Geotech Report No 11-19 Ghiglione Final Foundation Report.pdf

Ghiglione Bridge February 2020

Table of Contents 1-i

Geotechnical Report No. 11-19

Ghiglione Bridge

FINAL GEOTECHNICAL & FOUNDATION

REPORT

AK PRA DENA 10(36)

Denali Borough, Alaska February 2020

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Table of Contents i

TABLE OF CONTENTS

1 INTRODUCTION

1.1 Project Description

1.2 Purpose and Scope

2 SITE CONDITIONS

2.1 Topograhpy, Drainage, and Vegetation

2.2 Climate

2.3 Subsurface Investigation

2.4 Subsurface Conditions

2.4.1 Groundwater

2.4.2 Permafrost

2.5 Laboratory Testing

2.6 Seismic Hazard

2.6.1 AASHTO LRFD Seismic Specifications

2.6.2 Seismic Hazard Analysis

2.6.3 Liquefaction

2.7 Scour

3 BRIDGE FOUNDATIONS

3.1 Design Methodology

3.2 Group Considerations

3.3 Axial and Lateral Resistance

3.4 Service Limit State Analysis

3.5 Frost Heave

3.6 Pile Driving Considerations

3.7 Pile Plug and Pile Fill

3.8 Pile Corrosion

4 RETAINING WALLS

4.1 Abutment and Wing Wall Recommendations

5 EARTHWORK RECOMMENDATIONS

5.1 Slope Recommendations

5.1.1 Soil Cut Slopes

5.1.2 Soil Embankment Slopes

ii Table of Contents

6 CONSTRUCTION

6.1 Excavations

6.2 Cold Weather Embanking and Compaction

7 LIMITATIONS

8 REFERENCES

List of Figures iii

LIST OF FIGURES

Figure 1. Project Location Map

Figure 2. Vicinity Satellite Image

Figure 3. Ghiglione Bridge Boring Location Map

Figure 4. 5-Percent Damped Design Response Spectrum

Figure 5. Definition of Loading Direction and Spacing for Group Effects (After AASHTO, 2017)

Figure 6. Pile frost jacking isolation sleeve

LIST OF TABLES

Table 1. Period of Record Monthly Climate Summary for Denali Park Headquarters, Alaska

Table 2. Summary of Water Level Observations

Table 3. Summary of Seismic Parameters (7% PE in 75 years) - General Procedure

Table 4. Scour Summary

Table 5. Estimated Pile Tip Elevations

Table 6. Lateral Deep Foundation Soil Parameters

Table 7. AASHTO Recommended P-Multipliers for Lateral Analysis of Pile Groups

Table 8. Recommended Static Soil Parameters for Abutment and Wing Wall Design

APPENDICES

APPENDIX A

Site Photographs

APPENDIX B

Descriptive Terminology for Boring Logs Boring Logs GB16-01 – GB16-04, GB18-05 – GB18-06

APPENDIX C

Laboratory Test Reports

APPENDIX D

Axial Pile Calculations

Introduction 1

1 INTRODUCTION

Denali National Park and Preserve (Park), Alaska, is replacing the Ghiglione Bridge (Structure No. 9830-011P). This report provides the geotechnical investigation results, analysis, final foundation and geotechnical recommendations for the Replace Ghiglione Bridge Project. The project is located at approximately MP 41.9 on the Denali Park Road, Alaska. The Ghiglione Bridge is maintained by the Park. The project vicinity is shown in Figure 1. and a site aerial photo is shown in Figure 2. Western Federal Lands Highway Division (WFLHD) is advancing plans for the bridge replacement and will administer construction on the Park’s behalf.

1.1 PROJECT DESCRIPTION

As-built plans indicate the existing Ghiglione Bridge is a 3-span, steel girder structure supported on driven 10BP42 (H) piles with lengths varying from 30 to 50 feet. The existing structure was built in 1960. The existing structure is on an alignment with a curve radius of 229 feet with span lengths of approximately 45 feet (Bureau of Public Road, 1960). The proposed project involves replacing the existing bridge with a four-span, steel girder structure approximately 180 feet in length. The proposed bridge will be located north of the existing alignment, closer to the historic alignment.

1.2 PURPOSE AND SCOPE

This report describes the data gathering procedures and presents the results of the geotechnical investigation, laboratory testing, and analysis to support the final geotechnical design and construction recommendations for the Ghiglione Bridge Project. This final report supersedes the previous geotechnical reports and memos for this project. The recommendations within the report have been developed based on the 95% design package alignment and stationing.

Figure 1. Project Location Map

Figure 2. Vicinity Satellite Image

Ghiglione Bridge

N

USGS EarthExplorer

Coal Creek

Site Conditions 3

2 SITE CONDITIONS

2.1 TOPOGRAHPY, DRAINAGE, AND VEGETATION

The Denali Park Road traverses along the south slope of Sable Mountain and associated peaks, which reaches an elevation of nearly 6,000 feet, in the project vicinity. The roadway elevation is approximately 3,370 feet in the project area. The general topography is hilly, sloping to the south.

The drainage Ghiglione Bridge crosses is located approximately 30 to 40 feet below the existing road level. Below the road, the slope continues and the drainage intersects the west draining Coal Creek and eventually the braided channel of the East Fork of the Toklat River.

The mapped geology of the area indicates the mountains above are primarily comprised of sedimentary rocks of the Cantwell Formation with intrusions of volcanic rocks of the Teklanika Formation. The gentler slopes closer to the roadway are comprised of alluvial, colluvial, and glacial deposits while the drainages are alluvium. The opposite slope west of the bridge is mapped as coal bearing rocks of the Usibelli group of formations (Gilbert and Redman, 1975;

Thornberry-Ehrlich, 2010). Below the road at approximate MP 42.5 a coal mine operated from the 1920’s to as late as 1940 along Coal Creek (Capps et al., 2016).

Vegetation in the project area generally consists of shrubs and willows.

Selected site photos are presented in Appendix A.

2.2 CLIMATE

The climate of the project site is greatly influenced by Alaska Range. Locations north of the Alaska Range, such as the project site, are typical of the interior Alaska climate with warm summers and very cold winters. Table 1 summarizes average temperature ranges, precipitation, and snow depth measurements from Denali Park Headquarters, located approximately 27 miles northeast of the project site (NPS, 2019).

4 Site Conditions

Table 1. Period of Record Monthly Climate Summary for Denali Park Headquarters, Alaska.

