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9In many instances, CPT is increasingly being valued as a pro- ductive and cost-efficient means of site investigation for highway projects. Because many diverse geologic forma- tions can be found across the North American continent, TRB decided that a synthesis on the state of practice in CPT would be a helpful guide in its upcoming utilization. One purpose of this synthesis was to gather information from all state and provincial DOTs with the objective of defining and sharing common experiences, successes and failures, and value in applying cone penetrometer technology in highway design and construction. Toward this goal, a survey ques- tionnaire was prepared as an initial step in determining the individual practices from highway departments and their consultants. The questionnaire was directed at geotechnical engineers in the 52 state DOTs in the United States and their equivalents at 12 provincial DOTs in Canada. Where perti- nent, the state and provincial geotechnical engineers were offered the opportunity to engage responses from selected consultant testing firms to aid in the survey results. Appen- dix A contains a summary of the findings derived from the responses to the 59 questions posed in the survey. A total of 56 surveys (of 64 sent) were returned; an overall response rate of 88%. Despite the advantages of CPT, currently 37% of respond- ing state and provincial DOTs do not use any CPT technol- ogy whatsoever. Another 36% of the DOTs use CPT only on 10% of their site investigation studies. Fifteen DOTs (or 27% of the respondents) use CPT on a fairly regular basis on their geotechnical projects (see Figure 4). Much of the CPT work is conducted by outside consultants working under contract to the DOT. The CPT is used to investigate a variety of different geo- materials, but is particularly focused on studies involving soft to firm clays, loose sands, organic soils, and fills. With regard to geotechnical project type, CPT has been used for an assortment of purposes, with the primary applications being bridge design, embankments, and deep foundations (see Figure 5). Reasons for DOTs not to use the CPT vary considerably across the United States and Canada, as summarized in Fig- ure 6. The most frequently cited obstacle reported was that many geologic settings were apparently too hard and not con- ducive to successful penetration by standard CPT equipment. Other common reasons for nonutilization included limited accessibility, lack of expertise, and nonfamiliarity with the technology. This synthesis addresses these major issues. More than two-thirds of the DOTs have not had any unfa- vorable experiences with the CPT on their projects (see Fig- ure 7). Only 6% of responses indicated difficulties, with another 25% mentioning an occasional problem. Based on the survey results, it appears that the majority of DOTs are aware of the CPT technology and its availability. Approximately 64% of the respondent DOTs indicated having made plans to increase their use of CPT in coming years for site exploration and geotechnical investigations (see Figure 8). CHAPTER TWO SURVEY QUESTIONNAIRE ON CONE PENETRATION TESTING FIGURE 4 Results from survey questionnaire on annual use of CPT by DOTs.
10 FIGURE 6 Reasons that CPT is not used by state and provincial DOTs. FIGURE 7 Survey results of unfavorable experiences with CPT by DOTs. FIGURE 5 Types of geotechnical projects that CPT is used on by state and provincial DOTs.
11 FIGURE 8 Projected use of CPT on future DOT geotechnical projects.
