HomeMy WebLinkAboutSubsoil Study for Foundation Design 09.30.15~ .
HEPWORTH-PAWLAK GEOTECHNICAL
September 30. 2015
Jim Little
10250 Clubhouse Circle
Magnolia, Texas 77354
jjml@wcnx.org
l-lt.pwonh-P;l\1 l.1k G.:11tnlinic.1I, In ~
5020 County Ro;1J 154
Glcmw10J Sprm:,~. 01lor:1du 81601
Phnnc· 970 -945 i9SR
Fax 970-94; 6-15-1
un.111 hpi;:co@hri:.:nr.;ch Clim
Job No.115 439A
Subject: Subsoil Study for Foundation Design, Proposed Residence, Homestead 51,
Panorama Ranch, Elk Range Road, Garfield County, Colorado
Dear Mr. Little:
As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study for design
of foundations at the subject site. The study was conducted in accordance with our
proposal for geotechnical engineering services to you dated September 15, 2015. The
data obtained and our reconunendations based on the proposed construction and
subsurface conditions encountered nre presented in this report.
Proposed Construction: At the time of our study, design plans for the residence had not
been developed. We understand our findings will be considered in the purchase of the
property. The proposed residence is assumed to be a 1 to 2 story structure over a walkout
basement located on the upper portion of the property, to the south of the ridge and
irrigation ditch. Grading for the structure is assumed to be relatively minor with cut
depths between about 8 to 10 feet. We assume relatively light foundation loadings,
typical of the proposed type of construction.
When building location, grading and loading information have been developed, we
should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The site was vacant at the time of our investigation and the ground
appeared mostly natural. The northern portion of the lot along Elk Range Road is a
generally flat grassy field. Moving south, away from .the road, a basalt ridge with an
irrigation ditch bisects the Jot. The majority of the lot is located to the south of this ridge
and is comprised of a moderately steep south facing hillside with numerous basalt cobbles
and boulders on the surface. The abundance of surface rock dissipates moving down the
Parker 303-841-7119 • ColoradoSprings 719-633-5562 • Silverthorne 970-468-1989
' .
-2-
hillside . Vegetation on the site is comprised of mostly scrub oak and juniper trees on the
upper part of the lot with sagebrush, scattered cacti, and assorted grasses and weeds on
the lower part of the lot.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavacing two exploratory pits at the approximate locations shown on Figure l. The
logs of the pits arc presented on Figure 2. The subsoils encountered, below about one
foot of topsoil, consist of basalt cobbles and boulders in a sandy silt and clay matrix.
Results of a gradation analysis performed on a sample of gravel subsoils obtained from
the site are presented on Figure 3. No free water was observed in the pits at the time of
excavation and the soils were slightly moist to moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread
footings placed on the undisturbed natural basalt rock soil designed for an allowable soil
bearing pressure of 2,000 psf for support of the proposed residence. The matrix soils tend
to compress after wetting and there could be some post-construction foundation
settlement. Footings should be a minimum width of 16 inches for continuous walls and 2
feet for columns. Loose and disturbed soils 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 . Voids below footing grode created
by basalt boulder removal should be backfilled with concrete or well-compacted W'
aggregate base course. Exterior footings should be provided with adequate cover above
their bearing elevations for frost protection. Placement of footings at least 36 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
should be designed to resist a lateral earth pressure based on an equivalent fluid unit
weight of at least 50 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, arc suitable to support lightly
to moderately loaded slab-on-grade construction. 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
Job No.I IS 439A
. .
-3-
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 Jess than 50% passing the No. 4
sieve and Jess than 2% 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.
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
also create a perched condition. We recommend below-grade construction, such as
retaining walls, crawlspace and basement areas, 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 I fool below lowest adjacent finish
grade and sloped at a minimum l % to a suitable gravity outlet. Free-draining granular
material used in the underdrain system should contain less than 2% passing the No. 200
sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The
drain gravel backfill should be at least l 1h feet deep.
