GM_28-17_Repair_Mather_Memorial_Slide_Area,_Short_Term_Repairs.pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

Subject: GEOTECHNICAL INFORMATION Date: October 25, 2017 Repair Mather Memorial Slide Area Short Term Repairs Mather Memorial Parkway (SR 410) Mount Rainier National Park

From: Robert Kraig, Geotechnical Engineer Reply to: HFL-17, Geotechnical Services GM 28-17

To: Kirk Loftsgaarden, Project Manager Repair Mather Memorial Slide Area Short-Term Repairs

WA NPS MORA 12(1)

Introduction

The Mather Memorial Parkway (SR 410) is located to the east of Mt. Rainier in the east-central portion of Mount Rainier National Park (the Park or MORA), near the boundary of the Wenatchee National Forest in Pierce County, Washington. It lies within a National Historic Landscape District. This segment of SR 410 is located in the Park and serves as a critical link serving as the primary east access to the northeast section of the Park and to the Sunrise Developed Area. Seasonally, it also serves as one of five primary east/west cross-cascade highways in the state, linking Puget Sound and central Washington. The road is closed during the winter months and although it is located in the Park, it is otherwise maintained through contract with the Washington State Department of Transportation (WSDOT).

A moderate-size, active, modern-day landslide (Mather Landslide or Slide) crosses the road for approximately 600 to 650 feet at about milepost (MP) 64 on the SR 410, approximately 1.2 miles north from the juncture of SR 410 with SR 123, and is located at coordinates 46o 53’ 11.08” north latitude and -121o 32’ 29.31” west longitude. Photos of the slide area are attached to this memorandum.

Based on our studies of historical data, the slide has been studied since at least the early 1980s, but earlier studies may exist. Most slide movement occurs during the wet season following winter road closure. Historical studies state that movements were typically minor (< 3 inches) and once the road was opened in the spring the road typically required patching or repaving prior to opening it to the public. It was reported that in the spring of 2015 the nature of the movement changed with movements observed to be >3 inches in addition to several inches of highway uplift.

We interpret the slide to be located within the boundary of a much larger ancient landslide having a footprint that extends about 1300 to 1400 feet along the road and approximately 2000 feet or more up slope from the road. Refer to Figure 1 for the Slide location and Figure 2 for the Slide vicinity relative to Ashford, Washington and Mt. Rainier.

Figure 1: Mather Slide location

The Western Federal Lands Highway Division (WFLHD) attended a scoping review on site in September, 2016. We were met by members of the Park and WSDOT. We reviewed the site and the immediate corridor area and discussed historic maintenance issues with the WSDOT and Park maintenance personnel. Following the scoping review the WFLHD was tasked with a two-fold goal to:

1) Provide recommendations for safety improvements and, if possible, reduce maintenance efforts. The recommendations will seek an assumed short-term goal of approximately three to seven-year design life until a longer-term solution can be developed. The short-term improvements are described as simple solutions that can be made without conducting in-depth geotechnical design studies or analyses. Safety improvements may include re-grading the roadway (including removing some of the existing asphalt patching that has accumulated over the years), adjusting the horizontal and vertical alignments, cleaning the ditches, adding a low wall, RSS or sliver fills, or patching. Additional cuts would be avoided.

2) Develop a plan and estimate for future actions that will lead to long-term solutions to address the underlying cause(s) of landslide movement. These solutions will have the goal of controlling the magnitude of movement at the road caused by landslide movement.

Figure 2: Mather Slide vicinity

This document contains background information and construction recommendations for short-term repairs across the active slide area. Long-term mitigation solutions will require further study to better understand the character of the landslide, its complexity, and subsurface conditions over time. Recommendations pertaining to the long-term study will be presented in a separate memorandum.

Geology

The site is in the South Cascades geologic province. An excerpt from the Surficial Geology of Mount Rainier National Park, Washington (1969, Crandell, F.R., U.S. Geological Survey B- 1288), is provided as Figure 3. As shown in the figure, the landslide is identified as landslide deposits (Ql mapped unit) that is flanked by talus (Qt) to the north and to the east, and mapped Evans Creek Drift deposits (Qe) to the south (consisting of till as well as stream-deposited sand and gravel). The head of the slide is bounded by the Tbr mapped unit (rock formations older than Mount Rainier comprised of undifferentiated volcanic, sedimentary, and intrusive igneous rocks). Klickitat Creek (not shown in the excerpt) is located to the west at the toe of the slope.

