GM14-23 Granite Hill Final Foundation Memorandum.pdf

158377846

M E M O R A N D U M Western Federal Lands Highway Division

610 E. Fifth Street Vancouver, WA 98661

DATE: March 8, 2024

TO: Sean Hayter Project Manager

FROM: Evan Garich Geotechnical Engineer

SUBJECT: Geotechnical Memorandum GM14-23 Final Foundation Recommendations Granite Hill Road Reconstruction

OR FLAP GRANT 24(2)

Grant County, Oregon

INTRODUCTION

This memorandum provides final foundation recommendations for the Granite Hill Reconstruction Project Phase Two. The project is located approximately 45 miles west of Baker City, Oregon, on Highway 410. Figure 1 shows the project location map.

PROJECT DESCRIPTION

The original Granite Hill Road Reconstruction project consisted of pavement reconstruction, subgrade improvements, and replacing five culverts along Granite Hill Road in Grant County, Oregon. The project was later divided into two phases; the first phase, OR GRANT 24(1), included pavement reconstruction and subgrade improvements. The second phase and current project, OR FLAP GRANT 24(2), includes five culvert replacements. Construction for OR GRANT 24(1) was completed in 2022. Two geotechnical memorandums were published before the project was separated into two phases. A final geotechnical report was published after the division of the two phases and focuses on the pavement reconstruction and subgrade improvements for the OR GRANT 24(1) Phase One project. The three geotechnical engineering documents published for Phase One include the following:

• Geotechnical Memorandum GM41-20 Granite Hill Reconstruction Preliminary Geotechnical Recommendations dated August 13, 2020.

• Geotechnical Memorandum GM43-20 Granite Hill Reconstruction Preliminary Geotechnical Investigation Results dated August 19, 2020.

• Geotechnical Report, GR04-21, Granite Hill Reconstruction Final Geotechnical Recommendations dated April 2021.

All three documents above include discussions, boring location figures, boring logs, and laboratory test reports that discuss the geology, subsurface conditions, and observed site conditions for this project. Italicized text in this memorandum denotes text copied directly from Geotechnical Report, GR04-21.

Exploration location maps, boring logs, field rock core photos, and laboratory test results are provided in GR04-21 and not repeated herein. The reader should refer to GR04-21 for that information.

The current phase of the Granite Hill Road Reconstruction project includes replacing five culverts along Granite Hill Road in Grant County, Oregon. The existing 7.5-foot by 5-foot arch corrugated metal pipe (CMP) culvert at Bull Run Creek Crossing No.1 will be replaced with a 15-foot wide and 9-foot tall concrete box culvert with 15-foot high wing walls. The existing 10-foot by 7-foot arch CMP culvert at Bull Run Creek Crossing No.2 will be replaced with a 22-foot by 9-foot tall concrete box culvert with 15-foot high wing walls. The existing 6-foot by 3-foot arch CMP culvert at Boundary Creek will be replaced with a 13-foot by 12-foot concrete box culvert with 18-foot wing walls.

The existing culverts at Bull Creek Crossings No.3 and No.4 are 10-foot wide and 7-foot high CMP arch culverts. The proposed Bull Run Creek Crossing No. 3 consists of an approximately 54-ft. single span precast voided slab girder bridge supported on deep foundations. The proposed Bull Run Creek Crossing No. 4 consists of an approximately 101-ft. single span precast concrete bulb-T girder bridge supported on deep foundations. The out-to-out width of the bridges is approximately 28-feet, and the bridges are skewed approximately 25° to 30° from the centerline of the roadway.

Figure 1 – Project location maps.

REGIONAL SETTING

Geology

Geology along the corridor has various of rock types mapped (Ferns, Brooks, and Ducette, 1982; Brooks Ferns and Mullen, 1982). Table 1 synthesizes geologic units, map symbols, and basic descriptions along the Granite Hill Road Reconstruction project.

Regionally rocks of the Blue Mountains are an agglomeration of many rock types from an island arc system that was accreted (added) onto the North American plate by tectonic forces. The island arc rocks were also modified by igneous intrusions that caused further metamorphism and structural deformation. Regionally, geologic processes produced complex sulfide ores that supported mining districts with historically significant gold and silver, and lesser amounts of lead, zinc, copper, and chromite. Hard rock, dredge, and placer mining methods were historically used in the local mining districts.

The primary rock type encountered along the alignment is the Elkhorn Ridge Argillite, a mainly dark colored metamorphosed, fine grained, muddy, siliceous oceanic sedimentary rock with chert and small amounts of felsic-tuff (lithified volcanic ash), sandstone, and conglomerate. The argillite has undergone significant structural deformation and metamorphosis due to regional tectonics and intrusions, as mentioned above. Other units encountered in smaller amounts along the alignment are a mixed mélange of tectonically juxtaposed materials such as peridotite, serpentine, gabbro, basalt, silicic-andesitic volcanics, and volcanic derived sedimentary rocks.

Intrusive rocks found along the roadway are considered part of the Grays Peak Stock and are compositionally norite and tonalite rock types. Table 1 is a synthesis of geologic units, map symbols, age, and basic descriptions from published geologic mapping within the project vicinity.

As the road alignment loses elevation and curves down toward Granite, the valley widens and becomes less constrained. These areas have significant amounts of placer and dredge-mine tailings piled up along the main drainage next to the road corridor along Bull Run Creek.

Table 1: Synthesis of geologic units, map symbols, and basic descriptions along the Granite Hill Road Reconstruction project.

Geologic Unit

Map Symbol Age Description

Alluvium Qal Holocene, Pleistocene

Unconsolidated, poorly sorted fluvial deposits of gravel, sand, and silt.

Terrace gravel Qtg Holocene, Pleistocene

Unconsolidated to weakly consolidated, poorly sorted fluvial deposits of gravel, sand, and silt at higher levels than present stream flood plains.

