idf-nezpr221-1_GEO_GR0625.pdf

National Forest System Road 221 Rehabilitation OCTOBER 2025

Table of Contents 1-i

Geotechnical Report No. 06-25

National Forest System Road 221 Rehabilitation

FINAL GEOTECHNICAL ENGINEERING

REPORT

ID NEZPR117 221(1)

Idaho County, Idaho

OCTOBER 2025

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Table of Contents i

TABLE OF CONTENTS

1 INTRODUCTION

1.1 Project Description

2 GEOLOGIC SETTING

2.1 Local Geology

2.2 Faulting and Seismicity

2.2.1 Shallow Crustal Faults

3 SITE CONDITIONS

3.1.1 Site Conditions and Observations

3.1.2 Deep Patch and RSS Repairs

SUBSURFACE INVESTIGATION

3.2 Soils and Rock

3.3 Groundwater

4 GEOTECHNICAL CONCLUSIONS AND RECOMMENDATIONS

4.1 MP 19.8 RSS Slope Stability Analyses

4.2 MP 19.8 Reinforced Soil Slope

4.3 Deep Patches

5 CONSTRUCTION CONSIDERATIONS

5.1 Site Preparation

5.2 Proofrolling and Subgrade Verification

5.3 Wet Weather Conditions

5.4 Excavation

5.5 Material and Aggregate Source

5.6 Traffic Control and Accessibility

6 LIMITATIONS

7 REFERENCES

LIST OF FIGURES

In Text:

Figure 1-1. Project Location Map

As Attachments:

Figure 1 Vicinity Map and Site Plan

Figure 2 Detail Map 1: MP 6.7 to MP 11.7 ii Table of Contents

Figure 3 Detail Map 2: MP 12.1 to MP 20.8

Figure 4 Detail Map 3: MP 21.1 to MP 24.0

Figure 5 Detail Map 4: MP 26.4 to MP 33.6

LIST OF TABLES

Table 1. Deep Patch and RSS Locations and Conditions Summary

Table 2. Geotechnical and Subgrade Boring Locations and Depths

Table 3. Subgrade Borings Summary

Table 4. Soil Units and Engineering Properties

Table 5. Summary of Slope Stability Analysis Results

APPENDICES

Appendix A GRI Geotechnical Data Report

Appendix B Slide Models for Slope Stability Analysis

1 INTRODUCTION

This report provides the geotechnical investigation results, analysis, and final recommendations for the ID NEZPR117 221(1) – National Forest System Road 221 Rehabilitation Project. The project is located approximately 5 miles south of Grangeville, Idaho along National Forest System

Road (NFSR) 221 between milepost (MP) 6.8 and MP 36.5, as shown in Figure 1-1.

1.1 PROJECT DESCRIPTION

The NFSR 221, known locally as the Grangeville-Salmon Road, is a vital public and administrative access road to the Salmon River Ranger District, and., a major route for traffic in the wildland-urban interface (WUI). The road supports the forest products industry, vegetation management, fire protection, and truck traffic, particularly for hauling activities south of Grangeville, and provides access for the Nez Perce Tribe, public recreation, including skiing, hunting, fishing, hiking, motor sports, and is the main corridor to the western Gospel Hump Wilderness.

The NFSR 221 Rehabilitation Project includes:

• Roadway pavement rehabilitation between MP 6.8 and 34.3, repairing road shoulders, and flattening road embankment slopes along the road edge;

• Installing deep patches and reinforced soil slopes (RSS) in unstable areas;

• Replacing several culverts with either like-in-kind or upsized pipes; and,

• Paving intersection aprons where NFSR 221 and aggregate surface forest roads branch.

IDAHO

PROJECT

LOCATION

Road No. 221

Figure 1-1. Project Location Map

2 GEOLOGIC SETTING

The project alignment is on the western boundary of the Nez Perce-Clearwater National Forests and winds roughly south to north between the Columbia Plateau and Rocky Mountain physiographic provinces in north-central Idaho (Lewis et al., 2012). The basement rocks underlying the project area include cratonic and accreted terrane assemblages juxtaposed along a north-south zone. The cratonic assemblage consists of Proterozoic metamorphic and

Cretaceous intrusive rocks. The accreted terrane assemblage includes Permian to Cretaceous volcanic, volcaniclastic, sedimentary, and intrusive rocks with varying degrees of metamorphism.

Miocene Columbia River Basalt Group lava flows and minor interbedded sediments cover much of the ground surface and lie unconformably on the older basement rocks. Remnants of Tertiary gravels locally cap the flows. Pleistocene glacial deposits are present in the higher elevation and

Pleistocene to Holocene alluvial deposits form terraces and stream deposits along the major rivers and tributary streams. Landslide and mass-wasting deposits, also of Pleistocene to

Holocene age, are common throughout area, especially in areas of steep relief.

2.1 LOCAL GEOLOGY

Based on the geologic maps in the area (Kauffman et al., 2008; Kauffman et al., 2011; and, Kauffman et al., 2014), the project alignment traverses over the juxtaposed cratonic and accreted assemblages bedrock formations that are unconformably capped with Columbia River Basalts and mantled with younger, unconsolidated Pleistocene and Holocene glacial and alluvial deposits, and artificial fill.

Unconsolidated Deposits

Holocene alluvial deposits in local drainages (Qas) Stratified silt, sand, and clay typically between 5 and 20 feet thick.

Columbia River

Basalts

Miocene Grande Ronde Basalt, R2 unit (Tgr2) Medium to dark gray, fine-grained basalt, commonly with a sugary texture with uncommon to common plagioclase phenocrysts and reverse magnetic polarity. Consists of one or two flows and a unit thickness generally less than 100 feet. Local thickening and thinning may result from structures developed on earlier

Grande Ronde Basalt or from erosion on the earlier basalt surface.

Miocene Grande Ronde Basalt, N1 unit (Tgn1) Dark gray, fine-grained generally aphyric to plagioclase-microphyric basalt and normal magnetic polarity. The number of flows is estimated to be from three to five with a total unit thickness from 400 to 600 feet The flows near the top of sequence commonly 50 to 70 feet thick with a sugary texture and flows lower in the sequence are typically thicker, generally from 100 to 200 feet. Colonnades of thin flows and entablatures of thick flows tend to form tiered cliffs on steep canyon slopes.

Miocene Grande Ronde Basalt, R1 unit (Tgr1) Dark gray, fine-grained aphyric to microphyric basalt with uncommon and reverse magnetic polarity. Outcrop characteristics of flows are similar to those in the Grande

Ronde N1 unit and an exposed thickness of about 700 to 800 feet.

Intrusive Rocks Cretaceous Tonalite and trondhjemite (Kto) The tonalite is biotite- and hornblende-bearing, with large biotite plates that create a distinctive mottled appearance and weathers to light tan grus, medium-grained. This unit belongs to a group of tonalite and trondhjemite plutons along the

Salmon River suture of an age of around 111 million years.

Metamorphic Rocks

Permian to Cretaceous Ultramafic rocks (KPum) Metamorphosed pyroxenite or peridotite with clusters of anthophyllite, talc, and chlorite.

