HomeMy WebLinkAbout938400542 Geotech Assessment~~
NORTHWESTERN TERRITORIES,INC.
1 ~ A JLS GROUP COMPANY-
~ 717 SOUTH PEABODY STREET, PORT ANGELES, WA 98362
Engineers .Land-Surveyors Geologists
~~~ Construction trfspection .Materials Testing _ _ _ _ . _ _~
(360)452-8491 FAX 452-8498 www.nti4u.COm E-Mail: info@nti4u:com ~ ((*1~ r~ n "~ ~~ ~'
JLS GROUP, ~ ~ ''' ~. - n_ , : ~
INC. -
~:
GEOTECHNICAL REPORT
Prepared For John Gieser
August 15, 2003
- For the Properties Described As
Lots 43 and 44, Block 5, Division 3 of Cape. George Colony
- Tax #'s 938400542 and .938400543
Section 12, Township 30 North; Range 2 West, W.M.
Jefferson County, Washington
Prepared by
NORTHWESTERN TERRITORIES, INC.
717.S: Peabody Street
Port Angeles, Washington 98362
Phone 360-452-8491 Fax 360-452-.8498 -
Web Site www:nti4u.com
E-mail- info@nti4u.com
Geotechnical-Report for-
Tax #'s 938400542 and 938400543
August 15, 2003
~` ~ n n'j ~ r __l
' ~ I
I ~ ~ ;i
., '
~~PT. OF Cab, ;.... .:.:vE~O~'~+r`_-~(
John Gieser
P.O. Box 2073
Port Townsend, WA 98368-0250
Subject: Geotechnical Report for the Property Described as Lots 43 and 44, Block
5, Division 3.of Cape George Colony, -Tax #'s 938400542 and .938400543
Dear Mr. Gieser:
Background
At your request, Bill Payton, Engineering Geologist, with Northwestern Territories, Inc.
(NTI} conducted a geotechnical .inspection of the above-mentioned property on June 9,
2003. The purpose of this inspection was to examine the slope and, subsurface soils at
the property by visual means-and provide soil index properties to assist in-the --
construction of asingle-family residence on-each lot (Figure 1 }.
The inspection included research of available geologic literature of the .area, visual
observations of the,slope on the property and the visual examination of two backhoe
test pits excavated to a depth of approximately 8 feet. The test pits-were excavated in
the area of the. proposed .houses.
Site Description
The subject property consists of two adjacent undeveloped lots .and is located on San
Juan -Drive in Cape George Colony. The property is well vegetated with trees, brush
and grass Photo 1). Most of the trees on the slope face have straight trunks, indicating
tha# little or no slope creep is occurring. No springs or seeps were noticed on-the slope
face.
The lots are situated on a slope that is approximately 70 feet high and rises up towards-
the northeast at 29 degrees +/-. This- angle is below the "angle of repose" -which is
defined as the maximum slope or angle at which- loose, cohesionless material remains.
stable. It commonly ranges between 33 and 37 degrees on natural slopes.
-1-
_ r -~
~~ ~ ~~ Its ~ s
Geologic Conditions. ~~PT~o~ t;'~~~ , ._ ~~r,'..ot'r~~:~ ~r
The SCS Soil Survey of Jefferson County maps the soil in the area of the. subject
property as the Clallam gravelly sandy loam. -This soil formed in glacial till. Runoff is
classified as slow to medium and the hazard of water erosion is slight to moderate. The
Survey classifies this. soil as a .Silty Sand (SM) from 0" to 23"-and as a :Silty Gravel (GM)
or Silty -Sand (SM) from 23" to 36" using the Unified Soil Classification System (USCS}.
The Survey labels the shrink-swell .potential as low, the corrosivity to uncoated steel and
concrete as moderate, and the-frost action potential as none. This soil is typically.-
cemented below a depth of 20" to 40" and water may- move laterally above the
cemented layer during the wet season.
The Washington State Department of Ecology in their "Geology and Ground-Water
Resources of Eastern Jefferson County, Washington" maps-the soil in-the area of the
subjec# property as Lodgement tilt (Qvt) or as Recessional outwash (Qvr). These units
are associated with the Fraser Glaciation and consist of primarily of gravel and sand
with boulders, cobbles, silt and clay. .
Visual observations of the two test pits revealed the soiF to be compact light brovun to
tan-sandy rounded gravel (GW or GP using the USCS} with a trace of cobbles (Photo
2). There was about 10" of organic topsoil on the surface.
