地震扰动的泥石流源区砾石土强度恢复动态过程实验研究

Wenchuan Earthquake, Lushan Earthquake and Ludian Earthquake happened from 2008 to 2014 in the southeastern margin of Tibetan Plateau. A substantial rise in debris flow was apparent following the Wenchuan Earthquake. The critical rainfall intensity, amount of the loose source, magnitude and frequency of post-seismic debris flow has become research hotspots. But it is still uncertain that how long the earthquake would affect on triggering debris flows due to the lack of strength recovery mechanism of loose gravelly soil during the re-consolidation process. The applicant has already collected many post-seismic data of the physical and mechanical properties of gravelly soil. In this study, the researcher first will choose two sites of loose landslides located in debris flow gullies of the seismic intensity level 8 in Wenchuan Earthquake, Lushan Earthquake and Ludian Earthquake. The gravelly soils will have similar physical and mechanical properties when their grain compositions are similar. The porosity, grain composition, filtration coefficient, shear strength and soil anti-scourability will be obtained through field experiments and laboratory tests every year from 2016 to 2018. So the physical and mechanical properties of the similar loose gravelly soils will be derived for time that is 2-4 years after Ludian Earthquake, 3-5 years after Lushan Earthquake and 8-10 years after Wenchuan Earthquake respectively. The change mechanism of physical and mechanical properties of gravelly soils will be obtained during the consolidation process, as well as the control effect of physical properties on soil strength. How long it will take the properties of gravelly soil to restore to the level before the earthquake can be estimated using the “strength-time post seismic” function. The results will guide the recovery and reconstruction activity in the earthquake stricken area, and provide theoretical and experimental evidence for post seismic debris flow research.

青藏高原东南缘2008年至2014年先后发生了汶川地震、芦山地震和鲁甸地震。地震后物源增多泥石流高发，泥石流活跃期成为研究热点。目前对松散物源在固结过程中强度恢复规律的研究较少，对震后泥石流活跃期的预测缺乏机理性依据。申请者在前期工作中收集到较多的震后砾石土物理力学数据。本课题拟在鲁甸地震、芦山地震和汶川地震的Ⅷ度烈区，分别选取1处泥石流沟内的土质滑坡松散堆积物进行实验，逐年测定扰动砾石土的孔隙比、颗粒级配、渗透系数、抗剪强度、抗冲蚀系数，获得级配相近的土体在鲁甸地震后第2-4年、芦山地震后第3-5年和汶川地震后第8-10年的物理力学指标。通过数据拟合出松散砾石土物理力学指标在固结过程中的动态变化规律，研究物理性质对力学参数的控制机制，进而得出“土体强度-震后时间”函数来预判砾石土性质恢复到震前水平所需时长。本课题对灾区恢复重建具有重要的实际意义，并将为震后泥石流研究提供理论和实验依据。

青藏高原东南缘2008年至2014年先后发生了汶川地震、芦山地震和鲁甸地震。地震后物源增多泥石流高发，泥石流活跃期成为研究热点。目前对松散物源在固结过程中强度恢复规律的研究较少，对震后泥石流活跃期的预测缺乏机理性依据。本课题在鲁甸地震、芦山地震和汶川地震的Ⅷ度烈区，分别选取1处泥石流沟内的土质滑坡松散堆积物进行实验，逐年测定扰动砾石土的孔隙比、颗粒级配、抗剪强度，获得级配相近的土体在鲁甸地震后第2-4年、芦山地震后第3-5年和汶川地震后第8-10年的物理力学指标。随着震后松散土体的固结，土体的颗粒级配发生变化，细颗粒流失；土体的干密度增大，孔隙比降低。土体的内摩擦角φ与粘聚力c均随固结增长，土体的抗剪强度也随之增大。泥石流物源减少，启动难度增加。干密度对土体的抗剪强度具有较大的影响，随着干密度的增加，土体的内粘聚力c和内摩擦角φ均增加。这种变化符合指数函数。当干密度恢复到1.7g/cm3时，土体的抗剪强度可能恢复到震前未扰动的水平。以土体强度恢复的速率来看，震后泥石流的活跃周期约为25年。由于土体固结和剥蚀导致松散物源变少，二者满足任何一种条件，泥石流既有高频率转为中低频率，活跃期结束。本课题对灾区恢复重建具有重要的实际意义，并将为震后泥石流研究提供理论和实验依据。.