S. R. Rubenstein Engineering and Research Center Bureau of Reclamation October 1970 Petrographic and Physical Properties Techniques for Study of Foundation Rock - ~ITwPoint Damsite 7. AUTHOR(S) 8. PERFORMING ORGANIZATION S. R. Rubenstein REPORT NO. REC-OCE-70- 39 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. WORK UNIT NO. Division of General Research Engineering and Research Center 11. CONTRACT OR GRANT NO. Bureau of Reclamation Denver, Colorado 80225 13. TYPE OF REPORT AND PERIOD COVERED 12. SPONSORING AGENCY NAME AND ADDRESS 14. SPONSORING AGENCY CODE I 15. SUPPLEMENTARY NOTES 16. ABSTRACT king the foundation investigation of schists and gneisses at Mom Point damsite, the rock (Pix cores) was petrographically described and classified for structural tests. Petrographic and physical tests of the core were grouped to give an overall picture of the foundation. Methods are described for determining the petrographic characteristics such as articulation, mineral composition, and microstructure of the rock. Ar- ticulation and texture of the grains were determined on the basis of microscope examination for evaluation of bond strength. Composition of the rock was determined by modal analysis (by a method of intercept distances) and the rocks were grouped according to minerals present. Oriented microstructures in foliated rocks were determined by the photo- meter method for analysis of structure. The relationship between elas- ticity and the texture composition, and structure was compared. The relationship between ~.bsorptionand seismic wave velocity w9e examined. Physical properties by means of laboratory and seismic methods were measured for individual rock types. (7. KEY WORDS AND DOCUMENT ANALYSIS a. DESCRIPTORS--/ Wtrographic investigations/ *rock foundations/ rock mechanics/ gneisses/ mineralogy/ petrofabrics/ compressive strength/ elas ticity/ geology/ micros tructurea/ mica/ *physical properties/ *rock properties/ absorption/ schists/ specific gravity/ static tests 1 a. IDENTIFIERS-4Morrow Point Bm, ~olo/photomicrographs/ thin sections .C. COSATI Fleld/Group 18. DISTRIBUTION STATEMENT 19. SECURITY CLASS '21. NO. OF PAGE (THIS REPORT) Available from the Material Technical Information UN~~~~~l~lED23 Service, Operations Mvision, Springfield, '20. SECURITY CLASS 22. PRICE CAGE) Virginia 22151. UNCLASSIFIED(THIS 53.00 REC-OCE-70-39 PETROGRAPH IC AND PHYSICAL PROPERTIES TECHN IQUES FOR STUDY OF FOUNDATION ROCK MORROW POINT DAMSITE Determining petrographic characteristics of the rock and their relationship to modulus of elasticity. by S. R. Rubenstein October 1970 Applied Sciences Branch Division of General Research Engineering and Research Center Denver, Colorado UNITED STATES DEPARTMENT OF THE INTERIOR * BUREAU OF RECLAMATION Ellis L. Armstrong Commissioner ACKNOWLEDGMENT This study was conducted by S. R. Rubenstein under the s:Jpervision of W. Y. Holland, Head, Applied Physics Section (retired). L. O. Timblin, I:- ,10. Jr., is Chief of the Applied Sciences Branch. The author extends his appreciation to members of the Petrographic Laboratory, Rock Mechanics and Structures Unit, Concrete and Structural Branch, and Geophysics Branch. The work was done at the Bureau of Reclamation, Division of General Research, Denver, Colorado. Reprint or republication of any of this material shall give appropriate credit to the Bureau of Reclamation, Department of the Interior. CONTENTS Page Introduction. 1 Conclusion. 1 Application. 1 Test methods. 2 Chemical Analysis and Correlation. 2 Rock Groupings by Hardness. 2 Rock Classification by Texture. 2 Macrostructure (foliation and fractures) . 2 Modal Analysis (composition) ,... 2 Photometer Method of Petrofabric Study. 2 Specific Gravity and Absorption. 2 Compressive Strength and Elasticity. 2 Comparison of Petrographic and Structural Properties . 3 References. 4 LIST OF TABLES Table 1 Chemical composition. 5 2A Modal analysis of Pre-Cambrian rocks. 5 2B Results of combined rock and thin section analysis of specimen. 6 3 Preferredorientation of quartz in foundation rock. 6 4 Physicalproperties. 7 5 Static laboratorytests. 7 6A Articulationcomparedto elasticity. 8 6B Textural and mineralogical classification of rocks versus physicalproperties. 8 7 Angleof foliationcomparedto elasticity. 8 8 Micacomparedwith elasticityand strength. 9 9 Absorption compared to elasticity . 9 LIST OF FIGURES Figure 1 Photograph of hand specimens of schist. 10 2 Photograph of hand specimens of schist. 10 3 Rock classification relationshipf'. 11 4 Comparison of percent mica and angle of foliation with strength. 12 5 Rock texture versus elasticity. 13 6 Comparison of percent quartz with elasticity . 14 7 Absorption versus elasticity. 15 CONTENTS-Continued Page .:. APPENDIX .'- Lithologic logs of drill holes. 