soil density 5

[massagung]

i have problem regarding embankment, in specification agreement writen that density per layer (30 cm) is 95%, but due to in rush target we can not conduct compaction test for each layer (30 cm) but for increment 1 meter,. the height of embankment is 30 meter stand in soft clay,

but now we have problem because occur consolidation, but i ask to my mentor (certified GE), that the settlement occur is not because poor compaction but is more caused by foundation load. but the main contractor blame us that it occured because poor compaction.

but i need to make sure that soil density is already meet the specification, is there any method to know soil density with precision in 30 cm, for depth 30m?? no correlation method, with meet international standard.

pls hlp.

M.A.

 

[GeoPaveTraffic]

A good example of why rushing is a really bad idea.

Your best option at this point is to drill through the embankment and collect continous, undistrubed samples (such as Shelby tubes), and then run density tests on those samples. Once you have dry densities, you can compare those densitys to the standard compaction densities (assuming you took time to get those during construction). If you don't have standard densities, you may be able to make enought holes and collect enough sample to run standard densities after the fact.

Now that I have provided you an answer, why would any one build a 30 meter high embankment without performing a proper design and providing proper testing? In the end, if it was your company that made the decision not to test the material; your company deserves to pay out the nose to identify the extent of the problem and for the repair. Just no excuse.

Mike Lambert

 

[Ron]

Agree with GPT. Placing soil in 1 meter lifts is a bad idea, without regard to the soil type. If the soil is clayey, it is a recipe for big problems.

Settlement could be caused by numerous things.....including poor compaction. If the compaction increases after placement, settlement will occur...the void ratio will change with compaction, thus the volume will change. When you are only dealing with a volume change in one direction, that turns out to be....settlement.

Test as GPT noted...then open your checkbook.

 

[massagung]

thanks all,
settlement occur in bottom of embaknment (near with stand clay, isn't this can be proof that settlement is because of embankment loading? i have conduct spt test for embankment and N value about 20, this indicate that our compaction is not really poor or already met the specsification. the project are access road for mining.

M.A.

 

[Ron]

There is no good correlation between SPT and percent compaction in accordance with a laboratory standard. Don't depend on that.

Settlement might have occurred in the clay layer below the fill; however, insufficient compaction will cause additional settlement.

I'm surprised that consideration was not given to the clay layer and the consolidation that would occur with such a large overburden increase.

 

[massagung]

Hi Ron,
yap we understand that correlation SPT and percent of compaction is not a good way to know the actual percent of compaction. but we also need to stand up for oneself due to my Scope of Work in this project only for embankment work.

I have learn a lot in this case, now we need to install inclinometer pipes to monitoring lateral movement of embankment and currently already installed. i just need to proof that compaction is already meet the specification (another method) althougt we measure each 1 meter which it should each 30 cm (layer). and we will do UDS for many holes to conduct density test of course this its need extra cost but this is our mistakes missed the test each layer due to rush in time. and now the good news that owner will paid the UDS density test if all samples are pass with specification.

thanks all for your suggestion,




M.A.

 

[TomDOT]

Okay, let me see if I understand this:

You were contracted to verify compaction every 30 cm.

You chose to do it every 100 cm instead.

This means you performed 30 tests instead of 100. Did you give the owner a discount for to 70 tests you never performed?

You have settling, so something is obviously wrong.

You convinced the owner to pay for (more expensive) post-facto testing to replace the testing you should have done in the first place.

I'm also puzzled by this lack of time to verify compaction - I strolled down the hall to the soils guys, and they say it should take maybe one minute with a nuc gauge to verify compaction.

 

[massagung]

i never use nuc gauge before, and i do not know the accuracy same like CBR? or more accurate?
is really nuclear gauge just take one minute? and whether nuc gauge already met the standard ASTM or others?
how if we need to test each area 20 m x 50 m? and the total area is 20 m x 8000 m ?

M.A.

 

[TomDOT]

I pulled up a random manufacturer, their standard test time is 1 minute. Several ASTM and AASHTO standards are quoted in the data sheet. As for comparisons with other methods - I'm not a soils guy, they live down the hallway. This is their standard method in the field.

http://www.humboldtscientific.com/download/pdf/HS-5001SD_datasheet_0912.pdf

If you are compacting 20m x 8000m, I can't believe that it is all being compacted simultaneously. You can follow the equipment, verifying compaction as you go. You can also deploy multiple inspectors each with a gauge. One guy ought to be able to cover the whole thing in about 5 hours at your stated test frequency of every 50 meters. Less if he walks fast.

 

[massagung]

thanks tomDOT,

M.A.

 

[aeoliantexan]

If settlement is continuing, you can install settlement telltales at various depths including at the base of the embankment and monitor the settlement at various levels to determine whether the foundation or the embankment is compressing. Most likely, the embankment is compressing some; 1% to 2% strain would be common even with good compaction and should have been anticipated by the designer. If the foundation is soft clay, it is probably compressing more.

