Calcareous sand erosion under natural environment changes or human activities is a major concern to many coastal zones, where weak and loose calcareous sands are usually encountered. To improve the tensile behavior and structural integrity of such sands, we combine the fiber reinforcement method and the bio-cementation technique based on microbially induced carbonate precipitation (MICP) for calcareous sand treatment. Various fiber-sand mixtures are prepared by mixing calcareous sand with different amount of fibers, including 0.00%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30% and 0.40%, before the bio-cementation process. To investigate the tensile strength as well as the post-peak response, we conduct the direct tensile test on these bio-cemented, fiber-reinforced sand samples. Experimental results highlight the interplay of MICP and fiber inclusions in strengthening microscale inter-particle binding and improving macroscopic tensile behaviors. The tensile strength of the sample increases with the increasing calcium carbonate content. The inclusion of fibers increases the sand ductility, but excessive amount of fibers may cause negative effects on the sand tensile strength due to the possible presence of more micro-voids and the resulting structural heterogeneity. Given varying fiber contents, we identify two types of stress-strain responses under the direct tensile load. With higher fiber content, the overall stress strain response follows four phases, with phase I representing the linear breakage of cemented sand body, phase II responding to the sudden stress drop due to the brittle failure of cemented sand, phase III related to the elastoplastic deformation of fibers, and phase IV for the pull-out or snapping of fibers. In comparison, with lower fiber content, phase III does not exist because of the much higher stress distributed to each individual fiber. Scanned Electron Microscopy observations further reveal that the increasing calcite precipitations strengthen the fiber reinforcement effect and the increasing fibers provide more surfaces that facilitate the calcite precipitations. This study provides new insights into the tensile behavior of bio-cemented, fiber-reinforced sands and contributes to possible future implementations for coastal erosion control.

自然环境变化或人类活动下的钙质砂侵蚀是许多沿海地区的主要关注点，通常会遇到弱而松散的钙质砂。为了改善此类砂的拉伸行为和结构完整性，我们将纤维增强方法和基于微生物诱导碳酸盐沉淀 (MICP) 的生物胶结技术相结合，用于钙质砂处理。在生物胶结过程之前，通过将钙质砂与不同量的纤维（包括0.00%、0.05%、0.10%、0.15%、0.20%、0.25%、0.30%和0.40%）混合来制备各种纤维-砂混合物。为了研究拉伸强度以及峰值后响应，我们对这些生物胶结的纤维增强砂样品进行了直接拉伸测试。实验结果突出了 MICP 和纤维夹杂物在加强微观粒子间结合和改善宏观拉伸行为方面的相互作用。样品的拉伸强度随着碳酸钙含量的增加而增加。纤维的加入增加了砂的延展性，但由于可能存在更多的微孔和由此产生的结构异质性，过量的纤维可能对砂的抗拉强度产生负面影响。鉴于不同的纤维含量，我们确定了直接拉伸载荷下的两种应力应变响应。随着纤维含量的增加，整体应力应变响应遵循四个阶段，阶段 I 代表胶结砂体的线性破坏，阶段 II 响应由于胶结砂脆性破坏引起的突然应力下降，第三阶段与纤维的弹塑性变形有关，第四阶段与纤维的拉出或折断有关。相比之下，在纤维含量较低的情况下，第三阶段不存在，因为分布到每根单独纤维的应力要高得多。扫描电子显微镜观察进一步表明，增加的方解石沉淀加强了纤维增强效应，增加的纤维提供了更多的表面，有利于方解石沉淀。这项研究为生物胶结、纤维增强砂的拉伸行为提供了新的见解，并有助于未来可能实施的海岸侵蚀控制。由于分布在每根单独纤维上的应力要高得多，因此 III 相不存在。扫描电子显微镜观察进一步表明，增加的方解石沉淀加强了纤维增强效应，增加的纤维提供了更多的表面，有利于方解石沉淀。这项研究为生物胶结、纤维增强砂的拉伸行为提供了新的见解，并有助于未来可能实施的海岸侵蚀控制。由于分布在每根单独纤维上的应力要高得多，因此 III 相不存在。扫描电子显微镜观察进一步表明，增加的方解石沉淀加强了纤维增强效应，增加的纤维提供了更多的表面，有利于方解石沉淀。这项研究为生物胶结、纤维增强砂的拉伸行为提供了新的见解，并有助于未来可能实施的海岸侵蚀控制。