有机质对黏性土热传导系数的影响与机制

Influence and mechanism of organic matter on thermal conductivity of clay soil

有机质是土中常见组分,对土体热性质有显著影响。为明确有机质对黏性土热传导系数影响与机制,以膨润土为基质,通过添加腐殖质制备不同有机质含量土样。利用热探针法测定其热传导系数λ,分析λ随干密度ρ_(d)、含水率w(饱和度S_(r))和有机质含量w_(u)的变化规律;并通过分析膨润土对有机质的吸附特征,探讨了有机质对土热传导系数影响机制。试验结果表明:有机质含量w_(u)相同时,热传导系数λ随干密度ρ_(d)、含水率w、饱和度S_(r)增大而增大。在土体饱和、ρ_(d)相同条件下,λ随w_(u)增大而减小,但并非单调线性递减关系;可分为急剧下降段、过渡段和平缓下降段3个阶段。过渡段对应的w_(u)大致范围为7.5%~15.0%。通过傅积平法测试得出膨润土对紧结态有机质饱和吸附量w_(u,1)大致为8.0%,对紧结态+稳结态有机质的饱和吸附量w_(u,2)约为14.0%;即有机质赋存形态变化的两个阈值(w_(u,1)、w_(u,2))和λ-w_(u)关系曲线过渡段对应的w_(u)基本吻合。机制分析表明:除有机质含量外,土中有机质赋存形态变化也是影响土热导系数的重要因素。分析了几种热导系数理论预测模型对含有机质黏性土的适用性。

Organic matter is a common component in soil and has a significant effect on the thermal properties of soil.To clarify the influence and mechanism of organic matter on the thermal conductivity of clay,bentonite was used as the matrix to prepare soil samples with different organic matter contents by adding humus.Thermal conductivity coefficient λ was measured by thermal probe,and the variation of λ with dry density ρ_(d),water content w(degree of saturation S_(r))and organic matter content w_(u) were examined.By analysing the adsorption characteristics of bentonite to organic matter,the influence mechanism of organic matter on soil thermal conductivity was discussed.The results show that the thermal conductivity coefficient λ increases with the increase of dry density ρ_(d) water content w and degree of saturation S_(r) when w_(u) is the same.When the dry density ρ_(d) of saturated soil is the same,λ decreases with the increasing of w_(u),but is not a monotone linear decline.It can be divided into three stages:sharp descent stage,transition stage,and gentle descent stage.The approximate range of w_(u) corresponding to the transition stage is 7.5%to 15.0%.The saturated adsorption capacity w_(u,1)of bentonite to compact organic matter is about 8%,and that of w_(u,2)to compact+stable organic matter is about 14.0%.In other words,the two thresholds(w_(u,1),w_(u,2))of the variation of organic matter occurrence form are consistent with the w_(u) corresponding to the transition section of the λ-w_(u) relation curve.Mechanism analysis shows that in addition to the content of organic matter,the change of organic matter occurrence form is also an important factor affecting the thermal conductivity of the soil.The applicability of several theoretical prediction models of thermal conductivity for clay soil containing organic matter was analysed.