HomeMy WebLinkAboutGeoTech Report Revision for BLD2007-01923 and 01922 - BLD Engineering / Geo-tech Reports - 2/6/2008 V e c t o r
E N G I N E E R I N G I N C
309 WASHINGTON STREET NE • OLYMPIA WA 98501 • TEL: 360 352-2477• FAX: 360 352-0179
www.vectorengineeringinc.com
TO BE KEPT IN THE
February 15,2008 PARCEL FILE
Mr.Robert D.Fink,AICP �*
Mason County—Department of Community Development fiq .
Mason County Bldg 1
P.O.Box 279
Shelton,WA 98584 0
Subject: Geotechnical Report Acceptance
Permit#s:BLD 2007-01923 BLD 2007-01922
Parcel No.3222-45-000031 or 3222-35-000031
Applicant:NORRIS N&MARY M SUDER
Planner: Chuck McCoy
VEI#: 7054-031
Dear Mr.Fink,
The geotechnical report dated May 14, 2004 and revised geotechnical report dated December
31, 2007, and second revised report dated February 6, 2008 prepared by GeoResources, 5113
Pacific Hwy, Suite 1-I, Fife, Washington 98424.2649 for a proposed single family residence
addition and a retaining wall at 11031 NE North Shore Road, Belfair, WA 98528 was
received and reviewed by Vector Engineering,Inc.
No further review by Vector Engineering is necessary.
We have enjoyed working with you on this geotechmcal review to support the goals of the
Department of Community Development of Mason County, Washington. We look forward to
cooperating with you on any future project or review.
The buffer reduction request will need to go through the variance process.
The invoice, the geo tech work order, the geotechnical report, revised geotechnical report,
second geotechnical report,and our review are enclosed.
Please feel free to contact me if you have any questions regarding these comments, or if you
feel any features need further discussion or attention.
Sincerely,
Russell W. La Force, P.E.
Design Engineer
Enc.
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V e c t o r
E N G I N E E R I N G I N
309 WASHINGTON STREET NE • OLYMPIA WA 98501 • TEL: 360 352-2477• FAX: 360 352-0179
www.vectorengineeringinc.com
Review of Geotechnical Report
February 15,2008 gig,
s
Permit#s:BLD 2007-01923 BLD 2007-01922 F2 0 3
Parcel No.322245-000031 or 3222-35-000031 1 -
Applicant:NORRIS N&NARY M SUDER ; "A IC D - PLA i N'+ ' d
Planner: Chuck McCoy
VEI#: 7054-031
The geotechnical report dated May 14, 2004 and revised geotechnical report dated December
31, 2007, and second revised report dated February 6, 2008 prepared by GeoResources, 5113
Pacific Hwy, Suite 1-1, Fife, Washington 98424.2649 for a proposed single family residence
addition and a retaining wall at 11031 NE North Shore Road, Belfair, WA 98528 was
received and reviewed by Vector Engineering, Inc. The Department of Community
Development requested the review for the purpose assisting the Department in determining
the amount of potential for landslide activity and the proposed development would not cause
significant adverse impacts or there is adequate geological information available on the area to
determine the impacts of the proposed development and appropriate mitigating measures. The
Department of Community Development reviews all development applications to determine if
they are likely to be in or near a landslide hazard area per Mason County Resource Ordinance
(MCRO), Geologically Hazardous Areas,Landslide Hazard Areas 17.01.100, Seismic Hazard
Areas 17.01.102,and Erosion Hazard Areas 17.01.104 approved December 27,2006.
The geotechnical report states the site has an existing residence on the shore of Hood Canal, a
parking area, a rockery, outside stairs from the parking area, and an existing concrete wall
along the toe of the slope. A site sketch with locations of the existing residence, a parking
area, a rockery, outside stairs from the parking area, and an existing concrete wall was
provided with the report.
A revised geotechnical report was submitted upon the request of the private reviewer as the
report was more than three years olds and there have been changes to the critical areas
ordinance of Mason County.
The second revised geotechnical was submitted upon the request of the private reviewer to
clarify location,retaining wall details and other items.
Findings
1. Areas identified on the Mason County Soil Survey Map as having slopes greater than
15%is one guide used by the County to indicate areas that have a higher likelihood of
meeting the classification criteria for landslide hazard areas. MCRO 17.01.100 A.2.a.
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• The site slopes south down to Hood Canal at inclinations of 85 to 135 percent.
The vertical relief of the entire slope is approximately 310 feet. The vertical relief
from the highway is 60 feet.
2. A 50-foot buffer of undisturbed natural vegetation is required around the Landslide
Hazard Area or as recommended by the geotechnical engineer. MCRO 17.01.100
D.6.a.
• No buffer or hazard is noted on the site plan.
• The second revised geotechnical report states a buffer would reduce the envelope
of the proposed development, slope appears stable, and to facilitate the proposed
development. At the toe of the slope is a retaining wall and the area is currently
disturbed. The response is adequate.
3. Based upon the results of the Geotechnical Report or Geological Assessment, the
Director may increase the buffer.MCRO 17.01.100 D.6.b.
4. Development proposed within 300 feet of areas with slopes greater than 40 percent
will require a geotechnical report.MCRO 17.01.100 E.La.
• The existing residence is within 35 feet of the toe of the landslide hazard area.
The addition is within 8 feet of the toe of the landslide hazard area.
5. The geotechnical report shall be prepared by a licensed civil engineer or a licensed
engineering geologist. MCRO 17.01.100 E.3
• Bradley Biggerstaff, a licensed engineering geologist, and Kurt Groesch, a
licensed civil engineer, prepared the 2004 report. Bradley Biggerstaff and Glen
Coad, a licensed civil engineer, prepared the revised 2007 report and the second
revised report.
6. The report includes a discussion of geologic conditions in the general vicinity,
including soil types, groundwater conditions, upslope geomorphology, location of
upland waterbodies and wetlands, and a history of the landslide activity. MCRO
17.01.100 E.S.(1).
• The revised report states the geology of the site is glacial drift with soils of Everett
gravelly loamy sand deposited during the Vashon Stade of the Fraser Glaciation in
the upper portions of the slope and Salmon Springs sediments in the lower
portions.No groundwater was encountered or observed. It was mentioned than an
adjacent area southwest of the site is mapped as unstable. No evidence of
sloughing or deep-seated movement was observed in the slope above the
residence. There was no mention of upslope geomorphology and upland
waterbodies.
• The second revised report states no upland water bodies or ravines were observed
and no slope instability was observed.The response is adequate.
7. The report is to include a site plan identifying important development or geologic
features.MCRO 17.01.100 E.S. (2).
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• The second revised report includes a site plan showing locations of the existing
residence, a parking area, a rockery, outside stairs from the parking area, and an
existing concrete wall.
8. The report is to include the locations and logs of exploratory holes or probes. MCRO
17.01.100 E.S. (3).
• Three locations were hand augured. The logs are in the report. The locations are
shown on the site sketch.
9. The report is to include a geologic map of the site showing the area of the proposed
development with the boundaries of the hazard, and associated buffers and setbacks
delineated on the map.MCRO 17.01.100 E.S.(4).
• A geologic map of the site showing the area of the proposed development with
boundaries of the hazard, and associated buffers and setbacks needs to be
provided.
• A geologic map of the site showing the area of the proposed development with
boundaries of the hazard, and associated buffers and setbacks was provided in the
second revised report. The response is adequate.
10. The report is to include a cross-section at a scale adequately depicting the subsurface
profile.MCRO 17.01.100 E.S.(5).
• A cross-section showing the subsurface profile was provided in the report. The
building, road, parking area, existing retaining wall and proposed concrete
bulkhead is also shown on the cross-section
11. The report is to include a description and results of the slope stability analysis. The
analysis should include the Simplified Bishop's Method of Circles. The minimum
static factor of safety is 1.5. The minimum seismic safety factor is I.I. The quasi-
static analysis coefficient should be 0.15.MCRO 17.01.100 E.S.(6).
• The revised report states on page 6 in the section titled SLOPE STABILITY
METHODOLOGY slope stability was modeled using WinStabl but PCSTABL6
appears to have been used. The revised report also mentions on page 9 in the
section titled STABILITY ANALYSIS,XSTABL was also used. The quasi-static
analysis coefficient used was 0.15.The minimum calculated factors of safety were
estimated to be 1.50 static and 1.18 dynamic.Two soil types were identified.
• The second revised report states the slope stability program used was
WinStabl(PCSTABL6). The response is adequate.
12. The report is to include appropriate restrictions on placement of drainage features,
septic drainfields and compacted fill and footings,including recommended buffers and
setbacks from the landslide hazard areas.MCRO 17.01.100 E.S.(7).
• The report includes the restrictions on drainage of concentrated surface water or
significant sheet flow onto the sloped areas; structural fill, including floor slab
support and retaining walls,and setbacks.
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13. The report is to include recommendations for the preparation of a detailed clearing and
grading plan which specifically identifies vegetation to be removed, a schedule for
vegetation and replanting, and the method of vegetation removal. MCRO 17.01.100
E.S. (8).
• The report includes recommendations for clearing and grading.
14. The report is to include recommendations for the preparation of a detailed temporary
erosion control plan, which identifies the specific mitigating measures to be
implemented. MCRO 17.01.100 E.S. (9).
