HomeMy WebLinkAboutSubsoil Study for Foundation Design 07.25.15~tech
HEPWORTH · PAWLAK GEOTECHNICAL
July 25, 2013
Deborah and Craig Mulligan
60 Monroe Ctr. Street NW
Suite l lA
Grand Rapids , Michigan 49503
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Job No .113 215A
Subject: Subsoil Study for Foundation Design and Percolation Test, Proposed
Residence, Lot 25, Stirling Ranch, Schooner Lane, Missouri Heights,
Garfield County, Colorado
Dear Mr. & Mrs. Mulligan:
As requested, Hepworth-Pawlak Geotechnical, Inc. perfonned a subsoil study and
percolation test for foundation and septic disposal designs at the subject site. The study
was conducted in accordance with our proposal for geotechnical engineering services to
you dated June 10, 2013. The data obtained and our recommendations based on the
proposed construction and subsurface conditions encountered are presented in this report .
Proposed Construction: The proposed residence will be a one story wood frame
structure over a walkout basement level located on the site as shown on Figure I. A
detached one story garage will be located northwest of the house. Ground floors are
proposed to be slab-on-grade. Cut depths are expected to range between about 2 to 8 feet.
Foundation loadings for this type of construction are assumed to be relatively light and
typical of the proposed type of construction . The septic disposal system is proposed to be
located south of the house as shown on Figure l.
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 report.
Site Conditions: The site is vacant and the building area is vegetated with pinon forest
mixed with juniper, scrub oak and sagebrush with an understory of grass, weeds and
cacti. The upper part of the lot in the driveway and garage area is relatively flat with a
slight slope down to the south. The house is located on a moderate slope down to the
septic disposal area which is gently sloping down to the south-southeast. Numerous basalt
boulders were visible on the ground surface in the proposed building area.
Parh:r 303-S-41-7119 • C .ilorado Spring~ 719-633-5562 • S1lvcrrl1nmL' ll/\1.cl68·1989
-2-
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating two exploratory pits in the building area and one profile pit in the septic
disposal area at the approidmate loca t ions shown on Figure I . The logs of the pits are
presented on Figure 2. The subsoils encountered in the building area, below about Yi to I
foot of topsoil, consist of basalt rocks up to boulder size in a silty sand and gravel matrix.
Results of a gradation analysis perfurmed on a sample of the matrix soils (minus l 'll inch
fraction) obtained from the site are presented on the top of Fibrure 3. No free water was
observed in the pits at the time of excavation and the soils were slightly 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 natw-al soil designed for an allowable soil bearing
pressure of2,000 psffur 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 18 inches for continuous walls and 2 feet for
columns. Loose and distw-bed soils encountered at the foundation bearing level within
the excavation should be removed and the rooting bearing level extended down to the
undisturbed natural soils. Holes below footing grade due to basalt boulder removal
should be backfilled with concrete or ~-inch road base compacted to at least 98% of the
maximum standard Proctor density at a moisture content near optimum. Loose material
should be scraped out of the holes prior to backfilling. Exterior footings should be
provided with adequate cover above their bearing elevations for frost protection.
Placement of fuotings at least 36 inches below the exterior grade is typically used in this
area. Continuous folllldation 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 SO pcffor the on-site soil as backfill,
excluding rock larger than about 6 inches.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly
loaded slab-on-grnde construction. To reduce the effects of some differential movement,
floor slabs should be separated from all bearing walls and columns with expa nsion 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 less than 50% passing the No. 4 sieve and less than 2% passing the No.
200 sieve.
Job No. l 13215A
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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.
Undcrdrain System: Although free water was not encountered during our exploration, it
has been our experience in mountainous areas 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 reconunend below-grade construction, such as
retaining walls, crawlspace and basement areas, be protected from wetting and
hydrostatic pressure buildup by an underdrain system Slab-at grade construction (such
as the garage and downhill side of the house) should not require 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 minimum I% 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 of2 inches. The
drain gravel backfill should be at least l Yi feet deep.
Surface Drainage: The following drainage precautions should be observed during
construction and maintained at all times after the residence has been completed:
l) 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 wall backfill should be
capped with about 2 feet of the on-site, finer graded soils to reduce surface
water infiltration.
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 t 0 feet in unpaved
areas and a minimum slope of3 inches in the first 10 feet in pavement and
walkway areas.
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 5 feet from the building. Consideration should be given to the use of
xeriscape to limit potential wetting of soils below the building caused by
irrigation.
