Eagle Point Bluff Documents
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MEMORANDUM
January 9, 2006
TO:
The Honorable Mayor and City Council Members
FROM:
Michael C. Van Milligen, City Manager
SUBJECT: Work Session - January 12, 2006
Eagle Point Bluff
Attached is the PowerPoint that will be presented at the Work Session on Thursday
night, January 12, 2006. The Work Session will be held at the 3rd Floor Auditorium at
Carnegie-Stout Public Library, instead of Five Flags. The session will begin at 5:00
p.m. There will be no pre-meeting meal.
The PowerPoint presentation will take almost one hour. The presenters will be Dr. Bill
Gates, Ph.D. of Kleinfelder, Inc. Also there from Kleinfelder, Inc. will be Geological
Engineer Chad Lukkarila, PE.
City staff in attendance will be City Engineer Gus Psihoyos, Assistant City Engineer Bob
Schiesl, Civil Engineer" Deron Muehring, Assistant City Manager Cindy Steinhauser
and Corporation Counsel Barry Lindahl. As you are aware, I will not be able to attend.
Also attached is a page from the Fiscal Year 2007 budget recommendation that you will
receive for the January 17, 2006 City Council meeting. This Capital Improvement
Program recommendation does not assume any City liability or financial contribution, it
just provides funds should the City Council decide that is an appropriate course of
action.
Finally, included with the packet is the November 17, 2005 memorandum asking that
this Work Session be scheduled.
Michael C. Van Mi igen
MCVM/jh
Attachments
cc: Barry Lindahl, Corporation Counsel
Cindy Steinhauser, Assistant City Manager
Gus Psi hoyos, City Engineer
,
Results of Phase I of the Eagle Point Bluff Study
City Council Work Session
January 12,2006
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Presentation Overview
. Project Background
. Historical Information
. Geological Information
. 2003 Excavation Summary
. Bluff Cross-Section
2 Evaluation
. Rock Mass Characteristics
. Rock Mass Kinematic
(Potential Motion) Analysis
. Rock Mass Stability
Assessment
. Bluff Stabilization Options
K L E I N F E L 0 E R
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Project Background
. In 2003, developer initiated
excavation of portions bluff
. Utilized mechanical methods and
blasting for excavation,
concluded blasting in Nov. 2003
. Section of bluff collapsed in
2004
. Initial investigation indicated that
sections of bluff are unstable
. City retained Kleinfelder in June
2005 to conduct Rock
Engineering Investigation
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Eagle Point Bluff 1885
4
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2
Eagle Point Bluff History
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. 1885 - Eagle Point Lime
Works and Quarry
. Early 1900's - Eagle
Point Toll Bridge
5 - Used quarry stone for
bridge foundation
- Bluff was excavated
for toll booth and
bridge approach
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Eagle Point Bluff History
. Toll Bridge Restaurant
- Original bridge foundation
. Built 1985
. Demolished Circa 2002
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3
2003 Excavation: Blastin
. Excavation began on
September 16, 2003
. Type of Blasting
- Production
- Controlled
. Pre~split
7 . Cushion (Trim)
. Blasting plan review indicated
standard blasting techniques
- Blasting technique within limits
. Blasting completed on
November 19,2003
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>EXPECT MORE
Controlled Blasting
Half Casts
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. Used for wall control
. Cushion (Trim) Blasting
. Presplit (Preshear)
Blasting
8 . Evidence: Half casts
- Suggests good blasting
technique
- Good wall control
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4
2003 Mechanical Excavation
9
. Utilized mechanical
methods to excavate
bluff
. Track hoe used to
remove rock, loose
sections and excavate at
base of bluff
. Wrecking ball used in
January 2004
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2003 Site Inspection Summary
. City of Dubuque
Personnel
- Onsite during excavation
activities
10
. Field notes &
Observations
- Blasting techniques
appeared good
- Noted slides composed of
mud, rock & trees during
excavation
- Identified safety concerns
- Inspected bluff daily for
rock slides & unstable areas
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5
II
2004 Bluff Collapse
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March 9, 2004
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2004 Bluff Collapse
, '- ~.t< . '...
'-'#: ,..""'"
