GENERALIZED STRENGTH DEVELOPMENT MODEL OF SOLIDIFIED DREDGED MARINE SOILS WITH GRANULAR FILLER ADDITION

Abstract

Dredged marine soils (DMS) are the sediment and debris removed in the dredging process.
Large amount of DMS is generated from the dredging operations yearly, especially from the maintenance of
existing shipping channels and the development of various coastal infrastructures. In practice, DMS are
generally disposed of at designated offshore dump sites. Inadvertently, these discarded DMS would in time
be deposited back near shore due to tidal dynamics, necessitating dredging works again. Considering that
DMS are essentially soils with poor engineering properties, particularly low shear strength, there could be
potential for the materials’ reuse as acceptable or good geomaterials if the original conditions can be
improved. Pre-treatment for enhancement of the soil’s strength, such as solidification, is a feasible option. In
the present study, the solidification of 3 DMS samples was examined with the admixing of cement and/or
bottom ash, where cement acts as a binder while the bottom ash functions a filler material to lend structure to
the weak soil. The strength improvement of the solidified DMS was monitored with the unconfined
compression tests. The key factors that influence strength development in solidified soils were investigated,
i.e. curing period, water-binder ratio and binder-filler mix ratio. The curing period was prefixed at 3, 7, 14,
28 and 56 days, while the water-binder ratio examined were 1, 3 and 5. The test results indicated that strength
increased with curing time and higher water-binder ratio. The optimal binder-filler mix ratio determined was
75 % cement to 25 % bottom ash. The bottom ash was found to contribute to strength gain too, albeit in a
minor way compared to the highly reactive cement. For the generalized strength development plots, the
unconfined compressive strength of a particular day (q) was divided with the strength on day 28 (q28). The
resulting q/q28 vs. curing period plots were linear with varying gradients dependent on the water-binder ratio,
though it was apparent that the gradient of the plot decreased with increased water-binder ratio. In summary,
solidification with cement-bottom ash is expedient in improving the original low strength of the DMS, and
the generalized strength development model is useful for modeling, design and prediction on site.