多层堤基中土层结构变化对管涌影响的试验研究

Experimental researches on effect of foundation structure on piping in multilayer embankment

不同土层结构的堤基,管涌的发生和发展情形不同。利用室内试验,通过改变下伏砂层内夹砂层的级配组成,对3种不同夹砂层的多层堤基进行了管涌破坏过程的模拟,研究了不同颗粒级配组成的夹砂层对管涌发生及发展过程和机理的影响。试验结果表明,多层堤基夹砂层均为细砂时,承受的水压力较大,临界水力梯度较高,一旦发生管涌破坏后其渗透流量、涌砂量以及破坏范围都比较大,所以此类堤基发生管涌破坏时具有一定的突然性和剧烈性,应及早采取防治措施;夹砂层均为粗砂时,管涌破坏时的情形与双层堤基类似,管涌破坏的范围局限于砂砾层顶部,破坏深度有限;夹砂层为细砾时,发生管涌破坏的临界水力梯度较小,管涌破坏程度逐步增加且破坏速度较快,由于涌砂量较大容易使堤基产生明显的渗透变形。

The situations of the occurrence and development of piping are different because of different soil layer structures of embankment.Based on the laboratory tests,the destruction processes of piping of multilayer embankment with three kinds of different sand layers are simulated.By changing the grain-size distribution of the underlying sand layers,the effect of sand layers with different grain-size distributions on the mechanism and process of the occurrence and development of piping is analyzed.The test results show that when the sand layer of multilayer embankment is fine sand,it bears larger water pressure,and the critical hydraulic gradient is high.Once piping occurs,the seepage discharge,erosion mass and damage range are large.The piping failure of this kind of embankment is sudden and dramatic,and prevention measures should be taken as early as possible.When the sand layer is coarse sand,the situation of piping is like that of sand gravel layer.The damage scope of piping is confined to the top of the gravel layer,and the damage depth is limited.When the sand layer is fine gravel,the critical hydraulic gradient is small,the damage extent gradually increases,and the speed of piping is quick because large amount of erosion embankment can generate obvious seepage deformation.