B08_Attachment_13_Camp_Muir_Final_Geotechnical_Report_0004.pdf

3203 South Russell Street Missoula, MT 59801

T 406.721.4320 F 406.549.6371 djanda.com

December 23, 2020

Mr. Josh Boisvert Concessions Management Specialist Mount Rainier National Park 55210 238th Avenue East Ashford, WA 98304

RE: Geotechnical Engineering Report

Evaluate Geotechnical and Structural Stability of Camp Muir Developed Area Mount Rainier National Park, Washington

PMIS #2668

Dear Josh, DJ&A, P.C. (DJ&A) and Terracon Consultants, Inc. (Terracon) are pleased to submit the enclosed Final Geotechnical Engineering Report for the Camp Muir Developed Area in Mount Rainier National Park. This project was completed in accordance with the Statement of Work described in Task Order No.

140P8520F0076 under Contract No. 140P8519D0004.

The enclosed report describes site conditions observed during the August 2020 field investigation, presents findings of geotechnical engineering analyses, and provides geotechnical recommendations for future improvements planned at Camp Muir. The final report also incorporates key points from your team’s review comments.

The final report can be downloaded via the project ftp site and is saved in a folder titled “20.12.23 - Final Geotechnical Report for Camp Muir Developed Area”; instructions to access the ftp site follow.

1) Copy/paste the link below into Windows Explorer ftp://mail.djanda.com/Camp_Muir

2) Enter Username: CampMuir

3) Enter Password: Rainier@2020

The DJ&A and Terracon team thanks you the opportunity to assist the National Park Service and to be part of this exciting and unique project. Additionally, we thank you for your continued support and coordination throughout the planning, field investigation, and reporting phases. Please let us know if we can be of any further assistance in planning repair and improvements at Camp Muir.

Sincerely, DJ&A

Jon Pederson, PE Project Manager ftp://mail.djanda.com/Camp_Muir

Geotechnical Engineering Report Evaluate Geotechnical and Structural Stability of Camp Muir Developed Area

Mount Rainier National Park, Washington

PMIS #2668

cc: Ms. Liset Gomez, Contracting Officer, National Park Service, Interior Regions 8, 9, 10, & 12 Ms. Jara Woodard, Contract Specialist, National Park Service, Interior Regions 8, 9, 10, & 12 Mr. Matthew Hoffmann, Senior Associate/Geotechnical Engineer, Terracon Consultants, Inc.

Enclosure (electronic version of final report)

REPORT COVER PAGE

Geotechnical Engineering Services Report

Evaluate Geotechnical and Structural Stability of Camp Muir Developed Area Mount Rainier National Park, WA

PMIS #266786

Title I – Geotechnical Services

Contract No. 140P8519D0004; Task Order No. 140P8520F0076

December 23, 2020 Terracon Project No. C4205024

Prepared for:

DJ&A, P.C.

2000 Maple Street Missoula, MT 59808

On behalf of National Park Service

Interior Regions 8, 9, 10, & 12

Prepared by:

Terracon Consultants, Inc.

1392 13th Ave SW Great Falls, MT 59404

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REPORT TOPICS

INTRODUCTION

SITE GEOLOGY

PROJECT DESCRIPTION

GEOTECHNICAL OVERVIEW

GEOTECHNICAL CHARACTERIZATION

EXISTING STRUCTURE EVALUATION

GEOHAZARD MITIGATION

EARTHWORK CONSIDERATION

SHALLOW FOUNDATIONS

HISTORIC GUIDE SHELTER (RANGER STATION) UNDERPINNING CONCEPTUAL

OPTION

SEISMIC CONSIDERATIONS

FLOOR SLABS

RETAINING WALLS

SLOPE STABILITY

SEQUENCING CONSIDERATIONS

GENERAL COMMENTS

FIGURES

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the GeoReport logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

PHOTOGRAPHY LOG

SITE LOCATION AND EXPLORATION PLANS

GEOHAZARD AND DEVELOPABLE AREAS

EXPLORATION RESULTS

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

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INTRODUC TION

Geotechnical Engineering Services Report Evaluate Geotechnical and Structural Stability of Camp Muir

Developed Area

PMIS #266876

Mount Rainier National Park, WA Terracon Project No. C4205024

December 23, 2020

INTRODUCTION

This report presents the results of limited subsurface exploration, geologic reconnaissance, and geotechnical engineering services performed for the Camp Muir Developed Area in Mount Rainier National Park, WA. These services were provided to achieve specific geotechnical engineering objectives and inform recommendations relative to:

■ Subsurface soil and rock conditions ■ Foundation design and construction

■ Regional geologic setting ■ Floor slab design and construction

■ Groundwater/Permafrost conditions ■ Geohazards

■ Site preparation and earthwork ■ Retaining wall considerations

■ Structural evaluation ■ Conceptual geohazard mitigations

■ Seismic site classification per International Building Code (IBC) (1)

