Experimental Study On Backfill Strength Testing By Ultrasound Guided Wave And Filling Effect

The filling effect and strength of the backfill are the most important two indexes of filling slurry during the process of downward slicing cut-and-fill.The strength and the filling effect of the filling body directly restrict the progress of the mining and affect the security and stability of the stope.The characteristics of convenience and non-destruction make ultrasonic guided wave a new way to detect the strength of the backfill.The high fluidity of foam concrete makes it a new kind of suitable promising material to fill the gob area.The acoustic parameters of the artificial roof’s strength are studied in this thesis based on the indoor test and under the guidance of ultrasonic guided wave theory.The type and addition of the foam agent were optimized.And the experiment is conducted to explore the filling effect of the foam filling slurry at the same time.Conclusions can be draw as follows.(1)The acoustic parameters of the wave-guiding rod and backfill-reinforcement system were studied by the way of experimental simulation.Expe rimental results demonstrate that the wave in different frequencies have different wave velocities and attenuation characteristics.There is an optimum excitation signal which makes the clearest reflection and makes the relationships of backfill strength between wave velocities and attenuation obvious.(2)The propagation laws of longitudinal guided waves which propagate in the backfill-reinforcement system were analyzed at the specific frequencies.The results show that the wave velocities and attenuation o f the backfill-reinforcement system are directly related to the backfill strength.With the addition of filling body strength,the wave velocity of longitudinal guided waves which propagate in the backfill-reinforcement system shows an exponentially decreasing trend,while the attenuation shows an exponentially increasing trend.The fitting equation between wave velocities,attenuations and backfill strength were obtained and it provides reference for the stope artificial roof’s testing.(3)The stability of two common commercially available kinds of foaming agent was examinated.The dilution ratio,the foaming multiple and the settlement of the two kinds of foaming agent were tested.The test result shows that the foaming agent B is more stable than foaming agent A.And then,fluidity of the foam filling slurry and the general one were tested by the Glue Sand fluidity determinator.The effects of addition of foam agent and concentration of the filling slurry to the fluidity of filling slurry were examinated.The results show that foam agent makes contribution to the filling slurry fluidity.And the more foam agent the better fluidness.When the addition of foam agent comes to 1.5%,the concentration can be increased from 75% to 79% while the change of filling slurry’s fluidness and strength controlled in an acceptable range.(4)The slicing and filling model was built;the experiment was conducted to explore the filling effect of the slurry.The result shows that the tangent angle which between the filling slurry surface and the horizontal decrease from 0.0064 to 0.0029.And the conclusion can be draw that a right amount of foam agent can improve the filling effect.