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Simple Hints on Characterizing Complex Bimrocks Simple Hints on Characterizing Complex Bimrocks Dr. Edmund Medley PE, CEG Consulting Geological Engineer, Belmont, California Noon Seminar Geotech Group, UC Berkeley November 10, 2004

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Who I am Prospector in Canada Prospector in Canada Educated in Geological/Geotech. Engineering Educated in Geological/Geotech. Engineering Geotechnical Eng. Consultant Geotechnical Eng. Consultant Principal Engineer at Exponent in Geology/Geotech/GeoEnvironmental Principal Engineer at Exponent in Geology/Geotech/GeoEnvironmental Licensed Geologist/Engineer in US, Canada and United Kingdom Licensed Geologist/Engineer in US, Canada and United Kingdom

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BIG CONCLUSION 1: Remember this picture!!! Matrix Scale: 1:?????? Blocks, inclusions, lenses, etc Actual Distribution of Blocks Medley, 2000

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Matrix Willis, 2000 Apparent Distribution of Blocks BIG CONCLUSION 2: Remember this picture as well!!!

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Melanges and Similar Bimrocks Melanges: (French mélange) : UN CHILE mixtures of competent blocks composed of sedimentary/ metamorphic blocks in weaker matrix of sheared shale or serpentinite Melanges: (French mélange) : UN CHILE mixtures of competent blocks composed of sedimentary/ metamorphic blocks in weaker matrix of sheared shale or serpentinite Bimrocks: block-in-matrix rocks Bimrocks: block-in-matrix rocks – mixtures of rocks composed of geotechnically significant blocks within a bonded matrix of finer texture Similar Bimrocks: Saprolites, Breccias, Fault Zones, Lahars, Tillites, etc. Similar Bimrocks: Saprolites, Breccias, Fault Zones, Lahars, Tillites, etc.

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Bimrocks are NOT Bimbo Rock(stars), and have not yet made me a millionaire…

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Mixture with weaker soil and strong blocks (decomposed granite at Hwy 50, California) Example of weathered rock bimrock Example of weathered rock bimrock soil Corestones, blocks, boulders

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Brecciated rock….

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer … or bathbim…

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Fault Rocks and Shear Rocks Riedmueller et al, 2001 ExEx Fault zones and Shear zones may have blocks millimeters to 100s of meters wide: BLOCK SIZE DISTRIBUTIONS TEND TO BE SCALE INDEPENDENT

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Limestone Olistolith (Block) Embedded in an Irregularly Foliated Matrix of Shale, Siltstone and Sandstone Egnatia Motorway, Greece Photo by Prof. Gunter Riedmueller

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Global distribution of melanges Medley, 1994

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Franciscan Complex melanges From Medley, 1994; after Ellen and Wentworth, 1995

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Franciscan Complex melange (Point Delgada, California) shear block

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Often severe spatial variability Often severe spatial variability Heterogeneity in properties Heterogeneity in properties Design and construction shortcomings in characterizations cost someone $$$$, (usually the Owner and/or Contractor) Design and construction shortcomings in characterizations cost someone $$$$, (usually the Owner and/or Contractor) $$Problems with Melanges

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Geology 101 Subsurface characterization of layer cake geology Linear interpolation is geologically justified only SOMETIMES; extrapolation RARELY exploration borings Layer 2 Layer 3 Layer 1 ? ?

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Difficult geology Difficult geology: lots of layers (“complex formations”) Layer 1 exploration borings Layer 2 Layer 1Layer 2 Layer 1Layer 2 Fault soil Layer 4 Layer 3 fault

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The complexity of a turbidite sequence - interbedded sandstones and shales (Devil’s Slide, Pacifica, California)

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Chaotic Geology: apparent “layers” are blocks, lenses, inclusions….. exploration borings soil Fault?? Characterization is NOT a piece of cake!

