HomeMy WebLinkAboutBLD2012-00182 Geotechnical Report - BLD Engineering / Geo-tech Reports - 5/30/2012 GEOTECHNICAL ENGINEERING REPORT
HILLIS RESIDENTIAL EXPANSION
TAHUYA, WASHINGTON
FOR
MS. EMILY HILLIS
MAY 2012
Mason County Review Checklist
For a Geotechnical Report
Instructions:
This checklist is intended to assist Staff in the review of a Geotechnical Report. The Geotechnical Report
is reviewed for completeness with respect to the Resource Ordinance. If an item is found to be not
applicable, the Report should explain the basis for the conclusion.The Report is also reviewed for clarity
and consistency. If the drawings, discussion, or recommendations are not understandable, they should be
clarified. If they do not appear internally consistent or consistent with the application or observations on
site, this needs to be corrected or explained. If resolution is not achieved with the author, staff should
refer the case to the Planning Manager or Director.
Applicant's Name: U 5
Permit# 10 IT C1 1 0618j Parcel# 22� � r
Date(s) of the Document(s) reviewed:
(1) (a)A discussion of general geologic conditions in the vicinity of the proposed development,
OK? Comment: fig " 2
(b) A discussion of specific soil types
OK? Comment: �.
..(c) A discussion of ground water conditions.
OK? Comment:
(d) A discussion of the upslope geomorphology
OK? Comment:
(e) A discussion of the location of upland wate bodie .and wetlands
OK? Comment: G
(f) A discussion of history of landslide activity In .he activity in the vicinity, as available in the
..
referenced maps and records
OK? Comment:
(2) A site plan which identifies the important pvelopment and geologic features.
OK? Comment:_ , 17/
(3) Locations and logs of exploratory holes or probes.
OK? Comment:
(4) The area of the proposed development,the boundaries of the hazard, and associated buffers and
setbacks shall be delineated(top, both sides and toe)on a geologic map of the site.
OK? Comment: � a ?/
(5) A minimum of one cross section at a scale which adequately depicts the subsurface profile, and
which incorporates the details of proposed grade changes.
OK? Comment: .v
(6) A description and results of slope stAbilify analyses performed for both static and seismic loading
conditions.Analysis should examin worst case failures. The analysis should include the
Simplified Bishop's Method of Circles. The minimum static safety factor is 1.5, the minimum
seismic safety factor is 1.1. and the quasi-static analysis coeffients should be a value of 0.15.
OK? Comment: - 26ya G
(7) (a)Appropriate restrictions on placement of d ainage features
OK? Comment: I V151 i
(b) Appropriate restrictions on placerrlent of septic drain fields
OK? Comment:
(c) Appropriate restrictions on place nt ck pm acted fills and footings
OK? Comment:
(d) Recommended buffers from the land lid h zard areas shoreline bluffs and the tops of other
slopes on the property.
Page 1 of 2 Form Effective June 2008
OK? Comment:
(e) Recommended setbacks from the land is edl hazard areas shoreline bluffs and the tops of
other slopes on the property.
OK? Comment: rtal.
(8) Recommendations for the preparation of a detailed clearing and grading plan which specifically
identifies vegetation to be removed, a schedule for vegetation removal and replanting, and the
method of vegetation removal. iQ
OK? Comment:
(9) Recommendations for the preparation of a detailed temporary erosion control plan which
identifies the specific mitigating measures to be implemented during construction to protect the
slope from erosion, landslides and har f I n truction methods.
OK? Comment:
(10) An analysis of both on-site and off-sit impacts of the roposed development.
OK? Comment: ►��j
(11) Specifications of final development conditions such as, vegetative management, drainage,
erosion control, and buffer widths.
OK? Comment:
(12) Recommendations for the preparation of strLfctural mitigation or details of other proposed
mitigation.
OK? Comment: F-
(13) A site map drawn to scale showing the properTyb6undaries, scale, north arrow, and the location
and nature of existing and proposed d elopment on the site.
OK? Comment:
Are the Documents signed and stamped?
Type and#of License:
If not approved, what is the next action/recommendation for further action?' i
41
Reviewed by , on
Time spent in review:
SECOND REVIEW/UPDATE:
Reviewed by , on
Time spent in second review:
THIRD REVIEW/UPDATE:
Reviewed by , on
Time spent in third review:
Disclaimer: Mason County does not certify the quality of the work done in this Geological Assessment
Page 2 of 2 Form Effective June 2008
y
ROBINSON-
NOBLE
May 17, 2012
Ms. Emily Hillis
9421 Tacoma Avenue South
Tacoma, Washington 98444
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
RN File No. 2456-001 B
Dear Ms. Hillis:
This letter transmits three copies of our report for your residential expansion project. The
project is located on a north facing slope on the south side of Haven Lake and consists of the
expansion of your residential structure at the property. The residential structure is being
expanded to the south due to site line limitations on the lake side (north) of the property. The
property has a steep slope greater than 40% and taller than 10 feet in height and therefore is
considered by the Mason County Resource Ordinance (June 16, 2009) to be classified as a
"landslide hazard area." Since the site has a landslide hazard area and the improvements are
within 300 feet of the hazard, a geotechnical report is required to address the planned
improvements.
We appreciate the opportunity of working with you on this project. If you have any questions
regarding this report, please contact us.
