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Home My WebLink AboutSUB201800171 Correspondence 2019-03-27 (5)i `' Charlottesville, VA 2294:3 www.timmons.com March 26, 2019 Justin Deel VDOT Culpeper District Structure & Bridge Charlottesville, VA RE: Lewis & Clark Ext. Culvert #1 Plan Review - Comment Response Letter Dear Mr. Deel: We have reviewed all of your emailed comments from March 11, 2019 and made the necessary revisions. Please find our responses to the comments below in bold lettering. Culpeper District Structure & Bridge Section: 1. Structural information and calculations have not been provided, only hydraulics. Based on the graphic depictions on the Timmons profile sheet, the height of both boxes is 5'. Both are skewed to the roadway. The designer has not identified the specific VDOT standard (such as BCD-20) for either box, and the designer has not identified the specific standard for the wingwalls. VDOT end wall standards have been specified on profiles. 2. Culvert #1 is a 250' long double 5'x5' box with approximately 20' of fill. Skew is approximately 35 degrees. The geotechnical report incorrectly identifies this as a single 7'x5'. The correct culvert size will is shown in updated geotechnical report. 3. Culvert #2 is a 164' long single 7'x5' box with approximately 10' of fill. Skew is approximately 10 degrees. The geotechnical report incorrectly identifies this as a single 5'x4'. VDOT standard box culvert sizes are 7'x4' and 7'x6', but no standard 7'x5'. 4. The correct culvert size is shown in updated geotechnical report. (;antorhnirnI- 5. General: Please provide additional information regarding the design of Culvert #1, such as: a. Height of fill overtop of culvert. OV111l I II::::: Ill III II:II 11Allll I ' U11?,VII:Y]1NG I (pq,'S I I �,6.DII�' Illl a➢�,II,q,6.Dll� : Il',II°�Aq�,ll',' This is described in updated geotechnical report. b. Culvert material — i.e. Reinforced Concrete Pipe (RCP) This is described in updated geotechnical report. c. Invert elevations. This is described in updated geotechnical report. 6. General: Boring logs should be provided using the "gINT" software on the VDOT template. This is provided in updated geotechnical report. 7. General: Soil descriptions provided on the boring logs should follow the guidelines provided in Chapter 3 of the VDOT Manual of Instruction (MOI). This is provided in updated geotechnical report. 8. General: The GER makes references to "weather rock". Based on the description of this material in the GER, this material appears to be "Intermediate Geomaterial (IGM)". Please refer to Chapter 3 of VDOT MOI for further information. This is provided in updated geotechnical report. 9. General: In the report narrative, please provide a table of soil parameters used for engineering analyses based on the soil strata encountered. A table of values has been added to the Slope recommendations section in the updated geotechnical report 10. General: Provide engineering analysis calculations for culvert bearing resistance. What is the anticipated loading pressure? Updated calculations are provided in the updated geotechnical report. 11. General: Provide the engineering analysis calculations for culvert settlement. Updated calculations are provided in the updated geotechnical report. 12. Executive Summary, 81" bullet states "Undercutting of at least 4 to 6 feet of soft soils is anticipated for the culvert and end walls". Based on review of the invert elevations provided on the storm culvert profile as well subsurface soil information provided on Boring Logs B-09 and B-10, there does not appear to be a need for an undercut of material. Please Clarify: a. The elevations of the proposed undercut. We agree with VDOT's undercut assessment, except at the culvert ends where the culverts tie into the streams and soft alluvial soils are likely present. We have assumed about 4 feet of undercut is needed in these isolated areas. b. Why Timmons believes an undercut/replacement is necessary. Please see Item a. above. This is discussed in the updated geotechnical report. 13. Narrative, Page 1, Section 1 "Project Information". Sixth sentence states that the first crossing will consist of 60 x 84-inch box culvert. The Storm Culvert Profiles call out this culvert to be a 60 x 60-inch double box culvert. Please clarify. The corrected culvert information is described in updated geotechnical report. 14. Narrative, Page 2, Section 2 "Field Exploration", third paragraph states "Water levels were measured in open boreholes at the time of drilling. Upon completion, boreholes were then backfilled up to the original ground surface with drill cuttings". Please clarify why 24-hour water levels were not measured, specifically, at Culvert #1. The borehole water levels are expected to coincide with the existing creek level for borings near the culverts. This is mentioned in the updated geotechnical report. 15. Narrative, Page 2, Section 3 "Laboratory Testing". Please clarify why there does not appear to be lab testing performed on soil samples below the Culvert #1 invert elevation. Given the anticipated amount of fill proposed to be placed over this culvert (approx. 20 to 25 feet according to the Storm Culvert Profile), this information may be useful in engineering analyses. We do not disagree with this statement. However, the undisturbed soils are expected to be very stiff to hard beneath most of the culvert invert and not very settlement sensitive. Where any soft soils are present, they are recommended for undercut. In addition, we have laboratory tests for similar soils on the site. 16. Narrative, Section 11 "Culverts and End Walls" a. Please provide discussion regarding proposed thickness of fill over Culvert #1 and resulting loading pressure on subgrade soils. This is provided in the updated geotechnical report. b. Please provide discussion regarding potential culvert settlement. This is provided in the updated geotechnical report. c. Please provide discussion regarding culvert bearing resistance. This is provided in the updated geotechnical report. d. Please refer to VDOT Road and Bridge Standards PB-1 (Installation of Box Culvert Bedding and Backfill — Method A) and VDOT Road and Bridge Specifications Section 302.03 (2) with regards to bedding and backfill recommendations. This is addressed and referenced in the updated geotechnical report. e. 111 Paragraph, second sentence states that the first crossing will consist of 60 x84 inch box culvert. The Storm Culvert Profiles show this culvert to be a 60 x 60-inch double box culvert. Please clarify (see comment #9). The corrected culvert information is described in the updated geotechnical report. 17. Narrative, Section 11 "Culverts and End Walls", 111 paragraph, fourth sentence states "Based on past experience and test borings in the proposed culvert vicinity, we anticipate undercutting of at least 4 to 6 feet of soft soils will be required to reach an acceptable, stiff subgrade for culvert and end wall construction". a. Based on review of the invert elevations provided on the storm culvert profile as well subsurface soil information provided on Boring Logs B-09 and B-10, there does not appear to be a need for an undercut of material. (See Comment #8). Please refer to our response for Item 12. b. If undercutting is not necessary and water is still anticipated to enter the culvert exploration, please provide recommended thickness of #57 aggregate to be capped with 4 inches of VDOT #25 or #25 aggregate. This information is provided in the updated geotechnical report. We have included copies of the plans for your review. If you have any questions or comments, please feel free to give me a call at 434.295.5624. Sincerely, Jonathan Showalter, PE Project Engineer