A/CSP15R31018 Page 1 of 1 December 2, Kleinfelder

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1 December 2, 2015 Kleinfelder Project No A/CSP15R31018 Ms. Sara Hartley City of Manitou Springs Flood Recovery Project Manager 606 Manitou Avenue Manitou Springs, CO 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 Respectfully submitted, KLEINFELDER, INC. Ronald F. Gibson, PE Senior Principal Professional A/CSP15R31018 Page 1 of 1 December 2, List Drive, Unit 115, Colorado Springs, CO p f

2 STRUCTURAL ASSESSMENT REPORT SPENCER RETAINING WALL WEST END OF SPENCER AVENUE MANITOU SPRINGS, COLORADO KLEINFELDER PROJECT # A DECEMBER 2, 2015 KLEINFELDER PROJECT A 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 A/CSP15R31018 Page i of iii December 2, 2015

3 A Report Prepared for: Ms. Sara Hartley City of Manitou Springs Flood Recovery Project Manager 606 Manitou Avenue Manitou Springs, CO 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 Phone: Fax: December 2, 2015 Kleinfelder Project No A A/CSP15R31018 Page ii of iii December 2, 2015

4 TABLE OF CONTENTS Section Page 1 INTRODUCTION PROJECT DESCRIPTION DESCRIPTION OF STRUCTURE STRUCTURE DESCRIPTION INSPECTION FINDINGS GENERAL COMMENTS RETAINING WALL CONCLUSIONS AND RECOMMENDATIONS EXTENT OF FLOOD DAMAGE RECOMMENDATIONS FOR REPAIR AND MAINTENANCE Solider Pile Wall Details COST ESTIMATES GENERAL LIMITATIONS REFERENCES 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 A/CSP15R31018 Page iii of iii December 2, 2015

5 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, 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 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) A/CSP15R31018 Page 1 of 12 December 2, 2015

6 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) 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) A/CSP15R31018 Page 2 of 12 December 2, 2015

7 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 A/CSP15R31018 Page 3 of 12 December 2, 2015

8 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. 3.2 RETAINING WALL Figure 1: Retaining Wall, Looking North 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 A/CSP15R31018 Page 4 of 12 December 2, 2015

9 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 A/CSP15R31018 Page 5 of 12 December 2, 2015

10 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 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 A/CSP15R31018 Page 6 of 12 December 2, 2015

11 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 A/CSP15R31018 Page 7 of 12 December 2, 2015

12 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, $5, " CIDH Solider Pile Wall LF 85 $1, $85, Timber Lagging SF 1200 $2.50 $3, Tree Removal EA 5 $ $1, Remove Modular Blocks LS 1 $1, $1, SUBTOTAL $95, % of Subtotal Utility Relocations 15% $14, Misc. Construction 30% $28, SUBTOTAL $138, Construction Contingency 20% $27, Total Construction Cost $166, % of Construction Cost ROW/Easement 10% $16, Construction Management 15% $24, Additional Fees Project Management (City) $16, $16, Engineering/Design/Survey $33, $33, Total Project Cost $257, Total Project Cost (Rounded) $258, A/CSP15R31018 Page 8 of 12 December 2, 2015

13 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 A/CSP15R31018 Page 9 of 12 December 2, 2015

14 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 A/CSP15R31018 Page 10 of 12 December 2, 2015

15 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 A/CSP15R31018 Page 11 of 12 December 2, 2015

16 7 REFERENCES American Concrete Institute (ACI), 2002, Building Code Requirements for Structural Concrete (ACI ) 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 A/CSP15R31018 Page 12 of 12 December 2, 2015

17 APPENDIX A ALL PHOTOS A/CSP15R31018 December 2, 2015

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