TIMPANOGOS CAVE NATIONAL MONUMENT ROCKFALL MITIGATION MEASURES UT FLTP TICA 10(992)

GEOTECHNICAL DESIGN REPORT Report # UT-PX-TICA-13-01

Geotechnical Services Branch July 2013

TABLE OF CONTENTS

REPORT PAGE

1.0 INTRODUCTION ...... 1 1.1 Scope of Rockfall Hazard Evaluation ...... 1 1.2 Previous Reports and Investigations ...... 2

2.0 GEOLOGY AND SEISMICITY ...... 3 2.1 Site Geology ...... 3 2.2 Regional and Local Seismic Setting ...... 3 2.3 Geologic Hazards ...... 4 2.4 NPS Geologic Hazard Policy ...... 5

3.0 PROCEDURES AND RESULTS ...... 7 3.1 Findings ...... 7

4.0 ANALYSIS AND RECOMMENDATIONS ...... 12 4.1 Rockfall Analysis ...... 13 4.2 Rockfall Mitigation Recommendations ...... 16 4.3 Rock Scaling Recommendations ...... 17 4.4 Rockfall Hazard Rating System Assessment ...... 17 4.5 Construction Considerations ...... 19

5.0 DISCLAIMER/LIMITATIONS CLAUSE ...... 20

6.0 REFERENCES ...... 21

APPENDICES

Appendix A – Figures Appendix B – NPS Geologic Hazards Management Policy Appendix C – Rockfall Mitigation Methods Appendix D – Rockfall Analysis Data Appendix E – Rockfall Fence Details Appendix F - Special Contract Requirements Appendix G – Photos

Page i 1.0 INTRODUCTION

This report presents the findings of a visual reconnaissance and provides geotechnical recommendations to support the development of a rockfall hazard evaluation and associated mitigation measures within the Timpanogos Cave National Monument (TICA). TICA is located within the American Fork Canyon along Utah State Highway (SH) 92, approximately 3 miles east of Highland, Utah in Utah County.

The main resource at the National Monument is the cave system providing access to Hanson Cave, Middle Cave, and Timpanogos Cave. To reach the cave, visitors must hike the strenuous, 1.5-mile-long cave trail, which rises steeply just over 1,000 feet. The Visitor Center and caves are open from late-May to late-September. A Project Vicinity Map and Project Location Map are presented in Appendix A.

Regular rockfall events within the park coupled with seasonal visitation emphasizes the need for proactive, systematic evaluation of natural slope hazards. For example, rock scaling efforts are conducted by Park staff on an annual basis on the readily accessible slopes within the Park. In addition, the United State Geological Survey (USGS) has conducted several rockfall hazard assessments of specific locations within the Park, as well as locations within American Fork Canyon.

To support ongoing efforts to improve the safety and performance of unstable natural slopes within the Park, this project focused on the following objectives:

1. Relate slope hazards and qualified risks with broader efforts to identify rockfall hazards within the Park; 2. Recommend a range of rockfall hazard mitigation strategies suited to Park resource management objectives and the effective use of maintenance resources, and apply these strategies toward site-specific hazard mitigation recommendations; and 3. Frame identified rockfall hazards and risks within the assest management architecture, emphasizing the need to treat specific rockfall hazard locations as assets requiring proactive, life-cycle type management.

This study provides an assessment and prioritization of rockfall hazards for unstable natural slopes adjacent to the current location of the TICA Visitor Center and along the cave access trail. Recommended mitigation measures, and strategies for effectively deploying these measures, are provided along with order-of-magnitude cost estimates for general mitigation measures.

1.1 Scope of Rockfall Hazard Evaluation

The rockfall hazard evaluation is focused on the current location of the TICA Visitor Center, located at the base of near-vertical rock cliffs comprised of highly fractured quartzite bedrock. The cliffs begin approximately 150 feet from the Visitor Center and extend to more than 600 feet in height. A talus slope is located below the cliffs and extends downslope to the Visitor Center. The talus slope is approximately 100-feet-high with an overall slope ratio of 1V:1H. Rockfall debris from the cliffs generally reach the vicinity of the Visitor Center and have occasionally impacted and penetrated the roof of the

Page 1 Visitor Center. A 6-foot-high chain link fence is currently located between the toe of the talus slope and the Visitor Center. The fence has been damaged and is retaining material from numerous rockfall events.

TICA is currently completing final design plans to move the Visitor Center away from these cliffs and increase parking capacity. The proposed location for the Visitor Center is at the east end of the existing parking lot. Relocating the Visitor Center will distance the structure from the runout zone of the active talus slope; thereby, providing greater protection from rockfall impacts. Relocation plans also include minor realignment of SH 92 in the vicinity of the Visitor Center to accommodate increased parking capacity.

While the proposed site is better protected from rockfalls, the demolition and removal of the existing Visitor Center and associated structures increases the rockfall hazard to the proposed parking area. As a result, TICA has requested technical assistance with the evaluation of rockfall hazards and development of rockfall protection measures.

A cursory hazard evaluation was also conducted of natural slopes along the length of the cave trail. Lower portions of the cave trail cross beneath near vertical cliffs comprised of intensely fractured Mutual Quartzite. Rocks falling from these cliffs commonly reach the vicinity of, or impact, the Visitor Center. Upper portions of the trail abut Deseret Limestone, which at this location consist of a sequence of fractured, interbedded limestones, dolomites, and quartzites. Steep gullies in the cliffs between the cave entrance and exit have been the site of numerous rockfalls. These rockfalls resulted in one fatality in 1933 and several near misses, which has prompted the construction of suspended, weighted fences to attenuate rockfall, as well as rockfall shelters at the cave entrance and exit in 1976.

During the summer months, thousands of visitors per day access the trail and visit the cave system. Areas along the trail with known, significant rockfall hazards are marked with a red stripe. Trail users are advised to be cautious and not stop to rest in these areas.

1.2 Previous Reports and Investigations

Geotechnical personnel from CFLHD were originally consulted for technical expertise on this project in August 2009. A trip report was prepared during the initial consultation which provided preliminary geotechnical recommendations on a rockfall catchment system. The recommendations were based on a visual inspection and estimates of rock slope geometry and characteristics.

Page 2 2.0 GEOLOGY AND SEISMICITY

American Fork Canyon is a deeply incised canyon that transects the Wasatch Mountain Range in central Utah. Specifically, the Canyon is within the deeply dissected Wasatch Front of northern Utah. The Wasatch Range is characterized by rugged mountain faces and narrow, east-west trending, steep sided canyons. Rapid regional uplift has caused many of the streams that drain the west side of the Wasatch Front to erode headward, carving back canyons, until they reach the mountain crests.

The Wasatch Range is an uplifted block that extends approximately 120 miles. The range is 8- to 16-miles-wide and is bounded on the west by the scarp of the seismically active Wasatch Front. The Wasatch Front rises dramatically from the valley floor and separates the geologic province of the Basin and Range to the west from the Middle Rocky Mountain province to the east. The Wasatch range is geologically complex and is characterized by the normal faults along which the Basin and Range deformation occurred. There are many parallel ranges throughout the Timpanogos region due to the extensional tectonics pulling the crust apart in an east-west oriented pattern. Many westward flowing, high gradient, parallel streams dissect the Wasatch Front into isolated peaks separated by deep, narrow canyons.

The lower part of the America Fork Canyon is V-shaped as a result of downcutting by the American Fork River. The upper reaches of the canyon were glaciated in Pleistocene time. American Fork Canyon trends east-west, and extends approximately 20 miles to a fault zone responsible for the formation of the Timpanogos Cave complex.

2.1 Site Geology

Currently, the Visitor Center is located at the base of near-vertical cliffs that rise over 600 feet above the floor of American Fork Canyon. A talus slope extends from the base of the cliffs to the rear of the Visitor Center. The cliffs above the Visitor Center are truncated along a north-draining side canyon and a talus slope extends along the east-facing part of the cliffs. The trail to the Timpanogos Cave complex crosses the lower portion of the east talus slope and the top of the talus slope immediately behind the Visitor Center.

The cliffs above the Visitor Center are comprised of highly fractured, Precambrian Mutual Quartzite, as are the talus slopes adjacent to the Visitor Center. Cobbles and boulders predominate on the talus slope behind the Visitor Center, where most boulders have an intermediate dimension of 6 to 12 inches, with some as large as 4 feet. The east talus slope has boulders of larger size, with most having an intermediate dimension of 1 to 2 feet, with some as large as 6 feet.

2.2 Regional and Local Seismic Setting

The Wasatch Range is tectonically active. The western flank of the range forms the eastern boundary of the Basin and Range province. This boundary is marked by a zone of active faults known as the Wasatch fault zone. The surface expression of this zone is a series of fault scarps which trend north-south along the western flank of the range. The average recurrence interval between surface-rupturing earthquakes in the central part of the

Page 3 fault zone, including the area near the mouth of American Fork Canyon is about 400 years (Machette and others, 1992).

Recommended seismic response parameters for design are based on the (AASHTO) LRFD Bridge Design Specifications, 5th edition, 2010, and represents horizontal peak ground acceleration (PGA) with 7 percent probability of exceedance in 75 years (approximately 1000-year return period). The 1000-year return period uniform hazard spectrum for the project site, located at 40.444º N latitude and -111.669º W longitude, was obtained in accordance with the AASHTO ground motion maps for the probabilistic horizontal acceleration values corresponding to specific peak ground acceleration (PGA) and the spectral coefficients, namely the short- and long- period ground acceleration (Ss and S1 respectively) and corrected for the soil profile at the site. Based on visual analysis of native soils, the soils are classified as Class D according to the site class definitions specified in Table 3.10.3.1-1 of AASHTO.

A seismic hazard analysis to establish ground motions for seismic design was conducted. The recommended spectral acceleration coefficient values for probabilistic design with a return period of 1000 years were calculated using the program provided with the AASHTO LRFD Bridge Design Manual developed by the USGS (2008) entitled “Seismic Design Parameters”, version 2.10 and are summarized in Table 1, Summary of Seismic Parameters Corrected for Class D Soils.

Horizontal Peak Ground Acceleration, (As) 0.364g Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDs) 0..862g Horizontal Response Spectral Acceleration at Period of 1.0 sec, (SD1) 0.465g Site Factor at Zero-Period of Acceleration Spectrum, (Fpga) 1.22 Site Factor at Short-Period Range of Acceleration Spectrum, (Fa) 1.25 Site Factor at Long-Period Range of Acceleration Spectrum, (Fv) 1.92

Table 1. Summary of Seismic Parameters Corrected for Class D Soils.

Based on the long acceleration coefficient SD1 value of 0.465 g, calculated as FvS1, the site is assigned to seismic hazard Zone 3 according to Table 3.10.6-1 in AASHTO. Seismic hazard zones reflect the variation in seismic risk in different regions needing different requirements for design.

