ak pfh 58(1)_GR0818.pdf

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NECK LAKE ROAD, AK PFH

58(1), GEOTECHNICAL

INVESTIGATION

Final Geotechnical Design Report

WFL Geotechnical Report No. 08-18

Contract No. DTFH7015D00007

Task Order No. 69056718F000007

Prepared For: Federal Highway Administration Western Federal Lands Highway Division 610 East Fifth Street Vancouver, WA 98661

Submitted To: Jeff Key, PE Robert Peccia & Associates 3147 Saddle Drive Helena, MT 59601

Submitted By: Golder Associates Inc.

2121 Abbott Road, Suite 100 Anchorage, AK 99507 USA

Distribution:

1 PDF – Robert Peccia & Associates 1 Copy – Golder Associates Inc.

January 21, 2019 1788309

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January 2019 i Neck Lake Road

Reconstruction

AK PFH 58(1)

Final Geotechnical Design Report

Table of Contents

1.0 INTRODUCTION

1.1 Project Description

1.2 Scope of Work

1.3 Project Alignment

2.0 PROJECT SETTING

2.1 Regional Geology

2.2 Seismic Design Parameters

3.0 FIELD EXPLORATION

3.1 Geotechnical Boreholes

3.2 Geotechnical Test Pits and DCPT

3.3 Soil Probes

3.4 Surficial Engineering Geologic Mapping

3.5 Rock Mapping Sites (RMS)

3.6 Material Source Investigation

4.0 LABORATORY TESTING

5.0 GEOTECHNICAL ENGINEERING DISCUSSIONS

5.1 Cut and Fill Slopes

5.1.1 Soil Slopes

5.1.1.1 Cut Slopes

5.1.1.2 Fill Slopes

5.1.2 Rock Cuts

5.1.2.1 Rock Cut - 01 STA 76+00 to 78+00

5.1.2.2 Rock Cut - 02 STA 82+50 to 83+25

5.1.2.3 Rock Cut - 03 STA 87+25 to 90+50

5.1.2.4 Rock Cut - 04 STA 91+50 to 98+50

5.1.2.5 Rock Cut - 05 STA 107+50 to 109+00

5.1.2.6 Rock Cut - 06 STA 121+50 to 127+50

5.1.2.7 Rock Cut - 07 STA 141+65 to 146+35

5.1.2.8 Rock Cut - 08 STA 156+75 to 158+80

5.1.2.9 Rock Cut - 09 STA 213+50 to 214+50

5.1.2.10 Ditch Width Assessment

5.1.2.11 Constructability of Rock Cuts

5.2 Retaining Structures – MSE Walls

5.2.1 Analysis

5.2.2 Recommendations

5.2.2.1 General Geotechnical Parameters (STA 274+00 to 277+75, 280+00 to 281+75, 365+00 to 365+90)

January 2019 ii

5.2.2.2 Seismic Design Parameters (STA 274+00 to 277+75, 280+00 to 281+75, 365+00 to 365+90)

5.2.2.3 General Geotechnical Parameters (STA 407+50 to 413+50)

5.2.2.4 Seismic Design Parameters (STA 407+50 to 413+50)

5.2.2.5 Drainage

5.3 Precast Concrete Block Gravity Retaining Wall – Fish Hatchery Bulkhead

5.3.1 Analysis

5.3.2 Recommendations

5.3.3 Lateral Earth Pressure – Fish Hatchery Bulkhead

5.3.4 Seismic Design Parameters– Fish Hatchery Bulkhead

5.4 Road Embankment

5.4.1 Roadway Construction Berms

5.5 Material Utilization and Disposal

5.5.1 Reuse of Existing Material

5.5.2 Material Sites

5.5.2.1 Material Source Investigation Sites (MSIS)

5.5.2.2 Rock Cuts

5.5.3 Material Disposal

5.6 Construction over Soft Soils

5.6.1 Analysis Method

5.6.1.1 Stability Analysis

5.6.1.2 Settlement Analysis

5.6.2 Summary Recommendations

5.6.2.1 Summary

5.6.2.2 Surcharge Fill

5.6.2.3 Surcharge Staging

5.6.3 Station by Station Recommendations

5.6.3.1 STA 46+75 to STA 59+00

5.6.3.2 Causeway 1, STA 78+38 to STA 79+50

5.6.3.3 STA 130+00 to STA 131+50

5.6.3.4 Causeway 2, STA 147+50 to STA 152+50

5.6.3.5 Causeway 3, STA 167+80 to STA 169+79

5.6.3.6 Causeway 4, STA 177+00 to STA 180+00

5.6.3.7 Causeway 5, STA 184+00 to STA 186+75

5.6.3.8 Causeway 6, Station 381+25 to 382+75

5.6.4 Considerations

5.6.4.1 Surcharge Fill

5.6.4.2 Site Preparation and Geotextile

5.6.5 Geogrid Reinforced Embankment

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5.6.6 Culverts

5.6.7 Long Term Embankment Performance

5.6.8 Construction Monitoring

5.6.8.1 Settlement Plates

5.6.8.2 Pore Water Piezometers

5.6.9 Construction Considerations

5.6.10 Result Summary

5.7 Bridge Foundations

5.7.1 Lateral Earth Pressures

5.7.2 Bridge 1 Segment 1 (STA 35+69 to 36+89)

5.7.2.1 West Abutment

5.7.2.2 East Abutment

5.7.2.3 Seismic Design Parameters

5.7.2.4 Shallow Foundation – Service Limit State

5.7.2.5 Shallow Foundation – Strength Limit State

5.7.3 Bridge 4 Segment 2 (STA 346+80 to 347+50)

5.7.3.1 Seismic Design Parameters

5.7.3.2 Strength Limit State

5.7.3.3 Service Limit State

5.7.3.4 Lateral Soil Response

5.7.3.5 Downdrag Forces

5.7.3.6 Axial Uplift Resistance

5.7.4 Bridge 6 Segment 2 (STA 391+50 to 392+15)

5.7.4.1 West Abutment

5.7.4.2 East Abutment

5.7.4.3 Seismic Design Parameters

5.7.4.4 Shallow Foundation – Service Limit State

5.7.4.5 Shallow Foundation – Strength Limit State

5.8 Drainage

5.9 Acid Rock Drainage

5.9.1 Field Investigation

5.9.2 Laboratory Test Results and Interpretation

5.9.3 Determination of ARD Potential

5.9.4 Discussion of ARD Potential

6.0 USE OF REPORT

7.0 CLOSING

8.0 REFERENCES

January 2019 iv