Gravel, tuff, tuffaceous sediments

Tgt Miocene- Oligocene

Unconsolidated to weakly consolidated interlayered deposits of gravel and silicic and andesitic tuff and tuffaceous sand and silt.

Basalt Tb Miocene- Oligocene Basalt

Grays Peak Stock KJgp L. Cretaceous, U. Jurassic Intrusive satellite of Bald Mountain Batholith; norite and tonalite.

Mixed rock terrane mt, sp varies

Structurally chaotic assemblage of rocks with differing compositions and ages; serpentinite, peridotite, basalt, gabbro, diorite, limestone.

Elkhorn Ridge Argillite TRPer

Triassic, Permian, Pennsylvanian

Mainly dark colored argillite with chert some felsic tuff, sandstone, and conglomerate. Multiple episodes of structural deformation and metamorphosis.

Geologic Hazards

Our research did not discover any published geologic hazard maps for the vicinity and within the Statewide Landslide Information Database for Oregon (DOGAMI, 2020). Geologic maps have potential landslides near the project area, but nothing was identified during our literature review or was observed during our site visits within the project corridor.

SUBSURFACE INVESTIGATION

Geotechnical Drilling

A subsurface exploration program to support the design and construction of the project was completed on the project between April 13 and 22, 2020. Eight geotechnical subsurface borings and 22 subgrade borings were drilled and sampled on-site 2020, by Haz-Tech Drilling Incorporated with a truck-mounted CME 75 drill rig. Geotechnical logging services were subcontracted through Haz-Tech Drilling with Materials Testing and Inspection (MTI). Figures A- 2 through A-6 show satellite images of the locations of the borings. Table 2 lists coordinates, station, depths, centerline offsets, and brief descriptions of each boring location. Borings denoted with the prefix SG are subgrade borings, and this memorandum does not discuss information from these borings. Boring logs, field rock core photos, and lab results are provided in GR04-21

The following site conditions are discussions taken directly from Geotechnical Memorandum GM43-20, Granite Hill Road Reconstruction Preliminary Geotechnical Investigation Results, dated August 28, 2020. This memorandum italicizes these discussions.

One geotechnical boring was drilled at the AOP Bull Run Creek Crossings No. 1 and 2, and two were drilled at the AOP Boundary Creek Crossing. One boring was also drilled at each bridge abutment. Geotechnical borings were advanced between 17.5 feet to 85.0 feet below the ground surface.

Table 2: Borehole ID coordinates, station, depths, centerline offsets, and brief descriptions of borings.

Borehole

ID

Coordinates1 Station2 Centerline Offset (ft)

Depth

(ft) Description

Latitude Longitude BH20-02 44.7756 -118.3444 244+94 Left (8) 35.5 Bull Run Cr. Crossing No.1, AOP

BH20-03 44.7801 -118.3501 270+57 Left (8) 39.5 Bull Run Cr. Crossing No.2, AOP

BH20-04A 44.7874 -118.3749 343+49 Right (8) 17.5 Redrill of BH20-04

BH20-04 44.7874 -118.3749 343+63 Right (8) 21.5 Boundary Cr. Crossing, AOP

BH20-05 44.7892 -118.3876 379+15 Right (8) 50.0 Bull Run Cr. Crossing No.3, Bridge

BH20-06 44.7891 -118.3875 379+59 Left (8) 50.0 Bull Run Cr. Crossing No.3, Bridge

BH20-07 44.8078 -118.4224 494+51 Left (6) 85.0 Bull Run Cr. Crossing No.4, Bridge

BH20-08 44.8076 -118.4226 495+39 Right (6) 70.0 Bull Run Cr. Crossing No.4, Bridge

Notes:

1 Coordinates based on WGS 84 mapping.

2 Stations are approximate

SITE CONDITIONS

General

The roadway crosses mountainous terrane with the project beginning at 5,710 feet elevation and dropping to 4,575 feet elevation at the project end. The roadway crosses numerous drainages with large embankment fills and there are roadway cuts in both soil and bedrock.

Mostly vegetated embankment slopes ranged from 34 to 36 degrees and had slope distances up to 100 feet. Fill slopes were observed to be performing well in their current condition, although some slightly steeper areas exhibit minor creep and sloughing movement when not vegetated.

As noted, only minor embankment creep and sloughing was observed.

Natural slopes observed along the alignment appear to be performing well with no indication of large-scale instability. Similarly, existing roadway cut slopes are generally performing well with no evidence of global instability. However, in some areas, over-steepened cuts in rock overlain by soils were observed from 40 to 80 degrees and at least 75 feet high with little to no vegetation. Raveling-type rockfall is associated with these slopes, but discussions with

Grant County Maintenance did not identify any problematic or nuisance sites. Roadway ditches reportedly, and appear to, catch most rockfall generated from raveling of soil overlying rock slope material from those cut slopes.

In some circumstances, similar to the one described above, debris within ditches is affecting drainage flow and efficiency. As ditches fill with debris, water flow is impeded, allowing water to pond and seep into the adjacent roadway base and subgrade leading to possible structural weakening impacting overlying pavement. Adding to impeded water flow, debris filled ditches also have less catchment for raveling and falling slope material. Ditch vegetation growth can also impede drivers’ site distance.

Some stretches of the alignment are in low gradient areas, such as meadows, where positive drainage away from the roadway is difficult. Also, along the lower stretch of the alignment Bull Run Creek flows close to the road in some locations.

Dredge and placer mine tailings at the confluence of Boundary Creek with Bull Run Creek were investigated as a potential material source; it is designated as the Boundary Creek tailings area for ease of discussion. This area runs along Bull Run Creek on WNF managed land but has active mining claims for mineral rights. Grab samples of material were collected at this site (GB20-01) for its characterization and aggregate quality testing.

