HomeMy WebLinkAboutSoils & Foundation Investigation 12.12.2006ffi CTL ITHONIPSON
December 12,2006
Ms. Arianna Lightfoot
{23 Rosewood Way
Parachute, CO 81635
Subject:Soils and Foundation lnvestigation
Lightfoot Residence
Lot 9, Monument Ridge
Garfield County, Colorado
Project No. G504906-1 20
This report presents the results of our soils and foundation investigation
for the Lightfoot Residence proposed on Lot 9, Monument Ridge in GarÍield
County, Cotorado. We conducted this investigation to evaluate subsurface
conditions at the site and provide foundation recommendations for the proposed
residence. Our report was prepared from data developed during observation of
subsurface conditions exposed in exploratory pits excavated at the site,
engineering analysis and our experience with similar conditions. This report
includes a description of the subsurface conditions observed in exploratory pits,
recommendations and design criteria for the foundation and floor systems, and
geotechnical and construction crlteria for details influenced by the subsoils.
Recommendations contained in this report were developed based on our
understanding of the planned construction. lf plans differ significantly from the
descriptions contained in the report, we should be informed so that we can check
that our recommendations and design criteria are appropriate.
Site..Gonditions
Lot 9 is northeast of the County Road 300 and Monument Ridge Road
intersection. Access to the lot will be from Monument Ridge Road. The building
lootprint witl be near the center of the lot. Grades at the lot are relatively flat and
vegetation is a sparse cover of native ground flora'
Proposed Construction
We did not have building plans to prepare this report, We understand that
the Lightfoot Residence will be a two-story, wood-frame building with an attached
234 Center Þrive lGlenwood Springs, Colorado I'1601
Telephone: 97 A-945-2809 Fax: 970"945-7 411
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garage. No basement \¡ìtlll be constructed. A crawl space will be below thê ma¡n
floor living area. The garage floor will be a slah-on-grade. Maximum foundation
excavatíon depths will likely be about 5 feet, Completed wall backfill depth may be
slightly more than excavation depth as final grades are adJusted for drainage.
Foundation loads are expected to vary between 1,000 and 3,000 pounds per lineal
foot of foundation wall with maximum interior column loads of 30 kips. lf
construction will differ significantly from the descriptions above, we should be
informed so that we can adjust our recommendations and design criteria, if
necessary.
Subsurface Conditions
We observed subsurface conditTons exposed in two exploratory pits (TP-1
and TP-2) excavated at the site. The approximate locations of our exploratory pits
are shown on Figure l. Subsurface conditions observed in the pits were logged
by our laboratory/field manager who obtained samples of the excavated soils.
Graphic logs of the soils observed in the exploratory pits are shown on Figure 2.
Subsurface conditíons observed in our exploratory pits consisted of about
l2 inches of sandy clay "topsoil" underlain by silty sand with gravel and scattered
cobbles to the total explored depth of 11 feet below existing ground sur-face. Free
ground water was not observed in the exploratory pits at the time of excavation.
A sample of the natural soil selected for gradation analysis contained 41
percent gravel, 26 percent sand, and 33 percent silt and clay size particles
{passing the No. 200 sieve). Two samples of the soils were subjected to one
dimensional consolidation tests. The samples were flooded while subjected to a
.1,000 psf load. Both samples showed consolidation potential. Laboratory test
resutts are shown on F¡gures 3 through 5.
Site Ea.rthwork
Excavations
We anticipate excavations for the building foundation and utilities can be
accomplished using conventional, heavy-duty excavation equipment. Excavation
sides will need to be sloped or braced to meet local, state and federal safety
regulations. We believe the natural sands will classify as a Type C soil based on
OSHA standards governing excavations. Ternporary slopes deeper than 5 feet
should be no steeper than 1.5 to I {horizontal to vertical} in Type C soils.
Contractors should identify the soils encountered in the excavations and refer to
OSHA standards to determine appropriate slopes.
Soils removed from the excavation should not be stockpiled at the edge of
the excavation. Excavated soils should be placed at a dístance from the top of the
excavation equal to at least the depth of the exeavation.
MS. AR¡ANNA LIGHTFOOT
LIGHTFOOT RESIDENCE
PROJECT NO, GS04906 145
sics04906,o00tl2ol3, Letler31c50490S 120 Ll doc
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Fill and Backfill
Grading plans were not províded to us. We are providing criteria for
footings supported on structural fill (see Foundation section). Fill may be
required to obtain subgrade elevations for parts of the driveway. Areas which will
receive fill should be stripped of vegetation, organic soils and debris. The on-site
soils free of organic matter, debris and rocks larger than 3 inches in diameter can
be used as structural fill below footings or as fill to achieve subgrade for exterior
{latwork or the drivewaY.
