compaction test

[Ahmesaad]

Dear all
if we compact a soil, and we neet to test this soil , we found that the degree of compaction in sample at depth 10 cm is higher then at surface
i need to know why, and i need a paper explain that
thanks

 

[Ron]

The most common reason for this is lack of confinement at the surface. As the soil dries at the surface, it can move a bit thus reducing the apparent compaction. It is also more susceptible to disturbance from traffic or other influences. This is common with granular soils, particularly fine sands.

Check any of the classic geotechnical texts.

 

[Ahmesaad]

thank Ron, can you name a paper explain this i want scientific answer to introduce it

 

[BigH]

Do a search of D'Appolonia. This is explained well, if I remember correctly, in Terzaghi Peck and (now) Mesri. Another reason that the surface might show a bit less compaction is that the compactor needs to "grip" the soil in order to move forward and therefore will disturb the immediate surface. If testing in sand (say river sand), it is, in my view, better to test the layer placed previously. Test the current layer after placement and compaction of the succeeding layer.