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March 30,2004
Pedersen Architectural Sç'rvices
Attn: Jess Pedersen
220 Main Street
Carbondale, Colorado 81 623
Job No.104 200
Subject:Subsoil Study for Foundation Design and Percolation Test, Proposed
Addition, 1451 County Road 102, Missouri Heights, Garfield County,
Colorado
Dear Mr. Pedersen:
As requested, Hepworth-Pawlak Geotechnical, Inc. performrid a subsoil study and
percolation test for foundation and septic disposal designs at the subject site. The study
was conducted in accordance with our agreement for geotechnical engineering services to
you dated March 10,2004. The data obtained and our recolnr.nendations based on the
proposed constmction and subsurface conditions encountercd are presented iri lhis repon.
Pro¡rosed Construction: The proposed acl<.lition will be a single story wr-rud fianle
structure approximately 1,500 square-feet in size located off the east sicle of the existing
residence as shown on Figure l. Ground floor is proposed to be slab-on-grade and
approxintately 2 feet higher than the existing finished floor elevation. Cut cleptlis are
expe*ted to range between about 3 to 4 feet. F-oundation loadings are assr¡nled to be
relatively light and typical of the proposed type of construction. A nerv septic disposal
system is proposed to be located north of the existing systent.
If building conditions or founclation loadings are significantly different {i'om thoss
describ¡¡d above, we should be notified to re-evaluate the recommendations preserrted in
this report.
Site Conditions: The property consists of 2 lots with a. combined area of about 5 acres
suûounded by a working ranoh. Lot 1 is occupied by a single family residence at the
south end with scatterccl outbuildings and Lot 2 consists mainiy of a grass pasture as
shown on Figure 1. Minor ground disttubance at the site consists of shallow cuts and fills
for the current developrnent. The topography in this area of Missouri Heights generally
consists of rolling hills. The ground surface in the project area is slightly irregular but
mostly flat with a moderate slope down to the north-northwest. Tltere is about 2 feet of
elevation difference across the proposed addition footJxint and 4 feet across the proposed
leach field area. Vegetation consists of lawn areas adjacent to the existing residence rvith
scattered trees and sluubs throughout the prcrject area.
'fhe existing resiclence on Lot I consists of a single story log structure with a recent
addition to tlre east sicle. The original purtion of the r¡:sidence is constructecl over a
.'
shallow crawlspace (approximately l% feet high) with a deeper (6 feeQ portion near the
center of the house which serves as a mechanical room. Ground floor in a small addition
on the east end of the house is slab-on-grade. The building did not show obvious signs of
major distress.
Subsurface Conditions: The subsuface conditions at the site were evaluated by
excavating one exploratory pit at the proposed addition area and one profile pit in the
septic disposal area at the approximate locations shown on Figure 1. The logs of the pits
are presented on Figure 2. The subsoils encountered at the proposed addition, below
about %footof organic topsoil, consist of 2 feet of brown stiff sandy silty clay overlying
whitish medium dense silty sand and clay with scattered basah fragments up to cobble
size down to the bottom pit depth of 7 feet. Results of swell-consolidation testing
performed on a relatively undisturbed sample of the upper brown clay in Pit 1, presented
on Figure 3, indicate low compressibility under exisiing moisture conditions and light
loading, and a moderate expansion potential when wetted. Similar testing on a sample of
lower whitish silty sand and clay in Pit 1, presented on Figure 3, indicates low
compressibility under existing moisture conditions and light loading, and a low collapse
potential (settlement under a constant load) when wetted. The sample showed moderate
compressibility with increased loading after wetting. No free water was observed in the
pit at the time of excavation and the soils were slightly rnoist to moist.
Foundation Recommendations: Considering the subsoil conclitions encountered in the
exploratory pit excavated at the proposed addition and the nature of the proposed
construction, we recommend spread footings placed on the urdisturbed natural whitish
soil below the upper expansive brown clay designed for an allowable soil bearing
pressure of 1,500 psf for support of the proposed addition. The soils tend to compress
after wetting and there could be some post-construction foundation settlement. Footings
slrould be a minimum width of 16 inches for continuous walls andL feet for columns.
Loose and disturbed soils, expansive clay and existing fill encountered at the foundation
bearing level within the excavation should be removed and the footing bearing level
extended down to the undisturbed natural soils. Exterior footings should be provided
with adequate cover above their bearing elevations for fi'ost protection. Placement of
footings at least 42 inches below the exterior grade is typically used in this area.
