Abstract
Permeability is an import character of soil, especially in excavation and tunnelling. Hollow cylindrical apparatus (HCA) is often used to determine soil anisotropy, particularly soil strength and stiffness under different directions of major principal stress, so complex stress paths can be simulated and the corresponding soil properties can be examined. It can also be used to determine the permeability coefficient if a special mode is added, therefore the seepage test can be expected. Owing to no seepage test has been conducted by HCA before, the complete procedure of HCA seepage tests after static and dynamic loading are respectively studied. And the seepage stability stage is discussed since only data in this stage are valid and reliable for permeability calculation. The results show that:1) when the difference in average permeability coefficient within unit time (3600 seconds) less than 2% in 24h, it is reliable to take the average permeability coefficient in this period as the ultimate permeability in static seepage test; 2) for dynamic test, if the average permeability in 3600 seconds varies with 5% in 24h, the average permeability coefficient in this period can be taken as the ultimate value. Research in this paper provides a solid foundation for HCA seepage test under complex stress paths.
Highlights
Since the concept of "permeability coefficient" was published in the 1850s [1], many scholars have devoted themselves to study the influencing factors and measuring methods of permeability coefficient
Permeability from triaxial permeameter is much better since the confining pressure pushing the latex film closely attached to the soil surface, which makes the elimination of sidewall leakage possible [6]
Considering the test efficiency and result accuracy, when the difference in average permeability coefficient within unit time (3600 seconds) less than 2% in continuous 24h, and the permeability coefficient in each unit time has no obvious increasing or decreasing tendency, this stage can be defined as the stage of seepage stability, and average permeability coefficient in this period can be taken as the ultimate permeability coefficient
Summary
Since the concept of "permeability coefficient" was published in the 1850s [1], many scholars have devoted themselves to study the influencing factors and measuring methods of permeability coefficient. One of the major difficulties in the seepage test is the sidewall leakage [3] In response to this difficulty, scholars are committed to reduce the errors by smearing water proof materials and adding O-rings [4,5], but there is no significant effect. From this perspective, permeability from triaxial permeameter is much better since the confining pressure pushing the latex film closely attached to the soil surface, which makes the elimination of sidewall leakage possible [6]. This paper focuses on stable stage study in static and dynamic permeability test and aims to provide a theoretical basis for HCA permeability test and dynamic loading effect on permeability
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