Tailings in the site were river transported before placement and consist of silt, sand, and gravel with cobble to boulder sized (up to 3 feet) material of varying lithologies. All material in this location has been displaced from dredge mining of in-situ river sediments and piled-up at its current location. Minimal vegetation is currently growing on the tailing piles.

Bull Run Creek Crossing No.1, Station 244+66, AOP

Bull Run Creek flows northward under the roadway, which is skewed approximately 48 degrees to the channel. The current crossing is an existing 60-inch by 90-inch corrugated metal pipe (CMP) arch culvert. A concrete box culvert is planned as a replacement at this crossing.

The location of this crossing is near a geologic contact between the Elkhorn argillite rock unit down station and the intrusive Gray’s Peak Stock tonalite rock unit up station. The tonalite is observable in a road cut bank outcrop directly up station of the crossing. The argillite bedrock exhibits more metamorphism due to proximity of the intrusive igneous rock unit east of the site.

The channel is moderately constrained in this location with banks mostly vegetated with trees, shrubs, and grasses with little exposed soil. Surficial channel material was seen to be sand with gravel, and cobbles and some silt. Boulders up to 4 feet in dimension were observed in the channel, but larger (up to 10 feet in dimension) were observed in the meadow above the channel banks and are likely within the channel as well.

Subsurface conditions were observed and documented in boring BH20-02 on the northwest bank. Underground utilities were located under the northern shoulder. Roadway fill composed of dense, poorly graded SAND and GRAVEL with clay was interpreted to a depth of 3.8 feet. In-situ, medium dense to very dense poorly graded GRAVEL with clay and sand was observed from 3.8 to 12 feet bgs, where argillite rock (metamorphosed siltstone, i.e. slate) was encountered. The rock unit was characterized as very weak to weak down to 25.5 feet bgs.

Groundwater was encountered approximately 4 feet bgs, about the elevation of Bull Run Creek.

Roadway fill was interpreted to a depth of 3.8 feet with in-situ CLAY and silt supporting cobbles below the fill.

Bull Run Creek Crossing No.2, Station 270+08, AOP

Bull Run Creek flows eastward under the alignment at this location with the roadway skewed approximately 55 degrees to the channel. The current crossing is an existing 84-inch by 120-inch CMP arch culvert and a concrete box culvert is planned as a replacement at this crossing.

The location of this crossing is mapped as the Elkhorn argillite rock unit.

The channel is moderately constrained at this location with banks mostly vegetated with trees, shrubs, and grasses and little exposed soil. Surficial channel material was seen to be sand with gravel, and cobbles and some silt. Boulders up to 3 feet were observed in the channel, but larger (up to 4 feet in dimension) were observed above the channel banks and are likely within the channel as well. Some large woody debris was observed downstream of the crossing on the upper banks of the channel. Deep Creek confluences with Bull Run Creek approximately 400 feet upstream from this creek crossing.

Subsurface conditions were observed and documented in boring BH20-03 on the northwest bank. Medium dense to very dense, poorly graded GRAVEL with clay and sand fill was interpreted to 5.0 feet bgs. In-situ dense to very dense, poorly graded GRAVEL with clay and sand was observed below 5.0 feet to a depth of 26.6 feet. Weak to moderately strong argillite rock was encountered at 26.6 feet bgs. Groundwater was encountered about 5.5 feet bgs, approximately the elevation of Bull Run Creek. Underground utilities are located at this site as well.

Subgrade boring SG20-13 was also drilled approximately 245 feet up station of BH20-03.

Aggregate base, poorly graded GRAVEL with clay and sand, was observed to 0.6 feet bgs.

Clayey GRAVEL with sand supporting 6-inch minus cobbles is interpreted as roadway fill to a depth of 5.0 feet. Groundwater was observed at 3.8 feet bgs in this subgrade boring.

Boundary Creek Crossing, Station 343+55, AOP

Boundary Creek flows southward under the roadway at this location with the alignment 45 degrees to the channel. The current crossing is an existing 48-inch by 60-inch CMP culvert. A concrete box culvert is planned as a replacement at this crossing. The location of this crossing is mapped as the Elkhorn argillite rock unit.

The channel is within an alluvial fan and not well constrained at this location. The area has been dredge and placer mined, particularly below the crossing along Bull Run Creek. Piles of dredge and placer mine tailings are located throughout the area south of the crossing and are approximately 10 feet to 20 feet above the channel elevation. Boulders up to 4 feet in dimension were observed in the mine tailings. Mine tailing piles currently deflect Boundary Creek westward and confine the creek near the base of the roadway alignment’s embankment for approximately 600 feet.

Banks are vegetated with trees, shrubs, and grasses, but exposed soils were observed at numerous locations along the channel above and below the crossing. This is due to the unconsolidated nature of the mine tailings. Surficial channel material was seen to be sand with gravel, and cobbles and some silt. Boulders up to 3 feet were observed in the channel, but larger (up to 4 feet in dimension) were observed above the channel banks and are likely within the channel as well.

Subsurface conditions were observed and documented in borings BH20-04 and BH20-04A on the southwest bank. These borings were drilled near each other with an approximate 15-foot offset. Medium dense to dense, poorly graded GRAVEL with clay and sand fill was interpreted to 4.0 feet bgs. Loose to medium dense, clayey GRAVEL and SAND was encountered with zones of firm to very stiff, gravelly and sandy fat CLAY or elastic SILT was encountered below the fill from approximately 4.0 feet to at least 21.5 feet bgs. Observations from borings BH20-04 and BH20-04A suggest subsurface conditions are not uniform and highlight the indeterminate nature of an alluvial fan depositional environment at this site. Groundwater was observed between 8.0 feet and 19.7 feet bgs during drilling.