A previous WSDOT study described bedrock in the vicinity as greenish to brown and maroon dacite to basaltic-andesitic lithic breccia, tuff, tuff breccia, and volcaniclastic siltstone, sandstone, and conglomerate of the Ohanapecosh Formation (credited to Schasse, 1987).

Figure 3: Excerpt from the surficial geologic map. (Surficial geology of Mount Rainier

National Park, Washington (1969, Crandell, F.R., U.S. Geological Survey B-1288)

It is worth noting that two small lakes (Deadwood Lakes) are located above the landslide area.

The lakes appear to be located above a possible ancient head scarp.

We interpret that the slide occurred in the Qt and Qe units. The active slide appears to be occurring within the Qt mapped unit.

Climate

The climate of Pierce County is greatly tempered by winds from the Pacific Ocean.

Summers are fairly warm, but hot temperatures are not common. Rainfall is generally very light and sporadic during summer. During the rest of the year precipitation is frequent, especially late in fall and in winter as is shown in Tables 1-A and 1-B.

The data in the tables is based on observations recorded at Packwood, located along US 12 approximately 25 miles driving distance to the south-southeast at elevation 1060 feet, and Paradise to the southwest near the summit of Mt. Rainier (elevation 5427 feet). As can be observed in the tables the higher elevation (Paradise) generally experiences more precipitation and seasonally cooler temperatures. Note that the data is for the most recent available climate normal (1981 to 2010) and is not a summary of all possible observations at those stations. Precipitation taking the form of snow is included in the tables. (Snow accumulations are not shown.) Seasonal mean snowfalls are reported to be about 30

Mather

Slide

N inches for Packwood and 670 inches for Paradise (November into April and September into July at the Packwood and Paradise stations, respectively).

Table 1-A: Temperature and Precipitation Data* 1981 – 2010 (Packwood)

Month Temperature (°F) Precipitation Mean (inches) Daily Max. Daily Min. Mean

January 43.7 31.9 37.8 8.96

February 48.8 31.7 40.3 6.05

March 53.5 35.0 44.2 5.43

April 59.0 38.1 48.6 3.67

May 65.9 44.1 55.0 2.88

June 71.0 49.5 60.3 2.09

July 78.0 53.6 35.8 0.91

August 78.9 52.9 65.9 0.87

September 73.6 46.8 60.2 2.06

October 61.2 40.3 50.7 5.02

November 48.3 35.5 41.9 9.95

December 41.7 30.8 36.3 8.11

*Data obtained from the National Climatic Data Center (NCDC), Station: Packwood, WA US USC00456262.

Table 1-B: Temperature and Precipitation Data* 1981 – 2010 (Paradise Station)

Month Temperature (°F) Precipitation Mean (inches) Daily Max. Daily Min. Mean

January 34.9 22.5 28.7 18.24

February 35.7 22.1 28.9 12.69

March 37.9 23.7 30.8 12.56

April 42.1 25.9 34.0 8.30

May 49.3 31.8 40.5 5.89

June 54.7 36.2 45.5 4.11

July 63.3 42.7 53.0 1.95

August 64.5 43.9 54.2 1.97

September 58.1 39.7 48.9 4.71

October 47.9 32.3 40.1 10.43

November 37.3 24.7 31.0 20.28

December 33.8 21.1 27.4 17.17

*Data obtained from the National Climatic Data Center (NCDC), Station: Rainier Paradise RNG, WA US USC00456898.

Of the total annual mean precipitation, about 22 percent (approximately 12.5 inches) usually falls during the period April through September near Packwood, and about 23 percent (nearly 27 inches) at Paradise. The annual mean average precipitation (not shown in the tables) is about 56 inches at Packwood and about 118 inches at Paradise.

