HomeMy WebLinkAboutSubsoils Study for Foundation Designrcrf iffi,ffifffiii'iiå**
An Emdoycc olrncd Compony
5020 Counfy Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Offrce Locations: Denver (HQ), Parker, Côlorado Springs, Fon Collins, Glenwood Springs, and Summit Corurty, Colorado
PRELIMINARY SUBSOIL STUDY
FOR FOT]NDATION DESIGN
PROPOSED RESIDENCES
LOTS I - 4, BLOCK I AND LOTS | - 4, BLOCK 2
THE FAIR\ryAYS, BATTLEMENT MESA
IIOGAN CIRCLE
GARFIELD COUNTY, COLORADO
PROJECT NO.2t-7-229
JtiLY 21,2021
PREPARED FOR:
VINCENT TOMAST]LO
C/o RUSSELL CARTWRIGHT
35 }YILLOWVIEW WAY
PARACHUTE' COLORADO 81635
russecart@gmail.com
TABLE OF COIYTENTS
PURPOSE AND SCOPE OF STUDY.......
PROPOSED CONSTRUCTION .....
SITE CONDITIONS
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS ...............
FOUNDATIONS
FOL]NDATION AND RETAINING WALLS ......
FLOOR SLABS
UNDERDRAIN SYSTEM
SURFACE DRAINAGE...............
LIMITATIONS
FIGURE 1 . LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 through 6 - S\MELL-CONSOLIDATION TEST RESULTS
FIGURE 7 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. @ Project No.21-7-229
PURPOSE AND SCOPE OF'STTTDY
This report presents the results of a preliminary subsoil study for proposed residences to be
located on Lots I to 4,Block I and Lots I to 4, Block 2, The Fairways, Battlement Mesa, Hogan
Circle, Garfield County, Colorado. The project site is shown on Figure l. The purpose of the
study was to develop preliminary recommendations for foundation designs. The study was
conducted in accordance with our agreement for geotechnical engineering services to Russell
Cartwright dated March 1,2021.
A field exploration progrrim consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obt¿ined during the field
exploration were tested in the laboratory to determine their classification, compressibility or
swell and other engineering characteristics. The results of the field exploration and laboratory
testing were analyzedto develop reçommendations for foundation types, depths and allowable
pressures for the proposed building foundation. This report summarizes the data obtained during
this study and presents our conçlusions, design recommendations and other geotechnical
engineering considerations based on the proposed construction and the subsurface conditions
encountered.
PROPOSED CONSTRUCTION
The proposed residences will be one- and two- story structures with attached garages. Ground
floors will be structural over crawlspace for the living areas and slab-on-grade for the garage.
Grading for the structures is assumed to be relatively minor with cut depths between about 2 to 5
feet. We assume relatively light foundation loadings, typical of the proposed type of
construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The subject site was vacant at the time of our field exploration. The glound surface is sloping
down to the east at an estimated grade of about l0 percent. Vegetation consists of grass and
sparse weeds.
Kumar & A¡¡oci¡tar, lnc. ñ Proioct No, 21-7-229
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FTELD EXPLORATION
The field exploration for the project was conducted on March 26,2021. Four exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
The borings were advanced with 4-inch diameter continuous flight augers powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates,Inc.
Samples of the subsoils were taken with l%-inch and 2-inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140-pound hammer falling 30
inches. This test is similar to the st¿ndard penetration test described by ASTM Method D-1586.
The penetration resist¿nce values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing-
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about 1 foot of topsoil overþing mainly sandy silt soils to depths betwcen
12 and20 feet where dense, siþ clayey sand and gravel with cobbles was encountered to the
maximum explored depth of 24 feet deep. Drilling in the dense granular soils with auger
equipment was difficult due to the cobbles and possible boulders and drilling refusal was
encountered in the deposit at Borings I and 4.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation anaþses. Results of swell-consolidation testing performed on
relatively undisturbed drive samples of the silt soils, presented on Figures 4 through 6, indicate
low compressibility under existing low moisture conditions and light loading and varied low
collapse to low swell potential when wetted under constant light surcharge. Results of gradation
analyses performed on small diameter drive samples (minus lYz-nch fraction) of the coarse
granular subsoils are shown on Figure 7. The laboratory testing is summarizedinTable 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
Kumar & Associates, lnc. o Project No, 21-7-225
a-J-
FOT]NDATION BEARING COI\DITIONS
The upper silt soils encountered in the borings possess low bearing capacity and varied
compression/expansion potential when wetted. Our experience indicated the upper fine-grained
soils are mainly compressible when wetted under loading. The underþing gravel soils possess
moderate bearing capacity and typically low settlement potential. Spread footings placed on the
upper fine-grained soils can be used for support of the proposed residences with a risk of
foundation movement. A lower risk option would be to extertd the bearing level down to the
underþing gravel soils with a deep foundation system such as drilled piers or micro-piles.
