HomeMy WebLinkAbout612 E. PITKIN, CARRIAGE HOUSE - FDP - FDP160007 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTOctober 12, 2015
Pat McGaughran (pat@riograndemexican.com)
824 Whedbee Street
Fort Collins, CO 80524
Re: Geotechnical Subsurface Exploration
612 East Pitkin Street
Fort Collins, Colorado
EEC Project No. 15-01-197
Mr. McGaughran:
Earth Engineering Company, Inc. (EEC) personnel have completed the geotechnical subsurface
exploration you requested for the single-family residence and detached garage/carriage house to be
constructed at 612 East Pitkin Street in Fort Collins, Colorado. Results of that subsurface exploration
are provided with this report.
We understand the proposed single-family residence will be a two story wood frame structure supported
over a full basement and the detached garage/carriage house will be supported over a slab-on-grade type
foundation system. We expect foundation loads for the proposed structure will be light with continuous
wall loads less than 3 kips per lineal foot and individual column loads less than 50 kips. Small grade
changes are expected to develop final site grades for the structures.
The purpose of this report is to describe the subsurface conditions encountered in the test borings
completed within the identified building envelopes and provide geotechnical recommendations for
design and construction of foundations and support of floor slabs.
The residence site is located at 612 East Pitkin Street in Fort Collins, Colorado. The property is presently
developed with an existing residence located within the house building envelope. The existing structure
is to be removed prior to construction of the new residence.
To develop information on existing subsurface conditions in the area of the proposed residence, two soil
borings were advanced to a depth of approximately 25½ feet below site grades at the identified building
envelopes.
The borings were completed using a truck-mounted CME-55 drill rig equipped with a hydraulic head
employed in drilling and sampling operations. The borehole was advanced using 4-inch nominal
Earth Engineering Company, Inc.
EEC Project No. 15-01-197
October 12, 2015
Page 2
diameter continuous flight augers and samples of the subsurface materials encountered were obtained
using split-barrel and California barrel sampling procedures in general accordance with ASTM
Specification D-1586. In the split-barrel and California barrel sampling procedures, standard sampling
spoons are driven into the ground using a 140-pound hammer falling a distance of 30 inches. The number
of blows required to advance the samplers is recorded and is used to estimate the in-situ relative density
of cohesionless materials and, to a lesser degree of accuracy, the consistency of cohesive soils. All
samples obtained in the field were sealed and returned to the laboratory for further examination,
classification and testing.
EEC field personnel were on-site during drilling to evaluate the subsurface conditions encountered and
direct the drilling activities. A field log was prepared based on observation of disturbed samples and
auger cuttings. Based on results of the field boring and laboratory testing, subsurface conditions in the
area of the residence can be summarized as follows.
Brown sandy lean clay soils were encountered at the surface at the boring locations. The sandy lean clay
soils were medium stiff to very stiff in consistency, contained calcareous deposits and exhibited a low
to moderate potential for swelling with variation in moisture content at current moisture/density
conditions. The moderately plastic sandy lean clay soils were underlain by brown sand and gravel
materials at a depth of approximately 22 feet below present site grades. The sand and gravel materials
were very dense in consistency and extended to the bottom of the borings at a depth of approximately
25½ feet below present site grades where the boring was terminated.
Observations were made at the time of drilling and approximately 24 hours after drilling to evaluate the
presence and depth to free water at the test boring locations. At the time of drilling, free water was
observed at a depth of approximately 22 and 23 feet below present site grades at borings B-1 and B-2,
respectively. Free water was observed at a depth of approximately 22 and 22½ feet below present site
grades approximately 24 hours after drilling at borings B-1 and B-2, respectively. Longer term
observations in holes that are cased and sealed from the influence of surface water would be required to
more accurately determine fluctuations in groundwater levels over time. Fluctuations in groundwater
levels can occur based on hydrologic conditions and other conditions not apparent at the time of this
report. Zones of perched and/or trapped water may also be encountered in more permeable zones within
the subgrade soils at times throughout the year.
The stratification boundaries indicated on the boring logs represent the approximate locations of changes
in soil types; in-situ, the transition of materials may be gradual and indistinct. In addition, the test borings
provide an indication of subsurface conditions at the test locations; however, subsurface conditions may
Earth Engineering Company, Inc.
