C04g Attachment 7 Recommendations1240BH26R0013.pdf

REPORT

Geological Assessment Findings and Recommendations for Repairs and Corrective Actions Blanchard Springs Caverns - Geological Assessment and Design

Submitted to:

United States Forest Service Southern Region (R08) Ozark-St. Francis National Forest Sylamore Ranger District

Submitted by:

Golder Associates Inc.

13515 Barrett Parkway Drive, Suite 260, Ballwin, Missouri, USA 63021

+1 314 984-8800

19129310

July 31, 2020 - Rev1

July 31, 2020 - Rev1 19129310 i

Distribution List Golder Associates Inc.

United States Forest Service

Robert Peccia & Associates, Inc.

Executive Summary

The United States Forest Service (Forest Service) contracted Golder Associates Inc. (Golder) through Robert

Peccia & Associates, Inc. (RPA) in September 2019 to perform various tasks associated with the Blanchard

Springs Caverns – Geological Assessment and Design Project (the Project) at Blanchard Springs Caverns, located near Fifty-Six, Arkansas (Project Site or Site).

This report of Geological Assessment Findings and Recommendations for Repairs and Corrective Actions

(Report) presents the findings from Golder’s geotechnical investigation and site assessment, presents the methodology and results of geotechnical analyses completed to determine recommendations for permanent repairs, presents recommendations for permanent ground support in the assessment areas, presents recommendations for instrumentation and monitoring, presents replacement options for airlock doors and security doors, and includes a preliminary construction cost estimate and schedule.

Golder visited the Site to complete the Site investigation/assessment on January 13-15, 2020. During the Site assessment, Golder gathered additional data and samples to aid in our geological assessment and design recommendations for five separate areas (assessment areas); the Dripstone Cave Entrance, Dripstone Cave

Bypass Tunnel, Dripstone Cave Exit, Discovery Cave Exit, and Surface Sinkhole Area. For all areas, Golder visually observed rock and existing support conditions and used measuring devices to collect data. Samples of cavern roof rock were collected from loose rock bulk samples that were recently scaled from the cavern roof in the

Dripstone Cave Entrance and were submitted for laboratory geotechnical testing. Photographs were also taken of the various assessment areas. In the Discovery Cave Exit, Golder drilled a series of probe holes in the shotcrete roof structure on either side of the inner airlock doors. Once drilled, a borescope camera was inserted into the drillhole to check shotcrete thickness, view rock conditions, and check for the presence of steel beams/reinforcement. Golder inspected the existing canopy structure in the Dripstone Cave Exit that is composed of steel I-beams and plate roofing with supporting masonry/steel column supports. The structure itself appeared in relatively poor condition due to deterioration/weathering of the steel. The void space between the steel plating and tunnel roof has been filled with masonry/cement. Rock conditions behind the structure were not visible but are assumed to be poor to necessitate the support structure.

In general, the rock mass quality in each formation appeared relatively uniform laterally between assessment areas. The rock quality in the roof of the assessment areas is generally fair while the quality in the limestone units in the floor and side walls is generally good. The Chattanooga Shale, which is present in thicknesses ranging from 2.5 to 4.0 feet in the side walls of the assessment areas, is generally poor quality. Most of the discontinuities encountered were bedding planes between bedrock units, with some near-vertical joints. Several rock ledges with potentially loose material were noted in the roof rock above the Dripstone Cave Entrance and Dripstone Cave

Bypass tunnel.

Analysis of the unsupported span openings in the assessment areas using empirical relationships based on rock mass quality indicates that the unsupported spans are “potentially unstable” without the use of permanent ground

(rock) support (rock bolts, mesh, shotcrete, etc.). The geotechnical analyses suggest the use of permanent ground support to improve stability in the Elevator Room and Dripstone Cave Entrance, Dripstone Cave Bypass

Tunnel, and Dripstone Cave Exit. Due to the relatively long design life and use as a public facility, Golder recommends that permanent ground support be added to each of these areas.

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The existing airlock and security doors were installed in the 1970s and have deteriorated considerably over approximately the last 50 years. Various construction material options and door options were reviewed by Golder as a part of this Report. Construction materials were considered for both new door and frame installations, as well as bulkhead installations that join the tunnel and cave walls to the structure of the door frame.

Golder’s overall recommendations for each assessment area are detailed in the following paragraphs.

Elevator Room and Dripstone Cave Entrance Recommendations: Recommended work includes replacement of the airlock door systems and installation of permanent ground support (rockbolts, mesh, and shotcrete) through the entry tunnel; scaling (removal) of loose rock, demolition and replacement of existing false ceilings and utilities/ducting, instrumentation installation near the interface with the natural cavern, and protection of existing features and the natural cave environment.

Dripstone Cave Bypass Tunnel Recommendations: Recommended work includes replacement of the door between the tunnel and the surface shaft and installation of permanent ground support (rockbolts and mesh) through the tunnel; scaling of loose rock, instrumentation at both ends near the interface with the natural cavern, and protection of existing features and the natural cave environment.

Dripstone Cave Exit Recommendations: Recommended work includes replacement of the airlock and security door systems and installation of permanent ground support (rockbolts, mesh, and shotcrete) through the exit tunnel; scaling of loose rock, demolition of existing canopy structure and replacement with structural shotcrete, instrumentation near the interface with the natural cavern, and protection of existing features and the natural cave environment.

Discovery Cave Exit Recommendations: Probe drilling of the existing shotcrete and steel beam ground support found the structure to be in good condition. Recommended work is limited to replacement of the airlock and security door systems and protection of existing features and the natural cave environment.

Surface Sinkhole Area Recommendations: Security of the cave is the primary concern. Golder recommends that the sinkhole be filled with crushed limestone and that a water diversion berm be constructed to divert surface water from the adjacent roadway and limit man-made water inflows.

For Forest Service budgeting purposes, estimated construction costs related to the recommended scope items outlined above are approximately $3,800,000 and total Project duration is estimated to be approximately 23 weeks. We have estimated costs based on our prior experience on similar projects and conservatively assumed a contingency factor of 25%, based on the logistical factors involved. We have also included an estimate of costs related to engineering construction management during Project construction. The preliminary cost estimate should be considered order of magnitude and will continue to be refined as the design phase advances.

