GM5124 - Final Memo 67th Place Public Enhancement Revised.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: December 02, 2024

TO: Sean Hayter Project Manager

FROM: Leah Wilmot Geotechnical Engineer

SUBJECT: Geotechnical Memo 5124 Final Geotechnical Recommendations - Revised 67th Place Public Enhancement to Willapa NWR

WA FLAP PACIFI 12800(2)

Pacific County, WA

INTRODUCTION

This memorandum has been revised to include additional options for temporary diversion.

This memorandum provides geotechnical investigation results, design, and construction recommendations for the 67th Place Public Enhancement to Willapa National Wildlife Refuge (WNWR) Project being performed for Pacific County, Washington. The project stationing referenced in this memo is from 70% Design Set, dated May of 2024.

PROJECT DESCRIPTION

The geotechnical scope of work for this project included review of existing published geologic and geotechnical literature for this area combined with a site reconnaissance and a subsurface investigation program consisting of dynamic cone penetrometer tests (DCP) along the proposed alignment. The DCP’s were completed by Western Federal Lands Highway Division

(WFL).

This memorandum provides geotechnical recommendations for subgrade improvements, shoulder construction, temporary cofferdam use, and cut and fill slope angles.

This memorandum supersedes all other previous memorandums for this project.

Project Description

The project is located on the Long Beach Peninsula in southwest Washington along 67th Place in Pacific County, Washington as shown in Figure 1. This road serves as sole access to the

Riekkola Unit of the WNWR and is designated as a tsunami evacuation route leading to a designated assembly area for the surrounding communities of Long Beach and Ilwaco, Washington.

Figure 1: Project Location

The project starts at the west end of the 67th Place at stationing 12+25 (approximate milepost 1.2) and ends on the east end of 67th Place at stationing 18+30 (approximate milepost 1.42) as shown in Figure 2. The existing travel way is 16 feet wide at its narrowest with no shoulders.

The project consists of widening 605 feet of the existing roadway to 10-foot travel lanes with 1-foot shoulders and constructing ditches in select locations. Roadway widening will involve subgrade improvements, fills to construct the shoulders, and cuts to place ditches along the roadway. One culvert will be replaced as part of this project. Temporary cofferdams are expected to be used along the shoulder to hold a temporary traffic lane that will allow traffic through the project site.

Figure 2: Project Vicinity Map

GEOLOGY

The general area lies along the Willapa Hills geologic province of Washington and is in an area with several major estuaries and adjacent highlands that reach elevations of 2000 feet above mean sea level (MSL). Natural bedrock exposures in the wider areas are typically restricted to stream courses along larger drainages but were not observed near the project (Western Federal Lands, 2019). The elevation at the project location is approximately 10 feet above mean sea level (MSL).

According to the Geologic map of the Cape Disappointment-Naselle River area, Pacific and Wahkiakum Counties, Washington (Wells, R.E, 1989), the site is mapped as “Qf” for the approximate first third of the project and “Qm” for the last two thirds of the project as shown in Figure 3.

The “Qf” unit is defined as fluvial and estuarine deposits of Holocene-age (10,000 years to present) and is described as unconsolidated clay, silt, sand, and gravel alluvium deposited along rivers and streams and includes stabilized tidal flat deposits.

The “Qm” unit is defined as the Sand of Mountain Springs of Pleistocene-age (2.5 million to 11,000 years ago) and is described as semi-consolidated, laminated to massive, fine to coarse sand, commonly with yellow-orange to red iron oxide staining and is characterized by planar laminations, broad gently dipping cross laminations, trough cross laminations, and localized channel fills. This unit may represent remains of an older barrier beach and dune field.

