engineering geology field manual
TRANSCRIPT
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
1/449
ENGINEERING
GEOLOGY
FIEL
MANUAL
SECOND EDITION
VOLUME I
998
REPRINTED 2001
U S Department of the Interior
Bureau ofReclamation
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
2/449
The Mission of the
Department
of the
Interior
is to
protect and provide access to our
Nation s natural and
cultural
heritage and
honor
our
trust
responsibilities to
tribes
.
The Mission
ofth
e Bureau ofReclamation is to manage
develop and protect water and related resour es n
an
environmentally and
economically
sound manner in
the
interest of
the American public.
Information contained in this manual regarding
commercial products
or
firms
may not be used
for
advertising or promotional purposes and is not an
endorsement
of
any product or firm by the
Bureau of
Reclamation.
The
information contained in this manual was developed
for
th
e
Bureau
of Reclamation; no wtuT8Ilty
as to the
accuracy usefulness or completeness is expressed or
imolied.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
3/449
Aclm owledgmenu
t r
Second dition
The
original compilation and p ~ p a r a t i o n
of this manual
involved
many
engineering geologists
and
geophysicists
withinReclamation. Theirinput sgreatlyappreciated.
This
second edition incorporates comments on the first edition
and
technological changes since the
first
edition was
prepared appro:limately 10 years ago. Without the
comments and
i JJ put
from the Denver, Regional, and Area
Offices
the
revision would not
have
happened. Special
thanks
to Sam
Bartlett, Engineering Geology Group 1
Manager, for
his support
and
input
throughout
the
preparation of the manual.
Although
there are
too
many
people to acknowledge
individually who contributed to the revisions and the second
edition,
Frank
Calcagno, Mel ill retired), Sandy
Kunzer
,
Jeff
Farrar,
SharoJ;l
Hebenstreit
, Linda Arrowwood, and
Peter
Rohrer
made
especially significant contributions.
Mark
McKeown contributed
to
and
edited
the
second edition.
Continued
recognition
ili
given
to Jerry
S. Dodd retired),
who initiated the
manual;
Jeny s
successor, Newcomb
Bennett
(retired),
who kept
the manual
moving; and
to
Steve D. Markwell retired), who
saw the first
edition
completed.
We extend
our thanks and appreciation
to
Louis
R
Frei, who helped establish
and document many
geological standards ofpractice,
and
to Richard H. Throner,
who wrote much of the original manual, who assembled
and
served on committees for preparation
and
review, to Sam
R
Bartlett
who compiled and printed the
early
loose
leaf
v e n ~ i o n of the
manual, and to Mel Hill
who completed the
publication of the first edition. To the g i o n a l Geologists
and their staffs and
the
many geotechnical
engineers
who
offered comments
that
have
been
mcorporated into
the
manual
we extend our thanks
and
appreciation for their
work s
well. The manual would not be oeomplete
with-out
the drawings
and
figures; to the engineering and physical
science
technicians
we extend our gratitude and thanks.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
4/449
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
5/449
FOREWORD
TO THE SECOND
EDITION
Approximately
10
years have gone by since the first
editionwas published,
and technolOgy
and
missions
have
changed
significantly. his second
edition
incorporates
many modifications and additions.
The
Global
Positioning System GPS) baa revolutionized how we
survey and locate OU1'8elves in the field
,
computers
are
used extensively ta
collect and evaluate
data, and
computer
aided
modeling, design, and drafting
are
almost
universal
. Reclamation
has
a
greater emphasis on
maintenance
and
safety
of
infrastnicture,
dam
safety
analyses
and modifications, and water resource
management
than
on
design and
construction
of
new
hydraulicstructures. Techniques
for
these
activities
and
environmental
restoration/hazardous
waste remediation
activities are reflected ill this edition.
A few
of
the
moat
significant
changes
to
the
manual
are
the
addition
of a section on concrete core logging, a
chapter
on hazard
ous waste site investigations, and
an
index to facilitate
finding
relevant information. Many
other
suggested
revisions and
improvements
collected
since the manual
was first published
also are
incorporated. he manum
now
is in
two uolumes
Volume I contains
material
commonly needed
in
the
field,
and
Volume II includes reference
or other material
.
As in the first edition, the
Engineering
Geolcgy kld
Manual presents
the practices for the collection of
geologic data obtained by the Burcnu of Reclamation.
The manual establishes common guidelines, procedures,
and
concepts for the collection,
evaluation,
and
presen-
tation
of
geologic
i.onnation. The
analyai.l
of
geologic
conditions, the
preparation
ofdesigns and specifications,
and
effective
construction monitoring and use of
geo-
logical information to assess site characteri.l tics and ri.l k,
require
consi.l tent, comprehen8ive,
and timely
geologic
v
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
6/449
information.
The
use
of
these guidelines by all Recla-
mation engineering geologists collecting documenting
evaluating and presenting geological and geotechnical
data promotes consistency helps assure that the requind
evaluations
and
data
are
complete
and
promotes inte-
gration and coordination
of
geological
and
engineering
activities.
The Engineering Geology Field Manual
in
conjunction
with
the
Engineering
Geology Office Manual
forms the
basis for the mutually beneficial exchange of ideas by
Reclamation geologists. Experienced geologists w ll find
useful reminders
and
new procedures
and
special tech-
niques while less experienced engineering geologists and
those from
other
disciplines
can
use
the manual to
expand
their
familiarity
with
geology
as
practiced
in
the
Bureau of Reclamation.
Review and comments on the
manual are
encouraged
and
if
you
have
comments
or
suggested additions please
forward
them to the
Technical Service Center
Engineering Geology Groups.
Richard Throner
Leadership Team Member
Geotechnical Services
vi
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
7/449
CONTENTS
Page
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . i i iForeword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Chapter 1 Introduction . . . . . . . . . . . . . . . . . 1
Chapter 2 Geologic Terminology andClassifications for GeologicMaterials . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Established References for GeologicalTerminology . . . . . . . . . . . . . . . . . . . . . . . . 3
Geologic Classi fi cat ion of Mater ials . . . . . . . 4
Engineer ing Classificat ion of GeologicMater ials . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Appl ication and Use of Standard Indexes,Terminology, and Descr iptors . . . . . . . . . . 9
Uni ts of M easur ements for Geologic Logsof Explorat ion, Drawings, and Reports . . 12
Bibl iography . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Chapter 3 Engineering Classification andDescription of Soil . . . . . . . . . . . . . . . . . 17
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Classificat ions of Soi ls . . . . . . . . . . . . . . . . . . 21Abbreviated Soil Classif icat ion Symbols . . . 39Descr ipt ion of t he Physical Proper t ies
of Soi l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Narrat ive Descr ipt ions and Examples . . . . . 48Use of Soil Classification as Secondary
Ident i ficat ion Method for Mater ials
Other Than Natural Soi ls . . . . . . . . . . . . . 51
Bibl iography . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Chapter 4 Classification of Rocks andDescription of PhysicalProperties of Rock . . . . . . . . . . . . . . . . . 57
Int roduct ion . . . . . . . . . . . . . . . . . . . . . . . . . . 57Rock Classificat ion . . . . . . . . . . . . . . . . . . . . 57
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
8/449
FIELD MANUAL
viii
Chapter 4 Classification of Rocks andDescription of PhysicalProperties of Rock(continued)
Page
Descr ipt ion of Rock . . . . . . . . . . . . . . . . . . . . 59
Example Descr ipt ions . . . . . . . . . . . . . . . . . . 86
Bibl iography . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Chapter 5 Terminology and Descriptionsfor Discontinuities . . . . . . . . . . . . . . . . . 91
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Indexes for Descr ibing Fractur ing . . . . . . . . 94
Descr ipt ion of Fractures . . . . . . . . . . . . . . . . 98Descripti ons of Shears and Shear Zones . . . 114
Bibl iography . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Chapter 6 Geologic Mapping andDocumentation . . . . . . . . . . . . . . . . . . . . 129
Responsibi l i t ies of t he Engineer ingGeologist . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Development of a St udy Plan . . . . . . . . . . . . 130
Speci fic Mapping Requi rements . . . . . . . . . . 133Global Posit ioning Syst em . . . . . . . . . . . . . . 135
Site Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 153Dozer Trench Mapping . . . . . . . . . . . . . . . . . 157Backhoe Trench Mapping . . . . . . . . . . . . . . . 161
Const ruct ion Geologic Mapping . . . . . . . . . . 167
L ar ge Excavat ion M apping . . . . . . . . . . . . . . 168Steep Slope Mapping . . . . . . . . . . . . . . . . . . . 169
Canal and Pipel ine Mapping . . . . . . . . . . . . 170
Underground Geologic Mapping . . . . . . . . . 171Underground Geologic Mapping Methods . . 185
Photogeologic Mapping . . . . . . . . . . . . . . . . . 196
Analysis of Aer ial Photographs . . . . . . . . . . 198
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
9/449
CONTENTS
ix
Chapter 6 Geologic Mapping andDocumentation(continued)
Page
Photoanalysis for ReconnaissanceGeologic Mapping . . . . . . . . . . . . . . . . . . . . 199
Availabi l i ty of Imagery . . . . . . . . . . . . . . . . . 200
