盾构隧道壁后注浆材料的介电常数测定

DIELECTRIC COEFFICIENT TESTING OF GROUTING MATERIAL BEHIND SEGMENTS IN SHIELD TUNNEL

在利用地质雷达对盾构隧道壁后注浆进行探测的过程中,电磁波在注浆浆液中的传播速度是影响探测精度的关键参数之一。首先,提出一种测量介质介电常数的终端开路同轴探头技术,该技术将同轴探头紧贴有导电衬底的介质,通过测量探头终端的反射系数来确定介质的介电常数;然后,通过这种室内同轴探头法,测试在频率为1 GHz范围内,上海地区盾构隧道所使用的两种不同配比惰性浆液在第1天龄期的介电常数值以及一定配比的双浆液在第3天和第14天龄期的介电常数,进而得到在不同频率下电磁波在浆液中精确的传播速度。通过对试验结果的分析可知,不同的测试频率、不同的浆液配比以及不同的龄期等因素都影响电磁波在浆液中的传播速度。

The estimation of electromagnetic wave velocity is very important for the use of ground penetrating radar(GPR) to detect the existence or the thickness of the grouting slurries behind segments in shield tunnel.Firstly,a laboratory coaxial probe method for measuring dielectric coefficient of dielectric materials are proposed.The dielectric materials,backed by an electric conductor,are placed flush with the coaxial probe.The values of the dielectric coefficients of the dielectric materials are determined from the coaxial aperture reflection coefficients,which are measured by a network analyzer.With this method,a series of experimental measurements are carried out to test the dielectric coefficient of inertia slurry in two different proportions during the first day and the dielectric coefficients of double slurry in a certain proportion in the third and fourteenth days within the frequency of 1 GHz(the slurries are the ones used in shield tunnels in Shanghai).Then the electromagnetic wave velocities according to these slurries under different test frequencies can be obtained.Through the numerical analysis of the testing datai,t is concluded that different testing frequencies,different proportions and ages of the slurries can have influences on the electromagnetic wave velocities.Therefore,to improve the precision of GPR to detect the existence or the thickness of the grouting slurries behind segments in shield tunnel,the accurate determination of the dielectric coefficient of the grouting slurries is necessary.