砂土地层盾构隧道施工对地层扰动的室内掘进试验研究

LABORATORY TEST STUDY OF SOIL DISTURBANCE CAUSED BY SHIELD TUNNELLING IN SANDY STRATA

土压平衡式盾构机在穿越流塑性差、渗透系数大的砂土地层时容易对隧道周围土体产生扰动，导致地表沉降不易控制和作用在衬砌结构上的土压力发生改变。针对地铁盾构隧道穿越砂土地层引起的地层扰动，采用一种能完全反映盾构隧道动态施工全过程的分析方法尤为重要。以城市地铁盾构区间隧道施工采用的土压平衡式盾构机为原型，研制妒800mm土压平衡式模型盾构机，该机主要包括推进机构、掘削机构和出土机构，能实现盾构始发、刀盘切削、螺旋出土、管片拼装等主要功能，以此开展砂土地层中盾构施工的室内掘进试验。试验过程中对盾构掘进引起的地层沉降及衬砌结构上的土压力进行量测，分析地层沉降形态和衬砌结构上土压力的分布形态，同时将试验结果同理论计算、数值分析及现场资料进行对比。研究结果表明，土体性状和盾尾注浆对地层沉降具有重要影响，地层损失是地层发生沉降的主要原因。未注浆情况下盾尾脱环引起的地表沉降值占总沉降值的60％以上，且由于未注浆而增大的地表沉降所占比例为20％-30％，沉降时程曲线具有阶段性和时效性。地表沉降槽宽度系数i与现场测试数据具有一致性。衬砌结构上的土压力分布类似于上下端为长半轴、左右端为短半轴的椭圆形，数值上试验实测值较理论计算值要小。

Sandy stratum with poor plasticity and large permeability can easily be disturbed when the earth- pressure-balance（EPB） shield machine passes through; the induced ground surface settlement is difficult to control; and the earth pressure acting on the segment lining structures changes. It is particularly important to employ an analysis method, which could represent the whole dynamic process of shield tunnelling, to study the soil disturbance caused by shield tunnelling in sandy stratum. The ~ 800 mm EPB shield model machine was developed and manufactured on the basis of the EPB shield machine used in the city metro tunnel projects. The EPB model shield machine consists mainly of a jacking system, a cutting system and a slag discharge system. It can achieve some main function such as shield machine originating, cutter head cutting, muck discharging, segment assembling, etc. Ground settlements caused by shield tunnelling and earth pressure acting on the lining structure were monitored in the laboratory test to find out the settlement features and earth pressure distributionrule; and then the results were compared with the theoretical and numerical results and field test. Results show that, soil characteristics and shield tail grouting have significant influence on the ground settlement; and the ground loss is still the main reason of ground settlement. The surface settlement values caused by the tail void are more than 60% of the final settiement values without grouting; and a 20% to 30% proportion due to that without grouting. The settlement time-history curves show periodic and timeliness. The width parameter of surface settlement trough is consistent with the field test values. The distribution of the earth pressure acting on the lining structure is like an oval, which upper and lower side is the semimajor, left and right side is semiminor. The tested earth pressures are smaller than the theoretical values.