软黏土地层顶管隧道掌子面稳定性数值研究

Numerical Research on Face Stability of Pipe Jacking Tunnel in Soft Clay

土压平衡式顶管施工中顶进支护压力是维持前部掌子面稳定的重要施工控制参数。在软黏土地层中考虑分段顶进和开挖土体受扰动强度折减,采用数值模拟分析顶进掌子面支护压力不足引起的前部土体主动破坏模式、塑性区发展、地层扰动以及土体应力释放,在此基础上进一步研究顶管隧道埋深、管径、土层性质和不同扰动强度折减等因素对极限顶进支护压力的影响规律。结果表明:(1)当掌子面顶进支护压力逐步减小时,前部土体呈现半梨形外鼓破坏模式;塑性区在一定范围内发展近似形成半椭球形;掌子面应力释放率逐步增大,但不同部位处的应力释放率存在差异,掌子面中心处应力释放率大于顶部和底部;(2)主动极限顶进支护压力随着埋深和管径增大而不同程度地增大;土层性质参数对极限顶进支护压力影响的敏感程度依次为内摩擦角、粘聚力和弹性模量,其中内摩擦角和粘聚力受扰动折减程度对极限顶进支护压力有较为显著的影响,弹性模量扰动折减则几乎无影响。

Jacking support pressure is a significant control parameter to maintain the front face stable during earth-pressure balance pipe jacking construction. Considering segmented jacking and excavated soil strength reduction in clay,numerical simulation was applied to analyze the active failure mode of jacking face,plastic zone,stratum displacement and stress release which were induced by insufficient jacking support pressure. In addition, the influence rules of tunnel depth,diameter,soil properties and different strength reduction on the limit jacking support pressure were studied. The results show that:( 1) when the jacking support pressure goes down,the front soil plumps up as half pear-shaped; plastic zone develops into a semi-ellipsoid within a certain range; stress release rate of tunnel face increases step by step,while different positions show differences,stress release rate of face center is higher than that of the top and the bottom.( 2) as the tunnel depth and diameter go up,active limit jacking support pressure increases in different degree; the sensitive degree of soil parameter on limit jacking support pressure is followed by the internal friction,cohesion and elastic modulus,the strength reduction of internal friction and cohesion have obvious influence on limit jacking support pressure,however,the elastic modulus has not.