Discussion

Bull Eng Geol Env (2001) 60 : 75–76 7 Q Springer-Verlag 75

Discussion on the paper by A. Tugrul and I.H. Zarif,“Engineering aspects of limestone weathering in Istanbul,Turkey”,Bull Eng Geol Environ 58 : 191–200Concetta I. Giasi

Received: 22 May 2000

C.I. Giasi (Y)Associate Professor of Environmental Engineering Geology,Technical University of Bari, 70125 Bari, Italy

In their paper, Tugrul and Zarif report and comment on aseries of physico-mechanical characteristics (minimum,maximum and mean values) of limestones. I would like tomake the following observations. It would be interesting toalso see the standard deviations for all the groups ofsamples reported. Concerning calculated linear correla-tions between different properties, it would appear that insome cases it is better to use non-linear laws; in particularfor regression between elasticity modulus and uniaxialcompression strength and between uniaxial compressionstrength and P-wave velocity.Figure 1 shows the line indicated by Tugrul and Zarif usingthe linear law and two curved lines using different lawswhich I consider provide a better fit, i.e.:

EpP98.6c2.04!scP0.0072!sc2 (1)

with a correlation coefficient r1p0.927;

EpP307.59P2.267scc56.68 ;sc (2)

with a correlation coefficient r2p0.924.For these two equations r1 and r2 are greater than 0.90, thevalue quoted by Tugrul and Zarif using the linear law.In Fig. 2 I have plotted the points for uniaxial compressionstrength and P-wave velocity, with the linear law (rp0.90)quoted by Tugrul and Zarif in their Fig. 12b and two non-linear laws:

scp194.16P2.647V2pc0.467V3

pP186.76

;Vp

(3)

with an improved correlation coefficient r3p0.95.A simpler non-linear equation is:

scp82.67c0.217V3pP

35.11Vp

(4)

also having r4p0.95.

Fig. 1Linear and non-linear laws (Eqs. 1 and 2) correlating elasticitymodulus (E) with uniaxial compression strength (sc)

Fig. 2Linear and non-linear laws (Eqs. 3 and 4) correlating uniaxialcompression strength (sc) with P-wave velocity (Vp)

76 Bull Eng Geol Env (2001) 60 : 75–76 7 Q Springer-Verlag

My final comment concerns that of undertaking straightline regression using different techniques (Troutman andWilliams 1982; Cherubini and Giasi 1997). For example,RMA has been found to give good results when re-arranging an equation, equating two different equations orsubstituting an equation with another, all statisticallyvalid.

References

Cherubini C, Giasi CI (1997) Limits and abuses in the use ofregression techniques in applied geology and geotechnics (inItalian). Medit 3 : 41–48

Troutman BM, Williams GP (1982) Fitting straight lines inearth sciences. In: Size WB (ed) Use and abuse of statisticalmethods in earth sciences. Oxford University Press, New York,pp 107–128