EEC Project No. 15-01-197
October 12, 2015
Page 3
vary in relatively short distances away from those locations. Potential variations in subsurface conditions
can best be evaluated by close observation and testing of the subgrade materials during construction. If
significant variations from the conditions anticipated from the test borings appear evident at that time, it
may be necessary to re-evaluate the recommendations provided in this report.
ANALYSIS AND RECOMMENDATIONS
General
It is our understanding the existing residence and foundation located at the site will be removed prior to
construction of the new residence. We recommend the existing concrete foundation and any other
concrete elements be entirely removed from the proposed residence location prior to construction of the
new residence. Some areas of backfill near the old residence may be encountered during demolition and
removal of the structure. We recommend removing those fill materials down to the natural in-situ sandy
lean clay soils prior to construction of the new foundation.
Foundations
Based on the materials observed at the test boring locations, it is our opinion the proposed lightly loaded
single-family residence could be supported on conventional footing foundations bearing on undisturbed
natural sandy lean clay soils. For design of footing foundations bearing in the natural, low swell potential
medium stiff to very stiff sandy lean clay soils, we recommend using a net allowable total load soil
bearing pressure not to exceed 1,000 psf. The net bearing pressure refers to the pressure at foundation
bearing level in excess of the minimum surrounding overburden pressure. Total load should include full
dead and live loads.
Exterior foundations and foundations in unheated areas should be located at least 30 inches below
adjacent exterior grade to provide frost cover protection. We recommend formed continuous footings
have a minimum width of 12 inches and isolated column foundations have a minimum width of 24
inches.
We recommend the foundation footing design loads be balanced to promote relatively uniform
settlement, thereby reducing the potential for differential settlement. As an alternative to balancing the
design loads solely on settlement, designing the foundation such that the dead-load pressure is balanced
throughout the foundations could be considered. Balancing the dead-load pressure would also reduce the
Earth Engineering Company, Inc.
EEC Project No. 15-01-197
October 12, 2015
Page 4
potential for differential settlement between adjacent footings. We estimate the long-term settlement of
footing foundations designed and constructed as recommended above would be less than 1 inch.
While most of the site cohesive soils did not exhibit appreciable swell potential with variation in moisture
content, moderate swell potential was observed in one of the near surface sandy clay soil samples tested
on this lot. Close observation and testing will be needed to evaluate the volume change characteristics
of the in-situ soils at the time of foundation excavation. If moderately expansive soils are observed at
that time, reworking of the subgrade or removal and replacement may be necessary to develop suitable
foundation bearing.
Groundwater was observed in the test borings at a depth of approximately 22 to 22½ feet below the
present site grades. We recommend maintaining a minimum vertical separation of three feet between
foundation bearing elevation and the peak seasonal groundwater level. We have typically observed peak
seasonal groundwater levels in mid to late summer.
No unusual problems are anticipated in the construction of the footing foundations. Care should be taken
to avoid disturbing the bearing soils. The natural site soils may be easily disturbed by construction
activities. Soils which are disturbed by the construction activities or materials which have become dry
and desiccated or wet and softened should be reworked or removed from the foundation excavation prior
to the placement of foundation concrete.
Floor Slab and Exterior Slab-on-Grade Subgrades
In any slab-on-grade areas, those slabs may be supported on existing site soils or newly placed and
compacted fill. All existing vegetation and/or topsoil should be removed from the floor or flatwork
areas. After stripping and completing all cuts and prior to placement of any fill, floor slabs or other
flatwork, we recommend the in-place soils be scarified to a minimum depth of 9 inches, adjusted in
moisture content and compacted to at least 95% of the material's maximum dry density as determined in
accordance with ASTM Specification D-698, the standard Proctor procedure. The moisture content of
the scarified soils should be adjusted to be within the range of ±2% of standard Proctor optimum moisture
at the time of compaction. Scarification and compaction of subgrades in the basement area of the
structure would not be required.
Fill soils required to develop the floor slab subgrades should consist of approved, low-volume change
materials which are free from organic matter and debris. It is our opinion the on-site sandy lean clay
Earth Engineering Company, Inc.
EEC Project No. 15-01-197
October 12, 2015
Page 5
soils could be used as low-volume change fill in the floor areas. Those fill materials should be placed in
loose lifts not to exceed 9 inches thick, adjusted in moisture content as recommended for the scarified
soils and compacted to at least 95% of standard Proctor maximum dry density.
After preparation of the subgrades, care should be taken to avoid disturbing the in-place materials.
