Geotech report.pdfI
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Dennis M. Bruce,. P.E.
M:S:C.E., M.B A, Geoterhnicai XMI Engineer
RECEIVED
July 10; 200$ JUL 28 2008
DEVELOPMENT SERVICES
COUNTER
City of Edmonds
c/o Paul Tomlin
7530 1841h Pl. SW
Edmonds, WA 98026 - 5$27
Subject: Geotechnical "Update" — ECDC Requirements
Tomlin — New Single -Family Residence
.7530 184th PI. SW
File No. S-08-24
This engineering report presents additional "language updates" with regard to the
proposed new Tomlin residence at the above referenced address. This additional
report was required by City of Edmonds request for compliance with current code
stipulations.
REFERENCES: <..
• Original GeotechnidaI'Report;by D.` Bruce,P E. dated:October 8, 2001
Geotechnical "Exemption" clarification by D. Bruce, P.E. dated August 2, 2002
• March 6, 2008 Geotechnical Update Report by. D_ Bruce, P.E.
o Project Plans (submitted by Tomlin)
• City of Edmonds June 5, 2008 request for additional information
BACKGROUND:
As previously stated, this engineer performed an extensive geotechnical
investigation in 2001 for Mr. Paul Tomlin (for the proposed new residence).
Development of the house project was delayed, and is now currently in permit.
The October 8, 2001 report specified the extremely dense, native, sub -grade
soils "dense sandy silt with occasional gravels". No evidence of any geotechnical
distress was observed in 2001 (nor any distress observed in the 7 years since). No
slides, no soil tension cracks, or any evidence of erosional degradation.
Sacs • FOUNDAnO SIS * SITE DEMOMEMT • rMSPEcrtvM * DRAMGE ! DESIGN, & PERMrr • LEGAL
P.0. Box 55502 Shoreline, WA.98155 (206) 546-9217 FAX (206) 546-8442
City of Edmonds
c/o Paul Tomlin
July 10, 2008
Page 2
it is understood that this area is categorized a critical area due to the portions of
the slope that slightly exceed 40 percent grade. This declination in slope is well
documented on the topographic map by Western Surveyors.
The August 2, 2002 geotechnical exemption report clearly addresses categories
of the ECDC regarding exemptions to critical areas restrictions.
This engineer undertook a reassessment of the site in March of 2008 and
verified the stability of the slope and the findings and recommendations of the previous
geotechnical reports.
It is understood that the City of Edmonds has updated its code and re -numerated
critical area requirement numbering systems.
Hence, City of Edmonds permitting planner requests an updated "symantic — re-
numeration" in order to comply with current City of Edmonds Codes.
NOTE: No actual geotechnical conditions have changed from 2001. The findings
and recommendations of the 2001 geotechnical report are valid.
The Tomlin property is not a land slide hazard, nor is it an erosion hazard. The
slope is neotechnicaly stable f as previously declared many times.
The proposed development (new residence) will imp rove slope stability by
means of the reinforced concrete foundation, stem walls and improved drainage.
ECDC CURRENT CODE NUMERATION AND REQUIREMENTS:
1) 23.80.050:
This section enumerates a number of requirements for plans and
.geotechnical report. As previously discussed (in 2001 and 2002), the site is
stable with soils categorized as Advanced Outwash". These soils are extremely
stable and provide excellent foundation bearing support.
The 2001 and 2002 reports provide all geotechnical information required
under 23.80.050.
It is :understood that project plans (provided by Mr. Tomlin) address the
speck site and construction plans, as well as the buffer and setback distances
from property lines.
City of Edmonds
c/o Paul Tomlin
July 10, 2008
Page 3
There are no specific geotechnical mitigations required for this project,
other than normal geotechnical inspections by D. Bruce, RE. for: excavation,
foundation bearing verification, review of foundation footings (formwork,
reinforcing steel), subsurface drainage, backfill, final grading, and any landscape
stabilization rockeries. It is understood that D. Bruce, P.E. will perform these
geotechnical inspections during construction.
2) 23.80.060:
"The proposed Tomlin residence... will not increase the threat of the
geologic hazard to the adjacent properties beyond pre -development conditions."
This project will not adversely impact other critical areas.
The design of the Tomlin residence does not impose a hazard to the site —
in fact the construction of the Tomlin residence improves the stability of the slope
better than pre -development conditions.
The proposed Tomlin residence is certified as safe, as designed, under
the anticipated conditions by Dennis M. Bruce, P.E. an experienced geotechnical
engineer licensed in the State of Washington.
3) 23.80.070(3):
a) The proposed Tomlin residence shall not decrease the factor of safety for
landslide occurrences developed below the limits of 1.5 for static
conditions and 1.2 for dynamic conditions.
b) There are no geologic hazardous areas on the site, thus no "clustering" is
required for this single-family residence.
c) This engineer agrees that the foundation shall be tiered in order to
minimize excavation into the slope.
d) The overall site is not critical, thus the current proposal for house location
is geotechnically valid.
e) The proposed Tomlin residence shall not result in a greater risk or need
for increased buffers on the neighboring property.
City of Edmonds
c/o Paul Tomlin
July 10, 2008
Page 4
D The Tomlin project plans do not incorporate any retaining wall for
geotechnical purposes. Small rockeries are proposed for landscaping
stabilization and erosion control purposes.
g) See project plans for impervious lot coverage.
4) Ve-getation Retention:
This engineer agrees that the current vegetation on the modest Tomlin
slopes should be maintained and not "clear cut". This engineer supports the City
of Edmonds decisions to delineate vegetation preservation zones.
5) Seasonal Restriction:
Given the sandy sub -grade soils, this site does not require any
geotechnical restriction for excavation and construction. Geotechnical
inspections by D. Bruce, P.E. are required.
SUMMARY:
• The proposed Tomlin residence at 7530 184'h Pl. SW will not create any adverse
geotechnical impacts to the slopes. The 2001, 2002 and 2008 reports clearly
demonstrate the stability of the slope and stability of the sub -grade soils.
• Construction of the Tomlin residence will actually improve overall slope stability,
as discussed herein.
• Geotechnical inspections are required by D_ Bruce, P.E.
If there are any questions, do not hesitate to call.
DMB:abt +twa�s
3nnis M. Bruce, P.E.
eotechnical / Civil Engineer