GR15-21 Dickey Creek Bridge Replacement Geotech Recomendations Rev. 1.pdf

Geotechnical Recommendations for Dickey Creek Bridge Replacement (Rev. 1) October 2021

Table of Contents 1-i

Geotechnical Report No. 15-21

Geotechnical Recommendations for Dickey Creek Bridge Replacement (Rev. 1)

GEOTECHNICAL ENGINEERING REPORT

WA KITTITAS 5880(1)

Kittitas County, Washington

October 2021

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Table of Contents iii

TABLE OF CONTENTS

1 INTRODUCTION

1.1 Project Overview

1.2 Scope of Work

1.2.1 Reporting

1.2.2 Geotechnical Investigation

1.3 Project Datums

2 SITE CONDITIONS

2.1 Topography, Drainage, and Vegetation

2.2 Climate

3 SUBSURFACE CONDITIONS

3.1 Site Geology

3.2 Subsurface Investigation

3.2.1 Geotechnical Borings

3.2.2 Test Pits…

3.2.3 Sampling and Testing

3.3 Subsurface Profile

3.3.1 West Abutment

3.3.2 East Abutment

3.3.3 Embankment

3.4 Groundwater Observations

4 LABORATORY TESTING

4.1 Laboratory Testing

5 SEISMIC

5.1 Seismic Hazard

5.2 Liquefaction

5.3 Lateral Spreading

5.4 Surface Rupture

6 ANALYSIS AND RECOMMENDATIONS

6.1 Scour

6.2 Lateral Parameters

6.2.1 Lateral Earth Pressures

6.2.2 Foundations

6.3 Abutments

6.3.1 Downdrag

6.3.2 Settlement

6.4 Global Stability

6.4.1 Static Stability

6.4.2 Seismic Stability

iv Introduction

6.5 Embankment Slopes

7 CONSTRUCTION CONSIDERATIONS

8 LIMITATIONS

9 REFERENCES

LIST OF FIGURES

Figure 1. Dickey Creek Bridge Replacement vicinity map

Figure 2. Mapped geology for the Dickey Creek Bridge Replacement project in Kitittas County, Washington (Tabor, et al., 1982)

Figure 3. 5% Damped Response Sprectra – Site Class B

LIST OF TABLES

Table 1. Monthly Climate Summary for Cle Elum, Washington (USC00451504) from January 1, 1960 to December 31, 2020

Table 2. Summary of boring locations, total depths, and groundwater observations

Table 3. Soil laboratory testing summary

Table 4. Uniaxial compressive strength (UCS) testing summary

Table 5. Summary of Seismic Parameters (7% PE in 75 years) - General Procedure

Table 6. Approximate rock contact elevations

Table 7. Recommended soil parameters for wing walls

Table 8. Recommended soil parameters for lateral analysis of drilled shafts

Table 9. Global stability C/D ratios for west and east abutments

Table 10. Global seismic stability C/D ratios for west and east abutments

Introduction v

Appendices

APPENDIX A

Axial Foundation Capacity Charts

Foundation Global Stability Analysis Results

APPENDIX B

Boring Location Plan

APPENDIX C

Field Classifications for Soil and Rock Boring Logs Test Pit Logs

APPENDIX D

Laboratory Test Reports Rock Core Photos

Introduction 1

1 INTRODUCTION

1.1 PROJECT OVERVIEW

The project area is located 19 miles northeast of Cle Elum, Washington on North Fork Teanaway Road at milepost 2.84. The coordinates of the existing Dickey Creek Bridge are 47.2895° North, 120.8595° West. The total project length is 0.28 miles, which includes realignment of the proposed bridge approaches as shown in Figure 1. Kittitas County will be the primary partner for the project.

The existing Dickey Creek Bridge crosses over the North Fork Teanaway River and consists of a 52-foot-long single span, prestressed concrete girder bridge. One abutment is founded on a spread footing bearing on bedrock, and one abutment is founded on piles. The existing bridge has a travel way width of 24-feet and an overall width of 25-feet. The new roadway alignment and bridge will be relocated approximately 100-feet south. The planned single span replacement bridge will be a concrete bulb-tee girder and with a span length of 135-feet and an increased final grade height of about 3 feet. The new bridge will include two 11-foot lanes with 5-foot shoulders on each side. Proposed earth approach embankments will be constructed on both sides of the new bridge with sides slopes of 1V:2H (vertical:horizontal).

2 Introduction

Figure 1. Dickey Creek Bridge Replacement vicinity map.

1.2 SCOPE OF WORK

1.2.1 Reporting

This report presents the geotechnical engineering recommendations for the replacement of Dickey Creek Bridge. This report is based on information provided by WFLHD Structural and Hydraulic sections and data collected during the subsurface investigation completed in the summer of 2020.

This will be a new structure having the following characteristics:

• Single span

• Overall length of 135 feet

• Overall width of 32 feet

• Two-lane, 22-foot overall travel way width

• Two, 5-foot wide shoulders

• Begin bridge station: 207+49.44

• End bridge station: 208+84.58

1.2.2 Geotechnical Investigation

The geotechnical investigation program was designed to provide information required to adequately characterize the subsurface conditions for the design and construction of the Dickey Creek Bridge. The locations of the geotechnical borings and test pits are shown in Appendix B.

The investigation consisted of two borings near the proposed bridge foundations and six test pits along the alignment of the proposed embankments. The six test pits were completed on June 25, 2020 and were terminated between Elevation 2,378 feet and 2,379.5 feet (depths between 6- and 8-feet below ground surface (bgs)). The two borings, DC20-01 and DC20-02, were completed September 22 and 23, 2020 and were terminated at Elevation 2,344 feet (42-feet bgs) and Elevation 2,345 feet (40.5-feet bgs), respectively.

Laboratory testing of samples collected during investigation operations was performed to evaluate index properties and strength characteristics of the soil and rock. Laboratory testing was completed by FHWA WFL.

1.3 PROJECT DATUMS

The coordinate system is the Washington South SPCS NAD83 CORS96. The vertical datum is based on the NAVD88 GEOID03. All elevations presented in this report are approximate.

4 Site Conditions

2 SITE CONDITIONS

2.1 TOPOGRAPHY, DRAINAGE, AND VEGETATION

The project site is located within the Cascade Mountain Range approximately 8 miles northeast of Cle Elum, Washington. The location of the project site is bound within a confined valley through which the North Fork of Teanaway River flows generally from north to south.

