拱形双排隔离桩对既有隧道的保护效果研究

采用隔离桩来保护邻近基坑的既有隧道是工程中常用方法,目前隔离桩平面排列形式多采用传统的矩形行列式。以杭州市某房建地下室基坑工程为例,提出由直线形排桩和弧形排桩组成的拱形双排隔离桩及相应的优化方案,采用ABAQUS有限元软件建立三维模型,研究了隔离桩中心距、桩半径、平面位置以及弧形排桩曲率半径等因素对隔离效果的影响,并与实测结果进行对比。结果表明:隧道衬砌总位移存在最大值和最小值,隧道衬砌总位移最大值点位于拱底,最小值点位于拱顶,隧道衬砌整体呈现出沉降的趋势。减小隔离桩中心距或增大隔离桩半径均可减小隧道衬砌的位移,拱形双排隔离桩的保护效果优于传统形式;将拱形双排隔离桩设在距基坑10 m处,并将弧形排桩设在隧道一侧更合理;弧形排桩曲率半径对隧道保护效果存在合理值;采用优化方案时隧道位移比原方案减小45.7%,隧道更趋于安全。

Study on Protective Effect of Arched Double Row Piles onExisting Tunnel

Isolated piles are often used to protect existing tunnels at the edge of foundation pits in engineering practices. Currently, traditional rectangular pile layouts are mostly adopted in the arrangement of isolated piles. For the excavationof a building basement in Hangzhou, the arch double row isolated pile, which iscomposed of straight row piles and curved row piles, and the corresponding optimization scheme were proposed. A three-dimensional model was established by using the finite element software ABAQUS, and the influence of center distance, pileradius, plane position, and radius curvature of pile on the isolation effect was studied, together with a comparison with measured results. The results show that there is a maximum and minimum value of the total displacement of tunnel lining; the maximum total displacement of tunnel lining is located at the arch bottom, the minimum value occurs at the arch top, and the lining of the tunnel showsa general trend of subsidence. A reduction of the center distance and an increase of the pile radius can reduce the tunnel displacement, and the isolation effect of double row piles is better than traditional ones. Moreover, a reasonable arrangement is that the arch double row isolation pile is located at about 10 m away from the foundation pit, and the curved row piles are deployed at one side ofthe tunnel; there is a critical value of the curvature radius of curved row pilefor maximizing the protection effect on the tunnel. Finally, the tunnel displacement is reduced by 45.7% using the optimized scheme as compared to the originalscheme, and hence the tunnel tends to be safer.