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Bimrock – Mapped or cored Matrix Willis, 2000

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The Benefits and Dangers of Drawing Straight Lines Matrix

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Actual Distribution of Blocks Matrix Willis, 2000; after Medley, 2000

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So What? Who Cares*? * Answer: Owners, Contractors and Lawyers

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Characterization of Melanges and Similar Bimrocks

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Steps in Characterization of Bimrocks 1. Determine you are working in a bimrock 1. Determine you are working in a bimrock 2. Select the Characteristic Engineering Dimensions of interest 2. Select the Characteristic Engineering Dimensions of interest 3. Perform field mapping of geological and geotechnical features 3. Perform field mapping of geological and geotechnical features 4. Drill using careful drillers! 4. Drill using careful drillers! 5. Measure areal and linear block proportions 5. Measure areal and linear block proportions

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer More Steps in Characterization of Bimrocks 6. Select specimens for laboratory testing with blocks 6. Select specimens for laboratory testing with blocks 7. Test a variety of specimens with different block proportions 7. Test a variety of specimens with different block proportions 8. Adjust your linear block proportion to account for uncertainty 8. Adjust your linear block proportion to account for uncertainty 9. Estimate overall bimrock strength 9. Estimate overall bimrock strength

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer 1. Determine you are working in a bimrock

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Really obvious melange…. Really obvious melange…. Gwna Melange, N. Wales photo Ed Medley

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Geomorphic clues: subtle!! Protruding blocks Vegetation contrasts=blocks

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer 2. Select the Characteristic Engineering Dimensions of interest

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Q: What is Block Size?? A: Rarely the “diameter” maximum observed dimension

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Blocks in Franciscan Melange Blocks range in size between mountains and sand and will always be found Blocks range in size between mountains and sand and will always be found Block size distributions are scale independent and fractal ( power law) Block size distributions are scale independent and fractal ( power law) Largest reasonable block is: Largest reasonable block is: 0.75 A aka d max 0.75 A aka d max Block/matrix threshold is 0.05 A Block/matrix threshold is 0.05 A Characterization must take blocks into account Characterization must take blocks into account

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Use these guidelines at any scale of interest smallest blocks are: smallest blocks are: 0.05L c or 0.05 A or 0.05d max largest block is: largest block is: 0.75Lc or 0.75 A or 0.75d max 0.75Lc or 0.75 A or 0.75d max

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When is a block not a block? depends on scale of interest 100 m R. of W. 20m 1 m block 100 mpipeline trench

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer 3. Perform field mapping of geological and geotechnical features

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Some elements of CHARACTERIZATION Block/matrix discrimination Matrix lithology, block lithology, block size, block shape, block orientation Block size distribution Block discontinuities Etc… ALL are straight forward geological engineering during field investigation…

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Systematic investigation of chaos Wakabayashi & Medley, 2004 Matrix strength

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Right and wrong way to map melanges Outcrops (blocks) WRONG!! Right!!

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Observe block/matrix contacts

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer 4. Drill using careful drillers! Log using your painfully learned Engineering Geology! (Bless Professors….)

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer right way and the wrong way… Wrong!!! Right!!! Wakabayashi & Medley, 2004

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer 5. Measure areal and linear block proportions

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Drilling and coring bimrocks boreholes

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Scott Dam melange (California) photo Prof. R Goodman Matrix- rich core Measure core/block intercept (chord) Measure block linear proportion

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Measuring Linear Proportion

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer 6. Select specimens for laboratory testing with blocks

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Scott Dam melange photo Prof. R Goodman Take samples of matrix

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer 7. Test a variety of specimens with different block proportions

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Different orientations and volumetric block proportions Lindquist, 1994

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Increase in friction angle with volumetric block proportion Lindquist, 1994

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Decrease in cohesion with volumetric block proportion Lindquist, 1994

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Scott Dam melange strength testing results Prof. R Goodman

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer 8. Adjust the linear block proportion to account for uncertainty

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Determination of volumetric block proportions Application of stereological principle: Application of stereological principle: linear proportion = volumetric proportion Determine linear proportion from drill core Beware uncertainty! Beware uncertainty!

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Warnings!!!! So, although stereology says that volumetric % = linear % So, although stereology says that volumetric % = linear % It is TRUE ONLY when you have sufficient linear measurements!! (lots of $$$ drilling!!) It is TRUE ONLY when you have sufficient linear measurements!! (lots of $$$ drilling!!)

