下伏缓倾煤层开采对既有铁路隧道安全性影响分析

Influence of Excavation in Underlying Gently-Inclined Coal Layer on the Safety of Existing Railway Tunnel

为量化下伏煤层开采对上部既有铁路隧道的显著影响,以近接缓倾煤层开采区的某铁路隧道为工程背景,构建三维数值分析模型并分别采用现场监测和理论计算的方式进行验证;通过数值模拟分析煤层开采全过程中隧道衬砌的变形,对比煤层开采前与开采至Ⅵ边界时隧道最不利截面内力,并利用最小安全系数和最大裂缝宽度2个指标评价煤层开采对上部铁路隧道安全性影响,确定煤层开采的竖向影响范围。结果表明:现场监测和理论计算2种方法均证明了数值模拟参数取值合理、方法可行;煤层开采过程中隧道洞口位置变形最大,沉降增加了7.38倍;煤层开采造成隧道近煤层侧仰拱和边墙内力增大,加剧了隧道洞口的偏压程度;自煤层开始开采到开采至Ⅵ边界的整个过程中,隧道安全系数降低了68.97%,隧道结构裂缝宽度最大达到2.01 mm且与现场检测得到的隧道结构裂缝病害情况相一致;煤层开采的竖向影响范围为自开采区竖向往上2449 m。

In order to quantify the significant influence of the excavation in underlying coal layer on the upper existing railway tunnel,a threedimensional numerical analysis model was constructed with a railway tunnel adjacent to the goaf in gentlyinclined coal layer as the engineering background and the model was verified by onsite monitoring and theoretical calculations respectively.The deformation of the tunnel lining during the whole process of the excavation in coal layer was analyzed by numerical simulation,and the internal forces of the most unfavorable tunnel section were compared before the excavation of the coal layer and when the coal layer was mined to the VI boundary.Using the two indicators of the minimum safety factor and the maximum crack width,the influence of the excavation in coal layer on the safety of the upper railway tunnel was evaluated.The vertical influence range of the excavation in coal layer was determined.The results show that the two methods of onsite monitoring and theoretical calculation all prove that the numerical simulation parameter values are reasonable and the method is feasible.During the process of the excavation in coal layer,the deformation of the tunnel entrance is the largest with the settlement increase by 7.38 times.The excavation of coal layer causes the increase of internal forces in the inverted arch and side wall near the coal layer,which intensifies the degree of bias at the tunnel entrance.In the whole process from the beginning of the excavation to excavating to the VI boundary in coal layer,the safety factor of the tunnel is reduced by 68.97%.The maximum crack width of the tunnel structure is 2.01 mm,which is consistent with the crack disease of the tunnel structure detected on site.The vertical influence range of the excavation in coal layer is 2449 m vertically upwards from the area of excavation.