HomeMy WebLinkAboutSubsoils Report for Foundation DesignlGn [ffifi:,{Tl:ffinn:'i*"'
An Employcc Orncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (FIQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT F-10, ASPEN GLEN
RIVERPARK LANE
GARFTELD COUNTY, COLORADO
PROJECT NO.22-7-472
NOVEMBEIK-9,2022
PREPARED FOR:
STANLEY BARTLOMINC JZUK
cio JORDAN ARCHITECTURE
ATTN: BRAD JORDAN
4IO 2ffII STREET
GLENWOOD SPRINGS, COLORADO 81601
brad i ordanarch itect@sm ail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
SUBSIDENCE POTENTIAL
FIELD EXPLORATION
SUBSURFACE CONDITIONS
DESIGN RECOMMENDATIONS .
FOUNDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
IJNDERDRAIN SYSTEM
SURFACE DRAINAGE
LIMITATIONS
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - GRADATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESUL'I'S
APPENDIX _ DEVELOPMENT IN SURFACE DEPRESSION AREAS
1
I
-3-
n
.|
-L-
-3-
-4-
-5-
-5-
-6-
-6-
Kumar & Assoclates, lnc. o Project No.22-7.&2
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot F-10, Aspen Glen, River Park Lane, Garfield County, Colorado. The project site is shown
on Figure 1. The purpose of the study was to develop recommendations for the foundation
design. The study was conducted in accordance with our agreement for geotechnical engineering
services to Stanley Bartlomiecjzuk dated June 29,2022.
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 and other engineering
characteristics. The results ofthe 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
Plans for the proposed residence were conceptual at the time of our study. The proposed
residence is assumed to be a two-story wood-frame structure with a walkout lower level and
attached garage. Ground floor could be slab-on-grade or structural over crawlspace. Grading for
the structure is assumed to be relatively minor with cut depths between about 2to 6 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 subject site was vacant at the time of our field exploration. The ground surface was
moderately to gently sloping down to the southwest with around 6 feet of elevation difference
across the assumed building area. Vegetation consists of grass and weeds. Minor overlot
grading likely occurred during subdivision development. A drainage ditch was flowing near the
northeast lot line.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen Subdivision
These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some
Kumar & Associates, lnc. o Project No.22-7-472
-2-
massive beds of gypsum and limestone. There is a possihility that massive gypsrrm deposits
associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the
gypsum under certain conditions can cause sinkholes to develop and can produce areas of
localized subsidence. During previous work in the area, several sinkholes were obscrvcd
scattcrcd throughout the Aspen Glen Development. The nearest sinkhole was mapped
approximately 700 feet to the north of the subject site. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas ofthe Eagle Valley. The site is identified as
being within and near the northeast perimeter of a broad subsidence surface depression area.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory borings were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on Lot Fl0 throughout the service life of the proposed residence, in our
opinion, is low; however, the owner should be made aware of the potential for sinkhole
development. Recommendations for development in surlbce depression areas are attached as an
Appendix to this report. If further investigation of possible cavities in the bedrock below the site
is desired, we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on July 5, 2022. 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,Inc.
Samples of the subsoils were taken with a l%-inch I.D. spoon sampler. The sampler was 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-l586. 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
siiown on ihe Logs of Expioratory Borings, Figure 2. The sampies were returneci to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Craphic logs of the subsurface coudiLiuls cnuuulleretl at the site are shown on Figure 2. The
subsoils consist of about t/2to I foot of topsoil overlying dense, sandy gravel with cobbles and
Kumar & Associates, lnc. @ Project No.22-7.472
-J-
probably boulders. A one-foot-thick layer of medium stiff, sandy clay was encountered below
the topsoil in Boring l. Drilling in the dense gtanular soils with auger equipment was difficult
due to the cobbles and boulders and drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of gradation analyses performed on small diameter drive
samples (minus l%-inch fraction) ofthe coarse granular subsoils are shown on Figure 4. The
laboratory testing is summarizedin Table l.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
DESIGN RECOMMENDATIONS
FOTINDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural granular soils below the topsoil and clay soil.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 2,500 psf. Based on experience, we expect
settlement of footings designed u t ucted as discussed in this section will
be about I inch or less.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
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
area.
4) Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 12feet.
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.
