HomeMy WebLinkAboutPermit File 3500 Oakes Avenue 08/12/94 12:47 206 679 9445 YONITAAN CONSTRUCTION PAGE 01
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FAX COVER SHEET
FIX # : (204) 679-9445
FROM t SCOTT.YONEMAN KEN MARSH
GREG YONfAN GEORGE YONKMAN
STUART GROVDAHL _... JEAN EASTWOOD
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06l12!94 12: 47 206 679 9445 YONRMAN CONSTRUCTION PAGE 02
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august 11, 1994 Job 214
Mr. Baron Diegel
2400 Summit
Escondido, CA 92025
RE: Ceotechnical evaluation of a Parcel located in Block 1001 ,
Northern Pacific Addition to Anacortes, and just west of 3502
Oakes Avenue, Anacortes , Skagit County, WA.
Dear Mr. Dieget:
At the request of your agent , Yonkman construction , Inc . , an
evaluation was made of the subject parcel . Since the northern
portion of the parcel is within an area classed as being
unstable, a geotechnical evaluation is required before the City
of Anacortes will issue a building permit for the parcel .
The subject evaluation consisted of (1) review of Coastal Sone
Atlas of Washington volume 2 , Skagit County , Washington ,
Department of Ecology, 1978, (2) review of Soil Survey of Skagit
County Area. Washington, USDA, Soil Conservation Service, 1989,
(3) review of City of Anacortes West Fidalgo Island Sensitive
Area Inventory , Jones 6 Stokes Associates , 1991 and (4) a
reconnaissance over the parcel to determine surface conditions,
foundation conditions , slope stability. and surface drainage.
Also a hand level-compass-tape survey was conducted in order to
obtain data to prepare a draft topographic map and geologic
section. The field work was done on August 9, 1994 .
In summary, on the portion of the parcel located up slope of the
steep bluff, good foundation conditions exist in regard to any
proposed structure. A portion of the bluff slope, in places, is
vertical and bare of vegetation, This indicates recent erosion
and shallow slope failures have occurred. Since thes bluff slope
is much steeper than the angle of repooc, it will fail in the
future . Therefore, in regard to slope stability, the further the
set-back for a proposed structure, the better. However, if you
desire to place a structure any closer than 50 feet to the
closest point of the bluff , placement of cast in-drill -hole
(c. I .b.H. ) or jet piles, should be considered.
Based on the Soil Conservation Service soil map, the foundation
material above the bluff , is classed as Clallam gravelly loam, 8
08/12/94 12: 47 206 679 9445 YONKMAN CONSTRUCTION PAGE 03
Mr. Baron Mews]. August 11 . 1994
-2-
to 15% slope. This soil type consists of gravelly sandy loam
(ce-OM) , which grades into slightly cemented Vashon till at a
depth of two to three feet . Then , at depth , the Whidbey
formation is encountered (see Figure 1) .
Bearing capacities in the Clallam gravelly loam and the
underlying Vashon till , after stripping the surface soil and
forest floor organic material , should cacced 2 TSP which will be
ample for any residential type structure. The recent logging has
left the surface rather "torn up" and dcprcaaiona (low areas)
exist, where water can pond. Also, it appears that a shallow
trench, located 8 feet back and parallel to the bluff face, was
placed along a portion of the bluff some years ago, to intercept
surface drainage. Drainage from this trench may have contributed
to the current erosion problem. The existing conifer trees , at
all points on the parcel , all show a alight bending down slope,
which is normal when soil creep occurs.
In the exposed face of the bluff, about 10 feet from the top of
the bluff, is where the Whidbey formation, a rather volt youth,
cemented (indurated) clayey and sandy silt , is encountered. This
formation, in both Island and Skagit Counties , is notorious for
being unstable and triggering slope failures . The surface soil
in the bluff and down to the high tide line, is shown on the soil
Conservation Service soil map as Dystric Xerochrepts, 70 to 90%
slopes. This soil type is very gravelly loam (SM, GM) . However,
this soil does not reflect the sandy silt and clayey silt nature
of the underlying Whidbey formation. It is quite obvious that
the gravelly loam is the result of down slope migration or slope
wash of the Vashon till , and at a shallow depth either sandy silt
or clayey silt will be encountered.
In the past, a railroad was constructed along the high tide zone
along the northern portion of your parcel , and the water side of
the railroad grade was armored with rip-rap. This has tended to
protect the shoreline and has arrested wave erosion. This will
add many years to the project life of the parcel , in regard to
slope instability being caused by removal of toe material . The
upslope grading cut for the railroad, probably unbalanced the j
slope and thus triggered a number of landslides in the past. The
railroad has since been abnndnned. i
Other than the potential for sudden slope failures in the upper
portion of the steep bluff during a seismic event, the greatest
danger is from erosion of the rather soft Whidbey formation
material . For this reason, surface drainage water should never
he allowed to concentrate and then flow down the face of the
bluff or into the existing draws on both sides of the parcel .
Paso, all low spots in the area above the bluff should be filled
and sloped to drain. Such low spots, could result in the ponded
water seeping into the subsurface and down to the cemented till .
