SUBJECT: Structural Assessment Report Spencer … saturated soil weakened the stability ... debris...

20162539.001A/CSP15R31018 of 1 December 2, 2015 © 2015 Kleinfelder

4815 List Drive, Unit 115, Colorado Springs, CO 80919 p | 719.632.3593 f | 719.632.2648

December 2, 2015 Kleinfelder Project No. 20162539.001A/CSP15R31018 Ms. Sara Hartley City of Manitou Springs Flood Recovery Project Manager 606 Manitou Avenue Manitou Springs, CO 80829 SUBJECT: Structural Assessment Report Spencer Retaining Wall West End of Spencer Avenue Manitou Springs, Colorado Dear Ms. Hartley: Kleinfelder is pleased to present this report summarizing our structural assessment for the Spencer Retaining Wall located near the U-turn on Spencer Avenue, Manitou Springs, Colorado. The purpose of our structural assessment was to provide the City of Manitou Springs with an initial inspection for this structure and to evaluate the structural condition of the retaining wall for possible flood damage during the May 2015 storm event (FEMA DR 4229). We appreciate the opportunity to provide structural engineering services to you on this project. If you have any questions, please contact the undersigned at 719.632.3593. Respectfully submitted, KLEINFELDER, INC. Ronald F. Gibson, PE Senior Principal Professional

20162539.001A/CSP15R31018 Page i of iii December 2, 2015 © 2015 Kleinfelder

STRUCTURAL ASSESSMENT REPORT SPENCER RETAINING WALL WEST END OF SPENCER AVENUE MANITOU SPRINGS, COLORADO KLEINFELDER PROJECT #20162539.001A

DECEMBER 2, 2015

KLEINFELDER PROJECT 20162539.001A

Copyright 2015 Kleinfelder All Rights Reserved

ONLY THE CLIENT OR ITS DESIGNATED REPRESENTATIVES MAY USE THIS DOCUMENT AND ONLY FOR THE SPECIFIC

PROJECT FOR WHICH THIS REPORT WAS PREPARED.

20162539.001A/CSP15R31018 Page ii of iii December 2, 2015 © 2015 Kleinfelder

A Report Prepared for: Ms. Sara Hartley City of Manitou Springs Flood Recovery Project Manager 606 Manitou Avenue Manitou Springs, CO 80829 STRUCTURAL ASSESSMENT REPORT SPENCER RETAINING WALL WEST END OF SPENCER AVENUE MANITOU SPRINGS, COLORADO Prepared by: Garrett Erickson, P.E. Project Professional Reviewed by: Ronald F. Gibson, P.E. Senior Principal Professional KLEINFELDER 4815 List Drive, Unit 115 Colorado Springs, Colorado 80919 Phone: 719.632.3593 Fax: 719. 632.2648 December 2, 2015 Kleinfelder Project No 20162539.001A

JWilliams

Ron Gib Seal Stamp

20162539.001A/CSP15R31018 Page iii of iii December 2, 2015 © 2015 Kleinfelder

TABLE OF CONTENTS

Section Page

1 INTRODUCTION ............................................................................................................. 1 1.1 PROJECT DESCRIPTION ................................................................................... 1

2 DESCRIPTION OF STRUCTURE ................................................................................... 3 2.1 STRUCTURE DESCRIPTION .............................................................................. 3

3 INSPECTION FINDINGS................................................................................................. 4 3.1 GENERAL COMMENTS ...................................................................................... 4 3.2 RETAINING WALL ............................................................................................... 4

4 CONCLUSIONS AND RECOMMENDATIONS ............................................................... 6 4.1 EXTENT OF FLOOD DAMAGE ........................................................................... 6 4.2 RECOMMENDATIONS FOR REPAIR AND MAINTENANCE .............................. 6

4.2.1 Solider Pile Wall Details ........................................................................... 6

5 COST ESTIMATES ......................................................................................................... 8 5.1 GENERAL............................................................................................................ 8

6 LIMITATIONS ................................................................................................................. 9

7 REFERENCES .............................................................................................................. 12

TABLES Table 1: Engineering Cost Estimate ........................................................................................... 8 FIGURES

Figure 1: Retaining Wall, Looking North ..................................................................................... 4 Figure 2: Retaining Wall, Looking East ...................................................................................... 5 Figure 3: East Side of Retaining Wall, Note Timber and Drainage Pipe ..................................... 5 APPENDICES A All Photos

