An Experimental Study On The Pore Diameter Distribution Of NMR Expansive Soil Dry And Wet

At present,there are many studies on the measurement of macroscopic indexes in the dry and wet cycle,and the micro index of measurement is less.The reason was that the precision of the micro test was not ideal after the dry and wet cycle test.Nuclear magnetic resonance（NMR）has the characteristics of nondestructive and high precision,which was suitable for the study of some microscopic effects of dry and wet cycle.There were mainly two ways to study dry and wet cycling test,one way was without load,the ring knife limits the lateral volume of the soil and that the dry and wet cycle test was carried out under no load condition;another was also a ring knife limits the lateral volume of the soil,and the vertical load was applied to the pattern on the ring knife by the weight.In this paper,a set of simple device which can simulate dry and wet cycle and test NMR under the action of load was developed,which can simulate vertical load of soil at different depths.There was no unloading phenomenon in the process of dry and wet cycle test using this device,which were well realize the simulation of actual load of the project.In order to study the characteristics of NMR under the action of expansive soil dry and wet circulation,which that nanning expansive soil was selected as the research object,on the sample 0 kPa,10 kPa,20 kPa under,this level 3 load 0⁶ times of the dry and wet cycle test,magnetic resonance（NMR）measurement of soil samples after dry and wet cycle test,then the area of the NMR T₂ curve、the volume of the specimen and the shear strength were compared.The result as followed:（1）Using Teflon material,an indoor test device was designed to simulate the dry and wet cycle by the lever applied load.The device has been tested and verified to be able to complete the combination of dry and wet cycle test and nuclear magnetic resonance（NMR）test,which can keep the sample under load during water absorption saturation and dehydration.（2）The peak value of the pore distribution curve of Nanning weak expansive soil and the peak value of NMR T₂ curve are calculated by the peak method,which the relaxation rate is0.085×10^-6m/ms.By comparing different dry densities and the same test conditions,the error is within 8%.（3）By comparing the NMR T₂ distribution curves of the dry and wet cycle tests under the0kPa,10kPa and 20kPa loads,The increase of pore diameter distribution along with the increase of pore size is inhibited with the increase of load.（4）Discovered by NMR test,With the increase of dry and wet cycles,the area of T₂ curve was gradually increasing.When the volume of T₂ was compared with the size of the sample,the measured area of the NMR T₂ atlas changes when the volume of the sample was changed during the cycle.With the increase of the load in the effective range,the development of the total pore volume represented by the area of the T₂ curve was gradually limited.（5）Using nuclear magnetic resonance test,measuring volume and direct shear test found,With the increase of load during the dry-wet cycle,the change of T₂ curve area,sample volume and shear strength will gradually approach stability.