盾构法是城市地铁隧道开挖的常用方法之一。盾构法施工引起地表下沉的主要原因包括：覆土条件、土仓压力、掘进速度、盾尾注浆、开挖面扰动以及盾构施工过程中引起的地层损失。在富水砂卵石地层盾构施工中，由于该地层的特殊性，为了确保地铁隧道施工安全有序进行，迫切需要对富水砂卵石地层盾构法隧道施工沉降规律进行研究。砂卵石地层无胶结、松散、单个石块强度高、自稳能力差、渗透系数大、粘聚力小、颗粒之间孔隙大，是一种典型的力学不稳定层，其物理和力学特性与黄土、软土及复合地层有较大差别，砂卵石地层中的卵石颗粒在无水状况下点对点传力，受扰动后地层反应灵敏。因此研究砂卵石地层中盾构施工造成的地表沉降规律十分必要。 本文选择西安地铁二号线二期工程航天城～韦曲南站区间全断面富水砂卵石地层的特点和周边环境对盾构施工的要求为工程实例，辅以MIDAS/GTS数值模拟计算，预先对隧道施工过程中地表的沉降规律进行预测，从而有针对性的制定施工方案。具体的研究工作与结果如下： （1）地铁隧道盾构开挖的覆土条件、掘进速度、盾尾注浆、土仓压力及开挖方式等都对地表沉降有一定的影响，且造成的地表沉降时间历程及影响范围不同。 （2）在砂卵石地层中，相同开挖条件下，隧道上覆土厚度越厚，地表沉降量越小；盾构的土仓压力以及掘进速度对地表沉降影响比较大；砂卵石地层双孔隧道同时同向开挖是较好的开挖方式；不同地层在相同开挖方式条件下，地表沉降空间和时间效应变化趋势基本一致，但最大沉降量有一定差异。所以，在不同地层条件下，盾构施工参数的确定对地表沉降的控制有着明显的不同。 （3）对隧道盾构施工进行现场实时监测，监测结果与盾构施工数值模拟结果基本一致，沉降值 18mm，地表沉降变化趋势相当。模拟数据和现场监测数据的线性回归拟合误差 10%在允许范围内，说明西安地铁二号线航天城～韦曲南站区间富水砂卵石地层盾构法施工设计方案的合理性，对以后类似的工程具有参考价值。

Shield method is one of the commonly used method of urban subway tunnel excavation. The main reasons for the surface subsidence caused by shield method construction include: the overburden thickness of tunnel, soil pressure, driving speed, shield tail grouting, excavation surface disturbance and formation damage caused by shield construction process. In water-rich sandy gravel stratum shield construction, because of the particularity of the formation, in order to ensure safe and orderly subway tunnel construction, the tunneling shield settlement rule for water-rich sandy gravel stratum needs to be researched urgently. The features of sand cobble stratum is briquetting binderless, unconsolidated, no single stone high strength, poor stability, permeability coefficient, small cohesion and large particles, it is a typical mechanical unstable layer, the physical and mechanical properties is very different with loess, soft soil and complex formation, under dry condition sand and gravel formation pebble particle point-to-point transmission force, formation responsive after disturbance. Therefore, studies on the surface settlement caused by the shield construction in pebble stratum settlement is very necessary. In this paper, we choose Xi’an Metro Line 2 HangTianCheng～WeiQu south station interval total water-rich sandy gravel stratum section characteristics and surroundings of shield construction requirements as the project example, to study the tunnel surface subsidence regularity through Midas/GTS numerical simulation Expand research work and results are as follows: (1) Subway tunnel shield excavation overburden conditions, driving speed, shield tail grouting, soil pressure and the excavation way have some impact on the surface subsidence, and cause different surface subsidence time history and influence scope. (2) In the sand and gravel stratum, under the same conditions, the thicker the tunnel overburden, the smaller the amount of surface subsidence; soil pressure and driving speed have relatively large impact on surface subsidence; the same time and direction excavation for the sand and gravel stratum double orifice tunnel is the better excavation way; under the same conditions of excavation, surface subsidence spatial and temporal trends are the same effect basically, but the maximum settlement amount is different. Therefore, under different formation conditions, the different parameters of shield construction is significantly different to surface subsidence control. (3) For the real-time monitoring of shield tunnel construction site, monitoring results are consistent with the results of numerical simulation, sedimentation value is 18mm, surface subsidence trends fairly. Analog data and on-site monitoring data linear regression error of 10% is within the allowable range, indicating the rationality of Xi’an Metro Line 2 HangTianCheng～WeiQu south station interval water-rich sandy gravel stratum shield construction design scheme, for similar projects in the future as a reference value.