Done Construction. We are getting ready to break ground on the project. I need all of your survey control so I can set up my machine control.”
Surveyor: “I’m sorry. I wasn’t under contract to provide construction surveying services for this project. Please provide the name and contact information for the surveyor doing the construction layout. I’ll provide them with the primary survey control used for the design surveys.”
Contractor: “We bought a Trimble R12 GPS. We do our own construction surveying now. Please send the survey control information as soon as possible. You are delaying the start of construction.”
Alternatively, if you are the surveyor providing construction surveys, you may have a phone call like this at the start of construction:
Surveyor: “I’m working for Build It Right Construction Company. I’m the licensed surveyor in charge of construction layout. I’m calling to request the survey control information for the project.”
Civil Engineer: “We have control survey information on the plans.”
Surveyor: “I’ve carefully reviewed your plans. There is only information for a single benchmark on the plans. I searched for the benchmark, but the city destroyed it in a sidewalk repair last year. I need more control information to properly layout the design.”
Civil Engineer: “Every other surveyor we’ve worked with can layout the design with a single benchmark. What is your problem?”
These two (2) example phone calls are opposite sides of the same problem: There isn’t enough survey control information on the approved civil engineering plans (or other contract documents) to perform the construction surveying needed to build a project correctly.
Why Do We Get The Phone Call (The Causes Of The Problem)
What are the root causes of this problem? I’ve identified four (4) causes based on my experience as a licensed land surveyor:
The First Cause: Survey control monuments of poor quality are set during design surveys. These monuments become disturbed or destroyed before construction begins. (I recently worked on an infrastructure project spanning over 25 miles. The company performing the main design surveys set short magnetic nails in the dirt. We found very few of the nails less than a year later.)
The Second Cause: The surveyor performing design surveys uses sloppy methods to establish control coordinates. (For example, I recently retraced a survey of 1200 acres on a renewable energy project. The previous survey company set a handful of points using RTK GNSS with radial ties from a single base station.
The Third Cause: The design surveyor doesn’t properly document the control survey – or doesn’t document it at all. (In contrast, I believe the project surveyor should provide a survey control report on every design survey. This report includes information on the project coordinate reference system. It also includes information on the control survey methods.) Often, civil engineering plans include only the description of a single benchmark. This benchmark often has an elevation value with no metadata. That doesn’t cut it for proper documentation of survey control.
The Fourth Cause: The survey control set for design surveys isn’t suitable for construction surveying. The design survey control may not be:
- Dense enough for construction surveying.
- In the suitable locations for construction surveying.
- The right type of monument for construction surveying.
- Have imprecise coordinates for construction surveying.
This fourth cause is often not the fault of the surveyor performing the design surveys. (See the sidebar “How Technology Is Making The Problem Worse)
When Should Survey Control For Construction Be Set?
There are three (3) basic options for when survey control for construction can be set.
During Design Surveys: Survey control for construction can be set during design surveys. There are a couple of advantages to this approach:
- Survey control for construction is set by the same surveyor performing the design surveys.
- The construction control should be well connected to the primary survey control for the design surveys.
- The design surveyor can document the survey control on the civil engineering plans. There are two disadvantages of this approach.
- The extra cost incurred during design surveys.
- The risk that survey control will be destroyed or disturbed before construction.
Between Design and Construction: Survey control for construction can be set after design surveys are complete but before construction. I most often see this when a good construction manager or savvy contractor. They use this approach to get in front of potential construction surveying problems hopefully, before the heavy equipment arrives.
Immediately Before and During Construction: Survey control can be set immediately before and during construction. This approach has a couple of advantages:
- The lower cost of design surveys. (In this approach, the project owner is moving the construction surveying control cost to the project’s construction phase.)
- The close connection in time between the placement of the control monuments and actual construction. This closeness reduces the risk that control monuments will be disturbed or destroyed before construction. There are a couple of disadvantages to this approach.
- This option hides the cost of survey control for construction from the project owner. (This results in the civil engineer, design surveyor, and contractor all point fingers at each other.)
- It often leads to the wrong person setting the survey control for construction.
None of the above options are always “right” or “always” wrong. The best approach will change depending on the project, design team members, and construction team members. But each option has advantages and disadvantages. There is a set of tradeoffs. Significant problems occur when the project owner, design team, and construction team don’t discuss these tradeoffs. They should agree on the timing of survey control for construction in advance.
Who Should Set Survey Control For Construction?
As mentioned above, the choice of timing for establishing survey control for construction can lead to a problem: the wrong person doing the control survey. As you move closer to the start of construction, the risk of an unqualified person setting the survey control increases.
Who shouldn’t set the survey control for construction? Here is a short list:
- The civil engineer. (They usually aren’t qualified – but often think they are. It’s just math, right?)
- The construction manager. (They aren’t qualified either.)
- The contractor. (They aren’t qualified – but I think they are after your survey equipment vendor sells them the stuff.)
- The point-and-shoot construction surveyor. (This is especially true on large or complicated infrastructure projects.)
Who should set the survey control for construction? There are two (2) options:
- The licensed surveyor is responsible for the design surveys.
- The licensed surveyor is responsible for construction surveys.
Because technology is removing the second option from most construction teams, the first option may be the only option. That means establishing survey control for construction must likely be in the design surveyor’s scope of services.
Conclusion
Project teams can avoid phone calls like the two (2) examples used to introduce this article. This requires up-front conversations about who, when, and how survey control for construction will be established. Everyone (including the project owner) loses when the project team avoids this conversation. All project team members should agree on what survey control will be provided, what it costs, and who pays for it. Good land surveyors can help enable these conversations.
In a future article, I’d like to discuss how civil engineers’ responsibilities for survey control support construction.
Sidebar: How Technology Is Making The Problem Worse
Major improvements in measurement technology is making this problem worse. How?
First, technology enables the non-surveyor to perform more layout of design improvements during construction. Although not inherently evil, this layout by non-surveyors can cause major problems on the construction site. Many of the modern measurement technologies are black boxes. The non-surveyors using them for layout don’t understand how they work. They also don’t understand basic surveying principles.
Second, technology now allows a surveyor to complete design surveys with much less control than was needed even two (2) decades ago. This means there are fewer control monuments from the design surveys available during construction surveying. For example, I recently completed supplemental surveys on a project site for a major infrastructure project. On this site the only primary control point set by the initial surveyor was an active GNSS station several miles away.
Third, design teams are now trying to integrate disparate geospatial datasets. Many of these datasets are publicly available. Most lack good metadata and information on their coordinate reference system. Project teams can use reasonable survey control can to tie these disparate datasets together during design and then during construction.
Sidebar: What Is Construction Surveying?
In this article, I use the term “construction surveying” to refer to all types of surveying supporting heavy infrastructure construction. This includes construction layout (staking), monitoring surveys, and as-builts.