Jub No.113 215A
- 4 -
Pcrcoiation Testing: Percolation tests were conducted on June 21, 2013 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 diameter 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 P it shown on Figure 2 and consist of 1 Yl
feet of topsoil overlying sandy silt (silt loam) and fine gravelly loamy sand with basalt
rocks down to 8 feet deep. Gradation test results are shown on the bottom of Figure 3 and
Figure 4. The percolation test results are presented in Table l and ranged from 20 to 60
minutes per inch with an overall average of37 minutes per inch. 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.
Subsidence Potential: Stirling Ranch is underlain by Pennsylvania Age Eagle Valley
Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum
under certain conditions can cause sinkholes to develop and can produce areas of
localized subsidence . During previous work in the area, sinkholes have been observed in
the lower Roaring Fork River Valley. Sinkholes were not observed in the immediate area
of the subject lot. The exploratory pits were shallow, for foundation design only. Based
on our present knowledge of the site, it cannot be said for certain that sinkholes will not
develop. In our opinion, the risk of ground subsidence at Lot 25 is low and similar to
other lots in the area but the owner should be aware of the potential for sinkhole
development.
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 expressed 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, the proposed type of construction and our experience in
the area. Our serv ices 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 wttil excavation is perfonned. If conditions encowttered 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.
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
Job No.113 215A
-5 -
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-s ite 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 .
Respectfully Submitted ,
HEPWORTH -PAWLAKGEOTECHNICAL, INC .
Reviewed by:
Steven L. Pawlak, P.E.
DEH/ksw
attaclunents Figure I -Locations of Exploratory Pits and Percolation Test Holes
Figure 2 -Logs of Exploratory Pits
Figure 3 -Gradation Test Results
Figure 4 -USDA Gradation Test Results
Table l -Percolation Test Results
cc: Confluence Architecture -Angela Loughry (angela({b confl ue ncearchitecture.com)
Job No.113 215A
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LOCATIONS OF EXPLORATORY PITS
AND PERCOLATION TEST HOLES FIGURE 1
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PIT 1
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PIT2 PROFILE PIT
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LEGEND:
10
~ TOPSOIL; organic sandy gravelly clay and silt, slightly moist to moist, dark brown.
~ ~
COBBLES ANO BOULDERS (GM); In a saty sand and gravel matrix, medium dense to dense. slightly moist,
light brown, rocks consist of basalt Calcareous.
I . . . SAND (SM); silty, gravelly with cobbles, sandy silt lenses, medium dense, sllghtly moist, light brown, rocks
consist of basalt. Calcareous .
Disturbed bulk sample.
NOTES:
1. Exploratory pits were excavated on June 20, 2013 with a mlni-trackhoe.
2. Locatlons of exploratory pits were measured approximately by pacing from features shown on the site plan provided.
3 . Elevations of exploratory pits were not measured and the logs of exploratory pits are drawn to depth.
4. The exploratory pit locations and elevallons 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 Resul ts:
WC • Water Content ( % )
+4 = Percent retained on the No. 4 sieve
-200 = Percent passing No. 200 sieve
G = Gravel fraction per USDA Classification (%)
S = Sand fraction per USDA Classification (%}
M = Silt fraction per USDA Oassificallon (%)
C = Clay fraction per USDA Classification (%)
113 215A ~tech
HEPWORTtU'AWLAK GEOTEC HNICAI.
LOGS OF EXPLORATORY PITS FIGURE 2
HYOHUMt: 1 CH ANAi.. YSIS SIEVE ANAl.:T;>1::>
I TIME READINGS I U.S STANDARD SEAIES I Cl.EAR SQUARE OPENINGS I
r~IN. 1s'ti1N. 60MINJ9MIN.4 MIN 1 MIN.
0
#200 #100 #50 #30 #16 #B <114 3/B" 314• 1 112' 3· s·e· e·
ICO
10 ..
0 20 .,
w (!)
z 30 JO z
~ en en
a: 40 .. ~
..... !z z 50 IO w w
u (.)
a: 60 Cl a:
w w
Q.. a.
70 llO
80 "'
90 10
100 II
CIDI 11111 cm cot °"' tR7 111' ISO XO 11111 ... t» .,, tS IU ltO ... IU l!a :zm
127
DIAMETER OF PARTICLES IN MIWMETERS
o..&Y10Sl.T I rK I ~-Im.Ml I -Si!!jllli~ I coaae
GRAVEL 32 % SAND 35 % SILT AND CLAY 33 %
SAMPLE OF: Silty Sand and Gravel FROM: Pit 1 at 2 to 3 Feet
I HYOAOMETal ANAL= l>ll:vtANALl'::>aS
2 ~ 7 HA TIMEAEAOINGS I U S. STANDARD SERIES I Cu:AA SQUARE OPENINGS I
#200 #100 150 #30 #16 #8 #4 318' 3/4' 1 1/2' 3• 5'6' 8' i3 . 15 MIN. 60MINJ9MIN 4 MIN. 1 MIN 100
10 90
0 20 so
w Cl
~ 30 70 z en ~ en
a: 40 60 ~
I-50 ~ z so w w
(.) (.)
a: 60 40 ffi w c. 11.
