HomeMy WebLinkAboutGeoTech Report Review for Slope Investigation Report - PLN General - 8/6/1996 MASON COUNTY
PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER
Swit ,WuImptm 96M81
DATE: August 6, 1996
INTER-DEPARTMENTAL COMMUNICATIONS
TO: Randy Neff, DCD -Planner
FROM: Alan A. Tahja, P/W- Co. Hydr. Engr.
SUBJ: Geo-Tech Report Review NAME: Manke Lumber Co.
SP - Theler's Home& Garden Trcts MDNS 96-101
Randy,
The Geo-Tech assessment prepared for Manke Lumber Company's proposed short plat in the
Theler Home& Garden Tracts in Belfair appears to adequately address stability issues relating to
this property.
The recommendations made by Mr. Hal Parks should be made conditions of approval for this
proposal.
Sin erely,
Al An A. Tahja
File: H:\WP\GEO\REVIEWS\MNKE-BLF.AIR
August 5, 1996
To: Jerry Hauth/Alan Tahja
From: Randy Neff 1661;12
RE: Geo-tech Assessment for Manke Lumber Co.
Jerry & Alan:
D.C.D. received this geo-tech assessment for the Manke Short
Plat. Would you please review and comment on this assessment.
Thanks for all your help.
SQ
'V480N COUNTY go ND
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SLOPE
INVESTIGATION
REPORT
BELFAIR SHORTPLAT
Parcel # 123325000085
For
Manke Lumber Company
Shelton WA
By
Geotechnical Testing Laboratory
July, 1996
r
G EOTECHNICAL
TESTING LABORATORY
MANKE LUMBER CO. INC.
926 FAIRMOUNT AVE.
SHELTON, WA 98584
Attn: Harry Rydell
Re: Manke Subdivision
Mason Co.,WA
Gentlemen:
This letter presents the results of our slope stability and soils investigation regarding the above referenced site in Belfair,
Washington. Tile existing site comprises two lots, identified as Lot A and Lot B. The relief on Lot A was gentle with a
I vertical to 4 horizontal angle; Lot B has a I vertical to I horizontal angle, with a stream near the base of the slope.
No buildings currently occupy either site.
SUBSURFACE EXPLORATION PROGRAM
The subsurface exploration program consisted of a reconnaissance and observation of the lots. Information from our
files was reviewed. Hal Parks,Engineering Geologist, collected soil samples from soil log holes previously dug on the
lots. The soil strata observed on the slope profiles were from spot locations across the site and on the slope. The soil on
the site was uniform and consistent. It is mapped by the USDA Soil Conservation Service as an Everett Gravely Loamy
Sand.
SITE CONDITIONS
Lot A: The slope began at the road access and gently progressed toward the west and was covered with large trees and
low shrubs. This type of vegetation produces excellent protection against erosion on the immediate bank. Partially
decayed leaves and other organic material covered the native soil. A gentle slope continued off the property and beyond
the scope of this study. Runoff is slight because of the rapid internal drainage of the soil. No evidence of rotational
movement or deep seated instability was observed.
Lot B. From the access road to the crest of the slope,this lot is relatively level. This level area is the most propitious
spot for the building of a home. Tile lot drops suddenly to a small stream at the bottom of a well-defined drainage
channel. Tile entire lot was covered with trees and brush. Most of the water from the upper terrace drains away from
the slope to the east. All surface runoff from the crest of the slope and eastward runs toward the gully. All runoff enters
the ground and at discharge areas, the flows tend to swing normally in the direction of the surface flow.
An access road runs between the two lots(see map). The best location for a home on Lot B was assumed to be on the
terrace above and back from the crest. From this area,a new home could be built with no special engineering
considerations except setback distance. A home located 40 feet from the crest would not destabilize the slope along the
gully.
A close examination of the crest of the gully in regard to the subject lots showed no signs of cracking and slumping. It is
our opinion that the slopes are sound, but we recommend that any building built on lot B observe a setback of 40 ft. from
the crest of the slope and any building built on lot A follow the(DAYLIGHT)principle mentioned in the following
paragraph. Low shrubbery and vegetation should be encouraged to grow on the bank to mitigate erosion. Should the
owner of a particular lot desire to build closer than 50 ft. to the crest, an engineering geologist should be consulted to
insure stability of the home and the slope.