2.3 Geologic Hazards

There are a variety of geologic hazards present in the Timpanogos Cave area; however, most hazards are associated with mass wasting. The presence of highly fractured Mutual Quartzite along the high cliffs above the existing Visitor Center indicates that all areas in the general vicinity are exposed to hazards from rockfall. The presence of mature talus slopes with little or no vegetation is indicative that rockfall has been occurring for some time and that these cliffs continue to actively produce rockfall. In general, the risk of rockfall is highest near the base of the cliffs and adjacent talus slopes, and lowest in the center of the canyon floor. Rockfall events are typically most common in the winter and spring seasons, as hydraulic forces from precipitation events or snowmelt remove blocks from the cliff faces that were previously loosened as a result of physical weathering by

Page 4 freeze-thaw cycles and associated ice wedging. There are documented cases of rockfall occurring as a result of human and animal activities (hikers, mountain goats) in the Timpanogos Cave area. There are also documented cases of rockfall occurring as a result of seismic activity in canyons adjacent to American Fork Canyon.

A debris fan exists just to the east of the current Visitor Center. The debris fan has built up over time and is a result of recurring debris flows. The debris fan extends to the American Fork River on the north and to the existing Visitor Center parking lot on the west. The toe of this debris fan has been excavated to accommodate SH 92 and the Visitor Center parking lot, exposing debris flow deposits. The debris fan originates in the side canyon east of the existing Visitor Center. This side canyon is heavily forested, except for a narrow debris flow channel in the middle of the canyon. The debris flow channel lacks significant vegetation and organic material indicating that the channel remains active. The debris flow channel flattens as it reaches the mouth of the side canyon and disperses to feed the debris fan. The debris flow does not pose a significant hazard and has likely not been active for several decades, as evidenced by the mature forest cover atop the debris fan. This mature forest cover also provides a screen from future debris flow significantly impacting SH 92 or adjacent Park Service facilities.

The project site is located in a seismically active area. Ground motions caused by an earthquake are influenced not only by the distance from the fault planes, but also by the geology found at the site. Amplified ground motions are expected in areas underlain by alluvial materials within American Fork Canyon.

In general, saturated, loose clean sand is prone to liquefaction or lateral spreading during seismic events. Groundwater depths are relatively shallow within the canyon in areas adjacent to the American Fork River. The relative density of observed soils within the canyon indicates that these soils are generally not prone to liquefaction or lateral spreading. Although not anticipated, localized liquefaction and lateral spreading may occur in small zones under seismic loading conditions.

American Fork Canyon is prone to sporadic flood events. These events usually occur in the summer monsoon months, between June and September. Past flood events have caused damage to Park Service facilities adjacent to the American Fork River. Road closures within the canyon have also been enacted at various times as a result of flooding and associated mudslide damage.

2.4 NPS Geologic Hazard Policy

Based on current rockfall hazard evaluation efforts by the Central Federal Lands Highway Division and previous efforts by the USGS, Timpanogos Cave National Park is undertaking proactive measures to address at-risk facilities and minimize visitor exposure to rockfall events. The following excerpt from NPS Director’s Order #50C demonstrates a clear understanding of the extent to which rockfall may be managed and/or mitigated within the Park:

“In fulfilling [it’s] mission, the NPS must balance issues of access against those of safety. Toward this goal, the NPS, “…must strive to prevent visitor injuries and

Page 5 fatalities within the limits of available resources.” – National Park Service Director’s Order #50C: Public Risk Management Program

Further, Director’s Order #50C states that Park Superintendents “…should strive to minimize the frequency and severity of visitor incidents by developing a range of appropriate prevention strategies and implementing risk reduction mitigation plans.” Examples of such strategies include “…conducting periodic risk assessments to identify and appropriately mitigate hazards,” and “…integrating safety measures into the design and maintenance of park facilities, as appropriate, feasible, and consistent with NPS and park mandates.” – Section 4.1 Management and Incident Reduction, Operational Policies and Procedures.

These directives, and others presented in Appendix B, not only compel the Park to undertake measures to enhance visitor safety, but require hazard mitigation strategies that are cognizant of both natural and financial resource preservation needs.

Page 6 3.0 PROCEDURES AND RESULTS

The Central Federal Lands Highway Division (CFLHD) Geotechnical Section completed a field exploration program for Project UT FLTP TICA 10(992) on June 5 and 6, 2013. The scope of work for the field exploration program included a visual investigation and measurements, as well as the completion of a LiDAR scan of the slopes adjacent to the existing Visitor Center. LiDAR is a remote sensing technique that measures distance by illuminating a target with a laser and then analyzing the reflected light. The LiDAR scan was used to create a three-dimensional model of the cliffs and slopes adjacent to the existing Visitor Center. The three-dimensional model was then used in completing rockfall analyses.

3.1 Findings

In general, the visual reconnaissance at the project site concentrated on the area immediately behind the existing Visitor Center, including the active talus slope and cave access trail crossing the upper reaches of the talus slope. The Mutual Quartzite cliffs that rise above the talus slope and Visitor Center were only observed from a distance or along the cave trail where access to the cliffs could more easily be obtained.

The vertical height of the talus slope is approximately 100 feet with an overall slope ratio of 1V:1H. The majority of material on the talus slope has an intermediate dimension less than 6 inches. A 6-foot-high chain link fence is located in the breakout zone of the talus slope, a level area between the toe of the talus slope and the Visitor Center. The fence has been damaged and is retaining material from numerous rockfall events.

Wolman counts were performed on representative rock particles on the talus slope, as well as particles within the breakout zone of the talus slope (within 4 feet of the existing chain link fence behind the Visitor Center). The Wolman count is a method used to determine the size distribution of riprap rock based on a random sampling of individual particles within a matrix. While the method is typically used to size riprap sources, it works equally well on talus slopes, or other areas predominately covered with rock particles. The gradation curves as a result of these Wolman counts are presented in Figure 1.

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Figure 1. Size Distribution of Rock Particles Associated With Talus Field.

An interesting observation from review of these size distribution curves is that particles within the talus slope are generally smaller than those which reach the breakout zone of the talus slope. Therefore, it can be concluded that individual rockfall particles with an intermediate dimension of 6 inches or less are generally retained within the talus slope and do not reach the breakout zone. Rockfall particles with an intermediate dimension greater than 6 inches generally have sufficient mass and energy to reach the breakout zone and cause damage to nearby structures, property, or Park users.

The existing 6-foot-high chain link fence located in the breakout zone of the talus slope provides a minimal level of rockfall retention and protection. This fence was clearly not intended to serve as a rockfall barrier and should not be relied upon as a future rockfall protection measure. While the fence is currently retaining small rocks, the fence has been penetrated several times by larger rockfall.

Observations and measurements of the cliff face indicate the presence of a predominant joint set dipping out of the face of the cliff. Dip and dip direction measurements yield a joint orientation of 50/000. There is also a fracture set which is oriented roughly 90 degrees from the predominant joint set, resulting in the release of fairly blocky rockfall particles. The size of rockfall particles is a function of the fracture spacing, which in the cliffs immediately behind the existing Visitor Center ranges from approximately 4 to 24 inches. Numerous unstable rock blocks, which pose a potential threat to Park users, were observed on slopes immediately behind the existing Visitor Center, as well as slopes adjacent to the entire cave trail. The cliffs above the side canyon to the east of the existing Visitor Center have a significantly wider fracture spacing, which yields rockfall particles with an intermediate dimension ranging between 12 and 48 inches, as observed on adjacent talus slopes.

There are several prominent features on the cliff face that contribute to the rockfall issue at TICA, specifically the concentration of rockfall in talus runout zones. A north-south Page 8 trending ridgeline abuts the cliff face on its lower portion, separating the talus slopes adjacent to the existing Visitor Center. There is also a concave feature west of the ridgeline which channels rockfall through a chute and into the talus slope directly behind the existing Visitor Center. While no single rockfall source area was observed during field reconnaissance efforts, it is thought that rockfall generation is evenly and widely distributed along the cliff face. These features are labeled in Figure 2.

Figure 2. Cliff Features.

Page 9 Along the cave access trail, numerous locations of unstable, overhanging blocks were observed within the Mutual Quartzite and Deseret Limestone units. Many of these unstable blocks are created due to adverse bedding and fracture plane orientation within the rock mass. In several locations, daylighting joint sets were observed immediately adjacent to or above portions of the trail. Figure 3 highlights some of the adverse joint orientations. In addition USGS studies have noted the presence of a section of limestone cliff pulling away from overlying bedding layers in the vicinity of the cave exit (Harp, Dart, and Reichenbach, 2010).

Figure 3. Adverse joint orientation of Quartzite rock mass along the cave access trail.

Based on the findings of this study, it is generally recommended to:

1. Construct a flexible rockfall fence behind the current location of the Visitor Center to protect facilities from ongoing, natural rockfall events, as well as future scaling efforts; 2. Hand-scale isolated, loose Quartzite and Limestone blocks posing imminent safety threats to Park users on slopes above the current location of the Visitor Center and along the cave access trail (the scaling effort should be commenced shortly after construction of the flexible rockfall fence is complete;

Page 10 3. Complete a detailed Rockfall Hazard Rating System (RHRS) assessment of all slopes adjacent to critical Park facilities, namely the Visitor Center area and the cave access trail; and 4. Develop a systematic and prioritized approach to mitigating specific rockfall hazard locations, as identified in the RHRS assessment, which maximizes available resources using a life-cycle management system.

Following this general approach will mitigate immediate hazards, cost-effectively raise the rockfall hazard “health” of the Park’s facilities, and systematically improve the highest risk slopes in the Park with appropriately timed and measured expenditures.

Page 11 4.0 ANALYSIS AND RECOMMENDATIONS

Once general corrective measures are selected for a rockfall site, the project goals are typically considered to establish the appropriate level of response and the specific design criteria. The goal of rockfall mitigation measures can range from continued maintenance, to hazard reduction, to hazard elimination. Ideally, mitigation decisions optimize life- safety, property, and mobility risk reduction with available financial resources.

The main categories of engineered rockfall mitigation measures are avoidance, stabilization, and protection. Avoidance measures relocate facilities or persons away from hazardous rockfall sites without reducing the potential for rockfall. Stabilization measures seek to inhibit the fall from occurring by anchoring rock blocks in place with rock bolting techniques or by strategically removing unstable blocks in a controlled manner with rock scaling or blasting methods. Protection measures are intended to capture falling rocks and prevent them from reaching protected areas. A more detailed presentation of available rockfall mitigation methods with associated costs is presented in Appendix C.

Due to the nature of Park Service facilities within American Fork Canyon, namely the limited footprint of existing structures and the need to maintain access to the cave trail, relocation beyond all rockfall impacts is not a feasible rockfall mitigation alternative. The Park Service has taken steps to relocate the Visitor Center to a more protected location; however, rockfall will still pose a threat to the parking area. The potential risk of rockfall impacting the parking area will be greater than it currently is, as the existing Visitor Center serves a function as a rockfall barrier.

Mitigation measures focused on stabilization are not feasible at this site because of the geology on adjacent slopes and cliff faces. The Mutual Quartzite that comprises the cliff faces above the existing Visitor Center is intensely fractured, such that stabilization techniques (rock bolting, lashing, buttressing) would be ineffective. The source zone for rockfall generation is thought to be uniformly distributed along the cliff face, as evidenced by the wide talus fan. While there are features on the cliff face that channel falling rock, there does not appear to be one specific source zone that could readily accommodate stabilization measures in a cost effective manner. Rock scaling methods in accessible areas could have a limited effect on reducing the rockfall potential in selected areas.

