River Baling Geotech Report 31-1-20083-006 (Reference Material).pdf

SUBMITTED TO:

HDR, Inc.

2525 C Street, Suite 500 Anchorage, Alaska 99503

BY:

Shannon & Wilson, Inc.

2355 Hill Road Fairbanks, AK 99709

AECC125

(907) 479-0600 www.shannonwilson.com

GEOTECHNICAL ENGINEERING REPORT

Baling Improvements, Chena River Lakes Flood Control Project

NORTH POLE, ALASKA

August 2018

Shannon & Wilson No.: 31-1-20083-006

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Baling Improvements, Chena River Lakes Flood Control Project FINAL Geotechnical Engineering Report

31-1-20083-006 August 2018

PAGE INTENTIONALLY LEFT BLANK FOR DOUBLE-SIDED PRINTING

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CONTENTS

CONTENTS ........................................................................................................................................ iii

ACRONYMS ........................................................................................................................................ v

1 Introduction

1.1 Purpose and Scope

1.2 Project Understanding

2 Site Geological Setting and Seismicity

2.1 Geological Setting

2.2 Seismicity

3 Site and Subsurface Conditions

4 Earthquake Hazards Analysis

4.1 Design Earthquake Ground Motion

4.2 Liquefaction Analyses

4.3 Seismically Induced Settlement Analysis

4.4 Soil Strength Reduction during Liquefaction

4.5 Lateral Spreading

5 Cellular Sheet Pile Cofferdam

5.1 Earth and Water Pressure Loads

5.2 Global Stability

5.3 Engineering Soil Parameters

6 Construction Considerations

6.1 Sheet Pile Installation

6.2 Backfill and Compaction

6.3 Construction Erosion Control

6.4 Snow and Weather Considerations

6.5 Plans Review and Construction Observation

7 Closure

8 References

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Exhibits Exhibit 4-1: Peak Ground Accelerations (PGAs) Exhibit 4-2: Residual Internal Friction Angles for Loose to Medium Dense Alluvium Exhibit 5-1: Design Water Level Elevations Exhibit 5-2: Global Stability Cases Considered Exhibit 5-3: Global Stability Analysis Results Exhibit 5-4: Design Water Level Elevations Exhibit 6-1: Gradation Requirements for Structural Fill

Figures Figure 1: Vicinity Map Figure 2: Site and Exploration Plan Figure 3: Regional Geology Map Figure 4: Subsurface Profile A-A' Figure 5: Subsurface Profile B-B' Figure 6: Subsurface Profile C-C' Figure 7: Recommended Design Loads on Cellular Sheet Pile Cofferdam Figure 8: Profile B-B' Stability Analysis, Static Condition, Water Level El. 487.2 ft Figure 9: Profile B-B' Stability Analysis, Seismic Condition, Water Level El. 493.5 ft Figure 10: Profile B-B' Stability Analysis, Post-Seismic Condition, Water Level El. 493.5 ft Figure 11: Profile B-B' Stability Analysis, Post-Seismic Condition, Deeper, Water Level

El. 493.5 ft Figure 12: Profile B-B’ Stability Analysis, Existing Condition, Post-Seismic Safety Map

Appendices Appendix A: Engineering Analyses Important Information

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ACRONYMS

ASCE American Society of Civil Engineers bgs below ground surface DSHA Deterministic Seismic Hazard Analysis FPGA site factor FS factor of safety g gravity GDR Geotechnical Data Report IBC International Building Code MS earthquake magnitude MCE maximum credible earthquake MCEIBC IBC maximum considered earthquake MDE maximum design earthquake OBE operating basis earthquake PGA peak ground acceleration PGAM mean peak ground acceleration SPT Standard Penetration Test SSZ Salcha seismic zone USACE United States Army Corps of Engineers USGS United States Geological Survey

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1 INTRODUCTION

1.1 Purpose and Scope

This geotechnical engineering report presents the results of our geotechnical study for the new baling deck and civil site improvements at the Chena River Lakes Flood Control Project in North Pole, Alaska. Figure 1 presents a vicinity map showing the project location.

We conducted our services for the project in accordance with Geotechnical Subconsultant Agreement number 1000100026434 with HDR, dated February 2018. Our scope of services, described in Attachment D of the above-referenced Agreement, included:

Development of a Drilling Program Plan, Performing baling deck geotechnical field investigation, Performing geotechnical laboratory testing, Preparation of a Geotechnical Data Report (GDR), and

Preparation of this Geotechnical Engineering Report.

We received authorization to proceed with our scope of work from Jon Zufelt on March 1, 2018, via email.

We understand this report will be used for the development of construction drawings and specifications for the proposed improvements. This report should not be used for other purposes without Shannon & Wilson's review. The recommendations in this report supersede those provided in all previous versions of this report and those provided via email or other correspondence during the development of our report.

This report was prepared for the exclusive use of our client, HDR, Inc. and their representatives for this project.

1.2 Project Understanding

Based on our communications with the United States Army Corps of Engineers (USACE) and HDR and the project statement of work dated January 19, 2018, we understand the proposed project includes constructing a new baling deck and civil site improvements at the Chena River Lakes Flood Control Dam in North Pole, Alaska, as shown in Figure 2. The USACE currently bales debris, including spruce, birch, and willow logs with stumps, that is trapped upstream of the bays of the control structure. Baling is currently performed from the top of the Control Works deck. The deck is narrow with limited room to maneuver, and

31-1-20083-006 August 2018 the line of sight from the crane operator to the debris is limited; in some areas, the crane operator is unable to see the debris that needs to be removed. The proposed improvements will allow a crane operator to view the work area, provide maneuvering room to place debris in piles, provide room for sawyers to cut debris, and provide space for sorting and loading debris with a medium-sized excavator into 26-cubic-yard side-dump trucks, which haul the debris to a staging area.

The USACE plans to construct a cellular sheet pile retaining wall to create a baling deck on the north side of the Chena River, as shown in Figure 2. The sheet pile wall will extend about 34.5 feet above the design mudline (elevation 480 feet). The baling deck will be about 155 long and consist of three 50-foot-diameter cells with two connecting arcs between the cells.

2 SITE GEOLOGICAL SETTING AND SEISMICITY

2.1 Geological Setting

The project site is within the Tanana Lowlands physiographic province, which forms a large arcuate band of alluvial sediments between the Alaska Range and the Yukon-Tanana Uplands, as shown in Figure 3. The Lowlands consist of vegetated floodplains and low benches cut by the Tanana River and its tributaries. Soils in the Tanana Lowlands consist of interbedded alluvial sand and gravel covered by silty overbank deposits.