Bull Run Creek Crossing No.3

Bull Run Creek flows northward under the alignment at this location with the roadway skewed approximately 65 degrees to the channel. The current crossing is an existing 84-inch by 120-inch CMP arch culvert. An approximate 54-foot single span bridge is planned as a replacement at this crossing. The location of this crossing is mapped as alluvial and river terrace deposits overlying silicic volcanic flows or serpentinite derived from a peridotite rock unit.

The channel is not well constrained at this location with banks mostly vegetated by shrubs, grasses, and a few trees. Exposed soil was observed along stream cut banks directly downstream of the crossing. Surficial channel material was seen to be sand with gravel and silt supporting cobbles and boulders up to 3 feet in dimension. Boulders up to 4 feet were observed above the channel banks and are likely within the channel as well. Dredge and placer mine tailing piles are located downstream of this crossing also.

Subsurface conditions were observed and documented in borings BH20-05 and BH20-06. Due to overhead utilities at this site both borings were located on the south side of the roadway (east and west banks of the channel. Loose to dense, poorly graded GRAVEL with clay and sand fill was observed from 7.0 feet (BH20-06) to 11.0 feet (BH20-05) bgs. In-situ loose to very dense, silty SAND (with and without gravel) was observed overlying extremely weak to moderately strong, silicic volcanic breccia rock between 17.7 feet (BH20-05) and 21.6 feet (BH20-06) depth.

Groundwater was encountered about 7.6 feet bgs in BH20-05 and 7.0 feet in BH20-06; similar elevation of Bull Run Creek.

Bull Run Creek Crossing No.4

Bull Run Creek flows westerly under the alignment at this location with the roadway skewing approximately 25 degrees to the channel. The current crossing is an existing 84-inch by 120-inch CMP arch culvert. An approximate 105-foot single span bridge is planned as a replacement at this crossing. The location of this crossing is mapped as alluvial and river terrace deposits overlying silicic volcanic flows.

The channel is meandering within a meadow and not constrained at this location with banks mostly vegetated with grasses and very few trees and shrubs. Little exposed soil was observed along the low stream banks. Surficial channel material was observed to be silty sand with gravel and some clay supporting cobbles and boulders up to 1 foot in dimension.

Boulders up to 2 feet were observed above the channel banks and are likely within the channel as well. Due to the nature of the deposits, it is anticipated that larger boulders will be present and should be anticipated. Dredge and placer mine tailing piles are located around this crossing as well.

Subsurface conditions were observed in borings BH20-07 and BH20-08. Boring BH20-07 was located on the southeast bank of the creek and BH20-08 was placed on the northwest bank of the creek. Roadway fill was observed to a depth of about 9 inches and is a medium dense, poorly graded GRAVEL with clay and sand. It transitions to a loose, medium dense, clayey GRAVEL with sand to a depth of 7 feet bgs (BH20-07) and 8 feet bgs (BH20-08). In-situ soils observed below the roadway fill are similar in both borings but described separately below.

Boring BH20-07 has loose, poorly graded SAND with clay and gravel to a depth of 12.5 feet bgs, and then transitions to a loose, silty SAND to 15 feet bgs. Underlying this material are very stiff, fat CLAY and SILT layers interpreted as completely weathered (to a residual soil) andesitic rock. More competent, but extremely weak to weak weathered andesitic rock was encountered approximately 53.5 feet bgs. Groundwater was observed and recorded at 8.4 feet bgs.

Boring BH20-08 has a soft SILT to 9.5 feet bgs, and transitions to a stiff, sandy SILT to 14.5 feet bgs. Completely weathered rock was encountered between 14.5 and 18 feet bgs and is described as a stiff, sandy lean CLAY. From 18 to 31 feet bgs a very stiff, elastic SILT with sand was encountered before more competent, but extremely weak to weak, andesitic rock was encountered at a depth of 31 feet bgs. Groundwater was observed and recorded at 10.8 feet depth.

CORROSION

Factors that influence the rate and amount of corrosion include:

• The amount of moisture.

• The conductivity of the solution (soil and/or water).

• The hydrogen activity of the solution (pH).

• The oxygen concentration (aeration).

The presence of high acidity in the soil can react with the lime in concrete to form soluble reaction products that leach out of the concrete. Resistivity testing is an indicator of a corrosive environment. Chloride ions from soil, water, or de-icing salts can lead to the corrosion of steel reinforcement in concrete and steel structures. Sulfate ions react with lime in the concrete, which forms the growth of minerals caused by a reaction of chemicals in the cement that causes concrete to soften and crack. Sulfate ions may lead to accelerated corrosion of steel reinforcements.

According to AASHTO BDS, Article 5.10.1, corrosive water or soil contains more than or equal to 500 parts per million (ppm) chlorides. Sites considered corrosive due solely to sulfate content greater than or equal to 2000 ppm and/or a pH of less than or equal to 5.5 are considered non-corrosive in determining minimum concrete cover.

Article 5.14.2.4 further discusses water-soluble sulfates in the soil above 0.1 percent (1,000 ppm) or sulfates in water above 150 ppm and recommends special construction procedures, including avoiding construction joints at low and upper water levels. Special concrete mixes may be justified for sulfate content above 0.2 percent (2,000 ppm) in soil or 1,500 ppm in water.

AASHTO BDS, Article 10.7.5, states the following conditions should be considered as indicative of a potential pile deterioration or corrosion situation:

• resistivity less than 2,000 ohm-cm,

• pH less than 5.5,

• pH between 5.5 and 8.5 in soils with high organic content,

• sulfate concentrations greater than 1,000 ppm,

• soils subject to mine or industrial drainage.

The following criteria for water conditions should be considered as indicative of a potential pile deterioration or corrosion situation:

• chloride content greater than 500 ppm,

• Sulfate concentration greater than 500 ppm, or

• pH less than 5.5,

• mine or industrial runoff,

• high organic content.