Because relocation and stabilization mitigation measures were not considered feasible, rockfall protection measures were given due consideration. Protection measures are considered passive systems, as they do not actively reinforce or remove the hazard, but provide a barrier, control rockfall trajectory, reduce rockfall energy, or provide a catchment area. The most common protection measures include: catchment areas, rigid barriers, flexible fences, and drapery.

Rockfall catchment areas (ditches) are designed to catch and retain a high percentage of moving rocks before they impact adjacent facilities by dissipating their energy with the catchment zone. Using a variety of design criteria and the given geometry of the rock slopes at TICA, a catchment area approximately 30 feet wide is required to achieve a reasonable improvement in the retention level of rockfall from existing conditions. The

Page 12 required catchment area width is not practical without significant excavation into the talus slope and revision of the existing plans for the relocated Visitor Center and parking area.

Rigid barriers can deflect or contain rockfall depending on their location and orientation with respect to rockfall trajectory. Rigid barriers have been constructed with a variety of materials over the years, including earthen/rock berms, and structural walls (e.g., concrete gravity walls, soldier pile walls, MSE walls). A barrier designed to achieve a reasonable retention level of rockfall would either have a significant footprint, larger than could be accommodated at the site, or would be cost prohibitive because of its required height. Aesthetic considerations could be a major drawback to the use of rigid barriers to retain rockfall.

Drapery systems are commonly used to control the velocity and energy of rockfall at or near its source. Drapery consists of wire mesh suspended down the slope from anchors at or near the slope crest. The drapery system allows rockfall to occur between the slope and the mesh, controlling its descent into a catchment area at the base of the slope. Drapery systems can be used to shorten the effective height of a slope, which reduces rockfall velocity, energy, bounce height, and runout distance. Due to the extensive nature of the rockfall source area at the project site, difficult high slope access, and extreme slope height, drapery systems are considered cost prohibitive from both an installation and continued maintenance perspective. Drapery will also create a substantial visual impact on the high slopes.

Flexible rockfall fences are also used to deflect or retain rockfall. The fence systems use a net suspended from anchored posts to intercept falling rocks. The system also relies on anchored tieback and lateral cables fitted with energy dissipation devices to contain rockfall and reduce fence damage. Flexible fences are generally cost effective solutions to rockfall issues and have versatile placement options along slopes. For these reasons, flexible rockfall fences are considered a suitable mitigation alternative for the project site. Therefore, flexible rockfall fences will be further evaluated and analyzed to determine the minimum height and energy rating that will be most effective for this site.

4.1 Rockfall Analysis

Using the actual three dimensional slope geometry, derived from a ground-based LiDAR scan, a rockfall analysis was performed on the cliff faces and talus slopes directly behind the existing Visitor Center using CRSP-3D. The CRSP-3D analysis program is a numerical modeling tool for evaluating rockfall events and provides design criteria for rockfall fences, catchment ditches, catchment berms and other rockfall protection structures. CRSP-3D uses the Discrete Element Method for dynamic model simulation using the equations of motion for a more accurate approximation of rock and slope interaction than the methods employed by previous versions of CRSP. CRSP-3D allows the slope profile to be generated from slope survey data, including LiDAR scans, which produce much more representative slope conditions and, subsequently, a more accurate three dimensional rockfall analysis. The use of a three dimensional slope provides the ability to model possible rockfall paths on a section of slope, and has the capability to model the rotational movement of non-spherical rocks giving a more accurate portrayal of rockfall dispersion, runout distance, trajectory, bounce height, and energy along the slope.

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The CRSP-3D software requires various, site specific rockfall parameters to be input, in an effort to create a more accurate simulation model. Mechanical properties of the slope, including hardness and roughness values were input into CRSP-3D, based on observations and estimations made during the field reconnaissance and as recommended in the CRSP- 3D user’s manual (Andrew et al., 2012). Various analysis points along the slope were input into the program to determine various characteristics of simulated rockfall, including velocity, bounce height, kinetic energy, and rollout distance. These characteristics are critical to the design of rockfall protection structures. Falling rock parameters, including rock density, shape, and size were input into the program and were based on field observations and measurements along the talus slope behind the existing Visitor Center. It was assumed that the rockfall source zone originates from a widely dispersed area on the cliffs above the existing Visitor Center. These input parameters are included in the rockfall analysis report in Appendix D.

The input parameters, as described above, were varied over a number of rockfall simulations, in an effort to create a parametric analysis to determine the sensitivity of the model to various input parameters. Through this calibration effort a refined model was created that closely matches observed rockfall parameters at this site. Simulation results of the refined model are presented in Appendix D.

As mentioned previously, a number of points along the slope were analyzed as to their rockfall characteristics, in an effort to determine an optimal location to place a flexible rockfall fence. Rockfall fences placed high on the slope were found to be ineffective at retaining a large percentage of rockfall due to significant bounce heights of individual rocks. Fences placed high on the slope would also be difficult to maintain and inspect. Rockfall analyses indicated that the optimal location for a rockfall fence was near the base of the talus slope immediately behind the existing Visitor Center. A fence placed in this location would provide a suitable level of rockfall protection, as well as provide a reasonable level of access for cleanout, maintenance, and inspection. Analysis indicated a rockfall retention of 5% at the analysis point. A summary of rockfall analysis results are presented in Figures 4 and 5, with respect to an analysis point placed at an idealized rockfall flexible fence location, approximately 17 feet behind the existing Visitor Center.

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Figure 4. Rockfall Bounce Height Results.

Figure 5. Rockfall Energy Results.

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Based on the above results with respect to bounce height, the existing conditions on the talus slope behind the Visitor Center, including the effect of the existing chain link fence, provide a rockfall retention level of approximately 95%. This retention level is likely somewhat lower when rockfall energies are considered, as the fence is not designed to withstand impact loads from rockfall.

The level of desired rockfall retention for a given rockfall fence is based on a number of site specific risk factors, including the exposure of Park users and facilities to rockfall, as well as the likelihood of rockfall events, which considers the geology and weather conditions of the site. Cost considerations also have a significant effect on the desired level of rockfall retention. In most cases of highway rockfall protection structures, these mitigation measures must show an appreciable increase in the level of rockfall retention to justify their use and construction. It is generally cost prohibitive for rockfall protection structures to be designed to achieve a level of rockfall retention of nearly 100%.

4.2 Rockfall Mitigation Recommendations

A flexible rockfall fence placed on the talus slope behind the existing Visitor Center is the recommended rockfall mitigation measure for this site. As shown in Figure 4, the incremental increase in rockfall retention decreases significantly for fence heights greater than 10.0 feet (3.0 meters) in height. Therefore, it is recommended to install a flexible rockfall fence with a height of 10.0 feet (3.0 meters) to offer the most practical level of rockfall protection. While the initial capital cost of the recommended fence will be higher when compared with lower fence heights, the increased level of protection over the performance life of the fence will make it a worthwhile investment. The recommended rockfall fence provides a high level of risk protection from a life-safety perspective, while balancing the need for continued maintenance of the fence and catchment area.

A rockfall fence with a minimum energy rating of 500 kJ is recommended at this site. As shown in Figure 5, the maximum anticipated energy from simulated rockfall is 66 kJ. Rockfall fence manufacturers do provide fences rated at 100 kJ; however, they do not vary significantly, cost or otherwise, from rockfall fences rated at 500 kJ. Fences rated at 500 kJ provide additional support to fence posts from cable anchors, while fence posts in systems rated at 100 kJ are unsupported, besides their foundation components. A rockfall fence rated at 500 kJ will provide protection, and a suitable level of risk reduction, from typical rockfall events at this site, but will also provide protection against anomalous rockfall events that may produce rockfall debris of significant size.

Detail drawings and a preliminary cost estimate of the recommended rockfall fence are provided in Appendix E. Special Contract Requirements (SCR’s) for the rockfall fence are presented in Appendix F. The specified rockfall fence catches the rockfall debris and can be periodically maintained by detaching the fence from the posts and removing rockfall debris into a catchment area behind the fence. A concrete barrier is recommended to separate the proposed, expanded parking area from the rockfall catchment area. Sections of this concrete barrier can be removed, as needed, and rockfall debris in the catchment area can be excavated and removed.

Page 16 NPS plan sheets, presented in Appendix E, detailing the relocated Visitor Center and expanded parking area show head-in parking and a concrete sidewalk where the existing Visitor Center is located. It is recommended that the concrete sidewalk be deleted and replaced with a dedicated asphalt walking path that is literally an extension of the asphalt parking area, as shown in Appendix E. This will allow for easier access to maintain the rockfall fence and catchment area, while preventing significant and costly damage to adjacent structures during maintenance operations. It is assumed that the concrete barrier and asphalt sidewalk will not be part of the rockfall fence construction and will be included as part of the Visitor Center relocation contract.

4.3 Rock Scaling Recommendations

During the field reconnaissance effort on the slopes immediately above the Visitor Center and subsequent visual inspection of slopes adjacent to the entire cave trail, several areas immediately above and adjacent to the trail with unstable and fractured rock blocks were observed. Many of these blocks pose a threat to downslope structures, but more importantly, pose a potential threat to trail users. TICA staff currently performs scaling operations along the trail before the Park opens each spring, but these operations are limited by the lack of specialized equipment and expertise. It is recommended that TICA complete an extensive scaling effort in the very near term. This effort should include the expertise of a geotechnical engineer to identify locations or individual rock blocks that require scaling, in connection with a trained scaling crew capable of performing the identified scaling. The extensive scaling effort will likely reduce the amount of scaling required by TICA staff on an annual basis, but will also ensure that identified areas requiring scaling, currently beyond the capabilities of TICA staff, receive the level of attention that they require. These scaling efforts will ultimately contribute to an increased level of safety, as well as rockfall risk reduction, along the cave trail.

4.4 Rockfall Hazard Rating System Assessment

It is recommended to develop a systematic and prioritized approach to mitigating specific rockfall hazard locations adjacent to Park facilities and along the cave access trail, using the Rockfall Hazard Rating System assessment, which maximizes available resources using a life-cycle management system.

Oregon DOT first began developmental work on the “Rockfall Hazard Rating System” in 1984. An FHWA pooled fund study provided the research funding needed to complete exhaustive testing and refinement of the system, resulting in publication of the methodology in the early 90’s (Pierson, 1991; Pierson and Van Vickle, 1993). Since that time, the RHRS methodology and variants of the original rating system have been deployed nationwide by federal, state and municipal transportation agencies to quantify rockfall hazards and characterize associated risks. As noted in the 1993 FHWA RHRS manual (Pierson and Van Vickle, 1993), the tool provides a “…legally defensible, standardized way to prioritize the use of the limited construction funds available by numerically differentiating the apparent risks at rockfall sites.”