Continuous foundation walls should be reinforced top and bottom to span local anomalies
such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as
retaining structures, if any, should be designed to resist a lateral earth pressure based on
an equivalent fluid unit weight of at least 55 pcf for the on-site soil as backfill excluding
expansive clay and oversized rock.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly
loaded slab-on-grade construction. The upper clay soils possess an expansion potential
and slab distress could occur if the subgrade soils becotne wet. 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 shlinkage cracking. The
requirements for joint spacing and slab reinforcement should be established by the
designer based on expedence and the intended slab use. A minimum -inch layer of sand
Job No. I 04 200
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and gravel (road base) should be placed beneath interior slabs for support. This material
should consist of minus 2-inch aggregate with less than 50% passing the No. 4 sieve and
less than 12% passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95% 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.
Surface Drainage: The following drainage precautions should be observed during
construction and maintained at all times after the addition has been completed:
1) Inundation of the foundation excavations and underslab areas should be
avoided during construction.
2) Exterior backfill should be adjusted to near optirnum moisture and
compacted to at least 95% of the maximum standard Proctor density in
pavement and slab areas and to at least 90% ofthe maximum standard
Proctor density in landscape areas.
3) T'he ground surface surrounding the exterior of the building should be
sloped to clrain away from the foundation in all directions. We
recommend a minimum slope of 6 inches in the first 10 feet in unpaved
areas and a minimum slope of 3 inches in the first l0 feet in pavement and
walkway areas.
4) Roof downsponts and drains shoukJ discharge well beyond the limits of all
backfill.
5) Sprinkler heads and landscaping which requires regular heavy irrigation,
such as sod, should be located at least 5 feet from the building.
Percolation Testing: Percolation tests were conducted on March 19,2004 to evaluate
the feasibility of an infiltration septic disposal system at the site. One profile pit and three
percolation holes were dug at the locations shown on Figure 1. The test holes (nominal
12 inch diarneter by 12 inch deep) were hand dug at the bottom of shallow backhoe pits
and were soaked with water one day prior to testing. The soils exposed in the percolation
holes are similar to those exposed in the Profile Pit shown on Figure 2 and below % foot
of organic topsoil, consist of 3Yz feet of sandy silty clay overlying silty sand and clay with
basalt fragments down to the bottom pit depth of I feet. No free water was encountered
in the pit at the time of excavation and the soils were slightly moist to moist.
The percolation test results are presented in Table 2. Percolation testing indicates
infiltration rates between 20 and26 minutes per inch with an average of 23 minutes per
inch. P-l was run in the upper clay soils and could account for the slightly slower
percolation rate. P-2 and P-3 were run in the underlying silty sand and clay with basalt
fragments. 'We understand that Garfield Cotrnty is designing the septic disposal system.
Limitations: This study has been conducted in accordance with generally acceptecl
geotechnical engineering principles ancl practices in this area al this time. 'We make no
wan'anty either expressed or irnplied. The conclusions and recommendations submitted
in this report are based upon the data obtained from the exploratory pits excavatecl at the
locations inclicated on Figure I, the proposed type nf construstion and our experience in
Job No.l04 200
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the area. Our services do not include determining the presence, prevention or possibility
of rnold or other biological contaminants (MOBC) developing in the future. If the client
is concemecl about MOtsC, then a professional in this special field of practice should be
consulted. Our findings include interpolation and extrapolation af the subsurf'aco
conditions identified at the exploratory pits and variations in the subsurface conditions
may rrot become evident until excavation is"perforrned" If conditions encounterecl during
construction appear different from those described in this report, we should be notified at
once so re-evaluation of the recommendations may be made.
'fhis report has been prepared for the exclusive rrse by our client for design purposes. We
are not responsible frlr technical interpretations by otliers of our inforrnation. As the
project evolves, we should provide continued consultation and field services during
construction to review and monitor the irnplementation of out recommendations, and to
verify that the recorniltendations have been appropriately inter¡reted. Significant desigrr
changes may require additional analysis or rrrodifications to the recommendations
presented herein. We recommend on-site observation of excavations and foundation
bearing strata and testing of structural fill by a representative clf the geotechnical
engineer,
If you have any questions or if we may be of further assistance, please let us know
Respectfully Submitted,
HEPWORTH . PAV/LAK GEOTECHNICAL, INC.