■ Recommendations on developable areas

The geotechnical engineering Scope of Services for this project included a site visit to perform geologic reconnaissance and limited geotechnical subsurface explorations on August 17, 18, and 19, 2020. The site visit included the following geotechnical exploration elements:

■ Geologic site reconnaissance of the developed area

■ Site reconnaissance and review of existing structure performance (including shelters, retaining structures, foundations)

■ Limited subsurface exploration using hand tools to excavate a total of two shallow test pits

■ Use of Dynamic Cone Penetrometer (DCP) at eight locations for determination of shallow soil penetration resistance for foundation analysis

■ Geophysical survey lines/arrays at four locations for acquisition of shear-wave velocities of subsurface profile

■ Limited laboratory testing (additional testing in process) for determination of slope material strength properties

Geotechnical Engineering Services Report

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Maps showing locations of test pits, DCP’s and geophysical lines/arrays are shown on the Exploration Plan. Logs of test pits, DCP data summary, and completed laboratory testing are shown as separate graphs in the Exploration Results section.

SITE GEOLOGY

The following description of geologic site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic reports and maps available on the United States Geologic Survey website(2),(3),(4), a previous 2002 geotechnical reconnaissance report performed for the National Park Service (NPS) by Pullman Group(5), a 2011 engineering report by Western Geotechnical Consultants, Inc.(6) completed for NPS, and topographic maps (provided by NPS within the West Toilet Design Set)(7).

Present-day Mount Rainier is the direct result of volcanic activity over the past 500,000 years.

These eruptions occurred as a direct result of the subduction of the Juan de Fuca plate off the west coast of the North American Continent which was responsible for the volcanism in the region.

Mount Rainier is situated upon a base of granodiorite that was emplaced just below the earth’s surface approximately 14 to 18 million years ago. Evidence suggests an archaic Mount Rainier once stood at the present location, but as the western edge of North America was uplifted, the overlying volcanic rock was eroded and stripped down to the granodiorite base rock approximately 1 to 2 million years ago. Approximately 500,000 years ago, the present-day Mount Rainier began to form as a series of andesitic lava flows, pyroclastic flows, pumice eruptions, and lahars created the present edifice of the mountain. The most recent lava flow and pumice eruptions are believed to be approximately 2,200 years in age, with a more recent pyroclastic flow occurring about 1,100 years ago.

Glaciation and other geomorphological processes have had a significant role in the shaping of the present-day Mount Rainier. At present, some 29 named glaciers(8) occupy the cone of the mountain, and it is believed glaciers have been a present occurrence on the mountain since its formation nearly 500,000 years ago. Within the last 170,000 years, glaciers extended from the precipice of Mount Rainier to distance of up to 63 miles away during the Hayden Creek Period (170,000 to 130,000 years ago) and somewhat less impactful during the Evans Creek Period (22,000 to 15,000 years ago). Numerous more recent glacial advances also occurred in the past 12,000 years including the McNeeley Drift that deposited moraines dated at roughly 11,300 and 9,500 years ago. The most recent 10,000 years have also seen several resurgences of ice up until the mid-1800’s. The actions of the glaciers carved large valleys, deposited lateral and terminal moraines, deposited glacial outwash, have broken and plucked bedrock, and have even impacted the path of lava flows over the past 500,000 years. In addition to glacial action, numerous lahars, mudflows, and debris flows helped shape the present-day Mount Rainier as we see it.

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The Camp Muir site is situated on an andesite bedrock ridge that is covered with glacial drift, talus, and considerable accumulations of pumice. The surficial pumice is believed to be the residual remnant of the last pumice eruption approximately 2,200 years ago. The pumice accumulations are primarily restricted to the south side of the east-west trending ridge at the project site where it forms very loose and unconsolidated slopes. The site is bound to the north by the Cowlitz Glacier and to the south by the Muir Snow Fields, and the deposits within the vicinity are likely to be those of the Evans Creek Period along with local, recent deposits of moraine from the aforementioned glaciers. Glacial action from the Cowlitz Glacier has significantly broken and fractured the rock on the north side of the ridge. Variations in ice/snow depth year to year severely weather the rock through the abrasive action of the glacier grinding on the rock and the repetitive freeze-thaw cycling, both of which combine to create vast exposures of large, broken and loosely held together slabs of andesite. Some very rocky morainal till also covers the surface where the two icefields (Cowlitz Glacier and Muir Snow Fields) separate, leaving a very rubbly surface of andesite boulders atop the andesite bedrock ridge. The rubbly moraine and broken bedrock tend to ravel down the steep slopes, particularly in the vicinity of the Butler Shelter to the west and the newly constructed restroom to the east. Underlying the pumice deposits, permafrost is encountered at roughly 24 to 36 inches below ground surface and incorporates the pumice and moraine deposits into a frozen mass of ice.

We collected numerous photographs at the time of our field exploration program and representative photos are provided in our Photography Log.

