HomeMy WebLinkAboutIR 8155 'INFORMAL REPORT TO CITY COUNCIL MEMBERS No. 8155
ySr To the Mayor and Members of the City Council 1 of 2
October 13, 1998
s 6x1 Subject: COMMERCE STREET TUNNEL INFORMAL REPORT
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On January 20, 1998 (M&C C - 165549), City Council authorized the City
Manager to execute a contract with Southland Contracting Inc. for the Commerce
Street Sewer Rehabilitation, Phase I from Bluff Street to Third Street. The
purpose of the project was to replace an existing 21" sanitary sewer with a new
24" line using tunneling methods. The project became necessary due to high
maintenance and increased risk of collapse of the existing system that was built
in the early 1900's. The existing Commerce Street sewer was laid within a hand
mined tunnel that was left unsupported and was not backfilled.
A future phase of the project was planned which would have completed a new
sewer from Third Street to Lancaster. In the interim, the pipe south of Third
Street was evaluated and several areas were identified which needed limited
pipe replacement or point repairs. These point repairs would have allowed the
existing sewer to have an extended service life before the future phase would
become necessary.
The point repairs required that the pipe be exposed by open cut. During
excavation it was discovered that the void around the pipe was larger than
anticipated. The city's consulting engineer on the project, Carter and Burgess,
Inc., recommended that the city take immediate remedial action to relieve the risk
to the public from possible collapse of the void. Ground penetrating radar (GPR)
was ordered to map the extent of the void without disturbing the pavement and
risking possible collapse. Based on the results of the GPR and recommendations
from the consultant, the Department of Engineering, coordinating with
Transportation and Public Works and the Water Department, consulted the
Department of Law to allow that contracts be procured outside normal
competitive bid statutes to protect the safety of citizens.
Carter and Burgess performed preliminary investigations and produced
engineering documents that were used to define the magnitude of the problem.
The consultant firm of Black & Veatch was retained to provide guidance and to
prepare necessary construction contract documents for stabilization of the tunnel.
Black and Veatch had previous success in providing tunnel inspection for the
West Fork Tunnel project in the Central Business District.
The approved plan was to seal the existing 21" sanitary sewer line and manholes
from the inside and then follow up with a grouting process to fill the void. To
accomplish this, a total of three construction contracts were executed. All three
contracts were with Insituform Texark. The first two were for the internal lining of
the existing 21" pipe and the third was for manhole rehabilitation and grouting of
the void. °
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ISSUED BY THE CITY MANAGER � "T"WOR t4,
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NFORMAL REPORT TO CITY COUNCIL MEMBERS N o. 8155
RTE To the Mayor and Members of the City Council 2 of 2
October 13, 1998
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The GPR data reflected a void of approximately 2500 cub,ic yards, however the
actual void was closer to 500 cubic yards based on the grout used. The repair
has been completed.
The contracts staff is requesting to be confirmed by City Council are summarized
on the attached sheet. In addition to these an amendment will be requested to
compensate Carter and Burgess for work on this project which was clearly
outside the original scope of their contract.
Formal KA&C' ill be forwarded to Council requesting approval of these
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Bob Terrell
City Manager
Attachment
ISSUED BY THE CITY MANAGER FORT WORTH,TEXAS
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