Fill should be placed in loose lifts of 10 inches thick or less and moisture
conditioned to within 2 percent of optimum moisture content. Fill placed outside
the building footprint should be compacted to at least 95 percent of standard
proctor {ASTM D 69S) maximum dry density. Structural fill below footings or
exterior flatwork should be compacted to at least 98 percent of ASTM D 698
maximum dry density. Moisture content and density of fill and structural fill
should be checked by a representative of our firm during placement'
Baekfill placed adjacent to foundation wall exteriors should be free of
organic matter, debris and rocks larger than 3 inches in diameter. Backfill should
be moisture conditioned to within 2 percent of optimum moisture content and
compacted to at least 95 percent of standard Proctor (ASTM D 698) maximum dry
density.
Free ground water was not ohserved in the exploratory pits during our site
visit We do not anticipate excavations for foundations or utilities will penetrate
ground water, however, excavations should be sloped to a gravity discharge or to
a temporary sump where water ,can be removed by pumping' The ground
surrounding the excavations should be sloped as much as practical to direct
runoff away from the excavations.
Foundation
Our exploratory pits indicate that natural silty sands are present at
anticipated foundation elevations for the Lightfoot Residence. These soils are
slightly moist to dry and are susceptíble to collapse and consolidatíon when
wetted. Some increase in moisture should be assumed after the residence is
completed and the yard is landscaped. We recommend constructing the
residence on footing foundations. The footÍngs can be supported by either a
minimum 3 feet of densely compacted structural fill (see Figure 6) or on the native
soils in the in-situ state. The placement of densely compacted structural fill below
footing will reduce the risk of footing settlement and the potential for differentÍal
settlement of the building foundation. Our representative should be called to
observe and check the placement of structural fill. We should also observe the
compteted foundation excavation prior to placing forms, to confirm that the soil
exposed is suitable for support of the designed footings. Recommended desfgn
and construction criteria for footings âre presented below.
M5, ARIANNA LIGHTFOOT
LIGHTFOOT RESIDËNCE
PRoJECT NO. GS049t6 '145
s:lGSû4906,000\12013, !ótterstGSo,1906 1 20 Ll.doc
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Footing foundatlon.s should be supported by structural fill or tho
undlsturbed, natural soils, Soils loosened during excavation or the
forming process forthe footings should he rernoved or the soils can
be re-compacted prior to placing concrete.
Footings supported by structural fill or the natural soils can be
designed for a maximum allowable soil pressure of 3,000 psf.
Gontínuous wall footings should have a mínimum width of at least
16 inches. Foundations for isolated columns should have minimum
dimensions of 24 inches by 24 inches. Larger sizes may be
required, depending upon foundation loads.
4.Grade beams and foundation walls should be well reinforced, top
and bottom, to span undisclosed loose or soft soil pockets. We
recornmend reinforcement sufficient to span an unsupported
distance of at least 12îeet Reinforcement should be designed by a
qual ified structural engineer.
The soils beneath exteríor footings should be protected from
freezing. We recommend the bottom of footings be constructed at a
depth of at least 36 inches below finished exterior grades for soil
frost protection.
Floor Svstem and Slabs-On-Grade
We understand the main level living area will be constructed with a crawl
space below the floor. From a geotechnical perspective structural floors are very
positive. We understand that the garage floor is planned as a slab-on-grade.
Based on our experience, we judge slab-on-grade construction can be supported
by the undisturbed, natural soils with a low to moderate risk of differential
movoment and associated damage, The potential for slab-on-grade settlement can
be reduced by the placementof atleast {2 inches of structural fill belowthe slab,
$tructural fill placed to attain subgrade elevations for exterior concrete flatwork
should be in accordance with the recommendations outlined in the Fill and
Backfill section.
We recommend the following precautions for slab-on-grade construction at
this site.
Slabs should be separated from exterior walls and interior bearing
members with slip joints which allow free vertical movement of the
slaÞs.
Underslab plumbing should be pressure tested for leaks before the
slabs are constructed. Plumbing and utílíties whích pass through
MS. ARIANNA LIGHTFOOT
LIGHTFOOT RESIÐENCE
PROJECT NO. GS04906 145
slËS04906'Ù00\120\3. LettsrE\G504906'l 20 L1,doc
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slabs should be isolated from the slabs with sleeves and provided
with flexible couplings to slab supported appliances.
