Large sections of roadway may consist entirely of viaduct , sections with no connection to the earth other than through vertical columns . When concrete columns are used , the detailing is critical . Typical failure may be in the toppling of a row of columns due either to soil connection failure or to insufficient cylindrical wrapping with rebar . Both failures were seen in the 1995 Great Hanshin earthquake in Kobe , Japan , where an entire viaduct , centrally supported by a single row of large columns , was laid down to one side . Such columns are reinforced by excavating to the foundation pad , driving additional pilings , and adding a new , larger pad , well connected with rebar alongside or into the column . A column with insufficient wrapping bar , which is prone to burst and then hinge at the bursting point , may be completely encased in a circular or elliptical jacket of welded steel sheet and grouted as described above
Great Hanshin earthquake
Great Hanshin earthquake
Seismic retrofit