HomeMy WebLinkAboutSubsoil Study for Foundation Design 02.07.2022rcnfiffifi:ffi*#*:$:'i*."
An Employes O!trrtd Csnpony
5020 Counff Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
wwwkumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
F'OR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT E-43, ASPEN GLEN SUBDIVISION
284 WEST DIAMOND A RANCH ROAI)
GARFTELD COUNTY, COLORADO
PROJECT NO.22-7-134
FEBRUARY 7,2022
PREPARED FOR:
SMITH MOUNTAIN BUILDERS
ATTN: ZACHSMITH
2IOII HERITAGE DRIVE
CARBONDALE, COLORADO 81623
smithm o untain builderlj@gngil-Qs4
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY ..
PROPOSED CONSTRUCTION
SITE CONDITIONS.......
SUBSIDENCE POTENTIAL
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS ....................
FOLINDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
LIMITATIONS
REFERENCES ........
FIGURE 1 _ LOCATION OF EXPLORATORY BORINGS
FIGURE 2 _ LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 _ GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
APPENDIX 1 - DEVELOPMENT IN SURFACE DEPRESSION AREAS
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Kumar & Associates, lnc. @ Project No.22-7-134
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
LotE-43, Aspen Glen Subdivision,284 West Diamond A Ranch Road, Garfield County,
Colorado. The project site is shown on Figure 1. The purpose of the study was to develop
recofllmendations for the foundation design. The study was eonducted in accordance with our
agreement for geotechnical engineering services to Smith Mountain Builders dated Jawary 2I,
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 of the field exploration and laboratory testing were analyzedto
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 is assumed to be a one and two-story wood-frame structure over
crawlspace and an attached slab-on-grade garage. Grading for the structure is assumed to be
relatively minor with cut depths between about 3 to 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, with about 4 inches of snow
covering the ground. The lot fronts on West Diamond A Ranch Road, with the golf course to the
rear. The ground surface is relatively flat with a strong slope at the front up from West Diamond
A Ranch Road and a strong slope at the rear down toward the golf course. The elevation
difference across the proposed building area is estimated at about 2 feet. Vegetation consists of
grass and weeds.
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SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanianage Eagle Valley Evaporite underlies the Aspen Glen
development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and
siltstone with some massive beds of gypsum and limestone. There is a possibility that massive
gypsum 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 studies in the area, broad subsidence
areas and smaller size sinkholes were observed scattered through the Aspen Glen development,
predominantly on the east side of the Roaring Fork River (Chen-Northern, Inc., 1993). LotE-43
is mapped as being in the southeastern portion of a broad depression. Two sinkholes were
mapped in the general area of Lot E-43, one about 900 feet to the east, and one about 700 feet to
the south. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in
areas of the lower Roaring Fork River valley.
No evidence of cavities was encountered in the subsurface materials during our field exploration;
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 E-43 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. If further investigation of possible cavities in
the bedrock below the site is desired, we should be contacted. We have, in the attached
appendix, the Chen-Northern recommendations for building in a broad surface depression area.
We believe these recommendations are conservative but will reduce structural distress in the
event of future ground movement and should be considered in the design.
FIELD EXPLORATION
The field exploration for the project was conducted on January 24,2022. Two 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-45B drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Samples of the subsoils were taken with a ltA-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-1586. The
penetration resistance values are an indication of the relative density or consistency of the
Kumar & Associates, lnc. @ Project No.22-7-134
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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. The
subsoils encountered in Boring 1, below about Yzfoot of topsoil, consist of relatively dense, silty
sandy gravel with cobbles and probable boulders down to the drilled depths of 8% feet. In
Boring 2, below about Yzfootof topsoil, about 2%feet of relatively dense, silty sandy gravel
with cobbles and probable boulders was encountered, which was underlain by medium dense,
slightly clayey sand and silt down to a depth of about 5Yz feet, where relatively dense, silty sandy
gravel with cobbles and probable boulders was encountered, down to the explored depth of
l l feet. Drilling in the coarse granular soils was difficult due to the cobbles and boulders and
practical auger drilling refusal was encountered in both borings 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%-inc,h fraction) of the coarse granular subsoils are shown on Figure 4. The
laboratory testing is summarizedinTable 1.
No free water was encountered in the boring atthe time of drilling and the subsoils were slightly
moist.
FOUNDATION BEARING CONDITIONS
The natural sandy gravel and cobble soils possess moderate bearing capacity and typically low
settlement potential. Spread footing bearing on the granular soils below the topsoil and sand and
silt soils should be suitable for support of the proposed residence with a low risk of settlement.
