HomeMy WebLinkAboutEisenbeis Block 160, 165, 166 - Geotechnical Report - 2005.02.24ffi )
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GEOTECHNICAL REPORT
San Juan e"pti5%f,urch Addition
- lzolDis"oveffiitfl|it
"*nsend, wASection 10, Township go No.tn, R;ft;1 West, W.MJefferson County, Wasniijton
san ,":;8ffi,?Jilnu."r,,
Nn Engine"lruH:t ?ld surveying717 S. peabody Streetport Angeles, Washington gAgOZphone 360_4s2_8491 r"i ioo+s 2_8498Web Site www.nti4u.com
E_mail info@nti4u.com
February 24,2OOs
l8
NORTHWESTERN TERRITORIES, INC.A JLS GROUP COMPANi' '
71 7 SOUTH PEABODY STREET, PORT ANGELES, WA 9S362t7 Engineors a Land Surueyors n Goologats
(360) 452-849r FAX 452-8498 www.nti4u.corn E-Mait: inlo@nti4u.conr
NTI
JLS GROUP.tNc.
1.0 lntroduction
2.0 Site Description
Geotechnical Report for san Juan Baptist church Addition
During February
"f^3-0-o-5r
NTl.Engineering and Land surveying (NTr) conducted a geotechnicartnvestigation for a proposed class"room aodition to tne san Juan Baptist church rocated at 1704Discovery Rd in Port ro*n."no, wu"rnington. The inu"-rt,:gution included research of availablegeotogic data for the area and a.ro.rrrJ"I.i"rijiii,in'""tygution. The purpose of theinvestigation was to verify soir
"onoitL].,, at tne olitoing [.utions and provide geotechnicar soirparameters to assist in the design of ne project. .'v .--
It is our understanding that plans include the construction of a 5,5001 s.F. footprint high baysingle storv buildinq witn p"itiui *"ri""ine. The f;r;;;;;; wir be conventionat spread andS:.fi::XH;l[: gmn::**Anm;fi;;##,?:1il was carried out at *e request or
The subject property is^bounded on the north by 2oth street, on the.south by Discovery Road, onthe east bv Mccreilan street ;il ;; il; ;;;i;i
"-;".i"iJ;;;iar neishborhood. Existingimprovements to the property include ttre sanctuary];lu,;"r buirdings, out buirdings andffi*ar''tsing areas' Tnb pt6pettvis roughrv nat airo-reveiano vegetated in grass, shrubs and
3.0 Regional/Site Geotogy;, r.slisht to moderate' r|"-.s-;,,*i, i"iJ!"tninn" r"ir ii 3i"tiLt"o p"rt ot i["iiile ouring the rainy;?XTiL:11fii'T?'"[,fl':iiil:Jj',J3f'urrv, in pri."i,"Jolu*tn"::Tgrted rayer
're-soir
su^iey ,.,
The washinqton Department of Ecology, "9g.o-lg^gic Map of Eastern Jefferson county,, mapsthe soil at th6 subied"r;rffi;;";;';;:!i"f,f.[1,3; 1it?iF.:J]!'ll,"S#l:jJ[q;5:T"%3:1,*ilJH"?,.* i?.:,.Bx# "J3l"i?R'a'y,^7*[,,fui*'ni{i*#$rns::l,Tjt"J,[":".""""?,8,i,:,flli3l]i;Jl]?
stability and good for,seismic it"oiritv lno .tut"ri[uiiii. i"irstands-in steep naturar and cutslopes for long periods' eot "o-tiuiiiJn prrposes, the veriicar bluffs in downtown port,i?gio'b"L[fl':3fl,,Yf:"J,ig?"J"*SiH,t,.i;#.::$lH', ,uo" rnrormation-rrom the test pit
1
Reviews of 6 water well reports in the vicinity of the subject property were also conducted as
part of this investigation. Static water levels in three of the wells ranged from 30'to 43', and from
190' to 298' in the other three wells. Based upon this information, we conclude that the
groundwater table is well below the footing elevation. However, it is possible that seasonal
perched water may be present above the till layer during the wet season, as was encountered in
TP-1.
4.0 Site lnvestigation
On February 9, 2005, Bill Payton, Engineering Geologist with NTI conducted the test pit
investigation. Seton Construction was the excavation contractor.
Two test pits were excavated at the approximate locations shown on Figure 1. The test pits
were advanced to a maximum depth of 10 feet using a John Deere 410C Turbo rubber tired
backhoe. The soils were visually classified and individual soil logs were constructed (See
Appendix). Upon completion of the test pit investigation, the test pits were backfilled with the
excavated material but were not compacted. The test pits remained open during the
investigation. A small amount of groundwater was seeping out of the side of TP-1 at about 2.5'
during the excavation.
