HomeMy WebLinkAboutSubsoil StudyHEPWORTH - PAWLAI< GEOTECHNICAL
October 31, 2005
Jordan Architecture
Attn: Darryl Anderson
P.O. Box 1031
Glenwood Springs, Colorado 81602
Hc1�tr, rt1,-r'a�;^laL (3eoteQlsnical, l t.
502( Counry Road 154
Glenwood Spring:, Colorado 81601
PIir ne: 970-9'15-7(M
Fa':: 970-945..S45N
email: hpg lftilpgr<)tec1;.c,.nn
Job No.105 855
Subject: Subsoil Study for Founc:ation Design, Proposed Burkholder Residence,
Lot A-14, The Peninsula at Aspen Glen, Whispering Water and River's
Bend, Garfield County, Colorado.
Dear Mr. Anderson:
As requested, Hepworth-Pawiak Geotechnical, Inc. performed a subsoil study for design
of foundations at the subject site. The study was conducted in accordance with our
agreement for geotechnical engineering services to Jordan Architecture dated September
23, 2005. 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 two story wood frame
structure with an attached garage. Ground floor will either be structural over a
crawlspace or a basement level with slab -on -grade floor. Cut depths are expected to
range between about 3 to 10 feet. Foundation loadings for this type of construction are
assumed to be relatively light and typical of the proposed type of construction.
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 was vacant at the time of our field exploration. There is sone
fill on the lot from overlot grading as part of the subdivision development. The ground
surface is relatively flat with a slight slope down to the south. There is about 2 to 3 feet
of elevation difference across the lot. Vegetation consists of scattered grass and weeds.
Cobbles are exposed on the ground surface.
Subsidence Potential: Aspen Glen 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 studies in the area, sinkholes were observed in
Aspen Glen development. Sinkholes were not observed in the immediate area of the
subject lot. The nearest mapped sinkhole is approximately 1540 feet to the north-
northwest of the lot. The exploratory pits were relatively 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 A-14
Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989
FILE copy
-2 -
throughout the service life of the residence is low and similar to other lots in the area but
the owner should be aware of the potential for sinkhole development.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating three exploratory pits at the approximate locations shown on Figure 1. The
logs of the pits are presented on Figure 2. The subsoils encountered, below about 1/2 to 3
feet of clay fill, generally consist of relatively dense, slightly silty sandy gravel with
cobbles and scattered boulders. A 1 to 3 foot thick slightly silty to silty sand layer was
encountered within the gravels in Pits 1 and 2. Results of a gradation analysis performed
on a sample of the gravels (minus 5 inch fraction) obtained from the site are presented on
Figure 3. The laboratory testing is summarized on Table 1. 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 natural gravel soil designed for an allowable soil
bearing pressure of 3,000 psf for support of the proposed residence. Footings should be a
minimum width of 16 inches for continuous walls and 2 feet for columns. Topsoil and
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 gravel 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 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 45 pcf for the on-site soil as backfill,
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 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 flee -draining gravel should be placed beneath
basement level slabs to facilitate drainage. This material should consist ofminus 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 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
create a perched condition. We recommend below -grade construction, such as retaining
Job No, l 05 855
satech
_3 -
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 1 foot below lowest adjacent finish
grade and sloped at a minimum 1% to a suitable gravity outlet dry well or sump and
pump, 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. Free -draining wall backfill should be
capped with about 2 feet of the an -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 6 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.
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 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 xnold 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.
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.105 855
-4 -
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,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
Jordy Z. Adamson, Jr., P.E.
Reviewed by:
Daniel E. Hardin, P.E.
JZA/ksw
attachments Figure 1-- Location of Exploratory Pits
Figure 2— Logs of Exploratory Pits
Figure 3 -- Gradation Test Results
Table 1-- Summary of Laboratory Test Results
Job No.105 B55
1
LOT Aly
APPROXIMATE SCALE
1"=30'
wRf `SPtR/!vC 1yq
TER
7
r
1
\ ,.' 1
i 1
PIT 1
1
1
1
LOT A14 I
1
1 PIT 2
L1
1 ■
` //
1 /
W......_„
/
\\ PIT ■
` //
r r
r r
LOT A13
1 � `
~~ '� -
BENCH MARK; GROUND SURFACE AT PROPERTY
CORNER; ELEV. = 100.0; ASSUMED.
RIVER'S BEND
105 855
Hepworth -Pawl* Geot- foal
LOCATION OF EXPLORATORY PITS
Figure 1
5
10
LEGEND:
PIT 1
ELEV.= 102.6'
WC=1.9
DD=97
-200=5
PMT 2
ELEV.= 101.0'
a y i
+ 1 +4=62
j -200=6
WC=2.7
DD=101
-200=4
PIT 3
ELEV.= 101,2'
FILL; sandy silty clay, organics in Pit 3, firm, slightly moist, brown to reddish brown.
