Bank Weight of Soil Same as Max. Dry Density 3

[jafcon1]

If soils report states that Maximum Dry Density of Sandy Silt is 121.5 lbs/cu ft, would this also represent the Bank, or Natural State Weight? The soils report has no shrink/swell percentages, and I am trying to arrive at some reasonable adjustment factors. Any help would be appreciated.

 

[ashjun]

Hi,
If I understand your query right; it is difficult to make an approximation of the natural density from the maximum dry density test results. (if someone has seen one please let me have a copy, would be interesting).

To evaluate the natural density, you definitely need to obtain some cores or do sand replacement tests at site. These are very cheap tests and can be conducted easily.

Having said this, 121.5 pounds per cubic feet is approx 19.5 kN/m3; this is not much for a maximum dry density; which can be up to 21 or so for a well graded material. For all approximations, you could assume a natural density of 17 kN/m3. I presume it is an embankment and generally could be clayey silts. Any case, you must state you density assumption clearly (you have to save your back).

Cheers

 

[Ron]

jafcon1...you need to provide a bit more context for your "maximum dry density" statement. This term is usually associated with a laboratory test to determine such for field comparison to in-place density after compaction. If they are using the term to imply bank density, then you should ask the Geotech to clarify.

Get the terms clarified as I have seen lawsuits over such. The 121 value may or may not be high, depending on the nature of the material. Densities can vary all over the board....90 pcf to 130pcf or more.

 

[jafcon1]

Perhaps I aked my question in the wrong way. What I'm trying to determine is if it is reasonable to use the Geo Lab's Max Dry Density Weight as Loose Weight Estimates for trucking? Or am I way out in left field?

 

[BigH]

Not only in left field, but in foul territory. I might estimate that the loaded truck is 85% of MDD standard - typically, when you dump sand it is in this round figure. Ashjun - our silty sand here has a MDD modified of only 1.55 to 1.6g/cc. We are below the specified "minimum" MDD value but we've passed it for use - why pass up a good sand for embankment construction just to use a heavier clay with PI of 40?

 

[Ron]

Jafcon1...BigH is right. Now you are in litigation territory. 85% is a reasonable estimate of bank density to maximum dry density; however, it is very easy to determine the in-place density of a material, excavate a small amount and determine its density again after the "bulking" associated with excavation. If you are moving a lot of soil, a small error in these estimates can cost a lot of money in the transportation/placement/compaction of the materials.