HomeMy WebLinkAboutSubsoil Study for Foundation.pdf~tech HEPWORTH -PAWLAK GEOTECHNICAL April 17, 2013 Frontier Paving Attn: Debbie Ellsworth 1014 County Road 311 New Castle, Colorado 81647-9614 (deb b ie@li-onlierpaYin!!inc. co Ill)
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i4 (' Illa il: hp}!\',)§l lPJ.!c, '(~'\.h. nl l\ l Job No. III 2838 Subject: Subsoil Study for Foundation Design, Proposed Office Building, Frontier Paving Plant Site, County Road 315,
Garfield County, Colorado Dear Mrs. EllswOlth: As requested, Hepworth-Pawlak Geotechnical, Inc. perfonned a subsoil study for design of foundations at the subject site. The study was
conducted in accordance with our agreement for geotechnical engineering services to Frontier Paving dated April 3, 2013_ The data obtained and our recommendations based on the proposed
construction and subsurface conditions encountered are presented in this repOlt. We previously conducted a preliminary geotechnical engineering study for the plant site and submitted
our findings in a repOlt dated September 26, 20 II, Job No. III 283A. Proposed Construction: The office building will be a single story, wood frame modular type structure, 60 feet by
24 feet in plan size and located on the site as shown on Figure I. The floor will be over crawlspace. Cut depths are expected to be up to about 3 feet. Foundation loadings for this type
of construction are assumed to be relatively light and typical of the proposed modular building construction. The drive and parking areas will be asphalt paved. If building conditions
or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this repolt. Site Conditions: The
proposed office building site is located on the east side of County Road 315 and about one-half mile south of the Interstate Highway 70 Mamrn Creek exit. The site was vacant and devoid
of vegetation at the time of our field exploration. The site has been previously graded relatively flat with on-site cut soils. Prior to the grading the telTain was west facing hillside.
The fill is up to about 8 to I 0 feet deep on the downslope, Parker 303-841-7 119 • Colmad() Springs 719-633-5562 • Silverrhorne 970-468-1989
-2 -western side ofthe building area. The ground surface across the proposed building area has a slight slope down to the west. There are fairly steep roadway cuts to the east and steep
fill embankment slopes for the building site grading to the north, south and west. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory
pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered at Pit 1, below about 2 feet of fill, consisted of medium
hard weathered claystone. Man-placed fill was encountered to the depth explored of7 feet at Pit 2. The fill consisted of medium stiff to stiff; sandy to very sandy silty clay with gravel
and small cobbles. The gravels and small cobbles vary fi'om shale fi'agments to rounded hard rocks. Laboratory testing of samples obtained fi'om the pits included natural moisture content
and density and percent finer than sand size gradation analyses. Results of swellconsolidation testing performed on a relatively undisturbed sample of the fill, presented on Figure 3,
indicate low compressibility under existing moisture conditions and light loading, and a moderate collapse potential when wetted. This sample showed moderately high compressibility when
loaded after wetting. The sample may be pal1ly disturbed due to the rock content. Results of swell-consolidation testing performed on a relatively the weathered claystone and another
sample ofthe fill, presented on Figure 4, indicate low compressibility under existing moisture conditions and light loading and a minor expansion potential when wetted under a constant
light surcharge. No free water was observed in the pits at the time of excavation and the soils were slightly moist to moist and the weathered claystone slightly mo ist. Foundation Bearing
Conditions: The existing fill soils are somewhat variable and the placement and construction, to the best of our knowledge, has not been documented. In general, the fill appears at least
moderately compacted. The fill soils possess low bearing capacity with generally moderate settlement potential. The weathered claystone encountered below the till has moderate bearing
capacity and a relatively low potential for movement. At typical excavation depth, the clay fill so i1s will be exposed at sub grade. Spread footings bearing on these soils can be used
for foundation support with some risk of settlement. We understand adjustments up to a few inches can be made to the modular type structure as needed ifsome differential settlement occurs.
We should further evaluate the suitability ofthe fill for toundation support at the time of construction. Extending the footings down to natural soils or weathered bedrock would provide
a lower risk of settlement. Foundation Recommendations: Considering the subsoil conditions encountered in the explol'atolY pits and the nature of the proposed construction, we recommend
spread fuotings designed for an allowable soil bearing pressure of 1,500 psffor support of the proposed building with a risk of differential settlement. The risk ofsettlement is Job
No. 111 2838
-3 -primarily ifthe fill soils were not adequately compacted. Precautions should be taken to prevent wetting of the bearing soils. Footings should be a minimum width of 18 inches tor
continuous walls and 2 feet tor columns. Loose and disturbed soils encountered at the foundation bearing level within the excavation should be removed and the subgrade moistened and
compacted. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement offootings at least 36 inches below the exterior grade
is typically used in this area. Continuous foundation walls should be well 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 should also be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcffor the on-site
soil as backfill. Surface Drainage: Positive surface drainage is an important aspect of the project to prevent wetting of the bearing soils. The following drainage precautions should
be observed during construction and maintained at all times after the office building has been completed: I) Inundation ofthe foundation excavations areas should be avoided during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% 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 !,'found 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 6 inches in the first 10 feet in nnpaved areas and a minimum slope of2Yz inches in the first 10 feet in pavement and walkway areas. 4) Roofdownspouts
and drains should discharge well beyond the limitsofall backflll. 5) Landscaping which requires regular heavy irrigation, such as sod, should be located at least 10 feet from the building.