SAND (SP -SM); slightly silty to silty, medium dense, slightly molst, light brown.
GRAVEL (GP -GM); sandy, slightly silty with cobbles and scattered boulders, dense, slightly moist,
light brown, subrounded to rounded rock.
2' Diameter hand driven liner sample.
Disturbed bulk sample.
0
5
10
NOTES:
1. Exploratory pits were excavated on October 11, 2005 with a Caterpillar 420D backhoe.
2. Locations of exploratory plts were measured approximately by pacing from features shown on the site plan
provided,
3. Elevations of exploratory pits were obtained by interpolation between contours shown on the site plan provided and
checked by instrument level.
4. The exploratory pit locations and elevations 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 Results:
WC = Water Content (%)
DD = Dry Density (pcf)
+4 = Percent retained on the No. 4 sieve
-200 = Percent passing No. 200 sieve
105 855
M
Hap worth—PawIat atatttnical
LOGS OF EXPLORATORY PITS
Figure 2
•
.MMM.••..
Ha, HYDROMETER ANALYSIS j SIEVE ANALYSIS
TIME 1
p 24 MIN. 15 MIN. 6QM N19M44 MIN, READINGS, 1 RAIN. #2100 #100 U # 0 #30S. S#EROIES#e ' 3/ SQUAREOPENINGS 58' 100
10
20
30
40
▪ 50
d 60
70
80
90
100
.001 .002 .005 .009 .019 .037 .074 ,150 .300 .600 1.18 2.36 4.75 9.5 19.0 37.5 76.2 152 203
12.5 127
r MII I •OIPIpMI __M MMS Pa•—.s i^
-- MIMII. •aii
MITI MMIIIMrr MI. aarai aa�
r MMMiM i M=MINIMIAPIPUNIM— NM= MI_
.MIiaMMMiMi..i= >KaMai
KININ—=min MEINI_i .MM•
l�.i MI 01•••1111111aMMINO I MOM IMmil.MM
—M_..ar il..—
—MMM r�a-_ MIilMP.....•.INN •r.lr!i a..r!!•.r...+1011.iiMIdtIa.MI
Mraa•rMri
ra• i I MINOM �I•NM= i —
—
aM•aii i
N—Ma•—i i.M MIM
M.NliMpl MIMI— MMI•I_Mi
ii MINM i I=M111=1111 1=M= i ill!
SaMI•rl i _aai i M..
lMaaMMai MIMI I i•ii al i ii
NIIN i W •_MiM11 LM =NM ii
..Miiair _ ail! I.=AO.= lMi raM 1....
l MMM.r.MMM.• MOW 1.m—MMS
•MIMIM•Milliil i -------
••III^i MINIM marIMINIMIIIMINIMPE
---
MMMM IIMIi..— m MINIMEMIMMI_
•�Mrrrr•— i• MI— ____B
MMIMI I _MPP iMMi!i•M MIMrrr
aM• •a•iM11111Mi . I MI.MIi
—lMM MEN.— =MOM= MMaI II. ONIMMMIIIOO IMMMII'MI IM PINIO —___ �il� i!
N UMNI •M= i•!INMiMM Maar
=MN=Mi_r i a• MMM..arM�
=1.=•aaM ==MIIi r=1•r•r.ii
!moi i.11l I aMMIM. a l+ii�r
MIi•NMI FI.Mii i i:! aMMaU MINIM i.MIIIMANIMMIR piffil IN NM=i
---
•___li WI• FMM.I NTMI•• IMMUNE MI
! Muir— Mia M— iir i ffiI
F— •ria M. MIMIM;Mr•i -Mi NEi
liMMaai Email IIIIii i • _'MI __ i M•
•M.MMw ai_ •^ i il. =moo .MMMM.•M• iia rri
a• a•M il.wl..IM.
INI MMIN1==.ww M• i•NMO lrrii
r•.•Mi i• i -- —J 1•1•111Mri_ I= =MP
aaai •.MI•MI IMS aiaa• l i i i
III MIII !Mai Mg WPM iai! -- iri
li..iIM iMil iriia.. p•i M.Ii NUi
!M•Mi— _•.TIMI.! _ilii
! i•ia M• BF a• _.PITT — i aar
all li+i Frac MIM. r____.