The thickness of alluvial sediments overlying bedrock is unknown at the project site;

however, it has been established to be as great as 600 feet below ground surface (bgs) near the control structure site. Former slough channels are commonly filled with organic silt and peat deposits. These deposits are laterally discontinuous and vary in thickness. The portion of the Tanana Lowlands in which the site is located has not been glaciated.

The project area is in a subarctic zone underlain by discontinuous permafrost. Permafrost is defined as ground that has remained at a temperature of 32 degrees Fahrenheit or less for two or more continuous years. The depth of permafrost measured in the project area is more than 200 feet. The thickness of the "active layer," the portion of the ground at or near the surface that undergoes an annual freeze-thaw cycle, is largely dependent on the type of ground cover and snow depth. Seasonal frost depths can exceed 12 feet bgs in areas kept clear of insulating snow cover, such as roads, runways, taxiways, and parking areas. In natural, undisturbed, vegetated areas with thick organic surface cover, seasonal frost depths may be less than 2 feet bgs.

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2.2 Seismicity

The project site lies between right-lateral shear systems: the Denali Fault System approximately 90 miles south of the Moose Creek Dam and the Kaltag and Tintina Fault Systems approximately 80 miles north. The shear along these systems is believed to be the result of crustal adjustments in the North American Plate due to convergence with the Pacific Plate along the Gulf of Alaska.

Seismicity in the area has historically been concentrated in clusters or bands with a northeast-southwest trend that indicates active faulting, although no faults with Holocene displacement have been recognized in the Fairbanks area (Page et al., 1991). These seismic zones include the Salcha Seismic Zone (SSZ) just south of the Moose Creek Dam and the Fairbanks Seismic Zone and Minto Flats Seismic Zone about 35 miles northwest. Page et al.

(1995) hypothesized these bands delineate the edges of blocks rotating clockwise between two right-lateral shear systems. Outside these northeast-trending linear seismic zones, recorded seismicity appears diffuse. Earthquakes in the area typically occur at depths of less than 25 miles.

Within the past century, interior Alaska has been subjected to four large earthquakes. On July 22, 1937, a magnitude (MS) 7.0 event occurred in the SSZ about 19 miles east of the project site. This event, widely felt throughout central Alaska, produced extensive ground failures in the epicentral area (Page et al., 1995). Two other earthquakes, an October 16, 1947, MS 7.2 event about 65 miles southwest of the Moose Creek Dam, and an August 27, 1904, MS 7.3 event, suggest thrust-faulting, in contrast to the strike-slip faulting suggested in the area. The epicenter of the 1904 earthquake is uncertain. The November 3, 2002, MS 7.9 event on the Denali Fault, approximately 90 miles south of the project site, was felt widely throughout central and southern Alaska and resulted in minor liquefaction in the Fairbanks area. The peak horizontal ground acceleration of this event recorded on bedrock at the University of Alaska Fairbanks campus was 0.09 g (gravity).

3 SITE AND SUBSURFACE CONDITIONS

The project site is located northeast of the Moose Creek Dam (Figure 2). The proposed baling deck will be constructed on an existing fill embankment. This embankment has an approximately 2.5 Horizontal to 1 Vertical (2.5H:1V) to 3H:1V side slope facing the Chena River channel.

The existing embankment fill slope is covered in approximately 4 to 5 feet of riprap. During our site visits, we observed rock riprap approximately 8 to 24 inches in equivalent diameter. The material was open graded and contained trace to few sand and gravel.

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We developed our interpretation of the subsurface conditions at the site based on four borings we drilled in May 2018. Logs of these borings, results of geotechnical laboratory testing of soil samples retrieved from them, and descriptions of our exploration procedures and methods are presented in our GDR (Shannon & Wilson, 2018).

Our subsurface interpretations are presented in generalized subsurface profiles A-A’ through C-C’ (Figures 4 through 6).

In general, our borings encountered a pad of medium dense to dense sand and gravel fill material underlain by a deposit of loose to medium dense sand and gravel alluvium about 30 to 60 feet deep. We encountered medium dense sand and gravel alluvium deposits at the bottoms of our borings.

4 EARTHQUAKE HAZARDS ANALYSIS

The project is in a seismic area where major earthquakes can and have occurred. In accordance with USACE manual, Earthquake Design and Evaluation for Civil Works Projects, EM 1110-2-1806 (USACE, 2016), a seismic hazard analysis should be performed to evaluate the risk associated with those hazards. Earthquake-induced geologic hazards that may affect the site include ground-surface fault rupture and liquefaction and its associated effects (e.g., loss of shear strength, bearing-capacity failures, loss of lateral support, ground oscillation, lateral spreading, and ground settlement due to soil densification).

Our analyses of earthquake ground motions and earthquake-induced geologic hazards that may affect the site are described in the following sections.

4.1 Design Earthquake Ground Motion

We developed seismic ground motions for the liquefaction analyses in general accordance with the USACE manual, Earthquake Design and Evaluation for Civil Works Projects, EM 1110-2-1806 (USACE, 2016). This document provides three design earthquakes:

Maximum Credible Earthquake (MCE), Maximum Design Earthquake (MDE), and

Operating Basis Earthquake (OBE).

USACE describes the MCE as the “largest earthquake that can reasonably be expected to be generated by a specific source on the basis of seismological and geologic evidence” (USACE, 2016). EM 1110-2-1806 recommends the MCE be determined using a site-specific Deterministic Seismic Hazard Analysis (DSHA). In lieu of a DSHA, we used the

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International Building Code (IBC) 2015 code to determine ground motions for the IBC maximum considered earthquake (MCEIBC) and assumed it to be equivalent to the MCE.

We estimated the MCEIBC using maps for bedrock ground motions published by the United States Geological Survey (USGS) for ground motions with a 2 percent chance of occurrence in 50 years (USGS, 2008; USGS, 2018a). We adjusted these values assuming Site Class D conditions at the site by applying a site factor (FPGA) of 1.11 (USGS, 2018a). We derived the mapped MCEIBC geometric mean peak ground acceleration (PGAM) using 2010 American Society of Civil Engineers (ASCE) 7 (with 2013 errata).

