1 of 7_GeoRpt_White River_OR Hwy 35(Preliminary).pdf

Draft Geotechnical Data

OR FS ERFO 2007(1)-11(1)

Highway 35 Betterment

This document is a draft and should NOT be relied upon to determine final conditions for bidding.

Final documents will be available during the advertisement period.

Preliminary Geotechnical Report No. 01-09

Oregon Highway 35 White River Bridge Replacement Foundation Investigation

OR FS ERFO 2007(1) - 11(1), Mount Hood National Forest

Hood River County, Oregon

March 2009

CONTENTS

PAGE

1. Introduction 1

2. White River Debris Flows 1 3 Surface Conditions 2

4. Subsurface Investigations 2

4.1 Drilling Investigations 2

4.2 Investigation Results (2007 & 2008 Borings) 2

4.3 Subsurface Water Levels 4

4.4 Pressuremeter Testing 5

5. Laboratory Materials Testing 6

5.1 Soil Classification, Atterberg Limits, and Natural Moisture 6

5.2 Shear Strength Testing 6

6. Bridge Foundation Considerations 7

7. Lateral Loading by Debris Flow Impacts 7

8. Drilled Shaft Foundation Analysis and Design 8

8.1 Scour Recommendations 8

8.2 Earthquake Effects 8

8.3 SPT N-value Corrections 9

8.4 Liquefaction 10

8.5 Subsurface Soil Profile and Soil Strength Parameters 11

8.6 Drilled Shaft Analysis and Design 12

8.6a Design Loads 12 8.6b Preliminary Drilled Shaft Recommendations 12 8.6c Settlement 14 8.6d Lateral Analysis 15

9. Drilled Shaft Construction Considerations 15

10. Approach Embankments and Abutment Backfill 16

11. Use of this Report 18

12. References 19

FIGURES

FIGURE 1. Project Location Map iii FIGURE 2. White River Bridge after November 2006 Debris Flow 1 FIGURE 3. 5-Percent-Damped-Design Response Spectrum 9 FIGURE 4. Corrected SPT (N1)60 Values Plotted Versus Depth 10 FIGURE 5. View of Depression Looking North Toward Existing Bridge 16 ii

TABLES

TABLE 1. Boring Locations, Elevations, and Groundwater Observations 3 TABLE 2. Summary of Pressuremeter Test Results 5 TABLE 3. Summary of Seismic Parameters (7% PE in 75 years) 8 TABLE 4. Subsurface Layers and Strength Parameters 11 TABLE 5. Preliminary Drilled Shaft Recommendations 14 TABLE 6. Recommended Soil Parameters for Lateral Analysis 15 TABLE 7. Recommended Soil Parameters for Abutment Wall Design 17

APPENDICES

APPENDIX A: Preliminary Bridge Layout with Boring Locations and Soil Profile APPENDIX B: Boring Logs APPENDIX C: Pressuremeter Testing Report APPENDIX D: Laboratory Test Reports APPENDIX E: Unified Soil Classification System APPENDIX F: SPT N-Value Corrections APPENDIX G: Drilled Shaft Design Charts iii

Figure 1. Project Location Map.

WHITE RIVER BRIDGE

GOVERNMENT CAMP

1 MILE

N

BEGIN

PROJECT

END

PROJECT

1. INTRODUCTION

This report provides geotechnical investigation results, analysis, and preliminary foundation recommendations for replacement of the White River Bridge on Oregon Highway 35 on the southeast side of Mount Hood (Figure 1). Replacement of the White River Bridge is part of a larger project encompassing sections of Highway 35 located at White River and between Clark and Newton Creeks about three miles north of White River.

This report provides preliminary foundation recommendations for initial bridge design based on preliminary loading information. A second report containing finalized foundation recommendations will be provided to the WFLHD Structures Section once the bridge design process has begun and the actual bridge geometry and design loads of the new structure have been determined.

2. WHITE RIVER DEBRIS FLOWS

The history and nature of debris flows at White River were comprehensively addressed in the report “White River Highway 35 Betterment Project, OR FS ERFO 2007 (1)- 11(1): Geomorphic Assessment (December, 2007)”, prepared for the WFLHD’s Hydraulic Section by Pacific Water Resources, Inc., and R W Beck. The reader is referred to that report for additional geological, geomorphological, and hydrological information regarding White River debris flows.

Figure 2. White River Bridge after November 2006 Debris Flow (taken by Doug Jones, Mount Hood National Forest).

3. SURFACE CONDITIONS

The project site is located on the alluvial fan of White River, which at the bridge site is approximately 3000 feet wide. The fan is an aggrading deposit consisting predominantly of poorly-graded, fine to coarse silty sand, gravel, cobbles, and boulders that is classified as SM, SP-SM, and GP-GM soil in the Unified Soil Classification System (USCS).

