Experimental study on flow resistance due to multi-pier of tunnel drainage system

Abstract

Hydraulic experiments are conducted to investigate the Manning roughness coefficient of the tunnel drainage system. Multi-pier with a rectangular cross-section is used for obstacles. Various uniform flows are achieved by adjusting the discharge and the bottom slope for each experiment to evaluate the Manning roughness coefficient easily and accurately. The Manning roughness coefficients for the multi-pier are evaluated for the various cases of longitudinal and lateral pier spacing and water depth. The results show that the Manning roughness coefficient increases with increasing water depth. It is also found that, when the water depth is fixed, the Manning roughness coefficient increases as the longitudinal pier spacing increases up to approximately the pier width. However, it decreases as the longitudinal pier spacing increases further beyond the pier width. On the other hand, when the lateral pier spacing increases, the Manning roughness coefficient decreases. The major findings in this study can be used for the derivation of an empirical formula to estimate the flow capacity of the tunnel drainage system if further experiments are conducted for various shapes and alignments of multi-pier.

利用多排矩形基桩模型进行水力试验，并在改变纵向及侧向模型间距及水深等条件下，研究隧道排水系统 的曼宁籼糙系数特性。曼宁粗糙系数则是由调整流萤及底床坡度所获得的均匀流来进行计算的，试验结果表明， 曼宁粗糙系数随水深深度的增加而增加。值得一提的是，当水深维持不变时，曼宁粗糙系数也会持续增加直至纵 向基桩间距与其宽度相同为止。然而，如纵向基桩的间距超过其宽度，曼宁租糙系数则会呈现衰减现象。当侧向 基桩的问距增加时，曼宁粗糙系数则会递减。对于不同形状的多排基桩及其配置的水力试验．该试验结果仍然可 用于计算隧道排水系统的排水能力，进而可总结出一条经验公式。