【作者】 庞烈鑫；

【导师】 王明年；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2006， 硕士

【摘要】 论文根据神朔铁路新小则沟隧道的地质情况、围岩类别及荷载状况，应用荷载—结构模型计算得出了基底所需要的承载力，通过与原地基承载力进行比较，得出现有地基不能满足隧道修建要求的结论。并对树根桩加固隧道地基进行了初步设计，为了验证设计正确与否，在DK52+382～+540段进行了树根桩单桩承载力现场载荷试验及群桩复合地基承载力现场载荷试验，对黄土及砂土地区树根桩的设计提供了较好的实践参考。首先查明了试验场地黄土的物理力学性质，得出了相关的物理力学参数，接着共进行了11根单桩载荷试验和3个群桩复合地基的载荷试验，3个群桩复合地基分别包含3根、8根和3根树根桩。根据现场实测数据，作出了每次试验的P-s曲线，并依该曲线确定了每一单桩及群桩复合地基的承载力及其对应的沉降量。作出了群桩复合地基的S-t曲线，并分析了复合地基在每级荷载作用下的变形情况。在上述结果的基础上，分析了单桩承载力的影响因素，分析了成桩材料、桩长、桩径、配筋情况等对单桩承载力的影响；分析了群桩复合地基承载力的影响因素。得出了如下有益的结论：成桩骨料的改进能明显地增加单桩承载力，在条件允许且必要的情况下，应采取先填石子然后压力注浆成桩的施工工艺；对于摩擦桩来说，桩长增大到一定程度后，继续在很大程度上增加桩长并不能在很大程度上增加单桩承载力；桩身配筋对于摩擦桩来说，并不能明显地提高单桩承载力，但可明显地是高桩身强度；黄土地基中，可直接采用S法来确定树根桩的单桩承力，即直接采用桩顶位移S=0.03d(d为桩直径)时所对应的荷载为其单桩承载力，而可不用P-S曲线来确定；树根桩群桩经过合理的布置，与原路基岩土体形成的复合地基，能在较大程度上提高路基的承载力，是路基加固行之有效的方法。试验表明，树根桩根数增多，复合地基承载力也将随之提高，当然，当桩根数增大到一定程度时，承载力将达到一极限；树根桩多的复合地基在相同的荷载作用下，沉降完成所需的时间要比桩根少的复合地基少。由试验结果得出，树根桩单桩承载力比理论计算的单更多还原

【Abstract】 The requisite bearing capacity for the tunnel construction is firstly calculated in this paper with the loading-structure model considering the geological condition, wall-rock class and the loading condition. The calculation result is compared with the academic. And the result is drawn out that the requisite bearing capacity is larger than the academic. So the soundsill consoliding is necessary with root piles. Then some load tests of root piles in loess groundsill are developed in this paper. The tests in the ground of Xinxiaozegou tunnel including 11 single piles and 3 composite foundations are completed in DK52+382～+540. The results from the tests offer many important references for the root piles in loess groundsill. This paper inquires into the characteristics, application and theory of root piles underpinning. After combining the features of engineering geology and actural situation in the tunnel and using the way of comprehensive techniques and contrasting, the author believes that choosing root piles have less influnce to the building and its foundation, and more sensitivity to bearing capacity to reinforce the foundation of the tunnel.After continuous subsidence watching of the reinforce work, it is proved through practice that this technique is both economical and convenient, and working efficiency is improved greatly, and the equipments used are usual and the time cost is short and the technique is uncomplicated, especially, it can improve the earth under the foundation effectively. It not only opens up the scope of the root piles application, but also has the unique effect on the similar questions in our country. The three composite foundations respectively include three, eight and three single piles. Basing the data from field investigation, the carrying capacities of single piles and composite foundations are educed from the P-s curves. And the distortion of the composite foundations are analyzed更多还原