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Peshawa Mahmod

University of Brighton

Major steps in the evolution of idea about engineering description and classification of weathered rock

Introduction The continuous problem that faced during the engineering construction in area of weathered rock leads to draw several schemes by several experts and working parties to classify and analyse the weathered rock for engineering purpose. They tend to have a kind of classification and description to apply to all type of weathered rocks. First international consultation about foundation and soil mechanic take place in 1936 to discuss about the Panama Canal slides; and other remarkable interested works done in early twentieth century on rock behaviour by different experts, for example, Lde (1936) and Terzaghi (1946) (Hoek, 2006). However, according to Dearman (1976) the developing of classification and description of weathered rocks for engineering purpose was derived from Moye 1955 classification of rock for engineering purpose. This essay argue different scheme of classification and description of weathered rock done by different experts and group work party; firstly, Terzaghi, Moye and (Ruxton and Berry) classification, secondly, Little classification and thirdly, Party group classification and description. Finally, some Individual works with conclude attempting to publication and Standard of the classification and description of weathered rock.

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Peshawa Mahmod

University of Brighton

Terzaghi, Moye and (Ruxton and Berry) classification Terzaghi classification was attempted to classify rock for engineering purpose in 1946. In this classification Terzaghi recognized the importance of discontinuities in the engineering purpose in describing the rock spacing and their material filling. He used this information to describe certain kind of ground that could suitable for load forced steel arch in tunnel (Dearma, 1977). Moye classification was developed a method of classification of weathered rock throughout site investigation in Granite outcrop. The term was schemed that it could serve as an indication of engineering function for weathered Granitic rocks; also it might be useful as constant term by other peoples in doing investigation (dearman, 1995). In his classification Moye describe six classes of materials with weathering degrees in weathered Granit rock on Snowy Mountain, Australia. several parameters was taking to account as a recognition factors in the classification, for example, degree of Feldspar and Biotite disintegrating, joint with rock and soil materials strained, decomposition in water and presence and absence of original texture (Moye, 1955) (fig. 1.).

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Peshawa Mahmod

University of Brighton

The other classification was done by (Ruxton and Berry 1957) for the weathering granite in Hong Kong (Dearman, 1976). The classification was done in geological and pedological term together and based on the exposure of Granite to weathering (Dearma, 1995). The important part of this classification is that it could be applicable and equivalent to a mature chemical weathering and lateral profile in Granite core stone in the same weathering sketch. Four chemical and mechanical weathering terms was described with in rock weathering stage each term has particular results. (fig.2)

(Ruxton and Berry 1957) classification takes to account the sequence of variation containing physical disintegration and chemical decomposition for the martial of granite core stone; also allocation of these changes by demonstrating the weathering profile in the rock. On the other hand, the classification of Moye concentrated on the creating engineering quality of the granite material spatially on drilling sample (Dearman 1976). These classifications could consider being a complementary of each other in that the Moye classification and description of sample rock in small scale while (Ruxton and Berry) classification was describing mass of weathered rock in larger scale. Followed these classification several other approaches which have been recommended as weathered 3


Peshawa Mahmod

University of Brighton

classification and description of different rock types, however, all are slightly differ from the Moye, Terzaghi and (Ruxton and Berry) classifications that they also concentrate on the large scale weathering feature of material included the description of their zone. With the beginning of 1960s the development of rock engineering became more important because of number of disastrous failures built on rock and soil foundations (Hoek, 2006).

Little classification In the (1967 and 1969) Little published his classifications for engineering purpose for different stages of weathering procedure and different number of grades (Dearman 1995). This classification described various stage of weathering process based on evaluation of amount of discoloration of different materials (soil to fresh rock) with a grade number started from VI to I and conceding to the field description and recognizing of the materials with rock and soil ratio (Little, 1969). Also the description contains the indication of the engineering properties of rock (see table 1). Generally, the interested feature in this classification is that the grade to apply for weathering rock was recognized also by Moye 1955 (Dearman 1976).

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Peshawa Mahmod

University of Brighton

Group working party classification and description Two classifications of weathered rock and rock mass for engineering purpose have been come to stage by a group of expert in United Kingdom and they published a report as an engineering group of Geology Society of London (Pinho et al, 2006). The first classification of Working Party was structured with the purpose of recommending scheme for core drilled rock for engineering method and based on the degree of weathering in core logging rocks (Anon, 1970). The weathering classification is clearly evident that mainly based on the classification of Moye 1955 however, some improvement has been done to progress the classification and description of weathered rock for example, the term granitic soil in Moye 1955 was changed to residual soil and the classes were changed from six to seven classes. The working method of this classification based on general observation and description while in Moye classification was based on particular index. Another difference between this classification and previous one is that this classification was used for widely rang of different type rock but the previous classifications was derived for weathered granite only (Dearman, 1995). The second classification of weathered rock for engineering purpose was measurement of rock mass in engineering geological mapping (Dearman 1976). This work was done also by engineering group of the Geological Society of London (Anon, 1972). In this classification the same expressions was used with some different in definition and also it deals with various type of rocks and also applied to engineering soil with referencing to material strengths (Dearman, 1995), but the most important point in this classification is concerning on mass classification of rock instead of material classification.