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Estimated volumetric properties on the basis of Scott Dam linear boring measurements x40% = 6%: use 34% block proportion Linear proportions assumed to be same as volumetric proportions Uncertainty: error in the assumption

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer 9. Estimate overall bimrock strength

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Strength of Franciscan below Scott Dam Medley, 2002; after Goodman and Ahlgren, 2001 Approx 39% friction for 34% volumetric block proportion

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Strength of bimrock depends on volumetric block proportion

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Strength and deformation properties of Melange Bimrocks Strength and deformation of melanges are independent of block strengths (Lindquist and Goodman,1994) Strength and deformation of melanges are independent of block strengths (Lindquist and Goodman,1994) Overall strength is directly related to volumetric block proportion Overall strength is directly related to volumetric block proportion Blocks adds friction, stiffen the mixture and reduce cohesion. Blocks adds friction, stiffen the mixture and reduce cohesion. Must perform geotech tests with blocks in specimens Must perform geotech tests with blocks in specimens

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Slope Stability: Recent Research

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Blocks added strength to matrix? Photo: Exponent

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer shears Tortuous Shears in Melange

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Tortuousity of Failure Surfaces Medley, 2004

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Developed profile of failure surface Medley, 2004

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Tortuousity is not Roughness Medley, 2004

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Measuring Tortuosity Medley, 2004

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Findings: Tortuosity depends most on block proportion (and orientation??) Width of shear zones approx to 0.15 L c Proportion block/shear contact closely related to volumetric block proportion Medley, 2004

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer What are the influences on tortuosity and slope stability in bimrocks? Block/matrix vol. proportion; matrix c, ϕ ?? Block shape, block&shear orientation?? Block size, location, orientation?? Bimrock weak zones, variability?? Medley & Sanz, 2004

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Tortuosity depends most on volumetric block proportion and, intuitively, block orientations So: what are the effects of block proportion, block orientation on slope stability? Answer: let’s investigate!!

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Simple Model Analysis Critical failure surface in matrix Φ = 25º c = 10 kPa FS ~ 1.26 Using Slope/W

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Simple, random arrays of blocks 50% 25% 13%

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Analysis of Influence of Blocks on Slope Stability Using Simple Models horizontal rectangular blocks BSD= partial Franciscan Random arrays trial surfaces negotiate blocks, tortuosity reflects many factors A A =V V 5m

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Locate critical matrix-only and tortuous trial surfaces and compute F of S

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50% block proportion: FS for a tortuous trial surface FS ~ 1.65

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Slope stability of Boulder Colluvium Hong Kong GEO TN 4/92

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Trial tortuous failure surfaces with blocks oriented out-of-slope After Irfan & Tang, 1993

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Combining the results of analyses

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Bimrock strength increases with block proportion (>~15%-25% V v )

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer Slope Stability Conclusions Increased tortuosity of failure surfaces results in increased slope stability Increases in tortuosity are most influenced by block volumetric proportion and block orientation Or: strength of bimrocks increases because of presence of blocks

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BIG CONCLUSION 1: Remember this picture!!! Matrix Scale: 1:?????? Blocks, inclusions, lenses, etc Actual Distribution of Blocks

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Matrix Willis, 2000 Apparent Distribution of Blocks BIG CONCLUSION 2: Remember this picture as well!!!

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Other CONCLUSIONS Melange bimrocks and other bimrocks mixtures are chaotic but can be characterized in a disciplined fashion Melange bimrocks and other bimrocks mixtures are chaotic but can be characterized in a disciplined fashion Strength and deformation properties of bimrocks are determinable Strength and deformation properties of bimrocks are determinable Uncertainties in estimates must be considered Uncertainties in estimates must be considered

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Conclusions continued: Bimrocks are NOT: Bimrocks are NOT: – “soil with boulders”, – “interlayered shale and sandstone” – “miscellaneous soils” Block volumes, sizes and lithologies are $important$ to Contractors/Owners and some effort should be made to determine them Block volumes, sizes and lithologies are $important$ to Contractors/Owners and some effort should be made to determine them Block sizes should be estimated very conservatively for construction Block sizes should be estimated very conservatively for construction

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For more information, see contents of the CDROM and Felsbau Oct /2004 Characterizing melanges Characterizing melanges Medley, 1998 (IAEG, Vancouver) Medley, 1998 (ASCE ISC, Atlanta) Medley, 1999, 2001 (Feldsbau, Austrian J. Geomechanics) Medley, 2002 ( Eng. Geol. Practice No. Cal. ) Block size distributions in melanges Block size distributions in melanges Medley and Lindquist, 1995 (35th USRMC, Tahoe) Medley 2002 (NARMS Toronto) Uncertainties from boring data in melanges Uncertainties from boring data in melanges Medley, 1997 (IAEG, Athens)

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Copyright: Dr. Edmund Medley, PE, CEG Consulting Geological Engineer

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