These rocks are light green to orange on fresh surfaces and gray where weathered, occurring as elongate, discontinuous bodies forming low, rounded ridges within the KPgs unit.

Permian to Cretaceous Gneiss and schist (KPgs) Fine to medium grained gneiss that grades into schist. Also includes calc-silicate rocks and quartzite. Light gray or green to black, weathering to a fine gray brown soil.

Although some plagioclase-amphibole gneiss may be metavolcanic in origin, most (if not all) of the unit is probably metasedimentary.

2.2 FAULTING AND SEISMICITY

The NFSR 221 is in a tectonically active region, experiencing low to moderate seismicity, with occasional events with magnitudes between 2 and 4, influenced by faulting associated with the

Basin and Range province, strike-slip faults like the Salmon River Fault Zone, and thrust faulting.

The NFSR 221 alignment traverses close to and crosses several fault zones, particularly those structures associated with the nearby Salmon River Fault Zone and other regional fault systems.

2.2.1 SHALLOW CRUSTAL FAULTS

The northeast-southwest trending Goodwin Meadows Fault projects through Goodwin Meadows and then bends northward along the South Fork Clearwater River and intersects NFSR 221 at

MP 14.1 near the Twin Cabins Quarry. The fault primarily offsets Grande Ronde Basalt units, with a maximum displacement of approximately 300 feet (Kauffman et. al., 2008). The Goodwin

Meadows Fault is considered a minor vertical fault with poorly documented activity.

The Dairy Mountain Fault is a thrust fault mapped 2,400 feet west of subgrade boring SG24-05 and does not intersect NFSR 221. Various rock units surround the Dairy Mountain Fault, including

Miocene lava flows of the Columbia River Basalt Group and Permian to Cretaceous metamorphic rocks (Kauffman et. al., 2011).

The northeast-trending Mill Creek Fault parallels the Dairy Mountain fault and intersects

NFSR 221 near MP 28.6. This fault more or less traces the Salmon River suture and is probably a reactivated compressional structure.

3 SITE CONDITIONS

The NSFR 221 winds through foothills and low mountains in the southern portion of the Nez

Perce-Clearwater National Forests.

3.1.1 SITE CONDITIONS AND OBSERVATIONS

The NFSR 221 in the southwest part of the Idaho panhandle, approximately 8 miles south of

Grangeville and leads into the Nez Perce-Clearwater National Forests, is used by several active timber harvest operations for hauling product to mills along with recreational and local users. The road is between 24 and 32 feet wide depending on the shoulder widths with an average gradient of approximately 2.5 percent with a maximum gradient of 4.5 percent. The elevations (EL) range between EL 5,000 and EL 5,900 feet, generally increasing and peaking near MP 25.5 and then descends to the end of the project limits.

Road settlement and pavement deterioration are common, with cracks in the asphalt, potholes, and scalping along the edges. Road maintenance has primarily been surficial and includes flexible crack sealing with tar, patches for individual potholes and lane sections, and chip seals. The road edges are scalped and narrowed in many sections due to erosion and oversteepened embankments slopes. Open potholes are commonly 12 to 18 inch in diameter and up to 12 inches deep with many marked with white paint to help travelers avoid them.

The vegetation surrounding the road is primarily dense stands of coniferous trees, deciduous trees, shrubs, and other underbrush. In most areas, the tree line is approximately 15 to 30 feet from the road centerline and few trees grow within the upper portion of the embankment fill slopes.

3.1.2 DEEP PATCH AND RSS REPAIRS

On August 20, 2024, we conducted a reconnaissance of the NFSR 221 project alignment, identifying six road sections requiring subsurface improvements due to slope instabilities. Table

1 includes the six sites along the road that were identified for repair, five deep patches to reinforce the upper subgrade beneath the pavement and one reinforced soil slope (RSS) to replace a failed gabion basket wall and improve the slope stability.

Table 1. Deep Patch and RSS Locations and Conditions Summary

Repair Mile Post Description

DP-01 17.9 130 feet of pavement deformation and cracking along the downslope side.

RSS-01 19.8

45 feet of deformation and separation, compounded by a failing gabion basket wall.

DP-02 21.6 50 feet of cracks, indicating a slow progressive failure mechanism.

DP-03 22.3 55 feet of pavement deformation, with underlying embankment issues.

DP-04 31.3 280 feet of deformation, with potential voids beneath the embankment.

DP-05 32.8 120 feet of deformation, showing signs of gradual deterioration.

SUBSURFACE INVESTIGATION

Between October 10 and October 16, 2024, Western States Drilling, advanced 6 geotechnical borings and 10 subgrade borings with truck mounted CME-75 drill rigs using a combination of solid flight augers, hollow stem augers (HSA), and rock core barrels. Disturbed soil samples were obtained in our borings at 2.5- to 5-foot intervals using the Standard Penetration Test (SPT) in general accordance with the American Society for Testing and Materials International (ASTM)

D1586, Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of

Soils (ASTM, 2025). Rock samples were collected using HQ3 triple tube wireline coring system.

Boring details are presented in Table 2 below. Boring logs summarizing the subsurface conditions are presented in GRI’s Geotechnical Data Report (2024) in Appendix A.

Table 2. Geotechnical and Subgrade Boring Locations and Depths

Boring Repair Depth (ft) MP Latitude(a) Longitude(a) EL (ft)(a)

BH24-01 DP-05 5.5 32.8 45.6172 -116.0295 4,947

BH24-02 DP-04 10.8 31.3 45.6321 -116.0168 5,109

BH24-03 DP-03 16.5 22.3 45.7178 -116.0347 5,310

BH24-04 DP-02 12.6 21.6 45.7236 -116.0223 5,435

BH24-05 RSS-01 15.1 19.8 45.7434 -116.0125 5,177

BH24-06 DP-01 11.6 17.9 45.7654 -116.0306 5,436

SG24-01 Pavement 5 32.9 45.6160 -116.0292 5,449

SG24-02 Pavement 5 29.9 45.6437 -116.0250 5,363

SG24-03 Pavement 5 29.0 45.6465 -116.0398 5,381

SG24-04 Pavement 5 27.1 45.6629 -116.0497 5,603

SG24-05 Pavement 4.7 23.2 45.7104 -116.0408 5,627

SG24-06 Pavement 5 19.2 45.7506 -116.0181 5,041

SG24-07 Pavement 5 17.6 45.7700 -116.0289 4,958

SG24-08 Pavement 5 14.4 45.7826 -116.0686 5,235

SG24-09 Pavement 5 10.7 45.8102 -116.0699 5,157

SG24-10 Pavement 5 7.0 45.8549 -116.0809 5,116

Notes: a – Based on WGS84.

