船坞坞口水上基坑力学性状数值分析

Numerical analysis on performance of waterfront dock entrance excavation

结合某船坞坞口水上基坑围护结构的设计,采用有限元数值模拟研究了基坑施工全过程中支护结构的受力与变形性态。采用Plaxis 2D建立考虑结构与土体共同作用的平面应变计算模型,并考虑不同水位及波浪荷载、地形地质条件及复杂施工工况的影响。研究表明:外部条件的不对称导致水上基坑围护结构的变形及受力与陆上基坑存在明显差异,基坑开挖并降水至坑底并非结构受力的最不利状态;基坑外坡护坡、压脚未施工前坑内降水是基坑围护结构变形的最不利状态;不同水位及波压条件对单排钢板桩的影响比对双排钢板桩的影响明显,两种不同类型围护桩的整体受力状态也存在明显差异;随基坑开挖和降水深度的增加,第1道混凝土支撑的受力会从受压变成受拉,下部各道钢支撑均处于受压状态;施工中应密切关注第1道支撑受力状态的变化。

In combination with the design of waterfront excavation for a ship dock entrance, a two- dimensional finite element numerical simulation is conducted to investigate the performance of the retaining structures during the excavating and dewatering process of the dock entrance. The geotechniea] analysis program Plaxis 2D is adopted to establish the plain-strain numerical model which takes into account the interaction between the retaining structures and the surrounding strata, different tide levels and wave conditions, on-site topographical and geological conditions, as well as the complicated construction sequences. The numerical results indicate that there are obvious distinctions of the performance of retaining structures between waterfront excavation and conventional onshore excavation. The most disadvantageous construction stage of the waterfront excavation is during the process of dewatering and before the construction of protecting berms outside the retaining steel sheet piles. Tide and wave conditions exert more detrimental impacts on the single-line steel sheet piles than on the double- line compound steel sheet piles filled with sand. More concerns should be focused on the alteration of the axial force of the first-level struts which may change from compression to subsequent tension; correspondingly, the overall cast-in-situ concrete beams ought to be used for the first-level struts to strengthen the integrative stiffness of the retaining structures.