09/12/94 12: 47 206 679 9445 YONKMAN CONSTRUCTION PAGE 04
Mr. Baron Diegel August 11, 1994
-3-
This water would then migrate down slope, seep out of the bluff
slope, and also contribute to erosion.
To control both surface and subsurface water , the placement of a
"tight line" system is recommended. This will collect and
discharge the water into the sip-tap zone or at the high tide
line. The system should include all water collected from the
roof of any proposed structure . Also , yuu should place au
140\0 intercept ditch-curtain drain just up slope (10 to 15 feet) of
the bluff to intercept and culled surface sheet flow, which will
tette then also be removed by the "tight line". General data on "tight
line" installation is given in Attachment A. Since the blurt
height is low, the "tight line" will only need a minimum of
anchorage points.
vegetation is you'. g'.eatest protection against erosion, therefore
never remove any vegetation unless necessary. I would suggest
that you contact the Skagit County Planning Department and
obtain the following FREE publications - Vegetation Management: 'A
Guide for Puget Sound Bluff property Owners, Publication 93-31
and Slope Stabilization and Erosion Control Using Vegetation,
Publication 93-30 , both published in 1993 by the Washington
Department of Ecology.
In order to prepare the geologic section, showing both relative
topography and known or expected subsurface conditions (see
Figure 1 ) , a "hand level -compass-tape" survey was made. The
accuracy of distances and elevations, will be plus or minus 5
feet. This geologic section will aid you in selecting a building
site. Also, I have shown what I consider a reasonable slope
failure condition with allowance for a MODERATE sized seismic
event . Such a seismic event could result in lurching and
possibly , if the Whidbey formation beds are saturated ,
liquefaction at depth, which could then result in failure back 20
to 30 feet into the bluff. slope . In my judgment , a seismic
acceleration of 0.15g is reasonable for this area.
As you know, your parcel slopes toward the north. That means
that any accumulated winter snow or ice will take longer to melt .
Therefore, a steep access road could make for a dangerous
condition. You wilt note in Figure 1, that the 13 foot slope
distance fill slope, down from Oakes Avenue, is quite steep (50
degrees ) . A large ramp ( if the access road alignment is
perpendicular to Oakes Avenue) will be required in order to
obtain a reasonable grade for the road, Also, before placing an
access ramp or any fill material on the existing ground surface, 1
all loose surface soil which consists of vegetation and organic
( forest floor) material , must be stripped and wasted. However, a
second option could be considered. It is my understanding that
the owner of the parcel immediately to the west of your parcel
will build in the near future. If an entry and exit ramp was
99/12/94 12: 47 296 679 9445 YUNKMAN CONSTRUCTION PAGE 95
Mr . Bacon Diego' Auyus1 11, 1994
-4-
placed for access to both parcels, at an angle to and from Oakes
Avenue and crossed both parcels, then the road grades could be
made quite low.
I would suggest that any spoil (free of organic material )
that is developed during grading on your parcel , be placed on the
lower part of the bluff , especially in the draw along the west
side of your parcel , to obtain a flatter bluff slope and in that
way reduce the erosion potential and later slope failures .
Such a fill should be armored. Specifications or a guide, for
your contractor, will have to be prepared if you fill against the
bluff slope. Also, once you have selected a building site, then
if it is determined that C . I . D .H . piles are needed, then
secondary exploration (backhoe trenches or drilling) will be
required . Based on the exploration data obtained . pile tip
elevations will then be determined.
The recommendations provided herein are based on my understanding
of the project at this time. I expect the on-site surface and
subsurface conditions to reflect my findings . However , some
variations may occur. Should conditions he encountered that have
not been discussed herein,. .I should be contacted immediately to
determine if additional nr alternate recommendations are
required. This report has been prepared for specific application
to the proposed placement of a structure on the subject parcel ,
in accordance with generally accepted geotecbnical engineering
practices. No other warranty, expressed or implied, is made.
sincerely,
B. s
James B. Scott, P. E. %Q ii YWAsy4�TpA
Yonkman Construction
Attachment A •� 9�CrsTgSt9 ‘it -
ors
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08/12/94 12: 47 206 679 9445 YONKMAN CONSTRUCTION PAGE 06
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INSTALLATION OF TIGHT LINE SYSTEM
This general and standard design statement , regarding the
placement of a " tightline" system, is to be considered as a guide
only. Bluff or slope conditions along with the volume of water
to discharge , will dictate the actual design of the system.
Figure 1 shows a typical section view of such a system, It
should be pointed out that the system shown. could he ennsidered
to be "over designed " . However , it is known that many
"lightline" systems have failed because of poor anchorage nr the
use of under strength pipe. Therefore . it is better to err in
favor of over design than to have a system fail . Failure of a
tightline system can and does result in very rapid erosion with
associated unbalancing of the slope , which then leads to slope
instability and landslides . The typical system, as shown, can
have a project life of up to 15 years for the exposed portion of
the pipe which will ultimately deteriorate. Polyethylene pipe
becomes brittle after extended exposure to molar UV . However.
buried pipe is reported to have a project life estimated to
exceed 100 years . This system design was prepared with the
understanding that the system will be placed . using your own
labor . This data and the description of how the system will be
placed, was not prepared as "plans and specifications" for a bid
(nontract ) item.
