PHONE No. : 206 828 0333
From' .THIELSEN .=iRCHiTECTS ':Jl-~.)-l!i,I'-=- ~.,:;: 1~1-'1'1
l.,,l!'o-t.e-oh Loncu J t.ar,-ti.,
Jan.03 1996 1::1../1::JI~..:,.:;_:;
Jan1.1ary 3, 1 e~Hs
GEOTECH CONSULTANTS .. INC.
1~256 !-:.t. ~th St. (N~•,thur W11,r~- Suitt ;_6
8t':llt1·ue:. WA 91400:i (206) 747,5618
Thlelsen Arr..hltects 720 Mark.&t Street, Suito C Kirkland. Wathln;ton · SS::>33
AUentiQn: David Thiel$9n Subject:
Response to King County Letter ,cooomber 1a, 1OOS) 425 Ea;t Lake Sarnmamlsh Lane Northeast King County, Washington King County FIie #905~ 1 ~
Dear Mr. i hlelsen:
J!3/7-!) ,fj Jg)~
In response to a request from Nancy Brown of the Kln9 County Land Use Division, this letter provlde1 ·lurtl'\er Information re;ardlng soil auaceptlbllfty to sel$mlcally Induced llquefactlon or aelamlcall)' Induced ••ttlement. Ms. Brown el10 requested Justification for the estimated plle length glv,m In our latter of September 26, 1995. Geotech Consultant., Inc. originally oonducted o geotechniccl engineering study of the subject site for Clno Simone. For thi$ feporl, dale,d Jamuary 21, 1992, we excavated three teat plt5, which revealed sllty Hrtd wllh gri'.ivel. Slnc1t this report was Issued, we have provided geotachnlcal engineerlr.g services at 201 e&Sl Lake S11mmamlsh Shoreline Northeast and 2f51 EHt Lake Sammamish Shoreline Northe:,tuil. Explorations end foundation Installations for theae housea revealod loo$e 1011 down to II dspth of approximately 2S to 20 ft=et, where the soil became denser. It Is our opinion that seismic llquefactlon could occur under certain conditions at the subject site, and It Is propoaed that th6' house be supported on driven. pipe piles or augercast piers. These deep four.datlons wlll tranefer the atructural loads to the underlying dense strata., reducing the potential effects of seismic llquefactlon. This Is a standard engineering practice. Bl!lsed on the information obtained from les\ b~rlngs and foundation ln•talletlona at the nearby altea, we atisume thet denee zsoll will be found at a depth of 25 to SO feet bel'-'1vv the ground syrface. Therefore; we e8tlmate that II plur hmgth on the order of 3e to 40 feet wlll be required to acbieve a 10-foot penetration into tho den•• soll. Our engineers wlll be on the :>He during the Installation .:)f the deep foundation to verify that adequate soil bearing Is achieved. Somo $ettloment could occur between u·,e &Ile and the building, which wlll be suppcrtad on deep f oundatlon•. and utility connection• should therefore be relatively flexible. Fl~Xlble materials, such as copper. PVC, or ductlle Iron pipe, $hould be used. Where the utilltlea penetrate the foundation, a large opening should be provlde.d 110 tha\ any potentl•I •ettlement will not cause damage le the utilities. FloaUng slabs adjacent to the bulldlng should be $tn.Jcturally attached to
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From: THIELSEN ARCHITECTS 01-D3-1996 0J:11FM
PHONE No. : 206 828 0333 Geotech Concultan~c lne
Thlelsen Archlttcts January 3. 1996
~Jan.~~ 1996 6:08FIM 8280333
F'.02 JN 92001
Y'e building. and ralnfqrclng should be provided within the slabs so that the •lebG can hinge ~ff the structure. Thia would roduoe the tendency for a step to occur at the bulldlng, If e stab settles due
to soil conaolidation. If you have any questions, or If we oen be of further eervlcc, please do not hesitate to contact u,.
@§as j / 17 /r:f?.: James R.. Finley, Jr., P.E. Principal JRF:dJs
OFDTECH CONSt.n.T.ANT.S. l'NC.