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
Bibl iography . . . . . . . . . . . . . . . . . . . . . . . . . . 203
Chapter 7 Discontinuity Surveys . . . . . . . . 205General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205Bibl iography . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Chapter 8 Exploration DrillingPrograms . . . . . . . . . . . . . . . . . . . . . . . . . 213
Int roduct ion . . . . . . . . . . . . . . . . . . . . . . . . . . 213
Preparation of Dr i l l ing Speci ficati onsand Format . . . . . . . . . . . . . . . . . . . . . . . . . 223
Chapter 9 Groundwater Data AcquisitionMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Int roduct ion . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Design and Installation of ObservationWel ls and Piezometers . . . . . . . . . . . . . . . 229
Methods Used t o Measure Groundwater
Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Methods and Techniques Used t o EstimateFlows fr om Seeps, Spr ings, and Small
Drainages . . . . . . . . . . . . . . . . . . . . . . . . . . 241
Computer-Based Monitoring Systems . . . . . 242Definit ions . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 246Bibl iography . . . . . . . . . . . . . . . . . . . . . . . . . . 247
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
10/449
FIELD MANUAL
x
Chapter 10 Guidelines for Core Logging . 249General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Format and Requir ed Data for the Final
Geologic Log . . . . . . . . . . . . . . . . . . . . . . . . 252Method of Repor t ing Or ientati on of Planar
Discontinuit ies and Str uctural Features . 284
Core Recovery and Core Losses . . . . . . . . . . 285Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
Core Photography . . . . . . . . . . . . . . . . . . . . . 288
Equipment Necessary for Preparing
Field Logs . . . . . . . . . . . . . . . . . . . . . . . . . . 291Inst ruct ion to Dr i l lers, Dai ly Dr i l l Repor ts,
and General Dr i l ling Procedures . . . . . . . . 294
Chapter 11 Instructions for Logging Soils 313General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313Formats for Test Pit s and Auger Hole Logs 325
Format of Word Descr ipt ions for Dr i l l Hole Logs . . . . . . . . . . . . . . . . . . . . . . . . . . . 333Except ions to Test Pit and Auger Hole
Format and Descr ipt ions for Dr i l l
Hole Logs . . . . . . . . . . . . . . . . . . . . . . . . . . 339Equipment Necessary for Preparing the
Field Log . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
Example Descr ipt ions and Format . . . . . . . . 349
Laboratory Classi ficat ions in Addit ion t oVisual Classificat ions . . . . . . . . . . . . . . . . 349
Word Descr ipt ions for Var ious Soi lClassificat ions . . . . . . . . . . . . . . . . . . . . . . . 351
Repor ting L abor at ory Dat a . . . . . . . . . . . . . . 351
Special Cases for USCS Classificati on . . . . . 363Repor t ing In-Place Densi ty Tests . . . . . . . . . 364
Bibl iography . . . . . . . . . . . . . . . . . . . . . . . . . . 366
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
11/449
CONTENTS
xi
Page
Chapter 12 Hazardous Waste Site
Investigations . . . . . . . . . . . . . . . . . . . . . 367General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
Common Terminology and Processes . . . . . . 368Documentat ion . . . . . . . . . . . . . . . . . . . . . . . . 369
Contaminant Character ist ics and
Migrat ion . . . . . . . . . . . . . . . . . . . . . . . . . . 375Classif icat ion and Handling of Materials . . 381
Field Sampling Protocol . . . . . . . . . . . . . . . . 383Sample Analysis . . . . . . . . . . . . . . . . . . . . . . 402Safety at Hazardous Waste Si tes . . . . . . . . . 405
Sample Quali ty Assurance and
Quali ty Cont rol . . . . . . . . . . . . . . . . . . . . . 406Sample Management . . . . . . . . . . . . . . . . . . . 410
Decontaminat ion . . . . . . . . . . . . . . . . . . . . . . 417
AppendixAbbreviations and Acronyms CommonlyUsed in Bureau of ReclamationEngineering Geology and Related toHazardous Waste . . . . . . . . . . . . . . . . . . . . 419
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433
TABLES
Table Page
2-1 Ground behavior for eart h tunnelingwith steel suppor ts . . . . . . . . . . . . . . . 10
2-2 Useful conversion factorsmetr ic andEngl ish unit s (inch-pound) . . . . . . . . . 14
3-1 Basic gr oup names, pr imar y gr oups . . . 26
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
12/449
FIELD MANUAL
xi i
TABLES (continued)
Table Page
3-2 Basic group names, 5 to 12 percent
fines . . . . . . . . . . . . . . . . . . . . . . . . . . . 263-3 Cr iter ia for descr ibing dry st rength . . . 31
3-4 Cr iter ia for descr ibing di latancy . . . . . . 32
3-5 Cr iter ia for descr ibing toughness . . . . . 333-6 Cr iter ia for descr ibing plast ici ty . . . . . . 34
3-7 Identif icati on of inorganic f ine-grainedsoi ls from manual tests . . . . . . . . . . . 36
3-8 Crit eria for describing angularit y of
coar se-gr ained par ticles . . . . . . . . . . . 41
3-9 Cr it er ia for descr ibing par t i cl e shape . . 423-10 Cri teri a for describing moisture
condit ion . . . . . . . . . . . . . . . . . . . . . . . 43
3-11 Cri teri a for describing react ionwith HCl . . . . . . . . . . . . . . . . . . . . . . . 43
3-12 Cr it er ia for descr ibing consistency of
in-place or undisturbed fine-grainedsoi ls . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3-13 Cr it er ia for descr ibing cementat ion . . . 44
3-14 Cr it er ia for descr ibing st ruct ur e . . . . . . 453-15 Par t icle sizes . . . . . . . . . . . . . . . . . . . . . . 46
3-16 Checkl ist for the descr iption of soilclassi ficat ion and ident i ficat ion . . . . . 48
3-17 Checkl ist for the descr iption of in-place
condit ions . . . . . . . . . . . . . . . . . . . . . . . . 49
4-1 Igneous and metamorphic rock grainsize descr iptors . . . . . . . . . . . . . . . . . . 70
4-2 Sedimentary and pyroclastic rock
par ticle-size descr ipt or s . . . . . . . . . . . 714-3 Bedding, fol iat ion, or f low texture
descr iptors . . . . . . . . . . . . . . . . . . . . . . . 74
4-4 Weather ing descr iptors . . . . . . . . . . . . . 774-5 Durabi l i ty index descr iptors . . . . . . . . . 79
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
13/449
CONTENTS
xiii
TABLES (continued)
Table Page
4-6 Rock har dness/st rengt h descr ipt or s . . . 835-1 Fracture density descr iptors . . . . . . . . . 97
5-2 Fracture spacing descr iptors . . . . . . . . . 102
5-3 Fr act ur e cont inuit y descr ipt or s . . . . . . . 1025-4 Descriptors for recording fracture ends
in joint surveys . . . . . . . . . . . . . . . . . . 1035-5 Fr act ur e openness descr ipt or s . . . . . . . . 1045-6 Fracture fi ll ing thickness descr iptors . . 104
5-7 Fracture heal ing descr iptors . . . . . . . . . 107
5-8 Fr act ur e r oughness descr ipt or s . . . . . . . 1095-9 Fracture moisture condit ions
descr iptors . . . . . . . . . . . . . . . . . . . . . . 110
6-1 U.S. State plane coordinate systems 1927 datum . . . . . . . . . . . . . . . . . . . . . 137
6-2 U.S. State plane coordinate systems
1983 datum . . . . . . . . . . . . . . . . . . . . . 14311-1 Checkl ist for the descr iption of soil s in
test pi t and auger hole logs . . . . . . . . 326
12-1 EPA recommended sampling containers,preservation requirements, and
holding t imes for soi l samples . . . . . . 38512-2 Summary of soi l sampl ing devices . . . . 38812-3 Common laboratory test ing methods . . 404
FIGURES
Figure Page
3-1 Modifiers t o basic soi l gr oup names . . . 223-2 Flow chart for i norganic f ine-grained
soi ls, visual method . . . . . . . . . . . . . . 23
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
14/449
FIELD MANUAL
xiv
FIGURES (continued)
Figure Page
3-3 Flow chart for organic soils, visual
method . . . . . . . . . . . . . . . . . . . . . . . . . 24
3-4 Flow chart for coarse-grained soils,visual method . . . . . . . . . . . . . . . . . . . 25
3-5 Plast ici ty char t . . . . . . . . . . . . . . . . . . . . 35
3-6 Sample of test results summary . . . . . . 534-1 Field classi fi cat ion of i gneous rocks . . . 60
4-2 Field classif ication of sedimentary
rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . 614-3 Field classif icat ion of metamorphic
rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4-4 Field classi ficat ion of pyroclast ic rocks . 634-5 Chart s for estimating percentage of
composit ion of rocks and sediments . 644-6 Descriptor legend and explanation
example . . . . . . . . . . . . . . . . . . . . . . . . 67
4-7 Permeabil i ty conversion char t . . . . . . . . 87
5-1 Rock Quality Designation (RQD)computat ion . . . . . . . . . . . . . . . . . . . . . 96
5-2 Comparison of tr ue and apparent
spacing . . . . . . . . . . . . . . . . . . . . . . . . . 1015-3 Examples of roughness and waviness of
fr acture sur faces, typical roughness
profi les, and t erminology . . . . . . . . . . 1085-4 Uniform shear zone . . . . . . . . . . . . . . . . 115
5-5 Str uctured shear zone (two zones or
layers) . . . . . . . . . . . . . . . . . . . . . . . . . 116
5-6 St ructured shear zone (three layers) . . 1165-7 Uniform shear zone wit h veinlet s . . . . . 116
5-8 Unifor m shear zone (composit e) . . . . . . 1175-9 Standard descriptors and descriptive
cr it er ia for di scont inui ti es . . . . . . . . . 121
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
15/449
CONTENTS
xv
FIGURES (continued)
Figure Page
6-1 Process of engineer ing geology
mapping . . . . . . . . . . . . . . . . . . . . . . . . 131
6-2 Sample t rench log . . . . . . . . . . . . . . . . . . 1606-3 Sample completed t rench log . . . . . . . . . 165
6-4 Tunnel mapping form wi th key
alphanumeric descr iptors andmapping data . . . . . . . . . . . . . . . . . . . 173
6-5 Tunnel mapping form with blocks for
