HomeMy WebLinkAboutSoils Report for Foundation Design and Perc Test 06.22.2017H -PKU MAR
Geotechnical Engineering I Engineering Geology
Materials Testing 1 Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
June 22, 2017
Michael Redmond
466 Ponderosa Pines Way
Carbondale, Colorado 81623
(mredntond900 @gmail.com)
Office Locations: Parker, Glenwood Springs, and Silverthome, Colorado
Project No.17-7-467
Subject: Subsoil Study for Foundation Design and Percolation Test, Proposed Residence,
Lot 12, Pinyon Peaks, 89 Sage Swale Road, Garfield County, Colorado
Dear Mr. Redmond:
As requested, H-P/Kumar performed 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 February 24, 2017. 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 one story wood frame construction
above a crawlspace with a detached garage. The house and garage will be located on the site as
shown on Figure 1. Garage floor is proposed to be slab -on -grade. Cut depths are expected to
range between about 3 to 9 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 downhill and west of the residence.
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 property is vacant. The lot is vegetated with a pinion and juniper forest
with a ground cover of sage brush, cactus, grass and weeds. The building site is located on a
knoll on a northwest trending ridgeline. The ridge slopes steeply down to the west above the
building area, becomes slightly sloping at the building site and steepens again west of the site.
The slope down from the building area to the north is very steep and down from the building area
Foundation Recommendations:
-2 -
to the west is moderately steep down to the sage swale road. Numerous basalt cobbles and
boulders are visible on the ground surface.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits in the building areas 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, below about 12 to 18 inches of topsoil, consist of basalt gravel, cobbles
and boulders in a sandy clay and silt matrix. Results of swell -consolidation testing performed on
relatively undisturbed samples of the matrix soils, presented on Figures 3 and 4, indicate low
compressibility under existing moisture conditions and light loading. The sample tested from Pit
1 at 4 feet showed a low expansion potential (settlement under constant load) when wetted. The
sample tested from Pit 2 at 4 feet showed a low collapse potential when wetted. Results of a
USDA soil texture gradation analysis performed on a sample of very gravelly sandy loam with
cobbles (minus 5 inch fraction) obtained from the profile pit are presented on Figure 5. The
laboratory test results are summarized in Table 1. No free water was observed in the pits at the
time of excavation and the soils were slightly moist to moist.
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 soil designed for an allowable soil bearing pressure of 2,000
psf for support of the proposed residence. The matrix soils tend to expand or 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. Utility trenches and
deep cut areas below about 3 feet may require rock excavating techniques such as chipping or
blasting. Loose and disturbed soils 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 created from boulder removal at footing grade should be filled with a
structural material such as road base compacted to 98 percent standard Proctor density at a
moisture content near optimum or concrete. 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 10 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.
H -P 4. KUMAR
Project No. 17-7-467
-3 -
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly 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 clue
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.
All fill materials for support of floor slabs should be compacted to at least 95% of maximum
standard Proctor density al 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 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 recommend below -grade construction, such as retaining walls and
crawlspace 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 1 foot below lowest adjacent finish grade and sloped al 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 of 2 inches. The drain gravel backfill should be at least 11/2 feet deep.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence 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 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.
H -Pt KUMAR
Project No. 17-7-467
-4 -
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 10 feet in unpaved areas and a minimum slope of 3
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.
Percolation Testing:
Percolation tests were conducted on June 13, 2017 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 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 consist of 18 inches of topsoil overlying basalt
gravel, cobbles and boulders in a sandy silt matrix. The percolation test results are presented in
Table 2. Based on the subsurface conditions encountered and the percolation test results, the
tested area should be suitable for a conventional infiltration septic disposal system.
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 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,
H-PT_KUMAR
Project No. 17-7-467
5
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.
Respectfully Submitted,
H-PKIJMAR
Louis E. Eller
Reviewed by:
Daniel E Hardin, P.E. ;+n 2 443 r'
-o' G (D t'17
LEE/kac
attachments Figure 1 L.oca on t- Exploratory Pits and Percolation Test Holes
Figure 2 a- Logs of Exploratory Pits
Figures 3 and 4 -- Swell -Consolidation Test Results
Figure 5 -- USDA Gradation Test Results
Table 1 - Summary of Laboratory Test Results
Table 2 - Percolation Test Results
H-P=-KUMAR
Project No. 17-7-467
PROFI; .E
PIT 1
LOT 12
LOT 11
PROPOSED
GARAGE
PROPOSED
RESIDENCE
100 0 100 200
APPROXIMATE SCALE -FEET
17-7-467
H—PkeKUMAR
LOT 4
LOCATION OF EXPLORATORY PITS
AND PERCOLATION TEST HOLES
LOT 19
Fig. 1
W
W
1
0▪ .
a
W
-
— 5
PIT 1
WC=11.9
D0=94
PIT 2
WC=8.3
D0=87
PROFILE PIT
GRAVEL= 42
SAND=29
SILT=26
CLAY=3
0 -
10 10
LEGEND
TOPSOIL; ORGANIC SANDY SILT
• MOIST, DARK BROWN.
BASALT GRAVEL, COBBLES AND
SLIGHTLY MOIST, LIGHT BROWN,
HAND DRIVEN LINER SAMPLE.
DISTURBED BULK SAMPLE.
PRACTICAL DIGGING REFUSAL.
