膨胀土是一种特殊土，具有特殊的矿物成分和复杂的结构特征，为工程建设和灾害 预防中时常面临的“问题土”。膨胀土的改良技术一直是岩土工程和工程地质领域的研究 热点问题。目前工程应用比较多的膨胀土改良技术以物理加固和化学改良为主，但现有 技术还存在改良效果不理想、污染环境、造价高等问题，而生物岩土技术的兴起为人们 解决膨胀土工程问题提供了一种新思路。论文以安康地区天然膨胀土为研究对象，采用 试验与数值模拟相结合的方法，探索了植物源脲酶诱导碳酸钙沉淀（Enzyme Induced Carbonate Precipitation，EICP）和生物聚合物（Biopolymer，BP）协同改良膨胀土的工程 性能及改良效果。主要研究内容与成果如下： （1）确立了改良膨胀土的EICP最优固化参数和BP改良方案。通过开展脲酶活性 测试和钙化试验，得到了豆源种类、脲酶溶液浓度、尿素溶液浓度、尿素溶液体积、脲 酶-胶结液体积比、尿素-钙液体积比对脲酶活性和钙化效率的影响规律，确定了EICP最 优固化参数。依据在干湿循环条件下改良膨胀土的直剪试验和无侧限单轴压缩试验结果， 分析了不同生物聚合物及不同掺量对膨胀土的改良效果，探明了BP最优改良方案。 （2）通过宏观试验及微观测试相结合的方法，得到了EICP-XG（（原胶胶）改良膨胀 土的力学特性、渗透特性及微观结构特征。通过开展直剪试验、无侧限单轴压缩试验， 得到了不同改良方式对改良膨胀土力学强度的影响规律；通过变水头渗透试验，得到了 不同改良方式对改良膨胀土渗透性的影响规律；借助扫描电镜（SEM）观测、X射线衍 射（XRD）分析、核磁共振（1H NMR），得到了改良膨胀土的微观结构特征。根据以上 试验结果，确定EICP-XG改良膨胀土的力学性质最优、抵抗干湿劣化的能力最强。 （3）借助有限元数值软件对EICP-XG改良膨胀土的改良效果进行分析，验证了其 有效性。利用MIDAS GTS NX有限元分析软件建立膨胀土边坡模型，数值重现降雨-蒸 发（干湿循环）和持续强降雨影响下的膨胀土边坡滑移破坏过程，发现经EICP-XG技术改良的膨胀土边坡稳定系数和未经改良的膨胀土边坡相比更高，且在降雨工况下的稳定 系数降幅更小。 研究成果将有助于揭示EICP-BP改良膨胀土对干湿循环效应的力学响应机制，深化 半干旱地区膨胀土灾害绿色防护与科学治理的认识，对提升半干旱地区膨胀土工程韧性 与发展膨胀土工程绿色生态处置技术具有重要意义。

Expansive soil is a special type of soil with unique mineral composition and complex structural characteristics, which is often encountered as a "problem soil" in engineering construction and disaster prevention. The improvement technology of expansive soil has always been a hot research topic in the fields of geotechnical engineering and engineering geology. At present, the most commonly used techniques for improving expansive soil in engineering applications are physical reinforcement and chemical improvement. However, existing technologies still have problems such as unsatisfactory improvement effects, environmental pollution, and high cost. The rise of bio geotechnical technology provides a new approach for solving expansive soil engineering problems. The paper takes natural expansive soil in Ankang area as the research object, and uses a combination of experimental and numerical simulation methods to explore the engineering performance and improvement effect of enzyme induced carbonate precipitation (EICP) and biopolymer (BP) synergistic improvement of expansive soil. The main research contents and achievements are as follows: (1) Established the optimal EICP solidification parameters and BP improvement plan for improving expansive soil. By conducting urease activity testing and calcification experiments, the influence laws of soybean source type, urease solution concentration, urea solution concentration, urea solution volume, urease cement volume ratio, and urea calcium volume ratio on urease activity and calcification efficiency were obtained, and the optimal solidification parameters for EICP were determined. Based on the direct shear test and unconfined uniaxial compression test results of improving expansive soil under wet dry cycle conditions, the improvement effects of different biopolymers and dosages on expansive soil were analyzed, and the optimal BP improvement scheme was identified. (2) The mechanical properties, permeability characteristics, and microstructure characteristics of EICP-XG (xanthan gum) modified expansive soil were obtained through a combination of macroscopic and microscopic testing methods. By conducting direct shear tests and unconfined uniaxial compression tests, the influence of different improvement methods on the mechanical strength of improved expansive soil was obtained; The influence of different improvement methods on the permeability of improved expansive soil was obtained through variable head permeability tests; The microstructure characteristics of the improved expansive soil were obtained through scanning electron microscopy (SEM) observation, X-ray diffraction (XRD) analysis, and nuclear magnetic resonance (1H NMR). Based on the above experimental results, it is determined that EICP-XG has the best mechanical properties and the strongest ability to resist dry and wet deterioration for improved expansive soil. (3) The improvement effect of EICP-XG on expansive soil was analyzed using finite element numerical software, and its effectiveness was verified. Using the MIDAS GTS NX finite element analysis software, a model of expansive soil slope was established to numerically reproduce the sliding and failure process of expansive soil slope under the influence of rainfall evaporation (dry wet cycle) and continuous heavy rainfall. It was found that the stability coefficient of the expansive soil slope improved by EICP-XG technology was higher than that of the unmodified expansive soil slope, and the decrease in stability coefficient under rainfall conditions was smaller. The research results will help reveal the mechanical response mechanism of EICP-BP improved expansive soil to the wet dry cycle effect, deepen the understanding of green protection and scientific management of expansive soil disasters in semi-arid areas, and have important significance for enhancing the engineering resilience of expansive soil in semi-arid areas and developing green ecological disposal technology for expansive soil engineering.