3.2 SOILS AND ROCK

Subsurface conditions were inferred from the subsurface field explorations, laboratory testing on the collected soil samples, and review of applicable geologic literature. The soil and rock units observed in the borings include the road embankment and culvert fill, (Qam) Alluvium of the

South Fork Clearwater River, (Qas) Alluvial deposits in local drainages, (Kgt) Granodiorite and tonalite (Cretaceous), (KPgs) Gneiss and schist (Permian to Cretaceous). Additional units within the local area include (Tgr2) Grande Ronde Basalt, (Tgn1) Grande Ronde Basalt, (Tgr1) Grande Ronde, Basalt, (Kto)Tonalite and trondhjemite, (KPum) Ultramafic rocks (Permian to Cretaceous).

The subsurface units summaries, in stratigraphic order, encountered in the geotechnical and subgrade borings, grouped by milepost and the proposed improvement, are presented below.

MP 17.9 – Deep Patch

BH24-06

Ground Surface and Road Embankment Fill

The ground surface in boring BH24-06 consists of 5 inches of hot mix asphalt (HMA) pavement over 5 inches of aggregate base which is underlain by brown and gray silty SAND with gravel (SM) fill to a depth of approximately 5 feet bgs.

The silty sand fill is damp with a medium dense apparent density, with an N-value of 11 blows per foot (bpf). The fill layer was underlain by silty SAND with gravel in a loose, damp condition which became medium dense and micaceous below 7.5 feet.

(KPgs) Gneiss and schist (Permian to Cretaceous)

The embankment fill layer is underlain by SCHIST from approximately

10.5 feet to the depth explored of 11.5 feet bgs.

MP 19.8 – RSS

BH24-05

Ground Surface and Road Embankment Fill

The ground surface in BH24-05 consists of 6 inches of HMA pavement over 9 inches of aggregate base which is underlain by brown silty SAND with gravel (SM) fill to a depth of approximately 11.5 feet bgs.

The embankment fill layer was encountered in a loose, damp condition, which became very loose at 5 feet bgs. The fill layer was underlain by silty SAND with gravel in a medium dense, moist condition to a depth of 14.5 feet bgs.

(KPgs) Gneiss and schist (Permian to Cretaceous)

The medium dense silty sand layer was underlain by SCHIST to the full depth explored in BH24-05 of 15.1 feet bgs.

MP 21.6 – Deep Patch

BH24-04

Ground Surface and Road Embankment Fill

The ground surface in boring BH24-04 consists of 5 inches of HMA pavement over 12 inches of aggregate base which is underlain by brown silty SAND with gravel (SM) fill to a depth of approximately 7.5 feet bgs.

The embankment fill layer was encountered in a medium dense, damp condition, which became loose at 5 feet bgs. The fill layer was underlain by silty GRAVEL with sand in a medium dense, damp condition and became very dense at 10 feet bgs to a depth of 12.5 feet.

(KPgs) Gneiss and schist (Permian to Cretaceous)

The medium dense silty gravel layer was underlain by SCHIST to the full depth explored in BH24-04.

MP 22.3 – Deep Patch

BH24-03

Ground Surface and Road Embankment Fill

The ground surface in boring BH24-03 consists of 3 inches of HMA pavement over 10 inches of aggregate base which is underlain by brown silty SAND with gravel (SM) fill to a depth of approximately 13 feet bgs.

The embankment fill layer was encountered in a loose, damp condition, which became very loose at 5 feet bgs and brown and white below 7.5 feet bgs. The fill layer was underlain by sandy SILT in a soft, damp condition to a depth of 15 feet bgs.

The soft, sandy silt layer was underlain by brown and white silty SAND with gravel in a medium dense, damp condition to the full depth explored in BH24-03.

(KPgs) Gneiss and schist (Permian to

Cretaceous)

Unit not explored at depth.

MP 31.3 – Deep Patch

BH24-02

Ground Surface and Road Embankment Fill

The ground surface in boring BH24-02 consists of 6 inches of HMA pavement over 9 inches of aggregate base which is underlain by brown and white SAND with silt and gravel (SW-SM) fill to a depth of approximately 7.5 feet bgs.

The embankment fill layer was encountered in a very dense, damp condition, which became medium dense at 5 feet bgs. The fill layer was underlain by brown SAND with silt and gravel in a dense, damp condition to a depth of 10.5 feet bgs.

(Kgt) Granodiorite and tonalite (Cretaceous)

The dense SAND with silt and gravel layer was underlain by TONALITE to the full depth explored in BH24-02.

MP 32.8 – Deep Patch

BH24-01

Ground Surface and Road Embankment Fill

The ground surface in boring BH24-01 consists of 1 inch of HMA pavement over 8 inches of aggregate base which is underlain by brown and white SAND with silt and gravel (SW-SM) fill to a depth of approximately 5 feet bgs.

The embankment fill layer was encountered in a dense, damp condition.

(Kgt) Granodiorite and tonalite (Cretaceous)

The dense SAND with silt and gravel layer was underlain by TONALITE to the full depth explored in BH24-01.

Subgrade Borings

Haz-Tech Drilling advanced 10 subgrade borings using large-diameter solid flight augers to collect bulk samples for laboratory tests to measure the existing pavement section and classify near surface subgrade soils for pavement design. Table 3 summarizes the subgrade boring conditions.

Table 3. Subgrade Borings Summary

Boring MP Depth (ft) HMA (in) Stratigraphy

SG24-01 32.9 5 2

0.2 to 0.8 feet: Aggregate base

0.8 to 5.0 feet: SAND with silt and gravel (SW-SM)

SG24-02 29.9 5 1.5

0.1 to 0.4 feet: Aggregate base

0.4 to 5.0 feet: Sandy SILT, with sand and gravel

(MH)

SG24-03 29.0 5 1.5

0.1 to 0.6 feet: Aggregate base

0.6 to 5.0 feet: Sandy SILT with gravel (ML)

SG24-04 27.1 5 1

0.1 to 0.6 feet: Aggregate base

0.6 to 3.5 feet: Silty SAND, with gravel (SM)

3.5 to 5.0 feet: Clayey SAND with silt and gravel (SC)

SG24-05 23.2 4.7 1

0.1 to 1.1 feet: Aggregate base

1.1 to 3.5 feet: Clayey SAND with silt and gravel (SC)

3.5 to refusal: TONALITE

SG24-06 19.2 5 5

0.4 to 0.8 feet: Aggregate base

0.8 to 5.0 feet: Clayey SAND with gravel (SC)

SG24-07 17.6 5 5

0.4 to 0.8 feet: Aggregate base

0.8 to 5.0 feet: GRAVEL with silty and sand (GM-GC)

SG24-08 14.4 5 4

0.3 to 1.0 feet: Aggregate base

1.0 to 3.5 feet: GRAVEL with silt and sand (GM-GC)

3.5 to 5.0 feet: SILT with sand (ML)

SG24-09 10.7 5 4

0.3 to 0.8 feet: Aggregate base

0.8 to 5.0 feet: GRAVEL with silt, sand, and cobbles

(GM-GC)

SG24-10 7.0 5 6

0.5 to 1.3 feet: Aggregate base

1.3 to 5.0 feet: Sandy SILT with gravel (MH)

3.3 GROUNDWATER

Groundwater was not encountered while drilling the explorations. Groundwater measurements were taken during the summer and groundwater conditions should be expected to fluctuate during precipitation, snow melt, nearby irrigation, and as a result of other local and regional seasonal factors.