DESIGN RECOMMENDATIONS
FOI.INDATIONS
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.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 3,000 psf. Based on experience, we expect
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3)
settlement of footings designed and constructed as discussed in this section will
be about I inch or less.
The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
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
4)
atea.
Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 12 feet.
Foundation walls acting as retaining structures should also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section ofthis report.
The topsoil, sand and silt soil, and any loose or disturbed soils should be removed
and the footing bearing level extended down to the natural granular soils. The
exposed soils in footing area should then be moistened and compacted.
A representative of the 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 arelaterally 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 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 40 pcf for backfill consisting of the on-site granular soils. Backfill
should not contain organics or rock larger than 6 inches.
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 ahorizontal
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.
2)
s)
6)
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Backfill should be placed in uniform lifts and compacted to at least 90Yo of the maximum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at least 95%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 wall
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 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 0.50 for the gravel soils. Passive pressure of compacted
backfill against the sides of the footings can be calculated using an equivalent fluid unit weight
of 450 pcf. The coefficient of friction and passive pressure values recommended above 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 a granular material
compacted to at least 95Yo of the maximum standard Proctor density at a moisture content near
optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction with a possible risk of movement due to the upper sand and silt soils. 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 base course should be placed beneath the
garage slab for support. This material should consist of minus 2-inch aggregate with at least
50o/o retained on the No. 4 sieve and less than I2oh passing the No. 200 sieve.
All fil1materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
onsite granular soils devoid of vegetation, topsoil, and oversized rock.
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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
rscommend 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 lo/o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yo passing the No. 200 sieve, less than 50olo passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least llz 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 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 95o/o of the maximum standard Proctor density in pavement and slab areas
and to at least 90%o 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 6 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 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.
5) Landscaping which requires regular heavy inigation should be located at least
5 feet from foundation walls.
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.
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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 determining the
presence, prevention or possibility of mold or other biological contaminants (MOBC) developing
in the future. If the client is concemed about MOBC, then a professional in this special field of
practice should be consuited. 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-evaluation of theiecommendations may be made.
This report has been prepared for the exclusive use by our client for design pu{poses. 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 veriff that the recommendations
have been appropriately interpreted. Significant design changes may require additional anaiysis
or modifications to the recommendations presented herein. We recommend on-site observation
of excavations and foundation bearing strata and testing of structural fili by a representative of
the geotechnical engineer.
Respectfully Submitted,
.Kpxamar &. ,Asse*3a€esu En*,
-k-j g *
\ & %_fu*-*
David A. Noteboom, Staff Engineer
Reviewed by:
Daniei E.
DEH/kac
W:ur*wr & A*seeiat*s, lne" 6 ?r*ie#,t*a.22"7-134
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REFERENCES
Chen-Northern, Inc., 1991, Preliminary Geotechnical Engineering Study, Proposed Aspen Glen
Development, Garfield County, Colorado, prepared for Aspen Glen Company, dated
December 20,199I, Job No. 4 lL2 92
Chen-Northern, Inc., 1993, Geotechnical Engineering Studyfor Preliminary Plat Design, Aspen
Glen Development, Garfield County, Colorado, prepared for Aspen Glen Company, dated
May 28,1993, Job No. 411292
Kumar & Associates, lnc, @ Project No.22-7-134
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APPROXIMATE SCALE-FEET
22-7 -134 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
s
t
BORING 1
EL. 6051'
BORING 2
EL. 5053'
0 0
34/6, 5O/5 COMBINED
5 5
FtrlIJl!
IrF(L
lrjo
37/5, 47/6 14/6,50/6 FIJ
lJJtL
I-FL
trJo
10 1050/4
15 15
WC=1.4
+4=47
-2OO=1 4
Fig. 2Kumar & Associates LOGS OF EXPLORATORY BORINGS22-7-134
.*
LEGEND
TOPSOIL; SILTY SANDY CLAY WITH ORGANICS, FIRM, MOIST, RED.
SAND AND S|LT (SM-ML); SLIGHTLY CLAYEY, MEDIUM DENSE, SLIGHTLY MOIST, BROWN.
w
w
GRAVEL (GM); SANDY TO VERY SANDY, COBBLY WITH PROBABLE SMALL BOULDERS, SILTY
VERY DENSE, SLIGHTLY MOIST, BROWN, PALE TAN, AND GRAY.
I DRTVE SAMPLE, 1 s/g-INCH l.D. SPLIT SPOON STANDARD PENETRATIoN TEST.