Kumar & Associates, lnc. @ Project No.22-7472
-4-
The topsoil, clay soil and any loose or disturbed soils should be removed and the
footing bearing level extended down to the relatively dense natural granular soils.
The exposed soils in footing area should then be moistened and compacted.
A rcpresentative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
F'OUNDA'I'ION 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 45 pcf for backfill consisting
of the on-site granular soils. Cantilevered retuining structurcs whioh are separate from the
residence and can be expectcd to deflect sufficiently to mobilize the full active eafth pressure
condition should be designed for a lateral earth pressure computed on the basis of an equivalent
fluid unit weight of at least 35 pcf for backfill consisting of the on-site granular soils. Backfill
should not contain organics, debris or rock larger than about 6 inchcs.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, 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%o of themaximum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at least 95o/o of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or use large equipment near the wall, since
this could cause excessive lateral pressure on the wall. Some settlement of deep foundation r,vall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill.
The lateral resistance of foundation or retaining w-all footings wiii 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 0.50. Passive pressure of compacted backfill against the
sides of thc footings can bc calculated using an equivalclt {Iuitl unit weight of 400 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
5)
6)
Kumar & Associates, lnc. o Project No. 22-7-472
5
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 a granular material compacted to at least
95% of the maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive oftopsoil, 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 free-
draining gravel should be placed beneath basement level slabs to facilitate drainage. This
material should consist of minus 2-inch aggregate with at least 5004 retained on the No. 4 sieve
and less than29io passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least9lo/o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
on-site granular soils devoid of vegetation, topsoil and oversized rock.
IJNDERDRAIN 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 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 lYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yopassingthe 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%feet deep and covered
with filter fabric such as Mirafi 140N or 160N.
Kumar & Associates, Inc. @ Prcject No.22-7472
-6-
SURFACE DRAINAGE
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 95a/o of the maximum standard Proctor density in pavement and slab areas
and to at least 90% ofthe 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 6 inches in the first l0 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 about 2 feet of the on-site finer graded
soils to reduce surface water infiltration.
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 arcaatthis time. We make no warranq/ either express or implied.
The conclusions and recommendations submitted in this report are based upon the data obtained
from the cxploratory 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 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 borings 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 so
that re-evaiuation of the recommenciations 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 construction to review and
monitor the implementation of our recommendations, and to verifu that the recommendations
Kumar & Associates, lnc, @ Project No.22-7.472
-7 -
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 foundationbearing strata and testing of structural fill by a representative of
the geotectrnical engineer.
Respectfully Submitted,
Kumar & A
James H.
Reviewed by:
ffi*/.
Steven L. Pawlak, P.E.
JHPlkac
Kumar & Associates, lnc. o Proiect No, 22-7-472
lftj-3tvJS SrVf{tXOUddv
I L
I
l
l
e.acoe aoq
N,PIHY
il
:l\t
I
TB
q^
?
CJI
I
I
7.-c
\Af.
/ /[ /07 I
\
I
I\
\
\
)
A'--
I
\
9' ..6
b$e
{L\
\
Ji'
\
\
\
\
\
$$
Xl c\ruoaoe
(
I
I
I
I
\
'\ti'
.up'{*t
t oNtuo8
o
,y'::,,
\g* '\r",8t9',O
V/
\
\
\
I
\er
\7
\
I
I
/07\
\\\\
cNtuoS
.62
)n
t
ot
t
6[ /o7
zLn- L-27,solercossv g JeunyscNluo8 uorvuotdxl J0 N0[v301t'6u
BORING 1
EL. 6053.5'
BORING 2
EL. 6055.5'
BOR
EL.
ING
605
3
8'
0 0
12/6, so/s
WC=3.1
+4=45
-2O0=17
8s/12
WC=1.4
+4=47
-2OO=1 4
s1/12
5 542/6, 5o/3 43/6, 50/5 44/12
F
Lrl
LrJt!
IIF(L
LJo
10 10
F
Lrj
LJt!
IIF(L
tJo
46/12
15 15
20 20
Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 222-7-472
E
*
I
E
LEGEND
N
TOPSOIL; SAND, CLAYEY, SILTY, GRAVELLY, ORGANIC, FIRM, SLIGHTLY MOIST, BROWN
CLAY (CL); SANDY TO VERY SANDY, SILTY, STIFF, SLIGHTLY MOIST, TAN.
w
GRAVEL (GM) VERY SANDY TO SANDY, COBBLES, SILTY" PROBABLE BOULDERS, DENSE,
SLIGHTLY MOIST, MIXED TAN TO BEIGE.
