INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Select Fill Materials

Select Fill Materials

(OP)
Could someone help me in understanding the term "Select Fill" materials. I understand these fills are not expansive and can substitute the expansive soils in order to decrease the potential vertical rise of the sub-grade soil due to moisture variations. What are the typical ingredients of select fill materials. I presume they are sand and clay. How many percent clay do they have? Thank you.

RE: Select Fill Materials

We have a standard specification for Select Fill. I think it's defined as a granular material with no material than can't pass through a 3 inch sieve and a PI less than 15 (maybe 30). If the Geotechnical Engineer has a different definition we adjust this.

RE: Select Fill Materials

Where I work, "Select Fill" is a general terms that means the best locally available material for the intended purpose. If the specification gave ideal properties, the material may have to be brought in from a long distance away (say, > 100 miles). Not cost effective... unless absolutely necessary.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Select Fill Materials

select fill is defined by our specifications. Our specifications are likely consistent with the FHWA.

f-d

ípapß gordo ainÆt no madre flaca!

RE: Select Fill Materials

Usually is is granular material with no plasticity (very little if any silt or clay). A common material is that used as fine aggregate for concrete.

RE: Select Fill Materials

As others have alluded, "Select Fill" is not a clearly defined term within the profession and depends a lot on what is available at a particular site as SRE notes. In my area, "Select Fill", presumably meaning "Select Structural Fill" is generally taken to mean relatively clean fine sands having less that 10% passing a No. 200 sieve, non-plastic and having less than 5% organic loss on ignition. In other areas, that specification will change depending on the nature of the materials available.

RE: Select Fill Materials

(OP)
Thanks for all enlightening answers. This is related in a project in North Texas. The select fill has a PI of less than 15. But the gradation is not available. For soil expansion analysis,I require the typical percentage of clay in the select fill. I wonder if someone can provide me an answer to this as well. Thanks.

RE: Select Fill Materials

select fill or select material is locally defined and generally project specific. It will be different if this for use in a landfill, structures, landscaping or for road construction. For instance, landfill select fill would be lean clay, clayey sand or clayey gravel. Structural select fill would be GW, GP, SW, SP with low PI. you will need a sample of the proposed material if there is no spec. However, with a PI less than 15, I would assume that the percent clay would be need to be very low

RE: Select Fill Materials

is it a highway job?

f-d

ípapß gordo ainÆt no madre flaca!

RE: Select Fill Materials

(OP)
Thanks fattdad and cvg. The select fill in here's context is for replacement of usually top expansive soils to reduce the heave of footings due to seasonal moisture changes for low rise structures. It has similar application in roads and highways. The FHWA did not have any any item on this when I carried out a word search. Maybe it is more of the states rather than federal scales. E.g. TX LA, CA, ..

RE: Select Fill Materials

I agree that the terms "select fill" and/or "structural fill" have different meanings across the US as noted above. In areas where expansive and fat clays are common and granular materials are not, select fill may be a clay of low expansion/plasticity. In these areas it is necessary to call a material "select granular fill" if that is desired and provide the appropriate specifications

As an example, if one has an highly expansive foundation material, removal and replacement with compacted lean clay may be a better solution to keep water from the expansive soil foundation than sand as an example. Usually a LL and PI requirement would be specified and possibly expansion/swell testing to confirm that the material does not have the same problem as the material being replaced.

TX, CO, KS, MS all have their issues with expansive & fat clays so I would look in those areas for local standards of practice regarding foundation treatment in expansive soils.


RE: Select Fill Materials

(OP)
Thanks Doctormo for letting me know which states have expansive soils. The information I received from all respondents were useful and conclusive and thanks to all.

One more aspect of expansive soils that I have been looking for is the estimation of uplift pressures on the bored pile's skin, when the dry soil swells. I very much appreciated a feedback on this subject, too, if possible.

RE: Select Fill Materials

I work in North Texas, and our earthwork specs include a section on earth fill classifications. For select fill we commonly specify Class 4 Earth Fill, defined as SP, SM, SC, CL, or dual classifications thereof, which have a liquid limit less than or equal to 35 and a plasticity index of a minimum of 4 and a maximum of 15, which are free of organic materials.

This may have some swell potential, but much less than the CH it may be replacing. Materials used are often sandy clay or clayey sand.

We will amend the specification to meet the particular needs of the project.

RE: Select Fill Materials

I'm afraid the OP has missed my point, so I'll restate it.

On a project with federal DOT funding, there is a likelihood that, "Select Fill" is as defined by the FHWA. I've provided that link. On jurisdictional or private projects, I'd agree that there is local convention that may allow such select fill to include USC classifications, CL, or ML, or other? Clearly in private practice, the specifying engineer can define it at will. Nobody in DOT work would defer to such local custom; however, as the FHWA definitions would prevail.

f-d

ípapß gordo ainÆt no madre flaca!

RE: Select Fill Materials

(OP)
aeoliantexan, I wonder if I should start a new string or you could kindly let me know how you choose the uplift pressures on pier footings. I have seen 0.5 to 1.1 tsf but wonder on waht base they are recommended. Thanks.

RE: Select Fill Materials

I haven't done much of this. I think it is pretty common local practice to assign about 0.5 tsf upward skin friction to the pier through the seasonally active zone of expansive soil. One would expect that this would vary with the strength of the material, but apparently it is conservative enough. I will check with some of my associates.

RE: Select Fill Materials

(OP)
aeoliantexan,

I am still looking for the uplift pressure estimation - theoretical or empirical values. Das textbook has a section on this but it is complicated and I guess overestimates.

RE: Select Fill Materials

(OP)
Okiryu,many thanks for the link. Is there any upper bound for the uplift pressure as the PI of soil increases. The local consultants in Texas use much lower values for high PIs. I wonder if aeliantexan could also give me an opinion on this. Thank you.

RE: Select Fill Materials

I do not deal too much with expansive clays, so I would also like to see aeoliantexan's input.

RE: Select Fill Materials

Sorry to be slow; I've been distracted.

My associate confirmed that local practice (Dallas area) is some variation on about 1000 psf upward skin friction or adhesion applied over the depth of seasonal variation (commonly about 10 to 15 feet). He prefers a higher skin friction applied to about 2/3rds of the seasonal variation.

In dry weather, the undrained strength of our clays can be much higher than 1000 psf. But is the soil swelling and heaving at that time? Has the clay in the top few feet shrunk away from the wall of the pier? In wet seasons, will it both swell and soften from the top down?

Like a lot of rules of thumb, the practice generally seems to work most of the time. I would be cautious about applying it in other parts of the country.


RE: Select Fill Materials

Thank you aeoliantexan to open the blackbox. Trying to understand better, you referred to the undrained strength of clays in Dallas areas. Is there any rule of thumb between the uplift pressure and the undrained strength? The one discussed earlier was between the PI and uplift pressure, which I thought to be very conservative. I would appreciate your comments on this too. I have also seen that they use 1000 psf but is this uplift pressure the same in all clay soils in Dallas area? The question is still how to estimate the uplift pressure and based on what soil parameters (in Dallas area). Hope you can shed some more lights on this.

RE: Select Fill Materials

I don't have any handy relationships or rules of thumb for swell pressure. You can address it with swell testing in the oedometer, of course. One would think that there should be a relationship between unconfined strength and swell pressure, because both are related to relative water content. I just assume that if the soil is highly plastic, hard, and dry it will probably swell too much. Locally, the PVR, Potential Vertical Rise, is used a lot by practitioners and derided by academics. You can find it in the TXDOT Soil Manual. This just estimates the potential movement under overburden load, not pressure.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close