Gilson Pneumatic Direct/Residual Shear Machines are tabletop units that use Karol-Warner's proven CONBEL® loading system to apply vertical confining pressures to the specimen with increased accuracy. Confining loads are applied pneumatically using a small, rolling diaphragm piston for light loads of 4—100lbf (0.018—0.44kN) and a larger diameter piston for loads up to 1,500lbf (6.67kN).
Direct and residual shear values give important information for evaluating the strength and stability of soils. The test is performed on a variety of soil types with either undisturbed or remolded samples. The specimens are carefully trimmed into a Direct Shear Box, which is split to allow individual movement of the upper and lower halves. A vertical confining load is applied to the specimen, and a horizontal shear force is applied to the lower half of the shear box, while the upper half remains stationary. After shear failure has been measured, the force direction is reversed to determine residual shear values.
Loading is controlled using the precision regulator with included calibration chart. Load settings are displayed digitally and are accurate to ±0.25%. Both pneumatic shear machines are completely self-contained, and the need for loading weights is eliminated.
A stepper motor drive controls strain rates to ±1% from 0.0001—0.3in/min (0.0025—7.62mm/ min), and is easily set with digital thumbwheels. Total shear capacity is 1,500lbf (6.67kN). HMA-735, 2.5in (63.5mm) diameter stainless steel shear ring, porous stones, drainage plates and a water chamber constructed of Teflon coated, anodized aluminum for corrosion resistance are included.