波致粉质土海床剪切破坏及其强度演化的试验研究

The Experimental Study on Wave-Induced Shear Failure and Strength Evolution of Silty Seabed

本文以黄河三角洲粉质土为研究对象,开展了波致海床剪切破坏过程中孔压响应与土体强度变化的室内水槽试验研究,试验过程中,先后在模拟海床床上施加5、10、15cm波高的模拟波浪荷载,同步测量海床内不同深度处的孔压变化,并对海床进行贯入阻力测试和不排水抗剪强度测试。研究发现:海床中孔压响应过程的规律为孔压快速累积-孔压缓慢消散,在该过程中海床内最容易形成大幅度的孔压累积、孔压响应最强烈的位置,也是海床内土体强度的逐渐丧失以及土体剪切破坏是处开始发育的深度;波浪作用下粉质海床剪切破坏后会在海床内部一定深度处出现明显的弧形破坏界面,破坏土体沿界面随波浪作振荡运动,且破坏范围经历先扩展后回缩的过程,剪切破坏界面以下会有强度硬层的发育,强度硬层的形成与演化直接受剪切破坏过程控制,最终整个海床出现明显的强度非均质化;在孔压响应过程中孔压比即超孔压与上覆有效应力比值存在临界值K(本文水槽试验所得K=0.5),当超过K值时,土体贯入阻力和不排水抗剪强度降低,发生剪切破坏,这是波浪作用提供的剪切力以及超孔压累积导致海床内部抗剪强度降低共同作用的结果。

This study is a wave-flume experiment about wave-induced pore pressure response and seabed strength evolution during the shear failure process based on the silty soil from the Yellow River delta area.During the experiment wave loadings of 5,10,15 cm wave height were applied on the seabed,pore pressure at different depths,penetration strength and un-drained shear strength of seabed were measured synchronously.The results show that pore pressure response inside the seabed experienced the process of rapid accumulation,slow dissipation.There was a certain depth that always showing the strongest pore pressure response and accumulating the largest excess pore pressure.Strength attenuation and structural failure of seabed originated right here.Arc shaped sliding surface inside the seabed would appear after a certain wave loading time,and the failure soil did oscillatory motion along the interface.A hard layer developed beneath the sliding surface and eventually resulted in nonhomogeneous strength of seabed.The shear failure of seabed directly controlled the formation and evolution of the hard layer.When the ratio of excess pore pressure and overlying effective stress exceeded the critical value K（K=0.5in this experiment）,penetration resistance and un-drained shear strength of seabed would decrease significantly,result in shear failure,and it was caused by the joint effects of wave-induced shear force and pore pressure accumulation inside the seabed.