:-),*.-Q. h-Q
Trevor L,. Knell
Reviewed by:
l¡'\,
i:r -. "f a¡,-.-i,-.L
.Daniel E. [{ardin, l'
l'LK/ksw
attachments Figure i - Locations of Exploratory Pits and Percolation Test lloles
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test R.esults
Table I - Percolation -fest Results
Job No.l04 200
cå5teor
APPROXIMATE SCALE
1":40'
EXISTING
CABIN
P-2
AP-1 t P-JÀ pnorlr A
PIT
LOT 1
LOT 2
(PASruRE)
APPROXIMATE
LOCATON OT
EXISTING LEACH
FIELD
o
EXISÏNG
WELL
PIT 1
PROPERTY
BOUNDARY
PRIVATE ROAD<___
COUNW
ROAD
102
EXISTING
RESIDENCE
1451 COUNTY
ROAD 102
104 200 HEPWORÏH*PAWLAK
GEOTECHNICAL, INC
LOCATION OF EXPLORATORY PITS AND
PERCOLATION TEST HOLES Figure 1
PIT 1 PROFILE PIT
0 o
t¡YC=10.7
DD=l10 o
{¡)lL
I
-coqto
ook-
I
-c
o-
o)ô
WC=l9.7
DD=73 5Â
10 10
LEGEND:
TOPSOIL; sondy silty cloy, orgon¡c, firm, moist, dork brown to blsck.
þ
l
CLAy (CL); silty, sondy, stiff ond slightly moist .to medium ,
stiff ond moist with depth in the
È-n¡"'p¡{, ¡rown to reã¿¡sfr brown, colCoreous troces, blocky ot Pit 1.
SAND AND CLAy (SC-CL); silt¡ with bosolt frogments up to cobble size, medium dense,
slighty moist to moist, light brown to whíte, colcoreous'
2" Diometer hond driven liner somple.
¡
I
J
Disturbed bulk somPle"
NOIES:
1. Explorotory pits were excovoted on Morch 18, 2004 with o CAT 420D bockhoe.
2. Locotions of explorotory pit's were meosured opproximotely by toping from existing building corners'
3. Elevotions of explorotory pits were not meosured ond the logs ore drown to depth.
4. The explorotory pit locctions should be considered occurote only to the degree implied by the rnethod
used.
S. The lines between moteriols shown on the explorotory pit logs represent the opproximote boundories
between moteriol tlpes ond tronsitions moy be grcduol.
6. No free wster wos encountered in the pits ct the time of excovoting. Fluctuotion in woter level moy
occur with time.
7. Loborotory Testing Results:
WC:WoterContent(Z)
DD = Dry Density ( pcf )
Figure 2LOGS OF EXPLORATORY PITSHEPWORTH _ PAWLAK
GEOTECHNICAL, INC.104 200
2
bQ
c1
Õ'6coôıo
I
co<-6 1
l:1,
t¡J
ocoz
C)
3
0.1 1.0 10
APPLIED PRESSURE - ksf
100
o
1
bs
co'6
øoLa
Eo(J
2
3
4
5
6
0.1 1.0 10
APPLIED PRESSURE - ksf
100
Moisture Content : 10.7
Dry Density - 110
Somple of: Sondy Silty CloY
From: Pit 1 of 1.5 Feet
percent
pcf
\_
Exponsion
upon
wetting \\
I )
Moisture Content : 19.7
Dry Density = 73
Somple of: Silty Sond ond Cloy
Frorn: Pit 1 of 3,5 Feet
percent
pcf
Compression\ upon
wetting
(
\)
104 200 HfPWORTH*PAWLAK
GEOTECHNICAL, INC SWELL-CONSOLIDATION TIST RESULTS Figure 3
iI EPWORTH-PAWLAK GEOTECH NICAL, INC.
|-ABLE 1
PERCOLATION TEST RESULTS
ItB NO. 104 ?-0ti
Note: percolation test holes were hand dug in the bottom of backhoe pits and soaked on
March 18, 2004. Percolation tests were conducted on March 19, 2004. The average
percolation rates were based on the last three readings of each test.
HOLE NO HOLE DEPTH
(rNCHEs)
LFNGTH OF
INTERVAL
(MIN)
WATER
DEPTH ÂT
STARÏ OF
INTËRVAI,
(TNCHES)
WATER
DEPTH AT
END OF
INTERVAL
(INCHEs)
DROP IN
WATER
LEVEL
(rNCHEsi
AVERAGE
PERCOLATION
RATF
(MiN./INCH)
P-1 43 15 11 91/z IVz
1^
91/z B3/a
83/,,B 3/q
B 71/q 3/q
7Va 61/2 44
6Vz 6 Vz
6 5Vq 3/q
5W 43/q Vz
P-Z 59 15 tIYq L}V+1
z0
70Y+9Vq 1
9Yq 81/q 1
81/a 7Va 1
71/a 6Vz 3/+
6Vz 53/c 3/q
53/q 5 3/q
5 4V4 3/+
P-3 5B 15 lAVz 91/s IY+
LJ
9Yq BVz r/4
BVz 71h 1
71/z 63/+3/q
63/+6 '/4
6 5Vq 3/a
5W 4Vz 3/+
41/z 4 Vz