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.” Bimrocks universally frustrate the economic and accurate characterization, design and construction of civil engineering works and are troublesome to geotechnical engineers, geologists, contractors and owners.
Bimrocks are very common. So there is no excuse to ignore them. So I don’t… Anyway: 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.
My research and professional contributions on bimrocks are freely available at my bimrocks website. 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. For some overall guidance see the Introduction and Summary Lectures for the Short Course taught in 2017 at Medellín, Colombia (Lecture PDFs can be downloaded); or, the annotated “Introduction to Bimrocks”,
Despite the thousands of geological papers, there are few engineers who specialize in, or research, bimrocks. I am one of those few. Some example projects:
- Investigated Differing Site Condition claim for landslide repair and tie-back wall in Franciscan Complex melange at Polhemus Road, Hillsborough, California; plaintiff withdraw claim after deposition.
- Investigated Differing Site Condition claim for micro-tunneled sewer in mixed-face conditions in Northern California. Testified for defendant at deposition and trial, case found in favor of defendant.
- Technical Reviewer, Geological and Hydrogeological Investigations for aggregate quarry located in fault-sheared rock mass in major fault zone, Northern California.
- Characterized chaotic rock mass, investigated rock mass integrity, and evaluated static and seismic slope stability of chaotic shear zone in Franciscan Complex rocks at a steep 300 foot slope in an old quarry in Richmond, California. Presented findings at public meetings of the California State Mining and Geology Board.
- As part of three-expert team, investigated causes of major landslide in Franciscan Complex melange that damaged several private properties in the Pinehurst Court-Crestview Drive area of Millbrae, California. Resultant litigation case settled prior to testimony.
- Investigated landslide in rural San Mateo County in Franciscan Complex melange that damaged several homes. Testified at deposition for defendant; case settled before trial.
- Performed reconnaissance study of failing high wall in complexly sheared Franciscan Complex rock at the Homestake McLaughlin gold mine in Lake County, California.
- Investigated the uncertainty in estimates of volumetric block proportion of Franciscan Complex melange in the foundation of Scott Dam, Eel River, Northern California.
- Principal reviewer for an investigation of extent of collapsible, bouldery debris flow soils; and definition of remediation and constructability strategies, for proposed Indian Cultural Center in Southern California.
- Principal reviewer of geotechnical characterization and proposed earthwork design in Franciscan Complex melange at the Lehigh/Hanson Permanente Quarry in Cupertino, California.
- Provide consultations on characterization of landslides and excavated slopes bimrocks located throughout Northern California to geotechnical consultants and attorneys.