For the proposed RHRS assessment in TICA, a two-phase approach is recommended to scope slope hazards adjacent to Park facilities and along the cave access trail: (1)

Page 17 preliminary screening of natural slopes within the Park, including a simple, relative slope hazard/maintenance level rating (1-5 scale) with Park maintenance staff; and (2) RHRS rating of slopes with potential rockfall hazards.

The RHRS was developed as a process to allow agencies to actively manage the rock slopes along their highway system. The RHRS is comprised of ten rating elements (risk factors), as follows:

1. Slope Height 2. Ditch Effectiveness 3. Average Vehicle Risk 4. Percent of Design Site Distance 5. Roadway Width 6. Geologic Character (Case 1) - Case 1 refers to slopes where joints, bedding planes, or other discontinuities are the dominant features leading to rockfall. 7. Geologic Character (Case 2) - Case 2 refers to slopes where differential erosion or oversteepening is the dominant condition that leads to rockfall. Erosion features included failing debris slopes, unsupported rock units, or exposed resistant rocks either locally or throughout the slope. 8. Block Size Range/Volume of Rockfall Per Event 9. Slope, Water, and Ice Conditions 10. Rockfall History

Because the proposed RHRS assessment in TICA is not focused on slopes along a highway system, it will have to be modified slightly to reflect the specific assessment needs. This modification is easily done by deleting elements 4 and 5. Slight adjustments will also need to be made to elements 2 and 3. Element 2 will become a factor of natural slope catchment and will qualitatively evaluate the amount of rockfall that reaches the trail or adjacent facility. Element 3 becomes a factor of average trail user risk and will quantitatively measure the percentage of time a hiker will be present in the rockfall zone based on slope length, number of trail users, and average hiking speed.

The purpose of the rating system is to numerically differentiate the risks at the identified sites. Slopes are given a score for each rating element and the individual rating element scores are then totaled. Slopes with higher scores present the greater risk. Once rated, the sites can be sorted and prioritized on the basis of their scores.

Based on results of RHRS assessment in other National Parks, it is not appropriate to believe that failure to mitigate rockfall hazards on the highest rated slopes first assigns liability to the park should an accident occur at one of these locations. Engineering “standard of care” requires that available means for characterizing, assessing, managing and mitigating hazards be taken as fiscally practicable. By conducting the RHRS evaluation and then devising a prudent strategy for the expenditure of funds, addressing localized, low cost immediate hazards first, systematic modest cost hazard over large areas next, and then high cost localized hazards as possible – the overall health of natural slopes within the Park is methodically improved year-to-year, optimizing user safety per dollar spent.

Page 18 4.5 Construction Considerations

Overhead Power Line: Currently, there is an overhead power line located above the talus slope behind the existing Visitor Center. This power line will require special attention during construction of the rockfall fence. There is a possibility that the power line may need to be relocated, at least temporarily during fence construction.

Construction Access: During field reconnaissance efforts, Park Service staff expressed a desire for construction of the rockfall fence to proceed prior to demolition of the existing Visitor Center. The area behind the existing Visitor Center is very confined and while compact, specialized construction equipment could be used, it would significantly add to the construction costs. It is recommended that construction of the rockfall fence proceed immediately following demolition of the existing Visitor Center, but prior to construction of the expanded parking area.

Page 19

5.0 DISCLAIMER/LIMITATIONS CLAUSE

The Analysis and Recommendations section in this report include interpretations and recommendations developed by the Government in the process of preparing the design. These interpretations are not intended as a substitute for the personal investigation, independent interpretation, and judgment of the Contractor.

Page 20

6.0 REFERENCES

Andrew, R.D., R. Bartingdale, H. Hume, A. Rock, and R. Zhang, 2012, CRSP-3D User’s Manual, FHWA-CFL/TD-12-007, available at www.cflhd.gov, February 2012, 64 pp.

Harp, E.L., Dart, R., and Rechenbach, 2010, “Rock fall simulation at Timpanogos Cave National Monument, American Fork Canyon, Utah, USA”, Landslides, published online January 27, 2011.

Machette, M.N., Personius, S.F., and Nelson, A.R., 1992, “Paeleoseismology of the Wasatch Fault Zone: A summary of recent investigation, interpretations, and conclusions”, Assessment of regional earthquake hazards and risk along the Wasatch Front, Utah: U.S. Geological Survey Professional Paper 1500-A, p. A1- A71.

Pierson, L.A. and R. Van Vickle, 1993,Rockfall Hazard Rating System, Federal Highway Administration Publication No. FHWA-SA-93-057, November 1993, 104 pp.

Pierson, L.A., 1991, “The Rockfall Hazard Rating System”, Oregon Department of Transportation, Federal Highway Administration Publication No. FHWA-OR-GT- 92-05, November 1991, 16 pp.

Page 21 APPENDIX A – Figures

Project Site

UT FLTP TICA 10(992) Timpanogos Cave National Monument

Figure 1 Project Location Map APPENDIX B – NPS Geologic Hazards Policy

APPENDIX C – Rockfall Mitigation Methods Excerpt from DeMarco, M., 2012, “Yosemite National Park Engineered Slope Rockfall Study”, Geotechnical Report No. CA-PX-YOSE-12-01, Central Federal Lands Highway Division, FHWA, October 2012, 108 pp.

C.0 ROCKFALL MITIGATION METHODS

The goals of a successful rockfall mitigation program for engineered cut slopes should include:

o Consistently increasing slope safety in alignment with existing and future slope performance objectives for the route; o Deploying long-life mitigation measures not requiring excessive or expensive maintenance, whenever possible; o Maximizing the use of available construction/maintenance skills and materials within the park; o Applying measures that best meet aesthetic, cultural and historic requirements of the roadway corridor, and balancing these requirements with asset safety; and o Consistent application of repair options park-wide for strategic expenditure allocations.

With these in mind, rockfall mitigation measures (summarized in Section C.11) should be deployed in an escalating fashion regarding effectiveness (maintainable vs. permanent solutions), installation cost, long-term maintenance cost, and visual impact to the facility. This section describes, in ascending order of complexity and cost, some of the more frequently used methods for rockfall mitigation and describes their application per a variety of slope types.

Additional information regarding application of the RHRS to selecting rockfall mitigation measures can be found in the recent rockfall engineering study completed by the FHWA Western Federal Lands Highway Division (WFLHD) for Crater Lakes National Park (Lofgren and Jenks, 2010). Detailed descriptions of slope stabilization and rockfall management systems can also be found in the CFLHD Technology Deployment Program publication entitled, “Context Sensitive Rock Slope Design Solutions” (Andrew et.al, 2011), available at www.cflhd.gov.

C.1 SLOPE SCALING

Slope scaling is the removal of loose, broken, or partially detached rock from the slope using manual methods, excavation equipment, or trim blasting techniques. Manual, or “hand-scaling”, methods commonly involve 2-3 man crews consisting of experienced scalers skilled at systematically removing loose, isolated rockfall hazards with a variety of specialized hand tools, manual and pneumatic jacks, and light blasting options. Scaling crews typically work off ropes, but may occasionally work from crane baskets or lifts, and always require spotters on the roadway to continually survey the slope for unsafe working conditions. Slope excavation, or “machine-scaling”, methods commonly involve excavators using buckets to pry rock from the slope, hydraulic hammers to bring down larger unstable rock masses, and/or heavy chains to brush large quantities of loose debris from the slope. Machine scaling uses similar crew sizes and clean-up/haul equipment as hand-scaling, and also relies on roadway spotters to ensure operation safety. Hand-scaling and machine-scaling may be done in tandem on raveling slopes where high, localized rockfall exists outside the reach of common excavators (30-40 ft). For high slopes with substantial rockfall hazard, long-reach excavators are available that extend to well over 100 ft.

Figure 1. Slope scaling and top-slope rounding using long-reach excavator, Hyampom Road, Hyampom, CA (Andrew, et.al, 2011).

Systematic scaling along a route is the most efficient and effective option for rapidly upgrading the safety and maintenance performance of engineered slopes in the park. Coupling top-slope rounding on eroding slopes and ditch improvements with slope scaling, which utilizes the same equipment and crews, may greatly mitigate pending rockfall hazards and extend the service life of slope improvements, thereby substantially deferring routine slope maintenance expenditures.

Key attributes of slope scaling include:  For slopes with moderate to low volumes of loose rock, scaling crews can quickly dress slopes with minimal delays to traffic. For slopes with large rockfall volumes, large localized rock masses to be removed, dangerous rockfall exposures high on the slope, or requiring slope crest excavation, roadway closures may be required.  Scaling cannot be expected to remove the entire loose rock hazard from the slope. Hand- scalers will generally do a better job of removing small, loose rock to ensure safe overhead conditions as work progresses downslope. Machine-scaling operations typically remove larger volumes of larger rock from the slope, but tend to leave small slope debris behind. “Chaining” or “brushing” by dragging chains, dozer tracks, etc. over the slope can be effective in removing small rock debris.  Scaling results are proportional to the skill and experience of the scalers. Experienced crews cost more, but typically work faster and produce higher quality results (buying years of slope performance in many cases).

 Unsupervised scaling may turn into small mining operations if expected results are not well communicated, resulting in substantial over-excavation and quantity and schedule cost overruns.  Scaling is not a permanent solution to rockfall. Scaling frequency is dependent on many factors, including the erosional/weathering durability of the slope, extent and persistence of structural features producing loose rock, and presence of other effective mitigation measures such as catchment ditches or barriers.

Figure 2. Hand-scalers systematically removing loose material from high cut slope, South Fork Smith River Road, Crescent City, CA (Andrew, et.al, 2011).

Rock removal may leave behind obvious fresh rock exposures that impact visual aesthetics. Consideration may be given to rock staining options in such cases.

Effective scaling programs require clearly communicated expectations during contracting (pre- bid on-site meetings and special contract specifications), and supervised operations by knowledgeable construction management staff. Scaling measures for each major type of slope –

jointed rock, raveling weathered rock, colluvial boulder accumulations, etc. – should be evaluated early in the scaling program for continuity of work products.

C.2 ROCKFALL CATCHMENT DITCHES

When space permits, engineered catchment ditches are effective measures for controlling the amount of rock falling onto the roadway. State-of-the-practice catchment ditch design currently follows the guidance provided in the 2001 Oregon Dept. of Transportation (ODOT) manual, entitled “Rockfall Catchment Area Design Guide” (Pierson, et.al, 2001). In the ODOT study, over 11,000 rocks, ranging 1-3 ft in diameter, were rolled from slopes of various heights and slope ratios to catchment ditches of varying width and inclination to determine rockfall retention percentages for different slope/ditch configurations. Salient highlights of the ODOT design charts include:

 The greater the ditch inclination the greater the retention percentage. Flat-bottomed ditches, including engineered catchments that have not been well-maintained and have subsequently filled with debris, provide the worst retention, promoting rock roll-out into the travelway. Ditch slopes of 4H:1V provide for superior catchment and clear zone recovery.  The manner in which rock travels down a slope affects catchment design and effectiveness. For example, rock rolling and bouncing down flatter slopes (e.g. 1:1 to 2V:1H) tend to travel further from the slope toe than rocks falling from steep, near-vertical cuts.  Vertical slopes 40+ ft in height achieve 50% rock retention with ditch widths averaging 8-10 ft for inclined ditch profiles. For similar slope heights and ditch configurations, 4V:1H slopes achieve 50% rock retention with ditch widths averaging 3-7 ft, illustrating the positive effect a little slope roughness can have on diminishing roll-out energy. However, as slopes flatten to 1V:1H, 50% rock retention requires increased ditch widths averaging 8-14 ft.

