Attachment 004 FLH Soil Identification Guidelines_2025.pdf

Federal Lands Highway

Soil Description, Interpretation, and Reporting Guidelines

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025 i

TABLE OF CONTENTS

1 INTRODUCTION

1.1 PURPOSE AND INTENT

1.2 REFERENCED PROCEDURES

2 EXPLORATION AND SAMPLE IDENTIFICATION

2.1 EXPLORATION NAME AND NUMBER CONVENTION

2.2 SAMPLE COLLECTION AND LABELS

3 SOIL IDENTIFICATION

3.1 COARSE-GRAINED SOILS – GRAVEL & SAND (<50% FINES)

3.2 FINE-GRAINED SOIL – SILT & CLAY (≥ 50% FINES)

3.2.1 INORGANIC FINE-GRAINED SOIL

3.2.2 ORGANIC FINE-GRAINED SOIL

3.3 PEAT

3.4 COBBLES AND BOULDERS

4 SOIL DESCRIPTORS

4.1 APPARENT DENSITY AND CONSISTENCY

4.2 COLOR

4.3 MOISTURE

4.4 PARTICLE SIZE AND ANGULARITY (COARSE-GRAINED SOIL)

4.5 PLASTICITY (FINE-GRAINED SOIL)

4.6 STRUCTURE

4.7 OTHER DESCRIPTORS

4.7.1 CEMENTATION

4.7.2 HCl REACTION

4.7.3 MICA CONTENT

4.7.4 FROZEN SOIL

4.7.5 REMARKS

4.8 GROUNDWATER OBSERVATIONS

5 FIELD: SOIL EXPLORATION LOGS

5.1 DEFINING AND DELINEATING STRATIFICATION

5.2 ORDER OF DESCRIPTORS

5.3 FIELD SOIL EXPLORATION LOG EXAMPLES

6 REPORT: SOIL EXPLORATION LOGS

6.1 DATA AND SAMPLE REVIEW AND LABORATORY TESTS

6.2 FIELD SOIL EXPLORATION LOG MODIFICATIONS

6.3 ORDER OF DESCRIPTORS

6.4 REPORT SOIL EXPLORATION LOG EXAMPLES

7 REFERENCES

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025 ii

ATTACHMENTS

APPENDIX A Example Field Soil Boring Logs

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

1 INTRODUCTION

This guide outlines the standard practice for field identification and classification of soils on Federal Lands Highway (FLH) projects. The intent of this guide is to produce consistent and uniform field descriptions for soil by FLH personnel and consultants working on FLH projects.

1.1 PURPOSE AND INTENT

The purpose of performing geotechnical investigations is to characterize the in situ subsurface conditions underlying a site. Some common explorations used to collect soil and groundwater data include boreholes, test pits, cone penetration test (CPT) probes, and geophysical surveys, among many others, and each can be performed with variable types of equipment and sampling methods. Typically, no single method will collect all the needed data due to various limitations.

Assumptions, interpretations, and extrapolations will be necessary to properly characterize a site.

The intent of these guidelines pertains specifically to describing soils based on direct field observations of exploration surface walls, existing slope cuts and outcrops, and physical soil samples collected by advancing and/or driving samplers. Determining in situ subsurface conditions from boreholes can be particularly challenging due to, for example, the drill rig type, drill method, sample intervals, sampler type and size, etc., which can eliminate, limit, or preferentially collect soil constituents. Since soil identification, for engineering purposes, is based on the distribution and behavior of the fine-grained and coarse-grained soil constituents, this absence and/or excess will cause erroneous soil classification of the in situ subsurface characterization unless critical interpretations are made during and after field data collection based on sample reviews, laboratory tests, and the holistic assessment.

Prior to performing the field investigations, a desktop study of the area should be performed to determine the mapped surface and bedrock geology stratigraphy, presence of geologic hazards, review past geotechnical data and reports in the vicinity, and other available information.

Two important notes to consider:

• The field identifications in the exploration logs should not solely be an assessment of the collected materials in a sample. They should consider the above discussed variables, along with drill action and other observations, that are included as detailed notes.

• The exploration logs with detailed notes should be carried forward to assist in:

o Developing the laboratory test program, and, o Digitization of the exploration for report presentation.

1.2 REFERENCED PROCEDURES

In this guide, an important distinction is made between field identifications during exploration and the soil descriptions on the digital logs provided in memorandums and reports. The referenced documents include:

• Field Soil Identification: Based on modified procedures outlined in ASTM D 2488 – Standard Practice for Description and Identification of Soils (Visual-Manual Procedure) and Publication No. FHWA NHI-01-031, Subsurface Investigations – Geotechnical Site Characterization Reference Manual (2002). The visual-manual identification utilizes

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025 visual observation and simple manual tests to identify the characteristics of the soil constituents whereas soil classification is based on prescribed laboratory tests to determine particle size characteristics, liquid limit, and plasticity index.

• Memorandum and Report Soil Descriptions: Based on soil classification according to ASTM D2487 – Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System) and the AASHTO Classification System (AASHTO M 145). After a laboratory testing program has been completed on representative samples, the USCS Group Symbols are added behind the group name to indicate that it is a classification in accordance with ASTM D 2487 based on the laboratory test results.

AASHTO soil classifications may be added to the boring log at the discretion of the project geotechnical engineer or engineering geologist. The AASHTO soil classifications are determined in accordance with AASHTO M 145 based on the results of prescribed laboratory tests. Please note, not every sample has to be tested to be considered classified and professional judgement should be used to extrapolate similar materials at other depths and between borings to assign the same soil classifications within a stratigraphic unit.

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

2 EXPLORATION AND SAMPLE IDENTIFICATION

Exploration naming conventions and sample labels should adhere to the following guidelines.