The alluvial fan consists primarily of fluvial deposits of White River, but has been built in part by periodic debris flows that result from the mobilization and rapid downslope transport of large amounts of sand, gravel, cobbles, and boulders following “rain-on-snow” events in the upper reaches of the White River drainage.

4. SUBSURFACE INVESTIGATIONS

4.1 Drilling Investigations

Two foundation drilling investigations were performed for the current bridge replacement project. Four investigation borings were drilled on the west (upstream) side of the highway in October, 2007, to obtain preliminary foundation information. The locations of 2007 boring numbers 1 and 2 are shown on the White River Bridge Preliminary Layout in Appendix A. Borings 3 and 4, not shown on the Preliminary Layout, were located on the highway shoulder south and north, respectively, of the map boundaries.

Eight additional foundation borings were drilled in October, 2008, on the downstream side of the existing bridge. Those borings, which were drilled at the abutment and pier locations of the bridge to be constructed, are also shown on the Preliminary Layout in Appendix A.

4.2 Investigation Results

Logs of the 2007 and 2008 borings are contained in Appendix B. A summary of the materials encountered in the borings is provided below:

2007 Borings

Borings B-1 and B-2 were drilled to 100 feet depth. Boring B-3 was drilled to 85 feet and boring B-4 was drilled to 96 feet depth. The 2007 borings were begun with 5 inch diameter casing hammered in to 3 feet depth and advanced from the surface to 10 feet depth with a 4 inch diameter tri-cone bit and mud rotary drilling. Below 10 feet depth, the borings were advanced with HQ3 diamond coring tools.

All of the materials in borings B-1 and B-2 and to 45 feet depth in B-3 and 26 feet depth in B-4 were described by the drill inspector as “alluvium” consisting predominantly of loose to very dense, damp to wet, poorly graded mixtures of silty, fine to coarse gravelly sand containing cobbles and boulders that were field classified as SM, SP, and SP-SM materials in the Unified Soil Classification System (USCS) and lesser amounts of more gravelly material classified as GP-GM.

Below 45 feet depth in B-3 and 26 feet in B-4, the boring inspector described the materials as “mudflow deposit”. The mudflow deposit consists primarily of brown to purplish-colored, very dense gravel with silt, fine to coarse sand, cobbles, and boulders that was generally classified as GM with occasional zones of GP-GM material.

Although the materials in all four borings were typically medium dense to very dense, a zone of very loose (“0” blow count), wet, brown, fine to coarse sand was encountered at 40-41.5 feet in boring B-2. The blow count of “0” may represent a thin zone of wet, very loose silt or a void between boulders, and is considered to be an anomalous value that is not representative of material density as a whole.

Boulders ranging in size from 12 to 24 inches were encountered in the 2007 borings.

2008 Borings

The 2008 borings were numbered in continuing sequence with the 2007 borings, beginning with boring B-5 and ending with boring B-12. Boring locations are shown on the White River Bridge Preliminary Layout in Appendix A. The locations, ground surface elevations, and water level observations of the 2008 borings are summarized in Table 1 below.

Table 1. 2008 Boring Locations, Elevations, and Groundwater Observations

Boring No. Station and Offset

Ground Surface

Elevation1 (feet)

Depth (feet)

Water Level Observations2

Water Level

Elevation (feet)

B-5 40+33, 20 ft LT 4254 100.5 29.8 ft 4224.2

B-6 40+33, 20 ft RT 4252 101.0 28.3 ft 4223.7

B-7 41+19, 20 ft LT 4240 100.4 NR -

B-8 41+19, 20 ft RT 4238 99.8 NR -

B-9 42+34, 20 ft LT 4240 101.0 13.8 ft 4226.2

B-10 42+34, 20 ft RT 4240 91.0 NR -

B-11 43+20, 20 ft LT 4256 99.8 NR -

B-12 43+20, 20 ft RT 4250 99.9 NR -

NOTES:

1Determined from contours on Preliminary Layout.

2NR = Water level not recorded due to use of drilling mud to advance boring.

The 2008 borings were advanced by mud rotary drilling with an HWT casing advancer and tri-cone rock bit their entire depths. SPT samples were taken at 2.5 foot intervals to 15 (+/-) feet depth and at 5 foot intervals below 15 feet.

