微生物矿化作用改善不同孔隙砂岩抗冻融特性试验研究

砂岩是地质遗迹和石质文物最为常见的岩石类型，冻融循环导致的风化劣化是引起其发生地质灾害的主要原因。降渗加固是解决该问题的根本途径。文章引入国际上新型的岩土体加固技术—微生物诱导碳酸钙沉淀（MICP），以中粒砂岩和微粒砂岩为例，通过开展MICP处理和冻融循环试验，研究其改善不同孔隙砂岩抗冻融特性的可行性，分析其改善机理。研究结果表明：（1）MICP作用能显著提高两类砂岩的抗冻融特性，主要改善机理是MICP过程生成的碳酸钙不仅填充了岩石孔隙，减小了孔隙水的体积和冻融损伤作用力，同时也加强了岩石颗粒之间的胶结强度，但孔隙因素对该过程有一定影响；（2）3轮次MICP处理后的岩样在冻融循环40次后未见明显表观破坏，而未经处理的岩样当冻融循环达到40轮次时在棱角处出现局部表观破坏且中粒砂岩破坏程度略大于微粒砂岩；（3）40轮次冻融循环作用后，中粒砂岩和微粒砂岩岩样孔隙率增加率从17.0%和14.8%降低到了4.4%和6.3%，质量损失率从0.22%和0.14%下降到了0.04%和0.02%，吸水率从6.8%和4.4%减小到了0.75%和1.5%，波速降低率从18.5%和12.4%降低到了7.3%和3.8%；（4）由于中粒砂岩孔隙大于微粒砂岩，其碳酸钙沉淀效率更高，有效处理深度更深，表层孔隙间距更大，从而在进行相同轮次MICP处理时，其孔隙率降低率、吸水率降低率、质量增长率、波速增长率均较大。

Experimental Investigation of Microbial Induced Calcite Precipitation(MICP) Improvement on Freeze-Thaw Resistance ofSandstone with Various Types of Porosity

Sandstone is the most common rock type for geological relic and historic stone. Lithologic deterioration induced by freeze-thaw is the dominant reason that cause sandstone geological disaster. Permeability reduction and physico-mechanical property improvement is an effective way to solve this problem. In this study, the feasibility using Microbial Induced Calcite Precipitation (MICP) to improve the freeze-thaw resistance of sandstone with various types of porosity was studied as well as its mechanism was analyzed. MICP treatment and freeze-thaw test were carried out based on two types of sandstone with mediumgrain size and fine-grain size. Experimental results indicate that (1) MICP treatment could improve the freeze-thaw resistance of the two types of sandstone, which is contribute to the production of the CaCO3 crystals during the MICP process. These CaCO₃ crystals occupy the porosity and reduce the volume of pore water and damaging force as well as enhance the bonding of the stone particles. However, MICP improvement performance is affected the effect of porosity. (2) After 40 cycles of freeze-thaw test, apparent damages at angular position were only observed from the samples without MICP treatment compared to the samples with MICP treatment. (3) The reduction rate of porosity of sandstone with medium-grain size and fine-grain size were reduced to 4.4% and 6.3% from 17.0% and 14.8% due to the MICP improvement when subjected to 40 cycles of freeze-thaw test. The same phenomenon can also be observed from the mass loss rate, water absorption, the reduction rate of wave velocity, corresponding values are 0.04% and 0.02% from 0.22% and 0.14%, 0.75% and 1.5% from 6.8% and 4.4%, 7.3% and 3.8% from 18.5% and 12.4%. (4) The efficiency of MICP process, effective treatment depth, distance of pore near surface of sandstone with mediumgrain size were higher because that its pores are larger, inducing higher values of the reduction rate of porosity and water absorption, growth rate of mass and wave velocity.