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January 9, 2004
March I, 2004
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6
Existing Bluff Conditions
. 300 feet in length and 90 feet
in height
. Bluff face dips to the east
. North end of bluff that dips
to the south/southeast
IJ . Vertical to overhanging
. Fractures primarily sub-
vertical with prominent sub-
horizontal bedding
. Colluvium (loose soil/rock)
and tree roots along brow
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General Approach to Bluff Design
. Geomechanical rock
mass information and
classification
. Rock quality designation
(RQD)
. Strength
]4 . Markland analysis
. Hoek-Brown strength
- Overall strength of rock mass
. Rockfall hazard
mitigation
. Stabilization design
options
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Phase I: Investigation
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. Conduct geotechnical
investigation
- Conduct horizontal and
vertical geological
mapping
- Collect specific
geological and
geomechanical
information of the rock
mass
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Geologic Mapping Locations
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Bluff Distance Reference
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Geologic Mapping
. Number of fracture
17 sets
. Strength
. Fracture spacing
. Aperture/filling
. Weathering
. Water
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I. Dip and dip direction of
rock discontinuities
2. Rock mass
characteristics
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Rock Quality Designation
RQD % = liS - (3.3 Jv)
Jv = Ifxs (x+y+z/mJ)
Example:
18 RQD=115-(3.3(2+ 1+2))
RQD = 99% ::::-
Excellent Rock
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9
Uniaxial Compressive Strength
IRS
IlIt&elrock
~trel1~h ',i1l1Vl~ mUll" ~1
rangt
(}(Pal
<'\.25 crurubko<.mhlllld
I 2~ . 5 thin Wal.K bro!"ak t~,~, in Mnd
]9 S -12.5 Thin \lab\ brtak by hta,')' hand p'fi-
,~,
125-50 hll11p'> brokm by b~hl h.mllUff blow'!>
5(}.100 l~brol.:mb...Ma"yh:wuuer
blow"
100 - 200 lun~ ollly (hip by lu-ny MllIn-.n
blo....."
>200 rocb rill! on l"'Il1D\t'I" blOln - \~lb
fly
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Stability Analysis and Design
20
Conduct analysis and design of
bluff
Gcomcchanical rock mass
classifications
Slope stability analyses via
Markland Analyses &
Kinematic Analysis
. Study of potential motion
Rock slope stability design
methodology via Hock-Brown
Strength Analysis
RockfaIl hazard analysis
Stability design options
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Rock Mass Rating (RMR)
l. Strength of intact rock
material
2. Rock quality designation
(RQD)
3. Spacing of
discontinuities
21 4. Condition of
discontinuities
5. Groundwater conditions
6. Orientation of Rock Mass Rating (RMR). otherwise
discontinuities relative to known as the Gcomechanical Cla.;;sification,
the rockslope was developed by Z.T. Bieniawski in the
early 1970's and revised in the latc 1980's.
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Rock Mass Rating (RMR)
Descriptors
Rock Mass 81-100 61-80 41-60 21-40 <20
Ratin
Class No. I II III IV V
22 Description Very Good Fair Poor Very
good rock rock rock poor
rock rock
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II
Rock Mass Properties
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. Moderately strong to strong
rock (7,000-14,000 psi)
. Good quality rock (RMR>60)
. Fracture aperture < 2mm
. Fracture surface: Rough and
undulating
. Fracture filling: No filling or
unconsolidated soillrock
. Bedding spacing: I to 4 feet
. Fracture spacing: I to 6+ feet
. No groundwater observed
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Markland Stability Analysis
. Plot of the orientation of
the discontinuities
. Dip, dip direction and
friction angle of rock
mass
24 . Ifplunge of intersecting
fractures exceeds
friction angle => FOS <
1.0
. IdentifY translational
sliding or toppling
failures
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>EXPECT MQR!;
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I
Example: Structurally-Controlled Rock Slope:
Planar & Toppling Failures
"~
,. +-........
I.' ,"'. \
~';.'.',.'
"-. ..-. .
\.,. -
"- '/<
. -~- .,/"
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Bluff Stability - Unstable Blocks
~1 J"...~
Ifuvhl '.,.