Exterior patio and porch slabs should be isolated from the
residence. These slabs should be well-reinforced to function as
independent units.
Frequent control joints should be provided, in accordance with
American Concrete lnstítute (ACl) recommendatíons, to reduce
problems associated with shrinkage and curling.
B rade Constru ction
Foundation walls which extend below-grade should be designed for lateral
earth pressures where backfíll is not present to about the same extent on both
sides of the wall. Many factors affect the values of the design lateral earth
pressure. These factors include, þut are not limited to, the type, compaction,
slope and drainage of the backfill, and the rigidi$ of the wall against rotation and
deflection. For a very rigid wall where negligible or very little deflection will occur,
an "at-rest" lateral earth pressure should be used in design. For walls which can
deflect or rotate 0.5 to 1 percent of wall height (depending upon the backfill types),
lower "active" lateral earth pressures are appropriate. Our experience indicates
typical foundatíon walls can deflect or rotate slightly under normal design loads,
and that this deflection results in satisfactory wall performance. Thus, the earth
pressures on the wallg will likely be between the "active" and "at-rest" conditions.
lf the on-site soils are used as backfill, we recommend design of below-
grade walls using an equivalent fluid density of at least 50 pcf for this site, This
equ¡valent density does not include allowances for sloping backfill, surcharges or
hydrostatic pressures. The recommended equ¡valent density assumes deflection;
some minor cracking of walls may occur. lf very little wall deflection is desired, a
higher equivalent fluid density may be appropriate for design. Our recent
experience indicates most below-grade walls designed with 45 pcf to 55 pcf
equivalent fluid density have performed satisfactorily. Backfill should be placed
in accordance with recornmendations in the Fill and Backfill section.
Water from rain, snow melt and surface irrigation of lawns and landscaping
frequently flows through relatively permeable backfill placed adjacent to a
residence and collects on the surface of relatively impermeable soils occurring at
the bottom of the excavation. This can cause wet or moist conditions in below-
grade areas after construction. To reduce the likelihood water pressure will
develop outside foundation walls and reduce risk of accumulation of water in tlre
crawl space, we recommend provision of a foundation drain. The drain should
consist of a 4-inch díameter, slotted pipe encased ín free draining gravel. The
drain should lead to a positive gravity outfall, or to a sump pit where water can be
removed by pumping. A typical foundation drain detail is presented on Figure 7.
ln addítfon, adequate crawlspace ventilation should be provided.
MS. ARIANNA LìGHTFOOT
LIGHTFOOT RESIDENCE
PRoJEcr No. Gs04906 145
sloso4906.00O\12013. Lsllers\G$04906 t20 Ll doc
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Surface D-rqinsgg
Surface drainage is critical to the pefformance of foundations, floor slabs
and concrete flatwork. We recommend the following precautions be observed
during construction and maintained at alltimes after the residence is completed:
The ground surface surrounding the exterior of the residence should
be sloped to drain away from the residence in afl directions. We
recommend providing a slope of at least f 2 inches in the first l0 feet
around the residence, where possible. ln no case should the slope
be less than 6 inches in the first 5 feet.
Backfill around the exterior of foundation walls should be placed in
maximum 10 inch thick loose lifts, moisture cond¡t¡oned to within 2
percent of optimum moisture content and compacted to at least 95
percent of standard Proctor {ASTM D 698} maximum dry density.
The residence should be provided with roof gutters and
downspouts. Roof downspouts and drains should discharge well
beyond the limits of all backfill. $plash blocks and downspout
extensions should be provided at all discharge points.
4.Landscaping should be carefully designed to minimize irrigation.
Plants used near foundation walls should be limited to those with
low moisture requirements; irrigated grass should not be located
within 5 feet of the foundation. Sprinklers should not discharge
within 5 feet of the foundation and should be directed away from the
building.
lmpervious plastic membranes should not be used to cover the
ground surface immediately surrounding the residence. These
membranes tend to trap moisture and prevent normal evaporation
from occurring. Geotextile fabrics can be used to control weed
growth and allow some evaporation to occur.
Limitations
The exploratory pits provide a reasonably accurate picture of subsurface
conditions. Variations in the subsurface conditions not indicated by the pits will
occur. Our representative should be called to observe and check fill placement
and to observe the completed foundation excavation to confirm the soil exposed
is suitable for support of the footings as designed'
ThÍs investigation was conducted in a mânner consistent with that level of
care and skill ordinarily exercised by geotechnical engineers currently practicing
under similar conditions in the locality of this project. No warranty, express or
implied, is made. lf we can be of further service in discussing the contents of this
MS. ARIANNA LIGHTFOOT
LIGHTFOOT RESIDENCE
PROJECT HO. GS04900 145
S lGâ04906.000\120\3. Letlerslcs04906 120 Ll.doc
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report or in the analysls of the influonce of the subsoll condltlons on the deslgn of
the structure, please call.