Figure 3. Wide and deep catchment ditch beneath exfoliating granite cut along Tioga Road, Yosemite National Park.

Figure 4. Well-maintained, wide and deep catchment ditch beneath eroding colluvial slope on Tioga Road in Yosemite National Park.

The ODOT design guidance provides a good index for catchment ditch design and expected performance. However, factors such as rock shape and density, slope roughness, slope hardness, and slope profile configuration (e.g., linear, benched) will also affect catchment performance.

It is generally recommended throughout the slope inventory to clean and reestablish ditch widths, depths and profiles wherever possible, mindful of safe travelway foreslope requirements. However, there are occasions when marginal gains in ditch width may result in decreased rockfall retention. In cases where the toe slope above a modest ditch (e.g., 3-5 ft wide) contains a substantial accumulation of soft soil and talus material, or nested angular rock, consideration should be given to the attenuating characteristics of this “landing pad” feature. At many locations within the park, soft toe slopes and nested rock appeared to be effectively slowing or stopping small to moderate size rockfall.

Figure 5. Hybrid ditch catchment including short wall with armored facing supporting elevated roadway section (Andrew, et.al, 2011)

Regardless of whether a ditch was engineered for rockfall retention or only surface water drainage, regularly cleaned and maintained ditches will provide some degree of effective rockfall mitigation for all park cut slopes.

C.3 ROCK BOLTS AND DOWELS

Rock bolts – tensioned, steel reinforcing bars grouted into small-diameter drillholes within a jointed, fractured rock mass – are considered “active” reinforcing elements providing a normal, confining component of compressive force across rock mass discontinuities. Relatively small normal loads applied across rock failure surfaces can result in enormous gains in rock mass shear strength, putting rock-on-rock frictional resistance to work for immediate enhancements to slope stability. Unlike massive earth retention projects requiring high-capacity ground anchor systems, rock reinforcement commonly works at surficial scales using much smaller reinforcing elements (e.g., No. 8-14 deformed bar) installed to manageable hole depths (10-30 ft) .

Rock dowels are similar to rock bolts with the exception that they are untensioned reinforcing elements primarily used to “key” loose blocks together, allowing the blocks to work against one another to achieve rock mass stability. Dowels may be used to resist sliding blocks; however, even though the sliding mass must overcome the shear resistance of asperities along the slide plane discontinuity, for design purposes only the shear resistance of the steel bar can be counted upon. As a result, many dowels may have to be placed to provide the sliding resistance of just one tensioned rock bolt when used to resist sliding blocks.

Figure 6. Rock bolt installation at site of December 30th, 2010, sliding-block rockfall, El Portal Road, Yosemite National Park. Hand-drilling can be accomplished from lifts and baskets to depths exceeding 25 ft.

Both reinforcing options can be anchored within the rock mass with either cement grout or polyester resin grout. In general, cement grouts require more time for bolt or dowel installation, require reaccessing the installation for anchor and/or final grouting, and risk overruns if the rock mass is highly fractured. Resin grouting generally allows single-pass reinforcement installation as resin cartridges are placed prior to bar insertion, mixed as the bar spins to depth, and then cure rapidly (typically, 5-30 minutes). Because resin grouting relies on very small anchor annuluses (~0.125 in), installations depths are limited to the means used to push the bar through the viscous resin, commonly limiting fully-grouted resin installations to less than 20 ft. Combination cement/resin systems may provide feasible solutions for rapidly installing rock bolting systems. For example, resin grouted anchorage zones, followed by cement grouting of the free-stressing length, allow rapid, same-day bar tensioning for long rock bolts that could not otherwise be installed full-column with resin. Rapid resin anchor tensioning allows crews to systematically reinforce slopes without having to wait for cement anchors to cure several days. Cement grouting of all bolts at one time following completion of bolt installation and tensioning expedites the process and provides for better control of grout overruns. Cement grouting also has the added benefit of ground improvement beyond the bolt hole as grout permeates and fills discontinuities intersected by bolt drilling, thereby providing additional bonding within the rock mass.

Both tensioned rock bolts and dowels can be placed inconspicuously within the slope. Once the final, full-column grout has set, nuts, washers and bearing plates can be removed without loss of reinforcement performance. Extruding lengths of bar are cut flush with the rock surface or countersunk within precut depressions in the rock or by using bar couplers close to the collar of

the hole. The small drillhole and bar end are then grouted or epoxy painted to match the surrounding rock mass.

“Spot bolting”, incorporating both dowel and tensioned rock bolts, has been successfully used at to address localized rock instabilities. Additional spot bolting (based on engineering judgment) and large-area “systematic bolting” is recommended at several additional locations per the current RHRS slope assessment. Systematic bolting may include spot bolting and/or pattern bolting (regularly-spaced bolt pattern), and is always based on detailed slope stability mapping and kinematic analyses, as opposed to engineering judgment.

Figure 7. Tensioned rock bolts with colored bearing plates. Fully-grouted rock bolts can have the bearing plates removed once the reinforcement tension is locked-in with the grout anchorage.

C.4 GROUT STABILIZATION

Grouting is a stabilization technique where cementitious or chemical grouts are injected into the ground mass through small diameter drill-holes under low pressures to fill voids, open joints and cracks, and fine fractures. Groundmass strength improvements are realized through adhesion of the grout across discontinuities (“gluing” effect), consolidation of loose ground, and control of water seepage contributing to groundmass erosion, weathering and ice wedging.

Grouting may be used as a stand-alone solution for stabilizing very weak ground or may be used to supplement primary rock stabilization measures. For example, highly fractured, severely weathered and/or highly permeable rock masses susceptible to global failures (similar to soil mass failures) may not be successfully stabilized with more conventional ground reinforcement or buttressing techniques. Such ground masses at Yosemite might include tightly jointed, weathering granites; highly fractured, raveling metamorphic schists; and unstable talus and

boulder deposits. Permeation and/or void-fill grouting – with grouts specifically formulated to fill small fractures to large voids – can be used to consolidate and strengthen these materials.

In situations involving blocky, adversely jointed rock, where rock bolting may be required to provide a high degree of confidence in slope stabilization, fracture and joint grouting may be used to assist bolting performance by improving discontinuity shear strength, sealing the rock mass to limit water damage and reinforcement corrosion, and consolidating smaller blocks into larger cohesive units. Grouting can also be used to offset bolting costs by minimizing the amount of bolting required.

Figure 8. Demonstration sample of rock fragments encased in hardened polyurethane resin (PUR). PUR is pumped into rock joints and fine fractures to “glue” the rock mass together – resulting in an adhesive bond typically much stronger than the tensile strength of the rock (Arndt, et.al, 2008).

A variety of cementitious and chemical grouting products exist that can be applied to both rock and soil mass stabilization (e.g., bouldery colluvial masses). Cement grouts range from very low slump products used to mechanically compact and densify loose ground to microfine products used to permeate fine fractures and small void spaces. A number of admix products are also available to control set times, viscosities, bleed and other grout properties, greatly expanding the realm of application. Cement grouts tend to be significantly cheaper than chemical grouts, but may not meet strength requirements and may be more difficult to control during placement (“Where’d all the grout go?”). Cement grouts may also run from the exposed slope face creating clean-up and aesthetics issues.

Chemical grouts commonly involve some variant of polyurethane, polyurethane resin or epoxy resin, and similar adhesive compounds. These materials may be used for void filling applications (foaming products), but are more commonly used as adhesives, gluing fractured rock masses together. Advantages to chemical grouting products include very fine fracture grouting, very high adhesion strength, simple installation equipment, rapid installation, fast set times (one to a few minutes), and good control of product overruns. Chemical grouts are substantially more expensive than cementitious grouts, but project aesthetics and performance requirements may determine that chemical grouts are the better long-term value. Examples of and specifications for the use of high-strength polyurethane resin (PUR) can be found in the CFLHD Technology Deployment Program publication entitled, “Polyurethane Resin Injection for Rock Mass Stabilization” (Arndt, et.al, 2008), available at: http://www.cflhd.gov/programs/techDevelopment/CompletedProjects.cfm.

Grouting oftentimes provides a cost-effective alternative for preserving the natural aesthetics of an otherwise unstable rock slope. Since the stabilizing consolidation and adhesion properties of grouts is within the groundmass, there is no visual impact to this mitigation measure – assuming proper installation and cleanup procedures are closely followed. Grouting can be used in conjunction with rock reinforcement to greatly reduce the number of surficial anchorage assemblies, further enhancing the stabilization of the slope while minimizing visual impacts.

C.5 BUTTRESSING

Buttressing may be used to provide foundation support for overhanging rock masses or large undercut boulders deemed too large to excavate safely and/or too aesthetically significant to remove from the roadway viewshed. Buttressing may involve the placement of mortared rock rubble or stone masonry, formed concrete, reinforced shotcrete, mechanical support or some combination of these components. The work can be hazardous (high rockfall exposure) and may require temporary support measures and roadway closure. Buttressing requires complete and solid contact between the buttress foundation and the stabilizing rock mass, and performs best when used in conjunction with other rock mass stabilization measures, such as bolting and chemical grouting.

Buttressing has been used at several locations within the park involving large rocks sitting atop eroding colluvial soils to both stabilize the rock mass and mitigate further undermining of the soil foundation. Mortared stone masonry buttresses or formed concrete/shotcrete with mortared stone facings provide aesthetic solutions matching the context of the roadway. Sculpted, colored and stained shotcrete options are available that mimic natural rock so well as to be nearly invisible to the traveling public. Sculpted shotcrete installations are, however, susceptible to discoloration and relief weathering over time, and may crack and peel due to seasonal freeze/thaw.

Figure 9. Sculpted and stained reinforced shotcrete buttress constructed beneath unstable overhang along Going to the Sun Road, Glacier National Park, MT (Lofgren and Jenks, 2010).

C.6 SHOTCRETE STABILIZATION

In addition to buttressing applications, reinforced shotcrete can also be used to stabilize localized areas of highly jointed, fractured, spalling or deeply weathered rock. Shotcrete provides a measure of “surface control” to the weak rock mass, protects weathering-susceptible slopes, and may be used in conjunction with ground mass reinforcements (e.g., bolting or soil nailing). Shotcrete is typically applied in structural (reinforced) and architectural (facing) lifts, and can be colored and textured to blend with the surrounding ground mass. Colored, stained, and sculpted finishes can range from mundane, manufactured appearances to near exact replicas of adjoining rock, and can be combined with natural rock inlays and stone masonry.

As previously noted, shotcrete applications may suffer performance issues related to discoloration, surficial weathering and drainage freeze/thaw damage. Reinforced structural sections several inches thick generally outperform decorative veneers. Discrete weep hole placement and the use of polystyrene insulation behind structural sections has increased service life in many cold weather applications.

