GM03-16_Spruce_RR_Trail_Segment_C_WA_NPS_OLYM_2015(4)__Geotech_Recomm_8Jan2016.pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

In Reply Refer To: HFL-17

TO: Kirk Loftsgaarden, P.E.

Project Manager

FROM: Diann Morehouse, P.E.

Geotechnical Engineer

DATE: January 8, 2016

SUBJECT: Intermediate Geotechnical Recommendations Spruce Railroad Trail Segment C

WA NPS OLYM 2015(4)

Geotechnical Memorandum: GM03-16

This memorandum provides geotechnical recommendations for the Spruce Railroad Trail, Segment C project located in Olympic National Park, Clallam County, Washington. Location and vicinity maps are shown in Figures 1 and 2 contained in the attachment. These recommendations are based on the plan set provided by Kirk Loftsgaarden on January 4, 2016 and is shown in Figure 3 contained in the attachment. At the time of the field review, stationing was not set. A recreational grade Global Positioning System (GPS) was used to identify sites.

Referenced stationing within this memo is approximate.

Scope of Project

This project extends from the southern end of Spruce Railroad Trail, Segment D, at project station 27+50 (BOP) to the south side of the east (1st) tunnel at project Station 56+85 (EOP). The project involves reconstruction of the existing variable width trail to a 13-foot wide aggregate surfaced multi-use trail. The reconstruction will include horizontal and vertical alignment improvements, new fill slopes, drainage improvements, and spot stabilization at select locations.

This memo will cover geotechnical recommendations for the trail between BOP and Station 48+50 and Station 55+50 and EOP. Others will provide geotechnical discussions and recommendations for work inside the tunnel, portals, and cut slopes adjacent to the tunnel entrances in a separate document.

Geotechnical Memorandum GM 03-16 Page 2 January 2016

Spruce Railroad Grade

The alignment of this project will be constructed above the Spruce Production Division Railroad No. 1 railroad grade. The purpose for the railroad was to transport Sitka spruce logs for WWI airplanes and was constructed in 1918 through a government contract. The east tunnel and west tunnel were known as McFee and Daley-Rankin Tunnels, respectively. (Magnuson, 2007)

Site Geology

The Olympic Mountains are a mostly Tertiary-aged subduction complex comprising underplated deep-marine siliciclastic rocks and the overlying marine basalt and autochthonous marginal marine basin fill. Between these two provinces lies the Puget Lowland, which was invaded repeatedly in Pleistocene time by ice of the Cordilleran ice sheet that covered the contact between the North Cascades and Olympic Mountains provinces with unconsolidated sediments as much as 3280 feet thick. The Cordilleran ice sheet extended to where Lake Crescent is now located. Lake Crescent was inundated by ice during the last maximum glacial ice extent that occurred approximately 25,000–21,000 years ago during the Late Wisconsin-age. (Schasse, 2003) Figure 5 shows an excerpt of the Geologic Map of the Washington Portion of Port Angeles 1:100,000 Quadrangle where the project is located.

Bedrock in this area consists of Aldwell Formation (EM2a) and the lower Crescent Formation (Evcp). The middle Eocene-age Aldwell Formation (EM2a) consists of thin to medium-bedded, well-indurated marine siltstone and sandy siltstone with interbeds of fine sandstone. Massive lenses of pebbles, cobbles and boulders of basalt occur sporadically, as well as lenses of basalt breccia and pillow lava. The middle and lower Eocene-age Crescent Formation (Evcp) consists of marine basaltic rocks dominated by tholeiitic pillow basalt, but also contains basalt breccia, and volcanoclastic sandstone and conglomerate. (Schasse, 2003)

Site Investigation

Surface Conditions

The trail follows Lake Crescent’s northwestern shoreline at an elevation of approximately 600 feet. A utility box is located near Station 38 between the existing trail and the lake. (Picture 2)

Several site visits were completed for observation of the geologic materials and geologic processes, and of existing cut slope and fill slope conditions along the corridor. Fieldwork also included observation of geologic materials excavated during construction activities along Spruce Railroad Trail Segment D between August and October 2015. The original construction method of the railroad grade is interpreted to be partial bench to sidecast, to full benching and typical of methods used at the time. Rock outcrops and raveling rock slopes are present on the uphill side of the trail.

