Geotechnical model - Axis pile resistance This is a description of the input for axial pile resistance (T-z curve) in the geotechnical model. Select the checkbox labeled Calculate Axial Pile Resistance to enable. Three more parameters will then have to be specified. Pile Type Open end or closed end: Clay: Closed-ended piles – K=1.0 Sand: Closed-ended piles – K=1.0 Open-ended piles – K=0.8 Zone of influence, Zi: A dimensionless zone of influence, defined as the radius of the zone of influence around the pile divided by the radius of the piles, R. Curve fitting factor, Rf: This parameter adjusts curve shape. The figure below shows curves with different curve fitting factors - 0.5, 0.9 and 0.98.