20162539.001A/CSP15R31018 Page 1 of 12 December 2, 2015 © 2015 Kleinfelder

STRUCTURAL ASSESSMENT REPORT

SPENCER RETAINING WALL

WEST END OF SPENCER AVENUE

MANITOU SPRINGS, COLORADO

1 INTRODUCTION

This report presents the results of our structural assessment for the Spencer Retaining Wall

located near the west end of Spencer Avenue in Manitou Springs, Colorado. The purpose of our

structural assessment was to perform an initial inspection and to evaluate the structural condition

of the Spencer Retaining Wall for possible flood damage during the May storm event (FEMA DR

4229). The scope of our services was presented in our proposal titled, “City of Manitou Springs

Structural Engineering Services Assessment of Historic Bridges and Structures,” dated September

18, 2015.

Our report includes a description of the work performed, a discussion of the structural conditions

observed at the site, cost estimates for repair and maintenance, and recommendations developed

from our engineering analyses of field data. We recommend that all individuals utilizing this report

read the limitations (Section 6.0).

1.1 PROJECT DESCRIPTION

Kleinfelder understands that the Spencer Retaining Wall and 24 other structures are located in

the vicinity of FEMA DR 4229. These structures consist of historic arch bridges, concrete

structures, one earthen slope, one retaining wall, and one tank foundation mainly along Ruxton

Creek and Fountain Creek that may have been damaged in the May storm event. The full list of

structures includes:

1. Spring Street Bridge (Ruxton Creek) 2. Beckers Lane Bridge (Ruxton Creek) 3. Serpentine Road Bridge (Fountain Creek) 4. Spencer (Retaining Wall) 5. Canon Avenue 7x7 RCBC 6. Church Street Bridge (Ruxton Creek) 7. Capitol Hill Bridge (Ruxton Creek) 8. Manitou and Park Bridge (Fountain Creek)


9. Soda Springs Park Footbridge (Fountain Creek) 10. Cheyenne Springs Bridge 11. Canon and Lover’s Lane Bridge (Fountain Creek) 12. Lafayette at Lover’s Lane Bridge (Fountain Creek) 13. Wichita Parking Bridge (Fountain Creek) 14. El Paso Bridge (Fountain Creek) 15. Old Man’s Trail Bridge (Fountain Creek) 16. Mayfair Bridge (Fountain Creek) 18. 356 Ruxton Ave (Ruxton Creek) 19. Brook Street Bridge (Ruxton Creek) 20. Winter Street Bridge (Ruxton Creek) 21. Iron Spring Bridge (Ruxton Creek) 23. Ruxton Avenue, uppermost bridge (Ruxton Creek) 24. Washington by-Pass and Lover’s Lane (Slope Failure) 25. Mesa Tank (Foundation)


2 DESCRIPTION OF STRUCTURE

2.1 STRUCTURE DESCRIPTION

This structure was constructed primarily of a dry stacked stone masonry with timber on the west

side forming a retaining wall located south of Spencer Avenue. Stones ranging in size from 3”

inches to 3 feet in diameter were used as a gravity retaining wall. Spencer Avenue was

immediately uphill of the wall, and a private residence was constructed immediately below the

wall.


3 INSPECTION FINDINGS

3.1 GENERAL COMMENTS

This structure was not one of the structures originally evaluated for the Historic Structures

Assessment Report. The roadway was closed on the south shoulder near the failed portion of the

wall. Precast modular blocks were placed on the downhill side to protect the private residence

from further slope failure. Vegetation was present along the top of the wall. A drainage pipe was

present on the far west side of the wall.

Figure 1: Retaining Wall, Looking North

3.2 RETAINING WALL

This structure was constructed of a dry stacked stone masonry and timber forming a gravity

retaining wall with stones ranging in size from 3” inches to 3 feet in diameter and lagging of

approximately 6 feet in length and 4 inches by 6 inches in width. The total length of the wall was

approximately 85 feet, and the failed portion was approximately 20 feet. The western 15 to 20

feet of the retaining wall was composed of the timber. The wall thickness ranges from 6 inches to

2 feet, largely depending on the sizes of the stones.


