地铁暗挖下穿富水黄土建筑沉降特性及规律
Settlement characteristics of underground excavation metro tunnelling beneath existing building in water？？rich loess strata

为了研究富水黄土地区暗挖地铁下穿既有建筑时地表和建筑的沉降特性及规律，确保其施工安全，基于西安地铁3号线长通（长乐公园站―通化门站）暗挖区间，采用MIDAS/GTS建立三维有限元模型，对浅埋暗挖下穿建筑进行动态模拟，得到有无超前注浆时的建筑沉降曲线、工后沉降分布曲线以及工后地表沉降云图，并结合现场实测数据，对比分析下穿过程中建筑的竖向位移、沉降差值随开挖的变化规律以及施工后地表的变形分布。研究结果表明：2种工况下建筑的沉降均主要受其下方左洞开挖的影响，左线下台阶开挖后沉降速率达到最大值，当建筑下部土体全部挖空后沉降达到最大值，施工完成后建筑的沉降以左线为中心呈对称分布；未注浆时建筑的最大沉降发生在基础底部，为119.5 mm，差异沉降值为120.5 mm，采用超前注浆时最大沉降和差异沉降分别减小了74.7%和75.6%；地表沉降范围为施工区域的2.5～3.0倍，整体呈斜W形分布，左侧变形稍大；未注浆加固时其沉降槽较深，达到了112.3 mm，注浆后其最大值仅为15.1 mm；与模拟数据相比，现场监测值略大，产生偏差的原因可能是其实际地质条件更复杂，且沉降受地表各种荷载及施工爆破的影响，依托工程实测累计沉降为16 mm，可满足控制要求，现场实测数据与数值计算结果吻合较好，可为黄土地区类似工程设计与施工提供一定参考。
To investigate the settlement characteristics of the building and surface during the tunnelling beneath existing building in water？？rich loess areas and to ensure the safety of construction, based on the underground excavation section of Changtong Line (Changle Park Station to Tonghumen Station) of Xi？？an Metroline 3 Tunnel, a three？？dimensional finite element model is established by using MIDAS/GTS.The building settlement curve, the post construction settlement distribution curve and the surface settlement cloud image after construction under the condition of pre？？grouting or no pre？？grounting. At the same time, combined with the field measured data, the settlement of the building, along with the excavations and the distribution of the surface deformation after the construction, was compared and analyzed. The results show that the settlement of the building is mainly affected by the excavation of the left tunnel under the two conditions, and the settlement rate reaches the maximum after the excavation of the lower section in left line. Moreover, the settlement reaches the maximum after the excavation of all the soil beneath the building. After the construction, the settlement of the building is symmetrical at the center of the left line. The maximum settlement of the building occurs at the foundation, which is 119.5 mm, and the differential settlement value is 120.5 mm. The maximum and differential settlement decreases by 74.7% and 75.6%, respectively, under the condition of pre？？grouting, respectively. The surface subsidence area is 2.5 to 3 times of the construction area, and the overall distribution is oblique W type, with a left groove that is slightly deeper. When the grouting is not reinforced, the settlement groove is deeper, reaching 112.3 mm, and the maximum value after grouting is 15.1 mm. Compared with the simulation, the field monitoring value is slightly larger. The reason for the deviation maybe that the actual geological conditions are more complex, and the settlements are