2.3 SUBSURFACE INVESTIGATION

Four subsurface borings were completed at the site in September 2016 (GB16-01 through GB16-

04) and two additional borings were completed in August 2018 (GB18-05 and GB18-06). The borings locations are shown in Figure 3.

Figure 3. Ghiglione Bridge Boring Location Map

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual

Average Max.

Temp. (F)

11.1 17.3 25.6 39.4 54.4 65.0 66.7 60.9 50.2 31.6 16.5 14.9 37.9

Average Min.

Temp. (F)

-4.9 -2.1 1.2 16.4 31.2 40.6 44.6 40.4 30.6 14.2 1.3 -1.2 17.8

Average Total Precipitation

(in.)

0.63 0.54 0.39 0.40 0.87 2.15 3.22 2.71 1.70 0.78 0.75 0.92 15.06

Average Total Snow Fall (in.)

9.0 8.4 6.8 6.1 3.1 0.1 0 0 4.7 9.9 13.2 15.4 76.7

Average Snow Depth (in.)

20 22 23 22 10 0 0 0 4 8 13 18 n/a

Notes:

1. Period of Record: 1981 to 2010.

2. Data from https://www.nps.gov/dena/learn/nature/climate.htm, accessed November 7, 2019.

100 FEET

N https://www.nps.gov/dena/learn/nature/climate.htm

Site Conditions 5

The 2016 subsurface borings were completed on site between September 25 and September 29, 2016. The bridge alignment had not been finalized and the borings were located at potential abutment locations under consideration at the time. The borings were advanced by the Alaska Department of Transportation and Public Facilities (AKDOT&PF) with a CME 55 drill rig. Hollow-stem augers were used to advance the borings. The borings were logged in the field by AKDOT&PF personnel.

The selected alignment was finalized following the 2016 borings. The proposed alignment was located between the 2016 boring locations therefore, two additional borings were advanced. The 2018 subsurface borings were completed on site between August 28 and August 30, 2018 at the proposed abutment locations. The borings were advanced by GeoTek Alaska utilizing a Geoprobe 6620DT drill rig. The borings were logged in the field by a WFLHD engineering geologist.

Disturbed soil samples were collected at intervals ranging from 2.5 to 10 feet. The Standard Penetration Test (SPT) method was generally followed to collect soil samples. The SPT consists of using a 140-pound hammer with a 30-inch drop to drive a split-barrel sampler 18 or 24 inches below the bottom of the bore hole and recording the number of blows for each 6-inch increment of penetration. Standard SPT split barrel samplers (2-inch outside diameter) and 3.0-inch outside diameter samplers were used. The last two 6-inch penetration resistances shown in the boring logs (for 18-inch drives) or the middle two resistances (for 24-inch drives) are added together to determine the blows per foot (bpf), which is known as the Field N-value when the standard 2-inch OD sampler is used. The 2016 soil samples were obtained using a 340-pound (rather than 140-pound) hammer to drive 3-inch diameter samplers. For analysis, corrections are applied to the blow counts to correct for non-standard sampler size, hammer weight, overburden pressure, and hammer energy to calculate the (N1)60 value. Hammer efficiency of the 2016 borings was assumed to be 80%. Hammer energy of the automatic hammer on drill rigs used on 2018 borings was tested in accordance with ASTM D4633. The test reports indicate and average energy transfer of 97%.

Borings were logged in the field by an AKDOT&PF geologist (2016) and WFLHD engineering geologists (2018) in general accordance with Federal Lands Highways (FLH) Soil Description and Identification Guidelines. Samples were collected and shipped to WFLHD in Vancouver, Washington. Selected samples of soil and rock were submitted to the WFLHD Materials Laboratory for testing. Boring logs are presented in Appendix B.

2.4 SUBSURFACE CONDITIONS

Fill was encountered at the ground surface in GB16-01, GB16-02, GB18-05, and GB18-06. The fill consists of layers of silty sand with gravel, poorly graded sand with silt, silty gravel with sand, poorly graded gravel, and silt with sand. Many of the fill layers contain cobbles. The fill extends to the following approximate depths:

• 10.5 feet in GB16-01,

• 29.4 feet in GB16-02,

• 4.3 feet in GB18-05,

• 3.3 feet in GB18-06.

6 Site Conditions

Below the fill, the borings encountered layers of mostly fine-grained soil consisting of silt and lean clay with varying amounts of sand. Layers of poorly graded sand and silty sand were encountered in GB16-03, GB16-04, GB18-05, and GB18-06. Layers of peat and layers of coal were also encountered in all the borings.

Penetration resistances generally increased with depth. The penetration test is considered to encounter refusal when one of the 6-inch increments exceeds 50 blows. Refusal blow counts were encountered below the following depths in the borings:

• GB16-01 below 69 feet,

• GB16-02 below 79 feet,

• GB16-03 below 34 feet,

• GB16-04 below 49 feet,

• GB18-05 below 30 feet,

• GB18-06 below 65 feet.

2.4.1 GROUNDWATER

Groundwater observations are summarized in Table 2.

Table 2. Summary of Water Level Observations.

Boring No. Water Level Depth (feet) Time of Observation

GB16-01 62.5 At completion

GB16-02 35 After drilling

GB16-03 43 At completion

GB16-04 17.3 After drilling

GB18-05 38.5 At completion

GB18-06 48.1 At completion

The groundwater table is expected to be coincident with the flowing drainage under the bridge.

Perched water may be encountered at higher elevations in the valley walls. Groundwater levels fluctuate, and seasonal fluctuations in groundwater levels should be anticipated, especially during spring thaw and following periods of heavy precipitation.

2.4.2 PERMAFROST

Permafrost is present within the Park and has been encountered during construction of other projects. However, no surface features indicating the presence of underlying permafrost at the project site have been observed during site visits. Additionally, the subsurface explorations performed did not encounter permafrost.

Permafrost is not expected to be encountered at the project site, although deep seasonal frost (±10 feet) is expected.

Site Conditions 7

2.5 LABORATORY TESTING

Selected soil samples were submitted to the WFLHD Materials Laboratory for soil index testing.

Laboratory test reports are contained in Appendix C.

The following is a list of tests that were completed on the selected soil samples and the standards that were followed:

● Particle Size Analysis - AASHTO T 88

● Liquid Limit, Plastic Limit, and Plasticity Index – AASHTO T 89/90

● Natural Moisture – AASHTO T 265

● Resistivity – AASHTO T 288/ASTM G 57

● Organic Content – AASHTO T 267

The results of the soil index tests were used to classify the samples according to the Unified Soil Classification System (USCS). The USCS is reported on the boring logs.