!—!rI FMi i _ran rd rrr__
— i •!aaa.i__ MMS
l=NON •Iii MMiM.aaM.i =MEM! =MNii
lMli�i Aliximr-r—ii prom=
iMP MMMT• il_M•IMMPMIM •s! U.Mar�MMIi
M—moi i!!!M--- lrMMMi IM—_r_MII MMi .Tai—
! iri a• alai _NUMMI !__.ilii
!1— ■.f =AMM=!! I.I.triii
M—aMIMirMii ra•aMaMMPM_.ili ii
—IMP.leMMi
I.ilr.wri
—Iii i M�� MMMM•i IMIM•Mi P—MINIMI MIi
IIIMN. MN 1.11MINM .'s =====..p. ii i—ii.^
• MN= . i•! — Iiiii
!—i MaaM-_aMINIIM.i —i •! rMrr MMMT iaar
! i ===•r lI NMrM.l MIM• MMIN _MINIMI 1•i! MMMMM III M•
!I^Iit.lMEMEN MIai MMM._! !r— M.iPIN •—i,II ! MINIM= ■•ii
!I M• =MrM•MMMMrr .ii
I�.i.Ial.—r. .111I M.Ii• l..Il ii
M.....AI!lriii•! i ...!•..
l MI! — antrala— Mllllll.11or i• l.MIIIMIIMM.M iaMi
MaaMMaMl..it a. MI. -/m .1^IIII..I ai i am.!! M• MINIMUM
MINIMI MMwNI Mi UNWOME ! MAiI.M Mi M.! N.0••• •IIIII im liM
SIIIIIIIIIIMIN— iiM= M—1 Mm i•iaaa_ li iiMIi
NIMH.Iii— i•!! iii Mi =MIME Elmll -MMS
aa•
100. MINN .a.MMIMI Iii♦! .MINI_• M—! M• MIM•
MINIM■MMMM•i .—M—lli•! MINNOW IMM MI .1M NII
mum= MEM=MO milmw mu
.M.—MaMMM•iimil i iii
IMIMMIMI 1MMMM•i [! nig lir MMM. MINIM=!_ ii
!MMrMM♦Mi MI. i NIA l!!M•iMIMi MMIM MmolmNaa•M• MIMIM.Ia
! MM.MiiMM MINIM• Neal N• i
! i• M•!! MMI• MMM.! •Ar. MMI..!! MMMMr_MI •!! MIMMar MM
i1111 lalMai i.MMIMMMM_ar MOMPIPIIII IMii lMr WWI FIIMMEMM i•M NE ar a MN=
lMMM—=MIN =1" •iMMIi lIONA mommI__ ! !—aMOM
liMar i MM'_!!! MIM• ImVii MMIMIi. MMMIMIM M• i aar
M.MM.MOM aa•MMMarMnUw_MM— = •MMM•! MII MI -M•
.•MIM.MIIMMI _MUNI.— ai UNUM._ l
MEN.M
l IIIIMM..M ir'"...IrIIIIIMMi M—miminlold_ i•!!=NM _
i
!MIiiR mgmil m,i!!!MINIMIi• MIYMi l— iMMIll •• MilW. MM
i I.Ir.I.i
rr►�=NEM
MEN MMr•laMi AMi
IUP•_
lr Ml•i
M—••I MAMA
WMMMMM.a•1..I11I111•M
!—.M•i
MM•01 =M.MI
lMMMii
iMIr�"Ii i011 `�MO
.MMMT ..Mi
=U MMI !li
IMIM Mr•r iMa.l i•MIMM 0=ZMI
M• MIMIi
l aMMM i
=• M•••• mi !MIEN
I
MiI••••••=1M NII^ Mt Ili.Ia
CLAY TOSILT
DIAMETER OF PARTICLES IN MILLIMETERS
SAND dRAVEi
FINE 1 IJEDIUM }COARSE fl i mum
GOBBLES
GRAVEL 62 %
LIQUID LIMIT q
SAMPLE OF: Slightly Silty Sandy Gravel with Cobbles
SAND 32 %
SILT AND CLAY 6 %
PLASTICITY INDEX %
FROM: Pit 2 at 5 to 7 Feet
90
80
70
60
50
40
30
20
10
0
T PAS ,r
105 855
•
H
GRADATION TEST RESULTS
Hepworth—Powlak Geotec1 nTeal
Figure 3
0
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1 Job No. 105 855
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION
PIT
DEPTH
(ft)
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(p)
GRADATION
GRAVEL
((XI)
SAND
(%)
PERMIT
PASSING
NO. 200
SIEVE
ATTERBERG LIMITS
LIQUID PLASTIC
LIMIT INDEX
(°)
(%)
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
SOIL OR
BEDROCK TYPE
1
6
1.9
97
5
Slightly silty sand
2
5-7
62 32
6
1
Slightly silty sandy gravel
with cobbles
i
7
2.7 101
4
sand