Limitations: This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either
express or implied. The conclusions and recommendations submitted in this repOit are based upon the data obtained from the exploratory pits excavated at the locations indicated on Figure
I and to the depths shown on Figure 2, the proposed type of construction, and our experience in the area. Our services do not include detellnining the presence, prevention or possibility
of mold or other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in Job No. III 2838
-4-this special field of practice should be consulted. Our fmdings include interpolat ion and extrapolation of the subsurface conditions identi fied at the exploratory pits and variations
in the subsurface conditions may not become evident until excavation is perfonned. If conditions encountered during construction appear different from those described in this repol1,
we should be notified at once so re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for 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 implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require addit ional 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 representative
of the geoteclmical engineer. If you have any questions or if we may be offinther assistance, please let us know. Respectfully Submitted, HEPWORTH -PAWLAK GEOTECHNICAL, INC. ~ Robert
E. Stempihar, E.!. Reviewed b : \\,tlllll"" ",\,\\'...,,00 RE"Q(:'" ~ ~A,J:;;"""" U". ~_ ~~ ", ~ L--C:~-1iLf'.·~l . .. = fa . : -q \ -216' h: :: DavIdA. Young,P.E. ~~" d ' /IZ/W:: -:,~··.
7 · 18'-~~~ ~ ~~ ....•..... ~~ ,~ RES/ljg "'" lONA!..~'" \\,\" 11/"11111\\\ attachments: Figure I -Locations of Exploratory Pits Figure 2 -Logs of ExploratolY Pits Figures 3 and 4 -Swell-Consolidatio
n Test Results Table I -Summary of Laboratory Test Results cc: SGM -Jeff Simonson (jeftS@sgm-inc.com) Job No. III 2838 ~1ech
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l ' = 50' LOCATIONS OF EXPLORATORY PITS FIGURE 1
o 5 10 LEGEND: NOTES: PIT 1 ElEV.=5449' we = 11 .8 00=108 we = 10.7 00=127 PIT 2 ElEV.=5449' o 5 10 Fill: silty sandy gravelly clay, medium stiff to still, moisl, mixed brown, angular
to rounded rocks, organics and roots encountered at 5~ to 6~ feet at Pit 2 only. WEATHERED CLAYSTONE; medium hard, moist, grey· brown, Relatively undisturbed 2-inch diameter liner sample.
Disturbed bulk sample. 1. Exploratory pits were excavated on April 2, 2013 with a mini·trackhoe. Iii w LL J: Ii: w 0 2. locations of exploratory pits were measured approximately by pacing
from features shown on the site plan provided. 3. Elevations of exploratory pits were obtained by interpolation between contours shown on the site plan provided. The logs of exploratory
pits are drawn to depth. 4. The exploratory pit locations and elevations should be considered accurate only to the degree implied by the method used. 5. The lines between materials shown
on the exploratory pit logs represent the approximate boundaries between material types and transitions may be gradual. 6. No free water was encountered in the pits at the time of excavating.
Fluctuation in water level may occur with time. 7. laboratory Testing Results: WC = Water Content ( % ) DD = Dry Density ( pef) -200 = Percent passing No. 200 sieve 111 2838 ~tech HEPWORTH·PAWLAKGEOT
ECHNICAL LOGS OF EXPLORATORY PITS FIGURE 2
Moisture Content = 11.8 perce nt Dry Density = 108 pel Sample of: Very Sandy Silty Clay with Gravel ( Fill) From: Pit 1 at 2 Feet 0 1 r---i'--I -i'-. I Compression 'i/I. I i'-/'" upon
z~ 1' 1, f.-D, wetting 2 0 ~1'1~I1tr1 (ij en w a: 3 n. ::;: 0 U 4 5 1\ 6 \ , 7 1\ 8 1 9 1\1, ' I, 10 0.1 1.0 10 100 APPLIED PRESSURE ( ksf ) 1112836 ~tech SWELL-CONSOLIDATION TEST RESULTS
FIGURE 3 HEPWORTH·PAWlAKGEOTECHNICAL
Moisture Content = 10.7 percent Dry Density = 127 pel Sample of: Weathered Claystone From: Pit 1 at 4 Feet 1 ~ ;I{ z~ 0 0 I I I I I III ~I I 1ii ~ 1 I I I I I I I I " I 1 I (Ii , ~Ili
z 2 0 1 1ii Expansion en upon w aa.:. 3 wetting ::;: 0 u 4 0.1 1.0 10 100 APPLIED PRESSURE ( ksf ) I Moisture Content = 8.3 perce nt Dry Density = 129 pel Sample of: Sandy Silty Clay
with Gravel (FiIQ From: Pit 2 at 4 Feet 1 ~ *-~ z 0 0 1ii N-+UI ~ 1 I]~ I (Ii I , z 2 0 ~ ~ I""N 1ii ffi aa.:. 3 ::;: , ExpanSion u0 upon 4 welling I I 0.1 1.0 10 100 APPLIED PRESSURE
( ksf ) 111 283B ~tech SWELL-CONSOLIDATION TEST RESULTS FIGURE 4 HEPWORTH-PAWLAK GEOTECHNICAL
HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 Job NO. 111283B SUMMARY OF LABORATORY TEST RESULTS SAMPLE LOCATION NATURAL GRADATION ATIERSERG LIMITS MOISTURE NATURAL PERCENT UNCONFINED PIT
DEPTH DRY DENSITY GRAVEL SAND PLASTiC COMPRESSIVE SOIL OR CONTENT PASSING NO. lIQUIO LIMIT (%) (%) 200 SIEVE INDEX STRENGTH BEDROCK lYPE (ft) (%) (pcf) (%) (%1 (PSF) 1 2 11.8 108 Very
Sandy Silty Clay with Gravel (Fill) 4 lO.7 127 Weathered Claystone 2 3 8.9 134 61 Gravelly Sandy Silty Clay with Gravel (Fill) 4 8.3 129 Sandy Silty Clay with Gravel (Fill) I i