• The report does include recommendations for the preparation of a detailed
temporary erosion control plan on page 9 in the section titled EROSION
HAZARD.
15. The report is to include an analysis of both on-site and oil site impacts. MCRO
17.01.100 E.S.(10).
• The revised report includes an analysis of on-site and off-site impacts. The
analysis states the proposed development will not decrease slope stability at the
site or on adjacent properties and the risk for such occurrence would be minimal.
16. The report is to include specifications of final development conditions, such as,
vegetative management, drainage control, and buffer widths. MCRO 17.01.100 E.S.
(10).
• The revised report includes incomplete recommendations for final development
conditions,such as vegetation management,and drainage control.
• The report should include recommendations stressing the need to maintain the
natural vegetative cover on the landslide hazard area and its buffers.
17. The report is to include recommendations for the preparation of structural mitigation
or details of other proposed mitigation.MCRO 17.01.100 E.S.(11).
• The report includes recommendations for mitigation.
18. The report is to include a site map drawn to scale showing the property boundaries,
scale, north arrow, and the location and nature of the proposed development on the
site.MCRO 17.01.100 E.S. (12).
• A site sketch drawn to scale showing the nature of the proposed development
except for the concrete retaining wall in relation to the existing residence, a
parking area, a rockery, outside stairs from the parking area, and an existing
concrete wall is a part of the report.
• A site plan drawn to scale showing the property boundaries, scale, north arrow,
and the location and nature of the proposed development on the site is a part of the
report.
19. If the site is in a Seismic Hazard Area, then the Geological Report shall include a
description of the geology of the site,conclusions and recommendations regarding the
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effect of geological conditions on the proposed development, and opinions and
recommendations for compensating for the seismic hazards present.MCRO 17.01.102
D.3.a.
• The report includes an analysis of the seismic hazard and the site was determined
to be not susceptible to liquefaction.
20. If the site is in an Erosion Hazard Area,then the Geological Report may include a Soil
Erosion and Control Report as an attachment.MCRO 17.01.104 D.3.
• The report mentions that the site does not meet the requirements of an erosion
hazard area.
Conclusions and Recommendations
In the reviewer's opinion,the report, revised report, and second revised report were prepared
by a qualified engineering geologist and qualified civil engineers and does provide sufficient
information to determine the proposed residence will not decrease slope stability at the site or
on adjacent properties and the risk for such occurrence would be minimal.
It is recommended that the geotechnical report, first revised report, and second revised report
be accepted. No further review by Vector Engineering is necessary.
Adequate erosion and sediment control features need to be implemented during land
disturbing activities to protect neighboring properties and State waters from adverse
stormwater runoff impacts. The migration or release of silty water or mud from the
applicant's property will be considered a violation of County and State water quality
protection regulations.
The conclusions presented in this report are based on Vector Engineering, Inc.' understanding
of the project requirements.Vector Engineering,Inc.warrants that its services were performed
with the level of care and skill ordinarily exercised by members of the same profession
currently practicing in the same locality under similar conditions. No other warranty or
representation,expressed or implied,is included or intended hereunder.
Sincerely,
—&A4� ,`g, vim— &. 1 Sa .o Y
(Signature) (Date)
Russell W. La Force, P.E. Seal:
Design Engineer A o
Vector Engineering, Inc. 44, S 2-0 ii
309 Washington Street NE 9 42651 �
Olympia, WA 98501 fcisTEA�`° J
(360) 352-2477 S/0NAL
EXPIRE=05-25-('
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GeoResources, LLC
Ph. 253-279-1023 5113 Pacific Hwy. E., Ste. 1-I
Fx. 253-638-8992 Fife, Washington 98424-2648
February 6, 2008
Mr. Norris Suder
13035 15th Avenue NE
Seattle, WA 98125
Ph: 206-367-6251
D nn 2 L Revised Geotechnical Report
DU Proposed Residential Remodel
11031 North Shore Road
F E B 1 3 440 Lot 17 Div 14
Mason County, WA
PN:322245000031
VECTOR ENGINEERING, INC. Job No: SuderN.NoShoreRd.RG.r
INTRODUCTION
This revised report summarizes our site observations, provides our opinion
regarding development of the site and addresses the current Mason County critical area
regulations. The site is located at 11031 North Shore Road along the shoreline of Hood
Canal, approximately 11 miles northwest of Belfair, Washington. The general location of
the site is illustrated on the Vicinity Map, Figure 1a. According to the Mason County
Assessor/Treasurer parcel information, the site is identified as 3222-45-00031. The
Mason County Map Web Viewer identifies the site as parcel number 3222-35-00031.
A site location map with the distance to the nearest intersection is included as
Figure 1 b.
Our previously prepared Geotechnical Report dated December 31, 2007 was
returned to us with comments from Vector Engineering. Their comments were
documented in a January 11, 2008 letter, a copy of which is attached. We have
since included additional text and figures, as appropriate.
Our services are provided at your request and are based on our site meeting with
you, our experience in the area, and our site observations, and discussions with County
staff. We visited the site on several occasions in March and April of 2004. We
understand that you propose to remodel the single-family residential structure at the site.
We further understand that conventional construction methods will likely be used.
Portions of the lot slope at greater than 40 percent and have a vertical height of
greater than 10 feet. Mason County therefore requires a geotechnical report be
prepared to address slope stability and provide geotechnical recommendations and
design criteria for the proposed single-family residence addition at the site. A site sketch
is included as Figure 2.
The purpose of our services is to address the landslide and erosion hazard issues
at the site per the Mason County SAO (Sensitive Area Ordinance) and provide
geotechnical recommendations and design criteria for the proposed residential site
improvements. Specifically, the scope of services for this project will include the
following:
1. Review the available Critical Area, geologic, hydrogeologic and geotechnical
data for the site area.
• rc
Suder: Residential Remodel
February 6, 2008
Page 2
2. Conduct a detailed geologic reconnaissance and slope mapping of the site area,
including exposures of the dense, native "hardpan", supplemented by hand
auger test borings at selected representative locations.
3. Conduct a computer generated slope stability analysis using the WINSTABL
program.
4. Address the appropriate geotechnical regulatory requirements for the proposed
site development, and slope mitigation measures.
5. Provide geotechnical recommendations for site grading including site
preparation, subgrade preparation, fill placement criteria, suitability of on-site
soils for use as structural fill, temporary and permanent cut and fill slopes, and
drainage and erosion control measures.
6. Provide recommendations and design criteria for foundation and floor slab
support, including allowable bearing capacity, subgrade modulus, lateral
resistance values and estimates of settlement.
7. Provide recommendations and design criteria for design of conventional
subgrade/retaining walls, including backfill and drainage requirements, lateral
design loads, and lateral resistance values, and the possible use or extension of
the existing wall to support the new construction.
8. Provide stormwater runoff control recommendations.
SITE CONDITIONS
Surface Conditions
The site is located at 11031 North Shore Road between Tahuya and Belfair State
Park in Mason County, Washington. The existing home at the site is located above
beach level and is currently accessed by steps descending from a parking area located
approximately 6-feet below the grade of North Shore Road. North Shore Road is
situated east of the residence and dissects the property. The site is bounded by existing
residential structures on the west, northeast and southwest and Hood Canal on the
southeast.
The site is located on the shoreline margin of the glacial uplands near
Tahuya. No upland water bodies or ravines were observed near the site. The
Tahuya River is located greater than 3000 feet from the site and is separated from
the site by a glacial upland area. The site is a located on a southeast-facing slope
north of Hood Canal. The upper sloping area east and above North Shore Road is
densely vegetated and currently undeveloped. The site extends across North Shore
Road and topography slopes down toward the shoreline of Hood Canal. The existing home
on the subject property is a waterfront cabin, accessed by stairs that extend down from a
parking area and North Shore Road. An existing retaining wall is located at the base of a
steeply descending hillside that is situated between the existing residence and North Shore
Road. The proposed remodel of the existing residence and the new addition to be
constructed is located between the rear of the existing residence and the concrete retaining
wall and will utilize conventional construction methods. The new addition will be two stories
in height. The shoreline area is protected by an existing concrete bulkhead.
The ground surface in the proposed residential addition area is generally flat.
The uphill side of the addition area is protected by the existing concrete retaining wall.
The construction details of the existing wall (age, reinforcement, foundation size) are
unknown, and portions of the walls are out of plumb and leaning outwards slightly from
the slope. We understand that this is related to construction, and not movement of the
Suder: Residential Remodel
February 6, 2008
Page 3
wall. We have not been provided a site plan at this time. However we have
included a parcel map with landslide hazard areas, buffers, and boundaries as
Figure 2b.
The slope area between the wall and the upper parking area is densely vegetated
with mature evergreen trees and sparse underbrush. The trees are vertical in orientation
and do not exhibit "pistol' butt trunks or other evidence indicative of slope instability or
soil creep. The site slope between the residence and parking area ranged between 85
and 100 percent. We measured slopes as steep as 135 percent east of and across
North Shore Road from the area of proposed development. The vertical height of the
steep slope area above the residence and wall is approximately 40-feet. No evidence of
significant erosion or slope instability were observed at the site or the adjacent areas. A
Cross-Section is included as Figure 3.
