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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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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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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

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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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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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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.

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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

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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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(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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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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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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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.