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Table of Contents

1.0 INTRODUCTION

1.1 Background

2.0 GEOLOGIC SETTING

2.1 Geological Structures

2.2 Stratigraphy

2.2.1 St. Peter Sandstone

2.2.2 Joachim Dolomite

2.2.3 Plattin Limestone

2.2.4 Kimmswick Limestone

2.2.5 Fernvale Limestone

2.2.6 Cason Formation

2.2.7 Silurian Limestones

2.2.7.1 St. Clair Limestone

2.2.7.2 Lafferty Limestone

2.2.8 Chattanooga Formation

2.2.8.1 Sylamore Sandstone Member

2.2.8.2 Chattanooga Shale

2.2.9 Boone Formation

2.2.9.1 St. Joe Limestone

3.0 GEOTECHNICAL INVESTIGATION

3.1 Underground Inspection

3.1.1 Rock Quality

3.1.2 Discontinuities

3.2 Geotechnical Laboratory Testing

3.2.1 Testing Results

4.0 GEOTECHNICAL ANALYSES

4.1 Rock Mass Classification and Material Geotechnical Properties iii

4.1.1 NGI-Q System

4.1.2 Rock Mass Rating

4.1.3 Material Geotechnical Properties

4.2 Roof Beam Analysis

4.3 Ground Support Analysis

4.4 Finite Element Analyses

4.4.1 Model Inputs and Method

4.4.2 RS2 Model Results

5.0 GEOTECHNICAL RECOMMENDATIONS

5.1 Design Criteria

5.2 Elevator Room and Dripstone Cave Entrance Support Recommendations

5.2.1 Elevator Room

5.2.2 Outer Airlock Door to Inner Airlock Door

5.2.3 Inner Airlock Door to Cave Interface

5.3 Dripstone Bridge Recommendations

5.4 Dripstone Cave Bypass Tunnel Support Recommendations

5.5 Dripstone Cave Exit Support Recommendations

5.5.1 Cave Interface to Inner Airlock Door

5.5.2 Inner Airlock Door to Outer Airlock Door

5.5.3 Outer Airlock Door to Security Door

5.6 Discovery Cave Exit Recommendations

5.7 Surface Sinkhole Area Recommendations

5.8 Recommendations for Instrumentation and Future Monitoring

6.0 AIRLOCK DOORS AND SECURITY DOORS

6.1 Design Criteria

6.2 Door Replacement Options

6.3 Reference Product Lines

6.4 Door Information and Recommendations

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6.4.1 Dripstone Cave Entrance – Outer Airlock Doors

6.4.2 Dripstone Cave Entrance – Inner Airlock Doors

6.4.3 Dripstone Cave Bypass Tunnel Door

6.4.4 Dripstone Cave Exit – Inner Airlock Door

6.4.5 Dripstone Cave Exit – Outer Airlock Door

6.4.6 Dripstone Cave Exit – Security Doors

6.4.7 Discovery Cave Exit – Security Doors

6.4.8 Discovery Cave Exit – Outer Airlock Door

6.4.9 Discovery Cave Exit – Inner Airlock Door

7.0 PRELIMINARY CONSTRUCTION COST ESTIMATE AND SCHEDULE

8.0 CLOSING

9.0 REFERENCES

TABLES

Table 1: Generalized Stratigraphic Sequence for Blanchard Caverns

Table 2: Discontinuity Log

Table 3: Laboratory Testing Results

Table 4: Summary of the Q Values by Formation

Table 5: Summary of RMR 89 Values by Formation

Table 6: Summary of Material Properties Used in Geotechnical Analyses

Table 7: Roof Beam Analysis FS Crushing and Buckling Limits

Table 8: Door, Frame, and Bulkhead Material Options Reviewed

Table 9: Proposed Replacements Summary

Table 10: Preliminary Construction Cost Estimate

Table 11: Preliminary Construction Schedule

FIGURES

Figure 1: Cavern Map and Assessment Area Locations

Figure 2: A:Sidewall of the Dripstone Trail exit displaying the St. Joe Limestone, Chattanooga Shale and Silurian Limestones. B: Fossils present in the Chattanooga Shale

Figure 3: Boone Formation outside of Dripstone Trail exit v

Figure 4: Upper portion of the St. Joe Member in the roof of the bypass tunnel

Figure 5: Empirical Design Span Chart

Figure 6: Empirical Support Design Chart (after NGI, 2015)

Figure 7: Elevator Room RS2 Model Geometry

Figure 8: Dripstone Cave Entrance RS2 Model Geometry

Figure 9: Dripstone Cave Bypass Tunnel RS2 Model Geometry

Figure 10: Dripstone Cave Exit RS2 Model Geometry

Figure 11: Hollow Aluminum Doors with Brushed Aluminum and Bronze Finishes (Source: CDF)

Figure 12: Stainless Steel Storefront System (Source: CRL)

Figure 13: Aluminum Balancer Storefront System (Source: CRL)

Figure 14: FRP Door with Full Kick Plates, Push Bars, and Closers in RAL 5015 Blue (Source: Dortek)

Figure 15: Solid Fiberglass Door with Aluminum Frame and Glass/Fiberglass Panels (source: Metropolitan Door Industries)

Figure 16: Stainless Steel Door with Window Kit in #4 Stain Stainless Finish (source: Trudoor)

Figure 17: Tubelite E4500 Hollow Aluminum Storefront System with Wide Stile Doors in Clear Class Finish (source: Tubelite)

Figure 18: Dripstone Entrance - Airlock Entrance (Existing Conditions). Existing stacked stone masonry bulkhead visible on left side of doors

Figure 19: Dripstone Entrance - Airlock Exit (Existing Conditions)

Figure 20: Dripstone Bypass Door (Existing Conditions)

Figure 21: Dripstone Exit – Airlock Entrance (Existing Conditions)

Figure 22: Dripstone Exit - Airlock Exit (Existing Conditions)

Figure 23: Dripstone Exit - Security Door (Existing Conditions)

Figure 24: Discovery Exit - Security Door (Existing Conditions)

Figure 25: Discovery Exit - Airlock Entrance (Existing Conditions)

Figure 26: Discovery Exit - Airlock Exit (Existing Conditions)