PROJECT DESCRIPTION

Camp Muir is currently undergoing a multi-year redevelopment plan including removal of unsightly and condemned buildings and construction of new visitor facilities, which will serve concessions operations and park climbing rangers. This geotechnical assessment has been conducted to assist in determining appropriate locations for redevelopment and construction of new climbing concession facilities and to provide mitigation recommendations to stabilize existing structures and landscape features including the historic ranger station, retaining walls, helipad, and pathways.

During our site visit, we interviewed climbing rangers as well as Mr. Joshua Boisvert (local project representative), regarding the possibility of redevelopment planning with some consideration to the use of temporary structures as well as permanent structures. From a geotechnical standpoint, temporary structures, if found to be of merit (based on anticipated useful life and construction costs), may be considered. Based on our conversations, we understand that NPS desires the aesthetics and architectural style of the high camp structures be considered in redevelopment planning, with knowledge that the existing Client Shelter/Gombu is in stark contrast to the aesthetics of the historic shelters.

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Following submittal and review by NPS of our draft geotechnical report, we participated in a call on December 1, 2020 with NPS stakeholders along with DJ&A to present the geotechnical findings, review NPS comments, and collaborate on development of the final report. Comments provided by NPS have been addressed within this report, where applicable, and the discussions held during the conference call have provided Terracon with a more in-depth understanding of NPS needs. As such, sequencing recommendations have been provided based on acceptable risk tolerances and long-term site development planning goals. Of note within the NPS comments was the potential for long-term, or cumulative impacts of glacial and perennial snow thinning overtime and its potential effects on the stability of the Camp Muir Developed Area. The focus of these comments by NPS was primarily on the impacts of climate change and the prediction of impacts on the glaciers/ice field over time. It was noted that this specialty is not within the scope of the geotechnical engineer’s services or expertise. If future development of models by ice/glacier engineering experts can establish the loss of ice versus time based on climate change impacts on ice/snow cover, a geotechnical approach to the slope stability could incorporate predictions from climate/ice/glacier engineering experts.

GEOTECHNICAL OVERVIEW

The primary geotechnical considerations for the redevelopment of the Camp Muir site is providing relatively stable bearing support for existing, relocated, or new structures within the developed area that meet the needs for the NPS and climbing concessionaires to provide shelter and amenities. The current developed area includes structures that are situated on various bearing layers with varying risk for differential performance. The stability of existing structures is not at a point of critical need for immediate relocation or underpinning, but consideration has been given to future needs, with the understanding that the area will be redeveloped with shelters moved, and existing temporary toilet facilities on the east side of the camp removed in favor of more permanent toilet structures. We understand NPS desires to maintain the historic appearance for future buildings, with consideration being given to both temporary and permanent structures.

The site is located on the southeastern slope of Mount Rainier, an active volcano located in the Ring of Fire as part of the North American Cordillera. Because of the potential for complete destruction of the site, geohazards discussed within this document are exclusive of the potential for volcanic activity which is not part of the scope of these services. As such, the geohazard evaluations are focused on effects of glaciation, landsliding, rock plucking, rockfall, and potential rock toppling issues within the developed area. Geotechnical considerations are presented for support of new structures on shallow foundations, as well as conceptual mitigation alternatives for existing foundations that are currently undermined at the Historic Guide Shelter (Ranger Station).

Based on site reconnaissance and limited subsurface exploration discussed within the report, there are locations within the Camp Muir development area that are suitable for redevelopment if careful

Mount Rainier National Park, WA ■ Terracon Project No. C4205024 December 23, 2020

Responsive ■ Resourceful ■ Reliable 5 consideration is given to siting new structures within these areas. In general, the saddle located between the Client Shelter/Gombu and the Helipad provides a suitable, stable platform to host locations of new structures where shallow foundations would bear within the permafrost layer. The Helipad and area east, toward the Historic Men’s Comfort Station, is situated on a limited thickness of existing fill overlying shallow bedrock and is also suitable for redevelopment. The stability of these two areas could accommodate various concepts and configurations or structures, especially with the planned removal of the temporary toilet structures east of the Helipad.

The existing conditions and evaluations of current structures is discussed in more detail within this report, but of note the Historic Guide Shelter (Ranger Station) is situated on a portion of glacial moraine mass that is undergoing substantial glacial action resulting in undermining of the foundations. This structure does not currently appear to be in a condition of imminent foundation failure, but the undermining of the foundation will need to be addressed or relocation of the structure should be considered. Conceptual alternatives for support of existing foundations and/or relocation are provided for the Historic Guide Shelter (Ranger Station). Evaluation of the remaining structures, which are in less precarious conditions, are also addressed in this report.

A preliminary geohazard and developable areas map that depicts areas that are suitable for redevelopment, areas that should be avoided, locations of existing structures, and geohazards such as rockfall and slope instabilities is presented in the attachments.

The General Comments section provides an understanding of the report limitations.

GEOTECHNICAL CHARACTERIZATION

We have developed a general characterization of the subsurface conditions based upon our review of the geologic setting, our limited subsurface exploration, our understanding of the project, available laboratory data, and analysis of geophysical field data gathered during our field studies.

