GM 28-21_Grand Loop Road - Old Faithful to West Thumb_Revised Final Geotechnical Recommendations .pdf

158377846

M E M O R A N D U M Western Federal Lands Highway Division

610 E. Fifth Street Vancouver, WA 98661

DATE: July 23, 2021

TO: Nathan Jones Project Manager

FROM: Robert Kraig Geotechnical Engineer

SUBJECT: Geotechnical Memo 28-21 REVISED Final Geotechnical Recommendations Grand Loop Road - Old Faithful to West Thumb

WY NPS YELL 10(23)

Yellowstone National Park

INTRODUCTION

This memorandum provides updated final recommendations from those provided in Geotechnical Memorandum GM 08-15, Final Geotechnical Recommendations, WY NPS YELL 10(23), West Thumb to Old Faithful, dated March 17, 2015. The recommendations appearing in this memorandum supersede those appearing in GM 08-15 where substantive differences exist between the two memorandums. The subject project was developed to 90 percent design completion in 2017 and then shelved before being picked back up in 2021 to complete the design. The recommendations appearing herein are provided to the project Design Team for project design completion and to document the revised final geotechnical recommendations.

These recommendations resulted from the review of previous project documents, reevaluation of project needs after being shelved for several years, discussions between the WFL Design Team and Agency Partners, and incorporating the results from the recent Plan-in-Hand (PIH) site review conducted in June 2021. During the PIH site review the sites were evaluated for possible changes in condition and to verify/modify the repair limits. During this review several repair locations were added to the project. Also observed and noted during the site visit were several locations where ditch reconditioning may be beneficial to the adjacent roadway subgrade.

DISCUSSION AND RECOMMENDATIONS

Repair at 3097+82 to 3099+22 During the 2021 PIH site review the proposed repair at 3097+82 to 3099+22 was noted to be adjacent to a ditch area that had standing water and grasses, as can be seen in the photo below. There is severe rutting in the road adjacent to the ditch, thus indicating weak subgrade conditions. We consider this site to rank among the worst observed during the recent PIH site review.

The National Park Service (NPS) has informed us that the grasses in the ditch appear to be hydrophilic and thus require the ditch area to be designated as a wetland. The project environmental documents restrict permanent impacts to wetlands, which precludes work in this ditch. The site is located over relatively flat ground on a shallow fill with poor drainage even though there is a culvert located at the end of the section. The pullout located in the left of the photo was also constructed over a shallow fill offering limited ability to drain the subgrade to that side.

Approximately Station 3097+82 looking ahead

Pullout

Standing water and hydrophilic grasses

Subexcavation Types Four subexcavation types were developed for the project. The designs were reassessed based on the current site conditions and project requirements, with only slight modifications having been made to provide design clarity and to improve constructability. The final revised full-width subexcavation recommendations are provided in the Attachment. Note that some of the subexcavation locations and types may require full-width as others may require half-width construction, constructed left of centerline or right of centerline, depending on field conditions.

Refer to Table 1 for design width requirements at each planned repair site. Note also that the proposed repair at 3097+82 to 3099+22 (discussed above) is a Type 1 Subexcavation and that a Type 1 Subexcavation is daylighted for drainage. The previous recommendation at this site was for a Type 2 Subexcavation; however, it would not be possible for the Type 2 subexcavation to collect and carry the ground water away from the source (i.e., adjacent to the ditch). It is thought to be equally unlikely that a Type 3 Subexcavation will be effective given the flat terrain, shallow fill, and the difficulty in constructing sufficient slope into the outlet pipe for effective drainage to occur. Given these difficulties, we anticipate that this repair site will require field adjustments for fit. Such adjustment may require reducing the depth of the repair to achieve daylighting to the left of the turnout. Note that the repair at this site will require it to be constructed full-width, which will include the pullout area.

Revised Final Subexcavation Recommendations Updated subex types and limits are provided in Table 1. Table 1 contains final recommended Station Limits, Length, Subex Type, Width, Daylight Side, and Outlet Side.

Table 1: Revised Final Subexcavation Limits Station Length Type Width Daylight

Side Outlet Side Start End

3097+82 3099+22 140 1 Full LT NA 91+45 96+20 475 3 Full NA RT 99+40 102+25 285 5 Full Both NA

116+90 118+30 140 2 Full NA LT 177+95 179+10 115 3 Full NA LT 185+85 187+30 145 2 Full NA RT 197+10 200+55 345 2 Full NA RT 202+70 203+60 90 1 Full RT NA

204+70 206+05 135 1 RT RT NA

206+70 207+00 30 1 RT RT NA

240+80 242+30 150 3 Full NA RT 285+25 287+65 240 3 Full NA RT

Table 1: Revised Final Subexcavation Limits (cont.)

290+35 292+00 165 2 Full NA LT

296+10 297+40 130 1 LT LT NA

297+40 298+65 125 1 Full LT NA

298+65 302+50 385 1 LT LT NA

347+80 350+15 235 2 Full NA RT 362+80 368+55 575 2 Full NA RT 385+50 388+90 340 2 Full NA RT 403+15 405+25 210 2 Full NA RT 414+05 415+35 130 2 Full NA RT 416+50 418+80 230 2 Full NA RT 419+90 421+50 160 2 Full NA RT

450+60 452+30 170 2 RT NA RT

511+70 513+20 150 3 Full NA RT

734+75 736+25 150 2 RT NA RT

783+50 787+05 355 2 Full NA RT

1074+75 1075+25 50 5 Full Both NA 1075+95 1078+50 255 2 Full NA RT 9213+85 9219+00 515 2 Full NA RT

Proposed Areas for Ditch Reconditioning During the site visit we noticed several areas where the ditches have filled with material that had sloughed or eroded off the slopes or had filled-in with other debris or sediments. It is our opinion that these locations would benefit from ditch reconditioning. The proposed areas are listed in Table 2. Note that the limits should only be considered as approximate as the limits were obtained during a project drive-through and that field adjustments may be necessary.

Table 2: Proposed Ditch Reconditioning Areas Station (approx.) Length Side

Start End

97+00 101+50 450 LT

160+00 164+00 400 LT

363+10 370+00 690 LT

414+00 422+00 800 LT

554+00 555+50 150 LT

600+50 603+50 300 LT

682+00 682+50 50 LT

CLOSING

Please contact Robert Kraig at (360) 619-7699 or robert.kraig@dot.gov with any questions regarding this memorandum.

RK

CC: Nathan Jones, Project Manager Ben Vincent, Highway Design Manager Katie Alexander, Designer

Erin Chipps, Environmental Protection Specialist Megan Chatfield, Materials Engineer Charles Dissen, Construction Operations Engineer Katie Carlos, Safety Engineer Jim Neighorn, Hydraulics Engineer Eben Babb, Designer Rafael Castanon, Project Engineer Douglas A. Anderson, Geoteam Functional Manager

Geotechnical File

Attachments: Final Subexcavation Typical Details

(Intentionally blank)

Type 1 Subexcavation Typical Detail

Type 2 Subexcavation Typical Detail

Type 3 Subexcavation Typical Detail

Attachment 1 of 2

Type 5 Subexcavation Typical Detail

Type 5 Subexcavation Typical Detail A and B

Attachment 2 of 2