整体桥高性能混凝土桩−土相互作用试验研究

高性能混凝土（高性能复合水泥基材料engineered cementitious composite，简称ECC与超高性能混凝土ultra-high performance concrete pile，简称UHPC）桩基具有良好的抗开裂性能和较高的承载能力，能较好地满足整体桥纵桥向变形。开展了砂土中高性能混凝土桩低周往复拟静力试验，得到了桩基的破坏特点、抗开裂能力以及极限承载力，分析了其桩身变形、桩侧土抗力以及桩身应变等分布规律，并与钢筋混凝土（RC）桩进行了比较。在此基础上，讨论了几种常用规范的适用性。试验结果表明，ECC、UHPC材料能有效减轻桩基的破坏程度、提高桩基的抗开裂能力以及水平承载力；相比RC桩基，高性能混凝土桩基的破坏位置更深，桩基的有效桩长更大，抗震性能更好；其中，ECC桩基的抗开裂能力最强，开裂荷载可达5.8 kN，开裂位移可达15 mm。试验结果还表明，高性能混凝土桩基的变形沿埋深方向不断的减小，埋深1.5 m以下位置基本为0；桩侧土抗力先增大后减小，桩底土抗力和变形量为0；桩身应变分布较为对称，且呈“橄榄”形，在埋深4D～6D（D为桩径）区间内桩身应变较大。分析计算表明，当桩顶位移在10 mm以内时，“m”法与API新规范法均能较好地计算高性能混凝土桩的桩身变形；当位移超过10 mm后，“m”法与实际数值相差较大。“m”法与API新规范法均不能较好地计算桩身弯矩，适用性不高；桩侧土抗力建议采用API新规范法。

Experiment on Interaction of High Performance Concrete Pile-Soil in IAJBs

High-performance concrete (ECC and UHPC) pile foundations have the advantages of excellent crack resistance and high bearing capacity, which can better meet the longitudinal deformation of piles in integral abutment jointless bridges (IAJBs). Low-cycle reciprocating pseudo-static tests were carried out on interaction of high-performance concrete pile-soil. The failure characteristics, crack resistance and bearing capacity of the pile were obtained. The distribution laws of pile strain, pile deformation and pile side soil resistance were analyzed and compared with the reinforced concrete (RC) pile. Meanwhile, the usability of commonly used codes were discussed. Some findings were as follows. ECC and UHPC materials can significantly reduce the damage of the pile foundation, increase the horizontal bearing capacity and crack resistance compared to RC. The damage position of the high-performance concrete pile is deeper, the effective pile length of the pile is longer, and the seismic performance is better. In special, the ECC pile has the strongest anti-cracking ability, its cracking displacement and cracking load can reach 15 mm and 5.8 kN, respectively. The deformation of high-performance concrete piles continuously reduces along the buried depth, and approaches zero at 15 m and deeper. The soil resistance of pile side increases first and then decreases, the resistance and deformation of the pile bottom soil are both 0; the strain of the pile shaft is symmetrically distributed with an “olive” shape, and there is larger strain in the interval of 4D to 6D buried depth. Furthermore, both the “m” method and the new API standard method can estimate the high-performance concrete pile displacement better when the displacement of pile top is within 10 mm. When the displacement exceeds 10 mm, the “m” method is no longer applicable. Neither the “m” method nor the new API standard method can predict the bending moment of the high-performance concrete pile well, indicating poor applicability. The new API standard method is recommended for estimating soil resistance of pile side.