4 GEOTECHNICAL CONCLUSIONS AND RECOMMENDATIONS

Based on the site reconnaissance, subsurface borings, and laboratory testing, we present the following recommendations that should be considered in the project design and construction:

4.1 MP 19.8 RSS SLOPE STABILITY ANALYSES

The stability of the slope descending to the southwest, below the roadway, for the proposed RSS was evaluated with information developed from available data. Based on the developed cross section, a limit-equilibrium slope stability was modelled using the Slide2 software (RocScience, 2022).

Multiple soil units are described within the boring, which were grouped based on type and origin into:

• Aggregate base

• Road embankment fill

• Upper silty sand layer, residual soil from the Blue Mountain Island-Arc Complex

• Schist bedrock layer, Blue Mountain Island-Arc Complex

In addition, during the field reconnaissance:

• Groundwater was observed to daylight from the bottom of the existing ganoin basket wall and this perched groundwater table was used in the model as the likely controlling scenario for slope stability.

The soil engineering properties used in the analyses are summarized in Table 4 and were modeled using Mohr-Coulomb failure criterion.

Table 4. Soil Units and Engineering Properties

Soil Unit

Unit Weight

(pcf)

Saturated

Unit Weight

(pcf)

Strength Parameters

Cohesion

(psf)

Friction Angle

(degrees)

Aggregate Base 125 130 0 40

MSE Wall 150 N/A 0 50

Gravel Backfill 135 N/A 0 35

Road Embankment Fill 120 125 0 32

Silty Sand/Sandy Silt – Residual

Soil (Blue Mountains Island-Arc

Complex)

125 130 0 30

Schist (Blue Mountains Island-Arc

Complex) 150 N/A 0 45

Notes: pcf = pounds per cubic foot psf = pounds per square foot

A general back-analysis of these landslides was conducted using the subsurface information and soil units described above in Table 4. Slide2® performs slope stability computations based on the modeled conditions and calculates a factor of safety against slope failure, which is defined as the ratio of resisting forces to driving forces. A factor of safety of 1.0 indicates a “just-stable” condition, and a factor of safety less than 1.0 would indicate unstable conditions. The typical factor of safety for a landslide slope mitigation is 1.3. Risk reduction efforts are considered at a reduced factor of safety when appropriate. These back-analyses were utilized to determine soil and rock strength parameters and possible landslide subsurface geometry for the design of long-term solutions. The parameters were adjusted under static conditions until the FOS was 1.0 or less.

The results of the slope stability analysis for existing and proposed conditions are summarized in

Table 5 and the slope stability models are shown in Appendix B.

Table 5. Summary of Slope Stability Analysis Results

Scenario Calculated Factor of Safety

Existing 0.79

RSS 1.49

4.2 MP 19.8 REINFORCED SOIL SLOPE

The proposed RSS at MP 19.8 is intended to protect the roadway from further erosion and undermining from the failing gabion basket wall. Based on the available materials that would be sourced from the Twin Cabins Quarry site, we designed the RSS to use these government-provided materials as RSS backfill.

The RSS should be a welded wire face with reinforcement geogrid. At the site, we propose a minimum length of reinforcement, L, of 18 feet and a maximum reinforcement spacing of 1.5 feet.

The current RSS profile shows a maximum height of approximately 11 feet with a face angle of

1V:1H.

The subsurface drainage system for the RSS consists of partial coverage of the temporary cut slope with a geocomposite sheet drain meeting FP-24 Standard Specification 714.02. This partial coverage is intended to reduce hydrostatic pressure should incidental groundwater be encountered after construction. If areas of active seepage are encountered or identified during construction, these seepage areas should include additional coverage with the geocomposite sheet drains. A perforated pipe system is included at the RSS base and we anticipate that groundwater will flow through the geocomposite sheet drain to the perforated pipe system and out the face of the RSS.

4.3 DEEP PATCHES

Deep patches are short-term, partial- to full-width road repairs intended to reduce the differential settlement, cracking, and abrupt grade changes, caused by shallow slumps, typically within sidecast fills along older rural roads in steep terrain. While deep patches will generally not fully mitigate deep-seated landslide movements, the repairs are occasionally used to improve lateral transitions on low-volume roads. and extend the time before major repairs are necessary.

Deep patch thicknesses are typically between 2 and 5 feet thick and based on design charts and/or equations developed by the U.S. Forest Service (Musser and Denning, 2005), by WFLHD, and the Western Transportation Institute (Cuelho et al., 2012), or by the analysis and judgement of the geo-professional. Input parameters for design include the fill slope angle, friction angle of the soil, distance of the crack from the top of the slope (hinge point), slope distance, and other factors. The required tensile strength of the geosynthetic reinforcement can also be determined using one of the above references. Alternatively, deep patches can be designed similar to RSSs using limit equilibrium methods.

Alternating layers of geosynthetic reinforcement and select borrow backfill are vertically placed at between 8 and 12 inch spacing. Research by the FHWA Turner-Fairbank Highway Research

Center indicates that vertical spacing of 12 inches or less results in a geosynthetic reinforced soil

(GRS) composite behavior (Adams and Nicks, 2018). WFLHD standard of practice is to use a maximum vertical spacing of 12 inches when using the preferred biaxial stabilization geogrid or geotextile, which reduces the effects of creep effect of these types of products (Lim, 2025). A minimum of 3 layers of geosynthetic should be used on a minimum 2-foot-thick reinforced section.

Incorporating subsurface drainage in the design should also be considered when using high permeability backfill (e.g., select borrow) that can create a bathtub effect. The drainage system could include a perforated underdrain pipe on the cut-side of the road draining by gravity to an outlet on the fill slope, or by sloping the subgrade and daylighting the deep.

Areas slated for deep patch repairs can grow in area between the time that the initial field review is performed, and construction begins. The deep patch should extend past the cracked areas at least 10 feet along the roadway length (up and down station), and ideally at least 5 feet past the primary tension crack along the road width.

5 CONSTRUCTION CONSIDERATIONS

Earthwork is typically most economical when performed under dry weather conditions.

Appropriate erosion control measures should be implemented prior to beginning earthwork activities in accordance with regulations. In our opinion, excavation can generally be accomplished using standard excavation equipment. While not directly observed in our subsurface explorations, the presence of potential obstructions, such as small boulders, buried logs, or other debris, in the fill or other deposits could be encountered.

5.1 SITE PREPARATION

Site preparation within the proposed construction footprint should include removal of fill and soils containing roots, organics, debris, and any other deleterious materials. The contractor must use care during site preparation and excavation operations, so that any bearing surfaces are not disturbed. If disturbance does occur, the disturbed material should be removed to expose undisturbed material or be compacted in place to acceptable criteria as determined by the PE.

5.2 PROOFROLLING AND SUBGRADE VERIFICATION

Following site preparation, and prior to placing the base RSS or deep patch layer, or an aggregate base for the pavement sections, the exposed subgrade should be evaluated either by proofrolling or another method of subgrade verification. The subgrade should be proofrolled with a fully loaded dump truck or similar heavy, rubber-tire construction equipment to identify unsuitable areas. If evaluation of the subgrades occurs during wet conditions, or if proofrolling the subgrades is infeasible or will result in disturbance, it should be evaluated using a steel foundation probe.