Table 3 shows select samples submitted for pH, resistivity, sulfate, and chloride testing to determine if the soils within the project contained markers for aggressive soils. Based on the markers discussed above, none of the sulfate or chloride markers were met for soil concentrations. Only sample S-3 from boring BH20-04 met the marker for a pH level below 5.5 in soil. A sample, not shown in Table 3, from boring BH20-08 between 8 and 8.9 feet, was the only sample tested for organics, and the result of the organic content test was 8.02 percent.

Three samples met the requirements based on resistivity testing for pile deterioration or corrosion potential. These samples include BH20-04, sample S-5, BH20-07, samples S-8 and S-10, and BH20-07, samples S-15 and S-16.

Table 3: Corrosive Soils Laboratory Test Results.

Boring ID Sample

Depth ft.

pH

Resistivity Ohm-cm

Sulfate ppm

Chloride ppm

BH20-04 S-3 5.0-6.5 5.2 2800 3.5 122

BH20-04 S05 10.0-11.5 7 - - -

BH20-04 S-7 15.0.16.5 7.4 410 3.4 613

BH20-04 S08B 18.0-19.0 7.8 - - -

BH20-04A S02 10.0-11.5 6.9 7300 4.6 9.5

BH20-05 S-3, S-4, & S-7 7.5-9, 10-11.5, & 15-15.4 5.9 3500 3.5 52.1

BH20-05 S06 13.2-14.0 7.1 - - -

BH20-06 S04 10.0-11.5 6.6 - - -

BH20-06 S-5B, S-6, & S-8 12.5-14.0,15-15.8, &20-20.3 6.8 3200 13.6 7.2

BH20-07 S-8 & S-10 15.0-16.5 & 25-26.5 6.1 890 2.3 6.8

BH20-07 S-15 & S-16 45.0-46.5 & 50.0-52.0 7.8 1250 <2 8.9

BH20-08 T-1 9.0-11.0 6.5 4000 4 35.3

SCOUR

Scour elevations were provided by the WFLHD Hydraulics Group in the Bull Run Creek Crossing No. 3 and 4, Design Hydraulics Memorandums, dated September 2, 2020. Based on preliminary scour calculations, the 100-year and 500-year total scour elevations are 4663.6 and

4662.7 feet for Crossing No. 3 and 4560.3 and 4559.9 feet for Crossing No. 4, respectively.

SITE SEISMICITY

The procedures outlined in Section 3.10 of the 9th Edition of the AASHTO LRFD Bridge Design Specifications (BDS) were followed to characterize the seismic hazard. The seismic hazard at the site and the importance of the proposed bridge dictate the level of seismic analysis that is required for the design. The seismic hazard principles within the AASHTO BDS are that bridges shall be designed to have a low probability of collapse but may suffer significant damage and disruption to service when subject to earthquake ground motions with a 7-percent probability of exceedance (PE) in 75 years. Partial or complete replacement may be required (AASHTO, 2020).

According to the USGS Quaternary Fault and Fold Database for the United States, the Sumpter Valley, Fault ID 711, is a middle to late Quaternary, normal fault. The western mapped terminus of this fault is located about 8.5 and 10.8 miles east-southeast from Bull Run Creek Crossings No.1 and No. 3, respectively. The West Baker Valley, Fault ID 804, is a late Quaternary, normal fault located about 16 miles north-northeast from the closest structure. According to AASHTO BDS Article 3.10.2.2, a site-specific study of a near-field motion is required if the project site is less than 6 miles from an active fault. Therefore, no site-specific analysis was performed.

Based on the AASHTO procedures and the N60 standard penetration resistance in the top 100 feet of the soil profile at the project site, we recommend a Site Class of “D” for bridge sites. The Unified Hazard Tool website (USGS, 2022) was used to determine the base peak ground acceleration and spectral accelerations at the project site for the underlying rock. The spectral accelerations were then scaled to Site Class D using the site factors recommended by AASHTO to represent the seismic accelerations amplified at the ground surface. The results of this analysis are presented in Tables 4 and 5 for bridge sites No. 3 and No.4, respectively. The difference between the results of SS, AS, SDS, and SD1 from each site is no more than 0.001g.

The values in Table 4 were used to develop the 5-percent-damped-design response spectrum shown in Figure 2 below for the project site. The data set obtained in this analysis is from the Unified Hazard Tool website, Dynamic: Conterminous, version 3.3.3.

Table 4: Summary of Seismic Parameters (7-Percent PE in 75 Years) Bull Run Creek Crossing No.3.

Parameter Value Site Latitude 44.78915°

Site Longitude -118.3855° Site Class D

Horizontal Peak Ground Acceleration on Site Class B Rock (PGA) 0.1 g Horizontal Response Spectral Acceleration at a Period of 0.2 sec on Site Class B Rock (Ss) 0.227 g Horizontal Response Spectral Acceleration at a Period of 1.0 sec on Site Class B Rock (S1) 0.073 g

Mapped Peak Ground Acceleration Coefficient (FPGA) 1.6 g Mapped Short-Period Spectral Acceleration Coefficient (Fa) 1.6 g Mapped 1-sec Period Spectral Acceleration Coefficient (Fv) 2.4 g

Scaled Peak Ground Acceleration for Project Site, Site Class C (As) 0.16 g Scaled Horizontal Response Spectral Acceleration at a Period of 0.2 sec for Project Site, Site Class C (SDS) 0.363 g Scaled Horizontal Response Spectral Acceleration at a Period of 1.0 sec for Project Site, Site Class C (SD1) 0.175 g

AASHTO Seismic Zone 2

Table 5 : Summary of Seismic Parameters (7-Percent PE in 75 Years) Bull Run Creek Crossing No.4.