Sculpted shotcrete has been used at several locations within the park, both as structural support to inboard rock cuts and for MSE wall architectural facing. There are several additional areas in the park involving localized pockets of eroding decomposed granite creating surrounding rockfall hazards where shotcrete stabilization may be preferred option.

Figure 10. Sculpted and stained reinforced shotcrete slope retention constructed along El Portal Road, Yosemite National Park (approximately MP 6).

C.7 RIGID BARRIERS

Rigid rockfall barriers may be used to prevent all or a substantial portion of rock rolling and bouncing down engineered slopes and immediate top-slopes from reaching the roadway. Rigid barriers can be constructed from a wide range of materials, providing an array of novel structures meeting various performance and aesthetic requirements, including:

o Earthen berms; o Single- or multiple-course boulder barriers; o Removable concrete Jersey barrier or “K-Rail”, with or without extended fencing; o Removable or permanent decorative concrete blocks (e.g., form-lined, stained concrete); o “Montana Rockfall Fence” utilizing steel or steel-backed wood guardrail variations (Figure 11); o Stacked gabion baskets stained or filled with decorative rock; o High-capacity GRS/MSE barrier walls (geosynthetic reinforced soil/mechanically stabilized earth), typically with modular block architectural treatments; and o Soldier pile walls with timber lagging or decorative concrete panels.

Figure 11. “Montana Rockfall Fence” – optional barrier to the more commonly used Jersey barrier. (Lofgren and Jenks, 2010).

Rigid rockfall barriers are widely used in the U.S. to mitigate rockfall hazards, are very familiar to motorists, and typically result in minor view shed impacts. Clearly, constructing with natural materials, such as the earthen berm or rock barrier options listed above, creates the least visual impact along the roadway. However, building barrier structures with common architectural elements may also help to minimize motorist awareness of barrier presence. For example, common guardrail or Jersey barrier systems may go largely unnoticed by the traveling public. In contrast, efforts to employ colored architectural facings, such as form-lined concrete, may actually attract attention and may be out of context for the roadway.

In general, rigid barriers require regular maintenance to achieve both performance and aesthetics objectives, including regular removal of rockfall accumulations from behind the barrier and repair of visible damage or non-functioning elements. Removable barriers or barriers constructed of less expensive components, such as the guardrail or concrete barrier options, are desired by maintenance staffs, can be used in areas where little room otherwise exists behind the barrier for clean-out equipment, and address roadway geometrics safety requirements. Natural stone “boulder barriers” can be cost-effective, aesthetically pleasing, easily maintained options when large rock is readily available, but may not meet clear-zone safety requirements. For locations subject to regularly occurring, high volume rockfalls, particularly involving large rock, more permanent, expensive to construct and maintain wall systems are required.

C.8 DRAPED OR ANCHORED WIRE MESH

Slope meshing has been used for decades to provide surface control to highly weathered, fractured, jointed, raveling and/or eroding slopes. Originally employing eye-catching, off-the- shelf galvanized chain link fencing subject to “unzipping” failures, slope meshing has evolved to variable-gage, scaled opening, double-twist steel wire and high-strength wire rope products. A substantial range of corrosion protection options and color coatings, including PVC, epoxy and powder-coating selections, are also available. In addition, erosion control measures, including turf mat, 3-D high run-off geo-netting and bonded-fiber options, can be easily incorporated into slope meshing, with even minor revegetation of the slope often making the mesh invisible to the traveling public. These products have come a long way in recent years with regards to installation, aesthetics and performance, and are becoming widely accepted throughout the U.S.

Figure 12. Nearly invisible draped colored mesh along upper two-thirds of the rock cut. The judicious use of draped mesh can mitigate the need to excavate large catchments beneath otherwise tall, hazardous slopes (Andrew, et.al, 2011).

Two basic applications may be deployed:

1) Draped Mesh: Draped installations suspend mesh from the top of a slope using grouted ground anchors or rock bolts. The mesh lays loose against the slope providing surface control for loose rock and talus, allowing the loose material to gradually migrate down the slope behind the mesh as weathering and erosion processes occur. Draped installations are particularly useful on slopes subject to high volume rockfall resulting from highly weathered rock or colluvial deposits. In situations where loose rock, cobbles or boulders tend to accumulate in pockets behind the mesh, draped installations can be easily cleaned by temporarily lifting the mesh from the slope. Draped mesh may be

installed full-slope; however, it is more common to customize the length to shorten effective rockfall heights to meet catchment requirements and cut installation costs.

2) Anchored Mesh: Anchored mesh installations are intended to constrain loose rocks along the slope, rather than allow them to pass to roadside catchments like draped systems. As such, meshes are generally heavier and additional large-opening, wire-rope netting may be used over the mesh to provide added strength. Mesh/netting is secured to the slope with patterned ground anchors, commonly using resin or cement grouted dowels. Whereas draped installations controlled raveling surface material, anchored mesh systems provide a significant measure of near-surface ground reinforcement. Similar to draped installations, anchored meshes and netting products come in an array of corrosion protection and color coating options.

Figure 13. Scaled slope treated with colored anchored mesh that is beginning to revegetate. (Courtesy Geobrugg; www.Geobrugg.com)

Both applications are engineered systems that account for such things as mesh, rock and snow loads, corrosion, anchorage service life, coating life, etc. Both systems require occasional maintenance to repair broken elements and bagged material accumulating behind the mesh. Colored mesh is nearly invisible with minor revegetation; can blend in well on relatively smooth, bare slopes; and may be highly visible from side approaches where slope asperities lift the mesh off the ground. Although color coatings are subject to weathering, meshes can be restained in- place years down the road.

Although draped and anchored mesh has been used successfully in U.S. national parks, applications are rare and generally many years old (before quality aesthetic treatments were available).

C.9 FLEXIBLE ROCKFALL FENCES AND ATTENUATION BARRIERS

Flexible rockfall barriers include an array of fencing products and structure configurations commonly consisting of a steel wire or wire rope net stretched between anchored steel fence posts or suspended from high-strength steel cables. For rockfall and high-capacity debris flow fences, the netting is secured to posts or anchors across the top and bottom of the fence, ensuring containment of captured rock and debris. For attenuator systems, the bottom of the draped netting is left unsecured and extended a short distance downslope. Unlike barrier fences that are designed to stop rolling/sliding rock, attenuator systems only slow falling rock, providing managed control of the rock as it moves downslope. Attenuator systems may be used in conjunction with catchment ditches, rigid barriers or flexible fences to optimize barrier performance, as well as limit the size and expense of the overall integrated barrier system.

Figure 14. Ring-net flexible rockfall barrier (Andrew, et.al, 2011).

Although flexible barrier systems are commonly used around the world to protect roads and structures, they are limited in application by installation and maintenance costs, accessibility to desired installation locations, needed operating room adjacent to roads (mesh fencing can deform many feet upon impact and/or be damaged by winter maintenance vehicles), anchor/post strength and maximum capacity. Although the highest capacity fences (~10,000 kJ rated) can stop sizeable volumes of small rock debris and large single rocks, for a sense of scale, the recent January 2012 rockfall impacting lower Big Oak Flat Road was estimated to hit the roadway with almost 50 times the energy of the highest capacity barrier fence available on the market today.

Flexible barriers require regular maintenance to repair broken elements and braking systems, and need be cleared of excessive debris accumulations – which may require time-consuming dismantling of the netting. Post and anchorage systems are particularly susceptible to damage,

and can be costly to repair. In many cases, flexible fencing, and especially attenuator systems, are installed high within rockfall chutes, complicating maintenance access.

Figure 15. Rockfall “attenuator” system consisting of draped rockfall fencing unsecured at the bottom to allow slowing and controlled release of high-energy rockfall (Andrew, et.al, 2011).

Fencing and attenuator systems are not aesthetically appealing structures and, thusly, have not been widely embraced for use in the national parks. Nonetheless, consideration should be given to using these systems when they can be discretely placed out of the viewshed of the public. As with all mesh systems, fence and attenuator components can be coated and stained to blend with the natural surroundings.

C.10 SLOPE FLATTENING AND ROADWAY REALIGNMENT

More extreme measures to mitigating rockfall hazards involve excavating cuts to flatter slope angles less prone to rock sliding and rolling, or moving the road alignment to provide for adequate inboard ditch catchment. Roadway realignment is often infeasible or involves the construction of substantial outboard embankment and/or retaining wall systems.

Slope flattening may occasionally require excavating the entire slope, but more commonly involves flattening or rounding of the upper reaches of the cut. Top-of-cut areas are commonly comprised of surficial soils and colluvium transitioning to broken, weathered bedrock – a highly erosive groundmass that commonly produces rockfall during storm events and globally unstable, soily erosional scarps beneath overlying vegetation mats. Such rockfall-prone conditions were commonly observed along park roads during the RHRS assessment wherever cobble and boulder colluvium and/or decomposed granite were exposed high on the cut. Recommendations for

mitigating these features includes heavy slope rounding or flattening, placement of erosion control matting and seeding, and establishing surface water run-off furrows and run-downs to control slope erosion. In some cases, where a large volume of cobbles and boulders are being produced from thick colluvium, recommendations may also include draped or anchored mesh treatments within the rounded section – often well out of the passing motorist viewshed. In addition to the steel mesh options, a number of manufacturers also provide lightweight anchored geosynthetic meshes and steel mesh/three-dimensional geosynthetic erosion mat combination products for customizing top slope mitigation measures. These products come in a variety of colors and can be designed as permanent or semi-permanent installations.

C.11 SUMMARY OF MITIGATION MEASURES AND RELATIVE COSTS

Table C.1 summarizes the escalation of rockfall mitigation measures that may comprise a comprehensive strategy for a given roadway. Table C.2 provides generalized cost estimates for the various mitigation options.

Table C.1: Relative comparison of rockfall mitigation measures.

Installation Maintenance Maintenance Method Function Slope Type Cost Cost Schedule Slope Hazard All slopes Low Low 2-5 Years Scaling Removal Small-block, jointed granite; Catchment Rockfall Low to Annually to raveling, weathered schist; Low Ditch Containment Medium Bi-annually cobble/boulder colluvium Slope Medium- to large-block, Low to Rock Bolting Very Low 10-50 Years Reinforcement jointed/fractured granite Medium Jointed/fractured granite; Slope Medium to Grouting raveling schist; medium-to- Very Low 5-25 Years Reinforcement High large, angular talus Isolated overhangs of Foundation jointed/fractured granite; Medium to Buttressing Low 5-15 Years Stabilization isolated large granite High boulders atop eroding soils Surface Raveling, rapidly Control and Medium to Medium to Shotcrete weathering, schist and 2-5 Years Weathering High High decomposed granites Protection

Table C.1 cont’d.: Relative comparison of rockfall mitigation measures.