DRAWINGS

G-01 – Provinces of Northern Arkansas and Stratigraphic Column

G-02 – Geologic Map and Cross Section vi

APPENDICES

APPENDIX A

Photo Log

APPENDIX B

Laboratory Testing Reports

APPENDIX C

Material Properties and Rock Mass Characterization Analysis

APPENDIX D

Roof Beam and Ground Support Calculations

APPENDIX E

RS2 Model Output Figures

1.0 INTRODUCTION

The United States Forest Service (Forest Service) contracted Golder Associates Inc. (Golder) through Robert

Peccia & Associates, Inc. (RPA) in September 2019 to perform various tasks associated with the Blanchard

Springs Caverns – Geological Assessment and Design Project (the Project) at Blanchard Springs Caverns, located near Fifty-Six, Arkansas (Project Site or Site). The Project scope includes various technical support services related to an assessment and design for stabilization and repairs at the Site. These technical support services include:

On-site assessments and investigations

Detailed findings and recommendations reporting

Complete design packages for permanent repairs in identified areas

This report of Geological Assessment Findings and Recommendations for Repairs and Corrective Actions

(Report) presents the findings from Golder’s geotechnical investigation and site assessment, presents the methodology and results of geotechnical analyses completed to determine recommendations for permanent repairs, presents recommendations for ground support in the assessment areas, presents replacement options for air lock doors and security doors, and includes a preliminary construction cost estimate and schedule.

1.1 Background

Blanchard Springs Caverns and Visitor Center is located in North Central Arkansas in the Sylamore Ranger

District of the Ozark-St. Francis National Forest. The Blanchard Springs Visitor Center opened to the public in

1973 and is the initial access point for the caverns, and the portal for the Dripstone Cave. The Caverns are unique in that limited access has prevented cavern features from being damaged by man. It is an active “living” cave with large rooms “decorated” with crystalline formations that are still growing. The Site is on the Forest

Service Regional Priority Investment list and plays a vital role in the local tourism economy in that part of the

State.

During a March 2015 inspection, a Forest Service geologist identified potential hazards associated with horizontal tension fractures in the natural rock above the Dripstone Cave Entrance tunnel. Temporary mitigation measures were installed in this area of the tunnel in 2015. The mitigation work was recommended and approved by the

Roof Control Division, Mine Safety & Health Administration (MSHA) as a temporary solution, with the intention of following this work with a professional mining/tunneling assessment and design of a permanent solution.

Golder performed an initial Site visit and attended a preliminary assessment meeting with Forest Service personnel on October 8th and 9th, 2019 at the Project Site. During overall Project discussions at the conclusion of the meeting, Golder discussed conceptual recommendations for improving ground support and/or providing remedial measures at the following five separate areas (assessment areas):

Dripstone Cave Entrance

Dripstone Cave Bypass Tunnel

Dripstone Cave Exit

Discovery Cave Exit

Surface Sinkhole Area

Those areas and preliminary construction scope items were discussed in Golder’s October 21, 2019 technical memorandum. All of the underground areas are manmade tunnels excavated to provide access to the caves and are only representative of natural cave conditions at the points where the tunnels transition into the cave areas.

They were not located in critical bat hibernation areas. A plan view map of the cavern system that displays the relative location of the assessment areas is included in Figure 1.

Golder visited the Site to complete the Site investigation/assessment on January 13-15, 2020. During the Site assessment, Golder gathered additional data and samples from the assessment areas to aid in our geological assessment and design recommendations.

Figure 1: Cavern Map and Assessment Area Locations

2.0 GEOLOGIC SETTING

The Site area lies within the Ozarks Plateaus Physiographic Province (Ozark Province) in northern Arkansas, as shown in Drawing G-01. This Ozark Province is on the southern flank of an asymmetrical dome (or uplift) with a center located in the St. Francois Mountains in southeastern Missouri. Typically, units dip gently away from the center of the dome, which produces the slight southward to southwestward dip of bedrock strata in northern

Arkansas. The Ozark Province is commonly divided into three different plateaus in Arkansas based on elevation and age of the rock units present at the surface. These three plateaus are (Arkansas Geological Survey (AGS), 2020):

Salem Plateau – Oldest of the three plateaus and made up of Ordovician dolostones, sandstones, and limestones. The formations forming the Salem Plateau are present along the northern end of the Blanchard

Cavern grounds and typically present in the Discovery Trail and the lower portions of the Dripstone Trail.

Springfield Plateau – Mostly Mississippian limestone with chert that extents down to the Boone Formation.

The formations forming the Springfield Plateau are present in the upper portions and roof of the Dripstone

Trail.

Boston Mountains Plateau – the youngest and southernmost of the three plateaus, typically Pennsylvanian sandstones and shales with minor amounts of limestone. The formations comprising the Boston Mountains

Plateau are not present in the Blanchard Cavern trail system.

2.1 Geological Structures

No references that discuss the local geological structures in detail have been discovered, however, a geological map for the Fifty-six quadrangle (Braden et al., 2002) displays several structural features present in the area near the cave (See Drawing G-02). Approximately one mile north of the Site is the southeast trending North Sylamore

Monocline. This monocline folds the sedimentary units and causes a steepening of the dip towards the southeast.

Based on the cross section presented on the quadrangle map, the units flatten near North Sylamore Creek, north of the site. Mapping also displays a series of steeply dipping normal faults striking from northwest to southeast that are spaced approximately 1.5 to 2 miles apart. Geological mapping displays one of these features just south of Highway 14, 0.75 miles southeast of the site; and another ~0.75 miles to the northeast, near North Sylamore creek.

2.2 Stratigraphy

The stratigraphy of the Blanchard Caverns area consists of Ordovician, Silurian, Devonian, and Mississippian aged limestone and dolostone with lesser amounts of shale and sandstone. Table 1 presents the generalized stratigraphic sequence encountered at the cave, including general unit thicknesses and rock descriptions based on site specific observations and local/regional geological reports (McFarland, 1998, and Braden et al., 2002).

Detailed descriptions of the units are provided in the following sub-sections. Blanchard caverns developed due to solution activity between the Boone and the St. Peters formations.

