How can I account for pile spacing out of plane?

Any 2D program, whether it be RS2 or Slide, can only model support with out of plane spacing using some smearing technique out of plane.  For true 3D behaviour you need a 3D program.  In the case of Slide, support is smeared by dividing the capacity by the out of plane spacing to get an equivalent capacity per unit length out of plane.   To model support with bending stiffness in RS2, such as piles, you need to do something similar to the modulus and moment of inertia.  This can be done by using the reinforced concrete liner model and spacing the support.  Tutorial 24 discusses tunnel lining design.  The same concept can be used for piles.

Another option is to determine factored properties using area weighting.  The paper cited below presents one method by which to do this (see section 4, page 10). 

Carranza-Torres, C., Diederichs, M. (2009)  Mechanical analysis of circular liners with particular reference to composite supports.  For example, liners consisting of shotcrete and steel sets.  Tunnelling and Underground Space Technology.  24(5):506-532

 

This is the method that the reinforced concrete liner model uses.  In RS2, in the reinforced concrete liner material properties, you want to turn off the concrete and simply enter the piles as reinforcement with their respective moment of inertia, etc. (see image below).  In the RS2 Interpreter, you can go into the support capacity plot and look at the moments, axial forces, and shear forces in the piles.  Tutorial 24 illustrates how to do this.

Phase2-linerproperties.png

Define Liner Properties dialog:  Specifying reinforcement only
 

In addition, Evert Hoek's Kersten lecture deals with the spacing of steel sets.