Practices for Construction-Ready Digital Terrain Models (2021) / Chapter Skim
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11 State of Practice As noted in Chapter 1, an online survey questionnaire was built in Qualtrics and distributed by email to members of the AASHTO Committee on Construction (COC)
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12 Practices for Construction-Ready Digital Terrain Models State DOTs that participated State DOTs that did not participate Figure 6. Map of DOTs responding to the survey, N = 40.
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State of Practice 13 Note: Numbers do not add to 100% because of rounding. Figure 8.
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14 Practices for Construction-Ready Digital Terrain Models that 11% of the DOTs have been using DTMs for less than 3 years, 16% of the responding DOTs have between 3 and 7 years of experience using DTMs, 29% reported experience of 7 to 10 years using DTMs, and 45% of the respondents indicated that their DOT has been using DTMs for more than 10 years. Figure 10 depicts the DTM usage timeline of the 40 responding DOTs.
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State of Practice 15 Figure 11. Variation in the sources of DTM across DOTs, N = 32.
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16 Practices for Construction-Ready Digital Terrain Models DTMs are least used for Pavement Thickness Checks (UC9) ; QA/QC, Class Detection, or Reducing Plan Discrepancies (UC8)
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State of Practice 17 Respondents also had the option to report other types of training that were not listed in the survey. One respondent indicated reliance by the DOT on the training provided by a contractor or vendor when using GPS rovers for earthwork quantity checks.
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18 Practices for Construction-Ready Digital Terrain Models that the DOTs created or received from designers but also the levels of quality and usefulness of the models according to the contractors. Given that the survey is distributed to DOT personnel, the question had to be posed as seeking the perspective of the contractors as perceived by the agency.
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State of Practice 19 3.2.2 Project Type Respondents were asked to identify the types of projects for which their DOT uses DTMs. As illustrated in Figure 18, most responding DOTs use DTMs for widening corridors (87%)
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20 Practices for Construction-Ready Digital Terrain Models discussions in Chapter 4, states note that DB and CM/GC, in particular, enable better DTM use in construction, given the ability to have early contractor involvement. 3.2.4 DTM Construction Inspection Respondents were asked to specify the party responsible for construction inspection on projects that used DTMs.
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State of Practice 21 • Performing quantity verifications on contractors' models, • Performing survey stake-out and grade control, • Identifying areas in excess materials in right of way, and • Staging. 3.3.2 DTM Long-Term Benefits Respondents were asked to indicate their level of agreement with a list of long-term benefits associated with the use of DTMs using a five-point scale of strongly disagree (1)
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22 Practices for Construction-Ready Digital Terrain Models Responses are grouped into major and relevant phases for a highway construction project's life cycle and are provided in the following as direct quotes. • Design – Developed a DTM to support a new alignment on a multi-bridge project and a 4.5 million cubic yard earthwork project.
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State of Practice 23 • Surveying – Our office is responsible for producing DTMs by photogrammetry and LiDAR methods. – Have used kinematic equipment to obtain terrain model to determine areal measurements for vegetative establishment quantities.
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Figure 22. Perceived barriers to implementing DTMs, N = 37.
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State of Practice 25 Although 11% of the respondents indicated that they were not aware of any written specifications related to contractors' use of DTMs, the majority of respondents acknowledged the presence of language related to DTM in their DOT's policy manual(s) or contract documents.
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26 Practices for Construction-Ready Digital Terrain Models provided in the survey, some respondents from South Carolina (SCDOT) , Alabama (ALDOT)
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