Table 1: Generalized Stratigraphic Sequence for Blanchard Caverns

System

(Age)

Formation Member Thickness

(Feet)

Brief Geological Description

Mississippian

Boone Boone

Limestone

250+

Light to medium gray, fine to coarse grained fossiliferous limestone with interbedded chert.

Mississippian Boone St. Joe Member

0-12

Dark gray, fine-grained crinoidal limestone with small round green spheres that are sometime flattened and appear to be composed of green clay at the top of the unit.

Devonian Chattanooga Chattanooga

Shale

0-6 Black, fissile clay shale that may contain pyrite.

Devonian Chattanooga Sylamore

Sandstone

0-1.5 Basal unit that is a white to dark gray quartz sandstone.

Silurian

Silurian

Limestones

Lafferty

0-20 Sparsely fossiliferous, finely crystalline, medium gray

Silurian Silurian

Limestones

St. Clair

0-3 A coarse-grained, thickly bedded to massive, highly fossiliferous, light gray to pinkish gray

Silurian Cason Cason Shale 0-8 Clay shale with abundant black phosphate pebbles, dark gray, with reddish siltstone in upper portion.

Ordovician

Fernvale

Undifferentiated 0-30 Massive with occasional cross beds, coarsely crystalline, light gray to pink, clinoidal limestone

Kimmswick

Undifferentiated 0-15 Thin to massively bedded, light- to dark-gray, fine- to coarse-grained bioclastic limestone with a very sugary texture.

Plattin

Undifferentiated 20-180 Very fine grained, light to dark gray, thinly bedded, micritic limestone

Joachim

Dolomite

Undifferentiated 0-90 Fine grained sandy dolostone or dolomitic limestone with thin shale beds throughout.

St. Peter

Sandstone

Undifferentiated 20-300 Massively bedded, medium to very fine grained, friable, quartz sandstone

2.2.1 St. Peter Sandstone

The oldest and lowermost unit present in the Blanchard Caverns area is the St. Peter Sandstone. This formation is described as a massively bedded, very fine to medium grained, well sorted, friable, quartz sandstone with calcite cementation. Fresh exposures of the unit are typically white and the unit weathers to a buff to brownish color. The unit is also an important regional aquifer and is a frequent bluff-former. The St. Peter Sandstone was not encountered in the cave during this field investigation and forms the base of the lowest portions of the

Discovery Trail. Outcroppings of the St. Peter Sandstone are present near Blanchard Springs.

2.2.2 Joachim Dolomite

The Joachim Dolomite lies conformably above the St. Peter Sandstone and is described as a fine grained to finely crystalline, sandy dolostone or dolomitic limestone with thin shale beds throughout. The unit is light to medium gray where fresh and weathers to dark gray or tan in color. The Joachim Dolomite was not encountered in the cave during this field investigation; however, it is typically present in the lower sections of the Discovery Trail.

Outcroppings of the Joachim Dolomite are also present near Blanchard Springs.

2.2.3 Plattin Limestone

The Plattin Limestone lies unconformably above the Joachim Dolomite and is described as a very fine grained, thinly bedded, micritic limestone. While some fossils are present in the upper portions of the Plattin Limestone, the unit is less fossiliferous than the overlying units. The unit is light to dark gray on fresh surfaces and weathers to dark gray. The Plattin Limestone was encountered in the Discovery Trail; however, detailed descriptions of the unit were not established as it is not present in any of the areas of concern. The discharge of Blanchard Springs is formed in the Plattin Limestone.

2.2.4 Kimmswick Limestone

The Kimmswick Limestone lies unconformably above the the Plattin Limestone and is described as thin to massively bedded, medium crystalline, bioclastic limestone with a very sugary texture. Some beds of dolomite and sandstone have been noted, but they are not prevalent. The grains of the Kimmswick are typically a well-mixed accumulation of fossil fragments. The unit is light gray on fresh surfaces but weathers to a dark gray. The

Kimmswick Formation was encountered in the Discovery Trail; however, detailed descriptions of the unit were not established as it is not present in any of the areas of concern.

2.2.5 Fernvale Limestone

The Fernvale Limestone lies conformably above Kimmswick Limestone and is described as massive with occasional cross beds, coarsely crystalline crinoidal limestone with occasional vugs and often contains traces of bluish to olive gray clays. The unit is white to light gray with a pink to reddish mottling on fresh surfaces and weathers to a dark gray color. The Fernvale was encountered in the Dripstone Trail and makes up the lowest portions of that trail.

2.2.6 Cason Formation

The Cason Formation is unconformable to the underlying Fernvale Limestone and is described as clay shale with abundant phosphate pebbles. The unit is dark gray on fresh surfaces and weathers to a buff or light brown color.

Regionally, the unit has been described as also having flattened oncolites (algal buttons) and to be blue/green to dark gray/black in color. The unit was not specifically identified in the cave and is known to be missing in some parts of the region. However, in the main rooms of the cave, locations of walkways and large amounts of flowstone on the walls limit access to and observation of the geological units. Where present, the Cason

Formation would likely have weathered quickly after exposure, exposing the overlying limestone. If present in the cave, the Cason Formation would be at or below the floor of the Dripstone exit tunnel.

2.2.7 Silurian Limestones

In northern Arkansas there is a thin, typically 5 to 20-foot-thick series of Silurian limestones. In the area around

Blanchard Cave in the Fifty-six Quadrangle, two of these units can exist, the Lafferty Limestone and the St. Clair

Limestone.

2.2.7.1 St. Clair Limestone

The St. Clair Limestone is not laterally extensive throughout the area and is described as coarsely grained, thickly bedded to massive, and highly fossiliferous. The unit is typically light gray to white with small round spots on fresh surfaces but weathers to a medium gray. The St. Clair Limestone was not identified in the cave.

2.2.7.2 Lafferty Limestone

The Lafferty Limestone is unconformable to the underlying St. Clair Limestone, Cason Formation, or Fernvale

Limestone, depending on which units are present. The unit is described as having few fossils, finely crystalline, thin to thickly bedded, and with frequent styolites along bedding planes. The unit is fairly persistent throughout the area and is medium gray with small red spots on fresh surfaces and weathers to a light gray. The unit also often has pyrite cubes near its upper contact. In the Dripstone Cave, this unit was present in the lower sections of the entrance, exit, and bypass tunnels.

