测定堆石体密度的附加质量法理论分析研究

附加质量法是一种新兴的堆石体密度检测方法,它具有方便、无损等优点,近年来有较为广泛的应用,但该方法的应用效果会受到震源、雨水、双峰频谱等因素的影响.本文则考虑堆石体系统振动的阻尼因素,以及附加质量块与堆石体之间的非刚性连接,分别基于质弹阻模型以及双自由度-质弹阻模型对这些因素的影响进行了理论分析.结果表明,质弹阻模型可以解释主频随震源频率和雨水而变化的现象;而双自由度-质弹阻模型则可以解释主频随质量块偏移距和触地面积而变化的现象.在此基础上,本文对附加质量法的测试过程提出了几点改进建议.

Theoretical analysis on density measurement of rockfill body by additive mass method

Additive mass method is a new rockfill body density detection method, which is convenient and nondestructive, so it's widely used. But the effectiveness of this method will be affected by the source,rainwater,and double-peak spectrum. The damping of the rockfill system and the non-rigid connecting between the additive mass and rockfill object are analyzed.The theoretical analysis is carried out by using mass-spring-damping model and TDF-mass-spring-damping model. Firstly, the vibration of the rockfill system is analyzed by using a mass-spring-damping model considering the rockfill damping. The influence of the damping of the rockfill body on the measured vibration frequency and the mass-frequency curve are analyzed. Secondly, the vibration of the rockfill system is analyzed by using a two-degree-of-freedom mass-spring-damping model considering the non-rigid connecting between the additive mass and rockfill body. The influence of the non-rigid connecting on the measured vibration frequency and the mass-frequency curve are also analyzed.Based on mass-spring-damping model, the formula of received signal spectrum is presented. It shows that the received signal dominant frequency varies with source frequency and also the damping value of the rockfill body. For a given model, the theoretical computed received signal dominant frequencies fit well with the FEM simulated received signal dominant frequencies. It also shows that the received signal dominant frequency becomes higher with the increasing additive mass for low source frequency and small additive mass. This cause some abnormal mass-frequency curves. On the other hand, based on TDF-mass-spring-damping model, another formula of received signal spectrum is presented. This formula causes different received signal spectrum results from the results for simple mass-spring-damping model. The mass-frequency curve obtained from a small stiffness connection TDF-mass-spring-damping model has a very small intercept which means small vibration mass of the rockfill body. These results fit well with some FEM simulated mass-frequency curve. For a moderate stiffness connection TDF-mass-spring-damping model, the theoretical computed received signal spectrum has two peaks when source frequency is high. The first peak fits well with the natural frequency of total mass of the rockfill vibration system for small additive mass. For a big stiffness connection TDF-mass-spring-damping model, the theoretical computed received signal spectrum only has one peak near the natural frequency of total mass of the rockfill vibration system.The mass-spring-damping model can be used to explain the phenomenon that the received signal frequency varies with source frequency and rainwater. It can also be used to explain the down-to-up type and decreasing type of abnormal mass-frequency curve in the additive mass testing. The TDF-mass-spring-damping model can be used to explain the phenomenon that the received signal frequency varies with the offset and the contacting area of the additive mass. It can also be used to explain the small-intercept type of abnormal mass-frequency curve and double-peak spectrum of the received signal.