List of Tables Table 2.1 USGS Seismic Design Parameters – Site Class D (in text) Table 5.1 Stationing with Soil Cut Slopes (in text) Table 5.2 Summary of Rock Slope Stability Analysis and Slope Design Recommendations Table 5.3 Rock Cut – 01 Discontinuity Sets (in text) Table 5.4 Rock Cut – 01 Barton-Bandis Input Parameters (in text) Table 5.5 Rock Cut – 02 Discontinuity Sets (in text) Table 5.6 Rock Cut – 03 Discontinuity Sets (in text) Table 5.7 Rock Cut – 04 Discontinuity Sets (in text) Table 5.8 Rock Cut – 05 Discontinuity Sets (in text) Table 5.9 Rock Cut – 05 Barton-Bandis and Mohr-Coulomb Input Parameters (in text) Table 5.10 Rock Cut – 06 Discontinuity Sets (in text) Table 5.11 Rock Cut – 07 Discontinuity Sets (in text) Table 5.12 Rock Cut – 07 Barton-Bandis Input Parameters (in text) Table 5.13 Rock Cut – 08 Discontinuity Sets (in text) Table 5.14 Rock Cut – 08 Barton-Bandis Input Parameters (in text) Table 5.15 Rock Cut – 09 Discontinuity Sets (in text) Table 5.16 Rock Cut – 09 Barton-Bandis and Mohr-Coulomb Input Parameters (in text) Table 5.17 MSE Wall Information (in text) Table 5.18 USGS Seismic Design Parameters – Site Class B (in text) Table 5.19 USGS Seismic Design Parameters – Site Class D (in text) Table 5.20 Lateral Equivalent Fluid Pressure (in text) Table 5.21 USGS Seismic Design Parameters – Site Class B (in text) Table 5.22 Estimated Excavation Depths of Organic/Soft Soil (in text) Table 5.23 Stationing with Embankment Soil not Suitable for Reuse (in text) Table 5.24 Material Testing Results and Material Use Table 5.25 Strength Parameters used for Stability Analysis, Long Term Conditions (in text) Table 5.26 Strength Parameters used for Stability Analysis, Short Term Conditions (in text) Table 5.27 Settlement Analysis Parameters (in text) Table 5.28 Summary of Causeway and Soft Soil Areas (in text) Table 5.29 Summary of Causeway and Soft Soil Areas (in text) Table 5.30 USGS Seismic Design Parameters – Site Class B (in text) Table 5.31 USGS Seismic Design Parameters – Site Class D (in text) Table 5.32 USGS Seismic Design Parameters – Site Class B (in text) Table 5.33 Acid Base Accounting Results and Interpretation

List of Figures Figure 1 Project Location Map Figure 2 Typical Cut/Fill Section in Soil Figure 3 2V:1H Rock Cut Typical Section Figure 4 Rock Dowel Typical Section Figure 5 Summary Catchment Criteria Figure 6 Map of Material Source Investigation Sites (MSIS) and Rock Mapping Stations (RMS) Figure 7 Proposed Unsuitable Construction Material Disposal Site from USFS Figure 8 Typical Surcharge Schematic Figure 9 Map of Sampling Locations, ARD Classification, and Observed Iron Staining Locations

List of Appendices Appendix A Updated RPA Plan and Profile Set Appendix B Kinematic Analysis of Rock Cuts Appendix C MSE Wall Slope Stability Figures Appendix D Precast Concrete Block Gravity Retaining Wall Slope Stability Figures

January 2019 v

Appendix E Causeway and Soft Soil Slope Stability Figures Appendix F Bridge Calculations Appendix G Acid Base Accounting Laboratory Data

January 2019 1

1.0 INTRODUCTION

1.1 Project Description

The Alaska Department of Transportation & Public Facilities (ADOT&PF) in cooperation with the US Forest

Service (USFS) is proposing approximately eight miles of road upgrades for the Neck Lake Road on Prince of Wales Island in southeast Alaska. The project begins at the intersection of National Forest Service Road

(NFSR) 25 and Forest Highway (FH) 43, and ends southeast of the Whale Pass float plane dock (Figure

1). The road improvements will include widening the existing gravel roadway to a two-lane, paved road, improving drainage, and reducing horizontal and vertical curves. Western Federal Lands Highway Division

(WFLHD) of the Federal Highway Administration (FHWA) is delivering the project on behalf of ADOT&PF and the USFS. WFLHD has selected Robert Peccia and Associates (RPA) to provide engineering services for the project. RPA contracted Golder Associates Inc. (Golder) to conduct the geotechnical investigation and provide initial comments on geotechnical engineering issues. The geotechnical investigation was completed by Golder in 2016, and WFL Geotechnical Report No. 15-16 (2017) was submitted by Golder to

RPA on November 13, 2017.

RPA contracted Golder to produce a Geotechnical Design Report (this document) presenting the geotechnical analysis, design, and construction recommendations as well as recommendations for the material source development plan. WFL Geotechnical Report No. 15-16 for the project should be referenced when utilizing this Geotechnical Design Report.

1.2 Scope of Work

The scope of work for this project involved producing a Geotechnical Design Report that includes:

An introduction containing project location, brief location description, scope of work, and general geology of the project area.

An exploration and testing section with a summary discussion of the field investigation and testing procedures.

A discussion section, containing in-depth discussions of individual project elements.

A constructability section, discussing specific construction concerns, including sequencing, potential problem areas and recommended solutions.

A summary of recommendations that reiterates construction recommendations and concerns expressed in the "Discussion" section. At a minimum, the recommendations shall include (as applicable):

Cut and fill slope analysis/design

Retaining wall locations/design

Bridge foundation design

Materials utilization and disposal

Construction over soft soils

January 2019 2

Embankment design

Type, location of drainage improvements

Potential Acid Rock Drainage (ARD) locations and mitigation recommendations including disposal of ARD producing materials

Suitability of excavated materials

Earthwork recommendations

Applicable figures, including vicinity map, plan maps with boring and test pit locations, cross sections, and similar information.

Appendices containing supportive information such as project photos, stability analyses, and geotechnical analysis and design calculations.