Discussion of the use of DCP and geophysical field data is presented below, with the reduced data shown as separate graphs in the Exploration Results section. This characterization, termed GeoModel, forms the basis of our geotechnical evaluation of site development, slope stability, site preparation, and foundation options. As part of our analyses, we identified the following model layers within the subsurface profile.

Model Layer Layer Name General Description

1 Fill

Fill soils were encountered throughout the site, located beneath or adjacent to the primary structures (Historic Public Shelter, Helipad, Historic Guide Shelter (Ranger Station), East Toilet, and Historic Men’s Comfort Station) and at retaining walls to access the Ranger Station, Butler Shelter and Public Shelter area. The fill appears to have been constructed of existing site materials, inclusive of

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Model Layer Layer Name General Description pumice, sand, and boulders/cobbles to level areas for the shelters, and to provide backfill within the retaining walls constructed for the level areas. The fill is likely relatively uncontrolled in nature; that is, the fill was placed with limited compactive effort due to the location and resources available at the time.

2 Talus

Loose talus materials were encountered on the south-facing slope of the ridge west of the Client Shelter/Gombu and Butler Shelter.

The material was very loose to loose on the surface, with larger talus particles on the order of 18 to 36 inches in maximum particle size. In general, the larger talus overlaid a loose pumice sand material over permafrost (encountered in TP-01 at a depth of 36 inches). Localized slope instability within the talus was noted west of the Butler Shelter. Talus was also noted to the east of the Historic Public Shelter and New Toilet Building, with more slab rock predominating the talus slope.

3 Pumice

The saddle located between the Ranger Station and the Helipad and the south side slope of the east-west ridge is generally comprised of pumice within the upper two to three feet. The pumice within the saddle (as observed in TP-02) was of generally uniform size, ¾ to 1 inch diameter, and was very loose to medium dense in consistency based on Dynamic Cone Penetration (DCP) correlations to Standard Penetration Test (SPT) “N” values. The pumice sand/gravel encountered on the south slope was generally very loose to loose, coarse-grained, and appeared unconsolidated overlying a permafrost layer at depths on the order of 24 to 36 inches below existing grade.

4 Glacial Moraine

Very rocky morainal till covers the surface where the two icefields (Cowlitz Glacier and Muir Snow Fields) separate, leaving a very rubbly surface of andesite boulders atop the andesite bedrock ridge. The morainal till includes very limited gravel, sand, or silt/clay matrix. The rubbly moraine and broken bedrock tend to ravel down the steep slopes, creating talus slopes, particularly in the vicinity of the Butler Shelter to the west and the newly constructed restroom to the east.

5 Andesite

Andesite bedrock was the predominant rock encountered along the east-west ridge line, with prominent exposures north and west of the Historic Guide Shelter (Ranger Station) that have been rubbelized/abraded by glacial action. Andesite was also prevalent on the east portion of the site composing the large resistant outcrop that stands east of the Historic Public Shelter. Based on the shear wave data collected, there appears to be two distinct flow profiles within the upper 100-foot profile. The first flow is

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Model Layer Layer Name General Description encountered approximately 20 feet below existing grade at the saddle and Helipad areas, which is highly fractured and increases in density with depth. A second flow is encountered around 50 feet below existing grade, which is less fractured (based on shear wave data) and of higher density.

6 Breccia

A zone of volcanic breccia was mapped to the immediate west of the Historic Men’s Comfort Station, in which moderately hard, weathered, fine-grained matrix with large angular andesite/basalt cobble and boulder-sized fragments were observed.

As noted, we performed limited subsurface exploration inclusive of two test pits. The test pits were excavated by hand shoveling and limited picking of surficial soils to shallow depths, approximately two to three feet below existing grades. The test pit excavations were logged by our Geotechnical Engineer based on visual classification using the Unified Soil Classification System (USCS) with observations summarized in the table below as well as individual logs in the Exploration Results section:

Test Pit ID Location Total Depth (inches) Material Description

TP-01

South Slope, approximately 30’ S & 13’ E of SE Corner of Gombu Shelter

0” – Large gravel and cobbles up to 18 inches at the surface.

2” – surface poorly-graded sand with gravel, dark brown with some reddish brown/black, very loose to loose, moist (SP)

24” – poorly-graded gravel with sand, brown/black, medium dense to dense, moist to very moist (GP)

36” – permafrost, frozen layer of sand with gravel matrix (SP)

TP-02 Middle of Saddle, approximately 70’ E & 20’ N 26 0” – pumice, light brown/tan, very loose to

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Test Pit ID Location Total Depth (inches) Material Description of NE Corner of Gombu Shelter loose, uniform pumice particle size between ¾ inch and 1 inch observed throughout layer (GP)

24” – permafrost, frozen layer of pumice with sand and limited gravel matrix

(GP)