The topography of the surrounding area generally consists of west/east trending valley and ridge sequence. Multiple streams and creeks flow within the surrounding valleys and discharge into the North Fork of Teanaway River. WFL Hydrualics Section estimated the drainage area at the location of Dickey Creek Bridge as 82 square miles. The 100-year flow velocity was estimated at 10 feet/second. WFL Hydraulics Section observed ordinary-high-water channel width to be about 65-feet, which was noted as being wider than the existing bridge span.

West and north of the project site, the densely forested terrain gains elevation with an average slope of 14 percent and maximum slope of 37 percent. The material is generally comprised of landslide deposits and avalanche debris from the 1980 Mt. St. Helens event. The eastern portion of the project site consists of 8.5 acres of generally level ground comprised of grasses. A thin line of trees runs north/south through the center of the cleared area. This location was once a campground that has since been abandoned and likely serves as a flood plain given the ground surface elevation is 2 to 3 feet above the river elevation. the south portion of the project site, west of the river, is comprised of moderately forested terrain that gently slopes down to the south.

The west bridge approach embankment appears to be cut-and-cast into the side of the existing slope. The fill side is primarily vegetated with grasses with a 1V:2H slope and a maximum height of about 25 feet. The east approach embankment appears to be a fill embankment with 1V:2.5H slopes and a maximum height of about 5 feet.

The existing bridge was constructed in 1963 and consists of a 53-foot long prestressed girder bridge. The bridge is currently owned and maintained by Kittitas County (County). The west abutment has experienced scour, and County maintenance where observed to be placing riprap to protect the abutment during the Fall of 2020. Streambed material consists of sands, gravels, and cobbles. Woody debris was also observed within the river channel. Rock outcrops can be observed within the stream channel and surrounding areas.

2.2 CLIMATE

Table 1 summarizes average temperatures, precipitation, and snowfall measurements for the Cle Elum weather station (USC00451504), located approximately 7 miles south of the site.

Table 1. Monthly Climate Summary for Cle Elum, Washington (USC00451504) from January 1, 1960 to December 31, 2020.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual

Average Max.

Temperature (°F)

35.3 41.3 49.2 56.9 65.6 72.2 80.3 80.5 72.5 58.9 43.4 35.2 80.5

Average Min.

Temperature

(°F)

21.7 24.2 28.3 33.5 40.2 47.2 52.0 51.1 42.3 33.8 28.5 22.6 21.7

Extreme Max.

Temperature (°F)

47.9 53.1 63.3 73.3 83.7 89.5 95.2 95.6 87.6 74.6 56.2 47.4 95.6

Extreme Min.

Temperature

(°F)

0.9 6.9 15.8 23.4 28.5 36.2 40.5 39.0 29.1 21.4 13.6 4.5 0.9

Average Temperature

(°F)

28.5 32.8 38.8 45.2 52.9 59.6 66.2 65.8 57.4 46.4 35.9 28.9 46.5

Average Total

Precipitation (in.)

3.6 2.5 1.8 1.3 1.0 0.8 0.4 0.6 0.8 2.0 3.6 4.0 22.5

Average Total

Snowfall (in.)

23.5 12.4 7.3 0.8 0.1 0.0 0.0 0.0 0.0 0.3 11.0 24.6 80.1

3 SUBSURFACE CONDITIONS

3.1 SITE GEOLOGY

The project site is located along the eastern portion of the Central Cascade Mountain Range.

According to the Geologic Map of the Wenatchee 1:100,000 Quadrangle, Central Washington (Tabor, et al., 1982), the site is primarily mapped as “Qs” with “Qkis”, “Qkss”, and “Trl” also mapped in the area.

The “Qs” unit is defined as Sidestream Alluvium (Holocene) described as moderately sorted boulder to pebble gravel composed of the few rock types that outcrop in relatively small drainage basins. The age range is reported as less than 10,000 years old.

The “Qkis” unit is also defined as Sidestream Alluvium (Pleistocene). This unit is specific to Kittitas Valley and is similar to the “Qs” unit. This unit forms distinct terraces on the northern side of Yakima River paired to mainstream outwash (“Qkim”) south of the river. It is traceable up Dry Creek and Green Canyon Creek valleys. The age range is reported as between 18,000 and 140,000 years old.

The “Qkss” unit is another Sidestream Alluvium (Pliestocene) specific to northern Kittitas Valley.

It is described as sand, gravelly sand, and sandy gravel which form broad terraces above the floor

6 Subsurface Conditions of each fork on the Teanaway River. The age range is also reported as between 18,000 and 140,000 years old.

The “Trl” unit is the bedrock mapped in the project area and is considered the lower member of the Roslyn Formation (Eocene). The unit is described as mostly white, weathering to yellowish and pale orange, medium to coarse grained, micaceous, lithic, feldspathic, and lithofeldspathic sandstone with crossbedding, pebble stringers, and cut-and-fill structures. Abundant conglomerate and pebbly sandstone with rounded pebbles of granitic and aphanitic extrusive or hypabyssal rock. The age range is reported as 40 to 44 million years old.

3.2 SUBSURFACE INVESTIGATION

The investigation consisted of two borings near the proposed bridge foundations and six test pits along the alignment of the proposed embankments. The six test pits were completed on June 25, 2020 and were terminated between Elevation 2,378 feet and 2,379.5 feet (depths between 6- and 8-feet below ground surface (bgs)). The two borings, DC20-01 and DC20-02, were completed September 22 and 23, 2020 and were terminated at Elevation 2,344 feet (42-feet bgs) and

Project Site

Figure 2. Mapped geology for the Dickey Creek Bridge Replacement project in Kitittas County, Washington (Tabor, et al., 1982).

Elevation 2,345 feet (40.5-feet bgs), respectively. The boring locations are summarized in Table 2 and shown on the Boring Locations Map in Appendix B. The boring logs are presented in Appendix C.

Table 2. Summary of boring locations, total depths, and groundwater observations.

Exploration No. General Location Latitude Longitude Total

Depth Groundwater Depth/Elev.

DC20-01 West Abutment 47.28921° -120.85966° 42.0 ft. 3.0 ft. / 2,383.0 ft.

DC20-02 East Abutment 47.28941° -120.85923° 40.5 ft. 2.0 ft. / 2,384.0 ft.

TP20-01 West Embankment 47.28877° -120.86046° 7.0 ft. 6.5 ft. / 2,378.5 ft.

TP20-02 West Embankment 47.28889° -120.86018° 7.0 ft. 6.5 ft. / 2,378.5 ft.

TP20-03 West Embankment 47.28911° -120.85965° 8.0 ft. 3.4 ft. / 2,382.6 ft.

TP20-04 East Embankment 47.28934° -120.85925° 6.5 ft. 2.0 ft. / 2,384.0 ft.