We used the USGS Unified Hazard Tool (USGS, 2018b) to estimate bedrock peak ground acceleration (PGA) values for the MDE and OBE earthquakes. We multiplied the same FPGA value of 1.11 used for the MCEIBC to the bedrock values from the MDE and OBE earthquake PGA values. These values are tabulated in Exhibit 4-1.

Exhibit 4-1: Peak Ground Accelerations (PGAs)

Earthquake Return Period Bedrock PGA (USGS, 2018b)

Site Modified

PGAM = FPGA×PGA

=1.11×PGA

Maximum Credible Earthquake

(MCE)

2,500 years 0.39 g 0.44 g

Maximum Design Earthquake

(MDE)

950 years 0.26 g 0.29 g

Operating Basis Earthquake

(OBE)

144 years 0.10 g 0.11 g

We used the MCE in our liquefaction, global stability, and earth pressure analyses; this is the controlling earthquake.

4.2 Liquefaction Analyses

In the borings drilled for this project, numerous samples from below the groundwater table had uncorrected penetration resistance values (blow counts) of less than 20; some had blow counts of less than 10. In our experience, soil in the Moose Creek area with blow counts as low as these are susceptible to liquefaction and dynamically induced densification if subjected to earthquake ground motions implied by the 2015 IBC.

Liquefaction of loose, saturated, cohesionless, unfrozen soil occurs when excess pore pressures are generated because of earthquake shaking. Additionally, densification of the granular soils above and below the water table could occur when subjected to earthquake shaking, resulting in differential ground settlement at the site.

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The methods to evaluate liquefaction potential are empirical and based on correlations between standard penetration test (SPT) resistance (N-value), PGA, and earthquake magnitude. We performed liquefaction analysis using four deep borings at the project site.

Based on earthquakes that have occurred within 90 miles of the site in the last 100 years, we assumed an earthquake MS of 7.3 for our analyses. We assumed the MCE PGAM of 0.44 g for our liquefaction analyses.

We used three procedures to evaluate liquefaction potential at this site:

Youd and others (2001), Cetin and others (2004), and

Boulanger, Idriss, and Izzat (2014).

In these procedures, the SPT N-value (blow count) is correlated to the liquefaction resistance of the soil (expressed as cyclic resistance ratio). The soil resistance is compared to the earthquake-induced loading (expressed as cyclic stress ratio) to calculate a corresponding factor of safety (FS) against liquefaction. The blow count data obtained during drilling was collected with a large-diameter sampler. The large sampler is frequently used in the area to obtain more representative samples and reduce the occurrence of large gravel particles interfering with the accuracy of the blow count data. N-values obtained with the large-diameter sampler were corrected to SPT N-values by multiplying the N-value by

1.3 (Daniel and others, 2003). We did not perform liquefaction analyses at depths where the samples were frozen.

We performed our liquefaction analyses using the MCE PGAM provided in Exhibit 4-1 above. Triggering of liquefaction is predicted for an FS of less than one. Our analyses, presented in Appendix A, indicate the loose to medium dense alluvial deposits would liquefy following the design earthquake ground motions. The primary effects of liquefaction at the site are settlement, reduction in soil shear strength, and a potential for lateral spreading.

4.3 Seismically Induced Settlement Analysis

An associated effect of earthquake shaking is densification (and the potential for associated settlement) of loose to medium dense, cohesionless soil that undergoes liquefaction. We used the relationships developed by Youd, Idriss, and Andrus (2001); Tokimatsu and Seed (1987); and Idriss and Boulanger (2008); relating earthquake ground motion and penetration resistance with volumetric strain, to estimate the potential for free-field ground settlement.

Using these relationships, in conjunction with the three procedures used to evaluate liquefaction potential at this site, our liquefaction analyses of in situ soil suggest 4 to

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8 inches of free-field settlement could occur at the ground surface, all of which could be differential within the new baling deck area.

4.4 Soil Strength Reduction during Liquefaction

We calculated reduction in soil shear strength during liquefaction in borings using relationships by Olson and Stark (2003), Idriss and Boulanger (2007), and Kramer (2008), correlating SPT blow counts with apparent shear strengths. Based on the calculated mean of the residual strength from the three methods, the average residual internal friction angle of soils below the water table during liquefaction could be about 8 to 12 degrees for in situ soil conditions.

Exhibit 4-2: Residual Internal Friction Angles for Loose to Medium Dense Alluvium

Elevation (feet) Residual Friction Angle

Above 460 8 degrees

Below 460 12 degrees

4.5 Lateral Spreading

Lateral spreading is a phenomenon that can occur in loose to dense, saturated, granular soils beneath even very gently sloping ground surfaces and on level ground near slopes (i.e., free faces) such as riverbanks or lakes.

We note that limited lateral spreading was observed along streams in the Tanana Valley east of Fairbanks following the 2002 Denali Fault MS 7.9 earthquake. The Northway Runway and portions of the Glenn Highway in the Mentasta area sustained considerable damage as a result of lateral spreading during the earthquake.

We do not anticipate lateral spreading will be widespread; however, localized areas of spreading may occur at the higher ground-motion levels.

5 CELLULAR SHEET PILE COFFERDAM

We understand HDR is designing the proposed baling deck structure as a cellular sheet pile cofferdam. We understand the structure will be designed in accordance with the USACE manual, Design of Sheet Pile Cellular Structures Cofferdams and Retaining Structures

(USACE, 1990).

A preliminary layout of the proposed cofferdam cells is presented in Figure 2. The cofferdam footprint is also indicated in the geologic profiles (Figures 3 through 5).

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Geotechnical design recommendations for the proposed cellular cofferdam structure are provided in the following sections.

5.1 Earth and Water Pressure Loads

We understand HDR will evaluate the loads acting on the proposed cellular cofferdam structure following the design procedures summarized by Schroeder (1990). We estimated lateral earth and water pressure design parameters for this method based on the findings from our subsurface explorations and laboratory tests. These parameters are presented in Figure 7.

We calculated lateral earth pressure coefficients using the Coulomb method with interface friction angles between the sheet piles and the adjacent soil of 14 and 17 degrees for soil above and below 460 feet elevation, respectively.

We obtained design Chena River water levels from HDR drawing S-301 and an email from Julie Anderson of USACE on April 13, 2018. Exhibit 5-1 below summarizes the design water levels we used in our geotechnical analyses.

Exhibit 5-1: Design Water Level Elevations

Case Water Level Elevation in Chena

River (feet) Water Level Elevation in Cell and

Retained Soil (feet)

Static 487.3 514 (Ground Surface)

Seismic 493.5 503.5

We understand the static water level of 487.3 feet is the lowest anticipated Chena River water level and the 493.5 feet elevation represents the minimum operational Chena River water level. We interpreted the latter elevation as most appropriate for use for seismic conditions.

