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Simple shear

Fugro uses two types of simple shear machines. The Geonor machines were developed in Norway for research into the behaviour of quick clays and the Marshall Silver machine was developed in America to study behaviour of soils subjected to earthquake loading.

The test is similar in some ways to the direct shear box, except that great care is taken to ensure that shear strains throughout the test specimen are uniform during shearing, with soil behaviour during pure shear loading being more accurately simulated. Fugro says boundary effects prevent Mohr circles being drawn, so the primary purpose of the test is to determine soil strength and monitor strain and pore pressure development.

The test is used to assess soil behaviour under earthquake loading and for ground response beneath large offshore gravity base structures under storm wave loading. Simple shear machines are not usually equipped to measure pore-water pressure.

Instead, the specimen height is kept constant (within around 0.002mm) by changing the applied vertical load. As the sample volume remains constant, the change in load applied to the specimen may be equated to the change in pore-water pressure.

The hydraulic system allows high frequency testing (up to 20Hz). The control system is updated up to 2,000 times per second to keep maximum control of the test specimens as they approach failure.

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