Is Gypsum Rippable?

[LCruiser]

We have a large quantity of gypsum that needs to be removed for a roadway. Due to velocities over 16,000 fps, it will be classified as rock exc. However, it seems gypsum would be easily rippable. Has anyone had any experience with that?

 

[epongra2]

For most all bedrock materials, once you get past 10-11,000 ft/sec you are getting to the point where it would per considered non-rippable. However, using only velocities to determine rippability is considered old school. Parameters such as uniaxial tensile strength, weathering, abrasiveness, and spacing of discontinuities should be considered.

16,000 ft/sec sounds pretty high for gypsum. Is the gypsum hosted in another rock type?

 

[LCruiser]

No mention of any underlying strata. Close to the surface the velocity is 2,000 to 4,000 (a couple of feet down) but cores indicate gypsum as deep as they go. It's a pretty large area - at least 5 miles long on the surface.

 

[epongra2]

How deep or high are the excavations going? Are there any outcrops of the gypsum in the immediate area that one could map? Perhaps one of the local geotech consultants has some experience with excavations in this material.

 

[LCruiser]

Some cuts will be 15' - well into the "high velocity" strata. Drilling shows continuous gypsum, and of course penetration tests go to refusal pretty quickly as the gypsum bulbs out.

 

[civilperson]

A large dozer with a ripper tooth could do this excavation (D-8 or bigger), Comparative costing will probably lead to drill and shoot blasting on a 6 foot or bigger grid. Use of the excavated material for on site fill may weigh the cost/method analysis to another method.

 

[LCruiser]

Which brings up another point. Our geotech says we can't use the gypsum as roadway fill. I know it should not be used with lime treatment, but other than that, as long as it's covered with a non-dispersive layer, why not?

 

[eric1037]

Gypsum is soluble in water. That's probably why they won't let you use it for roadway fill.

You may be able to excavate with high-pressure water.

I don't have any experience or knowledge of anybody actually doing it though.