Experimental Study On Air Permeability Of Malan Loess And Uniformity Of Reshaped Samples Based On Air Permeability

The air permeability is closely related to the structure and properties of the soil itself,and is an important parameter often used in engineering practice.Soil air permeability characteristics are directly related to the stability and safety of engineering construction,and are also crucial in environmental engineering issues such as landfills.Using the improved ZC-2015 type air permeation device in this paper,taking the Malan loess from Heifangtai in Gansu,Yanan in Shaanxi and Xi’an in Shaanxi as the research objects,the effect of different factors on the air permeability of the sample was explored.And on the basis of indoor air permeability test,combined with different in-situ air permeability test devices to explore the air permeability test method suitable for Malan loess layer.An index for evaluating the uniformity of the sample is obtained by performing the indoor air permeability test on the reshaped samples of different uniformity.The results showed that:(1)The influence of the sample area,permeation length,dry density,water content and sample depth on the air permeability of the samples are very significant.The samples in Heifangtai area have coarse particles and large pores,resulting in the highest air permeability rate;the samples in Xi’an area have fine particles and few pores,resulting in the minimum air permeability rate.As the permeation length of the sample increases,the air permeability rate decreases due to the increase of the permeability path,but the final air permeability rate tends to be stable.With the increase of dry density,the decrease of water content and the increase of the buried depth of the sample,the air permeability rate gradually decreases.(2)Taking the results of the original sample indoor air permeability test as a reference,comparing the results of the insert in-suit and contact in-situ air permeability test devices.It is found that the results of the in-suit air permeability test are reliable.Comparing the results of the three kinds of air permeability tests,it is found that in the field with coarser particles and smaller water content,the insert probe and the indoor test have greater disturbance to the sample,air permeability test has a large result.The contact probe has the smallest disturbance and the result are the most accurate.In the field with finer particles and larger water content,the air permeability obtained by the three tests is basically the same.(3)The sample prepared by the indoor sample preparation method found that the dry density of the upper part of the sample is larger,the dry density of the lower part of the sample is smaller,and the dry density distribution in the middle of the sample is more uniform.Comparing the change of layered dry density of the test sample,it is found that the hit sample is less uniform than the compact sample.Sample preparation using the compaction method found that with the increase in the overall preparation height and dry density of the sample,the uniformity of the sample was significantly enhanced.And as the uniformity of the sample increases,the air permeability rate of the sample gradually decreases,so it is feasible to use the permeability to evaluate the uniformity of the reshaped sample.However,the problem of the connectivity of the pores of the original sample will be affected by natural factors,so the use of gas permeability to evaluate the uniformity of the original sample needs further research and discussion.