Kaya dolgu yapılar ve kaya dolgulardaki son gelişmeler
Advances in rockfill structures
Yazar: EKREM GENCO GÜNAY
Danışman: DOÇ. DR. HÜSEYİN YILDIRIM
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü
Derece: Yüksek Lisans, 1995
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Jeoteknik = Geotechnics ; Kaya dolgu = Rock fill

Özet:
ÖZET Dolgu inşaatı, hızla gelişen inşaat teknolojisi ve süratle yapılanan uygun boş arazilerin az alımı ile ayrı bir önem kazanmıştır. Artık günümüzde tesviye' edilmiş, uygun ve sağlam yapı zeminlerinin oluşturulması, en az üst yapının inşaası kadar zahmetli ve önemli bir konu haline gelmiştir. özellikle dolgu baraj inşaatlarında, dolgunun kalitesi ve laboratuvardaki teorik çalışmalar ile arazi araştırmalarının paralelliği, dolgu yapımı sırasında, bir mühendis için birinci derece önem arz etmektedir. Kaya dolguların, gerek laboratuvar, gerekse de arazi de neyleri ile incelenmesi, 1920'li yıllarda başlamış ve 1970 *li yıllarda hız kazanmıştır. Laboratuvarda yapılan yoğunluk, permeabilite ve kayma gerilmesi testleri, arazide test dolgusu üzerinde yapılan in-situ araştırmaları ile karşılaştırılarak, hesapların gerçekselliği irdelenmektedir. Ancak buradaki esas problem, araştırmaların; kompaksiyon araçlarına, su muhtevasına, geçiş sayısına, dane dağılımına, poroziteye vb. bağlı olarak farklılıklar gösterebilmesidir. Bu çalışmada, özellikle laboratuvar ve arazi deneyleri üzerinde yıllardır yapılmış olan araştırmalar incelenmiş, sonuçları; uygulanan yöntem ve kullanılan malzeme bazında karşılaştırılmıştır. Ayrıca, dolgulardaki filtrasyonda, ana gövde ile filtre malzemesi arasındaki kesitin, dane çapı oranlarına bağlı olarak, borularıma adı verilen olayı başlatması incelenmiştir. Araştırmanın bir diğer özelliği, dünyada yapılmış olan mevcut barajları örnek alması ve inşaaları esnasında sağlanan gerçek değerleri irdelemesidir.

Abstract:
SUMMARY ADVANCES IN ROCKFILL STRUCTURES Rockfill structures are used all over the world, but their role and importance are not generally recognised. For instance, when reference is made to dams, the public in general, immediately thinks in terms of concrete dams, ignorant of the fact that embankment dams are by far the most numerous; and the surprise is total when it is said that the highest dams in the world (more than three hundred meters) are earth-rockfill dams. Nevertheless, progress in this area is relatively recent and is centered in three domains: - construction technology, where compaction by vibration has a leading role; - constitutive laws, subject to which fundamental research on particulate media, laboratory and field tests, as well as monitoring, have made important contributions ; - numerical methods, because they allow the application of constitutive laws, and thus, the forecasting of rockfill structure behaviour. It is important to stress that rockfills, when compared with soils, present additional difficulties, when a theoretical approach to their behaviour is attempted. One of the most significant, is that for the range of stresses found in civil engineering problems, particles of granular materials undergo important breakage, even for very low stress levels. This means that when travelling along their stress paths, rockfills are continuously changing not only the void ratio - as is the case with soils - but also the grain size. For each new step in this path, a new material is obtained. It therefore becomes clear how hard it is to design a rockfill structure when we aim to tackle all the safety problems involved. vxnFrom time immemorial man has used rockfill as a construc tion material for different structures. For better or for worse, empiricism always guided design and construc tion of those structures; in fact only in the 1950s did all phases of a construction projection begin to be approached in a rational way. After the fundamentals of soil mechanics have been established and some further development in this domain have been a achieved, attention began to focus on rockfills. In this case too, Terzaghi played a leading role when he rightly disapproved of the construction technique usually adopted at his time, i.e. applying high pressure water jets to remove fines in rockfills for dams construction. A number of important steps followed, of which we should mention: - laboratory characterization studies of the mechanical behaviour of rockfill, namely their shear strength and deformability, which called for design and construction of large-size equipment intended for direct shear tests, oedometric tests and triaxial shear tests (with axisymmetry) ; - acknowledgement of the role of particle fracturing in the mechanical behaviour of rockfills; - microstructural studies and their important contribution to sucess of the macro structural approach:, - assessment of the non-linear characteristics of the Mohr-Coulomb envelope and of the possibility of significant deviation in the normal trend of the initial phase (low stresses) of the stress- strain curve obtained in ID compression tests; - important results in grain size modelling; - marked progress in studying rock alteration and weatherability processes; - increase understanding of the role of water in the rheologie behaviour of rockfills; - great progress in developing constitutive laws, which, together with suitable numerical techniques, have brought about increasing success in description and prediction of stresses and strains in complex rockfill structures; - in situ tests for physical and mechanical characterization of rockfills; - monitoring and observation of the most varied rockfill structures. ixThe above steps associated with important developments in the domaine of quarrying and of transportation, laying, wetting and compaction of rockfill materials. It is only fair to emphasize the role played by powerful vibrating rollers in qualitative advance of rockfill structures. This progress brought about an impressive worldwide dissemination of rockfill uses in varied areas such as power production, agriculture, water supply, protection against natural calamities (earthquakes, slope slidings, floods), transportation (roads, railways, ports and airports), etc. What will be the future role of rockfills and rockfill structures? In an attempt to gather opinions on the matter, a panel entitled "Rockfill Future" took place during the ASI on Rockfill Structures. Next the main trends of the discussion are summed up. First the material itself has to be considered, i.e. whether it seems there may be large investment in laboratory tests in future for its physical, mechanical and hydraulic characterization. The index properties, for instance, in the near future will have a growing importance on the estimation of the main rockfill characteristics. There is no doubt that the design of rockfill structures, especially when they are integrated in high - precision projects should always be based on appropriate "design" tests carried out in situ and in the laboratory and performed on rockfill samples. However, in many circumstances, index properties obtained in stone pieces are of great interest whenever a rough estimate of the rockfill behaviour is desirable and more sophisticated tests are not available. Simple structures do not always justify expensive tests and pre-design analysis of large structures may greatly benefit from simple tests on small samples that are easy to obtain and transport, namely access when access to sites is difficult or outcrops are scarce. Recent experience shows that the estimate of design parameters of rockfill is possible although it is not a simple task. Much more data will be necessary for xevaluating the exact meaning of the first correlations and for assessing the degree of accuracy that may be expected from this procedure. Laboratory tests will also have an important role in the mechanical characterization of rockfills. Certainly we will not see the design and construction of large apparatus for testing the real material. As a matter of fact, some institutions have already done a lot in this very difficult, expensive and complex area to demonstrate that laboratory mechanical testing of rockfills needs larger equipment than that used for soils, but the testing of the integral that used for soils, but the testing of the integral granulometry is not always necessary. We owe a tribute to those institutions for this remarkable work. Laboratory testing in the research area will be mainly devoted to the study of rockfills consisting of uncommon rocks (weak rocks included) and of important phenomena such as the collapse (due to wetting and submersion) and creep of rockfill as well as its response to cyclic and seismic actions. Once the question of materials was dealt with, it matters to discuss what is expected for the different types of rockfill use, starting by dams. As a result of recent progress in the understanding of low-strength rock behaviour, this material will be more widely applied in dam embankments, which will surely contribute to more frequent choice of earth-rockfill solutions. Mainly for high dams, research on the mathematical modelling of the strain-hardening or strain- softening, elastic-plastic behaviour, mainly of the core material, as well as on the filter criteria, will make very important contributions to increase the safety of those structures. The parametric studies using the f.e.m. will be also an indispensable and decisive tool. Concrete face rockfill dams (CFRD), in turn, will attain heights that had never been reached before. This will be the result of important progress in the design and construction technology of the concrete revetments of the upstream slopes, and avoidance of vertical and horizontal joints. The recognition of the important role of the transition zone immediately under the concrete slab as a potential filter and discharge control as well as support zone with adequate deformabilitiy, will