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      <title>Research in Progress (RIP)</title>
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      <title>Design and Verification of Blast Densification for Highway Embankments on Liquefiable Sands</title>
      <link>https://rip.trb.org/View/1236624</link>
      <description><![CDATA[This proposal summarizes the progress and describes the scope of work in year 3 of the three year effort to develop a quantifiable design methodology and attendant verification approach for improving loose sands deposits underlying highway embankments in seismically active regions.  The project involves a major field project where blast densification of loose sands is undertaken periodically to improve the loose sands beneath a large fill.  Originally envisioned as a two year project the field work was delayed because of the recession of 2009 as it slowed the owner's plans for development of the site.  The production blasting now is scheduled for early 2011, delayed from its original time of August 2009.  The delay has allowed Northwestern to conduct a detailed laboratory evaluation of the liquefiable soils from the site, and as a result, the focus of the field work has changed somewhat since first envisioned, as will subsequently be explained. The proposed work is a joint effort between GeoSyntec Consultants, the engineering consultant for the project, and Northwestern University.  Matching funds are derived from GeoSyntec's analytical and field efforts for the project, as well as from the blasting contractor at the site.    Transportation systems included many embankments for highways and railroads.  In seismically sensitive areas west of the Rocky Mountains and over broad areas of the eastern and central US - estimated to cover as much as 40% of the continental US, earthquake engineering for highway facilities is very important (FHWA 1997).   A key design issue for such facilities is whether or not liquefaction - or the loss of shear strength of sands - will occur during an earthquake.  If such a possibility exists, then one must either relocate the embankment or improve the potentially liquefiable soil to the point where the improved soil will not liquefy under the expected earthquake.  Loose sands are the soils most susceptible to liquefaction.  Two questions arise during design: (i) will liquefaction occur under a given earthquake loading, and (ii) what are the consequences of liquefaction? The most egregious effect is a flow failure of the embankment through the liquefied soil.  Because highway and railroad embankments traverse large areas, the costs of mitigating the effects of the liquefiable soils are large, as are costs related to realignment, if this option is followed in design.    To improve the ground over large areas, densification of loose sands by controlled blasting is an economical approach.  Design methods for this approach are empirical, as will be described later.  A few case studies have shown that loose sands apparently compress almost immediately after blasting, but when common verification tests are conducted, such as the cone penetration test (CPT) and the standard penetration test (SPT), the outcomes provide rather counterintuitive results.  If taken soon after the blast, the CPT tip resistance decreases, and at times never increases to levels above the pre-blast level, at least for the amount of time the studies included.  At the same time, the ground surface settles almost immediately after blasting, implying that loose sands in the subsurface have increased density.  However, the lack of increase in penetration resistance suggests that the strength and stiffness of the soil apparently does not.   This leads to questions about future performance.  Have the loose sands really been improved to the point where liquefaction is not a possibility?   One simple, yet common approach for evaluating liquefaction potential (answer to question (i) above) is to compare SPT N-values at a site with those needed to prevent liquefaction for a given magnitude of earthquake.  Similar relations have been proposed for CPT results.  Because there is much evidence to show the relation between penetration resistance and liquefaction susceptibility, it is not clear why such field measures of resistance do not increase after blasting has apparently increased the density of the loose soils.  Consequently there is a need to understand the fundamental mechanics behind the effects of blasting on the constitutive responses of the soil and to develop reliable and meaningful ways to provide quality control of the process.  Also, since the design is large empirical, a rational way to define how much improvement is required to meet the design objective required.]]></description>
      <pubDate>Thu, 03 Jan 2013 15:50:10 GMT</pubDate>
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      <title>Development of Effective Multihazard Seismic Blast Design Guidelines</title>
      <link>https://rip.trb.org/View/1236093</link>
      <description><![CDATA[There is increased awareness toward vulnerabilities due to blast and other accidental damage to highway bridges since the September 2001 attack on the World Trade Center(WTC) in New York. The recent collapse of the I-35 Bridge in Minnesota, on August 1, 2007, has demonstrated the psychological, societal and economic impacts of the collapse of bridges in urban areas. Recently, the principal investigator (PI) carried  out an extensive investigation on blast load effects on highway bridges, to develop multi-hazard blast-seismic correlations by investigating blast effects on the same type of bridge designed for different levels of seismic resistance. It has been observed that a bridge designed for better seismic resistance is capable of withstanding a large magnitude of blast pressures. One very significant outcome of this research has been the identification of various failure modes during blast loads and their correlations with seismic failure modes. This information can be utilized to develop guidelines that can prevent  the occurrence of catastrophic failure modes by optimizing detailing for both seismic and blast loads. The objectives of the proposed research are to be achieved through numerical simulation of blast loads on a typical three span highway bridge model. It should be noted that a recent National Cooperative Highway Research Program report (NCHRP 645, Williamson et al. 2010) has presented guidelines on the blast resistant design of bridges that is likely to be adopted by NCHRP. However, there is very limited information on the effectiveness of these guidelines. To investigate their effectiveness, as presented in NCHRP 645, this research will use high fidelity numerical simulations. The proposed work is important and urgently needed for designing the multi-hazard aspects of highway bridges. The proposed research will be carried out by the PI, Professor Anil K. Agrawal. Doctor Mohammed Ettouney, Principal of Applied Research at Weidlinder Associates, New York, and Doctor Sreenivas Alampalli, Director of Bridge Program and Evaluation Services Bureau at the New York State Department of Transportation will be members of the advisory committee, to evaluate research work, progress and reports. The outcome of this project will provide necessary tools on the design of blast resistant highway bridges that engineers and departments of transportation (DOTs) decision makers across the country can use.]]></description>
      <pubDate>Thu, 03 Jan 2013 15:40:56 GMT</pubDate>
      <guid>https://rip.trb.org/View/1236093</guid>
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