Engineering Description or Classification of Weathered Rocks

Engineering Description or Classification of Weathitherd Rocks creationThe exposition and Classification of Weathered gemstones brought together a series of chief(prenominal) studies by leading geologist and unioniseing researchers due to the countless difficulties encountered by engineers in weather shake up candy areas, how it affects lay exploration, plan and evaluation steps during projects. In the 1950s there has been a considerable amount of literature create on the characterisation of withstand flutters and engineering properties of weathered textiles, but there was little or no mensurationisation of descriptive terminology during this period, the physical exercise of these create data for the prediction of the engineering behaviour away from the headmaster study areas is limited. Thereafter the publications by the Geological Society Engineering concourse running(a) companionship the world(prenominal) Society of Rock Mechanics, the British Standards Institu tion, the International Association of Engineering Geologist and Dearman have rationalised the terminology by the engage of standard descriptive indices and simple forefinger testing. These objects enable the geologist or Civil engineer to disclose the materials and rock structure in engineering terms, and how it has been adopted for command practice worldwide. However the choice of which scheme to use is generally certified on the p bring up of the engineer responsible.Background AnalysisThe earliest attempts to shed light on weathered rocks in such a manner that will study useful to engineering goes back to the early 1950s when weathering compartmentalisation of granite was introduced by Moye in the Snowy Mountains of Australia. Moye proposed the scheme for the promotion and identification of engineering properties of weathered rock materials and how it would help to formulate the weathering terms of granite when they are apply during situation investigation by various group of persons.Six classes of rock materials were exposit based on the concept that logging of cores would be done on the basis of recognition of weathering events irrespective of order surface or downwards and without any attempt fitting the initial results of the logging into a formatted or general weathering profile with subsequent zones appointed in the rock cud. littler (1967), discussing laterites, suggested that the Moye motley could be applied to other lateritic-type soils and would be more booming for the purpose, than the usual temperate soil classification into clay, silts etc. The engagementing device characteristic was that Little applied grade numbers to the various degrees of weathering recognised by Moye (1955) grade I was refreshed rock and grade VI was rock weathered to a residual soil.Then the classifications of weathered rock came to a stage where a group of specialist came together in the UK and published a report on the first formalised weathering classification of rocks low the name of Geological Society Engineering Group Working Party narration on The Logging of Rock Cores for Engineering Purposes (Anon, 1970 in (Dearman, 1995). Its discernible that this was also mainly based on the classification of (Moye, 1955) scheme. However, few amendments were do the Moyes bouldery soil term was changed to residual soil thereby increase the number of categories from six to seven classes. Thus the new scheme was suggested to founder for a broader range of rocks while it was initially devised to granite. A nonher point of interest was that of the Working Party scheme which relied mostly on general descriptions and observations, which includes crumbliness while that of Moye was based on classification on specific index test.To pave the way for the mass scheme recommendation in BS5930 1981 (Anon, 1995), and so the latter scheme grades were reduced back to 6 as it was in the first place done by (Moye, 1955) and the same terminolog y was used with a pad different meaning. The argument over using the description of the materials or the mass scales for a classification came on. However, the required different approaches was advocated and grading the materials recommended to be decomposed, disintegrated, fresh and discoloured. Duncan (1969) also proposed a scheme based on texture, structure, composition and classification (calcareous or non-calcareous), colour and grain size.Following the publication of BS5930 1981, attempts have been suck at developing classification schemes which allow the degree of weathering to be delimitate for different lithologies, (Table.2) (Anon 1970, Anon 1977, BS 5930 1981). The early schemes (Anon 1970, for instance) were based on the chemical substance weathering of granite rocks and represented a hybrid material grade and zone scheme. In 1977, the working party of the Engineering Group of Geological Society on the Description of Rock Masses (Geological Society of London 1977) cle arly quarantined the description of weathering on a rock mass scale. This scheme, corresponding the preferably ones, placed great emphasis on the weathering profiles unquestionable on granitic rocks in tropical and sub-tropical environments, although, little guidance was given for the description of weathering.The British Standard proposed that weathered rock materials may be described or graded using four terms