北京地铁粉细砂层PBA车站沉降规律研究

PBA工法工序转换复杂，易引起地表沉降，不同地层条件下的沉降规律难以掌握。尤其在含水粉细砂地层等不良地质条件下的地表沉降难以控制，对周边环境造成一定安全隐患。为研究粉细砂地层PBA车站沉降规律，通过调研北京地铁粉细砂地层PBA车站分布情况，基于监控量测数据分析不同降水条件下PBA车站地表沉降规律，并依据有限元方法进行计算验证，研究表明： 1）大于相应地表沉降值的发生概率与地表最大沉降值的关系符合正态分布，有效降水和未有效降水车站地表最大沉降值分别为-85.31～-93.29 mm、-126.16～-131.35 mm，由数据拟合得出地表最大沉降值超过-60 mm的概率分别为53.30%、74.96%； 2）沉降变形主要发生在导洞施工及扣拱施工阶段(约占90%)，上导洞施工、下导洞施工、梁柱体系施工、扣拱施工阶段沉降比例约为4∶3∶1∶2； 3）沉降槽与Peck曲线趋近一致，沉降槽宽度系数在9.82～15.51 m，有效降水车站的沉降槽宽度系数比未有效降水车站的大3～5 m； 4）地层损失率普遍在0.56%～0.70%，沉降槽宽度参数受降水效果影响显著，普遍在0.51～0.89。研究结论可用于初步判断粉细砂层PBA车站的地表最大沉降。

Study on Settlement Law of PBA Station of Beijing Metro in Fine Silty Sand Stratum

The process conversion of PBA method is complex, and it is easy to cause surface settlement. It is difficult to clear the settlement law under different stratum conditions, especially under bad geological conditions such as water bearing silt formation, which would cause certain safety hazards to the surrounding environment. As a result, the distribution of PBA stations in fine silty sand stratum of Beijing Metro is investigated, the surface settlement laws of PBA station under different precipitation conditions are analyzed based on monitoring data, and the calculation and verification are carried out according to the finite element method. The research results show that: (1) The relationship between occurrence probability of surface settlement value greater than correspondance and maximum surface settlement shows a normal distribution; the maximum surface settlement values of effective precipitation and non effective precipitation station are -85.31～-93.29 mm and -126.16～-131.35 mm, respectively, and the probabilities of the maximum surface settlement value exceeding -60 mm are 53.30% and 74.96%, respectively according to data fitting. (2) The settlement deformation mainly occurs in the construction stage of the pilot tunnel and the arch lining, accounting for about 90%, and the settlement ratio in typical construction stage of top heading excavation,lower bench excavation,bean column system construction and arch lining construction is about 4∶3∶1∶2. (3) The settlement trough is consistent with Peck curve, the settlement trough width is 9.82～15.51 m, and the settlement trough width in the effective precipitation station is 3～5 m wider than that of the non effective precipitation station. (4) The ground loss rate is 0.56%～0.70% generally, and settlement trough width parameter is affected by precipitation effect significantly, ranging from 0.51 to 0.89. The conclusions can be used to preliminarily judge the maximum surface settlement of PBA station．