A subsurface profile showing White River 2008 investigation borings 5, 7, 9, and 11 is contained in Appendix A. With the exception of the materials described in the 2007 borings as “mudflow deposit”, the materials encountered in the 2008 borings were virtually identical to those encountered in the 2007 borings, consisting predominantly of damp to wet, loose to very dense, silty, fine to coarse gravelly sand with cobbles and boulders. None of the materials described in the 2008 borings were described by the drilling inspector as “mudflow deposit”. It is possible that “mudflow deposit” materials were encountered in the 2008 borings, but, because the borings were not cored, were not recognized as such by the drilling inspector.

Because the borings were advanced by casing advancer rather than coring, it was not possible to determine the actual sizes of boulders that were encountered by direct measurement of cored boulders. Instead, boulder sizes were estimated by the driller.

Most boulders were estimated to be in the range of 1 to 2 feet diameter; however, the driller reported a few boulders that may have been as large as 4-6 feet in diameter. This is consistent with the size of boulders exposed in the slopes adjacent to the White River at the bridge location.

The tri-cone rock bit was able to penetrate boulders of up to possibly 6 feet diameter.

Observations of the surface cobbles and boulders in the flood plain of White River indicate that material is primarily andesite lava and pyroclastic volcanic rock typical of the Cascade volcanoes.

4.3 Subsurface Water Levels

Direct water level measurements were not made in most of the borings because drilling mud was pumped into the holes to advance the borings. Water level measurements were made in boring B-5 and B-6 after leaving the casing in the ground overnight and in boring B-9 after leaving the casing open for an hour. Water levels in those borings were measured at elevations between 4223.8 and 4226.2 feet, which is approximately coincident with the White River elevation at the time of drilling.

Groundwater levels fluctuate, and the ground water level at the bridge location is likely to rise and fall with the level of the White River, particularly during spring thaw and following periods of heavy precipitation. The WFLHD Hydraulic Section provided water surface elevations of 4223.0 feet and 4225.0 feet for the 2-year and 500-year flow events, respectively. Based on these values the groundwater table near the bridge location is likely to be less than 4225 feet throughout most of the year.

4.4 Pressuremeter Testing

Pressuremeter testing (PMT) was performed at White River Bridge by INSITU TECH INC. of Beaverton, Oregon. The results of pressuremeter testing are presented in “Pressuremeter Testing Report – Proposed Hwy 35 Bridge, White River, Mt Hood, OR (November, 2008)” in Appendix C.

The PMT was completed in pre-bored holes using a TEXAM hydraulic unit operating a long NX probe. PMT tests were conducted in borings B-7 and B-10. Five PMT tests were completed in each boring at depths between 12 and 72 feet. Results of the pressuremeter tests are summarized in Table 2 below.

Table 2. Summary of Pressuremeter Test Results.

B-10 (ground surface elevation = 4240)

Test #1 Depth (ft) Elevation

Net Limit Pressure, pL*

(ksf)

Menard Initial Modulus, E0

(ksf)

PMT Reload Modulus, Er

(ksf) 3 14.5 4225.5 >100 2228 6635 4 22 4218.0 68 723 3648 5 31 4209.0 >90 1248 5342 6 51.25 4188.75 95 2205 4868 7 72 4168.0 >120 2987 6041

B-7 (ground surface elevation = 4240)

Test # Depth (ft) Elevation

Net Limit Pressure, pL*

(ksf)

Menard Initial Modulus, E0

(ksf)

PMT Reload Modulus, Er

(ksf) 8 12 4228.0 >105 2052 8140

9 16 4224.0 >105 1496 4877

10 26.75 4213.25 >110 2308 7478

11 51.3 4188.7 80 1408 4066

12 72 4168.0 >120 1934 5170

NOTES:

1. Missing numbers are calibration tests.

The presence of a significant percentage of gravel and cobbles in the subsurface profile influenced the results of many of the SPT tests as shown by the scatter of data points in Figure 4 in Section 8.3 below. The PMT results provided verification that the subsurface profile consisted of dense to very dense cohesionless soils.

Procedures for calculating ultimate bearing capacity using PMT results (Briaud, 1989) were used to check the results for ultimate bearing capacity determined from procedures using N60 values. Modulus values determined from the PMT were used to directly estimate settlement of the proposed drilled shafts and also to estimate lateral capacity of the proposed shafts.

5. LABORATORY MATERIALS TESTING

5.1 Soil Classification, Atterberg Limits, and Natural Moisture

Nine samples comprised of Standard Penetration Test samples from borings 7 and 8 were submitted to the WFLHD’s Vancouver, Washington, materials testing laboratory for soil classification, Atterberg Limits, and natural moisture content. Two of the nine submitted samples consisted of a single SPT sample interval and seven samples consisted of two or more SPT samples of similar materials combined as one test sample.