2.6 SEISMIC HAZARD

Denali National Park and Preserve is within an area of active seismicity with numerous faults cable of producing earthquake activity. The Denali Fault is a major fault system which approximately 13 miles south of the project site. The results of a regional seismic hazard analysis (USGS, 2007) indicate that the ground motion hazard is dominated by the Denali Fault and shallow crust seismicity. The Alaska-Aleutian subduction zone and intraslab events contribute to the seismic hazard to a lesser extent.

2.6.1 AASHTO LRFD SEISMIC SPECIFICATIONS

AASHTO LRFD Bridge Design Specifications (8th Edition, 2017) use earthquake design ground motion with a 7 percent probability of exceedance in 75 years, approximately equivalent to a return period of 1000 years. The seismic hazard at the site and the importance of the proposed bridge dictate the level of seismic analysis that is required for the design. The seismic hazard principles within the current AASHTO Specifications are: 1) small to moderate earthquakes should be resisted without significant damage, 2) realistic seismic ground motion intensities and forces should be used in the design, and 3) exposure to shaking from large earthquakes may cause damage to the bridge, but the probability of collapse will be low and the damage will be limited to areas of the structure that are accessible for inspection and repair.

AASHTO Specifications require site specific hazard analysis if any of the following conditions exist:

• The site is located within 6 miles of an active fault,

• The site is classified as site class F,

• Long duration earthquakes are expected, or

• The importance of the bridge is such that a lower probability of exceedance should be considered.

8 Site Conditions

2.6.2 SEISMIC HAZARD ANALYSIS

The General Procedure outlined in Section 3.10 of the AASHTO LRFD Bridge Design Specifications (2017) was followed to characterize the seismic hazard. The General Procedure uses mapped gridded values of peak ground acceleration, 0.2 second spectral acceleration, and

1.0 second spectral acceleration to develop the 5-percent-damped-design response spectrum chart.

These procedures use a design earthquake with a return period of 1000 years, or a 7 percent probability of exceedance (PE) in 75 years. The USGS Seismic Design Reports Application was used to determine the peak ground acceleration and spectral accelerations (USGS 2018). Site class D was selected based on standard penetration test “N” values from the geotechnical investigation. Site factors were selected from Table 3.10.3.2-1 through 3.10.3.2-3 in AASHTO (2017) and multiplied by the mapped peak ground accelerations and spectral accelerations in order to determine the modified peak ground acceleration and spectral accelerations. The results of the hazard analysis are presented in Table 3.

Table 3. Summary of Seismic Parameters (7% PE in 75 years) - General Procedure.

Site Class (by Soil Type and Profile) D

Horizontal Peak Ground Acceleration (PGA) Latitude 63.557°, Longitude -149.754° 0.42g

Horizontal Response Spectral Acceleration at Period of 0.2 sec (Ss) 0.94g

Horizontal Response Spectral Acceleration at Period of 1.0 sec (S1) 0.38g

Site Factor for Zero-Period on Acceleration Spectrum (Fpga) 1.08

Site Factor for Short-Period Spectral Acceleration (Fa) 1.12

Site Factor for Long-Period Spectral Acceleration (Fv) 1.64

Modified Horizontal Peak Ground Acceleration (As) 0.46g

Modified Horizontal Response Spectral Acceleration at Period of 0.2 sec (SDS) 1.06g

Modified Horizontal Response Spectral Acceleration at Period of 1.0 sec (SD1) 0.62g

Seismic Zone 4

The modified peak ground acceleration and spectral acceleration values in Table 3 were used to develop the 5-percent-damped-design response spectrum shown in Figure 4.

Site Conditions 9

Figure 4. 5-Percent Damped Design Response Spectrum

2.6.3 LIQUEFACTION

Liquefaction is not anticipated to occur during a design seismic event because loose, cohesionless soils were not encountered below the water table in any of the borings at the site.

2.7 SCOUR

WFLHD Hydraulics group provided scour recommendations in the Ghiglione Bridge Hydraulic TS&L Report, dated April 5, 2019. The recommendations from the report are summarized in Table 4.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

El as tic S ei sm ic C oe ffi ci en t, C sm

Period, Tm (seconds)

5-Percent-Damped-Design Response Spectrum

10 Site Conditions

Table 4. Scour Summary

Item 100 Year

Flood 500 Year

Flood

Scour Base Elevation (ft) (Channel Thalweg) 3338.0 3338.0

Contraction Scour Depth (ft) 0 0

Stream Degradation Scour Depth (ft) 3.0 3.0

Abutment Scour Depth (ft) 0 0

Total Abutment Scour Elevation (ft) N/A N/A

Pier Scour Depth (ft) 6.7 7.2

Total Pier Scour Elevation (ft) 3328.2 3327.8

Bridge Foundations 11

3 BRIDGE FOUNDATIONS

Deep foundations are recommended at this site due to the axial and lateral bridge loads, the deep soil profile, and the potential for scour. Open-end pipe piles are the recommended foundation type. Other foundation types were not considered due to the Park’s desire for the proposed bridge to have exposed pile bents that looked similar to the timber trestle bridge that was replaced by the current bridge at the project site.

The recommended pile sizes for the new bridge are as follows:

PIER and ABUTMENT locations:

• 18-inch outside diameter (OD) pipe pile with 0.5-inch wall thickness

Foundation loads have been provided by the Central Federal Lands Structural Team in the 95% plan set. The maximum factored axial load per pile for the Strength I load case is 195 kips at Abutments 1 and 2, 235 kips at Piers 1 and 3, and 250 kips at Pier 2.

3.1 DESIGN METHODOLOGY

Pile foundations were designed in general accordance with the 8th Edition of the AASHTO LRFD Bridge Design Specifications (2017) [AASHTO]. Piles were designed using a combination of side resistance (skin friction) and tip resistance (end bearing). Pile lengths and tip elevations were initially selected to satisfy the maximum factored Strength Limit State axial loads. Then settlement for the maximum Service Limit State axial loads was calculated based on those pile lengths.

Settlement was evaluated using the equivalent footing method for the pile group.