TP20-05 East Embankment 47.28951° -120.85887° 6.5 ft. 4.0 ft. / 2,382.0 ft.

TP20-06 East Embankment 47.28971° -120.85847° 7.5 ft. 7.0 ft. / 2,380.0 ft.

3.2.1 Geotechnical Borings

The geotechnical borings were completed by Budinger and Associates of Spokane, Washington over September 22 and 23, 2020. Soil and rock logging was completed by a WFLHD geotechnical engineer. The borings were drilled with a track mounted Geoprobe 7822DT. Borings were advanced with 8-inch diameter hollow stem auger and HQ wireline coring was used to advance the holes and retrieve samples in bedrock. Groundwater readings were taken during drilling.

Borings were backfilled with soil cuttings and bentonite chips following completion.

3.2.2 Test Pits

The test pits were completed by Kittitas County personnel on June 25, 2020. Soil logging was completed by a WFLHD geotechnical engineer. The test pits were advanced using a wheeled backhoe. Groundwater observations were completed during the advancement of the test pits.

Representative bulk soil samples were collected for each soil type encountered. Upon completion, the test pits were backfilled with the excavated soil.

3.2.3 Sampling and Testing

Penetration tests were completed at 2.5-foot to 5-foot intervals in overburden material. The penetration tests consist of using a 140-pound hammer with a 30-inch drop to drive a three inch outside diameter split-barrel sampler 18 inches below the bottom of the bore hole and recording the number of blows for each six-inch increment of penetration. The total number of blows

8 Subsurface Conditions required to drive the sampler the second and third 6-inch intervals is known as the N-value (blows per foot).

Samples collected during all subsurface investigations were transported to the WFL laboratory in Vancouver, Washington by WFL personnel. The samples and draft logs were reviewed by the WFL geotechnical engineer and engineering geologists assigned to the project. Selected samples of soil were submitted to the WFL materials laboratory for testing.

3.3 SUBSURFACE PROFILE

In general, the borings and test pits encountered material interpreted as fill and native alluvial deposits overlying bedrock.

3.3.1 West Abutment

Boring DC20-01 was completed near the west bridge abutment. The subsurface observations for this boring consisted medium dense to dense sand with silt, gravel, and cobbles to Elevation 2,374 feet (12-feet bgs), interpreted as Sidestream Alluvium (Qs). An estimated 24-inch diameter boulder was encountered at Elevation 2,374 feet (10-feet bgs). Underlying the alluvium, the boring encountered moderately to highly weathered, very weak siltstone with interbedded layers of silty clayey sand. At Elevation 2,372 feet (17-feet bgs), the boring encountered an approximately 2-foot thick layer of medium strong siltstone. Underlying the siltstone, weak sandstone was encountered to Elevation 2,363 feet (29-feet bgs), interpreted as Roslyn Formation (Trl). At this elevation, the sandstone generally begins to increase in strength with depth to a medium strong sandstone. The boring was terminated in the medium strong sandstone at Elevation 2,344 feet (42-feet bgs). Ground water was observed at Elevation 2,383 feet (3-feet bgs), which was approximately the same elevation as the nearby Dickey Creek.

3.3.2 East Abutment

In boring DC20-02, located near the east bridge foundation, the boring encountered dense silty gravel with sand and cobbles to Elevation 2,376 feet (10-feet bgs). Underlying the gravel, dense to very dense clayey and silty sand with gravel and cobbles was encountered to Elevation 2,370.5 feet (15.5-feet bgs), interpreted as Sidestream Alluvium (Qs). Underlying the alluvium, the boring encountered very weak sandstone to Elevation 2,364.5 feet (20.5-feet bgs), interpreted as Roslyn Formation (Trl). Similar to DC20-01, the sandstone generally increases in strength with depth to a medium strong sandstone. The boring was terminated at Elevation 2,345 feet (40.5-feet bgs).

Ground water was observed at Elevation 2,384 feet (2-feet bgs), which was approximately the same elevation as nearby Dickey Creek.

3.3.3 Embankment

All test pits generally encountered medium dense to dense sand and gravel with cobbles and boulders up to 24-inches in diameter with varying silt content, interpreted as Sidestream Alluvium (Qs). In TP20-04 and TP20-05 on the east side of Dickey Creek, approximately 1- to 2-feet of fill was encountered. This fill was likely the result of grading that had previously occurred in the area as this location was once a campground. The fill is interpreted as reworked alluvium.

Groundwater was encountered at approximately Elevation 2,383 feet (approximately 3-feet bgs) at TP20-03 and TP20-04, nearest to Dickey Creek. This was observed to be similar to the water level elevation of the Dickey Creek at the time of the investigation. In test pits located further from Dickey Creek, lower ground water was observed at Elevation 2,377.5 feet (6.5-feet bgs) and Elevation 2,379 feet (7-feet bgs) at TP20-01 and TP20-06, respectively. Test pits were terminated between Elevation 2,378 feet and 2,379.5 feet (depths between 6- and 8-feet bgs). All test pits experienced moderate to severe caving of the sidewalls and generally coincided with ground water elevation.

3.4 GROUNDWATER OBSERVATIONS

Water level observations made during the subsurface investigation are summarized in Table 2.

In the borings near the proposed abutments, groundwater was observed at approximately Elevation 2,383 feet, which was similar to the water elevation of Dickey Creek at the time of drilling. As observed in the test pits, the groundwater level decreased as the test pits moved further from the creek. The furthest tests pits from the river, TP20-01 and TP20-06, were located approximately 300 feet from Dickey Creek, and groundwater was observed at approximately Elevation 2,379 feet.

4 LABORATORY TESTING

4.1 LABORATORY TESTING

Selected split-barrel soil samples, rock cores, and bulk samples from tests pits were submitted to the WFLHD Materials Laboratory for routine laboratory testing. Laboratory test results are discussed below, and test reports are contained in Appendix D.

The following laboratory tests were performed on the selected soil and rock samples:

• Soil Classification (AASHTO M145)

• Sieve Analysis (AASHTO T11/T27)

• Atterberg Limits (AASHTO T89/T90)

• Specific Gravity (AASHTO T100)

• Moisture Content (AASHTO T265)

• Organic Content (AASHTO T267)

• Resistivity (AASHTO T288)

• pH of Soil (AASHTO T289)

• Uniaxial Compressive Strength, Rock (ASTM D7012 Method D)

The results of the soil tests were used to classify the samples according the Unified Soil Classification System (USCS). The USCS classification is reported on the boring logs. A summary of the soil testing results is presented in Table 3. The soil types displayed in Table 3 varied but primarily consisted of silty, clayey Sand, silty, clayey Gravel, or lean Clay with sand. Table 4 presents the results of the Uniaxial Compressive Strength (UCS) tests completed on select rock samples.

