Importance of Automatization on Dry Funnel Deposited Specimens for Liquefaction Testing

Dry funnel deposition is one of the most commonly utilized specimen reconstitution methods for both triaxial and simple shear testing of sandy soils. The basic procedure of the method is simple, where the dry soil is deposited through a funnel, which is raised gently along the axis of symmetry of the specimen allowing the soil to gradually fill the space encapsulated by a split mold or stack of rings. The specimen can then be saturated by CO₂ flushing and de-aired water percolation. During funnel raising process, experimentalists could lose the control of the raising speed, vertical alignment (i.e. asymmetrical raising), or even could shake the funnel, which could influence the initial fabric and therefore the dynamic response of specimens. In this study, an automated funnel was designed and developed for an NGI type cyclic simple shear apparatus. The funnel has a control unit which allows various computer controlled funnel raising speeds. The funnel also has six extensions, each having 35 mm length. The present study investigates the influence of funnel raising speed and the height of the funnel (by using extensions) on relative density and cyclic liquefaction resistance of a clean and silty sand (with 10% fines content). An equation is developed showing the relationship between funnel raising speed and relative density of specimens. Accordingly, the relative density of specimens increase with increasing funnel raising speed in a logarithmic manner. Also as the number of extensions on the funnel increase, relative density of resulting specimens also increase. This is an important observation which shows that deposition process actually starts much earlier than the initial funnel movement, perhaps as soon as the experimentalist starts to deal with the soil. It was observed that both manual and automatic dry funnel deposited specimens have the same liquefaction resistance for a given relative density and CSR, implying that specimens at the same D_r have similar fabric. However, it was found that for a given funnel raising speed (frs), the fabric achieved by automatic dry funnel deposition is systematically looser than the one achieved by manual dry funnel deposition. Possible reasons are discussed.