Geotechnical Memorandum GM 03-16 Page 3 January 2016

Subsurface Soils

No geotechnical subsurface exploration (borings or test pits) were conducted for this project.

Subsurface information obtained from test pit sampling and hand augered test holes within Segment D of the Spruce Railroad trail project is used, in part, to generally characterize the native soils within this project, Segment C.

The native surface soils interpreted to be generally comprised of sandy silt, silty sand with gravel, clayey gravel with sand. Generally, soils comprised primarily of gravel and sand are considered to be excellent for subgrade support, soils comprised of silty or clayey gravel and sand are considered good, and soils comprised of silt are considered fair to poor for subgrade support. It is thought that some type of gravel or ballast underlies the surficial layer of organic and soil surfacing material along the railroad grade. However, no evidence of ballast material was seen during the field visit. Materials underlying the surface of the railroad grade may include cobble and boulder size rocks.

In Situ Testing

In situ testing consisted of Dynamic Cone Penetrometer (DCP). The DCP test consists of a 0.6-inch diameter steel rod with a steel cone attached at one end, which is driven into the ground by means of a sliding hammer weighing 17.6 lbs. and having a drop height of 22.6 inches.

Ten DCP tests were performed at approximately 600-foot intervals along the alignment (not including the tunnel) with one test performed in the center of the existing trail and one test performed near the outside fill slope (the anticipated left shoulder hinge point). DCP tests were completed up to depths of 32 inches below the existing ground. All of the DCP tests within the center of the trail had refusal prior to a depth of 8 inches. The five DCP test performed near the anticipated left shoulder hinge point penetrated to depths between about 8 inches and 32 inches.

The US Forest Service and the Minnesota Department of Transportation (MNDOT) have established correlations between the DCP penetration rate (mm/blow) and California Bearing Ratio (CBR) values. MNDOT have established correlations between the DCP penetration rate (mm/blow) and Standard Penetration Test (SPT) N60 values.

The DCP test results and correlations to CBR and SPT values are provided in Table 1.

Geotechnical Recommendations

The focus of the geotechnical investigation was to identify sections of the alignment that require subgrade stabilization, areas of embankment instability necessitating the use of reinforcing geosynthetic layers, and areas where poor surface drainage conditions warranted the installation of a cross-drain. Table 2 shows areas of geotechnical issues and possible mitigation methods.

This memorandum discusses alternative mitigation methods to open the discussion about risks to this project.

Geotechnical Memorandum GM 03-16 Page 4 January 2016

Surfacing Section and Subgrade Based on DCP tests, the surface of the existing trail along its centerline appears dense to very dense and DCP tests performed in the left shoulder found, the top 1 to 2.5 feet of the embankment material less dense. The DCP tests were performed after a very dry summer. It is also important to understand that, at least in some instances, DCP values shown in the table may have been influenced by the presence of large gravel, cobbles, and boulders, which would tend to overstate the strength of the subsurface materials. It is assumed that the embankment fill material varies considerably throughout the project. It is likely that these soils, especially off the railroad grade and near the existing embankment slope, will not support conventional earth moving equipment.

During a February 2014 site visit, one site was observed to have standing water in the area. The stationing or length of this site is not currently known, but based on the cross sections it is believed to be between stations 37+00 and 39+00.

It is recommended to install a Class 2, Type C stabilization geotextile between the top of the subgrade and grade fill if there is a fill, or under the structural surfacing section if there is no grade fill along the entire length of project stopping and starting 50 feet outside of the tunnel and portal. The geosynthetic will provide stability and separation between the different subgrade materials.

