CANOD.pdfADAMS
RESC]URCE
CONSULTANTS
Slavik Miniaylo
7316 -164th Street SW
Edmonds, WA 98026
APPROVED DA°ra
BLDG. OFF10AL:
PERMIT INUMBER
Re: REVISED Geotechnical Assessment for New Retaining Wall at
7316-1641h Street SW
Edmonds, Washington
Transmitted electronically to: nwstonecraft@yahoo.com
Our Reference: J 111- 01-16
Dear Slavik:
Adams Resource Consultants (ARC) is pleased to provide this brief letter report addressing the need to
apply for a permit to allow the newly constructed (March, 2016) concrete block retaining wall (Figures 1
through 3) at your above listed residence. As part of our assessment we have reviewed the following:
1) Letter dated January 7, 2005 from Cornerstone Geotechnical, Inc, to Clay Enterprises.
2) Plan Map titled: "Site Plan for House Construction," by Partners Architectural, dated June 10,
1999.
3) Applicable City of Edmonds codes: a) Chapter 23.40 Environmentally Critical Areas General
Provisions, b) Chapter 23.80 Geologically Hazardous Areas and c) Retaining Wall Permit Submittal
Requirements #1362.
In summary, based on our site observations and the previously listed information, the site area in question
that contains a newly constructed cement block wall is located in a Critical (steep (>40 percent) slope and
landslide hazard) Area. It is our professional opinion that this wall does not create a hazard to
neighboring properties, the older block wall above (south) nor to the slope beyond the lawn (north). The
construction of the new wall improves the slope and planting area by removing an older (degraded) wall.
We provide the details of our observations, opinions and recommendations below for your review and
submittal to the City in support of a permit to build and maintain the block wall.
BACKGROUND
RECEIVED
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Miniaylo - New Retaining Wall J-111-01-16
April 21, 2016
We understand from our conversations that two older block walls were overgrown and leaning prior to
new re -construction. The lower block wall was replaced with the new wall (subject of this letter report).
We understand the new wall was completed by excavating to a firm and stable base and provided with a
3/4 -inch crushed rock leveling surface about 8 inches thick. The blocks were placed with interlocking pegs
at a slight facing batter. A footing drain was placed along the front foot of the wall. Filter fabric and 1
inch diameter drain rock was placed behind the wall to create a blanket drain approximately 12 inches
wide that extends from the top of the wall to the foot. The upper (older) leaning wall was left in place as
shown in Figures 1through 3. We noted that during a site visit in the past a geotechnical engineer noted
(2005) the condition of the two walls and indicated that these walls complied with their
recommendations.
GENERAL OBSERVATIONS
We used a hand auger and shovel to investigate the soil in front and behind the new wall. Our
explorations extended to less than or equal to 4 feet deep and confirmed that the soil conditions
associated with the new wall was as described. We also found determined that soil material behind the
new wall consisted of between 1 and 1.5 feet of loose topsoil and sandy fill that overlies at least 2 to 3
feet of native sand. We did not observe any indications of significant movement, settlement, wet or soft
areas along the wall foundation. The blocks appear level and the wall in good condition.
OVERALL SLOPE STABILITY
We observed soil conditions north and below the wall area where the slope exposes native sand, Figure 2.
This slope extends down at an angle of between 45 and 50 degrees to a creek that flows to the west
within and near the north property line. We did not observe any indications of groundwater seepage,
slope movement or creep in this hillside north and below the block wall. It does not appear that past
movement of the two block walls is related to a larger slope stability issue or landsliding.
CONCLUSIONS AND RECOMMENDATIONS
In our opinion the observed movement of the old wall is an indication of settlement from construction on
loose fill soil materials. The lawn to the north and slope below do not exhibit any signs of landsliding and
though this region has been mapped as containing old landslide features, the slopes described and noted
on Figure 3 seem to be at equilibrium and have not moved for a very long time.
In order to be assured that this area continues to perform well we recommend the following as a
condition of permit:
1. All watering should be kept to a minimum. Planting should include draught resistance vegetation.
No vegetation should be removed from the area between the new wall and the previously
mentioned creek without advice from both a geotechnical and vegetation specialist. RECEIVED
2016
Miniaylo - New Retaining Wall
April 21, 2016
)-111-01-16
2. With the exception of completing drain rock placement behind the new wall, no additional
construction should take place in the area without the advice of a geotechnical specialist.
3. Surface survey monitoring points should be placed at several locations along the new wall and
north edge of the lawn. These monitoring points should be tied back to nearby fixed (stable)
reference points, such as the house foundation corners or established monuments in the street.
Readings should be taken twice yearly or more often if movement is observed (before and after
the rainy season) by a licensed surveyor or engineer. The readings should be tracked by a
geotechnical specialist.
4. All retaining walls should be no more than a maximum height of 4 feet without specific
engineering design recommendations and engineering construction observations/approval. (The
existing block walls were designed by others for a maximum height of 48 inches.)
5. All new drainage lines from the wall area should be located. Drains should extend down to
positive discharge at the creek on our client's property.
In addition to the recommendations previously provided we also suggest that the owner consider
extending two geotechnical boreholes in the lawn area in front (north) of the new wall. These boreholes
would extend to elevations of the stream to the north and should be fitted with standpipe piezometers so
that the engineer can monitor both groundwater levels and any slope movement. If these boreholes are
completed as described we would recommend that data from the boreholes be collected and tracked in
the same way during the same time frame as the surface survey readings.
In our opinion if the walls noted in Figure 3 are built according to our recommendations, the construction
will improve site conditions and stability.
LIMITATIONS
Subsurface conditions interpreted from observed soil materials and seepage conditions encountered
formed the basis for developing the recommendations in this report. The nature and extent of conditions
may change over time, often vary between observation locations and differences may not become
evident until after the start of site work. If significant variations then appear evident, we should be
consulted to re-evaluate the conclusions and recommendations in this report. It should be noted that
groundwater seepage and any fluctuations in the level of the groundwater are dependent on seasonal
variations in rainfall, temperature, and other climatic factors.
Our work for this project was performed, and this report prepared, in accordance with our original
contract with you, executed on April 13, 2016, including any approved changes. We have completed this
work in accordance with generally accepted professional practices for the nature and conditions of the
work done in the same, or in similar localities, at the time the work was performed. This report is
intended for the exclusive use of you and your contractors and/or consultants for specific application to
the referenced property. We make no other warranty, express or implied.
Miniaylo - New Retaining Wall
April 21, 2016
J-111-01-16
If we may provide any additional information or clarification about this report, please do not hesitate to
contact Wayne by cell at 425.466.2891 or by message at 425.788.3244.
Sincerely,
ADAMS Resource Consultants Company
WAYNE C. ADAMS, PE, PENG, EG
President/CEO
ADAMS Resource Consultants
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ARTHUR J. FLEMING, PE
Associate Engineer
ADAMS Resource Consultants
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RECEIVED
APR 2 6 2016
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Figure I Site Plan Sketch.
Note: All locationsand dlmensionsshown are approximate.
RECEIVED
APR 2 6 2016
DEVELOPMENT SERVICES