Preferred injection method and curing mechanism analysis for the curing of loose Pisha sandstone based on microbially...

As a loose rock formation with low lithogenic property, low structural strength, and poor intersand cementation, Pisha sandstone is susceptible to chemical weathering and extreme soil erosion and has become an important source of sediment for the Yellow River. There is limited information available on the conditions of microbial distribution homogeneity under grain-mediated conditions in Pisha sandstones, as well as on the influence of dissolved minerals on calcium carbonate morphological mechanisms. In this paper, microbially induced calcium carbonate deposition was used to reinforce and improve the loose Pisha sandstone. First, the influence laws of the single-phase/self-absorption two-phase injection method and added solvent on the curing indexes such as curing volume, curing depth, calcium carbonate yield, and unconfined compressive strength of the specimens were discussed. Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction spectroscopy were used to analyze the microstructure of the cemented sand columns, as well as the mineral phases and distribution of the biomineralization products mechanistically. The results demonstrated that the single-phase injection treatment could only achieve local solidification of the Pisha sandstone sand column, whereas the self-absorption two-phase injection method could result in a more uniform spatial distribution of bacteria and a monolithic specimen, in which the calcium carbonate yield increased with increasing low concentration CaCl₂ injection. The compressive strength appeared to increase significantly, and the effect of the applied liquid CO(NH₂)₂ was not obvious. Montmorillonite underwent dissolution during the mineralization process, eliminating the characteristics of Pisha sandstone swelling in water. Under the effect of biomineralization, calcium carbonate crystals are formed to wrap around the Pisha sandstone particles, changing their particle size and increasing the interparticle roughness. Meanwhile, the interstices between particles are filled via calcium carbonate precipitation, effectively forming cementation points that can significantly improve the strength of the Pisha sandstone. The results of this study provide a theoretical basis for the application of biomineralization technology in the ecological restoration of Pisha sandstone areas.