Due to a lack of curb on the roadway, and the roadway sloping towards the retaining wall, the soil

behind the wall likely became saturated due to the flood event. The saturated soil weakened the

stability of the wall, ultimately causing the failure seen below.

Figure 2: Retaining Wall, Looking East

Figure 3: East Side of Retaining Wall, Note Timber and Drainage Pipe


4 CONCLUSIONS AND RECOMMENDATIONS

4.1 EXTENT OF FLOOD DAMAGE

Based on our findings, previous experience, and known data, we believe that the Spencer

Retaining Wall was damaged due to the flood event. It should be noted that the roadway slopes

downward toward the failed retaining wall; therefore, larger forces of water could accumulate at

this location. In addition to a higher water volume, there is also an increase in the likelihood of

debris impact due to the curvature and slope of the roadway. The soil behind the retaining wall

has a higher likelihood of becoming saturated, ultimately resulting in the wall failure seen at this

structure. Ground stabilization failures have an exponential potential to increase once they have

begun; therefore, the wall failure at this structure was likely caused by the flood.

4.2 RECOMMENDATIONS FOR REPAIR AND MAINTENANCE

The structure was inspected for damage due to the flood event. Some conditions were preexisting

such as loose stones and missing mortar and not negatively impacted by the flood. The extent of

damage caused by flooding from FEMA DR 4229 is often difficult to determine due to lack of data

before and after the storm event. Based on our findings and previous experience, we have the

following recommendations for the Spencer Retaining Wall:

Replace the current retaining wall with a soldier pile wall.

Remove the modular blocks after the retaining wall has been repaired.

4.2.1 Solider Pile Wall Details

A soldier pile wall is constructed by using vertical steel or concrete piling with horizontal lagging.

Piles are driven or placed in predrilled holes at the appropriate depths required to stabilize the

slope. Lagging consisting of wood, steel, or concrete is placed between the piling to ensure

proper earth retention. The lagging resists the loads and transfers it to the piles, which act as

cantilever supports. We recommend using 24” diameter cast-in-drilled-holes (CIDH) with timber

or concrete lagging. A geotechnical study and additional engineering will be required to ensure

the retaining wall is properly designed.

The soldier pile wall is the most feasible and safe method of repairing the wall because the

roadway can remain open while the soldier pile wall is installed. Additionally, this method is

preferred due to the limited access between the retaining wall and the private residence below.


Compared to a soil nail wall, this method requires little-to-no access requirements on the private

residence. Additionally, the slope becomes stabilized as the piles and lagging are constructed.

A drainage ditch or curb will be incorporated into the design with a drainage inlet at the bottom

of the wall.


5 COST ESTIMATES

5.1 GENERAL

Cost estimates are based on our past experience with similar projects, historical data derived

from the City of Colorado Springs, and CDOT cost data. The following table shows the summary

of approximate cost to repair and maintain the Spencer Retaining Wall. Costs are broken down

within Table 1 below. This table is limited to items that need repair, maintenance, replacement,

or rehabilitation due to the flood event and is subject to the limitations set forth in section 6. These

costs include only construction, design, and management fees and do not include environmental

or permitting costs. The total estimated is $258,000.

Table 1: Engineering Cost Estimate

Item Units Quantity Unit Price Cost

Mobilization LS 1 $5,000.00 $5,000.00

24" CIDH Solider Pile Wall LF 85 $1,000.00 $85,000.00

Timber Lagging SF 1200 $2.50 $3,000.00

Tree Removal EA 5 $250.00 $1,250.00

Remove Modular Blocks LS 1 $1,500.00 $1,500.00

SUBTOTAL $95,750.00

% of Subtotal

Utility Relocations 15% $14,362.50

Misc. Construction 30% $28,725.00

SUBTOTAL $138,837.50

Construction Contingency 20% $27,767.50

Total Construction Cost $166,605.00

% of Construction

Cost

ROW/Easement 10% $16,660.50

Construction Management 15% $24,990.75

Additional Fees

Project Management (City) $16,500.00 $16,500.00

Engineering/Design/Survey $33,000.00 $33,000.00

Total Project Cost $257,756.25

Total Project Cost (Rounded) $258,000.00


6 LIMITATIONS

This structural assessment has been prepared for the exclusive use of the City of Manitou Springs

and their agents for specific application to evaluate possible flood damage to the existing

structure. The findings, conclusions and recommendations presented in this report were prepared

in accordance with generally accepted structural engineering practice. No other warranty, express

or implied, is made.

