Cementation of Shale Soils by MICP Technology and Its Damage Characteristics Due to Freeze–Thaw Weathering Processes

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Abstract
This paper describes an application for microbial induced calcite precipitation (MICP) on the cementation of shale soils for ground reinforcement in cold regions. The micro and macrostructures of the cemented body were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) imaging techniques. The results showed that MICP can cement shale particles effectively with a significant amount of generated calcites on the surfaces of particles. Cementation tests for shale soils with various size distributions indicated that shale allows easy deposition of calcium carbonate (CaCO3) crystals with high bond strength. The optimal particle size distribution to achieve high strength should include particles with good grading in all size ranges. To investigate the damage characteristics of the cemented body in response to freeze–thaw weathering processes, tests were carried out on samples with four different water contents. The apparent damage characteristics of the cemented body and the development of pores and fissures due to freeze–thaw weathering were studied in detail. The results showed that the freeze–thaw failure of the cemented body was a physical process occurring when the frost heave force exceeded the bond strength created by MICP. When the number of freeze–thaw cycles exceeded a certain threshold, large areas of damage were formed, leading to significant spalling on the surface of the cemented body. More severe spalling damage was observed for cases with higher water content and more numbers of freeze–thaw weathering cycles. The T2 spectrum curves of the cemented body showed that the development of small to medium size pores was dominant for the cemented body with low water content and for high water content, the continuous expansion of large size pores was dominant. In addition, this feature was consistent with the observations from magnetic resonance imaging (MRI) images.

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