Sincerely,
Rick B. Powell, PE
Principal Engineer
MP:JRW:RBP:am
Three Copies Submitted
Appendix A and B
Two Figures
3011 South Huson Street, Suite A 17625 130th Avenue NE, Suite 102
Tacoma,Washington 98409 www.robinson-noble.com Woodinville,'Washington 98072
P:253.475.7711 1 F: 253.472.5846 P: 425.488.0599 1 F:425.488.2330
TABLE OF CONTENTS
INTRODUCTION............................................................................................................................................1
PROJECTDESCRIPTION..............................................................................................................................1
SITECONDITIONS........................................................................................................................I...............1
SurfaceConditions.....................................................................................................................................I
Geology......................................................................................................................................................2
Explorations ...............................................................................................................................................2
SubsurfaceConditions...............................................................................................................................3
HydrologicConditions................................................................................................................................3
GEOLOGICHAZARDS............................,.......................................................................................I..............4
LandslideHazards......................................................................................................................................4
ErosionHazard...........................................................................................................................................4
SeismicHazard ..........................................................................................................................................4
CONCLUSIONSAND RECOMMENDATIONS..............................................................................................5
General.......................................................................................................................................................5
GlobalStability .............................................................................5
SitePreparation and Grading.....................................................................................................................6
TemporarySlopes......................................................................................................................................6
Foundations ...............................................................................................................................................7
LateralLoads..............................................................................................................................................7
Drainage.....................................................................................................................................................8
CONSTRUCTIONOBSERVATION.................................................................................................................8
USEOF THIS REPORT....................................................................................................................I.............8
Robinson Noble, Inc
INTRODUCTION
This report presents the results of our geotechnical engineering investigation at your proposed
single-family residential project in Mason County, Washington. The site is located at 491 Haven
Lake Drive, as shown on the Vicinity Map in Figure 1.
On April 27, our geologist visited the site to evaluate the area and review the request for
additional information from the County. We met Mr. Steve Ates of Family Classic Homes on
site. During our site visit, he provided the letter from Mason County as well as additional details
regarding your planned remodel and addition to the existing cabin. Mason County has
expressed concerns regarding slope stability and has requested a Geological Assessment of
the property. This request was provided in a Notification of Incomplete Application from the
Mason County Department of Community Development dated April 26, 2012. This letter
addresses Mason County's concerns.
PROJECT DESCRIPTION
The project will consist of an addition to the existing single family residential structure. The
new addition is planned on the northeast and southeast sides of the house. The addition is not
planned on the northwest side of the house due to view line restrictions. We have not been
provided with a grading plan, but we expect that site grading will include minor excavation cuts
in the area of the planned addition. The planned addition will have a conventional foundation
system with a crawlspace.
SITE CONDITIONS
Surface Conditions
The lot is located at 491 Northeast Haven Lake Drive, near Tahuya, Washington, and is
referenced as tax parcel 22330-50-00103 by the Mason County Assessor's office. The lot
stretches from NE Haven Lake Drive on the south to the shore of Haven Lake on the north, and
is located in a small community of homes surrounding the lake in rural Mason County. As such,
while the development immediately surrounding the lake is made up of lots smaller than 1/2
acre, there are no public utilities serving the area.
A single family residence and associated outbuildings currently sits within the site. A drain field
g Y
is located in the southeastern portion of the lot and is located approximately 30 feet southeast
of the existing structure. A water well is located near the southwest corner of the site and has
an Ecology Well ID of BAJ 010.
A majority of the vegetation has been removed from the site. In addition to the mature
evergreens on the southern portion of the property, forested areas lie on the northeastern and
southwestern property lines and contain medium to large diameter evergreen trees. Some
native shrubs and vines exist on the steeper portions of the site in the northern region. Grass
is beginning to reestablish in the southern region of the site, but exposed soils are observed
near the existing structure where there is increased foot traffic.
The site and neighboring properties slope downwards from Northeast Haven Lake Drive in the
southeastern region of the site to Haven Lake in the northwestern region of the site. The
rectangular shaped property is about 0.32 acres in size and has maximum dimensions of
approximately 278 feet in the approximate northwest-southeast direction and 50 feet in the
approximate northeast-southwest direction. According to information available from Mason
County, the site slopes down from about 460 feet near Northeast Haven Lake Drive to
Robinson Noble, Inc
L --
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
May 17, 2012
RN File No. 2456-001 B
Page 2
approximately 380 feet at the shore of Haven Lake. A site plan showing the location of the
residence and hazard area is shown in Figure 2.
A cross section has been developed based on the 20 foot interval contour maps from Mason
County and from our site observations, as shown in Appendix B, Figure B-1. The steep slope
and lower portion of the site has an inclination of approximately 41% to 50%. The upper
portion of the lot where the cabin, septic drain field, and new well are located has a slope angle
of approximately 21 % to 30%.
Geology
Most of the Puget Sound Region was affected by past intrusion of continental glaciation. The
last period of glaciation, the Vashon Stade of the Fraser Glaciation, ended approximately 14,000
years ago. Many of the geomorphic features seen today are a result of scouring and overriding
by glacial ice. During the Vashon Stade, areas of the Puget Sound region were overridden by
over 3,000 feet of ice. Soil layers overridden by the ice sheet were compacted to a much
greater extent than those that were not.
A review of the most recent geologic map of the area, Geologic Map of the Lilliwaup and Lake
Wooten 7.5 Minute Quadrangles Kitsap and Mason Counties, Washington, by Michael A.
O'Neal maps the lot and surrounding area as the Vashon till, with the Vashon advance outwash
exposed at lower elevations (near 360 feet) in the valley 2000 feet east of the site.