Bluff Distance Reference
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Wedge 1 Stability Analysis
27
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Bluff Cross Section Evaluation
. Prior to 2003 excavation Before 2003
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- Angle of 65 to 85 degrees ,
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- Height of20 to 55 feet ~
. After the 2003 excavation ~ After 2003
- Angle of77 to 89 degrees
28 with average of 80
degrees
- Some sections overhang : i \
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past vertical
- Height of 35 to 90 feet
From McGhie and Betts, 2004
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14
Bluff Stability Assessment
Park Stairwa
. Bluff stability prior to
2003 excavation
- Angle of bluff face
matched angle of
fractures
29 .
Bluff stability after
2003 excavation
- Bluff face is steepened
potential for wedges
- Overhanging rock
- Colluvium exposed
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Pre-excavation
Post excavation
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Bluff Stability - Unstable Blocks
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Bluff Distance Reference
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Bluff Stability - Repeating Fractures
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Bluff Stabilit - Unstable Blocks
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Wedge I - 100 ft Block I -120 ft
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Bluff Stability - Unstable Blocks
33
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Tower 3 - 180 fI
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- Unstable Blocks
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Blocks 3 and 4 - 200 fI
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Bluff Stability - Unstable Blocks
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Blocks 5 and 6 - 230 ft Blocks 7 to 12 - 240 to 255ft
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Bluff Stability - Colluvium and Trees
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Colluvium - 230 to 260 ft
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Example: Tree Pry Bars
37
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Risk of Failure
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. Risk of failure in identified
blocks ranges from low to
high
- Function of the geometry
. Tension fractures present
- Indicate movement of
block(s)
. Overhanging blocks
. Stability analyses indicate
Safety Factors < 1.0
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Stabilization Options
Three land-use scenarios for stabilization options:
I. Commercial development
2. Residential development
3. Undeveloped
Stabilization options:
1. Controlled blasting
2. Controlled blasting and rock bolt reinforcement
3. Rock bolt reinforcement
4. Wire mesh drape slope protection
.
.
39
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Commercial Zoning Options
Stabilization Steps:
. Tree removal
- 15 - 20 ft behind brow
. Scale loose rock
Stability Options:
40. Controlled blasting or
stabilize in place with rock
bolts
. Install horizontal drains
. Scale colluvium or drape
with wire mesh
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>EXPECT MORE
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Residential Zoning Options
Undeveloped Options
Stabilization Steps:
. Tree removal
- 15 - 20 ft behind brow
. Scale loose rock
Stability Options:
42. Controlled blasting or
stabilize in place with rock
bolts
. Install horizontal drains
. Scale colluvium
. Fence off area
K LEI N F E L D
Stabilization Steps:
. Tree removal
- 15 - 20 ft behind brow
. Scale loose rock
Stability Options:
41. Controlled blasting or stabilize in
place with rock bolts
. Tecco@ Mesh Slope Protection
. Install horizontal drains
. Scale colluvium or drape with
wire mesh
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21
43
44
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Artist's Rendition of Bluff
Controlled-Blasting of Bluff
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Artist's Rendition of Bluff
45
~-
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Stabilization of Bluff by Rock Bolting
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F E
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US 97, Washington
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48
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Artist's Rendition of Bluff
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Wire Mesh Drape Example
J(
@
From Geobl1Jgg~
LEI
Cheyenne Mountain, Colorado Springs, CO
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>EXPECT MORE
24
Tecco@ Mesh Example
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Slope Monitoring
. Tension fractures present
behind blocks
. Tower 3 - tension fracture
ranges from 3 to 18 inches
wide
50 . Monitoring recommended if
stabilization does not occur
in the next 6 to 12 months
. Options include survey
points, surface jointmeters,
or displacement transducers
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25
Estimate of Stabilization Cost
. Commercial Development
I. Option 1: Blasting - Approx. $180,000
2. Option 2: Rock bolts, wire mesh - Approx. $200,000
. Residential Development
1. Option I: Blasting - Approx. $180,000
2. Option 2: Rock bolts, wire mesh - Approx. $200,000
3. Option 3: Tecco Mesh - Approx. $350,000
. Undeveloped
I. Option I: Blasting - Approx. $180,000
2. Option 2: Rock bolts - Approx. $190,000
51
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Conclusions
>EXPECT MORE
The bluff is unstable
Future collapses are possible
Potential for:
a) Wedge and toppling-type failures
Causes for instability and failure
a) Oversteepening of bluff
b) Exacerbated by mechanical excavation methods
Risk of failure: low to high based on geometry
Stability options include a combination of:
a) Controlled blasting, slope scaling, rock bolts, horizontal
drains, and wire mesh slope protection
7. Stabilization costs range from $180,000 to $350,000
K lEI N FE l D E R
I.