Figure 3: Geologic Map of the Project Vicinity

A resource report was compiled from the Web Soil Survey Map (USDA, 2024) for the project vicinity. Soils are mapped as Ilwaco silt loam and Ocosta silty clay loam. The Ilwaco silt loam unit consist of residuum soils weathered from sandstone. The Ocosta silty clay loam unit consist of clayey alluvium. The Unified Soil Classifications for these deposits include ML, MH, CL, CH, OL, and OH. These soils have a high rating of corrosion to steel, and a moderate to high rating of corrosion to concrete, respectively, according to the Soil Survey.

Geologic Hazards

The Washington Geologic Information Portal website (2024) was used to screen the project vicinity for geologic hazards. The Washington Geologic Information Portal maps show the following geologic hazards:

Table 1. Geologic Hazards

Geologic Hazard Mapping Description

Earthquake Hazards:

- Active Faults

Nearest active fault is the Willapa Bay fault zone approximately 5.25 miles northeast.

Based on the distance to the site, the risk of surface rupture is considered low. Cascadia Subduction

Zone - approximately 18 miles west.

- Liquefaction "Moderate to High" The risk is considered high based on the mapping.

- Expected earthquake shaking

“Very Strong” to “Severe” mapping over the entire vicinity.

Very strong ground motions expected.

Tsunami Hazard Within Tsunami hazard area Risk is considered high.

Volcanic Hazard No areas mapped within project vicinity.

Risk is considered low.

SITE CONDITIONS

The project is located along 67th Place, running west to east and is bound on each side by private landowners. The western half of the alignment runs through gently rolling hills, while the eastern half is generally flat topography.

The slopes are typically well vegetated with grasses and deciduous trees, while the flatter section is covered in thick grassy matting with ponding water typically just below the top of the existing roadway throughout the year.

The 67th Place as it runs through the project is narrow with an oiled gravel or chip sealed surface.

The road shows a high degree of distress and disintegration, as evident in the form of large potholes that in some areas extend the full width of the road (Photographs A-1, A-3, and A-4).

It is our understanding that the roadway surface is a result of several chip seals rather than from a formal hot mix asphalt pavement structure. Photographs of the site are provided in Appendix A.

The existing embankment is constructed of fill from an unknown source, which appears to have been in place since the time of original road construction. During our site visit on December 19th, 2023, a local property owner informed us that he had encountered buried logs while constructing a fence along the east side of the alignment. It is our understanding that the current roadway was constructed on top of a “corduroy road” section consisting of logs placed over the soft subgrade for roadway support.

Average Temperatures and Precipitation

The project site is a wet and rainy climate with precipitation expected throughout the year.

Table 2 shows the average maximum and minimum temperatures, average monthly precipitations, and the average monthly snowfall data for the period of 1967 to 2016 for the Long Beach EXP STN, Washington (454748) weather station (Western Region Climate Center, 2024).

Table 2: Climate Data Summary

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual

Average Max.

Temp. (F)

48.8 51.1 52.9 55.3 59.4 62.5 65.5 66.5 66.6 60.5 53.3 48.8 57.6

Average Min.

Temp. (F) 36 36.5 38.2 40.5 45 49.2 51.8 51.6 47.8 42.7 39.1 36.1 42.9

Average Total

Precip.

(in.)

11.57 8.69 8.87 5.99 3.83 2.93 1.56 1.81 3.25 7.04 11.5 12.58 79.61

Average Total

Snowfall (in.)

0.4 0.3 0 0 0 0 0 0 0 0 0 0.3 1.1

Average Snow Depth (in.)

0 0 0 0 0 0 0 0 0 0 0 0 0

Note: Period of Record 1967 to 2016

SUBSURFACE CONDITIONS

A subsurface exploration was conducted for the project. The exploration included using a hand-operated, 17.6-pound, pavement DCP starting at approximate stationing 13+80 on the southside of the roadway to 17+78 for a total of five DCP’s. The DCP testing was performed in general accordance with ASTM D6951. The approximate DCP locations are shown in Figure 4 and Table 3. The DCP was advance on average to 3.2 feet below ground surface (bgs).