Surface Drainage: The following drainage precautions should be observed during
construction and maintained at all limes after the residence has been completed:
I) Inundation of the 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 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. Free-draining waJI backfill should be
capped with about 2 feet of the on-site, finer graded soils to reduce surface
waler infiltration.
3) The ground surface surrounding the exterior of the building should be
sloped to drain away from the foundation in all directions. We
Job No .115 439A
..
recommend a minimum slope of 12 inches in the first I 0 feet in unpaved
areas and a minimum slope of 3 inches in the first I 0 feet in pavement and
walkway areas. A swale may be needed uphill to direct surface runoff
around the residence.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Percolation Testing: Percolation tests were conducted on September 22. 2015 to
evaluate the feasibility of an infiltration septic disposal system at the she. Two profile
pits and three percolation holes were dug at the locations shown on Fig. l. The test holes
(nominal 12 inch diameter by 12 inch deep) were hand dug at the bottom of shallow
trackhoe 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 Pits shown on Fig. 4 and
consist of gravelly loam with cobbles.
The percolation test results are presented in Table I. Based on the subsurface conditions
encountered and the percolation test results. the tested area should be suitable for a
conventional infiltration septic disposal system. A civil engineer should design the
infiltration septic disposal system.
Limitations: This study has been conducted in accordance with generally accepted
geotechnicaJ 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 report are based upon the data obtained from the exploratory pits excavated at the
locations indicated on Figure 1 and to the depths shown on Figure 2, 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 pits 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.
Job No.115 439A
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 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 representative of the geotechnical
engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectf uJly Submitted,
HEPWORTH -PAWLAK GEOTECHNICAL, INC.
er;:: c '6:-u--
Tom C. Brunner
Reviewed by:
Daniel E. Hardin, P. E.
TCB/ksw
attachments Figure 1 -Location of Exploratory Pits
Figure 2 -Logs of Exploratory Pits
Figure 3 -Gradation Test Results
Job No.11.S 439A
Figure 4 -USDA Gradation Test Results
Table 1 -Percolation Test Results
APPROXIMATE SCALE
1· = 100'
HOMESTEAD 50
115 439A
_ --_ ""-IRRIGATION DITCH ,,-....-
'-.... ------~
P1
PIT2 •
P2
PIT 1 •
I:::!.
.6, P3
• .6. • PROFILE PIT 1 PROFILE PIT 2
HOMESTEAD 51
_,.
LOCATION OF EXPLORATORY PITS
HOMESTEAD 52
Figure 1
1i3
Q) u.
I
£ c.
IU 0
PIT 1 PIT2 PROFILE PIT 1 PROFILE PIT 2
0
'
, __ +4=52
-.J .200 .. 20
-jCOBBLE ·7
1GRAVEL a 13 --
5 I
-.J SAND .. 27 I
SILT •44 I
-.J
CLAY •9
10
LEGEND :
TOPSOIL; silty, sandy, granular, with basalt cobbles and boulders, dry to slightly moist. dark brown,
root zone .
0
5
10
GRAVEL (GM); basalt cobbles and boulders in sandy silt and clay matrix, very dense, slightly moist-moist,
pale/white.
Disturbed bulk sample.
T Practical refusal to digging with lrackhoe.
NOTES:
1. Exploratory pits were excavated on September 21, 2015 . The pits were dug with a CAT 307 trackhoe .
2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan
provided .
3. Elevations of exploratory pits were not obtained and the logs of exploratory pits are drawn to depth .
4. The exploratory pit locations 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 lhe pits at the time of excavating. Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
+4 = Percent retained on No . 4 Sieve
-200 = Percent passing No. 200 Sieve
Gravel= Percent retained on No. 10 Sieve
Sand = Percent passing No. 1 O sieve and retained on No . 325 sieve
Silt = Percent passing No. 325 sieve to particle size .002mm
Clay = Percent smaller than particle size .002mm
Si u..
