© 2017. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The feasibility of using ultrasound transmission method to assess raw earthen materials is investigated. Results indicate that this technique is effective at controlling the drying process of raw earthen materials. Near the hygrometric equilibrium, there is a linear relationship between the moisture content of the earthen material and the ultrasound transmission speed, which increases during the drying process. For the tested compressed earth, the hygrometric equilibrium is reached when the ultrasound transmission speed is over 1100 m/s. In addition, ultrasound transmission method is useful to reliably calculate the dynamic Young's modulus of raw earthen materials.Peer ReviewedPostprint (author's final draft

Interaction between microbially induced calcium carbonate precipitation (MICP) and compaction procedures to stabilise raw soil materials has been studied with the aim of producing earthen engineering structures. Initial tests to optimise MICP in aqueous medium and in selected soils were performed. MICP and compaction were finally applied to assess medium-size elements. The main result was that sandy soils should be compacted before irrigation treatment to close the existing voids and prevent bacterial sweeping, whereas clayey soils should be compacted after irrigation treatment to avoid the plugging effect. MICP improved small sand soil compressive strength by up to 32% over the value reached by compaction alone. However, MICP had no positive effect on coarse soils and soils with an optimum particle size distribution: MICP treatment was not able to fill large connected voids in the first case and it caused little void generation due to bacteria sporulation in the second.

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