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HomeMy WebLinkAboutLetter-DesimoneDESIMONE MEMORANDUM Date: January 26, 2005 Re: River Front West NEW YORK SLBMITTEDsitiZTHE PUBLIC RECORD FOR ITEM ez.a ON Oc Proposed Tunnel Alignment Expert Analysis Based Upon City of Miami Requirement as Presented by City of Miami Assistant City Manager Alicia Cuervo Schreiber This letter follows up on our meeting yesterday at the Miami City Hall with Alicia Cuervo Schreiber, Assistant City Manager. In this meeting, we discussed various issues related to a proposed tunnel that may cross under the Miami River and through the River Front West parcel. We were informed that the City of Miami has engaged consultants to study tunnel alignment and construction methods. This study is to be concluded after a six-month period, which began approximately 2 weeks ago. Ms. Cuervo Schreiber informed us that an initial feasible location for the tunnel would be directly under the River Front West parcel running in a north -south direction. We were informed that one feasible tunnel alignment would be somewhere within 150 feet of the west property line. We were further informed that the two-lane tunnel (one each direction) would require a right-of-way [ROW] of approximately 50 feet. We are scheduled to deliver permit drawings to the City of Miami Building Department next week for Phase I of the project. Foundations for the project are designed in accordance with a geotechnical report prepared by KACO dated November 30, 2004. The currently designed Phase I tower foundation consists of 24-inch diameter auger -cast piles supporting the 46-story tower and individual shallow spread footings supporting the low-rise podium. The piles extend to a depth of -90.0 NGVD. There are three major pile cap groups that support the shear walls providing lateral stability to the building. A shallow mat foundation is not possible for the proposed towers due to the soil conditions on the site. The piles are generally placed 6 feet apart across the footprint of the tower creating a "forest" of piles 90 feet into the ground. Therefore, it would be impossible for a tunnel alignment to pass below the building with the present foundation system. This building design effort to date has required over 1,000 man hours. Much of this work will be of no use if the tunnel alignment passes below the building. DESIMONE CONSULTING ENGINEERS, PLLC 2600 DOUGLAS ROAD SLATE 900 CORAL GABLES, FLORIDA 33134 P. 305.441.0755 F. 305,447.9023 River Front West Proposed Tunnel Alignment January 26, 2005 Page 2 of 3 DES ONE A possible technical solution being proposed by the City of Miami for the River Front West parcel is to provide a foundation system that "bridges" over the tunnel ROW. Essentially, a very deep and very wide beam would span a minimum of 50 feet across the ROW and support the 46-story tower above. We have not had an opportunity to fully evaluate the technical merits of this proposed solution. However, if possible, the depth of this beam could be 30 feet deep or more. With a top of pile cap elevation of +6.5 NGVD, this places the bottom of beam at approximately elevation -23.5 NGVD. The proposed tunnel alignment below the proposed towers will need to pass below elevation -23.5 NGVD. Assuming a minimum clearance of six feet between the bottom of building foundations and top of tunnel, the top of tunnel elevation would be approximately -29.5 NGVD. Therefore, the solution proposed by the City of Miami would require the top of the tunnel to remain very deep throughout the River Front West parcel to clear the tower foundations. With this in mind, it does not appear possible to link the tunnel roadway with S.W. 3rd Street as proposed in the City of Miami Downtown Transportation Master Plan, Section 7.2.15. Assuming a roadway elevation 20 feet below the tunnel roof at elevation -49.5 NGVD, it would require approximately one -quarter of a mile to bring the roadway up to ground level assuming a design standard 5-percent incline. The closest street meeting the one -quarter mile criteria is north of N.E. 1st Street. See Exhibit A for a representative section. There will be other impacts to the proposed towers. The tunnel will require ventilation shafts and emergency exit shafts. It is probable that these will extend up from the tunnel within the River Front West parcel disrupting or prohibiting above ground uses. Ms. Cuervo Schreiber suggested that we design and submit for permit review an alternate foundation system that would be coordinated with the proposed tunnel alignment. She added that the city proposed foundation solution would cost 30 to 50 percent more than what is presently designed. In this manner, a foundation system that could accommodate a tunnel could be reviewed concurrently with the present foundation system and thus minimize project delays. We believe, however, that this alternate foundation system will exceed a 50-percent cost increase as compared to the current foundation design, further a new foundation design cannot be developed until the specifics of the tunnel are determined by the city. River Front West Proposed Tunnel Alignment January 26, 2005 Page 3 of 3 DESIMONE, Further foundation redesign will likely be required for the 9-story podium. The shallow foundations will likely be replaced with a smaller version of the tower "bridge". Other issues to consider are the effects of tunnel construction upon the building foundations. Deep piles or caissons obtain load capacity through direct bearing on the tip and through skin friction along the length of the pie. Disruption of soil near a pile or caisson could cause a loss of capacity. Currently, we are submitting plans for permit at the end of this month and plan to commence construction in June 2005. Due to the new city recuirement to accommodate a possible tunnel alignment, the general information of which was given to us on January 25, 2005, and the tunnel alignment which will take a minimum of 6 months to determine although could extend from that date, a foundation cannot be designed until the completion of the study. Please note that the exact horizontal and vertical alignment, width, and depth must be determined before a foundation system can be designed. It would then take another 2 to 3 months to finalize a design and produce construction documents for the alternate foundation system. Permit reviews in the City of Miami can then take another 3 to 6 months. This amounts to a 12 to 15 month project delay. Based upon the foregoing, it is clear that the proposed River Front West parcel use is not compatible with the proposed tunnel alignment through the site. Submitted by, William R. O'Donnell, P.E. Managing Partner WOD/dhm Attachment: Exhibit A: Representative Section A PHASE II luNNI I I XII IN NI 1ST I DESIMON I MIAMI RIVER RIVER FRONT WEST EXHIBIT A REPRESENTATIVE SECTION S-1