桩侧注浆与扩底抗拔桩的极限载荷试验研究

相比于传统等截面抗拔桩,桩侧注浆抗拔桩和扩底抗拔桩能大幅提高抗拔承载力,具有较高的工程应用前景。笔者开展了有效桩长19 m的桩侧注浆抗拔桩和扩底抗拔桩的极限载荷对比试验,各3根试桩,均加载至极限破坏状态,同时开展桩身轴力与变形量测。从荷载位移曲线、桩身轴力分布规律、桩侧摩阻力发挥特性等方面对两种桩型进行了对比分析。试验表明,两种桩型相比于等截面抗拔桩的承载力提高机理不同:桩侧注浆使得有效桩长范围内各层土桩侧摩阻力普遍得到增强,实测桩侧摩阻力比勘察建议值提高33%~73%。扩底抗拔桩中等截面段侧摩阻力的发挥与勘察报告建议值相当,扩大头提供的抗拔承载力随加载值的增大而逐步发挥,在最大加载值时,扩大头承载力达到总加载的55%,超过等截面段桩侧摩阻力,扩大头的存在对于提高抗拔承载力作用明显。

Comparison on Bearing Behavior of Uplift Piles with Side-grouting and Enlarged Base by Full-scale Tests

Compared with traditional uplift pile with uniform cross section, bearing capacity of uplift piles with side-grouting and enlarged base are higher. A series of loading tests on two types of uplift piles with side-grouting and enlarged base having effective pile lengths of 19 m were carried out. For each type, three test piles were loaded to failure. The deformations of the testing piles at the top and toe were continuously monitored throughout the test. The axial force of pile shaft was measured as well. Load-displacement curves, distribution of axial force of pile shaft and shaft resistance are investigated. Tests showed that, the bearing capacity strengthening mechanism is different. Side resistance of piles is reinforced by side-grouting on full pile, and the tests showed that the measured data are larger than the proposed data nearly 33%~73%. The uplift capacity of uplift pile with enlarged base is composed of shaft resistance of the uniform section and the uplift resistance of the under-reamed part. When the pile is pulled up, the shaft resistance of the uniform section works firstly, follows by the under-reamed part. At the ultimate state, the uplift resistance which is provided by the under-reamed part accounts for about 55% of the total uplift capacity. The enhancement of the bearing capacity by the enlarged base is significant.