Wednesday, March 5, 2014

Pumice/Scoria as Low Mass Fill

Pumice/scoria distribution is a side a business for a trucking company that otherwise specializes in agricultural trucking services.  

This scoria is a Washington State product from the Goldendale area. The Cascades of south-central Washington better reflect what one might call the pure Cascade Range - a broad uplift covered with volcanoes including considerable number of cinder cones. The North Cascades are really a multiple tectonic mélange of various accreted terrains. Cinder cones are rare in the North Cascades, but there is one near Mount Baker (nwgeology/the-cinder-cone-in-schreibers-meadow).

Those holes of course make the rock very light - so light in mass that they can float as long as the air pockets do fill with water. As such the material makes excellent fill where light weight is important. A sizeable potion of the pile at the trucking company had recently been hauled to a bridge approach project. The low density fill to support the road approaching the bridge was a cost effective approach to crossing an area that would otherwise sink when loaded with a mass of heavier fill material.

The availability of this material for geotechnical engineering or engineering projects can solve some tricky problems where low density fill is needed. And an added benefit is the light weight for trucking gives it a better range for use as hauling costs per ton is no small thing. 


magmatist said...

Pumice and scoria are two different critters, though both are characterized by having lots of holes left by gas bubbles during eruption. Pumice is high in silica, usually associated with big explosive eruptions from dacite and rhyolite volcanoes such as St. Helens, Glacier Peak or the Crater Lake caldera. Only rarely is pumice erupted at andesite volcanoes such as Baker. Scoria is basaltic or andesitic, denser and lower in silica content. Think of 'pumice' as a light-colored pyroclastic volcanic rock that is mostly gas bubbles (though most are microscopic) and scoria as a red or black volcanic rock that is around 50% gas holes.
Dave Tucker

Dan McShane said...

I needed a magmatist's help on claification on this. Went with the dual name inthe title but the particular stuff pictured is scoria. The general public calls this stuff pumice and I have found mysef using the term wrongly and self correcting.
I will add that the denisty of this particular scoria is way under 50% of basalt - very frothy stuff and hence great for low density fill projects