GM05-14_Dene_Tene_Path-Eska_Creek_Bridge_Preliminary_Foundation_Recommendations_05Feb2014.pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

Date: February 5, 2014 In Reply Refer To: HFL-17

From: Diann Morehouse, Geotechnical Engineer

To: Neal Christensen, Project Manager

Subject: GEOTECHNIAL MEMORANDUM GM05-14 Preliminary Foundation Recommendations Dene Tene Path, Eska Creek Bridge

AK TTP CHIC 2013(1)

INTRODUCTION

This memorandum provides general geologic site conditions, analysis, and preliminary foundation recommendations for the proposed Dene Tene Pedestrian Path Bridge across Eska Creek. This bridge will connect a one-mile pedestrian path from the Chickaloon Village Traditional Building in Sutton to an existing trail system located on the opposite side of Eska Creek. This is a new pedestrian bridge which will lie about 25 feet north of the Glenn Highway, Eska Bridge over Eska Creek. The proposed Eska Creek Pedestrian Bridge has a total length of 160 feet and a width of 16 feet.

The proposed use of this bridge includes pedestrian, bicyclists, ATVs and snowmobiles.

This memorandum provides investigation results, analyses, and recommendations only for the Eska Creek Pedestrian Bridge abutment foundations and approach embankments.

Project Location The proposed pedestrian bridge will be located 25 feet north of the existing Glenn Highway Bridge across Eska Creek. The project location is shown in Figures 1 and 2, attached at the end of this memorandum. The location of the proposed pedestrian bridge is shown in Figure 3.

Previous Geotechnical Reports A previous geotechnical investigation was completed at this site by the Alaska Department of Transportation and Public Facilities for the replacement of the Glenn Highway Bridge over Eska Creek. The results of that investigation and recommendations for bridge foundations are

Dene Tene Pedestrian Path – Eska Creek Bridge Preliminary Bridge Foundation Memorandum

Geotechnical Memorandum No. GM05-14

AK TTP CHIC 2013(1)

provided in the report by the Engineering and Operations Headquarters Material Section, titled, Foundation Report Glenn Highway: MP 55-61 Moose Creek to Sutton, Eska Creek Bridge No.

542, September 1997.

SITE CONDITIONS

Surface Conditions Eska Creek is a tributary to the Matanuska River whose confluence is approximately three-fourth of a mile southwesterly from the project site.

The terrain at the proposed bridge location is generally level. The creek banks are vegetated with willows and deciduous trees. The material in the creek bed consisted of sand to boulder sized material. In September of 2013 during a site visit the maximum depth of water at the proposed pedestrian bridge location was estimated to be about 3 feet.

The 1997 Foundation Report stated that the previous bridge across Eska Creek “ices” or “glaciates” each winter resulting in ice building and aggrading up to the steel bridge girders.

Annual scheduled deicing or steam thawing for drainage was required at the bridge prior to replacement in 1998.

Geology The project lies within the Matanuska River Valley. The Quaternary-aged Castle Mountain Fault is within 10 miles north of Sutton. This fault parallels the Denali Fault and major earthquakes have occurred on this fault about every 700 years in the last 2,700 years. The last significant earthquake along this fault occurred about 650 years ago (Haeussler, 2002).

Within the surrounding area of Sutton, the surficial geology includes Holocene-aged unconsolidated deposits of stratified glaciofluvial sand and gravel.

Sutton is built on a gravel alluvial fan protruding into the river valley. Eska Creek consists of reworked glaciofluvial gravel and sand. Eska Creek floods periodically (Péwé, Reger, 1983).

Subsurface Conditions The Alaska DOT drilled two borings and conducted two penetrometer test soundings for the construction of a new bridge (AKDOT Bridge No. 542) across Eska Creek site in July-August 1996. See Figures 4, 5, and 6 attached at the end of this Memorandum. The borings were performed with NW (3.5-inch O.D) casing and BW (2.1-inch) rotary drilling tools. In situ tests included standard penetration tests (SPT) and friction penetrometer tests that consisted of driving a 2.5-inch diameter flush coupled blunt-tipped steel rod with a 342-pound automatic hammer.

The general subsurface profile consists of alternating layers of silty sandy gravel, gravelly sand, and cobbles and boulders in a matrix of sandy gravel. SPT N-values ranged from 6 to greater than 100 blows per foot (bpf). SPT N-values are influenced by the presence of gravel, cobbles, and boulders, and may erroneously indicate soil relative density values that are above actual.

The approximate locations borings relative to the proposed bridge are shown in Figure 3.

Geotechnical Memorandum No. GM05-14

AK TTP CHIC 2013(1)

Groundwater Groundwater was not encountered in the two borings. After the casing was removed boring 96-1 remained dry and open to an elevation of 438 feet and boring 96-2 to an elevation of 444.5 feet, even though the creek level was at an elevation of 457 feet. Stream flow and ground water will vary with seasonal precipitation and snow melt. The cohesionless soils, indicated by the boring logs, will have a tendency to cave in unsupported excavations below the groundwater table.

Stream Scour Stream scour information is not available at the time of this memorandum. Megan Frye, WFLHD Hydraulic Engineer, indicated during a CFT meeting on January 31, 2014 that scour at the proposed pedestrian bridge foundation locations will be minimal since the foundations are located outside the floodplain.

