GM_04-18_Rehabilitate_Staircase_Road_WA_NPS_207(1).pdf

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

610 E. Fifth Street Vancouver, WA 98661

DATE: October 17, 2018

TO: Kirk Loftsgaarden Project Manager

FROM: Diann Morehouse Geotechnical Engineer

SUBJECT: Geotechnical Memorandum GM04-18 Final Geotechnical Recommendations Rehabilitate Staircase Road

WA NPS 207(1)

INTRODUCTION

This memorandum provides geotechnical information gathered during a site reconnaissance trip and final geotechnical recommendations for the proposed Rehabilitate Staircase Road project. The project stationing referenced in this memorandum is from 70% Plan Set, dated December 4, 2017. A project specific elevation datum is used for elevations provided in this memorandum.

PROEJCT DESCRIPTION

This project is located at the end of State Highway 119 on Staircase Road, approximately 15 road miles northwest of Hoodsport, Washington, Mason County, Olympic National Park.

Figures 1 and 2, shows the project location and vicinity maps, respectively. This project starts at the Olympic National Park and Olympic National Forest Boundary. The coordinates for the beginning of project are approximately 47.5056°, -123.3154° (WGS84). The project includes re-establishing a uniform road profile by installing a leveling course and apply an asphalt concrete overlay over the length of road, and pave the existing gravel surfaced trailhead access road and Overflow Parking area. The project also includes constructing a utility trench under the road from the beginning of the project to the Staircase Ranger Station.

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Figure 1: Location Map.

Staircase Road within the Park

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Figure 1: Project Location Map

Figure 2: Project Vicinity Map (Project shown in red)

GEOLOGY

Figure 3 shows an excerpt from Geologic Map of Washington – Northwest Quadrant (Dragovich, J.D., 2002). Surficial soil along the project alignment consists of Quarternary- Aged glacial outwash deposits. The glacial alpine outwash is described as stratified sand and gravel and locally contains silt and clay.

Underlying bedrock observed in outcropping rock is interpreted to be Lower-Middle Eocene- Aged Crescent Formation consisting of basalt flows, basaltic flow breccia, and volcaniclasitic conglomerate. The Crescent Formation is described to also contain interbeds of basaltic tuff, chert, red argillite, limestone, siltstone, dacite, and rhyolite. Rock strength field testing of grab samples indicates the rock is weak to strong rock (R2 to R4) with an approximate unconfined compressive strength ranging between 730 to 15,000 psi.

Figure 2: Excerpt of Geologic Map of Washington - Northwest Quadrant (Dragovich, J.D., et al, 2002)

Quarternary-Aged

Oligocene-Eocene-Aged

Lower-Middle Eocene - Aged

Eocene-Paleocene - Aged

SITE CONDITIONS

The general topography of the region consists of mountainous terrain of the Olympic Mountain Range. The road within the project generally traverses relatively flat terrain along the Skokomish River valley floor at an elevation between 700 and 800 feet with surrounding mountain peaks rising above 5000 feet.

The section of Staircase Road within the project is a paved road varying in width between 18 and 24 feet wide and over steepen embankment slopes of nearly 1V:1.25 in some areas. Cut slopes are also over steepen and showing signs for creep. The current pavement surface is chip seal. The road profile, through much of the project, is uneven due to differential settlement. Vertical deformations in the profile varies up to about 2.5 inches (Picture 1).

Arcuate pavement cracking is also exhibited in isolated areas (Picture 2).

The ditch line along the project is choked with vegetation and soil. Near Station 14+00 surface water from the slope above the road fills the ditch and flows across the road.

(Pictures 3 and 4).

Foreign material, such as metal, within the pavement surface was noted along the alignment.

Areas of relative uniformed settlement were also noted along the alignment (Picture 5). The embankment slope along the entire length of the project exhibits areas with large boulders, extending from the fill (Picture 6). Boulders up to 3 feet in diameter were observed. Areas of exposed bedrock is also located on both cut and fill slopes along the project alignment (Picture 7).

The Overflow Parking Area is currently gravel surfaced (Picture 8). The access road to the Overflow Parking area appears to be surfaced with a chip seal (Picture 9).

SUBSURFACE INVESTIGATION

On June 29, 2017, Western Federal Lands Highway Division (WFLHD) Materials Group conducted subsurface investigation using hand tools in Staircase Campground Overflow Parking Area consisting of two test pits. A memorandum discussing the investigation and test results was issued August 7, 2017 and is contained at the end of this memorandum.

