Soil Resistivity Testing And Its Application In Dynamic Slaking Test

Many water-related subgrade diseases are appeared during the development of heavy haul railway, such as mud pumping, subgrade subsidence, uneven settlement etc, these problems hinder the reformation of existing railway seriously, it can be found that coupling effect of constant dynamic stress and water reaction is the main factor that causes these diseases. Therefore, it is significant to learn moisture migration and dynamic slaking deformation for treating them. Dynamic triaxial apparatus is used to study the dynamic properties of soil, however, due to the limit of pressure chamber, the change of water content along the height of sample can’t be tested during the process of testing mechanical parameters. Under the support of National Natural Science Fund “Research on subgrade dynamic slaking deformation mechanism and adaptability of existing heavy haul railway”, A moisture migration test system and test methods that based on van der pauw method are developed in this paper, which can test soil resistivity to reflect water content in real time. This system is applied in indoor dynamic slaking triaxial test in order to analyze the dynamic slaking properties of subgrade. The main content and test results are as follows:(1)A set of moisture migration test system and test measures that based on VDP method are developed.(2)The relationships between soil resistivity and water content of flat unit sample under different compactness are studied, the test results of 4 compaction degrees are fitted by exponential function, which has a good correlation, and the formula is verified. Soil resistivity sensitive factors such as porosity ratio, saturation,compactness and mass water content are analyzed. The relationship between soil resistivity and porosity ratio of flat unit specimen under different water content is linear and finally converge to one point. The relationships between soil resistivity and compactness, mass water content are more distinct than saturation.(3)The sensitivive factors of VDP method to test resistivity is defined,theoretically, the applicable objects of this method is flat specimen, so it is necessaryto study the effects of temperature, electrode size, sample height and other sensitive factors on testing resistivity with VDP method, the influence law of these factors on this method is mastered by making some corresponding test. The concept of“conversion factor η”, “Influence line of height effect” are proposed by analyzing the test results of titanium electrodes(5×10 mm), the conversion of soil resistivity from different location along the non-flat specimen height to flat specimen is realized successfully, and the general formula of water content which consider height effect is deduced, it provides theoretical support for testing moisture migration.(4)Moisture migration test system is applied in GDS dynamic triaxial apparatus in dynamic slaking test, moisture migration and slaking deformation of the specimens under different dynamic stress amplitudes are studied, the result shows that the inflow is less when the dynamic stress amplitude is higher, and the slaking deformation is synchronous bigger.(5)A modified slaking backbone curve that can reflect the actual wetting process is proposed, which can provide reference for subgrade future deformation in dynamic slaking.