A total of eight Dynamic Cone Penetration (DCP) tests were conducted as part of the field exploration efforts. The DCP tests were conducted in general accordance with the Sower’s Cone Method, developed by George F. Sowers and Charles S. Hedges and referenced in Dynamic Cone for Shallow In-Situ Penetration Testing, Vane Shear and Cone Penetration Resistance Testing of In-Situ Soils(9). In this method, a 15-lb steel mass is dropped from a height of 20 inches where it strikes an anvil to drive a 1.5-inch diameter 45-degree cone into the in-situ soils. The cone is seated into the in-situ soils, approximately 2 inches, and then maintaining a plumb position with the rod assembly the mass is lifted and dropped on the anvil in a free fall. The number of blows to advance the cone in 1-¾-inch depth increments is recorded, and each subsequent 1-¾-inch interval is recorded as desired. The recorded blows to advance the DCP cone for the 1-¾-inch depth interval can be correlated to traditional Standard Penetration Test (SPT) measurements to determine an N-value as if a conventional drill rig and automatic hammer was utilized. The SPT is conducted using an exploration drill rig in a similar fashion where a standard 2-inch outer diameter split-barrel sampling spoon is driven into the ground by a 140-pound automatic hammer falling a distance of 30 inches. The number of blows required to advance the sampling spoon the last 12 inches of a normal 18-inch penetration is recorded as the Standard Penetration Test “N” resistance value (SPT N-value).

The Sower’s cone DCP is utilized in locations where a drill rig and automatic hammer are unable to access an exploration location, such as Camp Muir, to correlate similar blow count measurements to SPT N-values. The SPT N-value is generally utilized to determine the relative density of a soil deposit for use in analyzing the soil for bearing capacity and settlement response under loading. The correlations utilized in our data reduction have been modified from those developed by Sowers and Hedges to account for the lack of available DCP to SPT N-value direct correlations in the geologic setting. We have used two of the correlation curves developed by the authors; a curve for virgin piedmont soils and another for 95 percent compacted soils, and averaged the two to develop correlations for this site. The raw reading, correlation based on the above reference, and relative density of the soil is presented in the Exploration Results section for each DCP point performed.

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Exploration Point ID Location

Total Depth

(inches)

Average Recorded DCP Value

Average Correlated SPT

“N” Value Remarks

DCP-01 On slope, adjacent TP-01 26 10 9 Refusal in permafrost

DCP-02

On slope at trail access to Camp Muir

63 9 8 Driven to full depth, no refusal (pumice)

DCP-03 On saddle, adjacent TP-02 23 8 7 Refusal in permafrost

DCP-04 Near NE corner of Gombu Shelter 19 10 9 Refusal in permafrost

DCP-05 Below Helipad 19 8 7 Refusal in permafrost

DCP-06 Within west lower retaining wall fill 14 10 8

Refusal in three attempts, all within upper 14 inches

DCP-07 Helipad fill, 6 feet east of stairs 51 16 13 Refusal blow counts, likely cobble/boulder

DCP-08

South of Historic Men’s Comfort Station

49 24 18 Medium dense to dense fill zone

Terracon performed refraction microtremor (ReMi) shear-wave profiling and multi-channel analysis of shear wave (MASW) measurements at the site. A total of four seismic survey lines were conducted, as shown on the Exploration Plan, throughout the site to develop depth profiles of the measured shear wave velocity (VS) values. The development of the depth of measured shear wave values was used to assist in delineating the subsurface profile as described above, at depths unobservable by test pit or DCP exploration. The acquired data was reduced and Seismic Line Profiles are attached in the Exploration Results section. The shear wave data was reviewed and compared with previously acquired Terracon shear wave profiles for similar velocities to correlate relative density of the subsurface conditions with assumed soil/rock materials.

Based on our findings, the predominant soil profile utilized in our analysis of slope stability and foundation support for new buildings consists of the following generalized layers. All layers are generally considered to be pumice, morainal till, or talus materials overlying bedrock. The upper two to three foot zone is generally very loose to loose sand with gravel (as appears on the south slope below the Client Shelter/Gombu, or pumice over the saddle), with average shear wave velocities on the order of 300 to 550 feet per second (fps). This layer is underlain by an

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Responsive ■ Resourceful ■ Reliable 10 approximately two to five foot thick zone of medium dense gravel with sand (also includes the permafrost materials based on test pit observations) with shear wave velocities ranging from 600 to 900 fps. Below this layer is another loose to medium dense layer of sand or gravel three to five feet thick with shear wave velocities on the order of 400 fps. Below this loose layer, the density begins to increase at approximately 12 to 16 feet below existing grade within a likely gravel layer prior to what appears to be a highly fractured bedrock layer based on shear wave velocities at approximately 20 to 24 feet below existing grade. The bedrock velocities near the interface are in the range of 1,300 to 1,500 fps and increase to approximately 4,000 to 5,000 fps at depths greater than 50 feet. This generalized profile was used in the development of the slope stability analysis and conceptual micropile foundational alternatives, discuss in the following sections.

EXISTING STRUCTURE EVALUATION

A brief description of each structure observed during the site visit is provided below. Photos of the structure and conditions discussed are provided in the Photography Log.

