板桩加固护岸桩身受力现场试验研究*

板桩侧摩阻力的大小和分布模式对板桩的沉降有较大影响,进而对板桩加固护岸结构的稳定产生影响,桩端至于相对硬土层的板桩护岸结构,对板桩沉降是一项重要研究内容。为了研究加固护岸板桩桩侧摩阻力的分布模式和大小,结合长湖申航道湖州段板桩加固护岸实体工程,通过在板桩预制过程中将钢筋应力计埋入板桩轴心处,完整测试了板桩在凝固硬化过程中钢筋应力计受力情况和护岸荷载施加过程中的板桩荷载传递机制,详细介绍了钢筋应力计的焊接及埋设方式。现场试验结果表明:混凝土凝固硬化过程对埋入板桩的钢筋应力计会产生较大的拉压应力并逐步趋于稳定;施工荷载对钢筋应力计受力的影响较大,在分析护岸荷载施加过程中板桩荷载传递机制时,需要对钢筋应力计进行重新标定;在护岸荷载作用下,桩身的上部轴力变化较大,而中部及下部轴力不仅变化较小而且轴力较大,即桩顶荷载易于向下传递;桩侧摩阻力在靠近桩顶附近得到了较大发挥,在距桩顶0.3 m范围内的桩侧摩阻力约占整个桩身摩阻力的40%;JGJ 94—2008《建筑桩基技术规范》推荐的极限桩侧摩阻力较大,实测最大值仅为推荐值的63.9%。

Field experimental study on force on the body of sheet pile reinforced revetment

The magnitude and distribution mode of the skin friction resistance has considerable influence on the settlement of the sheet pile,and further on the stability of the revetment reinforced by the sheet pile.The settlement is an important study content while the sheet piles of the revetment structure are driven to the relatively hard layer.Field experiment is carried out in the actual sheet pile improved revetment project at Huzhou section of Chang-Hu-Shen waterway to research the distribution mode and magnitude of the sheet pile’s skin friction resistance.Stress gauges are arranged on the axial line in the pre-process of the sheet pile,and the jointing and embedding manner are presented.Through detected stress gauges,the axial force and the load transfer mechanism are adequately studied respectively in the harden progress and the loading procedure.The stress gauges in the sheet pile will bear pull force firstly then turn into press force and tend to be stable during the concrete solidify progress.Stress gauges should be recalibrated to analyze the load transfer mechanism under increasing loading,owing to the great inference of construction load on the stress gauges.The axial force of the top pile exhibited considerable variation,but the middle and under part of the pile show small changes but large values,and the pile load on the top is easily transformed.The skin friction resistance is fully played near the top pile;it accounts for 40 percent of the all skin friction resistance for distance shorten than 0.3 meters to the top pile.The recommended value of the ultimate skin frictional resistance in the Technical Specifications(JGJ 94—2008)is much larger,and the measured maximum friction is only 63.9% of the recommended value.