10 Seismic

Table 3. Soil laboratory testing summary.

Test Tests Completed Range of Values

AL – Plastic Limit 10 NP to 21%

AL – Liquid Limit 10 NP to 28%

AL– Plasticity Index 10 NP to 7%

Moisture Content 4 4.7% to 13.6%

Organic Content 8 1.9% to 3.9%

Resistivity 4 4,200 to 12,000 ohm-cm pH 4 6.5 to 7.1

Table 4. Uniaxial compressive strength (UCS) testing summary.

Material Tests Completed

Range of UCS Values (psi) Average UCS (psi) Average ISRM

1981 R Scale

Siltstone 1 4,390 4,390 R3

Weathered Sandstone 2 1,790 to 2,080 1,935 R2

Sandstone 8 2,870 to 6,770 4,026 R3

5 SEISMIC

5.1 SEISMIC HAZARD

The General Procedure outlined in Section 3.10.2 of the AASHTO LRFD Bridge Design Specifications, 9th Edition (2020) was followed to characterize the seismic hazard. The General Procedure uses mapped gridded values of peak ground acceleration (PGA), 0.2 second spectral acceleration, and 1.0 second spectral acceleration to develop the 5-percent-damped-design response spectrum.

These procedures use a design earthquake with a return period of 975 years, or a 7 percent probability of exceedance (PE) in 75 years. The USGS Seismic Design Reports Application was used to determine the peak ground acceleration and spectral accelerations (USGS, 2017). Site Class B was selected at the abutment locations based on the penetration resistance of the soil in general accordance with Section 3.10.3, Method B (AASHTO, 2020). Site factors were selected from Table 3.10.3.2-1 through 3.10.3.2-3 in AASHTO (2020) and multiplied by the mapped PGA and spectral accelerations in order to determine the modified peak ground acceleration (As) and spectral accelerations. The results of the hazard analysis are presented in Table 5 and Figure 3.

Table 5. Summary of Seismic Parameters (7% PE in 75 years) - General Procedure.

Site Latitude 47.28921° Site Longitude -120.85966°

Site Class at Project Site (by Soil Type and Penetration Resistance in Top 100 feet of Soil Profile) B

Horizontal Peak Ground Acceleration on Site Class B Rock (PGA) 0.197 g

Horizontal Response Spectral Acceleration at a Period of 0.2 sec on Site Class B Rock (Ss) 0.449 g

Horizontal Response Spectral Acceleration at a Period of 1.0 sec on Site Class B Rock (S1) 0.154 g

Mapped Peak Ground Acceleration Coefficient, FPGA 1.000 Mapped Short-Period Spectral Acceleration Coefficient, Fa 1.000 Mapped 1-sec Period Spectral Acceleration Coefficient, Fv 1.000

Scaled Peak Ground Acceleration for Project Site, Site Class B (As) 0.197 g

Scaled Horizontal Response Spectral Acceleration at a Period of 0.2 sec for Project Site, Site Class B (SDS) 0.449 g

Scaled Horizontal Response Spectral Acceleration at a Period of 1.0 sec for Project Site, Site Class B (SD1) 0.154 g

AASHTO Seismic Zone 2

Figure 3. 5% Damped Response Sprectra – Site Class B.

12 Analysis and Recommendations

5.2 LIQUEFACTION

Soil liquefaction refers to the condition by which vibration or shaking of the ground, usually from earthquake forces, results in the collapse of the soil structure, the development of excess pore pressures in saturated soils, and a subsequent reduction in soil shear strength. Evaluation of liquefaction potential is dependent on numerous parameters, including soil type, grain-size distribution, soil density, depth to groundwater, in-situ static ground stresses, earthquake magnitude, PGA, and associated earthquake-induced ground stresses. In general, soils that are susceptible to liquefaction include very loose to medium dense, clean to silty sands and very soft to stiff non-plastic silts that are below the water table.

Based on the geology in the project vicinity and results of the subsurface investigation, the risk for soil liquefaction is low.

5.3 LATERAL SPREADING

Lateral spreading related to seismic activity typically involves lateral displacement of large, surficial blocks of non-liquefied soil when a layer of underlying soil loses strength during seismic shaking. Lateral spreading usually develops in areas where sloping ground or large grade changes are present. Based on the planned improvements, site topography, and liquefaction potential explained above, the risk of lateral spreading impacting the site is low.

5.4 SURFACE RUPTURE

According to the Washington State Department of Natural Resources (DNR) Interactive Natural Hazards Map (accessed June 15, 2021), the closest mapped fault is the Frenchman Hills structures, which is approximately 13 miles southeast of the project site. The fault is described as a normal fault with a southwest dip direction. Slip rate is estimated at less than 0.1-inches per year. Based on the proximity of the site to the nearest known fault, the risk for surface rupture is at the project site is low.

6 ANALYSIS AND RECOMMENDATIONS

Foundation recommendations are discussed below. The abutments are expected to be founded on 2.5-foot diameter drilled shafts socketed in rock.

Major stratigraphic contacts observed during the subsurface investigation are presented in Table 6.

Table 6. Approximate rock contact elevations.

Location Approx. Planned1 Ground Elev. (ft.)

Approx. Existing Ground Elev. (ft.)

Approx. Top of Weathered Rock

Elev. (ft.)

Approx. Top of Competent

Rock Elev. (ft.)

West Abutment 2,390 2,386 2,367 2,356

East Abutment 2,388 2,386 2,370 2,365

1 Planned ground elevation represents bottom of pile cap.

6.1 SCOUR

Scour recommendations were provided by WFLHD Hydraulics Section in their Dickey Creek Bridge Replacement Scour Hydraulics Memo dated June 1, 2021. The total scour elevation, which includes abutment scour plus long-term degradation, is Elevation 2,377 feet.

6.2 LATERAL PARAMETERS

6.2.1 Lateral Earth Pressures

Select borrow should be used behind wing walls. Geocomposite sheet drains connected to drain pipe and weep holes should be installed behind walls to ensure adequate drainage. The soil parameters listed in Table 7 should be used to estimate the lateral earth pressures exerted on the abutment walls and wing walls. The parameters listed in Table 7 assume a vertical wall with level ground at the top of the wall. Passive pressure should be neglected from the surface to a depth of 2 feet.

Table 7. Recommended soil parameters for wing walls.

