How much is too much? too much is when gravity becomes stronger than the sum of friction, cohesion, and adhesion.
As water is added to the sand castle, the pores (spaces between particles) begin to fill with water and the pressure in the pores changes from negative to positive.  These pictures show what happens as more water is added. Take a close look near the bottom of the castle, where the water first becomes visible at the surface.	The castle at first leans, then begins to slump.  The surface begins to glisten as water appears in the pores. Water can be seen in most of the pores even near the top of the castle.	Finally, the castle collapses on itself as the adhesive/cohesive forces weaken as the pores fill with water.  Then gravity does its job and pulls the castle down. This is the same principle that happens in mudflows. Some ponded water can be seen in the dish.
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Updated 06-23-2005. Copyright 2005. Clay Robinson, Ph.D., as to all resources: Materials may not be reproduced without Dr. Robinson's written consent. Students are prohibited from selling (or being paid for taking) notes or webpages during this course to or by any person or commercial firm without the express written permission of the developer of these pages.

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