1.3 Project Alignment

Stationing (STA) in LandXML format and cross sections in PDF file format have been provided by RPA to

Golder for this project. In this report, the term proposed alignment refers the following alignment segments and cross sections:

Segment 1: STA 7+35 (begin project) to STA 221+85

Segment 2A: STA 220+50 to STA 355+00

Segment 2B: STA 355+00 to STA 433+25 (end project)

The proposed alignment LandXML files analyzed in this report include:

Segment 1 (dated 8/13/2018)

Segment 2A and Segment 2B (dated 2/13/2018)

Cross sections analyzed in this report include:

Segment 1 (dated 7/19/2018)

Segment 2A and Segment 2B (dated 2/13/2018)

Plan and profile sheets are provided in Appendix A for:

Segment 1 (dated 8/8/2018)

Segment 2A and 2B (dated 2/13/2018)

January 2019 3

2.0 PROJECT SETTING

The Neck Lake Road project is located in the northern portion of Prince of Wales Island in southeast Alaska

(Figure 1). The topography of the project area is characterized by mountainous terrain less than about

1,000 feet in elevation. The mountains are divided by valleys and lakes trending generally either north to northwest, or to the west. Neck Lake is found in the western portion of the proposed alignment. At the eastern end of Neck Lake, the existing road spans an arm of Neck Lake through the use of causeways connecting two islands. The outlet of the lake is located at the eastern end of the lake. Water from the lake outlet then flows east under the Hatchery Bridge, approximately between STA 217+50 to 218+50, and out into Whale Passage. The eastern portion of the alignment traverses around the northern extents of Whale

Passage. At the Lower 108 Bridge at approximately STA 353+00, Big Creek flows southeast down a southeast-trending valley into the tidal flats of Whale Passage and out into marine waters.

2.1 Regional Geology

The regional geology of northern Prince of Wales Island is comprised of bedrock of the Alexander Terrane, a block of bedrock units that collided through plate tectonic processes with the western coast of North

America. This collision may have occurred by the late Jurassic (Saleeby, 2000), approximately 145 to 164 million years ago (Ma)1.

The bedrock units of the Alexander Terrane in the project area consist of three regional geologic units listed in order from the beginning of project to end of project: Heceta Limestone, Bay of Pillars Formation, Descon

Formation (Brew and others, 1984). The Heceta Limestone is of Silurian age (444 to 419 Ma) and consists primarily of limestone with additional units of limestone breccia, sandstone, mudstone, and conglomerate.

The Bay of Pillars Formation is of Silurian age (444 to 419 Ma) and consists of graywacke, slate, limestone, conglomerate, and volcanic breccia. The Lower Ordovician to Lower Silurian age (485 to 433 Ma) Descon

Formation contains volcanoclastic graywacke and siliceous shale.

Several regional bedrock faults trend north northwest to north across the project area. These bedrock faults cross-cut regional geologic units, or juxtapose two different regional geologic units. Based on the regional geologic maps by Brew and others (1984) (1:250,000 scale), Gehrels and Berg (1992) (1:600,000 scale), and Golder interpretation of digital elevation data (NED, 2013), four regional bedrock faults in the project area are interpreted to cross the proposed alignment at the following station ranges:

North northwest-striking fault in the vicinity of STA 77+50 to 87+50

North-striking fault in the vicinity of STA 138+00 to 153+50

North northwest-striking fault in the vicinity of STA 215+50 to 224+00

1 Numerical geologic ages in this report from Walker and others (2012).

January 2019 4

North northwest-striking fault in the vicinity of Big Creek (approximately STA 350+50 to 375+00). Big Creek appears to follow the general trend of the fault into Whale Passage.

The station ranges where these regional bedrock faults are interpreted to cross the proposed alignment are approximate and cover several hundred feet due to applying broad scale geologic maps to the proposed alignment.

The glacial history of southeast Alaska plays an important role in the present topography and distribution of sedimentary deposits. The bedrock units in the project area have been covered by extensive glacial ice.

During the late Pleistocene (130,000 to 10,000 years ago), glacial ice reached up to approximately the

3,000 to 4,000-foot elevation level over the project area (Coulter and others, 1962). The ice flow direction was generally to the southwest or west (Carrara and others, 2003). As the glacial ice retreated, southeast

Alaska experienced glacial isostatic adjustment as the glacial ice load diminished, causing the depressed land surface to rebound.

2.2 Seismic Design Parameters

The project alignment has various depths to bedrock which will directly affect the seismic site classification.

Due to the variable nature of the depth to bedrock, Golder recommends utilizing seismic soil “Site Class D” as a conservative estimate of site response, which is defined as stiff soil. This category has an average

SPT blow count (N) between 15 and 50 blows per foot, or range of average shear wave velocities (VS-100) between 1,200 and 2,500 feet/second in the upper 100 feet of the soil/rock profile. Structure-specific seismic design parameter recommendations are provided on a structure by structure basis for bridges and specific retaining structures in later sections of this report.

Seismic properties from the USGS Design Maps, based on 2009 AASHTO standard specifications, are summarized in Table 2.1 (USGS 2018).

Table 2.1: USGS Seismic Design Parameters – Site Class D Peak Ground Acceleration (PGA) 0.105 g

Short Period Spectral Acceleration (SS) 0.23 g

One Second Period Spectral Acceleration (S1) 0.18 g

Site Amplification Coefficient (Fpga) 1.59

Site Amplification Coefficient (Fa) 1.60

Site Amplification Coefficient (Fv) 2.08

Short Period Site Factored PGA (As) 0.167 g

Design Short Period Spectral Acceleration (SDS) 0.368 g

Design One Second Period Spectral Acceleration (SD1) 0.374 g

Notes: Calculated for coordinates 56.11807°N, 133.12804°W

January 2019 5

3.0 FIELD EXPLORATION

Golder completed a geotechnical exploration along the project area between August 18, 2016 and

September 21, 2016. The geotechnical program consisted of the following:

Advancing geotechnical boreholes

Advancing geotechnical test pits

Advancing Dynamic Cone Penetration Tests (DCPT)

Advancing T-handle soil probes

Performing surficial engineering geologic mapping

Performing rock mass and discontinuity surveys

Performing a material source investigation

The following sections present a brief summary of the field exploration methods. WFL Geotechnical Report

No. 15-16 should be referenced for additional detail and subsurface logs developed during the field program.

