基于核磁共振的土体有效孔隙比及其渗透性研究

Study on effective void ratio and permeability of soil based on nuclear magnetic resonance

为了探究水头差和孔隙结构对土体渗透性的影响,测定重塑土样在8种水头差作用下的核磁共振T_(2)曲线。将土体孔隙划分为有效孔和无效孔,并定量分析有效孔与水头差的关系,最后引入水头差、有效孔隙比对Kozeny Carman渗透模型进行修正。研究显示,随着水头差从0增大到50 m,T_(2)曲线积分面积和T_(2)最大值均逐渐减小,T_(2)最小值几乎不变;有效孔隙比随水头差的增加而呈指数增大,而无效孔隙随水头差增加呈指数减小。孔径尺寸是影响土体渗流的关键因素;水头差作用下,土体大孔隙优先排水,并逐渐向微孔隙发展;水头差的增大会提高土体的有效孔隙比,导致更多孔隙参与渗流,渗透率显著增大。基于有效孔隙比的修正Kozeny Carman模型更适用于黏性土路基稳定性分析与防渗设计。

To explore the effects of hydraulic head and pore structure on soil permeability,the NMR T_(2) curves of disturbed soil were measured under 8 kinds of hydraulic head.The pore of soil was divided into effective pore and invalid pore,and the relationship between effective pore and hydraulic head was quantitatively analyzed.Finally,the hydraulic head and effective void ratio were introduced to revise the Kozeny Carman permeability model.It was found that the integral area and the maximum value of T_(2) curve decreased gradually as the hydraulic head increased from 0 to 50 m,and the minimum value of T_(2) was almost unchanged.The effective void ratio increased exponentially with the increase of hydraulic head,while the invalid pore exponentially decreased.Pore radius is a key factor affecting seepage of soil.Affected by the hydraulic head,pore water starts to drain firstly from macropore and gradually develops to micropore.The increase of hydraulic head raises the effective void ratio,leading to more pore participating in seepage and a significantly increase of soil permeability.The modified Kozeny Carman model based on effective void ratio is more suitable for subgrade stability analysis and anti seepage design in clay soil.