Very Truly Yours
cTL ITHOMPSON, lNC.
J
l"
i-.;,: J 'r
(5 copies sent)
MS. ARIANNA LIGHTFOOT
LIGHTFOOT RESIDENCE
PROJECT NO. GS04906 1a5
S:\GS01906,000112013. Lolt6rslcs04006 l¡0 Ll.dæ
7
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ProJect No. G9O49O6-1 2O
LOT 5
7.117 AC. r
FENCE
LOT 9
6.555 AC. t
WELL FOR LOTS 9 AND 10, PERMIT _
I NO. 57703F
TP-2
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COUNTY ROAD 5OO
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LEGEND:NOTES:
El SondYbC moisl,
oloy "topsoll", orgonlcs,
brown.
1. Explor.olory pÌis nÇrc ôxcovolcd
with o bockhos on December 6,
2006. Plls wero bockfillad
immediolely ofler axcovolion
operollons wer€ compleled.
2. No free ground wotsr wos
obscrvcd ln lhc explorotory
pÍls of lhe llme of excovolion,
3. Locolions of explorotory pits ore
opproximole.
4. These explorolory pits ore
subJecl lo lhe explonofions,
llrnilotlons qnd conclusions os
contslned ln lhis report.
Ø
L
þ
Sqnd, silty, grovel' cobbles,
occoelonol bouldcrs, mcdiurn
dcnss to d¡nsc, slighlly moisl
to dry, lighl ton, whlle.
(SM-Gl,l)
lndlcotes hond drìve somPle.
lndlcotss bulk somPle.
SUMMARY LOGS OF EXPLORATORY PITS
Projecl No. GS04906-145 Flg. 2
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7
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5
4
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zI(nz
o-xIu
\9
zIûo
trlÉ
0.Eo(J
0
-2
-3
4
-6
-8
0.1 1.0
APPLIED PRESSURE. KSF
10
NATURAL DRY UNÍT WEIGHT=
NATURAL MOISTURE CONTENT=
100
71
10.1
PCF
o/o
Somple ol SAND, SILTY (SM)
FTom TP.1 AT 3 FEET
Swell Consolidation
Test Results Frc 3
,/i
,/i DUE INTOREWETT
ON UNDER
i
PROJECT NO, G504906-120
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7
6
5
4
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Somple of SAND, SILTY (SM)
1.0
APPLIED PRESSURE . KSF
10
NATURAL DRY UNIT WEIGHT=
NATUR TMOISTURECONTENT=
100
PCF
FTOM TP.2 AT4 FEET
7A
10.9 o/.
Swell Gonsolidation
Test Results FrG 4
¡
:
ADDITfONA
CONST G
o N
DUE TOE
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I
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PROJECT NO, GSO4906-120
--frir.-
-J,l-fä'
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SANBS GRAVEI
FINE MEÐIUM COARSE FINE COARSE CÔBBtESçLAY {PTÁSTIC) TO SILT {NON.FLASTIC)
SIEVE ANALYSISHYDROMETER ANALYSIS
90
ao
7A
60
50
40
30
2t
10
.005 _oos .01s .037 .c74 .149 .297 _ __.590 1.19 2.0 2.38 4.76 9.52 19.1 36.1 76.2 't27-,2O0o.42 152
DIAMET€R OF PARTICLE IN À'ILLIMETERS
:- l-- l-''-l', ,.1.-, i.---,.-J--:--'J "-'-l'-":-_. -- l.:-----f:-.::-.'l -.---- l-.. .l:---:.rr.l - ì..-. - -l
,
.-'--..-l-----
_l_l .__ . -.----.-t_
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---t-____
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@oÈ
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CLEÁR
a
d&
tszd
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0.002
3/a'xt4"
s0
lnn
TIME
1Ul
STANDARD SERIES
,50-40'30.1ô.1Ô,s6û MtN. re MrN. 4 MlN. 1 MlN. '200 '100
2g HR. 7 HR,
d5 MtN. 15 MlN.
