考虑有机质赋存形态的含有机质土一维压缩与渗透特性研究

One-dimensional compression and permeability characteristics of organic soil considering the occurrence of organic matter

有机质在土壤中常以不同形态赋存,结合态和自由态是其主要类型,2种赋存形态有机质理化性质有较大差异。但一直以来,土力学领域主要关注有机质含量对土宏观工程性质的影响,有机质赋存形态方面鲜有报道。文章通过人工调配不同有机质含量土样,并基于傅积平法测试土样中不同赋存形态有机质的含量;利用改装的一维固结-渗透仪和常规一维固结仪对相同初始孔隙比e_(0)、不同有机质含量w_(u)土样进行一维渗压和蠕变试验,以期在明确压缩、蠕变及渗透性相关参数随有机质含量变化规律的同时,也厘清有机质赋存形态与上述指标的关联;最后基于压汞(MIP)试验结果,分析不同w_(u)土样在相同初始孔隙比(e_(0)=1.5)以及分级加载下的孔隙特征演变规律。试验结果表明:(1)压缩指数C_(c)总体呈现随w_(u)增大而增大的趋势,但C_(c)-w_(u)关系并非单调而是分段线性关系,分段点对应的w_(u)接近阈值w_(u), 2;次固结系数Ca与w_(u)呈单调线性增大关系。表明有机质赋存形态对C_(c)-w_(u)关系有一定影响,但对Ca-w_(u)关系影响不明显。(2)初始渗透系数kv0随w_(u)增大而减小,减小过程也可分为2个阶段,有机质赋存形态对kv0-w_(u)关系有影响;渗透指数Ck与w_(u)呈线性正相关关系,和有机质赋存形态无明显关联;(3)从MIP结果可知,对于相同e_(0)(=1.5)土样,w_(u)越大,其累积进汞体积减小,封闭型孔隙占比增多,PSD曲线从孔径分散的不规则型向孔径集中的单峰型转变;分级加载下,含结合态有机质为主的土样(w_(u)=4%)与含自由态有机质的土样(w_(u)=20%),二者PSD曲线演变过程不同。

Due to the interfacial interactions between mineral soil particles and soil organic matter(SOM),SOM occurs in various forms in the soil,and the mineral-associated particulate are fundamental.Many recent studies have focused on the effects of SOM content(w.)and type on the geotechnical behavior of soil.However,the researches on SOM occurrence form are insufficient.Hence,in this work,a study was carried out on the one-dimensional compression and permeability characteristics of organic soils with different SOM occurrence forms.Firstly,the soil samples with different w_(u) were prepared artificially,and the content of SOM with different occurrence forms in the soil samples was tested based on Fu's method.Then,one-dimensional consolidation and creep tests were carried out on the soil samples with the same initial porosity ratio(eo)and different w_(u),using the modified one-dimensional consolidation-permeability and the conventional one-dimensional consolidation instruments,to clarify the changing laws of the relevant parameters of compression,creep and permeability with w_(u) as well as the association of the occurrence forms of SOM with the above parameters.Finally,based on the results of Mercury-in-pressure(MIP)tests,the evolution of pore characteristics of soil samples with dfferent w.but with the same initial pore ratio(e_(0)=1.5)were analyzed under graded loading.The test results show that:(i)the compression index C increases with the increase of w_(u),and the fitted curves of C.and w_(u) were not monotonic but piecewise-linear,which can be divided into two straight lines with different slopes;the value of w_(u) corresponding to the inflection point of C_(c)-w_(u) curves was close to the threshold value W_(u),2.The fitted curves of secondary consolidation coefficient C_(c)and w_(u) were monotonically linear.It is shown that the SOM occurrence form has certain influence on the relationship between C and w_(u),but the influence on the relationship between Ca and w_(u) was not evident.(ii)Theinitial permeability coefficient kvo decreased with the increase of w_(u),and the decrease process can be divided into two stages,and the relationship between kvo and w_(u)was related to the SOM occurrence form;the permeability index C_(c)showed a linear positive correlation with w_(u),but there was no obvious correlation with the SOM occurrence form.(iii)From the MIP test results,for the soil samples with the same eo(=1.5),the larger w_(u) was,the cumulative mercury feed volume decreased,the percentage of closed-type pores increased,and the pore sizes distribution(PSD)curves changed from irregular types with scattered pore sizes to single-peak types with concentrated pore sizes.Under the graded loading test,the PSD curves of soil samples containing predominantly mineral-associated SOM(w_(u)=4%)and soil samples containing particulate SOM(w_(u)=20%)evolved differently.