HomeMy WebLinkAboutSubsoil Study for Foundation Design 05.28.2024l(* Hffiffiiis'**'"
An Emdoycc Orncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
wwrv.kumarusa.com
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Office Locations: Denver (HQ), Parker, Colorado Spnn5, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 1, RrVER VIEW RANCH SUBDfVISTON
113 SHORE DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO.24-7-219
MAY 28,2024
PREPARAD FOR:
DEAN KARSTENSEN
3772 I\IINOOKA ROAI)
MORRIS, nLINOTS 60450
dean.karstensen@gmail.com
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY.............
PROPOSED CONSTRUCTION
SITE CONDITIONS..
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
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FOUNDATIONS
FOTINDATION AND RETAINING WALLS
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5-I.JNDERDRAIN SYSTEM
SURFACE DRAINAGE................
A LIMITATIONS..
FIGURE I - LOCATION OF EXPLORATORY BORINGS
FIGTJRE 2. LOGS OF EXPLORATORY BORINGS
FIGURE 3 . LEGEND AND NOTES
FIGURES 4,5, and 6 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1. SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. 6 Projec't No.2&7-219
PURPOSE AI\[D SCOPE OF STUDY
This report presents the results of a subsoil study .for a proposed residence to be located on Lot 1 ,
River View Ranch Subdivision, 113 Shore Drive, Garfield County, Colorado. The project site is
shown on Figure l. The purpose of the study was to develop recommendations for the
foundation design. The study was conducted in general accordance with our agreement for
geotechnical engineering services to Dean Karstensen dated March27,2024.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their classification, compressibility or
swell and other engineering characteristics. The results of the field exploration and laboratory
testing were analyzed to develop recommendations for foundation types, depths and allowable
pressures for the proposed building foundation. This report summarizes the data obtained during
this study and presents our conclusions, design recommendations and other geotechnical
engineering considerations based on the proposed construction and the subsurface conditions
encountered.
PROPOSED CONSTRUCTION
The proposed residence will be a single-story wood-frame structure over a walkout basement
level with a detached garage. Floors in the residence and garage will be slab-on-grade. The
structures will be located as shown on Figure l. Grading for the structures is assumed to be
relatively minor with cut depths up to about 12 feet. We assume relatively light foundation
loadings, typical of the proposed type of construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The building site was vacant at the time of our field exploration. The driveway access is off
Shore Drive which crosses Lot I south of the building envelope. The ground surface through
the building area is gently sloping to the north, toward the Colorado River. The lot then drops
steeply down to the shoreline trail then again down to the Colorado River. Vegetation through
the building area consists of sparse grass and weeds.
FIELD EXPLORATION
The field exploration for the project was conducted on April 24,2024. Three exploratory
borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions.
The borings were advanced with 4-inch diameter continuous flight augers powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates.
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Samples of the subsoils were taken with 1% inch and 2-inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140-pound hammer falling 30
inches. This test is similar to the standard penetration test described by ASTM Method D-I586.
The penetration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. Below
about 1 foot of topsoil the subsoils consist of stiff to very stiff,, slightly clayey, slightly sandy silt
down to depths of about 24 to 27 feet, underlain by dense silty sandy gravel and cobbles. Drilling
in the coarse granular soils with auger equipment was difficult due to the cobbles and probable
boulders and drilling refusal was encountered in all three borings in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density, and finer than sand size gradation analyses. Results of swell-consolidation
testing performed on relatively undisturbed drive samples of the silt soils, presented on Figures
4, 5, and 6, indicate low compressibility under natural low moisture content and light loading.
The samples showed relatively minor compressibility when wetted under light load and moderate
compressibility under additional loading after wetting. The laboratory testing is summarized in
Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
typically slightly moist.
FOUNDATION BEARING CONDITIONS
The silt soils have low bearing capacity and generally moderate compressibility potential under
loading. Shallow spread footings placed on the natural soils can be used for foundation support
with a risk of settlement and distress mainly if the bearing soils are wetted. A deep foundation
such as micro-piles or drilled piers could be used to achieve a low settlement risk foundation and
could be 25 feet or more in depth to reach suitable dense gravel soils. If a deep foundation is
desired, we should be contacted for additional evaluation and recommendations.
The foundation bearing level should be set back from the steep slope an adequate distance to not
adversely impact the slope stability. It appears a horizontal setback of 8 feet (edge of footing to
slope face) should be adequate provided construction activity does not disturb the slope. Surface
water from the development should not be directed to the steep slope near the residence and be
by sheet flow rather than concentrated.1
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DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature
of the proposed construction, the building can be founded with spread footings bearing on the
natural soils with a risk of settlement and distress. Precautions should be taken to prevent
wetting of the bearing soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of!J00 psl-Based on experience, we expect initial
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. Additional differential settlement of around I to 2 inches
could occur depending on the depth and extent of wetting.
2) The footings should have a minimum width of 20 inches for continuous wall and
2 feet for isolated columns.
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
atea.
4) Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 14 feet and
built in a box-like configuration. Foundation walls acting as retaining structures
should also be designed to resist lateral earth pressures as discussed in the
"Foundation and Retaining Walls" section of this report..
5) The topsoil and any loose disturbed soils should be removed in the footing
areas. The exposed soils should then be moistened and compacted.
6) A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected
to undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site soils. Cantilevered retaining structures which are separate from the residence and
can be expected to deflect sufficiently to mobilize the full active earth pressure condition should
be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight
of at least 45 pcf for backfill oonsisting of the on-site soils.
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All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffrc, construction materials and equipment.
The pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at near optimum moisture content. Backfill placed in pavement and
walkway areas should be compacted to at least 95% ofthe maximum standard Proctor density.
Care should be taken not to over-compact the backfill or use large equipment near the wall, since
this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill. Backfill should not contain organics, debris, or rocks larger
than about 6 inches.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 300 pcf. The
coefficient of friction and passive pressure values recommended abbve assume ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be compacted to at leastg5%o of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade
construction with a risk of settlement like that for footing foundations. 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 relatively well graded sand and gravel should be
placed beneath ground level slabs for support. This material should consist of minus 2-inch
aggregate with at least 50% retained on the No. 4 sieve and less than 12% passing the No. 200
sieve.
Kumar & Associates, lnc. o Project No. 24-7-219
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All fill materials for support of floor slabs should be compacted to at leastglYo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
onsite soils devoid of vegetation, topsoil and oversized rock.
LINDERDRAIN 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 runoffcan also create a perched condition. We
recommend below-grade construction, such as retaining walls and basement areas, be protected
from wetting and hydrostatic pressure buildup by an underdrain system. If a shallow crawlspace
or slab-on-grade construction is used, an underdrain should not be provided to help keep the
shallow footings dry.
If installed, the drains should consist of 4-inch diameter perforated PVC pipe 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 I foot below lowest
adjacent finish grade and sloped at a minimumllYo 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 l%feetdeep. An impervious membrane such as 20 milPVC
should be placed beneath the drain gravel in a trough shape and attached to the foundation wall
with mastic to prevent wetting of the bearing soils.
SURFACE DRAINAGE
Development of proper surface grading and drainage will be critical to keeping the bearing soils
dry and limiting building movement and distress throughout the building life. The following
drainage precautions should be observed during construction and maintained at all times after
the residence has been completed:
l) Inundation ofthe 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 95V" 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.
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 l0 feet in paved areas. Free-draining wall backfill should be
covered with filter fabric and capped with at least 2 feet of the on-site soils to
reduce surface water infiltration.
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Kumar & Associates, lnc. 6 Project No.24P7-219
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4) Roof downspouts and drains should dischmge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least
10 feet from foundation walls. Consideration should be given to use of xeriscape
to reduce the potential for wetting of soils below the building caused by irrigation.
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 borings drilled at the locations indicated on Figure 1, the proposed type of
construction and our experience in the area. Our services do not include deterrnining the
presence, prevention orpossibility ofmold or otherbiological 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 borings and variations in the subsurface
conditions may not become evident until excavation is perfonned. If conditions encountered
during construction appear different from those described in this report, we should be notified so
that re-evaluation of the recomme,ndations may be made.
This report has been pre'pared 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 veriry 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.
Respectfu lly Submitted,
Kumar & Associrtes, Inc.
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David A. Noteboom, Staff
Reviewed by:
Robert L. Duran,
DANlkac
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Kumar & Aesociates, lnc. o Project No.24-7-219
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HOUSE
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COLORADO RIVER
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'+2E.55'185.59'-75'
40'66'79.39 BLDG LOT
ENV LINE
10'
50'
PRO
EXTEND BUILDING
ENVELOPE BY 50'
2A'
42'
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0'
FoJ
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FoJ
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55'L*L 21'
L_J
SHORE DRIVE
APPROXIMATE SCALE-FEET
24-7-219 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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BORING 1 BORING 2 BORING 3
0 0
1a/ 12
18/12
WC=6.5
DD=97
3s/12
WC=5.1
DD=1 00
5
30/12
WC=9.5
DD=1 1 6
-20A=73
20/12
WC=8.1
DD=95
s/12
WC=6.5
DD=93
5
10 e/12
WC=14.4
DD=98
1o/ 12
WC=8.6
DD=98
8/
WC
12
=12.9 10
DD=95
Fl!trjL
IIFo-lrj6
15
12/ 12 8/12 10/12
15
F
Ld
LJlr
I-Fo-LIo
20 s/12
20
25 15/12 35/4, 1s/o 37/5,15/O
25
25/5, 15/A
30 50
24-7-219 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEOEND
TOPSOIh SANDY SILT WITH SCATTERED ROOTS AND ORGANICS, FIRM, SLIGHTLY MOIST, LIGHT
BROWN-TAN.
9l!,I_(r!!)i sLrcHTLy sANDy, sLlcHTLy cLAyEy, sTtFF TO HARD, DRy TO SLtcHTLy MOIST,
LIGHT BROWN TO LIGHT BROWN AND TAN.
