Exprimental Study On Damping Characteristic And Mechanism Of Sandstone And Granite

It's the significant parameters, which are damping ratio and damping coefficient of rock,for the designing and safety evaluating of anti-seismic engineering. But there is not test procedures about rock damping parameters. Cyclic loading tests and external vibration test are carried out about sandstone and granite in this paper. The rules are studied that damping parameters and dynamic elastic modulus changes with frequency, strain amplitude and stress level, to do some basic researching work for the rock dynamic test procedures. The main results follow:(1) Based on the visco-elastic theory, the formula calculating damping ratio of the rock is put forward under cyclic load from the perspective of energy conservation.(2) Damping ratio decreases with increased frequency on the high frequency range and damping ratio increases with the frequency on the low frequency range. It is speculated that there exists the peak when the damping ratio changes with frequency. When frequency is less than the peak, the damping ratio increases with the frequency and when frequency is greater than the peak,the damping ratio decreases with increasing frequency. The law about damping coefficient is opposite damping ratio. The physical model is used to determine the peak, which are 2.23 Hz and 4.08 Hz.(3) Under the condition of high frequency, damping ratio and the damping coefficient increases with the increasing of strain amplitude, the damping ratio can be divided into three stages with strain amplitude changing, which are early growth stage, stable stage and tardy growth stage. The stage of damping coefficient is not obvious. Under the condition of low frequency,damping ratio and the damping coefficient increases with the strain amplitude increasing.(4) Damping ratio decreases with the increasing of stress level and the damping coefficient increases with the increasing of stress level. With stress level increasing, it makes soft gypsum compacting and granite microcracks compacting and consumption of energy reducing and cohesive mechanism start hardly so that the damping ratio decreases and the damping coefficient increases.(5) The dynamic elastic modulus increases with the increasing of frequency and stress level,and decreases with strain amplitude increasing.(6) The law is consistent that is damping parameters and dynamic elastic modulus of sandstone and granite with frequency, strain amplitude and stress level changing. But damping ratio is sensitive to the stress level about sandstone and damping parameters and dynamic elastic modulus is sensitive to strain amplitude about granite. It reflects the influence of damping parameters and dynamic elastic modulus because of the difference between formation and structure about clastic rocks and crystalline rock.