基于互相关法的土体波速测量方法改进与应用

    Improvement and Application of the Cross-Correlation Method for Wave Velocity Measurement in Soils

    • 摘要: 岩土工程的声学测试中,不同的波速确定方法(初达波法和互相关法)计算的波速结果通常不一致,误差较大,且尚未形成广泛使用的标准。为解决这一问题,通过改进互相关法,提出了一种更加客观、准确的波速测量方法。该方法以第一谐振频率作为激励频率,采用高斯调制正弦脉冲(GMSP)作为激励信号,结合互相关法获取波速。由于GMSP与接收信号形状接近,提高了互相关法的准确性。此外,给出了上述方法的适用频率范围,在该范围内EE和BE振动模态仅产生P波或S波,消除了近场效应。测量了干密度为1.6 g/cm3不同含水量砂土的波速,以及含水率为7%时不同干密度砂土的波速。试验结果显示采用该方法测试砂土的信号中没有近场效应的产生,并且通过互相关法与初达波法得到了一致的波速。砂土的P波波速在饱和状态下由于水的高模量而达到1700 m/s,但随着含水率的降低,波速迅速下降至350-400 m/s,并略有回升,S波波速在干燥条件下为150 m/s,随着含水率的增加而下降至约100 m/s,并在接近饱和状态时进一步降低,这种变化与吸附水和基质吸力密切相关。不同干密度的试验结果表明,随着干密度增加,S波波速增长速度快于P波。

       

      Abstract: In the experimental study on wave propagation in soil, wave velocities calculated using the start-to-start method and the cross-correlation method often yield inconsistent results with significant errors, and no widely accepted standard has yet been established. To address this issue, a more objective and accurate method for wave velocity measurement is proposed by improving the cross-correlation method. This method uses the first resonant frequency as the excitation frequency and a Gaussian-modulated sinusoidal pulse (GMSP) as the excitation signal, combined with the cross-correlation technique to determine wave velocity. Since the shape of the GMSP closely matches that of the received signal, the accuracy of the cross-correlation method is significantly improved. Moreover, the applicable frequency range of this method is defined, within which the vibration modes of EE and BE generate only pure P-waves or S-waves, effectively eliminating near-field effects. The wave velocity of sand at different water content and dry density was measured, and the results show that, the proposed method eliminates near-field effects in signals measured, and consistent wave velocities are obtained using both the cross-correlation and first arrival methods. In saturated conditions, the P-wave velocity in sand reaches 1700 m/s due to the high modulus of water. As the water content decreases, the velocity drops sharply to 350–400 m/s, followed by a slight rebound. The S-wave velocity is approximately 150 m/s under dry conditions, decreasing to around 100 m/s as water content increases, and further declines near saturation. These variations are closely related to adsorbed water and matric suction. The test results of different dry densities show that with the increase of dry density, the growth rate of s wave velocity is faster than that of P wave.

       

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