井点降水措施对大断面海底隧道施工安全影响分析

EFFECT OF DEWATERING WITH WELLS ON CONSTRUCTION OF SUBSEA TUNNEL WITH LARGE CROSS-SECTION

正在施工的厦门东通道海底隧道是我国第一条大断面海底隧道,其地质条件差,地下水丰富,翔安端进口段施工过程中结构变形严重。为了提高围岩强度,降低地下水的影响,根据国内外类似工程的施工经验,现场采用了井点降水措施。为探知井点降水的施工效果,首先通过在现场试验(如浸水崩解试验及剪切试验等)获得施工阶段围岩的物理力学参数;然后利用有限差分法进行数值模拟,分析井点降水前后隧道施工安全性的变化情况;最后通过对数值模拟结果与现场监控量测数据进行综合分析,确定井点降水的施工效果:在采用井点降水工程措施后,可以使隧道拱顶下沉量减小约50%,水平收敛减小约30%,且拱部塑性区范围大幅度减小,支护安全性系数显著提高。

Xiamen East Passage subsea tunnel is the first subsea tunnel with large cross-section in China,and its geological conditions are complex and unfavorable with enriched groundwater. The deformation of tunnel support in the entrance of Xiang′an part is great. To reinforce the surrounding rock and reduce the effects of groundwater, the constructor dewaters the water level with wells based on in-situ experiences of similar engineering. To ascertain the effect of dewatering with wells,the parameters of wall rock by field experiment,i.e. disassemble experiment,shear experiment,are gained;and then,the construction safety was calculated with numerical analysis. Finally,the effects of the dewatering wells were achieved with the results of numerical analysis and locally measured data. The effects are mainly shown as follows:the arch-crown settlement of tunnel will be decreased to 50%,that of and horizontal convergence will be decreased to 30% after considering the dewatering wells; meanwhile,the range of plastic area also will be reduced to large extent,and the tunnel support safety will be increased.