Subgrade materials loosened or disturbed by the construction activities or materials which become dry
and desiccated or wet and softened should be removed and replaced or reworked in place prior to
placement of the floor slab concrete.
As a precaution, the floor slabs should be isolated from structural portions of the building to prevent
differential movement to those elements causing distress to the structure. That isolation is typically
developed through the use of a voided wall which is suspended from the overhead first floor joist. Care
should be taken in door framing, drywalling and finishing to maintain a voided space which will allow
for movement of the floor slab without transmission of stresses to the overlying structure.
While most of the site soils exhibited relatively low potential for swelling with increases in moisture
content at current moisture/density conditions, some swelling was observed in one of the near surface
samples tested on this lot. Slight swelling of the subgrade soils could lead to post-construction
movement of lightly loaded slabs. Reworking of the slab subgrades (i.e. scarification, moisture
conditioning and compacting) would reduce the potential for post-construction movement; however, that
risk cannot be eliminated.
Below Grade Areas
We recommend a perimeter drain system be constructed around all below grade areas to reduce the
potential for water seepage into below grade areas and/or development of hydrostatic loads on below
grade walls. In general, a perimeter drain system should consist of perforated metal or plastic pipe placed
around the exterior of the structure and sloped to drain to a sump area where water can be removed
without reverse flow occurring in the system. The drain line should be surrounded by a minimum of 6
inches of appropriately sized granular filter soil and either the granular filter soil or the drain line should
be surrounded in a filter fabric to prevent the accumulation of fines in the drain system.
Backfill placed adjacent to below grade walls above the drain system should consist of approved, low-
volume change materials which are free from organic matter and debris. The on-site sandy lean clay soils
could be used as backfill adjacent to the below grade walls. If free draining granular soils are used as
backfill adjacent to the below grade areas, we recommend the top 2 feet of material be an essentially
Earth Engineering Company, Inc.
EEC Project No. 15-01-197
October 12, 2015
Page 6
cohesive material to reduce surface infiltration in the backfill. Those soils should be placed in loose lifts
not to exceed 9 inches thick, adjusted in moisture content and compacted to at least 95% of the material's
standard Proctor maximum dry density. The moisture content of the fill soils should be adjusted to be
within the range of ±2% of standard Proctor optimum moisture at the time of compaction.
Care should be taken in placing and compacting the wall backfill to avoid placing undue lateral stress
on the below grade walls. We recommend compaction using light mechanical or hand compaction
equipment.
For design of below grade walls where appropriate steps have been taken to eliminate the buildup of
hydrostatic loads, we recommend using an equivalent fluid pressure of 50 pounds per cubic foot. That
recommended equivalent fluid pressure is based on an active stress distribution analysis which includes
an assumption of slight wall rotation. The assumed wall rotation for an active case analysis may cause
deflection on the order of 0.5% of the wall height. The recommended equivalent fluid pressure does not
include a factor of safety nor an allowance for hydrostatic loads. Point loads placed in the backfill or
surcharge loads placed adjacent to the structure could add to the lateral forces on the below grade walls.
Other Considerations
Positive drainage should be developed away from the structure with a minimum slope of 1 inch per foot
for the first 10 feet away from the building. Care should be taken in planning of landscaping adjacent
to the residence to avoid features which would pond water adjacent to the foundations or basement walls.
Placement of plants which require irrigation systems or could result in fluctuations of the moisture
content of the subgrade materials should be avoided adjacent to the structure. Lawn watering systems
should not be placed within 5 feet of the perimeter of the building and spray heads should be designed
not to spray water on or immediately adjacent to the structure. Roof drains should be designed to
discharge at least 5 feet away from the structure and away from the pavement areas.
GENERAL COMMENTS
The analysis and recommendations presented in this report are based upon the data obtained from the
soil borings performed at the indicated locations and from any other information discussed in this report.
This report does not reflect any variations which may occur across the site. The nature and extent of
such variations may not become evident until construction. If variations appear evident, it will be
necessary to re-evaluate the recommendations of this report.
