the Water in the Soil - GN6 Articles

Since the time of his first involvement in Civil Engineering projects dealing with soil dynamics, Hodge became increasingly uncomfortable with having to use the standard method and means of Geotechnical Theory. These are based on dry Soil Mechanics principles with the influence of water being a simply buoyant add-on. Over time (~ 20 years), he developed his own understanding of how the ground would naturally behave while undergoing forced deformations in the time-domain.

Following established practice, he offered his insights to Geotechnique, the ICE journal, and apart from having it rejected out of hand, this rejection came with the further dismissive diktat that "it should not be revised nor resubmitted". So, for the purpose of offering my reasoning to others in the profession I wrote, in non-academic language, the Water in the Soil. This work appeared as six separate articles in Geotechnical New over the fifteen months between December 2010 and March 2012.

For easy reference, those six articles are available here through the following links to PDF versions:

GN Part 1 GN Part 2 GN Part 3 GN Part 4 GN Part 5 GN Part 6

For anyone who might want to verify the numerical values printed in these articles, or better still, improve on them, the full source code (un-compiled FORTRAN) is provide through the following links to the three main computer programs which Hodge wrote for that specific purpose.

Fall-Velocity Relationship Soil Permeability Deformation-Gradient Relationship

In the intervening time since publication I have had a chance to think about what I wrote then, and will take this chance to clarify one point, and add some emphasis to another:

Silts and Liquefaction

Although non-cohesive deposits of silt- and clay-sized particles (for instance, tailings slimes) will not liquefy under dynamic loading, it needs to be said that they will temporarily loose much, if not all, of their shear strength. Whereas sand-sizes, when turned to a heavy fluid, become subject to the high hydraulic gradients resulting from the energy transferred from solid particles to the surrounding water, silt and clay sizes become a viscous fluid, without involving any increase in pore pressures. Sands normally manifest liquefaction failure by concentrated venting of supernatant void water through a few weak spots in the overlying deposit. And, in these circumstances, because each "volcano" carries the flow from a relatively large area of surrounding ground, exit velocity can be sufficient to transport sand (and even gravel) particles out of the ground. This is not the case with sub-sand sized particles.

Loose Ends

I am happy with where I got to by the end of GN Part 6, but as I see it, that was really only the starting point for building a new coherent and rational hydrodynamic approach to geotechnical design. In particular I did not do a good job in making the clean link I wanted between void ratio changes and pore water gradients. But I believe I did set out a robust skeleton that can be fleshed-out by researchers younger than my 75 years. And the triaxial compression machine is, most certainly, not for the junkyard. It is the ideal piece of laboratory apparatus (in its drained configuration) for evaluating the "Crowding" K-factor.