Soil Parameter Design Value Unit weight 120 pcf

Angle of internal friction 36 degrees Active earth pressure coefficient, Ka 0.24

Active equivalent fluid pressure 29 psf/ft At-rest earth pressure coefficient, Ko 0.42

At-rest equivalent fluid pressure 50 psf/ft Passive earth pressure coefficient, Kp 10.14

Passive equivalent fluid pressure 1,000 psf/ft Wall-backfill interface friction angle, δ 27 degrees

14 Analysis and Recommendations

6.2.2 Foundations

Table 8 presents the soil parameters recommended to analyze lateral loading and foundation capacity with software such as LPile. The values in Table 8 do not include factors of safety or load factors. A resistance factor of 1.0 is specified in AASHTO (2020) for lateral geotechnical resistance of single or group shafts.

For lateral pile or shaft loading, reductions in the soil response p-y curves are necessary if the piles are spaced close enough to influence the other piles in the group. The values of P shall be multiplied by Pm to account for group effects. The values of Pm presented below should be used, if applicable.

Longitudinal Direction

For pile loading in the longitudinal direction, it is necessary to reduce the P values in the soil response p-y curves if the center-to-center spacing of the piles is less than five equivalent pile diameters. The p-y multiplier can be determined from the equation below:

Pm = 0.1(S) + 0.5

Where:

Pm = p-y multiplier

S = center-to-center pile spacing, expressed in number of equivalent pile diameters

Transverse Direction

For pile/shaft loading in the transverse direction, it is necessary to reduce the P values in the soil response p-y curves if the center to center spacing of the piles/shafts is less than 5 equivalent pile/shaft diameters. The p-y multiplier for the first pile/shaft can be determined from the equation below:

Pm = 0.1(S) + 0.5

The second pile will be influenced by the “shadow” of the first pile if the pile spacing is less than

5.7 equivalent pile diameters. The p-y multiplier for the second pile/shaft can be determined from the equation below:

Pm = 0.225(S) - 0.275

The third and subsequent piles/shafts will be influenced by the “shadow” of the piles/shafts in front if the pile/shaft spacing is less than 6.5 equivalent pile/shaft diameters. The p-y multiplier for the third and subsequent piles/shafts can be determined from the equation below:

Pm = 0.2(S) - 0.3

Table 8. Recommended soil parameters for lateral analysis of drilled shafts.

6.3 ABUTMENTS

Drilled shafts are recommended for foundation support at both abutments and have been analyzed at the proposed abutment locations. Factored axial capacity charts for 2.5-foot diameter drilled shafts socketed into rock are provided in Appendix A. Permanent casing is recommended to extend to competent rock elevation; therefore, the compressive side resistance was reduced.

Factored resistances were developed using the following resistance factors in accordance with

AASHTO LRFD BDS (2020):

Properties for

Sand Properties for Strong Rock and

Weak Rock Elev.

(feet)

LPile Material γ (pcf) γ’ (pcf) φ’ (deg) k (lb/in3) qu

(psi) Erm

(psi)

RQD

(%) krm

West Foundation (ground surface assumed = Elev. 2,386 feet, use effective unit weight below Elev. 2,383 feet) >2,383 Sand (Reese) 120 - 34 130 - - - - 2,383- 2,376 Sand (Reese) - 58 34 70 - - - -

2,376- 2,356 Weak Rock - 94 - - 1,500 150,000 10 0.0005

<2,356 Strong Rock - 103 - - 2,000 - - -

East Foundation (ground surface assumed = Elev. 2,386 feet, use effective unit weight below Elev. 2,384 feet) >2,384 Sand (Reese) 125 - 36 135 - - - - 2,384- 2,371 Sand (Reese) - 53 36 75 - - - -

2,371- 2,365 Weak Rock - 98 - - 1,250 150,000 30 0.0005

<2,365 Strong Rock - 98 - - 3,000 - - -

NOTES:

1. γ = moist unit weight.

2. γ’ = effective unit weight.

3. φ’ = effective internal angle of friction.

4. k is the constant giving the variation of soil modulus with depth in the equation Es = kz, where Es = soil modulus, and z = depth below the ground surface.

5. qu = unconfined compressive strength.

6. Erm = elastic modulus of rock mass.

7. RQD = rock quality designation.

8. krm = rock strain factor.

16 Analysis and Recommendations

• Compressive side resistance in sand – 0.55

• Side resistance in rock – 0.55

• Tip resistance in rock – 0.50

WFL Structural Section provided loads for the proposed bridge via email dated June 16, 2021.

Factored axial Limit State loads per abutment are:

• Axial Service I – 1,036 kips

• Axial Strength I – 1,434 kips

• Axial Extreme I – 650 kips

Drilled shafts should extend a minimum of one shaft diameter into competent bedrock. Deeper drilled shafts may be required for lateral resistance. Competent bedrock elevations observed during our subsurface explorations are:

• West foundation – Elevation 2,356 feet

• East foundation – Elevation 2,365 feet

6.3.1 Downdrag

Because of the location and depth of the foundation elements relative to the proposed embankments, downdrag loads resulting from embankment settlement are not anticipated.

6.3.2 Settlement

An evaluation of settlement for foundation elements has been performed. Settlement is anticipated to occur immediately (during construction) and is estimated to be less than 0.5 inches.

6.4 GLOBAL STABILITY

Global slope stability analyses were performed for the west and east abutments. The slopes were analyzed for static, seismic (pseudo-static), and liquefied stability using Slide2 (Rocscience, Inc.

2020). Three force/moment equilibrium methods were used: Bishop simplified, Spencer, and GLE/Morgenstern-Price. Soil properties used in the analyses were informed by the subsurface exploration boring logs and associated laboratory results. Results of the global stability analyses are discussed below and presented in Appendix A.

6.4.1 Static Stability

Under static conditions a minimum capacity to demand (C/D) ratio of 1.5 is required for the slope to be considered stable. A summary of the C/D ratios for the west and east abutments are displayed in Table 9.

Table 9. Global stability C/D ratios for west and east abutments.

Global Static Stability Method West Abutment East Abutment

Bishop Simplified 1.64 1.70

Spencer 1.65 1.71

GLE / Morgenstern-Price 1.66 1.72

These results were determined without using the shear resistance of the piles as a stabilizing force, and therefore these results are considered conservative. The analysis shows that the stability at both abutments is acceptable.

6.4.2 Seismic Stability

Pseudo-static slope stability analyses were performed at the west and east abutments using the estimated drained strength of the foundation soils and a horizontal seismic coefficient of 0.11 g, which is half of the calculated surface peak ground acceleration based on values presented in Table 5. This analysis models conditions during an earthquake before loss in soil strength occurs.