DRILLING AND EXPLORATION
DRILLING & SAMPLING SYMBOLS:
SS: Split Spoon - 13/8" I.D., 2" O.D., unless otherwise noted PS: Piston Sample
ST: Thin-Walled Tube - 2" O.D., unless otherwise noted WS: Wash Sample
R: Ring Barrel Sampler - 2.42" I.D., 3" O.D. unless otherwise noted
PA: Power Auger FT: Fish Tail Bit
HA: Hand Auger RB: Rock Bit
DB: Diamond Bit = 4", N, B BS: Bulk Sample
AS: Auger Sample PM: Pressure Meter
HS: Hollow Stem Auger WB: Wash Bore
Standard "N" Penetration: Blows per foot of a 140 pound hammer falling 30 inches on a 2-inch O.D. split spoon, except where noted.
WATER LEVEL MEASUREMENT SYMBOLS:
WL : Water Level WS : While Sampling
WCI: Wet Cave in WD : While Drilling
DCI: Dry Cave in BCR: Before Casing Removal
AB : After Boring ACR: After Casting Removal
Water levels indicated on the boring logs are the levels measured in the borings at the time indicated. In pervious soils, the indicated
levels may reflect the location of ground water. In low permeability soils, the accurate determination of ground water levels is not
possible with only short term observations.
DESCRIPTIVE SOIL CLASSIFICATION
Soil Classification is based on the Unified Soil Classification
system and the ASTM Designations D-2488. Coarse Grained
Soils have move than 50% of their dry weight retained on a
#200 sieve; they are described as: boulders, cobbles, gravel or
sand. Fine Grained Soils have less than 50% of their dry weight
retained on a #200 sieve; they are described as : clays, if they
are plastic, and silts if they are slightly plastic or non-plastic.
Major constituents may be added as modifiers and minor
constituents may be added according to the relative
proportions based on grain size. In addition to gradation,
coarse grained soils are defined on the basis of their relative in-
place density and fine grained soils on the basis of their
consistency. Example: Lean clay with sand, trace gravel, stiff
(CL); silty sand, trace gravel, medium dense (SM).
CONSISTENCY OF FINE-GRAINED SOILS
Unconfined Compressive
Strength, Qu, psf Consistency
< 500 Very Soft
500 - 1,000 Soft
1,001 - 2,000 Medium
2,001 - 4,000 Stiff
4,001 - 8,000 Very Stiff
8,001 - 16,000 Very Hard
RELATIVE DENSITY OF COARSE-GRAINED SOILS:
N-Blows/ft Relative Density
0-3 Very Loose
4-9 Loose
10-29 Medium Dense
30-49 Dense
50-80 Very Dense
80 + Extremely Dense
PHYSICAL PROPERTIES OF BEDROCK
DEGREE OF WEATHERING:
Slight Slight decomposition of parent material on
joints. May be color change.
Moderate Some decomposition and color change
throughout.
High Rock highly decomposed, may be extremely
broken.
HARDNESS AND DEGREE OF CEMENTATION:
Group
Symbol
Group Name
Cu≥4 and 1<Cc≤3
E GW Well-graded gravel
F
Cu<4 and/or 1>Cc>3
E GP Poorly-graded gravel
F
Fines classify as ML or MH GM Silty gravel
G,H
Fines Classify as CL or CH GC Clayey Gravel
F,G,H
Cu≥6 and 1<Cc≤3
E SW Well-graded sand
I
Cu<6 and/or 1>Cc>3
E SP Poorly-graded sand
I
Fines classify as ML or MH SM Silty sand
G,H,I
Fines classify as CL or CH SC Clayey sand
G,H,I
inorganic PI>7 and plots on or above "A" Line CL Lean clay
K,L,M
PI<4 or plots below "A" Line ML Silt
K,L,M
organic Liquid Limit - oven dried Organic clay
K,L,M,N
Liquid Limit - not dried Organic silt
K,L,M,O
inorganic PI plots on or above "A" Line CH Fat clay
K,L,M
PI plots below "A" Line MH Elastic Silt
K,L,M
organic Liquid Limit - oven dried Organic clay
K,L,M,P
Liquid Limit - not dried Organic silt
K,L,M,O
Highly organic soils PT Peat
(D30)2
D10 x D60
GW-GM well graded gravel with silt NPI≥4 and plots on or above "A" line.
GW-GC well-graded gravel with clay OPI≤4 or plots below "A" line.
GP-GM poorly-graded gravel with silt PPI plots on or above "A" line.
GP-GC poorly-graded gravel with clay QPI plots below "A" line.
SW-SM well-graded sand with silt
SW-SC well-graded sand with clay
SP-SM poorly graded sand with silt
SP-SC poorly graded sand with clay
Silts and Clays
Liquid Limit 50 or
more
CGravels with 5 to 12% fines required dual symbols:
Kif soil contains 15 to 29% plus No. 200, add "with sand"
or "with gravel", whichever is predominant.
