HomeMy WebLinkAboutSubsoil Study 09.16.2022TC'T Kumar & Asmciates, Inc.'
Geotechnical and Materials Engineers
and Environmental Scientists
5020 CountyRoad 154
Glenwood Springs, CO 81601
phone: {970)945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.eom
www.kumarusa.comAn Employcc Owncd Compony
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
September 16,2022
Joe O'Malley
45105 Highway 6
Glenwood Springs, Colorado 81601
j oe@soundstructural. com
Project No.22-l-561
Subject: Subsoil Study for Underpinning Design, Existing Residence, 45705 Highway 6,
Garfield County, Colorado
Dear Mr. O'Malley:
As requested, Kumar & Associates perfoûned a subsoil study for the design of foundation
underpinning at the subject site, The data obtained and our recommendations based on the
proposed construction and subsurface conditions encountered are presented in this reporl. The
study was conducted in accordance with our agreement for geotechnical engineering seryices to
you dated August 10,2022.
Background: The existing residence is a single-story wood frame structure with an attached
garage located as shown on Figure 1. The building floors are slab-on-grade. Vy'e understand the
building has undergone excessive settlement, on the order of 1 to 2 inches, causing distress to the
structure including cracks in the walls. Helical piers are desired to underpin the building
foundation. The residence is reportedly founded on 16-inch-wide spread footings and concrete
foundation walls. The spread footings are probably about 3 feet below ground surface and likely
bearing on the previously placed fill material.
Subsurface Conditions: The general subsurface conditions at the site were evaluated by
drilling one exploratory borin g îear the southwest corner of the residence, see Figure 1 , A
graphic log of the subsurface conditions encountered in the boring is show on Figure 2.
The subsoils consisted of about 6 feet of previously placed fill material underlain by relatively
dense, silty sandy gravel and cobbles with probable boulders down to the depth drilled of 7 feet.
The fill included cobbles and possible boulders. Drilling in the subsoils with auger equipment
was difficult due to the cobbles and boulders and drilling refusal was encountered in the natural
dense coarse granular soils deposit after shallow penetration.
Results of gradation analyses performed on samples of the silty sand and gravel f,rll material
(minus \%-inch fraction) obtained from the boring are presented on Figure 3. The laboratory
1
testing is summari zed in Table 1 . No free water \ilas encountered in the boring at the time of
drilling and the subsoils were slightly moist.
Foundation Recommendations: The filI material encountered in the boring consists of silty
sand and gravel with scattered cobbles and probable boulders. Considering the subsoil
conditions encountered in the exploratory boring and the nature of the proposed construction, we
believe helical piers may have some difficulty penetrating the previously placed fill and minor or
no penetration into the natural coarse granular soils. It may be feasible to use helical piers to
underpin the residence provided the allowable downward design capacities are limited to about
10 kips and relatively shallow embedment in the dense coarse granular soils is acceptable to the
designer.
An alternative underpinning method that should be considered is excavation to native soils
(estimated to be on the order of about 3 feet below the existing footing) and extending the
foundation walls down to new spread footings bearing on the dense coarse granular soils. The
new foundation areas should be excavated and poured in segments to avoid undermining the
existing foundation. Spread footings placed on the undisturbed natural coarse granular soils can
be designed for an allowable bearing pressure of 3,000 psf. The footings should be a minimum
width of I 8 inches for continuous walls and 2 feet for columns. All fill, topsoil and any loose
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 coarse granular
soils. 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 loca1
anomalies such as by assuming an unsupported length of at least 10 feet. Foundation walls
acting as retaining structures, if any, should be designed to resist alateral earth pressure based on
an equivalent fluid unit weight of at least 50 pcf for the on-site granular soil as backfill.
Micro-piles are also a feasible foundation altemative with proper design and construction.
Micro-piles should have a minimum embedment length of 15 feet and are typically design/build
by contractors with experience in the area.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this arca aI 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 boring drilled at the location indicated on Figure I
and to the depth shown on Figure 2,Ihe proposed construction, and our experience in the area.
Kumar & Associates, lnc.6 Project No. 22-7-561
3
Our findings include extrapolation of the subsurface conditions identified at the exploratory
boring and variations in the subsurface conditions may not become evident until underpinning is
performed. If conditions encountered during construction appear different from those described
in this reporto we should be notified at once so re-evaluation of the recommendations maybe
made. We recommend on-site observation of excavations and foundation bearing strata, and
obse¡vation of pile or pier installation 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,
Ku¡nar & Associates. T
Robert L. Duran, P.E.
Reviewed by:
David A. Y
RLDlkac
attachments Figure I - Location of Exploratory Boring
Figure 2 -Logof Exploratory Boring
Figure 3 - Gradation Test Results
Table I * Summary of Laboratory Test Results
P
o î/,lotJ¿
Kumæn & Asg*eiates, i¡¡s.6"Frojeet No. ??.7"S*1
O,MALLEY RESIDENCE
4507 HIGHWAY 6
APPROXIMATE SCALE-FEET
22-7 -s61 Kumar & Associates LOCATION OF TXPLORATORY BORING Fig. 1
E
E
!