t i t le and geologic data . . . . . . . . . . . . 1746-6 As-bui lt summary geology tunnel map . 179
6-7 Ful l per iphery mapping method
layout . . . . . . . . . . . . . . . . . . . . . . . . . . 1866-8 Ful l per iphery geologic map example . . 188
6-9 Map layout of a tunnel for geologicmapping . . . . . . . . . . . . . . . . . . . . . . . . 191
6-10 Relationship of planar feature t race to
map project ions . . . . . . . . . . . . . . . . . . 192
7-1 Equator ial equal area net . . . . . . . . . . . 2097-2 Discont inuity log field sheet . . . . . . . . . 210
10-1 Dr i l l hole log, DH-123 . . . . . . . . . . . . . . 253
10-2 Dril l hole log, B-102, for Standard Penet rat ion Test . . . . . . . . . . . . . . . . . 255
10-3 Dr i l l hole log, DH-SP-2 . . . . . . . . . . . . . 259
10-4 Dr i l l hole log, SPT-107-2 . . . . . . . . . . . . 26110-5 Dr il l hole log, DH-DN/P-60-1 . . . . . . . . . 270
10-6 Daily dr i l l repor t . . . . . . . . . . . . . . . . . . 292
10-7 Water test ing record . . . . . . . . . . . . . . . 299
10-8 Use of hal f-round to protect core . . . . . . 30110-9 Standard N-size core box . . . . . . . . . . . . 303
10-10 Log of concrete and rock core . . . . . . . . . 30811-1 L og of t est pit or auger hole . . . . . . . . . . 314
11-2 Clean coar se-gr ained soi ls . . . . . . . . . . . 315
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
16/449
FIELD MANUAL
xvi
FIGURES (continued)
Figure Page
11-3 Fine-grained soi ls . . . . . . . . . . . . . . . . . . 316
11-4 Soil classificat ions based on laboratory
test data . . . . . . . . . . . . . . . . . . . . . . . . 31711-5 Auger hole wit h samples t aken . . . . . . . 318
11-6 Repor t ing laboratory classificat ion in
addi t ion to visual classi ficat ion . . . . . 31911-7 Undisturbed soi ls . . . . . . . . . . . . . . . . . . 320
11-8 Coarse-grained soi ls wi th fines . . . . . . . 321
11-9 Coarse-grained soil s wit h dualsymbols . . . . . . . . . . . . . . . . . . . . . . . . 322
11-10 Repor t ing in-place density tests and
percent compact ion . . . . . . . . . . . . . . . 32311-11 Soil wi th measured percentages of
cobbles and boulder s . . . . . . . . . . . . . . 32411-12 Field form - soi l logging . . . . . . . . . . . . . 32911-13 Soil with more than 50 percent cobbles
and boulders . . . . . . . . . . . . . . . . . . . . 334
11-14 Border l ine soi ls . . . . . . . . . . . . . . . . . . . . 33511-15 Test pit wit h samples t aken . . . . . . . . . 336
11-16 Disturbed samples . . . . . . . . . . . . . . . . . 337
11-17 Two descr ipti ons from t he samehor izon . . . . . . . . . . . . . . . . . . . . . . . . . 338
11-18 Dr i l l hole advanced by tr i-cone
rock bit . . . . . . . . . . . . . . . . . . . . . . . . . 34011-19 Log showing poor r ecovery . . . . . . . . . . . 342
11-20 Log of l andsl ide mater ial (a) . . . . . . . . . 343
11-21 Log of l andsl ide mater ial (b) . . . . . . . . . 344
11-22 Log of bedrock . . . . . . . . . . . . . . . . . . . . . 34511-23 Geologic int erpretat ion in t est pit
(sheet 1) . . . . . . . . . . . . . . . . . . . . . . . . 35011-24 Geologic int erpretat ion in test pit
(sheet 2) . . . . . . . . . . . . . . . . . . . . . . . . 352
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
17/449
CONTENTS
xvii
FIGURES (continued)
Figure Page
11-25 Geologic int erpretat ion in test pit using
a geologic profi le (1) . . . . . . . . . . . . . . 353
11-26 Geologic int erpretat ion in test pit(sheet 3) . . . . . . . . . . . . . . . . . . . . . . . . 354
11-27 Geologic int erpretat ion in test pit
(sheet 4) . . . . . . . . . . . . . . . . . . . . . . . . 35511-28 Geologic int erpretat ion in test pit using
a geologic profi le (2) . . . . . . . . . . . . . . 356
11-29 Geologic int erpretat ion in test pit(sheet 5) . . . . . . . . . . . . . . . . . . . . . . . . 357
11-30 Geologic int erpretat ion in test pit
(sheet 6) . . . . . . . . . . . . . . . . . . . . . . . . 35811-31 Geologic int erpretat ion in test pit
(sheet 7) . . . . . . . . . . . . . . . . . . . . . . . . 35911-32 Geologic int erpretat ion in test pit
(sheet 8) . . . . . . . . . . . . . . . . . . . . . . . . 360
11-33 Geologic int erpretat ion in test pit using
a geologic profi le (3) . . . . . . . . . . . . . . 36112-1 Aquifer types . . . . . . . . . . . . . . . . . . . . . . 379
12-2 Typical monitor ing well const ruct ion for
wat er qual i t y sampling . . . . . . . . . . . . 39912-3 Soil and water sample identificati on
labels . . . . . . . . . . . . . . . . . . . . . . . . . . 412
12-4 Chain-of-custody record . . . . . . . . . . . . . 41312-5 Custody seal . . . . . . . . . . . . . . . . . . . . . . 415
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
18/449
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
19/449
Chapter 1
INTRODUCTION
This manual provides guidelines and instructions for
performing and documenting field work. The manual is
a ready reference for anyone engaged in field-oriented
engineering geology or geotechnical engineering. The
manual is written for general engineering geology use as
well as to meet Reclamation needs. The application of
geology to solving engineering problems is emphasized,
rather than academic or other aspects of geology. Themanual provides guidance for:
Geologic classification and description of rock and
rock discontinuities
Engineering classification and description of soil
and surficial deposits
Application of standard indexes, descriptors, and
terminology
Geologic mapping, sampling, testing, and
performing discontinuity surveys
Exploratory drilling
Soil and rock logging
Acquisition of groundwater data
Core logging
Soil logging
Investigation of hazardous waste sites
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
20/449
FIELD MANUAL
2
Although the methods described in this manual are
appropriate for most situations, complex sites, conditions,
or design needs may require modification or expansion of
the suggestions, criteria, and indices to fit specificrequirements.
Many of the chapters in this manual will always need
revision because they cover material that changes as
technology changes. Critical comments, especially sug-
gestions for improvement, are welcome from all users,
not just the Bureau of Reclamation.
The appendix contains abbreviations and acronyms
commonly used in engineering geology.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
21/449
1Brackets refer to bibliography entries at end of each chapter.
Chapter 2
GEOLOGIC TERMINOLOGY
AND CLASSIFICATIONS FOR
GEOLOGIC MATERIALS
Established References for Geological
Terminology
Adaptations or refinements of the Bureau of Reclamation
(Reclamation) standards presented in this and subse-quent chapters may be established to meet specific design
requirements or site-specific geologic complexity when
justified.
The Glossary of Geology, Fourth Edition [1]1, published by
the American Geological Institute (AGI), 1997, is accepted
by Reclamation as the standard for definitions of geologic
words and terms except for the nomenclature, definitions,
or usage established in this chapter and chapters 3, 4,
and 5.
The North American Stratigraphic Code (NASC) [2] is the
accepted system for classifying and naming stratigraphic
units. However, Reclamation's engineering geology pro-
grams are focused primarily on the engineering prop-erties of geologic units, not on the details of formal
stratigraphic classification. Stratigraphic names are not
always consistent within the literature, often change from
one locality to another, and do not necessarily convey
engineering properties or rock types. Use of stratigraphic
names in Reclamation documents normally will be
informal (lower case) (see NASC for discussion of formalversus informal usage). Exceptions to informal usage are
for names previously used formally in the area in discus-
sions of geologic setting or regional geology. Normally,
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
22/449
FIELD MANUAL
4
the first use of formal names in a report should include a
reference to a geologic map or publication in which the
term is defined.
Geologic Classification of Materials
The following definitions of geologic materials more fully
satisfy general usage and supersede those in the Glossary
of Geology. These definitions are for geologic classifica-
tion of materials. They should not be confused with engi-neering classifications of materials such as rock and soil
or rock and common excavation.
Bedrockis a general term that includes any of the gen-
erally indurated or crystalline materials that make up the
Earth's crust. Individual stratigraphic units or units sig-
nificant to engineering geology within bedrock may in-clude poorly or nonindurated materials such as beds,
lenses, or intercalations. These may be weak rock units
or interbeds consisting of clay, silt, and sand (such as the
generally soft and friable St. Peter Sandstone), or clay
beds and bentonite partings in siliceous shales of the
Morrison Formation.
Surficial Depositsare the relatively younger materialsoccurring at or near the Earth's surface overlying bed-
rock. They occur as two major classes: (1) transported
deposits generally derived from bedrock materials by
water, wind, ice, gravity, and man's intervention and
(2) residual deposits formed in place as a result of
weathering processes. Surficial deposits may be stratified
or unstratified such as soil profiles, basin fill, alluvial orfluvial deposits, landslides, or talus. The material may be
partially indurated or cemented by silicates, oxides,
carbonates, or other chemicals (caliche or hardpan). This
term is often used interchangeably with the imprecisely
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
23/449
TERMINOLOGY
5
defined word overburden. Overburden is a mining
term meaning, among other things, material overlying a
useful material that has to be removed. Surficial
deposit is the preferred term.