Parameter Value Site Latitude 44.8077°

Site Longitude -118.4225° Site Class D

Horizontal Peak Ground Acceleration on Site Class B Rock (PGA) 0.1 g Horizontal Response Spectral Acceleration at a Period of 0.2 sec on Site Class B Rock (Ss) 0.226 g Horizontal Response Spectral Acceleration at a Period of 1.0 sec on Site Class B Rock (S1) 0.073 g

Mapped Peak Ground Acceleration Coefficient (FPGA) 1.6 g Mapped Short-Period Spectral Acceleration Coefficient (Fa) 1.6 g Mapped 1-sec Period Spectral Acceleration Coefficient (Fv) 2.4 g

Scaled Peak Ground Acceleration for Project Site, Site Class C (As) 0.159 g Scaled Horizontal Response Spectral Acceleration at a Period of 0.2 sec for Project Site, Site Class C (SDS) 0.362 g Scaled Horizontal Response Spectral Acceleration at a Period of 1.0 sec for Project Site, Site Class C (SD1) 0.176 g

AASHTO Seismic Zone 2

Figure 2: 5-Percent-Damped-Design Response Spectrum Bull Run Creek Crossings No. 3.

LIQUEFACTION

Following the AASHTO BDS Article 10.5.4.2 procedures, this site was determined to be in Seismic Zone 2. There is a potential for liquefaction in Seismic Zone 2 where loose to very loose saturated sands (e.g., (N1)60 is less than ten blows per foot (bpf) are present to a sufficient extent within the subsurface profile and the acceleration coefficient, As, is 0.15 or higher. Based on the soil stratigraphy and seismic hazard; it is our opinion that a liquefaction analysis is not needed.

FOUNDATION DISCUSSION

Both shallow and deep foundation concepts were considered to support the bridges on this project. The major factors considered when evaluating foundation alternatives were site conditions, subsurface conditions, scour, design loading, constructability, and cost.

Due to the proximity of Bull Run Creek and the required excavation depth, a consensus between WFLHD Structural and Geotechnical Groups is that both bridges will be supported on deep foundations. Both driven piles and drilled shafts are feasible deep foundation options;

however, with typical costs for drilled shaft construction, a driven pile foundation is the preferred option. It is typically more cost and time effective to install driven piles when compared to drilled shafts.

Final Foundation Loads

Final bridge loads per abutment were provided by the WFLHD Structural Group on 6/22/2023 and are summarized below:

• Bull Run Creek Bridge Site 3 o Unfactored Load – 369 kips o Factored Service I Load – 369 kips o Factored Strength I Load – 540 kips

• Bull Run Creek Bridge Site 4 o Unfactored Load – 722 kips o Factored Service I Load – 722 kips o Factored Strength I Load – 1,016 kips

Final Driven Piling Recommendations

The 95% plan set show HP10X57 piles for both bridge locations, with 5 piles per abutment. At Crossing No 3 breccia was encountered approximately 18 feet below the ground surface at abutment 1 and andesite was encountered at approximately 22 feet below the ground surface at abutment 2. It is recommended to drive the piles to these units.

At Crossing No. 4 andesite was encountered approximately 54 and 31 feet below the ground surface at abutment 1 and abutment 2, respectively. It is recommended to drive the piles to these units. If the required nominal capacity is achieved above the andesite unit at abutment 1, it is acceptable to stop pile driving once the required minimum tip elevation is reached.

Because it is recommended to drive the piles to rock units, it is expected the structural capacity of the pile will limit the pile resistance. Geotechnical recommendations have been developed based on this design condition. The Structures group should confirm the piles are adequately sized to resist the required nominal capacities.

It is recommended to perform wave equation analyses for drivability analyses and pile acceptance. A resistance factor of φ = 0.65 is recommended. This resistance factor is higher than the typical φ = 0.5 and is based on the anticipated driving of the piles to rock and Design and Construction Recommendations for Steel Driven Piles in Intermediate Geomaterials (Ng et al., 2023).

Table 6 presents final pile recommendations. The recommendations in this table attempt to capture some site uncertainty. The minimum pile tip elevations are slightly higher than the elevations bedrock was encountered in the borings, while the estimated tip elevation is slightly lower. The intent is for the piles to be driven to rock or weathered rock where the explorations encountered refusal blowcounts while obtaining soil samples.

Table 6: Pile Recommendations for Bull Run Crossing Nos. 3 and 4

Abutment Minimum Pile Tip Elevation (ft)

Estimated Pile Tip Elevation (ft)

Required Nominal Capacity (kips)

Crossing No.3, Abutment 1 (East) 4,662 4,656 167 Crossing No.3, Abutment 2 (West) 4,662 4,651 167 Crossing No.4, Abutment 1 (South) 4,536 4,520 355 Crossing No.4, Abutment 2 (North) 4,548 4,540 355

Settlement

The settlement at the bottom of the pile cap elevation due to service limit state load is anticipated to be less than ½ inch.

Lateral Analysis

Table 7 provides the recommended soil parameters to analyze lateral foundation loads at Crossings No.3 and No.4. The values in these tables do not include load factors. A resistance factor of 1.0 is specified in AASHTO BDS Table 10.5.5.2.3-1 for horizontal geotechnical resistance of a single pile or shaft or pile group. Ground slope effects can be accounted for in the L-Pile parameters by the input of the ground surface inclination. Group effects can be modeled in L-Pile by applying an appropriate p-modifier. The p-modifier is a function of the center-to-center spacing, where D is the width of the pile, and is provided in Table 10.7.2.4-1 of the AASHTO BDS.

Table 7: Recommended Soil Parameters for Lateral Analyses.