2.2.8 Chattanooga Formation

The Chattanooga Formation is typically broken up into two members, the upper Chattanooga Shale and the lower

Sylamore Sandstone member. Both units are not laterally predominant in the Fifty-six quadrangle and are missing in many areas.

2.2.8.1 Sylamore Sandstone Member

The Sylamore Sandstone is unconformable with the

Silurian limestones and is a medium grained, moderately sorted, sub-rounded to sub-angular, friable, iron-cemented sandstone. The unit has white to dark gray appearance were fresh but weathers to a light tan. The unit was not identified during the field investigation.

2.2.8.2 Chattanooga Shale

The Chattanooga Shale lies unconformably above the

Silurian Limestones when the Sylamore is not present.

The unit is described as a fissile clay shale, with small abundant pyrite, and is not laterally continuous. The unit is black on both fresh and weathered surfaces. In the Fifty-six quadrangle, the Chattanooga Shale often contains small lenticular sand bodies.

In the Dripstone Cave, the Chattanooga Shale is present in the side walls of the entrance, exit and bypass tunnels, where it is approximately 1.5 to 4.5 feet thick. In the cave, the unit is black to green with some large

A B

Chattanooga

Shale

St. Joe

Limestone

Silurian

Limestone -

Lafferty

Figure 2: A:Sidewall of the Dripstone Trail exit displaying the St. Joe Limestone, Chattanooga Shale and Silurian Limestones. B: Fossils present in the Chattanooga Shale.

clasts of sandstone/limestone. The unit is soft and slightly to moderately weathered. Additionally, the unit is very iron rich near the top, with some pyrite present in fresh samples, and some fossils present throughout the unit.

2.2.9 Boone Formation

The Boone Formation has an unconformable contact with the underlying Chattanooga Formation and is described as a fine to coarse grained fossiliferous limestone with interbedded chert. This unit is typically light to medium gray on fresh surfaces and weathers to a dark gray. This unit is known throughout the region for having frequent springs and sinkholes. The Boone Formation is present in the natural roof portions of the Dripstone Cave. Additionally, this unit is present in unstained exposures just outside of the Dripstone

Cave exit. In this area, the unit is a medium strong, slightly weathered limestone with very thing beds and frequent chert nodules.

2.2.9.1 St. Joe Limestone

At the bottom of the Boone Formation is the St. Joe Limestone member. This member, which is widespread throughout the Ozark region, is mostly a fine-grained, thin bedded, crinoidal limestone with occasional chert and thin shaley limestone beds. The unit is typically dark gray to reddish with some greenish mottling. The upper portion of the St. Joe in the Fifty-six Quadrangle is described as a prevalent and distinguishable unit containing small round green spheres that are sometime flattened and appear to be composed of green clay. Additionally, the lower portion of the St. Joe can contain a basal sandstone that is a fine to medium grained, moderately sorted, iron or quartz cemented sandstone.

In the Dripstone Trail, the St. Joe Formation is present at or within the roof in the entrance to the cave, the bypass tunnel and the exit from the cave. The Upper portion of the St. Joe

Formation is a distinguishable bed in each of the areas due to the presence of the green spheres of clay like material.

In some areas, this unit has undergone moderate weathering and is very weak to weak. There are also trace amounts of pyrite cubes. Below the upper clayey member is an approximately 2 to 5 foot-thick thinly bedded limestone with frequent fossils and calcite mineralization that was slightly weathered and was much stronger than the upper member, with a medium strong strength.

Boone Formation

Figure 3: Boone Formation outside of Dripstone Trail exit

Figure 4: Upper portion of the St. Joe Member in the roof of the bypass tunnel

3.0 GEOTECHNICAL INVESTIGATION

Golder completed a geotechnical underground Site assessment on January 13-15, 2020. During the Site assessment, Golder gathered additional data and samples from the assessment areas to aid in geotechnical analyses and design recommendations and supplement data collected during the initial Site visit.

3.1 Underground Inspection

The assessment areas of the caverns consist of the Dripstone Cave Entrance, Dripstone Cave Bypass Tunnel, Dripstone Cave Exit, and Discovery Cave Exit. For all areas, Golder visually observed rock and existing support conditions (using A-frame ladders provided by the Forest Service, where necessary) and used measuring devices such as tape measures, laser distance meters, and handheld Brunton compass to collect data. Photographs were also taken of the various assessment areas.

In the Discovery Cave Exit, Golder used a battery powered handheld hammer drill to drill a series of 1-inch diameter probe holes in the shotcrete roof structure on either side of the inner airlock door. Once drilled, a borescope camera was inserted into the drillhole to check shotcrete thickness, view rock conditions, and check for the presence of steel beams/reinforcement. Probe holes were sealed with hydraulic cement following inspection.

3.1.1 Rock Quality

The rock quality as described by Rock Quality Designation (RQD) (Deere, 1988) data was estimated during the underground inspection. In general, the rock quality in each formation appeared fairly uniform laterally between assessment areas. The observed RQD was generally good (75 – 90%) to excellent (90 – 100%) except in the

Chattanooga Shale, where it was observed to be poor (25 - 50%). Rock mass qualities as defined by the

Norwegian Geotechnical Institute Rock Quality Index (NGI-Q index) system and Rock Mass Rating (RMR) system are further described in Section 4.1.

3.1.2 Discontinuities

Detailed description of structural discontinuities in the rock units in each assessment area were logged, including fracture type, strike/dip, shape, roughness, and infilling type and character. Most of the discontinuities encountered were bedding planes occurring between the bedrock units, with some near-vertical joints. These near-vertical discontinuities were primarily irregular surfaces with clean faces. Discontinuities observed in each assessment area are described in Table 2 below.

