Liquefaction-induced lateral spreading is a critical design consideration for many bridges in highly seismic regions of the Pacific Northwest, with broad impacts on safety for the general public. The current design procedures used to estimate liquefaction-induced lateral spreading in bridge-foundation-soil systems are often overly conservative, with the result that the construction of bridges may be more costly than necessary. <\/p>\n\n\n\n
A modified design procedure, an equivalent static analysis (ESA) procedure based on a\ntwo-dimensional pile pinning concept, has been developed as a means to\nmore appropriately consider relevant factors, and it has been shown to be\neffective at reducing some of the excessive conservatism associated with\nmore simplified design approaches. However, only limited testing and analysis have\nbeen conducted to verify and benchmark the relative safety of the\nresulting design solutions for a range of bridges, foundations, and soil\nconditions. <\/p>\n\n\n\n
Before local agencies adopt this modified design\napproach, it is important to verify the safety of the resulting bridge and\nfoundation designs for conditions typical in the Northwest, and to develop a\ndatabase and benchmarking framework useful for future evaluations. <\/p>\n\n\n\n
This\nwork aimed to verify the modified simplified design procedure by using three-dimensional\n(3-D) finite element analysis (FEA) and to increase understanding of the site\ngeometry conditions that necessitate a more comprehensive consideration of 3-D\neffects in foundation design. The project objectives were accomplished by\nanalyzing 200 distinct cases using both 3-D FEA and simplified ESA models of\nthe soil-foundation system. The cases for these parameter studies considered\ndifferent combinations of bridge approach embankment width, non-liquefiable\ncrust thickness, liquefiable layer thickness, and foundation size\/stiffness.<\/p>\n\n\n\n
This modeling effort provided evidence\nthat consideration of the 3-D geometry of a site is an important factor in the\nanalysis of bridge foundations subject to lateral spreading, and the modeling\ndetermined that for a given level of lateral spreading deformation, the lateral\nresponse of the foundation for a particular site is governed by the interaction\nof multiple site parameters, including the location and size of the liquefied\nlayer, the width of the approach embankment, and the size and stiffness of the\nfoundation. Overall agreement in the qualitative and quantitative assessments\nof the results obtained from the 3-D FEA and simplified ESA modeling efforts\noffered important verification of each modeling approach and the assumptions\nassociated with each. <\/p>\n\n\n\n
Verification of the modified lateral spreading\ndesign approach will not only lead to potential cost savings in the design\nand construction of future bridges but will also increase public safety by\nreducing the potential for bridge collapse and minimizing the time\nassociated with lost bridge service immediately following\nlateral spreading caused by an earthquake.<\/p>\n\n\n\n