Explorations
Subsurface conditions were observed during previous excavations at the site and nearby
properties. During our 2008 site work, we observed an excavation for a new residential
structure southwest of the subject property and have evaluated open test pit excavations when
the septic system was being designed for the subject property. The description of the soils
was not documented during our observation of the excavations
We have also reviewed well logs for this site and an adjacent site. In 2008, we prepared a
request for a variance in water well construction for the site, which involved the research of
local geologic conditions, an analysis of the well logs for water wells in the area, and a visit to
the site. This variance was granted with the requirements that the well be drilled at least 100
feet deep with a surface seal extending to at least 30 feet below surface. A satisfactory well,
BAJ 010, has been drilled on the property in compliance with this variance. Additionally, the
septic drain field has been constructed since our last site visit.
We have also referenced the Ecology Well ID BCA 503, which is located at 501 Northeast
Haven Lake Drive, the parcel immediately to the east of the subject. This boring log has more
detailed geologic descriptions in the upper 100 feet than the boring log for the subject property;
therefore, we have used it within our cross section. The log is also provided in Appendix A.
Robinson Noble, Inc
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
May 17, 2012
RN File No. 2456-001 B
Page 3
Subsurface Conditions
We provide a brief description of the subsurface conditions below. A more detailed description
of the subsurface soils can be reviewed in the boring logs provided in Appendix A.
Our direct observations of the subsurface conditions during the 2008 excavation for the
foundation of a new house being constructed on a lot located southwest of the site, as well as
observations made in the test pits for the proposed septic system on the subject lot indicate a
brown to reddish-brown silty fine sand with gravel to cobbles present at and near the surface.
The subsurface material becomes denser and has a higher silt and clay content with increasing
depth and grades to more of a brown color. At approximately six feet below grade, the color
changes to gray, and the material becomes dense to very dense. This suggests that the
surficial material present at this location is consistent with Vashon Till.
Analysis of the local water well reports indicates that the site is underlain by a thick sequence
of glacial till or till-like deposits. Locally, there thin sands and gravels were reported within the
till. These were not noted in the water well report for the well on site or the well to the west of
the subject. Similarly, the Vashon advance outwash was not observed in all of the water well
reports reviewed, but where observed, it was typically identified at elevations of approximately
360 feet above sea level, approximately 100 feet below the elevation at the southern portion of
the site. The advance outwash is underlain by another low-permeability unit primarily consisting
of silt and clay with some sand and gravel. The aquifer serving the well on the subject, as well
as those to the east and west of the subject is a sand and gravel deposit found below the lower
permeability material at depths between 235 and 276 feet below grade.
Hydrologic Conditions
The dense to very dense till interpreted to underlie the site is considered poorly draining.
During the wetter times of the year, we expect perched water conditions will occur as pockets
of water on top of the till layer. Perched water does not represent a regional groundwater
"table" within the upper soil horizons. Volumes of perched groundwater vary depending upon
the time of year and the upslope recharge conditions.
The first significant aquifer beneath the site is within the Vashon advance outwash, which is
typically present at an elevation of approximately 360 feet above sea level, approximately 100
feet below land surface. Water levels in this aquifer are approximately 95 feet below land
surface. The well on site and those on the adjacent parcels were completed in a deeper sand
and gravel aquifer, encountered at an elevation of 200 feet above sea level. Water levels in this
deeper aquifer are approximately 225 feet below land surface.
The parcel is bounded by the southern shore of Haven lake, which is the nearest surface water
in the area. The surface slopes upward from Haven Lake until just to the southeast of
Northeast Haven Lake Drive, then slopes gently downward in a southeasterly direction. There
was no evidence of seepage on the steep slope during either of our site visits.
Robinson Noble, Inc
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
May 17, 2012
RN File No. 2456-001 B
Page 4
GEOLOGIC HAZARDS
Landslide Hazards
The core of the site is inferred to be composed of glacially overridden soils. We consider these
soils to be of high strength and considered to be stable with regards to deep-seated slope
failures. We did not observe indications of surficial seepage on the site, nor did we observe
indications of shallow or deep seated slope failures. The mature fir trees in the immediate area
exhibit straight trunks, which also is indicative of a stable slope. A number of the trees on the
property were damaged during the recent winter storms and have been cut down. Images
collected during our site work in 2008 indicate that these trees were all standing relatively
straight and had no pronounced curvature in the trunks that would indicate slope instability.
Erosion Hazard
The erosion hazard criteria used for determination of affected areas includes soil type, slope
gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to
vegetative cover and the specific surface soil types (group classification), which are related to
the underlying geologic soil units. We reviewed the Web Soil Survey by the Natural Resources
Conservation Service (NRCS) to determine the erosion hazard of the on-site soils. The site
surface soils were classified using the NRCS classification system as Alderwood gravelly sandy
loam, 5 to 15 percent slopes. The corresponding geologic unit for these soils is glacial till which
is in agreement with the soils encountered in the site explorations. The erosion hazard for the
soil is listed as being moderate for the gently to moderately sloping conditions at the site. As
previously documented steeper slopes exist within the site. We would expect the erosion
hazard for the steeper sections of the site to be moderate to high.
Seismic Hazard
It is our opinion based on our subsurface explorations that the Soil Profile in accordance with
Table 1613.5.2 of the 2009 International Building Code (IBC) is Site Class C. As referenced in
the 2009 IBC,we used the US Geological Survey program "Seismic Hazard Curves and
Uniform Hazard Response Spectra." That program uses 2003 NEHRP Seismic Design
Provisions to obtain values for S., S,, Fa, and F, The seismic design parameters are:
SS 124.7% g
S, 63.6% g
Fa 1.0
F,, 1.32
Site specific coefficients and adjusted maximum considered earthquake spectral response
acceleration parameters apply as shown in Section 1613.5 of the IBC. Based on the USGS data
and Tables 1613.5.60) and (2), the site has Seismic Design Category D.