Iä
BORING 1
LEGEND
0 FILL; SAND AND GRAVEL, SILTY, \tVlTH SCATTERED COBBLES
AND PROBABLE BOULDERS, MEDIUM DENSE, SLIGHTLY MOIST,
GRAY-BROWN37 /12
WC=1.6
*4=42
-200=14
w
fi'"41.,/ÞJV¡' I
GRAVTL AND COBBLES (GM); SltlOy, SILTY, PRIMARILY
BOULDERS, SUBROUNDED TO ROUNDED ROCKS, DENSE, SLIGHTLY
MOIST, LIGHT BROWN.
F
t¡J
L¡ltL
I
:Et-fLt¡lo
5
40/12
WC=1.0
+4=59
-.¿uu= tJ i DRTVE SAMPLE, 1 3/8-|NCH t.D. SpLrT Sp00N STANDARD
PENETRATION TIST.
zz ¡r o DRIVE SAMPLE BL0W COUNT, INDICATES THAT ?? BLOWS 0Frt/ '' A r40-pouND HAMMER FALLTNG J0 rNcHEs WERE REQUTRED
TO DRIVE THE SAMPLER 12 INCHTS.
'10
f nnncrrcll AUGIR DRTLLTNc RTFUSAL.
NOTES
1 THT EXPLORATORY BORING WAS DRILLED ON AUGUST 22,
2022 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER
AUGER.
2. THE LOCATION OF THI IXPLORATORY BORING WAS MTASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE
FIGURT 1 SITE PLAN,
3. THE ELEVATION OF THE TXPLORATORY BORING WAS NOT
MEASURED AND THE LOG OF THE TXPLORATORY BORING IS
PLOTTIO TO DEPTH.
4. THE EXPLORATORY BORING LOCATION SHOULD BE
CONSIDERED ACCURATE ONLY TO THE DEGRIE IMPLIED BY
THE METHOD USED.
5. THE LINES BETWTTN MATERIALS SHOWN ON THE
TXPLORATORY BORING LOG REPRESINT ÏHE APPROXIMATE
BOUNDARIES BETWEEN MATERIAL TYPES AND THE
TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT
ÏHE TIME OF DRILLING.
7 LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
+4 = PERCENTAGI RETAINED ON NO. 4 SIEVE
(rsrv o ogr¡);
-200 = PERCENTAGE PASSING N0. 200 SIEVE
(ASTM D 1140).
LOG OF EXPLORATORY BORING Fi1. 222-7 -561 Kumar & Associates
ı
100
90
ao
50
50
40
30
20
10
0
o
10
20
30
40
50
60
70
80
90
ãtr
.oot .oo2 4.t9 38.1 76.2
152
DIAMETER OF INM
CLAY TO SILT COBBLES
GRAVEL 42 % SAND 44 %
LIQUID LIMIÏ - PLASTICITY INDEX
SAMPLE OF: Silty Sond ond Grovel (Fill)
SILT AND CLAY 14 %
FROM:Boringl@2.5'
6
r00
90
80
70
60
50
10
30
20
10
o
0
10
20
30
40
50
60
70
a0
90
.oot 4.t9 3a.t 76.2 127 200
I
DIAMETER OF PA IN MILLI
CLAY TO SILT COBBLES
GRAVET 39 % SAND 4A %
LIQUID LIMIT - PLASTICITY ÍNDEX
Sia,MPLE OF: Silty Sond ond Grovel (Fill) FROM: Boring 1 @ 5'
SILT AND CLAY 13%
Th€sc losl rosulls opply only lo lh€
sompl€s which w€re lsslod. Th€
iosl¡ng roporl sholl nol bo reproduced,
sxc€pl ið full, wllhout lhs wrlltenqpprovql of Kumqr & Assoclql€s, lnc,
Sl€ve qnolysls l€stlng ls pgrformed ln
occordone€ wlth ASTM 06913, ASTM 07928,
ASTM Cl56 qnd/or ASTM 0t140.
HYDROMETER ANALYSIS SIEVE ANALYSIS
I MIN
24 HRS 7 HRS¡4 MIN 15 MIN
fIME REÄDINGS
6OMIN IEMIN ¡M¡N
U-S. SIANDARD SÊRIES CLEAR SOUARE
-1.
. -. 1.-
-:. .. 1.- .-i-
... ...1 .
- l_
. -._-t..
-. 1
.... f..
. ... --.-i ..1.''..t
-l-__l
--...,-t..-.. ¿ -
.....1
I
SAND GRAVEL
FINE MEDIUM COARSE FINE COARSE
HYOROMETER ANALYSIS SIEVE ANALYSIS
TIME REAÐINCS
24 HRS 7 HRS I
CLEAR SQUARE OPENINGS
\/ur a/^i I 1/.'t
U.S. STÀNOARO SERIES
SAND GRAVEL
FIN E MEDIUM COARSE FINE COARSE
22-7 -561 Kumar & Associates GRADATION TEST RTSULTS Fig. 3
lcrtH,ffit*ffifffi[.Få*"'TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.22-7-561152%BORINGDEPTHSAMPLE LOCATION1.01.6lololNATURALMOISTURECONTENTLIQUID LIMIT(%)GRAVEL(%)SANDNATURALDRYDENSITYPERCENTPASSING NO.200 srEVEPLASTICINDEX39424844IaJt4lpsflUNCONFINEDCOMPRESSIVESTRENGTHSilty Sand and Gravel (fill)Silty Sand and Gravel (fill)SOIL TYPE