甘肃岷县浑水沟泥包砾成因机制及其灾害意义

2020年8月, 甘东南地区持续降雨且伴随多个强降雨过程, 岷县梅川镇浑水沟暴发泥石流, 左岸方家山滑坡失稳下滑, 严重威胁沟口成兰铁路安全。基于野外调查、遥感解译和室内测试结果, 分析泥包砾的形态结构、矿物组成以及堆积特征, 研究泥包砾形成的地质环境和机制, 探讨泥包砾的灾害意义。研究结果表明: 泥包砾分布于浑水沟流通区下游及堆积区, 呈球形且具多层结构, 由石英、方解石、黏土矿物等组成, 其形成主要受控于流域第四系黄土和古近系泥岩中的黏土矿物, 而较缓的沟道、岸坡黄土滑坡和崩塌的发育以及适宜的水动力条件, 促进了泥包砾的形成和自生加大; 泥石流冲击力随着泥包砾粒径的增大而增大, 再起动所需临界泥石流流速相较于块石较小; 泥包砾是古近系泥岩与泥石流共同作用的结果, 具有加剧泥石流危害的作用, 因此亟需治理浑水沟泥石流以保证成兰铁路的安全运营。 

Genesis mechanism and disaster-causing significance of the mud-coated gravel in the Hunshui gully,Min County,Gansu Province

In August 2020, due to the continuous rainfall in southeast Gansu, especially the heavy rainfall processes, debris flows broke out in the Hunshui gully. The left bank of the Fangjiashan landslide was destabilized and sliding, seriously threatening the safety of the Chengdu-Lanzhou Railway at the mouth of the gully. Based on the field investigation results, remote sensing interpretation, and laboratory tests, we studied the mud-coated gravel's morphology, mineral composition, and accumulation characteristics, analyzed the geological environment and mechanism for its formation and discussed its disaster-causing significance. The results show that mud-coated gravels are distributed in the lower reaches of the circulation area and the accumulation area. It presents a spherical and multi-layered structure composed of quartz, calcite, clay minerals, etc. Its formation is mainly controlled by the clay minerals in the Quaternary loess and Paleogene mudstone in the basin. The slow-moving gullies, landslides, and collapses developed on the bank slope as well as appropriate hydrodynamic conditions, promoted the formation and autogenesis of the mud-coated gravel. The impact force of debris flow increases with the particle size of mud-coated gravel, and the critical velocity required for restarting a debris flow is smaller than that of block rock. Mud-coated gravel is the result of the joint action of the Paleogene mudstone and debris flow, and it can aggravate the debris flow hazard. Therefore, it is urgent to control the debris flows in the Hunshui gully to ensure the safe operation of the Chengdu-Lanzhou Railway.