Additional seismic considerations include liquefaction potential and amplification of ground
motions by soft soil deposits. The liquefaction potential is highest for loose sand with a high
Robinson Noble, Inc
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
May 17, 2012
RN File No. 2456-001 B
Page 5
groundwater table. The underlying dense till and advance outwash soils are considered to have
a very low potential for liquefaction and amplification of ground motion.
CONCLUSIONS AND RECOMMENDATIONS
General
It is our opinion that the site is compatible with the planned development. Due to the natural
steep slopes in the northwestern portion of the property, this parcel is characterized as a
landslide hazard area, as defined in Mason County Resource Ordinance 17-01-100. The
ordinance items are addressed below:
a. Evidence of past or current earth movement on the subject was not observed.
b. Oversteepened or unengineered slopes were not noticeably observed.
c. The soils on the subject are not soft and have an extremely low potential for
liquefaction.
d. There was no undercutting evident along the lake shore.
e. While the slope is greater than 15%, the geology is uniform across the site and for a
considerable thickness, glacially overconsolidated and there is no evidence of seepage.
f. The northern portion of the site exceeds 40% slope, and has more than 10 feet of
vertical relief.
While the slopes on site do locally exceed 40% and have a relief in excess of 10 feet, there
was no evidence of past slope failures at the time of our site inspections. Undisturbed glacial till
is not typically prone to deep-seated slope failures. There is always a risk of shallow slough
type failures on steep slopes.
The location of the planned addition to the existing structure is on the side of the residence and
will not reduce the existing geologic buffer. In our opinion the existing buffer is adequate for
the planned improvements based on the subsurface information and our analyses. We
recommend that the construction zone be minimized on the downslope side of the residence
to reduce the risk of affecting the steep slope.
Global Stability
We analyzed global stability using a computer program known as XSTABL, version 5.2.
XSTABL is a two-dimensional, limit-equilibrium slope stability program. The sections were
analyzed using the Modified Bishops method of slices. XSTABL generates random potential
failure surfaces and determines their corresponding factors of safety with respect to failure.
The factor of safety is defined as the ratio of the internal soil strength divided by the gravity
driving forces that cause failure. By generating a large number of random surfaces, the factor
of safety can be obtained as the lowest number calculated.
Robinson Noble, Inc
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
May 17, 2012
RN File No. 2456-001 B
Page 6
The site is underlain by glacially consolidated soils. Based on the geologic environment of the
materials encountered relatively high strengths can be used. We did not perform laboratory
shear testing of the soils but we have utilized typical values commonly used for similar soils.
Existing conditions were used to calculate static slope stability in Cross-Section A-A'. Cross
Section A-A' can be observed in Appendix B, Figure B-1. We modeled groundwater as a free
water surface in our analysis rather than as a piezometric surface. The parameters and results
are shown in Appendix B, Figures B-2 through B-3. Factors of safety against deep-seated
failures under static conditions were above 1.5 for Cross-Section A-A'.
We evaluated the slope stability for seismic conditions, using a pseudostatic analysis with a
design input horizontal acceleration of 0.17g, which correlates to approximately a 1 in 100 year
event.
We used the static soil parameters in our seismic evaluation. We expect that for short intervals
of dynamic forces, such as those created in a seismic event, the cohesion within the
subsurface soils will be greater than the long-term internal resisting forces. We have included a
free water surface in the analyses. The parameters and results are shown in Figures B-4
through B-5. Factors of safety against deep-seated failures under seismic loading were above
1.1 for Cross-Section A-A'.
Site Preparation and Grading
The first step of site preparation should be to strip the vegetation, topsoil, or loose soils to
expose medium dense or firmer native soils in the building areas. The excavated material
should be removed from the site, or stockpiled for later use as landscaping fill. The subgrade
should be evaluated to confirm that a medium dense or better condition is encountered. Areas
observed to pump or yield should be repaired prior to placing hard surfaces.
The on-site glacial till likely to be exposed during construction is considered highly moisture
sensitive, and the surface will disturb easily when wet. We expect these soils would be
difficult, if not impossible, to compact to structural fill specifications in wet weather. We
recommend that earthwork be conducted during the drier months. Additional expenses of wet
weather or winter construction could include extra excavation and use of imported fill or rock
spalls. During wet weather, alternative site preparation methods may be necessary. These
methods may include utilizing a smooth-bucket trackhoe to complete site stripping and
diverting construction traffic around prepared subgrades. Disturbance to the prepared
subgrade may be minimized by placing a blanket of rock spalls or imported sand and gravel in
traffic and roadway areas. These methods can be evaluated at the time of construction.
Temporary Slopes
Temporary cut slope stability is a function of many factors, such as the type and consistency of
soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains
open, and the presence of surface or groundwater. It is exceedingly difficult under these
Robinson Noble, Inc
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
May 17, 2012
RN File No. 2456-001 B
Page 7
variable conditions to estimate a stable temporary cut slope geometry. Therefore, it should be
the responsibility of the contractor to maintain safe slope configurations, since the contractor is
continuously at the job site, able to observe the nature and condition of the cut slopes, and able
to monitor the subsurface materials and groundwater conditions encountered.
