CHAPTER 6 CONCLUDING REMARKS AND RECOMMENDATIONS

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1 CHAPTER 6 CONCLUDING REMARKS AND RECOMMENDATIONS

2 CHAPTER 6 SUMMARY OF DISCUSSIONS ON TEST RESULTS AND CONCLUSIONS 6.1 The summary of discussion on the results of the initial study With reference to section 3.7; the discussion on the results of the initial study can be summarised as; Percentage drop of magnitude of an index property vs. temperature is more accurate than drop of magnitude of an index property vs. temperature in this type of study. Even though the unconfined compressive strength and slake durability index of quartzo-feldspathic gneiss is higher than that of biotite gneiss at room temperature, quartzo-feldspathic gneiss deteriorates faster than biotite gneiss subjected to heat treatments. Percentage drop of magnitude of index property vs. temperature plots for the index tests of unconfined compressive strength and slake durability test results depict that curves drawn for quartzo-feldspathic gneiss and biotite gneiss intersect at temperature of 573 C. Hence this particular temperature is significant in any investigation in cooling heating done on these two rock types. 6.2 The summary of discussion on the results of the detailed investigation on thermal sensitivity of biotite gneiss With reference to the Section 4.4; the discussion on the results of the detailed study on thermal sensitivity of biotite gneiss can be summarised as; Deterioration of magnitude of an index property with the increment of temperature of biotite gneiss follows a second order polynomial plot in the form of y = - Ax 2 - B x + C (where A, B and C are constants) Naturally decomposed biotite samples belonging to different weathering classes show a reasonable variation in ultrasonic pulse velocity (UPV) and unconfined compressive strength (UCS) values but not in slake durability index (S.I) values. Hence UPV and UCS tests are more meaningful for a similar study. Index values obtained for different weathering classes by means of UPV and UCS tests are compatible and illustrated in Table 6.1.

3 100 Table Comparison of normalised index values obtained for biotite gneiss Change of class UPV (Normalised) UCS (Normalized) S.I (Normalized) Class I Class II Class III Class IV Class V This table implies that heat stress does not significantly affect the changing of slake durability index of biotite gneiss. This behavior is also depicted in Figure 4.3 in which S.I values of naturally decomposed biotite gneiss are confined to a limited range. Heat stress can affect weakening of slake durability of biotite gneiss above temperature 630 C only. In addition, physical weathering might not significantly affect the deterioration of slake durability index of biotite gneiss. A smaller number of micro fractures are naturally present in competent rock mass as well. These are propagated due to heat stress and number of micro fractures is increased accordingly. Thin section study done on heat-treated and non-heat treated rock cores illustrate that micro fractures are propagated in longitudinal and transverse directions of rock cores during heat treatments. These micro -fractures could enlarge and expand further when the rock mass is loaded reducing the bearing capacity of rock. Figure 4.2 illustrates that weakening process is enhanced with the increment of temperature, by reducing the bearing capacity of rock core samples. Therefore micro fracturing is a dominant deformation mechanism in the process of deterioration. 6.3 The summary of discussion on the results of the detailed investigation on thermal sensitivity of quartzo-feldspathic gneiss With reference to the Section 5.4; the discussion on the results of the detailed investigation on thermal sensitivity of biotite gneiss can be summarised as; Deterioration of magnitude of an index property with the increment of temperature of quartzo-feldspathic gneiss follows a second order accurate polynomial plot in the form of y = - Px 2 - Q x + R (where P, Q and R are constants). Selection of quartzo-feldspathic gneiss representing different weathering classes was quite difficult. The main reason was that the weathering had not penetrated in to the quartzo-feldspathic gneiss rock mass. Decomposition was confined to the bottom of the overburden soil strata or the top of the quartzo-feldspathic gneiss rock mass. This is further verified by the test results given in Figures 5.2, 5.3 and 5.4.

4 101 As per Figure 5.2, UPV of naturally decomposed quartzo-feldspathic gneiss is confined to a limited range of values, which confirms that the decomposition has not penetrated into the quartzo-feldspathic gneiss rock strata. This is verified by the results of the slake durability index test in Figure 5.4 where there is a certain overlapping of S.I values. Figure 5.4 illustrates that heat stress can affect weakening of slake durability of quartzo-feldspathic gneiss above temperature 690 C only. In addition, physical weathering might not significantly enhance deterioration of quartzo-feldspathic gneiss measured by slake durability index test. Comparison of test results of the detailed investigations done on biotite gneiss and quartzo-feldspathic gneiss Results obtained for both rock types in the detailed investigations carried out are compared and illustrated in Figure 6.2 to 6.4. Figure 6.2 illustrates the fact that heat-treated fresh quartzo-feldspathic gneiss deteriorates faster than that of biotite gneiss when tested for ultrasonic pulse velocity of each. Figure 6.3 also illustrates the fact that heat-treated fresh quartzo-feldspathic gneiss deteriorates faster than that of biotite gneiss when tested for unconfined compressive strength of each. Figure 6.4 also further confirms that heat-treated fresh quartzo-feldspathic gneiss deteriorates faster than that of biotite gneiss when tested for slake durability index of each. Results of the above index tests done in the detailed study prove that quartzofeldspathic gneiss deteriorates faster than biotite gneiss.