Test pitsTP17-01 and TP17-02 extended to a depth of 12 inches and 18 inches, respectively.

Soil encountered in TP17-01 consists of well-graded gravel with sand and silt (GW-GM). Soil encountered in TP17-02 consists of well-graded gravel with sand (GW).

Based on field observations during site visit, soils within cuts are interpreted to be classify as sandy clay and clayey sand. These soils can be moisture sensitive.

DESIGN RECOMMENDATIONS

Deep Patch The road exhibits areas of settlement along Staircase Road. Many of the areas exhibit varying amounts of settlement across the entire width of the road while other areas are localized. The following are some possible reasons for roadway subsidence at various locations.

• Ditch or groundwater migrating under the roadway fill resulting in soil piping and loss of pavement structure support.

• River erosion undercutting the embankment slope resulting in loss of lateral support.

• The timber crib walls decomposed over time and the area was filled in with borrow.

Many of the areas exhibit pavement distress are in the left lane (outboard lane) and the outside shoulder is soft. It is interpreted groundwater is piping under the road is the general cause of subgrade failure and pavement distress.

In other areas, pavement distress takes the form of tension cracking that is predominantly arcuate or sinuous longitudinally along the road. This type of distress is usually indicative of slope creep and/or settlement of fill materials due to river undercutting the toe of the embankment slope.

Areas of uniform settlement, shown in Photo 6, is suspected to have organic material such as a log within the subgrade material.

Deep patch is recommended at locations that are currently exhibiting signs of poor subgrade support and slope instability. These locations are at the top of a relatively steep slope that is not supported directly on firm soils or bedrock. These areas are likely to have creeping slopes which may result in continuing cracking and settlement of the pavement on the outboard side without some form of mitigation. Table 1 shows deep patch locations.

The deep patches should be constructed to subexcavation depths of either 1.5 feet or 2.25 feet measured vertically below top of subgrade elevation, based on the interpreted severity of potential instability. Line the bottom and side of the subexcavation with Class 1 Type A, non-woven filter geotextile. Deep patch reinforcement should consist of layers of biaxial geogrid at 9-inch vertical spacing with the first reinforcement overlying the geotextile lining the bottom of the excavation. Deep patch sections 1.5 feet deep will have 3 layers of biaxial geogrid and deep patch 2.25 feet deep will have 4 layers. The biaxial geogrid should be lapped back 4 feet at the slope face, matching the existing slope. A thin layer of gravel should be placed between the lap and the overlying layer to prevent direct contact between adjacent geogrid layers. The slope face should be covered with a Type 5.B rolled erosion control product.

Reinforced Soil Slope (RSS) Table 1 shows a RSS is recommended at one location. The RSS should be constructed similarly to a Type 2 deep patch except to a subexcavation depth of 6 feet measured vertically below top of subgrade elevation and 18-inch vertical spacing. The RSS will require construction around a 24-inch pipe culvert. Where pipe culverts are placed within the reinforced zone construct as follows:

(a) If more than half the pipe cross section is above the geogrid reinforcement layer, then the geogrid should be trimmed along the length of the pipe.

(b) If more than half the pipe cross section is below the geogrid reinforcement layer, then the geogrid should be placed over the pipe as a continuous reinforcement layer.

Underdrain System An underdrain system should be installed at the back side of all deep patch and RSS locations. The underdrain system should consist of a 6-inch diameter perforated collector pipe in a 12-inch wide by 12-inch deep trench backfilled with granular backfill and lined with Class 1, Type A filter geotextile running the length of the deep patch. Non-perforated outlet pipes should be installed that drain across the road and daylight on the slope about every 100 feet along the deep patch and at all low points in the deep patch profile.

Utility Trench Utility trench is proposed for the entire length of this project. Due to the anticipated boulders and cobbles in the fill and the volume of groundwater expected for this area, migration of trench backfill is a concern. Install a Class 1, Type A, non-woven, separation- stabilization geotextile along the sides and bottom of the trench excavation. After backfilling and compacting the trench backfill material lap over the geotextile at the top of the subgrade prior to placing the base course material.

Table 1: Deep Patch and RSS Locations

CONSTRUCTION CONSIDERATIONS

Cobbles, boulders, and bedrock outcrops are visible on the embankment and cut slopes. It is interpreted fill under the road may include boulders and cobbles and bedrock may be shallow.

