HomeMy WebLinkAbout10 01 2018 Retaining Walls PresentationBLUFFS &
RETAINING WALLS
Prior Lake City Council Work Session
October 1, 2018
2040 Vision & Strategic Plan
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Goal: Environmental Stewardship & Recreation
Objective: Protect and enhance the quality of Prior
Lake’s surface waters.
City Retaining Wall Policy –March 2010
Retaining Walls Outside of a Bluff –In 2010, no new retaining walls were permitted
inside a bluff.
■Building code requires all retaining walls over 4’ in height require a building permit
before construction.
■The permit application must be accompanied by a design certified by a registered
engineer.
■The City will submit the plans to a third-party consulting engineer for review. The
applicant is responsible for the cost of this review.
■Once the City’s consultant approves design, they will provide a cost estimate to
complete the necessary inspections during the wall construction. The applicant is
responsible for the cost of this review.
■The contractor must coordinate the construction and inspections with the City’s
designated inspector. No construction may take place without the necessary
inspections.
■Once construction is complete, the City’s consultant will provide a letter stating the
wall was constructed in accordance with the approved plans before a CO is issued.
1104.303 Bluff Impact Zones
Structures and accessory facilities, excluding stairways, lifts, and landings, shall not be
placed in bluff impact zones except for the following:
(2)Retaining walls shall not be permitted in the bluff impact zone or bluff setback
except for the following:
a.Construction on an existing retaining wall that consists of the repair or exact
replacement of the existing wall, provided the grade of the land within the bluff
impact zone or bluff setback and the location and size of the retaining wall do not
change and the new retaining wall will create no more impact in the bluff impact
zone or bluff setback than was caused by the existing retaining wall.
b.Construction of a new retaining wall that does not exceed four feet in height,
construction that consists of an addition to an existing retaining wall that does not
increase the height of the wall above four feet, or construction that decreases the
height of an existing retaining wall; provided the proposed drainage patterns
and/or erosion control methods are an improvement over the existing conditions
on the site as determined by the City.
Construction of retaining walls under provisions (a) and (b) above shall require
a grading and filling permit as well as engineering reports as required by
subsection 1104.305.
1104.305 Engineering Reports Required
For any construction within a bluff impact zone or bluff setback, including work on any building, platform or structure, the following shall be provided:
(1) Prior to any construction, a report and calculations prepared and signed by a professional engineer licensed by the State of Minnesota on the bluff stability and the impact any excavation, fill or placement of structures will have on the site and whether the excavation, fill, or placement of structures will cause any slope to become unstable or will impose loads that may affect the safety of structures or slopes.The report shall include the following:
■The global failure plane determination of the slope substantiated by at least one soil boring at an appropriate depth and location.
■Analysis of the land influence zone and its intersection with the failure plane based on the soil type
■The Engineer's recommendations for the proper design and maintenance of a drainage system so the site development will not interfere with adequate drainage for the site or adjacent properties, will not obstruct, damage or adversely affect existing sewer or drainage facilities, will not adversely affect the quality of stormwater runoff, will not adversely affect downstream properties, wetlands or bodies of water and will not result in erosion or sedimentation.
■If the initial determination indicates that the load influence zone intersects or falls within the global failure plane, a global stability analysis of the bluff shall be required.
(2)After construction is complete, an as-built survey and post-construction report completed by a professional engineer licensed by the State of Minnesota that the final grading of the site was completed in compliance with an approved grading plan and that the recommendations contained in the engineer's report have been adhered to.
Bluff
Bluff** -A topographic feature such as a hill, cliff,
or embankment having the following
characteristics:
•Part or all the feature is in a Shoreland area;
•The slope rises at least 25 feet above the
ordinary high-water level of the water body;
•The grade of the slope from the toe of the bluff
to a point 25 feet or more above the ordinary
high-water level averages 30% or more; and
•The slope must drain toward the water body.
**An area with an average slope of less than
18% over 50 feet or more shall not be considered
part of the bluff.
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Submit Detailed Plans/Reports Consultant Review Plans Inspection of Installation
Retaining Walls Under 4'
(non-riparian) No No No
Retaining Walls Under 4'
(on Riparian Lots)
Yes, but the City Engineer can
grant an exception to this
requirement if the wall is short or
located a significant distance
from the lake.
No
No city inspection; however,
applicant's Engineer will need to
sign off to certify wall was
inspected by Engineer and
installed per plans, unless City
Engineer grants an exception to
this requirement
Retaining Walls Over 4'
(outside of Shoreland Dist.)Yes
Yes, but the City Engineer can
grant an exception to this
requirement if the wall failure
would not affect public or
adjacent private property
Yes, City Engineer may grant an
exception or allow applicant's
engineer to sign off to certify wall
was inspected by Engineer and
installed per plans
Retaining Walls Over 4'
(in Shoreland Dist.)Yes Yes, City Engineer may grant an
exception.
Yes, City Engineer may grant an
exception or allow applicant's
engineer to sign off to certify wall
was inspected by Engineer and
installed per plans
Retaining Walls or Structures
of any height
(in Bluffs)
If building permit is required YES
require detailed plans including
soil reports
Yes, City Engineer may grant an
exception.
Yes, City Engineer may grant an
exception or allow applicant's
engineer to sign off to certify wall
was inspected by Engineer and
installed per plans
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Green Heights Trail
Sycamore Trail
Sycamore Trail
Breezy Point
Shore Trail
Shore Trail
Bluffs of Northwood Meadows Bluffs of Northwood Meadows
Candy Cove Trail (Before)
Candy Cove Trail (After)
Pixie Point Cir.
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Summary
■Prior to 2016, no new retaining walls were permitted in a bluff, only maintenance or
exact replacement of existing walls.
–Now retaining walls under 4’ may be permitted in a bluff.
■Prior to 2016, City required a third-party engineer contracted by the city, and paid for by
the applicant, to review engineering plans, inspect and certify the wall after construction.
–Now the City Engineer may allow the applicant’s engineer to certify wall was
installed per plan, eliminating the third-party engineering fee.
■Soil Testing -Some residents have objected to this; staff feels this is a necessary
component of the engineered plans.
■Post-Project Certification -Some residents have objected to this; staff feels this is
necessary to ensure the wall has been installed per plan. City Engineer may allow the
applicant’s engineer to certify the wall, eliminating the third-party engineering fee.
■As-Built Survey -Some residents have objected to this; staff feels this is necessary to
ensure the walls were placed in the proper location and at the approved height. As-built
surveys are required for all commercial projects and projects within the shoreland
district.
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QUESTIONS?
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