GRAVEL (eU); COeeLV, SANDY, S|LTY, VERY DENSE, SLtcHTLy MOIST, cRAy.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRtvE SAMFLE, 1 s/8-tNcH t.D. spllr spooN STANDARD PENETRATIoN TEsr.
1n/i2 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 10 ELOWS OF A 140-POUND HAMMER'-,.- FALLING 30 INCHES WERE REQUTRED TO DRIVE THE SAMPLER 12 INCHES.
f enlcrtcaL AucER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 24, 2024 WTH A 4-INCH-DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PI-AN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF
THE EXPLORATORY BORINGS ARE PLOTTED TO DEPTH.
1. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE
DEGREE IMPLIED 8Y THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. I.ABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216)I
DD = DRY DENSTTY (pct) (mrU D2216);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM Dl14O).
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24-7-219 LEGEND AND NOTES Fis. 3Kumar & Associates
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SAMPLE OF: Slightly Sondy Gloyey Silt
FROM:Boringl@9'
WC = 14.4 %, DD = 98 pcf
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NO MOVEMENT UPON
WETTINGA0N
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=UI
t_2
zotr
(f
=-Jo
anzoQ-4
- KSF 100
24-7-219 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
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SAMPLE OF: Sllghily Sondy Cloycy Sllt
FROM:Boring3O2'
WC = 5.1 %, DD = 100 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1
0N
l-1lrl
=vl
t_2
zotr
6
=-roazoo_4
-b
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-8
t.0 APPUEO PRESSURE -
24-7-219 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
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SAMPLE OF: Sllghtly Sondy Slightly Cloyey Slli
FROM;Borlng26.4'
WC = 8.1 %, DD = 95 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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zotr
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Jotnzo(J
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-2
-5
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-6
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24-7-219 Kumar & Associates SWELL.CONSOLIDATION TEST RESULTS Fig. 5
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Geoledrnbal ard Materhlr Engineers
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
PrcJect No.2{.7-219
SAIIPL LOCAT|OIt NATUML
MOISIURE
CONIENT
t%t
NAIURAL
DRY
DEilSfi
an.A
GRAD,'noN
PERCENT
PASSIG NO.
200 srE\c
AT LIMITS
UNCOI{FINED
COMPRESSTVE
STREN6TH
Imtl
SOIL TYPEBORINGDEPTII
tfil
GRAI/EL
(%)
SAT{D
(Yol
UQUID IIMIT
t%l
Pt-ASIIC
IIIDEX
l%l
I 4 9.5 l16 73 Slightly Sandy Clayey Silt
9 14.4 98 Slightly Sandy Clayey Silt
2 2 6.3 97 Slightly Sandy Slightly
Clavev Silt
4 8.1 95 Slightly Sandy Slightly
Clavev Silt
9 8.6 98 Slightly Sandy Slightly
Clavev Silt
J 2 5.1 ,100 Slightly Sandy Clayey Silt
4 6.6 93 Slightly Sandy Clayey Silt
9 t2.9 95 Slightly Sandy Clayey Silt
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1. DRAIN PIPE - consists of 4-inch perforated pVC, sunounded
by a minimum of 4 inches of drain gravel on the top and
sides, sloped at I percent to a gravity discharge or sump pit
where the water can be removed by pumping. Bottom ol
pipe al the high point should be a minimum of 12 inches
below the top of the floor.RELATIVELY IMPERVIOUS
BACKFILL IN THE UPPER 2
FEET OR FLATWORK/
ASPHALT
2. DRAIN GRAVEL - consists of minus l|inch aggregate with
less than 50 percent passing the No. 4 sieve and less than 2
percent passing the No.
lhe entire trench and be
sieve. Drain gravel should fill
BACKFILL SURFACE
1O PERCENT MINIMUM
SLOPE FORLANDSCAPE
AREAS OR 3 PERCENT FOR
FLATWORK/ASPHALT FOR
10 FEEr
minimum of 4 inches of
of 18 inches deep. A
is recommended under
basement level concrete
drain gravel under tlu slab
perimeter or pit
by lhe in the
sump pit by the the
doumhlllside method
of a minimum 10'mil vapor
rquirements of ASTM E17'15
overlaped and sealed. Vapor
FOUNDATION in accordance with the
WALL DRAIN drain gravel and drain pipewith
or equivalent.
DAMPPROOFING 5.of Mhadrain 6000, or equilalent,
MEMBRANE - consists of 20 or B0 mil. F/C, or
attached to foundation uallwith mastic.
FILTER FABRIC
TOP OF SLAB
I
1'MINIMUMDRAIN GRAVEL
DRAIN PIPE 1 VAPOR RETARDER
1 DRAIN GRAVEL (minimum 4" depth)F/C
Class C malerial,
FILTER FABRIC
rslarder
1rtoN
t
)
NOTTO SCALE
TYPICAL DRAIN DETAIL Flg. 1