I
.l:. a.
QJ
0
115 439A LOGS OF EXPLORATORY PITS Figure 2
0
UJ z < ..... w
0::
..... z w u
0:::
UJ a..
. .
I HYDROMETER ANALYSIS I SiEVE ANALYSIS I ~ 7 H~ TIME READ:NGS US STANDARD SERIES I CLEAA SQUARE OPENINGS
O ~2 ~ . 15 Ml 60MJNJ9MIN.4 M;N 1 MIN #200 #100 #50 #30 #16 #8 #4 31e· 3/4' 11/2' 3· 5'6" a· 100
10 90
20 80 . .
30 70
40 60
50 50
40 60 ~ -
70 30
80 20
90 10
0 100
00\ 002 005 .009 .019 .037 074 .150 .300 .600 1 18 2 38 4 75 95 190 375 76 2 152 203
12 5 127
DIAMETER OF PARTICLES IN MIWMETERS
QJ.110::LI
COBBLES 13 % GRAVEL 39 % SAND 28 % SILT ANO CLAY 20 %
LIQUID LIMIT %
SAMPLE OF : Slightly Clayey Silty Sandy Gravel with
Cobbles
PLASTICITY INDEX %
FROM: Pit 2 at 1 ~ to 2 Feet
(.!) z
iii
Ul < a..
~ z w u
0:: w a..
115 439A GRADATION TEST RESULTS Figure 3
I HYDROMETER ANALYSIS I SIEVE ANALYSIS
HR TIME READINGS M N US. STANDARD SERIES j CLEAR SQUARE OPEN NGS
O ~~ ~~ 1~ MIN . 60MINJ9MIN 4 MIN 1 1
t11325 #140 11160 fll35 #18 #10 1114 318' 3/4' 11t'Z' a· 5'6' e· 1oo
10
20
30
c
~ 40
~ IJ.J
Q::
I-50 z
tj
Q::
LIJ a.. 60
70
BO
90
100
001 002 005 009 019 045 106 025 500 100 200 475 95 190 37.5 762 152 203
DIAMETER OF PARTICLES IN MIWMETERS
CIA• I 1-I -,, r,...oa:,......,j"""1"'"'H,..,j.-.,..~s;.-..,.,,awG"==. ""fr""a:NC1~1--~,.,.,...,.L-j ___,.IK,.,,~,.,.,,.,..;1:"6....,...t1'.._l -lNU=----11 axaL5
COBBLE 7 % GRAVEL 13 % SAND 27 % SILT 44 % CLAY 9 %
USDA SOIL lYPE: Gravelly Loam with Cobbles FROM : Profile Pil 1 al 3 ~ to 5 Feet
90
80
70
60
so
40
30
20
10
0
C> z
iii
(/)
< a..
1-z w u
Q::
LIJ a.
115 439A USDA GRADATION TEST RESULTS Figure 4
HOLE HOLE
NO. DEPTH
(INCHES)
P-1 56
P-2 77
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1
PERGOLA TION TEST RES UL TS
LENGTH OF WATER WATER DROP IN
INTERVAL DEPTH AT DEPTH AT WATER
(MIN} START OF ENO OF LEVEL
INTERVAL INTERVAL (INCHES)
(INCHES) (INCHES)
10 6'..4 4% 2%
4% 2% 2
Water added 6% 5 1%
5 3% 1%
3Y:a 2% 1
Water added 6 41/:a 1Y:a
4% 3% %
3% 2% 1%
Water added 6Y:a S'h 1%
5% 3% 1%
3% 2% 11..4
Waler added 6 4% 11..4
10 5 3 2
3 H~ 1%
Water added 5% 3% 1%
3% 2% 1
2'..4 1% 1%
Water added 5% 4% 1
4% 3% 'A
3% 2% 1
Water added 5% 4% %
4% 3% 1%
3% 2% 1
Water added 5% 4 1%
JOB NO. 115 439A
Page 1 of2
AVERAGE
PERCOLATION
RATE
(MIN./INCH)
71/z
8
Note: Percolation lest holes were hand dug in the bottom of trackhoe pits and soaked
on September 21, 2015. Percolation tests were conducted on September 22,
2015. The average percolation rates were based on the last three readings of
each test.