<0.75 OH
Primarily organic matter, dark in color, and organic odor
ABased on the material passing the 3-in. (75-mm)
sieve
612 EAST PITKIN ST.
FORT COLLINS, COLORADO
EEC PROJECT No. 15-01-197
OCTOBER 2015
612 EAST PITKIN STREET
FORT COLLINS, COLORADO
PROJECT NO: 15-01-197 DATE: OCTOBER 2015
LOG OF BORING B-1
RIG TYPE: CME55 SHEET 1 OF 1 WATER DEPTH
FOREMAN: SM START DATE 10/6/2015 WHILE DRILLING 22'
AUGER TYPE: 4" CFA FINISH DATE 10/6/2015 AFTER DRILLING 22'
SPT HAMMER: AUTO SURFACE ELEV N/A 24 HOUR 22'
SOIL DESCRIPTION D N QU MC DD A-LIMITS -200 SWELL
TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF
_ _
SANDY LEAN CLAY (CL) 1
brown _ _
stiff 2
silty with calcareous deposits _ _
CS 3 9 9000+ 11.4 104.3 36 24 82.2 2200 psf 2.0%
_ _
4
medium stiff _ _
SS 5 5 5500 10.4
_ _
6
_ _
7
_ _
8
_ _
9
_ _
CS 10 7 9000+ 12.5 98.9 < 500 psf None
_ _
11
_ _
12
_ _
13
_ _
14
stiff _ _
SS 15 10 6500 16.5
_ _
16
_ _
17
_ _
18
_ _
19
_ _
CS 20 12 7500 18.5 115.4 < 1000 psf None@1000
_ _
21
_ _
22
_ _
SAND AND GRAVEL (SP-GP) 23
brown _ _
very dense 24
_ _
25.5' BOTTOM OF BORING SS 25 50/10" -- 10.3
612 EAST PITKIN STREET
FORT COLLINS, COLORADO
PROJECT NO: 15-01-197 DATE: OCTOBER 2015
LOG OF BORING B-2
RIG TYPE: CME55 SHEET 1 OF 1 WATER DEPTH
FOREMAN: SM START DATE 10/6/2015 WHILE DRILLING 23'
AUGER TYPE: 4" CFA FINISH DATE 10/6/2015 AFTER DRILLING 23'
SPT HAMMER: AUTO SURFACE ELEV N/A 24 HOUR 22.5'
SOIL DESCRIPTION D N QU MC DD A-LIMITS -200 SWELL
TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF
_ _
SANDY LEAN CLAY (CL) 1
brown _ _
stiff 2
silty _ _
3
_ _
4
_ _
CS 5 10 9000+ 16.7 111.1 < 500 psf None
_ _
6
_ _
7
_ _
8
_ _
9
_ _
CS 10 8 9000+ 17.5 105.8 < 500 psf None
_ _
11
_ _
12
_ _
13
_ _
14
_ _
CS 15 8 9000+ 18.5 112.6 < 1000 psf None@1000
_ _
16
_ _
17
_ _
18
_ _
19
brown/rust _ _
very stiff SS 20 15 5000 17.8
with calcaroeus deposits _ _
21
_ _
22
_ _
SAND AND GRAVEL (SP-GP) 23
brown _ _
very dense 24
_ _
25.5' BOTTOM OF BORING SS 25 50 -- 11.0
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Brown Sandy Lean Clay
Sample Location: B-1, S-1 @ 2'
Liquid Limit: 36 Plasticity Index: 24 % Passing #200: 82.2
Beginning Moisture: 11.5% Dry Density: 104.3 pcf Ending Moisture: 20.0%
Swell Pressure: 2200 psf % Swell @ 500 psf: 2.0%
Project: 612 East Pitkin Street
Fort Collins, Colorado
Project No.: 15-01-197
Date: October 2015
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Brown Sandy Lean Clay
Sample Location: B-1, S-3 @ 9'
Liquid Limit: -- Plasticity Index: -- % Passing #200: --
Beginning Moisture: 12.0% Dry Density: 98.9 pcf Ending Moisture: 23.2%
Swell Pressure: < 500 psf % Swell @ 500 psf: None
Project: 612 East Pitkin Street
Fort Collins, Colorado
Project No.: 15-01-197
Date: October 2015
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Brown Sandy Lean Clay
Sample Location: B-1, S-5 @ 19'
Liquid Limit: -- Plasticity Index: -- % Passing #200: --
Beginning Moisture: 17.3% Dry Density: 115.4 pcf Ending Moisture: 17.8%
Swell Pressure: < 1000 psf % Swell @ 1000 psf: None
Project: 612 East Pitkin Street
Fort Collins, Colorado
Project No.: 15-01-197
Date: October 2015
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Brown Sandy Lean Clay
Sample Location: B-2, S-1 @ 4'
Liquid Limit: -- Plasticity Index: -- % Passing #200: --