Below a surface covering of grass, the upper -1' to 1.5' is organic topsoil. Below this layer and
down lo -2.5'in TP-1, and 5' inTP-2, the soil is loose to medium dense brown silty sand (SM)
with gravel and occasional cobbles. Groundwater was seeping out of the side of TP-1 at about
2.5'. Below this second layer, the soilwas gray, dense to very dense silty sand/silty gravel till to
the limits of exploration (Photo 1). The sidewalls of the test pits did not cave in. Please see the
attached soil logs for detailed descriptions and the attached site plan for approximate test pit
locations. All soils were classified by visual means. The boundary lines between soiltypes on
the logs are approximations. Actually, the transitions may be gradual and subsurface conditions
may vary between exploration locations.
5.0 Conclusions and Recommendations
5.1 Foundations
The proposed construction appears feasible from a geotechnical perspective. The upper
1.5' or so of dark topsoil should not be used under structures or pavements. This material
should be removed from the site or only used in places such as landscape areas. lt is
recommended that any existing utilities within proposed building footprint areas be rerouted
outside the footprint area or abandoned in place.
The native undisturbed subgrade should be free of deleterious material such as grass,
stumps, roots, trash, etc. The subgrade should be in a firm and unyielding condition and
near its optimum moisture content. Loose areas should be compacted to a firm unyielding
condition or over excavated and replaced with properly placed and compacted structurallill
or otherwise stabilized in order to achieve the desired condition. Wet areas may need to be
removed and replaced with structural fill, or allowed to dry to near optimum moisture and
replaced as structural fill.
The on site silty sand/silty gravel material can be used for structural fill, provided that
deleterious material and stones over 6" diameter are removed and that the soil is at near
optimum moisture content. However, this soil is moisture sensitive and may not be suitable
2
for use during the wet season or if it is already wet, as was the case in TP-1 during the
investigation. Preparation for placement of structural fill should include the removal of
vegetaiion, topsoil and other deleterious material and proper sub grade preparation as
described above.
lmported structural fill should conform to the specifications for Gravel Backfill for
Foundations listed in Section 9-03.12(1 ) of the 2004 WSDOT Standard Specifications, or
similar material subject to approval of the engineer. Structural fill should be placed in
horizontal lifts not to exceed 8" thick, with each lift being compacted to at least 95% of the
modified proctor value, at near optimum moisture content. Compaction testing should be
performed in order to verify that proper compaction is being achieved.
The test-pits were backfilled with the excavated material but not compacted. lf any portion of
the proposed building foundations will be constructed over a test-pit location, the material
should be over excavated 3' and replaced in compacted lifts as described above in order to
reduce the potential for settlement.
We recommend that foundations be located in the undisturbed compact glacial till found at
depths ranging from 2.5'to 5' in the test pits. For spread and continuous footings located in
this material, the recommended allowable fodndation pressure is 4000 pounds per square
foot (psf) With a minimum 18 inch wide footing. The lateral bearing of this soil is 200 lbs.
psf/ft of depth below natural grade. These values may be increased by 113 when
considering load combinations, including wind or earthquake loads. The lateral sliding
coefficient of this soil is 0.35, to be multiplied by the dead load.
The recommended allowable foundation pressure for the silty sand material encountered
below the topsoil and above the glacial till is 2000 pounds per square foot (psf). The lateral
bearing of this soil is 150 lbs. psf/ft of depth below natural grade. These values may be
increased by 1t3 when considering load combinations, including wind or earthquake loads.
The lateral sliding coefficient of this soil is 0.25, to be multiplied by the dead load.
Expected settlement for foundation elements founded in properly prepared material is
estimated to be about one inch for total settlement andV2" for differential settlement and
should occur during construction.
5.2 Drainage Considerations
During Construction, all excavations should be rolled with a compactor as soon as possible
to reduce the impact of rain on the exposed surface. Water should not be allowed to stand in
any area where foundations, slabs or pavements are to be constructed. Constructing
excavations to slope to a low spot and installing a sump pump discharging to a storm
drainage system can accomplish this.
Based upon the subsurface test pit information, we expect localized perched groundwater to
be encountered above the glacialtill. The amount of groundwater present likely fluctuates
with the seasons and is expected to be wettest during winter and early spring.
We recommend the use of perforated footing drains at the base of all footings. These drains
should be surrounded by at least six inches of washed drain rock. At the highest point, the
invert of the drain should be at least as low as the bottom of the looting and it should be
3
sloped for drainage. All roof and surface water drains must be kept separate from the
perforated footing drains. All drains should be connected to a storm drain system.
