Geopractitioner approaches to working with antisocial mélanges

Abstract

Although mélanges are exciting, puzzling, and controversial to geologists, it is geopractitioners and contractors who must work with them to engineer the constructed works of Society. Geopractitioners include geotechnical engineers, geological engineers, engineering geologists, and rock engineers. Mélanges are the most intractable bimrocks (block-in-matrix rocks), complex geological mixtures composed of hard blocks of rocks surrounded by weaker matrix, and are famously exemplifi ed by those within the Franciscan Complex of Northern California. Bimrocks also include olistostromes, weathered rocks, fault rocks, and lahars. The conventional characterization, design, and construction procedures used by geopractitioners for well-behaved stratifi ed rocks and soils are not well suited to mélanges. The considerable engineering and construction diffi culties related to mélanges burden Society to the extent that they can be considered "antisocial." Case histories exemplify a recommended systematic procedure for characterization, design, and construction with mélanges. Geopractitioner approaches to characterizing California's chaotic Franciscan mélanges are applicable to geologists and geopractitioners working in fault zones, weathered rocks, lahars, and other bimrocks, and suggestions are offered for collaborative research between geologists and geopractitioners.

An approach to predicting the overall strengths of unwelded bimrocks and bimsoils

“…For this case, when the volumetric block proportions (VBPs) in a bimrock increase, the internal friction angle tends to increase and cohesions tend to decrease (Lindquist, 1994 andLindquist and. But, Medley and Zekkos (2011) emphasized that under sufficient high normal or confining stresses, failure surfaces may actually penetrate blocks regardless of the mechanical contrast between block and matrix.…”

“…: 1:10,000) may be part of a matrix at a smaller scale (e.g. : 1:1000) (Medley and Zekkos, 2011). Note that for reasons of geometrical probability, the sizes of blocks (the maximum observed dimensions, or "d mod ") measured from field mapping or drilling are almost always shorter than the true "diameter" of blocks (Medley and Zekkos, 2011).…”

“…Although this topic is widely discussed in related literature, it was summarized by Medley and Zekkos (2011). Based on the studies performed by Medley (1994) and Medley and Lindquist (1995) on Franciscan Complex ("Franciscan") mélanges, the block size distributions of Franciscan mélanges are scale independent, having similar appearances regardless of the scale of interest.…”

“…1. Medley and Zekkos (2011) provided a comprehensive review of geopractice with mélanges and similar bimrocks. …”

Engineering Geological Characterisation of Block-in-Matrix Rocks

“…The expression "block-in-matrix rocks" was introduced by Raymond (Raymond, 1984) and incorporates similar terminologies such as mega-breccias, olistostromes, argille scagliose, friction carpets, wildflysch, varicoloured clays and sedimentary chaos (Medley and Zekkos, 2011).…”