EagleCreekBridgeFoundationInvestigationFINAL.pdf

Foundation Investigation

EAGLE CREEK BRIDGE

Columbia River Gorge National Scenic Area

July 19, 2019

Ryan Cole, R.G.

Engineering Geologist

Chris Martin, P.E.

Geotechnical Engineer i Eagle Creek Bridge Foundation Investigation

Contents Table of Figures ............................................................................................................................................. ii

List of Tables ................................................................................................................................................. ii

Introduction

Geologic Setting

Subsurface Investigation

Subsurface Conditions

Groundwater

Foundation Recommendations

Attachments

Attachment A - Location Map

Attachment B – Site Plan

Attachment C – Drill Logs

Attachment D – Photographs

References ii Eagle Creek Bridge Foundation Investigation

Table of Figures Figure 1. track mounted Terrasonic International TSi 150CC Sonic Drill Rig operated by Cascade Drilling. 6 Figure 2. location of borehole in the vicinity of the proposed north bridge abutment Figure 3. core sample from 10-15', upper portion of sample is shown at top of photo Figure 4. SPT sample from 15', upper portion of sample is shown at top of photo Figure 5. core sample from 15-20', upper portion of sample is shown at top of photo; no SPT was taken at 20’ due to refusal Figure 6. core sample from 20-25’, upper portion of sample is shown at top of photo Figure 7. core sample from 25-30', upper portion of sample is shown at top of photo Figure 8. SPT sample from 25', upper portion of sample is shown at top of photo Figure 9. core sample from 30-35', upper portion of sample is shown at top of photo Figure 10. SPT sample from 30', upper portion of sample is shown at top of photo Figure 11. core sample from 35-40', upper portion of sample is shown at top of photo Figure 12. SPT sample from 35', upper portion of sample is shown at top of photo Figure 13. core sample from 40-45', upper portion of sample is shown at top of photo Figure 14. SPT sample from 40', upper portion of sample is shown at top of photo Figure 15. core sample from 45-50', upper portion of sample is shown at top of photo Figure 16. SPT sample from 45', upper portion of sample is shown at top of photo Figure 17. core sample from 50-55’', upper portion of sample is shown at top of photo Figure 18. SPT sample from 50', upper portion of sample is shown at top of photo Figure 19. core sample from 55-60’', upper portion of sample is shown at top of photo Figure 20. SPT sample from 55', upper portion of sample is shown at top of photo

List of Tables Table 1. Recommended range of unconfined compressive strength (Qu) values for deep foundation design Table 2. ODOT rock hardness classification chart

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Introduction The Eagle Creek Fire initiated on September 2, 2017 and resulted in nearly 50,000 acres burned. The fire swept through the project site and resulted in damage to an existing suspension trail bridge. The irreparable damage required removal of the bridge, which was completed in early 2018. A plan to replace the bridge has been developed and a subsurface investigation is required to confirm design assumptions for a replacement structure. The proposed replacement structure is a 150 foot long prefabricated steel truss bridge with timber decking founded on concrete-filled steel piles.

A geotechnical investigation of the Eagle Creek bridge site was completed by the Forest Geotechnical Engineer and Engineering Geologist on July 19, 2019. The investigation consisted of historical project records research, field reconnaissance and subsurface investigation. The site is along Forest Service road 241, approximately ½ mile from exit 41 on Interstate 84, in the SE ¼ of Section 22, T. 2 N., R. 7 E., Willamette Meridian. The site is located in the Columbia River Gorge National Scenic Area (see Attachment A - Location Map).

Geologic Setting Regional geologic mapping indicates that the site is underlain by the lower Miocene (17 to 20 m.y.a.)

Eagle Creek Formation, which is described as a thick fluvial outwash deposit that was derived from local volcanic sources (Korosec, 1987). It is composed of interstratified conglomerate, debris flow breccia-conglomerate, volcaniclastic sandstone, tuffaceous sandstone and siltstone, and minor air-fall tuff. The boulder and conglomerate typically consists of poorly sorted andesite clasts in a matrix of clay that includes channel deposits. The breccia conglomerate typically forms from poorly sorted beds up to 10 feet thick of boulders and cobbles in a matrix of clay and pumice fragments. The sandstone is thinly-bedded, well-sorted and typically includes lensoidal bars up to 12 feet thick. Eagle Creek Formation exposed in the headscarp of the Bonneville Landslide Complex at Greenleaf Peak is greater than 1,200 feet thick. The Eagle Creek Formation rests unconformably on late Oligocene age (23-34 m.y.a.)

volcaniclastic rocks and is unconformably overlain by a thick sequence of flood basalts belonging to the Columbia River Basalt Group (Rapp and Imbrie, 2018).

Subsurface Investigation One exploratory borehole was drilled at the site near the proposed northern abutment on July 19, 2019.

The borehole was drilled by Cascade Drilling of Clackamas, Oregon utilizing a track-mounted Terrasonic International TSi 150CC Sonic Drill Rig to a depth of 60 feet. Continuous core samples, in addition to standard penetration tests were obtained generally every 5 feet of depth, and were continuously logged by SREO engineering staff. The final logs (see Attachment C – Drill Logs) were prepared based on a review of the field logs and site literature. The approximate locations of the borings are shown on the site plan (see Attachment B – Site Plan). The subsurface conditions are discussed below.

