HomeMy WebLinkAboutObservation of Excavation 05.20.2016HEPWORTH-PAWLAK GEOTECHNICAL
May 20, 2016
Stephen Self
1098 County Road 214
Silt, Colorado 81652
stephen@willowwisp.nel
Hq'Wl)rth p I\\ I 1\,, o~llt~chni " ,1[, l n l
5020 Count; Rc1 aJ 1 5~
Gkm11>nJ Sr rin: Cnl ·r1du 8160 1
Phnn .: 970 9-t5 ~9 ~'
r;ix 9 70·9-f j l:lfrl
u m1l hrgu1@h r grnru .. h ClHll
Job No. 116 154A
Subject: Observation of Backhoe Pit, Proposed Barn/Auxiliary Dwelling Unit, 1098
County Road 214, North of Silt, Garfield County, Colorado
Dear Stephen:
As requested, a representative of Hepworth-Pawlak Geotechnical observed the backhoe
pit excavation at the subject site on May 2, 20 J 6 to evaluate the soils exposed for
foundation support. The findings of our observations and recommendations for the
foundation design are presented in this report. The services were performed in
accordance with our agreement for professional engineering services to you, dated April
29, 2016.
The garage/auxiliary dwelling unit (ADU) wiJI be located north of the existing residence
on the property. The building will be a two story wood frame structure with a slab-on-
grade ground floor. The ground floor will be at an elevation near to slightly above the
adjacent ground surface. We assume relatively light foundation loads.
At the time of our site visit, one backhoe pit (Pit I) had been excavated in the proposed
building area, about 60 feet north of the residence. The soils exposed in the pit, below
about 8 inches of topsoil, consisted of generally stiff, sandy clay and silt that extended
down to the pit depth of 6V:z feet. Results of swell-consolidation testing perfonned on a
sample taken from the pit, shown on Figure 1, indicate the soils are slightly to moderately
compressible under conditions of loading and wetting. The laboratory testing is
summarized in Table I. No free water was encountered in the pit at the time of
excavation and the soils were slightly moist to moist with depth.
Considering the conditions exposed in the pit and the nature of the proposed construction,
spread footings placed on the undisturbed natural soil designed for an allowable bearing
pressure of l,500 psf can be used for support of the proposed barn/ADU building. The
soils may tend to compress when wetted and there could be some post-construction
settlement of the foundation if the bearing soils become wet, and precautions should be
taken to prevent wetting. Footings should be a minimum width of 18 inches for
continuous walls and 2 feet for columns. Prior to the footing construction, all fill, topsoil
and any loose disturbed soils should be removed and the bearing level extended down to
the undisturbed natural soils, and the subgrade moistened and compacted. Exterior
footings should be provided with adequate soil cover above their bearing elevations for
Parke r 303-841-7119 • Co lnrad o Spring~ 71 9-63 3-5 562 • Silvert horn e 970-46 8-198 9
Stephen Self
May 20, 2016
Page2
frost protection. 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 (if any) should also be designed to resist a
lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for on-site
soil as backfill . Structural fill placed within floor slab areas can consist of the on-site
soils compacted to at least 95% of standard Proctor density (SPD) at a moisture content
near optimum. Backfill placed around the structure should be compacted to at least 90%
SPD (95% in pavement areas) and the surface graded to prevent ponding within at least
10 feet of the building. Landscape that requires regular heavy irrigation, such as sod, and
sprinkler heads should not be located within 5 feet of the foundation.
This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at this time. The conclusions and
recommendations submitted in this report ore based upon the data obtained from the
exploratory pit excavated at the location and to the depth indicated, the proposed type of
construction, and our 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 concerned about MOBC, then a professional in
this special field of practice should be consulted. Our findings include interpolation and
extrapolation of the subsurface conditions identified at the exploratory pit and variations
in the subsurface conditions may not become evident until excavation is performed. If
conditions encountered 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. We recommend on-site observation of excavations and foundation bearing strata
and testing of structural fill by a representative of the geotechnical engineer.
If you have any questions or need further assistance, please call our office.
Sincerely,
attachments Figure l, Swell-Consolidation Test Results
Table 1, Summary of Laboratory Test Results
cc: Kurtz and Associates -Brian Kurtz (kurtzen~i n eer@yahoo .com )
Job No. 116 154A
Moisture Content = 17.0 percent
Dry Density = 105 pcf
Sample of: Sandy Clay and Silt
From: Pit 1 at 6 Feet
0 No Movement -:--..--'tfi. -,.....
-~--f"-....r--., upon ~
c 1 .......... wetting
0 "'-.. ·u;
(/) "'~ Q) a
E 2 ....... 0
(.) ~)
3
0.1 1.0 10 100
APPLIED PRESSURE · ksf
116 154A ~ SWELL·CONSOLIDATION TEST RESULTS Figure 1
He11worth-Powlok Geotechnlc;ol
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1 JobNo. 116154A
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION NATURAL NATURAL GRADATION ATTERBERG LIMITS UNCONFINED PERCENT
MOISTURE DRY GRAVEL SAND PASSING LIQUID PLASTIC COMPRESSIVE SOIL OR PIT DEPTH CONTENT DENSITY N0.200 LIMIT INDEX STRENGTH BEDROCK TYPE (%) (%)
(ft) (%) loco
SIEVE
t%l (%) (PSF)
1 4 13.6 100 88 Sandy Clay and Silt
6 17.5 105 Sandy Clay and Silt