Site Soils
The USDA Natural Resource Conservation Service web soil survey for Mason
County indicates that the site and steep slope area soils consist of Everett gravelly
loamy sand (Ek) that form on 15 to 30 percent slopes. The Everett soils are
generally derived from gravelly glacial outwash and are listed as having
"moderate" potential for erosion hazard, when exposed. A copy of the USDA SCS map
for the site is included as Figure 4. As previously discussed, we observed no evidence of
surficial erosion at the time of our site visit.
Geologic Conditions
The Geologic Map of Washington State, by Eric Schuster, (2005) maps soils in
the vicinity of the site to consist of Pleistocene Continental Glacial Drift (Qgd). The
glacial drift soils are described as undifferentiated glacial till and outwash sand and
gravel. Based on our experience in the area, the soils in the upper portion of the slope
were deposited during the Vashon Stade of the Fraser Glaciation, approximately 12,000
to 15,000 years ago. The soils in the lower portion of the slope, exposed along North
Shore Road, are likely older Salmon Springs sediments. The glacial soils in the site area
consists of sand and gravel with variable silt, cobbles and boulders that was deposited
and overridden by the continental ice mass. As such, the undisturbed soils in the site
area are considered overconsolidated and have high strength and low compressibility
characteristics. The near surface recessional outwash deposits consist of a poorly
stratified mixture of sand and gravel that were deposited by meltwater streams and rivers
emanating from the continental ice mass. The surficial soils in the site area have been
weathered by natural processes to a loose to medium dense condition. An excerpt of
the above referenced map is included as Figure 5a. Since a detailed geologic map
of the area is not yet available, a map of the proposed development with boundaries
of landslide hazard areas as defined by Mason County are shown on Figure 2b.
We also reviewed the Relative Slope Stability of the Southern Hood Canal Area,
Washington by Smith and Carson dated 1977. This map indicates the site, located on
the flatter upland area north of the Hood Canal, is in a Class I area for slope stability.
The shoreline bluff at the site is identified as "S" or Stable by the Department of Ecology
Coastal Zone Atlas. An area of "U" or Unstable shoreline is located just southwest of the
site. An excerpt of the Coast Zone Atlas map for the site area is included as Figure 5b.
Suder: Residential Remodel
February 6, 2008
Page 4
Subsurface Conditions
As part of our site reconnaissance, we completed a series of hand auger
explorations at selected representative locations across the site. Soil conditions at
specific exploration locations were logged in the field. The conditions encountered in the
individual hand auger explorations were logged in accordance with the Soil Classification
system summarized on Figure 6. Logs of the individual hand auger explorations are
included as Figure 7.
Near surface soils at the site generally consist of dense sands and gravel with
variable silt, cobbles and boulders. The dense sands and gravels are exposed in outcrop
in numerous locations on the uphill side of North Shore Road in the project vicinity.
These soils are interpreted to be older glacial outwash related to the Salmon Springs.
Our site exploration encountered cemented sands and gravels in the crawl space below
the cabin. These soils are likely the older glacial deposits (Salmon Springs) and were in
a very dense and cemented condition. The slope area above the home and retaining
wall is mantled by a thin deposit of topsoil and forest duff. The native sand and gravel
soils below the topsoil in this area were generally in a dense to very dense condition. No
groundwater seepage or spring activity was observed in the sloping areas at or near the
site at the site at the time of our site visit, or in our explorations. Portions of the slope
area below the home, outboard the concrete bulkhead are intermittently submerged,
depending on tidal fluctuations.
GEOLOGIC HAZARDS
Landslide Hazard Indicators per Mason County Resource Ordinance 17.01.100
According to the Mason County Resource Ordinance 17.01.100, the purpose of
the landslide hazard section is to identify areas that present potential dangers to public
health and safety, to prevent the acceleration of natural geological hazards, to address
off site environmental impacts, and to minimize the risk to the property owner or adjacent
property owners from development activities. The following shall be classified as
Landslide Hazard Areas:
a. Areas with any indications of earth movement such as debris slides,
earthflows,
slumps and rock falls (see figure F.100).
b. Areas with artificial oversteepened or unengineered slopes, i.e. cuts or fills.
c. Areas with slopes containing soft or potentially liquefiable soils.
d. Areas oversteepened or otherwise unstable as a result of stream incision,
stream bank erosion, and undercutting by wave action.
e. Slopes greater than 15% (8.5 degrees) and having the following:
I. Hillsides intersecting geologic contacts with a relatively permeable
sediment overlying a relatively impermeable sediment or bedrock (e.g.
sand overlying clay); and
ii. Springs or groundwater seepage.
f. Any area with a slope of forty percent or steeper and with a vertical relief of ten
or more feet except areas composed of consolidated rock. A slope is delineated
by establishing its toe and top and measured by averaging the inclination over at
least ten feet of vertical relief.
In addition, the following information may be used as a guide by the County to indicate
areas that have a higher likelihood of meeting the classification criteria above:
a. The areas identified on the Mason County Soil Survey Map as having slopes
greater than 15%.
Suder: Residential Remodel
February 6, 2008
Page 5
b. The areas identified on the Coastal Zone Atlas, Volume 9, of Mason County,
Washington as:
I. Unstable - "U"
ii. Unstable Old Slides - "UOS"
iii. Unstable Recent Slides - "URS"
iv. Intermediate Slopes - "I"
v. Modified Slopes - "M"
c. The areas identified as Class 2, 3, 4, or 5 of the maps: "Relative Slope Stability
of the Southern Hood Canal Area, Washington", by M. Smith and R.J. Carson,
Washington State Department of Natural Resources, Division of Earth
Resources, 1977; and `The Geological Map of North Central Mason County,
Washington", by R.J. Carson, 1976, U.S. Geologic Survey OFR 76-2;
d. Areas mapped as landslide deposits (Map Unit Qls) on the: Geologic map of
the Longbranch 7.5-minute quadrangle, Thurston, Pierce, and Mason Counties,
Washington, by R. L. Logan, T. J. Walsh, and Michael Polenz. 1 sheet, scale
1:24,000, 2003; Geologic map of the Squaxin Island 7.5-minute quadrangle,
Mason and Thurston Counties, Washington, by R. L. Logan, Michael Polenz, T.
J. Walsh, and H. W. Schasse. 1 sheet, scale 1:24,000, 2003; Geologic map of
the Shelton 7.5-minute quadrangle, Mason and Thurston Counties, Washington,
by H. W. Schasse, R. L. Logan, Michael Polenz, and T. J. Walsh. 1 sheet, scale
1:24,000, 2003; and Geologic map of the Summit Lake 7.5-minute quadrangle,
Thurston and Mason Counties, Washington, by R. L. Logan and T. J. Walsh. 42 x
36 in. color sheet, scale 1:24,000, 2004.
SLOPE STABILITY METHODOLOGY
The computer program WinStabl (PCSTABL6) was used to determine the overall
stability of the site in its current configuration for both static and seismic conditions, and
in the post-development configuration for both static and seismic conditions. Slope
failure surfaces were analyzed using the Bishop Method, which is a circular failure force
equilibrium method. All calculations were performed by the computer model WinStabl,
which requires user input of the topographic surface, soil strength properties,
groundwater information, and other loads, including seismic and building loads. The
surface data was provided by the topographic site section developed during our evaluation.
The soil parameters used in the analysis are interpreted, estimated, and/or assumed based
on our visual observations, field explorations, empirical correlations, and experience with
similar soil and groundwater conditions in the area.
Once the parameters have been determined, the critical failure surfaces and
associated factors of safety for the modeled slope and development conditions can be
calculated. The critical surface is the surface or plane most likely along which the soil
mass will slide. The factor of safety is the ratio of the sum of moments resisting movement
over the sum of moments driving movements. Accordingly, a slope with a factor of safety
less than 1.0 has more driving forces than resisting forces, while a factor of safety greater
than 1.0 has more resisting forces than driving forces. Industry standard requires that a
site have a factor of safety of 1.5 and 1.1 against failure for static and seismic conditions,
respectively.
1 .
Suder: Residential Remodel
February 6, 2008
Page 6
Slope Stability Analysis
To analyze the stability of the site, we performed our analysis on the 85 to 100
percent slope area observed between the residence and North Shore Road. The slope
across from and above, on the east side of North Shore Road has slopes greater
than 40 percent with more than 10 vertical feet. This slopes is in an area identified
as Class 2 for slope stability based on inclination by the "Relative Slope Stability
of the Southern Hood Canal Area, Washington" by Smith and Carson (1977). We
do not anticipate any development on this slope area. The width of North Shore
Road also acts as a buffer for this up- slope area and therefore is not addressed in
our slope stability analysis. In our professional opinion, the analysis on the slope
below North Shore Road and the shoreline is adequate to address the slope
stability in the area of proposed development. Based on our site observations, site
topography, and the encountered subsurface soil and groundwater conditions, we
established both dry and saturated unit weight, isotropic strength intercept (cohesion),
and isotropic strength angle (phi angle) for the various soil units at the site.
GeoResources assigned soil unit weight and strength parameters based on our
experience, field explorations accomplished in the site area, as well as index laboratory
testing accomplished on this parcels and adjacent properties. Based on our review, we
conclude the assumed values for the various soil types appear to fall well within the range
of tabulated values in the literature, and in some instances, the values appear to be
conservative. The following table summarized our assigned soil strength properties.