Subsurface Conditions Borehole (DH-1) was drilled in the vicinity of the proposed northern abutment location. Asphalt pavement was encountered for ±4 inches followed by gravel fill to a depth of ±16.5 feet. Underlying the gravel fill was material belonging to the Eagle Creek Formation. This material generally consisted of loose to very dense silty gravel (GM) with sand and ash to poorly graded gravel (GP) with silt and sand to a depth of ±30 feet. Underlying the silty gravel to poorly graded gravel was a dense to very dense clayey silt (ML-MH) with gravel and trace cobble to a depth of 45 feet. Underlying the clayey silt was a dense to very dense clayey to silty sand (SC-SM) with gravel and cobble to the final borehole depth of 60 feet.

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Material below ±35 feet was interpreted to be intact Eagle Creek Formation based on SPT blow counts and drilling observations. However, recovered material was pulverized by sonic drilling methods. (see Attachment C – Drill Logs, and Attachment D – Photographs).

Groundwater Groundwater was not observed during drilling, but saturated soil conditions were noted during drilling at ±30 feet.

Foundation Recommendations Due to the location of existing structures and infrastructure at the northern abutment (abutment 1), the utilization of deep foundations is recommended. Drilled shafts or pre-drilled pipe piles are favorable to the constraints of this site and the anticipated loads. Due to the vertical variability of strength characteristics of the Eagle Creek Formation, we recommend the use of the unconfined compression strengths (Qu) for deep foundation design as outlined in Table 1.

Table 1. Recommended range of unconfined compressive strength (Qu) values for deep foundation design.

Depth (top) Depth (Bot) Qu (psi) 35 ft 45 ft 1000-1250 45 ft 50 ft 1250-1500 50 ft 60 ft 1500-1750

*depths are measured from surface elev. of DH-1

Installation of deep foundations will require drilling through rocky materials ranging from R0 to R3, according to the ODOT Rock hardness classification chart (Table 2). Drilling and equipment and tooling will need to be appropriate for the conditions. Minimum pile depths should be determined by a minimum rock socket of 10 ft, or 40 ft based on DH-1 observations. Drilled pipe piles should be analyzed as end-bearing piles and skin friction should be neglected.

Table 2. ODOT rock hardness classification chart.

ODOT Rock Hardness Rating

Field Criteria Unconfined Compressive Strength

Typical Equipment Needed for Excavation

Extremely Soft (R0)

Indented by thumbnail <100 psi Small Excavator

Very Soft (R1) Scratched by thumbnail, crumbled by rock hammer

100 – 1000 psi Small Excavator

Soft (R2) Not scratched by Thumbnail, indented by rock hammer

1000 – 4000 psi Medium Excavator

Medium Hard (R3)

Scratched or fractured by rock hammer

4000 – 8000 psi Medium to Large Excavator

Hard (R4) Scratched or fractured w/ difficulty

8000 – 16000 psi Slow chipping with hydraulic hammer

Very Hard (R5) Not scratched or fractured after many blows, hammer rebounds

>16000 psi Blasting

Abutment 2 will utilize shallow foundations with nominal bearing capacities based on Williamson drive probe data. A nominal bearing capacity of 4 kips/ft2 should be assumed for footing depths beyond 3 feet.

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Attachments Attachment A - Location Map

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Attachment B – Site Plan

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Attachment C – Drill Logs

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Attachment D – Photographs

Figure 1. track mounted Terrasonic International TSi 150CC

Sonic Drill Rig operated by Cascade Drilling.

Figure 2. location of borehole in the vicinity of the proposed north bridge abutment.

Figure 3. core sample from 10-15', upper portion of sample is shown at top of photo.

Figure 4. SPT sample from 15', upper portion of sample is

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Figure 5. core sample from 15-20', upper portion of sample is shown at top of photo; no SPT was taken at 20’ due to refusal.

Figure 6. core sample from 20-25’, upper portion of sample is

Figure 7. core sample from 25-30', upper portion of sample is

Figure 8. SPT sample from 25', upper portion of sample is

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Figure 9. core sample from 30-35', upper portion of sample is

Figure 10. SPT sample from 30', upper portion of sample is

Figure 11. core sample from 35-40', upper portion of sample is shown at top of photo.

Figure 12. SPT sample from 35', upper portion of sample is

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Figure 13. core sample from 40-45', upper portion of sample

Figure 14. SPT sample from 40', upper portion of sample is

Figure 15. core sample from 45-50', upper portion of sample

Figure 16. SPT sample from 45', upper portion of sample is

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Figure 17. core sample from 50-55’', upper portion of sample

Figure 18. SPT sample from 50', upper portion of sample is

Figure 19. core sample from 55-60’', upper portion of sample

Figure 20. SPT sample from 55', upper portion of sample is

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References Rapp, B.K., and Imbrie, J.D., 2018, Geotechnical engineering report, Cascade Hatchery: GeoPacific

Engineering, Inc. job no. 18-4825.

Korosec, M.A., 1987, Geologic map of the Hood River quadrangle, Washington and Oregon: Washington Division of Geology and Earth Resources Open-File Report 87-6, scale 1:100,000.

References