East Toilet

The East Toilet structure is located on the extreme east of the existing developed area. The structure was constructed in the 2014-2015 season using shallow foundations bearing within the fill zone overlying the andesite bedrock in this area of the site. The structure is relatively new, along with the West Toilet (the newest structure at the site), and is constructed with reinforced concrete shallow foundations (assumed as no design or as-built drawings were reviewed), concrete slab-on-grade for the split level (upper level toilets, lower level depository for waste), and a composite concrete/steel pan deck roof structure. A rock façade has been constructed as a veneer around the exterior of the building. No signs of differential movement or adverse performance were observed at this structure during the site visit.

Historic Public Shelter

The Historic Public Shelter is located on the east side of the Camp Muir Developed Area and was erected in memory of John Muir in 1921. The structure is constructed of rock with concrete slab-on-grade and an isolated concrete foundation/stem wall on the north side of the structure. The interior rock has been plastered and exterior mortar joints for the rock have been recently pointed (within the last five years). This structure shows some signs of structural distress at the corners, with shear cracks developing at the rock/mortar joints apparent at all four corners and varying in separation/width. There are also distress cracks propagating from the door and window lintels observed from the interior of the structure. This type of crack is not atypical for rock/brick and mortar construction in which wall movement differs from the middle to edge of walls and results in shear cracking. This result is due to the relatively brittle nature of the façade material, and is typically repaired with pointing of mortar joints to reseal were necessary. The floor slab on the

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Responsive ■ Resourceful ■ Reliable 11 interior exhibited limited cracking or sloping, and the structure appears to be in good condition for its age and environment.

Historic Men’s Comfort Station

The Historic Men’s Comfort Station was constructed in or around 1916 of rock with concrete slab-on-grade and currently has a concrete roof. The structure is currently being utilized for storage, and has a limited footprint. The structure appears to have been constructed on a minimum thickness of fill overlying bedrock in the area, with the breccia intrusion located directly north of this structure. The structure shows no signs of distress or differential movement, and the mortar/rock joints are tight with some signs of more recent pointing efforts (within last five years).

Helipad

The helipad is located just east of the center of the ridge saddle at the Camp Muir Developed site.

The dry-stack, or rockery retaining wall, constructed to level the area for the helipad has a maximum height of approximately seven feet on the south side, where it intercepts a relatively level walking path perpendicular to the south slope. On the north side, the maximum wall height is on the order of five feet where it intercepts a relatively steep glacial moraine mass above the Cowlitz Glacier. The retaining wall is performing well as currently constructed, and appears to have been constructed utilizing locally available bedrock slabs/boulders for the wall face and backfilled within the approximate 25-foot diameter using available sand/gravel/cobble matrix materials. The wall has a minimal batter, less than 1H:10V (horizontal:vertical) as currently constructed; however, it shows no obvious signs of tilt or deformation that would indicate distress or failure of the as-built system. A Dynamic Cone Penetration (DCP) test was conducted on the west end of the helipad approximately 6 feet east of the access stairs, in which the average correlated SPT N-value of 13 was determined within the upper 4.3 feet of the helipad subsurface.

This correlates to a medium dense fill placed within the retained area, consistent with a modest compactive effort. The DCP probe was driven to approximately 4.3 feet below top of pad before encountering refusal blows (>50 blows per 1-¾-inch increment). It is likely that, at that depth, the backfill material was generally cobble size or larger, as it would be in the lowest reaches of the retained mass and near the glacial moraine material elevation on the north edge of the helipad.

A geophysical line was also conducted that traversed over the helipad (Line 4) toward the east, in which the shear wave velocity in the upper five feet was found to be consistent with a medium dense material (approximately 1,250 fps).

Retaining Walls South of Historic Guide Shelter (Ranger Station)

On the west side of the developed area, three short dry-stack or rockery retaining walls have been constructed below the Historic Guide Shelter (Ranger Station). The lower retaining wall is approximately six feet tall at maximum height near the radius at the east end of the wall, and tapers to approximately two feet tall near the west toilets. The wall appears to have been

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Responsive ■ Resourceful ■ Reliable 12 constructed utilizing locally available bedrock slabs/boulders for the wall face and backfilled using available sand/gravel/cobble matrix materials. The lower retaining wall has experienced a localized failure near the radius on the east side of the wall, in which the lower level rocks forming the base of the wall appear to have pushed out. This has resulted in a mobilization of the backfill material, increasing lateral pressures on the wall until a full wall failure occurred. The wall failure has not been repaired, but the rock appears to have been stacked to limit potential for additional failure or loss of backfill materials.