I suggest installing Sondex settlement gages in several of the holes you are drilling to take undisturbed samples. The Sondex can be installed using 3-inch corrugated drainage tubing with 2-1/2-inch flush-jointed PVC pipe inside it and weak cement/bentonite grout outside it. You can do the same thing with your slope inclinometer wells. Tie and solder wire rings around the corrugated tubing every few feet. The Sondex device is on a calibrated cable and is lowered down the PVC pipe to detect the position of each ring. If you extend the boring to incompressible material below the soft clay, you can get the data without surveying, because the bottom ring becomes your bench mark. See Slope Indicator Company's website for more information.

Am I correct in understanding that the fill was placed and compacted in 30-cm lifts, but only every third lift was tested? If the inspector confirmed that all lifts were properly moisture conditioned and compacted with the same procedure, your approach is defensible.

 

[BigH]

All,

I think we might all step back a bit . . . the OR stated that each lift was placed in 300 mm lifts - not 1 m. They carried out testing every third lift. It is difficult to determine whether this was actually the field density tests or the Proctor test - I will assume (hoping not to be the first part of the word) that the hiccup was in the taking of the field density tests in which to compare to the MDD value.

I am not sure of the OR's location, but given the syntax of his OR and subsequent responses, it is clear to me that he is not "practicing" in North America or Europe. It is quite likely that this is in Asia. Nukes are not typically used in many countries in Asia - rather the reliance is placed on the sand cone. (Why no nukes? In China, they were afraid that they would go sterile; in India, they were so afraid that the guy wore a lead vest when they did the test - go figure). Now with a sand cone, depending on the type of material being placed, it might take a day to get the moisture content (clayey soil) which is slower than the "desired" placement rate. (Not all labs will have done the needful and determine the rate of moisture loss in the oven so they could use a reduction from 24 hours if the dry mass has stabilized). As a result, the timing of receiving values is slow . . . This is my take on why compaction testing wasn't done every layer. It should have been done - and if they had chosen to risk placing subsequent layers prior to confirming the relative compaction - that is a risk many contractors will take. At least, having done the test, they would have, in the end, been able to prove compliance - their risk was thus justified . . . . or, on the other hand, they get reamed pretty badly.

I don't think that the OR suggested that the "stability" of putting a 30 m high embankment on soft clay was a problem - it would be hoped that engineering did go into the design of the embankment (In India we put 11 m on 6 m of Su = 20) clay - but used wick drains, stage loading and the like). So let's take at face value that the embankment is stable. It will, however, undergo settlement. There is settlement of the fill placed (even if placed at 95% or better) and then there is settlement of the underlying clay. Given the OR, it would not be a long leap of faith in that the underlying clay will settle more than the embankment fill (say embankment fill 1.5% of total height or 450 mm) and the underlying clay - depends. Many contracts (most I would say) state that payment for the embankment will be on "final" cross section and any settlement of the foundation and embankment would be included in the unit rate - hence any make-up fill would be included in the unit rate at tender - we had this problem big time on asphalt pavement work on a low embankment on soft clay.

The question then becomes - is the contractor trying to blame the OR (is he a testing consultant? or a subcontractor?)? As a first step, if it is available, I would go with a piezocone (ConeBoy - help me out) - and push it through the fill and into the underlying "soft" clay. One would be able to see if there is a uniformity of the embankment fill - that could then be correlated to the layers that were, in fact, tested. One might also, too, be able to determine the contact between the original approved foundation level on which the fill was placed and the embankment fill. This would be my first step. The second, as GPT stated, would be do do some continuous sampling of the fill to obtain "practically undisturbed" samples of the embankment fill for determining the wet/dry density. We just used a Japanese method of coring with a triple tube through residual soil - the system places a plastic sleeve between the inner core tube and the recovered soil - better than 95% recovery. In this system, one could do continuous density determinations.

Aeoliantexan has a good idea if you are needing to monitor the settlement. There are magnetometers that can be attached to the outside of inclinometer casing (with movement slip joints between each of the tube sections) - so if one is monitoring the movement by inclinometer, one can also have the settlement instrumentation as well.

Anyway - these are my thoughts at the moment. Seems to me that the contractor might just be trying to squeeze the OR because he didn't build in the settlement into his rate(s) or if he did, trying to get more out of it.

 

[massagung]

thanks all for the helpfull input and suggestion.

M.A.

 

[fattdad]

sorry to arrive late. Interesting problem. . .

In addition to all the great advice so far, I'd also consider a piezometer in the foundation soil to evaluate excess pore pressures. If the pore pressure is over the phreatic level, you have a consolidation process ongoing that is influencing the performance of the embankment.

f-d

¡papá gordo ain’t no madre flaca!