1001 1 Blomberg Street SW, Olympia, WA 98512
GEOTECHNICAL
TESTING LABOR
ATORY
HILLSIDE FOUNDATIONS DAYLIGHT DIMENSION
Structures built on sloping sites offer a number of potential problems. Fig. I illustrates a basic consideration for what is
called the"daylight"dimension, which is the horizontal distance from the bottom of the footing to the adjacent ground
surface. Many building codes require a minimum distance for this dimension in order to assure some safety against the
pushing out of the footing in the downslope direction. Logically, the limit for this distance depends on the type of soil
and the angle of the slope of the ground surface. For low slope angles,a reasonable daylight dimension is assured simply
because of the usual requirements for the minimum depth of the bottom of the footing below the surface in a vertical
direction. As the slope increases,the daylight dimension is less assured and should be limited to some minimum distance.
A depth of 32 inches will provide the critical exposure necessary.
A common problem with hillside construction is that shown in Fig.2,where recontouring of the construction site results
in a portion of the building being placed on some significant depth of fill. If possible,all of the footings should be carried
down to a depth below the fill. If structural fill is used and placed with reasonable compaction, it may be possible to rest
the footings in the fill,provided that this is done only with inspection and supervision by a qualified soils consultant.
RECOMMENDATIONS:
All material excavated from the site cannot be dumped on the site without adequate subgrade preparation at the spoil
location and proper fencing and runoff controls. All spoils soil must be compacted to 90%MDD as per ASTM D 1557
and protected from erosion. Footing drains must be installed around the footing or basement and the invert of the drain
shall be lower than the bottom of the footing. In the footing area,the foundation for any homes must be placed in the
firm native soil.
The conclusions and recommendations in this report are based on our interpretation of site conditions as they presently
exist,anticipated future construction activities,and the expectation that our exploratory efforts adequately define the
subsurface conditions throughout the site. In the event that the scope or location of the project should change,or
subsurface conditions different from those encountered during our study be observed or suspected,we should be advised.
At that time,a review of the changed conditions will be made and alternative or remedial recommendations given as
requested.
f�Sincerely 1)1"
Harold Parks,
Engineering Geologist
1001 1 Blomberg Street SW,Olympia, WA 98512
G EOTECIINICAL
TESTING LABORATORY
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10011 Blomberg Slreet SW, Olympia, WA 98512
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Slope Analysis for Cohesionless Soils
angle: 42 Unit Weight: 134.2 Critical Slope Angle,Saturated: 25.7
Saturated Saturated Unsaturated Unsaturale
X Y Z Height Horizontal Slope Total Total Total Total Section Total Section 'Total
Grid Grid Elevation Change Distance Slope Angle florizonta Change Slope Angle (3> 13> > >
Line Line Feet Feet Feet % p Feet Feet % 11 Critical Critical
Lot A 0 104 0 0 0 10 0 0 0 0
Lot A 1 105.25 1.25 10 12.5% 7.1 10 1.25 12.5% 7.1 Safe Safe Safe Safe
Lot A 2 106.5 1.25 8 15.6% 8.9 18 2.5 13.9% 7.9 Safe Safe Safe Safe
Lot A 3 107.75 1.25 7 17.9% 10.1 25 3.75 15.0% 8.5 Safe Safe Safe Safe
Lot A 4 109 1.25 6 20.8% 11.8 31 5 16.1% 9.2 Safe Safe Safe Safe
Lot A 5 110.25 1.25 5 25.0% 14.0 36 6.25 17.4% 9.8 Safe Safe Safe Safe
Lot A 6 111.5 1.25 5 25.0% 14.0 41 7.5 18.3%" 10.4 Sale Safe Safe Safe
Lot A 7 112.75 1.25 5 25.0% 14.0 46 8.75 19.0% 10.8 Safe Safe Safe Safe
Lot A 8 • 114 1.25 5 25.0% 14.0 51 10 19.6% 11.1 Safe Safe Safe Safe
Lot A 9 115.25 1.25 5 25.0% 14.0 56 11.25 20.1% 11.4 Safe Safe Safe Safe
Lot A 10 116.5 1.25 5 25.0% 14.0 b 1 12.5 20.5% 11.6 Safe Safe Safe Safe
Lot A 11 117.75 1.25 5 25.0% 14.0 66 13.75 20.8% 11.8 Safe Safe Safe Safe
Lot A 12 119 1.25 5 25.0% 14.0 71 15 21.1% 11.9 Safe Safe Safe Safe
Lot A 13 120.25 1.25 5 25.0% 14.0 76 16.25 21.4% 12.1 Safe Safe Safe Safe
Lot A 14 121.5 1.25 5 25.0% 14.0 81 17.5 21.6% 12.2 Safe Safe Safe Safe
Lot A 15 122.75 1.25 5 25.0% 14.0 86 18.75 21.8% 12.3 Safe Safe Safe Safe
Lot A 16 123 0.25 25 1.0% 0.6 1 I 1 19 17.1% 9.7 Sale Safe Safe Safe
Slope Graph
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