Based on elevational considerations alone, it is likely that the climate at the site (elev. 4340) lies somewhere between that experienced at Packwood (elev. 1060) and at Paradise (elev.

5427), but is more likely to be nearer to the type of climate experienced at the Paradise reporting station. There is another NCDC reporting station (Rainier Ohanapecosh, WA US USC00456896 at elev. 1950 feet) that is located off SR 123 at approximately 14 miles driving distance to the south; however, the data from that station is incomplete as it only reports precipitation data, although for same climate normal period (1981 to 2010). This reporting station is at a somewhat higher elevation than the Packwood reporting station (1950 feet vs 1060 feet, respectively), but is much lower than the project site (4320 feet) and even lower compared to the Paradise site (5427 feet). The mean precipitation recorded at this site is only slightly higher than that recorded at the Packwood site. Since the Ohanapecosh reporting station data is limited but is similar to that reported at the Packwood reporting station, it is not listed in the tables.

Site Conditions

In the vicinity of the project, the Mather Memorial Parkway is cut into the side of an approximately 25 degree, westward-dipping slope that extends from a ridge on the east (≈ elev.

5800 feet) and down to Klickitat Creek (≈ elev. 3800 feet). Approximately 15 to 50-foot-high, over-steepened cutslopes that stand up to 55 degrees (or more) from horizontal comprise the eastern side of the highway. In many areas, the cutslopes are unvegetated and actively ravel rock and debris into the uphill ditch and into the northbound travel lane, as can be seen in Photos 1, 2, 8 and 9. In an earlier report, WSDOT reported seeps in the cut(s) where rockfall/sloughing is occurring. This section of road is typically closed during the winter months.

The interpreted boundaries of the active slide limits at the road are shown in red dashed line in Figure 4. The interpreted limits are based on historical data (not discussed in this memorandum) and the observance of distress and evidence of repairs in the roadway. At this stage of study, we are uncertain as to whether the road crosses within the toe area, or closer to midpoint of the active slide; however, the historical data suggest that the road crosses near the toe.

Figure 4: Interpreted active landslide limits

Horizontal and vertical geometry of the road has changed over the years to a condition in which the alignment became undrivable at the posted 35 mph speed limit; thus, requiring WSDOT to post a 20-mph speed limit through the landslide zone. Note the apparent distortion in the horizontal alignment (lateral bulge) of the road in Photos 3 and 5 where it crosses within the slide limits. Photo 4 shows the alignment taken from south of the active limits. Note the vertical distortions within the active limits.

Based on the information obtained from the historical data, we interpret that the slide is moving along the interface of the soil units and the top of bedrock.

For the last several years, as the slide has become more active, this 600 to 650-foot section of road has required annual efforts by the WSDOT to improve drivability and perform maintenance such as ditch cleaning, patches, restriping, signing, etc. on an annual basis.

Anecdotal reporting suggests that some sections inside the landslide limits may contain pavement that is up to 3 feet (or more) thick as a result of the annual patching. Note recent patching in the photos appearing in Photos 3 and 13 taken near the beginning and end of the interpreted active limits, respectively. It was reported anecdotally that in previous years, sections of the roadway have typically slumped over the winter months, but over the winter of 2014/2015 some areas were reported to have heaved, particularly at the beginning of the interpreted landslide limits.

Historical data noted that numerous springs were present in the cutslope above the highway and within the downhill slope. During our site visit we observed an active seep in the cutslope and wet ditch near the beginning of the project, but did not traverse the downhill slope. See Photos 21 through 24.

WFLHD attempted to visit the site in early May 2017 to see firsthand how the road survived the previous winter shutdown. We were unable to visit the site and had to turn back because of a road closure resulting from a spring storm. We observed the site several weeks later after the road had been repaired by the WSDOT and after it had already been opened to the public.

Prior to these repairs, the Park visited the site and provided photographs that showed the damage sustained during the seasonal shutdown. See photos 14 through 20 showing the site conditions on May 5, 2017.

Figure 5: Interpreted active landslide limits and features present along the highway.