In some localities, where the distinction between bedrock
and surficial deposits is not clear, even if assigned a
stratigraphic name, a uniform practice should be estab-
lished and documented and that definition followed for
the site or study.
Guidelines for the collection of data pertaining to bedrock
and surficial deposits are presented in chapter 6.
Engineering Classification of Geologic
Materials
General
Geologic classification of materials as surficial deposits or
bedrock is insufficient for engineering purposes. Usually,
surficial deposits are described as soil for engineering
purposes, and most bedrock is described as rock; however,
there are exceptions. Contract documents often classify
structure excavations as to their ease of excavation. Also,classification systems for tunneling in geologic materials
have been established.
Classification as Soil or Rock
In engineering applications, soilmay be defined as gener-
ally unindurated accumulations of solid particlesproduced by the physical and/or chemical disintegration
of bedrock and which may or may not contain organic
matter. Surficial deposits, such as colluvium, alluvium,
or residual soil, normally are described using Recla-
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
24/449
FIELD MANUAL
6
mation Procedure 5005, Determining Unified Soil
Classification (Visual Method) [3]. American Society for
Testing and Materials (ASTM) Standards D2487-85,
Standard Test Method for Classification of Soils forEngineering Purposes or D2488-84, Standard Practice for
Description and Identification of Soils (Visual-Manual
Procedure), which are based on Reclamation 5000 and
5005 [3] also may be used. Instructions for the
description and classification of soils are provided in
chapter 3. Chapter 11 provides instructions for the
logging of soils in geologic explorations. In some cases,partially indurated soils may have rock-like
characteristics and may be described as rock.
The United States Department of Agriculture (USDA)
Agricultural Soils Classification System is used for drain-
age and land classification and some detailed Quaternary
geology studies, such as for seismotectonic investigations.
Rock as an engineering material is defined as lithified or
indurated crystalline or noncrystalline materials. Rock
is encountered in masses and as large fragments which
have consequences to design and construction differing
from those of soil. Field classification of igneous,
metamorphic, sedimentary, and pyroclastic rocks are
provided in chapter 4. Chapter 4 also presents asuggested description format, standard descriptors, and
descriptive criteria for the lithologic and engineering
physical properties of rock. Nonindurated materials with-
in bedrock should be described using the Reclamation soil
classification standards and soil descriptors presented in
chapter 3. Engineering and geological classification and
description of discontinuities which may be present ineither soil or rock are discussed in chapter 5.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
25/449
TERMINOLOGY
7
Classification of Excavations
The engineering classification of excavation as either rock
excavation or common excavation or the definition of rockin specifications must be evaluated and determined for
each contract document and should be based on the
physical properties of the materials (induration and other
characteristics), quantity and method of excavation, and
equipment constraints and size.
Classification of Materials for Tunneling
Classification systems are used for data reports, speci-
fications, and construction monitoring for tunnel designs
and construction. When appropriate for design, other
load prediction and classification systems may be used
such as the Q system developed by the Norwegian Geo-
technical Institute (NGI), Rock Mass Rating System
Geomechanics Classification (RMR), and Rock Structure
Rating (RSR).
The following terms for the classification of rock [4] for
tunneling are suggested:
Intact rockcontains neither joints nor hairline cracks.
If it breaks, it breaks across sound rock. On account ofdamage to the rock due to blasting, spalls may drop off
the roof several hours or days after blasting. This is
known as spalling condition. Hard, intact rock may also
be encountered in the popping condition (rock burst)
involving the spontaneous and violent detachment of rock
slabs from sides or roof.
Stratified rockconsists of individual strata with little
or no resistance against separation along the boundaries
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
26/449
FIELD MANUAL
8
between strata. The strata may or may not be weakened
by transverse joints. In such rock, the spalling condition
is quite common.
Moderately jointed rockcontains joints and hairline
cracks, but the blocks between joints are locally grown
together or so intimately interlocked that vertical walls
do not require lateral support. In rocks of this type, both
the spalling and the popping condition may be
encountered.
Blocky and seamy rockconsists of chemically intact
or almost intact rock fragments which are entirely
separated from each other and imperfectly interlocked.
In such rock, vertical walls may require support.
Crushed but chemically intact rockhas the char-
acter of a crusher run. If most or all of the fragments areas small as fine sand and no recementation has taken
place, crushed rock below the water table exhibits the
properties of a water-bearing sand.
Squeezing rock slowly advances into the tunnel
without perceptible volume increase. Movement is the
result of overstressing and plastic failure of the rock mass
and not due to swelling.
Swelling rockadvances into the tunnel chiefly on ac-
count of expansion. The capacity to swell is generally
limited to those rocks which contain smectite, a
montmorillonite group of clay minerals, with a high
swelling capacity.
Although the terms are defined, no distinct boundaries
exist between rock categories. Wide variations in the
physical properties of rocks classified by these terms and
rock loading are often the case.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
27/449
TERMINOLOGY
9
Table 2-1, Ground behavior for earth tunneling with steel
supports, provides ground classifications for different
reactions of ground to tunneling operations.
Application and Use of Standard Indexes,
Terminology, and Descriptors
This section and subsequent chapters 3, 4, and 5 provide
definitions and standard descriptors for physical
properties of geologic materials which are of engineeringsignificance. The ability of a foundation to support loads
imposed by various structures depends primarily on the
deformability and stability of the foundation materials
and the groundwater conditions. Description of geologic
and some manmade materials (embankments) is one of
the geologist's direct contributions to the design process.
Judgment and intuition alone are not adequate for the
safe and economical design of large complex engineering
projects. Preparation of geologic logs, maps and sections,
and detailed descriptions of observed material is the least
expensive aspect and most continuous record of a sub-
surface exploration program. It is imperative to develop
design data properly because recent advances in soil and
rock mechanics have enabled engineers and geologists to
analyze more conditions than previously possible. Theseanalyses rely on physical models that are developed
through geologic observation and which must be
described without ambiguity.
The need for standard geologic terminology, indexes, and
descriptors has long been recognized because it is
important that design engineers and contractors, aswell as geologists, be able to have all the facts and quali-
tative information as a common basis to arrive at
conclusions from any log of exploration, report, or draw-
ing, regardless of the preparer. Geologic terminology,
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
28/449
FIELD MANUAL
10
Table 2-1.Ground behavior for earth tunneling withsteel supports (after Terzaghi, 1977) [4]
Ground classification Reaction of ground to tunneling operation
HARD Tunnel heading may be advanced without roof support.FIRM Ground in which a roof section of a tunnel can be left
unsupported for several days without inducing a
perceptible movement of the ground.
RAVELING Chunks or flakes of soil begin to drop out of roof at some
point during the ground-movement period.
SLOW RAVELING The time required to excavate 5 feet of tunnel and
install a rib set and lagging in a small tunnel is about
6 hours. Therefore, if the stand-up time of raveling
ground is more than 6 hours, by using ribs and lagging,
the steel rib sets may be spaced on 5-foot centers. Sucha soil would be classed as slow raveling.
FAST RAVELING If the stand-up time is less than 6 hours, set spacing
must be reduced to 4 feet, 3 feet, or even 2 feet. If the
stand-up time is too short for these smaller spacings,
liner plates should be used, either with or without rib
sets, depending on the tunnel size.
SQUEEZING Ground slowly advances into tunnel without any signs
of fracturing. The loss of ground caused by squeeze and
the resulting settlement of the ground surface can be
substantial.
SWELLING Ground slowly advances into the tunnel partly or chiefly
because of an increase in the volume of the ground. The
volume increase is in response to an increase of water
content. In every other respect, swelling ground in a
tunnel behaves like a stiff non-squeezing, or slowly
squeezing, non-swelling clay.
RUNNING The removal of lateral support on any surface rising at
an angle of more than 34E(to the horizontal) is
immediately followed by a running movement of the soil
particles. This movement does not stop until the slope
of the moving soil becomes roughly equal to 34E if
running ground has a trace of cohesion, then the run is
preceded by a brief period of progressive raveling.
VERY SOFT SQUEEZING Ground advances rapidly into tunnel in a plastic flow.
FLOWING Ground supporting a tunnel cannot be classified as
flowing ground unless water flows or seeps through it
toward the tunnel. For this reason, a flowing condition
is encountered only in free air tunnels below the
watertable or under compressed air when the pressureis not high enough in the tunnel to dry the bottom. A
second prerequisite for flowing is low cohesion of soil.
Therefore, conditions for flowing ground occur only in
inorganic silt, fine silty sand, clean sand or gravel, or
sand-and-gravel with some clay binder. Organic silt
may behave either as a flowing or as a very soft,
squeezing ground.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
29/449
TERMINOLOGY
11
standard descriptors, and descriptive criteria for physical
properties have been established so that geologic data are
recorded uniformly, objectively, consistently, and accu-
rately. The application of these indexes, terminology,descriptors, and various manual and visual tests must be
applied consistently by all geologists for each particular
project. The need to calibrate themselves with others per-
forming similar tests and descriptions is imperative to
ensure that data are recorded and interpreted uniformly.