Installation Maintenance Maintenance Method Function Slope Type Cost Cost Schedule Rigid Rockfall Medium to Annually to All slopes Low to High Barriers Containment High Few Years High-volume, small-block Draped Surface Medium to granite; raveling schist; Medium 2-5 Years Mesh Control High cobble/boulder colluvium Small- to medium-block, Slope jointed/fractured granite; Anchored Reinforcement Medium to raveling schist; high- Medium 2-5 Years Mesh and Surface High volume, large boulder Control colluvium Rockfall All slopes producing high Flexible Medium to Annually to Control and rockfall volume of medium High Barriers High Bi-annually Containment to large rock size Weak, eroding, raveling slopes at risk of small global Slope Hazard 10 Years - failures/pot-outs; eroding Low to High Very Low Flattening Removal Never top-of-cut colluvium and decomposed granite Large area, high volume, large to very large Roadway Hazard High to rock/debris, high failure risk Very Low Never Realignment Avoidance Very High slopes where alignment is cost feasible

Table C.2: Generalized pay item costs per method (modified from Lofgren and Jenks, 2010).

Method Unit Cost1 Estimation Considerations Includes either 3-man hand-scaling crew plus foreman and Slope Scaling $350-$500/hr cleanup or long reach excavator, operator, foreman, and site cleanup. Assumes excavator, grader and site cleanup by the Catchment <$5/lnft Ditch equipment-hour for moderate toe slope excavation. Includes drilling access (lift/crane), drilling equipment, 2 Rock Bolting $150-$200/lnft drillers, foreman and ground crew, light scaling, placement, grouting, testing and finishing of rock bolts, site cleanup. Includes drilling and placement of cement grout (~$25/cuft) or chemical grout (~$140/cuft). Typically, much smaller Grouting $25-$140/cuft quantities of chemical grouting are used. Cost is highly dependent on type of grouting and volume/area to be treated. Includes reinforced shotcrete and form work as well as stone masonry and rockery construction. Rockery/nested boulder Buttressing $50-$100/sqft inlays are least expensive options; reinforced sculpted shotcrete foundational buttresses are most expensive. 1Does not include engineering, traffic control, mobilization, construction management, etc.

Table C.2 cont’d: Generalized pay item costs per method (modified from Lofgren and Jenks, 2010).

Method Unit Cost1 Estimation Considerations Cost is highly dependent on sculpting and staining Shotcrete $55-$75/sqft requirements, site access, and need for reinforcement/drainage features. Generally includes guardrail variants and Jersey barriers, but Rigid Barriers $60-$100/lnft may include geosynthetic reinforced soil (GRS) structures or earthen structures. Cost is highly dependent on site access, total coverage area, Draped $4-$8/sqft Mesh drapery anchorage requirements, and coatings and finishes. Includes mesh anchors and anchor plates on common 10X10 pattern. Cost may escalate with requirements for wire rope Anchored $30-$50/sqft Mesh cable systems, dual mesh systems, or elaborate erosion control systems. Rockfall fences range in price according to energy ratings. Slope location, construction access, and foundation and $200-$800/ft Flexible anchorage requirements for fence posts also greatly affect Barriers $15-$40/sqft installed cost. Attenuators are typically cheaper to construct and maintain, Excavation and blasting costs are shown for slope flattening. $10/cuyd Slope This cost does not reflect erosion control or drainage Flattening $35/drilled lnft measures. Realignment costs typically include outboard slope Roadway Realignment $250K+/site construction involving walls, large embankments or reinforced fills – all of which are expensive options. 1Does not include engineering, traffic control, mobilization, construction management, etc.

C.12 REFERENCES

Andrew, R.D., R. Bartingdale and H. Hume, 2011, Context Sensitive Rock Slope Design Solutions, FHWA-CFL/TD-11-002, available at www.cflhd.gov, January 2011, 122 pp.

Arndt, B., M.J. DeMarco, and R.D. Andrew, 2008, Polyurethane Resin (PUR) Injection for Rock Mass Stabilization, FHWA-CFL/TD-08-004, available at www.cflhd.gov, September 2008, 75 pp.

Lofgren, D. and N. Jenks, 2010, “Crater Lake National Park Rockfall Engineering Study”, Geotechnical Engineering Report No. 15-09, Western Federal Lands Highway Division, FHWA, March 2010, 104 pp.

Pierson, L.A., C.F. Gullixson, and R.G. Chassie, 2001, Rockfall Catchment Area Design Guide – Final Report, Oregon Dept. of Transportation Research Group pub. No. SPR-3(032), November 2001, pp.92. APPENDIX D – Rockfall Analysis Data Colorado Rockfall Simulation Program -- CRSP-3D

CRSP Rockfall Analysis

CRSP was used to determine the expected kinetic energy and bouncing height of falling rocks at various points along the slope. In the analysis, it was assumed that irregular shaped boulders with a maximum diameter of 3.0 feet would impact the rockfall retaining system. For each simulation, the model rolled 500 shaped rocks from a source area at 236 - 582 feet. A slope surface roughness of 2.0, and hardness of 0.7 - 0.9 were used.

PROJECT INFORMATION

Project Name TICA2

Material Properties English Units SI Units Material 1 ID Hard Bedrock Hard Bedrock Color Green Green Roughness 2 ft 0.61 m Hardness .9 .9 Material 2 ID Talus Talus Color Yellow Yellow Roughness 2 ft 0.61 m Hardness .7 .7 Material 3 ID Other Other Color Red Red Roughness 2 ft 0.61 m Hardness .9 .9

Analysis Partition Properties English Units SI Units Analysis Partition 1 ID AP-1 AP-1 Color Red Red Dir X X Location 810 ft 247 m

Rockfall Parameters English Units SI Units Rockfall Parameter 1 Release Zone Other Other γ 180 pcf 28.3 kN/m3 Rocks to Release 350 350 Shape One_Element_Sphere One_Element_Sphere Size .5-1 ft 0.1524 - 0.3048 x 0.1524 - 0.3048 x 0.1524 - 0.3048 m Rockfall Parameter 2 Release Zone Other Other γ 180 pcf 28.3 kN/m3 Rocks to Release 100 100 Shape One_Element_Sphere One_Element_Sphere Size 1-2 ft 0.3048 - 0.6096 x 0.3048 - 0.6096 x 0.3048 - 0.6096 m Rockfall Parameter 3 Release Zone Other Other γ 180 pcf 28.3 kN/m3 Rocks to Release 50 50 Shape One_Element_Sphere One_Element_Sphere Size 2-3 ft 0.6096 - 0.9144 x 0.6096 - 0.9144 x 0.6096 - 0.9144 m

Colorado Rockfall Simulation Program -- CRSP-3D Project Name: TICA2

CRSP Rockfall Results for Analysis Partition AP-1

Summary of Results Max Bounce Ht, ft Max Velocity, ft/s Max Energy, ft-kips Max Energy, kJ Percent Passing 21 81 49 66 5%

Cumulative Probability Cumulative Probability Bounce Ht, ft Velocity, ft/s Energy, ft-kips Energy, kJ Rollout X, ft Rollout Z, ft 50% 2.2 36 5 7 830 136 75% 4.5 47 10 14 854 153 90% 8.0 58 30 40 876 169 95% 17.8 65 39 53 889 178 98% 21.1 81 49 66 903 188

Colorado Rockfall Simulation Program -- CRSP-3D Project Name: TICA2

CRSP Rockfall Results for Analysis Partition 1

Height (ft)

Velocity (ft/s)

Kinetic Energy (ft-kips)

Kinetic Energy (kJ)

Rollout Stop X (ft) for rocks passing Analysis Partition 1

Rollout Stop Z (ft) for rocks passing Analysis Partition 1

APPENDIX E – Rockfall Fence Details

Timpanogos Cave National Monument Estimate July 2013

Item No. Description Unit Quantity Unit Price Amount Notes 15101-0000 Mobilization LPSM ALL $26,829.17 $26,829.17 15701-0000 Soil Erosion Control LPSM ALL $1,000.00 $1,000.00 62201-0350 Backhoe HOUR 80 $101.50 $8,120.00 62302-0100 Special Labor, Slope Scaling HOUR 160 $350.00 $56,000.00 62302-1000 Special Labor, Hired Technical Services HOUR 40 $200.00 $8,000.00 Geotechnical Engineer to identify rockfall hazards 65201-0000 Rockfall Fence LN FT 196 $660.00 $129,360.00 Contingency Items (30%) PERC % 30.00% $68,792.75

Total Construction Amount $298,101.93

Assumptions 1. Access road subsidiary to mobilization

APPENDIX F– Special Contract Requirements

Section 204. - EXCAVATION AND EMBANKMENT

Construction Requirements

204.13 Sloping, Shaping, and Finishing.

Add the following:

(e) Slope scaling. Stabilize or scale all loose rock and other unstable materials greater than 1 ft3 in volume as directed by the CO. Remove and dispose of all spoil resulting from the scaling operation. Scaling should be done by hand methods to remove potentially unstable boulders, rocks, and trees, thereby reducing the rockfall hazard and maintenance requirements following scaling efforts. The CO will approve the use of power equipment for scaling on an as needed basis. Use concrete barriers where required to prevent safety hazards.

(1) Submittals. Two weeks prior to commencing the rock slope scaling, provide the following to the CO:

(a) Personnel Qualifications. The Foreman and scaling crew shall have a minimum of five years of demonstrated experience in rock scaling in similar capacities. (b) Submit a detailed work plan for each rock slope to be scaled. The plans shall detail the following:

(1) Proposed construction sequence and schedule. (2) Types and number of machinery and tools to be utilized for scaling. (3) Number of scaling crews required for the project. (4) Rock and soil removal and disposal plan for materials generated from the scaling work. (5) Protection plan to be implemented by the Contractor during scaling to protect personnel, facilities, and other structures from damage caused by scaling activities. (6) Traffic interruptions and controls required.

Do not begin the work until the CO has approved the submittals.

(2) Scaling Crew Requirements. Provide scaling crews with one Foreman present at all times when scaling is performed. A scaling crew is defined as three qualified scalers, one of which could be the scaling Foreman (if a crewmember must leave for any reason that member shall be replaced by a qualified replacement).

(3) Protection of Properties. Provide adequate protection in the areas being scaled to prevent damage to property and structures and utilities by falling rock from the scaling operation. The Contractor is also responsible for the protection of personnel from the danger inherent in scaling. Provide devices, measures, and procedures to protect the public and any adjacent facilities or structures from danger or damage caused by scaling. This plan must be in effect prior to commencing the scaling. Any injuries or damages caused by scaling are the responsibility of the Contractor.

(4) Sequencing. Begin scaling at the top of the slope and proceed downward. Remove all materials scaled off the slopes.

204.14 Disposal of Unsuitable or Excess Material. Add the following:

Secure environmental clearances according to Subsection 107.10.

Unsuitable or excess material may not leave Government property without a contract for the sale of mineral material (if applicable).

Coordinate with Town or Georgetown for potential placement locations for excess material from the reconstruction of Argentine Street.

Measurement

204.16

(a) Roadway Excavation.

(1) Include the following volumes in roadway excavation:

(e) Delete the text and substitute the following:

Conserved topsoil stripped from cuts.

(h) Delete the text and substitute the following:

Conserved material taken from stockpiles and used in Section 204 work except topsoil measured under Section 624. Only materials required to be conserved by the CO are eligible for measurement under this item.

(2) Do not include the following in roadway excavation: Add the following:

(m) Conserved topsoil stripped from fills. (n) Mine waste material if measured and paid under separate item.