AND CLAY WITH COBBLES AND BOULDERS, FIRM, SLIGHTLY
BOULDERS (GM); SILT, CLAY AND SAND MATRIX, DENSE,
CALCAREOUS.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI EXCAVATOR ON JUNE 12, 2017.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT DETERMINED.
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 THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATING. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC - WATER CONTENT (%) (ASTM D 2216);
DO = DRY DENSITY (pcf) (ASTM 0 2216);
GRAVEL = PERCENT RETAINED ON NO. 10 SIEVE;
SAND = PERCENT PASSING NO. 10 SIEVE AND RETAINED ON NO. 325 SIEVE;
SILT = PERCENT PASSING NO. 325 SIEVE TO PARTICLE SIZE .002mm;
CLAY = PERCENT SMALLER THAN PARTICLE SIZE .002mm.
17-7-467
H-P%KUMAR
LOGS OF EXPLORATORY PITS
Fig. 2
.. 0
CONSOLIDATION - SWELL
—1
—4
nnatoot ....n. ar, w, b w
.orr.. uM.a. se. wwy ,w *
v.o1 UP. ra-.w..-, .1•=r0
tdeitts Imo 0010 iffet000d
iM 1rW410,, 10- Sw/
Cpe.m1nt ►'fM N
+wna.
oce+.��•.f•a.
17-7-467
SAMPLE OF: Sandy Silly Clay Matrix
FROM: Boring 1 0 4'
WC = 11.9 Y., DD = 94 pci
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
iA AAALIEO PRESSURE — K5r lc tic
H—PkeKUMAR
SWELL -CONSOLIDATION TEST RESULT
Fig. 3
2
— 2
-' —4
—6
W
— 8
z
0
1-
10
0
In
z
0
v-12;
—14 '
llumf.N .nW1 OW, NI' Ie IN
W*WH 4.0.4 Ths INV.] t..,.t
thug net 1* tip1e8W...t1111 tw
fLre,.NYINI Sn. w# tM qp0./ b
I..— Fl .._104a I. 3>.i
opew lits SpWG M1 IMO L
aardmx. •u f� 0 1MI
17-7-467
SAMPLE OF: Sandy Clayey Silt Matrix
FROM: Boring 2 0 4'
WC = 8.3 %. DD = 87 pcf
I.6 APPLIED PRESSURE KSr IA
H-P-M<UMAR
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
SWELL -CONSOLIDATION TEST RESULT
Fig. 4
f HYDROMETER ANALYSIS
SIEVE ANALYSIS
2
0 4n
[HI 7 FIR TIME READINGS 1 MIN
MIN 15 MlN 60MIN19MIN 4 MIN #325
U S STANDARD SERIES CLEAR SQUARE OPENINGS
#140 460 #35 418 410 44 3/8' 31.1' 1 1)2' 3' 5'6' 8'
PERCENT RETAINED
3 o $' o 8 `o" 0 0 "'o 0
' 0 0 0 0 0 0 0 0 0
PERCENT PASSING
or
f
r4"....4'1
001 002 005 009 019 0.1'; 106 0 5 100 00 4 75 9 5 19 0 37.5 76 2 152 203
DIAMETER OF PARTI E IN MI IM TER
G440-.1
1!- IF $1$ t.'1_1_1_11 5i=]'lllf� 14 w;
CONICS
GRAVEL 42 % SAND 29 % SILT 26 00 CLAY 3 %
USDA SOI TYPE. Very Gravelly Sandy Loam FROM: Profile Pit @ 3-5'
with Cobbles
17-7 467
"H-P- KUMAR
U':-DA GRADAT ON TEST RESULTS
Fig. 5
H-PKUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-467
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(Pcf)
GRADATION
PERCENT
PASSING
NO.200
SIEVE
USDA SOIL TEXTURE
SOIL TYPE
PIT
DEPTH
(ft)
GRAVEL
(%)
SAND
(%)
GRAVEL
(%)
SAND
(%)
SILT
(%)
CLAY
(%)
I
4
11.9
94
1
Sandy Silty Clay
Matrix
2
4
8.3
87
Sandy Clayey Silt
Matrix Y Y
Profile
Pit
3 to 5
42
29
26
3
Very Gravelly Sandy
Loam with Cobbles
H-PEKUMAR
TABLE 2
PERCOLATION TEST RESULTS
PROJECT NO. 17.7-467
HOLE NO.
-
P 1
HOLE DEPTH
(INCHES)
LENGTH OF
INTERVAL
(MIN)
WATER DEPTH
i AT START OF
INTERVAL
(INCHES)
WATER DEPTH
AT END OF
INTERVAL
(INCHES)
DROP IN
WATER LEVEL
(INCHES)
AVERAGE
PERCOLATION
RATE
(MIN./INCH)
35
15
6
5
1
6
5'/.
%
5%
5
5
4%
%
60/1
4%
4%
4'/,
4
'/+
P 2
32
15
7
6'/:
60/1
6%
6%
1/
61/4
6
6
5%
%
5'
5%
14
5%
5'/.
'/,
P 3
30
15
6
41/4
13/4
12/1
6%:
5
1%
6%=
5%
1%
5%
4
114
5%
4'/.
1%
41/4
3
1'/.
Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked on June 12,
2017. Percolation tests were conducted on June 13, 2017. The average percolation rates were
based on the last three readings of each test.