17 Photomicrographs of biotite schist, mica schist, and. 19 hornblende schist. 20 Stereopair of scheared rock surface. 21 Geology section-seismic measurements of rock elasticity. 22 Conversion factors-British to metric units of measurement iNTRODUCTION CONCLUSIONS In the investigation of foundation rocks at Morrow 1. The rock grouping of the cores by hammer hardness Point Damsite, Colorado,! rock cores were from soft, moderately hard, to hard showed fairly good petrographically classified and logged. Certain physical correlation with elasticity. Those wh ich had a good tests were also performed and related to engineering "ring" were harder than those with a duller "ring." The properties of design. soft group had a lower elasticity. Morrow Point damsite is located on the Gunnison a. The petrographic identification and classification River, upstream from the confluence with Cimarron was a good method for determining the Creek. Geologically, the Gunnison River cuts through characteristics that effect the engineering properties Pre-Cambrian gneisses, sch ists, and pegmatite at the of the rock. Trends were obtained between texture, damsite. structure, composition, and strength and elasticity. Strength increased as the amount of quartz Because the dam will be a thin arch, double-curvature increased and mica decreased. The increase in designed dam, extensive geologic investigations were strength appears to result from greater locking of undertaken. In addition to the geological studies, the crystals as the transition from parallel to structural properties of the rock were determined. This anhedral (shapeless crystals) to euhedral (bounded paper is concerned with the description of some of the by its own crystal faces) fabric occurs. petrographic techniques which are used in the investigation of geological conditions in rock b. Modal compositional analysis by the thin section foundations and the manner in which such information method gave more accurate mineral percentages as can be presented in engineering terms. compared to visual estimation. The mineral percentages then can be used in the identification of Twenty-nine representative samples of Nx (2-1/8 the rock. The data can also be used in the inches) core from exploration drill holes and tunnels correlation with structural properties. There was a were examined. For the petrographic examination, decrease in strength when the quantity of mica was each piece was selected so that its location in the drill greater than 40 to 50 percent. hole was as close as possible to another core piece which was tested for compressive strength, elasticity, c. The anistropy of the biotite schists caused and other properties by the Rock Mechanics and notable differences in strength in core samples Structures Unit of the Division of Research. tested along their isotropic planes of weakness. Microscopic examination was performed for 2. Absorption data was related to the elasticity of the determination of composition, internal structure, rock. The absorption was low and when compared to texture, secondary minerals, and microcracks. Modal elasticity showed the lower the absorption the higher analysis was used to provide a quantitative composition the elasticity. of the rock. The photometer technique provide a method to determine the lineation and microstructure 3. Photomicrographs can be an. aid to determining of the rock by the orientation of the quartz grains. texture and articulation in the classification of rock types. Stereo photomicrographs can be an aid to X-ray diffraction analysis for determination of explain surface roughness. fine-grained minerals was made as well as spectrograph ic analysis for sem iquantitative determ ination of elements. Clay stain ing tests for APPliCATION qualitative determination of clay were done when necessary. Determinations of porosity, absorption, and Petrographic techniques such as classification, modal bulk specific gravity (specific gravity with the analysis, petrofabric study, chemical analysis, and permeable voids filled with water) by the immersion hardness tests with strength and modulus of elasticity method were made to obtain these physical properties tests provided a good method for determining the of the rock. Elasticity and unconfined compressive behavior of the foundation rock at Morrow Point site. strength tests were performed.2 ! Numbers refer to references at end of paper. TEST METHODS TEXTURAL CLASSIFICATION Chemical Analysis and Correlation Group Rock Articu lation Textun It was important in the investigation of the foundation Biotite schist Very poorly Sch istos ~ to determine the petrogenesis of the rock for interlocked .~ excavation and structural purposes. The chem ical II Mica schist Very poorly Sch istos compounds were obtained