In accordance with USACE recommendations, we assumed a long-term retained water level within the cells at the ground surface and a 10-foot head differential between the retained water and the Chena River channel water level for seismic conditions.

We calculated seismic lateral earth pressure coefficients using a horizontal acceleration coefficient equal to one half of the PGAM (½ × 0.44 g = 0.22 g).

Appendix A includes our earth and water pressure load calculations.

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5.2 Global Stability

We evaluated global, deep-seated stability of the proposed cofferdam structure in general accordance with the USACE manual, EM 1110-2-2503 (USACE, 1990), and the USACE Slope Stability Manual, EM 1110-2-1902 (USACE, 2003).

Methodology and Software

A global stability analysis is an evaluation of the overall stability of a structure. The result of this analysis is a FS defined as the ratio of resisting forces/moments to driving forces/moments.

We performed global slope stability analyses using the program SLOPE/W, Version 9 (Geo-Slope International, 2018). We used the Spencer method (1967), which satisfies both force and moment equilibrium, to compute FSs along possible failure surfaces. We used a two-step process to calculate critical failure surfaces for each analysis case. First, we specified circular slip surface entry and exit ranges on the ground surface behind the proposed cells and within the Chena River channel, respectively. Then we employed the SLOPE/W optimization technique, which systematically modifies the most critical circular failure surface, to find a non-circular failure surface with a lower FS.

Conditions Evaluated

We selected generalized geologic profile B-B' (Figure 5) for our global stability analysis, because it represents the location along the proposed cofferdam structure with the largest exposed wall height and is close to boring AP-3018, which encountered the deepest liquefiable soil.

We evaluated three primary loading cases for our global stability analyses. FS target and water level assumptions for these cases are summarized in Exhibit 5-2 below.

Exhibit 5-2: Global Stability Cases Considered

Case Target Factor of

Safety (FS) Water Level Elevation in

Chena River (feet) Water Level Elevation in Cell and Retained Soil (feet)

Static 1.5 487.3 514 (Ground Surface)

Seismic (Pseudostatic) 1.3 493.5 503.5

Post-Seismic (Liquefied) -- 493.5 503.5

We understand the USACE has decided not to design the proposed cellular cofferdam structure for liquefied conditions. We present these analyses for informational purposes.

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Global Stability Analyses Results and Conclusions

The results of our global stability analyses are presented as Figures 8 through 11 and tabulated below.

Exhibit 5-3: Global Stability Analysis Results

Figure Case Sheet Pile Tip

Elevation (feet) Target Factor of Safety

(FS)

FS Obtained from

Analysis

8 Static 450 1.5 2.1

9 Seismic (Pseudostatic) 450 1.3 1.3

10 Post-Seismic (Liquefied)

450 -- 0.9

11 Post-Seismic (Liquefied)

441 -- 1.4

Based on discussions with HDR, we understand the current design tip elevation for the proposed cellular cofferdam structure is 450 feet. Our stability results suggest that this tip elevation would result in adequate FS values for the seismic and static case but would result in a FS value below 1.0 for the post-seismic (liquefied) condition following the design earthquake. A FS of 0.9 suggests the proposed structure would be at risk to suffer lateral displacement and loss of functionality following the design earthquake.

We note that, although our analyses show the post-seismic FS for the proposed cellular cofferdam structure would be about 0.9, it would be an improvement over the existing conditions. Figure 12 presents the results of a post-seismic global stability analysis of the existing slope at profile B-B'. This figure presents the FS results as a safety map, with color bands representing groups of failure surfaces within a given FS range. As shown in Figure 12, our analyses suggest the FS of the existing slope would be as low as 0.3 under liquefied conditions following the design earthquake.

Appendix A includes our global stability calculations.

5.3 Engineering Soil Parameters

We understand HDR will perform all external stability analyses required by USACE EM 1110-2-2503 (USACE, 1990) except for deep-seated global stability. Recommended soil parameters for these units are provided below.

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Exhibit 5-4: Design Water Level Elevations

Soil Unit

Saturated Unit Weight

(pcf)

Cohesion (psf)

Friction Angle, φ’ (degrees)

Static and Seismic

Post-Seismic (Liquefied1)

Static and Seismic Post-Seismic (Liquefied1)

New Compacted Backfill

135 0 0 35° 35°

Existing Embankment Fill

130 0 0 36° 36°

Sand and Gravel Alluvium

125 0 0 34° 8° (above Elev. 460 ft) 12° (below Elev. 460 ft)

Notes:

1 See Section 4.4.

6 CONSTRUCTION CONSIDERATIONS

The applicability of the geotechnical design parameters we provide in the report is contingent upon good construction practice. Poor construction techniques and methods may alter conditions from those upon which our recommendations are based. The following sections discuss some construction considerations for this project.

6.1 Sheet Pile Installation

Construction of the cellular cofferdam will require installation of steel sheet piles. Sheet piles may be installed with a vibratory and/or impact hammer. Vibratory hammers may be an efficient installation method for penetration through the loose to medium dense sand and gravel. However, if pockets of cobbles are encountered, an impact hammer would likely be more efficient. The Contractor should be prepared with both types of hammers to install the sheet piles. Existing riprap should be removed prior to installation of the sheet piles.

We recommend the Contractor be prepared to encounter obstructions (e.g., boulders or logs) during sheet pile installation. In our experience, these objects are present in sand and gravel alluvial deposits in this region. We encountered wood debris in Boring AP-3015 at depths of approximately 5 and 31 feet bgs.

Care should be taken during sheet pile installation to maintain proper interlocking of the sheet piles. Because of the presence of gravel and larger-sized rocks in the subsurface soil, the sheet piles may deflect as they are driven or vibrated into the ground. The Contractor should use an iterative process to install adjacent sheet piles. For example, a series of piles can be installed to a depth of about half the required penetration. Then further penetration

31-1-20083-006 August 2018 can be achieved by driving each pile a few feet and then the adjacent piles a few feet, etc.

This iterative method would allow for better control of deflections and thereby result in greater success with maintaining the proper interlocking between the sheet piles. There is the possibility that soil setup could occur. Iterative driving should be accomplished in a timely manner.