2.1 EXPLORATION NAME AND NUMBER CONVENTION

Identify each exploration with an alphanumeric identification (ID) that includes the two-digit year the exploration was completed followed by a dash and then a two-digit sequential number. Letters used in the ID should either describe the exploration type, instrumentation(s) installed, or location of the boring. Use the same total numerical digits in all exploration identifications for each project (i.e., BH24-01 and BH24-10).

The following abbreviations are recommended:

BH Conventional boring CP Cone penetrometer test hole

IT Multiple instruments MW Monitoring well/open standpipe

PM Pressuremeter test hole SA Shape array

SG Subgrade boring SI Slope inclinometer casing

TD Time domain reflectometer TM Thermistor

TP Test pit VW Vibrating wire piezometer

Example Boring IDs are listed and described below:

BH24-01 indicates boring number 1 drilled in 2024 with no instrumentation

SG24-22 indicates subgrade boring number 22 drilled in 2024

VW24-04 indicates boring number 4 drilled in 2024 with a vibrating wire piezometer installation

SI24-22 indicates boring number 22 drilled in 2024 with slope inclinometer casing installation

TP24-01 indicates test pit number 1 excavated in 2024

TM24-01 indicates boring number 1 drilled in 2024 with thermistor installation

INST24-01 indicates boring number 1 drilled in 2024 with multiple instrument installations, i.e., slope inclinometer casing and vibrating wire piezometer

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

2.2 SAMPLE COLLECTION AND LABELS

Soil, rock, and other material samples collected during drilling should be handled with care.

Depending on the volume, disturbed soil samples should be placed in 1-gallon airtight resealable bags (e.g., Ziploc), plastic jars with lids, plastic bulk sample bags, or 5-gallon buckets (with lids).

Shelby tube and modified California brass liner samples should be kept vertical at all times with the end caps taped securely and kept from freezing and transported in a stable frame to prevent jostling and general disturbance of the in-situ sample.

The bags, jars, buckets, and tubes should be labeled with permanent black marker and in clear penmanship with the following information:

1. Project Name and Project Number

2. Exploration ID

3. Sample ID

4. Sample Depth or Sample Depth Range (in feet with increments in tenths of feet, i.e., 12.5’ to 15.3’)

5. Sample Collection Date

6. For disturbed driven samples, the blow counts in 6-inch increments (i.e., 5-8-15). If refusal is encountered, then the 6-inch increments and the final blow counts over inches driven (i.e., 4-25-50/3”)

7. For Shelby tube samples, the pressure to push the casing into the ground (in pounds per square inch)

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

3 SOIL IDENTIFICATION

The first step in identifying soils is to categorize the sample into one of the two broad categories listed below:

• Coarse-Grained Soils (passing 3-inch (75 mm) sieve and retained No. 200 sieve [0.075 mm opening]): Soils that contain less than 50% fines. These soils are composed primarily of sand and gravel. See Subsection 3.1.

• Fine-Grained Soils (passing No. 200 sieve [0.075 mm opening]): Soils that contain

50% or more fines. These soils are composed primarily of silt and clay. See Subsection 3.2.

Peat is a highly organic soil that does not fall into either of the categories listed above. Peat is material composed primarily of vegetative tissue in various stages of decomposition that has a fibrous to amorphous texture, dark brown to black color, a spongy consistency, and an organic odor. See Subsection 3.3 for guidance on describing peat.

The soil Group Name does not take into account the presence of cobbles and boulders (> 3 inch material) within the soil mass. See Subsection 3.4 for guidance on describing soils containing cobbles and/or boulders.

3.1 COARSE-GRAINED SOILS – GRAVEL & SAND (<50% FINES)

Coarse-grained soils have less than 50% fines. Coarse-grained soils are identified by estimating the percentages of gravel + sand compared to the fines content and determining the behavioral characteristics of the fine-grained material. The particle sizes of gravel, sand, and fines are defined in Exhibit 3.1-A.

Exhibit 3.1-A PARTICLE SIZE DEFINITIONS FOR GRAVEL, SAND, AND FINES

Component Grain Size Limits

Gravel #4 to 3-inch Sieve

(4.75 mm to 75 mm opening)

Sand #200 to #4 Sieve

(0.075 mm to 4.75 mm opening)

Fines Smaller than #200 Sieve

(0.075 mm opening)

Rounded to the nearest 5%, the percentage of fines in the soil should be estimated as: 5% or less, 10%, or 15% or more. Exhibit 3.2.1-A in Subsection 3.2.1 can be used to identify the soil group of the fines.

Identify coarse-grained soil as well-graded if it has a wide range of particle sizes and substantial amounts of the intermediate particle sizes. Identify coarse-grained soil as poorly graded if it contains predominantly one size (uniformly graded) or if it has a wide range of sizes with some intermediate sizes obviously missing (gap graded).

Once the major component is identified, use the flow chart in Exhibit 3.1-B to determine the Soil Group Name.

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

Exhibit 3.1-B FLOW CHART FOR IDENTIFICATION OF COARSE-GRAINED SOIL

(AFTER ASTM D 2488)

3.2 FINE-GRAINED SOIL – SILT & CLAY (≥ 50% FINES)

Fine-grained soils have 50% or more fines. Identify inorganic fine-grained soil according to Subsection 3.2.1. Identify the soil as organic fine-grained soil according to Subsection 3.2.2.

