Rock-Socketed Shafts for Highway Structure Foundations (2006) / Chapter Skim
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Appendix B - Survey Questionnaire and Responses
Appendix B - Survey Questionnaire and Responses
Pages 110-135
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From page 110... ...
111 APPENDIX B Survey Questionnaire and Responses The survey questionnaire is presented in the following pages. Responses to each question are summarized below each question.
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From page 111... ...
This questionnaire is designed to be completed by the state DOT Geotechnical Engineer, assuming that individual has the most knowledge regarding the issues identified above. However, it is recognized that practice varies between states and that other branches within a state DOT may have considerable involvement in drilled shaft engineering.
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From page 112... ...
University Ave. Fax: 307-766-2221 Laramie, WY 82071 e-mail: turner@uwyo.edu After completing the survey, if there are issues pertaining to rock-socketed drilled shafts that you believe are important but that are not addressed adequately by the questionnaire, please feel free to contact the author directly.
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From page 113... ...
California mudstone, sandstone, siltstone, phyllite, slate, and weathered rock Colorado claystone, siltstone, weakly cemented sandstone Florida weathered limestone Georgia partially weathered rock Illinois weathered limestone, hard clay/shale, cemented sand/sandstone Iowa shale, siltstone, sandstone, limestone, dolomite Kentucky weathered shale Massachusetts till Michigan soft shale, hardpan Minnesota noncemented sandstone, highly weathered granite Missouri softshale Montana claystones, siltstones, uncemented sandstones New Jersey v. dense sands with N > 50 New Hampshire glacial till New Mexico Santa Fe Formation (N > 75)
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From page 114... ...
GA: Geotechnical -- Selection of shafts is recommended foundation type or alternate; bearing pressures, rocksocket length, and tip elevations. Bridge -- Selection of shaft diameters, lateral analysis, and possible revision of tip elevations.
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From page 115... ...
MI: Geotechnical characterizes rock formation and determines rock-socket diameter and length. Bridge Design determines shaft location, shaft loading, and sizes reinforcement.
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From page 116... ...
When the contract requires a minimum penetration into a bearing layer, as opposed to a specified shaft tip elevation, and the bearing layer elevation at each shaft cannot be accurately determined, add subsection 3.05.E as follows: For those shafts with a specified minimum penetration into the bearing layer and no specified tip elevation the Contractor shall furnish each shaft steel reinforcing bar cage, including access tubes for cross-hole sonic log testing in accordance with subsection 3.06 of this Special Provision, 20% longer than specified in the plans. The Contractor shall add the increased length to the bottom of the cage.
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From page 117... ...
Design is generally based on the strength testing, regardless of material designation. The following is a list of rock properties that may be required or recommended to apply design methods specified in the FHWA Drilled Shaft Manual, as well as for other published design methods used for rock-socketed drilled shafts: qu = unconfined compressive strength (units of F/L2)
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From page 118... ...
AZ, CO, CT, FL, GA, IL, IA, KY, MA, MI, NH, NJ, NC, OR, TN, WA Method: AL: Correlation charts between qu and E IA: Theoretical KY: Correlation with UC strength ME: ASTM 7012-04 MA: Goodman, Jack, and tables/charts MI: Calculated from Ultrasonic Velocity test (ASTM D2845) or approximated from figures and tables in section 4 of the AASHTO Standard Specs MN: ASTM D3148 NH: Eintact determined from qu test, then correlated to Ein situ through RMR or other methods OR: From ASTM D2938 results with measured strains UT: either unconfined compression test or from AASHTO table VT: ASTM D3148 WA: Usually use published textbook values based on rock type RMR Always Never Varies Always: (5)
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From page 119... ...
AZ, CA, CO, NH, NJ, NM, NC, OR 10. List below any in situ test methods that are used by your agency to correlate with rock or IGM properties or to correlate directly to rock-socket design parameters (e.g., side or end bearing resistance)
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From page 120... ...
, SPT GA: Coring, RQD, compressive tests, split tensile IA: Strength, skin friction/end bearing; lab UC on cores, O-cell tests KS: Core, RQD RMR qu MN: Strength and stiffness; unconfined compression MO: Compressive strength; qu on core sample NC: Typically we core the rock and perform unconfined compression tests SC: Unconfined; load test TX: qu, skin friction, point bearing; ASTM, Tex-132-E; TxDOT Geotechnical Manual correlations UT: Same mentioned in Question 9 Soft shales or marls (14) AL, AZ, CA, GA, IA, KS, KY, MI, MO, NM, SC, SD, TX, UT State: Property; Test Method; Correlations Used AL: Rock strength, thickness and spacing of discontinuities; unconfined compression testing where possible, logged by a professional geologist from the cored rock (for all rock types checked)
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From page 121... ...
