上海盾构隧道壁后土体介电常数测试实验

Dielectric constant tests on soils behind shield tunnel segment in Shanghai

利用探地雷达方法探测盾构隧道壁后注浆注浆分布效果时,盾构管片壁后介质中的电磁波速的确定,是保证探测精度和图形识别的关键技术之一。运用网络分析仪同轴探头法对上海盾构隧道所穿越地层(第三层～第七层)的原状土样进行了介电常数测试实验和含水率实验,得到了这些土样含水率和其在测试频率为0.02～2.0GHz范围内的介电常数,通过计算得到了电磁波在这些土体中的传播速度,分析了其与含水率之间的关系以及随地层深度的变化趋势,为今后探地雷达用于上海地区盾构隧道壁后注浆效果的探测提供了重要的依据。

When GPR （ground penetrating radar） is used to detect the distribution of grouting behind the segment of shield tunnel, the determination of the velocity of the electromagnetic wave in the medium is one of the key techniques to ensure the detecting precision and image identification. The coaxial probe method with a network analytic instrument is introduced to test the dielectric constant of the undisturbed soil samples, which are taken in the soil layers （from the third layer to the seventh layer）, through which almost all shield tunnels are constructed in Shanghai. The water content and dielectric constant of the samples are tested under different frequencies, and the velocity of electromagnetic wave is computed by use of the dielectric constant. Some comparisons and directional deduction analyses on obtained images are done, and the relationship between the water content and the dielectric constant and that between the dielectric constant and the variation of soil strata are known. All these provide a basis for the GPR detection on the distribution of grouting behind segments.