Table 3. Approximate DCP Locations

DCP

Coordinates

Latitude Longitude

DCP23-01 46.357525 -124.011506

DCP23-02 46.357539 -124.011089

DCP23-03 46.357678 -124.010731

DCP23-04 46.357611 -124.010239

DCP23-05 46.357747 -124.009958

Notes:

World Geodetic System (WGS) 84 datum coordinates. Coordinates are approximate.

The first DCP (DCP23-01) was attempted within the roadway prism, but we were unable to drill through the pavement to drive the DCP. This location was abandoned and does not have any data. At the location of DCP23-02, we were unable to drive the DCP deeper than 2.5 inches into the road aggregate base course. The base material consisted of gravels at this location and the DCP was unable to be driven through this material. The location of DCP23-02 was moved to the left shoulder of the roadway to avoid the road base gravel materials.

No samples were collected during the exploration for testing.

Our observations and the results of the DCP tests suggest that the in-situ subgrade conditions are very poor to poor.

Groundwater was observed to be at the surface during our site visit on December 19, 2023. It is our understanding the groundwater is at the ground surface year-round (Photographs A-2 and A-5).

Figure 4: DCP Locations

ANALYSIS

The California bearing ratio (CBR) was calculated using the DCP field data, shown in Table 3 below. There is a down station trend in CBR values seen in the data. The CBR values range between 0.8 (DCP23-05) to 12.5 (DCP23-02), indicating clayey subgrade soils. This data suggests that the subgrade conditions are trending from a poor to very poor condition down station.

Table 4. Approximate Station and Offset, DCP Results and Calculated CBR Values

DCP

Depth Driven

Offset (ft)* Approx.

Stationing

CBR

DCP23-02 2.4 Right (15.5) 14+82 5.7 -12.5

DCP23-03 4.9 Left (15.1) 15+80 1.3 to 4.9

DCP23-04 2.3 Right (23.5) 17+00 1.2 to 1.8

DCP23-05 3.3 Left (18) 18+78 0.8 to 2.0 Notes:

* Offset measured from assumed center line and alignment from west to east.

DCP field data and graphs plotting the CBR value versus depth are presented in Appendix B.

The Salem Tool Companies Corp Style Dual Mass Dynamic Cone Penetrometer – Application and Maintenance and the DCP Excel Spreadsheet that accompanies the manual was used to process the field data and calculate and plot the CBR values versus depth shown in Appendix B.

DISCUSSION AND RECOMMENDATIONS

Based on our review of geologic and geotechnical publications and our limited subsurface exploration, the above information was analyzed to determine design recommendations for subgrade improvements, shoulder construction temporary cofferdam use, and cut and fill slopes angles. The following sections provide our final recommendations for roadway design.

Subgrade Improvements

In general, we recommend taking advantage of the existing, apparently well performing corduroy road for subgrade stabilization by leaving it in place. Removal of the corduroy road would result in a greater area of disturbance, additional costs for excavation and removal, as well as construction of a replacement stabilization section. Since the estuary water level appears to remain high throughout the year, the logs are likely in relatively good condition since they do not deteriorate when submerged and not exposed to oxygen. Since we were not able to verify corduroy section through our DCP explorations, there is some risk of poor log conditions under the existing roadway and future settlement. However, the use of geocells as explained herein, should provide additional strength to bridge over settling areas and mitigate future differential settlement concerns.

With this in mind, we recommend that a cellular confinement system, or geocell, with 8-inch-high cells be placed over the existing roadway after subgrade surface preparation. We recommend that the “corduroy road” section not be disturbed and remain in place for the proposed construction.

The existing roadway material should be excavated to the required depth and a separation-stabilization geotextile, class 1, type D (woven) meeting Section 714.01 should be placed between the subgrade and the geocell system. The geocell system meeting Sections 713.07 and Section 629.03 can be placed directly on the geotextile. The geocell system should then be filled with crushed aggregate conforming to Sections 703.06 and 302 to three inches above the top of the geocell system and compacted using vibratory equipment according to the manufacturer’s recommendation, as shown in Figure 5 below. All specifications presented refer to the FP-14 Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects as modified by the Special Contract Requirements (SCR)..