Table 2: Discontinuity Log

Notes:

1. “NM” = Not Measured

2. ft = feet

3. in = inches

4. mm = millimeters

Assessment Area Discontinuity

Type Dip Strike

Persistence (ft)

Spacing (in)

Roughness Shape Weathering Aperture

(mm) Infill

Water / Seepage

Elevator Room Bedding NM NM NM 4 Rough Undulating Slightly Weathered <1 Shale, Iron Oxide Damp

Joint 84 145 8 12-60 Rough Undulating Slightly Weathered 0 Clean Damp

Joint 86 351 4 8-60 Rough Undulating Slightly Weathered 0 Clean Damp

Bedding 9 65 40 6-24 Rough Undulating Moderately Weathered 0 Clay, Iron Damp

Bedding 4 91 40 4-18 Rough Undulating Moderately Weathered 0 Clay, Iron Damp

Bedding 9 45 40 2-8 Rough Undulating Moderately Weathered 0 Clean Damp Bedding 4 104 40 2-8 Rough Undulating Moderately Weathered 0 Clean Damp

Joint 62 270 2 60-80 Rough Undulating Moderately Weathered 10 Calcite Damp Joint 84 114 2 12-24 Rough Undulating Slightly Weathered 0 Clean Damp Joint 89 91 2 24 Rough Undulating Slightly Weathered 0 Clean Damp

Bedding 12 109 40 2-8 Rough Undulating Moderately Weathered 0 Clean Damp Bedding 16 59 40 2-8 Rough Undulating Moderately Weathered 0 Clean Damp Bedding 8 359 200 8-14 Rough Undulating Slightly Weathered 0 Clean Damp

Joint 88 161 12 24-36 Rough Undulating Highly Weathered 300 Clay Damp Joint 83 340 2 24-36 Rough Undulating Slightly Weathered 0 Clean Damp Joint 20 195 5 12-24 Rough Undulating Slightly Weathered 0 Clean Damp

Bedding 9 40 200 8-14 Rough Undulating Slightly Weathered 0 Clean Damp Joint 89 142 1-20 48-120 Rough Undulating Slightly Weathered 0 Clean Damp Joint 88 149 1-20 48-120 Rough Undulating Slightly Weathered 0 Clean Damp

Bedding 4 324 200 8-14 Rough Undulating Slightly Weathered 0 Clean Damp Joint 81 84 50 150 Rough Undulating Moderately Weathered 0 Clean Damp Joint 89 170 3-10 24-60 Rough Undulating Slightly Weathered 0 Clean Damp

Bedding 9 194 200 8-11 Rough Undulating Slightly Weathered 0 Clean Damp Bedding 8 326 200 8-11 Rough Undulating Slightly Weathered 0 Clean Damp

Joint 81 270 7 24-48 Rough Undulating Slightly Weathered 0 Clean Damp Joint 82 262 6 24-48 Rough Undulating Slightly Weathered 0 Clean Damp Joint 89 89 6 24-48 Rough Undulating Slightly Weathered 0 Clean Damp Joint 88 270 2-8 36 Rough Undulating Slightly Weathered 0 Clean Damp Joint 85 275 2-8 36 Rough Undulating Moderately Weathered 0 Clean Damp

Bedding 15 190 60 6-18 Rough Undulating Moderately Weathered 0 Clean Damp Bedding 9 157 60 6-18 Rough Undulating Moderately Weathered 0 Clean Damp

Joint 85 31 1-3 4-12 Rough Undulating Slightly Weathered 0 Clean Damp Joint 81 11 1-3 4-12 Rough Undulating Slightly Weathered 0 Clean Damp Joint 89 241 2-8 36 Rough Undulating Slightly Weathered 0 Clean Damp Joint 84 281 2-8 36 Rough Undulating Slightly Weathered 0 Clean Damp

Bedding 16 190 60 6-18 Rough Undulating Moderately Weathered 0 Clean Damp Joint 86 350 1-3 4-12 Rough Undulating Slightly Weathered 0 Clean Damp Joint 89 265 2-8 36 Rough Undulating Slightly Weathered 0 Clean Damp Joint 82 19 1-3 4-12 Rough Undulating Slightly Weathered 0 Clean Damp

Dripstone Cave Entry - First Air Door to Second Air Door

Dripstone Cave Entry - Second Air

Door to Cave

Dripstone Cave Bypass Tunnel

Dripstone Cave Exit Tunnel

3.2 Geotechnical Laboratory Testing

Five samples of cavern roof rock were collected from two loose rock bulk samples that were recently scaled from the cavern roof in the Dripstone Cave Entrance and were submitted to GeoTesting Express Inc. for laboratory geotechnical testing. The tests conducted included the following:

Unconfined compressive strength (UCS) (ASTM D 7012 - Method D)

Young’s Modulus (ASTM D 7012 – Method D)

Poisson’s Ratio (ASTM D 7012 – Method D)

A total of six rock core samples were cored form the bulk samples at the laboratory for geotechnical testing, however, due to breakage during lab preparation, only five were tested. The complete results of the laboratory testing are presented in Appendix B at the end of this Report.

3.2.1 Testing Results

The roof of the Dripstone Cave Entrance is made up of rock from the Upper and Lower St. Joe Formation. Bulk samples from the other formations present at the Site were not available, so estimates of their geotechnical parameters were made based on typical values for the rock type. Table 3 presents a summary of the laboratory results. Copies of the laboratory reports, including photographs of the rock samples, are included in Appendix B.

Table 3: Laboratory Testing Results

1. “N/A" Data not available

2. psi = pounds per square inch

3. ksi = thousand pounds per square inch

4. pcf = pounds per cubic foot

4.0 GEOTECHNICAL ANALYSES

The geotechnical analyses for the Site included the following:

Rock mass classification and rating

Material geotechnical properties

Roof beam analysis

Ground support analysis

Test Sample ID Rock Type / Formation

Broke Before Testing

UCS (psi) Young's

Modulus, E [ksi]

Poisson's Ratio, N

Bulk Density

(pcf)

Bulk Specific Gravity

DS Roof LS 1 St. Joe (Lower) No 21,081 27,800 0.46 150 2.40

DS Roof LS 2 St. Joe (Lower) No 19,010 37,900 N/A 151 2.42

DS Roof LS 3 St. Joe (Lower) No 10,732 11,000 0.28 146 2.34

DS Roof Clayey 1 St. Joe (Upper) No 18,047 N/A N/A 170 2.72

DS Roof Clayey 2 St. Joe (Upper) No 16,398 9,840 N/A 150 2.40

DS Roof Clayey 3 St. Joe (Upper) Yes N/A N/A N/A N/A N/A

GeoTesting Express 2020

- ASTM D7012D

Elastic Moduli of Rock in Uniaxial Compression

Joint kinematics analysis

Finite element analysis

Geotechnical analyses and detailed calculations are presented in Appendix C and Appendix D.