We recommend that cut slopes and inclinations made for the addition on the south side of the
existing residence conform to local and WISHA/OSHA standards. The cuts and slopes should
be protected from erosion. Measures taken may include covering cut slopes with plastic
sheeting and diverting surface runoff away from the top of slopes. We do not recommend
vertical slopes for cuts deeper than 4 feet, if worker access is necessary.
Foundations
Conventional shallow spread foundations should be founded on undisturbed, medium dense or
firmer soil. If the soil at the planned bottom of footing elevation is not suitable, it should be
overexcavated to expose suitable bearing soil. Footings should extend at least 18 inches below
the lowest adjacent finished ground surface for frost protection. Minimum foundation widths
should conform to IBC requirements. Standing water should not be allowed to accumulate in
footing trenches. All loose or disturbed soil should be removed from the foundation excavation
prior to placing concrete.
For foundations constructed as outlined above, we recommend an allowable design bearing
pressure of 2,500 pounds per square foot (psf) be used for the footing design. IBC guidelines
should be followed when considering short-term transitory wind or seismic loads. Potential
foundation settlement using the recommended allowable bearing pressure is estimated to be
less than 1-inch total and 1/z-inch differential between footings or across a distance of about 30
feet. Higher soil bearing values may be appropriate with wider footings. These higher values
can be determined after a review of a specific design.
Lateral Loads
The lateral earth pressure acting on retaining walls is dependent on the nature and density of
the soil behind the wall,the amount of lateral wall movement, which can occur as backfill is
placed, and the inclination of the backfill. Walls that are free to yield at least one-thousandth of
the height of the wall are in an "active" condition. Walls restrained from movement by
stiffness or bracing are in an "at-rest" condition. Active earth pressure and at-rest earth
pressure can be calculated based on equivalent fluid density. Equivalent fluid densities for
active and at-rest earth pressure of 35 pounds per cubic foot (pcf) and 55 pcf, respectively, may
be used for design for a level backslope. These values assume that the on-site soils or
imported granular fill are used for backfill, and that the wall backfill is drained. The preceding
values do not include the effects of surcharges, such as due to foundation loads or other
surface loads. Surcharge effects should be considered where appropriate. The above drained
active and at-rest values should be increased by a uniform pressure of 6.9H and 20.9H psf,
respectively, when considering seismic conditions. H represents the wall height.
Robinson Noble, Inc
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
May 17, 2012
RN File No. 2456-001 B
Page 8
The above lateral pressures may be resisted by friction at the base of the wall and passive
resistance against the foundation. A coefficient of friction of 0.45 may be used to determine
the base friction in the native glacial soils. An equivalent fluid density of 250 pcf may be used
for passive resistance design. To achieve this value of passive pressure, the foundations
should be poured "neat" against the native dense soils, or compacted fill should be used as
backfill against the front of the footing, and the soil in front of the wall should extend a
horizontal distance at least equal to three times the foundation depth. A factor of safety of 2.0
has been applied to the passive pressure to account for required movements to generate these
pressures. The friction coefficient does not include a factor of safety.
All wall backfill should be well compacted. Care should be taken to prevent the buildup of
excess lateral soil pressures due to overcompaction of the wall backfill.
Drainage
The finished ground surface should be sloped at a gradient of 5 percent minimum for a distance
of at least 10 feet away from the buildings, or to an approved method of diverting water from
the foundation, per IBC Section 1803.3. Surface water should not be allowed to have a direct
discharge over a steep slope. Methods to control the water such as rain gardens or dispersion
trenches should be used at the site. To reduce the effects on the steep slope, dispersion at
the base of the slope is preferred if possible.
We recommend that footing drains be used around all of the structures where moisture control
is important. The underlying till may pond water that could accumulate under slabs or within
crawlspaces. It is good practice to use footing drains installed at least 1 foot below the planned
finished floor slab or crawlspace elevation to provide drainage for the crawlspace.
Where used, footing drains should consist of 4-inch-diameter, perforated PVC pipe that is
surrounded by free-draining material, such as pea gravel. Footing drains should discharge into
tightlines leading to an appropriate collection and discharge point, Crawlspaces should be
sloped to drain, and a positive,connection should be made into the foundation drainage system.
Roof drains should not be connected to wall or footing drains.
CONSTRUCTION OBSERVATION
We should be retained to provide observation and consultation services during construction to
confirm that the conditions encountered are consistent with those indicated by the
explorations, and to provide recommendations for design changes, should the conditions
revealed during the work differ from those anticipated. As part of our services, we would also
evaluate whether or not earthwork and foundation installation activities comply with contract
plans and specifications.
USE OF THIS REPORT
We have prepared this report for Ms. Emily Hillis and her agents, for use in planning and design
of this project. The data and report should be provided to prospective contractors for their
Robinson Noble, Inc
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
May 17, 2012
RN File No. 2456-001 B
Page 9
bidding and estimating purposes, but our report, conclusions and interpretations should not be
construed as a warranty of subsurface conditions.
The scope of our services does not include services related to construction safety precautions,
and our recommendations are not intended to direct the contractors' methods, techniques,
sequences or procedures, except as specifically described in our report, for consideration in
design. There are possible variations in subsurface conditions. We recommend that project
planning include contingencies in budget and schedule, should areas be found with conditions
that vary from those described in this report.
Within the limitations of scope, schedule and budget for our services, we have strived to take
care that our services have been completed in accordance with generally accepted practices
followed in this area at the time this report was prepared. No other conditions, expressed or
implied, should be understood.
000
Robinson Noble, Inc
Geotechnical Engineering Report
Hillis Residential Expansion
491 Northeast Haven Lake Drive
Tahuya, Washington
May 17, 2012
RN File No. 2456-001 B
Page 10
We appreciate the opportunity to be of service to you. If there are any questions concerning
this report or if we can provide additional services, please call.
