硬软突变场地PHC桩沉桩可行分析评价研究

Research on Feasibility Analysis and Evaluation of PHC Pile Driving in Hard and Soft Mutation Ground

PHC桩经常会遇到需要穿越硬软突变的工况,当桩尖穿越硬土层进入软土层时,桩身形成的拉应力波会引起桩身开裂。通过GRLWEAP软件对硬软突变场地工况的PHC桩进行沉桩可行性分析,同时在工程现场开展高应变打桩监测试验。研究发现当硬土层和软土层土阻力相差较大且软弱土层相对较厚时,沉桩过程中桩身会产生较强的拉应力波,当拉应力超出桩身允许值时,就会引起桩身开裂,尽管采取很多措施如如采用预引孔措施、改变桩锤、改变桩型、打闭口桩、更换打桩设备以及供桩单位、重锤低击等,但坏桩率仍然偏高,最终证明引孔加静力压桩是最为行之有效的施工方法,可以将坏桩率降到最低。

PHC pile often need to cross the hard and soft mutation layer,when the pile tip driven through the hard soil layer into the soft soil layer,the tensile stress will lead to pile body fracture. In response to these circumstances.PHC pile driven through hard and soft mutation layer was analyzed by GRLWEAP software. The high strain monitoring test was also carried out. The research has found that when the soil resistance difference of the hard soil layer and soft soil layer was large and soft soil layer was relatively thick,in the process of pile driving,the pile would produce strong tensile stress wave,when the tensile stress beyond the accepted value of PHC pile,the pile body would be cracking,although many measures could be taken such as pre-drilling hole,changing the pile hammer,changing the pile type,driving the closing pile,changing the pile driving equipment and pile supply factory and application of heavy hammer with low drop distance,but the proportion of bad pile was still high,in the end it was proved that to drill holes with static pile driving was the most effective way and could minimize the proportion of bad piles.