×
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!
  • Students Click Here

*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.

Students Click Here

Jobs

Difference between Marl and Chalk

Difference between Marl and Chalk

Difference between Marl and Chalk

(OP)
Hello,

I recently had a site with two different geotechnical reports (same site, two reports from different years) and the subsurface conditions were similar (depth of clays, bearing stratum, etc), but one of them used Chalk for the bearing stratum, and the other used Marl". Both were found at the same depths.

Are these two types of soil basically the same?? can they be used interchangeably? Or what is the difference?

Thanks!

RE: Difference between Marl and Chalk

I really don't know, but. . .

In my world, chalk is a rock and marl is a soil - a soil composed of calcium carbonate.

f-d

ípapß gordo ainÆt no madre flaca!

RE: Difference between Marl and Chalk

Chalk is a rock but can be encountered in different Classes in the UK, from intact blocky Chalk to Chalk performing like fine grained soil. CIRIA report C574 (Engineering in Chalk) is the gospel in the UK for working with Chalk.




What type of tests were undertaken? For a Clay i would expect atterbergs, triaxials, odeometer. For a Chalk , depending on the grade (i.e. intact or structureless) it could range from UCS, NMC, saturated moisture content, atterbergs, PSD, to name a few.

Clay will obviously consolidate and this will be the primary cause of settlement, however for Chalk, consolidation settlement is relatively small and occurs quickly.

RE: Difference between Marl and Chalk

Geologist in the house- a marl is a lime-rich mudstone derivative i.e. a blend of lime and mud; chalk on the other hand is a biogenic limestone, usually almost pure lime derived from the skeletons of cretins on the ancient sea floor.

So the lime content is the main difference- in respect of bearing capacity the terms could safely be used interchangeably.

All the best,
Mike

RE: Difference between Marl and Chalk

In UK, "marl/marly" might be used for all grey/non-white chalk or even calcareous glacial clay by non-geologists. The term may be accurate according to what the geology actually is (on the map and in specimen), or written as a loose description of what a person saw having some knowledge.

RE: Difference between Marl and Chalk

To the OP: There's no chalk in Virginia (USA). We do have marl in our Coastal Plain. I like MadMike's explanation and it does make sense.

Unrelated to all this, I reflect on a rhetorical question, "What is the RQD of chalk?" I ask this question, because I'd expect if we had it in Virginia, the drillers would just drill through it with the auger or tricone, try an SPT and then make some claim of some sort. Who'd ever see a coring attempt!

Then I reflect on the other question, "If we actually had core, would it score an RQD?" According to the ASTM (the standards we follow mostly in the USA), rock core that can be broken by hand is excluded.

f-d

ípapß gordo ainÆt no madre flaca!

RE: Difference between Marl and Chalk

I like MadMike's description as well. One significant distinction, particularly in driven piles, is the ability for marl to remold after driving. I don't think the same happens with chalk. This is significant because in many of the coastal plains marls, driven piles that seem to have insufficient capacity during driving will usually reach capacity if they are left alone for a few days and upon retapping, the capacity is much higher.

RE: Difference between Marl and Chalk

Quote (Ron)

One significant distinction, particularly in driven piles, is the ability for marl to remold after driving. I don't think the same happens with chalk. This is significant because in many of the coastal plains marls, driven piles that seem to have insufficient capacity during driving will usually reach capacity if they are left alone for a few days and upon retapping, the capacity is much higher.

Is that gradual movement back towards the pile the "remolding" you mentioned?

RE: Difference between Marl and Chalk

@racookpe1978....yes

RE: Difference between Marl and Chalk

@Ron - remoulding of chalk is possible too. Driven CIP piles and CFA piles perform better that standard driven concrete or Steel piles

RE: Difference between Marl and Chalk

Thanks, EireChch......I have no experience with chalk, but have dealt with limestone marls as they are common in the Southeastern US coastal areas.

RE: Difference between Marl and Chalk

Here is an answer I recently received regarding chalk vs marl,

Generally, chalk is thought of a fine-grained sedimentary rock that is composed of a high percent (say 90%) of pelagic carbonate (forams, coccoliths, etc.). There can be a small component of siliceous microfossils, clay, and framework silicate silts.

Marl is usually though of as an impure chalk with a much higher content of clay and silt grains. The marls in the Alabama Coastal Plain, for example, are usually about one-third pelagic carbonate, one-third clay, and one-third silt (quartz and feldspars, mainly).

Chalk is oceanic, whereas marl may be oceanic or lacustrine. Chalk is most common in the Cretaceous System, whereas marl has no restrictions in the time scale.

The engineering properties of chalk and marl have some similarities, but also some differences (mainly due to clay content of the marl).

I have to say that there is some confusion in the literature about these two terms and that can be frustrating. Some early writers did not make much distinction between chalk and marl, for example, in the Alabama Coastal Plain. There is no agreed petrologic boundary between chalk and marl, as far as I know.

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! Already a Member? Login


Resources

eBook - 10 Reasons to Choose CATIA on the Cloud
To compete in today’s fast-paced and competitive market, smaller and newer firms need a powerful platform that will enable them to compete with bigger players, without the heavy investments needed in computer hardware, software and personnel. Download Now
White Paper - Smart Manufacturing for Electronics
This white paper describes a transformative approach to electronics manufacturing made possible by the addition of Mentor Graphics to the Siemens family. It describes a completely digitalized strategy that supports both printed circuit board (PCB) and mechanical design and manufacturing, uniting the entire product lifecycle – from idea and production to customers and back. Download Now

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