6.2 Backfill and Compaction

Prior to backfill installation, the Contractor should remove the existing riprap and bench the original ground where fill will be placed over the area of the existing slope. The face of each bench should be no more than 2 feet in height and should be vertical or near vertical as required to remain stable during material placement and compaction. The top of the bench should slope away from the cut face to drain and shall not be inclined steeper than 0.05 foot per foot. Benches damaged during work must be reestablished. The Contractor may need to place gravel backfill, pipe/ subsurface drains, or both, to drain any seepage.

We understand that the USACE desires a 24-inch-thick layer of aggregate base course surface covering the baling deck within the proposed cellular cofferdams to distribute crane loads. Below the aggregate base course surface, we recommend backfilling with non-frost-susceptible structural fill, meeting the following gradation limits:

Exhibit 6-1: Gradation Requirements for Structural Fill

Size Percent Passing

2-inch 100

No. 4 sieve 30-60

No. 200 sieve 0-5

Soil meeting this gradation requirement is commonly available from local sources as pit-run sand and gravel.

Most of the new structural fill will be installed within the proposed cellular cofferdams to achieve the desired baling deck grade. This fill will need to be installed after the sheet piles are in place. For typical wall designs, structural backfill is required to be compacted to at least 95 percent of the modified proctor value (ASTM D1557). We anticipate achieving this level of compaction within the cells will be difficult due to access constraints and wet conditions. However, based on our analyses and the material gradation specifications shown in Exhibit 6-1, an in-place dry density of 90 percent of the modified proctor value (ASTM D1557) would be sufficient, in our opinion, except within the upper 2 feet (relative to the bottom of the aggregate base course surface layer). In the upper 2 feet of fill, we

31-1-20083-006 August 2018 recommend compacting the fill to at least 95 percent of the modified proctor value.

Regardless of location, backfill should be placed in lifts no thicker than 12 inches.

ASTM D6938 Procedure A should be used to measure in-place densities. The fill should consist of unfrozen material and be placed at above-freezing air temperatures. If previously placed fill freezes, for instance, overnight, the frozen material should be excavated and wasted or allowed to thaw and recompact prior to the placement of additional fill.

6.3 Construction Erosion Control

The Contractor should employ proper erosion control measures during construction, especially if construction takes place during wet weather or it encounters wet conditions.

Covering work areas, soil stockpiles, or slopes with plastic, sandbags, sumps, and other measures should be employed as necessary to permit proper completion of the work. Bales of straw, geotextile silt fences, and drain inlet sediment screens/collection systems should be appropriately located to control soil movement and erosion.

6.4 Snow and Weather Considerations

We recommend performing excavation operations during warmer months when it is less likely that snow will fall or be present on the ground (e.g., June to September).

6.5 Plans Review and Construction Observation

We recommend that Shannon & Wilson be retained to review those portions of the plans and specifications that pertain to the cellular cofferdam and associated earthwork to determine if they are consistent with our recommendations. We recommend that we be retained to observe the geotechnical aspects of construction to check that the work is accomplished in accordance with the plans and specifications and our recommendations.

7 CLOSURE

Our interpretations, analyses, conclusions, and recommendations are based on the following:

The limitations of our approved scope, schedule, and budget.

Our understanding of the project and information provided by the Owner and our client.

Our previous experience near the project site and on similar projects in the area.

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Explorations performed by others. We did not review samples and cannot confirm that these explorations are representative of the site conditions.

This report was prepared for the exclusive use of HDR, Inc. for specific application to the design and construction of the baling improvements at Chena River Lakes Flood Control Project. The analyses and recommendations presented in this report apply to the proposed design developed by the Design-Build team. This report is not intended to be used or relied upon for any other purpose. Shannon & Wilson has prepared a document titled, “Important Information About Your Geotechnical Report,” which is enclosed. Please read this document to learn how you can lower your risks for this Project.

8 REFERENCES

American Society of Civil Engineers (ASCE), 2013, Minimum design loads for buildings and other structures (3rd printing): Reston, Va., American Society of Civil Engineers, ASCE Standard ASCE/SEI 7-10.

Boulanger, R. W. and Idriss, Izzat M., 2014, CPT and SPT based liquefaction triggering procedures: University of California at Davis, Center for Geotechnical Modeling, report no. UCD/CGM-14/01, 134 p.

Cetin, K.O., Seed, R.B., and others, 2004, Standard penetration test-based probabilistic and deterministic assessment of seismic soil liquefaction potential: Journal of Geotechnical and Geoenvironmental Engineering, v. 130, no. 12, pp. 1314-1340.

Daniel, C.R.; Howie, J.A.; and Sy, A., 2003, A method for correlating large penetration test (LPT) to standard penetration test (SPT) blow counts; Canadian Geotechnical Journal, Vol, 40, pp. 66-77.

Geo-Slope International, 2018, SLOPE/W v 9: Calgary, Alberta, Geo-Slope International.

Idriss, I.M., and Boulanger, R.W., 2007, Residual shear strength of liquefied soils in modernization and optimization of existing dams and reservoirs, 27th Annual USSD Conference, Philadelphia, Penn., 2007, Proceedings: Denver, Colo., U.S.

Society on Dams, P. 621-634.

Idriss, I.M., and Boulanger, R.W., 2008, Soil liquefaction during earthquakes: Earthquake Engineering Research Institute (EERI), MNO-12, 226 pp.

International Code Council, Inc., 2014, International building code 2015: Country Club Hills, Ill., International Code Council, Inc., 700 p.

31-1-20083-006 August 2018

Kramer, S.L., 2008, Evaluation of liquefaction hazards in Washington State: Olympia, Wash., Washington State Department of Transportation, Report no. WA-RD 668.1, 326 p.

Olson, S.M. and Stark, T.D., 2003, Yield strength ratio and liquefaction analysis of slopes and embankments: Journal of Geotechnical and Geoenvironmental Engineering, v. 129,

no. 8, p. 727-737.

Page, R.A.; Biswas, N.N.; Lahr, J.C.; and Pulpan, H., 1991, Seismicity of continental Alaska, in Slemmons, D.B.; Engdahl, E.R.; Zoback, M.D.; and Blackwell, D.D., eds., Neotectonics of North America: Boulder, Colo., Geological Society of America, Decade of North American Geology, p. 47-68.

Page, R.A.; Plafker, George; and Pulpan, Hans, 1995, Block rotation in east-central Alaska:

A framework for evaluating earthquake potential: Geology V. 23, no. 7, p. 629-632.

