Field Testing

[Nanyaro]

Hi,
We are living in arid area where summer temperatue rises up to 40 degree cengrade. During construction of road after laying the layers and compacted at optimum moisture content the next day you find the moisture content is very low especially if materials are non plastic.(eg say omc is 10% and next day you find mc is 4%). It happen in one of the project the field density was taken the next day using nuclear gauge and because of evaporation the moisture was found to be very low compare to OMC although densities were okay. The contrctor was intructed to re- do the work again by scarifying, addition of water and compacting to the requred denity and OMC. Is it fair for contractor to repeat the work? The instruction was given by engineer representing the client.

Best Regards,

 

[Ron]

The optimum moisture content is applicable at the time of compaction only, to aid the process of compaction. It has no relevance after the specified compaction is achieved. In fact, in most instances, the soil will not be at optimum after compaction. The comparison value to determine the percent compaction is the "maximum DRY density"...the moisture content is computed out.

The engineer was incorrect to require re-working. Once the specified compaction is achieved, you have no further need to compare to the optimum moisture.

 

[HSIII]

I have never heard of a contractor being required to add water after compaction was met.

If you have a sandy (pervious) material in your area, and temperatures reach in excess of 40C (104F), it is definitely not uncommon to lose moisture, either through evaporation of drainage.

I'm also wondering why the field densities were taken the following day as well as the previous day on the same material. Seems like a waste of time (I am not saying money because chances are cut/fill operations were continuing and the inspector needed to be there that day anyway) to have the same lift tested two sequential days.

If it was a contractor up here (RI) I can almost guarantee he would have said something along the lines of "I'll add water, but I'm not going to scarify and recompact it and waste time and money".

 

[BigH]

Ron hit it right on. Most specifications say that the compaction must be carried out within a certain moisture range of optimum - that is the compaction operation. This is why one compares the dry density to the maximum standard (or Proctor) dry density. The one caveat is with sands - uniform especially where after drying, they will be very susceptible (at the surface layer) to the loss of confinement - so if the material is a uniform sand, and the material sat for a while before the subbase is put on, then you might wish to water and recompact - but I certainly don't think you would need to scarify.

 

[Nanyaro]

Hi,

Thank you for your valuable contribution.

Best regards

 

[oldestguy]

This is why sometimes engineers get a bad name in the eyes of a contractor. Sounds like inexperienced inspection people on the job and a stupid contractor.

 

[0000005]

How to calculate soil bearing pressure from blow counts, cohisveless soil

 

[Ron]

0000005....start a new thread to ask a question. If you are a geotechnical engineer, you shouldn't need to ask that. If you are a student, go away. The forums are not for students.