3.1 Geotechnical Boreholes

A total of 63 boreholes were advanced along the road alignment at locations selected in coordination with

RPA and WFLHD. The primary boring method used was 4.25-inch-I.D. hollow-stem auger from a track-mounted CME 850 drill rig. Representative samples of the soils encountered in the borehole were obtained with Standard Penetration Tests (SPT) by driving a 2.0-inch O.D., 1.5-inch I.D. split-spoon sampler ahead of the auger with a 140-pound automatic hammer allowing for 30-inch free fall. When encountering bedrock or boulders, drilling operations switched to HQ triple tube (HQ3) rock coring. Rock coring was accomplished using a wireline HQ3 system. At nine borehole locations, a 12-inch diameter solid-stem auger was used to collect samples in the upper five feet of the roadway embankment.

3.2 Geotechnical Test Pits and DCPT

A total of 60 test pits were advanced along the road alignment at locations selected in coordination with

RPA and WFLHD. Test pits were excavated using a 2007 Hitachi Zx-120 excavator which had a maximum excavation depth of approximately 20 feet.

DCPT explorations were carried out at 15 locations along the project alignment by a Golder engineer.

These explorations were performed adjacent to select test pits to assist in determining the density of subsurface soil conditions. The DCPT testing was conducted using a Wildcat DCPT with a 35-pound hammer. During testing, the number of hammer blows required to advance the DCPT probe tip in increments of 4 inches was recorded.

January 2019 6

3.3 Soil Probes

T-handle soil probing was used to explore subsurface locations with organics or soft ground. The maximum length of the T-handle soil probe was 12 feet.

3.4 Surficial Engineering Geologic Mapping

Surficial geologic mapping was conducted by a two-person Golder mapping team along the project alignment, with the mapping objective to cover a region 50 feet left and right of the proposed centerline.

Mapping was conducted using a Trimble mapping-grade GEO7 GPS receiver, and QT Reader and ArcGIS

10.2 software.

3.5 Rock Mapping Sites (RMS)

Rock mass and discontinuity surveys were performed by a two-person Golder mapping team at select locations along the alignment. Discontinuity dip and dip directions were recorded using a Brunton GEO

Pocket Transit with magnetic declination set to 19° east.

3.6 Material Source Investigation

Material source investigations were conducted by a two-person Golder mapping team at four sites: STA

108+00, STA 144+50, STA 158+00, and USFS Quarry 27-1. At each site, approximately 350 pounds of rock samples were collected from rock faces and placed in canvas bags, for shipment to the WFLHD

Laboratory.

January 2019 7

4.0 LABORATORY TESTING

Soil and rock samples were collected in the field by Golder personnel and shipped to WFLHD for testing.

Most laboratory testing was arranged and completed by WFLHD, with some samples sent to additional laboratories. Results of the laboratory testing were provided to Golder, who then updated borehole and test pit logs with the data. Testing included the following:

Sieve Analysis (T 11/ T 27)

Plasticity Index (Atterberg Limits) (T 89/T 90)

Natural Moisture Content (T 265)

Particle Size Analysis to 0.02 mm (4 hr) (T 88)

Specific Gravity (T 100)

Organic Content by % Loss on Ignition (T 267)

R-Value, 300 PSI Exudation (T 190) pH Value (T 289)

Minimum Resistivity (T 288)

Durability (T 210)

Specific Gravity, Fine/Coarse (T 84/T 85)

Los Angeles Abrasion (T 96)

Soundness by Sodium Sulfate (T 104)

Accelerated Weathering (DMSO)

Immersion Compression (T 165)

Plasticity Index, Lab Manufactured (T 89/T 90)

SE, Lab Manufactured, Referee Method (T 176)

Acid base accounting and paste pH

January 2019 8

5.0 GEOTECHNICAL ENGINEERING DISCUSSIONS

5.1 Cut and Fill Slopes

Widening of the roadway corridor will require cut and fill soil slopes, and blasting of rock outcrops. The following sections provide recommendations for cuts and fills for soil slopes and rock cuts.

5.1.1 Soil Slopes

5.1.1.1 Cut Slopes

Widening of the road corridor will require cutting and filling of soil slopes. General criteria and key information is presented in Figure 2. In general, excavated slopes less than approximately 10 to 12 feet in height in natural (non-fill) granular soils should be sloped no steeper than 1V:1.5H. Slopes excavated in fine-grained or organic soils should be excavated no steeper than 1V:2H and should be evaluated on a case by case basis during construction. For tall cut slopes, slopes greater than 30 feet tall, it may be beneficial to install benches and swales to direct surface water away from the slope. In areas where groundwater seeps are observed in cut slopes, rock buttresses may be used to help reduce the potential for long-term instability. However, if the seepage is significant and the slope is not stable, other means such as dewatering trenches or horizontal drains may be required to achieve slope stability. Cut slopes should be vegetated and protected from raveling from surface water runoff and erosion. Table 5.1 provides station by station recommended slope ratios.

Table 5.1 Stationing with Soil Cut Slopes

Begin Station

End Station

Maximum Slope Height (feet)

Recommended Slope Ratio

Nearby Boreholes and Test Pits

7+35 24+50 10 ≥1V:1.5H TP16-01, -02, -03

24+50 26+25 14 ≥1V:2H TP16-04

26+25 33+26 12 ≥1V:1.5H BH16-01

33+26 34+00 28 ≥1V:2H1 N/A

34+00 66+49 11 ≥1V:1.5H BR16-01, -02; RR16-01; BH16-

02; TP16-05, -06, -07

66+49 69+50 28 ≥1V:2H1 TP16-08

69+50 75+00 12 ≥1V:1.5H TP16-09

78+00 82+50 26 ≥1V:2H1 BH16-03, -04; TP16-10

83+25 87+25 24 ≥1V:2H1 RR16-02; BH16-05

90+00 91+50 30 ≥1V:2H1 BH16-06, -07

98+50 107+50 56 ≥1V:2H1 BH16-07, -08, -09; TP16-11, -12

January 2019 9

Begin Station

End Station

Maximum Slope Height (feet)

Recommended Slope Ratio

Nearby Boreholes and Test Pits

109+00 121+50 26 ≥1V:2H BH16-10, -10A, -10B, -11, -11A, -

127+50 141+15 56 ≥1V:2H1 BH16-13, -14, -15; TP16-13, -14,

-15

146+85 157+00 55 ≥1V:2H BH16-17, -18, -19, -20, -21, -22;