Schroeder, W. L., 1990, Cellular sheetpile bulkheads, in Lambe, P. C. and Hansen, L. A., eds., Design and Performance of Earth Retaining Structures, 1990, Ithaca, N.Y., Proceedings: N.Y., American Society of Civil Engineers, p. 190-216.

Spencer, E., 1967, A method of analysis of the stability of embankments assuming parallel inter-slice forces: Geotechnique, v. 17, no. 1, p. 11-26.

Shannon & Wilson, Inc., 2018, Baling improvements, Chena River Lakes Flood Control Project, geotechnical data report, North Pole, Washington: Report prepared by Shannon & Wilson, Inc., Fairbanks, Alaska, project no. 31-1-20083-006, for HDR, Inc., Archorage, Alaska, June.

Tokimatsu, K. and Seed, H.B., 1987. Evaluation of Settlement in Sands Due to Earthquake Shaking: ASCE Journal of Geotechnical Engineering, Vol. 113, No. 8, August 1987.

U.S. Army Corps of Engineers (USACE), 1990, Engineering and design - design of sheet pile cellular structures cofferdams and retaining structures: U.S. Army Corps of Engineers Engineer Manual EM 1110-2-2503, 1 v., June 11.

U.S. Army Corps of Engineers (USACE), Engineering and Design, 2003, Slope Stability, Engineering Manual 1110-2-1902: Washington, D.C., October, available:

https://www.publications.usace.army.mil/Portals/76/Publications/EngineerManual s/EM_1110-2-1902.pdf.

U.S. Army Corps of Engineers, 2016, Engineering and design - earthquake design and evaluation for civil works projects: U.S. Army Corps of Engineers, Engineer Manual EM 1110-2-1806, 1 v, May 31, available:

https://www.publications.usace.army.mil/Portals/76/Publications/EngineerRegulat ions/ER_1110-2-1806.pdf https://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-2-1902.pdf https://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-2-1902.pdf https://www.publications.usace.army.mil/Portals/76/Publications/EngineerRegulations/ER_1110-2-1806.pdf https://www.publications.usace.army.mil/Portals/76/Publications/EngineerRegulations/ER_1110-2-1806.pdf

31-1-20083-006 August 2018

U.S. Geological Survey (USGS), 2018a, U.S. Seismic Design Maps Applications: Available:

https://earthquake.usgs.gov/designmaps/us/application.php, accessed May 2018.

U.S. Geological Survey, 2018b, Unified hazard tool: Available: https://earthquake.usgs.gov/hazards/interactive/, accessed May, 2018.

Youd, T.L.; Idriss, I.M.; Andrus, R.D.; and others, 2001, Liquefaction resistance of soils:

summary report from the 1996 NCEER and 1998 NCEER/NSF workshops on evaluation of liquefaction resistance of soils: Journal of Geotechnical and Geoenvironmental Engineering, V. 127, no. 10, p. 817-833.

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

© 2018 Microsoft Corporation © 2018 DigitalGlobe ©CNES (2018) Distribution Airbus DS

PROJECT

LOCATION

L a u r a n c e

R o a d

R i c h a r d s n

H i g h w a y

North Pole

Moose Creek

C h e n a R i v e r

M o o s e C r e e k

VICINITY MAP

Chena Baling Improvements

Chena River Lakes Flood Control Project

North Pole, Alaska

August 2018 31-1-20083-006

Fairbanks

Alaska

Map adapted from aerial imagery provided by

Google Earth Pro, reproduced by permission granted by Google Earth ™ Mapping Service.

NOTE

F i l e n a m e

J

V c i n i t y

M a p d w g

D a t e g i n a w p

5000 10000

Approximate Scale in Feet

Project

Location

MT

FIG. 1

AP-3018

AP-3016

AP-3017

AP-3015

F i l e n a m e

D

P r o j e c t s S

W

M o o s e

C r e e k

M o o s e

C r e e k

P l a n d y o u t s e p l a n t e g i n c a b r y

SITE AND EXPLORATION PLAN

Baling Improvements

Chena River Lakes Flood Control Project

North Pole, Alaska

31-1-20083-006August 2018

AP-3015

A

Boring Designation and

Approximate Location

Generalized

Subsurface Profile

LEGEND

NOTE

1. Figure adapted from client file, "CHENA EXHIBIT SK-001.dwg", received 6-6-2018.

50 100

Scale in Feet

FIG. 2

A

A'

B

B'

C

C'

Chena River

Wing Wall Footing Outline

Existing Top Wing Wall

Edge of Crane Track

PS31 Sheet Piles

155'

Moose Creek Dam

PROPOSED CELLULAR

COFFERDAM STRUCTURE

A p p r o x i m a t

E l e v a t i o n

F e t

A p p r o x i m a e v a t i o n e t

Distance in Feet

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420

Loose to Medium Dense Sand and Gravel (Alluvium)

Medium Dense to Dense Sand and Gravel (Fill)

Medium Dense to Dense Sand and Gravel (Fill)

Loose to Medium Dense Sand and Gravel (Alluvium)

Medium Dense Sand and Gravel (Alluvium)

Medium Dense Sand and Gravel (Alluvium)

05-13-18

AP-3017

05-10-18

AP-3018

6"

05-11-18

AP-3016

(Proj. 38' NE)

(Proj. 6' NE) (Proj. 5.5' SW)

West Cell Center Cell East Cell

GRAB

05-12-18

AP-3015

(Proj. 58' SW)

B C

F i l e n a m e

D

P r o j e c t s S

W

M o o s e

C r e e k

M o o s e

C r e e k

P l a n d y o u t p r o f i l t e g i n c a b r y

FIG. 4

GENERALIZED SUBSURFACE

PROFILE A-A'

30 60

Scale in Feet

1. Existing and proposed grades, proposed features, and design elevations are adapted from client file, "CHENA EXHIBIT SK-001.dwg", received 6-6-2018.

2. This subsurface profile is generalized from materials observed in soil borings. Variations may exist between profile and actual conditions.