Shoulder Construction

Shoulder widening is expected along the entire length of the project and the fill height varies.

Along the right side of the alignment the fill height required ranges between 0.3 and 3.4 feet with an average of 1.4 feet, while the left side of the alignment ranges between 0.9 to 2.1 feet with an average of 1.6 feet.

It is our understanding that the roadway edges will need to be steeply angled to minimize the footprint within the existing right-of-way. We recommend using a 3-foot wide geocell system with 4- to 8-inch-high cells where each geocell layer will be stepped at an overall angle of 2V:1H (63 degree batter). For example, an 8-inch thick geocell must be placed 4 inches away from the underlying layer.

We recommend placing a separation-stabilization geotextile, class 1, type D (non-woven) meeting Section 714.01 on top of the existing subgrade. Mechanically compacted foundation fill between 2 inches and 6 inches in diameter (i.e., quarry spalls) should be placed on top of the separation-stabilization geotextile and bucket tamped in 1-foot lifts. to create a level subgrade pad to build upon and to bridge the existing subgrade and shoulder material. If the the “corduroy road” section is encountered, then the subgrade can be built on top of the logs.

After this subgrade preparation, we recommend using a 3-foot wide geocell system with 4- to 8-inch-high cells filled with crushed aggregate meeting Section 703.06 as shown in Figure 5 below.

Figure 5: Cellular Confinement System Detail

Temporary Diversion

A temporary diversion will be required to construct the temporary lane through the project site.

The temporary diversion may consist of a berm or shoring depending on the Contractor’s means and methods. It will be the responsibility of the Contractor to determine the correct type of temporary diversion to perform the work. If the Contractor elects to use temporary shoring, the below information is provided to design temporary shoring.

We analyzed the above information collected during the site visit and the desktop study to evaluate the height and embedment depth of the temporary shoring using ShoringSuite Software by CivilTech Software. The reports and graphs from this analysis can be found in Appendix C.

Estimated wall height is four feet assuming the use of sheet piles with 8.54 feet of embedment, for a total length of 12.54 feet of pile. Table 5 provides the assumed soil parameters. It will be the contractors responsibility to confirm and design the final temporary shoring.

Table 5: Shoring Soil Parameters

Soil Type Unit Weight Phi Cohesion Assumed Nspt Assumed Soil Layer Depth (ft.)

Equivalent Clay 119.2 0 0.6 5 0 and below

Equivalent Clay 131.6 0 1.8 14 4 and below

Gravel 137.6 38.95 0 40 0 to 4

Cut Slopes

Cut slope areas are expected along the project alignment. Cuts slopes are anticipated to be approximately 5 feet or less. We recommended a cut slope inclination of 1V:1H along the alignment in soil. Anticipated soil conditions at cut slope locations include silty clays. Exceptions to these recommendations are possible with the approval of the project Geotechnical Engineer if field conditions should warrant changes.

Corrosion Considerations

The site is surrounded by salty or brackish water under tidal influence, as well as fine-grained soils that are mapped as having a high corrosion rating. Therefore, culverts and other features should be designed for a highly corrosive environment, which may include the use of plastic materials, aluminum pipe, or special coatings. Galvanized steel and concrete pipes is not recommended in these conditions.

CONSTRUCTION CONSIDERATIONS

No subsurface explorations were performed for this study. However, based on the information above, excavations will likely encounter soft silty clays. The majority of the “corduroy road” section will remain in place and should not be encountered during subexcavation. However, if encountered, we recommended to not disturb and leave the “corduroy road” section in place and work around the logs, or incorporate them into the subgrade stabilization section. If this is not possible, we recommend removing only sections of the “corduroy road” that are needed to complete the contract work.