ESTIMATED PROPERTIES OF ON-SITE SOILS FOR STABILITY ANALYSIS
Dry Unit Isotropic Internal
Soil Type Weight Sat. Unit Weight Strength Strength
(pcf) (pcf) Intercept Angle
(psf) (degrees)
Dense to Very Dense Sand 125 130 250 36
with Silt and Gravel
Older Salmon Springs Sand 138 145 750 40
and Gravel
The soil properties utilized were based on the soils observed in the site area and
relevant information provided in "Geotechnical Properties of Geologic Materials"by
Koloski, Schwarz, and Tubbs, Washington Division of Geology and Earth Resources
Bulletin 78, as presented in Volume 1, ENGINEERING GEOLOGY IN WASHINGTON.
The dense to very dense sand with silt and gravel is interpreted to be glacial till.
The site seismic stability conditions were analyzed by applying a horizontal acceleration
equal to one-half of the appropriate peak ground acceleration. Based on current
standard of practice, we used a design peak ground acceleration of 0.15g for the site.
Using the Bishop method, we generated several failure surfaces for the pre- and
post-development conditions using both the static and seismic loading conditions. Our
analyses yielded the following safety factors:
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Development Condition Factor Of Safety
Pre Development (Static) 1.50
Pre Development with 1 .18
Seismic
Post Development (Static) 1.50
Post Development with
1.18
Seismic
Graphical output of the WinStabl analysis, indicating the ten most critical failure
planes and corresponding factors of safety for the two post development models are
included as Appendix "A".
With respect to more substantial deep-seated failure modes, our analysis
indicates the factor of safety for the slope conditions are 1.50 for static conditions and
1.18 for seismic conditions. The factors of safety did not change with the proposed
addition at the site.
Based on the above and provided the recommendations presented in this report
are incorporated into the project design and construction, the proposed development will
not decrease slope stability at the site or on adjacent properties and the risk for such
occurrence would be minimal. In fact, the construction of additional retaining structures
above the addition area with improved drainage controls will improve slope stability at the
site.
CONCLUSIONS
Based on a review of the available geologic information and our site
reconnaissance, it is our opinion that the site is currently stable under the existing
conditions. The proposed addition will provide additional slope stabilization measures
and drainage controls. Proper retainage of the upslope area and improved surface
drainage and erosion control measures will reduce the risk for erosion and slope
instability at the site. The greatest risk of erosion and/or slope instability is during
construction. Appropriate erosion control measures will be installed to mitigate this risk.
We understand that grading at the site will be minimal, and will consist primarily of
excavating for the footings for the residential addition and new retaining structures for the
proposed addition, and any new site utilities and landscaping. Based on our
understanding of the project, it is our opinion that the site soils will provide adequate
support for the structure provided they are prepared in accordance with the standards of
practice for the Puget Sound area and the recommendations provided herein.
Geotechnical recommendations and design criteria for the proposed residential addition
are provided below.
Landslide Hazard
Based on our site observations, explorations and review of the available
published information, no evidence of past or ongoing earth movement, or landslide
activity was identified. No significant areas of fill material or unretained over-steepened
slopes were observed, nor were slopes with areas containing soft or potentially
liquefiable soils observed at the site. We did not observe areas oversteepened or
unstable soils as a result of stream incision, stream bank erosion, or undercutting by
f
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Page 8
wave action. The shoreline area is protected with a concrete bulkhead. While we did
observe areas of 15 percent slopes, we did not observe intersecting contacts or seeps
on the slope east of the building site. We also observed areas of greater than 40
percent slopes with more than 10 feet of vertical relief at the site. A portion of that slope
area is retained by a concrete retaining wall. No evidence of erosion or slope instability
was observed at the site or the adjacent areas. The site area is located in an area of
Class 2 slope stability with an area of Class 3 slope stability located south of the site
because of the steep slope areas by the "Relative Slope Stability of the Southern Hood
Canal Area, Washington."
Although portions of the site meet the technical criteria of a Landslide Hazard
area (slope greater than 40 percent with more than 10 vertical feet, Class II for slope
stability on the slope area), it is our opinion that the site soils are in a stable condition
based on our site observations and slope stability analysis.
The construction of the residential addition at the site will not have any adverse
impact on the stability of the slopes. Because the proposed addition area is currently
occupied by the existing shed roof addition and patio, no significant increase in
impervious area or storm water runoff is anticipated. Significant slope movement typically
occurs during or following significant or extended periods of rainfall/precipitation.
Although proper planning, design, drainage and construction techniques can reduce the
risk of significant erosion and slope instability, there is an inherent risk of instability
associated with steep shoreline sites.
Buffers per Mason County Resource Ordinance 17.01.100.D.6
We understand Mason County Resource Ordinance 17.0100.D.6a requires a
50 foot buffer of undisturbed, natural vegetation around a landslide hazard area
unless otherwise stated by a geotechnical engineer. The slope area nearest the
proposed residence has inclinations greater than 40 percent and approximately 30
feet of total relief. Therefore the slope with 40 percent or greater and 10 or more
vertical feet fit the criteria of a Landslide Hazard area. The required 50 foot buffer
would reduce the envelope of the proposed development. We understand a
reduction of the buffer around the Landslide Hazard Area is permitted as stated in
the Mason County Resource Ordinance 17.0100.D.6c. However, as demonstrated
by our slope stability modeling, the slope does have a factor of safety greater than
the required minimum by Mason County. Provided the recommendations in the
report are followed; we anticipate a reduction or elimination of the buffer should
be allowed, to facilitate the proposed development.
Again, based on our subsurface explorations and our slope stability analysis,
it is our opinion the slope near the proposed residence location appears stable in
both its current and proposed conditions.
Landslide Hazard Mitigation
Based on the results of our stability analysis and slope mitigation measures,
vertically extending the existing retaining wall will protect the proposed addition area. The
Vashon soils and Salmon Springs deposits at the site are in a dense to very dense
condition. Surficial soils at the site have been disturbed through natural weathering
processes and are presently in a loose to medium dense condition. The very dense site
soils have a moderate erosion hazard if undisturbed, especially in the heavily vegetated
area. Appropriate erosion control measures will mitigate this risk.
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Seismic Hazard Areas per Mason County Resource Ordinance 17.01.102
The purpose of the Seismic Hazard Section is to identify areas that present
potential dangers to public health and safety, and to prevent the acceleration of
manmade and natural geological hazards, and to neutralize the risk to the property
owner or adjacent properties from development activities. The following shall be
classified as Seismic Hazard Areas:
1. Areas susceptible to ground failure including the following:
a. Mapped geologic faults until proven inactive;
b. Deep road fills and areas of poorly compacted artificial fill;
c. Areas with artificially steepened slopes (i.e. old gravel pits);
d. Postglacial stream, lake or beach sediments;
e. River deltas;
f. Areas designated as potential Landslide Hazard Areas;
g. bluff areas;
In addition, the following criteria may be used as a guide by the County to indicate areas
that have a higher likelihood of meeting the classification criteria above:
a. Areas identified on the Coastal Zone Atlas of Washington, Volume 9,
Mason County as Af, Qa1, Qa2, Qvc, Qls, Qos and Qp.
b. Areas identified on the Mason County Soil Survey Map as having
slopes greater than 15 percent.
c. Faults identified on "Map Showing Known or Suspected Faults With
Quaternary Displacement in the Pacific Northwest", A.M. Rogers, T.J.
Walsh, W.J. Kockelman and G.R. Priest, US Geologic Survey, 1996; or
described in "Active Faulting Investigations on the Canyon River Fault,
Southern Olympic Ran a Washington", T.J. Walsh and K.G. Neal U.S.
9 9 ,
Geologic Survey, 1997.
Although the site has slopes greater than 15 percent and areas designated a
potential landslide hazard areas based on greater than 40 percent slopes on the site, no
other seismic hazard area indicators are located on the site.
Mason County and the state of Washington have recently adopted the 2003
International Building Code (IBC). Based on the soil conditions observed on site and the
mapped local geology, we interpret the site to correspond to a seismic Site Class "D" in
accordance with Table 1615.1.1 in the 2003 IBC (International Building Code)
documents. This is based on the likely range of equivalent SPT (Standard Penetration
Test) blow counts for the soil types observed in the site area. These conditions were
assumed to be representative for the conditions based on our experience in the vicinity
of the site.
Liquefaction is a phenomenon where there is a reduction or complete loss of soil
strength due to an increase in water pressure. The increase in pore water pressure is
induced by seismic vibrations. Liquefaction mainly affects geologically recent deposits of
loose, fine-grained sands that are below the groundwater table. The majority of the
outwash soils that underlie the site are in a very dense condition and have enough fines
to make them less likely to liquefy during a seismic event. Therefore, it is our opinion
that the risk for liquefaction to occur at this site during an earthquake is low.
Based on our site evaluation and slope stability analysis, the subject property is
located in an area underlain by very dense consolidated sand and gravel soils, and not
susceptible to design level seismic induced failures. Shaking of the already dense soil is
not apt to produce a denser configuration and subsequently excess pore water pressures
are not likely to be produced. Based on the density and coarse-grained nature of the
glacially derived soils observed on the site, and the lack of a groundwater table, it is our
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opinion that the risk for liquefaction to occur at this site during an earthquake is
negligible.