AL, AZ, FL, GA, KS, KY, MI, NM, TX State: Property; Test Method AZ: Core into rock after the excavation to check for voids FL: Coring, qu, qt, SPT GA: Coring, RQD, compressive tests, split tensile KS: Seismic KY: Rock Core Recovery NM: Discontinuities; test pits/seismic shear wave TX: qu, skin friction, point bearing; TxDOT Geotechnical Manual correlations Rock with steeply dipping discontinuities (7) AL, AR AZ, CA, GA, NM, WA State: Property; Test Method; Correlations AR: Visual observations of rock condition AZ: Down-the-hole camera to check for poorly oriented joint sets GA: Coring, RQD, compressive tests NM: Modulus; RMR WA: RQD and unconfined compressive strength; drilling and Point Load Interbedded rock with alternating strong and weak strata (11)
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From page 122... ...
Identify any other issues pertaining to IGM or rock characterization that you think should be addressed by the Synthesis. MO: Limited Osterberg load cell testing has indicated that we significantly overdesign shafts in IGMs based on compressive strength values from qu testing.
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From page 123... ...
NC: Depends on our design; we might use base or side resistance but most of the time we use both. OR: Combine side and base resistance only in very ductile rock formations as described in the FHWA Drilled Shaft Design Manual.
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From page 124... ...
to 3 UT: All types, φs 0.55 MA: All, FOS 2–2.5 or φs 0.55–0.65 VT: All, FOS 2.5 ME: Schist, FOS 2.5 WA: All, FOS 3.0 Static, 1.65 Seismic FL: By AASHTO LRFD 18. For calculating base resistance of rock sockets, please indicate the reference(s)
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From page 125... ...
If you include both side and base resistances in design of rock sockets, explain briefly how you account for the relative contribution of each to the socket axial resistance CA: Must determine the amount of each that can be mobilized at our allowable movement at the top of the pile. CT: The relative contributions would be based on the computed displacement/strain of the drilled shaft.
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From page 126... ...
NJ Other (please cite reference or provide a brief description) ME: FB Pier evaluation SC: Some lateral load resisting WA: S-Shaft Program developed by M
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From page 127... ...
Typically, this is about 10,000 ksi for basalt. We then use the unconfined compressive strength from point load tests along with E to define the curve.
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From page 128... ...
What branch or group within your agency is responsible for structural design of rock-socketed drilled shafts? AL: Bridge Bureau ME: Bridge Program AZ: Bridge Group MN: Bridge Office AR: Bridge Design MT: Bridge CA: Division of Engineering Services/ NH: Bridge and Geotechnical Sections Structure Design NJ: Structural and Geotechnical Engineering Units CT: No drilled shaft design has been done NM: Bridge Section with in-house engineering staff OR: Technical Services, Region Technical Centers GA: Office of Bridge Design PR: None, done by consultants HI: Bridge Design Section or Structural Consultants SC: Bridge Design Section ID: Bridge Design SD: Bridge Design
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From page 129... ...
NJ, WA 29. For structural design of drilled shafts, does your agency currently use Load Factor Design (LFD)
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From page 130... ...
: Unexpectedly high computed shear in the rock socket when using the p-y method of analysis. CA: "When the moments go from a maximum to zero over a relatively short length, then the corresponding shear demands that are reported are large." Difficulties or questions in applying p-y analysis to relatively short socket lengths CA, IA, NM NH: "One question is whether the drilled shaft length can be terminated even though the p-y analysis indicates some minor shear, moment, or deflection at the base of the shaft." Questions regarding transfer of moment to the rock socket or development length for reinforcing bars extending into the rock socket.
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From page 131... ...
MN: From our drilled shaft special provision: loose material shall be removed from drilled shafts prior to placement of reinforcement. After the shafts have been cleaned, the engineer will inspect the shafts for conformance to plan dimensions and construction tolerances.
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From page 132... ...
Rock type and special provision: AZ: Limestone; drill below tip elevation to check for karst conditions. ID: Special provisions for IGMs and hard rock.
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From page 133... ...
38. Indicate whether your agency has used any of the following field load testing methods on rock-socketed drilled shafts.
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From page 134... ...
Ultimate base resistance Proof load only 41. Additional comments regarding use of O-cell for load testing of rock sockets.
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From page 135... ...
47. Do you have case histories of design, construction, or testing of rock-socketed drilled shafts that, in your opinion, could provide useful information to your colleagues and, if so, are you willing to be contacted by the author of the synthesis to discuss your case histories further?
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