compaction test

[emad84]

i work in project of construction building, we have earth work and back fill .

we are facing problem in compaction of backfill ,we can not get 95% or over in first layer although we had checked in all sides of compaction operation many times ,including, porctor & compaction test .

NOTE : kind of soil of natural ground calcareous sandy silty clay .


pleas kindly . help us ?

 

[Ron]

Post some of your data. What is the classification of your fill material? What Proctor method are you using? What type of compaction equipment? What is the moisture content at the start of compaction? What type of soil is below this layer in the range of 12 to 24 inches? What is its compaction level?

How are you testing? (what methods for in-place density and moisture)

Are you required to get 95% of the standard Proctor or is the requirement for a modified Proctor?

 

[emad84]

the classification of fill material is A-1-b (thickness of the layer is 10 inch).

a modified Proctor is our method .

the moisture content at the start of compaction is 7-9.5%.

type of compaction equipment is roller 25 ton .

type of soil is below this layer in the range of 100 and more inches is a brown color & calcareous sandy silty clay stiff to vary stiff and dump to wet .


method for in-place density and moisture is nuclear gauge and sand cone ,same time .(we have same result ).

 

[oldestguy]

Something here seems missing. Sometimes for granular materials the act of compacting the sample causes a change in gradation, with coarser materials breaking down so the percent of voids is lower than "normal". One can check on this by using a fresh sample for each moisture point on the Proctor curve. There also may be an optimum somewhat below the moisture content of the fill used, explaining the situation, to wet a material.

Another point that may have to be addressed is "why 95 percent?". What is the use for this compacted backfill? That use may not require such a high density. In these cases, a discussion with the project engineer may be useful.

I have used another approach when faced with compaction problems with granular materials. Then the acceptable relative density is used for control, generally 70 percent or higher. Then, either a Proctor test or a vibration "compaction" method is used for the high end of the range.

 

[Ron]

What you have is a constructability issue. The subgrade soil below the layer you are compacting is likely not sufficiently stiff to accommodate the compaction of the overlying layer. It's a bit like trying to compact soil on top of a bed mattress.

I would suggest a couple of approaches you might use....

1. Use lighter compaction equipment but compact in 2 or 3 layers. Don't use vibratory. Consider a sheepsfoot roller if your fines content is greater than 15%. It will require more passes, but will prevent overexcavation and additional compaction of the natural subgrade.

2. Make sure your moisture content is slightly beyond optimum when you start compaction (not much...just about 1%). This will allow the material to dry during compaction and will allow faster densification.

3. Since you have an A-1-a material, it is likely you have quite a large fines content...this makes the material very sensitive to the proper moisture content.

Nothing wrong with your requirements. They are common and reasonable.

 

[darthsoilsguy2]

before you placed the fill, did you test the subgrade by driving a loaded dump truck all over it to see if the subgrade moves or have any weak spots to repair?

 

[emad84]

yeah sub-grad move down and weak ,it like Sponge piece .

 

[darthsoilsguy2]

well there's the problem.... and perhaps there may be a groundwater element to this that hasn't been discussed....

the 2 most typical things to do in that case are to 1.undercut the subgrade to suitable subgrade for compaction or 2. use of an engineered geotextile (geogrid or a woven, depending). item 1 requires knowing there is something down there. item 2 requires an understanding of how that material will interact with the subgrade, fill materials, suitability for the final design, and an understanding of the subgrade conditions to the point of knowing it will not affect final design

there are other approaches like lime stabilization, pushing surge stone into the soft spots (aka... rip-rap, or 4" nominal angular hard stone) but, the first 2 i discussed are the most common. the correct approach involves reviewing the plans, soils report, site visit with heavy equipment available, and observation of the implementation of the fix...

the placed fill needs to be assessed whether it needs to be cut out to do it again, or can be built on top of. i would assume cut until proven otherwise.

 

[bb29510]

look this not going be in the books but with the wet clayey material on the bottom, you won't never get compaction, its like beating on a trampoline , you going have to stabilize to give you something to work with, sand, two foot lift of clean sand, also your backfill lifts are too thick for that roller, 10 inch of clayey material is difficult, cut back to 6-8 loose lifts. if that still doesn't work, Jumping jacks