3.2.1 INORGANIC FINE-GRAINED SOIL

As outlined in ASTM D 2488, fine-grained soils are separated into four basic groups based on the physical characteristics of dry strength, dilatancy, and toughness. These physical characteristics are summarized in Exhibit 3.2.1-A. Field index tests can be performed on a representative handful-sized sample consisting of material smaller than the No. 40 sieve to determine physical characteristics of fine-grained soil. The field index tests outlined in Exhibit 3.2.1-B should be performed for each soil unit encountered to properly name the Soil Group. When describing and identifying similar soil samples, generally not all of the procedures need to be followed for field index testing as outlined in Exhibit 3.2.1-B.

Exhibit 3.2.1-A FIELD IDENTIFICATION OF INORGANIC FINE-GRAINED SOIL

Soil Group Dry Strength Dilatancy Toughness

SILT (ML) None to Low Slow to Rapid Low or thread cannot be formed elastic SILT (MH) Low to Medium None to Slow Low to Medium lean CLAY (CL) Medium to High None to Slow Medium fat CLAY (CH) High to Very High None High

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

Exhibit 3.2.1-B FIELD METHODS TO IDENTIFY INORGANIC FINE-GRAINED SOILS

FIELD TEST

Procedure

Description Criteria

DRY STRENGTH

Field Test Procedure: From the sample mold a 1-inch diameter ball until it has the consistency of putty, adding water as necessary. Make at least three specimens about ½ inch (13 mm) in diameter and allow the specimens to air dry in sunlight or other means at temperatures below 140°F (60°C). Test the dry strength of the balls by crushing between the thumb and forefinger.

No dry strength The dry specimen crumbles into powder with mere pressure of handling.

Low dry strength The dry specimen crumbles into powder with some finger pressure.

Medium dry strength The specimen breaks into pieces or crumbles with considerable finger pressure.

High dry strength The specimen cannot be broken with finger pressure but will break into pieces when pressed between the thumb and a hard surface.

Very high dry strength The specimen cannot be broken between the thumb and a hard surface.

DILATANCY

Field Test Procedure: From the sample mold a ball about ½ inch diameter, adding water as needed, until it has a soft but not sticky consistency. Smooth the ball on the palm of the hand with a soil knife or spatula and shake the specimen horizontally, striking the side of the hand vigorously multiple times. Note water appearing on the soil surface (dilatancy sheen) and squeeze the sample to observe disappearance of sheen.

No dilatancy No visible change in the specimen.

Slow dilatancy Water appears slowly on the surface of the specimen during shaking and does not disappear or disappears slowly upon squeezing.

Rapid dilatancy Water appears quickly on the surface of the specimen during shaking and disappears quickly upon squeezing.

FIELD TEST

Procedure

Description Criteria

TOUGHNESS AND PLASTICITY

Field Test Procedure: Shape the specimen into an elongated pat and roll by hand on a smooth surface or between the palms into a thread about ⅛-inch diameter. Repeatedly fold the specimen back together into a ball and reroll until the thread crumbles when it reaches ⅛-inch diameter - near the soil plastic limit. Note the pressure required to roll the thread and the thread strength. After reaching the plastic limit, lump the pieces of thread back together and knead until the lump crumbles and note the toughness during kneading.

Low toughness Slight pressure is required to roll the thread near the plastic limit and the lump is weak and soft.

Medium toughness Medium pressure is required to roll the thread to near the plastic limit and thread and the lump have medium stiffness.

High toughness Considerable pressure is required to roll the thread to near the plastic limit and the thread and the lump have very high stiffness.

Non-plastic ⅛-inch (3-mm) diameter thread cannot be rolled at any water content.

Low plasticity Barely rolls thread and lump cannot be formed when drier than the plastic limit.

Medium plasticity Easy to roll with little time required to reach plastic limit and thread cannot be rerolled. Lump crumbles when drier than plastic limit.

High plasticity Long time to roll and knead to reach the plastic limit and thread can be rerolled several. Lump can be formed without crumbling when drier than plastic limit.

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

Once the soil group has been determined, estimate the percentages of sand and gravel contained in the field sample to the nearest 5% (by weight) and use the flow chart in Exhibit 3.2.1-C to determine the Soil Group Name.

Exhibit 3.2.1-C FLOW CHART FOR IDENTIFICATION OF INORGANIC FINE-GRAINED

SOIL (AFTER ASTM D 2488)

3.2.2 ORGANIC FINE-GRAINED SOIL

If the soil has more than 50% fines and contains enough organic particles to influence the soil properties, identify it as an organic fine-grained soil. Organic soils usually have a dark brown to black color and may have an organic odor. Often, organic soils will change colors, for example from black to brown, when exposed to the air. Organic soils will not have a high toughness or plasticity. The thread for the toughness test will be spongy. Once the soil is determined as a fine-grained organic soil, estimate the percentage of fines, sand, and gravel in the field sample using the same procedures as for fine-grained inorganic soil. Use the flow chart in Exhibit 3.2.2-A (from ASTM D 2488) to determine the Soil Group Name and do not differentiate between organic silt and organic clay in the field.

Exhibit 3.2.2–A FLOW CHART FOR IDENTIFICATION OF ORGANIC FINE-GRAINED SOIL

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

3.3 PEAT

Soils composed primarily of vegetative tissue in various stages of decomposition that have a fibrous to amorphous texture, usually are dark brown to black, spongy consistency, and have distinctive organic odor are designated as peat. Peat is not subjected to any further identification procedures. Include color, moisture, odor, and any other relevant descriptors in the descriptive information on the soil log for the sample.

3.4 COBBLES AND BOULDERS

Soil identification is based on the minus 3-inch material and does not take into account the presence of cobbles and boulders within the soil mass. Cobbles and boulders are defined as follows:

• Cobbles – particles of rock that will pass a 12-inch (300 mm) square opening and are retained on a 3-inch (75 mm) sieve.