decomposes, disintegrated, fresh and discoloured, but they did non provide any guidance for determining and describing the degree or weathering. Attempts to use these schemes in the description of rock materials have met with difficulty. It is the opinion of the authors that any reference to the degree of weathering should be omitted from the description unless it is known with some certainty on the basis of experience and knowledge of the typical weathering profile for that rock type. For rock weathering in conditions where physical disintegration dominates, it is unli kely that the degree of weathering may be determined from examination of rock materials alone.The descriptive scheme for weathering was later criticized as being too restrictive in scope and not substantially applicable to a wide range of rock types and structural situation, though this was the original intention. As its indicated by (Cragg and Ingman, 1995) a number of problems may find when (BS5930 1981) is used for major projects. At the initial stage it is difficult to generalise the weathering pattern in two or three dimensions of rock cores. In some occasions this question cannot be fully answered unless closely position boreholes are cored, logged and then mass zones are ascribed after the complete bent grass has been logged. In profit, drill-hole may be insufficiently dense for a origin of a mass tract from material core logs.The critics of (BS5930 1981) do not always have more objective alternative schemes of classifications. For some the type of rock alternative sch emes may be preferred over the (BS5930 1981), including (Chandler, 1969) for Merica Mudstone and (Chandler, 1972) for fastness Lisa Clay and etc. In a situation where weathering dominates many aspects of geotechnics, the complementary classifications of (Moye, 1955) and (Ruxton and Berry, 1957) were essentially adopted as standards by the Hong Kong Government for engineering descriptions in 1979 (Anon, 1979) in (Anon, 1995), however, it is clear that all these alternatives are site or component part specified. They are generally rock mass schemes based and gradational or depth controlled.The IAEG (Anon, 1981c) in (Anon, 1995) recommended a presumably factual scale of percentages of weathering with no guidance for how this scale should be applied. According to the scheme, the degree of weathering can be expressed quantitatively by laboratory study. But these approaches remain apt(predicate) to lead to misunderstanding and disputes concerning descriptions.As far as the problems and difficulties prolonged in all engineering projects in the weathered rocks, the demand for such classification increased. Weathered rocks can cause particular difficulties especially in site investigations. They are frequently open textured and weakly bonded they can be very sensitive to disturbance during sampling. Also their profile are often complex and variability cannot be predicted with standard geological interpolation or extrapolation.The confusion, inapplicability of the suggested classification schemes combined with the lack of agreement between professionals working in the field has led to various bodies producing their own classifications, e.g. (Anon, 1988b). Similarly, many have off-key back to the (Anon, 1970) and (Anon, 1972). Some others keep using formation specified schemes like that of (Chandler, 1969).The Engineering Group of the Geological Society in an attempt to make critics see the ambiguity in its thesis has commissioned a Working Party to study the descri ption and classification of weathered rocks for engineering purposes. The Report of Working Party (1995) provides a scheme for describing the aver of weathering for uniform rock materials which are moderately strong or stronger in the fresh state which shows a clear gradation in engineering properties during weathering. The proposed classification scheme requires the use of appropriate index tests such as the point adulterate text and slaking tests.The most logical approach to the problem of classifying degree of weathering is to describe the rock material without attempting to provide a statement on how weathered it may be, apart from commenting on the presence of discolouration, decomposition, voids and softening. Once sufficient descriptive data on the rock material and the rock mass has been acquired to establish the mechanisms and stages of weathering present, a site specific weathering classification can be developed to provide a consistent means of describing both the rock material and, more importantly the rock mass.According to (Anon, 1995) The Working Party this duration preferred to make recommendations rather than attempting to deal with all aspects of weathering. In addition to circulating the draft at various stages among many correspondents and adding valued share to it, a three day meeting was held at the Leeds University, UK, in April 1994 for a more elaborate discussion. The Working Party report was then used during a day in the field and employed in the description of the weathered rocks in the laboratory (Anon, 1995).ConclusionApart from the potential confabulation problems, there is a strong argument for the need to devise a single modified version of the weathered rock classification proposed that superpower find more general acceptance and be more promptly applicable in field assessments, both rock material and rock mass.