地震作用下泥石流源区砾石土体强度的衰减实验

泥石流源区广泛分布着砾石土，从野外观察分析和理论计算可知，泥石流源区产流是由于土体强度降低的结果。经已往研究发现，地震作用产生的振动经常导致泥石流的发生，世界上许多地震活动带，同时也是泥石流活动带，这种分布的关联性使我们有理由推断地震的作用会使泥石流源区的砾石土体强度降低，导致土源大量激发，促进泥石流的暴发。基于这样的分析，利用土动三轴剪力仪，取泥石流源区的砾石土作为实验对象，以砾石土的含水量，土体的深度(围压)，土体的破坏标准和地震的震级(振动周次)为变量，取土体的粘聚力c、有效粘聚力c’、土体的摩擦角φ和有效摩擦角φ’作为土体强度衡量的指标进行实验。实验结果表明在地震作用下，土体的c值和c’值，随含水量的增加先是增加而后降低，其最大值时饱和度达84％左右。随着振动强度的增加，土体的粘聚力c、有效粘聚力c’逐渐减小，高含水土体的c’值在足够的振动强度条件下可以降为0。随着含水量的增加，φ和φ’值逐渐降低，但φ’值仅当饱和土体在强烈振动作用下会降低到0。一般地，土体的内摩擦角φ,总是随着振动周次的增加而减低，但减低的幅度较小：而有效内摩擦角φ’值的变化相对较复杂，在低地震强度(振动周次20周以下)的作用下，其值随着振动周次(震级)的增加有较小的降低。而在振动周次达到20周以上时，含水量与地震作用对φ’变化的联合影响作用显著，对于低饱和度的土体，当振动周次大于20周以后φ’值逐渐升高。但对于饱和土体，当振动周次达到一定的数值(50周)以后土体的φ’值迅速降低，直至为0。对于接近饱和的土体(本实验的饱和度为92％)，其φ’值随振动周次的升高变化不稳定，是受破坏标准等因素的影响或升高或降低。

TESTING STUDY ON STRENGTH REDUCTION OF GRAVELLY SOIL IN TRIGGERING AREA OF DEBRIS FLOW UNDER EARTHQUAKE

There is widely distributed gravelly soil in triggering area of debris flow. From the observation,analysis and calculation,it is found that triggering of debris flow results from soil strength reduction. In fact,debris flow areas are often located in earthquake belt. The distribution relation between debris flow and earthquake makes us to suggest that earthquake lead to the strength reduction of gravelly soil and make triggering of debris flow. On the basis of the suggestion,triaxial shear equipment is used to make testing study for the gravelly soil in the triggering area of debris flow. The variables are water content,soil depth or confining pressure,the destroy criterion and earthquake intensity or vibration times. The cohesion and friction are chosen to measure the strength of soil. As a result,it is found that the cohesion increases first and then drops with the increment of water content,and the max value appears when the saturation degree gets up to 84%. With the increment of vibration times the cohesion decreases. For the sample with high water content,the cohesion can drop to zero with enough vibration times. As usual the friction angle decreases with increment of water content and can drop to zero only for the nearly saturated sample. The friction angle always decreases slightly with increment of vibration time. The friction angle changes with vibration times unstably. When the vibration times are lower than 20 and earthquake intensity is under 7.5 grade,the friction angle decreases slightly with the increment of vibration times,but when the vibration times are higher than 20,the friction angle of low saturated sample increases. For the high saturated sample when the vibration times arrive 50 times,the friction angle drops to zero. For the nearly saturated sample with saturated degree of 92%,the friction angle increases or decreases unstably,which is dependent on the other factors. In conclusion,the tests show that earthquake may reduce the soil strength and under some special cases it may leads soil to be liquefied. Therefore earthquake makes an important role in triggering of debris flow.