杭州湾浅层储气砂土的持水特性试验研究

Experimental Study on Water Retention Characteristics of the Shallow Gas-bearing Sand in Hangzhou Bay

杭州湾嘉甬跨海高铁大桥遇到的储气砂土是一类特殊的非饱和土,以往砂土类主要以重塑样进行持水特性试验,而实际工程中,原状样的结构性对持水特性具有显著影响。以杭州湾储气砂土为研究对象,基于压力板仪试验研究了不同初始孔隙比砂土原状样与重塑样的持水特性,对比分析Brooks-Corey模型、Van Genuchten模型和Fredlund-Xing模型对砂土土-水特征曲线(soil water characteristics curve,SWCC)的适用性;利用等粒球状颗粒的不同排列方式分析了产生基质吸力差异的机理。结果表明:Van Genuchten模型更适用于描述和预测杭州湾储气砂土SWCC;对于相同孔隙比下的砂土原状样与重塑样,重塑样比原状样的失水斜率更小,但重塑样与原状样的进气值基本一致。原状砂土与重塑砂土不同的颗粒排列结构是造成其SWCC差异性的主要原因之一,重塑砂土比原状土具有更加均匀的孔隙分布,原状砂土结构性对SWCC的影响不可忽略,采用原状储气砂样的Van Genuchten模型可为实际工程提供更精准的预测和参考。

The gas-bearing sand of Jiayong High Speed Railway Bridge is a special kind of unsaturated soil.Due to the structure of the original specimen has a significant effect on the water holding capacity of soil,the experimental results of water holding characteristics for remolded sand do not represent the real situation.The water holding characteristics of the original and remolded sample of the Hangzhou Bay gas-bearing sand with different initial pore ratios were studied through the pressure plate test.The sand soil-water characteristic curve(SWCC)were compared and analyzed by Brooks-Corey model,Van Genuchten model and Fredlund-Xing model,and the mechanism of matrix suction difference was studied by using different arrangement of spherical particles.The results show that the Van Genuchten model is more suitable for describing and predicting the SWCC of Hangzhou Bay gas-bearing sand.The water loss slope of and remolded sand samples is smaller than that of undisturbed sand samples,but the air intake values of remolded sand samples are basically the same as that of undisturbed sand samples.The reason for the difference of SWCC is the different grain arrangement structure of undisturbed sand and remolded sand.There is more uniform pore distribution in remolded sand than the undisturbed sand,and the influence of the undisturbed sand structure on SWCC does not be ignored.The Van Genuchten model with undisturbed sand sample can provide more accurate prediction and reference for practical engineering.