Settlement and Slope Creep

The soils under the railroad grade appear to be conducive to the planned development.

However, based on the shallow DCP tests conducted near the outside fill slope indicate the possibility the soil is in a less compacted state than near the centerline. Differential settlement may occur within the embankments due to non-uniform embankment material (i.e. sand versus clay) and differential rates of settlement. In addition, differential settlement is likely to occur at cut/fill transitions, which may result in a transverse dip in the trail or longitudinal settlement where the trail is within a cut and fill section. Differential settlement can also occur due to increased loading over soils that are less dense than the soils under the railroad grade. Side cast cut and fill roadway construction methods have a high probability of experiencing differential settlement.

Lakeshore erosion at the toe of the embankment slopes can result in loss of lateral support and slope creep of the embankment slope. Typically, slope creep is more active during wet months of the year and may intensify during years of higher than normal precipitation, preceding high precipitation events, The cross sections show areas where the proposed trail appears to overlie interpreted sidecast fill material. The cross sections also show a grade raise ranging between about 1 to 4 feet and sections with sliver fills. The asphaltic-concrete pavement structure is not planned to be placed for another couple years; which should allow for most of the consolidation of the side cast fill material effected by the additional load. However, continuation of the lakeshore erosion will

Geotechnical Memorandum GM 03-16 Page 5 January 2016 most likely result in continuing active slope creep. Table 2 provides the locations where deep patches are recommended.

Two design approaches should be considered in regards to the risk of differential settlement resulting in future pavement distortion.

1. To mitigate potential differential settlement and future pavement distortion, a deep patch could be constructed. Deep patch is usually not considered complete mitigation; it is intended to slow the development and propagation of surface distress related to slope creep. The cost and environmental impacts of deep patches are much less when compared to other stabilization alternatives.

Deep patches would consist of excavating at 18 inches below the bottom of the pavement section and installing three layers of biaxial geogrid at 9 inch vertical spacing. The geogrid layers will extend from the face of the downhill slope back the full pavement width in order to develop embedment of soil reinforcement elements beyond the failure zone.

The deep patch must daylight and graded to drain towards the outboard slope.

If it is determined that deep, patches will be included in this project, the WFLHD project geotechnical engineer should be consulted for details.

2. The current plan for the entire Spruce Railroad Trail project within the Park is to construct this segment and two other segments over the next couple of years. This alternative does not construct the deep patches during the construction of this project. Instead, wait and observe the behavior of the gravel surface over a period of a few years. This approach would allow time for consolidation of the soils and provide some verification of settlement and/or creep of the embankment slope. However, if some mitigation is required, the cost of constructing the deep patches will most likely be higher.

Sliver Fills

The current design includes sliver fills in order to widen the embankment enough to support the proposed surfacing section. These areas may result in negative environmental impacts.

Reinforced soil slopes (RSS) can be constructed with the face nearly vertical; however, a sloping face is recommended in order not to create a drop off at the edge of the pavement structure.

Based on the cross sections the required depth of the RSS appears to be less than 5 feet. If it is determined that a reinforced soil slope is necessary for this project, the WFLHD project geotechnical engineer should be consulted for details.

Cut Slope Recommendations

Based on construction observations during Segment D, the existing cut slopes are interpreted to have 2 to 10 feet of soil overlying a siltstone and sandstone with slope ratios ranging between 30

Geotechnical Memorandum GM 03-16 Page 6 January 2016 and 40 degrees and 180+ feet high. These slopes show evidence of active or inactive slope creep.

It is recommended to avoid slope cuts in the inboard slope in order to reduce the possibility of reactivating creep or increasing the rate of creep within these slopes. This recommendation includes cutting the toe of the slope for a ditch.