I DRTVE SAMPLE, 1 3/8-INCH t.D. SpLtT SPOON STANDARD PENETRATTON TEST
1276 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 12 BLOWS OF A l4O-POUND HAMMER.., " FALLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 6 INCHES.
I enlcrrcaL AUcER REFUSAL
NOTES
1 THE EXPLORATORY BORINGS WERE DRILLED ON JULY 5, 2022 WITH 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 PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING 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 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. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
-2OQ= PERCENTAGE PASSING NO. 200 STEVE (ASTM Dl140).
22-7-472 Kumar & Associates LEGEND AND NOTES Fig. 3
€
I
5t
HYDROMETER ANALYSIS SIEVE ANALYSIS
IIME READIf,GS
24 HR:i 7 HRS
ta
U.S. $NDARD SERIES CUffi SOUARE PENINGS
/
/
/
I
l I
I
26
too
90
ao
70
60
50
40
50
20
10
o
o
to
20
30
40
60
50
70
ao
90
tm
a
p
50 1.t I 2.36 s.t 127.a2s 2.oOF PARTICLES IN MILLIMETERS
!52
CLAY TO SILT COBBLES
GRAVEL 15 % SAND
LIQUID LIMII
SAMPLE OF: Silly Very Sondy Grovel
58z
PLASTICITY INDEX
SILT AND CLAY 17 %
FROM:BorlnglO2.5'
ai
l@
90
ao
70
60
50
,io
50
20
to
o
o
10
20
50
4
50
30
70
m
90
100
-
-oo2 .o37 .o75 -t50 -600 t-1
DIAMETER OF INM
CLAY TO SILT COBBLES
GRAVEL 17 '6 SAND
LIQUID LIMIT
SAMPLE OF: Silly Very Sondy Grovel
39%
PLASTICITY INDEX
SILT AND CLAY 14 %
FROM: Borlng 2O2.5'
Thcc lcal resulls opply only lo lhe
sqmpls whlch r€re lo8lod. The
l€llng rcporl sholl nol be rsproducod,
oxc.pl ln full, wilhoul lhe *rlll€nqpprcvol of Kumor & Arsocioloa, lns.
Slov€ onolysk l€illng ls pgrtormsd ln
occordonc! with ASTM 05913, ASTM D7928,
ASIII C|JS qndlor ASIM 011,t0.
SAND GRAVEL
FINE MEDTUM lCOrnSr FINE COARSE
HYDROMETER ANALYSIS SIEVE ANALYSIS
TITE READIXCS
2a HRS 7 XF
U.S. SADARO SERIES CHR SQUffi€ OPENINGS
t/A. 111, 7 tfr'
/
/
/
I
I
I
I
/I
I.
I
I
I
1
I
,1,
SAND GRAVEL
FINE MEDIUM COARSE FINE COARSE
22-7 -472 Kumar & Associates GRADATION TEST RESULTS Fig. 4
rcnHffififfiffinriyi*"'
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SOIL TYPE
Silty Very Sandy Gravel
Silty Very Sandy Gravel
losfl
UNCONFINED
COMPRESSIVE
STRENGTH
PLASTIC
IilDEX
(ohl
ATTERBERG TIMITS
lolol
LIQUID LIMIT
PERCENT
PASSING NO,
200 slEvE
71
t4
SAND
P/"1
38
39
GRADATION
tf/"|
GRAVEL
45
47
(ocfl
NATURAL
DRY
DENSITY
lolol
NATURAL
MOISTURE
CON'IENT
t,.4
(ft)
DEPTH
3,72%
2%
SAMPLE LOCATION
BORING
1
2
No.22-7-472
I
practical due to the depth of the sintholes. The gmuting proedure should hclp reduce thc
settlement risk but not totally eliminae iL Therefore, we believe tlrat avoiding ttre sint*rolcs by
building setbac,k is the lowcr risk and the more appropriate approach that should bc heen.