5.3 Pavement Recommendations
For traffic bearing asphalt paving areas, the following pavement section is recommended for
all areas to be used for winter time staging during construction, with the final 2" asphalt lift
being placed after all heavy equipment is finished using this area:
2" class "B" asphalt
4" Asphalt Treated Base (ATB)
4" aggregate base course
For traffic bearing areas not being used for staging, an alternate paving cross section of 2"
class "B" asphalt, 2" crushed surfacing and 8" minimUm aggregate base Course is
recommended.
The current WSDOT Standard Specifications should be consulted for the material
specifications for these paving elements.
For concrete paving, 4" of "S-sack mix" is recommended for sidewalks and 6" of "S-sack
mix" is recommended for driveways over subgrade compacted to 95"/" of the modified
proctor value. A leveling course of 1"-2" of compacted crushed rock may be desirable to
expedite the grading process but is not necessary for structural purposes.
5.4 Seismic Parameters
Based upon visual observations, the seismic site class for the soils observed in the test pits
is site. class "D" based upon Table 1615.1.1 of the lBC. The USGS, in their 2002 National
Seismic Hazard Mapping Project, indicates a peak ground acceleration of 0.319 with a 10%
probability of being exceeded in 50 years.
Soil liquefaction is generally considered to occur in loose saturated granular soil. This
condition was present locally in the thin zone of loose material above the till where there is a
perched water table, as evidenced in TP-1. Therefore, the potential for soil liquefaction at
the subject site exists. However, the condition will be mitigated in the building areas by the
removal of the loose saturated material and replacement with compacted structural fill, and
by the recommended footing drains.
5.5 Wet Weather Construction
The silty sand at the site is moisture sensitive, thus wet weather oonstruction may pose
challenges. See comments in Section 5.3 regarding winter time staging areas.
6.0 Limitations
This report has been prepared for the exclusive use of San Juan Baptist Church and their
agents'in conjunction.with the above referenced project. The report has not been prepared for
use by others or for other locations or projects. Others may use it only with the expressed
written permission of the Engineer.
4
Within the limits of scope, schedule and budget, this report was prepared in general accordance
with accepted professiirnit engineering and leological principles and practices in this or similar
localities ht tnd time the report-was prdpared. No other warranty, expressed or implied, is made
as to the conclusions and irofessioiral advice included in this report.
The observations, conclusions and recommendations presented in this report were based on
our visual observations of the subject property at the time of our site visit. Soil and geologic
conditions can vary significantly between test holes and/or surface outcrops. lf there is a
substantial lapse of time, conditions at the site have changed or appear different than those
described in this report, we should be contacted and retained to evaluate the changed
conditions and make modifications to our report if necessary.
Sincerely,
NTI ENGINEERING & LAND SURVEYING
Robert A. Leach, P.E., MBA
Principal Engineer
,'\ t)
; )4,/ ( l.-r"jfr^
Bill Payton, L.E.G.
Engineering Geologist
G:\Gen\Bill\Reports\SJBC0502.1O(30-1).church addition geotech.Port Townsend.doc
EXPIRES 12t30t2006
Explres 1 1/06/05
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APPENDIX
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FOUNDATIOU*SO't LOGS
SAN JUAN BAPTIST CHURCH ADDITION
1704 DISCOVERY ROAD, PORT TOWNSEND
SECTION 10, TOWNSHIP 50 NORTH, RANGE 1 WEST, W.M.
JEFFERSON COUNTY, WASHINGTON
TEST PIT
#1
DEPTH
(FT.)
-0 Dork brown topsoil with gross on surfoce.
Loose to medium dense, brown, silty sond
(SM) with grovel ond troce cobbles; moistio iet; gr6undwoter seeping out of -2.5'.
Dense to very dense, groy, silty sond or
silty grovel (SM, GM) with troce cobbles;
moist; till.-3
-6
-9
-10 End of Test Pit 10'
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:J'
DATE: 2-9-05
FOUNDATION SOIL LOGS
FOR
SAN JUAN BAPTIST CHURCH ADDITION
1704 DISCOVERY ROAD, PORT TOWNSEND
SECTION 10, TOWNSHIP 30 NORTH, RANGE 1 WEST, W.M.
JEFFERSON COUNTY, WASHINGTON
TEST PIT
#2
DEPTH
(FT.)
-0 Dork brown topsoil with gross on surfoce.
Loose to medium dense, brown, silty sond
(SM) with grovel ond troce cobbles; moist.
-3
Dense to very dense, groy, silty sond or
silty grovel (SM, GM) with troce cobbles;
moist; till.-6
-8 End of Test Pit 8'
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DATE: 2-9-05