3.2 GROUP CONSIDERATIONS

Each abutment and pier will have a group of 4 piles. The nominal bearing resistance of pile groups in cohesionless soils is equal to the sum of the resistance of all the piles in the group and the efficiency factor of the group is 1.0 for a pile center-to-center spacing of 2.0 diameters or greater (Hannigan, 2016), as planned for this project.

3.3 AXIAL AND LATERAL RESISTANCE

Axial geotechnical resistances of the piles were calculated using the program Apile v.2015.7.8 following the FHWA method (Ensoft, 2018). Geotechnical capacities of single piles are expected to exceed the structural capacity of the pile section where driven to very dense, glacially overridden material. This is expected to occur at all bent locations. The top of very dense material was estimated based on the materials encountered in the borings. Borings were not performed at the interior piers and a higher level of uncertainty exists in the elevation estimation of this material at these locations. Estimated pile tip elevations required to achieve the factored capacities presented above are listed in Table 5. Estimated axial resistance charts for single piles at the Strength Limit State are presented in Appendix D.

12 Bridge Foundations

Table 5. Estimated Pile Tip Elevations

Location Estimated Tip Elevation (ft)

Abutment 1 3,323 Pier 1 3,307 Pier 2 3,289 Pier 3 3,303

Abutment 2 3,295

Recommendations for soil parameters for lateral analysis of the piles under static and seismic conditions are provided in Table 6. The k values in Table 6 are based on the representative values for sand found in the LPile Technical Manual (Eisenhower and Wang, 2015). Table 6 presents parameters for “dense/stiff” and “loose/soft” soils. This allows the structural team to analyze and design the substructure to bracket the potential range of conditions the built bridge will experience.

A “frozen condition” p-multiplier has been provided were appropriate. The values in Table 6 do not include resistance factors. A resistance factor of 1.0 is specified in AASHTO Table 10.5.5.2.3- 1 (2017) for lateral geotechnical resistance of a single pile or pile group.

Bridge Foundations 13

Table 6. Lateral Deep Foundation Soil Parameters

Elev. (feet) or Depth (feet) at

Piers LPILE Material γ’

(pcf) φ’

(deg) Cohesion, c (psf) k

(lb/in3)

Seismic Condition P-

Multiplier

Frozen Condition

P-Multiplier

Abutment 1 – Dense/Stiff Condition (ground surface assumed = el. 3365’, bottom of pile cap = el. 3364.7’)

3365-3336 Sand (Reese) 125 38 N/A 90 1 1

<3336 Sand (Reese) 125 45 N/A 225 1 1

Abutment 1 – Loose/Soft Condition (ground surface assumed = el. 3365’, bottom of pile cap = el. 3364.7’)

3365-3319 Sand (Reese) 110 32 N/A 25 1 1

<3319 Sand (Reese) 125 45 N/A 225 1 1

Piers 1 through 3 – Dense/Stiff Condition (ground surface varies from ~el. 3339 to 3351’, no scour condition)

0-10 Sand (Reese) 125 38 N/A 90 1 1

10-20 Sand (Reese) 63 38 N/A 60 1 1

20+ Sand (Reese) 63 45 N/A 225 1 1

Piers 1 through 3 – Loose/Soft Condition (ground surface varies from ~el. 3339 to 3351’, no scour condition)

0-20 Sand (Reese) 48 32 N/A 20 1

1,000 (depth 0-10’)

20+ Sand (Reese) 63 45 N/A 225 1 1

Abutment 2 – Dense/Stiff Condition (ground surface assumed = el. 3365’, bottom of pile cap = el. 3363.8’)

3365-3340 Sand (Reese) 125 40 N/A 125 1 1

3340-3310 Sand (Reese) 63 40 N/A 90 1 1

<3310 Sand (Reese) 63 45 N/A 225 1 1

Abutment 2 – Loose/Soft Condition (ground surface assumed = el. 3365’, bottom of pile cap = el. 3363.8’)

3365-3340 Sand (Reese) 110 30 N/A 25 1 1

3340-3290 Sand (Reese) 48 30 N/A 20 1 1

<3290 Sand (Reese) 63 45 N/A 225 1 1

NOTES:

1. γ’ = effective unit weight.

2. φ’ = effective internal angle of friction.

3. k is the constant giving the variation of soil modulus with depth in the equation Es = kz, where Es = soil modulus, and z = depth below the ground surface.

14 Bridge Foundations

For pile groups, Section 10.7.2.4 of AASHTO (2017) recommends application of p-multipliers (Pm) when pile center-to-center spacing is less than 5 pile diameters (B) to account for group effects in the direction of loading. The AASHTO recommended p-multipliers are summarized in Table 7.

These multipliers apply only to Service Limit State analysis of horizontal pile foundation movement. The definition of the loading direction and spacing is illustrated in Figure 5.

Table 7. AASHTO Recommended P-Multipliers for Lateral Analysis of Pile Groups.

Pile Center-to-Center Spacing in the Direction of Loading

P-Multipliers, Pm

Row 1 Row 2 Row 3 and higher

3B 0.8 0.4 0.3

5B 1.0 0.85 0.7

Figure 5. Definition of Loading Direction and Spacing for Group Effects (After AASHTO, 2017).

3.4 SERVICE LIMIT STATE ANALYSIS

Pile settlement was checked based on the Service Limit State axial pile loads. To estimate settlement the pile group was modeled as an equivalent pier embedded at the estimated pile depth following the procedures recommended in the FHWA Driven Pile Manual (Hannigan et al, 2016). Because the piles will be primarily end bearing, settlement was estimated in soil layers below the depth of the piles using the maximum Service Limit State axial load over a trapezoidal pressure distribution sloping at 2V:1H. Elastic compression of the pile was calculated based on the distributed axial compressive load along the pile length. Total settlement of the pile measured at the bottom of the pile cap elevation was determined by adding the soil settlement to the pile elastic compression. The estimated total settlement at the top of the pile for the Service I Limit State is expected to be approximately 0.25 inches.

Bridge Foundations 15

3.5 FROST HEAVE

Frost heave and frost jacking can occur in cold regions when soil freezes. Frost heave occurs in permafrost and non-permafrost soils. Frost heave is made up of two components; the first consists of moisture migrating to the freezing front and the associated formation of ice lenses, and the second is the volumetric expansion of water as it freezes. The migration of water to the freezing front results in heaves that are much larger than the volumetric expansion due to water changing to ice (ASCE, 1996).