Erosion Hazards per Mason County Resource Ordinance 17.01.104
The purpose of the Erosion Hazard Section is to identify areas that present
potential dangers to public health and safety, and to prevent the acceleration of natural
geological hazards, and to neutralize the risk to the property owner from development
activities. The following shall be classified as Erosion Hazard Areas:
Areas in Mason County underlain by soils which are subject to severe erosion
when disturbed. Such soils include, but are not limited to, those for which
potential for erosion is identified in the Soil Survey of Mason County, USDA Soil
Conservation Service, 1960, or any subsequent revisions or addition to this
source. These soils include, but are not limited to, any occurrence of River Wash
("Ra") or Coastal Beaches ("Cg") and the following when they occur on slopes
15% or steeper:
a. Alderwood gravelly sandy loam ("Ac" and "Ad")
b. Cloquallum silt loam ("Cd")
c. Harstine gravelly sandy loam ("Hb")
d. Kitsap silt loam ("Kc")
The area of planned development at the site is mapped by the USDA Natural
Resource Conservation Service Web Soil Survey for Mason County, formerly known as
the SCS, as Everett gravelly loamy sand (Ek) soils. Based on this USDA soil classification,
according to Mason County, the site is not classified as an erosion hazard area.
We recommend that temporary and permanent erosion control measures be
installed and maintained during and following construction, until permanent erosion control
measures or landscaping is in place. During wet weather conditions, erosion control
measures may include but should not be limited to berms and swales to channel surface
water runoff, and ground cover/protection in exposed or disturbed areas. Temporary
ground cover/protection such as jute matting, excelsior matting, wood chips or clear plastic
sheeting should be used during wet weather conditions until permanent erosion protection
is established. Silt fences should be utilized where appropriate.
Graded or disturbed areas shall be shaped to avoid concentrations of runoff onto
the site slopes or other erosion-sensitive areas. Cleared or denuded areas shall be
revegetated of covered with approved erosion control material such as straw or mulch. We
recommend reviewing the Washington State Department of Ecology pamphlets, "Surface
Water and Groundwater on Coastal Bluffs:A guide for Puget Sound property owners"and
"Slope Stabilization and Erosion Control Using Vegetation:A manual of practice for coastal
property owners"now available online.
Site Preparation
Based on our document review and our discussions with you, additional grading at
the site will be minimal and generally consist of the excavation of the foundation for the
addition. We expect that grading at the site can be accomplished with conventional earth
moving equipment. The site soils generally consist of sand and gravel with variable silt and
cobble content. These soils may be used as structural fill during dry and moderate wet
weather conditions.
Structural Fill
No additional significant earthwork is expected at the site. The following
recommendations are provided in the event that plans change. All fill material used to
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achieve design grades at the site should be placed as structural fill. The structural fill
should be placed in horizontal lifts of appropriate thickness to allow adequate and uniform
compaction of each lift. Fill placed in the building and pavement areas should be
compacted to a firm and unyielding surface.
The appropriate lift thickness will depend on the fill characteristics and compaction
equipment used. We recommend that the appropriate lift thickness be evaluated by our
field representative during construction. For planning purposes, we recommend a
maximum loose-lift thickness of 12 inches. We recommend that our representative be
present during site grading activities to observe the work and perform field density tests.
The suitability of material for use as structural fill will depend on the gradation and
moisture content of the soil. As the amount of fines (material passing No. 200 sieve)
increases, soil becomes increasingly sensitive to small changes in moisture content and
adequate compaction becomes more difficult to achieve. If it is necessary to import
structural fill material to the site, we recommend that fill material consist of well-graded
sand and gravel with less than 5 percent passing the No. 200 sieve based on that fraction
passing the 3/4-inch sieve. During prolonged dry weather conditions, a somewhat higher
(up to 10 to 12 percent) fines content will be acceptable.
Material placed for structural fill should be free of debris, organic matter, trash and
cobbles greater than 6 inches in diameter. Particle sizes larger than 3 inches should be
excluded from the top 1-foot of fill. The moisture content of the fill material should be
adjusted as necessary for proper compaction.
Suitability of On-Site Materials as Fill
During dry weather construction, any nonorganic on-site soil may be considered for
use as structural fill, provided it meets the criteria described above in the structural fill
section and can be compacted as recommended. If the material is over the optimum
moisture content (typically 2 to 4 percent) when excavated, it will be necessary to aerate or
dry the soil prior to placement as structural fill.
The workability of material for use as structural fill will depend on the gradation and
moisture content of the soil. As the amount of fines increases, soil becomes increasingly
more sensitive to small changes in moisture content and adequate compaction becomes
more difficult or impossible to achieve.
In general, the soils observed at the site consist of sand and gravel with variable silt
and cobble content. These materials are suitable for use as structural fill during dry and
moderately wet conditions. It may be necessary to moisture condition these soils prior to
use as structural fill, particularly during dry weather conditions.
Cut and Fill Slopes
Temporary cut slopes (foundation and utility excavations) may be necessary during
grading operations. As a general guide, temporary slopes of 1.5 to 1 (horizontal to vertical)
or flatter may be used for temporary cuts in the upper 3 to 5 feet of medium dense to
dense soils. Temporary slopes of 1 to 1 or flatter may be used in the unweathered dense
to very dense sands and gravels or till. These guidelines assume that all surface loads are
kept at a minimum distance of at least one half the depth of the cut away from the top of
the slope and that significant seepage is not present on the slope face. Flatter cut slopes
will be necessary if/where significant soil moisture or seepage occurs.
In the event that permanent cut and fill slopes are required, we recommend a
maximum of 2 to 1 slope. Where 2 to 1 slopes are not feasible, retaining structures should
be considered. Fill placed on slopes that are steeper than 5 to 1 should be "keyed" into the
undisturbed native soils by cutting a series of horizontal benches. The benches should be
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1'/2 times the width of equipment used for grading and a maximum of 3 feet in height.
Subsurface drainage may be required in seepage areas. Surface drainage should be
directed away from all slope faces. Some minor raveling may occur with time. All slopes
should be seeded as soon as practical to facilitate the development of a protective
vegetative cover or otherwise protected.
Foundations
Conventional spread footings are recommended for support of the residential
addition. For the new addition bearing on medium dense native soil, we recommend an
allowable soil bearing pressure of 2,000 pounds per square foot (psf) for combined dead
and long-term live loads, exclusive of the weight of the footing and any overlying backfill. A
higher bearing pressure of 3,000 psf may be used if the footings extend to the dense to
very dense soils encountered below 3-feet in the addition area. These values may be
increased by one-third for transient loads such as those induced by seismic events or wind
loadings.
We recommend a minimum width of 18 inches for isolated footings and 16 inches
for continuous wall footings. All exterior footing elements should be embedded at least
18 inches below the lowest adjacent finished grade. We recommend that any disturbed
soils in the footing excavations be removed, or if practical, recompacted prior to concrete
placement
We estimate that settlements of footings designed and constructed as
recommended will be less than 1/2 inch, with differential settlements between comparably
loaded footings of 1/2 inch or less. These settlements will occur essentially as loads are
applied. Disturbance of the foundation subgrade during construction could result in larger
settlements than predicted.
Floor Slab Support
Slabs-on-grade should be supported on dense native soil or on structural fill
prepared as recommended. We recommend that floor slabs at the site be underlain by a
6-inch thickness of uniformly graded gravel or sand containing no more than 3 percent
fines to provide a capillary break. The capillary break material should be placed in one lift
and compacted to a firm and unyielding surface. The capillary break material should be
connected to a suitable drain outlet to provide an exit for any accumulated seepage.
Where the native soils meet this criteria, they are considered suitable for use as the
capillary break.
A vapor barrier, such as a polyethylene liner is recommended where the native or
fill soils contain greater than 3 percent fines. A thin layer of"clean" sand may be placed
over the vapor barrier and immediately below the slab to protect the polyethylene liner
during steel and/or concrete placement.
A subgrade modulus of 250 kcf (kips per cubic foot) may be used for design. We
estimate that settlement of the floor slabs designed and constructed as recommended, will
be 1/2 inch or less over a span of 50 feet.
Lateral loads may be resisted by friction on the base of footings and floor slab and
as passive pressure on the sides of footings. We recommend a coefficient of friction of
0.65 be used to calculate friction between the concrete and very dense soil. Passive
pressure may be determined using an equivalent fluid weight of 300 pcf (pounds per cubic
foot) above the water table, and 160 pcf for saturated soils. This assumes that structural fill
is placed against the sides of the footings and that the top of the fill is confined by either a
concrete floor slab or pavement. A safety factor of 1.5 is conventionally applied to these
values.
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Retaining Walls
Thi s ctizn is not intended to provide construction details of a retaining wall
but rather a mr endations. Because of the uncertainties regarding the
construction of the existing concrete wall at the site, we do not recommend this wall be
relied upon to protect the new addition. In addition, even though adequate factors of safety
were indicated for deep-seated failures at the site, there is a risk of surficial sloughing in the
slope area above the residence. Because of the steep slope above the addition area, and
the presence of large trees on the slope, we recommend that a new retaining wall be
constructed against the toe of slope and extend above the existing top of wall by a
minimum of 5-feet. The wall extension would provide a catchment area to protect the
addition from surficial sloughing type failures. The existing wall can remain in place and
serve as a portion of the back form for the new wall. In addition, we recommend that no
penetrations or openings (windows or doors) be constructed in the addition on the side of
the structure facing the slope. We also recommend that the trees located above the
residence be removed (stumped) or trimmed to reduce the potential for damage in the
event of a shallow failure.