Provided below are recortmendations for a spread footing foundation system. If
recommendations for a deep foundation system are desired, we should be contacted to provide
them.
DE SIGN RECOMMENDATIONS
FOTINDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, rwe recommend the building be founded with spread footings bearing
on the natural fine-grained soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natwal fine-grained soils should be designed
for an allowable bearing pressure of 1,500 psf. Based on experience, we expect
initial settlement of footings derignä'ffi<lforrstructed as discussed in this section
will be about I inch or less. Additional post-construction differential foundation
movement could occur if the bearing soils become wetted. The magnitude of
additional movement would depend on the depth and extent of wetting but could
be on the order ofabout I to lYz inches.
2) The footings should have a minimum width of 18 inches for continuous walls and
2 feet for isolated pads.
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
aÍea, -=...--
4) Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 14 feet.
Kumar &Associates, lnc. o Project No. 21-7-225
4
Foundation walls acting as retaining structures should also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
Topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the firm natural fine-grained soils. The exposed
soils in footing area should then be moistened and compacted.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOLINDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site fine-grained soils. Cantilevered retaining structures which are separate from the
residences and can be expected to deflect sufficiently to mobilize the full active earth pressure
condition should be designed for a lateral earth pressure computed on the basis of an equivalent
fluid unit weight of at least 45 pcf for backfill consisting of the on-site fine-grained soils.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressurs imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at least 95o/o of the maximum standard Proctor density.
Care should be taken not to overcompact the backfrll or use large equipment near the wall, since
this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resist¿nce to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the
s)
6)
Kumar & Associates, lnc. o Project No.21-7-229
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sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The
coefficient of füction and passive pressure values recommended above assume ultimate soil
strength. Suitable factors of safety should be included in the desigu to limit the strain which will
occur at the ultimate strength, particularþ in the case ofpassive resistance. Fill placed against
the sides of the footings to resist laþral loads should be compacted to at least 95% of the
maximum st¿ndard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction with a risk of movement similar to that described above for footings. To reduce the
effects of some differential movement, floor slabs should be separated from all bearing walls and
columns with expansion joints which allow unrestrained vertical movement. Floor slab control
joints should be used to reduce damage due to shrinkage cracking. The requirements for joint
spacing and slab reinforcement should be established by the designer based on experience and
the intended slab use. A minimum 4-inch layer of free-draining gravel should be placed beneath
basement level slabs to facilitate drainage. This material should consist of minus 2-inch
aggregate with at least 50% retained on the No. 4 sieve and less than 2% passing the No. 200
sieve.
All fill materials for support of floor slabs should be compacted to at least 95Vo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
on-site soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area that local perched groundwater can develop during times of heavy precipitation or
seasonal runoff. Frozen ground during spring runoff can create a perched condition. We
recommend below-grade construction, such as retaining walls, crawlspace (greater than 4 feet
deep) and basement areas (if any), be protected from wetting and hydrostatic pressure buildup by
an underdrain system.
The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above
the invert level with free-draining granular material. The drain should be placed at each level of
excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimumLYoto
a suitable gravity outlet or sump and pump. Free-draining granular material used in the
underdrain system should contain less than 2Yo passrngthe No. 200 sieve, less than 50% passing
Kumar & Associates, lnc, o Project No.21-7-229
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the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at
least lYzfeet deep. An impervious membrane such as 20 mil PVC should be placed beneath the
drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting
of the bearing soils.
SURFACE DRAINAGE
Providing proper surface grading and drainage will be critical to limiting subsurface wetting and
potential building movement. The following drainage precautions should be observed during
construction and maintained at all times after the residences have been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95Vo of the maximum standard Proctor density in pavement and slab areas
and to at least 90% of the maximum standard Proctor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum
slope of 12 inches in the first l0 feet in unpaved areas and a minimum slope of
3 inches in the first l0 feet in paved areas. Free-draining wall backfrll should be
covered with filter fabric and capped with about 2 feet of the on-site soils to
reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least 10
feet from foundation walls. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by irrigation.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area at this timç. We make no warranty either express or implied.