Expect cobbles, boulders, and bedrock will be encountered during excavation activities for deep patch, RSS, and trenching construction.

The groundwater locations are not known based on the type of subsurface investigations performed for the project. Groundwater may be present at the culvert locations during construction. The Contractor should be prepared to dewater for proper construction of the new culverts.

Onsite soils are expected to be moisture sensitive. The Contractor may experience problems with poor support of construction equipment on wet subgrade. The Contractor should be prepared and take steps to manage moisture sensitive subgrade soils, including but not limited to limiting the amount of excavation or subgrade open at one time and use of geogrids and geotextiles and granular materials for equipment support.

REFERENCES

Dragovich, J.D., Logan, R.L., Schasse, H.W., et al (2002) Geologic Map of Washington- Northwest Quadrant, GM-50 Washington Division of Geology and Earth Resources, https://ngmdb.usgs.gov/Prodesc/proddesc_68659.htm

Final Pavement Memorandum, USDOT FHWA WFLHD, Rehabilitate Staircase Road WA NPS 207(1), August 7, 2017.

https://ngmdb.usgs.gov/Prodesc/proddesc_68659.htm

CLOSING

Please contact Diann Morehouse at (360) 619-7609 or Diann.Morehouse@dot.gov with any questions regarding this memorandum.

INITIALS

CC: PM and CFT Members Geotechnical File

Attachments: Attachment 1 – Project Pictures Attachment 2 – Final Pavement Memo mailto:Diann.Morehouse@dot.gov

ATTACHMENT 1

Project Pictures

Picture 1: Differential settlement near Station 30+00

Picture 2: Arcuate shaped cracks in the pavement near Station 17+00.

Picture 3: Surface water flowing over the road near Station 14+00

Picture 4: Surface water from upslope near Station 14+00.

Picture 5: Pieces of metal within the pavement surface were noted at three different locations. Metal are within the red circles.

Picture 6: Areas of relatively uniform settlement were noted.

Picture 7: The embankment slope along the entire length of project exhibits areas with large boulders extending from the fill. Areas of exposed bedrock is also located on both the cut and fill slopes along Staircase Road

Picture 8: Looking east across Overflow Parking Area.

Picture 9: Looking south along the access road from the trailhead kiosk towards Staircase Road.

ATTACHMENT 2

Final Pavement Memorandum

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

TO: Kirk Loftsgaarden, PM Curtis Jorgenson, HDM Thinh Phan, Designer Diann Morehouse, Geotechnical Engineer

In Reply Refer to:

HFL-17

FROM:

Stephen Henry, Assistant Materials Engineer

DATE: August 7, 2017

SUBJECT: INFORMATION:

Final Structural Pavement Recommendation Rehabilitate Staircase Road

WA NPS OLYM 207(1)

Background This project includes asphalt concrete paving and pavement preservation techniques at three facilities.

Approximately 0.9 miles of Staircase road from the boundary of NPS land to the Staircase campground entry fee station is paved, but the pavement profile has become distorted and needs to be restored. The remainder of Staircase road beyond the entry fee station and the Staircase campground are paved and will be micro-surfaced as a pavement preservation technique. The overflow parking for the Staircase campground is currently aggregate surfaced and will be finished with asphalt concrete pavement. This memorandum provides the final pavement structural recommendations for Staircase Road prior to the entry fee station and the Staircase campground overflow parking lot.

Parking Lot Subsurface Investigation A subsurface investigation of the Staircase campground overflow parking lot consisting of 2 test pits was completed on June 29, 2017. Test pits were opened with a shovel and pick. Samples were collected and transported to Western Federal Lands Highway Division (WFLHD) in Vancouver, Washington. Samples of soil and rock were submitted to the WFLHD Materials Laboratory for testing.

Test pit photo logs and notes are attached to this memorandum as Appendix A.

The typical existing surfacing material is 4 inches of well-graded gravel with sand, AASHTO classification A-1-a. Typical subgrade materials encountered were well-graded gravel with silt and sand, AASHTO classification A-1-a. These materials will provide high strength and good drainage characteristics; the overall quality of existing material can be considered very good.

Test results are attached to this memorandum as Appendix B.

