桩基负摩阻力沿桩长变化的试验研究

Field tests on changes of pile negative friction along its length

结合中国移动甘肃定西分公司新城区移动通信综合楼项目,在大厚度自重湿陷性黄土场地上进行长时间的桩基浸水载荷试验(试桩直径为800 mm,桩长26 m,试坑深度为2 m),对不同深度下、不同范围内的桩侧负摩阻力的变化特征以及土体的沉降过程进行分析。试验结果表明,特殊浸水条件下桩侧负摩阻力沿桩身出现多个峰值,并且正、负摩阻力出现交错分布的现象,无法给出建筑桩基技术规范[1]规定的平均负摩阻力值;桩周土体沉降量亦沿桩身出现多个峰值,并且其变化趋势直接影响桩侧正、负摩阻力沿桩身交替变化的走势;中性点位置并未得出建筑桩基技术规范[1]所提供的单一参考值而是沿桩身出现了多个中性点;黄土的实际湿陷情况是分段发生湿陷的,而不是如传统观点所述在单一中性点以上突然出现整段湿陷。

Combined with the project of mobile communication comprehensive building,Gansu Dingxi branch,China mobile in Dingxi new city,a lasting pile immersion test was made in the site of collapsible loess with large thickness;while the changing characteristics of pile negative friction and settlement process of soil were analyzed for different depths and limits(the diameter and length of test pile were 800 mm and 26 m respectively with 2 m pit in depth).The test results show that under the special immersion condition mentioned above,there appear multiple peak values along the pile,and positive and negative frictions presented staggered distribution phenomenon;so that the value of average negative friction couldn't be given by Technical code for building pile foundation[1];then with multimodal distribution of soil settlement amount,its changing tendency directly affects its trend in positive and negative friction along the pile;also,in the neutral point location,the single reference value provided by Technical code for building pile foundation wasn't given;but several neutral points appeared along the pile;and the actual collapsible condition of loess is in sections,but not is sudden collapsible in the whole section above a certain neutral point as the traditional view states.