• Boulders – particles of rock that will not pass a 12-inch (300 mm) square opening.

When cobbles and/or boulders are detected, either visually within a test pit or indicated by drilling action or core recovery, report the constituent(s) on the field logs.

Cobbles and/or boulders may be listed as the main soil constituent if the layer consists primarily of cobbles and/or boulders. An example description of the main constituents follows:

COBBLES and BOULDERS in a silty sand matrix

When cobbles and/or boulders are not the main constituent in the layer, report these constituent(s) on the field logs following the main soil type. If relevant, add notes at the end of the constituent description indicating the depths where cobbles and boulders are encountered.

Descriptors to be used include:

with cobbles - when only cobbles are present with boulders - when only boulders are present with cobbles and boulders - when both cobbles and boulders are present.

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

4 SOIL DESCRIPTORS

4.1 APPARENT DENSITY AND CONSISTENCY

The standard penetration test (SPT) is an in-situ field test (ASTM D 1586) that is widely used to approximate apparent density of cohesionless soil and the consistency of cohesive soil. Use Exhibits 4.1-A and 4.1-B to describe the apparent density or consistency, respectively, based on the field recorded uncorrected “standard penetration resistance” or “N-value”.

The standard penetration test consists of driving a 2-inch outside diameter (O.D.) split barrel sampler at the bottom of the borehole using a 140-lbs hammer with a 30-inch drop. The sampler is driven a total of 18 inches with the number of blows recorded for each 6-inch increment, or until practical refusal (refer to description below). The first increment is the “seating drive” of the sampler, and the sum of the number of blows required to advance the second and third increments is the “standard penetration resistance” or the “N-value” reported in blows per foot (bpf).

ASTM D 1586 indicates practical refusal if one of the following occurs:

1) A total of 50 blows is applied during any one of the 6-inch increments, or

2) A total of 100 blows has been applied, If the sampler sinks under the weight of the rods, or the weight of the rods and the hammer, record the depth of penetration and drive the sampler through the rest of the test interval. Record the blow count as either weight of rods (WR) or weight of hammer (WH), plus the blows per 6-inch increment, as relevant.

The type of hammer used to drive the sampler (e.g., automatic trip hammer, cathead and safety hammer, cathead and donut hammer) should be recorded on the field log. Also record the use of non-standard samplers (e.g., 3-inch split barrel samplers). Standard U.S. practice often omits the inside liner in the standard 2-inch O.D. split-barrel sampler. Therefore, if used, liners must be noted on the field log. Note that the use of an oversize sampler or other hammer weights and drops are not considered a “Standard Penetration Test.” Therefore, the blow counts are not considered an “N” value but should still be recorded at each 6-inch interval. The exception is when the driving refusal criteria for oversize samplers (with a 140-lb hammer) is 75 blows per 6-inch interval. For non-standard samplers shorter than 18 inches, the 6-inch seating increment should be omitted and the blows first two 6-inch increments are recorded as the penetration resistance.

Exhibit 4.1-A APPARENT RELATIVE DENSITY OF COARSE-GRAINED SOILS USING A 140-lb HAMMER WITH A 30-INCH DROP

2-Inch SPT N-value (blows per foot)

Apparent Density 3- to 3.5-Inch Sampler

(blows per foot)

0 to 4 Very Loose 0 to 6

5 to 10 Loose 7 to 15

11 to 30 Medium Dense 16 to 45

31 to 50 Dense 46 to 75

> 50 Very Dense > 75

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

Exhibit 4.1-B CONSISTENCY OF FINE-GRAINED SOILS USING A 140-lb HAMMER

WITH A 30-INCH DROP

2-Inch SPT N-value (blows per foot)

Apparent Density 3- to 3.5-Inch Sampler

(blows per foot)

0 to 1 Very Soft 0 to 2

2 to 4 Soft 3 to 6

5 to 8 Firm 7 to 12

9 to 15 Stiff 13 to 23

16 to 30 Very Stiff 24 to 45

31 to 60 Hard 46 to 85

> 60 Very Hard > 85

4.2 COLOR

Soil color is not a specific engineering property but may be an indicator of other significant geologic processes that may be occurring within the soil mass. Color may also aid in the subsurface correlation of soil units. Soil color should be determined in the field at the natural moisture content. Use basic color descriptions (i.e., brown, gray, black, green, white, yellow, red, etc.). Describe mixed colors by using a dash between the two basic colors (e.g., gray-green). Describe different shades or tints of basic colors by adding the terms light or dark in front of the basic color, for example, light brown.

Use Munsell color descriptions only when specified for a particular project.

The term mottled can be used to describe soil marked with spots of color; usually a result of the groundwater table rising and lowering in the soil column, causing reduction and oxidation of minerals in the soil. When using the term mottled, a color should be added to the description (e.g.

mottled orange-red).

4.3 MOISTURE

Make a visual estimation of the relative moisture content of the soil during the field identification.

Describe the field moisture content of the soil based on the criteria outlined in Exhibit 4.3-A.

Exhibit 4.3-A CRITERIA FOR DESCRIBING MOISTURE CONDITION

Moisture Description Criteria

Dry Absence of moisture; dusty; dry to the touch

Moist Damp but no visible water

Wet Visible free water

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

4.4 PARTICLE SIZE AND ANGULARITY (COARSE-GRAINED SOIL)

For coarse-grained soil (i.e., sand, gravel, cobbles and boulders) as the main constituent, include descriptors of particle size and angularity in the field description.

Conform to the field description of particle size of coarse-grained soil outlined in Exhibit 3.4-A.

The coarse-grained soil identification does not consider the presence of cobbles and boulders within the soil mass, which are often encountered in coarse-grained soil deposits. See Subsection

3.4 for guidance on describing cobbles and boulders. A range of grain size descriptors may be used when appropriate (e.g., fine- to medium-grained).