(All locations and limits approximate)

Recommendations

WFLHD has been asked to present recommendations for mitigating the landslide located on the Mather Memorial Parkway at about MP 64 that will improve drivability of the road and reduce maintenance efforts. The recommendations based herein are based on a review of historical data (not discussed in this memorandum), discussions with the Park and WSDOT maintenance personnel, and observations made during our site visits. This level of effort did not include in-depth studies and/or geotechnical analyses by the WFLHD. Long-term mitigation solutions for this moderately large and complex landslide will require further study to better understand the character of the landslide, its full complexity, and changes to the subsurface conditions over time. Long-term mitigation approaches and recommendations will be presented in a follow-up memorandum.

Low, welded wire faced, full road-width MSE walls have been designed for the project to provide the short-term mitigation. Because the walls are designed to be full width, they will essentially function like a deep patch with closely-spaced layers of reinforcements (typically 12 inches or less). It is anticipated that the multiple layers of reinforcement will reduce maintenance costs by bridging over the typical pavement crack areas thereby reducing the development of vertical and horizontal displacements at the road surface. The goal would be that cracks and displacements would still develop, but would be “softened” or less abrupt, and the time between maintenance intervals should be lengthened to several years instead of every season.

The MSE walls were designed to have a minimum height of 3 feet (exposed height 2.25 feet) and a maximum height of 6 feet (5.25 feet exposed height), thus avoiding the need for comprehensive geotechnical analysis, which was determined to be outside the scope of the

Start project

End project Active landslide limits

Active landslide limits Seep in cutslope

Zone of excessive patching

Zone of excessive patching

Wet ditch current project. Figure 6 contains a conceptual illustration of the wire faced MSE wall designed for the project. Refer to the contract documents for final construction requirements for the MSE walls.

Figure 6: Conceptual full-width wire-faced MSE wall

The MSE walls are constructed with free-draining granular backfill that is placed and compacted between multiple layers of closely-spaced geosynthetic reinforcement. Gabion rock fill is placed behind the wire face to protect the reinforcements from possible UV damage and to provide an aesthetic appearance. The wire-faced walls allow for additional support at the outside shoulder and avoids constructing a high embankment over the steep slope area.

An underdrain system is provided to minimize the effects of groundwater near the paved surface.

In addition to the underdrain system in the walls, additional design consideration should include culvert relocation, upsizing, and/or additional cross drainage, if determined to be practicable, and restoring positive drainage in the ditches. The geosynthetic reinforcements may be cut to accommodate the culverts as described in the contract; however, the welded wire facing elements should not to be cut for this purpose.

As described earlier and as can be seen in many of the photographs, many of the cutslopes through the project corridor are bare and over-steepened, which has led to surficial sloughing that collects in the ditches at the toe of the cutslopes and has required regular maintenance.

Since in-depth geotechnical analyses were outside the scope of this project, it is recommended that cuts to the existing cutslopes be minimized or avoided to prevent further destabilizing the cutslopes and the ground above. Cutslope recommendations have been provided to the Design Team during project development and are reflected in the final plan set.

Since additional cuts will be avoided or minimized, and because the road lies within a National Historic Landscape District, slope and/or toe treatments to prevent or reduce sloughing or its effects (i.e., rock inlays, permanent erosion control mats or mesh, rockery walls at the cutslope toes, etc.) have been eliminated from consideration due to visual impacts. Consequently, surficial sloughing on the cutslopes and continued ditch maintenance should be expected.

Construction Advisory

The construction zone lies within the limits of an ancient landslide, and as such, excavations into highly disturbed soils and rock materials should be anticipated. The contractor should be prepared to excavate into gravelly soils and cobbles and possible organics. Possible boulders more than 12-inch diameter may be encountered.

It is our understanding that construction will commence in Spring when the road becomes accessible. Snowy and/or wet conditions similar to those seen in Photos 14 through 20 may be encountered. The Contractor should expect to encounter wet subgrade conditions.

Measures such as staged construction, temporary shoring, or other approved methods may be required to ensure stability of the temporary excavations. Inspect all cutslopes for signs of instability during construction. If signs of instability develop such as the development of tension cracks, moving ground, or shallow failures, work should be ceased and the project geotechnical engineer should be notified immediately.