Sincerely,
Robinson Noble, Inc.
Hydrogeologist
{• 592 NCO
MICHAEL F. PIECHOWSKI
Michael F. Piechowski, LHG
Senior Hydrogeologist
rr S
Rick B. Powell, PE
Principal Engineer
MFP:JRW:RBP:am
Three Copies Submitted
Two Figures
Appendix A and B
Robinson Noble, Inc
f
_ n
f NE HAVEN WAYLD
W I
s
�a Project -
Site
jf> , .
q P
P
p 1276h
Note:Basemap Figure 1
taken from: PM: MFP Mason County
httpa/mapmason.co 2456-001B Vicinity Map
ROBINSON- .mason.wa.us on
NOBLE 5/16/2012 May 2012 Ms. Emily Hillis: Hillis Residential Expansion
Erosion Fence
108'
Proposed Addition
Footprint
Existing Deck
Existing Cabin
278'
Drainfield
Driveway
\ ...:..
sand Parking
135' :
ell 50,�a�e
0' 40'
I i
A A' Approximate Location
A of Cross-Section A-A'
Note: PM. MFP Mason County Figure 2
Basemap taken Site Plan
FROBINSON' from undated 2456-001B
untitled site plan. May 2012 Scale 1°= 40'
NOBLE Ms. Emily Hillis: Hillis Residential Expansion
Appendix A
r
WATER WELL REPORT
driller CURRENT
ECOLOGY Original&it copy-Ecology,2"dcopy-owner,3"copy-
Notice of Intent No.
Construction/Decommission("Yin circle) Unique Ecology Well ID Tag No. BAJ010
❑- Construction
❑ Decommission ORIGINAL INSTALLATION Water Right Peml it No.EXEMPT WELL
Notice of Intent Number Property Owner Name EASILY HILLS
PROPOSED USE: ❑x Domestic ❑ Industrial ❑Municipal
DeWater ❑Im ation ❑Test Well other Well Street Address 491 NE HAVEN LAKE DR -
TYPE OF WORK:Owners number ofwell(ifmore than one) City TAHUYA County MASON
Q New well ❑Reconditioned Method: ❑Dug ❑gored ❑ Driven
❑Deepened le ❑Roca ratted LocationN�l/4-1/4SW 1/4 Sec30 Twn23N R 2W acorn ❑ Check
DIMENSIONS:Diamdcr ofwell inches,dr lied 276 it Or
(s,t,r Still REQUIRED) tytyM❑One j
Dent
c w
CONSTRUCTION DETAILS Lat/Long Lat Deg LatMin/Sec
CasingEI Welded 6 Diem,from+1.5 R to 271 ft t."
Lon De Long Min/Sec
Installed: El Liner installed Diam.from_---: fL to R g g
" a o.(Required).223305000103
❑Threaded Diam From R to Tax Parcel N (Req __). _
Perforations: ❑Yes 0 No CONSTRUCTION OR DECOMMISSION PROCEDURE
Type of perforator used Formation:Describe by color,character,si=o£metarial and sovcture,and the kind and 71
SIZE o(perfs in.by in.and no.of perfs from ft.to ft. nature of the material in each stratum penetrated,with of least one entry for each change
of information.(USE ADDITIONAL SHEETS IF NECESSARY.)
Screens: ❑x yes ONO (]K-Pee Location 269 MATERIAL FROM TO
Manufacturers Name JOJ-1NSON SCREEN
Type SLOTTED BROWN CONGLOMERATE 0 3
Model No. -- -.
NARDP
Diam.5 Slot size 20 from 271 ft.to
C GRAY 3' 86
to 276 fL
Diam Slot sirs from ft.to ft. BROWN
CONGLOMERATE S6 ]53
BROWN HARDPAC WITH SEAPAGE AND 153
Gravel/Filter packed: ❑Yes []No Size ofgravd/sand SAND AND GRAVEL 273
Materials placed from fL to ft-
SAND AND GRAVEL H2O 273- — 276 -'
Surface Seal: ❑z yes ❑ No Towhatdepth7 38 ft-
Material used in seal BENTONITE CHIPS .. .- .
Did any strata contain unusable water? ❑Yes No
Type of water? Depenofraate ,___.-._... - - •-- -
Method of sealing strata off
PUMP:Manufacturers Name
i
Type: H.P. {
WATER LEVELS:Land-surface elevation above mean sea level
Static level 225 ft below top ofwell' Date 02/02/2009 _
Artesian pressure lbs.per square indr Date
- - Artesian water is controlled by — - (Cap,valve,etQ
WELL TESTS:Dnwdown is amount water level is lowered below static level Was a pump test made? ❑ Yes ❑Q No Ifyes,by whom? -
Yield: pUmin.with R drawdown after hrs.
Yield: gal.hnin.with R drawdown after In.
Yield: - gal./min.with f.drasvdown after }us.
Recoverydata(time taken aszero whenpump turned of0(wafer Level measured from well _
top to waterleveo
Time Water Level Time Water Level Time Water Level
• `n
Date of rest
u
.Railer Test 10 galhnin.with 12 RArawdown after bra.
Airtest gaUmin.with stem set at fL for hrs.
Artesian flow g"p.m. Dale
Temperature of water Was a chemical analysis made? ❑ Yes Z No Start Date 01/16/2049 Completed Date 02/02/2009
WELL CONSTRUCTION CERTIFICATION:I constructed and/or accept responsibility for construction of this well,and its compliance with all Washington well
construction standards.Materials used and the iriformation reported above are true tb my best knowledge and belief.