The proposed retaining wall can be supported on conventional shallow footings
founded on medium dense native soils or structural fill, if properly prepared. Footings
bearing on undisturbed native soils or structural fill as described above can be designed
using an average allowable bearing value of 2,000 psf with a maximum toe pressure of
3,000 psf. Footings extended to bear on the dense to very dense soils may be designed to
exert an average allowable bearing pressure of 3,000 psf, with a maximum toe pressure of
4,000 psf.
Lateral loads on conventional retaining structures founded as described above may
be resisted by friction on the base of the wall footings and as passive pressure on the sides
of footings. We recommend using an ultimate coefficient of friction of 0.65 to calculate
friction between the concrete and dense native soils or on structural fill. Passive pressure
may be determined using an equivalent fluid weight of 300 pcf. This assumes that
structural fill is placed against the sides of the footings. A safety factor of 1.5 should be
applied to these values, for sliding and overturning.
The lateral active soil pressures acting on reinforced concrete retaining walls
depend on the nature, density and configuration of the soil behind the wall. We
recommend that portions of walls supporting horizontal backfill be designed using an
equivalent fluid density of 35 pcf for a level back-slope behind the wall. For the condition of
the steep slope above the wall (85 per cent), we recommend a lateral design pressure
equal to 65 pcf be used. The recommended pressure does not include the effects of sur-
charges from surface loads.
Adequate drainage behind any retaining structure or subgrade wall is imperative.
The actual condition of the drainage system for the existing wall is not known. To promote
drainage through the existing wall, we recommend the wall be penetrated with small
diameter weep holes at the base of the existing wall on a horizontal spacing no greater
than 10-feet on center. Seepage from the weep holes should be collected and manifolded
to an appropriate discharge point. If the existing wall is utilized as a back form for the new
wall, we recommend the space between the walls include a drainage medium, such as
Miradrain or other proprietary drainage material. If the new wall is set forward of the
existing wall, in addition to the weep holes, we recommend that a drainage system
consisting of a minimum 12 inches of clean sand and/or gravel with less than 3 percent
fines be placed along the back of the wall. The drainage collector system consisting of 4-
inch perforated PVC pipe should be installed between the two walls to provide an outlet for
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Suder: Residential Remodel
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any accumulated water. The drainage material should be capped at the ground surface
with 1-foot of relatively impermeable soil or otherwise sealed.
Site Drainage
All ground surfaces, pavements and sidewalks at the site should be sloped away
from structure. Surface water runoff should be controlled by a system of sloping surfaces,
curbs, berms, drainage swales, and/or catch basins, and conveyed to an appropriate
discharge point at the shoreline. Drains should be provided behind all retaining walls.
We recommend that roof runoff at the site be collected and discharged to the
Hood Canal. No significant increase in hard surface area is anticipated because the
addition area is currently occupied by an existing patio and shed roof addition. Driveway
runoff should be sheet flowed to the adjacent vegetation.
Additional Explorations
Based on our site observations during our recent site visit and a review of
published geotechnical literature, it is our opinion that no additional subsurface
explorations or slope stability model is necessary.
LIMITATIONS
We have prepared this report for use by the Suder's and members of their design
team, for use in the design of a portion of this project. The data and report should be
provided to prospective contractors for their bidding or estimating purposes only. Our
report, conclusions and interpretations should not be construed as a warranty of the
subsurface conditions.
Variations in subsurface conditions are possible between the available explorations
(well) and may also occur with time. A contingency for unanticipated conditions should be
included in the budget and schedule. Although proper planning, design, drainage and
construction techniques can reduce the risk of significant erosion and slope instability,
there is an inherent risk of instability associated with steep shoreline bluff sites.
The scope of our services does not include services related to environmental
remediation and construction safety precautions. Our recommendations are not intended
to direct the contractor's methods, techniques, sequences or procedures, except as specifi-
cally described in our report for consideration in design.
If there are any changes in the loads, grades, locations, configurations or type of
facilities to be constructed, the conclusions and recommendations presented in this report
may not be fully applicable. If such changes are made, we should be given the opportunity
to review our recommendations and provide written modifications or verifications, as
appropriate.
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Within the limitations of scope, schedule and budget, our services have been executed in
accordance with generally accepted practices in this area at the time this report was
prepared. No other conditions, express or implied, should be understood.
Respectfully submitted,
GeoResources, LLC
Brad--P. Biggerstaff, LEG Glen Coad, PE
Principal` Principal
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Figure 3-Cross-Section
Figure 4:USDA SCS Map
Figure 5a:Geology Map
Figure 5b:Coastal Zone Atlas
Figure 6:Soil Classification System
Figure 7:Hand Auger Logs
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Approximate Site Location
GeoResources, LLC
5007 Pacific Highway East, Suite 20 Site Location Map
Fife, Washington 98424 11031 North
Phone: 253-896-1011 Mason County, WA
Fax: 253-896-2633
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number identified on the Mason Count Assessor/Treasurer web page 3222-45-000031
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Fax: 253-896-2633
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GeoResources, LLG FIGURES - S!ope Stability Cross
5007 Pacific Highway E., Suite 20 Project : -eA;9mit Section
Location : Nc)g r+
Fife, Washington 98424 MA50N ccw& y W A
Ph: (253) 896-1011 Fax: (253) 896 2633 Datet• f I.R 2is %m r
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15 to 39 PERCENT SLOPE AREA APPROXIMATE LOCATION OF Hand Auger HA-1 ■ GeoResources, LLC FIGURE 2b- Parcel Map
Scale 1:20 5007 Pacific Highway East, Suite Project: Proposed Residential Development
40 PERCENT OR GREATER SLOPE AREA Property Boundaries Fife,Washington 98424 Location: 11031 North Shore Road
Landslide Hazard areas I--� Landslide Hazard area boundaries Phone: 253-896-1011 Mason County, Washington
Fax: 253-896-2633 Client: Mr. Suder
Landslide Hazard area buffers Landslide Hazard area buffer boundaries •••••••••••••••••• Date: February 2008 Job#: Suder.North ShoreRd
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Approximate Site Location
GeoResources, LLC USDA SCS Soils Ma
5007 Pacific Highway East, Suite 20 p
Fife, Washington 98424 11031 NE North Shore Road
Phone: 253-896-1011 Mason County, WA
Fax: 253-896-2633
File:SuderN.NorthShoreRD.SCS January 2008 Figure 4
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Geologic Map of Washington State, by Eric Schuste (2005)
Approximate Site Location
s
Not to Scale
GeoResources, LLC USGS Geologic is Ma
5007 Pacific Highway East, Suite 20 p
Fife, Washington 98424 11031 North Shore Road
Phone: 253-896-1011 Mason County, Washington
Fax: 253-896-2633
File: Suder.NorthShoreRd.USGS February2008 Figuresa
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Approximate Site Location
GeoResources, LLC Coastal Zone Atlas
5007 Pacific Highway East, Suite 20
Fife,Washington 98424 11031 NE North Shore Road
Phone: 253-896-1011 Mason County, WA
Fax: 253-896-2633
File: SuderN.NorthShoreRD.CZA January 2008 Figure 5 6
SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS GROUP GROUP NAME
SYMBOL
GRAVEL CLEAN GW WELL-GRADED GRAVEL,FINE TO COARSE
GRAVEL GRAVEL
COARSE GP POORLY-GRADED GRAVEL
GRAINED More than 50%
SOILS Of Coarse Fraction GRAVEL GM SILTY GRAVEL
Retained on WITH FINES
No.4 Sieve
GC CLAYEY GRAVEL
More than 50% SAND CLEAN SAND SW WELL-GRADED SAND,FINE TO COARSE SAND
Retained on
No.200 Sieve SP POORLY-GRADED SAND
More than 50%
Of Coarse Fraction SAND SM SILTY SAND
Passes WITH FINES
No.4 Sieve SC CLAYEY SAND
SILT AND CLAY INORGANIC ML SILT
FINE
GRAINED CL CLAY
SOILS Liquid Limit
Less than 50 ORGANIC OL ORGANIC SILT,ORGANIC CLAY
SILT AND CLAY INORGANIC MH SILT OF HIGH PLASTICITY, ELASTIC SILT
More than 50%
Passes CH CLAY OF HIGH PLASTICITY, FAT CLAY
No.200 Sieve
Liquid Limit
50 or more ORGANIC OH ORGANIC CLAY,ORGANIC SILT
HIGHLY ORGANIC SOILS PT PEAT
NOTES: SOIL MOISTURE MODIFIERS:
1. Field classification is based on visual examination of soil Dry- Absence of moisture,dry to the touch
in general accordance with ASTM D2488-90.
Moist- Damp,but no visible water
2. Soil classification using laboratory tests is based on
ASTM D2487-90. Wet- Visible free water or saturated, usually soil is
obtained from below water table
3. Description of soil density or consistency are based on
interpretation of blow count data,visual appearance of
soils,and or test data.
