南水北调潞王坟段弱膨胀土膨胀性研究

Study of swelling characteristic of the weak expansive soil in Luwangfen for South-to-North Water Diversion Project

河南新乡潞王坟段膨胀土系第三系泥灰岩风化而成,以高岭石黏土矿物为主,具有弱膨胀性,其膨胀变形特性受孔隙结构影响比较大。为了清楚地研究试验段弱膨胀土的膨胀特性,从有荷膨胀变形、膨胀应力、循环胀缩变形3个方面进行研究,得出不同于以往其他膨胀土的膨胀变形特性:(1)当初始干密度比较小时,上覆压力超过膨胀应力,此时试样遇水不发生膨胀变形,反而出现明显的湿陷现象;当压实度大于96%后,即使上覆压力超过膨胀应力,试样遇水后也不发生湿陷现象,膨胀变形随上覆压力增大而趋于稳定值;(2)试验段弱膨胀土的膨胀应力随初始含水率的增加先增大后减小,出现膨胀应力峰值;(3)随着循环胀缩级数的增加,弱膨胀土的胀缩特性迅速降低,在循环级数达到4时,其胀缩特性就趋于稳定。上述3方面的膨胀特性充分表明,该弱膨胀土的膨胀特性与孔隙结构有着密切的关系。

The expansive soil in Luwangfen of Xinxiang in Henan is from the Tertiary marlite weathering, whose main clay mineral is kaolinite, and that owns weak expansive characteristic which is affected largely by the pore structure. In order to study the expansive characteristic of weak expansive soil in testing section, it studies of the expansion with loads, swelling stress and expansion-contraction cycle, and gets the different conclusions from other expansive soil before： （1） when the initial dry density is smaller and overlying loads are larger than expansive stress, the remolded weak expansive soil doesn＇t occur expansion, but collapsible phenomenon after immersing water; when the compaction degree is more than 96%, even when the overlying loads are larger than expansive stress, the remolded weak expansive soil doesn＇t occur collapsible phenomenon, and the swelling deformation tends to a constant value with the increasing of overlying loads; （2） The swelling stress of the weak expansive soil in testing section first increases then decreases with the increasing of initial water content, and occurs the expansive stress peak; （3） With the expansioncontraction recurring series increasing, the expansion-contraction characteristics of the weak expansive soil decrease rapidly, and the expansioncontraction deformation tends to be stabilized when the cycle progression reaches to 4th. The three expansive characteristics above show fully that the swelling characteristics of the weak expansive soil are related closely to the pore structure.