ODriller❑Engineer❑TraineeName(pri MARK ` L N Drilling Company ARCADIA DRILLING INC
Driller/Engineer/Trainee Signature t dress PO BOX 1790
Driller or trainee License No. 1992 City,State,Zip SHELTON WA 98584
IF TRAINEE:Driller's License No: Contractor's
-- ------------...------ - --- -- ------ —ation—No.—ARCADDI098K7-"— Datr 02102/2009- --
Drllerrs Signature: Registr
ECY 0504-20(Rev 06108)1•f ymf need this document in an alienateformaA please call the Water Resources Program at 360-407-6600.
Persons wilh hearing loss can call 711 for Washington Relay Sen•ice. Persons with a speech disability can call 877-833-6341.
WATER WELL REPORT
ECOLOGY Original copy-Ecology,2odcopy-owner, 3'°copy-driller CURRENT
<R Notice of Intent No.W 280101
Construction/Decommission (x"in circle)
❑X Construction Unique Ecology Well ID Tag No BCA 503
❑ Decommission ORIGINAL INSTALLATION Water Right Permit No
Notice of Intent Number
PROPOSED USE: 0 Domestic ❑ Industnal ❑Municipal _ Property Owner Name Ben Amende
❑DcWaler ❑Irrigation ❑Test Well El Other Well Street Address 501 NE Haven Lake Dr
TYPE OF WORK:Owoces number of well(if more than one) City Tahuya County Mason
0 New well D Reconditioned Method ❑Dug ❑Bored ❑ Driven
❑ Deepened O Cable DRolazy 0 3ellnd Location SW 1/4-1/4NE 1/4 Sec 30 Twn23 R 2 -m ❑ Check
DIMENSIONS:Diameter of well inches,dolled 2b0 ft (s,t,r Still REQUIRED) wwm❑• One
Dc th f coin ieted w IIII—XW ft ,
CONSTRUCTION DETAILS Lat/Long Lat Deg Lat Min/Sec
Casing Welded 6 Diam from +1 ft to 255 It
Installed: D Liner installed Diam from ft to ft Long Deg Long Min/Sec
❑'threaded Diam From it to It Tax Parcel No (Required) 223305000102
Perforations: ❑yes El No
CONSTRUCTION OR DECOMMISSION PROCEDURE
Type of perforator used Formation Describe by color,character,size of material and stmclnre,and the kind and
SIZE of perfs in by rn and no of perfs_from ft to ft nature of the matenal in each stratum penetrated,with at least one entry for each change
Screens: Eyes ❑No NK-Pac Location 253 of information (USE ADDITIONAL SHEETS IF NECESSARY)
ManufactureisName Johnson MATERIAL FROM 01
Type stainless Model No Silty sand&gravel,redish brown 0 10
Diam 5" Slot size 20 from 255 ft to 260 ft Brown till 10 29
Main Slot size from ft to ft Sand&gravel with some water 29 32
Gravel/Filter packed: ❑ Yes ❑x No Size of gravelfsand Gray till 32 54
Materials placed from ft to ft Brown till 54 86
Surface Seat: x❑Yes ❑No To what depth? 30 It Sandy brown clay with some water 86 105
Material used in seat Betonite Gray till 105 165
Did any strata contain unusable water? ❑Yes No Brown till 165 1215
Gray silty sand&gravel 215 220
Type of watery Depth of strata
Gray till 220 238
M
Method sealing strata off Cemented sand&gravel with water 238 254
PUMP: anufacturers Name Goulds • ' Sand&gravel with water 254 260
Type Sub I{p 11/2
WATER LEVELS:Land-surface elevation above mean sea level it
Static level 222 11 below lop of well Date
Artesian pressure Ibs per squam inch Date
Artesian water is controlled by (cap,valve,etc)
WELL TESTS: Drawdown is amount water level is lowered below static level
Was a pump test made? ❑ Yes Q No If yes,by whom?
Yield gal/min with ft diawdown after hrs
Yield gal/min with ft drawdown after his
Yield gal/min with ft drawdowm after hrs
Recovery data(time taken as zero when pump turned off)(water level measured from well
wpio waterfevel)Time Water Level Time Water Level Time Water Level APR 1 0n D I LV 1
A 61ctl L,r a ,r,A,t
Date or test Of r_l ry 1 l l"ZI
iv
Bailer Test 16 gal/min with 2 fl drawdown after 1 his
Airiest gal/min with siem set at ft for hrs
Artesian flow g p m Date
Temperature of water Was a chemical analysis made? ❑ Yes El No Start Date 1/9/11 Completed Date 2/24/11
WELL CONSTRUCTION CERTIFICATION:1 constructed and/or accept responsibility for construction of this well,and its compliance with all Washington well
construction standards Materials used and the information reported above are true to my best knowledge and belief
QDnller❑Engineer❑Trainee Name(Pnw)Stan Davis DrilhngCompany DavisDnllmg
Driller/Engineer/i•ramce Signature 7,, Address 340 NE Davis Farm Rd
Driller or trainee License No 967
1F TRAINEE Dntler's License No City,Stato zip Belfatr WA 98528
Contractol's
DrillcesSignature Registration No DAVISDI1100A Date Feb 2011
ECY 050-1-20(Rev 06108)ifyou need this document in an allenale formal,please call the Water Resources Program at 360-407-6600
Persons with hearing loss can call 71l for Washington Relay Service Persons ivith a speech disability can call 877.833-6341
Lai It �S r!r-� ---
File Original and First Copy with rl Card rto.�y(���� �1 7�'a
Second
of Ecology YyATER 'I (ALL REROR UEWELLLD.tt7�1_���L .__
Second Copy—Owner's Gopy
Third Copy—OnItar•s Copy STATE OF WASHINGTON Water Right permit No.
