Arghya Das

A Micromechanics Based Model for Cemented Granular Materials

Cemented Granular Materials (CGMs) consist of a particle skeleton and a solid matrix partially filling the interstitial space. In this broad class we encounter a number of typical geotechnical materials such as sedimentary rocks (Sandstones, Conglomerates and Breccia) as well as naturally and artificially cemented sands. These materials, while showing a brittle behavior under shearing at low confining pressures, are ductile at high confinements. The micro mechanisms involved, that are cement disaggregation, grain crushing and fragment rearrangement, are known to be different in these two cases.

Centrifuge model tests on rail embankments constructed with coal ash as a structural fill material

The objective of the present study is to understand the stability and deformation behavior of soil confined coal ash embankments through centrifuge model tests. A railway embankment of 11 m height configuration with a slope of 1V:2H was modeled at high gravities in a large beam centrifuge facility available at IIT Bombay. Considering the nature of railway embankments and possibility of building-up of ground water table due to rainfall, a seepage tank simulator was used to induce seepage into the rail embankment during centrifuge tests. After establishing steady-state seepage conditions, the crest of the embankment was subjected to an incremental static loading pressure distributed through a rigid strip footing up to 700 kPa or failure, whichever occurred first. Additionally, an option of provision of drainage at the mid-height of the railway embankment was also explored. Based on the analysis and interpretation of centrifuge model test results, for a soil confined coal ash embankment with 1V:2H slope with a confinement layer of 1.5 m thickness in the top-half height and berms in the bottom-half zone was observed to sustain an ultimate load bearing pressure of 400 kPa. Further, results of stability analysis of soil confined coal ash embankment models constructed with coal ash as a fill material were found to corroborate well with physically observed centrifuge test results.