Pneumatic Sinusoidal Loading System

Abstract

Current systems for the application of cyclic loads to soil specimens are reviewed, and a low-cost system which provides a sinusoidal load trace using normal shop compressed air is described. Loading systems employed for cyclic shear testing of soil commonly employ one of two principles. In one type, a double acting piston is coupled to the specimen and the pressure or load is varied by selection through a directional solenoid vave. In those employing the electrohydraulic closed loop, a double acting hydraulic piston is coupled to the specimen. The pneumatic sinusoidal loader developed from commercially available components has 3 elements: a mechanical sine wave signal generator, a volume booster relay, and double-acting piston. The since wave generator consists of an adjustable eccentric, driven by a variable speed motor, connected to a plunger-operated regulator through a crank arm. The volume booster relays and boosts the quantity of air flow required to keep the output pressure matching the signal pressure from the plunger regulator. The main features are outlined of the new piston which has been designed for low inertial mass and low friction. An advantage of this system is the ease of operation. A graph is presented which illustrates the actual recording of a triaxial liquefaction test performed with the system.