Three requirements must be met for frost heave to occur:

• Freezing temperatures in the soil,

• A source of water, such as the groundwater table, and

• Frost susceptible soil

These requirements are potentially present at the interior pier locations of the proposed bridge given the long cold winters in Denali, the drainage flowing below the bridge, and the silty soils present in the borings.

WFL has installed thermistors at several sites within the Park to understand the ground temperatures including at the Dog Kennels parking lot, Savage River Bridge, and Stoney Overlook. Temperature measurements over several seasons indicate an active layer of approximately 9 to 10 feet in depth.

Frost jacking of pile foundations occurs when, during the freezing season, the ground heaves and the adfreeze forces between the ground and the pile are large enough to lift the pile. When the ground thaws and settles back to its original level in the spring, the pile may not return to its original position because soil or water may have filled the void below it or there may be insufficient downward force to overcome the pile frictional resistance (ASCE, 1996).

Potential frost jacking forces were developed based on an average adfreeze adhesion force of 40 psi. Forty psi was chosen based on research conducted by the US Army Corps of Engineers (USACE, 1980). For an 18-inch diameter pile and an active frost depth of 10 feet, the frost jacking force was calculated to 273 kips. This jacking force exceeds the design dead load available to resist the jacking forces. The pile depths will be limited by encountering the glacially overconsolidated materials at the site. It is expected the piles will be able to penetrate no more than two to five feet into the glacially overconsolidated materials. While these conditions will allow for very high axial compressive resistances, they will limit the available skin friction resistance to values less than the jacking forces.

To protect the bridge from frost jacking it is recommend to isolate the piles from the jacking forces using a pile sleeve and non-frost susceptible soil. Figure 6 displays the recommended mitigation.

16 Bridge Foundations

Figure 6. Pile frost jacking isolation sleeve.

3.6 PILE DRIVING CONSIDERATIONS

The piles are expected to be tipped out in hard driving conditions; therefore, reinforced driving tips should be placed on the driven piles. It is estimated the proposed 18-inch diameter pipe piles will penetrate 2 to 5 feet into refusal material. Preboring may be required to achieve the minimum pile tip elevation provided in the plans.

Piling installed using non-impact hammers such as vibratory hammers may result in loss of axial resistance ranging from 15 to 55 percent (Doherty, 2015). Therefore, non-impact hammers are only recommended for installing piling above elevation 3,340. Impact hammers must be used to advance the piling when the tip is below this elevation.

It is recommended to perform at least one dynamic load test, in accordance with Section 551.13(a) per bent.

A resistance factor of φ = 0.65 is recommended to determine the factored capacity of the piles, assuming the dynamic load tests are performed to establish driving criteria for production piles.

3.7 PILE PLUG AND PILE FILL

It is expected a soil plug will form at some depth below the pile head. Piles will be concrete filled to depths specified on the plans. The pile will remain soil-filled below the depth of concrete. It may be necessary to drill out some of the soil in order to fill with concrete to the specified depth.

Bridge Foundations 17

Groundwater may be encountered inside the pile. Groundwater should be removed from inside the pipe or a tremie should be used to place concrete. If a plug does form and the void inside the pile is deeper than the required depth of concrete we recommend using a bentonite grout mix to fill the void up to the bottom of concrete elevation. The bentonite grout should be mixed at the following proportions:

1 bag cement (94 lbs.)

1/2 bag bentonite (25 lbs.)

30 gallons water

3.8 PILE CORROSION

The procedure recommended in AASHTO R 27 (2015), Assessment of Corrosion of Steel Piling for Non-Marine Applications, was generally followed to assess corrosion potential. Samples are first assessed based on saturated resistivity; if the saturated resistivity is greater than 2000 ohm-cm, the soil is determined to have a low possibility of uniform or macrocell corrosion according to R 27. The samples that were tested were determined to have a saturated resistivity ranging from 6200 to 8100 ohm-cm (much greater than 2000 ohm-cm) and therefore a low possibility of uniform or macrocell corrosion according to R 27.

18 Retaining Walls

4 RETAINING WALLS

4.1 ABUTMENT AND WING WALL RECOMMENDATIONS

Semi-integral abutments are proposed for Ghiglione Bridge. Bridge abutments will include wingwalls that will be approximately 6 feet in height. The wingwalls will extend approximately 8 feet back from the end wall.

Structural Backfill (FP-14 Subsection 704.04) should be used as backfill behind abutment end walls and wing walls. A drainage system should be installed behind all walls to prevent buildup of pore water pressure. The soil parameters listed in Table 8 are recommended to determine the lateral earth pressures exerted on retaining walls. The parameters listed in Table 8 assume a vertical wall with level ground at the top of the wall.

The values in Table 8 do not include factors of safety or load factors. Appropriate load factors should be used with these parameters when calculating lateral earth pressures. It is generally assumed that compacted backfill creates at-rest lateral earth pressure behind unyielding walls and that a slight movement at the top of the wall (0.002 x wall height) creates active lateral earth pressures behind walls. When passive lateral earth pressures are applicable, wall movements of

0.02 x wall height at the top of the wall are necessary to reach the earth pressures listed above.

The procedures outlined in Appendix A11 of AASHTO LRFD Bridge Design Specifications should be used to determine the seismic forces exerted on the walls.

Retaining Walls 19

Table 8. Recommended Static Soil Parameters for Abutment and Wing Wall Design

Parameter Design Value1

Backfill Moist Unit Weight 130 pcf

Backfill Angle of Internal Friction 34 degrees

Backfill Interface Friction Angle, δ 26 degrees

Active Earth Pressure Coefficient, Ka 0.28

Active Equivalent Fluid Pressure 36 psf/ft

At-Rest Earth Pressure Coefficient, K0 0.44

At-Rest Equivalent Fluid Pressure 57 psf/ft

Passive Earth Pressure Coefficient, Kp 3.54

Passive Equivalent Fluid Pressure 460 psf/ft

Base Soil Moist Unit Weight 120 pcf

Base Soil Angle of Internal Friction 34 degrees

Coefficient of Sliding Along the Base2, tan δ 0.65

Equivalent Height of Soil for Vehicle Loading of Abutment End Walls3, heq 4.0 ft

Equivalent Height of Soil for Vehicle Loading of Abutment Wing Walls and Guard Walls4, heq 2.0 ft

Notes:

1Design values based on a drained condition behind the wall.

2A resistance factor of 1.0 is recommended for sliding resistance of semigravity walls at the strength limit state (AASHTO Table 11.5.7-1) 3Interpolated from Table 3.11.6.4-1 in AASHTO.

