冻融循环作用下花岗岩损伤的宏微观尺度研究

A study of granite damage in the macro and microscopic scales under freezing-thawing cycles

岩石的冻融破坏是高原地区工程建设中不可忽视的自然灾害之一。冻融作用下岩石矿物的不均匀收缩和孔隙水冰相变导致岩石内部孔隙扩展造成的岩石损伤,对工程稳定具有极大的威胁。为了研究冻融循环下花岗岩的损伤规律,以川藏铁路沿线理塘县毛娅坝盆地乱石包高位远程滑坡为研究对象,针对滑带上花岗岩,通过冻融循环试验模拟高原寒冷的气候环境变化,对冻融循环后的花岗岩进行单轴压缩、电阻率和电镜扫描(SEM)试验,从宏微观多尺度综合探讨冻融循环作用对花岗岩损伤劣化的规律。从试验研究中发现:(1)冻融循环过程中花岗岩质量变化呈先减小后增大再减小的趋势,这与冻融循环引起试样表面颗粒掉落和内部裂隙扩展双重作用有关;(2)随着冻融循环次数增大,花岗岩的单轴抗压强度、弹性模量和黏聚力皆呈非线性衰减趋势,而内摩擦角仅在平均值附近微小波动;(3)当冻融循环次数增加时,由宏微观试验所确定的冻融损伤因子和冻融荷载耦合作用下的总损伤因子都呈增长趋势,说明冻融次数对于花岗岩的抗压强度影响较大。研究结果可为高原地区工程建设中衡量花岗岩冻融强度特性提供参考依据。

Freezing-thawing damage to rocks is one of the natural disasters that cannot be ignored in engineering construction in plateau regions.Under the action of freezing and thawing,uneven shrinkage of rock minerals and freezing of pore water lead to rock damage caused by pore expansion in rocks,which poses a great threat to engineering stability.In recent years,many researchers have conducted a lot of researches on rock properties under freezing-thawing conditions through theoretical and experimental methods.However,most of the previous studies focused mainly on sedimentary rocks such as sandstones,and very few studies were involved in freezing-thawing of granites in highland alpine regions.In this study,the granite on the landslide area was subjected to uniaxial compression,resistivity and electron microscope scanning(SEM)tests to discuss the damage of granite after multiple freezing-thawing cycles by simulating the cold climate changes on the plateau under freezing-thawing cycles.From the macro and micro multi-scale studies it can be found that:(1)the change of granite quality during freezing-thawing cycles tends to decrease,then increase and finally decrease,which is related to the dual effect of particle drop on the surface of the specimen and the expansion of internal fissures caused by freezing-thawing cycles.(2)As the freezing-thawing cycles increase,the uniaxial compressive strength,elastic modulus and cohesion of granite all show a non-linear decay,while the internal friction angle only fluctuates slightly around the mean value.(3)When the number of freezing-thawing cycles increases,both the freezing-thawing damage factor and the total damage factor under the coupling of freezing-thawing and load increase,which indicates that the number of freezing-thawing cycles has a greater influence on the strength of granite.The results of the study can provide a reference basis for measuring the freezing-thawing strength characteristics of granite in engineering construction in the plateau region.