软黏土中吸力锚循环失稳过程的模型试验

Model experiment on cyclic instability process of suction anchors in soft clays

开展了张紧式吸力锚在侧壁最优系泊点处遭受平均荷载和循环荷载共同作用下的模型试验,着重研究了软黏土中吸力锚在等幅及变幅循环荷载下的变形失稳过程。研究发现,循环累积位移过大是锚发生破坏的主要原因。对于等幅循环加载试验,由于竖向附加荷重的施加,锚在水平向的循环累积位移要明显大于竖向,表现为明显的水平破坏模式。在特定的平均荷载水平下,循环荷载水平越高,锚的累积位移发展得越快,达到破坏所需的循环次数就越少。循环位移随循环次数的增长变化不明显,但随循环荷载水平的增大而增大。对于变幅循环加载试验,系泊点各方向的循环累积位移与循环位移均与循环荷载水平成正比。不同的循环加载时程下,锚的竖向累积位移均比水平累积位移大,表现为偏向于竖向破坏的中间破坏模式。锚前期的循环加载历史对后续加载产生的累积变形有明显影响。与静力加载相比,循环加载时锚的运动方向角有所增大,这可能是由于锚底孔压的累积要大于锚侧孔压的累积,从有效应力的角度分析,锚底有效应力的减少相对锚侧明显,进而使得锚竖向承载力减小得更多,导致锚的竖向运动更明显。

Model tests of the suction anchors with taut mooring systems are conducted under combined average and cyclic loads at the optimal loading point on the side wall of anchors. The deformation instability process of suction anchor subjected to constant and variable amplitude cyclic loads are investigated. It is found that too large cyclic accumulative displacement is the main reason for the failure of anchor. The cyclic accumulative displacement of anchor in the horizontal direction is larger than that in the vertical direction due to application of the vertical additional loads, so the horizontal failure of suction anchors occurs for the constant amplitude cyclic loading tests. The accumulative displacement increases faster with higher cyclic load level at a given average load level, and the number of cycles to failure becomes less. The cyclic displacement does not change obviously with the increase of the number of cycles, but increases with the increase of cyclic load level. The cyclic accumulative displacement and cyclic displacement in each direction at the mooring point increase with the increase of cyclic load level for variable amplitude cyclic loading tests. The accumulative displacements are larger in vertical than in horizontal under different cyclic loading time histories, so the moderate preferring vertical failures of anchors occur. Besides, the previous cyclic loading histories have an obvious influence on the accumulative deformation produced by subsequent loading. Compared with the static loading, the movement direction angle of the anchor under cyclic loading increases, which may be due to the greater accumulation of pore pressure at the bottom of the anchor than that at the side wall. From the view of effective stress, the decrease of effective stress at the bottom is relative obvious than that at the side wall, thus vertical bearing capacity decreases more remarkably, and vertical movement of anchor is more obvious.