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    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
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    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
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      <title>Fragility Formulations for the BART System</title>
      <link>https://trid.trb.org/View/2149261</link>
      <description><![CDATA[This paper presents fragilities developed for the seismic risk analysis of the San Francisco Bay Area Rapid Transit (BART) system, including treatment of dependent and independent damage states. Categories of fragilities include aerial guideway structures, passenger stations, tunnels and the Transbay Tube, with fragilities developed based on a combination of analytical and experiential data.]]></description>
      <pubDate>Tue, 20 Jun 2023 10:09:52 GMT</pubDate>
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      <title>Seismic Assessment and Retrofit Concepts of the BART Transbay Tube</title>
      <link>https://trid.trb.org/View/2149252</link>
      <description><![CDATA[The Bay Area Rapid Transit (BART) system's Transbay Tube is 3.6 miles long and lies at the bottom of the San Francisco Bay, at a maximum depth of 132 feet below mean sea level. The tube is constructed of 57 segments with an average segment length of 330 feet. A ventilation structure is located at each end of the Transbay Tube — the San Francisco Ventilation Structure and the Oakland Ventilation Structure — and each is connected to the tube by a seismic joint. The Transbay Tube is a critical link in the BART system and a key system element analyzed as part of the BART Seismic Retrofit Program. Since the tube is submerged, it is important to ensure the structural integrity of the tube and the associated ventilation structures and seismic joints for the safety of passengers and BART personnel. Furthermore, for BART to provide an adequate level of post-earthquake transportation service to the public, satisfactory seismic performance of the tube is critical during any future strong earthquake in the Bay Area.]]></description>
      <pubDate>Fri, 21 Apr 2023 16:24:35 GMT</pubDate>
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      <title>Centrifuge Modeling of Seismically Induced Uplift for the BART Transbay Tube</title>
      <link>https://trid.trb.org/View/1112370</link>
      <description><![CDATA[The BART Transbay Tube (TBT) is an immersed cut-and-cover subway tunnel that runs from Oakland to San Francisco, California. The loose sand and gravel backfills placed around the tunnel are considered to be liquefiable, and the clays under the backfill are soft in some zones along the alignment. These conditions could potentially result in uplift of the tunnel during strong earthquake shaking. This paper describes centrifuge model tests performed to verify numerical methods used to assess the stability and to evaluate the potential uplift mechanisms of the TBT. The observed mechanisms of uplift were a ratcheting mechanism (sand migrating under the tunnel with each cycle of relative movement), a pore water migration mechanism (water flowing under the tunnel), and a bottom heave mechanism, involving soft soils below the base of the trench. A fourth potential mechanism, viscous flow of liquefied soil, was not observed. The volume of the tunnel relative to the volume of the trench and the densities and permeabilities of the nonhomogeneous backfill were important parameters affecting the uplift of the tunnel. From the experiments reported here and analyses reported by the designers, it was concluded that the magnitude of uplift is limited and, hence, that an expensive ground improvement project to densify the backfill was unwarranted.]]></description>
      <pubDate>Wed, 19 Oct 2011 12:52:52 GMT</pubDate>
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      <title>BART'S TRANSBAY TUBE RETROFIT</title>
      <link>https://trid.trb.org/View/761847</link>
      <description><![CDATA[This article gives an overview of a seismic retrofit project designed for the BART Transbay Tube in San Francisco. Work on the 3.6 mile steel-hulled, reinforced concrete-lined tube will be conducted in three phases involving the above-ground work at the east end of the tube where it connects with the Oakland vent structure, the underwater segment, and the San Francisco vent structure located at the west connection. A demonstration project will test different methods of vibrocompaction designed to make the backfill around and beneath the tube more dense and thus improve resistance to liquefaction. Funds for a system wide retrofit for BART will come from a voter-approved property tax increase.]]></description>
      <pubDate>Fri, 14 Oct 2005 08:27:59 GMT</pubDate>
      <guid>https://trid.trb.org/View/761847</guid>
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      <title>SEISMIC RETROFIT FOR BART</title>
      <link>https://trid.trb.org/View/700852</link>
      <description><![CDATA[This article discusses seismic retrofit projects for BART (Bay Area Rapid Transit) system with a focus on the Transbay tube between Oakland and San Francisco, one of the longest immersed tube tunnels in the world and also one of the longest continuous rigid structures, at 3.6 miles in length. It is comprised of 57 elements welded together, submerged up to 100 feet below the Bay's mean sea level and built to 1970s' state-of-the-art seismic standards.  New knowledge has raised concerns, including the understanding now of the behavior of the granular backfill around and beneath the tube, believed to be subject to liquefaction. Also of concern is the reduced displacement capacity of the patented seismic joints developed by the tube's builders and patented by them allowing movement between the tube and the fixed ventilation structures at either end. The joint on the Bay side has shifted so much that it has little play remaining. A top priority is the alignment from the West portal in the Berkeley Hills Tunnel through the Transbay tube to the Montgomery Station in San Francisco. The article describes funding, project schedules and proposed solutions.]]></description>
      <pubDate>Mon, 03 May 2004 00:00:00 GMT</pubDate>
      <guid>https://trid.trb.org/View/700852</guid>
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