Experimental Study for the Allocation of Ground-Sills Downstream of Check dams

The main purpose of this study is to understand the stabilizing effect of ground-sills on the riverbed through a series of flume model experiments.From results,although check dams have the ability to control upstream sediment transport,the mass energy produced by the free fall of the overtopping discharge still causes strong local scour downstream of the structure,and this Scour lcads to the instability of the check dam.Therefore,this study conducted model experiments on various types of serial ground-sills to determine the appropriate spacing to best protect the downstream bed.Based on the observations and analysis of channel geomorphology and sedimentation,this study concluded the following results:1)Serial ground-sills reduces the sediment transport ability perfectly,especially under a mild channel gradient equipped with 2-4 times the average channel width interval.But for steep slopes,it is suggested that the proper spacing should be shortened to 1-2 times the average channel width.2)Ground-sills can effectively protect the streambed from scouring under a suitable equipped condition and the concepts of guiding scour and riverbed inertia were used in the analysis of optimal ground-sill spacing.     

断裂带同震温度负异常机制分析

断裂带同震温度响应,可在震后钻孔测温中获得并识别,为发震断层摩擦特性与发震机制等基础研究提供了非常独特的思路和有效手段.集集、汶川及日本东北大地震后,实施了台湾车笼埔断层钻探项目(TCDP)、汶川地震断裂带科学钻探工程(WFSD)和日本海沟快速钻探计划(JFAST).钻孔测温结果表明:滑移面上下5～20m范围内存在温度正异常,这是同震摩擦生热所致,该机制已被广泛认识和接受;同时,距滑移面20～60m范围内也存在明显的温度负异常,但其成因机制几乎还未被真正关注和认识.虽然温度负异常峰值只有正异常峰值的1/4～1/3,但温度负异常分布范围却是正异常分布范围的3～4倍,即正、负温度异常区对应的总能量基本相当.因此,断裂带震后钻孔测温中的负异常及其成因不容忽视.在详细分析几种可能的同震温度负异常机制后(如岩层热物性分布差异、流体运移、表面自由能增大及同震应力释放),发现能在理论、实验及野外观测上都得到支撑的普适性机制只有同震应力释放.这可能是断裂带震后温度负异常的主要原因.