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Peshawa Mahmod

University of Brighton

Individual works Another classification was done by Bieniawski (1973, 1974) called RMR system and the classification of Lien and Lunde in 1974 that called Q system and also the classification of Dearman in 1974. These classifications developed from principally in the evaluation of tunnels work but then expanded to using widely. These classifications was dealing rock weathering in more details including the strength of intact rock material, surface spacing number and properties and the structural discontinuities also it include the influence of the subsurface water (Hoek, 2006) (Dearman, 1974) (see fig. 3).

Three year later another work done on description of classification of rock mass that obviously separate the classification of weathered materials from masses rocks (Anon, 1977). Depending on soil and rock contain in mass rock seven grad was used and it describe different type of rocks also the description contain other type of rocks that was not described before. 6


Peshawa Mahmod

University of Brighton

Standard publication After this classification several works have been adapted and it leads to word standard classification of weathered rock for engineering purpose and the first standard was BS5930 1981 (Anon, 1995). In this standard publication the grades reduced as first used by Moye 1955 but with different meaning. The scale of classification started with fresh rock in the first grad to residual soil in the sixth grade with description of each rock grades (see table 2).

However, it is apparent that there is agreement about the requirement to change the degree of weathered rock mass from six grades to five grades it mean that it started from fresh degree to completely weathered degree. The description that used in this classification lead to several arguments about type of scale used in the classification, and number of authors suppose that this classification system criticized, restricted and it was difficult to application to different type of rocks consequently, they suggested to revision (Pinho et al, 2006). According to (Cragg and Ingman 1995) some difficulty might arise in application of (BS5930: 1981, classification of weathered rock mass for engineering purpose) when it applied in major project. Furthermore, it is difficult to extend the application of this classification on three and also two dimension drilled core rocks (Pinho et 7


Peshawa Mahmod

University of Brighton

al, 2006). According to (Dearman, 1995) this classification criticized because it limited in range of application with comparison to the wide variety of rock type and structures condition. Furthermore, Cragg and Ingman (1995) claimed that The BS5930: 1981 for description of rock weathering is Inappropriate and it infrequently applied to core logging rock; also they argued that it is unsuitable in condition of uniformity lithological condition this difficulty related to deriving zonation mass form and they show an example for different geological situation. In fact, other schemes option used for some rock type as a replacement for (BS5930: 1981); in condition where rock were highly weathered the complementary classification of both (Moye 1955) and (Ruxton and Berry 1957) was tack a place in using. In addition, the (Moye 1955) and (Ruxton and Berry 1957) was used as standard for engineering description of rocks in 1979 by the Hong Kong government (Anon, 1979). The demand to produce weathering classification scheme of rock increased because of it is important and appropriate for different type of engineering projects with all difficulties that prolonged. In the field investigation weathered rock caused a lot of complications in that the weathered rock are weakly bonded and it easily deformed (Beaven, 1976), for that reason it might be sensitive to get an exact sampling. In addition the weathering rock profile is complex and it could not be collected with a standard geological scheme (Hencher and McNicholl, 1995). To become more understanding about the application of previous schemes in 1989 a group of working leaded to that the deferent weathering process caused different weathering type and different lithological rock weathered in deferent method. As well as they recommended that making description of weathering rocks instead of try to deal with all characteristic of rock weathering.

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Peshawa Mahmod

University of Brighton

(Anon, 1995) analysis that there is a difficulty to made a fundamental description of weathering rock profiles and this difficulty depends on number of factors for example, lithology of rock, type of discontinuities, elevation of ground surface, climate, and the fluctuation of the groundwater table. Furthermore, the state of weathering rock is not often characterized in suitable way (Pinho et al, 2006). The important future prospect in point view of increasing information is concerning about preparing digital type of standard format of weathering classification of rock. The new plan of the Association of Geotechnical and Geoenvironmental Specialists is to create global data of transfer format of classification of weathered rock called (DIGGS) (Anon, 2007b cited in Culshaw et al, 2007); this work with the (Anon, 2003a, d, and c) standard international formalised of classification of weathered rock lead to be an acceptable practice of international standard (Norbury, 2004 cited in Culshaw and et al 2007). This steps are the most significant to correspond to a final stage which started before 50 years. It could now saw geologists that describe weathered classification of rock in the same way (Culshaw et al, 2007).

