余震作用下堰塞坝体破坏及溃决过程大型振动台试验研究

LARGE SCALE SHAKING TABLE TESTS ON FAILURE AND BREACH PROCESS OF LANDSLIDE DAMS UNDER AFTERSHOCKS

山区特大地震往往导致大量堰塞湖,例如2008年汶川地震形成了至少257个堰塞湖,并且主震后发生了大量余震,这些余震可能会影响堰塞坝体的安全状态。通过大型振动台模型试验,研究了余震及库水耦合作用下堰塞坝体的破坏及溃决机理和过程。共进行了两组不同材料的振动台模型试验,分别模拟含黏粒较多且颗粒较小(坝体Ⅰ)和基本不含黏粒且颗粒较大(坝体Ⅱ)的两种坝体。在不同水位条件下进行振动台试验。研究成果表明:(1)地震和库水耦合作用下堰塞坝体的主要溃决方式是漫顶溢流,主要溃决过程为地震力使松散的堰塞坝体发生沉陷,库水渗入使沉陷加剧,最终水位上升漫过坝顶发生溢流冲蚀破坏。(2)地震一般不会直接引起堰塞坝体的破坏。地震力对坝体稳定性的主要影响是使坝体发生沉陷变形。在地震和库水耦合作用下,坝体沉陷比单一因素作用下更为剧烈,因此地震作用会使漫顶溢流提前发生。(3)地震和库水耦合作用下坝体Ⅰ沉陷量大于坝体Ⅱ,说明现实中由大粒径岩土体组成的堰塞坝体具有更好的稳定性。

Great earthquakes in mountainous areas usually cause large numbers of landslide dams. For example, at least 257 landslide dams formed during Wenchuan Earthquake in 2008. Lots of aftershocks occun＇ed after the major shock, which might influence the safety of these landslide dams. This paper presents the studies of large-scale shaking table tests on the breach mechanism and process of landslide dams under the coupled effect of aftershocks and waver. Two groups of shaking table tests were conducted to simulate the behaviors of two types of landslide dams ： one with cohesive materials and small particle size（ Dam I） and the other without cohesive materials and with large particle size （Dam Ⅱ ）. The shaking table tests were conducted under different water depths. The following conclusions are drawn： （1）The main failure mode of landslide darns under the coupled effect of aftershoeks and water is overtopping. The breach process is that： seismic force causes the subsidence of the loose landslide dams; seepage of water enlarges the subsidence value; finally, water level rises and overtops the darn crest and the darn fails by water erosion. （2）Earthquakes may not directly cause the failure of landslide dams. The main influence of earthquakes on landslide dams is causing subsidence of dam crest. The subsidence value under the coupled effect of aftershocks and water is larger than that under the effect of either factor. The subsidence induced by the earthquakes may bring forward the overtopping of landslide darns. （ 3 ） The subsidence of Darn I is larger than that of Dam Ⅱ under the coupled effect of earthquakes and waver, which shows that landslide darns composed of rock and soils with larger particle size are more stable.