隧道下穿河流施工时，盾构机在含水量丰富、渗透性较强的富水砂层掘进，施工中地层扰动变形控制难度大，高水位水头压使得施工安全性受到严重挑战。本文依托西安330kV电力盾构下穿灞河工程，采用理论分析、室内试验、数值模拟、现场监测等方法，对电力盾构下穿灞河的重大风险及技术难点展开研究并提出安全控制措施，研究成果为电力盾构下穿灞河施工提供安全指导，积累了相关工程经验，对盾构下穿河流盾构施工提供借鉴和参考意义。主要研究内容及结论如下：
（1）应用层次分析法和模糊综合评价法，对电力盾构下穿灞河施工风险等级进行评价，得到电力盾构施工中具有较高等级水平的风险因素。得到结论：电力盾构下穿灞河施工具有“中等风险”且易上升为“较高风险”，盾构重大风险主要源自施工方法因素和地质水文因素，因此需要采取合理有效的控制措施，降低施工安全风险。
（2）以粉质黏土、砂土为试验对象，泡沫剂、膨润土为改良剂，坍落度试验、黏附性试验、直剪试验、渗透试验为评价指标，进行渣土改良试验。试验结果表明：不同含水率的粉质黏土泡沫最佳注入比差别较大；含水率分别在18%、21%、24%、27%、30%时，最佳泡沫注入比分别为70%、55%、45%、30%、22%，改良粉质黏土可优先添加水提高土体含水率再用泡沫剂改良。砂土采用土水比为1:8的钠基膨润土泥浆可有效降低其渗透性，细砂、中砂、粗砂最佳体积添加比为8%、10%、16%。现场出渣情况显示试验结果用于盾构施工改良效果良好，粉质黏土基本无结泥饼现象，砂土无掌子面或螺旋输送机喷涌发生。
（3）综合使用正交试验和数值模拟方法，建立电力盾构下穿灞河三维模型，研究土仓压力、注浆压力、注浆层厚度对地层变形敏感性程度，确定出电力盾构下穿灞河主要掘进参数。结果表明：分别以地表最大沉降、地层最大竖向位移、地层最大水平位移为评价指标时，三个因素的影响敏感性主次顺序都是注浆压力、注浆层厚度、土仓压力。因此在穿河盾构施工中，应根据监测数据和参数反馈优先控制同步注浆压力、注浆量的变化，及时进行优化调整。
（4）通过理论计算，确定了盾构总推力、刀盘扭矩、土仓压力、注浆压力、同步注浆量等理论值，与现场实测掘进参数对比验证，并针对施工主要风险提出有效控制措施。得出下穿灞河小直径电力盾构掘进参数建议值为：总推力控制在9000kN，刀盘扭矩为1100kN·m，土仓压力为0.15MPa，注浆压力为0.18MPa，同步注浆量为4.05~5.06m³，施工速度保持在20～40mm/min之间。

When the tunnel is constructed under the river, the shield machine is excavated in the water-rich sand layer with rich water content and strong permeability. During the construction, it is difficult to control the disturbance and deformation of the stratum. The high water head pressure makes the construction safety seriously challenged. Relying on the Xi'an 330kV Power Shield Crossing Bahe Project, this paper uses theoretical analysis, laboratory tests, numerical simulation, on-site monitoring and other methods to study the major risks and technical difficulties of power shields crossing the Bahe River, and propose safety control measures. The research results provide safety guidance for the construction of electric shield tunnels under the Bahe River, accumulate relevant engineering experience, and provide reference and reference significance for the shield tunnel construction of shield tunnels under the river. The main research contents and conclusions are as follows:
(1) Apply the analytic hierarchy process and fuzzy comprehensive evaluation method to evaluate the risk level of the construction of the power shield under the Bahe River, and get the main risk factors with a higher level in the construction process, and get the conclusion: the power shield The construction under the Bahe River has "medium risk" and is easy to rise to "high risk". The major risks of shield tunneling are mainly derived from construction method factors and geological and hydrological factors. Therefore, reasonable and effective control measures need to be taken to reduce construction safety risks.
(2) Taking silty clay and sandy soil as test objects, foaming agent and bentonite as modifiers, and slump test, adhesion test, direct shear test, and penetration test as evaluation indicators, the slag soil improvement test was carried out. The test results show that the optimal injection ratios of silty clay foams with different moisture contents are quite different; when the moisture contents are 18%, 21%, 24%, 27%, and 30%, the optimal foam injection ratios are 70%, 70%, and 30%, respectively. 55%, 45%, 30%, 22%, for the improvement of silty clay, water can be added first to increase the moisture content of the soil, and then foaming agent can be used to improve it. Sodium bentonite mud with a soil-water ratio of 1:8 can effectively reduce its permeability for sand, and the optimal volume addition ratios of fine sand, medium sand and coarse sand are 8%, 10%, and 16%. The on-site slag discharge situation shows that the test results are good for shield construction improvement, the silty clay basically has no mud cake phenomenon, and the sandy soil has no face or screw conveyor spouting.
(3) Comprehensively using the orthogonal test and numerical simulation methods, a three-dimensional model of the power shield tunnel passing through the Ba River was established, and the sensitivity of the soil bunker pressure, grouting pressure, and grouting layer thickness to the formation deformation was studied, and the power shield tunnel passing through the Ba River was determined. Main excavation parameters. The results show that when the maximum subsidence of the surface, the maximum vertical displacement of the stratum, and the maximum horizontal displacement of the stratum are used as the evaluation indicators, the primary and secondary order of the sensitivity are grouting pressure, grouting layer thickness, and soil bin pressure. Therefore, in the construction of shield tunneling through the river, the changes of synchronous grouting pressure and grouting amount should be controlled preferentially according to the monitoring data and parameter feedback, and the optimization and adjustment should be carried out in time.
(4) Through theoretical calculation, the theoretical values of the total thrust of the shield, the torque of the cutter head, and the pressure of the soil bin are determined, which are compared and verified with the field-measured excavation parameters, and effective control measures are proposed for the main risks of construction. The recommended values for the tunneling parameters of the small-diameter electric shield tunnel through the Bahe River are: the total thrust is controlled at 9000kN, the cutter head torque is 1100kN m, the soil bin pressure is 0.15MPa, the grouting pressure is 0.18MPa, and the synchronous grouting amount is 4.05~5.06m³, and the construction speed is kept between 20~40mm/min.

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