2. Cracks, surrounding the object and extending out from the object 

 corners, formed during the initial displacement phase. The extent of cracking 

 appeared to vary with the relative force level. 



3. The soil near the object moved upward and outward away from 

 the object. The soil farther away from the object moved downward. An 

 elevation view of an object immediately after the initial displacement phase 

 is shown below. 



soil surface before 

 force application 



4. After the initial displacement, the object moved upward very 

 slowly until finally becoming detached from the soil. Cracking became 

 more extensive as time progressed. 



5. The depth of the hole left after breakout, relative to the initial 

 object embedment depth, varied inversely with the relative force level. In 

 fact, for immediate breakout there was virtually no hole; whereas for very 

 long-term breakout the hole depth approached the original embedment depth. 



6. It is uncertain whether or not the object bottom usually became 

 detached from the soil before final breakout. The quantity resulting from 

 subtracting the initial embedment depth from the total upward object dis- 

 placement before breakout and adding the final hole depth might equal the 

 thickness of a water pocket beneath the object. However, this quantity might 

 also reflect downward elastic deformation after breakout or even erosion caused 

 by water rushing in behind the object during final breakout. This quantity 

 was usually small but greater than zero. In a few of the very long-term tests 

 (for example, 2 weeks), this quantity was virtually zero. 



7. The upward displacement immediately preceding final breakout 

 varied directly with the relative force level. 



On the basis of these qualitative characteristics, a few tentative 

 conclusions were drawn: 



20 