Elevation Soil Unit LPILE Material γ’ ϕ’ c kpy Ɛ50

(lb/ft3) (deg) (lb/ft2) (lb/in3) Bull Run Creek Crossing 3, Abutment No. 1

4674’ - 4665’ Submerged Gravel and Sand, medium dense Reese Sand 57 30 - 60 - 4665’ – 4661’ Submerged Silty Sand, loose to dense Reese Sand 57 30 - 50 -

4661’ and below Residual Bedrock grading to bedrock (Breccia) Reese Sand 67 45 0 200 -

Bull Run Creek Crossing 3, Abutment No. 2 4673’ – 4668’ Submerged Grave, medium dense Reese Sand 57 30 - 60 - 4668’ – 4661’ Submerged Silty Sand, very loose Reese Sand 50 26 - 20 -

4662’ and below Submerged Silty Sand, very dense (residual bedrock grading to bedrock) Reese Sand 67 45 - 200 -

Bull Run Creek Crossing 4, Abutment No. 1 4571’ – 4661’ Submerged Sand, loose Reese Sand 50 25 - 50 - 4561’ – 4546’ Submerged Fat Clay Stiff clay w/o free water 60 - 1,500 - 0.010 4546’ – 4537’ Submerged Silt Stiff clay w/o free water 65 - 3000 - 0.005 4537’ – 4523’ Submerged Fat Clay Stiff clay w/o free water 65 - 4000 - 0.004

4523’ and below Andesite, R0-R2, Poor Strong Rock 75 qu - = 1,500 psi Bull Run Creek Crossing 4, Abutment No. 2

4570’ – 4557’ Submerged Sandy Silt Reese Sand 55 26 - 20 - 4557’ – 4544’ Submerged Elastic Silt Stiff Clay w/o free water 60 - 1,000 - 0.010

4544’ and below Andesite, R2, Fair Strong Rock 75 qu - = 1,500 psi

NOTES:

γ’ – Effective unit weight kpy – Reaction modulus (p-y modulus) ϕ’ – Effective internal angle of friction Ɛ50 – soil strain at 50% maximum deviatoric stress c – Cohesion qu – Uniaxial compressive strength

AQUATIC ORGANISM PASSAGE STREAM CROSSINGS

Three aquatic organism passages are proposed for this project. The following section discusses AOP recommendations based on the 95% plan set.

Bull Run Creek Crossing, AOP No.1

The proposed 15-foot by 9-foot AOP is located at ~STA 244+66 with 12-foot-long wing walls.

The elevation of the top of the bedrock at the outlet side is unknown. Boring BH20-02 was performed at this site from the existing roadway and encountered sands and gravels with cobbles over bedrock. Slightly to highly weathered, very weak to moderately strong argillite rock is expected to be encountered during the excavation of this AOP and wing walls at this site.

Bull Run Creek Crossing, AOP No.2

The proposed 22-foot wide, 9-foot high, and 56-foot long AOP is located at ~STA 270+09 with 12-foot-long wing walls. Boring BH20-03 was performed at this site. The AOP and wing wall footings are expected to bear on very dense, poorly graded gravel with clay and sand. Cobbles measuring 3 to 12 inches and boulders measuring up to 5-feet in diameter were encountered in this boring. Bedrock underlies the gravel and sand at depths beyond the expected excavation.

Boundary Creek Crossing, AOP No.3

The proposed 13-foot wide, 12-foot high, and 34-foot long AOP is located at ~STA 343+55 with12-foot-long wing walls. Borings BH20-04 and BH20-04A were performed at the site and a wide range of materials including gravels, sands, silts and clays ranging from firm/medium dense to very dense. Boulders up to 4 feet in diameter were observed in the vicinity.

Bearing Capacity

Bearing capacity for shallow foundations was determined using AASHTO BDS section

10.6.2.5.1 Settlement Analysis for Service Limit State Design. The presumptive bearing resistances for each site are shown below and are limited for settlement up to 1 inch.

• AOP No.1 - Slightly weathered, very weak to moderately strong (R1 to R3) bedrock, 12 ksf,

• AOP No.2 - Dense clayey sand and gravel, 10 ksf,

• AOP No.3 - Gravelly or sandy fat clay, clayey gravel, or elastic silt, 3 ksf.

Zones of soft clays or silts may be encountered with in the excavations, particularly at Boundary Creek. Soft clays are silts are considered unstable/unsuitable and should be excavated and replaced with foundation fill.

Wingwalls

Rigid, restrained walls or bridge abutments that can tolerate little or no movement should be designed for the at-rest earth pressure (Po). Structures able to tolerate sufficient rotation at the top of the wall or lateral translation equal to or greater than 0.002 times the wall or abutment height should be designed for an active-lateral-earth pressure (Pa). The resultant lateral load due to the earth pressure is assumed to act at a height of H/3 above the base of the wall.

Unbalanced groundwater behind walls and abutments adds significant lateral pressure and should be avoided by using permeable backfill and a free draining gravity outlet for water.

Backfill in the immediate vicinity of the retaining structure should consist of structural backfill in accordance with subsection 704.04.

The soil parameters listed in Table 8 may be used to determine the lateral earth pressures exerted on the wing walls.

Table 8 - Recommended Soil Parameters for Wingwall Design

Description Value

Minimum Depth for Frost 2 ft Assumed design depth for bearing, Df 2 ft

Backfill Soil Angle of Internal Friction, φb’ 34 deg

Backfill Moist Unit Weight, γb 130 pcf

At-Rest Earth Pressure Coefficient, K0 (Flat backslope only) 0.44

At-Rest Equivalent Fluid Pressure (Flat backslope only) 57 psf/ft

Active Earth Pressure Coefficient, Ka (Flat / 1V:2H backslope) 0.28 / 0.42

Active Equivalent Fluid Pressure (Flat / 1V:2H backslope) 37 / 54 psf/ln.ft Passive Earth Pressure Coefficient, Kp (at culverts locations, if scour is not expected) 6.15

Passive Equivalent Fluid Pressure (at culverts locations if scour is not expected) 369 psf/ft The above values are unfactored.

