HomeMy WebLinkAboutGeo-Tech Review for BLD2003-01256 - BLD Engineering / Geo-tech Reports - 10/15/2003 MASON COUNTY
PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER
Shelton,Washington 98584
DATE: October 15t', 2003
INTER-DEPARTMENTAL COMMUNICATIONS
TO: Diane Marcus Jones, DCD - Planner
FROM: Alan A. Tahja, P/W - Co. Hydr. Engr. WO# PLG-03
SUBJ: Geo-Tech Review NAME: Buchheit SFR k 681 Greenview Lane
BLD2003-01256
Diane,
The geotechnical report prepared for the Buchheit Single Family Residence (SFR)to be located
at 681 Greenview Lane, Mason County, has been received and reviewed by Public Works.
The report appears complete, and acceptance, as it pertains to the proposed development, is
recommended.
Recommendations made in the report should be incorporated into the site's development.
Please feel free to contact me at County extension 461 if you have any questions regarding these
comments, or if you feel any features need further discussion or attention.
erely
rk,4, 1 - I-
lan A. Tahj
TO BE KEPT IN THt
PARCEL FILE
File: H:\WP\GEo\Undetermined\Buchheit.doc
WORK ORDER - PUBLIC WORKS DEPT.
(A) Data: 10-15 a3 (q worts Order
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COST ESTIMATE
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0 C T 15 2003
MASON COUNTY PUBLIC WORKS
Geotechnical Report
681 Greenview Lane
Parcel #321352390011
Mason County, WA
Prepared for
Marc & Lydia Buchheit
by
Geotechnical Testing Lab
Olympia, WA
October 13, 2003
i
GEOTECHNICAL TESTING LABORATORY
IMARC AND LYDIA BUCHHEIT
P.O. BOX 344
SHELTON,WA 98584
RE: GEOLOGICAL ASSESSMENT
I 681 GREENVIEW LANE
PARCEL 321352390011
N47015.997' W 123°02.053'
I
INTRODUCTION
I -
This report summarizes the results of our geotechmcal consulting services for the proposed single-family residence
to be located at 681 Greenview Lane approximately 4.5 miles northeast of Shelton,Washington. The lot is located
I in an area of moderate residential development;the location of the site is shown relative to the surrounding area on
the Vicinity Map, Figure 1
I
View Looking East at Proposed Building Location
I Our understanding of the project is based on our discussions with you and our explorations and review of the site.
The site is accessed from a small gravel driveway off Greenview Lane. A septic system will be located onsite;
drinking water will be provided by a local well. Stormwater runoff from the site, roof and hard surfaces,will be
Icollected and controlled. The general layout of the site is shown on the Site Map, Figure 2.
We further understand that minor grading will be required at the site to reach design grade. In general,grading will
consist of the excavation of the foundation material,garage, and driveway.
IThe lot is gently sloping to the northeast. A large ravine curves around the south and east side of the proposed
building site. This ravine is no closer than 80 feet from the proposed building site. At the closest point,the top of
I the drainage is uphill of the building site. In anticipation of construction,the building site and immediate
surroundings have been cleared of vegetation. Slope angles on this site range from 5 percent to 20 percent at the
building site to over 100 percent along the ravine. Therefore, Mason County requires that a geotechnical report be
' prepared in accordance with the Critical Areas Ordinance.
' 10011 Blomberg Street SW, Olympia,WA 98512 1
Phone#: (360) 754-4612 Fax#: (360)7544848
GEOTECHNICAL TESTING LABORATORY
deposited less than 10,000 years ago,and weathering and erosion that has occurred since. A description of the
surficial soils is included in the"Site Soils"section of this report.
In general,the soils on the site are predominantly represented by Vashon recessional outwash material composed of
a mixture of sand and silt.
•.i-t ',x,t` A fi � �' �. "fir,.