Exhibit 4.4-A PARTICLE SIZE DEFINITION FOR COARSE-GRAINED SOILS

Component Grain Size Limits

GRAVEL

Coarse Gravel ¾ – 3”

(19 – 75 mm)

Fine Gravel #4 Sieve – ¾”

(4.75 – 19 mm)

SAND

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)

Conform to the criteria as outlined in Exhibit 4.4-B and shown in Exhibit 4.4-C for the field description for coarse-grained sized particle angularity of a soil (boulders, cobbles, and gravel).

A range of angularity descriptors should be used when appropriate (e.g., subrounded to rounded).

Exhibit 4.4-B CRITERIA FOR THE FIELD DESRIPTION OF ANGULARITY

(AFTER ASTM D 2488).

Description Criteria

Angular Coarse grained particles have sharp edges and relatively plane sides with unpolished surfaces

Subangular Coarse grained particles are similar to angular description but have rounded edges

Subrounded Coarse grained particles have nearly plane sides but have well rounded corners and edges

Rounded Coarse grained particles have smoothly curved sides and no edges

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

Exhibit 4.4-C ANGULARITY EXAMPLES (AFTER ASTM D 2488)

4.5 PLASTICITY (FINE-GRAINED SOIL)

Plasticity is an important index property of soil and should be included in the description for all fine-grained soil and in coarse-grained soils with greater than 15 percent fines. The range of the plasticity index can be estimated by using the results of the toughness test (ASTM D 2488) as outlined in Exhibit 3.2.1-B. General plasticity ranges for fine-grained soil types are shown in Exhibit 4.5-A below.

Exhibit 4.5-A GENERAL PLASTICITY DESCRIPTION RANGE FOR FINE-GRAINED SOILS

Soil Group Plasticity

Silt (ML & MH) Clay (CL & CH) Organic Soil (OL & OH)

Silt (ML) -- Organic Soil (OL) Non-Plastic

Silt (ML) -- Organic Soil (OL) Low Plasticity

Silt (ML & MH) Clay (CL) Organic Soil (OL & OH) Medium Plasticity

Silt (MH) Clay (CL & CH) Organic Soil (OH) High Plasticity

Silt (MH) Clay (CH) Organic Soil (OH) Very High Plasticity

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

4.6 STRUCTURE

Soil often contains depositional or physical features that are referred to as soil structure. These features should be described following the criteria as outlined in Exhibit 4.6-A.

Exhibit 4.6-A CRITERIA FOR DESCRIBING SOIL STRUCTURE

Description Criteria

Stratified

Alternating layers of varying material or color with layers at least 0.25 inch (6 mm) thick; note thickness and inclination.

Laminated*

Alternating layers of varying material or color with layers less than 0.25 inch (6 mm) thick; note thickness and inclination.

Fissured*

Breaks along definite planes of fracture with little resistance to fracturing.

Slickensided*

Fracture planes appear polished or glossy, sometimes striated.

Blocky*

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 been disturbed and moved substantially (i.e., placed fill or 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; note thickness

*Note: Do not use laminated, fissured, slickensided, or blocky for coarse-grained soils.

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

4.7 OTHER DESCRIPTORS

When applicable, use additional descriptors to describe specific geologic conditions encountered in the sample or non-soil material (i.e., HCl reaction, cementation, mica, gypsum, surface coatings on coarse-grained particles, wood, roots, root holes, odor, etc.). Guidelines for additional descriptors are provided in this Section. Do not include these additional descriptors unless they are relevant to the geology at the site. Include remarks on the observed performance of the drill or comments made by the driller when the conditions change between samples as described in Subsection 4.7.5.

4.7.1 CEMENTATION

If the soil particles are cemented, report the cementation of the soil sample in accordance with the criteria outlined in Exhibit 4.7.1-A. Only include a description of the soil cementation if the sample is cemented; however, it may be appropriate to indicate no cementation if adjacent samples or other soil layers encountered on the site have cemented particles.

Exhibit 4.7.1-A SOIL CEMENTATION

Description Criteria

Weak cementation Sample crumbles or breaks with handling or little finger pressure

Moderate cementation Sample crumbles or breaks with considerable finger pressure

Strong cementation Sample will not crumble or break with finger pressure

4.7.2 HCl REACTION

HCl reaction should be tested when the soil may contain carbonate minerals. Calcium carbonate is a common cementing agent in soil. To test for the presence of acidic reaction, the soil sample should be tested with dilute (3% to 10%) HCl. Report the reaction of the soil sample with HCl in accordance with the criteria outlined in Exhibit 4.7.2-A. Only include a description of the soil reaction to HCL when the sample has been tested.

Exhibit 4.7.2-A SOIL REACTION TO HYDROCHLORIC ACID

HCl Reaction Description Criteria

No HCl Reaction No visible reaction

Weak HCl Reaction Some reaction with bubbles forming slowly

Strong HCl Reaction Violent reaction with bubbles forming immediately

4.7.3 MICA CONTENT

Only include a description of the mica content if mica has been identified in the sample. Mica is common in residual soils and has been found to affect the compaction characteristics of fill/backfill and the compressibility and strength/stability, especially for cut slopes.

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

When the soil includes mica minerals, include one of the following expressions:

slightly micaceous – few shiny flakes micaceous – common throughout the soil highly micaceous – soil is almost all mica.

4.7.4 FROZEN SOIL

When frozen soil is encountered in areas that have seasonal frost penetration, use the following expression:

frozen from xx to xx feet

When frozen soil is encountered in permafrost areas, the project geotechnical engineer or engineering geologist should specify the use of ASTM D 4083 Description of Frozen Soils (Visual- Manual Procedure) for a systematic description of frozen soil and ice layers.

