The present study aims to improve shear strength of poorly graded sand using microbially induced calcite precipitation (MICP) technique. Two soil-based bacteria, namely Sporosarcina pasteurii (SP) and Bacillus sphaericus (BS), were bioaugmented in sand. The cementation solutions of 0.50 M concentration were prepared using distilled water (DWCS) and tap water (TWCS), maintaining sterile and non-sterile conditions, respectively. The biotreatment was carried out in direct shear test (DST) moulds using 12-hr treatment cycles up to 14 days. The biotreated sand samples were subjected to DST to determine shear strength parameters, and results were statistically explored using analysis of variance (ANOVA). The amount of calcite precipitation, XRD and SEM was used to interpret biocementation. The non-sterile treatment using TWCS showed significant strength. Additional biotreatment samples were prepared in DST and cylindrical PVC moulds using TWCS for 18 days but adopting different treatment cycles of 12, 24, 48 and 72 hr to explore inexpensive treatment option. All of these biotreated samples were tested for hydraulic conductivity, shear strength (based on DST and triaxial consolidated undrained (CU) tests) and three-layer calcite contents. In CU tests, stress-strain response of biocemented sands showed initial brittle behaviour followed by strain-softening, analogous to rock-like behaviour similar to sandstone. The maximum increase in strength was achieved with 12-hr treatment cycle. The 24-hr treatment cycle showed 1.7–1.8 times lesser strength than 12-hr treatment cycle specimens. However, a significant amount of calcite precipitation and strength in 24-hr treatment cycle showed its effectiveness in achieving cost reduction for large-scale field applications.

中文翻译：

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使用不同的尿素分解菌株和无菌条件对生物处理砂的剪切强度提高的比较

本研究旨在利用微生物诱导的方解石沉淀 (MICP) 技术提高等级差沙子的剪切强度。两种土壤细菌，即巴氏芽孢杆菌( SP ) 和球形芽孢杆菌( BS ))，在沙子中进行了生物强化。使用蒸馏水 (DWCS) 和自来水 (TWCS) 制备浓度为 0.50 M 的胶结溶液，分别保持无菌和非无菌条件。生物处理在直接剪切试验 (DST) 模具中进行，处理周期为 12 小时，最多 14 天。对生物处理过的沙样进行 DST 以确定剪切强度参数，并使用方差分析 (ANOVA) 对结果进行统计探索。方解石析出量、XRD、SEM用于解释生物胶结。使用 TWCS 的非无菌处理显示出显着的强度。额外的生物处理样品在 DST 和圆柱形 PVC 模具中使用 TWCS 制备 18 天，但采用 12、24、48 和 72 小时的不同处理周期来探索廉价的处理选择。所有这些经过生物处理的样品都进行了水力传导率、剪切强度（基于 DST 和三轴固结不排水 (CU) 测试）和三层方解石含量的测试。在 CU 测试中，生物胶结砂的应力-应变响应表现出最初的脆性行为，随后出现应变软化，类似于类似于砂岩的类岩石行为。在 12 小时的治疗周期中实现了强度的最大增加。24 小时处理周期的样本强度比 12 小时处理周期样本低 1.7-1.8 倍。然而，