CONSULT ANTS. INC. 13256 \.E. 20th St. (\orthup \\·ay). Suite 16 Bellevue. WA 98005
September 26, 1995
(206) 747-5618 FAX 747-8561
JN 92001 Art and Sally Holmboe c/o Thielsen Architects 720 Market Street, Suite C Kirkland, Washington 98033 Attention: David Thielsen Subject:
Supplemental Foundation Recommendations Proposed Holmboe Residence 425 East Lake Sammamish Parkway Northeast King County, Washington
Dear Mr. Thielsen: This letter is an addendum to the previous geotechnical engineering study that we prepared for this site. The original study, dated January 21, 1992, was conducted for Dino Simone. A copy of this previous study is attached, and we authorize you to use it for the currently planned development. We were provided with Sheets 1 through 3 of the architectural plans developed by Thielsen Architects and dated July 25, 1995. Based on these plans and discussions with David Thielsen, we understand that the proposed residence will have two stories with the lower floor constructed over a crawl space. A portion of the house will be elevated due to potential flooding. The structure will include a two-car garage and a large bay for boat storage. Three te:~ pits were conducted on the site for our previous geotechnical engineering study. These explorations encountered subsurface conditions consisting of several feet of loose sand fill and topsoil overlying medium-dense to dense, native, silty sands or sandy silts. Groundwater seepage was encountered at a depth of 4 to 5 feet in all of the test pits.
CONCLUSIONS AND RECOMMENDATIONS
We understand that the structural engineer has proposed to support at least a portion of the residence on deep foundations. In this case, conventional foundations should not be used to. support the remainder of the residence, as noticeable differential settlement between the foundation systems could result. We therefore recommend supporting all loads from house on driven pipe piles or augercast piers.
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'\ VICINITY MAP
425 E. LAKE SAMMAMISH PKWY
KING COUNTY, WASHINGTON o,,,., Pfot,: .lob No., Lon~d a,, 92001
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~ APPROXIMATE TEST PIT LOCATIONS
SITE EXPLORATION PLAN
425 E. LAKE SAMMAMISH PKWY KING COUNTY, WASHINGTON
~1-4;;.,.--_ -e: _____________________ , .,; 2NO.O 1 r Oo~A N
TEST PIT 1
uses fill ML
:rn: SM :ffi:
Gray, gravelly, slightly silty SAND, wet, loose to medium-dense (fill). Gray, mottled, sandy SILT, very wet, soft. Gray, fine grained, silty SAND with gravel, very moist to wet, dense Test pit tenninated at 6' below existing grade on 1-7-92. Groundwater seepage encountered at 5.5' during excavation. Minor caving above 2'.
TEST PIT 2
Gray, gravelly, slightly silty SAND, some debris, loose to medium-dense (fill). : ~: , Dark gray/black organic SILT, very wet, soft. : ~: Brown/gray, very gravelly, silty SAND, medium grained, Wt, \very wet, dense. rm Gray, sandy SILT, nonplastic, wet, medium-dense to dense. ··=· ! ~.) Becomes silty SAND, medium to coarse grained, very wet. Test pit terminated at 8' below existing grade on 1-7-92. Groundwater seepage encountered at 4.5' during excavation.
TEST PIT LOGS 425 E. LAKE SAMMAMISH PKWY KING COUNTY, WASHINGTON Job No: 92001
Date: JAN 1992
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TEST PIT 3
Gray, gravelly, slightly silty SAND, very moist, loose to medium-dense (fill). .Mh Grav/mottled, sandv SILT, verv wet, soft. ::;tJ;J;J:: Gray/tan, silty SAND with gravel, fine to medium grained, .w.i.: very wet to saturated, loose. •:1:1:1:1·: becomes medium-dense to dense. \
Test pit terminated at 5.5' below existing grade on 1-7-92. Slight groundwater seepage encountered at 5' during excavation.
TEST PIT LOGS
GEOTECH CONSULTANTS, INC.
425 E. LAKE SAMMAMISH PKWY KING COUNTY, WASHINGTON Job No: 92001
Date: JAN 1992