Slope displacement is expected to be less than two inches if the C/D ratio is greater than 1.1. A summary of the C/D ratios for the west and east abutments are displayed Table 10.

Table 10. Global seismic stability C/D ratios for west and east abutments.

Global Seismic Stability Method West Abutment East Abutment

Bishop Simplified 1.30 1.35

Spencer 1.32 1.38

GLE / Morgenstern-Price 1.34 1.38

These results were determined without using the shear resistance of the shafts as a stabilizing force; therefore, these results are considered conservative. The analysis indicates that the stability at both abutments is acceptable.

6.5 EMBANKMENT SLOPES

Soil embankment areas are limited to maximum slopes of 1V:2H and extend to heights of approximately 26 feet. Embankment material consists of imported unclassified borrow. The 1V:2H embankments slopes are appropriate for unclassified borrow. If steeper slopes are desired, the geotechnical engineer should be notified, and select granular material may be required.

Based on the subsurface investigation, embankment settlement is anticipated to occur during construction and is estimated to be less than 2-inches.

18 Construction Considerations

7 CONSTRUCTION CONSIDERATIONS

Drilled Shafts

Approach embankments should be constructed prior to shaft excavation. The overburden soils encountered during shaft excavation are very likely to slough above and below the water table.

Permanent casing is recommended to be advanced ahead of shaft excavation. A soil plug of at least 2 feet should be maintained during excavation; however, cobbles and boulders up to 24-inches should be anticipated which may require coring to advance the casing.

A 1.5-foot thick layer of medium strong (R3) siltstone was encountered in Boring DC20-01 at Elevation 2,369 feet. The Contractor should be prepared to core through the siltstone layer and into the underlying weak sandstone.

The bedrock at the project site is variable and UCS test results on rock core samples ranged from 1,790 psi to 6,770 psi. As shown in the Boring Logs in Appendix C, very weak and highly weathered sandstone was also encountered, and Table 6 provides the estimated elevation contact of competent bedrock. Soil infilling and seams were encountered in the rock. Drilled shafts should not be terminated within a soil seam. Permeant casing should be advanced to competent bedrock. The shafts should be socketed into the competent bedrock a minimum of one shaft diameter. Sounding should be used to verify that remaining cuttings in the bottom of the excavation are within the specified limits. Cross-hole Sonic Logging is not required for this project.

If an oversized hole is drilled for installation of permanent casing, the void between the outside of the casing and the soil must be sealed by tremie grouting or other approved methods.

Embankment

The proposed west approach embankment will be constructed south and adjacent to the existing embankment from approximately STA 201+00.00 to STA 206+00.00. The south slope of the existing embankment should be cleared and grubbed. The proposed embankment should be benched into the existing embankment.

After clearing and grubbing, ground conditions should be suitable for placement and compaction of embankment material. If ground conditions should differ from what is expected, the geotechnical engineer should be contacted to evaluate if the conditions impact the design.

8 LIMITATIONS

This report has been prepared to present final structural foundation engineering recommendations for this project. It should not be used, in part or in whole for other purposes without contacting the WFL Geotechnical Section for a review of the applicability of such reuse.

Subsurface exploration and associated laboratory testing describes subsurface conditions only at the sites of subsurface exploration and at the intervals where samples are collected. These data are interpreted by members of the WFL Geotechnical Section, who then render a professional geotechnical opinion regarding the general subsurface conditions. The distribution, continuity, thickness, and characteristics of identified (and unidentified) subsurface materials may vary considerably from that indicated by the subsurface data. In addition, the observed water levels and/or conditions indicated on the test boring logs are recorded at the time of the exploration. The water levels and/or conditions may vary considerably, with time, according to the climate, rainfall, and other factors and are otherwise dependent on the duration of, and methods used in, and interpretations made from the subsurface exploration program.

This report should be made available to prospective contractors for their information, or as factual data only, and not as a warranty of ground conditions.

Questions regarding this report should be addressed to Sean Hayter, WFLHD Geotechnical Engineer at (202) 934-0377 or Sean.Hayter@dot.gov.

20 Limitations

GEOTECHNICAL REPORT NO. 15-21

Geotechnical Recommendations for Dickey Creek Bridge Replacement (Rev. 1)

WA KITTITAS 5880(1)

Kittitas County, Washington October 2021

Prepared by: ________________________________________________ Sean Hayter, Geotechnical Engineer

Reviewed by: ________________________________________________ Evan Garich, Geotechnical Engineer

Approved by: ________________________________________________ Douglas Andersen, Geotechnical Functional Manager

9 REFERENCES

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

AASHTO (2020), Standard Specifications for Transportation Materials and Methods of Sampling and Testing, American Association of State Highway and Transportation Officials, Washington D.C.

ASTM International (2020), Annual Book of ASTM Standards, Section Four, Construction, Volume

4.08 and 4.09 Soil and Rock.

DNR (2019), Washington Geologic Information Portal, http://geologyportal.dnr.wa.gov, accessed June 15, 2021, Washington Department of Natural Resources.

FLH (2017), Federal Lands Highway Soil and Rock Characterization Guidelines, Federal Highway Administration, December 2017.

Rocscience, Inc. (2020), Slide2, Toronto, ON. M5T 1V1, CA.

USGS (2017), USGS Earthquake Hazards Program website, U.S. Seismic Design Maps, http://earthquake.usgs.gov/designmaps/us/application.php, accessed October 2, 2020, U.S. Geological Survey.

Tabor, R.W., Waitt, R. B., Frizzell, V.A., Swanson, D.A.; Byerly, G.R., and Bentley, R.D., 1982, Geologic Map of the Wenatchee 1:100,000 Quadrangle, Central Washington, Department of the Interior, U.S. Geological Survey.

http://geologyportal.dnr.wa.gov/ http://earthquake.usgs.gov/designmaps/us/application.php

Appendix A

• Axial Foundation Capacity Charts

• Foundation Global Stability Analysis Results

Western Federal Lands Highway Division 610 East Fifth Street Vancouver, WA 98661

Project No. Drilled Shaft Capacity FigureWA KITTITAS 5880(1) Scale

Dickey Creek Bridge Replacement A1

N/A File Name:

Date:

October 2021

2,322

2,332

2,342

2,352

2,362

2,372

2,382

0 1,000 2,000 3,000 4,000 5,000 6,000

El ev at io n (ft

Factored Axial Resistance (kips)

West 2.5-foot Diameter Drilled Shaft

Strength I Limit State Service I Limit State Extreme I Limit State

2,322

2,332

2,342

2,352

2,362

2,372

2,382

0 1,000 2,000 3,000 4,000 5,000 6,000

El ev at io n (ft

Factored Axial Resistance (kips)