The scope of services was limited to the extent described in the proposal. It should be recognized

that assessment and evaluation of structural conditions are difficult at times. Judgments leading

to conclusions and recommendations are generally made with incomplete knowledge of the

conditions present due to the limitations of data. The conclusions of this assessment are based

on our inspections, experience, and engineering analyses.

Kleinfelder offers various levels of investigative and engineering services to suit the varying needs

of different clients. Although risk can never be eliminated, more detailed and extensive studies

yield more information, which may help understand and manage the level of risk. Since detailed

study and analysis involves greater expense, our clients participate in determining levels of

service, which provide information for their purposes at acceptable levels of risk. The client and

key members of the design team should discuss the issues addressed in this report with

Kleinfelder, so that the issues are understood and applied in a manner consistent with the owner’s

budget, tolerance of risk and expectations for future performance and maintenance.

Recommendations contained in this report are based on our field investigations and our present

knowledge of the existing conditions. It is possible that soil, groundwater, or scour conditions

could vary between or beyond the points explored. If soil, groundwater, or scour conditions are

encountered during repair or maintenance that differ from those described herein, the client is

responsible for ensuring that Kleinfelder is notified immediately so that we may reevaluate the

recommendations of this report. If the scope of the proposed repair and maintenance, including

the locations of the improvements, changes from that described in this report, the conclusions

and recommendations contained in this report are not considered valid until the changes are

reviewed, and the conclusions of this report are modified or approved in writing, by Kleinfelder.


Our structural scope of services for this inspection and assessment report did not include

geotechnical or environmental assessments or evaluations regarding the presence or absence of

wetlands or hazardous substances in the soil, surface water, or groundwater at this site.

Kleinfelder cannot be responsible for interpretation by others of this report or the conditions

encountered in the field. Kleinfelder must be retained so that all structural aspects of repair and

maintenance will be monitored on a full-time basis by a representative from Kleinfelder. These

services provide Kleinfelder the opportunity to observe the actual soil, groundwater, and scour

conditions encountered during repair and maintenance and to evaluate the applicability of the

recommendations presented in this report to the site conditions. If Kleinfelder is not retained to

provide these services, we will cease to be the engineer of record for this project and will assume

no responsibility for any potential claim during or after construction on this project. If changed

site conditions affect the recommendations presented herein, Kleinfelder must also be retained

to perform a supplemental evaluation and to issue a revision to our original report.

This report, and any future addenda or reports regarding this site, may be made available to

bidders to supply them with only the data contained in the report regarding structural conditions

at the point and time noted. Bidders may not rely on interpretations, opinion, recommendations,

or conclusions contained in the report. Because of the limited nature of any structural

assessment, the contractor may encounter conditions during repair and maintenance which differ

from those presented in this report. In such event, the contractor should promptly notify the owner

so that Kleinfelder’s structural engineer can be contacted to confirm those conditions. We

recommend the contractor describe the nature and extent of the differing conditions in writing and

that the repair and maintenance contract include provisions for dealing with differing conditions.

Contingency funds should be reserved for potential problems.

This report may be used only by the client and only for the purposes stated, within a reasonable

time from its issuance, but in no event later than one year from the date of the report. Land use,

site conditions (both on site and off site) or other factors may change over time, and additional

work may be required with the passage of time. Any party, other than the client who wishes to

use this report shall notify Kleinfelder of such intended use. Based on the intended use of this

report and the nature of the new project, Kleinfelder may require that additional work be performed

and that an updated report be issued. Non-compliance with any of these requirements by the


client or anyone else will release Kleinfelder from any liability resulting from the use of this report

by any unauthorized party and the client agrees to defend, indemnify, and hold harmless

Kleinfelder from any claims or liability associated with such unauthorized use or non-compliance.


7 REFERENCES

American Concrete Institute (ACI), 2002, Building Code Requirements for Structural Concrete

(ACI 318-02) and Commentary (ACI 318R-02).

Historic Structures Assessment Report; for; City of Manitou Springs; Historic Stone Bridges and

Retaining Walls; Prepared by: the Collaborative Inc. and Atkinson Noland &

Associates, Inc.

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