NOTES

Northwest

A

Southeast

A'

Vertical = Horizontal

Baling Improvements

Chena River Lakes Flood Control Project

North Pole, Alaska

31-1-20083-006August 2018

Existing Ground Surface

PROPOSED

SHEET PILE

COFFERDAMS

SHEET PILE EMBEDMENT

TO BE DETERMINED

DESIGN MUDLINE

EL 480 FT

74/10"

AP-3015

05-10-18

(Proj. 50' E) Designation of Boring

Projected Distance and Direction

Sample and Penetration

Resistance in Blows/Foot or Blows per Inches Driven

USCS Symbol

Approximate Geologic Contact

Bottom of Boring

Date of Completion

LEGEND

Water Level

During Drilling

Frozen at

Time of Drilling p r o x i m a e v a t i o n e t

A p p r o x i m a e v a t i o n e t

Distance in Feet

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420

05-13-18

AP-3017

05-10-18

AP-3018

GRAB

05-12-18

AP-3015

Loose to Medium Dense Sand and Gravel (Alluvium)

Medium Dense to Dense Sand and Gravel (Fill)

Medium Dense Sand and Gravel (Alluvium)

(Proj. 16' NW)

(Proj. 73' SE)

(Proj. 4' NW)

A

DESIGN MUDLINE EL 480 FT

F i l e n a m e

D

P r o j e c t s S

W

M o o s e

C r e e k

M o o s e

C r e e k

P l a n d y o u t p r o f i l b t e g i n c a b r y

FIG. 5

GENERALIZED SUBSURFACE

PROFILE B-B'

30 60

Scale in Feet

1. Existing and proposed grades, proposed features, and design elevations are adapted from client file, "CHENA EXHIBIT

SK-001.dwg", received 6-6-2018.

2. This subsurface profile is generalized from materials observed in soil borings. Variations may exist between profile and actual conditions.

3. Bathymetric data is unavailable. Dashed line shown in this figure was developed by extrapolating the ground surface slope at the existing shorelines down to the proposed mudline elevation.

NOTES

Southwest

B

Northeast

B'

Vertical = Horizontal

Baling Improvements

Chena River Lakes Flood Control Project

North Pole, Alaska

31-1-20083-006August 2018

Existing Ground Surface

PROPOSED

SHEET PILE

COFFERDAMS

SHEET PILE EMBEDMENT

TO BE DETERMINED

74/10"

AP-3015

05-10-18

(Proj. 50' E) Designation of Boring

Projected Distance and Direction

Sample and Penetration

Resistance in Blows/Foot or Blows per Inches Driven

USCS Symbol

Approximate Geologic Contact

Bottom of Boring

Date of Completion

LEGEND

Water Level

During Drilling

Frozen at

Time of Drilling

Minimum Operational (Bailing)

Water El. 493.5 Ft

Lowest Water El. 487.2 Ft

See Note 3 p r o x i m a e v a t i o n e t

A p p r o x i m a e v a t i o n e t

Distance in Feet

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420

GRAB

05-12-18

AP-3015

6"

05-11-18

AP-3016

Loose to Medium Dense Sand and Gravel (Alluvium)

Medium Dense to Dense Sand and Gravel (Fill)

Medium Dense Sand and Gravel (Alluvium)

(Proj. 104' SE)(Proj. 19' NW)

A

F i l e n a m e

D

P r o j e c t s S

W

M o o s e

C r e e k

M o o s e

C r e e k

P l a n d y o u t p r o f i l

C t e g i n c a b r y

FIG. 6

GENERALIZED SUBSURFACE

PROFILE C-C'

30 60

Scale in Feet

Southwest

C

Northeast

C'

Vertical = Horizontal

Baling Improvements

Chena River Lakes Flood Control Project

North Pole, Alaska

31-1-20083-006August 2018

Existing Ground Surface

PROPOSED

SHEET PILE

COFFERDAMS

SHEET PILE EMBEDMENT

TO BE DETERMINED

74/10"

AP-3015

05-10-18

(Proj. 50' E) Designation of Boring

Projected Distance and Direction

Sample and Penetration

Resistance in Blows/Foot or Blows per Inches Driven

USCS Symbol

Approximate Geologic Contact

Bottom of Boring

Date of Completion

LEGEND

Water Level

During Drilling

Frozen at

Time of Drilling

DESIGN MUDLINE EL 480 FT

Minimum Operational (Bailing)

Water El. 493.5 Ft

Lowest Water El. 487.2 Ft

1. Existing and proposed grades, proposed features, and design elevations are adapted from client file, "CHENA EXHIBIT

SK-001.dwg", received 6-6-2018.

2. This subsurface profile is generalized from materials observed in soil borings. Variations may exist between profile and actual conditions.

3. Bathymetric data is unavailable. Dashed line shown in this figure was developed by extrapolating the ground surface slope at the existing shorelines down to the proposed mudline elevation.

NOTES

See Note 3

PARKS HIGHWAY

ST

EE

SE

EX

PR

ES

SW

AY

/H

IG

HW

AY

RICHARDSON HIGHWAY

EL

LIO

TT

HI

GH

WA

Y

|<yqm

|kp

|kp

|<yqs

|<yqsTKg

TKg

|kp |kp

|<yqs

|kp

|kp

Dmi

|kp

|kp

|<yqs

|<yqs

|kp

|<yqs

MDts

|<yqs

|kp |kp

|<yqs

|kp

|<yqm

Kmgr|<yqs|<yqs

TKg

|<yqs |<yqs

Kmgr |<yqs

|kp

|<yqs

|kp

|kp

|<yqs

|<yqm

|<yqm

|kp |kp

|<yqs

|<yqs

|<yqs |<yqs|<yqs TKg|<yqm

|<yqs

Moose Creek Dam Control Structure

0 1 2 3 4 5 6 7 80.5

Miles Bailing Improvements

Chena River Lakes Flood Control Project North Pole, Alaska

August 2018

REGIONAL GEOLOGY MAP

FIG. 3

31-1-20083-006p

LEGEND

Project_location

Qs Unconsolidated surficial deposits, undivided

Water

QTs Poorly consolidated surficial deposits

Tvu Volcanic rocks of southern Alaska

TKg Felsic granitic rocks

Kmgr Granitic rocks of central and southeast Alaska

Kmqm Quartz monzonite, monzonite, and syenite

Pze Eclogite and associated rocks

MDts Totatlanika Schist

Dmi Metamorphosed mafic igneous rocks

Pzkp Keevy Peak Formation and similar rocks

PzPxygs Gneiss, schist, and quartzite

MzPzyo Peridotite of dismembered ophiolite of the Yukon-Tanana region

MDag Augen gneiss and orthogneiss

CPxwn Wickersham and Neruokpuk units

PzPxyqs Quartzite and pelitic schist

PzPxyqm Pelitic schist, including Chena River sequence

Pzyms Mafic schist and amphibolite

Map source: Wilson and others, 2015, USGS

LEP Figure.xlsx-6/13/2018 pp1 = Kp1'd1 pp2 = Kp2'd1 pp3 = Kp2'd2

Source:

