What Does a Geotechnical Engineer do?
Will there be basements, multiple stories, grade changes, or special features on your proposed building project? One thing you may not be aware of is the tremendous value geotechnical engineers can bring to a project by selecting optimum foundations and site preparation techniques. They collect soil samples at critical depths for laboratory testing and explore various locations on the site to identify the greatest efficiency and can also provide guidance and recommendations to confirm a building or structure is compatible with the underlying soil. Earth is not a very sympathetic negotiator, so it is prudent to select a site improvement or foundation method that will be reliable at the lowest practical cost.
Realize Cost Savings
There is an art to supporting heavy loads on spread foundations and potential savings can be very high. With the right approach, a geotechnical consultant could justify bearing pressures that are three-to-four times higher than the typical values recommended in a conservative report. Ironically, the cost of sampling or in-situ testing required to justify higher bearing pressures is probably less than one deep foundation element.
Could the site be underlain by fat clays? The potential heave that a floor slab or foundation will experience is related to several factors, including current soil moisture content, soil plasticity, and the specific type of clayey soil. Currently, many consultants automatically recommend a correction of five feet below floors and foundations. The appropriate depth of overexcavation can be evaluated based on some simple tests that could add a few hundred dollars to the report. But reducing the overexcavation and replacement volume by one or two feet across the entire building while leaving the foundations on native soil can mean cost savings starting in the thousands for even a small building.
Create Clarity and Reduce Confusion
Project teams are usually led by an architect who selects trusted designers for the structural, civil, mechanical, and electrical systems. It’s a good idea to consider including the geotechnical engineer as part of that team at the beginning and throughout the design and construction of the project. During the design progress, a geotechnical consultant can guide the other designers as the details of the project are finalized. Frequently, designers struggle to implement the recommendations that are provided for several reasons. Maybe the original report was written for a previous building configuration and changes make those recommendations no longer appropriate. Another example is that the owner often directs the designer to choose a low bearing pressure that will be confirmed during construction, and to forego the geotechnical evaluation. Since the project is designed and practically constructed, any problems encountered will cost extra and cause a delay. The cost of the geotechnical report would have been about the same as performing the work during the design phase.
Having clear and coordinated specifications prepared by the geotechnical, civil, structural, and mechanical engineer creates clarity and reduces confusion. Confusion affects project schedules, and contractors will bid conservatively if they are not certain what to do. The geotechnical engineer frequently does not participate in the preparation of the specifications and plan notes, but could quickly confirm that they conform to the geotechnical recommendations for a project. Consistent terms, definitions, and direction are key.
Quality is Key to Constructability and Efficiency
A current trend is to solicit three bids from geotechnical consultants based on a provided scope, and select a consultant based on the lowest price. The trend of selecting a geotechnical consultant solely based on the lowest price has resulted in keeping bearing pressures very conservative, requiring massive overexcavation and replacement at the sign of potential trouble. To be competitive solely on price, the number of borings, laboratory testing, and engineering efforts are cut dangerously low to win projects. Additional unexpected construction costs and schedule delays based on these conservative recommendations often outweigh the cost of a thoughtful subsurface exploration and engineering evaluation conducted at the beginning of the project.
Hiring the geotechnical engineer with the design team to review the final building layout may result in changes that will improve constructability and efficiency. Value engineering ideas are often realized when a geotechnical consultant is engaged throughout the design and bid process. When selecting a member of the project team, include the geotechnical engineer and strive for quality with the understanding that their expertise can add value to your final project. For more information about our geotechnical engineering capabilities, contact Wes Dickhut.
This article was featured in “The North Dakota Engineer” magazine, a publication by the American Council of Engineering Companies (ACEC) of North Dakota.