关键词: 微生物诱导碳酸沉淀(MICP), 发泡聚苯乙烯(EPS), 强度, 破坏特征, 微观结构

Abstract:

[Objective] A method for preparing solidified lightweight red sandstone soil using microbial-induced calcium carbonate precipitation (MICP) technology was proposed for the recycle use of red sandstone residual soil in engineering. A design study was conducted on bio-based solidified lightweight red sandstone soil to investigate the solidification mechanism of the modified material. The effects of expanded polystyrene (EPS) mass content and cementation solution concentration on the strength of the lightweight solidified soil are analyzed. Based on this, the compression failure characteristics of the solidified lightweight red sandstone soil are studied, and its cementation mechanism is validated through both strength analysis and failure characteristics. [Methods] Bacillus pasteurii was selected as the target strain, and cementation solutions with concentrations ranging from 0.5 to 2.0 mol/L were prepared. Solidified lightweight red sandstone soil samples with EPS contents ranging from 0% to 1.125% were prepared. The internal microstructure of the modified red sandstone residual soil was analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Additionally, its mechanical properties were evaluated through slow shear tests and uniaxial compression tests. [Results] After MICP treatment, a substantial amount of calcite-type CaCO₃ precipitates was generated within the red sandstone residual soil. These CaCO₃ crystals formed a continuous and dense cementation network between soil particles, serving as the primary contributor to the strength of the solidified lightweight red sandstone soil. In contrast, only sparse crystal clusters were observed on the surfaces of hydrophobic EPS particles. When the cementation solution concentration was 1.5 mol/L and the EPS content was 0.375%, the solidified lightweight red sandstone soil samples exhibited the optimal performance combination. The compressive strength reached 0.76 MPa, meeting the standard requirement (≥0.6 MPa) for foam lightweight soil. The bulk density was 14.3 kN/m³, representing a 13% reduction compared to the undisturbed soil. Additionally, the internal friction angle and cohesion increased by 39% and 17%, respectively. Failure mode analysis revealed that samples with low EPS content (≤0.375%) exhibited typical brittle shear failure, with cracks propagating in a “Y” shape. In contrast, samples with high EPS content (≥1.125%) showed bulging failure, accompanied by surface spalling and debris detachment. [Conclusions] The combination of microbial solidification technology and EPS lightweight foam soil technology has effectively solidified lightweight red sandstone soil, overcoming the high energy consumption limitations of traditional cement-based solidification methods. A quantitative relationship between “cementation solution concentration, EPS content, and mechanical properties” was established. The proposed optimal mix ratio (1.5 mol/L cementation solution + 0.375% EPS) combines both lightweight characteristics (bulk density of 14.3 kN/m³) and high strength (0.76 MPa). This study provides a low-carbon and environmentally friendly solution for the resource utilization of red sandstone residual soil, demonstrating significant application value in engineering fields such as subgrade filling.

Key words: MICP, expanded polystyrene, strength, failure characteristics, microstructure