研究目的: 澳氹四桥主桥桩基永久钢护筒作为桩基成孔辅助措施,直径2.8 m,长度近100 m,不计入参与受力,钢护筒沉放采用搓管机或全套管全回转钻机施工。对于永久钢护筒,在后期不拔出的情况下,钢护筒合理壁厚至关重要,与施工安全和经济成本息息相关。为避免钢护筒壁厚过足造成经济浪费,壁厚不足导致在沉放过程中发生较大变形,通过建立考虑接触摩擦的钢护筒-周围水土三维模型进行钢护筒受压受扭沉放施工过程的力学仿真分析。
研究结论: (1)全回转全套管钻机或搓管机适用于海上超长大直径钢护筒的沉放,根据钢护筒回转和下压运动,给出了所受八项荷载的计算方式;(2)通过对不同桩位不同长度的桩基永久钢护筒管壁的环向应力和轴向应力、屈曲稳定进行研究,依据招标文件要求,钢护筒应按照永久结构设计,给出了静力计算和局部屈曲计算安全系数,确定了钢护筒的合理壁厚;(3)本文研究结论可为海上超长大直径利用全套管全回转或搓管机的钻孔桩成孔工艺中跟进永久钢护筒的稳定安全分析和合理壁厚提供参考。

Research purposes: As an auxiliary measure for hole formation of pile foundation, the permanent steel casing of the main bridge of Macao-Taipa Fourth Cross-sea Bridge has a diameter of 2.8 m and a length of nearly 100 m, which is not considered to participate in force. The steel casing of offshore pile foundation is usually constructed by pipe rolling machine or full casing rotary drilling machine. It was very important to ensure reasonable wall thickness of permanent steel casing without deformation when it was not pulled out eventually, which was closely related to construction safety and economic cost. In order to avoid economic waste caused by excessive wall thickness of steel casing, and large deformation caused by insufficient wall thickness in the process of sinking, a 3D model of steel casing and surrounding soil and water was established to simulate the construction process of steel casing subjected to torsion under pressure.
Research conclusions: (1) The full-rotary full-casing drilling machine or pipe rolling machine is suitable for sinking of super-long and large-diameter steel casing on the sea. According to the rotary and pressing motion of steel casing, the calculation method of eight loads is given. (2) By means of the research on hoop stress and axial stress, buckling stability of permanent steel casing wall of pile foundation with different pile positions and pile lengths, the steel casing should be in accordance with the permanent structure design on the basis of the bidding documents require. The static calculation and local buckling calculation of safety factor are given, and the reasonable wall thickness of steel casing is determined. (3) The research conclusion can provide a reference for the stability and safety analysis and reasonable wall thickness of permanent steel casing in the drilling pile drilling process using full casing full rotation or pipe rolling machine for super-long and large-diameter offshore pile.