Laboratory test reports are contained in Appendix D. Laboratory testing included determination of Atterberg Limits, natural moisture, and soil classification in the Unified Soil Classification System (Appendix E).

All of the tested samples were non plastic. Five of the nine samples were classified in the USCS as “SP-SM - poorly graded sand with silt and gravel”, three were classified as “SM

– silty sand and silty sand with gravel”, and one as “GP-GM – poorly graded gravel with silt and sand”. The natural moistures of the nine samples ranged from a low of 13.7 percent for the depth interval 2.5-15 feet in boring 7 to a high of 24.2 percent for the depth interval 59.5-61 feet in boring 8. The percent fines passing the no. 200 sieve ranged from a low of 9.3 for the depth range 39.5-41 feet in boring 8 to a high of 13.2 for the depth range 44.6-56 feet in boring 8.

Due to the observed consistency and similarity of the samples from the eight borings drilled in 2008 and the four borings drilled in 2007, it was not considered necessary to perform laboratory classifications for samples from every boring, and the samples tested from borings 7 and 8 are considered representative of the subsurface materials at the White River bridge site.

5.2 Shear Strength Testing

A test sample comprised of seven combined SPT samples from borings 1 and 2 of the 2007 investigation borings representing a depth of 30-55 feet was submitted to Cornforth Consultants of Portland, Oregon, for direct shear strength testing. The sample (Laboratory Report No. W-08-0205-SO in Appendix D) was classified as “SP-SM;

poorly graded sand with silt and gravel” in the Unified Soil Classification System (USCS). The test indicated that the peak strength parameters of the sample were cohesion = 0 and friction angle = 46 degrees.

6. BRIDGE FOUNDATION CONSIDERATIONS

Three foundation types were considered by the WFLHD Geotechnical, Structures, and Hydraulic Sections. The three foundation types considered were (1) spread footings, (2) driven piles, and (3) drilled shafts.

SPREAD FOOTINGS

Spread footings would be a suitable foundation in the predominantly dense to very dense, fine to coarse silty sand, gravel, cobbles, and boulders encountered in the investigation borings. However, the design scour elevation of 4200 feet recommended by the WFLHD Hydraulics Section would result in the need to place spread footings 25 feet below the existing White River stream bottom, which precluded their use at this location.

DRIVEN PILES

Driven pipe piles would be a suitable foundation for use in the cohesionless materials at White River. A static analysis indicated that pipe piles would need to be driven to depths on the order of 60-70 feet to achieve a desired ultimate capacity of 412 kips (206 tons) per pile below the scour elevation. A wave equation analysis indicated that pipe piles driven to 60-70 feet through dense to very dense gravels and sands would be structurally damaged before reaching the required tip depths. In addition, exposure of 25 feet of pile by scour would likely result in buckling of the piles and bridge failure. The difficulty of driving piles to bearing at White River and the potential for exposed piles to buckle precluded a pile foundation from further consideration.

DRILLED SHAFTS

Drilled shafts can be constructed at White River bridge. Lateral loads due to seismic events are anticipated to be a significant component of the bridge foundation design, and drilled shafts can be constructed to support the bridge in the event of 25 feet of scour below the top of the shafts. For constructability, scour concerns, and lateral load capacity, drilled shaft foundations were selected to transmit the bridge loads into the underlying soils at White River Bridge.

7. LATERAL LOADING BY DEBRIS FLOW IMPACTS

The potential for debris flows to exert significant lateral loads on the new bridge and its foundation elements was addressed during the preliminary design process. It was determined that the existing bridge had not sustained damage due to lateral loads from past debris flows. It was also determined that, due to the 3000 foot width and 6-8 percent gradient of the White River Valley at the bridge location, the energy available in debris flows by the time they reach the bridge to exert significant lateral loads is relatively low and not sufficient to warrant specific consideration in the foundation design.

8. DRILLED SHAFT FOUNDATION ANALYSIS AND DESIGN

8.1 Scour Recommendations

The elevation of the White River thalweg is approximately elevation 4224 feet along centerline of the proposed alignment. Based on analyses performed by the WFLHD’s Hydraulics Section, the following scour depths and elevations were recommended for the White River Bridge drilled shaft foundations:

• Scour elevation at bridge piers: 4200 feet (24 feet below the current stream bed).

• Scour elevation at bridge abutments: 4225 feet.

The estimated scour elevation of 4200 feet at the pier locations is based on a glacial outburst of 20,000 cfs, past debris removal operations, and a qualitative assessment of debris-related erosion (Browning, 2008).