Unsuitable areas identified during the field evaluation should be compacted to a firm condition or be excavated and replaced with structural fill.

5.3 WET WEATHER CONDITIONS

If earthwork is to be performed or fill is to be placed in wet weather or under wet conditions, when soil moisture content is above optimum and difficult to control, the following recommendations apply:

• Earthwork should be performed in small areas to minimize exposure.

• Excavation or the removal of unsuitable soils should be followed promptly by the placement and compaction of the specified structural fill.

• The size, type, and access of construction equipment used may have to be limited to prevent soil disturbance.

• The ground surface within the construction area should be graded to promote runoff of surface water away from the slopes and to prevent water ponding.

• The ground surface within the construction area should be properly covered and under no circumstances should be left uncompacted and/or exposed to moisture. Soils that become too wet for compaction should be removed and replaced with specified structural fill.

• Excavation and placement of fill should be observed by the geotechnical engineer to verify that all unsuitable materials are removed prior to placement, compaction requirements are met, and site drainage is appropriate.

• Erosion and sedimentation control should be implemented in accordance with best management practices (BMPs).

5.4 EXCAVATION

The near-surface soils at the site can be excavated with conventional earthwork equipment.

Sloughing and caving should be anticipated in loose, noncohesive materials. The intrusive granodiorite and tonalite and/or the metamorphic gneiss and schist bedrock may be encountered within the mass excavation when constructing the RSS. For the purposes of this report, rock excavation would apply to subsurface materials that require systematic drilling and blasting or the use of a pneumatic rock hammer. Based on the conditions observed in the borings, excavation within these materials should be possible using a Caterpillar 245 excavator, or equivalent, equipped with rock teeth. However, the actual subsurface conditions and excavation effort will not be fully apparent until the mass excavation is underway.

All excavations should conform to Sections 204 and 209 of the FP-24 (FHWA, 2024) and SCRs.

Large trees may need to be cleared for construction of the RSS slope. Clearing and grubbing of large trees should conform to Section 201 of FP-24 (FHWA, 2024).

Temporary slopes for the excavation of the RSS foundations are the responsibility of the contractor. Temporary slope angles will be determined based on OSHA requirements and on the conditions encountered, anticipated traffic/equipment loading above the temporary cut, and other factors under the control of the Contractor during construction. The Contractor should anticipate encountering perched groundwater, which was observed during the field reconnaissance, in the RSS temporary slope and excavation.

5.5 MATERIAL AND AGGREGATE SOURCE

We anticipate the excavated materials will not be suitable for reuse as RSS and deep patch backfill or road building material. The Twin Cabins Quarry, a potential government-provided material source along NFSR 221 has been identified and is currently being evaluated. The source will be described under a separate letterhead.

In the event suitable soils are encountered in the excavations and the Contractor desires to reuse the onsite materials, the Contractor is responsible for ensuring that the materials are processed to meet the contract requirements. Although possible the cut materials could be used for soil embankment fill during extended periods of dry weather, these primarily silt and silty sand soils are moisture sensitive with high natural moisture contents. Dry season grading is recommended if reuse is to be considered. Space and time for soil processing the soils during the construction season or admixtures, such as soil cement, may not be feasible.

5.6 TRAFFIC CONTROL AND ACCESSIBILITY

Considerations for maintaining public traffic through or around the work area should be considered, such as ramping in and out of the deep patch work/RSS area, or maintaining a stable cut or shoring for vehicles to pass around the excavation if a halfwidth deep patch is considered.

For half-road-width repairs, the ditches adjacent to the upslope side may be filled with quarry spalls overlain by one foot of aggregate base to create a temporary bump out for traffic to pass through. Full-road-width repairs may need to consider staged construction and temporary road closures.

6 LIMITATIONS

This report was prepared to provide data related to the subsurface investigation and laboratory test results for the proposed National Forest System Road 221 Rehabilitation project. At the time of this report, design plans and construction methods have not been finalized, and the information presented herein are based on project information. If project developments result in changes from the preliminary project information, WFLHD GEO should be contacted to determine if this report should be revised and/or expanded upon.

Variations may exist between the soil and groundwater conditions reported and those actually underlying the site. The nature and extent of such soil variations may change over time and may not be evident before construction begins. If any soil conditions are encountered at the site that are different from those described in this report, WFLHD GEO should be notified immediately to review the applicability of the geotechnical data contained herein.

Questions regarding this report should be addressed to Mark Swank, WFLHD Acting Functional

Manager, at (360) 210-6640, or mark.swank@dot.gov.

GEOTECHNICAL REPORT NO. 06-25

FINAL GEOTECHNICAL RECOMMENDATIONS REPORT

ID NEZPR117 221(1)

Clearwater County, Idaho

October 2025

Prepared by: _________________________________________

Nicholas Ferreira, Geotechnical Engineer

Approved by: _________________________________________

Mark Swank, GEO Team Functional Manager

10/3/2025

7 REFERENCES

ASTM International (ASTM), 2025, 2025 Annual Book of ASTM Standards, West Conshohocken, Pennsylvania.

Adams, M. and Nicks, J., 2018, Design and Construction Guidelines for Geosynthetic Reinforced

Soil Abutments and Integrated Bridge Systems, FHWA-HRT-17-080, Federal Highway

Administration, McLean, Virginia. Available at:

https://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/17080/17080.pdf

Cuelho, E., Perkins, S., and Akin, M., 2012, Deep Patch Repair, Phase I: Analysis and Design, Report No. FHWA-WFL/TD-12-003, Western Transportation Institute, Bozeman, Montana and

Federal Highway Administration, Western Federal Lands Highway Division, Vancouver, Washington, March 2012. Available at: https://westerntransportationinstitute.org/wp-content/uploads/2016/08/4W3350_Final_Report.pdf

Federal Highway Administration (FHWA), 2024, Standard Specifications for Construction of

Roads and Bridges on Federal Highway Projects FP-24, United States Department of

Transportation, Federal Highway Administration, Federal Lands Highways. Available at:

https://highways.dot.gov/federal-lands/specs

Geotechnical Resources, Inc., 2024, Geotechnical Data Report, Nez Perce Forest Road 221, (USFR 221) Rehabilitation, Idaho County, Idaho, dated January 24, 2025.