Recommended Pavement Structure - Parking Lot It is recommended to leave the existing parking lot material in place to function as a base layer for the asphalt concrete surface course. Due to the difficulty of finishing 6-inch minus material, it is highly recommended that any regrading of the parking lot not disturb more than 3-inches of existing material.

Specific traffic information is not available. A wide range of vehicles are expected. Traffic will be slow moving due to the parking lot environment. There are several locations in the parking lot that will have a tight turn radius. Slow moving, tight turning traffic will accelerate pavement distress types normally associated with traffic loading, specifically rutting and fatigue cracking. Based on these considerations, the following is recommended for the pavement structure:

3 inches – Asphalt Concrete Pavement, Type 1 (Item 40301-0100, estimated at 1.94 tons/cuyd)

Staircase Road Pavement Evaluation On April 12, 2017 a pavement evaluation was conducted by Steve Henry, Assistant Materials Engineer on Staircase Road from the beginning of the project at STA 10+00 to the entry fee station at the campground entrance STA 56+00 (approximately 0.9 miles). All stationing in this memo is based on the preliminary 30% plan set. This review was conducted with the purpose of evaluating the general pavement condition and identifying any locations where corrective action would be required to address pavement distress.

The review consisted of a visual evaluation of the pavement condition. The evaluation was accomplished by traversing the project on foot and assessing the pavement condition. Photos of the pavement were obtained to document the current conditions and show the type and severity of the pavement distress.

Staircase Road General Condition The overall condition of the Staircase Road pavement structure is very good. The current surface is a chip seal. Distress was limited to isolated cracking and edge raveling. The cracking did not appear to be caused by a failure of the pavement structure itself, rather the underlying subgrade appears to have settled. The primary cause of edge raveling appeared to be loss of subgrade support along the pavement edge.

The road profile was noticeably uneven along the entire length of the road. The severity of the unevenness varied, with 1/2-inch differences in profile height being common up to a 2-inch difference in an extreme case. This unevenness appeared to be caused by differential settlement of the underlying subgrade.

Large amounts of standing water were observed along the cut side of the road. Many ditches appeared choked with vegetation and debris.

Examples of the road condition and distress types present on the project are presented below, this list is not meant to be exhaustive of all distress on the project, but rather instructive as to the most common types of distress encountered.

Current Road Surface – Chip Seal

Isolated Cracking

Edge Raveling

Standing Water in Ditch

Recommended Corrective Actions – Staircase Road To improve the end-user experience when driving Staircase Road, a uniform road profile should be re-established. As the existing pavement structure is in good repair it is recommended that the existing pavement be left in place, and an asphalt concrete overlay placed atop it. Due to the large variance in the existing profile, it is unlikely that a uniform profile could be established in a single overlay lift. Therefore, prior to overlay placement it is recommended that a leveling course be placed to reduce existing unevenness. It is estimated that approximately 1/2-inch of leveling course over 50% of the project area will be sufficient. The following bid items are recommended for this work:

Asphalt Concrete Pavement, Type 1, Wedge and Leveling Course (Item 40303-0100, estimated at 1.94 tons/cuyd)

2 inches – Asphalt Concrete Pavement, Type 1 (Item 40301-0100, estimated at 1.94 tons/cuyd)

Specifications Materials will provide any required SCRs.

Should new information develop that impacts the information and assumptions made in this recommendation, the pavement design should be reexamined.

cc: Materials/Pavement File

Appendix A: Test Pits

Two test pits were opened at the following locations in the overflow parking lot:

TP17-01 was dug to a depth of approximately 1.0 feet. TP17-02 was dug to a depth of approximately

1.5 feet. The top 4-inches of both test pits contained a well-graded, angular, gravel material, approximately 1-inch minus in size. In TP17-01 this gravel layer sat atop a well-graded subgrade consisting of 2-inch minus rounded aggregate in a matrix of sand and silt. Field tests did not indicate plasticity. This layer extended to the bottom of the test pit. In TP17-02 the gravel layer sat atop a well-graded fill material consisting of 6-inch minus angular cobbles, aggregates and sand. This layer also extended to the bottom of the test pit.

TP17-01, Debris Cleared

TP17-02, Debris Cleared

TP17-01, Bottom of Gravel Layer, 4-inches

TP 17-02, Bottom of Gravel Layer, 4-inches

TP17-01, Bottom of Test Pit, 12-inches

TP17-02, Bottom of Test Pit, 18-inches

Appendix B: Test Results