强震区侵蚀-溃决型泥石流的动力特性定量分析

QUANTITATIVE ANALYSIS OF DYNAMIC FEATURES FOR ENTRAINMENT-OUTBURST-INDUCED CATASTROPHIC DEBRIS FLOWS IN WENCHUAN EARTHQUAKE AREA

强震作用导致流域内松散物源、微地貌及水文环境发生剧烈变化,致使强震区泥石流的形成机制和活动规律区别于普通泥石流。从启动判别、沟床侵蚀和溃决放大效应等3个方面入手,利用物理模型和数值模拟,定量分析了强震区泥石流启动-流通-堆积全过程的动力特性。结合案例验证了强震侵蚀-溃决型泥石流的力学机制。分析表明,泥石流沟床侵蚀是外部应力增加、内部强度衰减和松散物质基础3种机制的综合结果,沟道堰塞体溃决导致泥石流流量被瞬间放大,进而反馈到侵蚀机制中,导致泥石流规模剧增。红椿沟8·14泥石流案例验算显示,H02、H03堰塞体溃决导致泥石流流量放大至800.80m^3·s^(-1),沟床侵蚀物质总量达34.72×10~4m^3,约占总规模的50%。

Many causative factors have changed acutely after the Wenchuan earthquake. They included the loose material, micro-topography and hydrological environment. Hence, the earthquake-induced debris flows are different from the general one. A whole debris flow process mechanism is developed and analyzed quantitatively using initiation discrimination model, bed-matrix erosion model and outburst-discharge enlargement model. It includes the initiation, transition and deposition phases. Moreover, the failure mechanism of the erosion-outburst-induced debris flow is illustrated clearly with an example. The result indicates that bed-matrix entrainment mechanism is the comprehensive outcome of the stress enlargement, strength degradation and material basis. The landslide damoutburst-induced discharge enlargement and the above-mentioned erosion mechanism are contributed to the large- scale debris flow. The case study of Hong c h u n catchment indicates that debris-flow discharge increases to 800. 80m3 .s- 1 due to H 02-03 landslide-dam outburst, and the entrainment-induced solid materials are half of the total magnitude, about 34. 72×104m 3.