CYCLIC APPARATUS USING FRICTIONLESS AIR PISTON

A pneumatic cyclic shear apparatus constructed at the University of Texas at Austin has shown strong capabilities in testing soft clay samples under simulated wave loading conditions. Cyclic loads are applied to triaxial samples using a specially machined air piston having almost zero sliding friction. Varying air pressures are applied to this piston by an electro-pneumatic transducer. Thus, by applying a sinusoidal triangular variation in voltage to the transducer, a corresponding sinusoidal or triangular variation in output air pressure is obtained. The advantages of this new device are threefold. It is relatively inexpensive (about $2000); it is fairly simple with few moving parts and no complex electrical circuits and hence is dependable; and it is varsatile, having also been used in conducting stress-controlled static shear tests and short-term creep tests. The device can also perform cyclic compression tests at load frequencies less than 1 hz and with sinusoidal, triangular, and ramp pulse shapes. Due to the absence of friction in the loading piston, cyclic shear tests can be accurately performed on soft soil samples. The ability to apply to offset loads also gives the apparatus the capability of performing short-term creep tests under undrained conditions. In addition, by using a ramp function and varying the load frequency stress controlled shear stress can be performed with times to failure varying from great than 10 min to about 1 sec. Thus, viscosity effets can also be studied with the apparatus.

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  • Accession Number: 00179320
  • Record Type: Publication
  • Report/Paper Numbers: ASCE 13902 Proceeding
  • Files: TRIS
  • Created Date: Sep 14 1978 12:00AM