Kauffman, J.D., et. al., 2014, Geologic Map of the Idaho Part of the Grangeville 30 x 60 Minute

Quadrangle, and Adjoining Areas of Washington and Oregon, 1:100,000 quadrangle, Idaho

Geological Survey, Publication Order Number: GM-50

Kauffman, J.D., et. al., 2011, Geologic Map of the Dairy Mountain Quadrangle, Idaho County, Idaho 1:24,000 quadrangle, Idaho Geological Survey, Publication Order Number: DWM-97

Kauffman, J.D., et. al., 2008, Geologic Map of the Goodwin Meadows Quadrangle, Idaho County, Idaho 1:24,000 quadrangle, Idaho Geological Survey, Publication Order Number: DWM-97

Lewis, R.S., et. al., 2012, Geologic Map of Idaho, 1:750,000 quadrangle, Idaho Geological

Survey, Publication Order Number: M-9

Musser, S. W., and Denning, C., (2005), Deep Patch Road Embankment Repair Application

Guide, United States Department of Agriculture, Forest Service, October 2005. Available at:

https://www.fs.usda.gov/t-d/pubs/pdf/35dpi/05771204.pdf

Rocscience Inc. (2022). Slide2 (Version 9.026) [Computer software]. https://www.rocscience.com

DJ&A, P.C.

USFR 221 REHABILITATION

VICINITY MAP

JOB NO. 6999-AJAN. 2025 FIG. 1

0 4 8

1 INCH = 4 MILES±

BASEMAP PROVIDED BY USGS, 2024

PROJECT ALIGNMENT

LEGEND:

Tcr

Tcr

Qls

T_Pi

T_Psd

Ktt

KPro

Ktg

Qg

QTs

KJqd

JT_sv YqKg

Ym

Kog

CZs

T_Psd KJp

JT_sv

Tms

Kog

KPro

Tms

Kg

Ktt Tcr

KJp

Ktg

Qls

T_Pi

Ktt

Ktt

Qls

Ktt JT_sv

QTs

T_Pi

KJp

Ktt

JT_sv

KJcw

QTs Qg

T_Pi

Qg

Qg

Qls KJcw Qg

Qg Qaf

Tcr Tcr Qg

KPro

T_Pi

KPro

KJp

QTs Yq

Ym

T_Psd Kg

Yq Qg

QTsTcr

YqJT_sv

CZs

Kog Tcr

Ym

Tcr DJ&A, P.C.

USFR 221 REHABILITATION

LOCAL GEOLOGY MAP

JOB NO. 6999-AJAN. 2025 FIG. 2

0 4 8

1 INCH = 4 MILES±

LEGEND:

PROJECT ALIGNMENT

GEOLOGY MAP PROVIDED BY IDAHO GEOLOGIC SURVEY, 2012. COMPILED BY REED S. LEWIS, PAUL K. LINK, LOUDON R. STANFORD, AND SEAN P. LONG.

KPro - RIGGINS GROUP, OROFINO SERIES, AND RELATED ROCKS (CRETACEOUS TO PERMIAN)

METASEDIMENTARY AND METAVOLCANIC SCHIST, GNEISS, AMPHIBOLITE, AND MARBLE,

ALL OF UNCERTAIN AGE, ALONG EASTERN MARGIN OF ISLAND-ARC COMPLEX; TYPICALLY

HORNBLENDE-RICH. INCLUDES POLLOCK MOUNTAIN AMPHIBOLITE SOUTHEAST OF

RIGGINS AND GNEISS OF SWIFTWATER CREEK NEAR LOWELL.

Ktg - TONALITE, GRANODIORITE, AND QUARTZ DIORITE (CRETACEOUS)-TONALITE, GRANODIORITE, AND QUARTZ DIORITE, TYPICALLY HORNBLENDE-BEARING; INCLUDES

THE PAYETTE RIVER TONALITE (~90 MA) ALONG WESTERN BORDER ZONE OF THE

ATLANTA LOBE AND THE ~99 MA CROESUS PYROXENE-BIOTITE QUARTZ DIORITE SOUTH

OF HAILEY. ALSO INCLUDES GRANODIORITE WITH POTASSIUM FELDSPAR MEGACRYSTS

THAT IS TYPICALLY HORNBLENDE-BEARING AND FOLIATED (~90 MA IN CENTRAL IDAHO

AND ~100 MA IN NORTHERNMOST IDAHO) AND EARLY MAFIC PHASES OF THE

BITTERROOT LOBE (~70 MA).

Ktt - TONALITE AND TRONDHJEMITE (CRETACEOUS)-BIOTITE AND HORNBLENDE-BIOTITE

TONALITE AND BIOTITE-MUSCOVITE TRONDHJEMITE (120-110 MA); ROCKS CONTAIN

CONSPICIOUS MAGMATIC EPIDOTE IN PLUTONS ALONG EASTERN EDGE OF ARC

COMPLEX. INCLUDES TONALITIC PART OF HAZARD CREEK COMPLEX NORTHWEST OF

MCCALL, BLACKTAIL PLUTON SOUTHEAST OF GRANGEVILLE, AND SIXMILE CREEK PLUTON

SOUTHEAST OF OROFINO.

Qg - GLACIAL DEPOSITS (PLEISTOCENE)-TILL AND OUTWASH CONSISTING OF GRAVEL, SAND, SILT, AND CLAY. FORMED BY VALLEY GLACIERS AT HIGHER ELEVATIONS AND BY THE

CORDILLERAN ICE SHEET IN NORTHERN IDAHO. INCLUDES DEPOSISTS OF SEVERAL

GLACIAL EPISODES. INCLUDES ROCK GLACIER DEPOSITS AND SOME MODERN ALLUVIUM

DERIVED FROM REWORKED TILL AND OUTWASH.

COLUMBIA RIVER BASALT GROUP (MINOCENE)-LARGE-VOLUME LAVA FLOWS OF

THOLEIITIC BASALT, BASALTIC ANDESITE, AND SUBORDINATE ANDESITE IN WESTERN

IDAHO; CONSISTS OF IMNAHA BASALT (17.5-16.5 MA), GRANDE RONDE BASALT (16.5-15.6

MA), WANAPUM BASALT (15.6-14.5 MA), AND SADDLE MOUNTAINS BASALT (14.5-6 MA).

INCLUDES PORPHYRITIC BASALT AND BASALTIC ANDESITE IN WESTERN OWYHEE

COUNTY.

Tcr -

UNIT DESCRIPTIONS:

DJ&A, P.C.

USFR 221 REHABILITATION

SITE PLAN

JOB NO. 6999-AJAN. 2025 FIG. 3

DETAIL MAP 1

(FIGURE 4)

0 4 8

1 INCH = 4 MILES±

BASEMAP PROVIDED BY USGS, 2024

DETAIL MAP 2

(FIGURE 5)

DETAIL MAP 3

(FIGURE 6)

DETAIL MAP 4

(FIGURE 7)

PROJECT ALIGNMENT

LEGEND:

APPROXIMATE BORING LOCATIONS

SG24-09

SG24-10

JOB NO. 6999-A FIG. 4

0 4,000 8,000

1 INCH = 4,000 FEET

LEGEND:

DJ&A, P.C.

USFR 221 REHABILITATION

N

F-221

BASEMAP PROVIDED BY GOOGLE EARTH, 2024

HWY 14

PROJECT ALIGNMENT

APPROXIMATE LOCATION OF BORING DRILLED BY GRI

DETAIL MAP 1:

MP 6.7 TO MP 11.7

JAN. 2025

BH24-05

BH24-06

SG24-06

SG24-07

SG24-08

JOB NO. 6999-A FIG. 5

0 4,000 8,000

1 INCH = 4,000 FEET

LEGEND:

DJ&A, P.C.