Granite gravel was present in the test pits and there was a very large granite boulder
(glacial erratic) nearby which suggests that the material. is from the Fraser Glaciation as
granite is-not found locally on the Peninsula--but was carried -south from Canada by the
glaciers.
The test pits were standing vertical with no sloughing. (Photo 3) and no groundwater
was. present.
Conclusions and Recommendations
The hillside at the subject property appears grossly stable and the development of the
property seems feasible from a geotechnical perspective. The-slope is-well vegetated.-
The slope angle is below the angle of repose. No springs or-seeps were noticed on the
slope face and. no evidence of past slope failures were seen.
Due to the slope of the property and the proposed location of the houses. on the slope,
deepened foundations will be necessary. Also, retaining walls will be necessary to retain
cut :slopes and also to provide protection to the house from slope drainage, erosion and
shallow sloughing from the. hillside above..
Using the Uniform Building. Code (UBC) guidelines, we recommend that foundation
elements be embedded five feef below grade and founded in firm. undisturbed native
soil. As evidenced by the lack of sloughing of the-test pits, it appears that similar
-2-
;!~I
~ ', ,(
6
excavations for footing elements could be achieved at a cost advantage to typical auger
cast piers. Further, site access with a typical truck mounted drill rig would be difficult.
Foundation elements could consist of piers-cast into square holes dug with an excavator
or backhoe. The sidewalls would need to be approximately plumb; consistent in width
grid the bottom. would. need to be level and free of loose soil: Even-though the .test pits
did not cave in, there is a risk of the holes caving. in.-All codes and/or regulations should
be followed with regard. to trench excavations, shoring and-backfill in order to protect
workers. Based on Part N of Section 296-155 of the Washington Administrative Code
(WAC), the soils at-the site classify as Type C soils.
Based on Table 18-I-A of the Uniform Building-Code {IJBG), the allowable foundation
pressure of the sandy gravel found in the test pits is 2000 pounds-per square-foot (psf).
This-value can be increased up to 6000 psf subject to footnote 2 of the table. The lateral
bearing is 200 lbs. Per. square foot per foot of depth below natural grade. This -value
maybe increased per footnote 3 of the table..-The lateral sliding coefficient is 0.35 to be
multiplied by the dead-load.
For retaining structures, where free unrestrained walls are planned to retain level, clean,.
granular, nonexpansive backfill, an equivalent fluid pressure of 35 pcf for walls allowed
to deflect at-least 0.002 times the. wall height -(active condition) may be used. For walls
not allowed to deflect at least 0.002 times the wall height, the above value should be
increased to 67 pcf (at-rest condition). An appropriate safety factor should be applied for
the design of retaining structures. A safety factor of at least 1.5 for sliding and
overturning is recommended. Appropriate allowances should be made for anticipated
surcharge .loadings. Backdrainage systems- are recommended for solid retaining walls-.
For gabion baskets or rock walls, that are pervious., backdrainage systems-are- not
required, but may be used to direct water that might otherwise weep through- the wall
and be unsightly.
A typical batter angle for low gabionor rock walls-is 1 H:4U. The compact glacial till soils
found in the- test pits may temporarily stand at -this angle long. enough to face the cut
-with the wall (as evidenced. by the-test pits standing vertical). However, this steep of an
angle should not be considered stable and the slope should be monitored for any signs
of instability and layed back to a less steep angle if necessary. Surcharge-loads should.
be taken into consideration. Walls over 4 feet high generally require the design services
of a structural engineer. Lightweight compactors such as hand-operated tampers should
be utilized for compaction in close proximity to retaining walls in order to reduce he
possibility of excess wall loading and potential.-movement.
The following recommendations should also be considered with regards to development
of the subject property:
1. It will be necessary to maintain ground cover on the hillside to reduce erosion
from surface runoff:-Any bare areas that develop should be revegetated. Native
-3-
r'y r.~ r `~ i I r ~~ ,
~1 f`=, ~ -.~~
! F .~
3
deep rooted vegetation that requires little or no irrigation would be the most
beneficial. Bushes and small trees would be preferable to large trees in order to
.reduce the possible windthrow hazard.
2. Surface -runoff from upslope needs to be controlled and routed around the house.
This could, possibly be accomplished with swales, trench- drains, -etc.
