Differing Site Conditions

Exponent has been engaged by design-build engineering firms, general contractors, and specialty subcontractors to prepare and substantiate differing site conditions (DSC) claims brought by project owners and public agencies. We also evaluate claims submitted by contractors, and by professional liability insurance carriers to evaluate standard of care claims against design professionals. Exponent has the in-house multidisciplinary expertise of engineers, geologists, construction management professionals, schedulers, and estimators to analyze all aspects of DSC claims. The results of our development and evaluation of DSC claims have been presented in discussions with our clients, written reports, and testimony at review board hearings, arbitrations, mediations, and trials.

Construction projects necessarily involve the assessment of site surface and subsurface conditions to select the best means and methods to develop a construction schedule and bid and to complete the project. For traditional design-bid-build projects, the assessment of site conditions is typically based on information provided by the owner/agency in the bid package, familiarity gleaned from a site walk, as well as insight regarding conditions that could be reasonably expected. In some cases, contractors are encouraged to perform additional investigations, as needed, to become better acquainted with the field conditions. For design-build projects, the contractor typically accepts additional responsibility for evaluating site and subsurface conditions. Bidding contractors may be provided with a stipend to conduct additional subsurface investigations.

Differing site conditions in construction projects can cause schedule delays, cost increases, and dangerous working conditions. They can also invalidate design assumptions, putting short- and long-term project performance at risk.

Contractual provisions to deal with DSC claims in design-bid-build projects have evolved primarily in the transportation sector. The Federal Highway Administration (FHWA) developed a test system that defines a method of classifying claims—commonly referred to as Type I, Type II and Type III claims—according to the basis for the contractor’s pre-construction knowledge and understanding of site conditions, and the discovery of hazardous or toxic materials. A Type I DSC claim involves situations in which the site surface or subsurface conditions deviate substantially from those represented in the bid package. A Type II DSC claim refers to situations in which the site surface or subsurface conditions are substantially different from those that might be reasonably expected. A Type III DSC claim involves the discovery of hazardous or toxic materials. Some form of these FHWA provisions is contained in most construction contracts for public works projects. The language of the differing site conditions clause becomes a critical component of the construction contract.

In general, Exponent has expertise to evaluate issues related to:

  • Entitlement (technical merits of claim)
  • Cost analysis
  • Delay impacts
  • Acceleration

In Exponent’s evaluations of entitlement, our geologic, engineering, and construction professionals have used their education, training, and expertise to address issues related to the following types of site conditions:

  • Excavation and trench failure
  • Embankment failure
  • Pile-driving refusal
  • Rock suitability for drilled shafts
  • Import fill suitability
  • Borrow source characterization
  • Unsuitable material
  • Subgrade suitability
  • Embankment/subgrade R-value
  • Construction equipment mobility
  • Pumping and rutting of subgrade
  • Expansive soil
  • Collapsible soil
  • Liquefiable soil
  • Soil strength characterization for temporary excavation support systems
  • Cobbles and boulders (particle size)
  • Running ground”
  • Sinkholes
  • Excessive ground moisture
  • Groundwater and seepage
  • Groundwater pumping rates and volumes
  • Rock rippability
  • Back-cut slope stability
  • Landslides (mapped and unmapped)
  • Faults
  • Ground fissures
  • Hazardous and toxic materials (naturally occurring and manmade)


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