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SITE SOULS
The Soil Survey of Mason County, USDA Soil Conservation Service (1960)has mapped the site soils as Lystair
sandy loam, 5 to 15 percent slopes (Le). The report reads, "The Lystair series consists of somewhat excessively
drained, brown, sandy soils that occupy hilly kettles and kames and nearby level outwash plains. They have
developed from nearby gravel-free, loose, sandy glacial drift deposited mainly by outwash waters. The soils are
somewhat excessively drained and are droughty. They have a low capacity for available moisture. All layers of the
soil are porous."
The Coastal Zone Atlas, Volume 9, ofMason County(MA-22)maps the site as Vashon recessional outwash(Qvr).
The slope stability is described as "Generally stable in slopes up to the angle of repose." The foundation stability is
described as "Fair to excellent." Seismic stability is described as "good."
SUBSURFACE EXPLORATIONS
Subsurface conditions at the site were evaluated by observing the
exposed foundation material and the exposed northern steep slope as
well as local well logs. At the building location, unconsolidated
sandy loam was found to a depth of 36 inches and beyond. Well
logs indicate that hardpan may be expected from 3 to 22 feet below
the ground surface. A local well log follows this report.
SUBSURFACE CONDITIONS
In general, undisturbed unconsolidated sandy loam was observed throughout both the site and the proposed building
location. Groundwater seepage was not observed at the site. Seasonally perched groundwater conditions may not
be expected even during periods of extended wet weather.
10011 Blomberg Street SW, Olympia,WA 98512 3
Phone#: (360) 7544612 Fax#: (360)7544848
GEOTECHNICAL TESTING LABORATORY
No groundwater seepage was observed at the site. No wetland vegetation was observed at the site. Based on local
well logs,depth to groundwater is approximately 88 feet below ground surface. No surface water was observed in
the ravine.
SLOPE STABILITY
Slopes in excess of 100 percent were observed on the site. Since slopes of 40 percent or greater with 10 feet or more
of vertical relief occur on portions of the site, Mason County requires that a geologic hazards report be completed
according to the Critical Areas Ordinance.
The near-surface soils are in a dense to very dense condition except at the ground surface. The surficial soils are
generally in a medium dense condition.
In general,the subsurface undisturbed native soils of the site consist of a mixture of variable amounts of sand and
silt. These soil materials are in a dense condition except where they have been disturbed by weathering activity.
These soils are generally stable relative to deep-seated failure. No evidence of deep-seated landslide activity or
significant erosion was observed near or at the site during our investigation.
Weathering,erosion, and the resultant sloughing and shallow landsliding are natural processes that can affect steep
slope areas. Instability of this nature is typically confined to the upper weathered or disturbed zone,which has been
disturbed and has a lower strength. Evidence of minor surficial erosion was not observed at the site. Sloughing or
raveling was not observed along the steep ravine at the time of our investigative visit.
Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration,
wet/dry cycles,and freeze/thaw cycles. Erosion in steep slope areas such as this can be reduced by encouraging
vegetation and discouraging concentrated runoff on the steep slope. Erosion control recommendations for the
sloping areas are provided in the`Building Setback"and"Erosion Control'sections of this report.
CONCLUSIONS AND RECOMMENDATIONS
GENERAL
Based on the results of our site reconnaissance and subsurface observations, and our experience in the area, it is our
opinion that the site is suitable for the proposed single-family residence.
The site slopes are stable relative to deep-seated instability and will not be affected by the proposed single-family
residence. Proper drainage control measures will reduce or eliminate the potential for erosion in this area and
improve slope stability.
In general,the site soils are not suitable for use as structural fill material. Saturated soil conditions are associated
with these soils during or following extended periods of rainfall. Therefore we recommend that earthwork be
undertaken during favorable weather conditions to reduce grading time and construction costs.
Conventional construction equipment may be utilized for work at the site. Conventional spread footings may be
utilized for support of the structure. We do recommend that roof and footing drains be installed. Footing and roof
drains may not be connected. A vapor barrier is recommended for all slab-on-grades.
10011 Blomberg Street SW, Olympia,WA 98512 4
Phone#: (360) 754-4612 Fax#: (360)754-4848
i
GEOTECHNICAL TESTING LABORATORY
IPertinent conclusions and geotechnical recommendations regarding the design and construction of the proposed
single-family residence are presented below.