Notes:

1. Loads shown in this figure are nominal (unfactored).

2. pcf = pounds per cubic foot

KA = Static Active Pressure Coefficient for Retained Soil =

KP = Static Passive Pressure for Soil above Elevation 460 ft = 5.84 7.30

Ks AE = Dynamic Active Pressure Coefficient for Submerged Soil =

Ks PE = Dynamic Passive Pressure Coefficient for Submerged Soil = 4.97 6.35 kh = Horizontal Seismic Coefficient =

= Total Unit Weight of Soil (pcf) = 125 130

' = Submerged Unit Weight of Soil (pcf) = 62.6 67.6 w = Unit Weight of Water (pcf)=

Load Calculations:

Schroeder, W. L., 1990, Cellular sheetpile bulkheads, in Lambe, P. C. and Hansen, L. A., eds., Design and Performance of Earth Retaining Structures, 1990, Ithaca, N.Y., Proceedings: N.Y., American Society of Civil Engineers,

p. 190-216.

Above Elev. 460 ft

Below Elev. 460 ft

62.4

0.22

0.38

0.26

Recommended Input Parameters

August 2018

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants

31-1-20083-006

FIG. 7

Baling Improvements Chena River Lakes Flood Control Project

North Pole, Alaska

RECOMMENDED DESIGN

LOADS ON CELLULAR

SHEETPILE COFFERDAM

pp1 pp2 pp3 d1 d2

Elev.

460 ft

FS = 2.1

Distance (feet) 50 100 150 200 250 300 350 400

E le va tio n (fe et

E le va tio n (fe et

Lowest Water EL. 487.2 FT

10.5-Ft

Surcharge: 570 psf

PROPOSED

SHEET PILE

COFFERDAM

Elev. 450 ft

Elev. 514 ft

North Pole, Alaska

Bailing Improvements

August 2018 31-1-20083-006

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants

Color Name Model Unit Weight (pcf)

Cohesion' (psf)

Phi'

Piezometric Line

Loose Sand & Gravel Mohr-Coulomb 125 0 34 1

Loose Sand & Gravel [Confined in Cell]

High Strength 125 1

MD Sand & Gravel Mohr-Coulomb 130 0 36 1

MD Sand & Gravel [Confined in Cell]

High Strength 130 1

New Gravel Backfill High Strength 135 1

PROFILE B-B' STABILITY ANALYSIS

Notes:

1. SLOPE/W Analysis Name:

2 Lowest Water EL. 487.2 ft_Static (Tip Elev. 450 ft)

2. Factor of Safety Calculation Method:

Spencer

3. Analysis includes a horizontal acceleration coefficient of 0 g.

D ire ct or y:

SE

A

-F S1

\V ol

1\

EF

\O th er O ffi ce s\

-1 F

B X\

M oo se

C re ek D am \A na ly si s\

G lo ba l S ta bi lit y\

STATIC CONDITION

WATER LEVEL EL. 487.2 FT

Chena River Lakes Flood Control Project

FIG. 8

B B' Southwest Northeast

FS = 1.3

50 100 150 200 250 300 350 400

E le va tio n (fe et

E le va tio n (fe et

Minimum Operational (Bailing) Water EL. 493.5 FT

10.5-Ft

Surcharge: 570 psf

PROPOSED

SHEET PILE

COFFERDAM

Elev. 450 ft

Elev. 514 ft

North Pole, Alaska

Bailing Improvements

August 2018 31-1-20083-006

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants

Color Name Model Unit Weight (pcf)

Cohesion' (psf)

Phi'

Piezometric Line

Loose Sand & Gravel Mohr-Coulomb 125 0 34 1

Loose Sand & Gravel [Confined in Cell]

High Strength 125 1

MD Sand & Gravel Mohr-Coulomb 130 0 36 1

MD Sand & Gravel [Confined in Cell]

High Strength 130 1

New Gravel Backfill High Strength 135 1

PROFILE B-B' STABILITY ANALYSIS

Notes:

1. SLOPE/W Analysis Name:

3 Min. Operational (Bailing) Water EL. 493.5 ft_Seismic (Tip Elev. 450 ft)

2. Factor of Safety Calculation Method:

Spencer

3. Analysis includes a horizontal acceleration coefficient of 0.22 g.

D ire ct or y:

SE

A

-F S1

\V ol

1\

EF

\O th er O ffi ce s\

-1 F

B X\

M oo se

C re ek D am \A na ly si s\

G lo ba l S ta bi lit y\

Chena River Lakes Flood Control Project

SEISMIC CONDITION

WATER LEVEL EL. 493.5 FT

FIG. 9

FS = 0.9

50 100 150 200 250 300 350 400

E le va tio n (fe et

E le va tio n (fe et

Minimum Operational (Bailing) Water EL. 493.5 FT

10.5-Ft

Surcharge: 570 psf

PROPOSED

SHEET PILE

COFFERDAM

Elev. 450 ft

Elev. 514 ft

North Pole, Alaska

Bailing Improvements

August 2018 31-1-20083-006

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants

Color Name Model Unit Weight (pcf)

Cohesion' (psf)

Phi'

Piezometric Line

Loose Sand & Gravel (Liquefied - Above Elev. 460')

Mohr-Coulomb 125 0 8 1

Loose Sand & Gravel (Liquefied - Below Elev. 460')

Mohr-Coulomb 125 0 12 1

Loose Sand & Gravel [Confined in Cell and Liquefied]

High Strength 125 1

MD Sand & Gravel Mohr-Coulomb 130 0 36 1

MD Sand & Gravel [Confined in Cell]

High Strength 130 1

New Gravel Backfill High Strength 135 1

PROFILE B-B' STABILITY ANALYSIS

Notes:

1. SLOPE/W Analysis Name:

4 Min. Operational (Bailing) Water EL. 493.5 ft_Post-Static (Tip Elev. 450 ft)

2. Factor of Safety Calculation Method:

Spencer

3. Analysis includes a horizontal acceleration coefficient of 0 g.

D ire ct or y:

SE

A

-F S1

\V ol

1\

EF

\O th er O ffi ce s\

-1 F

B X\

M oo se

C re ek D am \A na ly si s\

G lo ba l S ta bi lit y\

Chena River Lakes Flood Control Project

POST-SEISMIC CONDITION

WATER LEVEL EL.