(f) Slope scaling. Delete the text and substitute the following:

Scaling in areas outside the limits noted above will be measured by scaling crew hour. A scaling crew is defined as three qualified scalers, one of which could be the scaling Foreman.

Power equipment required for the scaling operation will be included in the scaling crew hourly rate and will not be paid for separately. Measurements will not be made separately for individual equipment.

Removal and disposal of materials generated by scaling including equipment needed, loading/unloading, and transporting materials is incidental to the work and will not be paid for under this item.

Protection devices (such as barriers), measures, and procedures taken to protect adjacent property and structures from danger or damage and any repair required is incidental to the work and will not be paid separately.

Section 563. – Painting

Description

563.01 Add the following:

This work also consists of furnishing all materials, equipment and labor necessary for the application of penetrating desert varnish stain to all exposed surfaces of the rockfall fence.

Material

563.02 Add the following:

Furnish a desert varnish weathering material that is an aqueous solution containing salts of iron and manganese, built in oxidizers and other trace elements including copper and zinc. Furnish a stable, one-step component solution applied directly to the natural and galvanized surfaces.

Provide a material that has a projected life expectancy range from 50 to 100 years. Furnish a material that develops full coloration within two weeks of application. Supply a material where the final color is controlled or modified by custom blending of the basic ingredients, application techniques, dilution rate of the color concentrate with water or a combination of these methods.

Furnish a material that contains chemical components that have no adverse reactions or effects on soils, plants, or animals. The material can not contain corrosive by-products once the product has been applied. Only nitrate fertilizer products are permitted to be present as soluble residues.

For information, the following stain systems have been previously used on CFLHD projects or by client agencies:

NATINA manufactured by Natina Products, LLC 1577 First Street Coachella, CA 92236 Telephone: (877) 762-8462 www.natinaproducts.com

PERMEON manufactured by Soil-Tech, Co. 6420 S. Cameron Dr., Suite 207 Las Vegas, Nevada 89118 Telephone: (702) 873-2023 www.soil-tech.com

Alternate stain systems from various manufacturers may be proposed provided they meet the minimum material requirements.

Construction Requirements

563.03 Protection of Public, Property, and Workers. Add the following:

Comply with all applicable federal, state, and local regulations. Furnish material safety data sheets for all cleaning and staining products.

563.08 Painting Galvanized Surfaces. Add the following:

Clean the wire mesh and surfaces of other fencing components to be stained, prior to the stain being applied, in accordance with the manufacturer’s recommendations for the removal of all dirt, dust, efflorescence, scale or other foreign substances which could be detrimental to the stain penetration or color. At the time of application of stain, provide surfaces that are clean, completely dry, and free of frost or other foreign substances.

Apply the desert varnish stain in the presence of a manufacturer’s representative in accordance with the manufacturer’s recommendations.

Submit the name of the manufacturer of the desert varnish stain proposed for use, along with the manufacturer’s specifications for mixing and application, to the CO for approval.

Measurement and Payment 563.13 Add the following:

Do not measure stain for payment. Stain is considered subsidiary to Section 652.

Section 652. – ROCKFALL FENCE SYSTEM

Description

652.01 This work consists of designing, furnishing and installing rockfall fence systems. Installation shall be at the locations designated on the Plans or established by the CO. The rockfall fence system shall be manufactured and assembled in accordance with the contract documents and the manufacturer’s standards and requirements as follows:

The system shall be capable of absorbing impact design loads for a kinetic energy specified on the Plans and shall be able to absorb the ultimate impact loads without allowing the rock to pass. The system shall be designed with a sufficient safety factor above the design loading.

The rockfall fence system manufacturer shall be regularly engaged in designing and manufacturing rockfall protection systems, with a minimum of three years of documented experience with manufacturing of such systems used in a similar application and capacity. The manufacturer shall supply written evidence demonstrating certification of a quality assurance program.

The rockfall fence system product and installation within this section is manufactured by Brugg Cable System , Vancouver, WA, or equal. Products from different manufacturer may be proposed as an equal provider and shall meet the following minimum requirements:

Fence Type Design Impact Energy High Impact 500kJ

Rockfall fence systems shall be designed to withstand the Design Impact Energy (DIE) in the table and without allowing the rock to pass. The Contractor shall provide data to show that the fence system is capable of absorbing the DIE. The manufacturer shall design and prepare plans detailing the rockfall fence system and installation for the project. Transported materials shall be properly marked to identify the system components with manufacturer design plans.

Material

652.02 Conform to the following Subsections:

Foundation 209 Concrete 601 Rockfall fence 710.12 Painting 563

Construction Requirements

652.03 General. Rockfall fence systems shall be manufactured in accordance with the vendor’s standards and requirements as follows:

(a) The manufacturer shall design the fence system and submit copies of the layout and detail design drawings to the CO within two weeks from the receipt of an order for comments and/or approval. The manufacturer shall refer to data in the Geotechnical Report. Fabrication of the system shall commence only after the manufacturer has received the final approval from the CO. The manufacturer shall include one-day installation supervision by a qualified Field Engineer to ensure the system is properly installed.

(b) The designed rockfall fence system shall have a demonstrated satisfactory performance in a similar application and capacity.

(c) The vender shall provide documentation to show that fence system design can absorb the required ultimate load.

652.04 Excavation and Preparation

(a) Perform all excavation and foundation preparation work in accordance with Section 209. The following shall also be performed:

(b) Scatter excess excavated material around the vicinity of the rockfall fence system to match the existing ground surface and to prevent the creation of jumping ramps for falling rocks.

(c) Perform foundation work for the columns and rock and soil anchors in accordance with the typical sections shown on the plans. Column spacing, centerline to centerline, shall be in accordance to the typical section and shall not deviate more than 3.0 inches.

(d) Perform concrete placement according to Section 601. The minimum concrete strength is 4,000 psi at 28 days. The contractor shall determine the concrete consistency in the field by a slump test in accordance with ASTM C143 (AASHTO T119). After the concrete placement in the forms, the contractor shall maintain the concrete at a minimum temperature of 50oF for a period of 72 hours.

652.05 System Installation

(a) Erect the foundations, anchors, and columns in accordance with the design drawings. The columns shall not vary from the indicated pitch or from vertical by more than 2.0 inches from the top to bottom of the column and shall not deviate more than + 3.0 inches from centerline to centerline of the columns.

(b) Install and fasten support ropes, with the factory installed thimbles and breaking elements to the column and through the cable guide assemblies with the supplied wire rope clips as indicated on the design drawings. Distance from the column to the braking elements shall not exceed 5 feet. Support ropes shall not be fastened until the columns are properly set. Tension all ropes as necessary to eliminate slack, and tension the support ropes until there is no sag in the ropes.

(c) Place the wire mesh on the net support ropes and seam together with seam rope. Attach the bottom of the nets to the bottom support rope in a similar manner. Use the wire rope clips to securely fasten the seam ropes to the net system as shown on the design drawings once the seaming is completed. Do not attach the nets to the cable guide assemblies or to the columns. Bottom support rope braking elements should be oriented vertically and tied to the wire mesh using tie wire.

(d) Stain fence and components according to Section 563. Stain can be applied in the field or prior to shipping fence components to the site.

652.06 Shipping

(a) All materials shall be properly labeled and shipped by the manufacturer to the job site for the contractor to easily identify the system components with the manufacturer’s design drawings to minimize installation time. (b) The following spare parts are to be supplied by the manufacturer for the system:

(1) 3 each- Braking Element Replacement Kits (2) 2 each- Wire Rope Anchors (3) 1 each- Structural Steel Column

652.07 Acceptance. Rockfall fence system material and construction will be evaluated as follows:

Material for the Rockfall fence will be evaluated under Subsections 106.03 and 106.04.

Construction of Rockfall fence will be evaluated under Subsections 106.02 and 106.04.

Measurement

652.08 Measure rockfall barrier system by the linear foot.

Payment

652.09 The accepted quantities, measured as provided above, will be paid at the contract price per unit of measurement for item 65102-000 listed in the bid schedule. Payments will be full compensation for the work prescribed in this Section including material, freight, supervision, design drawing preparation and spare parts; plus labor, equipment, tools, and other incidentals necessary to install the complete rockfall fence system ready to use. See subsection 109.05.

Section 710. - FENCE AND GUARDRAIL

Add the following Subsection:

710.12 Rockfall Fence

(a) High Strength Wire Mesh: Wire mesh will be diamond shaped and of a woven construction. The mesh will be made with 0.118 inch diameter wire and the ends of the wire will be formed into a loop and twisted. The loops of the wire mesh will be fastened together to prevent unravelling of the mesh. The wire will be alloyed high strength carbon steel wire with a minimum tensile strength of 256,000 psi. The wire will be galvanized with a zinc/aluminum coating with a minimum weight of 0.655 oz/ft2. The size of the wire mesh opening will be 3.25 inches by 5.5 inches, and the depth of the mesh will be 0.59 inches.

(b) Net Support Columns: Columns shall be fabricated from wide flange structural members meeting ASTM A36 for preformed steel shapes. Columns shall be galvanized with a minimum of one coat. Column foundation shall be of shear pin assembly instead of direct buried foundation. All steel shapes shall comply with ASTM A36-84 and bolts, nuts and washers to ASTM A325-86.

(c) Support Wire Ropes: All support ropes shall be manufactured from a minimum 5/8 inch diameter wire rope, with a minimum breaking strength of 40,000 lbs. All wire ropes shall meet the Federal Specification RR-W-410D or equivalent.

(d) Rock and Soil Anchors: Wire rope anchors shall be manufactured from 19-mm diameter rope with a minimum breaking strength of 53,000 lbs. Anchors shall have minimum pullout strength of 33,000 lbs. for Medium Impact fence and 22,000 lbs. for Low Impact fence and must be verified in the field. The verification test shall consist of a pullout test incorporating 20% of the total number of anchors. The pullout test load shall be 1.2 times the minimum pullout strength. If more than 25% of the tested anchors fail, all anchors shall be tested. Failed anchors shall be replaced by the contractor. Testing shall be performed using a temporary yoke or load frame. No part of the yoke or load frame shall bear within 3.0 feet of the anchor.

(e) Miscellaneous Materials: All miscellaneous hardware such as wire rope clips, thimbles, bolts, shackles, etc. shall be hot dipped galvanized, and shall be supplied by the manufacturer with the system.

(f) Corrosion Protection: All materials shall be galvanized meeting the requirements of ASTM A641-92 for zinc coated carbon steel wire.

APPENDIX G– Photos

Talus slope behind existing Visitor Center

Talus slope behind existing Visitor Center Mutual Quartzite cliffs above existing Visitor Center

View of existing Visitor Center and adjacent slopes View of talus slope above existing Visitor Center, from Cave trail

View of talus slope above existing Visitor Center, from Cave trail View of Mutual Quartzite cliff face, from Cave trail

View of unstable blocks above existing Visitor Center, from Cave trail Talus slope within side canyon east of existing Visitor Center

Rockfall debris within lower portion of talus slope along side canyon east of existing Visitor Center