Between stationing 14+29.99 and 18+37.00, where shoulder construction will occur, we anticipate the groundwater levels to be above the ground surface and near the roadway elevation. A temporary diversion and dewatering should be anticipated. Contractor should also expect organics to be encountered while excavating within the above stationing.

Excavation

We anticipate the majority of the roadway materials from the excavations will be wet or contain a high fines content and will not be suitable for reuse and will need to be wasted from the site.

At the preparation time of this memorandum, a suitable waste site has not been provided or identified by Pacific County, Washington. If a waste site is not identified at the time of award, it should be the responsibility of the contractor to identify and procure a legal waste site in accordance with the contract terms.

Material and Aggregate Sources

Imported fill materials are planned for crushed aggregate and rock mulch, roadway aggregates and other materials. At the preparation time of this memorandum, there is no Government provided material source for this project. It is the Contractor’s responsibility to locate an approved material source from an available commercial or private source for all construction materials that meet the requirements of the contract.

If suitable soils are encountered and the Contractor should desire to use the onsite materials, it will be the Contractor’s responsibility to ensure the materials are processed and tested to meet the contract requirements.

LIMITATIONS

This memorandum was prepared to provide geotechnical recommendations for the design and construction of 67th Place Public Enhancement to Willapa National Wildlife Refuge (WNWR) Project being performed for Pacific County, Washington. Professional judgments and recommendations are presented in this memorandum. They are based on evaluation of the technical information gathered and on the Geotechnical Team’s general experience with subsurface conditions in the area. The observed water levels and/or conditions may vary considerably with time, according to the climate, rainfall, and other factors and are otherwise dependent on the duration of, and methods used in, and interpretations made form the subsurface investigation program.

If, during construction, soil conditions are encountered that vary from those discussed in this memorandum, or if project stationing, and/or configurations change, the WFL Geotechnical Team should be notified immediately to evaluate what effects, if any, the changes have on the recommendations contained in this memorandum. The recommendations presented in this memorandum are applicable only to this specific site. These data are not to be used for other purposes.

REFERENCES

Salem Tool Company, Corp Style Dual Mass Dynamic Cone Penetrometer – Application and Maintenance.

United States Department of Agriculture, Web Soil Survey, accessed January 2024, https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx.

Washington State Department of Natural Resources, accessed January 2024, https://www.dnr.wa.gov/programs-and-services/geology/geologic-hazards/geologic-hazard-maps#active-faults-and-earthquakes-in-washington-state.

Wells, Ray E., Geologic Map of the Cape Disappointment-Naselle River Area, Pacific and Wahkiakum Counties, Washington; U.S. Geological Survey; Map I-1832; 1989.

Western Federal Lands (WFL), 2019, GM 12-19, Final Geotechnical and Construction Recommendations, Public Access Enhancement to Willapa National Wildlife Refuge, prepared by WFL Geotechnical Section, December 2019.

Western Region Climate Center, accessed June 2024, https://wrcc.dri.edu/cgi-bin/cliMAIN.pl?wa4748.

CLOSING

Please contact Leah Wilmot at (360) 619-7697 or Leah.Wilmot@dot.gov with any questions regarding this memorandum.

LW

CC: Misbah Afshari, Highway Designer

Attachments: Appendix A: Photographs Appendix B: DCP Results and CBR Values Appendix B: Shoring Analysis

APPENDIX

Photograph A - 1: Beginning of project looking north. High severity patching, high severity potholing and high severity alligator cracking. Taken December 02, 2022.

Photograph A - 2: Looking west near end of the project. North side of the roadway with standing water near the shoulder elevation. Taken August 12, 2023.

Standing Water

Photograph A - 3: Looking West. Raveling and high severity potholing. Taken August 12, 2023.

Photograph A - 4: Looking East. Raveling and moderate to high severity potholing along center of the project alignment. Taken August 12, 2023.

Photograph A - 5: Looking east. Standing water to the shoulder elevation on the north side of the roadway. Taken August 12, 2023.