Foundation Fill per FP-14 subsection 704.01 should be used within a 1:1 splay beneath foundations unless the footings are founded on rock. Structural Backfill per FP-14 Subsection

704.04 should be used as backfill behind abutment foundation walls and wing walls.

Geocomposite sheet drains connected to a perforated footing drainpipe should be installed behind abutment/walls and drained to daylight to ensure adequate drainage.

CONSTRUCTION CONSIDERATIONS

Excavation

Excavations at the sites will encounter a wide range of soils. Gravels with varying amounts of cobbles, sand, silt, and clay are expected to be the most common soils encountered. However, sands, silts and clays were encountered in the explorations should also be expected. Boulders up to 5 feet in diameter were encountered in borings and similar sized boulders were noted within the streams and adjacent to the proposed crossings. A boulder 10 feet in dimension was observed near Bull Run Crossing No. 1. The contractor should be prepared to encounter large boulders and break them down, if required, to complete the required excavations.

Bedrock is expected near the elevation of the Bull Run Creek Crossing No. 1 wingwall footings and bottom of culvert. The contractor should be prepared to encounter and excavate bedrock at this location. It is expected a hydraulic ram or similar methods will be required to break up the bedrock to facilitate excavation. Bedrock is not expected to be encountered in excavations at the other project site locations.

Blasting is not allowed to remove bedrock or break up boulders.

Silty sands that run when excavated below groundwater are expected to be encountered at Bull Run Creek Crossing No. 3. These soils are expected below the abutment and wingwalls, but within the elevation of where riprap will be placed.

Excavated material is expected to generally be suitable material for embankment construction.

The contractor should expect to dry material with high fines content to enable proper placement and compaction. Perform structural excavation and backfill according to Section 209.

Dewatering and Shoring

Groundwater is likely to be encountered in the excavations at an elevation similar to the creek elevations. Once the creek is diverted at Bull Run Creek Crossings No.1 and No.2, and Boulder Creek Crossing it is expected submersible trash pumps will be sufficient for dewatering for all required excavations and work elements.

Persistent groundwater is not expected at the bottom elevation of the abutments and wingwalls for Bull Run Creek Crossings No. 3 and No.4. The bottom of the riprap is expected to be approximately 10 feet below the groundwater at these locations. Dewatering with a submersible trash pump is not expected to be successful, particularly at Bull Run Creek Crossing No. 4. The contractor should plan for alternative dewatering methods at these locations or to place the riprap in the wet.

Temporary slope angles and/or the need for shoring for excavation of the AOP and wingwall foundations is the responsibility of the Contractor based on the conditions encountered, traffic/equipment loading above the temporary cut, and other factors under their control during construction.

Pile Driving

Boulders were not observed in the borings at the bridge sites. If boulders are encountered during pile driving they are expected to be shallow enough to be excavated with conventional earth moving equipment. Hard driving conditions are expected as the piles near tip elevation. It is recommended to place driving tips on the H-piles. Pile capacity is expected to increase very rapidly as the piles tip out in rock; care should be taken to avoid overdriving or damaging the piles during installation.

SUMMARY

This memorandum presents final foundation recommendations for the Granite Hill Reconstruction Project.

For question regarding this memorandum, please contact Evan Garich at 360-619-7824 or evan.garich@dot.gov.

mailto:evan.garich@dot.gov

REFERENCES

AASHTO, 2020, AASHTO LRFD Bridge Design Specifications, 9th Edition, American Association of State Highway and Transportation Officials, Washington, D.C.

ACI, 2016, Guide to Durable Concrete, ACI201.2R-16. ACI Committee 201, American Concrete Institute, Farmington Hills, MI.

George, O., 2020, Geotechnical Memorandum GM43-20, Granite Hill Road Reconstruction, Preliminary Geotechnical Investigation Results, dated August 28, 2020, U.S. Department of Transportation, Federal Highway Administration, Western Federal Lands Highway Division.

George, O., 2021, Geotechnical Report GR04-21, Granite Hill Reconstruction Final Geotechnical Recommendations dated April 2021, U.S. Department of Transportation, Federal Highway Administration, Western Federal Lands Highway Division.

Leon, Sven, 2020, Granite Hill (Bull Run Creek Crossing No. 3) Hydraulics Scour Memorandum, dated September 2, 2020, U.S. Department of Transportation, Federal Highway Administration, Western Federal Lands Highway Division.

Leon, Sven, 2020, Granite Hill (Bull Run Creek Crossing No. 4) Hydraulics Scour Memorandum, dated September 2, 2020, U.S. Department of Transportation, Federal Highway Administration, Western Federal Lands Highway Division.

Ng, K., Bin Masud, N., Oluwatuyi, O., Wulff, S., 2023 Design and Construction Recommendations for Steel Driven Piles in Intermediate Geomaterials, Proceedings, Deep Foundations Institute Annual Conference, Seattle, WA, 2023.

USGS, 2020, Sumpter Valley Fault ID: Quaternary fault and fold database for the United States, accessed February 6, 2022, obtained from: http://earthquakes.usgs.gov/natural-hazards/earthquake-hazards/faults.

USGS, 2019, Dynamic: Conterminous U.S. 2008 Seismic Parameters: Unified Hazard Tool website, version 4.2.0, National Seismic Mapping Project (NSHMP), accessed February 6, 2022, obtained from: https://earthquake.usgs.gov/hazards/interactive/index.php, http://earthquakes.usgs.gov/natural-hazards/earthquake-hazards/faults/ http://earthquakes.usgs.gov/natural-hazards/earthquake-hazards/faults/ https://earthquake.usgs.gov/hazards/interactive/index.php