HOLE HOLE
NO. DEPTH
(INCHES)
P-3 46
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1
PERCOLATION TEST RESULTS
LENGTH OF WATER WATER
INTERVAL DEPTH AT DEPTH AT
(MIN) START OF END OF
INTERVAL INTERVAL
(INCHES) (INCHES)
10 81/a 61/a
61/a 5%
5Yz 4%
41/a 3%
33A 3
Water added 83A 8
8 7
7 6%
6% 5%
5% 41/a
4% 4
4 3%
DROP IN
WATER
LEVEL
(INCHES)
2
1
1
aA
:iA
%
1
•A
1
%
Ya
llA
JOB N0.115 439A
Page 2of2
AVERAGE
PERCOLATION
RATE
(MIN.llNCH)
15
Note: Percolation test holes were hand dug in the bottom of trackhoe pits and soaked
on September 21, 2015. Percolation tests were conducted on September 22,
2015. The average percolation rates were based on the last three readings of
each test
. . ' . .
September 22, 20l5
Hill Construction, Inc.
Attn: Gary Hill
P.O. Box l 735
Edwards, CO 81632
Job No. 112318B
Subject: Observation of Excavation, Proposed Fleeger Residence, Lot 2, Block 3,
Vail Village, 11 •h Filing, 2950 Booth Creek Drive, Vail, Colorado
Dear Mr. Hill:
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the
excavation at the subject site on September I 0 and 11, 2015 to evaluate the soils exposed
for foundation support. The findings of our observations and recommendations for the
foundation design are presented in this report. We previously conducted a subsoil study
for design of foundations at the site and presented our findings in a report dated October
19, 2012, Job No. 112 318A.
The proposed residence is essentially the same as described in our previous report and
will be supported on spread footings placed on the nautral soils and sized for an allowable
bearing pressure of 2,500 psf. No free water was observed within the excavation and the
dewatering wells appeared to be functioning properly.
At the time of our visit to the site, the foundation excavation had been cut in one level
from 4 to 8 !tl feet below the adjacent ground surface. The soils exposed in the bottom of
the excavation consisted of silly sand and gravel with cobbles. The results of a gradation
analysis performed on a sample of soil obtained from the northern portion of the
excavation are presented on Figure I. No free waler was encountered in the excavation
and the soils were slightly moist.
The soil conditions exposed in the excavation are consistent with those previously
encountered on the site and suilable for support of spread footings designed for the
, .
1 •
Error! Reference source not found.September 22, 2015
Page2
recommended allowable bearing pressure of 2,500 psf. Loose and disturbed soils should
be removed in the footing areas to expose the undisturbed naturnl soils. The existing
construction dewatering wells and pumps should remain in place. Other recommendations
presented in our previous report which are applicable should also be observed.
The recommendations submitted in this Jetter are based on our observation of the soils
exposed within the foundation excavation and the previous subsurface exploration at the
site. Variations in the subsurface conditions below the excavation could increase the risk
of foundation movement. We should be advised of any variations encountered in the
excavation conditions for possible changes to recommendations contained in this letter.
Our services do not include detennining 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.
If you have any questions or need further assistance, please call our office.
Sincerely,
HEPWORTH -PAWLAK GEOTECHNICAL, INC.
Tom C. Brunner -Staff Engineer
Reviewed by: David A. Young, P.E.
I
attachments FIGURE I -Gradation Test Results
cc:
Joh No. 112 3188