Earthwork and foundations fall early in most project schedules but are often beset with delays and unbudgeted costs for additional geotechnical evaluation, design changes, materials, and labour – all of which can easily propagate through the project timeline.

According to the US National Cooperative Highway Research Program (NCHRP) common causes of geotechnical claims and cost overruns result from a multitude of subsurface issues, including foundation depth overruns, groundwater and seepage issues, subgrade materials, and unanticipated or misidentified rock.

While a significant source of risk is realised in situations where actual ground or groundwater conditions are different than expected, there are also potential risks from design approaches, construction means and methods, quality of installation, and inspection and verification methods.

Changes to foundation type or configuration can also result in project complications or unintended consequences which can interact adversely with non-geotechnical construction based on the original design, creating further delays and costs, and potentially impact project integrity or performance.

Whose risk is it?

Managing these risks, both before and after unexpected challenges occur, is a challenge given the number of parties typically involved in a project. Ground conditions are rarely the only factor. Determination of design-appropriate subsurface material properties, stratigraphy, and spatial variability are inherent challenges to geotechnical investigation and interpretation.  

For instance, a contractor's chosen means and methods may change the ground reaction, influencing risks associated with construction efforts. But further uncertainty is added when, for a given unexpected geotechnical situation, there could be any number of problems and solutions. Some alternative procurement arrangements allow designers to more easily address construction issues; traditional design-bid-build arrangements are seldom as nimble in responding to these types of changes.

But as risks are identified, a frequently asked question is whether the distribution of risks, and associated costs, are fair.  For instance, does the owner, designer, contractor, and any subcontractors share the project risk equitably?

Risks are constantly introduced by parties based on choices made during geotechnical investigation and interpretation, final designs and specifications, construction means and methods, and the project delivery mechanisms. These are all heavily interrelated.

Risk allocation

Risk allocation is an area of current interest for deep foundations construction in the United States.  

Current practices, especially where risk is allocated poorly, often result in significant claims and disputes. As foundations become more expensive (due to material, labour, and energy costs) and as foundations are constructed in stressful circumstances (due to project demands including time, budget, location, and access constraints), each contributor looks to diminish their own potential liability and reallocate it to others.

Contract authors writing on behalf of owners have a financial interest in shedding as much risk as possible. Owners seek to make the designers and contractors responsible; designers seek to shed risk to owners and contractors; and contractors seek to put risk onto the project owners and designers.

While each party's preference to minimise its own risk is understandable, allocating risk fairly is a solution that can benefit all parties and result in better overall outcomes. This approach can be facilitated with an unusual, and currently underappreciated, type of geotechnical report.

Risk mitigation

In the early 1970s, geotechnical colleagues in the tunnelling industry developed a contract document to aid in the construction of horizontal features (tunnels) through the earth, and it has proven to be highly successful in managing risk for those works.

It is now being adopted by those in the deep foundations industry who have a similar interest in the construction of other in-ground elements, such as vertical features (foundations) through the earth, ground strengthening/improvement, and support of excavations.

A geotechnical baseline report (GBR) is a specialised contract document that defines anticipated subsurface conditions, including interpretations of those conditions, for the purposes of construction bidding.

Legal basis

GBRs allocate geotechnical and geologic risks among owners and other project parties for specific conditions identified as having a large impact on construction outcomes, such as groundwater conditions and rock elevations/strengths. It serves as a basis for bidding, allowing competing contractors to price risk consistently, and provides measurable standards for evaluating differing site conditions claims where conditions deviate from the defined conditions.

Unlike other geotechnical reports, a GBR is legally part of the contract documents and must be written collaboratively with authors of other plan requirements and specifications.

Geotechnical data reports, geotechnical interpretive reports, and geotechnical design memoranda and reports are far more common and are generally concerned with providing an accurate representation of actual ground conditions, while often avoiding providing an interpretation of those conditions that contractors can rely on (for certain procurement methods).

When the GBR is part of the contract, it defines the physical aspects of the ground conditions, known as "baselines," that should be provided for in the contractor's risk and the contract price. Conditions differing from those in the GBR are "unforeseen" under the contract and represent the owner's risk. The baselines are defined based on the owner's tolerance for risk and are used for the basis of measurement or payment and as a contractual tool to aid in addressing changed conditions resolving disputes.

GBR use

The use of GBR documents is evolving, and references to how to incorporate them into projects and use them effectively are expanding.

For instance, the 2022 revision to the AASHTO Manual on Subsurface Investigations (2) describes the use of GBR documents for general transportation applications. Also updated in 2022, the ASCE Manual of Practice (MOP) 154 Geotechnical Baseline Reports: Suggested Guidelines (3) contains recommendations for what should and should not be included in a GBR, provides general guidance for authoring the documents and presents examples of practices in creating baselines.

Most recently, Deep Foundations Institute (DFI), through its Subsurface Characterization for Deep Foundations Committee, developed a series of four GBR one-page primers and issued a position statement in support of the creation and use of GBR documents.

While claims, change orders, and cost overruns will still occur, with more widespread adoption of GBRs, the time and costs associated with changes, and associated administrative burdens, could lessen – at a minimum, initial bids on complex projects are more likely to be uniform and parties may appreciate that they are being treated fairly even while risks remain.

 

 ^* Derrick Dasenbrock is the Geotechnical Section Manager at the Minnesota Department of Transportation's Office of Materials & Road Research, and member of DFI's Subsurface Characterisation for Deep Foundations Committee. His article was written with input from Committee members Mary Nodine and Scott Walker