8.2 Earthquake Effects

Seismic sources that contribute to the regional seismic hazard include shallow crustal sources (local faults and gridded seismicity) and the Cascadia Subduction Zone interplate (mega-thrust) earthquakes.

The procedures outlined in Section 3.10 of the 4th Edition of the LRFD Manual with the 2008 Interims were followed to characterize the seismic hazard. Note that these procedures use a design earthquake with a return period of 1000 years, or a 7 percent probability of exceedance (PE) in 75 years. This is a departure from previous AASHTO Specifications which used a design earthquake with a return period of 500 years, or a 10 percent PE in 50 years. The USGS interactive deaggregation website was used to determine the 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).

Site Class (by Soil Type and Profile) C – very dense soil

Horizontal Peak Ground Acceleration (PGA) 0.166g

Horizontal Response Spectral Acceleration at Period of 0.2 sec (Ss) 0.392g

Horizontal Response Spectral Acceleration at Period of 1.0 sec (S1) 0.142g

As 0.199 g

SDS 0.470 g

SD1 0.236 g

Seismic Zone 2

The values in Table 3 were used to develop the 5-percent-damped-design response spectrum shown in Figure 3 below.

Figure 3. 5-Percent-Damped-Design Response Spectrum.

8.3 SPT N-Value Corrections

The SPT N-values taken in the 10 borings nearest the proposed bridge location were corrected for hammer energy and overburden pressure to determine the N60 values and the (N1)60 values. N60 values were corrected for hammer efficiency only. (N1)60 values were corrected for hammer efficiency and overburden pressure. The corrected N60 and (N1)60 values are contained in spreadsheet format in Appendix F. The (N1)60 values were averaged in 5-foot layers to produce a chart of average (N1)60 versus depth shown in Figure 4 below.

- 10 20 30 40 50 60 70 80 90 100

(N1)60 (blows/ft)

El ev at io n (ft

(N1)60 values

Avg (N1)60

Figure 4. Corrected SPT (N1)60 Values Plotted Versus Depth.

8.4 Liquefaction

The procedures outlined in Subsection 6.5.2 of the ODOT Geotechnical Design Manual (2008) were generally followed in order to assess the liquefaction potential at the site.

One of the conditions for preliminary screening of liquefaction potential is an assessment of the (N1)60 values in the upper 75 feet of the soil profile. (N1)60 values greater than 25 blows per foot (bpf) indicate that the soils are not susceptible to liquefaction and a detailed liquefaction analysis is not necessary. Figure 4 indicates that the average (N1)60 values were all greater than 25 bpf, indicating that none of the layers are susceptible to liquefaction.

Several of the individual (N1)60 values on Figure 4 are below 25 bpf, but liquefaction is still not of concern for two reasons: 1) most of the values less than 25 bpf were above the anticipated high groundwater table elevation (4225 ft) and therefore are not susceptible to liquefaction, and 2) the few values that are less than 25 bpf are widespread throughout the profile, indicating that these values are not representative of specific layers or depths and are more likely to be anomalies related to the presence of cobbles, boulders, and/or discrete pockets of loose materials in the profile. The use of drilled shaft foundations extending below the scour elevation will mitigate the potential for loss of support due to strength loss in any isolated thin layers during a seismic event.

Based on the foregoing discussion, no additional liquefaction analysis is considered necessary for the White River bridge foundation materials.

8.5 Subsurface Soil Profile and Soil Strength Parameters

Appendix A contains a subsurface profile along the bridge centerline with soil units projected into the profile from adjacent borings at the pier and abutment locations. The soil profile shows that, based on the eight subsurface borings, the subsurface materials can be divided into four zones or layers of differing density. Note that the soil profile was divided based on N60 values (N-values corrected only for hammer efficiency) rather than (N1)60 values since drilled shaft design procedures require N60 values for input. The layers and their associated soil strength parameters are shown in Table 4 below:

TABLE 4. Subsurface Layers and Strength Parameters.

Soil Layer

Elevation (feet)

Soil Description N60 φ’ (deg.)

Cohesion (psf)

Moist Unit Weight

(pcf)

1 > 4250 New Fill (Sandy Gravel) - 34 0 130

2 4234 – 4250 Gravelly Sand 32 36 0 130

3 4190 – 4234 Cohesionless

IGM 72 40 0 135

4 < 4190 Cohesionless

IGM 93 42 0 135

8.6 Drilled Shaft Analysis and Design

The proposed bridge will be a three span structure with a 115 foot-long main span and an 86 foot-long span at each end. The distance from the proposed bridge deck elevation to the scour elevation is about 50 and 75 feet at the abutments and piers, respectively. As discussed in Section 6, drilled shafts were selected over spread footings and driven piling as the preferred foundation type because drilled shafts can be more easily constructed to transmit loads below the scour elevation and they have relatively higher lateral load capacity than driven piles.