Beginning Moisture: 17.0% Dry Density: 111.1 pcf Ending Moisture: 20.3%
Swell Pressure: < 500 psf % Swell @ 500 psf: None
Project: 612 East Pitkin Street
Fort Collins, Colorado
Project No.: 15-01-197
Date: October 2015
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Brown Sandy Lean Clay
Sample Location: B-2, S-2 @ 9'
Liquid Limit: -- Plasticity Index: -- % Passing #200: --
Beginning Moisture: 18.7% Dry Density: 105.8 pcf Ending Moisture: 25.0%
Swell Pressure: < 500 psf % Swell @ 500 psf: None
Project: 612 East Pitkin Street
Fort Collins, Colorado
Project No.: 15-01-197
Date: October 2015
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Brown Sandy Lean Clay
Sample Location: B-2, S-3 @ 14'
Liquid Limit: -- Plasticity Index: -- % Passing #200: --
Beginning Moisture: 14.1% Dry Density: 112.6 pcf Ending Moisture: 20.9%
Swell Pressure: < 1000 psf % Swell @ 1000 psf: None
Project: 612 East Pitkin Street
Fort Collins, Colorado
Project No.: 15-01-197
Date: October 2015
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
Earth Engineering Company
Earth Engineering Company
ECu=D60/D10 Cc=
HIf fines are organic, add "with organic fines" to
group name
LIf soil contains ≥ 30% plus No. 200 predominantly sand,
add "sandy" to group name.
MIf soil contains ≥30% plus No. 200 predominantly gravel,
add "gravelly" to group name.
DSands with 5 to 12% fines require dual symbols:
BIf field sample contained cobbles or boulders, or
both, add "with cobbles or boulders, or both" to
group name. FIf soil contains ≥15% sand, add "with sand" to
Unified Soil ClaSSifiCation SyStem
Soil Classification
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests
Sands 50% or more
coarse fraction
passes No. 4 sieve
Fine-Grained Soils
50% or more passes
the No. 200 sieve
<0.75 OL
Gravels with Fines
more than 12%
fines
Clean Sands Less
than 5% fines
Sands with Fines
more than 12%
fines
Clean Gravels Less
than 5% fines
Gravels more than
50% of coarse
fraction retained on
No. 4 sieve
Coarse - Grained Soils
more than 50%
retained on No. 200
sieve
Silts and Clays
Liquid Limit less
than 50
IIf soil contains >15% gravel, add "with gravel" to
group name
JIf Atterberg limits plots shaded area, soil is a CL-
ML, Silty clay
GIf fines classify as CL-ML, use dual symbol GC-
CM, or SC-SM.
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90 100 110
PLASTICITY INDEX (PI)
LIQUID LIMIT (LL)
ML OR OL
MH OR OH
For Classification of fine-grained soils and
fine-grained fraction of coarse-grained
soils.
Equation of "A"-line
Horizontal at PI=4 to LL=25.5
then PI-0.73 (LL-20)
Equation of "U"-line
Vertical at LL=16 to PI-7,
then PI=0.9 (LL-8)
CL-ML
Limestone and Dolomite:
Hard Difficult to scratch with knife.
Moderately Can be scratched easily with knife.
Hard Cannot be scratched with fingernail.
Soft Can be scratched with fingernail.
Shale, Siltstone and Claystone:
Hard Can be scratched easily with knife, cannot be
scratched with fingernail.
Moderately Can be scratched with fingernail.
Hard
Soft Can be easily dented but not molded with
fingers.
Sandstone and Conglomerate:
Well Capable of scratching a knife blade.
Cemented
Cemented Can be scratched with knife.
Poorly Can be broken apart easily with fingers.
Cemented
Earth Engineering Company