4.1 Rock Mass Classification and Material Geotechnical Properties Estimates of rock mass classifications using the NGI-Q index and the RMR system were carried out for the Boone

Limestone, St. Joe (Upper), St. Joe (Lower), Chattanooga Shale, Lafferty Limestone, and Fernvale Limestone roof shale. Parameter values were determined based on the laboratory results and underground inspection performed as part of the geotechnical investigation.

4.1.1 NGI-Q System

The Q index incorporates six different rock parameters for the classification of the overall rock mass quality. The

Q system consists of the following parameters (Barton et al., 1974):

Where:

RQD = Rock Quality Designation

Jn = Joint Set number

Jr = Joint Roughness number

Ja = Joint Alteration number

Jw = Joint Water Reduction Factor

SRF = Stress Reduction Factor

For the rock mass characterization, the parameters were collected during the underground inspection. The stress reduction factors (SRF) were assumed to be 1 (medium stress) based on the rock strength, stress conditions, field observations, and professional judgement. Table 4 summarizes the Q rating for each unit based on the underground inspection.

Table 4: Summary of the Q Values by Formation

The analysis of rock mass quality, using the index developed by NGI, indicates the rock quality in the roof of the assessment areas is generally fair, while the limestone units in the floor and side walls are generally good quality.

The Chattanooga Shale, which is present in thicknesses ranging from 2.5 to 4.0 feet in the side walls of the assessment areas, is generally poor quality. It should be noted that the NGI-Q system does not account for rock strength and is primarily a measure of the rock mass structure and condition of the discontinuities.

4.1.2 Rock Mass Rating

The RMR system assigns ratings based on the following five parameters (after Bieniawski, 1976 with subsequent updates in 1989):

R1 = Rating based on uniaxial compressive strength of rock material

R2 = Rating based RQD

R3 = Rating based on Spacing of Discontinuities

R4 = Rating based on Conditions of Discontinuities

R5 = Rating based on Groundwater Conditions

Rating Adjustment based on Discontinuity Orientations

Where:

Since the various parameters are not equally important for the overall classification of a rock mass, importance ratings are allocated to the different value ranges of the parameters, with a higher rating indicating better rock mass conditions. The ratings for the five parameters are added to define the RMR values representing the rock mass condition of the formation under consideration. Five rock mass classes, based on the RMR values, classify the rock mass conditions from Very Good Rock (RMR > 80) to Very Poor Rock (RMR ≤ 20). For the RMR classification, the first four parameters (R1-R4) were taken from the laboratory testing and field observations. The

Formation RQD Jn Jr Ja Jw SRF Q

Rating Class

Description

Boone Limestone 79 9.0 3.0 1.8 0.66 1.0 10 Fair

St. Joe (Upper) 70 12.0 3.0 1.8 0.66 1.0 6 Fair

St. Joe (Lower) 90 9.0 3.0 1.2 0.66 1.0 17 Good

Chattanooga Shale 40 12.0 2.5 1.8 0.66 1.0 3 Poor

Lafferty Limestone 90 9.0 3.0 1.2 0.66 1.0 17 Good

Fernvale Limestone 90 9.0 3.0 1.2 0.66 1.0 17 Good groundwater parameter (R5) was assigned as 7 (wet) based on field observations. The Rating Adjustment was assigned based on field observations and the relative dip angles of the discontinuities.

Table 5 summarizes the RMR ‘89 rating for each formation using data from the field observations. Classification parameters and their ratings were evaluated for the given formation in each assessment area and overall classification parameters were calculated from these to give an overall RMR value for each formation. The analysis of RMR indicates the rock quality in the roof of the assessment areas is generally fair while the quality in the limestone units in the floor and side walls is generally good. The Chattanooga Shale, which is present in thicknesses ranging from 2.5 to 4.0 feet in the side walls of the assessment areas, is generally poor quality.

Table 5: Summary of RMR 89 Values by Formation

1. psi = pounds per square inch

2. RQD = Rock Quality Designation

3. ft = feet

4.1.3 Material Geotechnical Properties

Hoek Brown classification and equivalent Mohr-Coulomb cohesion and friction angle were calculated for the formations using the computer program RocDataTM from RocScience. Calculations were made using the geometric mean UCS and Young’s Modulus laboratory result values for the Upper St. Joe and Lower St. Joe formations. Bulk samples from the other formations present at the Site were not available to be tested, so estimates of their geotechnical parameters were made based on typical values for the rock types. Geological

Strength Index (GSI) values were estimated for each formation based on observed discontinuity condition and spacing. The rock mass modulus (Erm) was calculated from the intact Young’s modulus, GSI, and disturbance factor of the rock using a formula developed by Hoek and Dierderichs (2006). Material properties used in the geotechnical analyses are summarized in Table 6 below.

Geomean UCS (psi)

Rating Avg.

RQD

Rating Avg.

Discontinuity Spacing (ft)

Rating

Boone Limestone 14,000 9 79 16 0.3 8 22 7 -5 57 Fair

St. Joe (Upper) 17,203 12 70 14 0.7 9 18 7 -5 55 Fair

St. Joe (Lower) 16,262 12 90 19 1.2 10 22 7 -5 65 Good

Chattanooga Shale 2,600 4 40 8 0.7 9 16 7 -5 39 Poor

Lafferty Limestone 14,000 9 90 19 1.5 12 22 7 -5 64 Good

Fernvale Limestone 14,000 9 90 19 1.5 12 22 7 -5 64 Good

Rating Adj.

