正常固结黏土中平板锚基础的吸力和抗拉力

Tension resistance and suction of plate anchor foundation in normally consolidated clay

平板锚是新近出现的一种系泊深海浮式结构的基础型式。当黏土地基中的平板锚承受上拔力时,平板上、下表面超静孔压差形成的吸力使其抗拉承载力显著增加,对于风浪等快速加载条件尤其如此。利用有限元软件ADINA建立有效应力形式的轴对称动力有限元模型,研究圆形平板锚在缓慢加载与快速加载时的超静孔压分布与地基破坏型式。快速加载时重黏土和高岭土两组典型正常固结土样所得极限承载力系数与塑性极限分析解一致。进而通过变动参数分析,讨论加载速率和埋深对吸力和总抗拉力极限值的影响,并给出排水和不排水加载条件对应的临界加载速率。结果表明,不排水加载条件的总抗拉力可能达到排水总抗拉力的3倍。

The plate anchor is a new anchor foundation of moored deep-sea offshore floating structures. When a plate anchor is buried in the clay and subjected to uplift force, the difference of excess pore pressures on anchor top and base results in suction force, which may be beneficial to improve the uplift resistance of anchor, especially when wind and wave loadings apply quickly. A finite element software, ADINA, is used to establish axisymmetric dynamic finite element model in effective stress form. The distributions of excess pore pressure and failure mechanisms of foundation under fast and slow loadings of circular plate anchor are studied. In terms of two typical normally consolidated clays, gault and kaolin, under fast loading condition, the solutions of ultimate bearing capacity factor agree well with results from plastic limit analysis. By means of parametric analysis, the effect of loading rate and anchor embedment on suction force and limit value of total tension resistance are discussed. Furthermore, the critical loading rates corresponding to fully drained and undrained conditions are proposed. Numerical results show that the total tension resistance under undrained condition may be three times of the value under drained condition.