When I talk with people in the Architecture/Engineering/Construction industry, I often find that a lot of people working on building projects have complaints about the foundation engineering on those projects. These complaints have a few common themes:
- Inadequate scope or data collection for subsurface explorations and geotechnical reports;
- Excessively conservative foundation design recommendations;
- Inappropriate, incomplete or poorly applied foundation construction recommendations;
- Inability or unavailabilityof the geotechnical engineer to contribute to the design development process and refine their foundation design recommendations and parameters as the project evolves.
I have certainly seen my share of projects with incomplete, overly conservative, uncoordinated or even erroneous foundation engineering and perhaps you have too, but it doesn’t have to be that way.
The foundation is one of the most critical components of any structure. Poor foundation performance can impair the serviceability of the entire structure. In addition, there are risks unique to foundation systems, because to some extent, foundation construction is performed “in the blind” and it is difficult to access foundation elements for inspection and repair after construction. The construction methods used to build the foundation can also have a detrimental impact on adjacent structures. While these risks suggest that a conservative approach should be taken, the foundation system is one of the most expensive parts of the structure and adds little value beyond its capacity to support the structure. It is, therefore, necessary to balance performance, risk and cost in designing any foundation system.
A lot of problems resulting from foundation design and construction stem from the division of labor for foundation design on most building projects. Typically foundation parameters and recommendations are developed by a geotechnical engineer early in the design phase and used by a structural engineer to proportion and detail the foundation system. The structural and geotechnical engineers typically work for different firms and may have no interaction other than the former using the report prepared by the latter. As the project goes to construction, a general contractor and, perhaps, a specialty foundation contractor will use the geotechnical report to plan their work, but may also have no contact with the geotechnical engineer until work begins. Since the geotechnical engineer may not be consulted as the project is designed, his or her recommendation may be intentionally more conservative and unspecific, so as to envelope all possible needs of the project before it is designed. In addition to being incompatible with the iterative nature of the design process, this sort of narrow-scope, one-time involvement of the geotechnical engineer limits the value they can contribute to the project and commoditizes the services they provide.
Perhaps because they are accustomed to limited geotechnical services on their projects, some owners, architects and engineers are of the impression that soil is just another material to be tested. You can send out a technician, sample the soil, maybe do some laboratory testing and receive a report with all the answers. If you believe that a subsurface investigation is just a matter of running some standard tests and receiving the results, then you will believe that you can have the lowest bidding materials testing firm do the work. Of course, a low bid subsurface investigation is likely to be minimal in scope, with little project-specific engineering and no design assistance, since there will be no budget for an experienced professional to review the project requirements and the data and apply engineering judgment. This approach is always wrong, but if you are building a single family home or a shopping plaza, you may not see a difference unless something significant is missed. For larger projects, failing to apply some project-specific engineering analysis can lead to excessively costly foundation systems and incomplete or inappropriate recommendations leading to construction risks.
Thoughtful, project-specific foundation design parameters and recommendations can help contain construction cost and manage risk. Foundation parameters and recommendations should be well coordinated with site constraints, subsurface conditions, superstructure demands and likely construction methods. Support during construction should be available to the design team. A foundation engineering specialist can provide these services for your project. A good foundation engineer understands soil mechanics and geology, but also understands the behavior of the structure to be supported and the effects that construction methods have on new work and adjacent structures. This is not likely to be within the core competency of a construction materials testing laboratory, a special inspection agency or an environmental consultant, any of which may offer some geotechnical services so as to provide “one-stop shopping”.
A foundation specialist can be engaged at different stages in a project, but the most value can be contributed early in the design process, prior to the subsurface investigation. At this stage, the foundation specialist can assist with scoping the investigation to best reflect the needs of the project. However, it may not be apparent this early in the process what, if any, assistance the design team will need. Here are a few situations in which you should consider adding a foundation specialist to the project team:
- ExcessivelyConservative Design Parameters: If everyone on the design team believes that the design parameters in the geotechnical report are excessivelyconservative, they likely warrant a second opinion. Unlike structural tests, there are few design parameters that are derived directly and unambiguously from field and laboratory testing. Therefore significant engineering judgment is needed to determine what parameters are needed and how to determine them. A low bid subsurface investigation will often not have the budget to determine parameters on a project-specific basis and conservative values that have worked before will be provided. In some cases, there will be misinterpreted data. For example, the lowest value of a parameter may be used or reported, instead of an average. Data might not be properly correlated with geologic formations or the location of the new building on the site, resulting in unrepresentative data being used to develop parameters. Cutting corners in interpreting data can have real consequences. An incorrect seismic site classification can increase the seismic design loads on a building by 10 percent or more. Failing to account for standard penetration test hammer energy can make a site appear liquefaction susceptible when it is not. A foundation specialist will know what questions to ask to better use the subsurface information you have and can recommend supplemental explorations if necessary.
- Deep Foundations: Some buildings on some sites require pile or drilled shaft foundations, but I have seen too many projects where deep foundations were recommended when alternatives were available, if not more practical. On a large building, this can increase foundation cost by hundreds of thousands of dollars. Some geotechnical reports I have read seem to suggest that it is impossible to found a building on soil at all, which is just wrong. Unless the site is underlain by uncontrolled fill or organic soil, a second opinion might be warranted. There may also be multiple deep foundation alternatives applicable to the project. A foundation specialist can help you identify applicable foundation types, determine design parameters and evaluate contractor value engineering proposals.
- Deep Basements: Most geotechnical reports do not include complete recommendations and design parameters for a building with a deep basement. The report will provide some design parameters for permanent work, but additional information is usually required for the design of the excavation support system, protection and monitoring of adjacent structures and controlling of groundwater in the excavation. The design of these systems istypically delegated to the contractor, but create risk for the owner. The design team is typically not well experienced in these systems and may not be prepared to specify them or review the contractor’s designs. On some projects, there are advantages to integrating temporary systems with the permanent structure. These opportunities are lost if the design team lacks the expertise to evaluate them. A foundation specialist with construction systems experience can help the owner and design team identify and manage its risks from deep excavations and review contractor means and methods that affect the owner’s interests.
- Specialty Foundations: Some foundation systems, like slurry walls, secant pile walls, micropiles and ground improvement methods are outside the expertise of most structural engineers and need specific geotechnical inputs during the design process. The design of these systems is often delegated to specialty foundation contractors. A foundation specialist can perform type studies of these elements to determine their suitability and facilitate bidding, as well as help specify and review contractor submittals.
The engineering of well-performing and economical foundations is as much art as science and requires a unique understanding of structural behavior, soil mechanics and construction methods. Although many project teams forgo the benefits of having a foundation engineering specialist on the design team, some of the most common complaints about foundation engineering on building projects, as well as the associated, and avoidable, costs and risks, can be mitigated by engaging a foundation specialist to assist withyour project.
The information and statements in this document are for information purposes only and do not comprise the professional advice of the author or create a professional relationship between reader and author.