2.
3.
4.
52
5.
6.
>EXPECT MORE
26
Questions?
27
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WE
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\~k\lor)
1'F:r', S
THE CITY OF ~
DUB E
~ck~
MEMORANDUM
November 17, 2005
TO:
The Honorable Mayor and City Council Members
FROM:
Michael C. Van Milligen, City Manager
SUBJECT: Eagle Point Bluff Study - Results of Rock Slope Investigation
City Engineer Gus Psihoyos is recommending that a Work Session be scheduled to
discuss the results of the Eagle Point Bluff Study.
I respectfully request that the Mayor and City Council establish a date for the Work
Session, Staff will then verify availability with the consultant.
i/11J! tr~ //2111
Michael C. Van Milligen
MCVM/jh
Attachment
cc: Barry Lindahl, Corporation Counsel
Cindy Steinhauser, Assistant City Manager
Gus Psihoyos, City Engineer
Laura Carstens, Planning Services Manager
D~~~E
~<!k-~
MEMORANDUM
November 17, 2005
TO:
Michael C. Van Milligen, City Manager
Gus Psihoyos, City Engineer _up
SUBJECT: Eagle Point Bluff Study - Results of Rock Slope Investigation
FROM:
INTRODUCTION
The purpose of this memo is to transmit the findings of the Eagle Point Bluff Study -
Rock Slope Investigation performed by Kleinfelder, Inc (Bellevue, WA).
BACKGROUND
On August 2, 2004, the City Council authorized the solicitation of proposals from
qualified consulting/engineering firms for the Eagle Point Bluff Study. On December 17,
2004, the City Council endorsed the RFP for the Eagle Point Bluff Study and authorized
its release to the public. The RFP separated the project into three phases:
Phase I
The Consultant must obtain all necessary data either from City records or
site reconnaissance to thoroughly characterize the present stability of the
bluff and if the bluff is found to be unstable, the probable cause of
instability. Moreover, if the bluff is found to be unstable, the Consultant is
to draw on its experience and expertise in dealing with rock bluffs to
consider multiple stabilization techniques (such as rock removal, grouting,
bolting, etc.) and work with the City to identify which method best suits the
needs of the City.
Phase II (if necessary)
Consultant would prepare plans and specifications for the Eagle Point
Bluff Stabilization Project based on the optimum stabilization technique
identified in Phase I.
Phase III (if necessary)
Consultant would act as project engineer for the construction phase of a
stabilization project outlined in Phase II.
Page 2
The City received eight responses to the RFP. After careful review of the proposals,
presentations, review of fees, and reference checks, the proposal review committee
concluded that Kleinfelder, Inc. had the best combination of project experience, project
understanding, and project approach to best serve the City for the Eagle Point Bluff
Study.
On May 2, 2005, the City Council approved the selection of Kleinfelder, Inc. to provide
professional consulting services for the Eagle Point Bluff Study.
DISCUSSION
Kleinfelder, Inc. has completed Phase I of the Eagle Point Bluff Study and presented its
findings in two documents:
1. Eaqle Point Bluff Studv Phase I - Rock Slope Investiqation
This document is an unabridged guide to the Study and it includes the
engineering methods, testing, and analysis used to perform the bluff
investigation and establish recommendations.
2. Eaqle Point Bluff Studv Phase I - Rock Slope Investiqation Citizen Guide
This document contains a condensed version of the investigation. The
technical aspects of the engineering behind the Study are not included.