East 2.5-foot Diameter Drilled Shaft

Strength I Limit State Service I Limit State Extreme I Limit State

1.661.66

W

250.00 lbs/ft2

250.00 lbs/ft2 1.661.66

UCS

(psf)

Phi (deg)

Cohesion (psf)

Strength Type Unit Weight

(lbs/ft3) ColorMaterial Name

340Mohr-Coulomb120 Sand with Silt and Gravel

400Mohr-Coulomb105Riprap

350Mohr-Coulomb120Unclass. Borrow

380Mohr-Coulomb120Residual

1e+06 Generalized Hoek-Brown

120Sandstone

West

East

Min FSMethod Name 1.64Bishop simplified 1.65Spencer 1.66GLE / Morgenstern-Price

-80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200 220 240

West-Static Company FHWA WFFLHDDrawn By SAH File Name Abutments.slmdDate 4/14/2021, 3:55:32 PM

Project

Dickey Creek Bridge Replacement

SLIDEINTERPRET 9.003

1.341.34

250.00 lbs/ft2

250.00 lbs/ft2

1.341.34

UCS

(psf)

Phi (deg)

Cohesion (psf)

Strength Type Unit Weight

(lbs/ft3) ColorMaterial Name

340Mohr-Coulomb120 Sand with Silt and Gravel

400Mohr-Coulomb105Riprap

350Mohr-Coulomb120Unclass. Borrow

380Mohr-Coulomb120Residual

1e+06 Generalized Hoek-Brown

120Sandstone

West

East

0.1

Min FSMethod Name 1.30Bishop simplified 1.32Spencer 1.34GLE / Morgenstern-Price

-80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200 220

West-Seismic Company FHWA WFFLHDDrawn By SAH File Name Abutments.slmdDate 4/14/2021, 3:55:32 PM

Project

1.721.72

250.00 lbs/ft2

250.00 lbs/ft2

1.721.72

UCS

(psf)

Phi (deg)

Cohesion (psf)

Strength Type Unit Weight

(lbs/ft3) ColorMaterial Name

340Mohr-Coulomb120 Sand with Silt and Gravel

400Mohr-Coulomb105Riprap

350Mohr-Coulomb120Unclass. Borrow

380Mohr-Coulomb120Residual

1e+06 Generalized Hoek-Brown

120Sandstone

West

East

Min FSMethod Name 1.70Bishop simplified 1.71Spencer 1.72GLE / Morgenstern-Price

-80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200 220 240

East-Static Company FHWA WFFLHDDrawn By SAH File Name Abutments.slmdDate 4/14/2021, 3:55:32 PM

Project

1.381.38

250.00 lbs/ft2

250.00 lbs/ft2

1.381.38

UCS

(psf)

Phi (deg)

Cohesion (psf)

Strength Type Unit Weight

(lbs/ft3) ColorMaterial Name

340Mohr-Coulomb120 Sand with Silt and Gravel

400Mohr-Coulomb105Riprap

350Mohr-Coulomb120Unclass. Borrow

380Mohr-Coulomb120Residual

1e+06 Generalized Hoek-Brown

120Sandstone

West

East

0.1

Min FSMethod Name 1.35Bishop simplified 1.38Spencer 1.38GLE / Morgenstern-Price

-80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200 220

East-Seismic Company FHWA WFFLHDDrawn By SAH File Name Abutments.slmdDate 4/14/2021, 3:55:32 PM

Project

Appendix B

• Boring Location Plan

Vancouver, WA 98661

Project No. Subsurface Investigation Map FigureWA KITTAS 5880(1) Scale

Dickey Creek Bridge Replacement B1

N/A File Name:

Date:

October 2021

DC20-01: 47.28921; -120.85966

TP20-01: 47.28941; -120.86046

TP20-02: 47.28889; -120.86018

TP20-03: 47.28911; -120.85965

Boring

Test Pit

NOT FOR CONSTRUCTION

Vancouver, WA 98661

Project No. Subsurface Investigation Map FigureWA KITTITAS 5880(1) Scale

Dickey Creek Bridge Replacement B2

N/A File Name:

Date:

October 2021

DC20-02: 47.28941; -120.85923

TP20-04: 47.28934; -120.85925

TP20-05: 47.28951; -120.85887

TP20-06: 47.28971; -120.85847

Boring

Test Pit

NOT FOR CONSTRUCTION

Appendix C

• Field Classifications for Soil and Rock

• Boring Logs o DC20-01 o DC20-02

• Test Pit Logs o TP20-01 o TP20-02 o TP20-03 o TP20-04 o TP20-05 o TP20-06

SOIL CLASSIFICATION CHART

Criteria for Assigning Group Symbols and Group Name Using Laboratory TestsA Group

Symbol Group NameB

COARSE-GRAINED

SOILS

More than 50% retained on No. 200 Sieve

GRAVELS

More than 50% of coarse fraction retained on No. 4 Sieve

Clean GRAVELS Less than 5% fines E

Cu ≥ 4 and 1 ≤ Cc ≤ 3C GW Well-graded GRAVEL D

Cu < 4 and/or 1 > Cc > 3 C GP Poorly-graded GRAVEL D

GRAVELS with fines More than 12% fines E

Fines classify as ML or MH GM Silty GRAVEL D,F Fines classify as CL or CH GC Clayey GRAVEL D,F

SANDS

Less than 50% retained on No. 4 Sieve

Clean SANDS Less than 5% fines I

Cu ≥ 6 and 1 ≤ Cc ≤ 3 C SW Well-graded SAND H

Cu < 6 and/or 1 > Cc > 3 C SP Poorly-graded SAND H

SANDS with fines More than 12% fines I

Fines classify as ML or MH SM Silty SAND F,H Fines classify as CL or CH SC Clayey SAND F,H

FINE-GRAINED

SOILS

50% or more passes the No. 200 Sieve

SILTS and CLAYS Liquid limit less than 50

Inorganic PI > 7 and plots on or above the “A” line J CL Lean CLAY K,L,M PI < 4 or plots below “A” line J ML SILT K,L,M

Organic Liquid limit – oven dried Liquid limit – not dried < 0.75 OL Organic CLAY K,L,M,N

Organic SILT K,L,M,O

SILTY and CLAYS Liquid limit 50 or more

Inorganic PI plots on or above “A” line CH Fat CLAY K,L,M PI plots below “A” line MH Elastic SILT K,L,M

Organic Liquid limit – oven dried Liquid limit – not dried < 0.75 OH Organic CLAY K,L,M,P

Organic SILT K,L,M,Q

HIGHLY ORGANIC

SOILS Primarily organic matter, dark in color, and organic odor PT PEAT A Based on material passing the 3-inch sieve.

