大厚度湿陷性黄土地层浸水条件下承载桩基对近距隧道的影响研究

 承载桩基对近距隧道具有明显的附加荷载作用，对于水敏性的大厚度湿陷黄土地层其影响更加明显。为系统研究桩基对近距隧道的影响，基于改进的离心浸水试验系统开展考虑不同桩端荷载、不同桩距比和不同地层浸水厚度影响下，承载桩基对近距隧道影响的离心模型试验。试验结果表明：(1) 桩基附加荷载致使衬砌结构受力重分布，桩周土体对荷载传递具有削弱作用，桩端荷载越大，削弱作用越明显；土层浸水降低了其承载力，加剧了桩–隧间的荷载传递作用；随桩距比增大，桩基对隧道影响逐渐减小。(2) 桩端荷载较小时隧道弯矩变化均匀，随荷载增加隧道向桩基方向发生扭曲，荷载进一步增加，隧道扭曲作用加剧；桩距比较小时，增大桩距比对弯矩变化影响减弱较明显，随桩距比增大，进一步增加桩距比对弯矩影响逐渐减小；土层浸水厚度较小时，受桩周土体的荷载削弱作用，桩基对隧道的影响较小，随浸水深度的增加，桩周土体承载力减弱，桩基对隧道的影响随之增加。(3) 桩距比为1时，随桩端荷载的增加隧道最大下沉值达到16.7 mm，水平位移达到3.2 mm，随桩距比增加，隧道下沉和水平位移值均减小；随浸水厚度减小，隧道整体位移也减小，地基浸水导致的隧道位移主要表现为下沉，且浸水深度对隧道位移的影响弱于桩端荷载和桩距比。

Influence of pile foundation to adjacent tunnel with water immersion in collapsible loess layer of great thickness

The adjacent tunnel is influenced by pile foundation obviously due to the additional load，particularly in the area with loess layer of great thickness which is sensitive to water content. A serious of tests with the modified centrifuge testing equipment were conducted to systematically investigate the influence of the pile foundation to the adjacent tunnel. The influence factors considered in the tests are the pile foundation load，the pile-tunnel distance and the basement immersion depth. The soil around the pile was found to reduce the load-transfer effect，which led to the lining stress redistribution. The bigger the pile load，the more obvious the reduction effect. The bearing ability of the basement was reduced due to the water immersion，which increased the load-transfer between the pile and tunnel. The influence of pile to tunnel was decreased with the increasing of pile-tunnel distance. The bending moment of tunnel was evenly distributed when the pile load was small. The tunnel was distort with the pile load was bigger and was distort more as the pile load increased. The effect was obvious when the pile-tunnel distance was short. When the immersion depth in basement was small，the influence of pile to tunnel was weak due to the load-transfer effect，but the influence was more and more obvious with the increasing of immersion depth in basement. When the ratios of pile-tunnel distance to diameter of tunnel was 1，the vertical displacement reached 16.7 mm，the horizontal displacement reached 3.2 mm under the pile load increasing，and both reduced with the increasing of pile-tunnel distance. The tunnel displacement reduced with the decreasing of immersion depth in basement. The basement immersion affected mainly the vertical displacement. The effect of basement immersion to tunnel was smaller than pile-tunnel distance and pile load.