SASW测试相位差不确定性分析

NON-DETERMINACY ANALYSIS OF PHASE IN SASW TESTING

在SASW测试中,受高阶振型波及道距等的影响,从折叠相位差曲线中无法通过折叠展开方法确定各离散频率点的绝对相位差。绝对相位差与折叠相位差相差2p(弧度)的整数倍,整数取值不同,由一条折叠相位差曲线计算的相速度-频率曲线也不同,它们并不完全与表面波各阶振型频散曲线对应。若不同振型表面波影响在频率域是分离的,可以得到相应频率范围该振型波的频散曲线。在这些曲线中,总有一条相速度-频率曲线与常规折叠展开方法得到的相速度-频率曲线对应。将不同道距下得到的这些相速度-频率曲线堆叠在一起,并用灰度来表示各频散点出现的概率,由此可以研究基阶振型以及高阶振型波的频散。

Because of the effect of higher modes of surface waves and the distance between two receivers,it is very difficult to calculate absolute phase differences from the wrapped phase curve given in frequency domain by the conventional unwrapped technique. The difference between the absolute and the wrapped phases is 2p by an integer for each frequency point. The phase velocities calculated from a wrapped phase are varied with the integer, which do not correspond to the phase velocities of modes respectively. When the influences of different mode surface waves are separated in frequency domain,the dispersion curves of modes can be obtained in the corresponding frequency zones by the non-determinacy analysis of phase. Of these curves,one always corresponds to the so-called‘measured phase velocity vs frequency’ curve. When all curves of phase velocity for each distance are overlapped and the overlapped probabilities are figured by brightness,the dispersion curves of the fundamental mode and higher mode waves can be distinguished from brightness variation.