TP16-16, -17, -18

158+80 159+75 40 ≥1V:2H1 BH16-21, -22

159+75 171+10 9 ≥1V:1.5H RR16-03; BH16-23, -24

171+10 174+00 34 ≥1V:2H TP16-19, -20

174+00 187+85 10 ≥1V:1.5H BH16-25, -26, -27, -28, -29, -30;

TP16-21

187+85 191+50 15 ≥1V:2H1 TP16-22

191+50 213+50 10 ≥1V:1.5H BH16-31, -32; RR16-04; TP16-

23, -24, -25, -26

214+25 360+50 12

≥1V:1.5H

BH16-33, -34, -35, -36; RR16-05,

-06, -07; BR16-03, -04, -05, -06, -

07, -08, -09, -10; TP16-27, -28, -

28A, -29, -30, -30A, -31, -32, -33, -34, -35, -36, -37, -38, -39, -40, -

41, -42, -43, -44, -45

360+50 373+00 50 ≥1V:2H TP16-46, -47, -48, -49

373+00 385+75 18 ≥1V:2H BH16-37, -38; RR16-08; TP16-

50, -51

385+75 443+25 12 ≥1V:1.5H BH16-39; RR16-09; TP16-53, -

54A, -55, -56, -57, -58

Notes:

1) Slope can be steeper up to 1V:1H if cut into rock.

2) Stationing and maximum slope height based on the project plan and profiles dated February 13 and July 19, 2018.

3) Recommendations between the gap of station are provided in rock cut sections.

4) Gap in data between STA 33+26 and 34+00; 158+00 and 159+75, subsurface condition is estimated.

5.1.1.2 Fill Slopes

Fill slopes supporting the road embankment constructed of structural fill should be constructed with slopes no steeper than 1V:1.5H. Golder recommends constructing a compacted soil key at the toe of fill slopes greater than 10 feet high. With the exception of causeway fills and rock, the soil key excavation in granular soils should be approximately 2-3 feet deep, and approximately 8 feet wide. In areas where new fill slopes

January 2019 10 will be placed adjacent to existing slopes, Golder recommends regular benching into the existing slopes at the time of fill placement. Fill slopes should be vegetated and protected from raveling from surface water runoff and erosion.

In areas where material is required to be excavated and is unsuitable for reuse as embankment fill, the material may be suitable for use as topsoil, or can be used to flatten embankment slopes from the recommended grades. Flatter embankment slopes will provide better long-term performance of the road section.

5.1.2 Rock Cuts

Golder has developed design recommendations for Rock Cut - 01 through Rock Cut -09 within Segment 1.

The rock slope recommendations consist of a minimum rock cut slope angle and required ditch widths for

80 percent and 90 percent rockfall catchment. The rock cut slope angles are summarized in Table 5.2.

Figure 3 shows a typical rock cut for a 2V:1H cut. Figure 4 shows a typical dowel installation. Recommended ditch widths and a schematic showing the ditch and slope configurations are summarized in Figure 5. Slope dip direction and maximum slope height are based off of the July 19, 2018 cross sections and August 8, 2018 plan and profile sheets provided by RPA.

The subsequent sections provide a discussion of the investigation completed for each rock cut location along Neck Lake Segment 1, including data analyzed, discontinuity characteristics, kinematic analysis, and stability assessment (if sliding potential was identified). Data analyzed consists of observations made during reconnaissance site visits and drilling work conducted in August and September of 2016, and a plan in hand meeting April 2018. These data were provided in WFL Geotechnical Report No. 15-16. Data analysis was carried out using the computer program DIPS (Rocscience, 2017a) to identify major discontinuity sets

(above the 4 percent contour), and the stability assessments were completed using Swedge (Rocscience, 2017b). Pseudo-static stability assessments applied an alpha equal to half the PGA of 0.105 g horizontally for Site Class B-Rock (USGS 2018).

The descriptions, analyses, and recommendations are based on observations and measurements of limited bedrock exposures, relative to the proposed lengths and cut heights. Actual conditions may vary as the rock cut slopes are developed and should be verified by a qualified engineer or geologist during construction.

5.1.2.1 Rock Cut - 01 STA 76+00 to 78+00

Based on the plan and profile provided, the existing slope ranged from 40 to 90 feet in height with slope inclinations of approximately 35° to 55°. The geological and geotechnical data collection consisted of window mapping of one bedrock exposure at STA 77+50 and two rock core boreholes BH16-03 (STA

77+83, 81 feet right) and BH16-04 (STA 78+05, 10 feet right). During a field visit in April of 2018, an

January 2019 11 abandoned quarry adjacent to the roadway was identified and a near vertical rockface 30 to 40 feet high was observed. Bedrock was a slightly weathered (SW), light gray, very fine grained, strong (International

Society of Rock Mechanics (ISRM R4) to very strong (ISRM R5)), limestone.

5.1.2.1.1 Discontinuity Characteristics and Kinematic Analysis Structural information collected was plotted on a stereonet and four dominant discontinuity sets were identified, bedding (B) and three joint sets (J1, J2 and J3) (Table 5.3). The joint spacing on the joint sets were all generally less than 1.5 foot and the bedding had a spacing of approximately 1.7 feet. Blocks observed were blocky and generally medium to large (0.3 ft3 to 216 ft3). From field observations, the primary failure mechanism appeared to be planar with several joints acting as back and side release surfaces. The discontinuities were dry at the time of the site mapping but showed signs of previous water flow as evidenced by iron staining on the joint surface. The rock slope at the window mapping location, approximately STA 77+50, appeared blast damaged with dilated fractures generally up to 0.1 foot wide.

Table 5.3: Rock Cut – 01 Discontinuity Sets Discontinuity Dip (degrees) Dip Direction

(azimuth in degrees) B 60 322

J1 78 071

J2 52 060

J3 42 236

The kinematic analysis shown in Appendix B indicates that the probable modes of failure along Rock Cut -

01 are wedge or planar failures. For kinematic failure modes, 8 percent of the failure planes fell within the critical area of the stereonet plots for planar and 17 percent for wedge failure. None of the failure planes fell within the critical area for toppling failure. The analysis indicates a low planar failure potential along the bedding surface with minor joint sets providing steep release surfaces, and wedge failure potential along the intersection of joint set J3 and bedding planes with minor joint sets providing release surfaces. Although these joints are expected to daylight, the persistence, trace lengths, and intact rock strength need to be considered as these factors may also influence the stability of the face. Joint set J3 has very low persistence

(<3 feet) and wedge failure is likely not a major concern since the joint lengths are relatively short compared to the height of the cuts. While both planar and wedge failure modes were observed in the field, they were limited and the existing slope conditions suggest the rock mass is capable standing near vertical.

