冻融作用下岩石孔隙扩展演化特征研究

Study on characteristics of pore propagation and evolution in freeze-thawed rock

为探究岩石在冻融循环作用下的裂隙演化特征,利用CT扫描技术,获取不同冻融次数岩石的三维图像,并通过孔隙网络模型参数进行定量表征,研究岩石随冻融循环的裂隙形貌演化过程,以及孔隙结构随冻融次数的变化。结果表明:完整岩石冻融微裂隙主要集中在岩石外围,呈环形片状;而裂隙岩石冻融产生的微裂隙主要存在于预制裂隙周围和岩桥区域,且分布范围更广。冻融循环作用后,完整与裂隙岩石的PNM中各类孔隙变化特征不一。前者孔隙数量减少,小孔占比逐渐减小,中大孔占比增大,孔隙分布位置较为均匀;后者孔隙数量增加,但中孔占比减小,大孔占比迅速增大且主要集中在岩心上下端面。在冻融过程中,岩石各类孔喉结构主要参数均呈增长趋势,裂隙岩石孔喉网络发育更剧烈,冻融结束后其最大喉道半径增长幅度约为完整岩石的2倍。在冻融前期,冻融循环作用主要促进岩石孔隙相互连通,后期主要表现为孔喉加速扩张,且裂隙岩石孔隙率增长速率均大于完整岩石。研究结果可为寒区岩体破坏机理及灾害防治提供参考。

In order to explore the fracture evolution characteristics of rocks under freeze-thaw cycles,CT scan⁃ning technology was used to obtain three-dimensional images of rocks with different freeze-thaw cycles,and quantitative characterization was carried out by pore network model parameters to study the evolution process of rock fracture morphology with freeze-thaw cycles and the change of pore structure with freeze-thaw cycles.The results show that:the complete rock freeze-thaw microfracture are mainly concentrated in the periphery of the rock,showing annular flake;the microfracture generated by freeze-thaw action of fractured rock mainly exist around prefabricated cracks and rock bridge areas,and the distribution range is wider.After the freeze-thaw cy⁃cles,the characteristics of various pores in PNM of intact and fractured rocks are different:the number of pores in the former decreases,the proportion of small pores decreases gradually,the proportion of medium and large pores increases,and the pore location distribution is uniform;the number of pores in the latter increases,but the proportion of mesopores decreases,and the proportion of macropores increases rapidly and is mainly concen⁃trated in the upper and lower end faces of the core.During the freeze-thaw process,the main parameters of rock pore structure show an increasing trend,and the pore throat network of fractured rock is more intense,At the end of freeze-thaw process,the maximum throat radius increases by about twice that of intact rock.In the early stage of freeze-thaw process,the main effect of freeze-thaw cycles is to promote the connectivity of rock pores,and in the later stage,the main performance is the accelerated expansion of pore throats,and the porosity growth rate of fractured rock is greater than that of intact rock.The research results can provide reference for rock failure mechanism and disaster prevention in cold region.