4From Table 3.11.6.4-2 in AASHTO.

20 Earthwork Recommendations

5 EARTHWORK RECOMMENDATIONS

5.1 SLOPE RECOMMENDATIONS

5.1.1 SOIL CUT SLOPES

Slope cuts are not expected along the alignment as part of this project and should be avoided.

Once the existing bridge is removed the existing soil embankment fills will be removed and regraded to the natural ground line, to the extent possible. Final slopes should be 1V:2H or less where possible. Final slopes may be as steep as 1V:1.5H. Flatter slopes are recommended where possible because they will be less susceptible to erosion and will revegetate more readily.

It is understood that ditch construction may require short sections (50 feet or less) of cuts less than 5 feet in height. In these locations, a riprap blanket may be placed consisting of class 2 riprap at least 24-inches thick at angles up to 1V:1H.

5.1.2 SOIL EMBANKMENT SLOPES

Fill heights will be up to 25 feet (vertical). Fill slopes of compacted unclassified borrow can be constructed as steep as 1V:1.5H. It is understood that steeper slopes will reduce impacts;

however, flatter slopes should be used where possible because they are less susceptible to erosion and will revegetate more quickly.

Construction 21

6 CONSTRUCTION

6.1 EXCAVATIONS

The probability that permafrost will be encountered at the project site is interpreted to be low. If permafrost is encountered, the project Geotechnical Engineer should be contacted immediately to assess the effects, if any, it may have on the design.

Groundwater seepage should be anticipated in excavations below creek level (i.e. the drainage flowing below Ghiglione bridge. Groundwater seepage from the creek is likely to be encountered whenever the creek is flowing. Excavation slopes with groundwater seepage will not stand as steep as excavations into the same material above the water table and may require re-sloping or shoring. Bored excavations below the creek level will likely require casing to ensure sidewall stability.

Boulders are visible within the existing embankment. The contractor should anticipate encountering boulders while removing/regrading the existing embankment. The contractor should also anticipate encountering abandoned timber piles from previous structures during excavation of the existing embankment.

6.2 COLD WEATHER EMBANKING AND COMPACTION

Frozen material should not be used for constructing fill or backfill. If nighttime temperatures drop below freezing during construction, previously placed compacted fill and backfill material that freezes overnight shall be allowed to thaw before covering or shall be removed and replaced with unfrozen material.

22 Limitations

7 LIMITATIONS

This report was prepared to provide subsurface investigation results and geotechnical recommendations for the proposed Ghiglione Bridge Project. Professional judgments and recommendations are presented in this report. They are based partly on evaluation of the technical information gathered and partly on the Geotechnical Team’s general experience with subsurface conditions in the area. It should be noted the borings might not represent potentially unfavorable subsurface conditions away from the borings. The observed water levels and/or conditions indicated on the logs are as recorded at the time of the exploration. The water levels and/or conditions may vary considerably, with season/time, changes in climate, rainfall, and other factors and are otherwise dependent on the duration of, and methods used in, and interpretations made from the exploration program.

If soil conditions are encountered during construction that vary from those discussed in this report, or if design loads, project stationing, and/or configurations change, the WFLHD Geotechnical Team should be notified immediately in order to evaluate what effects, if any, the changes have on the recommendations contained in this report. The recommendations presented in this report are applicable only to this specific site. These data are not to be used for other purposes.

Questions regarding this report should be addressed to Evan Garich, WFLHD Geotechnical Engineer, at (360) 619-7824, or evan.garich@dot.gov.

mailto:evan.garich@dot.gov

Limitations 23

GEOTECHNICAL REPORT NO. 11-19

FINAL GEOTECHNICAL AND FOUNDATION REPORT

Ghiglione Bridge

AK PRA DENA 10(36)

Denali Borough, Alaska

February 2020

24 References

8 REFERENCES

American Association of State Highway and Transportation Officials (2017), AASHTO LRFD Bridge Design Specifications, 8th Edition, Washington, D.C.

American Association of State Highway and Transportation Officials (2019), Standard Practice for Assessment of Corrosion of Steel Piling for Non-Marine Applications, AASHTO Designation R 27-01

ASCE (1996), Cold Regions Utility Monograph, Third Edition, American Society of Civil Engineers

Bureau of Public Roads (1960), Ghiglione Creek as-built plans, DENA 9830-011P, Project No.

NP1-D1

Capps, D., McLane, S., and Chang, L. (2016), Denali National Park and Preserve Geology Road Guide. National Park Service, Denali National Park and Preserve, Denali Park, Alaska.

Doherty, P. (2015) Comparison of Impact Versus Vibratory Driven Piles, Deep Foundations Institute Deep Foundations Magazine, January/February, p 63-66.

Eisenhower, W.M., and Wang, S.-T. (2015) Technical Manual for LPile 2015, Ensoft, Inc.

Ensoft Inc. (2018), Apile version 2018.7.8

Gilbert, W.G. and Redman, E. (1975), Geologic Map and Structure Sections of Healy C-6 Quadrangle, Alaska, Alaska Division of Geological and Geophysical Surveys, Alaska Open File Report AOF 80.

Hannigan, P.J., Rausche, F., Likins, G.E., Robinson, B.R., and Becker, M.L. (2016a) Geotechnical Engineering Circular No. 12 – Design and Construction of Driven Pile Foundations, Volume 1 Report No. FHWA-NHI-16-009, National Highway Institute, US DOT, FHWA.

Hannigan, P.J., Rausche, F., Likins, G.E., Robinson, B.R., and Becker, M.L. (2016b) Geotechnical Engineering Circular No. 12 – Design and Construction of Driven Pile Foundations, Volume 2, FHWA-NHI-16-010, National Highway Institute, US DOT, FHWA.

National Park Service (NPS, 2019), Denali National Park and Preserve Climate Data, https://www.nps.gov/dena/learn/nature/climate.htm, (accessed 11/7/2019).

Thornberry-Ehrlich, T. (2010), Denali National Park and Preserve: geologic resources inventory report, Natural Resource Report NPS/NRPC/GRD/NRR—2010/244, National Park Service, Ft.

Collins, Colorado.