The second level wall is set back to the north from the top of the lower retaining structure by approximately eight to 10 feet, and is approximately six feet tall at maximum height. The wall has also been constructed using locally available bedrock slabs/boulders for the wall face and backfilled using available sand/gravel/cobble matrix materials. The second level wall face is also exhibiting distress near the radius on the east end of the wall, near maximum height, with the backfill material having settled and created a void space. The wall facing rock has a slight bulge and appears to be failing in the same vein as the lower wall section. A DCP test was conducted on the backfill for this level of the retaining wall near the radius of the wall. The DCP testing indicated a correlated average SPT N-value of 8 within the upper one foot of the backfill before refusal was encountered. We attempted three DCP tests in this backfill zone with each resulting in refusal near the one-foot depth. The resistance results correlate to loose fill prior to refusal within the retained area, consistent with limited compactive effort. It is likely backfill material is generally cobble size or larger, with non-uniform particle size.

The upper level wall is located immediately adjacent the Historic Guide Shelter (Ranger Station), and is approximately four to five feet tall at maximum height. This wall, too, appears to have been constructed using locally available bedrock slabs/boulders for the wall face and backfilled using available sand/gravel/cobble matrix materials. The wall facing and backfill at the upper wall appear to be performing well, with no visible indications of the failure mechanism encountered in the lower two levels.

All three dry-stack, rockery walls appear to have been constructed without consideration of proper base/foundation level rock sizing, incorporation of drainage, and the lower two walls have no apparent batter. That is, typical rockery wall construction includes selection of specifically sized base/foundation level rocks to provide for stable starting points for construction and allowance for battering of the wall face as constructed where the mass of the wall face will remain over the base rocks. It is recommended that reconstruction of the lower two levels of retaining walls be conducted in accordance with rockery design and construction guidelines provided within the document Rockery Design and Construction Guidelines, FHWA-CFL/TD-06-006, November 2006. Further support of this design can be provided following NPS determination of material sources, as the design is heavily dependent on material size and wall height.

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Historic Guide Shelter (Ranger Station)

The Historic Guide Shelter (Ranger Station), constructed in the 1920’s, is the primary structure of concern for the redevelopment plan as discussed with NPS. The Ranger Station is located on the west end of the developed area, situated on a precipice overlooking the Cowlitz Glacier to the north. The glacial action from the Cowlitz Glacier has significantly broken and fractured the rock on the north side of the ridge immediately northwest of the Ranger Station. Variations in ice/snow depth year to year, which have been reported to vary as much as 30 to 50 feet, severely weather the rock through abrasive action of the glacier grinding on the rock and the repetitive freezing and thawing, which create vast exposures of large, broken and loosely held together slabs of andesite.

The Ranger Station is situated immediately east of a very broken exposure of andesite slabs on a very rocky morainal till which covers the surface where the two icefields (Cowlitz Glacier and Muir Snow Fields) separate. The rubbly moraine and broken bedrock are continually being attacked/abraded by the Cowlitz Glacier acting from the north to undermine the existing north footing line of the Ranger Station.

There are two distinct concrete footing elements along the north footing line of the Ranger Station, with the most recent, and lower in elevation, placed approximately 10 years ago in an attempt to provide additional support to the structure. The older and upper concrete foundation was apparently placed in the 1970’s, and was subsequently undermined. The recently placed concrete at the lower elevation is ineffective in providing support as a majority of the foundation is currently undermined and in air. It appears the weight of the concrete foundation element may be pulling on the Ranger Station rock wall and creating additional distress. As a first move, consideration should be given to removing the latest concrete placed to relieve the structure from the added “dead” weight pulling on the rock. Separation of the upper level of concrete from the wall was also observed, with gaps between the concrete and rock/mortar line on the order of 1/8 to ¼ inches. Cracking of the upper (older generation) footing and rock walls of the Ranger Station were observed on the north wall, with separation of the north jamb of the entrance door from the door frame observed as well. The concrete roof was observed to slope toward the south to drain, and appeared to be in good condition with no cracking or adverse sloping near the north wall.

The slab-on-grade was found to be level with minimal cracking observed, all within typical performance expectations for a structure of its age. The superstructure appears to be in good condition in general, with the structure distress localized to the north wall/footing line and near the entrance door on the northeast portion of the building. These distress patterns are consistent with attritional loss of foundation support and differential movement. The structure does not appear to be in impending failure based on the condition of the superstructure and primary foundation elements (again the attempted concrete support at lower elevation appears to be having detrimental effects), but underpinning of the north foundation line or relocation of the structure should be considered if extension of the life of this approximately 100 year-old structure is desired.

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Client Shelter/Gombu

The Client Shelter/Gombu is located on the southwest portion of the developed area, immediately south of the Ranger Station. The structure is constructed of wood studs and plywood sheathing, supported by 4x4 timbers bearing on isolated concrete pad footings with cable anchors placed over the top of the structure and embedded below exiting grade near the lower retaining wall (reportedly within permafrost). The pad footings appear to be sitting directly on the unconsolidated talus/pumice slope materials and a large portion of the structure is exposed from beneath. This shelter is utilized by the climbing concessionaires during trips with customers from Paradise to the Summit of Mt. Rainier. It is our understanding that the temporary structure is to be replaced, and relocated. As this structure is not permanent and is programmed for replacement, evaluation of the existing structure was limited to the observations noted above.

Construction of a new climbing concessionaire shelter, or relocation of the existing shelter, are considerations provided in the foundation discussion.

