Thick-walled cylinder collapse strength

The so-called TWC-test (Thick-Walled Cylinder test) is carried out in a pressure vessel under hydrostatic loading.

The plug used for this test has a particular geometry: As usual in compressive strength testing, plugs are applied with a length to diameter ratio of 2:1. In addition to this, however, a central hole of 1/5 to 1/3 of the plug’s diameter is drilled and a thick wall cylinder remains. The most common diameters for TWC-tests are between 1.5" to 60 mm with a central hole of  0.5". At Gesteinslabor we use plugs of 60 mm diameter.

The sample is placed into a sleeve to avoid the intrusion of the confining pressure fluid into the sample. The inner hole remains atmospheric and the confining pressure is increased hydrostatically. At some point, the sample cannot withstand the pressure and fails, usually starting with failure of the central drill hole wall. The failure will be visible as a pressure drop and the failure stress point is recorded. Moreover, the confining pressure over time and the volume of pressure medium over time will be reported.

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In September 2019 the Swiss National Cooperative for the Disposal of Radioactive Waste (NAGRA) commisioned Gesteinslabor with UCS, Brazilian and triaxial tests on neighbouring rocks of the Opalinus Clay - the rock which will host Switzerland's future facilities for nuclear waste disposal.

Gesteinslabor receives funding from BMWi for the development of a new test rig. With this funding, our company will open up a new business field in renewable energies by implementing an innovative technology to determine the capillary threshold pressure with hydrogen on cap rock of underground gas storage facilities.