USACE (1980), Design and Construction of Foundations in Areas of Deep Seasonal Frost and Permafrost, Special Report 80-34, US Army Corps of Engineers, August 1980 https://www.nps.gov/dena/learn/nature/climate.htm

References 25

USGS (2007), Wesson, Robert L., Boyd, Oliver S., Mueller, Charles S., Bufe, Charles G., Frankel, Arthur D., Petersen, Mark D., Revision of time-Independent probabilistic seismic hazard maps for Alaska: U.S. Geological Survey Open-File Report 2007-1043.

USGS (2019), Unified Hazard Tool, Interactive Deaggregation, https://earthquake.usgs.gov/hazards/interactive/ (accessed 11/7/2019).

USGS (2018), U.S. Seismic Design Maps application, https://earthquake.usgs.gov/designmaps/us/application.php (accessed 10/29/2018).

WFLHD (2019), Neighorn, J., Ghiglione Bridge Hydraulic TS&L Report, April 5, 2019.

https://earthquake.usgs.gov/hazards/interactive/ https://earthquake.usgs.gov/designmaps/us/application.php

APPENDIX A – SITE PHOTOGRAPHS

Figure A1. Project site face west. Boring GB18-05 visible.

Figure A2. View of existing bridge and project site facing southwest.

Figure A3. South side of existing bridge/road, facing west.

Figure A4. South side of existing bridge, facing east. Note partially buried timber piles in embankment fill.

Figure A5. Facing east from north side of bridge. Note partially buried timber piles in embankment fill.

Figure A6. View facing downstream from the existing bridge.

Figure A7. View facing upstream from the existing bridge.

Figure A8. Facing north. Existing cut slope east of bridge.

APPENDIX B – BORING LOGS

10/04/2018

SOIL CLASSIFICATION CHART

Criteria for Assigning Group Symbols and Group Name Using Laboratory TestsA Group

Symbol Group NameB

COARSE-GRAINED

SOILS

More than 50% retained on No. 200 Sieve

GRAVELS

More than 50% of coarse fraction retained on No. 4 Sieve

Clean GRAVELS Less than 5% fines E

Cu ≥ 4 and 1 ≤ Cc ≤ 3C GW Well-graded GRAVEL D

Cu < 4 and/or 1 > Cc > 3 C GP Poorly-graded GRAVEL D

GRAVELS with fines More than 12% fines E

Fines classify as ML or MH GM Silty GRAVEL D,F Fines classify as CL or CH GC Clayey GRAVEL D,F

SANDS

Less than 50% retained on No. 4 Sieve

Clean SANDS Less than 5% fines I

Cu ≥ 6 and 1 ≤ Cc ≤ 3 C SW Well-graded SAND H

Cu < 6 and/or 1 > Cc > 3 C SP Poorly-graded SAND H

SANDS with fines More than 12% fines I

Fines classify as ML or MH SM Silty SAND F,H Fines classify as CL or CH SC Clayey SAND F,H

FINE-GRAINED

SOILS

50% or more passes the No. 200 Sieve

SILTS and CLAYS Liquid limit less than 50

Inorganic PI > 7 and plots on or above the “A” line J CL Lean CLAY K,L,M PI < 4 or plots below “A” line J ML SILT K,L,M

Organic Liquid limit – oven dried Liquid limit – not dried < 0.75 OL Organic CLAY K,L,M,N

Organic SILT K,L,M,O

SILTY and CLAYS Liquid limit 50 or more

Inorganic PI plots on or above “A” line CH Fat CLAY K,L,M PI plots below “A” line MH Elastic SILT K,L,M

Organic Liquid limit – oven dried Liquid limit – not dried < 0.75 OH Organic CLAY K,L,M,P

Organic SILT K,L,M,Q

HIGHLY ORGANIC

SOILS Primarily organic matter, dark in color, and organic odor PT PEAT A Based on material passing the 3-inch sieve.

B If field sample contains cobbles or boulders, add “with cobbles” or “boulders” or both, to group name.

C Cu = D60/D10 Cc = (D30)2 / (D10 x D60) D If soil contains ≥15% sand, add “with sand” to group name.

E Gravels with 5 to 12% fines require dual symbols:

GW-GM well-graded GRAVEL with silt GW-GC well-graded GRAVEL with clay GP-GM poorly-graded GRAVEL with silt GP-GC poorly-graded GRAVEL with clay

F If fines classify as CL-ML, use dual symbol GC-GM or SC-SM G If fines are organic, add “with organic fines” to group name.

H If soil contains ≥15% gravel, add “with gravel” to group name.

I Sand with 5 to 12% fines require dual symbols:

SW-SM well-graded SAND with silt SW-SC well-graded SAND with clay SP-SM poorly-graded SAND with silt SP-SC poorly-graded SAND with clay J If Atterberg limits plot in hatched area, soil is a CL-ML, silty

CLAY.

K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel”, whichever is predominant.

L If soil contains ≥ 30% plus No. 200, predominantly sand, add “sandy” to beginning of group name.

M If soil contains ≥ 30% plus No. 200, predominantly gravel, add “gravelly” to beginning of group name.

N PI ≥ 4 and plots on or above “A” line.

O PI < 4 or plots below “A” line.

P PI plots on or above “A” line.

Q PI plots below “A” line.

APPARENT DENSITY OF COARSE-

GRAINED SOIL

SPT N-value (blows per foot) Apparent Density

0 to 4 Very Loose

5 to 10 Loose

11 to 30 Medium Dense

31 to 50 Dense

> 50 Very Dense

CONSISTENCY OF

FINE-GRAINED SOIL

SPT N-value (blows per foot) Consistency

0 to 1 Very Soft

2 to 4 Soft

5 to 8 Firm

9 to 15 Stiff

16 to 30 Very Stiff

> 30 Hard

SOIL STRUCTURE TERMS

Stratified Alternating layers of varying material or color with layers > 1/4 inch (6 mm), note thickness and inclination.

Laminated(1) Alternating layers of varying material or color with layers < 1/4 inch (6 mm), note thickness and inclination.

Fissured(1) Breaks along definite planes of fracture with little resistance to fracturing.

Slickensided(1) Fracture planes appear polished or glossy, sometimes striated.

Blocky(1) Cohesive soil that can be broken down into smaller angular lumps which resists further breakdown.

Disrupted Soil structure is broken and mixed. Infers that material has moved substantially -landslide debris.

Homogeneous Same color and appearance throughout.

Lensed Inclusion of small pockets of different soil, such as small lenses of sand scattered through a mass of clay; < 1/4 inch (6 mm) note thickness.