5.1.2.1.2 Slope Stability Assessment

The shear strength of the discontinuity planes (J3 and Bedding) were modeled using the Barton-Bandis

(1990) strength criteria, based on the JRC/JCS values (JRC is the joint roughness coefficient, and JCS is the joint wall compressive strength) estimated in the field, and the normal force across the failure plane.

January 2019 12

Cohesion developed from rock bridging of intact rock between joints was not considered. The Barton-

Bandis inputs are summarized below in Table 5.4. A stability analysis was completed and revealed that for the static condition, with a 10 percent water filled fissure (with respect to the tension crack height), the minimum Factor of Safety (FS) of the slope is 1.4. The minimum FS for pseudo-static stability (PGA = 0.105

g) with a 10 percent water filled fissure is 1.2.

Table 5.4: Rock Cut – 01 Barton-Bandis Input Parameters

Discontinuity JRC JCS (psf) Phi (degrees)

J3 7 1,567,000 30

B 10 1,567,000 30 Notes: psf, pounds per square foot

The recommended maximum slope cut for Rock Cut – 01 is 2V:1H (63°) using controlled blasting to improve rock face stability and minimize long-term rockfall. There is potential for overburden to be greater than 3 feet thick above the cutslope. Refer to Figure 3 for recommended overburden slope treatments. The overburden thickness will vary and may be thicker in some areas. When accounting for this in Right-of-

Way (ROW) estimating an additional 5 to 10 feet should be added to the horizontal extent of the top of overburden slope to allow for field adjustments to be made during construction. Methods such as rock blanket stabilization could be used to steepen overburden slopes at the top of cuts and maintain ROW limits.

5.1.2.2 Rock Cut - 02 STA 82+50 to 83+25

Based on the plan and profile provided, the existing slope is roughly 30 feet in height with slope inclinations of approximately 35° to 40°. The geological and geotechnical data collection consisted of window mapping of one bedrock exposure at approximately STA 77+50 and two rock core boreholes BH16-03 (STA 77+83, 81 feet right and BH16-04 (STA 78+05, 10 feet right). Bedrock was a slightly weathered (SW), light gray, very fine grained, strong (ISRM R4) to very strong (ISRM R5), limestone. Rock Cut - 02 is assumed to be in the same structural domain as Rock Cut - 01 and the data used for Rock Cut - 02 are the same as that used for Rock Cut - 01.

5.1.2.2.1 Discontinuity Characteristics and Kinematic Analysis Structural information collected was plotted on a stereonet and four dominant discontinuity sets were identified, bedding (B) and three joint sets (J1, J2 and J3) (Table 5.5). The joint spacing on the joint sets were all generally less than 2 feet and the bedding had a spacing of approximately 1.7 feet. Blocks observed were blocky and generally medium to large (0.3 ft3 to 216 ft3). From field observations the primary failure mechanism appeared to be planar with several joints acting as back and side release surfaces.

January 2019 13

Table 5.5: Rock Cut – 02 Discontinuity Sets Discontinuity Dip (degrees) Dip Direction

(azimuth in degrees) B 60 322

J1 78 071

J2 52 060

J3 42 236

The joint spacing for discontinuity sets J1, J2, and J3 was moderate (0.8 inches to 2 feet) and bedding thickness was 1.7 foot creating “blocky” medium sized (0.3-8 ft3) blocks which is generally consistent with field observations. The discontinuities were dry at the time of the site mapping but showed signs of water flow (iron staining). The rock slope at the window mapping location, approximately STA 77+50, appeared blast damaged with dilated fractures generally up to 0.1 foot wide.

The kinematic analysis shown in Appendix B indicates that the probable modes of failure along Rock Cut -

02 are wedge or planar failures. For kinematic failure modes, 17-25 percent of the failure planes fell within the critical area of the stereonet plots for planar and 17-33 percent for wedge failure; percentage depends on slope orientation. None of the major joint sets fell within the critical area for toppling failure. Planar failure potential along the bedding surface with minor joint sets providing steep release surfaces, and wedge failure potential occurs along the intersection of J1-bedding, J2- bedding, and J3- bedding planes with minor joint sets providing release surfaces. Although these joints are expected to daylight, the persistence, trace lengths, and intact rock strength need to be considered as these factors may also influence the stability of the face. Joint sets J1, J2, and J3 have low to very low persistence (<3 feet) and wedge failure is likely not a major concern since the joint lengths are relatively short compared to the height of the cuts.

The recommended maximum slope cut for Rock Cut – 02 is 2V:1H (63°) using controlled blasting to improve rock face stability and minimize long-term rockfall. There is potential for overburden to be greater than 3 feet thick above the cutslope. Refer to Figure 3 for recommended overburden slope treatments. The overburden thickness will vary and may be thicker in some areas. When accounting for this in ROW estimating an additional 5 to 10 feet should be added to the horizontal extent of the top of overburden slope to allow for field adjustments to be made during construction. Methods such as rock blanket stabilization could be used to steepen overburden slopes at the top of cuts and maintain ROW limits.

5.1.2.3 Rock Cut - 03 STA 87+25 to 90+50

Based on the plan and profile provided, the existing slope ranged from 25 to 95 feet in height with slope inclinations of approximately 35° to 75°. The geological and geotechnical data collection consisted of window mapping of one bedrock exposure at approximately STA 88+50 and one borehole BH16-05 (STA

88+68, 8 feet left). Bedrock exposed at the window mapping location was a slightly weathered (SW), dark

January 2019 14 grayish green (fresh) to dark gray/black (weathered), fine grained, strong (ISRM R4) to very strong (ISRM

R5), graywacke. Boring BH16-05 indicates that at depth the rock consists of a slightly weathered (SW), greenish gray, fine to coarse multi-lithic clasts in a fine to medium grained matrix, strong (ISRM R4), conglomerate, with calcite infilled joints.

