一种原位测量非饱和土的气体扩散系数和渗透系数的方法与装置

Method and apparatus for measuring in-situ gas diffusion coefficient and permeability coefficient of unsaturated soils

气体扩散系数Dg和渗透系数Kg是研究非饱和土中气体运移的两个重要参数。推导了稳态条件下,非饱和土中气体运移参数的计算理论。该理论基于示踪气体浓度C与气体流量q1之间及压力梯度P与气体流量q2之间的变化规律,分别确定非饱和土的Dg,Kg。依据推导的理论公式,设计并研制了一种原位测量非饱和土的Dg,Kg的装置。开展土柱试验,利用新装置测量非饱和土的Dg,Kg,并采用单元试验和数值模拟验证新方法和装置的有效性。研究表明新方法测量的非饱和土的Dg,Kg与单元试验及数值模拟结果吻合良好。基于数值模拟开展的敏感性分析结果揭示:Dg测量准确度随土体的质量含水率w减少而降低,而Kg的测量准确度受含水量的影响不显著;非饱和土的Dg,Kg的测量准确度均随着注气球半径增加而降低,但是注气球半径对Kg的测量准确度的影响更为显著,当注气球半径增加到0.05 m时,其准确度约为55%;土体各向异性降低测量准确度,当竖向与水平向的气体运移参数的比值Dgv/Dgh和Kgv/Kgh均为0.1时,Dg,Kg的测量准确度仍可达到40%以上。

The gas diffusion(Dg)and permeability(Kg)coefficients are the two important parameters for the study on gas transport in unsaturated soils.In the present study,the theory of calculating Dg and Kg for unsaturated soils under steady state is derived.Dg and Kg of unsaturated soils are determined based on the relationship between tracer gas concentration(C)and gas flow rate(q1)and that between pressure gradient(p)and gas flow rate(q2),respectively.A device for in-situ measurement of Dg and Kg in unsaturated soils is designed and developed.The soil column tests are conducted to measure Dg and Kg of unsaturated soils with different water contents.Thereafter,the element tests and numerical simulation analysis are used to verify the effectiveness of the new method and device.It is found that Dg and Kg obtained by the new method are in good agreement with the results of the element tests and numerical simulations.The results of the sensitivity analysis show that the measurement accuracy of Dg reduces as the soil water content decreases,while the measurement accuracy of Kg is independent of water content of soil.The measurement accuracies of both Dg and Kg decrease with the increase of the radius of the aeration bulb,but the measurement of Kg is more sensitive to the change of the radius.The measurement accuracy of Kg is about 55%of the true value,when the radius of the aeration bulb is 0.05 m.The soil anisotropy reduces the measurement accuracy;when the values of Dgv/Dgh and Kgv/Kgh is 0.1,the measurement accuracies of Dg and Kg can still reach more than 40%.