Influence of compaction degree on the buffering mechanism of red mudstone cushion under rockfall impact
Rockfall hazards frequently occur in southwest China due to the numerous mountains.Because the red bed is widely distributed in the southwest,the red mudstone can be used as a buffer layer of rock shed to resist rockfall.However,the red mudstone is a fine-grained viscous material,which is different from the commonly used non-cohesive coarse-grained materials in properties,so the influence of compaction degree on the buffering mechanism is still unclear.Then,the model test and numerical simulation of the red mudstone buffer layer were carried out.By the test platform,model impact tests were conducted on red mudstone materials under different compaction degrees,monitoring the acceleration of the rockfall and the cushion layer and studying the influence of the compaction degree on the cushioning effect of the cushion layer.The model tests were compared and validated by coupling the discrete element method(DEM,PFC)and the finite difference method(FDM,FLAC).It could reveal the buffering mechanism of the red mudstone cushion.The results indicate that the lower the degree of compaction,the smaller the rockfall impact force among the three compaction degrees(K=0.9,0.8,and 0.7),and the impact force in the 0.7 compaction degree is reduced by 54.08%compared with the 0.9 compaction degree.The peak acceleration at the buffer layer decreases exponentially with the increase in horizontal distance,and the attenuation of acceleration is more significant with the decrease in compaction degree.The repeated rockfall impact can lead to the cushioning deterioration of the buffer layer,increasing rockfall impact force and acceleration in the buffer layer.It is necessary to pay attention to the deterioration influence of the buffer layer on the protection effect in engineering,which is caused by the repeated rockfall impacts.There are two reasons why the lower the degree of compaction,the better the cushioning effect.One reason is that when the compaction degree is low,the smaller the number of particles in series,the more unstable the force chain,and the force chain is prone to destruction by rockfall impact;therefore,the impact force is low.The other reason is that the loose cushion causes the shock wave propagation time to increase,so the dissipated energy increases.The results can provide a reference for the application of the red mudstone as the buffer layer in the southwest region of China.
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