I
LANDSLIDE—EROSION HAZARD AREAS
ICLASSIFICATION
The Mason County Critical Areas Ordinance(17.01.100)defines a landslide hazard area as one containing slopes
equal to or greater than 40 percent with more than a 10-foot vertical relief. The slope bordering the ravine is in
excess of 40 percent and the vertical relief is in excess of 10 feet. Based on this,this site does meet the technical
i criteria of a landslide hazard.
I The Relative Slope Stability of the Southern Hood Canal Area, by R.J. Carson(1977)classifies the site as Class 1.
Class 1 is expressed as,
Areas believed to be stable. Largely comprises rolling uplands underlain by very stable
material such as young glacial till, mantled in places by a thin layer of sandy gravel or
other permeable material; also includes flood plains, deltas, alluvial fans, and some beach
deposits. Class 1 areas immediately adjacent to steep slopes of class 3 areas may be
threatened by potential landsliding. Normal, proper engineering practices generally are
adequate to insure stability in these areas.
The Mason County Critical Areas Ordinance(17.01.104)defines an erosion hazard area as:
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 additions 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 1 S%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 soils at the site are mapped as Lystair sandy loam(LJ. This site does not meet the technical criteria of an
erosion hazard area. With proper drainage control and re-vegetation, potential erosion hazard concerns may be
overcome.
SLOPE STABILITY
I Based on our field observations,explorations and our experience with the soil types encountered on the property, we
conclude that although portions of the lot exceed 100 percent,they are generally stable relative to deep-seated failure
in their present configuration. The following figure represents a shear angle for the sandy loam. Shear angle and
Icohesion are variables used to model the site.
I
10011 Blomberg Street SW, Olympia,WA 98512 5
Phone#: (360) 7544612 Fax#: (360)754-4848
I
I
GEOTECHNICAL TESTING LABORATORY
I
Buchheit Site
Analysis Method: Morgenstern-Price
Direction of Slip Movement: Left to Right
Slip Surface Option: Grid and Radius
Seismic Coefficient: Horizontal and Vertical
240 J
200 1311.
= 1eo Proposed_ . . . . . . . .
I � Building . . v
16o ystair Sandy Loam area
CO
m
W 140 nit Weight: 119
I 120 —Cohesion:200
hi:41
100
0 50 100 160 200 250 300 350 400 450 500 550 600
Distance (ft)
I
A building setback from landslide hazard areas is required unless evaluated and reduced by an engineering geologist
or a licensed professional engineer. Based on our geotechnical evaluation of the site and our experience in the area,
a building setback will be needed for this lot. A setback of 25-feet from the crest of the slope to the bottom of the
footing should otherwise be observed. The building setback may be measured from the bottom of the footing to the
Iface of the steep slope, in accordance with the Unified Building Code.
As previously discussed, weathering, erosion and the resultant surficial sloughing and shallow landsliding are
I natural processes that affect slope areas. No significant surficial raveling or sloughing was observed in the sloping
portions of the site. To manage and reduce the potential for these natural processes,we recommend the following:
I 1. No drainage of concentrated surface water or significant sheet flow onto the sloped areas.
2. No filling within the setback zone unless retained by retaining walls or constructed as an engineered fill.
3. Drainage from the roof and footing drains should be collected and tight-lined to bottom of the ravine to the
south.
SEISMIC—LIQUEFACTION HAzARD
According to the Seismic Zone Map of the United States contained in Figure 16-2 of the 1997 UBC (Uniform
Building Code),the project site is located within Seismic Risk Zone 3.
Based on the subsurface conditions observed at the site,we interpret the site conditions to correspond to a seismic
Soil Profile Type Sc, for Very Dense Soil, as defined by Table 16-J (UBC). This is based on the range of SPT
(Standard Penetration Test)blow counts and/or probing with a '/Z-inch diameter steel probe rod. The shallow soil
conditions were assumed to be representative of the site conditions beyond the depths explored.
10011 Blomberg Street SW, Olympia,WA 98512 7
Phone#: (360) 7544612 Fax#: (360)7544848
� I
GEOTECHNICAL TESTING LABORATORY
percent of MDD (maximum dry density as determined in accordance with ASTM D-1557)to within 2 feet of
subgrade and 95 percent MDD in the upper 2 feet.
