汶川地震灾区松散土体岩土特性研究

汶川地震灾区地震诱发了巨量的松散固体物质,呈非均质、欠固结、空间结构复杂,岩土特性具有特殊性。以都江堰虹口深溪村锅圈岩沟为例,在地震诱发滑坡遥感解译的基础上,通过原位渗透、直剪和三轴实验,系统研究了汶川地震灾区松散土体的岩土力学特性。地震诱发的滑坡堆积体主要分布在源区坡度≥30°的区域,平均堆积厚度约为15 m,储量达20×10~4m~3。渗透实验表明,松散土体初始和稳定入渗率均较大,主要与其大空隙、大裂隙、欠固结等特性有关;此外存在内部侵蚀、细颗粒迁移现象。直剪实验中松散土体黏聚力和内摩擦角随黏粒含量增加而增加、但随含水率呈先增大后减小的趋势。三轴实验结果表明,应力随应变的增加而增加;且在不同含水率条件下增长速率不同。围压越小,剪应力达到峰值引起的土体应变越小,土体越易破坏。孔隙水压力随应力和应变的增加而增加,土体破坏后,孔隙水压迅速降低,之后随着应力和应变的增大,孔隙水压力呈现回升。研究成果可以为锅圈岩沟泥石流致灾机理、预警阈值、防治工程关键参数设计等提供科学依据。

Study on the Geotechnical Mechanical Characteristics of Loose Materials in the Wenchuan Earthquake-hit Areas

The earthquake induced a huge amount of loose materials in the meizoseismal areas of Wenchuan earthquake which was heterogeneous, the spatial structure was complicated and the geotechnical characteristics were particular. The Guo Juanyan gully in Du Jiangyan city is selected as the study area, based on the remote sensing interpretation of the landslide induced by the earthquake, the geotechnical mechanical characteristics of loose materials are explored by in situ permeability, direct shear, triaxial experiments. The landslide deposits induced by the earthquake is mainly distributed in the debris flow source area where the slope is larger than 30°, the average thickness is approximately 15 m and the accumulated reserve amounts to 20×104m3. The field in situ permeability tests show that initial and stable infiltration rates of loose materials are large which related to the large pores, large cracks and under-consolidated characteristics, as well as exists the transport and erosion of fine particles inside the soil. In the direct shear experiments, the cohesive force and internal friction angle increase with the clay content, but have the trend of first increases and then decreases with the moisture content. The triaxial experiments show the stress increases with the strain and the growth rate is various in different moisture content conditions, the smaller confining pressure and the smaller the peak shear stress caused by the strain and the soil is more easy to damage, pore water pressure increases with the stress and strain, when soil damaged, pore water pressure reduces rapidly, and the pore water pressure increases with the continuous increase of stress and strain. The study results can provide guide for debris flow disaster-causing mechanism, early warning threshold and key parameters of prevention engineering.