The conclusions and recommendations submitted in this report are based upon the dat¿ obtained
from the extrlloratory borings drilled at the locations indicated on Figure 1, the proposed type of
construction and ow experience in the area. Our services do not include determining the
presence, prevention or possibility of mold or other biological contaminants (MOBC) developing
in the future. If the client is concemed about MOBC, then a professional in this special field of
practice should be consulted. Our findings include interpolation and extrapolation of the
Kumar & Associates, lnc. @ Project No. 2l-7-229
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subsurface conditions identified at the exploratory borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
during construction appear different fiom those described in this report, we should be notified so
that re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for planning and preliminary
design purposes. We are not responsible for technical interpretations by others of our
information. As the project evolves, we should provide continued consultation and field services
during construction to review and monitor the implement¿tion of our recommendations, and to
verifu that the recommendations have been appropriatd interpreted. Significant design changes
may require additional analysis or modifications to the recommendations presented herein. We
recommend on-site observation of excavations and foundation bearing strata and testing of
structural fill by a rqlresentative of the geotechnical engineer.
Respectfrrlly Submitted,
Kumar & Associates, Inc.
James H. Parsons, P.E.
Reviewed by:
Steven L. Pawlak, P.E.
JHPlkac
Kumar & Associates, lnc. @ Project No. 21-7-229
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APPROXIMATE SCALE-FEEÏ
21 -7 -229 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1 BORING 2 BORING 5 BORING 4
o 2e/12
WC=4.8
DD=98
-2AO=92
0
4s/12 45/12
WC=5.7
DD=1 07 5s/ 12
5
22/ 12
WC=3.8
DD=1 O1
28/12
WC=5.8
DD=1 O4
18/12
WC=4.0
DD= f 03
5
24/ 12
26/12 23/12 23/12 24/12
10 10
24/12 22/12
WC=4.3
DD=99
24/ 12.
WC=6.4
DD=99
25/12
WC=4.8
DD= 1 O9
F
L¡J
t¡Jt!
I
:El-o-
hJô
15
25/6, sj/s
WC=4.6
+4=26
-2OO=43
15
t"-t¡J
L¡JL!
ITFû
L¡Jcl
31 /12
WC=5.5
DD=1 1 5
-2OO=94
4A/12 s2/12
20 20
43/ 12 50/1 50/2
25 25
50 50
21-7-229 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
IOPSOIL: SILT, SANDY, ORGANICS, FIRM, SLIGHTLY MOIST, BROWN.
SILT (ML): SLIGHTLY SANDY TO SANDY, SANDIER WITH DEPTH' SLIGHTLY CLAYEY' SLIGHTLY
CALCAREOUS, VERY STIFF TO HARD, SLIGHÏLY MOIST, TAN.
GRAVEL (CC-CV): SANDY, SILTY, CLAYEY, COBBLES, POSSIBLE BOULDERS, DENSE, SLIGHTLY
MOIST, GREY BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRTVE SAMPLE, 1 S/A-INCH l.D. SPLIT SPOON STANDARo PENETRATION TESÏ.
LEGEND
N
n
lt:-fi
kit
tÆi
F
I
/^ IA6 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 49 BLOWS OF A 140-POUND HAMMER+r/ t1 FALLTNG 30 TNcHES wERE REQUIRED To DRtvE THE SAMPLER 12 lNcHEs.
f eucrrcAL AUcER REFUSAI.
NOTES
1. TIIE EXPLORATORY BORINGS WERE DRILLED ON MARCH 26, 2A21 WITH A 4*INCH DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORÍNGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND ÏHE LOGS ARE
PLOTTED TO DEPÏH.
4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE
DEGRËE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (PCf) (ISTV D2216);
+1 = PERCENTAGE RETAINED ON N0. 4 SIEVE (aSfU O0glS);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140).
21 -7 -229 Kumar & Associates LEGEND AND NOÏIS Fig. 3
I
.i
SAMPLE OF: Sondy Silt
FROM:Boringl@4'
WC = 3.8 %, ÐD = 101 pcf
1
l
l
l
NO MOVEMENT UPON
WEÏTING
às
JJ
T¡J
=v,
I
zoË
ô
=ot/lzoo
1
0
-'l
2
-3
1 1.0 t00
N
JJ
L¡l
=v1
I
zotr
o
Jo
anzo()
2
1
0
-1
-2
1.0 100
SAMPLE OF: Silt ond Cloy
FROM: Boring 1 @ 15'
WC = 5.5 %, DD = 115 pcf
ln
ond
üE
l
l
I
t:l
rl
I
'i
|l;lii
¡it,
ir,l
llll
l
l
l¡
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EXPANSION UNDER CONSTANÎ
PRESSURE UPON WETTING
21 -7 -229 Kumar & Associates SWELL-CONSOLIDATION TTST RESULTS Fïg. 4
I
I
E
,:¡
I
F
.'¡
1
0
-1
-2
-3
-4
t
0
-1
2
-?
