黏性土中微型桩抗压和抗拔现场试验

Field Tests on Micropiles in Clay Subjected to Compression and Uplift

为了更好地研究一种新的施工工艺下微型桩的承载性状，选用两根微型桩做现场静栽试验，每根桩中12个振弦式钢筋应力计被均匀布置于微型桩中．通过静载试验的结果发现，微型桩在承受抗压及抗拔时最终呈刺入破坏或桩身被拔出．土层性状和桩土相对位移对微型桩侧阻的发挥有很大关系，桩身侧阻随桩土相对位移变化呈应变硬化关系．不同土层及同一土层受力状态不同时，桩的临界侧阻和临界位移各不相同．通过将微型桩实测单位侧阻与静力触探试验结果对比分析发现，抗压时实测单位侧阻为静力触探试验的锥尖侧阻平均值的0．57—0．99倍，抗拔时实测单位侧阻为静力触探试验的锥尖侧阻平均值的0．37～0．72倍．抗压桩实测单位锥尖端阻为静力触探试验结果的0.38倍．

In order to give a better insight into the behavior of a new type of micropile under compression and tension load, a load test program comprising two micropiles was conducted. Each pile was instrumented with 12 vibrating- wire strain gauges. The results show that failure occurs in plugging and pull-out manners under compression and ten- sion conditions, respectively. The soil properties and pile-soil relative displacement have great influence on the mobi- lization of shaft resistance. The relationship between shaft resistance and pile-soil relative displacement resembles the strain hardening model. Meanwhile, the critical displacement and the corresponding shaft resistance vary with soil profile and local stress state. Through a comparison with the average CPT sleeve friction, the measured shaft resis- tance is found to be 0.57--0.99 times the average CPT sleeve friction in compression and 0.37--0.72 times in tension, and the measured toe resistance is 0.38 times the average of CPT toe resistance.