3. Heavy irrigation. or other activities- that would contribute large- quantities of water
to the soil should be avoided. One cause of slope instability is the presence of
excessive groundwater.
4. Surface runoff from hard surfaces such as roofs, driveways, walkways and patios
should be controlled and routed to a drainage control device such that surface
water discharge to adjacent properties does not significantly exceed
predevelopment conditions. .
5. Silt fences or o#her sediment control devices may be needed during construction
such that sedimentation to adjacent properties does- not significantly exceed
predevelopment conditions.
6. All drainage control devices should be maintained in-good. working order and
inspected at least once a year.
7. Septic drain fields should not be located on the hillside above the home.
8. An engineered drainage and erosion control plan is recommended to address
items 2, 4, 5 and 6 above.
For further information please review the. three online publications published by the
Washington State Department of Ecology=(DOE) entitled: "Slope Stabilization and
Erosion- Control- Using Vegetation", "Vegetation- Management: A Guide for Puget Sound
Bluff Property Owners" and "Surface Water and Groundwater on Coastal Bluffs". These
publications are now out of print but can be obtained from the-DOE website at:
htt~ //www eey.wa.gov/bibliolsea.html under the 1993 and 1994 year heading. The DOE
website also contains much more useful information regarding slope stability and site
development; this reference is highly recommended.
Limitations
This- report-has been prepared for the exclusive use of John Gieser in conjunction with
the above referenced project. The report has not been prepared for use by others or for
other locations. It maybe used by others 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 professional engineering and geological principles and --
practices in this or similar ocalities at the time the report was prepared: No other
warranty, expressed or implied, is made as to the conclusions and professional 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; no
laboratory tests were performed. Soil and geologic conditions can vary significantly-
between -test holes and/or surface outcrops. If 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,.
NORTHWESTERN TERRITORIES, INC. ~oQ~ of®~sy~yc~y
ti °y
I f
/l ~ - -
'O~ ~F 13772 ~O ~,~
Robert A: Leach, P.E., MBA °~F ~isT~R ~~`~
Principal :Engineer ss~OnrA~ 'LNG
J/~/~~
Bill Payton, L.E.G.
Engineering Geologist
G:1GenlBill\Reports\GIES0301.geotech.12(30-2).Cape George.doc
EXPIRES 12!30/2004
~~ ~ ~~{~
~~; ~~: `~
~Wt#1lsr~ C. Pay#t~r~ ~
.Expires 11-pf'r43
r
~ ~ ~: ~ ~ -~
® cry ~~ _ ;~ ~~---., .
~,,.
~---- ,,
t
-5-
05/29/2003 22:23 2868819663
~~ ~~~
s r
"~~
~~ ~ ~ ~ +
~ 3c r
~~ ~ - ~,
S"o ~ t ql.t~~
. ~~ .n ~~~ ~ •900.54
~~ } ~~v
••1
e as ~ i
~;
I
. .___ . ~ r. - ~ ~' FAA
JDG INC. ' ,' ~E 01
1 ~-~---
I ~t:
;~
~ ~~s:
APT. OF C :;`~„ _ ~ __ .~~0°~„- `~ .
~. % o
0 S ~• Qr
'o•
M
~~~ I
Y m m ~ 1
~ _
1
S 2 G -r ' N
m
a
1
~~
+ m C -~i f'1
~y N
q . f
i'~
S s •e y + ~y ~
I ~
n '~~
~
~ m W
7 ~ 1
_
~ oY tmp ~
~ l
~
m
~ ~ ~ ~
~, ~Q r
I 3a
y ~
~ ~
~ ~
~
~ xa•o,~~4
aa-e .ta.cz.u~.-.
3 A
"` SAN JAUN D o • e 9 • ~
~ RIyE
»• ~
~~~o x ~ -•----•-' moot
~, I s
S1 f7, u
%~ •PE,CS.e
i~ MS'04•Jp'E
sa, ~ ~~o. , oo•o<z•ag
z r •
•t
~1e y~
`" I Q .
~
1~ ~H .~
m sn~"
tlr dl
~ .. a +~
J
n
w ~~
~
~ ,I
~n
//
m~ ~
to
I }
P
Im•4
.~ ~~ i
~ t
Y
~ ~
!
N / r ~
~
.>, tt ~ tb N
~ ~ ~ b
~m~~ a~ /y
i a ~y
s ~ ~ ~/
(7gVj ~ ~ ,t JO.oe
* / ~ ni•lo•4p^E
m s
~~= z
- z w'
~
ml m
N =
.~ ~
r ~
z
m °'
l~
~~ g ~~ ~ ~`
~
~o-i o~ ~ 1
~ m N 1
i~~P..