Z,l ZC DRIVE SAMPLE BLOW COUNT. INDICATES THAT 34 BLOWS OF A 14o_POUND HAMMER"-/ " FITIING 30 INcHES WERE REQUIRED TO DRIVE THE SAMPLER 6 INCHES.
I enacrtcAL DRTLLTNG REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 24, 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.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING LOCATIONS 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);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140).
22-7-134 Kumar & Associates LEGEND AND NOTES Fig. 5
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70
60
30
10
30
20
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20
30
10
50
60
76
60
s0
too
=tr,
ETER OF IN RS
CLAY TO SILT COBBLES
GRAVEL 47 % SAND
LIQUID LIMIT
SAMPLE OF: Silty Very Sondy Grovel
39%
PLASTICITY INDEX
SILT AND CLAY 14 %
FROM; Boring 1 O 2.5' & 5' (Comblned)
Th.tc lcsl rcrulls opply only lo lhc
somples whlch w€re l6El.d. Tho
loBllng roporl Eholl nol b! r.prcduccd,
.xc.pl ln full, wllhoul lhc wrllhn
opprcvol of Kumor & AsroclolcE, lnc.
Sl!y. onolysl3 l!3ilng ls prrtomld ln
occordoncc vlth ASTM 06913. ASTM D7928,
ASTM C156 ond/or ASTM Dll/rc.
SIEVE ANALYSISHYDROMETER ANALYSIS
u.s. STaNDARD sERrEs
I
cLE R SQUARE oPENTNGS
ItvlNaiZ' HRS 7 HRSli vtN t3 ultr
TIUE RilDINGS
60utN teultr aulN
GRAVELSAND
COARSEFINEMEDIUMCOARSEFINE
22-7 -134 Kumar & Associates GRADATION TTST RESULTS Fig. 4
K+n l(umar & Assoclates, lnc"@
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SOIL TYPE
Silty Very Sandy Gravel
(psfl
UNCONFINED
COMPRESSIVE
STRENGTH
(%l
PLASTIC
INDEX
ATTERBERG LIMITS
(%l
LIQUID LIMIT
PERCENT
PASSING NO.
200 stEvE
t4
SAND
$l
39
GRADATION
vt
GRAVEL
47
NATURAL
DRY
DENSITY
(ocfllol
NATURAL
MOISTURE
CONTENT
4I
(ft)
DEPTH
2% and 5
combined
SAMPLE LOCATION
BORING
1
No.22-7-134
APPENNIX 1
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Fire"*tical due t<l rhe depth of the sinkholes. The grcutilg procedure should help reduce rhe
sef*ement risk but not totally eiiminate it. Theref*tre, ws believe tha{ avciding fire sinkhales by
building setback is th* iower risk and the more appropriare approach that should be taken.
: Based cn our fi-nciings, development within the
ground surface depressi*n areas {shown *r: Fig. l) sh*uld be fsasible provided appropriat*
miiigative d*signs are implemented for the residentiat buitrdings, uliiities and rcadways as
described beiow. Thc appropriate level of the nritigative designs clepend on th* p*tential ground
def*rmaticn, tl:e buitding type, lacation and eonfiguration and level of tolerable maii:ienance
{mainly for raadways and utitities}. Bnitding design considerations include use of a relatively
rigid f*undation' {sueh as a stiffened slab or raft) and a simpiy shaped buitdir:g focrpri*t ro
reduce potential damage in the event of diff*rential movement. These design concepts woutrd
be included in the engineered foundations f*r residences located in tire depression areas,
Utilities sh*uld be designed and constructed to be reiatively ftexible and allcw for differentiai
movement witheiut rupturing" where possible, settlement sensitive main utility lines sftould be
routed cutside of th* ground surlace depr*ssion area$. Raaelways can be ccnve*tionally desigr:rrt
and constructed with prcvisi*ns for maintenance if subsidence r*iated clistress is experienced.
Ther* are several gectech*ical design concepts which ean be used to mitigate potenlial
subsidence darnage to rssidenlial buildings and undergrouns.! urilities. Speciat mirigative designs
for a specifie lot sh*uld be developed by the owner's archirect and structurai e::gineer a::d shouid
be basecl on the type of buiiding propcseel and the site specific foundati*n c*nditions. Tt-:*
follcwing design c*ncepts are presentcd to assist in evalualing eiesig* apti*ns prior to site
Consurl'nn pnn,',""rs and Screntrsts
Chen €Ncrthern,lne.