B If field sample contains cobbles or boulders, add “with cobbles” or “boulders” or both, to group name.

C Cu = D60/D10 Cc = (D30)2 / (D10 x D60) D If soil contains ≥15% sand, add “with sand” to group name.

E Gravels with 5 to 12% fines require dual symbols:

GW-GM well-graded GRAVEL with silt GW-GC well-graded GRAVEL with clay GP-GM poorly-graded GRAVEL with silt GP-GC poorly-graded GRAVEL with clay

F If fines classify as CL-ML, use dual symbol GC-GM or SC-SM G If fines are organic, add “with organic fines” to group name.

H If soil contains ≥15% gravel, add “with gravel” to group name.

I Sand with 5 to 12% fines require dual symbols:

SW-SM well-graded SAND with silt SW-SC well-graded SAND with clay SP-SM poorly-graded SAND with silt SP-SC poorly-graded SAND with clay J If Atterberg limits plot in hatched area, soil is a CL-ML, silty

CLAY.

K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel”, whichever is predominant.

L If soil contains ≥ 30% plus No. 200, predominantly sand, add “sandy” to beginning of group name.

M If soil contains ≥ 30% plus No. 200, predominantly gravel, add “gravelly” to beginning of group name.

N PI ≥ 4 and plots on or above “A” line.

O PI < 4 or plots below “A” line.

P PI plots on or above “A” line.

Q PI plots below “A” line.

APPARENT DENSITY OF COARSE-

GRAINED SOIL

SPT N-value (blows per foot) Apparent Density

0 to 4 Very Loose

5 to 10 Loose

11 to 30 Medium Dense

31 to 50 Dense

> 50 Very Dense

CONSISTENCY OF

FINE-GRAINED SOIL

SPT N-value (blows per foot) Consistency

0 to 1 Very Soft

2 to 4 Soft

5 to 8 Firm

9 to 15 Stiff

16 to 30 Very Stiff

> 30 Hard

SOIL STRUCTURE TERMS

Stratified Alternating layers of varying material or color with layers > 1/4 inch (6 mm), note thickness and inclination.

Laminated(1) Alternating layers of varying material or color with layers < 1/4 inch (6 mm), note thickness and inclination.

Fissured(1) Breaks along definite planes of fracture with little resistance to fracturing.

Slickensided(1) Fracture planes appear polished or glossy, sometimes striated.

Blocky(1) Cohesive soil that can be broken down into smaller angular lumps which resists further breakdown.

Disrupted Soil structure is broken and mixed. Infers that material has moved substantially -landslide debris.

Homogeneous Same color and appearance throughout.

Lensed Inclusion of small pockets of different soil, such as small lenses of sand scattered through a mass of clay; < 1/4 inch (6 mm) note thickness.

(1) Do not use laminated, fissured, slickensided, or blocky for coarse-grained soils.

Descriptive Terminology for Boring Logs

Field descriptions of borings are based on the FLH Soil and Rock Description and Identification Guidelines that generally follow the Visual-Manual Procedure (ASTM D 2488). The soil classifications shown on the boring logs are based on laboratory tests (ASTM D 2487) when the two-letter group symbol follows the group name in parenthesis.

Standard Penetration Test (SPT): the SPT consists of driving a 2 in (50 mm) O.D. split barrel sampler a depth of 18 in (450 mm) or 24 in (600 mm) using a 140 lb (63.6 kg) hammer with a 30 in (750 mm) drop. The blow count is the number of blows recorded for each 6 inch (50 mm) increment.

The N-value is the total number of blows for the second and third increments. Note that the N-values shown on the boring logs do not include any corrections for non-standard sampler size, hammers, drill rods, etc.

ANGULARITY OF

COARSE-GRAINED SOILS

Angular Sharp edges and relatively plane sides with unpolished surfaces

Subangular Similar to angular description, but with rounded edges

Subrounded Nearly plane sides, but will have well-rounded corners and edges.

Rounded Smoothly curved sides and no edges

PARTICLE SIZE OF COARSE-GRAINED SOILS

Component Grain Size Limits

Boulders > 12” (> 300 mm)

Cobbles 3 – 12” (75 – 300 mm)

Coarse Gravel 3/4 - 3" (19 - 75 mm)

Fine Gravel #4 Sieve - 3/4" (4.75 - 19 mm)

Coarse Sand #10 - #4 Sieve (2.00 - 4.75 mm)

Medium Sand #40 - #10 Sieve (0.425 - 2.00 mm)

Fine Sand #200 - #40 Sieve (0.075 - 0.425 mm)

GRAIN/CRYSTAL SIZE FOR ROCKS (MODIFIED AFTER WENTWORTH, 1972)

Grain Size Description Criteria

Less than 0.003 inches

(<0.075 mm) Very fine grained Cannot be distinguished by unaided eye. Few to no mineral grains are visible with a hand lens.

0.003 to 0.02 inches (0.075 to 0.425 mm) Fine grained

Few grain/crystal boundaries are visible; grains can be distinguished with difficulty by the unaided eye but can be somewhat distinguished by hand lens.

0.02 to 0.08 inches (0.425 to 2 mm) Medium grained Most grain/crystal boundaries are visible; grains distinguishable by eye and with the aid of a hand lens.

0.08 to 0.2 inches

(2 to 4.75 mm) Coarse grained Grain/crystal boundaries are visible; grains distinguishable with the naked eye and hand lens.

Greater than 0.2 inches

(>4.75 mm)

Very coarse grained

Grain/crystal boundaries are Clearly visible; grains are distinguishable with the naked eye.

GRAIN SHAPE (FOR SEDIMENTARY ROCKS)

Description Characteristic

Angular Showing very little evidence of wear. Grain edges and corners are sharp. Secondary corners are numerous and sharp.

Subangular

Showing definite effects of wear. Grain edges and corners are slightly rounded off. Secondary corners are slightly less numerous and slightly less sharp than in angular grains.

Subrounded Showing considerable wear. Grain edges and corners are rounded to smooth curves. Secondary corners are reduced greatly in number and highly rounded.

Rounded Showing extreme wear. Grain edges and corners are smoothed off the broad curves. Secondary corner are few in number and rounded.

Well-rounded Completely worn. Grain edges or corners are not present. No secondary edges or corners are present. DEGREE OF WEATHERING

Term Description Grade

Fresh No visible sign of…