Chotiros Nicholas R
Applied Research Laboratories, The University of Texas at Austin, 78713-8029, USA.
J Acoust Soc Am. 2002 Nov;112(5 Pt 1):1853-68. doi: 10.1121/1.1511199.
The discrepancy between acoustic measurements and the theoretical predictions was investigated in the case of water-saturated sand. Two theoretical models were considered: visco-elastic and poro-elastic solid models. The visco-elastic solid model could not be reconciled with reflection loss measurements and was rejected. The poro-elastic solid model using Biot's theory [J. Acoust. Soc. Am. 103, 2723-2729 (1998)] as formulated by Stoll [J. Acoust. Soc. Am. 70, 149-156 (1981)] was an improvement. It was investigated using an inversion process. Operative values of grain bulk modulus and the frame bulk and shear moduli of water-saturated sand were inverted from simple measurements--reflection loss, compressional and shear wave speeds and attenuations. Although the inversion process is nonlinear, in practice, it is well behaved and converges quite rapidly to a unique solution. The issue of imprecisely known parameter values was handled in a probabilistic manner. The inversion results, using published laboratory and in situ measurements, showed that further improvement was needed. In an attempt to find a solution, two possible hypotheses are put forward. (1) Composite materials: The possibility that the frame may contain fluid and that the pore fluid may contain loose grains. (2) Independent coefficient of fluid content: The possibility that porosity may change with pore fluid pressure. Inversion results were encouraging for both hypotheses. It is difficult to say which of the two hypotheses is superior, and the two hypotheses are not mutually exclusive. The new hypotheses represent a significant advance because they have the potential to resolve the remaining discrepancies. At this stage, alternative interpretations of the data are possible.
在水饱和砂的情况下，研究了声学测量值与理论预测值之间的差异。考虑了两种理论模型：粘弹性和多孔弹性固体模型。粘弹性固体模型与反射损耗测量结果不一致，因此被摒弃。由斯托尔[《美国声学学会杂志》70, 149 - 156 (1981)]按照比奥理论[《美国声学学会杂志》103, 2723 - 2729 (1998)]构建的多孔弹性固体模型是一种改进。使用反演过程对其进行了研究。从简单测量——反射损耗、纵波和横波速度及衰减中反演得到了水饱和砂的颗粒体积模量以及骨架体积模量和剪切模量的实际值。尽管反演过程是非线性的，但在实际应用中，它表现良好且能相当迅速地收敛到唯一解。以概率方式处理了参数值已知不准确的问题。利用已发表的实验室和现场测量数据得到的反演结果表明还需要进一步改进。为了找到解决方案，提出了两种可能的假设。(1)复合材料：骨架可能包含流体且孔隙流体可能包含松散颗粒的可能性。(2)流体含量的独立系数：孔隙率可能随孔隙流体压力变化的可能性。两种假设的反演结果都令人鼓舞。很难说这两种假设哪种更优，而且这两种假设并非相互排斥。新的假设代表了一个重大进展，因为它们有可能解决剩余的差异。在现阶段，对数据的其他解释也是可能的。