The use of these standard descriptors and terminology is
not intended to replace the geologist's or engineer's indi-vidual judgment. The established standard qualitative
and quantitative descriptors will assist newly employed
geologists and engineers in understanding Reclamation
terminology and procedures, permit better analysis of
data, and permit better understanding by other geologists
and engineers, and by contractors. Most of the physical
dimensions established for the descriptive criteria per-
taining to rock and discontinuity characteristics have
been established using a 1-3-10-30-100 progression for
consistency, ease of memory, conversion from English to
metric (30 millimeters [mm] = 0.1 foot [ft]) units, and to
conform to many established standards used throughout
the world. Their use will improve analysis, design and
construction considerations, and specifications prepara-
tion. Contractor claims also should be reduced due toconsistent and well defined terminology and descriptors.
Alphanumeric values for many physical properties have
been established to enable the geotechnical engineer and
engineering geologist to readily analyze the geologic data.
These alphanumeric descriptors also will assist in compi-
lation of data bases and computer searches when usingcomputer generated logs. For consistency, the lower the
alphanumeric value, the more favorable the condition
being described. However, alphanumeric codes do not
replace a complete description of what is observed. A
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
30/449
FIELD MANUAL
12
complete description provides physical dimensions
including a range and/or average in size, width, length or
other physical property, and/or descriptive information.
It is important to start physical testing of the geologic
materials as early as possible in an exploration program;
descriptors alone are not sufficient. As data are inter-
preted, index properties tests can be performed in the
field to obtain preliminary strength estimates for repre-
sentative materials or materials requiring special con-
sideration. The scope of such a program must be tailoredto each feature. Tests which are to be considered include
point load, Schmidt hammer, sliding tilt, and pocket
Torvane or penetrometer tests. These tests are described
briefly in chapters 4 and 5. Indexes to be considered
include rock hardness, durability (slaking), and Rock
Quality Designation (RQD). The type of detailed labora-
tory studies can be formulated better and the amount of
sampling and testing may be reduced if results from field
tests are available.
Units of Measurements for Geologic Logs of
Exploration, Drawings, and Reports
Metric Units
For metric specifications and studies, metric (Interna-
tional System of Units) should be used from the start of
work if possible. Logs of exploration providing depth
measurements should be given to tenths or hundredths of
meters. All linear measurements such as particle or
crystal sizes, ranges or averages in thickness, openness,and spacing, provided in descriptor definitions in
chapters 3, 4, and 5, should be expressed in millimeters
or meters as appropriate. Pressures should be given in
pascals (Pa). Permeability (hydraulic conductivity)
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
31/449
TERMINOLOGY
13
should be in centimeters per second (cm/s). In some
cases, local usage of other units such as kilogram per
square centimeter (kg/cm2) for pressure or centimeters
(cm) may be used.
English Units (U.S. Customary)
For specifications and studies using United States cus-
tomary or English units (inch-pound), depth measure-
ments should be given in feet and tenths of feet. Ranges
in thickness, openness, and spacing, are preferred intenths or hundredths of a foot, or feet as shown in the
descriptor definitions in chapters 4 and 5. Pressure
should be in pound-force per square inch (lbf/in2 or
PSI). Permeability should be in feet per year (ft/yr). The
exceptions to the use of English units (inch-pound) are for
describing particle and grain sizes and age dating.
Particle sizes for soils classified using American Society
for Testing and Materials/Unified Soil Classification
Systems (ASTM/USCS) should be in metric units on all
logs of exploration. For description of bedrock, particle
and grain sizes are to be in millimeters.
Age Dates
If age dates are abbreviated, the North American Strati-graphic Commission (NASC) recommends ka for thousand
years andMa for million years, but my or m.y. (million
years) for time intervals (for example, ". . . during a
period of 40 my . . .").
Conversion of Metric and English (U.S. Customary)
Units
Table 2-2 provides many of the most frequently used
metric and English (U.S. Customary) units for
geotechnical work.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
32/449
FIELD MANUAL
14
Table 2-2.Useful conversion factorsmetric and English units (inch-pound)
To convert units in column 1 to units in column 4, multiply column 1 by the factor in column 2.
To convert units in column 4 to units in column 1, multiply column 4 by the factor in column 3.
Column 1 Column 2 Column 3 Column 4
Length
inch (in) 2.540 X 10 1 3.937 X 10-2 millimeter (mm)
hundredths of feet 3.048 X 102 3.281 X 10 -3 millimeter (mm)
foot (ft) 3.048 X 10 -1 3.281 meter (m)
mile (mi) 1.6093 6.2137 X 10-1 kilometer (km)
Area
square inch (in2) 6.4516 X 10-4 1.550 X 10-3 square meter (m2)
square foot (ft2) 9.2903 X 10 -2 1.0764 X 101 square meter (m2)
acre 4.0469 X 10 -1 2.4711 hectare
square mile (mi2) 0.386 X 10 -2 259.0 hectares
Volume
cubic inch (in3) 1.6387 X 10-2 6.102 X 10-2 cubic centimeter (cm2)
cubic feet (ft3) 2.8317 X 10-2 3.5315 x 101 cubic meter (m3)
cubic yard (yd3) 7.6455 X 101 1.3079 cubic meter (ms)
cubic feet (ft3) 7.4805 1.3368 x 10-1 gallon (gal)
gallon (gal) 3.7854 2.6417 X 10-1 liter (L)
acre-feet (acre-ft) 1.2335 X 103 8.1071 X 10 -4 cubic meter (m3)
Flow
gallon per minute (gal/min) 6.309 X 10-2 1.5850 X 101 liter per second (L/s)
cubic foot per second (ft3/s) 4.4883 X 102 2.228 X 10-3 gallons per minute (gal/min)
1.9835 5.0417 X 10-1 acre-feet per day (acre-ft/d)
cubic foot per second (ft3/s) 7.2398 X 102 1.3813 X 10-3 acre-feet per year (acre-ft/yr)
2.8317 X 10-2 3.531 X 101 cubic meters per second (m3/s)
8.93 X 105 1.119 X 10-6 cubic meters per year (m3/yr)
Permeability
k, feet/year 9.651 X 10-7 1.035 X 106 k, centimeter per second
(cm/sec)
Density
pound-mass per cubic foot 1.6018 X 101 6.2429 X 10-2 kilogram per cubic meter
(lb/ft3) (kg/m3)
Unit Weight
pound force per cubic foot 0.157 6.366 kilonewton per cubic meter(lb/ft3) (kN/m3)
Pressure
pounds per square inch (psi) 7.03 X 10-2 1.4223 X 101 kilogram per square
centimeter (kg/cm3)
6.8948 0.145 kiloPascal (kPa)
Force
ton 8.89644 1.12405 X 10-1 kilonewton (kN)
pound-force 4.4482 X 10-3 224.8096 kilonewton (kN)
Temperature
EC = 5/9 (EF - 32 E) EF = (9/5 EC) + 32 E
GroutingMetric bag cement per meter 3.0 0.33 U.S. bag cement per foot
Water:cement ratio 0.7 1.4 water:cement ratio by weight
by volume
pounds per square inch 0.2296 4.3554 kilogram per square centi-
per foot meter per meter (kg/cm2/m)
k, feet/year 0.1 10 Lugeon
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
33/449
TERMINOLOGY
15
BIBLIOGRAPHY
[1] The Glossary of Geology, 4th edition, American
Geologic Institute, Alexandria, VA, 1997.
[2] The American Association of Petroleum Geologists
Bulletin, v. 67, No. 5, pp. 841-875, May 1983.
[3] Bureau of Reclamation,Earth Manual, 3rd edition,
part 2, Denver, CO, 1990.
[4 ] Proctor, Robert V., and Thomas L. White, "Earth
Tunneling with Steel Supports," Commercial
Shearing, Inc., 1775 Logan Avenue, Youngstown, OH
44501, 1977.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
34/449
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
35/449
Chapter 3
ENGINEERING CLASSIFICATION
AND DESCRIPTION OF SOIL
General
Application
Soil investigations conducted for engineering purposes
t ha t use test pits, t renches, a uger a nd dr ill holes, or ot her
explora tory meth ods a nd surfa ce sam pling a nd m a ppingare logged and described according to the Unified Soil
Cla ssif ica tion S yst em (U SC S) a s present ed in B ureau of
Recla ma t ion (Recla ma tion) sta nda rds U S B R 5000 [1] a nd
5005 [2]. Also, bedr ock ma t eria ls w ith t he engin eering
properties of soils are described using these standards
(cha pter 2). The Recla ma t ion sta nda rds a re consist ent
w ith t he America n S ociet y for Testin g Ma t eria ls (AS TM)
D esigna t ion D 2487 a nd 2488 on t he U S C S syst em [3,4].
Descriptive criteria and terminology presented are
prima rily for t he visua l classi f ica tion a nd ma nua l tests .
The ident ifica t ion port ion of t hese meth ods in a ssign ing
group symbols is l imited to soil particles smaller than
3 inches (in) (75 millimeters [mm]) and to naturally
occurr ing soils. P rovisions a re a lso ma de t o estima t e t he
percenta ges of cobbles a nd boulders by volume. Thisdescriptive system may also be applied to shale, shells,
crushed rock, and other materials if done according to
criteria est a blished in th is sect ion. C ha pter 11 a ddr esses
t he logging form a t a nd criteria for describing soil in t est
pits, t renches, a uger holes, a nd d rill hole logs.
All investiga t ions a ssocia t ed wit h la nd cla ssifica t ion forirriga t ion suita bility , da t a collect ion, a na lyses of soil
and substratum materia ls rela ted to drainage inves-
t igat ions, a nd Quat erna ry s tra t igraphy (e.g ., faul t a nd
pa leoflood st udies) a re logged a nd described using t he
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
36/449
FIELD MANUAL
18
U .S. D epa rt ment of Agricultur e terminology outlined in
appendix I to Agr i cul tu r e H and book N o. 436 (Soi l
Taxonomy), da t ed D ecember 1975 [5].