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.
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. During wet weather,we
recommend the use of well-graded sand and gravel with less than 5 percent(by weight)passing the No. 200 sieve
based on that fraction passing the%-inch sieve.
If prolonged dry weather prevails during the earthwork and foundation installation phase of construction,a
somewhat higher(up to 10 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. The moisture content of the fill material should be adjusted as necessary for proper compaction.
SUITABILITY OF ON-SITE SOILS AS FILL
On-site Lystair soils should not be used as structural fill. In general,the native soils(sandy loam)encountered on
the site have less than 10 percent fines (material passing the US No. 200 Sieve)and are not suitable for use as
structural fill.
CUT AND FILL SLOPES
All job site safety issues and precautions are the responsibility of the contractor providing services and/or work.
The following cut/fill slope guidelines are provided for planning purposes.
Temporary cut slopes will likely 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 4 feet of the glacially
consolidated soils that are weathered to a loose/medium dense condition. Temporary slopes of 1 to 1 or flatter may
be used in the unweathered dense to very dense sands and silts 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 where significant raveling or seepage occurs.
Subsurface drainage may be required if seepage areas are discovered. 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.
FOUNDATION SUPPORT
Where foundation elements are located near slopes of 5 percent or more,the footings should be located a minimum
of 2 times the footing width from the slope face(horizontally),and founded in medium dense or denser native soils
or properly prepared structural fill.
10011 Blomberg Street SW, Olympia,WA 98512 9
Phone#: (360) 754-4612 Fax#: (360)754-4848
GEOTECHNI TESTING LABORATORY
CAL S
We recommend a minimum width of 2 feet for isolated footings and at least 16 inches for continuous wall footings.
Footings founded as described above can be designed using an allowable soil bearing capacity of 2,000 psf(pounds
per square foot)for combined dead and long-term live loads in areas of medium dense to dense soils.
The weight of the footing and any overlying backfill may be neglected. The allowable bearing value may be
increased by one-third for transient loads such as those induced by seismic events or wind loads.
Lateral loads may be resisted by friction on the bases of footings and floor slabs and as passive pressure on the sides
of footings. We recommend that an allowable coefficient of friction of 0.40 be used to calculate friction between the
concrete and the underlying soil. Passive pressure may be determined using an allowable equivalent fluid density of
300 pcf(pounds per cubic foot).
We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch,for the
anticipated load conditions, with differential settlements between comparably loaded footings of/z inch or less.
Most of the settlements should occur essentially as loads are being applied. However, disturbance of the foundation
sub-grade during construction could result in larger settlements than predicted.
FLOOR SLAB SUPPORT
Slabs-on-grade should be supported on medium dense or dense native soils or on structural fill prepared as described
in the"Structural Fill"section of this report. We recommend that floor slabs be directly underlain by a minimum 6-
inch thickness of coarse sand and/or gravel containing less than 5 percent fines(by weight). The drainage material
should be placed and compacted to an unyielding condition.
A synthetic vapor barrier should be used for the control of moisture migration through the slab,particularly where
adhesives are used to anchor carpet or tile to the slab. A thin layer of sand may be placed over the vapor barrier and
immediately below the slab to protect the liner during steel and/or concrete placement. The lack of a vapor barrier
could result in wet spots on the slab,particularly in storage areas.
RETAINING WALLS
Retaining walls may be utilized on the sloping portion of the site to retain fill material. The lateral pressures acting
on the subgrade and retaining walls will depend upon the nature and density of the soil behind the wall. It is also
dependent upon the presence or absence of hydrostatic pressure. If the adjacent exterior wall space is backfilled
with clean granular,well-drained soil (washed rock),the design active pressure may be taken as 35 pcf(equivalent
fluid density). This design value assumes a level backslope and drained conditions as described below.
Retaining walls located on or near the toe of a slope that extends up behind the wall should be designed for a lateral
pressure, which includes the surcharge effects of the steep slope in proximity to the wall. Although not expected at
this site,the following data is provided for planning purposes.