Somple of
From
GR4VEL, CLAYEY, SILTY {Gç-GM)
TP-1 AT 10.11 FEET
GRAVEL 41 o/o
srlr & CLAY ,,_qx %
PLASTICITY INDEX
SAND 26%
Lte u ¡ o-I I lr¡ tî---l o/o
- o/o
SANDS GRÂVÊt
fINE MEDIUM coARsÉ FINE coARsËCLAY {PI-ESTIC} TO SILT (ÑON-PLASTIC)
COBBLÉS
HYDROMËTER ANATYSIS SIEVE ANALYSIS
45 MtN. 15 MtN. 60 MrN. le MlN. 4 MlN. I MtN. '200 ',100 '50 '40 '30 *16 '10 '8 '4 sls" 314" lW 3' .5',6" 8"
1û0
90
8û
7A
60
50
40
30
2D
10
o.o02 .005 -009 .0'19 .O37 .074 .'l4S .rg o.oi*O 1.19 2.0 2.38 4.76
DIAMËTER OF PARTICLE IN M'LLIMËTERS
.___I____-t,. -._i_
z
À
tszUoÉ!
od2a
EFz
!t¡
d
60
70
80
90
100s.52 19.1 38-1
25 HR 7 HR.
0
ì0
20
30
40
50
1Ë.2 12f 2æ
152
Somple of
From
GRAVEL % SANÞ %
stlr & ciÃY---% LleutD r-rrr¡rr %
PLASIC|TY l¡¡-orx -- %
Gradation
Test ResultsPROJECT NO, GSO49O6-120 FIG.5
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't
D (MrN. 3 ¡
2
P1
SIRIP FOOTING
B+D
DD)lI .=-,B P 2=
F
B+D
SQUARË COLUMN FOCITING
E'tr¡l''r=-Eu'
FP=
2
o
t
Þ
(e+D) 2
Distriþution of
Pregsure
q
STRUCTURAL FILL
B ;
I
\_*--\
p
Project No. GSO49O6-120
Below Footings
Flg,6
NOTË;
DRAIN SHOULD BE AT LEAST 2 INCHES
BELOW BOTTOM OF FOOTING AT THT
HIGHEST POINT AND SLOPE DOWNWARD
TO A POSITIVT GRAVITY OUTLfi OR TO
A SUMP WHERE WATËR CAN BE REMOVED
BY PUMPING.
sr_oPE
BELOW GRADE WALL
PROVIDI PVC SHTilING GLUTD
TO FOUNDATION WALL TO REDUCE
MOISTURE PINT|RAÏON.
REINFORCED STEEL
PIR STRUCTURAL
DRAWINGS
SLOPE
PER
OSHA
ENCASE PIPE lN WASHED
CCINCRETE ACGREGATE (ASTM
c53, NO. s7 0R NO. 67)
EXTEND GRAVI TO AT LEASÏ
1/2 HîlGHr or FoorlNG
I\ ror*r,rr ----
ICOMPOSIrION AND \
òoupncro¡r p¡R nEponD\
COVER GRAVEL WITH
FILTER FABRIC
MINIMUM
8" MINIMUM
OR BEYOND 1:1
SLOPË FROM BCITTOM
OF FOOTING,
{wHtcHEVER lS GREATER)
EOTTOM OF EXCAVATIÖN
PVC DRAIN PIPE
NETWORK IMBEDDED
CRAI#L
I
t)
J
IN WASHED CONCRII-T
AGGRIGATE
4-INCH DIAMETER PTRFORATED
DRAJN PIPE. THE PIPE SHOULD
BT PI-ACED IN A TRENCH WiÏH A
sLoPE RANGE BETWEEN 1/8 INCH
AND 1/4 |NCH DROP PtR FOOT
OF DRAIN.
êu
.l
¡
.ç
Ê
Exterlor
Foundation
Wall Drain
SUPFORTED
$totE ro oR¡,¡N
Project No. GSO4906-1 20 Flg.7
TABLE ISUMMARY OF LABORATORY TEST RESULTSPROJECT NO. GS04906-120SOIL CLASSIFICATIONSAND. SILry iSMìGRAVEL. CLAYEY, SILTY (GC-GM)SAND, SILTY (SM)PAliT'INGNO.200SIËVE('/")33'N TESTSPËRCENTSAND(o/ot¿ôGRADATI(PERCENTGRAVEL(o/o\41:RG LIMITSPLASTICITYINOEX(%\ATTËRBLIAUIDLIMIT(%jSWELL-(d/o\-1 .4-2.4NATURALDRYDENSITY(PCF)t170NATURALMOISTURË(a/o)10.18.310.9DEPTI.I(FEET)10-l 14BORINGI t -1TP-1TP.2'Note: swell due to wetting under en applied load of 1,00o psf" Negative values ¡ndicate consôlidationPage 1 of 1