Improved Site Stratigraphy and Layer Characterization Using Cone Penetration Testing Methods on Minnesota DOT Projects

In November of 2001, the Minnesota Department of Transportation (Mn/DOT) began using cone penetration testing (CPT) in addition to traditional borehole drilling as standard practice for geotechnical site characterization. Immediate benefits were observed. Use of the CPT system, in conjunction with drilling, sampling, and lab testing, has improved the ability to resolve small changes in soil stratigraphy and associated soil properties. Major transitions can be clearly identified and the location of the transition determined with greater precision and accuracy previously possible. As compared with traditional investigation techniques, CPT provides increased resolution for characterizing stratigraphic interfaces and the ability to develop continuous profiles of soil properties. Other practical advantages of the technique, of particular interest to geo-engineering agencies and companies, are discussed. The application of CPT methods has been useful on a broad range of transportation projects. Thickness and lateral extent of thin seams in soft clays have been identified. Limits of organic materials have been determined with precision and speed. Refined boring programs, based on CPT data have improved the efficiency of site investigations. Mn/DOT has also applied the CPT to a number of non-traditional projects including verification of contractor "remove and replace" operations and studying open-end pipe-pile plugging and pore-water pressure dissipation behavior. Four briefcase studies illustrating the use of CPT investigation techniques to identify thin seams and complicated site stratigraphy on Mn/DOT projects are discussed.