~ ~
t~
~
I;s~ 2 ~
,m•v•
``. R
~
• r
0 .
~
I (3 m ~
~F~~ c 0
v av-_
p
• ~ Z
~•
~ N ~i~uRC Z
3~
-•
2£ o~Z•h
S~
\4 ~ /
~'
.~ ~
f
o`'
' .4 LPOLL• y //,f/
174.19
C
a
QS
Or
N
'~°' ~'a
di' •~d
~ o~
:~
L~
~ v2;~°4.
s7
~ t
I~
~~
~'?
7~
1 ~Tr
f
9~'S9 L
tl
~5 t Of 0 ~'1
2 D
0 ~
G
R ~
Z -
i N
tw
p C
p 3
r ~
ro
a
0
n
M
-I
0
a
w
a
0
1lASH. STATE COORp. 6Y&TEF1
NAD t92'7
PEA YOLK 4 OF PLhT9 PAGE 23
~!1!
Q
-.,,
1
~,.~~_ _
~i
il. in,~
Photo 1. View of property looking northeast from road.
_ i '''111~~~
~ ~ "~ ~.
t '[ ~ '~
.
~ !i
~ °~u , ~
~ ~~
} lr
~` '~
_ - ~ 5,~~ h
~ z.
i ~lrs~ ri
(..' !Fa -'. ~ i .e~~ -`fit. ~ ?Sv~~ $- ~ ~ ~ ~''p~~ G •r~~ _ ~ ."'R _
~ ~ ~ ~~4 + ,t . -~ii*,v~ =':u mss`.- _ ~.~y _ ~g ~ _ ~ g' ~r~'
Q t
~" . t ~ :. ~
r
r ~-
!~ -t~ ,fit. ~ _ ~ , ,~ } ~~f ~ ~ ~ ' ~~~ .~F a• ~ ~ ti .~ - ' ~ '~ ~ '`ice
i~ is i -''~ ~; ~~_ - -
.$ ~, Sy. _~ ,~
~ ~
1 Y ~P "
'` ~°` ,°
~{ ~ '
-'Y' -"~/ '? ~ 'L~ : -~ ,rte' l 'S{ -~'
t
L 3~ ,~
ii'' ~ ~ 7
~.
t~ _ -1321_. _ -.~. .t. ._. _ -
_ pg;g/ ~ '~
1 ~ ,
Photo 2. View of test pit. __~~PT. of c~ ~. ; : , z r
~~
,'
Photo 3. 1/iew of test pit. ,_~~P7sor c~~ - _: ; ~. o~~r::-
05/29/2003 22:23 2068819663
~~
~ ~~ ,
Z Y~ S
J ~~ of
~i ~
~~s }
{~ae
f
~ Y ~
n .., v
2 m m
~ h
i x
~ "' ~ c
a x p ~
g'Si A~myy
~`7i A4
v r ~
a " ~
~ q W_ 7 ~
'.1 m ~
i ~~
~~~~ m
~ ~ y
pp m
3 A
m
~ ~ ~
04 N
~W ~~
~ ~
I m. 4 P m
~ #
f~D a~ °
5 .y
f0 ~
+ n
}
~~
m S
~~~
~m~ ~
S ti ~
~~
0
~~~
~'Q~r~
~~~ ~q~
G
~aro~
F~ ~ ~~
~~~p_
:~ ~
~zs~
~~
i3m~
'cy~
:~"'_?
~'~
i~~~ti
d
O A ~_
O K
JDG IN t.~ ~ ~~II ,PAGE 01
! ~ ,m
~~_ ~
o
-~ ~ ~
~ i
*
~
~
~
y i
y
~
7 N
* '
~
1
3JI n_p4.9 ~
i~~
f
° r 00•5p
~ ~ 1
I
n ~ '
f''
j _ 'YS
i
a
m, .
:o .-. wm
N Q'
1 ?
o
'+~a ~
~
~~~ ~ M
r~ '
.~ ~
I
JG r sa
~ ~
•'t6'0~•JA"E
~ 90'012 •1E
r SAN JAUN p c o• o p• ~~" •
RJV
E ~,+
~ ~ ooi
Z
z
m
t
rn
m
H
0
z
-a
u
O
N
' k
%i
:I 47.u PE.CS.e
"a'~•'oe•e
f . Zf'
'k
~
N r t9•
S
-
mI ~,ti
"~~n
mf
~ N
~
~
~ I ~ ~
W
}W / ~ _
H
N ~ fN
!
a / 'N
b
.