GeoResources, LLC Soil Classification System
5007 Pacific Highway East, Suite 20 Fife, Washington 98424 11031 NE North Shore Road
Phone: 253-896-1011 Mason County, Washington
Fax: 253-896-2633
File:SuderN.NorthShoreRd.SC January, 2008 Figure 6
J
HAND AUGER LOGS
SUDER RESIDENTIAL PROPERTY
SM North Shore Road
MASON COUNTY
HA-1-Located upper slope above residence
lDMh(ft.) Soil Type Description
0.0 - 0.5 Duff/Topsoil
0.5 - 1.0 SW Lt brn F-M SAND and GRAVEL w/silt,occ. cobbles
(med dense,moist),minor roots
1.0 - 2.0 SW Lt Brn F-M SAND and GRAVEL w/silt,occ.cobbles
(med dense to dense,moist)
2.0- 2.5 SM Lt brn SAND w/silt,cobbles
(dense to v.dense,moist)
Auger refusal at 2.5
Minor caving observed
No goundwater seepage observed
HA-2-Located mid slope above residence
Dotth(ft.) Soil Type Description
0.0 - 0.1 Duff/Topsoil
1.0 - 2.0 SM Brn SAND w/silt,trace gravel
(loose to med dense,moist)
2.0 - 3.5 SP Brn silty SAND w/trace gravel,
(loose to med.dense,moist)
3.5 - 5.0 GM Brn silty GRAVEL w/sand,occ.Cobbles
(med dense,damp)
5.0 - 5.5 SM/GM Brn silty SAND and GRAVEL w/occ. Cobbles
(wet,dense)
Minor caving observed
Minor groundwater seepage at 4.5 feet
HA-3-Located at base of concrete retaining wail
Depth(ft.) Soil Type Description
0.0 - 0.2 Duff/Topsoil
0.2 - 1.0 SP Lt.brn SAND w/silt,
(med dense,moist)
1.0 - 3.0 SW Brn/gray SAND w occ.gravel
(med dense,wet)
3.0 - 3.5 SW Gray SAND w/gravel,occ. Cobble,trace silt
(dense,wet)
Petroleum odor below 3-feet
Minor caving observed @1-foot
Minor goundwater seepage observed
F16URE
SvAGli?/.�,olle
HAND AUGER LOGS
SUDER RESIDENTIAL PROPERTY
AM North Shore Road
MASON COUNTY
HA4-Located in crawl space below residence
Depth(ft.) Soil Tvpe Description
0.0 - 1.0 SP/SW Brn Med SAND w/gravel,trace silt
(med.dense,moist)
>1.0 SW/GW Brn/gray SAND and GRAVEL w/cobbles,silt
(cementd, dense,moist-damp)
Auger refusal
No caving observed
No goundwater seepage observed
HA-5—Above rockery in parking area
Depth(ft.) Soil Type Description
0.0 - 0.5 SW Bm SAND w/gravel(FILL)
(loose,moist)
>1.0 SW Lt brn F-M SAND w/gravel
(dense to v.dense,moist),minor roots
Auger refusal at 1-foot
Minor caving observed
No goundwater seepage observed
Fttov�E �'
«d„ XIaN3ddV
r
SUd8 r8s-dencs. hlorth Shuors Road, Mcas®n County, pre-dsvcMopmsnl (staidc) Safety Factors
84.38 — — --
1.50
1.51
67.50 1 .54
1 .50
1 .59
1.59
50.63 1 .61
1 .62
1.63
33.75 1 .66
16.88
00 16.88 33.75 50.63 67.50 84.38 101.25 118.13 135.00
Suder residence: North Shore Road, Mason County, pre-development (sso& k) Safety Facb-s
84.38
1.18
1.19
67.50 1.22
1.26
1.27
1.27
50.63 1.28
1.28
1.29
33.75 1.30
16.88
0 16.88 33.75 50.63 67.50 84.38 101.25 118.13 135.00
Suder residence: North Shore Road, Mason County, post-development (static) Safety Factors
84.38
50
1.51
67.50 1.54
1.59
1 .59
1 .59
50.63 1.61
1.62
1.63
33.75 1 .66
16.88
0 16.88 33.75 50.63 67.50 84.38 101.25 118.13 135.00
1
•
Suder residence: North Shore Road, Mason County, post-development (seismic) Safety Factors
84.38 --
1.18
1.19
67.50 1.22
1.26
1.27
1.27
50.63 1 .28
1.28
1.29
33.75 1.30
16.88
00 16.88 33.75 50.63 67.50 84.38 101.25 118.13 135.00
Profile.out
PCSTABL6 *
by
Purdue University
modified by
Peter J . Bosscher
university of wisconsin-Madison
--slope Stability Analysis--
simplified Janbu, Simplified Bishop
or Spencers Method of Slices
PROBLEM DESCRIPTION suder residence: North Shore Road, Mason
County, post-development (static)
BOUNDARY COORDINATES
7 Top Boundaries
11 Total Boundaries
Boundary X-Left Y-Left X-Right Y-Right Soil Type
No. (ft) (ft) (ft) (ft) Below Bnd
1 0.00 10.00 35.00 10.00 1
2 35.00 10.00 35.00 14.00 1
3 35.00 14.00 42.00 14.00 1
4 42.00 14.00 89.50 56.00 1
5 89.50 56.00 100.00 56.00 1
6 100.00 56.00 100.00 62.00 1
7 100.00 62.00 135.00 62.00 1
8 0.00 4.50 31.00 6.00 2
9 31.00 6.00 57.00 23.00 2
10 57.00 23.00 72.00 38.00 2
11 72.00 38.00 92.00 56.00 2
ISOTROPIC SOIL PARAMETERS
2 Type(s) of soil
Soil Total Saturated Cohesion Friction Pore Pressure Piez.
Type unit wt. Unit wt. Intercept Angle Pressure Constant Surface
No. (pcf) (pcf) (psf) (deg) Param. (psf) No.
1 125.0 128.0 250.0 36.0 0.00 0.0 1
Page 1
Profile.out
2 125.0 128.0 250.0 35.0 0.00 0.0 2
BOUNDARY LOAD(S)
5 Load(s) specified
Load x-Left x-Right Intensity Deflection
No. (ft) (ft) (lb/sqft) (deg)
1 6.00 7.00 2500.0 0.0
2 15.00 25.00 2500.0 0.0
3 25.00 33.00 2500.0 0.0
4 34.00 35.00 1500.0 0.0
5 99.00 100.00 2000.0 0.0
NOTE - Intensity Is Specified As A uniformly Distributed
Force Acting on A Horizontally Projected Surface.
A Critical Failure surface searching Method, using A Random
Technique For Generating Circular surfaces, Has Been specified.
100 Trial Surfaces Have Been Generated.
10 Surfaces Initiate From Each of 10 Points Equally Spaced
Along The Ground surface Between x = 20.00 ft.
and x = 58.00 ft.
Each surface Terminates Between x = 80.00 ft.
and x = 110.00 ft.
unless Further Limitations were Imposed, The Minimum Elevation
At which A Surface Extends Is Y = 0.00 ft.
20.00 ft. Line segments Define Each Trial Failure surface.
Following Are Displayed The Ten Most Critical Of The Trial
Failure Surfaces Examined. They Are ordered - Most Critical
First.
* safety Factors Are calculated By The Modified Bishop Method
Failure Surface Specified By 5 Coordinate Points
Point x-Surf Y-Surf
No. (ft) (ft)
Page 2
J
Profile.out
1 45.33 16.95
2 64.71 21.92
3 82.24 31.54
4 96.85 45.19
5 107.60 62.00
Circle Center At x = 35.3 ; Y = 96.4 and Radius, 80.1
*** 1. 504 ***
Failure surface specified By 5 Coordinate Points
Point x-Surf Y-Surf
No. (ft) (ft)
1 45.33 16.95
2 63.90 24.38
3 80.99 34.77
4 96.13 47.84
5 107.88 62.00
Circle Center At x = 9.8 ; Y = 132.5 and Radius, 120.9
*** 1. 509 ***
Failure surface specified By 5 Coordinate Points
Point x-Surf Y-Surf
No. (ft) (ft)
1 49. 56 20.68
2 68.67 26.56
3 85.67 37.09
4 99.45 51. 59
5 105.18 62.00
Circle Center At x = 36.3 ; Y = 97.8 and Radius, 78.2
*** 1. 545 ***
Failure surface specified By 5 Coordinate Points
Point x-Surf Y-surf
No. (ft) (ft)
1 45.33 16.95
2 64.40 22.99
3 80.06 35.43
4 90.24 52.65
5 90.81 56.00
Page 3
Profile.out
Circle Center At x = 38.5 ; Y = 71.6 and Radius, 55.1
1. 585 ***
Failure surface specified By 5 Coordinate Points
Point x-surf Y-surf
No. (ft) (ft)
1 49.56 20.68
2 68.82 26.07
3 85.28 37.42
4 97.19 53.50
5 97.98 56.00
Circle Center At X = 43.0 ; Y = 81.2 and Radius, 60.8
** 1. 589 ***
Failure surface Specified By 5 Coordinate Points
Point X-surf Y-Surf
No. (ft) (ft)
1 45.33 16.95
2 65.13 19.79
3 82.71 29.33
4 95.89 44.37
5 102.63 62.00
Circle Center At X = 47.3 ; Y = 73.7 and Radius, 56.8
1.591 **
Failure surface specified By 5 coordinate Points
Point X-Surf Y-Surf
No. (ft) (ft)
1 49. 56 20.68
2 68.84 26.00
3 84.86 37.96
4 95.43 54.95
5 95.62 56.00
Circle Center At X = 45.1 ; Y = 74.5 and Radius, 54.0
1.605 ***
Page 4
Profile.out
Failure surface specified By 5 Coordinate Points
Point X-Surf Y-Surf
No. (ft) (ft)
1 53.78 24.41
2 72.95 30.11
3 89.60 41.19
4 102.26 56.67
5 104.43 62.00
Circle Center At X = 44.4 ; Y = 91.0 and Radius, 67.3
1.620 ***
Failure surface Specified By 5 Coordinate Points
Point X-surf Y-surf
No. (ft) (ft)
1 45.33 16.95
2 62.99 26.34
3 79.56 37. 54
4 94.87 50.41
5 106.04 62.00
Circle Center At X = -35.2 ; Y = 189.6 and Radius, 190.5
*** 1.625 ***
Failure Surface specified By 5 Coordinate Points
Point X-Surf Y-Surf
No. (ft) (ft)
1 49. 56 20.68
2 67.39 29.73
3 84.25 40.49
4 99.97 52.85
5 109. 51 62.00
Circle Center At X = -33.4 ; Y = 206.3 and Radius, 203.3
** 1.659 ***
Y A X I S F T
Page 5
Profile.out
0.00 16.88 33.75 50.63 67.50 84.38
x0.00 +--*--*---+---------+---------+---------+---------+
1/1
- /2
16.88 +
.2/3
A 33.75 + -4*4
- . . 1
x 50.63 + 3
. . 8
9'
. . . . . . . 612
I 67.50 + . . . 53 0
8.