8.6.a Design Loads

The WFLHD Structures Section provided preliminary axial dead and live loads for the abutments and piers. Individual load combinations for LRFD limit states were not provided. The unfactored loads are summarized as follows:

Abutments Piers Dead Load (DL) 771 kips 1542 kips Live Load (LL) 130 kips 130 kips DL + LL 901 kips 1672 kips

It should be noted that the dead load shown above includes 212 kips of a single 6 foot diameter by 50 foot long column dead load from approximately the ground surface elevation at the piers to the bridge deck elevation. The loads provided did not include the dead load of the drilled shaft above the scour elevation. Downdrag loads due to settlement are not anticipated.

WFLHD Structures has also indicated that up to ½ inch of settlement is tolerable for the loads listed above.

8.6.b Preliminary Drilled Shaft Recommendations

The soil layer depths and strength parameters discussed in Section 8.5 were used in drilled shaft design. Drilled shaft diameters of 6, 8, and 10 feet were analyzed for axial capacity provided by both skin friction and end-bearing by the methods recommended in the American Association of State Highway Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Specifications (2008) and the FHWA drilled shaft design manual (O’Neil and Reese, 1999).

Each bent will be supported by one or two drilled shafts with diameters between 6 and 10 feet. There will either be two 6- to 8-foot diameter drilled shafts or a single 10-foot diameter drilled shaft at each bent. After the final loads are determined, the diameter of the drilled shaft should be the minimum size required to carry the design loads, rounded up to the nearest 0.5 feet.

Charts of factored axial resistance versus depth for each bent are contained in Appendix G for 6, 8 and 10 foot diameter drilled shafts. Load versus settlement charts are also included in Appendix G for the uppermost tip elevations listed in Table 5.

The lines on the Charts in Appendix G for the service limit state were developed using a resistance factor of 1.0 and include the design scour.

The resistance factors listed in Table 10.5.5.2.4-1 of the AASHTO LRFD Specifications (2008) was used to calculate the factored axial resistance lines on the Charts in Appendix G and include the design scour. The resistance factors in the Table were reduced by 20 percent when used to calculate the factored axial resistance of a single 10 foot diameter drilled shaft to account for a lack of redundancy.

The lines on the Charts in Appendix G for the extreme event limit states were developed using a resistance factor of 1.0. Each chart includes both a capacity line for the extreme event limit state with and without the design scour included. Scour should be included in evaluation of the extreme event limit state when relevant.

It is assumed that if two 6- to 8-foot diameter drilled shafts are used, the unfactored axial live load and dead load on each shaft is half of the values listed in Section 8.6.a, i.e., 451 kips per shaft at the abutments and 836 kips per shaft at the piers.

The design charts provided in Appendix G were not modified for the dead load of the drilled shaft above the scour elevation. This load should be included in the design loads when using the charts.

It is assumed that if two drilled shafts are used at each bent, the center-to-center spacing of drilled shafts will be at least 4.0 diameters or more.

Constructability of drilled shafts will become more difficult with increasing depth. Most drilled shaft contractors are equipped to install drilled shafts up to 100 feet below the existing grade. The maximum depth of the drilled shafts should be limited to elevation 4145 feet at the piers and 4155 feet at the abutments.

Recommendations for drilled shafts are summarized in Table 5.

Table 5. Preliminary Drilled Shaft Recommendations.

Abutment 1 Pier 1 Pier 2 Abutment 2

Station at Centerline of Bridge 40+32.75 41+19.00 42+34.00 43+20.25

Finished Bridge Deck Elevation (feet) 4265.802 4266.722 4267.188 4266.967

Estimated Top of Drilled Shaft Elevation (feet) 4256 4225 4225 4257

Proposed Final Ground Surface Elevation (feet) 4266 4225 4225 4267

Design Scour Elevation (feet) 4225 4200 4200 4225

Recommended Uppermost Tip

Elevation* (feet)

B=6’ (2)

B=8’ (2)

B=10’ (1)

Recommended Lowest Tip Elevation (feet) 4155 4145 4145 4155

*B=Drilled Shaft Diameter, number in parentheses indicates number of drilled shafts per bent

Since factored load combinations were not provided, allowable stress design methods were used to develop the uppermost drilled shaft tip elevation. A factor of safety of 2.75 was applied to the loads provided in order to determine the minimum lengths of drilled shafts. In addition, the subsurface conditions, settlement criteria, and design scour elevations were also considered when setting the uppermost tip elevation. The uppermost tip elevations were set at least two diameters below the design scour elevation.