Figure 1 shows the location of the part of the bluff which is the subject of the Study. It is
below Eagle Point Park and adjacent to the remnant bridge abutment near Lock and
Dam NO.11.
Fi~ure 1. Location of the Eagle Point Bluff Study.
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Bluff Study Area
Page 3
Historical photographs show the Eagle Point Bluff tree covered except for the main high
bluff that is not part of the Study. The Eagle Point Toll Bridge was constructed circa
1901-1902 from Eagle Point on the Iowa side to Kimball's Slough on the Wisconsin side
of the Mississippi River. According to the Kleinfelder, Inc. Study, photographs taken
after the construction of the bridge show a "barren, steep rock slope" in the vicinity of
Eagle Point Bluff (see Citizen Guide, Appendix A: Photos 2-4). It appears that the bluff
was quarried and excavated to make room for the bridge. Deemed unsafe, the bridge
was torn down in 1982. The Toll Bridge Inn was constructed on the old bridge
foundation and operated as a restaurant until 2003.
Figure 2 is a photo taken in September of 2003, prior to the 2003 excavation.
In general, rock bluffs in the Dubuque area are near vertical in nature. Minor erosion
and weathering is prevalent and occasional rock falls are commonplace as witnessed at
the former quarry site just south of Eagle Point Bluff now occupied by C.R. Boats. The
Kleinfelder Study states, "because of the fractured nature of the rock mass, it is
suspected that minor rockfall occurred at the bluff (prior to the 2003 excavation)." Figure
2 shows the fractured nature of the bluff even prior to the 2003 excavation.
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The Kleinfelder Study concludes that there is now a high level of risk of a large-scale
failure on some parts of the bluff. The risk has been increased because of the 2003
excavation that steepened the slope from 75 to 80 degrees and increased the height
from 35 to 60 feet. While the Study finds no fault with the blasting operations on the
bluff, striking the rock face with a track hoe and wrecking ball "exacerbated the
instability of the rock slope." Figure 3 shows the wrecking ball hitting the rock face.
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The Kleinfelder Study presents multiple stabilization options for the bluff stabilization
depending on whether the use of the property below the bluff is commercial, residential,
or undeveloped. Although stabilization is recommended for all three uses, more
additional measures are recommended if the site is developed for commercial or
residential use. Options include controlled blasting, slopes scaling, rock bolts, horizontal
drains, and wire mesh slope protection. The construction cost estimates range from
$80,000 to $250,000.
The City Manager, the Corporation Counsel, and Engineering staff have begun
identifying potential actions that the City could take based on the Study findings. The
following list of actions is offered for consideration:
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1) Budget funds for a stabilization project by the City;
2) Explore the possibility of collaborating on the stabilization project with the
developer;
3) Consider declaring the risk of falling rock a public nuisance and requesting
the developer to install a fence to keep the public away from the area and
require implementation of one of the recommended stabilization methods
outlined by the Kleinfelder Study if and when the property is developed for
commercial or residential use.
This list is only offered as a starting point for discussions that will lead to the appropriate
response to the findings presented in the Eagle Point Bluff Study.
RECOMMENDATION
I recommend that the City Council schedule a work session at which time Dr. William
Gates of Kleinfelder, Inc. would present and discuss the Eagle Point Bluff Study.
BUDGET IMPACT
Phase I of the stabilization study has been completed at a cost of $49,800. If a
stabilization project is considered, the estimated costs are:
Engineering $ 45,000
(Phase II as outlined in the RFP)
Construction Observation $ 55,000
(Phase III)
Estimate Subtotal $100,000
Project Construction $ 80,000 - $250,000
(Dependent on Stabilization Method Used)
Total Project Estimate $180,000 - $350,000
ACTION TO BE TAKEN
I respectfully request the City Council be requested to schedule a work session to allow
Dr. William Gates of Kleinfelder, Inc. to present and discuss the Eagle Point Bluff Study.
Prepared by Deron Muehring
cc: Barry Lindahl, Corporation Counsel
Cindy Steinhauser, Assistant City Manager
Laura Carstens, Planning Services Manager
Bob Schiesl, Assistant City Engineer
Deron Muehring, Civil Engineer II