The weak points of any " tight line " system, depending on the
steepness of the slope , are ( 1 ) points where couplings are
located, ( 2 ) effect of UV on the exposed pipe, (3) strength of
the pipe ( the weight of the pipe tending to pull the pipe apart ) ,
and ( 4 ) vibration and movement caused by turbulent water flow.
Most couplings have been eliminated by using only flexible pipe.
However , couplings will be required at discharge points from roof
downspouts . Based on data from a manufacturer (see figure 2) , it
appears that the best pipe in regard to both resistance to UV and
strength for a very steep slope, allowing for the estimated flow
(25 year storm) generated from a 3000 square foot roof . will be 4
inch Heavy Duty-AASHTO or equivalent) flexible pipe as produced
by Hancor , Inc. The product code is HY P15 (Specification AASHTO
M252 ) , The Washington State distributor for Hancor pipe is H. D.
Fowler Company of Bellevue . Placement of anchors will be
required to reduce or dampen resulting from turbulent flow.
Two types of anchoring (concrete blocks and trenching) will be
discussed. In the case of a high or steep slope of a bluff,
during a very heavy storm. collected water as it discharges at
the high tide line , could be like a high pressure water fire
hose. To keep the pipe from moving from the vibration and surges
08/12/94 12: 47 206 679 9445 VONKMAN CONSTRUCTION PAGE 07
gf
y�= HEAVY DUTY-AASHTO PIPE
v / :,- HEAVY DUTY-AASHTO pipe it a flexible high density
polyethylene pipe, corrugated on the inside and c Rside.
HEAVY DUTY•AASHTO pipe is heavier than HEAVY
DUTY pipe. This extra weight provides additional
stiffness desired in some installations, It is often used for
highway-related drainage projects or for applications
es where heavy loads will be placed on the pipe, HEAVY
DUTY-AASHTO pipe also works well for general drainage
applications.
lealde Outside Prated
Disputer plamejer Cpartificstina ahig CMS SUGGESTED APPLICATIONS
3" 3.6" ' AASHTO Al2S2 flsln 11Y red 41
Part HY PPI a Slone dnWrtsge sterns
Pe t?Wnp HY Mt OS Culvefle grid Coss*teas
1" It' AASHTO MUS2 Male HY PLS 01 rkladort odor drains l
Pert ' icy Met
Peer/Wnp NY YIN NI ,
6" 7A" AASHTO M352 Plate HY PUSS
Pert HY PPI N
Pert/Wrap HY PW106
N r F.9" AASHTO M2S2 Fiala HY PM ss
Pell HY PFI 01
Pert/Wrap HY PW1 OS
te" tit" AASHTO M252 Male NY PLI to
Pert HY PFt a
reentry NY PW1 10
12" 11.t" AASHTO M294 Male MY PU 12 0
Per' HY PPI 11 i
Pere(AASHTO HY DM to e- 1.1_ s
M76 Frtteru)
Per/Wrap HY 1491/2 '
1!" 17.7" AASHTO M294 Main HY PW IS
Per HY PFt IS
Pere(AASHTO HY DM IS
pas Petters)
Pert/Wnp Hi nn 1$
1W' 21.!" AASHTO M294 Meta HY PIA II
Pert HY PPt IS CHECKLISTOF ITEMS TO coops
Pert(AAs1M'O HY OM II
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PerfWnp 11Y WWI 10
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Perf(AASWTI) flD3S24 et Gaolimdlie vat.
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08/12/94 12: 47 206 679 9445 YONKMAN CONSTRUCTION PAGE 08
1
INSTALLATION OP TIGHT LINE SYSTEM 08/11 /92
-2-
of water. a trench and then a series of anchor points will be
!coated along the pipe down the slope . These anchors will be 1/4
or 3/8 inch rebar . driven at least 2. 0 feet into the slope. bent
over to form a loop and then securea by vinyl coated wire.
A concrete anchor block (0.5 to 1 .0 cubic foot ) is recommended et
the point of discharge at the high tide line. The higher the
head (vertical height of bluff) . the larger the anchor block,
The function of the trench at the top of the bluff is to provide
a good anchor rue the up-hill portion of the pipe. The Mat
anchor point will be located about three feet down slope from the
point where the pipe appears out of the trench. Then anchors
(driven rebar) , will be placed every 20 to 50 feet (depending on
slope angle) along the pipe (see Figure 1 ) . If you do your own
labor, the cost of placing the anchor points and pipe , should be
quite economical with regard to material costa . However, the
labor effort to dig the trench. might he a difficult task. if
"hard pan" is encountered.
After the system has been placed into service . an annual
inspection of the pipeline is recommended . At the first sign of
the pipe becoming brittle, it should be replaced.
James B. Scott , P. E.
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