钱塘江冲海积粉土渗透破坏试验研究

钱塘江冲海积粉土以砂质粉土为主，呈“高粉性、低黏性”的地区特点，在地下水动水压力作用下极易产生渗透破坏。粉土是介于砂性土和黏性土之间的一种过渡类型土，工程性质既与砂性土不同又与黏性土有较大区别。采用自行研制的粉土抗渗强度测定设备，对钱塘江冲海积粉土5种典型样本和微层理原状样本进行了渗透稳定试验。结果表明，钱塘江冲海积粉土渗透稳定性差，抗渗强度低；砂质粉土临界水力比降icr为1.01～1.25，破坏形式为局部流土，从临界水力比降icr发展到破坏比降iF的过程是瞬间的，基坑开挖遇到该类土层极易产生渗透破坏；黏质粉土临界水力比降icr随黏粒含量增加而增加，从临界水力比降icr发展到破坏比降iF有个短暂的过程，是整体流土破坏；钱塘江冲海积粉土渗透稳定各向异性；渗流垂直微层理方向的临界水力比降icr最大，是渗流沿微层理方向icr的2.5倍左右。研究结果为粉土地基渗透破坏防治提供参考。

Experimental study of seepage failure of Qiantang River alluvial silts

Qiangtang alluvial layers are mainly composed of sandy silt and have “highly silty and weakly clayey” characteristics. Seepage failures can be easily induced in these layers by the hydrodynamic pressure of underground water. Silt is a kind of complex transitional soil between sand and clay; and its property is different from both sand and clay. Seepage stability tests are conducted with the testing apparatus developed by authors on samples of five typical types of silt in Qiangtang alluvial layers (including sandy silt and clayey silt) as well as samples of undisturbed soil with horizontal beddings. The results of the tests show that Qiantang alluvial silt has poor seepage stability and low impermeability. In terms of the sandy silt from Qiangtang alluvial layers. (1) The critical hydraulic gradient (icr) of sandy silt ranges from 1.01 to 1.25. (2) It turns into local flowing soil when failure occurs. (3) Its transition from the critical state to the failure state occurs instantaneously; and thus deep excavation in such sandy silt layers can very easily cause seepage failure. As with the Qiangtang clayey silt. (1) Its critical hydraulic gradient increases with the content of clay. (2) Its transition from the critical state to the failure state is relatively slow compared to the sandy silt. (3) It fails in the form of whole flowing soil. The tests also reveal that the seepage stability of Qiantang alluvial layers is anisotropic. The seepage perpendicular to the horizontal beddings has the maximum icr, which is about 2.5 times the icr of the seepage parallel with the beddings. The research provides more knowledge on the prevention of silt seepage failure.