All soil classification descriptions for particle sizes less
t ha n No. 4 sieve size a re t o be in m etric units.
Performing Tests and Obtaining Descriptive
Information
The U S C S g roups soils a ccord ing t o pot ent ia l engin eering
beha vior. The descriptive inform a t ion a ssists w ith esti-mating engineering properties such as shear strength,
compr essibility , a nd perm ea bilit y. These guidelines ca n
be used not only for ident ifica t ion of soils in th e field but
a lso in t he office, la bora t ory , or w herever soil sa mples a re
inspect ed a nd described.
Laboratory classification of soils [1] is not alwaysrequ ired but sh ould be perform ed a s necessa ry a nd can be
used a s a check of visua l-ma nu a l met hods. The descrip-
tors obtained from visual-manual inspection provide
valuable information not obtainable from laboratory
testing. Visual-manual inspection is always required.
The visual-manual method has particular value in
ident ifying a nd gr ouping simila r soil sa mples so t ha t only
a minimum num ber of la bora tory t ests a re required for
posit ive soil cla ssifica t ion. The a bilit y t o ident ify a nd
describe soils corr ect ly is lea rn ed more rea dily und er th e
guida nce of experienced personnel, but ca n be a cq uired by
compa ring la bora t ory t est r esult s for t ypica l soils of each
ty pe w ith their visua l a nd ma nua l cha ra cterist ics. When
identifying and describing soil samples from an area or
project , a ll t he procedures need not be follow ed. S imila rsoils m a y be gr ouped t ogether; for exa mple, one sa mple
should be ident ified a nd described complet ely, w ith t he
others identified as similar based on performing only a
few of the identification and descriptive procedures.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
37/449
SOIL
19
D escriptive inform a t ion sh ould be evalua t ed a nd r eport ed
on every sa mple.
The sa mple used for cla ssifica t ion m ust be representa t ive
of the s tra tum and be obtained by an appropriate ac-
cept ed or st a nda rd procedure. The origin of the ma t erial
mu st be corr ect ly ident ified. The origin descript ion ma y
be a boring n umber a nd d ept h a nd/or sa mple num ber, a
geologic stratum, a pedologic horizon, or a location
description with respect to a permanent monument, a
grid system, or a sta t ion num ber a nd offset .
Terminology for Soils
D efinitions for soil cla ssifica t ion a nd description a re in
accordance with USBR 3900 Standard Definit ions of
Terms a nd S ym bols Rela t ing t o S oil Mecha nics [6]:
Cobbles and boulderspa rt icles r eta ined on a 3-inch(75-mm ) U .S . St a nd a rd sieve. The follow ing t erminology
distingu ishes betw een cobbles a nd boulders:
Cobblesparticles of rock that will pass a 12-in
(300-mm ) sq ua re opening a nd be ret a ined on a 3-in
(75-mm) sieve.
Bouldersparticles of rock that will not pass a12-in (300-mm) sq ua re opening .
Gravelpa rt icles of rock t ha t w ill pa ss a 3-in (75-mm )
sieve a nd is ret a ined on a No. 4 (4.75-mm ) sieve. G ra vel
is furt her subdivided a s follow s:
Coarse gravelpa sses a 3-in (75-mm ) sieve a nd isret a ined on 3/4-in (19-mm) sieve.
Fine gravelpa sses a -in (19-mm ) sieve a nd is
ret a ined on No. 4 (4.75-mm) sieve.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
38/449
FIELD MANUAL
20
Sandpa rt icles of rock t ha t w ill pa ss a No. 4 (4.75-mm )
sieve a nd is r et a ined on a No. 200 (0.075-mm or 75-micro-
met er [m]) sieve. S a nd is furt her subd ivided a s follow s:
Coarse sandpa sses No. 4 (4.75-mm) sieve a nd is
ret a ined on No. 10 (2.00-mm) sieve.
Medium sandpa sses No. 10 (2.00-mm) sieve a nd
is r et a ined on No. 40 (425-m) sieve.
Fine sandpasses No. 40 (425-m) sieve and isretained on No. 200 (0.075-mm or 75-m) sieve.
Claypa ss es a No. 200 (0.075-mm or 75-m) siev e. S oil
ha s pla st icity w i thin a ra nge of wa ter contents a nd ha s
considera ble st rengt h w hen a ir-dry . For cla ssifica t ion,
cla y is a fine-gra ined soil, or t he fine-gra ined port ion of a
soil, w ith a pla stici ty index great er tha n 4 a nd t he plot ofpla st icity ind ex versus liquid limit fa lls on or a bove the
" A" -line (figur e 3-5, la t er in t his cha pter).
Siltpa sses a No. 200 (0.075-mm or 75-m) sieve. S oilis nonplastic or very sl ightly plastic and that exhibits
l it t le or no str ength wh en a ir-dry is a si lt . For
classification, a silt is a fine-grained soil , or the fine-gra ined port ion of a soil, wit h a pla st icity index less tha n
4 or t he plot of pla st icity index versus liqu id limit fa lls
below t he " A" -line (figur e 3-5).
Organic claycla y w ith sufficient orga nic cont ent t o in-fluence t he soil propert ies is a n orga nic cla y. For cla ssifi-
ca tion, a n orga nic clay is a soil t ha t w ould be classi f ied a s
a cla y except t ha t i t s l iqu id limit va lue a fter oven-dry ing
is less than 75 percent of i ts l iquid limit value before
oven-drying.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
39/449
SOIL
21
Organic siltsilt w ith sufficient orga nic cont ent t o in-
flu-ence th e soil propert ies. For cla ssifica t ion, a n org a nic
si lt is a soil th a t w ould be classi f ied a s a si lt except th a t
its l iquid limit value after oven-drying is less than
75 percent of it s liqu id limit va lue before oven-dr yin g.
Peatma t eria l composed prima rily of veget a ble t issuesin various stages of decomposition, usually with an or-
ganic odor, a dark brown to black color, a spongy con-
sistency, and a texture ranging from fibrous to amor-
phous. Cla ssifica t ion procedures ar e not a pplied to pea t .
Classifications of Soils
Group Names and Group Symbols
The ident ifica t ion a nd n a ming of a soil ba sed on result s
of visua l an d ma nua l tests is present ed in a subsequentsect ion. S oil is given a n ident ifica t ion by a ssigning a
group sym bol(s) a nd group na me. Im port a nt informa t ion
about the soil is added to the group name by the term
" w it h " w hen a ppropria t e (figu res 3-1, 3-2, 3-3, 3-4). The
group name is modified using with to stress other
significa nt component s in th e soil.
Figure 3-2 is a flow cha rt for a ssigning ty pica l na mes a nd
gr oup sy mbols for inorga nic fine-gr a ined soils; figure 3-3
is a flow cha rt for orga nic fine-gra ined soils; figure 3-4 is
a flow cha rt for coa rs e-gra ined soils. Refer to t a bles 3-1
a nd 3-2 for t he basic group na mes wit hout modifiers. If
t he soil ha s properties w hich do not dist inctly pla ce it in
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
40/449
FIELD MANUAL
22
FINE-GRAINED SOILS
Sandy BASIC
GROUP NAME
with sand
Gravelly with gravel
COARSE-GRAINED SOILS
with silt BASIC
GROUP NAME
with sand
with clay with gravel
Figure 3-1.Modifiers to basic soil group names
(for visual classification).
a specific group, bord erline sym bols ma y be used. There
is a distinction between dual symbol s a n d border l ine
symbols.
Dual Symbols.Dual symbols separated by a hyphen
a re used in la bora t ory cla ssifica t ion of soils a nd in visua lclassi f ication when soils are estimated to contain
10 percent fines. A dua l sym bol (t w o sym bols sepa ra t ed
by a hyphen, e.g. , GP-GM, SW-SC, CL-ML) should be
used to indicate that the soil has the properties of a
classi f ica tion w here tw o symbols a re required. D ua l sym-
bols are required when the soil has between 5 and
12 percent fines from la bora t ory t ests (t a ble 3-2), or fines
a re estima ted a s 10 percent by visual classi f ica tion. D ua l
symbols are also required when the l iquid l imit and
plasticity index values plot in the CL-ML area of the
pla st icity cha rt (figure 3-5, la t er in th is cha pter).
