中文摘要：

对盾构出洞口涌水、涌砂灾害问题作了分析，建立了地下水绕加固土体下卧层及井壁问隙渗流计算模型，利用半承压含水层渗流理论对一算例进行研究，结果表明，假定在井外加固土体完全隔水情况下，洞门涌土灾害的发生与否受到土体加固范围、井外地下水位及井壁间隙宽度等因素影响；土体加固长度的增加对工程安全有利，但成本较高；土体加固深度应根据具体工况经计算后确定，过深并不合理；井壁与加固土体之间的间隙控制也是工程安全进行的关键。各因素相互制约，需综合考虑工程安全性、经济性和工期等来确定合理的施工参数。

英文摘要：

The causes of piping and sand boiling of shield launching are analyzed; a model that groundwater permeates from reinforced soil pervious underlying layer to wall is established. Using semi-confined aquifer seepage theory, an example is given to demonstrate that, supposing that the reinforced soil is impervious, the accident that water and sand inflows from tunnel portal is influenced by range of soil reinforcement, groundwater level and the gap of wall; the cost and safety of engineering have the positive correlation with the length of reinforced soil; the depth of reinforcement isn＇t so deep but reasonable; the gap of wall also plays a key controlling role to shield launching＇s safety. The factors are mutual constraint; construction parameters are influenced by security, economy and time limit for a project.