砂岩疲劳特性的超声波速法试验研究

EXPERIMENTAL RESEARCH ON FATIGUE CHARACTERISTICS OF SANDSTONE USING ULTRASONIC WAVE VELOCITY METHOD

岩石地基或边坡在长期动荷载的作用下将产生疲劳损伤,岩石和混凝土材料都属于脆性材料,在疲劳损伤衰减规律上有很多相似的地方,但其变形及损伤特征也存在一些实质性的差别;另外,岩石材料由于其风化程度不同或所含成分及含量不同,其疲劳损伤演化进程也都不相同。对砂岩在循环荷载作用下的疲劳损伤特性进行实时超声波速的跟踪研究,研究结果表明:穿透砂岩试样的横向超声波速随着荷载的循环次数发生明显的三阶段衰减,即初始迅速衰减、稳定衰减与临近破坏的急速衰减三个阶段,它们分别约占疲劳寿命的10%,85%和5%,相比混凝土材料而言,到达第2阶段末波速的衰减幅度较小,且第3阶段经历的循环次数相比疲劳寿命而言极短;基于超声波速定义损伤变量,建立砂岩疲劳累积损伤的演化方程;最后对不同类型的砂岩疲劳特性进行对比分析,结果表明,含砾砂岩与粉砂岩疲劳过程中纵波波速都发生了明显的衰减现象,衰减速率前者高于后者;弱风化的砂岩疲劳损伤过程中纵波的衰减现象比强烈风化的砂岩明显。相关成果可为类似岩质地基、边坡的疲劳健康诊断提供理论依据。

Fatigue damage will be generated in rock foundation or slope under long-term dynamic loads. The rock and concrete belong to brittle materials. The attenuation laws for fatigue damage of rock and concrete are similar to certain extent, but there are some essential differences in deformation and damage of rock and concrete. Furthermore, the evolutionary processes for the fatigue damage of rock and concrete are different due to the differences of weathering degree, components and their contents. The histories of real-time ultrasonic wave velocity variations of sandstone specimen during cyclic compressive loading tests are researched. Results show that the attenuation of the transverse ultrasonic wave velocity follows inverse S-shaped line, which can be divided into three phases： initial fast attenuation phase, steady attenuation phase and rapid attenuation close to failure. The durations of the three phases are about 10%, 85% and 5% of fatigue life, respectively. Comparing with concrete materials, the attenuation amplitude of the ultrasonic wave velocity at the end of the second stage is little, and the cyclic times in the third phase are less in particular compared with fatigue life. A damage variable is defined based on the transverse ultrasonic wave velocity and used to describe the growth law of sandstones fatigue damage. The fatigue tests on the different sandstones indicate that the transverse ultrasonic wave velocities of the sandstone containing gravel and siltstone all attenuate obviously. The attenuation speed rates of the transverse ultrasonic wave velocity of the slightly weathered sandstone are greater evidently than that of the strongly weathered sandstone during the fatigue damage. The results may offer theoretical references for the fatigue health diagnosis of similar rock foundation and slope.