This can be applied to a variety of soil as related to glacial activity. I think the more common material under this class is that deposited by glaciers and usually having been under a substantial weight of ice.
thanks for your reply. I actually went to wikipedia and looked at.
The source of the question is we are driving steel sheet piles for a 1400' long dock. There's insufficient boreholes but what there are of them indicated the toe of the SSP would be around 3' into glacial till before bedrock. There's about 12' of soft organic sandy silt then 20' of silty clay then about 3' of glacial till then bedrock. Driving the piles is like a hot knife in butter through the silt and clay and it's turning out the till? as well. I would have thought the till would have slowed the vibro down but it barely notices the till. In the past when I've excavated in till it's dense and hard. In any case the word till was used the geotechnical report uses the following; clayey silt, few pieces of gravel, stiff qu = 2.5k/sq.ft. and/or sandy silt few pieces of gravel firm (SPT 8 blows for 0.5 feet).
Thoughts? Is this Till? Sure doesn't seem like it when driving through it?
Remember the word till refers mainly to the material, not it's density. Sort of like saying "butter" but not saying it is at room temperature as compared to just out of the freezer. So 8 blows in 5 inches is certainly not the dense stuff you had experienced. As an example for the St.Lawrence Seaway construction years ago, the glacial till was so hard that it nearly had to be blasted for loosening. I know of one earth moving contractor that went broke due to that difficulty and he had big equipment. He bid the job like the till he had been used to.
till can refer to any sort of heterogenous mixture of clay, silt, sand, gravel and boulders. just because silt and gravel were found in one or two borings does not mean you will not hit boulders or stiff clay. chances are high you will.