5.1.2.3.1 Discontinuity Characteristics and Kinematic Analysis Structural information collected was plotted on a stereonet and four dominant discontinuity sets were identified, bedding (B) and three joint sets (J1, J2 and J3) (Table 5.6). Two faults were also identified during the window survey, F1 and F2. The joint spacings were approximately 0.2 to 2.4 feet on J1, 0.05 to 0.2 feet on J2, 1.1 to 4.4 feet on J3, and the bedding had a spacing of 0.05 to 1.5 feet generally creating a blocky structure and small to medium (0.007 ft3 to 8 ft3) sized blocks. Both fault surfaces were smooth and showed slickensides. The major joint sets were generally dry at the time of the site mapping but showed evidence of water flow (iron staining). The faults were either dry or damp. During the window mapping, planar, wedge, and toppling failure modes were observed and mode varied by station.

Table 5.6: Rock Cut – 03 Discontinuity Sets Discontinuity Dip (degrees) Dip Direction

(azimuth in degrees) B 39 209

J1 57 263

J2 80 300

J3 56 055

F1 58 341

F2 60 312

The kinematic analysis shown in Appendix B indicates that the probable mode of failure along Rock Cut -

03 is wedge failure. For kinematic failure modes, 6 percent of the failure planes fell within the critical area of the stereonet plots for planar but none were major sets, and 33 percent of the intersecting planes for wedge. None of the major joint sets fell within the critical area for toppling failure. The recommended maximum slope cut is 2V:1H using controlled blasting to improve rock face stability and minimize long-term rockfall. The recommended 2V:1H cut should perform well since it is flatter than the existing cut and the persistence of discontinuities associated with the potential wedge failures are relatively short compared to the height of the cuts. There is potential for overburden to be greater than 3 feet thick above the cutslope.

Refer to Figure 3 for recommended overburden slope treatments. The overburden thickness will vary and may be thicker in some areas. When accounting for this in ROW estimating an additional 5 to 10 feet should be added to the horizontal extent of the top of overburden slope to allow for field adjustments to be

January 2019 15 made during construction. Methods such as rock blanket stabilization could be used to steepen overburden slopes at the top of cuts and maintain ROW limits.

5.1.2.4 Rock Cut - 04 STA 91+50 to 98+50

Based on the plan and profile provided, the existing slope ranged from 24 to 80 feet in height with slope inclinations of approximately 35° to 75°. The geological and geotechnical data collection consisted of window mapping at one bedrock exposure at STA 93+50 and one rock core borehole BH16-07 at STA

93+58, 30 feet left. Bedrock encountered varied by investigation location. At the window mapping location, a slightly weathered (SW), jointed, dark gray, very strong (ISRM R4), very fine to fine grained, graywacke with angular and sub rounded limestone clasts (up to 4 inches in size). Rock encountered in the boring consisted of a slightly weathered (SW), massive, jointed, medium gray, strong (ISRM R4), fine to coarse grain conglomerate with multi-lithic clasts in a fine to medium grained matrix.

5.1.2.4.1 Discontinuity Characteristics and Kinematic Analysis Structural information collected was plotted on a stereonet and four dominant discontinuity sets were identified, bedding (B) and three joint sets (J1, J2 and J3) (Table 5.7). The joint spacings were approximately 0.1 to 1.3 feet on J1, 1.3 to 3 feet on J2, 0.05 to 0.9 feet on J3, and the bedding had a spacing of 0.15 to 1 feet generally creating a blocky structure and small to medium sized blocks (0.007 ft3 to 8 ft3). The major of discontinuities were generally dry at the time of mapping but showed evidence (iron staining) of water in the past. During the window mapping, planar, wedge, and toppling failure modes were observed and mode varied by station.

Table 5.7: Rock Cut – 04 Discontinuity Sets Discontinuity Dip (degrees) Dip Direction

(azimuth in degrees) B 57 131

J1 79 111

J2 75 202

J3 57 240

The kinematic analysis shown in Appendix B indicates that there is a low probability of planar failure along

Rock Cut - 04. For kinematic failure modes, 3 percent of the intersection planes fell within the critical area of the stereonet plots for planar failure, none of which were major discontinuity sets. None of the failure planes fell within the critical area for wedge toppling failure. The recommended maximum slope cut is 2V:1H using controlled blasting to improve rock face stability and minimize long-term rockfall. Instability in the future will likely be characterized by local rockfalls of individual blocks (12 in3 to 8 ft3). There is potential for overburden to be greater than 3 feet thick above the cutslope. Refer to Figure 3 for recommended overburden slope treatments. The overburden thickness will vary and may be thicker in some areas. When

January 2019 16 accounting for this in ROW estimating an additional 5 to 10 feet should be added to the horizontal extent of the top of overburden slope to allow for field adjustments to be made during construction. Methods such as rock blanket stabilization could be used to steepen overburden slopes at the top of cuts and maintain

ROW limits.

5.1.2.5 Rock Cut - 05 STA 107+50 to 109+00

Based on the plan and profile provided, the proposed alignment passes through a previously quarried site.

The sections show the existing slopes range from 30 to 55 feet in height, and that the slope is benched.

The existing bench face inclinations were up to 80° in places. The geological and geotechnical data collection consisted of a scanline survey on the lower bench face, and one boring BH16-09 (STA 107+75, 6 feet left). Bedrock was a slightly weathered (SW), jointed, dark grayish green, very strong (ISRM R5), porphyritic basalt with calcite and hornblende phenocrysts up to one-quarter inch in size, in a fine-grained matrix, pillow structure.

5.1.2.5.1 Discontinuity Characteristics and Kinematic Analysis Structural information collected was plotted on a stereonet and two joint sets were identified, J1 and J2

(Table 5.8). Both joint sets were observed once over the length of the scanline survey and had low to medium persistence, 3 to 30 feet. Five bench-scale faults were also identified during the scanline survey, F1 through F5, and were generally infilled with silt/clay, rock breccia, and/or calcite (Table 5.8). The discontinuities were generally damp with no free water present. During the scanline survey, planar, wedge, and topple failure mechanisms were observed and varied by station. Additionally, the rock face showed evidence of blast damage with several blocks appearing “loosened” along faults and joints.