Seismicity The procedures outlined in Section 3.10 of the 6th Edition of the AASHTO LRFD Manual (2012) were followed to characterize the seismic hazard. These procedures use a design earthquake with a return period of 1000 years, or a 7 percent probability of exceedance (PE) in 75 years.

Horizontal response spectral acceleration coefficients were determined from maps within AASHTO LRFD manual. The locations of nearby faults are discussed in the Geology Section of this memorandum.

The spectral accelerations were scaled to the appropriate site class using the site factors recommended by AASHTO (2012). The results of the hazard analysis are presented in Table 1.

Table 1. Summary of Seismic Parameters (7% PE in 75 years).

Site Class (by Soil Type and Penetration Resistance in Top 100 Feet of Profile) D

Horizontal Peak Ground Acceleration on Site Class B Rock (PGA) 0.6

Horizontal Response Spectral Acceleration at Period of 0.2 sec on Site Class B Rock (Ss)

1.5

Horizontal Response Spectral Acceleration at Period of 1.0 sec on Site Class B Rock (S1)

0.5

Scaled Peak Ground Acceleration for Site Class Listed (As)

0.6

Scaled Horizontal Response Spectral Acceleration at Period of 0.2 sec for Site Class Listed (SDS) 1.5

Scaled Horizontal Response Spectral Acceleration at Period of 1.0 sec for Site Class Listed (SD1)

0.75

AASHTO Seismic Zone 4

Geotechnical Memorandum No. GM05-14

AK TTP CHIC 2013(1)

The values in Table 1 were used to develop the 5-percent-damped-design response spectrum shown in Graph 1 below.

Graph 1: 5% Damped Design Response Spectrum

BRIDGE FOUNDATION DISCUSSION

The preliminary bridge layout, provided by WFLHD Structural Group, is shown in Figure 7.

Preliminary bridge loads have not been provided.

The following are the foundation types which were considered for this site.

Spread footings A spread footing foundation can be considered based on preliminary design information.

Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) GRS-IBS is a fast, cost-effective method of bridge support that blends the roadway into the superstructure. GRS-IBS technology consists of closely spaced layers of geosynthetic reinforcement and compacted granular fill material to create a reinforced soil foundation, abutment, and integrated approach for the bridge. The application of IBS has several advantages. The system is easy to design and cost effective to construct. It can be built in variable weather conditions with readily available labor, materials, and equipment and can easily be modified in the field. GRS-IBS is relatively more flexible compared to other foundation alternatives during seismic events.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

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, T (sec)

5% DAMPED DESIGN RESPONSE SPECTRUM

Geotechnical Memorandum No. GM05-14

AK TTP CHIC 2013(1)

Deep Foundations According to the 2004 As-Built plans for the Glenn Highway Bridge crossing Eska Creek, bridge foundation consists of 12, HP 14x117, driven piles driven 138 feet. The cost of driven piles and drilled shafts are considered to be high compared to the other options.

RECOMMENDATIONS

Based on preliminary information that is available a GRS-IBS bridge foundation is recommended. The recommended design (allowable) bearing pressure on top of the GRS-IBS abutment, at the service limit state, is 4,000 lb/ft2 (allowable stress design method). Typical details for GRS-IBS have been provided to WFLHD Bridge via email on January 31, 2014.

Finalized foundation recommendations will be provided after design loads and scour analysis have been determined.

REFERENCES

Alaska Division of Geological & Geophysical Surveys, Quaternary Faults and Folds, Interactive Map, Alaska Department of Natural Resources, http://maps.dggs.alaska.gov/qff/#17900000:9100000:3, Accessed 28Jan2014

Haeussler, P. and Puckett, C. (2002), USGS Study Shows that Anchorage Area Fault is Capable of a Large Quake, U.S. Geologic Survey, http://www.usgs.gov/newsroom/article_pf.asp?ID=344, Accessed 30Jan2014.

Wilson.F.H, et al (2012) Geologic Map of the Cook Inlet Region, Alaska, U.S. Geologic Survey, Scientific Investigations Map 3153, Scale 1:250,000.

Attachments:

Figure 1 &2 - Vicinity Map and Project Location Site Map Figure 3 - Bridge Plan & Profile Drawing with AKDOT Investigation Locations Figure 4, 5, & 6 – AKDOT Test Hole Logs and Locations Figure 7 – Preliminary Bridge Layout http://maps.dggs.alaska.gov/qff/#17900000:9100000:3 http://www.usgs.gov/newsroom/article_pf.asp?ID=344

Figure 1: Project Vicinity Map

Figure 2: Project Site Location Map

Project Vicinity Site Location

Boring 96-1

Boring 96-2 Pent 96-1

Pent 96-2 Glenn Highway over Eska Creek

Diann.Morehouse Typewritten Text

Diann.Morehouse Typewritten Text

Diann.Morehouse Typewritten Text

FIGURE 3

Diann.Morehouse

FIGURE 4

Diann.Morehouse Typewritten Text

Diann.Morehouse

FIGURE 5

FIGURE 6

FIGURE 7