8.6.c Settlement

The estimated settlement at the top of the drilled shafts due to the working loads (DL + LL) listed in Subsection 8.6.a is up to 0.5 inches for the diameters and uppermost tip elevations of drilled shafts presented in Table 5. Charts of settlement versus load are presented in Appendix G following each bearing capacity chart. The settlement charts include scour and present settlement estimates for both the uppermost and lowest tip elevation listed in Table 5.

8.6.d Lateral Analysis

Lateral loads were not provided, but they are anticipated to be significant due to the seismic hazard at the site. Seismic lateral load analysis is an extreme event limit state so scour is not included in the analysis.

Table 6 provides the soil parameters that are recommended to analyze lateral foundation loads. The values in Table 6 do not include factors of safety or load factors. A resistance factor of 1.0 is specified in AASHTO (2008) for horizontal geotechnical resistance of a single shaft or shaft group.

Table 6. Recommended Soil Parameters for Lateral Analysis.

Layer No.

Elevation1

(feet) Soil

Type

Moist Unit Wt.

(pcf)

Effective Unit Wt.

(pcf)

Friction Angle

(degrees) k 2

(lb/in3) 1 > 4250 Sand 130 130 34 90

2 4234 – 4250 Sand 130 130 36 155

3 4225 – 4234 Sand 135 135 40 225

4 4190 – 4225 Sand 135 72.6 40 125

5 < 4190 Sand 135 72.6 42 125 Notes:

1 Layers 1 through 5 are applicable at the abutment locations and only layers 4 and 5 are applicable at the pier locations.

2 k is the constant giving the variation of soil modulus with depth in the equation Es = kx, where Es = soil modulus, and x = depth below the ground surface. k values from Table 3.6 and 3.7 in LPILE Technical Manual (Reese et al, 2004).

9. DRILLED SHAFT CONSTRUCTION CONSIDERATIONS

Based on both surface observations of the White River channel and adjacent flood plain and the subsurface investigation borings, it is anticipated that boulders at least as large as 6 feet in diameter may be encountered during the drilling and installation of drilled shaft foundations at the new White River bridge. The contractor should be prepared to remove boulders that are encountered during shaft installation that impede or prevent advancement of the shaft by approved methods.

The soils encountered in the borings will cave if excavated with an open hole. Full depth temporary casing or drilling slurry must be used to protect the side walls of the drilled shaft excavation during construction. The drilled shaft design includes a significant amount of skin friction along the sides of the drilled shaft. Therefore, any temporary casing must be removed from the completed drilled shaft. Very permeable layers of coarse gravel, cobbles and boulders are likely to be encountered which may exclude the use of drilling slurry. The contractor should consider the subsurface conditions carefully when choosing the method of drilled shaft construction. Wet methods of construction will be necessary. An adequate head of water (casing method) or drilling slurry should be maintained inside of the drilled shaft excavation to prevent heaving of the soils at the bottom of the excavation.

Cross-hole Sonic Logging (CSL) should be completed on each drilled shaft to insure the integrity of the shaft. Each rebar cage should include one CSL access tube per foot diameter of drilled shaft (i.e., at least 8 CSL access tubes for an eight-foot diameter drilled shaft). The access tubes should be spaced evenly on the rebar cage and securely fastened to either the inside or outside of the cage.

The WFLHD Geotechnical Team should be part of the reviewing effort of the contractor’s drilled shaft submittals to evaluate shaft design and construction appropriateness based on the subsurface conditions. A member of the Geotechnical Team should also be present during excavation of the drilled shafts to ensure that the subsurface conditions are consistent with the materials encountered in the subsurface exploration.

10. APPROACH EMBANKMENTS AND ABUTMENT BACKFILL

The approach embankment will likely be constructed with nearby material deposited during the 2006 debris flow event consisting of gravelly sand and cobbles or with shot rock material from a nearby Forest Service quarry. These materials are adequate for use as backfill and fill behind abutments and wing walls; however, the material should be screened with a grizzly or by other means to remove particles greater than 6 inches in size. A perforated corrugated polyethylene drain should be installed behind walls to ensure drainage. The soil parameters listed in Table 7 may be used to determine the lateral earth pressures exerted on the abutment walls and wing walls.

Table 7. Recommended Soil Parameters for Abutment Wall Design.

Parameter Design Value* Moist Unit Weight 130 pcf

Angle of Internal Friction 34 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

Wall-Backfill Interface Friction Angle, δ 26 degrees

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

The above values do not include factors of safety or load factors. Appropriate factors of safety or load factors should be used with these parameters. 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 LRFD (2008) should be used to determine the seismic forces exerted on the walls. Once the wall geometry is determined, the Geotechnical Team can assist in development of the seismic active pressure.