be also an outstanding factor. Moreover prediction of the movement of the perimetral joint will be improved as a result of progress in the extremely difficult task of relating dam xiprogress in the extremely difficult task of relating dam deformability and the movements in that joint. When compared with earth- rockf ill dams, CFRD allow a more versatile use of construction phases for tackling the important problem of river diversion. It is one more reason for their increasing use in the future. Their well-known good behaviour concerning seismic actions is also a feature that must be taken into account. One important application of rockfills is on through-flow or overflow dams. Usually these dams are not very height but for certain geomorphological and metereological local conditions their use will be expanded. Knowledge of the true water pressures in the rockfill medium percolated by the turbulent through water flow and the mechanisms associated with the scour effect on the structure slopes due to the overflow are of paramount importance. Theoretical approaches and physical modelling have been used to tackle those complex matters but the importance of accumulated experience must be underlined. Wide spread divulgation of results is therefore asked from those who possess that experience. Lastly, regarding the employment of rockfills in dams, one should stress the growing interest of using thin betuminous cores when the economic factor is determinant. On the other hand the demand for the use of betuminuous revetment in rockfill dams is not expected to exceed the present level. " To sum up, the future will show an increasing awareness of the safety of rockfill dams, structures already recognized among the other possible solutions as the most competitive from an economic point of view. An extension of the through-flow structure is the application of rockfills in spillways as an energy dissipator element (a solution whose main drawback is the low discharge capacity). Its use could be advised in some specific conditions. Another important area of use for rockfill is related with the transportation networks. Its use in embankments will certainly increase owing to the important progress in construction technologies. Efficient compaction at high rates of placement when compared with earthfills, (meteorological conditions are not an important constraint and embankment volumes are lower) will have both beneficial economic consequences and good post-construc tion behaviour, mainly as regards creep settlements. xiiIn certain countries there is expected to be an important application of rockfill in the construction of railways for high speed trains. In other regions (countries as Australia and Brazil, for instance) very heavy loads are to be supported by the railways and special attention must then be given to the ballast as well as to the embankments. The use of rockfills as well as the more recent knowledge of their behaviour will be an important factor in the design of those structures. The understanding of the reaction of maritime rockfill structures to the complex action of the waves will certainly be an important factor in choosing and improving those solutions. Finally as a consequence of research on the rockfill domain and observation of all types of rockfill structures, steeper embankment slopes will be employed. In many cases, waste rockfill type material from mining works has been accumulated in large areas. As a result of environmental problems or because different uses are now envisaged for these zones, special and important issues related with improvement of those rockfills must be solved in the future. Another important feature of rockfill structures (which is shared with the other fill structures) is their good answer to the ageing effects (the few exceptions do confirm the rule) when compared with other types of structures like concrete and steel, for instance. Because the rehabilitation of aged structures becomes a very important economic factor nowadays this is one more reason to choose rockfill solutions. Prospects about the use of rockfills in structures will certainly vary according to the region (for instance countries like U.K. and Germany hava practically no dams to be built which is by no means the case of Australia or Portugal). Nevertheless, when speaking of all the possible structures all around the world, there is no doubt that the future will show us an important increase in demanding for this type of structures and consequently large efforts will be made regarding rockfill structures safety (material properties, laboratory and in situ testing of rockfills, constitutive laws, mathematical and physical modeling) as well as construction technology (quarrying, transportation and compaction of rockfill, use of concrete and betuminuous material as an watertight element, etc). XlilFor all the presented reasons there is no doubt: rockfills will have a good future. xxv