4.7.5 REMARKS

Include remarks on the performance of the drill or comments made by the driller when the conditions change between samples, such as water color or fluid circulation, heaving sands, caving or sloughing of auger holes or test pits, difficulty in augering, etc.

Examples of additional remarks that may be included are:

driller remarks cobbles and boulders from 25 to 30 feet based on drill chatter driller remarks roots encountered from 1 to 4 feet driller remarks more drilling resistance below 13 feet driller remarks loss of water circulation from 18 to 20 feet

4.8 GROUNDWATER OBSERVATIONS

Groundwater observations are not a specific soil sample descriptor; however, the water table is an important consideration in almost any type of geotechnical design and therefore, it should be sought out in any type of geotechnical investigation.

As a general rule of thumb, water levels and borehole cave-in depths should be checked and recorded in the remarks section of the log in the following cases, as applicable:

• when advancing the borehole after wet soil samples are encountered, stop the drilling and measure the depth to groundwater and wait for it to equilibrate in the boring (e.g., water level observed at 16 feet while drilling).

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

• if borehole is stopped at the end of the work shift, and before resuming drilling (e.g., water level observed at 17 feet and casing is at 20.5 feet at end of work shift on 9/2/15, water level observed at 16.5 feet before resuming drilling on 9/3/15).

• after reaching the bottom of the borehole before pulling the augers/casing out of the ground (e.g., water level observed at 18 feet upon completion of boring with augers in).

• after pulling the augers/casing out of the ground (e.g., water level observed at 17.5 feet immediately after withdrawal of augers).

• at a set time after completion of the hole (e.g., water level observed at 15 feet 24 hours after withdrawal of augers).

When drilling fluids are introduced or groundwater instrumentation is being installed in the boring, the borehole should be baled to develop the hole. The groundwater will need to be allowed to recharge to measure the static water level following baling. In fine-grained soils, recharge to the static water level may take up to 24 hours and, in these cases, the borehole should be left open overnight and covered at the surface to allow this measurement the following day. However, in this absence of baling the drilling fluids, the groundwater should not be recorded to avoid collecting erroneous data.

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

5 FIELD: SOIL EXPLORATION LOGS

This section describes the linework to use and when to delineate stratigraphic changes and the order and content to include on the Field Soil Exploration Logs.

5.1 DEFINING AND DELINEATING STRATIFICATION

Indicate the thickness and type of groundcover encountered at the boring location. For example, the uppermost layer may be described as follows:

Asphalt Concrete (3.25 inches thick) over ¾-inch-minus base course aggregate (8 inches thick) Topsoil (5 inches thick) Duff/leaf litter (3 inches thick) Aggregate Roadway Surfacing (6 inches thick)

For borings through paved surfaces, record asphalt concrete pavement (ACP) or Portland cement concrete (PCC) pavement thickness to the nearest ¼ inch, and base course thickness, when present, to the nearest 1 inch.

Describe the first sample in every stratum using a full description as described under Section 5.2 Order of Descriptors. On subsequent samples, list changes to any of the descriptors from the first sample in that layer, if applicable (e.g., Becomes very dense and wet). Do NOT note apparent increases and decreases in constituent percentages (e.g., more sand or less silt) when comparing samples collected in the same Soil Group Name layer.

Use a stratification line to separate adjacent layers on the field logs where the Soil Group Name changes and where the geological origin of the material changes. Stratification lines may also be used if more than two of the descriptors change between samples (i.e., color and plasticity). Use:

• A solid horizontal line when a stratigraphic change is observed in a test pit wall or within a borehole sample.

• A dashed horizontal line when a change occurs between samples and is not observed, or when the driller notes a change in drilling behavior between samples. Place the dashed line midway between samples if the location of the change is unknown by drilling behavior.

Geologic origin or unit may be added if the information is available from geologic maps or the unit can be identified based on known area geology. When samples are interpreted as fill materials, or the geologic origin or unit is known, add a note at the end of the sample description with parentheses around the interpretation, e.g., (FILL) or (ALLUVIUM).

Groundwater observations must also be recorded on the boring logs. See Section 4.8 for guidance on recording groundwater.

5.2 ORDER OF DESCRIPTORS

Field Soil Exploration Log sheet title blocks should be completed in their entirety, including subsequent sheets for explorations that span multiple pages. Each soil sample should be fully described, ideally including the estimated percents of Fines, Sand, and Gravel (as the exploration log allows) along with the potential presence of cobbles and boulders. In addition to the soil

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025 identification descriptions, relevant notes should be recorded on changes in drill action, fluid losses, complications, depth to groundwater, artesian flow rates, and other possible indicators of in situ subsurface conditions.

The protocol for field identification of soil is to describe the soil properties in the following order, separating descriptors with a comma and each numbered descriptor using a semi-colon:

1. soil group NAME (main constituent in CAPS);

2. consistency or apparent density, colora, moisture;

3. plasticity of fine-grained constituent (non-plastic, low plasticity, medium plasticity, high plasticity)b, [optional: include dry strength, dilatancy, and toughness descriptions on the field exploration log];

4. size range (fine, medium, coarse grained) sand;

5. size range (fine, coarse), shape (rounded, subrounded, subangular, angular) gravel;

6. shape cobbles, shape boulders;

7. (as appropriate) organics type;

8. (as appropriate) structure, stratification, cementation, HCl reaction, mica content;

9. (as appropriate) sheen, odor, staining;

10. (as appropriate) lithology of gravel, cobbles, boulders.

