Use of gypsum in rock fill 1

[Bill13214]

I have a situation where we will potentially import fill material with a significant portion of fist sized, clear gypsum crystals throughout the fill. What are the risks on a site where there will be a one story building and a surface parking lot? Does anyone have any experience using this type of material?

 

[ishvaaag]

Volume change (swelling, settlement of free surface, washing and loss of material, local collapse of soils), greater earth push, loss of support of foundations, and of course environmental chemical aggression.

All this said where I leave there are soils with significant fractions of gypsum, and except for active settlement pits usually associated to active ongoing drainage at the subsoil, or caverns, which use to be avoided or bridged, not much particular precautions are used.

Walls of buildings, must be said, are externally waterproofed and/or resistant to sulfates, and typically 1 ft thick. Now we have geotechnical reports and follow their advice.

 

[hokie66]

"Walls of buildings, must be said, are externally waterproofed..." If only it were so.

 

[namron2]

bit off topic, but i have an additional question or 2 regarding rate of gypsum solubility

Does anyone have some experience in rate of disolution for shafts / tunnels etc in gypsum and gypsum bearing weak rock? Is it possible for disolution to occur (or rapidly worsen) within say the period of temp works for shaft construction if dewatering (say up to 1 or 2 years?). I suspect there would be a degree of solubilty in fresh water based on papers I have read, but what about saline groundwater.

How would swelling pressures factor in for shaft excavations in such materials?

 

[ishvaaag]

Sometimes here pits manifest during the duration of the works. The worst places are known but use to be avoided. To the press only made news some settlement in rail works not able of easily entirely avoid ample zones of problems.

I expect more worries from a zone south of Zaragoza where it is known there are gypsum settlement issues, starting development.

Normally, holes in the ground take more to develop. The more famous case here was the entire loss of support of some important footing at a building in Calatayud (around 30000 people living in the village). It seems over 25 years or so a cave of around 1000 m3 developed either from seepage from water pipes or just drainage from mountains around. It rest on a lake bed with gypsum issues, and was close to the Jalón river.

Caverns of even bigger volume have been found and bridged or infilled when making foundations for bridges on the Ebro river, but obviously subject to underground water currents.

Other villages near Zaragoza also experience agricultural surface subsidences (hole formation) associated to high watertable.

As said, these things almost never make the news, the usual practices of construction use to bar them gain preeminence, even without the mat foundations etc that only the recent years have made common for ordinary buildings with such problematics.

So in my opinion if there is not concurrence of significant and/or stable sources of water during the works I wouldn't expect cavern formation in such period. Even those manifest and active should have some source of water acknowledgeable.

Respect high pressures against a backface of crystalline gypsum I wouldn't expect it attain engineering significance for shafts properly/ordinarily dressed, the gypsum is quite adaptable and normally shall relieve the pressure someway, for if I understand well, these pressures are associated to gain of volume at very early age and the gypsum is not yet verily hardened. Even the advance of the hydration process itself could serve as a escape to the pressure, and then the dry gypsum also adsorb water from the new one in hydration.