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Pages 38-59

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From page 38...
... 38 The survey results presented in Chapter 3 were used to select five agencies for further case examination. The agencies were primarily identified on the basis of responses that indicated the agency had frequent experience with geophysical methods or experience on noteworthy projects.
From page 39...
... Case Examples 39 A three-person group consisting of a geologist, geologic engineer, and geophysicist is responsible for collecting and analyzing geophysical data when the need arises. This group works closely with MnDOT's drilling crews to provide supplementary information and fill in subsurface information between boreholes.
From page 40...
... 40 Advancements in Use of Geophysical Methods for Transportation Projects MnDOT Example Project: Bridge over Miller Creek in Duluth, Minnesota An early application of ER by MnDOT took place in 2006 in Duluth, Minnesota, at the site of a new bridge, roadway, and retaining walls. The decision to use a shallow or a deep foundation for the new bridge at this site required information about the depth to bedrock.
From page 41...
... Case Examples 41 the east end of the abutment, and deep foundation elements were designed for the west end with the option to switch to shallow foundations. When excavations were performed for the foundation, bedrock was encountered within 10 ft of the surface on both the east and the west side of the creek, which precluded the need for the deep foundation elements originally designed for the west side.
From page 42...
... 42 Advancements in Use of Geophysical Methods for Transportation Projects Chapter 3 of the agency's Manual of Instructions for the Materials Division (2019) , Section 303.02, states that "geophysical exploration is an appropriate adjunct to a subsurface exploration program." As stated in this manual and confirmed in the phone interview, VDOT requires that the methods score a 3 or 4 according to the U.S.
From page 43...
... Case Examples 43 Figure 30. Resistivity image with generalized interpretation and location of boreholes 14BH-001 and 14BH-002 (courtesy of VDOT)
From page 44...
... 44 Advancements in Use of Geophysical Methods for Transportation Projects Ohio Department of Transportation The synthesis survey revealed that the Ohio Department of Transportation (ODOT) applies geophysical methods on projects about six to 10 times per year, which the agency reported is more frequent than 5 years ago.
From page 45...
... Case Examples 45 further developed by the Field Exploration Group. When the group sees value in using geophysics for a project, it will suggest doing so in the field exploration program.
From page 46...
... 46 Advancements in Use of Geophysical Methods for Transportation Projects completed in 1967. In 2019, ODOT planned a project to replace the existing superstructure and widen the bridge.
From page 47...
... Case Examples 47 experiencing instability at all four quadrants of the overpass, with the northeastern quadrant exhibiting the greatest distress. The surface features indicated a shallow surficial sloughing of the outer embankment soils.
From page 48...
... 48 Advancements in Use of Geophysical Methods for Transportation Projects Informed by the results of this project, ODOT expects to use ER surveys in the future to image shallow embankment failures and to minimize the disturbance and effort needed for traditional drilling exploration at mid-slope locations. ODOT Example Project 3: Full Waveform Inversion to Characterize Abandoned Mines While many other seismic methods are based on matching first arrival times of recorded waveforms, full waveform inversion (FWI)
From page 49...
... Case Examples 49 ODOT: Lessons Learned ODOT has used geophysical measurements for a variety of applications, with many driven by issues associated with karst terrain (e.g., voids, irregular bedrock) and effects of abandoned mines on roadways.
From page 50...
... 50 Advancements in Use of Geophysical Methods for Transportation Projects History of Geophysics Use and Agency Practice Though NJDOT has used geophysical methods for approximately 20 years, it reported a slow build-up to its present level of use. NJDOT's earliest use of geophysics involved sporadic use of GPR until about 20 years ago, when the agency began to apply other geophysical methods to the problem of abandoned mine characterization.
From page 51...
... Case Examples 51 overlying shallow bedrock. In addition, a unique aspect of the project site was an extensive (approximately 600,000-square-ft)
From page 52...
... 52 Advancements in Use of Geophysical Methods for Transportation Projects Phase Three consisted of a series of borings, including rock coring, for a proposed widening of one of the existing ramps. To facilitate structural rock analysis and rock cut design along the ramp, borehole logging with optical televiewers was performed on all borings.
From page 53...
... Case Examples 53 now compared with 5 years ago. Caltrans was also the only agency interviewed that had a formal geophysics group within the agency.
From page 54...
... 54 Advancements in Use of Geophysical Methods for Transportation Projects provide a continuous record of the physical properties of the soil and rock; this augments the discrete information obtained from lab analysis. Caltrans reported extensive use of the acoustic televiewer in agency projects that seek to find orientations of failure surfaces, fractures, and bedding.
From page 55...
... Case Examples 55 refraction tomography for a freeway improvement project at Interstate 80 and Willow Avenue in Contra Costa County is presented here. The site is located near a heavily traveled urban freeway, whose traffic produced significant broad-band seismic noise.
From page 56...
... 56 Advancements in Use of Geophysical Methods for Transportation Projects Figure 38. Pseudo ray path model for velocity section shown in Figure 39 (courtesy of Caltrans)
From page 57...
... Case Examples 57 Figure 40. Pseudo ray path model using only surface sources, showing change in depth of investigation (courtesy of Caltrans)
From page 58...
... 58 Advancements in Use of Geophysical Methods for Transportation Projects Figure 42. GPR reflections interpreted to represent contact between Sherwin Till and overlying Bishop Tuff (courtesy of Caltrans)
From page 59...
... Case Examples 59 varies by project and has not been quantified by the agencies in most cases. The main source of cost savings mentioned by most of the agencies was avoidance of claims or unanticipated delays through better characterization of ground conditions.

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