N
JJ
l¡.¡
=t
I
zo
t-
(¡
:iovlzo()
JJl¡l
Èvt
I
z.otr
o
Jo
3/lzo()
10 t00
100
1.0I
SAMPLE OF: Sondy Sllt
FROM:Boring2o^2.5'
WC = 5.7 %, ÐD = 107 pcf
I
I
T
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
i
I
I
SAMPLE OF; Sondy Silt
FROM: Boring 2 Ct 10'
WC = 4.3 %, DD = 99 pcf
i
l
T
I
l
\li
I
l
j
i
I
EXPANSION UNDER CONSÏANT
PRESSURE UPON WETTING
Ê9rod$!d,
lhé
ônd
In
of
ll
l
ìl
it
tl
21-7-229 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
SAMPLE OF: Sondy Silt
FROM¡Boring5@4'
WC = 5.8 %, DD = 104 pcf
i
i
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
Lil
I
I
l
i'i
I
I
j
N
JJl¡l
=tn
I
zIt-
ô
=ovlzoc)
I
0
-1
*2
t.0 f0 t00
às
JJ
l¡J
=tn
I
zoË
tf
JoØzo()
1
0
-1
-2
.1 1.0
SAMPLE 0F: Sondy Silt
FROM: Borlng 4 6 10'
WC = 4.8 %, DD = 109 pcf
xtflbn
¡r
rlth
li I
I
-l
:
-i1l:ì
l
I
L
li,-i li;l
l
l
i
a- i -l-
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
21-7-229 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 6
HYDROMETER ÂNALYSIS SIEVÉ ANALYSIS
2a HRr¡ 7 HtilR ur! rl MrÙ
llTE REAONOS
m!r[ rþrr¡ &tf,'Btr l:
u.s. st No Ro s€¡tEs
¡h ¡6 ¡ü ¡i^
GTEAR SqUmE OPEXNq¡
tfar ltE | 1/r.
-l---
I+<
SAND GRAVEL
FINE MED]UM ICOARSE FINE COARSE
2
ø
E
Ë
100
90
go
70
60
50
Ã
30
20
lo
o
o
lo
ao
50
40
!o
60
,o
to
to
r00
q
3u
È
c
H
OF IN
CLAY TO SILI COBBLES
GRAVEL 26
'(
SANO 3f
LIQUID LIIIIT
SAMPLE OF: S¡lty Cloyôy Sond ond Grovel
PLASTICIW INOEX
SILT AND CLAY 13
'4
FROM: Boring ¿t O t ¿f'
fhc¡r t¡sl 7lrultt opply only io lh.
Lrl¡ñg ruporl lhqll ñot br raprcduc.d,
ilc€pl ln full, v¡lhoul lh! wrltlônqpprcwl oÍ Xumor t Asælot r. lno.
Sidc qnolyll! lr¡llng h p.rfômod ln
oooordonoa vllh ASftl 06913, ASTY D7¡28,
ASTI¡ Cl56 ondlor ASlll 01t40.
21-7-229 Kumar & Associates GRADATION TEST RESULTS Fig. 7
lGrtffiiffifffiiïiå**
TABLE I
SUMMARY OF LABORATORY TEST RESULTS
2
1
BORING
4
J
1 0
2%
I 5
4
lftl
DEPIH
SAi'PtE LOCATION
1 4
1 0
5
10
4
1
4.3
5.7
5.5
3.8
fYrì
I{ATURAL
[IOISTURE
CONTENT
4.6
4.8
4.0
6.4
3.8
4.8
99
107
115
I 0 I
NATURAT
DRY
DENSITY
locfl
109
103
99
104
98
('/6)
GRAVEL
26
SAND
(%)
GRAI'ATION
5 1
92
94
PERCEI{T
PASSING NO.
200 stEvE
43
LIQUID LMTT
lo/"1
PLASTIC
INDEX
(%l
ATTERBERG LITIITS
fosfl
UNCONFINED
COMPRESSIVE
STRENGTH
Sandy Silt
Slightly Sandy Silt
Sandy Silt
Sandy Silt
Silt and Clay
Sandy Silt
SOILTYPE
Siþ Clayey Sand and
Gravel
Sandy Silt
Sandy Silt
Sandy Silt
No.21-