USFR 221 REHABILITATION

NF-221

BASEMAP PROVIDED BY GOOGLE EARTH, 2024

PROJECT ALIGNMENT

APPROXIMATE LOCATION OF BORING DRILLED BY GRI

DETAIL MAP 2:

MP 12.1 TO MP 20.8

BH24-03

BH24-04

SG24-05

JOB NO. 6999-A FIG. 6

0 2,000 4,000

1 INCH = 2,000 FEET

LEGEND:

DJ&A, P.C.

USFR 221 REHABILITATION

NF-2

BASEMAP PROVIDED BY GOOGLE EARTH, 2024

PROJECT ALIGNMENT

APPROXIMATE LOCATION OF BORING DRILLED BY GRI

DETAIL MAP 3:

MP 21.1 TO MP 24.0

BH24-01

BH24-02

SG24-01

SG24-02

SG24-03

SG24-04

DETAIL MAP 4:

MP 26.4 TO MP 33.6

JOB NO. 6999-AJAN. 2025 FIG. 7

0 4,000 8,000

1 INCH = 4,000 FEET

LEGEND:

DJ&A, P.C.

USFR 221 REHABILITATION

NF

-2

BASEMAP PROVIDED BY GOOGLE EARTH, 2024

PROJECT ALIGNMENT

APPROXIMATE LOCATION OF BORING DRILLED BY GRI

DRAFT

GRI 6999-A: Nez Perce Forest Road 221 (USFR 221) Rehabilitation Geotechnical Data Report January 24, 2025

APPENDIX A

Boring Logs, Disturbed Sample Photographs, and Laboratory Testing

Table 1A

GUIDELINES FOR DESCRIPTION OF SOIL1

Description of Relative Density for Cohesionless (Coarse-Grained) Soils

Relative Density

Standard Penetration Resistance (N-values) blows/foot (ft)

3-inch Sampler, 140-lb hammer approx.

N-Value (blows/ft)2 Very Loose 0 - 4 0 – 6

Loose 5 - 10 7– 15 Medium Dense 11 - 30 16 – 45

Dense 31 - 50 46 – 75 Very Dense over 50 over 75

Description of Relative Consistency for Cohesive (Fine-Grained) Soils

Relative Consistency

Standard Penetration Resistance (N-values) blows/ft

3-inch Sampler, 140 lb hammer approx.

N-Value (blows/ft)1

Very Soft 0 - 1 0 – 2 Soft 2 - 4 3 – 6 Firm 5 - 8 7 – 12 Stiff 9 - 15 13 – 23

Very Stiff 16 - 30 24 – 45 Hard 31 – 60 46 – 85

Very Hard over 60 over 85

Grain-Size Classification Modifier for Subclassification Boulders:

>12 inches Cobbles:

3 inches - 12 inches Gravel:

No. 4 sieve - ¾ inch (fine) ¾ inch - 3 inches (coarse) Sand:

No. 200 - No. 40 sieve (fine) No. 40 - No. 10 sieve (medium) No. 10 - No. 4 sieve (coarse) Silt/Clay:

Pass No. 200 sieve

Adjective

Primary Constituent SAND or GRAVEL

Primary Constituent SILT or CLAY

Percentage of Other Material (By Weight) sand, gravel absent: <15 (sand, gravel) <15 (sand, gravel) with sand, gravel: >15 (sand, gravel) >15 (sand, gravel) silt, clay absent: <5 (silt, clay)

Relationship of clay and silt determined by plasticity index test with silt, clay: 5 - 15 (silt, clay) silty, clayey: >15 (silt, clay)

1. Soil descriptions are developed using visual-manual procedures (ASTM D2488) and generally follow the Federal Lands Highway (FLH) Soil Description and Identification Guidelines manual dated August 2024.

Table 2A

GUIDELINES FOR CLASSIFICATION OF ROCK

Relative Rock Weathering Scale

Term Field Identification Fresh No visible sign of rock material weathering; slight discoloration on major discontinuity surface is possible.

Slightly Weathered

Discoloration indicates weathering of rock material and discontinuity surfaces. All rock material may be discolored by weathering and the external surface may be somewhat weaker than in its fresh condition.

Moderately Weathered

Less than half the rock material is decomposed and/or disintegrated to a soil. Fresh or discolored rock is present either as a discontinuous framework or as corestones. A minimum 2-inch (50 mm) diameter sample cannot be broken readily by hand across the rock fabric.

Highly Weathered

More than half of the rock is decomposed and/or disintegrated to soil. Fresh or discolored rock is present either as a discontinuous framework or as corestones. A minimum 2-inch (50 mm) diameter sample can be broken readily by hand across the rock fabric.

Completely Weathered

All rock material is decomposed and/or disintegrated to soil. The original mass structure is still largely intact. Material can be granulated by hand. If rock is considered to be completely weathered, use FLH Soil Description and Identification Guidelines to describe the residual soil material.

Residual Soil All rock material is converted to soil. The mass structure and material fabric are destroyed but the apparent structure remains intact. There may be a large change in volume, but the soil has not been significantly transported. Material can be easily broken-down by hand. If rock is considered to be residual soil, use FLH Soil Description and Identification Guidelines to describe the residual soil material.

Relative Rock Strength Scale

Term

Hardness Designation

Field Identification

Approximate Unconfined Compressive Strength

Extremely Weak R0 Specimen can be indented by thumbnail. 35 - 150 psi

Very Weak R1

Specimen crumbles under sharp blow with point of geological hammer, and can be peeled with a pocket knife.

150 - 725 psi

Weak R2 Shallow cuts or scrapes can be made in a specimen with a pocket knife. A firm blow with a geological hammer point creates shallow indents.

725 – 3,500 psi

Medium Strong R3

Specimen cannot be scraped or cut with a pocket knife.

Specimen can be fractured with a single firm blow with a geologic hammer point.

3,500 – 7,250 psi

Strong R4 Specimen requires more than one firm blow of the geologic hammer point to fracture. 7,250 – 14,500 psi

Very Strong R5 Specimen requires many firm blows from the hammer end of the geologic hammer to fracture. 14,500 – 36,250 psi

Extremely Strong R6 Specimen can only be chipped with firm blows from the hammer end of the geologic hammer. >36,250 psi

1. Rock descriptions generally follow the Federal Lands Highway (FLH) Rock Characterization Guidelines manual dated December 2017.