5 Normalised Temperature : : -. : : : WO-r i i Figure Temperature vs. Normalised Temperature ( A reference graph for the analysis)

6 103 Temperature (Normalised) i Poly. (Fresh quartzo-feldspathic gneiss-heat treated) 0 r 2 0o- Figure Ultrasonic Pulse Velocity (Normalised) vs. Temperature (Normalised) (Comparison of biotite gneiss and quartzo-feldspathic gneiss)

7 104 Temperature (Normalised) Figure Unconfined Compressive Strength (Normalised) vs. Temperature (Normalised) (Comparison of biotite gneiss and quartzo-feldspathic gneiss)

8 105 Temperature (Normalised) - l-200-i -D- Q -0:800- J3! o K OJ e a.o n u 3 Q «55 A Slake Durability Index of Heat Treated Fresh Biotite Gneiss Fresh quartzo-feldspathic gneiss-heat treated Figure Slake Durability Index (Normalised) vs. Temperature (Normalised) (Comparison of biotite gneiss and quartzo-feldspathic gneiss)

9 6.5 Conclusions and Recommendations Conclusions As per the analysis of results of the research done, the following conclusions can be made: Strength of gneissic rocks drops significantly with increasing heat effect as applied in this study. Gneissic rocks deteriorate so that magnitude of an index property with the increment of temperature closely follows second order polynomial plots in the form of y = - X.x 2 - p x + y (where X, p and y are constants) within the range of temperatures used here. Out of all the tests carried out in this study, ultrasonic pulse velocity test and unconfined compressive strength test can be recommended as the best suitable index tests for a study on deterioration of gneissic rocks. Slake durability index property is insignificantly affected by application of heat followed by cooling up to 630 C for biotite gneiss and of 690 C for quartzo-feldspathic gneiss. Deterioration of slake durability in these rocks can be achieved by application of a temperature approximately exceeding the above values only. Observational studies of thin sections prepared from samples heated up to 700 C and of fresh samples indicate that micro-fracturing is the dominant deformation mechanism in the deterioration of gneissic rocks due to weathering as applied in this study. Different grades of weathering observed in the naturally weathered samples of rocks can be achieved in the laboratory by heating the fresh samples of rock to specific temperatures followed by cooling to ambient temperature. This was clearly established for biotite gneiss Recommendations Even though fresh quartzo-feldspathic gneiss has greater strength and higher durable properties than fresh biotite gneiss, it deteriorates faster than the biotite gneiss under similar processes of accelerated weathering. Therefore, this information may be taken into consideration when designing civil engineering structures on such geological formations. Attempts were made to simulate weathering by heating to a higher temperature and wetting. However to simulate natural weathering, it may be appropriate to heat to lower temperature for a long period of time and subjected to wetting. Furthermore since weathering is a long-term process, the above heating and wetting may be performed several times to simulate heating and subjecting to rains.

10 107 REFERENCES ASTM D 2216: Laboratory Determination of Water (Moisture) content of Soil, Rock and Soil-Aggregate Mixtures, American Society for Testing and Materials, ASTM D 2845: Laboratory Determination of Pulse Velocities and Ultrasonic Elastic Constants of Rock, American Society for Testing and Materials, ASTM D 2938: Unconfined compressive strength of Intact Rock Core Specimens, American Society for Testing and Materials, Bauer, S.J. and Jhnson, B. (1979). 'Effects of slow uniform heating on the physical properties of the westerly and Charcoal granites', Proc. 20 th U.S. Symp. Rock Mech.:7-18. Bell, F.G. (1994). 'Engineering Properties of Soils and Rocks', Blakwell Science Ltd., UK, pp Bieniawski, Z.T. (1989).'Engineering rock mass classifications', Wiley-Interscience, New York. Blyth, F.G.H. and de Freitas. M.H. (1974).'A Geology for Engineers', edward Arnold(Publishers)Ltd., UK, pp Brann, J., Friedman, M., and Hopkins, T.W.(1987). 'Strength and microfracturing of westerly granite extended wet and dry at temperatures to 8000C and pressures to 200MPa', 28 th US Symposium on Rock Mechanics, Tucson, USA. Clarke, G.M. and Cooke, D.(1992). 'A Basic Course in Statistics', ELBS(UK), pp Cooray, P.G. (1984). 'An introduction to the geology of Sri Lanka (Ceylon), National museums of Sri Lanka Publication, pp Goodman, R.E. (1993). 'Engineering Geology', John Wiley & Sons, Inc., UK, pp Gupta, A.N, and Rao, S.K (2001). 'Weathering indices and their applicability for crystalline rocks', Springer, Berlin, Germany, pp Kim, S. and Park, H.D.(2003). "The relationship between physical and chemical weathering indices of granites around Seoul, Korea', Bulletin of Engineering Geology and the Environmemnt, Springer, Berlin, Germany, pp MIN, K. and PARK.(2004).'Changes of rock properties by artificial weathering tests', Geological society of American Abstracts with Programs', Vol.36, No.5, pp.281. Oliver, H.J. (1976). 'Importance of rock durability in the engineering classification of Karoo rock masses for tunnelling', Proceedings of the Symposium on Exploration for Rock Engineering, Johannesburg, pp

11 108 Samaradivakara, G.V.I. (2004). 'Application of non-destructive methods for testing of index properties of gneissic rocks in large-scale geotechnical investigations', M.Eng. Thesis, University of Moratuwa, Sri Lanka, pp.47-48, 77-82, Worrall, W.E.(1969).'Raw Materials', Maclaren and sons Ltd., London, U.K., pp.5-15

A STUDY ON VARIATION IN ENGINEERING CHARACTERISTICS OF SOME GRANITIC ROCKS

A STUDY ON VARIATION IN ENGINEERING CHARACTERISTICS OF SOME GRANITIC ROCKS Int. J. Engg. Res. & Sci. & Tech. 2014 2013 Ajitesh Anurag and R K Yadav, 2014 Research Paper ISSN 2319-5991 www.ijerst.com Vol. 3, No. 1, February 2014 2014 IJERST. All Rights Reserved A STUDY ON VARIATION