Anecdotal evidence suggests that over-thickened pavement sections due to years of maintenance efforts may be present through some sections of the project. Notify the CO if thick pavement sections are encountered when reaching the design seating elevation of the MSE walls. All pavement must be removed prior to seating the MSE walls.

The MSE walls are designed to have a minimum setback of 2 feet from the face of the existing slope as shown in Figure 6. Notify the CO if the design footing elevations do not achieve a 2-foot minimum setback.

The project includes culvert installations, some of which are within the limits of the MSE wall sections. Geosynthetic reinforcements may be cut following the requirements of the contract to accommodate culvert installations. Do not cut the welded wire facing elements without CO approval.

Summary

This memorandum addresses the historic active landslide located at approximately MP 64 on the Mather Memorial Parkway (SR 410), which has been moving at a rate sufficient to require annual ongoing maintenance at the roadway, particularly, prior to opening the road to the public following the winter shutdown. It presents limited background information based on previous studies, discussion with Park and WSDOT personnel, and the results of our field reconnaissance. Recommendations are presented for repairing the SR 410 within the interpreted active limits of the landslide. These repairs are intended to have a short-term service life (approximately 3 to 7 years) to improve the drivability of the road and to reduce maintenance efforts.

Limitations

The information contained herein is intended for short-term mitigation of the landslide located on the Mather Memorial Parkway at approximately MP 64. The recommendations appearing herein were made without conducting geotechnical explorations, monitoring, or other long-term studies. They are based partly on limited background information, discussions with Park and WSDOT personnel, and field observations. Furthermore, the recommendations are based on

1) our understanding of the current conditions of the landslide and of the general vicinity, 2) our understanding of similar landslides in the region, and 3) professional judgements and experience. These recommendations and discussions are intended only for the site discussed in this memorandum and are not to be applied to any other site or used for any other purpose.

For questions regarding this memorandum, please contact Geotechnical Engineer, Robert Kraig, at 360-619-7699 or robert.kraig@dot.gov. If site, soil, or ground conditions are encountered during construction that vary from those discussed in this report, the WFLHD Geotechnical Team should be notified immediately in order to evaluate what effects, if any, the changes have on the recommendations contained in this memorandum.

mailto:robert.kraig@dot.gov

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Attachment Project Photographs

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Photo 1: Looking ahead toward the northerly flank from about mid-point of the active slide

Photo 2: Looking ahead toward the northerly flank of the active slide

Photo 3: Beginning of the active slide (south end limits). Note horizontal distortions and recent patching.

Photo 4: Beginning of the active slide (south end limits). Note vertical distortions.

Horizontal bulge

Vertical distortions

Photo 5: Fill-side slope near beginning of the slide (south end limits)

Photo 6: Bare over-steepened cut-side near the beginning of the active slide

Horizontal bulge

Photo 7: Bare fill-side slope before active slide area

Photo 8: Water-loving plants in the cut-side slope near the beginning of the active slide

Photo 9: Close-up of water-loving plants shown in Photo 9. Note moisture in cut.

Photo 10: Close-up of forest duff and root wad appearing in Photo 8.

Photo 11: Looking ahead near the middle of the active slide.

Photo 12: Cut near the middle of the slide.

Photo 13: End of active slide looking back. Note recent patching.

Photo 14: Photo taken by MORA staff on May 5, 2017 prior to road opening

Photo 15: Photo taken by MORA staff on May 5, 2017 prior to road opening

Photo 16: Photo taken by MORA staff on May 5, 2017 prior to road opening

Photo 17: Photo taken by MORA staff on May 5, 2017 prior to road opening

Photo 18: Photo taken by MORA staff on May 5, 2017 prior to road opening

Photo 19: Photo taken by MORA staff on May 5, 2017 prior to road opening

Photo 20: Photo taken by MORA staff on May 5, 2017 prior to road opening

Photo 21: Active spring near beginning of project

Photo 22: Active spring near beginning of project

Photo 23: Water observed at toe of cut south of the active spring

Photo 24: Vicinity where water at toe of cut vanishes before active slide area