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Peshawa Mahmod

University of Brighton

Conclusion

Terzaghi attempted to create first classification in 1946 however, the first publication in description of weathering rock related to Moye in early 1950th on the weathering of the granite rock in Snowy Mountains in Australia. In late 1950th the other publication work done by Ruxton and Berry in 1957s this scheme was also describe the weathering of granite rock in engineering sites of Hong Kong. After fifteen years these two schemes provide two group reports done by Geological Society Engineering Group Working in early 1970th and used as a good guide to site investigation practice. The declaration on the weathered situation of a rock include only the element of a description scheme of the sample of a rock as a mass or material to indicate the important engineering properties. The similar scheme descriptive was adapted with the publication of the first British standard BS5630:1981 and later it criticized to be limited in use and not easily application to wider range of rocks and different situation of structural discontinuities. It is useless to attempt creating a single weathering classification scheme of rocks in expects that would be appropriate with different type of rocks, however, the new (Anon, 2003a, d, and c) standard international formalised of classification and the plan of the global data of transfer format (DIGGS) could lead to an international scheme of weathered rock.

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Peshawa Mahmod

University of Brighton

Bibliography Anon (1970), the Logging of rock cores for engineering purpose: Engineering Group Working Party Report, Quarterly Journal of Engineering Geology, vol.3: pp 1-24. Anon (1972), The Preparation of maps and plans in terms of engineering geology Engineering Group Party Report, Quarterly Journal of Engineering Geology, vol.5, pp. 293-382. Anon (1977), The Description of rock masses for engineering purposes: Engineering Group Group Working Party Report, Quarterly Journal of Engineering Geology, vol.10, pp. 355-388. Anon (1979), Geotechnical Control Office Manual for Slopes, Hong Kong Government Printer, Hong Kong, (1st Ed.). Anon (1995), The Description and classification of weathered rocks for engineering purpose, Geology Society Engineering Group Working Party Report, Quarterly Journal of Engineering Geology, vol. (28), pp.207-242. Cragg D. J. and J. Ingman (1995), Rock Weathering descriptions: current difficulties, Quarterly Journal of Engineering Geology, vol. 28(3), pp. 277-286. Culshaw Martin G., Helen J. Reeves, and Michael S. Rosenbaum (2007), Two Hundred Years Of Engineering Geology, British Geological Survey, 31 March 2007, Nottingham, UK Dearman W. R. (1995), Description and classification of weathered rocks for engineering Purposes: the background to the BS5930:1981 proposals, Quarterly Journal of Engineering Geology, vol.28 pp.267-276.

Dearman W. R. (1976), Weathering Classification in the Characterisation of Rock: A Revision Bulletin of the International Association of Engineering Geology, vol.13, pp.123-127. Dearman W.R. (1977), The Description of Rock Mass For Engineering purposes, Report by The Geological Society Engineering Group Working Party, Quarterly Journal of Engineering Geology, vol.10 pp.355-388.

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Peshawa Mahmod

University of Brighton

Hoek Evert (2006), Practical Rock Engineering, [online],Rocscience Inc, www.rocscience.com /pdf/Partical_Rock_Engineering.pdf, accessed in 10/12/2009.

Heancher S. R. and McNicholl D. P. (1995), Engineering in Weathered Rock, Quarterly Journal of Engineering Geology, vol. (28), pp.267-276. Little A. L. (1969), Engineering Classification of Residual Tropical Soils, proceedings of the International Conference on Soil Mechanics and Foundation Engineering, Mexico Vol. (1), pp 1-10. Beaven (1976), Applied Geology for Engineering, Military Engineering, 1st ed., vol XV, chapter 5, London, Catalogue of army publication. Moye D. G. (1955), Engineering Geology of the Snowy Mountains Scheme, Journal of the Institution of Engineering of Australia, vol. (27), pp 281-299. Pinho Antonio, Jose Alcino Rodrigues-Carvalho, Celso Gomes and Isabel Maria Maria Duarte, (2006), Overview of the evolution of the state of rock weathering by visual inspection, IAE, paper number (260), pp 1-7. Ruxton R. B. and Berry L. (1957), Weathering of Granite and Associated Erosional Features in Hong Kong, Bulletin of the Geological Society of America, vol. (68), pp. 249-162.

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Major steps in the evolution of idea about classification of weathered rock