Developmcnt in Surfre DeFpqsion Arcas: Bascd on our fudiogs, dwdqpment witlin tlre
ground surface depression areas (shown on Fig. l) strould be ftasible pmvided apptogiab
mitigative designs are implemented for the rcsidential buildings, utilities and roaduays as
describ€d below, The appropriate lerrd of the mitigative desigrs d4ard on tlre poential ground
ddormation, the building type, location ud configuration and levcl of tolcrable maintcnane
(rnainly for roadurays and utilitics). Building dedgn considerations include rse of a rctatirnly
rigid foundafon, (such as a stifiFned slab or raft) and a sinply str@ building fmtprint to
reducc potential damage in ttre evcnt of diffcrential movement. thesc dcsign concepts would
be included in the cnginescd foundations for residenccs locaEd in Se dcpression arcas.
Utilitics strould b dcsigned and constntcted to be rclativdy flcxible and allow for diffcrelrtial
movernent without rupturing. Wherc posible, settlement sensitive main utility lincs should be
routcd outside of the gtound surface depression areas. Roaduays can bcconventionally designed
and construced witlt pmvisions for maintenance if subsidence relaled disness is experienccd.
There are several geotechnical design concepts whidt can be uscd to mitigate potential
subsidencc damage o residential buildings and undelground utilities. Special mitigative designs
for a specific lot strould be develo@ by the owneds architect and stnrchrral engineer urd should
be based on the tpe of building proposgd and the site gpccific foundation conditions. Thc
following design concepts uc prcscnrcd to assist in evaluating design options prior to sig
Chen€Nortlrern,lnc Cmalp€rgn 6lefitsci;1166
9
qpecific invcstigations for u individual building siE. Thc conccpt fon undergrcund utilities
should be incorporaEd into the utility design by the developer.
Building Configurations: the extent of damage to a building subjectcd to the surface effecg of
subsidence may be reduced by implernenting scveral architecrrnal measurEs in the buitding
design. fitese m.irures would includs the following:
* Relatively flexible struchral systcms such as wood frame construction, flexiblc
exterior siding, and dry wall interior partitions are pre,ferable to less flexiblc
na,$nry strncilral systcm and extcrior sidings.
* Interior non-bearing. partitions resting on the floor slab should bo provided witlr
slip joints so that slab movements arc not transmitred to the upper strucfi5e.
* The building should be a low struchre preferably limit€d to one or two sbries.
* The building should have relatively small plan dimensions of 60 feet or less. If
this is not practical then the building should bc divided into indepcndent modules.
* The building configuration should be a simple rectangular configuration with
straight foundation walls and a minimum of side projections from the main
building.
* The ground floor should be on a single level rather than using a split level design.
* Bascments are particularly susceptible to subsidence damage and arc not
- ^^*---,1-,l ..-l--- rlra xri.A €a..-l-l!^- :- ^. L^-^---. t---^r -- t ) r . .'rLt rllllllgllrlrrt ulllgito ul(, elll.Iv rvslllJ4ll(,ll rat d,l U6;tElll9lll ltvEl ifnu qc$gn€g IOf
lateral earth loading.
Chen€Nortlrern,lnc Corulrng €ngmcro rg Scatnr
*
ll
Elexible joina should be used between adjacent pipe segments for both gravity
and pressure lines.
Positive restnints should be providcd in pressure lines to prevent pipe separation.
A flexiblc joint should be providcd as close as practical to any building, manhole,
or other rigid sUuctural connection.
A soil cu$ion in the immediatc vicinity of the pipe should bc provided by not
over-compacting the bacldll soils close !o the pipe.
Check valves should bc placcd at appopriale locations on dl gas and water mains
to permit intemrption of flow in case of subsidence disupss.
tf
*
rf
DEBRIS FLOW RISK AND MITIGATTON
Hazard Evatpatiqn: This study shows that the alluvial and debris fans along the western side
of the development are potential sitcs of water flooding and debris flows. The area eraluatcd
is shown on the attachcd Fig lA. A summary of the basins urd fans evaluated is presented on
rhe attached Table II. Thc calculatcd flow depths and volumes are barcd on hydrological data
provided by Schmueser Gordon Meyer, Inc.
Potential water floods, with high sediment concentrations, should be considerd for dl
of the basins upslope of the fans. Appropriate surface water hydrologic methods should be used
to evaluate the flood hazards on all fans. Fans I and 2 in the southern Part of the area are not
subject to debris flows, but debris flows should be considered on Fans 3 through 25 and the area
to the north (sec Fig. lA).
Based on nurnerical debris flow modeling, we have designated three pobntial hazard
Chen€Norttrern,Inc Corsrlne Enryrrr3 and Schnts