Hydraulic Conductivity Procedure (Falling Head Test) for Compacted Soil

[ditapark]

Hello everyone, I'm doing some test for landfill design for my research.

I have some specimens that need to be tested, and all of the specimens are a mixed soil between four type of soils, which are organic/peat soil(in USDA classification it classified as loamy sand), kaolin (USDA classified as clay), bentonite (USDA classified as silty clay), and laterite soil (USDA classified as loam).

I've done the physical and mechanical characteristic test for all the four soils I'm using, which are water content test, specific gravity test, bulk density, atterberg limits, hydrometer & grain size distribution, compaction test, and also itself permeability (using falling head test).

So, after done with all the test, we mixed the soils between the organic and kaolin, organic and bentonite, laterite and kaolin, also laterite and bentonite with varies percentage. After mixing it, we do the compaction test for the mixed soil, and get the optimum water content for the permeability test.

So the problem is, I'm doing a permeability test with falling head method on these mixed compacted specimens using a mold with diameter 10.02 cm (3.94 in), and height 11.58 cm (4.56 in). After done the standard proctor compaction test using the water optimum content that we got from previous compaction test, and then we start install the mold permeameter to falling head test tool, and place the water to the standpipe, and wait until all the soil in the mold saturated. Since the mold I've been using is 11.58 cm height, it took a while to get saturated and being compacted itself also hard to make the specimen get saturated. My question is, is there a way to make the specimen get saturated quick? If yes, could you share with me how to do that? If no, is there a different method that I could use? What would you suggest? Should I use different mold?

Thank you so much before!

 

[GeoPaveTraffic]

For those soils, I would do a constant head test instead of a falling head test. Then you can use backpressure to improve you saturation.

Mike Lambert

 

[oldestguy]

If there are two floor levels in your building, go to a stairwell and use that height for a much higher head.

 

[RocEngineer]

Increase the hydraulic gradient by increasing H and/or decreasing the sample length L. Just a side note with regard to landfill design, organic soils are not typically desirable for use as liner material.

 

[Ron]

Agree with GPT....using a falling head test on low permeability materials has more room for error than constant head test. Evaporation is an issue with either, but more controllable for constant head test.

 

[ditapark]

Hi GeoPaveTraffic & Ron
I was told to try to use Rowe Cell. It just my problem right now is how do we know if our specimens are fully saturated or not. We could do triaxial test to make the sample saturated using Triaxial CD right? But the sample size for the triaxial test is different for the sample size for the permeameter mold which is the issue right now. Is it possible to use the disturbed soil samples for triaxial test? I bet the soil will be fragile. What you guys idea about to make the specimens saturated?

RocEngineer
So the original soil in the landfill site is classified as organic or peat which are like more than 10m depth and the landfill size itself is so huge. So we just trying to use the organic to see if it acceptable or not. We actually going to change the soil using the laterite soil. We just want to see which specimens have lower hydraulic conductivity.
About decreasing the sample length, we actually going to do it with molding the compacted soils using 3 cm height and diameter 7cm. But the problem right now is, we don't know about whether the soil is saturated or not. Whats your suggestion?

 

[RocEngineer]

See ASTM D5084, which touches upon the verification of saturation.

 

[fattdad]

the measurement of permeability in compacted samples is highly variable to compaction water content. Consider the work of Mitchell, Hooper and Campanella, ASCE, July 1965, "Permeability of Compacted Clay." The only way to benchmark the permeability is also to specify 100 percent saturation. Inundation in water does not guarantee saturation, as the blebs of air, may not be displaced by the trivial head of inundation. Triaxial-cell backpressure saturation is the traditional approach.

In compacted fine-grained soils, there can be orders of magnitude differences between a compacted sample prepared below the LOO (line of optimums) and above the LOO (again, refer to Mitchell, Hooper and Campanella). So, we would always specify compaction water contents for laboratory testing and in field compaction control, based on a degree of saturation - typically 90 percent saturation represents the LOO. With the compacted sample, we'd then run saturation to 100 in the laboratory.

Good luck in your research!

f-d

ípapß gordo ainÆt no madre flaca!