West Toilet

The West Toilet was constructed in the 2018-2019 season, with the exception of completion of façade rock materials. The toilet construction, as shown in the design drawings provided for our review by NPS, includes the foundation of the structure steel (Hollow Structural Section beam/column) on isolated reinforced concrete spread footings, or piers. The foundation elements consist of prefabricated BF-36 Forms (high density polyethylene plastic forms) 36 inches in diameter at bearing elevation, tapering to an 18-inch diameter pier (Sonotube) extending to the structural steel connection point. The foundations bear in the permafrost layer at approximately 42 inches below existing grade. It was reported that, during excavation of the foundations, a jackhammer was required to excavate to bearing level within the permafrost layer. The West Toilet is relatively new without the full rock façade constructed, therefore no distress was observed. This foundation alternative appears to provide a reasonable and reliable method for new construction, and has been proven to be able to be constructable with the resources that can be called on for use at the Camp Muir Developed Area.

Butler Shelter

The existing A-frame structure has been impacted by past rockfall, with rocks between two and three feet in diameter reportedly having struck the upslope side of the building. As such, the Butler Shelter has been condemned for use and is currently slated for demolition. It is anticipated that a cooking structure may be considered in the area, or slightly to the east of the Butler Shelter and above the Ranger Station. The Butler Shelter, aside from damage from rock impacts is in relatively good condition with a concrete slab-on-grade that is performing well.

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GEOHAZARD MITIGATION

There are several locations at Camp Muir that are potentially impacted by geohazard issues that include the effects of glaciation, rock plucking, rockfall, and potential rock toppling issues. Some of these areas, west-northwest of the current Historic Guide Shelter (Ranger Station) and north of the Historic Public Shelter, could benefit from the installation of rockfall mitigation structures, mesh netting, or potentially rock bolting or micropile installation. While some of these areas, such as the area directly downhill and north of the Historic Guide Shelter (Ranger Station), may be better served by operational controls to limit encroachment of tent camping to some distance from the rock face. There are also rockfall-generating zones adjacent to Camp Muir outside of the Camp Muir Historic District (and, in one instance, encroaching into the Wilderness Boundary) where no action is allowable, dictating that only operational controls are feasible.

The geohazard mitigation measures discussed below are intended to stabilize the subject geohazard issues, using construction methodologies feasible for installation using only helicopter-portable equipment, such as modular drilling equipment. When considering potential mitigation alternatives for the various geohazard issues present at the site, our focus has been to limit mitigation equipment or materials transported to the site to that equipment/material which can be broken down into load sizes capable of being lifted to the site by available KAMAX helicopters, a medium lift helicopter slightly larger than the support ship used during our August 2020 exploration at the site. Transport of larger equipment can be made by larger helicopters, but in all cases, helicopter availability and construction requiring helicopter lift capabilities is often very dependent on firefighting resource requirements in any given year.

In most cases, the potential geohazard mitigation can be made to conform to the appearance of the historic structures at Camp Muir. For several mitigation measures, such as the use of high-strength wire mesh slope stabilization fabric or the use of rock bolts/micropiles, the material can be stained or powder coated to mimic the appearance of the surrounding rock, but these materials will be visible (in the case of wire rope mesh) or may be visible (in the case of stacked rock veneer over gabions or the termination of rock bolts that are buried within rock veneer). In reviewing the proposed geohazard mitigation elements, NPS and other stakeholders will have to decide if the benefits of the various proposed alternatives outweigh the (potentially) adverse visual impact to the site.

The proposed mitigation concepts and methodologies are discussed below, with reference to exhibits included in the Figures section of this report. The attached Figures 7 and 8 are maps of the site, adapted from drawings provided in the NPS Camp Muir Rehabilitation Plan 2012, that delineate the historic/wilderness limits and the locations of facilities that are part of the currently preferred restoration alternative. Additional exhibits (Figures 9-16) reference photographs taken by Terracon during our August 2020 site visit, and refer to specific geohazard areas and the potential mitigation alternatives available and feasible for installation at the site.

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When reviewing this document, the reader is encouraged to consider the unique issues that steer design and construction efforts for a project such as Camp Muir Redevelopment. First of all, the site is remote, at an elevation of 10,080 feet. Access is only by alpine climbing or via helicopter lift. Delivery of most materials is only practical by helicopter lift, significantly limiting the type and weight of equipment that can be transported to the site. Regrading to facilitate slope safety could be easily accomplished on flat ground by driving a Caterpillar (CAT) 345 excavator with a bucket and thumb to the site and then flattening slopes or by simply reaching and moving potentially unstable boulders. Likewise, potentially unstable rock outcrops next to a highway would either be rock bolted into place or would be scaled or blasted off from their precarious position. None of these methodologies is feasible for the site, given the fact that a CAT 345 is simply too heavy to be lifted by a helicopter in one unit, and that same equipment is not modular, meaning that it cannot be readily broken down into modules that could be lifted by a helicopter.