北江大堤管涌加固工程问题剖析

Analysis of Problems in Reinforcement Project of Beijiang River Embankment Piping

北江大堤石角段尽管经历了4次大规模的加固工程,但在十年一遇的洪水中,堤防仍然面临管涌险情。经对北江大堤石角段的管涌进行分析,发现这些反复出现的问题主要集中在红砂岩层。所谓的管涌通道实际上是红砂岩中的一些溶洞,是红砂岩中的碳酸盐钙质胶结物在水岩反应中流失钙离子后形成的,属于化学侵蚀的结果。北江石角段断裂带发育,江水通过断裂带与左岸的地下水直接连通,河水与地下水通过断裂带与溶洞往复流动,在CO_(2)的参与下发生水岩反应,导致红砂岩中的钙质胶结物被溶蚀,从而形成溶洞。在洪水期间,随着江水位上涨,外江水位高于地表,江水压力通过溶洞传递到堤角覆盖层之下。当江水压力大于覆盖层的浮容重,则会发生流土破坏,进而演变成为管涌。研究认为,在枯水期通过钻孔灌浆的方法将红砂岩层中的溶洞填充,才能全面消除管涌危害。

Despite undergoing four large-scale reinforcement projects,the Shijiao section of the Beiji-ang River embankment still faces the risk of piping during once-in-a-decade floods.An analysis of the recurrent piping disasters in this section reveals that the primary issues are concentrated in the red sand-stone layers.The so-called piping channels are actually cavities in the red sandstone formed by the loss of calcium ions from the carbonate calcium cement during water-rock reactions,representing a result of chemical erosion.The fault zones are developed in the Shijiao section,and the river water is direct-ly connected to the underground water on the left bank through the fault zone.River water and ground-water flow reciprocally through the fault zone and cavities,and water-rock reactions occur with the participation of CO_(2).This process leads to the dissolution of calcium-cemented materials in the red sandstone,forming cavities.During the flood period,as the water level rises and the outer river water level is higher than the ground surface,the pressure of river water is transmitted through the cavities to the layer beneath the embankment cover.When the water pressure exceeds the buoyant unit weight of the cover layer,soil erosion occurs,eventually evolving into piping.Research suggests that filling the cavities in the red sandstone layer through grouting with boreholes during the dry season is neces-sary to comprehensively eliminate the hazards associated with piping.