"Ester"-A new ring-shear-apparatus for hydrate-bearing sediments.

Abstract

We developed a new thermostated ring-shear-apparatus for investigation on hydrate- or ice-bearing sediments. A fluid inlet at the bottom of the static part of the cell and a fluid outlet at the top of the rotating half-cell allow exchanging and pressurizing the pore fluid in the sample cell to a certain value below the pressure providing the normal load that is applied hydraulically via a seal disk using a syringe pump. The volume change in the sample can be derived from the volume received or injected by the pump. The system allows the use of different methods for the formation and controlled decomposition of hydrate before, after, and during a shear test. The ring-shear-cell is designed for a maximum hydraulic pressure of 30 MPa. A commercial hollow shaft servo actuator applies the torque to the rotating half of the sample cell, and a rotary encoder provides information for determining the shear displacement. Stress path investigations in shear rate controlled experiments with large strain are possible with shear rates up to 12.6 mm/s and torques up to 1440 N m. The system design allows for complex experiments studying the behavior of a shear plane in hydrate- and/or ice-bearing sediments, including the decomposition and reformation of hydrate and/or ice under varying pressure and temperature conditions. It is a useful tool to provide experimental data to support research and engineering in solving problems related to permafrost and hydrate-bearing formations. The system performance is demonstrated by examples of tests on hydrate- and ice-bearing sand samples.