Table 5.8: Rock Cut – 05 Discontinuity Sets Discontinuity Dip (degrees) Dip Direction

(azimuth in degrees) J1 48 002

J2 70 305

F1 50 303

F2 84 028

F3 75 225

F4 73 185

F5 67 064

The kinematic analysis shown in Appendix B indicates that the probable modes of failure along Rock Cut -

05 are planar and wedge failures. For kinematic failure modes, 8 percent of the planar failure discontinuities fell within the critical area of the stereonet plots, including approximately 50 percent of the F5 discontinuity

January 2019 17 range. Roughly 5 percent of the intersecting planes fell within the critical area for wedge failure which involved F2 an F4. None of the major joint sets fell within the critical area for toppling failure. The recommended maximum slope cut is 2V:1H (63°) using controlled blasting to improve rock face stability and minimize long-term rockfall. There is potential for overburden to be greater than 3 feet thick above the cutslope. Refer to Figure 3 for recommended overburden slope treatments. The overburden thickness will vary and may be thicker in some areas. When accounting for this in ROW estimating an additional 5 to 10 feet should be added to the horizontal extent of the top of overburden slope to allow for field adjustments to be made during construction. Methods such as rock blanket stabilization could be used to steepen overburden slopes at the top of cuts and maintain ROW limits.

5.1.2.5.2 Slope Stability Assessment

For the stability assessment, the shear strength of the F5 joint set was modeled using the Barton-Bandis

(1990) strength criteria, based on the JRC/JCS values estimated in the field, and the normal force across the failure plane (Table 5.9). Because both F2 an F4 discontinuity surfaces were smooth, planar, and infilled with silt, Mohr-Coulomb strength properties were used. A lower limit friction angle of 20° was used for the silt material and no cohesion was assumed. The Barton-Bandis and Mohr-Coulomb inputs are summarized below. A stability analysis was completed using the Rocscience software Swedge 6.0. This analysis revealed that for the static condition, with a 10 percent water filled fissure (with respect to the tension crack height), the minimum FS is 1.4. The minimum FS for pseudo-static stability (PGA = 0.105 g) with a 10 percent water filled fissure is 1.3.

Table 5.9: Rock Cut – 05 Barton-Bandis and Mohr-Coulomb Input Parameters

Discontinuity JRC Barton-Bandis Mohr-Coulomb

JCS (psf) Phi(base) Phi C (psf)

F5 8 2,600,000 30 -- --

F4 -- -- -- 20 --

F2 -- -- -- 20 -- Notes: psf, pounds per square foot

5.1.2.6 Rock Cut - 06 STA 121+50 to 127+50

Based on the plan and profile provided, the existing slope ranged from 10 to 58 feet in height with slope inclinations of approximately 34° to 74°. The geological and geotechnical data collection consisted of window mapping of one bedrock exposure at STA 124+00, and boreholes BH16-13 (STA 124+57, 15 feet left) and BH16-14 (STA 124+95, 174 feet right). Bedrock was a slightly weathered (SW), bedded, jointed, dark grayish green (fresh), dark gray/black (weathered), very strong (ISRM R5), graywacke with sub-rounded multi-lithic clasts in a fine-grained matrix.

January 2019 18

5.1.2.6.1 Discontinuity Characteristics and Kinematic Analysis Structural information collected was plotted on a stereonet and five major discontinuity sets were identified, bedding (B) and four joint sets (J1, J2, J3 and J4) (Table 5.10). The joint spacings were approximately 1.2 to 2.6 feet on J1, 0.6 to 2.5 feet on J2, 0.15 to 1.3 feet on J3, 0.6 feet on J4 and the bedding had a spacing of 0.2 to 1.1 feet generally creating a blocky structure forming medium sized blocks (0.3 ft3 to 8 ft3). The major discontinuities were generally dry to damp. During the window mapping, wedge failure was the primary failure mode observed. Apparent blast damage to the rock face was also observed at the time of the window mapping.

Table 5.10: Rock Cut – 06 Discontinuity Sets Discontinuity Dip (degrees) Dip Direction

(azimuth in degrees) B 30 287

J1 67 115

J2 84 208

J3 85 245

J4 83 360

The kinematic analysis shown in Appendix B indicates that the probable mode of failure along Rock Cut -

06 is toppling failure. For kinematic failure modes, 19 percent of the failure planes fell within the critical area of the stereonet plots for toppling, 100 percent of the J2 joint set. The joint sets have low to moderate persistence (3 to 30 feet). The recommended maximum slope cut is 2V:1H using controlled blasting to improve rock face stability and minimize long-term rockfall. Although kinematically feasible, the J2 joint set is of low persistence (3 -10 feet) and the toppling failure was not a dominant failure mode observed during the site visit. There is still the potential for minor block failures. Any unstable blocks encountered during excavation may be mitigated with scaling and/or spot dowels. There is potential for overburden to be greater than 3 feet thick above the cutslope. Refer to Figure 3 for recommended overburden slope treatments. The overburden thickness will vary and may be thicker in some areas. When accounting for this in ROW estimating an additional 5 to 10 feet should be added to the horizontal extent of the top of overburden slope to allow for field adjustments to be made during construction. Methods such as rock blanket stabilization could be used to steepen overburden slopes at the top of cuts and maintain ROW limits.

5.1.2.7 Rock Cut - 07 STA 141+65 to 146+35

Based on the plan and profile provided, the existing slope ranged from 16 to 40 feet in height with slope inclinations of approximately 35° to 70°. The geological and geotechnical data collection consisted of a scanline survey at one bedrock exposure at STA 144+00 and one borehole BH16-17 at 145+28, 28 feet

January 2019 19 left. Bedrock encountered varied by investigation. At the scanline survey location, a slightly weathered

(SW), jointed, dark grayish green (fresh), dark gray/black (weathered surface), fine grained, very strong

(ISRM R5), graywacke was observed. Rock encountered in the boring consisted of a slightly weathered

(SW), massive, medium gray, fine grained, jointed, strong (IRSM R4), argillite, joints filled with calcite.

5.1.2.7.1 Discontinuity Characteristics and Kinematic Analysis The structural information collected was plotted on a stereonet and three dominant joint sets were identified

(J1, J2 and J3), and six faults (Table 5.11). The joint spacings were approximately 0.05 to 0.3 feet on J1,

0.2 to 0.8 feet on J2, and 0.1 to 1.2 feet on J3. The observed faults cut the entire existing rock face, were generally planar, and contained crushed rock. The rock mass was generally blocky with small to medium block sizes (0.007 ft3 to 8 ft3). The major discontinuities were generally dry at the time of mapping but showed evidence (iron staining) of water in the past.