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ROCK CORE EVALUATION MANUALGEOTECHNICAL ENGINEERING MANUALGEM-23Revision #2AUGUST 2015

GEOTECHNICAL ENGINEERING MANUAL:ROCK CORE EVALUATION MANUALGEM-23Revision #2STATE OF NEW YORKDEPARTMENT OF TRANSPORTATIONGEOTECHNICAL ENGINEERING BUREAUAUGUST 2015EB 15-025Page 1 of 21

TABLE OF CONTENTSI.INTRODUCTION.4II.BRIEF GLOSSARY OF GEOLOGIC TERMS . 5-6III.ROCK CORE EVALUATION PROCEDURE .7A.Recovery. .7B.Rock Quality Designation (RQD) .7C.Rock Type. .81.Igneous. .82.Metamorphic. .83.Sedimentary. .8a.Compaction. .9b.Cementation. .9D.Color. .13E.Mineralogy, Grain Size, and Texture .13F.Bedding. .13G.Fractures. .14H.Size Range of Pieces .15I.Hardness. .16J.Weathering. .17K.Additional Observations .17L.Photographs.17M.Rock Core Logs .18REFERENCES . 19-20APPENDIX . .21ARock Core Evaluation Sheet. . A1-A2BSample Rock Core Log (International System of Units). . B1EB 15-025Page 2 of 21

LIST OF TABLESTable 1:Table 2:Table 3:Table 4:Table 5:Table 6:Table 7:Table 8:Igneous Rocks .10Metamorphic Rocks .11Sedimentary Rocks .12Sedimentary Rock Bedding.13Fracture Density .14Fracture Healing .15Rock Hardness .16Weathering Categories .17EB 15-025Page 3 of 21

I. INTRODUCTIONThis manual presents a procedure for describing rock core samples, obtained for the New YorkState Department of Transportation, by State work forces and/or private drilling companies, forfoundation, rockslope, and other engineering purposes. The evaluation is intended to provide acomprehensive word description of the core samples to those involved in the planning, design,construction, and maintenance processes.The procedure involves visual and manual examination of core samples with respect to rock type,color, composition, bedding, structure, hardness and degree of weathering. This information willbe used to generate an official Rock Core Log, for each evaluated boring, which will be madeavailable to interested parties, including designers and prospective bidders. NYSDOT obtainslarge quantities of rock core samples but only those samples necessary to advance the requiredgeologic designs are evaluated and the corresponding Rock Core Logs developed.The standardized charts and tables herein, used as descriptive aids in the evaluation procedures,are adopted from various organizations, such as the U.S. Department of Interior, GeologicalSurvey, the American Institute of Professional Geologists (AIPG), the U. S. Department of theNavy, Naval Facilities Engineering Command, etc.). It should be understood, however, that thefinal core descriptions and rock quality assessments are based on the judgment of the individualperforming the evaluation. Additional tests that may be performed, such as Point Load testsand/or Unconfined Compressive Strength tests, are not intended to be used to verify thedescriptions but to provide further information that will be reported separately.EB 15-025Page 4 of 21

II. BRIEF GLOSSARY OF GEOLOGIC TERMSBanding:Layering in the rock. The layers may be bedding, parallel to bedding, or be at anangle to bedding in sedimentary rock.In metamorphic rock, the layering is called foliation. The foliation is a result ofthe alignment of platy (flat) and/or elongated minerals due to the heat and pressureof metamorphism. The foliations may be parallel with or at an angle to theoriginal bedding. Sometimes the original bedding has been obliterated and onlythe foliations can be observed.Igneous rocks normally do not exhibit banding except in cases of differentialsettlement during hardening.Bedding:The layers in sedimentary rock parallel to the original surface of deposition. Theoriginal bedding planes were often, but not always, horizontal. The rock will oftentend to break along bedding planes.Cement:The material, usually chemically precipitated, which binds the particles of somesedimentary rocks together (see grains and matrix).Cleavage:Closely spaced parallel planes along which rock can break. The cleavage may bea result of weakness along bedding planes in sedimentary rock (fracture cleavage)or may be a secondary development by alignment of platy minerals inmetamorphic rock (slaty cleavage). Slaty cleavage may be parallel with or at anangle to original bedding.Diagenesis:The process of chemical, physical and/or biological change in deposited sedimentduring its conversion into rock, exclusive of metamorphosis and weathering (seelithification).Effervescence:The fizzing action that occurs when a carbonate rock (containing CaCO2 orCaCO3) is placed in contact with hydrochloric acid (HCl).Fault:A fracture in rock along which there has been observable movement (see joint).In rock cores, a fault can sometimes be recognized by the displacement of mineralveins.Foliation:The alignment of platy (flat) or elongate minerals, usually in metamorphic rocks,giving the rock a banded appearance. The foliation is usually a result of the heatand pressure rock is subjected to during metamorphism.EB 15-025Page 5 of 21