(1) Do not use laminated, fissured, slickensided, or blocky for coarse-grained soils.

Descriptive Terminology for Boring Logs

Field descriptions of borings are based on the FLH Soil and Rock Description and Identification Guidelines that generally follow the Visual-Manual Procedure (ASTM D 2488). The soil classifications shown on the boring logs are based on laboratory tests (ASTM D 2487) when the two-letter group symbol follows the group name in parenthesis.

Standard Penetration Test (SPT): the SPT consists of driving a 2 in (50 mm) O.D. split barrel sampler a depth of 18 in (450 mm) or 24 in (600 mm) using a 140 lb (63.6 kg) hammer with a 30 in (750 mm) drop. The blow count is the number of blows recorded for each 6 inch (50 mm) increment.

The N-value is the total number of blows for the second and third increments. Note that the N-values shown on the boring logs do not include any corrections for non-standard sampler size, hammers, drill rods, etc.

ANGULARITY OF

COARSE-GRAINED SOILS

Angular

Sharp edges and relatively plane sides with unpolished surfaces

Subangular

Similar to angular description, but with rounded edges

Subrounded

Nearly plane sides, but will have well-rounded corners and edges.

Rounded

Smoothly curved sides and no edges

PARTICLE SIZE OF COARSE-GRAINED SOILS

Component Grain Size Limits

Boulders > 12” (> 300 mm)

Cobbles 3 – 12” (75 – 300 mm)

Coarse Gravel 3/4 - 3" (19 - 75 mm)

Fine Gravel #4 Sieve - 3/4" (4.75 - 19 mm)

Coarse Sand #10 - #4 Sieve (2.00 - 4.75 mm)

Medium Sand #40 - #10 Sieve (0.425 - 2.00 mm)

Fine Sand #200 - #40 Sieve (0.075 - 0.425 mm)

10/04/2018

GRAIN/CRYSTAL SIZE FOR ROCKS (MODIFIED AFTER WENTWORTH, 1972)

Grain Size Description Criteria Less than 0.003 inches (<0.075 mm)

Very fine grained Cannot be distinguished by unaided eye. Few to no mineral grains are visible with a hand lens.

0.003 to 0.02 inches (0.075 to 0.425 mm) Fine grained

Few grain/crystal boundaries are visible; grains can be distinguished with difficulty by the unaided eye but can be somewhat distinguished by hand lens.

0.02 to 0.08 inches (0.425 to 2 mm) Medium grained Most grain/crystal boundaries are visible; grains distinguishable by eye and with the aid of a hand lens.

0.08 to 0.2 inches

(2 to 4.75 mm) Coarse grained Grain/crystal boundaries are visible; grains distinguishable with the naked eye and hand lens.

Greater than 0.2 inches

(>4.75 mm)

Very coarse grained

Grain/crystal boundaries are Clearly visible; grains are distinguishable with the naked eye.

GRAIN SHAPE (FOR SEDIMENTARY ROCKS)

Description Characteristic

Angular Showing very little evidence of wear. Grain edges and corners are sharp. Secondary corners are numerous and sharp.

Subangular

Showing definite effects of wear. Grain edges and corners are slightly rounded off. Secondary corners are slightly less numerous and slightly less sharp than in angular grains.

Subrounded Showing considerable wear. Grain edges and corners are rounded to smooth curves. Secondary corners are reduced greatly in number and highly rounded.

Rounded Showing extreme wear. Grain edges and corners are smoothed off the broad curves. Secondary corner are few in number and rounded.

Well-rounded Completely worn. Grain edges or corners are not present. No secondary edges or corners are present. DEGREE OF WEATHERING

Term Description Grade

Fresh No visible sign of rock material weathering; slight discoloration on major discontinuity surface is possible. I

Slightly Weathered

Discoloration indicates weathering of rock material and discontinuity surfaces. All rock material may be discolored by weathering and the external surface may be somewhat weaker than in its fresh condition.

II

Moderately Weathered

Less than half the rock material is decomposed and/or disintegrated to a soil.

Fresh or discolored rock is present either as a discontinuous framework or as corestones. A minimum 2-inch (50 mm) diameter sample cannot be broken readily by hand across the rock fabric.

III

Highly Weathered

More than half of the rock is decomposed and/or disintegrated to soil. Fresh or discolored rock is present either as a discontinuous framework or as corestones.

A minimum 2-inch (50 mm) diameter sample can be broken readily by hand across the rock fabric.

IV

Completely Weathered

All rock material is decomposed and/or disintegrated to soil. The original mass structure is still largely intact. Material can be granulated by hand. If rock is considered to be completely weathered, use FLH Soil Description and Identification Guidelines to describe the residual soil material.

V

Residual Soil

All rock material is converted to soil. The mass structure and material fabric are destroyed but the apparent structure remains intact. There may be a large change in volume, but the soil has not been significantly transported. Material can be easily broken-down by hand. If rock is considered to be completely weathered, use FLH Soil Description and Identification Guidelines to describe the residual soil material.

VI

RELATIVE STRENGTH OF SOIL INFILLING (ISRM, 1978 & 1981)

Grade Description Field Identification Approximate

Uniaxial Compressive

Strength

S1 Very Soft Easily penetrated several inches by fist

<3.5 psi (<25 kPa)

S2 Soft Easily penetrated severl inches by thumb

3.5 - 7 psi (25 - 50 kPa)

S3 Firm

Can be penetrated several inches by thumb with moderate effort

7 - 14.5 psi (50 - 100 kPa)

S4 Stiff

Readily indented by thumb but penetrated only with great effort

14.5 - 36 psi (100 - 250 kPa)

S5 Very Stiff Readily indented by thumbnail

36 - 72.5 psi (250 - 500 kPa)

S6 Hard Indented with difficulty by thumbnail

>72 psi (>500 kPa)

RELATIVE STRENGTH OF INTACT ROCK SPECIMENS (ISRM, 1978 &1981)

Grade Description Field Indentificaiton Approximate Uniaxial Compressive Strength

R0 Extremely Weak Rock Specimen can be indented by thumbnail 35 - 150 psi

(250 - 1,000 kPa)

R1 Very Weak Rock

Specimen crumbles under sharp blow with point of geological hammer, and can be peeled with a pocket knife.

150 - 725 psi (1,000 - 5,000 kPa)

R2 Weak Rock Shallow cuts or scrapes can be made in a specimen with a pocket knife. A firm blow with a geological hammer point creates shallow indents.

7…