For an irregular or composite slope,the equivalent slope angle may be determined by extending a line upward from
the toe of the wall at an angle of 1 to 1 (Horizontal to Vertical)to a point where the line intersects the ground
surface. The surcharge effects may be modeled by increasing the equivalent fluid pressure for flat ground by the
percentage given in the following table:
10011 Blomberg Street SW, Olympia,WA 98512 10
Phone#: (360)7544612 Fax#: (360)7544848
i
GEOTECHNICAL TESTING LABORATORY
ISLOPE INCLINATION: EQUIVALENT FLUID PRESSURE
Slope Angle Percent Increase Equivalent Fluid Pressure
Horizontal 0% 35 pcf
3H:1V 25% 44 pcf
214:1V 50% 53 pcf
I1H:1V 75% 61 pcf
If the walls are greater than 8 feet in height,exclusive of the footing,additional design considerations should be
Iapplied.
Positive drainage,which controls the development of hydrostatic pressure,can be accomplished by placing a zone of
I coarse sand and gravel behind the walls. The granular drainage material should contain less than 5 percent fines.
The drainage zone should extend horizontally at least 18 inches from the back of the wall. The drainage zone should
also extend from the base of the wall to within 1 foot of the top of the wall. The drainage zone should be compacted
to approximately 90 percent of the MDD. Over compaction should be avoided as this can lead to excessive lateral
pressures.
I A perforated PVC pipe with a minimum diameter of 4 inches should be placed in the drainage zone along the base of
the wall to direct accumulated water to an appropriate discharge location.
We recommend that a non-woven geotextile filter fabric be placed between the drainage material and the remaining
wall backfill to reduce silt migration into the drainage zone. The infiltration of silt into the drainage zone can,with
time, reduce the permeability of the granular material.
I ) The filter fabric should be placed in such a way that it fully separates the drainage material and the backfill, and
should be extended over the top of the drainage zone.
ILateral loads may be resisted by friction on the bases of footings and as passive pressure on the sides of footings and
the buried portions of the wall. We recommend that an allowable coefficient of friction of 0.40 be used to calculate
friction between the concrete and the underlying soil. Passive pressure may be determined using an allowable
equivalent fluid density of 35 pcf(pounds per cubic foot). Factors of safety have been applied to these values.
RETAINING WALL ALTERNATIVES
Typically, reinforced-earth block wall systems are more cost effective for long-term walls than the other options.
Specific design criteria for these options can be provided at your request by the block manufacturers.
SITE DRAINAGE
I All ground surfaces,pavements and sidewalks should be sloped away from the residences and associated structures.
Surface water runoff should be controlled by a system of curbs,berms,drainage swales,and/or catch basins. We
recommend that conventional roof drains be installed. Footing drains shall be installed for the home and garage.
I The roof drain should not be connected to the footing drain. For footing drains,the drain invert should be below the
bottom of the footing.
We recommend that the collected stormwater runoff at the site be directed to an appropriate area. Onsite irrigation
to lawn areas should be closely monitored. We do not expect any adverse affects on the recharge condition of the
groundwater system due to the use of on-site septic disposal.
10011 Blomberg Street SW, Olympia,WA 98512 11
Phone#: (360)7544612 Fax#: (360) 7544848
I
Geotechnical
r Testing
r
Laboratory
Geotechnical Services
QA/QC Services
O Testing Services
10011 Blomberg St.SW
Olympia,WA 98512
Phone:(360)754-4612
Fax:(360)754-4848
Date: 10/09/2003
Designed by: LL
Drawn by: LL
Checked by: LL
Dwg#:10-09-03-071
V
PROJECT NAME:
• BUCHHEIT SITE
681 GREENVIEW LANE
SHELTON, WASHINGTON
PARCEL 321352390011
Revisions:
1
i
SCALE 1'-40'
PRIVATE DRIVE 0.HS2
DATUM ASSUMED SCALE:1 inch=40 feet
THIS IS NOT A SURVEY
r 0 10 20 30 40 FIGURE 2
0
0