Gypsiferous soils

[killswitchengage]

Hello
Can someone point me toward any free content about problems relatd to Gypsiferous soils for foundations ?
What paramater can be affected by the presence of gypsum deposits , especially for clayey soils ?
Can we find Anyhdrite in arid regions like deserts ?
thnaks

 

[fattdad]

I think the concern is when sulfur is present (i.e., oxidized pyrite) there can be remineralization to form ettringite, which can provide uplift pressure. There are likely other factors and I'm mostly interested in the responses of others. Funny think is last Thursday or Friday, a buddy of mine called me to ask about shale in Kentucky with a similar concern.

f-d

ípapß gordo ainÆt no madre flaca!

 

[killswitchengage]

good i await others that dealt with such soils before .
Thing is a wise client decided to plant trees in the desert very close to his foundations , and shower the soil with endless irrigation water. Soil consists of gypsiferous clays and or clayer soils with heave potential . Funny thing is all constructions consists of a lobby building only , and suffered fissures in the masonery only ( no damage to the structure ) . I am interested on the effect of gypsum and anhydrite on soil behavior , although there are many articles around in the net .

 

[Ron]

I agree with f-d....water is the enemy in this case. Gypsum is relatively stable when dry, but not so much when wet. Further, as f-d noted, you have the potential with gypsum (calcium sulfate) to form ettringite, particularly delayed in the case of very dry conditions becoming wet over time. This will result in expansion. Also, there is a likelihood that you also have dolomitic conditions as well (CaMg(CO₃)₂). Within these, you have the potential of unreacted Calcium, unreacted Magnesium and significant expansion potential when exposed to water.

Additionally, all of these constituents will dissolve in water, thus changing the volume if sufficient water is available.

 

[killswitchengage]

Thanks Ron
What about collapse potential ?

 

[killswitchengage]

guys i see that Ettringite mostly form in the presence of a Gypsiferous soil treated with lime which provide the necessary chemicals

 

[fattdad]

Duh. . . I forgot to add that soil modification/stabilization can be the trigger - whether lime or cement stabilization.

I sort of know what you mean by, "gypsiferous" soil. I just don't know whether, "gypsum" is truly the bad actor. I mean gypsum already has the water in mineral form. Now anhydrite could be a bad actor, just like oxidized pyrite can lead to a very mobile form of sulfur.

f-d

ípapß gordo ainÆt no madre flaca!

 

[killswitchengage]

Why not ft ? of course gypsum is bad considering the client pour endless water on it , its soluble so materials are being washed away and create therefore cavities and karst

 

[fattdad]

according to Dana's manual of mineralogy, Gypsum is soluble in hot, dilute HCl. You do recall that alabaster is used for artistic carvings and the like. So, no, gypsum is not like limestone or other carbonates. It also only sheds its water at about 65 degrees C (150 degrees F) where it goes to CaSO4*1/2H2O.

To anybody reading this thread, a bit of research on gypsum and its distinctions between carbonate mineralogy and its distinction with anhydrite may be helpful.

Gypsum is quite stable and it takes the kiln to clinker it to cement (well along with a few other raw ingredients).

f-d

ípapß gordo ainÆt no madre flaca!

 

[emmgjld]

To follow up on fattdad, gypsum must be considered as a mineral AND by the in-place condition or crystal habit.
I live in a semi-arid to arid environment and deal with the entire range of anhydrite to crystalline gypsum to diffused sulfates in soils and weathered rocks. The problems range from minor/moderate expansion in specific operations of soil stabilization to potentially severe collapse due to water solution. Whether water is just wetting or is moving through the soil/rock (and transporting minerals out of the system) is as important as the mineralogy AND crystal habit.

 

[LRJ]

How would the gypsiferous soil behave if it were below the water table and fully saturated? Would heave no longer be an issue? Are there other concerns instead, i.e. relating to strength, void ratio/compaction? What about cyclic degradation?