Notes:

*Drilling notes and frozen soil ranges would be placed at or near the relevant depths where observed and not in the soil description.

a – Use basic color descriptions (i.e., brown, gray, black, green, white, yellow, red, etc., NO tan, olive, grey). Describe mixed colors by using a dash between the two basic colors (e.g., gray-green, NO ishes). Describe different shades or tints of basic colors by adding the terms light or dark in front of the basic color, for example, light brown) b – Used when soils contain silty or clayey in the name, or are fine-grained soils

5.3 FIELD SOIL EXPLORATION LOG EXAMPLES

Examples of this field logging protocol are as follows:

Poorly-graded GRAVEL with sand and cobbles; very dense, gray-brown, moist; fine to coarse sand; fine to coarse, rounded to angular gravel; rounded to subrounded cobbles up to 8 inches;

few roots up to 3 inches thick; moderate to strong cementation, weak to moderate HCl reaction, slightly micaceous; heavy sheen, organic odor; andesitic and granitic gravel and cobbles, phyllite boulders.

Sandy FAT CLAY; stiff, dark gray, wet; high plasticity [high dry strength, no dilatancy, high toughness]; fine sand; fine, rounded gravel; rootlets (anoxic), wood and plant fibers; organic odor.

Silty SAND; very loose, gray, wet; non-plastic; fine sand; fine, rounded to subangular gravel; few rootlets; clay lenses up to 2 inches thick, highly micaceous.

GRAVEL with silt and sand; dense, light brown, dry; fine to coarse sand; fine to coarse, subangular gravel; relict texture.

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

6 REPORT: SOIL EXPLORATION LOGS

This section describes examples of key interpretations and modifications to the Field Soil Exploration Logs when generating the Report Soil Exploration Logs, and reporting guidelines.

6.1 DATA AND SAMPLE REVIEW AND LABORATORY TESTS

When creating the Report Soil Exploration Logs, the responsible geotechnical engineer or engineering geologist should interpret the Field Soil Exploration Logs, based on:

• Review of published geologic information and previous work

• Further visual examinations of the field collected data and materials in the boring and across the project site for refinements, similarities, differences, and common stratigraphic units.

• Soil classification in accordance with ASTM D2487 – Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System) and the AASHTO Classification System (AASHTO M 145) after completing a laboratory testing program on representative samples

• Professional experience and judgment

6.2 FIELD SOIL EXPLORATION LOG MODIFICATIONS

The Report Soil Exploration Logs should be modified, with ongoing interpretations and iterations being made, as details are entered into digital boring software (i.e., OpenGround, RSLog, gINT, BoreDM, etc.) and reviews, including:

• After the laboratory tests are complete, as needed, update the soil group NAME and soil descriptors following ASTM D 2487 Testing and Soil Classification, including, for example, the field plasticity description based on results of ASTM D4318, and particle size distributions based on the results of ASTM D6913 and ASTM D7928. When multiple index tests are performed (i.e., ASTM D4318 and ASTM D6913), the results should be reviewed for the proper soil group NAME.

The soil plasticity descriptions should be based on Exhibit 6.2.1-A below.

Exhibit 6.2.1-A REPORT SOIL EXPLORATION LOG PLASTICITY DESCRIPTION

(AFTER BURMISTER, 1949)

Plasticity Index Range Description

0 Non-Plastic

1 to 10 Low Plasticity

11 to 20 Medium Plasticity

21 to 40 High Plasticity

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

• Soil classifications should be applied to the interpreted common stratigraphy. For example, if a common soil layer is identified as CLAY in the field exploration log and the ASTM D4318 test determines the material is SILT (ML), the soil within this similar stratum and in nearby borings should be assessed, and reclassified, as appropriate.

• Coalescing or removing general information that conflict with ASTM D2488 soil behavior notes (i.e., dry strength, dilatancy, and toughness) and soil classification if the soil types and descriptions have been submitted for testing and translated to ASTM D2487 USCS Soil Classifications from the field exploration logs to the draft digital report logs.

However, some field notes (i.e., fluid circulation losses, caving, heave, etc.) should always be included on the Report Soil Exploration Log at the observed depths. One exception would be if no soil laboratory testing was completed. In this case, include the ASTM D 2488 field test results.

• The stratigraphic contact depths and geologic units should be adjusted based on field observations and sample reviews that may indicate changes between samples.

For example, a field observation of “drill chatter at 12 feet bgs” and the sample at 15 feet contains gravel-sized constituents indicates the soil layer begins at 12 feet bgs. A solid stratigraphic line should be placed at 12 feet bgs and the field drill note can be removed.

If no observations were noted, the dashed stratigraphic line should be placed at the depth halfway between the previous sample and the sample the material was first recorded.

6.3 ORDER OF DESCRIPTORS

Classify the soils on the Report Soil Exploration Log based on ASTM D2487 if laboratory tests were performed and, if no laboratory tests were performed, on ASTM D2488. Describe the soil properties in a similar order and style as the Field Soil Exploration Log:

1. soil group NAME (main constituent in CAPS) with USCS Symbol (XX)a;

2. consistency or apparent density, colorb, moisture;

3. plasticity of fine-grained constituent (non-plastic, low plasticity, medium plasticity, high plasticity)c];

4. size range (fine, medium, coarse grained) sand;

5. size range (fine, coarse), shape (rounded, subrounded, subangular, angular) gravel;

6. shape cobbles, shape boulders;

7. (as appropriate) organics type;

8. (as appropriate) structure, stratification, cementation, HCl reaction, mica content;

9. (as appropriate) sheen, odor, staining;

10. (as appropriate) lithology of gravel, cobbles, boulders.

11. (GEOLOGIC UNIT).