Raveling Slope

At about Station 44, the topography upslope of the trail consists of a slope about 50 feet high and 40 feet wide at the toe with a slope angle about 30 degrees near the trail and steepening to about 40 degrees. This slope is poorly vegetated and displaying moderate degree of raveling and sloughing that has led to accumulations of silty/clayey sand and gravel, and cobbles covering the trail. (Picture 3) If no mitigation performed at this site is constructed the raveling and sloughing will lead to ditch infilling.

Two design approaches should be considered in regards to the reducing the risk of ditch infilling and loose material landing on the trail.

1. A cut side buttress will protect the ditch from infilling and will provide containment that will eventually promote the slope to flatten and revegetate resulting in a stabilized slope.

A cut side buttress can be constructed with concrete ecology blocks, gabion baskets, or boulder size rocks.

The buttress would be constructed at the base of the existing slope in order to build a flattened 1V:2H fill slope at the base of the cut (above the buttress) to promote revegetation and prevent raveling material from reaching the ditch and trail.

If it is determined a buttress is necessary for this project, the WFLHD project geotechnical engineer should be consulted for details.

2. Realign the trail to the left. This alternative will still accept a high risk of loose material infilling the ditch.

Fill Slope Instabilities

Several small slumps interpreted to be caused by erosion along the toe of the lake are present in the embankment at between approximately Stations 45 and 46 (Pictures 4, 5, and 6), between Stations 48+50 and 49+00 (Pictures 7 and 8), and between Stations 55+25 and 56+50 (Pictures 9 and 10).

Erosion and subsequent slumping has encroached up to the outboard trail shoulder. There is a high probability that these embankments will continue to display slope instabilities and may encroach up the roadway shoulder. In the current design, Site 55+25, is shown requiring a mitigation to construct the trail.

Geotechnical Memorandum GM 03-16 Page 7 January 2016

The following are a list of design considerations in regards to reducing the risk slope instability encroaching towards the trail surfacing structure and the constructability the trail at Station 55+25 site.

1. No mitigation proposed for these two areas. This is not an appropriate mitigation for Station 55+25 site.

2. Minimize fill heights and offset the trail as much as possible from the lakeshore.

3. The shoreline slope angle at Station 55+25 site is relatively shallow. A riprap revetment mitigation would reduce the erosion caused by wave action at this site. However, the floor of the lake, near the shore, appears to drop very quickly near Station 45, and Station 48+50 sites. It is unlikely that the embankment toe can be stabilized with riprap revetment mitigation.

4. A deep patch under the trail will probably be undermined over time; however, it would slow the development and propagation of surface distress related to slope creep and slope instabilities. The cost and environmental impacts of deep patches are much less when compared to other stabilization alternatives.

5. A RSS or a wall would provide a longer period of stability to the trail structure. The cost and environmental impacts of a RSS or a fill side wall mitigation would be higher than a deep patch mitigation.

6. A combination of above mitigations that is appropriate for each individual site.

7. The current plan for the entire Spruce Railroad Trail project within the Park is to construct this segment and two other segments over the next couple of years. This alternative does not construct any mitigation (except for realignment at Station 55+25) during the construction of this project. Instead, wait and observe the behavior of the gravel surface over a period of a few years. This approach would allow time to observe the rate and magnitude of the slope instabilities to determine the most appropriate mitigation for each individual site. However, construction of a mitigation at these site is typically higher after the project is completed.

Surface Drainage

To mitigate any potential drainage problems along the right shoulder between the edge of the trail and the toe of the cut slope, adequate grading should be performed to allow for drainage of accumulated water in recessed areas. Culverts and cross drains should be added to allow for adequate drainage.

Geotechnical Memorandum GM 03-16 Page 8 January 2016

Summary

This memorandum provides intermediate geotechnical recommendations based on the Plan and Profile sheets shown in Figures 4 and 5. The WFLHD project geotechnical engineer should be consulted if changes vertical or horizontal alignment changes are made.