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
41/449
23 Figure 3-2.Flow chart for inorganic fine-grained s
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
42/449
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
43/449
25 Figure 3-4.Flow chart for coarse-grained soils
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
44/449
FIELD MANUAL
26
Ta ble 3-1.B a sic group na mes, prima ry groups
C oa rse-gra ined soils Fine-gra ined soils
G W - Well gra ded gra velG P - P oor ly gr ad ed gr avel
G M - Si lt y gra vel
G C - C la y ey gr a vel s a n d
SW - Well graded sand
S P - P oor ly gr a ded sa n d
S M - S ilt y sa n d
S C - C la yey sa n d
C L - L ea n cla yML - S ilt
OL - Orga nic clay (on or
a bove A-line
- Orga nic silt (below A-line)
C H - F a t cla y
MH - E la st ic silt
OH - Organ ic clay (on or a bove
A-line)- Orga nic silt (below A-line)
B a sic group nameha tched a rea on P last icity Ch a rt
(La bora tory C lassifica tion)
C L-ML - S ilt y cla y
G C-G M - Si lt y , clayey gravel
S C -S M - S ilt y , cla y ey s a n d
Ta ble 3-2.B a sic group na mes, 5 t o 12 percent fines
(La bora tory Cla ssifica tion)
G W-G M - Well gra ded gra vel w it h silt
G W-G C - Well gra ded gra vel w it h cla y (if fin es =
C L-ML) Well gra ded gra vel w ith silty clayG P -G M - P oor ly gr a ded g ra v el w it h silt
G P -G C - P oor ly g rad ed g ravel w i t h clay (if fines =
CL -ML) P oorly gra ded gra vel w ith silty clay
S W-S M - Well gra ded sa nd w it h silt
SW-SC - Well graded sand wi th clay (if f ines = CL-ML)
Well gra ded sa nd w ith silty clay
S P -S M - P oorly gra ded sa nd w it h silt
SP -SC - P oor ly g rad ed sand w i t h clay (if fines = CL -ML) P oorly gra ded sa nd w ith silty cla y
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
45/449
SOIL
27
Borderline Symbols.Borderline symbols are used
w hen soil propert ies indica t e th e soil is close to a noth er
cla ssifica t ion group. Tw o sym bols sepa ra t ed by a sla sh,
such a s C L/CH , S C /C L, G M/S M, C L/ML , sh ould be used
to indicate that the soil has properties that do not
dist inctly pla ce t he soil int o a s pecific gr oup. B eca use th e
visual classification of soil is based on estimates of
pa rt icle-size dist ribution a nd pla st icity cha ra ct eristics, i t
ma y be difficult t o clea rly ident ify th e soil as belonging t o
one ca t egory. To indica t e t ha t t he soil ma y fa ll int o one
of t w o possible ba sic groups, a borderline symbol ma y be
used w i th the tw o symbols separa ted by a s lash. Aborderline classification symbol should not be used
indiscrimina t ely. E very effort should be ma de first to
pla ce th e soil int o a single group. B orderline symbols ca n
also be used in laboratory classification, but less
frequently.
A borderline symbol ma y be used w hen t he percent a ge offines is visua lly est ima t ed to be betw een 45 a nd 55 per-
cent . One symbol should be for a coa rs e-gra ined soil w ith
fines a nd t he ot her for a fine-gra ined soil. For exa mple:
G M/ML , C L/S C .
A borderline symbol ma y be used w hen t he percent a ge of
sand and the percentage of gravel is estimated to be
a bout t he sa me, for exa mple, G P /S P , S C/G C , G M/S M. It
is pra ct ica lly impossible t o ha ve a soil t ha t w ould ha ve a
border line sy mbol of G W/S W. H owever, a border line
symbol may be used when the soil could be either well
gr a ded or poorly gr a ded. For exa mple: G W/G P , S W/S P .
A bord erline sym bol ma y be used w hen t he soil could be
eith er a silt or a cla y. For exa mple: CL/ML, C H /MH ,S C /S M.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
46/449
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
47/449
SOIL
29
S oil ident ifica t ion procedures a re ba sed on t he minu s 3-in
(75-mm) pa r t icle sizes. All plus 3-in (75-mm) pa r t icles
must be manually removed from a loose sample, or
ment a lly for a n int a ct s a mple, before cla ssifying t he soil.
E st ima t e a nd n ot e th e percent by volume of t he plus 3-in
(75-mm ) pa rt icles, bot h t he percent a ge of cobbles a nd t he
percent a ge of boulders.
Not e: B eca use t he percent a ges of t he pa rt icle-
size distribution in laboratory classification
(AS TM: D 2487) a re by dry w eight a nd th e
estimates of percentages for gravel , sand, andfines are by dry weight, the description should
state that the percentages of cobbles and
boulders are by volume, not weight, for visual
cla ssifica t ion. E st ima t ion of the volume of cob-
bles a nd boulders is not a n easy t a sk. Accura te
estim a t ing req uires experience. While exper-
ienced loggers may be able to successfullyestimate the minus 3-in fraction to within
5 percent , th e ma rgin of error could be la rg er for
oversize pa rt icles. E st ima t es ca n be confirmed
or cal ibrated with large scale f ield gradation
t ests on crit ica l project s. G iven th e la rge pos-
sible errors in these estimates, the estimates
should n ot be used a s t he sole ba sis for d esign of
processing equipment. La rge sca le gra da t ions
should be obt a ined a s pa rt of th e process pla nt
designs.
In most cases, the volume of oversize is estimated in
three size ranges, 3 to 5, 5 to 12, and 12 inches and
la rger. Cobbles a re often divided int o t w o size ra nges,
because in roller compacted fill of 6-in compacted liftt hickness, t he ma ximum size cobble is 5 inches. If t he
purpose of the investigation is not for roller compacted
fill , a single size ra nge for cobbles can be est ima t ed.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
48/449
FIELD MANUAL
30
Estimate and note the percentage by dry weight of the
gra vel, sa nd, a nd fines of th e fra ct ion of t he soil sma ller
t ha n 3 in (75-mm ). The percenta ges a re est ima t ed to t he
closest 5 percent . The percent a ges of gr a vel, sa nd , a nd
fines must add up to 100 percent, excluding trace
a mount s. The presence of a component n ot in sufficient
quantity to be considered 5 percent in the minus 3-in
(75-mm ) port ion, is indica t ed by t he term " t ra ce." For ex-
a mple: t ra ce of fines. A t ra ce is not considered in t he
t ot a l of 100 percent for t he component s.
The first step in the identification procedure is todetermine the percentages of fine-grained and coarse-
gra ined ma t eria ls in t he sa mple. The soil is fine-gra ined
if it cont a ins 50 percent or more fines . The soil is coa rs e-
grained if i t contains less than 50 percent fines.
P rocedures for t he description a nd cla ssifica t ion of t hese
t w o prelimina ry ident ifica t ion groups follow .
Procedures and Criteria for Visual Classification
of Fine-Grained Soils
Select a representative sample of the material for
examination and remove particles larger than the
No. 40 sieve (medium sa nd a nd la rger) unt il a specimen
equiva lent t o a bout a ha ndful of represent a tive ma teria l
is a va ila ble. U se t his specimen for performing t he
ident ifica t ion test s.
Identification Criteria for Fine-Grained Soils.The
t ests for ident ifying propert ies of fines a re dry strength,
dilatency, toughness, and plasticity.
1. D r y st r en g th .S elect from t he specimen enough
material to mold into a ball about 1 in (25 mm) in
diam eter. Mold or w ork the ma teria l unt i l i t ha s the
consist ency of put t y, a dding w a t er if necessar y.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
49/449
SOIL
31
From t he molded ma teria l , ma ke a t lea st t hree test
specimens. E a ch test specimen should be a ba ll of
ma teria l a bout in (12 mm) in diam eter. Allow t he
t est specimens to dry in a ir or sun, or dry by a rt ificia l
mea ns, a s long a s t he tempera t ure does not exceed
60 degrees Cent igra de (EC ). In m ost ca ses, i t w ill be
necessa ry t o prepa re specimens a nd a l low th em t o
dry over night. I f the test specimen cont a ins nat ura l
dry lumps, those th a t a re about in (12 mm) in
dia met er ma y be used in pla ce of molded ba lls. (The
process of molding and drying usually produces
higher s trengths t ha n a re found in na tura l dry lumpsof soil). Test t he st reng t h of t he dry ba lls or lumps by
crushing them between the f ingers and note the
strength as none, low, medium, high, or very high
a ccording to t he crit eria in t a ble 3-3. If na t ura l dry
lumps a re used, do not use th e results of an y of t he
lumps t ha t a re found t o cont a in par ticles of coa rse
sand .
Ta ble 3-3.Crit eria for d escribing d ry st reng t h
None The dry specimen crumbles w it h mere
pressure of ha ndling.
Low The dry specimen crumbles w it h some
finger pressure.
M ed iu m Th e d ry specimen br ea k s in t o pieces or
crum bles w ith considera ble finger
pressure.
H igh The dry specimen ca nnot be broken w it h
finger pressure. S pecimen will brea k int o
pieces betw een t humb a nd a ha rd surfa ce.
Very High The dry specimen ca nnot be broken
betw een th umb an d a ha rd surfa ce.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
50/449
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
51/449
SOIL
33
3. Toughness.Following completion of the
dila ta ncy test , t he specimen is sha ped into a n
elonga t ed pat a nd rolled by ha nd on a smooth surfa ce
or between the palms into a thread about c in
(3 mm ) dia met er. (If t he sa mple is too w et t o roll
easi ly, spread the sample out into a thin layer and
a llow some w a ter loss by eva pora t ion). Fold the
sa mple threa ds a nd reroll repeat edly unt i l th e threa d
crumbles a t a dia meter of a bout c in (3 mm) when
th e soil is nea r the plast ic l imit . Note the t ime
required to reroll the thread to reach the plastic
limit . Not e t he pressure requ ired t o roll t he t hr ea dnea r t he pla st ic limit . Also, note t he st rengt h of t he
t hrea d. After t he thr ea d crum bles, the pieces should
be lumped together and kneaded unti l the lump
crum bles. Not e t he t oughn ess of t he ma t erial during
kneading.
Describe the toughness of the thread and lump aslow, medium, or high according to the criteria in
table 3-5.
Ta ble 3-5.C rit eria for describing t ough ness
Low Only slight pressure is req uired to roll t he
th rea d nea r the plast ic l imit . The th rea da nd the lump are wea k and sof t .
Medium Medium pressure is required to rol l the
th rea d to nea r th e pla stic l imit . The th rea d
a nd t he lump ha ve medium sti f fness.
H igh C on sid er a ble pr essur e is r eq uir ed t o r oll t heth rea d to nea r th e pla stic l imit . The th rea d
a nd t he lump ha ve very high sti f fness.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
52/449
FIELD MANUAL
34
4 . P las t i c i t y .On t he basis of observa tions m a de
during t he toughness t est, describe t he pla st icity of
the material according to the cri teria given in
t a ble 3-6 (figur e 3-5).
