落石冲击下压实度对红层泥岩垫层缓冲机制影响研究

Influence of compaction degree on the buffering mechanism of red mudstone cushion under rockfall impact

西南地区山地众多,落石频发,红层地质分布广泛,工程上红层隧道区可用红层泥岩作为棚洞垫层材料以抵抗落石冲击。但红层泥岩为细粒黏性缓冲材料,与无黏性粗粒材料不同,压实度对其缓冲机制影响仍不明晰,为此开展落石冲击红层泥岩垫层材料模型试验及数值模拟研究。通过搭建室内落石冲击试验平台,进行红层泥岩材料不同压实度下的模型冲击试验,监测落石及垫层内加速度大小,研究压实度对垫层缓冲效果的影响规律,并借助离散元(PFC)与有限差分(FLAC)耦合方法对模型试验进行了对比验证,揭示了压实度对红层泥岩垫层缓冲机制的影响规律。研究结果表明:1)不同压实度中(K=0.9、0.8、0.7),压实度越低,落石冲击力越小,K=0.7的冲击力较K=0.9减少54.08%;2)垫层内峰值加速度随水平距离增加呈指数衰减,且压实度越小,垫层加速度衰减越显著;3)重复冲击使垫层缓冲效果存在劣化现象,导致落石冲击力及垫层内加速度增加,工程中需加以注意;4)压实度低时,力链越不稳定,力链因易破坏重组而无法提供长期、稳定阻力,致使落石冲击力降低;同时垫层松散使冲击波传播时间增加,垫层吸收更多能量;因此,压实度低时垫层具有更好的缓冲效果。研究结果可为西南地区红层泥岩垫层材料的应用提供借鉴。

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.