. . . . . . . .49.
6 1 2
5 84.38 + . . . . .3.0
- 8 4
. . . . . . .612.9 7
. . . . .355/5
101.25 + . . . . . . 0 *5/
- . . . . . . . . . . .1
0
F 118.13 +
T 135.00 +
Page 6
r
Profile.out
PCSTABL6 **
by
Purdue university
modified by
Peter ) . Bosscher
university of Wisconsin-Madison
--Slope stability Analysis--
simplified 7anbu, simplified Bishop
or Spencers Method of slices
PROBLEM DESCRIPTION suder residence: North shore Road, Mason
County, post-development (seismic)
BOUNDARY COORDINATES
7 Top Boundaries
11 Total Boundaries
Boundary X-Left Y-Left X-Right Y-Right soil Type
No. (ft) (ft) (ft) (ft) BeloW Bnd
1 0.00 10.00 35.00 10.00 1
2 35.00 10.00 35.00 14.00 1
3 35.00 14.00 42.00 14.00 1
4 42.00 14.00 89.50 56.00 1
5 89.50 56.00 100.00 56.00 1
6 100.00 56.00 100.00 62.00 1
7 100.00 62.00 135.00 62.00 1
8 0.00 4. 50 31.00 6.00 2
9 31.00 6.00 57.00 23.00 2
10 57.00 23.00 72.00 38.00 2
11 72.00 38.00 92.00 56.00 2
ISOTROPIC SOIL PARAMETERS
2 Type(s) of soil
Soil Total Saturated Cohesion Friction Pore Pressure Piez.
Type Unit Wt. Unit Wt. Intercept Angle Pressure Constant Surface
No. (pcf) (pcf) (psf) (deg) Param. (psf) No.
1 125.0 128.0 250.0 36.0 0.00 0.0 1
Page 1
Profile.out
2 125.0 128.0 250.0 35.0 0.00 0.0 2
A Horizontal Earthquake Loading coefficient
of0.150 Has Been Assigned
A vertical Earthquake Loading coefficient
Of0.000 Has Been Assigned
Cavitation Pressure = 0.0 psf
BOUNDARY LOAD(S)
5 Load(s) specified
Load x-Left x-Right Intensit Deflection
No. (ft) (ft) (lb/sgft� (deg)
1 6.00 7.00 2500.0 0.0
2 15.00 25.00 2500.0 0.0
3 25.00 33.00 2500.0 0.0
4 34.00 35.00 1500.0 0.0
5 99.00 100.00 2000.0 0.0
NOTE - Intensity Is specified As A uniformly Distributed
Force Acting On A Horizontally Projected Surface.
A critical Failure Surface searching Method, using A Random
Technique For Generating Circular surfaces, Has Been specified.
100 Trial surfaces Have Been Generated.
10 surfaces Initiate From Each of 10 Points Equally Spaced
Along The Ground surface Between x = 20.00 ft.
and x = 58.00 ft.
Each Surface Terminates Between x = 80.00 ft.
and x = 110.00 ft.
unless Further Limitations were Imposed, The Minimum Elevation
At which A Surface Extends Is Y = 0.00 ft.
20.00 ft. Line segments Define Each Trial Failure surface.
Following Are Displayed The Ten Most Critical Of The Trial
Failure surfaces Examined. They Are ordered - Most critical
First.
Page 2
v
Profile.out
Safety Factors Are Calculated By The Modified Bishop Method
Failure surface specified By 5 coordinate Points
Point x-Surf Y-surf
No. (ft) (ft)
1 45.33 16.95
2 64.71 21.92
3 82.24 31. 54
4 96.85 45.19
5 107.60 62.00
Circle center At x = 35.3 Y = 96.4 and Radius, 80.1
1.185 �'
Failure surface specified By 5 Coordinate Points
Point X-surf Y-Surf
No. (ft) (ft)
1 45.33 16.95
2 63.90 24.38
3 80.99 34.77
4 96.13 47.84
5 107.88 62.00
circle Center At x = 9.8 ; Y = 132.5 and Radius, 120.9
pit 1.186 ***
Failure surface Specified By 5 Coordinate Points
Point X-Surf Y-surf
No. (ft) (ft)
1 49.56 20.68
2 68.67 26. 56
3 85.67 37.09
4 99.45 51. 59
5 105.18 62.00
Circle Center At x = 36.3 ; Y = 97.8 and Radius, 78.2
1.220 ***
Failure surface specified By 5 coordinate Points
Page 3
Profile.out
Point x-surf Y-surf
No. (ft) (ft)
1 49. 56 20.68
2 68.82 26.07
3 85.28 37.42
4 97.19 53. 50
5 97.98 56.00
circle center At x = 43.0 ; Y = 81.2 and Radius, 60.8
*�* 1.257 ***
Failure surface Specified By 5 coordinate Points
Point x-surf Y-surf
No. (ft) (ft)
1 45.33 16.95
2 65.13 19.79
3 82.71 29.33
4 95.89 44.37
5 102.63 62.00
circle center At x = 47.3 ; Y = 73.7 and Radius, 56.8
1.267 ***
Failure surface specified By 5 coordinate Points
Point x-Surf Y-Surf
No. (ft) (ft)
1 45.33 16.95
2 64.40 22.99
3 80.06 35.43
4 90.24 52.65
5 90.81 56.00
circle center At x = 38.5 ; Y = 71.6 and Radius, 55.1
** 1.269 ***
Failure Surface specified By 5 coordinate Points
Point x-Surf Y-Surf
No. (ft) (ft)
1 49.56 20.68
Page 4
l f
Profile.out
2 68.84 26.00
3 84.86 37.96
4 95.43 54.95
5 95.62 56.00
Circle Center At X = 45.1 ; Y = 74. 5 and Radius, 54.0
** 1.278 ***
Failure Surface Specified By 5 Coordinate Points
Point X-surf Y-Surf
No. (ft) (ft)
1 53.78 24.41
2 72.95 30.11
3 89.60 41.19
4 102.26 56.67
5 104.43 62.00
Circle center At X = 44.4 ; Y = 91.0 and Radius, 67.3
*** 1.280 ***
Failure Surface specified By 5 Coordinate Points
Point X-Surf Y-surf
No. (ft) (ft)
1 45.33 16.95
2 62.99 26.34
3 79.56 37. 54
4 94.87 50.41
5 106.04 62.00
Circle Center At X = -35.2 ; Y = 189.6 and Radius, 190. 5
*** 1.287 ***
Failure Surface specified By 5 Coordinate Points
Point X-Surf Y-surf
No. (ft) (ft)
1 49. 56 20.68
2 67. 39 29.73
3 84.25 40.49
4 99.97 52.85
5 109. 51 62.00
Circle Center At X = -33.4 ; Y = 206.3 and Radius, 203.3
Page 5
Y �
Profile.out
*** 1.300 °
Y A x I S F T
0.00 16.88 33.75 50.63 67.50 84.38
x0.00 +--*--*---+---------+---------+---------+---------+
1/1
/2
16.88 +
.2/3
A 33.75 + *4*4
1
x 50.63 + 3
- 8
9
. . . . . . . 512
I 67. 50 + . . . 43 0
- 8.
. . . . . . . .69.
. . . . 5 1 2
5 84.38 + . . . . .3.0 . .
8 6
. . . . . . . 512.9 7
- . . . . .344/5
101.25 + . . . . . . 0 *5/
. . . . . . 3
. . . . . . . . . . .
. . . . 1
- 0
F 118.13 +
T 135.00 +
Page 6