Improving the effectivity of dynamic compaction methods in silty sands through microbial induced desaturation (MID)

This study aimed to evaluate the potential of microbially induced desaturation (MID) to improve the compactibility of silty sands. Conventional soil compaction techniques for saturated silty sands often require either high compaction effort to achieve the desired results or even fail to reach aspired relative densities outright. A lab study was conducted on silt-sand mixtures with increasing amount of fines. The objective was to assess whether biogenic gas formation could be used as a pretreatment to increase the effectivity of soil compaction techniques. A two-stage method was carried out in which, firstly, a soil sample was desaturated by means of microbially induced desaturation (MID) through denitrification and, secondly, dynamically compacted using a vibrating table. The results of this method were compared to results acquired from dynamically compacting the same soil without pretreatment. The treated samples showed a considerable amount of swelling during the first stage as a result of gas formation. All treated soils were able to desaturate below the optimum water content. After compaction, the relative density of all treated samples with 15%-25% of fines was a factor 1.5 to 2 times higher compared to untreated samples using the same amount of compaction effort. At higher or lower fines content the MID pretreatment was less effective. The results of the lab tests provide proof of concept that MID through denitrification can be used as a pre-Treatment method to achieve higher degrees of compaction on silty sands. Further scale-up is still required to evaluate the full potential of this method at field scale.