RAILWAY EMBANKMENT CONSTRUCTED ON SOFT DELTAIC DEPOSIT: LONG-TERM BEHAVIOR AND EFFECT OF TREATMENT

Abstract

Railway construction over the soft soil of the active Ganges-Brahmaputra floodplain in the Padma Bridge Rail Link is the first of its kind in Bangladesh. A 2D finite element modeling using Plaxis investigated the long-term settlement behavior of ballast bottom as well as the factor of safety (FS) of this railway embankment. The contribution of cement-mixing piles (CMPs) in settlement reduction and FS improvement has been studied. Parametric study considers three train speeds, between 100–170 km/hr, and two soil profiles along different chainages: 82km+183m (Ch1) and 84km+102m (Ch2). The settlement of ballast bottom in both chainages are found higher in the long term, showing greater settlement in Ch2. Due to treatment, the short-term settlement of embankment bottom decreases by 13.8% at lower train speeds, and at 170 km/hr, the reduction increases to 18% and 16% for Ch1 and Ch2, respectively. The long-term settlement of ballast bottom is also reduced by 20% for lower speeds and 22% for a train speed of 170km/hr. CMP treatment is effective in settlement reduction, and the behavior was almost similar for both chainages, both short-and long-term. The treatment is seen to be more effective at higher train speeds. Due to treatment, increases of FS by 29–31% and 25–27% for Ch1, as well as 35–39% and 26–30% for Ch2, are obtained in the short and long term, respectively. The effect of treatment in providing stability is more prominent for Ch2 and its effect is also greater in the short term.