Notes:

*Drilling notes and frozen soil ranges would be placed at or near the relevant depths where observed and not in the soil description.

a – USCS Symbol should only be included if laboratory tests were performed b – Use basic color descriptions (i.e., brown, gray, black, green, white, yellow, red, etc., NO tan, olive, grey). Describe mixed colors by using a dash between the two basic colors (e.g., gray-green, NO ishes). Describe different shades or tints of basic colors by adding the terms light or dark in front of the basic color, for example, light brown) c – Used when soils contain silty or clayey in the name, or are fine-grained soils

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

6.4 REPORT SOIL EXPLORATION LOG EXAMPLES

Examples of this field logging protocol are as follows:

Poorly-graded GRAVEL (GP) with sand and cobbles; very dense, gray-brown, moist; fine to coarse sand; fine to coarse, rounded to angular gravel; rounded to subrounded cobbles up to 8 inches; few roots up to 3 inches thick; moderate to strong cementation, weak to moderate HCl reaction, slightly micaceous; heavy sheen, organic odor; andesitic and granitic gravel and cobbles with phyllite boulders up to 3 feet in dimension. (ALLUVIUM)

Sandy FAT CLAY (CH); stiff, dark gray, wet; high plasticity; fine sand; fine, rounded gravel;

rootlets (anoxic), wood and plant fibers; organic odor. (ESTUARINE DEPOSIT)

Silty SAND (SM); very loose, gray, wet; non-plastic; fine sand; fine, rounded to subangular gravel;

few rootlets; clay lenses up to 2 inches thick, highly micaceous. (COLLUVIUM)

GRAVEL (GP-SM) with silt and sand; dense, light brown, dry; fine to coarse sand; fine to coarse, subangular gravel; relict texture. (METACONGLOMERATE, COMPLETELY WEATHERED

GRADE V)

FLH Soil Description, Interpretation, and Reporting Guidelines March 2025

7 REFERENCES

AASHTO M 145. 2004. Classification of Soils and Soil-Aggregate Mixtures for Highway

Construction Purposes. American Association of State Highway and Transportation Officials. 8p.

ASTM D7928. 2021. Standard Test Method for Particle-Size Distribution (Gradation) of Fine-

Grained Soils Using the Sedimentation (Hydrometer) Analysis. ASTM International. 27p

ASTM D 1586. 2011. Standard Test Method for Standard Penetration Test (SPT) and Split-

Barrel Sampling of Soils. ASTM International. 9p.

ASTM D 2487. 2017. Standard Practice for Classification of Soils for Engineering Purposes

(Unified Soil Classification System). ASTM International. 13p.

ASTM D 2488. 2017. Standard Practice for Description and Identification of Soils (Visual-

Manual Procedure). ASTM International. 13p.

ASTM D 4318. 2017. Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils. ASTM International. 20.

ASTM D6913. 2009, Standard Test Methods for Particle-Size Distribution (Gradation) of Soils

Using Sieve Analysis. ASTM International. 34p.

ASTM D 4083. 2007. Standard Practice for Description of Frozen Soils (Visual-Manual

Procedure). ASTM International. 6p.

Burmister, D.M. 1949, "Principles and Techniques of Soil Identification" 29th Highway

Research Board Proceedings.

USDOT-FHWA, 2002. Subsurface Investigations - Geotechnical Site Characterization

Reference Manual, Publication No. FHWA NHI-01-031.

ATTACHMENTS

APPENDIX A

Example Field Soil Boring Logs

Bl ow s P er in ch es

Re co ve ry

(i n.

Mo ist ur e C on te nt (D

, M , W

Date Begin/End:

Logged By:

Location:

Drilling Company/Driller:

Equipment: Method(s):

Bit Type: Size:Coordinates (X/Y, Lat/Lon, Sta.):

De pt h

W ell

C on st ru ct io n

Dr ive n Le ng th

(i n.

) w ith

Sa m pl er

Ty pe

S ym bo l

Sa m pl e N um be r

ASTM Soil Name (Symbol);

Color Co ns ist an cy

/R . D en sit y

As Needed:

Organics; Structure, Stratification, Cementation, HCL Reaction, Mica Content; Sheen, Odor, Staining;

Lithology Gravel/Cobbles/Boulders;

(Geologic Unit) Pocket Pen., Torvane Drilling Rates and Conditions

Add. Soil Descriptors/Field Notes

Depth to GW (ft.) Initial/Time: Final/Time:

Boring Total Depth:

Elevation (ft.msl): Source:Surface Conditions: Hammer Type: Wt./Drop: Efficiency:

Pl as tic ity

(N P, L P, M P, H P)

Sh ap e o f G ra ve l (R

, S R, S A, A

Co bb les /B ou ld er s

(Y /N

Si ze

R an ge S an d

(F , M

, a nd

/o r C

Si ze

R an ge G ra ve l (F an d/ or C

Pe rc en t F in es

Pe rc en t S an d

Pe rc en t G ra ve l

Sheet: _____ of _____

SOIL BORING FIELD LOG

Project Name:Project Number:

Boring No.:

Soil Properties us cs

G , S

, F [d om in an t

M , C

C ol or

M oi st ur e (D

, M , W

Pa rt ic le

S iz e an d A ng ul ar ity

Pl as tic ity

(N , L

, H

St ru ct ur e

Additional Remarks, Notes, and Interpretation. May include Cementation, Odor, Weathering, Mineralogy, Max Particle Size, Organics, Contacts, Pocket Penetrometer, Drilling Action, Slip Plane Observations, Temperature or Gas Notes, Sample Testing Recommendations, and Genesis/Geologic Origin [in brackets].

If unsure if drilling through in-situ rock, log all soil and rock properties of sampled material.R ec ov er y

(ft

Sampling