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sp*cifi* investigations for an individual building site- The concept for underground utilities
shculd be inearp*rated into tle utility d*sign by the develcper"
Buitding Configurations: The exlcnt cf damage ta a building subjected to the surface effects of
subsidence may b+ reduced by implementing several archirccfural rneasures in the building
design. These measures w*uld include the f,ollawing:
* Relatively flexible strucfural systen:s such as wo*d frame e*nstruction, flexibie
ext*rj*r siciing, anci riry wall interior partiti**s are preferable to less fiexible
masonry strr}ctural systsm afid *xferiar sidings.
* Interior non-bearing partitic*s resting on the floor slab shculd be provided with
slip joints ss that slab mcvements are not tra*smitted to the upper strueture.
* The building sho*ld b* a l*w strucfure preferably limited to one *r fw* sicries.
* The building should have relatively smaii plan dimensions *f S* feet or less. Ef
this is not practic*3 ti:en the building should be divided into independent madules"
* The buitding configuratian should b* a simple rectangular e*nfiguraticn wjth
straight foundaticn walls and a minimum cf sirfe pr*jeerions from the main
building.
* The gr*und f3o*r sh*uld be on a single level rather than using a split levei design.
* *asements are parti*ulariy susceptible t* subsider':ee damage and ar* not
recomm*nded unless the entire foundation is at basement levei and designe.d for
lateral earth loading.
Chen€Northern,lnc.Consult,ng Enerr)eer s zinC Scrcntrsrai
3u I' Lr_r3r{}ffii.{ €} ri ei{:}
"t 3lg uo rr/Ror.ls ses-re uorssardep erruJns puno.l8 aql ur plie:o1 are sor]{r}n
puno:8"topun €Jaq/n pasn aq plnol{s saJnscatu uoqesilnu *q} uorurdo Jno uJ '*?eiuep -r*-; prlualod
?ql alnp*J 03 pasn 3q u?3 l.l3lqA\ slderuor u8lsap anrle3$ru1 fsJa^as €-ru eraql ffioleq po$lltns sV
'aeuaprsqns BarE Jo sS3JJJs €r{} 01 alqqdaxns e-re soi?rpln punorf,:opug :seq;Tnn punor8-rapug
'uc$reio:d 3so$ roJ peprno-rd aq pincqs raAo? Iros
tusrsljiJns ro qidap 1so4 rAoleq pereld sq plnoqs tJm *i{t JCI uoqE.{alo Suueoq aqJ, *
"silos ils8spunoj 3{.i? q3rrr4 lseluos ur s338jiJns lerrl-r3A
ne uo 13e fl paurnsse aq plnoqs fiq81em ?run prnlJ 1u*grn:nba lrd OOt ol 0g Jo
Jap-:s aqi uo) a:nssa.td quea ,,1$aJ le,r or.Il asri*l lseal le o1 pnba o:nssa.rd Fos eq;,
';ucuru.ld lualx€ 3E; *3 pa?Hr:ru{i$ 3q pln*qs clFns uor}spunoJ daap 3o *sn eqtr, ,(
'"radu1 pues aq? p're !5ff srlt uae*\jaq p*teJd
€q plniiq$ paqs aueJf{F,{1od g 'pilus ue.elr ,pelruduor {xrry} qourr? rrntun-rrur
e uo iler eql 8ur*e1d {q spos €u$eaq cql ffolJ pat*edas aq pl{lstis $sr aqJ *
"sucrlrelo:d lg*€.tea Js aaiJ pus q}*oriis eq pinoris giuj ew Jfi sseJrns iloitoq ciiJ {<
'suoqrpusi Srue-aq ircs cgrods €iis eql oi f;urp-ic,*re
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Flexible joints should be used between adjacent pipe segments for both gravity
and pressure lines.
Positive restraints should be provided in pressure lines to prevent pipe separation.
A flexible joint should be provided as close as practieal to any building, manhoie,
or olher rigid structural connection.
A soil cushion in the immediate viciniry of the pipe should be provided by nol
over-compacling the backfill soils close to the pipe-
Check valves shculd be placed at appropriate locations on all gas and water mains
to permit intem.rption of flow in case of subsidence distress-
DEBRIS FLOW RISK AND MITIGATION
Hazard E_valuation: This study shows that the alluvial and debris fans along the western side
of the development are potential sites of water flooding and debris flows. The area evaluated
is shown on the attached Fig 1A. A summary of the basins and fans evaluated is presented on
the attached Table II. The calculated flow depths and volumes are based on hydrological data
provided by Schmueser Gordon Meyer, Inc-
potential waler floods, with high sediment concentralicns, should be considered for all
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 (see Fig. lA).
Based on numericai debris flow modeling, we have designated three potential hazard
Chen€Nonhern,lnc.Consutr,no !-ng,neers anci Screnl,sts