Bimrocks

Franciscan melange in Headland at McKerricher State Park nr Fort Bragg Mendocino Co (E Medley)

Stopped by because you are looking for information on bimrocks? Then go to my bimrocks website for the current collection of resources on bimrocks for geological and geotechnical practitioners.

What are bimrocks? Bimrocks are block-in-matrix rocks, mixtures of stronger blocks of rock surrounded by weaker matrix rocks. Bimrocks are geologically, spatially, and mechanically heterogeneous. Bimrocks include melanges, fault rocks, weathered rocks, lahars and some “rock/soil mixtures.”

So What? Bimrocks universally frustrate the economic and accurate characterization, design and construction of civil engineering works.

Who cares? Bimrocks are troublesome to geotechnical engineers, geologists, contractors and owners.

Isn’t bimrocks a silly word? It looks silly, sure.  Nevertheless, it is a serious geological engineering term.  I coined the geologically neutral word bimrocks to focus engineers’ attentions on the fundamental and troublesome fabric of strong rock blocks in weak rock matrix, regardless of geological origins and euphonious geological names. Geology is important, but engineers generally do not understand the rich language of geology and are confused by (and even dismissive of) geological words.

Aren’t bimrocks rare? No, they are very common. So there is no excuse to ignore them.  I don’t: I live and work near San Francisco, which hosts the Franciscan Complex (“the Franciscan” for short), a regional-scale jumble of shards of earth’s crust, interspersed with some of the most spectacular melanges and bimrocks in the world. I have written some on such rocks, but others write far more: there are thousands of papers on melanges, a good proportion focused on those of the Franciscan.

In 2008 I organized a Field Trip for the American Rock Mechanics Association Conference in San Francisco. The tour had to be canceled, but many folk were so disappointed about that cancellation, that they asked me if I could lead a “private” tour. So, off on a small bus we went and had a jolly day looking at small bites of Franciscan Complex melanges. If you are interested in tidbits, then look at the informal Field Trip guide that I prepared for that frolic.

Also: the annotated presentation “An Introduction to Bimrocks“ is a useful review on bimrocks as is my most recent contribution: Geopractitioner Approaches to Working With Anti-Social Melanges, a chapter in the book in Special Paper 480: Mélanges: Processes of Formation and Societal Significance, by John Wakabayashi and Yildirim Dilek, published by the Geological Society of America. Wakabayashi and Dilek’s  full-text introduction to the volume is available at the GSA website and is a good place to start if you want to learn more about melanges.