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

Attachments: Figures 1 and 2: Location and Vicinity Maps Figure 3: Geologic Map excerpt Figure 4: Plan and Profile sheets Figure 5: Cross Sections Pictures: 1-10 Table 1: Dynamic Cone Penetrometer Test Results Table 2: Geotechnical Issues and Possible Mitigation

References

Magnuson, A.C., (2007) Spruce Production Division, Railroad #1, History Around Lake Crescent, Clallam County, Washington, http://www.craigmagnuson.com/spdrr01.htm.

Schasse, H.W (2003) Geologic Map of the Washington Portion of the Port Angeles 1:100,000 Quadrangle Washington Division of Geology and Earth Resources, Open File Report 2003-6, Scale 1:100,000.

mailto:Diann.Morehouse@dot.gov http://www.craigmagnuson.com/spdrr01.htm

Geotechnical Memorandum GM 03-16 Page 1 January 2016

Figure 1: Project Location Map.

Figure 2: Project Vicinity Map.

BOP

EOP

Project Location

RSS

N

NPS Drwg. No. 149/60510

CUYD

EXC.

CUYD

EMB.

25+00

D.1

STATE PROJECT

NUMBER

SHEET

WA

NPS OLYM 2015(4)

P

M

D e c e m b e r

U

S S u r ft

D

F F

H A

X

C A

D R

H S

H E

E T S o ly m d a .d g n

C h e c k e d b y

D e s ig n e d b y

27+00 29+00 31+00 33+00

N=XXX

E=XXX

El=XXX

Profile grade @ CL

Existing ground @ CL

P V I

.6

E L

.3

P V I

.0

E L

.6

P V I

.0

E L

.0

P V I

.0

E L

.2

-4.10%

0.99% -1.03%

172' V.C.

K=34 55' V.C.

K=27 132' V.C.

K=62

P O

T

.0

I

C

T

T

BEGIN PROJECT

27+50.00

FIGURE 3

FIGURE 4

CROSS SECTIONS

Geotechnical Memorandum GM 03-16 Page 6 January 2016

Figure 5: An excerpt from Geologic Map of Washington Portion of Port Angeles 1:100,000 Quadrangle (Schasse, 2003) where the project is located.

Holocene-Age Alluvium (Non-glacial)

Holocene and Pleistocene-age Landslide Deposits (Non-glacial)

Pleistocene-age Vashon Recessional Outwash (Fraser Glaciation)

Eocene and Paleocene-age marine sedimentary Rock (Blue Mountain Unit)

Middle and lower Eocene-age marine basaltic rocks, pillow dominated (Crescent Formation)

Middle Eocene-age marine siltstone and sandy siltstone (Aldwell Formation)

Maximum extent of the Cordilleran ice sheet; barbs point towards ice front

Thrust fault- sawteeth on upper plate; dashed where inferred, dotted where concealed.

BOP

EOP

Picture 1: Near Station 30+00, Back (2015)

Picture 2: Utility box near Station 37+00, (2014)

Geotechnical Memorandum GM 03-16 Page 2

Picture 3: Station 44, Back (2015)

Picture 4: Station 45, Ahead (2015)

Geotechnical Memorandum GM 03-16 Page 3

Picture 5: Station 45, Back (2015)

Picture 6: Station 45, Back LT (2015)

Geotechnical Memorandum GM 03-16 Page 4

Picture 7: Station 48+50 LT, Ahead (2015)

Picture 8: Station 49+50 LT, Back (2015)

Geotechnical Memorandum GM 03-16 Page 5

Picture 9: Station 55, Ahead (2014)

Picture 10: Station 56, Back (2015)

WA NPS OLYM 2015

Table 1: Dynamic Cone Penetrometer Results.

Geotechnical Memorandum GM 03-16 Page 2

Table 1: Dynamic Cone Penetrometer Results Continued.

Geotechnical Memorandum GM 03-16 Page 3

Table 2: Locations of geotechnical issues and possible mitigations.