Ta ble 3-6.Crit eria for describing plas t icity
Nonpla st ic A 3-mm t hread ca nnot be rolled a t a ny
w a ter content .
Low The th rea d ca n ba rely be rolled, a nd th elump ca nnot be formed w hen drier t ha n
t he pla st ic limit .
Medium The t hrea d is eas y t o roll , a nd not much
t ime is required t o rea ch t he pla st ic limit .
The t hr ead ca nnot be rerolled a fter
rea ching th e pla st ic limit . The lump
crumbles w hen drier t ha n t he plast ic
limit.
H igh I t t a kes considera ble t ime rolling a nd
knea ding to rea ch th e pla st ic limit . The
th rea d ca n be rolled severa l t imes a fter
rea ching th e pla st ic limit . The lump ca n
be form ed wit hout crum bling w hen drierth a n th e pla stic l imit .
After the dry strength, di latency, toughness, and
plasticity tests have been performed, decide on
whether the soil is an organic or an inorganic fine-
gra ined soil.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
53/449
35 Figure 3-5.Plasticity chart.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
54/449
FIELD MANUAL
36
Identification of Inorganic Fine-Grained Soils.Classify the soils using the results of the manual tests
a nd t he ident ifying crit eria show n in t a ble 3-7. P ossible
inorga nic soils include lea n cla y (C L), fa t cla y (C H ), silt
(ML), a nd ela st ic silt (MH ). The propert ies of a n ela st ic
silt a re simila r to t hose for a lea n cla y. H ow ever, the silt
w ill dry q uickly on th e ha nd a nd ha ve a smooth , silky feel
w hen dry. S ome soils wh ich cla ssify a s MH a ccording to
t he field cla ssifica t ion crit eria a re difficult to distingu ish
from lean clay s, CL . I t m a y be necessa ry to perform
la bora t ory t esting t o ensure proper cla ssifica t ion.
Ta ble 3-7.Ident ifica t ion of inorga nic fine-gr a ined
soils from ma nua l tests
Group
symbol
Dry
st rengt h D ila t a ncy Toughness
ML None t o low S low t o
rapid
Low or th read
cannot be formed
CL Medium t o high None t o slow Medium
MH Low to medium None t o slow Low t o medium
CH H igh t o very
high
None H igh
S ome soils undergo irreversible cha nges upon a ir dr ying.
These irreversible processes may cause changes in
a tt erberg limits a nd oth er index tests . E ven unsuspected
soils such as low plasticity silts may have differing
atterberg limits due to processes like disaggregation.
When t ested a t na tur a l moisture, clay par ticles cl ing t o
silt par ticles resulting in less pla st icity . When dried, t heclay disa ggregat es, ma king a f iner a nd more w ell gra ded
mix of pa rt icles w ith increa sed pla st icity.
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
55/449
SOIL
37
For foundation studies of existing or new structures,
na tur a l moisture a t terberg l imits a re preferred beca use
th e in-pla ce ma teria l w ill rema in moist . Na tur a l mois-
tur e a t terberg limits a re especial ly import a nt in cri t ica l
studies, such as earthquake l iquefaction evaluation of
silt s. On some founda t ion stu dies, such a s for pumping
pla nt d esign, consolida tion tests w ill govern, a nd na tur a l
moistur e a tt erbergs a re not required. For borrow st udies,
soils will l ikely undergo moisture changes, and natural
moistur e a tt erberg limits a re not required unless unusua l
minera logy is encount ered.
Identification of Organic Fine-Grained Soils.I f the
soil cont a ins enough orga nic pa rt icles to influence t he soil
propert ies, cla ssify th e soil as a n or gani c soi l, OL or OH .
Orga nic soils usua lly a re da rk brow n t o bla ck a nd usua lly
ha ve a n orga nic odor. Often orga nic soils w ill cha nge
color, (bla ck to brown ) w hen exposed t o a ir. Orga nic soils
norma lly do not ha ve high toughness or pla st icity. Theth read for th e toughness test is spongy. In some ca ses,
furt her identifica t ion of orga nic soils a s orga nic silts or
orga nic cla ys, OL or OH is possible. C orrela t ions betw een
the di la tancy, dry s trength, and toughness tests wi th
laboratory tests can be made to classify organic soils in
simila r ma teria ls.
Modifiers for Fine-Grained Soil Classifications.I f
ba sed on visua l observa t ion, t he soil is est ima t ed to ha ve
15 to 25 percent sa nd a nd/or gr a vel, th e words " w ith sa nd
a nd/or gr a vel" a re a dded t o t he group na me, for exa mple,
LE AN C LAY WITH S AND , (CL); S ILT WITH S AND AND
G RAVE L (ML). Refer t o figur es 3-2 a nd 3-3. I f th e soil is
visua lly est ima t ed t o be 30 percent or more sa nd a nd /or
gra vel , the w ords "sa ndy" or " gra vel ly " a re added to thegroup na me. Add the w ord " sa ndy" i f th ere a ppear s to be
more sa nd tha n gra vel . Add the w ord "gra velly" i f th ere
appears to be more gravel than sand, for example,
S AND Y LE AN C LAY (CL); G RAVEL LY F AT CLAY (CH );
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
56/449
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
57/449
SOIL
39
Classify the soil as a CLAYEY GRAVEL (GC) or a
C LAYEY S AND (S C ) if t he fines a re cla yey a s determ ined
by t he procedures for fine-gra ined soil ident ifica t ion.
Id entify t he soil a s a S IL TY G RAVE L (G M) or a S IL TY
S AND (S M) if the fines a re silt y a s determ ined by th e pro-
cedures for fine-gra ined soil ident ifica t ion.
If the soil is visually estimated to contain 10 percent
fines, give t he soil a dua l cla ssifica t ion us ing t w o group
sym bols. The first g roup sym bol should corr espond t o a
clea n gr a vel or sa nd (G W, G P , SW, SP ), a nd t he secondsym bol should corr espond t o a gra vel or sa nd w ith fines
(G C , G M, S C , S M). The typica l na me is the first group
symbol plus "with clay" or "with si l t " to indicate the
pla st icity cha ra ct eristics of t he fines. For exa mple,
WELL GRADED GRAVEL WITH CLAY (GW-GC);
P OORLY G RAD E D S AND WITH S IL T (S P -S M). Refer to
figure 3-4.
If t he specimen is predomina nt ly sa nd or gra vel but con-
tains an estimated 15 percent or more of the other
coarse-grained consti tuent, the words "with gravel" or
" w ith san d" a re a dded to th e group na me. For exam ple:
P OORLY G RAD E D G RAVE L WITH S AND (G P ); CL AY-
E Y S AND WITH G RAVE L (S C). Refer t o figur e 3-4.
I f t he field sa mple cont a ined a ny cobbles a nd /or boulders,
the words "with cobbles" or "with cobbles and boulders"
a re a dded to th e group na me, for exa mple, SI LTY G RA-
VE L WITH C OB B LE S (G M).
Abbreviated Soil Classification Symbols
I f spa ce is l imited, a n a bbrevia ted syst em ma y be used t o
indica t e the soil cla ssifica t ion sym bol an d na me such a s
in logs, da t a ba ses, t a bles, etc. The a bbrevia t ed syst em
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
58/449
FIELD MANUAL
40
is not a subst itut e for t he full na me a nd descriptive infor-
ma tion but ca n be used in supplementa ry present a tions.
The a bbrevia t ed syst em consist s of th e soil cla ssifica t ion
syst em ba sed on t his cha pter, wit h prefixes a nd suffixes
a s list ed below .
P refix: s = sa ndy g = gra velly
S uffix: s = w it h sa nd g = w it h gra vel
c = w it h cobbles b = w it h bou ld er s
The soil cla ssifica t ion sym bol is enclosed in pa rent heses.
E xamples a re :
C L, sa ndy lea n cla y s(C L)
S P -S M, poorly gra ded sa nd (S P -G M)g
w i th s il t a nd gra vel
G P , poor ly gra ded gra vel w it h sa nd, (G P )scb
cobbles, a nd boulders
ML, gra velly silt w ith sa nd g(ML)sc a nd cobbles
Description of the Physical Properties of Soil
Descriptive information for classification and reporting
soil properties such a s a ngula rity , sha pe, color, m oistur e
condit ions, a nd consist ency a re present ed in t he follow ing
paragraphs .
Angularity
Angularity is a descriptor for coarse-grained materials
only. The a ng ula rit y of t he sa nd (coa rse sizes only),
gra vel, cobbles, a nd boulders, a re described a s a ngula r,
-
8/9/2019 ENGINEERING GEOLOGY FIELD MANUAL
59/449
SOIL
41
suba ngula r, subrounded, or rounded a s indica ted by t he
cri teria in ta ble 3-8. A ra nge of a ngula ri ty m a y be sta ted,
such a s: sub-round ed t o round ed.
Ta ble 3-8.C rit eria for d escribing a ngu la rit y of
coa rse-gra ined pa rt icles
Angula r P a r t icles ha ve sha rp edges a nd rela t ively
pla na r sides with unpolished surfa ces.
Su bangula r P a r t i cles a r e s imila r t o angu la r d escr ipt ion
but h a ve rounded edges.
Su br ou nded P ar t i cles have nea r ly plana r s id es bu t w ell-
rounded corners and edges.
R oun ded P a r t icles h a ve sm oot hly cur ved sides a n d n o
edges.
Shape
D escribe the sha pe of t he gra vel, cobbles, a nd boulders a s
f la t , elonga ted or f la t a nd elonga ted i f th ey meet t he
criteria in ta ble 3-9. In dica t e the fra ct ion of t he pa rt icles
t ha t ha ve t he sha pe, such a s: one-t hird of gra vel pa rt icles
a re f la t . I f the ma