,y
aqf ~i ~
~
}
~~ ~ v!'io'~e"E
~
o
.~
/~
/ ?
W
0
~~'/ rn s
r ,,
!.
l~
`
1
~'
v
n
0
Z
~IC~URL
134.89
N~~10'4a'2
n ~
i ~ O
0
H ~
~
~ ~,
o.
i N
p C +
p
r 3
rn
d
~ ~
ro
a
0 ~
o
n
-I
..._ , _ ~ .e... . Q X47 ~ ,
Y .~
0
,2
jO ~
r
~O~
M
oJ~~ ~ ~~ ~
.r~ ~i
~ ~ f f f ~~
~r,~ o~.
pa s4,L
~ Z • °
°5~• 4p'~
/~L~
N
,A '9a..rP
C' dr' ~~d
~O~
.~ f
1
bar
p ~r~ `` C
e
4IASH. STATE COORp. 8TS'JEh
NAO t9~'7
PER VOL. 4 OF FLAT5 PAGE P3
W a.'
+~
~ --
t+t!
tJ-!
4
Cat
05/29/2003 22:23 2068819663
~~
~ t~ ~
~ ~~ n
~ ~
A~ ~
° ~~
.. ~~
~~~
~~ae
i~
n ... v
~ s m m
v c ~ .'„
i Z '~
~'"~ o
,~_~~
_g ~ [m~
A C .~i RI
s r ~
5 ~ ~ ~ ~
e `" w ~ ~
i ^~
i 2~
~T~~
~ m
c
~ R P
m
7~ ~N
~~ r ~
s`•'' ~~
:m.aP rn
~' >
i~5 i~ ~
Ip
Irr
I, ~QQ~
d []T
s
~~,
m ~
~~
°~ m ~ ~
~ ~
~ ~-
w K
doo+o
~g~~~
N~
gar c~
~~~ ~
w~
i~~p..
~~
e~
q
m$
:3~,.•
:~ r ~~
yam m
i~Fy~y~
Td
O A~
~-
Z
m
cn
H
m
n
a
z
u
0
z
fLt
JDG INC.
.~~
~~ ~ ~
~o
~!~ ~ ~~ J
{~ rn I I
'~ ~ ~ ~
~~y9.4r
~~ ~ ap•55
i
~~
• ~
~:
I I
I
1_
I, a
w m
~~ 1~ ~' ;u
a
~ ~ N r/I M
a 111
•~i .
I
I ~
so j so ~
r 1~ ,>, ,
+ .ia.cz,u~.-.
•'~'pa•Je~E
I 00'012•ti
ShN JAUN co•o9•~~~
~ bRIVE ~
b ~ ~~^••~'~ '1
~ Ne'oa'7~'•E '~r'---•_ _~-
~ r~ ~ '- - - -'-
n. f7. la .PE.cs.e
:~ MS•p.~~8'E
o. ~ oo•o<z•ag
~(~ .f• Er• IQ•~ ~
m% ~(^
1 ~ ~i•~
I ,I
I "'j or N
~~~ ~ ~ ~
a ~
N !N
' N
~ ~ ~S m
e ~,~ ~ ~
A `~
u~~ ~ ~ rao.ao
~ ~ ~~ ~ ~ vl•io~ae`E
Z
aw10 ~ §
r ch~~
r +~ :~ .'
1„
,a
~`
c
r
o
r~
0
2
~iC~u~C 2
~ -~ i
• ~~/
-~ i•
P o
i G O
H ~ ~ 4
.
Z - •~
i N
p C ^ c+
p 3 b
f ~ r
b
IV
~
b p
a
n
H
N
t
t'
I I'' ~~~Y •1 8 200~~ _ ,,
~-}
~_ _
=~cPI OF C'J`s r _~ ___. ~ rELO~t~i`_ : t
~• ~o 0
O ~ `• ~
ro•
F
uA5H. STATE CQORp. BYSTEfT
tlAO t927
PER VOLE 4 OF FLATS PA&E 23
C r
W o
y~
~m
(~11
6~
Q
Y
c.~
!nf
1~