70 30
80 20
90 10
100 0
.001 .002 .005 .009 .019 .037 .074 .150 300 .600 118 2.36 4 .75 9.5i 2.5 19.o 37.5 76.2 121/'2 203
DIAMETER OF PARTICLES IN MIWMETERS
ClAYIOSll I loE I ~ 1~1 fiii GRA):!).
I ~ I c:omn
GRAVEL 3 % SAND 18 % SILT AND Cl.A Y 79 %
SAMPLE OF: Sandy Silt FROM: Profile Pit at 2 to 4 Feet
113 215A r-k'l~tech GRADATION TEST RESULTS FIGURE 3
HEPWOATH-PAWl.AK GEOT£CHl'llCAL
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I HYDAOMElER ANALYSIS I SIEVE ANALYS IS I
7 HA TIME READINGS U.S. STANDARD SERIES I Cl.ENI SOUAAE OPENINGS
O ~ lfk 15 MIN. SJMIN19Ml ll.4 MW. 1 MIN. 41200 #100 150 130 #111 418 414 3k 'J/4' 11~ 3' 5'6" 8 ' 100
10
20
30
40
50
60
70
80
90
100
.001 .002 .005 .009 .019
Q.\Y I aT
GRAVEL 26 %
.037 .074 . UIO .300 .600 1.18 2.36 4.75 9.5 19.0 37.5
12.5
SAND 57 % SILT 10 %
76.2 152 203
127
CLAY 7 %
USDA SOIL TYPE: Rne Gravelly Loamy Sand FROM : Profile Pit at 4 to 6 Feet
90
80
70
60
50
40
30
20
10
0
~
!Z
~
113 215A ~ech USDA GRADATION TEST RESULTS FIGURE 4
HEPWORTH¥AWLAKGEOTECHNIC.o.L
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HOLE NO. HOLE
DEPTH
(FEET}
P-1 44%
P-2 52
P-3 41%
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1
PERCOLATION TEST RESULTS
LENGTH OF WATER WATER
INTERVAL DEPTH AT DEPTH AT
(MfN) START OF END OF
INTERVAL INTERVAL
(INCHES) {INCHES)
15 4% 3
3 1%
Water added 5% 4
4 ii4
2% 1%
1% y.
Water added 5% 4%
4% 3%
15 8 7%
7% 6%
6% 6%
6% 6
6 5%
5% 5%
5% 5
5 4%
15 7Yz 6%
6% ~h
5% 5%
5% 4%
4% 4%
4% 3%
3% 3%
3% 2%
DROPIN
WATER
LEVEL
(INCHES)
1%
1%
1%
1%
1%
1%
%
%
%
%
%
Yz
Yz
%
%
%
1
%
Yz
Yz
Yz
Yz
Yz
Yz
JOB N0.113 215A
AVERAGE
PERCOLATION
RATE
(MINJfNCH)
20
60
30
Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked
on June 20, 2013. Percolation tests were conducted on June 21, 2013. The
average percolation rates were based on the last two readings of each test
' .
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
Page: 1
5020 County Road 154
Glenwood Springs, CO 8160 I
Phone: 970-945,7988
fax: 970-945-8454
! Invoice for -Professional Services 11
i w::::::::::::-==s -=::J
lovolca Number : 0113985
Invoice Date : 7/26/2013
Job Number : 113215A
Profect Manager : DEH
Deborah and Craig Mulligan
60 Monroe Ctr. Streeet NW
Suite 11A
Grand Rapids, Ml 49503
Professional Services:
DATE
712612013
/LS
TASK DESCRIPTION
Lump Sum
Project : Proposed Residence
Lot 25, SUr11ng Ranch
Schooner lane
Mlsssouri Heights
Garfield County CO
PAYMENT TERMS, DUE UPON RECEIPT
WE NOW ACCEPT VISA & MASTERCARDfl
PLEASE INCLUDE INVOICE NUMBER ON CHECK
UNITS RATE AMOUNT
1.00 s 1,800.00 $ 1,800.00
Subsoil Study for FoundaUon Design and PercolaUon Test
WE APPRECIATE YOUR BUSINESS. THANK YOU. Invoice Total: S 1,800.00
PLEASE PAY FROM THIS INVOICE.
late ree of SJ0.00 or 1.5% per monlh (whichever Is greater) will be charged JO deys rrom the Invoice dale. Fed Tax ID: 84-1228299