o (1) OWNER: Hama Aitrsr,Ld�
CL �l-
4! (2) LOCATION OF WELL: c«xcyYm
ri
_ (29) STREET ADDRESS OF WELL(or mar"addrem) �QIGQ !nt IQY
3
�
( ) PROPOSED USE: Domestic�.' Industrial ❑ Municipal D (10) WELL LOG Or ABANDONMENT PROCEDURE DESCRIPTION
Irtipalion
Test Wee p Other
N D DBWaler ❑ Forme11u1:Deecube by molar,character,size of material and slruqura,erd chow thickness of aquXers
and the kind and nature of the material in ead,stratum pa"Iroled.with at Isom one arnq for each
(4) TYPE OF WORK: Owner's number of well change of information.
(If more than one)
= Abandoned❑ New well atATERIAL FROM TO
O � Method:Dug❑ Bored D
Deepened ❑ CaMe D Driven❑
1_ RecoMdioned❑ Rotary[� Jetted❑
(5) DIME IONS: Diameterotwell r.
Drilled 0 Teel. Depth of completed well A(00 h, Z
L (6) CONSTRUCTION DETAILS: _L c<
= Casing Installed: �' Dlam.hom�TJZ h.b i_IL
Welded Dfam,from ft.b —It.Unar insta119d❑
Threaded ❑ Diam.from h.to ry.
y. Parforatlons: Yes❑ No Cl
0 Type of perforator used
"ZS SIZE of perforatlarw In.by In. r
pedore(ions from >t.to ft
perforations from ft.in. fL C4
Mperforations from ft.to
Screens: Yes)fir' No❑(
Manufacturer's Name w� D
41 Type Model No.
Diem. Sb(size to n.to tpa ft
1= Diam._$lei size from tL to fL 1S
W
L Gravel packed: Yes❑ No❑ Sae of oravel
L —
ta Gravel placed from ft.to ry,
Surface a": Yes R5 No❑ whal depth? h.
O Material used in seal
Did any strata contain unusable water? Yes❑ No
N Type of water? Depth of strata
r� Method o1 saaling strata oil
O
(T) PUMP: Mamufamrer's Name
Type,- H.R.
O (8) WATER LEVELS: Landsahace-W 601 Work surfed v f9. Compbled — 19
V � above mean Na bv —
51etic brat al n.txlvw Icp of con Date
!,�
anesian raswr. ter Wa WELL CONSTRUCTOR CERTIFICATION:
LV D rbe. are fndi !)ale
y_, Artesian water is controlled by 1 constnxted and/or accept responsibility for construction of this well, and its
ep'TWiiii°�' compliance with all Washington well construction standards.Materials used and
(9) WELL TESTS: Drawdown is amount water level is lowered bebw static level the information reported ebovrre are true to my best knowledge and beliei.
WWas a pump fast made?Yes❑ No&�) If yes,by whom?with Yield- NAME
pel.lmin. ff.drawdown after _hrs, t asoer,rites.
� Address
CL
Lv
Recovery data(time taken as zero wtrn pump turned on)(water lard measured frorn wall (Signed) License No.
® top to water Ievaly tvrLL ota.LERt
a Time Water Level Time Water Level Time Water Level Contractor's
� Regislr$§��n
No. S HtA=A= Dale_ �(O 19—
(USE ADDITIONAL SHEETS IF NECESSARY)
Date of teat
Baiter test gal./min,with h.drattdown aner _hre-
Autast oal./min.with stem set at :2—'R5 ft.for_�_hra- Ecology Is an Equal Opportunity and Affirmative Action employer.For spe-
Arlesian lbw p.p.m. onto C(al accommodation needs,contact the Water Resources Program at(206)
Temperature of water Was a chemical analyse made? Yes❑ No k� 407-6500.The TDD number is(206)407-6006.
ECY 050-1-20(9183) r
Appendix B
Well
BAJO10
& BCA 503
Extrapolated
Approximate Lot 102,..., A'
Location of -
_____ Planned
460 _ l Addition
Approximate
Location of
Existing
Residence _f� '?- /� _ . _?_
430 -
/.�'� Qvt-SW-Sp
�400
.-Haven Lake Qvt-SM.--�"
A
i
370 _ . - . . . . . . .?- - - - - - -? . . . . . . .
? ?
Qva-SP-SW
- - • - - - ?- - - - - ?- - - -?- - -
340 Qvt-S M
310
Cross Section developed from the 20-foot interval contour map from Mason County and from our site observations.
PM: RBP Mason County Figure B-1
ROBINSON-
May 2012 Cross Section A-A
NOBLE 2456-001B Emily Hillis: Hillis Residential Expansion
NS1 5-14-** 11 :48
Existing cabin
480 10 most crifical surfaces, MINIMUM BISHOP F'OS 2.241
440
to 40 0
4—
r'r
V) r W 1
x
< 360
320 _.
280 - - —._ ------- r - - r--- —-
0 4-0 80 120 160 200 240 280 320
x ---AXIS ( feet
PM: RBP Mason County Figure 132
ROBINSON" May 2012 Non-Seismic Global Stability
NOBLE 2456-001B Emily Hillis: Hillis Residential Expansion