Embankments constructed with these materials can safely be constructed as steep as 1V:1.5H. However, embankments constructed 1V:2H or steeper with the nearby sandy gravel material will be highly susceptible to erosion and shallow failures during spring thaw and periods of heavy precipitation. Embankment protection (riprap or shot-rock) or aggressive revegetation and erosion control will be needed to protect slopes 1V:2H or steeper.

SHALLOW GROUND DEPRESSION

A shallow ground depression was observed in the southeast quadrant of the existing bridge. The depression is most likely due to piping of finer grained material from the soil matrix caused by melting of a large pile of snow and/or heavy precipitation runoff at this location. The depression measures approximately 150 feet long (parallel to the highway) by 40 feet wide. The material appears to have piped out about 6 to 8 feet below the original grade at this location.

Figure 5. View of Depression Looking North Towards Existing Bridge.

The embankment subgrade soils in the area of the depression should be removed to a depth of about 8 feet. The same material that is removed can be replaced and compacted.

The limits of the removal and replacement should be from approximately Station 38+00 to Station 41+00. The limits should extend from the right edge of the existing pavement (down a 1:1 slope) to approximately 65 feet right of the project centerline. All material above elevation 4240 feet should be removed and replaced. A typical section showing the area of removal and replacement and quantities for bidding should be shown in the project plans and specifications.

10. USE OF THIS REPORT

Professional judgments and recommendations are presented in this report. They are based partly on evaluation of the technical information gathered, partly on historical reports and partly on the WFLHD Geotechnical Team’s general experience with subsurface conditions in the area. It should be noted the borings might not represent potentially unfavorable subsurface conditions between borings. If, during construction, soil conditions are encountered that vary from those discussed in this report or historical reports, or if design loads and/or configurations change, the Geotechnical Team should be notified immediately in order that it may evaluate effects, if any, on foundation performance.

For questions regarding this report, please contact WFLHD Engineering Geologist Dave Lofgren at 360-619-7706 (david.lofgren@fhwa.dot.gov) or WFLHD Geotechnical Engineer Brian Collins at 360-619-7657 (brian.collins@fhwa.dot.gov).

11. REFERENCES

AASHTO LRFD Bridge Design Specifications 2008 Interim Revisions (2008) American Association of State Highway and Transportation Officials, Washington, D.C.

Briaud, J.-L. (1989) The Pressuremeter Tests for Highway Applications, Report No.

FHWA-IP-89-008, Federal Highway Adminsitration, McLean, Virginia, 156p.

Browning, M.C. (2008) November 6 Memorandum to Khoa Nguyen, Bridge Engineer, with subject heading “Hydraulic Information, White River Bridge, Highway 35, PFH 49, Oregon”, 8p.

ODOT Geotechnical Design Manual (2008) Oregon Department of Transportation, Technical Services Branch, Geo-Environmental Section, 325 p.

O’Oneil, M. W., and Reese, L. C. (1999) Drilled Shafts: Construction Procedures and Design Methods, FHWA Report No. FHWA-IF-99-025, Federal Highway Administration, Washington, D.C., 758 p.

Reese, L.C., Wang, S.T., Isenhower, W.M., and Arrellage, J.A. (2004) Computer Program LPILE Plus Version 5.0 Technical Manual, Ensoft, Inc.

U.S. Geological Survey, USGS Earthquake Hazards Program website, 2002 Interactive Deaggregations, http://eqint.cr.usgs.gov/deaggint/2002/index.php, accessed August 4, 2008.

APPENDIX A

Preliminary Bridge Layout with Boring Locations and Subsurface Profile

BH

BH4

SHEET

NUMBER

17-Aug-2009 03:36 PMX:\CAD_Services\Oregon\Hwy35\Design\Bridge_Plan.dgn

PROJECTSTATE

Checked by:Designed by:

N 41° 55’ 17" E

N

PRELIMINARY WHITE RIVER

BRIDGE LAYOUT

SHOWING APPROXIMATE

BORING LOCATIONS

Scale in feet

30 0 30 60

40+00 41+00 42+00 43+00

CENTERLINE PROFILE

WHITE RIVER BRIDGE

SHOWING INVESTIGATION

BORINGS B-5, B-7, B-9, B-11

SHEET

NUMBER

OR

FS ERFO 2007(1)-11(1)

30-Sep-2009 11:33 AMX:\CAD_Services\Oregon\Hwy35\Design\Bridge_Profile.dgn

PROJECTSTATE

Checked by:Designed by:

APPENDIX B

Boring Logs