Differing Site Conditions

Accurately assessing Differing Site Condition (DSC) claims requires a multidisciplinary team

For traditional design-bid-build projects, a site conditions assessment is typically based on information from the owner or agency in the bid package, site-walk observations, and reasonably expected insight into the conditions. In some cases, contractors are encouraged to perform additional investigations to become better acquainted with field conditions. Typically, for design-build projects, the contractor accepts responsibility for evaluating site and subsurface conditions.

In the United States (U.S.), the Federal Highway Administration (FHWA) developed a test system that defines a method of classifying claims according to the contractor's pre-construction knowledge, 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

Most construction contracts for public works projects in the U.S. contain some form of these FHWA provisions, and the language of the DSC clause is a critical contract component.

Internationally, the International Federation of Consulting Engineers (FIDIC) Yellow and Red books for construction and design and construction include an unforeseeable physical conditions clause where the contractor takes the risk of foreseeable site conditions. More recently, the Emerald Book, for underground works, included Geotechnical Baseline Report (GBR). The GBR is a compulsory contractual document with the purpose, among other things, of setting out a risk-sharing mechanism.

Exponent consults with design-build engineering firms, general contractors, and specialty subcontractors to prepare and substantiate DSC claims from project owners and public agencies, and to advise on risk-sharing strategies, including reviewing of GBRs. We also assess DSC claims from contractors and professional liability insurance carriers to evaluate standard-of-care claims against design professionals.

Exponent's multidisciplinary team of experts can present DSC claims development and evaluation results in discussions with clients, in written reports, and as testimonies at review board hearings, arbitrations, mediations, and trials in areas that include:

• Tunnels and underground structures
• Shallow and deep foundations
• Dams and water retaining structures
• Bridges
• Earthworks
• Retaining structures

• Support of excavations 

• Site grading 

• Ground improvement 

Dewatering 

• Geotechnical Baseline Reports (GBR)