Experiment Research On Electrical Frequency Characteristic Of Mable Stress

In the testing of the rock structure, the stress testing of rock is very difficult because of the complicate rock fracturing, the stress testing method of the rock structure have to use others field's knowledge. In recent years, there are some useful methods of the stress testing of rock but some limitation and shortage still existed to some extent. This paper choose marble as research object, then use electrical knowledge of rock to study the stress and electrical frequency effect of marble.The author of this paper has built the suitable experimental system for complete the experiment of electrical frequency characteristic of marble stress. The experimental system includes loading system and circuit system. The loading system is used for loading and measuring stress and strain value of marble specimen. The circuit system is used for offering AC signal of different frequency and acquiring the electrical resistance of marble specimen. At first, the stress, strain and electrical resistance experiment of marble specimen have finished under condition of invariable frequency of input AC signal. By analysis on the experimental data of two kinds of marble specimens which have different mineral compositions, the author has researched the change relation of electrical resistance with marble stress. On the basis of the stress, strain and electrical resistance experiments of marble, the author has done the experiment of electrical frequency characteristic of marble stress. When the pressure increases 5kN, the author stops loading and sustain loading until acquire the electrical spectrum line by changing the frequency of input AC signal. Then the experiment of loading-on and loading-off of marble specimen were carried out. When the pressure increases 10kN, the author starts unloading. The author has acquired electrical spectrum lines by changing frequency of input AC signal in suitable range when marble specimen stress has unloaded completely. The experiment is used for researching on electrical frequency memory characteristic of marble stress. By results we can discover several conclusions. If the frequency of input AC signal is invariable, the electrical resistance of marble specimen is increasing with the increase of stress. If the stress of rock specimen is invariable, the electrical resistance is changing with the change of the frequency.The electrical resistance of marble specimen can become electrical spectrum line by changing the frequency of input AC signal. With the increase of the stress, the electrical spectrum line moves up gradually. A piece of the spectrum line corresponds to a stress level. The stress electrical spectrum lines are obtained composed by several pieces of spectrum lines of different stress levels. According on analysis on the electrical spectrum lines, the author has studied the change relation of characteristic of electrical spectrum line with stress, then fitted mathematical formula to reflect electrical frequency characteristic of marble stress. The electrical spectrum line of rock specimen loaded off completely is different from the electrical spectrum line of initial zero stress. With the increase of the stress which had loaded on marble specimen, the electrical spectrum line moves up gradually, this phenomenon can show that the electrical memory characteristic of marble stress exists. The author has studied the memory characteristic of marble stress by using correlation between the electrical spectrum lines. These conclusions will be used for detection of rock stress and researching on inner structure of rock.