Fracture:Breakage in rock. The fracture may be parallel with or at an angle to banding,bedding, cleavage, foliation or lamination. Faults and joints are examples offracture.Grains:The particles of which a rock or sediment is composed (see cement and matrix).Joint:A fracture in rock along which there has been no observable movement (seefault).Lamination: Very thin layering in rock, less than 0.4 in. (10 mm). The layers may be a resultof physical or chemical variations. Laminations may be parallel with or at anangle to bedding (cross-laminations) in sedimentary rock.Lithification: The process by which loose sediment becomes rock (see diagenesis).Lithology:The character of a rock described in terms of its structure, color, mineralcomposition, grain-size, and arrangement of its component parts.Matrix:The fine-grained portion, not necessarily cement, of some sedimentary rocks(sandstone, conglomerate, etc.) in which the coarser particles are embedded. Thematrix may or may not be cemented (see cement).Mineral:An inorganic substance, not necessarily of inorganic origin, that has (1) a definitechemical composition, or range of composition and (2) distinctive physicalproperties and/or molecular structure. The basic building block of rock.Sediment:Solid material, either mineral or organic, that has been transported from its site oforigin, by air, water, ice or biological activity, and has been re-deposited on theearth's surface, above or below water.Weathering: The process by which rocks are broken down and decomposed by the action ofexternal agencies such as wind, water (rain and/or ground water), temperaturechange, plants and bacteria.EB 15-025Page 6 of 21

III. ROCK CORE EVALUATION PROCEDUREA proper description of rock obtained in drill cores is a valuable aid to the Engineering Geologistin determining the properties of bedrock with regard to rock slope and structure foundationdesign.When evaluating rock core, the Engineering Geologist should make note of the following:A. Recovery,B. RQD,C. Rock type,D. Color,E. Mineralogy, Grain size & Texture,F. Bedding,G. Fractures,H. Size range of core pieces,I. Hardness,J. Weathering,K. Additional observations,L. Photographs, andM. Rock Core Log. The results are to be recorded on a Rock Core Evaluation Sheet (SeeAppendix A) and used to prepare an official Rock Core Log (See Appendix B).A. RECOVERYThe recovery of each core run is usually determined by the Driller and recorded on the officialBoring Log. Where the recovery is not made available, the Engineering Geologist should recordthe recovery (in percent) as the length of core recovered divided by the total length of the corerun, multiplied by 100. Areas where loss is likely to have occurred (soft seams, fractures withedges that don't match, zones of decay, etc.) should be noted.B. RQDThe Rock Quality Designation (RQD) is a modified measure of recovery, calculated in order toestimate the quality of the intact rock mass. The Engineering Geologist is responsible for thedetermination of RQD. The RQD (in percent) is obtained by dividing the sum of all therecovered pieces of core equal to or greater than 4 in. (100 mm) in length by the total length ofthe core run, then multiplying by 100. In effect, the RQD is a measure of the spacing of thediscontinuities (bedding, fractures, faults, joints, shear zones, etc.) in the rock mass. Whencalculating RQD, it is important to try to distinguish between naturally occurring discontinuitiesand mechanical breaks which occur during coring procedure. Only naturally occurringdiscontinuities will be considered when calculating RQD. When there is uncertainty about abreak, it should be considered as natural in order to be conservative in the calculation of RQD.In addition, only sound bedrock is used in the calculation of RQD. Weak and/or weathered rockcore is not included in the RQD calculation.EB 15-025Page 7 of 21

Note: RQD was originally developed for use with NX-size (2.16 in. (54.9 mm)) core drilled incrystalline rock and used to describe rock quality for tunneling conditions. It has sincebecome virtually standard practice in drill core logging for a variety of core sizes and rocktypes. ASTM International indicates core sizes from BX (1.44 in. (36.6 mm)) to PX(3.35 in. (85.1 mm)) are normally acceptable for measuring RQD. RQD calculated forcores smaller than BX, e.g., AX-size (1.19 in. (30.2 mm)), may not be representative ofthe true quality of the rock mass.C. ROCK TYPEGeologists divide rocks into three groups based on origin and then subdivide them into smallergroups on the basis of composition and texture.1. IGNEOUS ROCKSRocks formed from the solidification of molten material (magma or lava). Igneousrocks can be intrusive (solidifying below the surface from magma) or extrusive(solidifying at the surface from lava).Intrusive igneous rocks are generally composed of larger crystals/grains (coarsertexture) while extrusive igneous rocks are generally composed of smallercrystals/grains (finer texture).In general, igneous rocks tend to have an interlocking, crystalline texture with little tono appearance of layering, banding, or bedding.2. METAMORPHIC ROCKSMetamorphic rocks are Igneous and/or Sedimentary rocks whose textures and /ormineral content have been changed by heat, pressure and/or chemically activesolutions (invading gasses and/or liquids). In some instances, metamorphic rockshave been re-metamorphosed into other higher or lower grade metamorphic rocks.Metamorphic rocks can appear banded or layered (due to the alignment of platy,tabular, or elongated mineral grains or the concentration of different minerals intodistinct bands).3. SEDIMENTARY ROCKSSedimentary rocks are formed by lithification of accumulated sediments that weretransported and deposited by water, wind, ice, biological activity and/or chem