Standing Water

DCP Results and CBR Values

DCP TEST DATA

File Name:

Project: WA FLAP PACIFIC 12800(2) Date: 19-Dec-23 Location: DCP23-02 Soil Type(s): Silts and Clays

No. of Accumulative Type of Blows Penetration Hammer

(mm)

0 0 1

1 27 1

2 55 1

4 86 1

4 113 1

3 148 1

2 174 1

2 200 1

2 241 1

2 275 1

3 300 1

3 333 1

3 362 1

4 391 1

2 418 1

2 451 1

2 491 1

2 530 1

1 561 1

1 594 1

1 626 1

2 663 1

3 699 1

1 725 1

0.1 1.0 10.0 100.0

0.1 1.0 10.0 100.0

D E

P T

H in

CBR

D E

P T

H m m

0 1000 2000 3000 4000 5000 6000

D E

P T

H in

BEARING CAPACITY, psf

Based on approximate interrelationships of CBR and Bearing values (Design of Concrete Airport Pavement, Portland

Cement Association, page 8, 1955)

10.1 lbs.

17.6 lbs.

Both hammers used

Soil Type

CH

CL

All other soils

Hammer

Project: WA FLAP PACIFIC 12800(2) Date: 19-Dec-23 Location: DCP23-03 Soil Type(s): Type in the soil type

No. of Accumulative Type of Blows Penetration Hammer

(mm)

0 420 1

1 560 1

1 660 1

2 739 1

1 788 1

1 847 1

1 912 1

1 975 1

1 1031 1

1 1081 1

1 1127 1

1 1174 1

1 1221 1

1 1257 1

1 1391 1

1 1329 1

1 1365 1

1 1400 1

1 1441 1

1 1482 1

0.1 1.0 10.0 100.0

0.1 1.0 10.0 100.0

D E

P T

H in

CBR

D E

P T

H m m

-12000 -10000 -8000 -6000 -4000 -2000 0 2000 4000

D E

P T

H in

BEARING CAPACITY, psf

Based on approximate interrelationships of CBR and Bearing values (Design of Concrete Airport Pavement, Portland

Cement Association, page 8, 1955)

10.1 lbs.

17.6 lbs.

Both hammers used

Soil Type

CH

CL

Project: WA FLAP PACIFIC 12800(2) Date: 19-Dec-23 Location: DCP23-04 Soil Type(s): Type in the soil type

No. of Accumulative Type of Blows Penetration Hammer

(mm)

0 0 1

0 609 1

1 704 1

1 792 1

1 884 1

1 974 1

1 1114 1

1 1134 1

1 1214 1

1 1294 1

0.1 1.0 10.0 100.0

0.1 1.0 10.0 100.0

D E

P T

H in

CBR

D E

P T

H m m

-12000 -10000 -8000 -6000 -4000 -2000 0 2000 4000

D E

P T

H in

BEARING CAPACITY, psf

Based on approximate interrelationships of CBR and Bearing values (Design of Concrete Airport Pavement, Portland

Cement Association, page 8, 1955)

10.1 lbs.

17.6 lbs.

Both hammers used

Soil Type

CH

CL

Project: WA FLAP PACIFIC 12800(2) Date: 19-Dec-23 Location: DCP23-05 Soil Type(s): Type in the soil type

No. of Accumulative Type of Blows Penetration Hammer

(mm)

0 0 1

1 85 1

1 225 1

1 420 1

1 565 1

1 665 1

1 765 1

1 870 1

1 990 1

0.1 1.0 10.0 100.0

0.1 1.0 10.0 100.0

D E

P T

H in

CBR

D E

P T

H m m

0 200 400 600 800 1000 1200

D E

P T

H in

BEARING CAPACITY, psf

Based on approximate interrelationships of CBR and Bearing values (Design of Concrete Airport Pavement, Portland

Cement Association, page 8, 1955)

10.1 lbs.

17.6 lbs.

Both hammers used

Soil Type

CH

CL