BH24-03 S-3 7.5 -- 13 -- -- -- -- SILT

S-5 12.5 -- 30 -- -- -- -- SILT

BH24-04 S-2 5.0 -- 16 -- -- -- -- SILT

S-4 10.0 -- 7 -- -- -- -- Silty GRAVEL

BH24-05 S-4 9.5 -- 14 -- -- -- 33 Silty SAND

S-5 11.5 -- 11 -- -- -- -- SILT

BH24-06 S-1 2.5 -- 6 -- -- -- -- SILT

S-2 5.0 -- 7 -- -- -- -- SILT

SG24-04 S-1 1.5 -- 13 111 32 11 27 Clayey SAND SG24-06 S-1 1.5 -- 10 123 24 7 24 Clayey SAND

Table 3B

SUMMARY OF LABORATORY RESULTS

Sample Information Atterberg Limits

Soil Type Fines

Content, % Plasticity Index, %

Liquid Limit, %

Dry Unit Weight, pcf

Moisture Content, %Elevation, ftSampleLocation Depth, ft

GRAVEL; clean to some silt, clay, and sand

Sandy GRAVEL; clean to some silt and clay

Silty GRAVEL; up to some clay and sand

Clayey SAND; up to some silt and gravel

Gravelly CLAY; up to some silt and sand

Sandy CLAY; up to some silt and gravel

Silty CLAY; up to some sand and gravel

Symbol Description

Flush-mount monument set in concrete

Concrete, well casing shown where applicable

Filter pack, machine-slotted well casing shown where applicable

1-in.-diameter solid PVC

FIELD MEASUREMENTS

Typical Description

Groundwater level after drilling and date measured

Symbol Typical Description

BASALT

MUDSTONE

SILTSTONE

PEAT

Symbol

FILL

Clayey GRAVEL; up to some silt and sand

SAND; clean to some silt, clay, and gravel

SILT; up to some clay, sand, and gravel

Gravelly SILT; up to some clay and sand

Sandy SILT; up to some clay and gravel

Clayey SILT; up to some sand and gravel

CLAY; up to some silt, sand, and gravel

Grab Sample

Rock core sample interval

Sonic core sample interval

INSTALLATION SYMBOLS

Symbol

Bentonite seal, well casing shown if applicable

Vibrating-wire pressure transducer

SymbolBEDROCK SYMBOLS

SOIL SYMBOLS

Typical Description

SAMPLER SYMBOLS

Sampler DescriptionSymbol

LANDSCAPE MATERIALS

Gravelly SAND; clean to some silt and clay

Silty SAND; up to some clay and gravel

Shelby tube sampler with recovery

(ASTM D1587)

Grout, vibrating-wire transducer cable shown where applicable

1-in.-diameter hand-slotted PVC

Grout, inclinometer casing shown where applicable

Groundwater level during drilling and date measured

SANDSTONE

SURFACE MATERIAL SYMBOLS

Symbol Typical Description

BORING AND TEST PIT LOG LEGEND

Rock quality designation (RQD, %)

Asphalt concrete PAVEMENT

Portland cement concrete PAVEMENT

Crushed rock BASE COURSE

2.0 in. O.D. split-spoon sampler and Standard Penetration Test with recovery (ASTM D1586)

3.0 in. O.D. split-spoon sampler with recovery

(ASTM D3550)

Push probe sample interval

Rock/sonic core or push probe recovery (%)

B O

R

IN

G A

N D

T E

S T

P

IT

L O

G L

E G

E N

D G

R I D

A T

A T

E M

P

LA

T E

.G D

T

/7 /2

Asphalt concrete PAVEMENT (1 inch) over crushed rock BASE COURSE (8 inches) SAND (SW-SM) with silt and gravel, dense, brown and white, damp, fine to coarse sand, fine to coarse subangular to angular gravel (POSSIBLE FILL)

TONALITE, white mottled black, coarse grained, moderately weathered to fresh, medium strong to very strong rock (R3 to R5) (IDAHO BATHOLITH) (10/14/2024)

Sand to gravel sized feldspar crystals found in sample S-1.

Practical refusal, potential bedrock at

5.5 feet.

Energy Ratio:

SA

M

PL

E

N O

CME 75 Truck-Mounted Drill Rig

Surface Elevation:

Hammer Type:

1.0

Weight:

Not Available IN

ST

AL

LA

TI

O

N

0.5

Logged By:

Drilling Method:

10/14/24

IN

ST

AL

LA

TI

O

N

8 in.

PLASTIC LIMIT, %

LIQUID LIMIT, %

FINES CONTENT, %

BLOWS PER FOOT

MOISTURE CONTENT, %

Hollow-Stem Auger

Drilled by:

140 lb Drop:

0.85See Legend for Explanation of Symbols

D

EP

TH

, F

T

SA

M

PL

E

TY

PE

BL

O

W C

O U

N T

Date Started:

Note:

K. Law Western States Soil Conservation, Inc.

D

EP

TH

, F

T

Equipment:

G R

AP

H

IC

L

O G

Auto Hammer

Hole Diameter:

CLASSIFICATION OF MATERIAL

30 in.

TORVANE SHEAR STRENGTH, TSF

UNDRAINED SHEAR STRENGTH, TSF

COMMENTS AND

ADDITIONAL TESTS

GPS Coordinates: 45.61722° N -116.02954° W ()

BORING BH24-01

FIG. 1A

G R

I B O

R

IN

G L

O G

G

P S

N O

E

LE

V G

R I D

A T

A T

E M

P

LA

T E

.G D

T

/2 4/

S-1

S-2 S-3

50/5" 100/0.5"

0.1

0.8

5.0

5.5

JAN. 2025 JOB NO. 6999-A

0 100

50/5" 100/0.5"

SAND (SW-SM) with silt and gravel; very dense, brown and white, damp, fine to coarse sand, fine to coarse angular gravel (POSSIBLE FILL)

---medium dense at 5 feet

SAND (SW-SM) with silt and gravel; dense, brown and white, damp, fine to coarse sand, fine to coarse angular gravel (COMPLETELY WEATHERED

TONALITE, IDAHO BATHOLITH)

TONALITE, white mottled black, coarse grained, moderately weathered to fresh, medium strong to very strong rock (R3 to R5) (IDAHO BATHOLITH) (10/14/2024)

Rough drill action.

Practical refusal, potential bedrock at

10.6 feet. Gravel sized rock fragments on auger flights.

Energy Ratio:

SA

M

PL

E

N O

CME 75 Truck-Mounted Drill Rig

Surface Elevation:

Hammer Type:

1.0

Weight:

Not Available IN

ST

AL

LA

TI

O

N

0.5

Logged By:

Drilling Method:

10/14/24

IN

ST

AL

LA

TI

O

N

8 in.

PLASTIC LIMIT, %

LIQUID LIMIT, %

FINES CONTENT, %

BLOWS PER FOOT

MOISTURE CONTENT, %

Hollow-Stem Auger

Drilled by:

140 lb Drop:

0.85See Legend for Explanation of Symbols

D

EP

TH

, F

T

SA

M

PL

E

TY

PE

BL

O

W C

O U

N T

Date Started:

Note:

K. Law Western States Soil Conservation, Inc.

D

EP

TH

, F

T

Equipment:

G R

AP

H

IC

L

O G

Auto Hammer

Hole Diameter:

CLASSIFICATION OF MATERIAL

30 in.

TORVANE SHEAR STRENGTH, TSF

UNDRAINED SHEAR STRENGTH, TSF

COMMENTS AND

ADDITIONAL TESTS

GPS Coordinates: 45.63208° N -116.01679° W ()

FIG. 2A

G R

I B O

R

IN

G L

O G

G

P S

N O

E

L…