下穿黄河盾构隧道管片衬砌结构受力特征模型试验
：The shield tunnel of Lanzhou metro undercrossing the Yellow River was driven under through high permeability sandy cobble stratum and under high water pressure. A device for external loading test was therefore developed， which introduced a controllable air pressure between the linings and grouting layer， and by regulating the pressure difference， the equivalent water pressure can be then simulated. Using this device together with a tunnel-ground simulation facility， a model test with a geometric similarity ratio of 1∶10 was conducted. The device can reach the point that the water pressure and earth pressure were controlled separately. The mechanical
characteristics of segment lining with different external water pressures， soil pressure， coefficient of side earth pressure and segment assembling methods was analyzed. The results suggest that， as external water pressure increased， a significant increasing trend of axial force and a gentle decrease trend of bending moment were observed while eccentricity decreased obviously； as soil pressure increased， a gentle increase of axial force， bending
moment and eccentricity was observed； Given a fixed water pressure， increasing effects on the bending moment and decreasing effects on axial force were shown with the increase of soil pressure； Given a normal pressure level， axial force of segment linings increased while bending moment decreased when the coefficient of side earth pressure increased， which made the eccentricity decrease. In addition， the coefficient of side earth pressure shows decreasing effects on the mechanical characteristics of segment linings with the increasing of water pressure； Under staggered assembling， internal force of the segment will produce a mutation at some parts of circumferential and longitudinal joints， besides， internal force of the segment under staggered assembling is larger than that under straight joint assembling.
目前，许多学者对外水压下盾构隧道管片的力学行为进行了研究，受成本和时间等因素的限制，目前研究整环管片受力特性的原型试验较少，封坤等[2]对南京长江隧道超大断面原型管片衬砌结构进行了原型加载试验，研究了不同荷载条件与拼装方式对管片结构力学特征的影响.数值模拟及理论分析是较常采用的手段，李围等[3]采用梁弹簧模型对通用管片结构进行有限元计算分析，研究了通用管片结构在不同拼装方式条件下的力学行
为，并得出施工中的控制拼装方式.黄清飞等[4]推导了水位位于隧道断面内工况下管片内力的弹性解，结合已有修正惯用法，针对国内4种典型盾构隧道分析了不同覆土条件下水位变化对管片内力的影响.康石磊等[5]将强度折减法引入刚体平动运动单元上限有限元并编制计算程序，针对椭圆形毛洞隧道围岩稳定性和破坏模式开展计算分析，并探讨了围岩强度折减极限状态对应的刚性块体破坏模式的形态特征.
在外水压下盾构隧道力学行为研究方面，模型试验是一种较为可靠的研究手段，目前已在隧道模型试验的材料制备、模型制作、设备研制等方面积累了宝贵经验[6]，何川等[7-9]在相似模型试验中采用盾构隧道地层复合体模拟试验系统结合自行研制的旋转式水压装置，重点讨论了外水压下各因素对管片力学行为的影响规律.唐志成等[10]同时考虑盾构隧道管片接头效应和管片与土体相互作用效应，用三维土盾构隧道相似模型试验对盾构隧道管片结构在不同拼装方式下的力学行为进行了研究.但已有的模型试验绝大部分基于软土地层开展，未有针对外水压下砂卵石地层管片力学特性的模型试验，且模型试验中的水压加载方式存在较大问题，未能实现真实水压对管片力学行为影响的模拟. 本文针对兰州地铁穿河段盾构隧道穿越强透水砂卵石地层和承受较高外水压的特点，研制了外水压加载装置，通过控制模型内外气压差来实现外水压的等效加载，同时结合隧道地层复合模拟试验系统开展了室内模型加载试验，实现了土压和水压的分