RMR '89

Rating

Class Description

R2

Formation

R1 R3

R4 R5

Table 6: Summary of Material Properties Used in Geotechnical Analyses

1. pcf = pounds per cubic foot

2. psi = pounds per square inch

3. ksi = thousand pounds per square inch

4.2 Roof Beam Analysis

The maximum design span was determined empirically using the following chart, developed by Pakalnis and

Vongpaisal (1993) and Pakalnis and Brady (2004). The design span chart uses RMR ’76 values, which were estimated using the RMR ’89 values presented in Section 4.1.2 using the relationship RMR ’76 = RMR ’89 – 5

(Hoek and Kaiser, 1997). The two RMR methods differ in the weight they give to discontinuity conditions.

mi mb s a Phi C (psi)

Boone Limestone 165.0 14,000 9,800 0.26 73 10 3.813 0.050 0.501 7,615 57.0 438

St. Joe (Upper) 149.0 17,203 9,840 0.32 62 7 1.802 0.015 0.502 5,563 56.0 309

St. Joe (Lower) 160.0 16,262 11,000 0.36 73 10 3.803 0.050 0.501 8,638 58.0 505

Chattanooga Shale 145.0 2,600 520 0.30 44 6 0.812 0.002 0.509 109 48.0 40

Lafferty Limestone 165.0 14,000 9,800 0.26 73 10 3.813 0.050 0.501 7,696 58.0 435

Fernvale Limestone 165.0 14,000 9,800 0.26 73 10 3.813 0.050 0.501 7,696 58.0 435

Young's Modulus, E (ksi)

Mohr-Coulomb Rock Type

Unit Weight

(pcf) UCS (psi)

Poisson's Ratio

Geological Strength

Index (GSI)

Generalized Hoek-Brown Parameters Young's

Modulus of the Rock Mass, Erm (ksi)

Figure 5: Empirical Design Span Chart

According to the empirical relationships in the above figure, the unsupported span openings in the Elevator Room, Dripstone Cave Bypass Tunnel, and Dripstone Cave Entrance are “potentially unstable”. The span in the

Dripstone Cave Exit plots in the “stable” area of the chart. This design span chart was developed for mining applications from cut and fill stopes and defines a stable span as standing for 3 months. The design life of the

Blanchard Springs Cavern tunnels is much greater than a typical mining application. Also, the chart does not factor in the effects of rock support and therefore represents conditions before supports are in place. It is important to note that these charts provide estimated ranges for span stability. Localized conditions may result in more or less stability. Also, it is important to note that the life span “to date” for these rooms, since the 1970s, has also far exceeded this time span, generally with no visible instability except in the Dripstone Cave Entrance. This indicates conservatism in the material properties and analysis.

The stability of an unsupported roof beam was analyzed using Golder's Roof Beam Analysis spreadsheet, which calculates Factor of Safety (FS) values against crushing and buckling values based on an algorithm developed in

Diederichs and Kaiser (1999). The maximum room span of each assessment area was analyzed. Each assessment area was analyzed to determine the minimum stable roof beam thickness at which the onset of potential buckling failure occurs. Discontinuity spacing present in the immediate roof less than these values will be in danger of buckling. Results of the analyses are summarized in Table 7 and presented in more detail in

Appendix D

Table 7: Roof Beam Analysis FS Crushing and Buckling Limits

1) Buckling Limits above 0.35 should be further examined due to potential failure. 0.02 is the lower limit of the buckling limit equation. A Buckling limit of 1.0 represents buckling failure.

The roof beam analysis suggests that the formations present in the roof of the assessment areas are capable of forming relatively thin stable beams. Due to the small span sizes, minimum stable beam thickness was calculated to be on the order of 1.9 to 2.5 inches. However, weathering over time and the effects of progressive-type failure could cause the roof conditions to degrade and for loose rock to occur if not supported, as evidenced by the current underground conditions.

It should be noted that these are two-dimensional analyses that do not take into account cases where the roof beam is open or unbound on one side, such as where the elevator shaft is present on one side or in the Dripstone

Cave Entrance and Dripstone Cave Bypass Tunnel, where the tunnels enter into the large cavern area. The beam stability is therefore only being evaluated “across” sections that are constrained by the rock mass on both sides, and stability is decreased anywhere there is a “brow” that causes a discontinuous beam.

4.3 Ground Support Analysis

The permanent conditions of the maximum span were checked using the Empirical Support Design Chart shown in Figure 6, developed by Grimstad and Barton (1993) and revised by the Norwegian Geotechnical Institute

(2015). The chart recommends support designs for underground excavations based on the relationship between the Equivalent Dimension (De) of the room and the NGI-Q value of the different formations that form the roof in the

Elevator Room (Boone

Limestone)

Dripstone Cave Entry (Upper St.

Joe)

Dripstone Cave Bypass Tunnel (Upper St. Joe)

Dripstone Cave Exit (Lower St.

Joe)

14.7 25.7 22.8 19.4

62.8 65.4 59.7 74.2

0.35 0.29 0.29 0.29

0.20 0.16 0.21 0.16

2.4 1.9 2.5 1.9

Factor of Safety - Crushing

Result Parameter

Factor of Safety - Sliding

Buckling Limit (1)

Minimum Stable Beam Thickness (feet)

Minimum Stable Beam Thickness (inches) assessment areas. De is defined by dividing the proposed span by a quantity called the Excavation Support Ratio

(ESR). The value of ESR is related to the intended use of the excavation and to the degree of security which is demanded of the support system installed to maintain the stability of the excavation. An ESR of 0.8 was selected for this facility on the basis of the tunnels being categorized as a public facility. NGI-Q values for the Boone

Limestone (10), Upper St. Joe (6), and Lower St. Joe (17) calculated earlier were used in the analysis. This resulted in all areas except for the Dripstone Cave Exit falling in the Number 3 (systematic bolting) category for the corresponding spans, as shown in Figure 6. The chart also suggests bolt lengths of 9.8 to 10.5 feet on spacings of 5.9 to 6.6 feet. In addition to bolts, 5-6 cm of fiber reinforced shotcrete and/or welded wire mesh may be applied.

Figure 6: Empirical Support Design Chart (after NGI, 2015)

Barton (1974) suggests the following equation to evaluate the roof bolt length (L) based on design span and ESR, where L is the roof bolt length in meters, B is the design span in meters, and ESR is the Excavation Support Ratio as defined above.

Using this equation results in the following suggested bolt lengths:

Elevator Room – De of 5.5 resulted in a Bolt Length (L) of about 2.8 m (9.3 ft)

𝐿 ൌ 2 0.15 ൬ 𝐵

𝐸𝑆𝑅

൰

Dripstone Entry – De of 4.3 resulted in a…