广州南沙深厚软基段盾构隧道长期沉降计算

为解决盾构隧道沉降预测现有计算方法考虑因素单一、以短期预测为主等问题,提出在软土固结和流变共同作用下的隧道沉降简化计算方法，并通过实际工程案例进行验证。首先，利用Merchant流变模型和太沙基-伦杜立克二维固结理论构建固结-流变耦合模型,该模型将盾构隧道的长期沉降分为2部分： 超静孔隙水压力消散引起的主固结沉降和土体流变引起的次固结沉降;然后，考虑地表荷载、土层性质、结构自重以及列车荷载等因素对沉降计算的影响，求解出隧道长期沉降解析式;最后，选取新建盾构隧道3个典型断面，利用该解析方法对隧道的长期沉降进行预测，并对超静孔隙水压力消散时间、沉降速率及最终沉降量进行对比分析。结果表明： 1）运营初期，隧道周围土体超孔隙水压力的消散速度较快，尤其是在最初的2年内最为明显；随着时间的推移，各断面的消散速度逐渐趋于稳定。2）盾构隧道的长期沉降与下卧土层的性质有关;下卧土层厚度越大，性质越差，所产生的沉降量越大;断面1、2、3最终沉降预测值分别为146.8 mm、97.6 mm和46.1 mm。

Long term Settlement Calculation of Shield Tunnel in Section of Deep Soft Ground in Nansha District,Guangzhou

In order to solve the problems of single factor and short term prediction in the existing calculation methods of shield tunnel settlement, a simplified calculation method of tunnel settlement under the combined action of consolidation and rheology of soft soil is proposed, which is verified by a practical engineering case. Firstly, the consolidation rheological coupling model is established based on the Merchant rheological model and Terzaghi Rendulic theory of two dimensional consolidation. The long term settlement of shield tunnel is divided into two parts by the model, i.e. the main consolidation settlement caused by excess pore water pressure dissipation and the secondary consolidation settlement caused by soil rheology. And then, the long term settlement analytical formula of the tunnel is solved by considering the influences of surface load, soil characteristics, structure self weight and train load. Lastly, three typical sections of the new shield tunnel are selected to predict the long term settlement of the tunnel, and the dissipation time of excess pore water pressure, settlement rate and final settlement are compared and analyzed. The results show that: (1) In the initial stage of operation, the dissipation speed of the excess pore water pressure of the soil around the tunnel is faster, especially in the first 2 years. With the passage of time, the dissipation speed of each section tends to be stable gradually. (2) The long term settlement of the shield tunnel is related to the character of the underlying soil; the greater the thickness, the worse the character of the underlying soil layer, and the larger the settlement. The final settlement prediction values of sections 1, 2 and 3 are 146.8 mm, 97.6 mm and 46.1 mm, respectively.