Geçirimsizlik perde ve şilteleri için kullanılan zeminlerin iyileştirilmesi

Abstract

İnşaat Mühendisliği' nde zemin olarak nitelendirilen malzeme, birbirinden çok farklı özelliklere sahiptir. Özellikleri geniş bir aralık içinde değişen tabii zeminlerin arazideki yüklemeler altoda davranışlarını analiz edebilmek ve mühendislik tasarımları için gerekli parametreleri saptayabilmek, diğer inşaat malzemelerine göre çok daha karmaşık bir problem oluşturmaktadır. Bütün zeminler için gerekli davranış modelleri ve malzeme katsayılarını tanımlayabilmek, çoğu durumlarda mümkün olmamaktadır. Bu nedenlerden dolayı, zeminler ile ilgili çalışmalarda deneysel çalışmalar esas alınmaktadır. Bu çalışmada da deneysel araştırmalardan yararlanılmıştır. Hızlı sanayileşme ve nüfus artışı sonucunda büyük boyutlarda kirlenme sorunuyla karşılaşılmıştır. Bu konunun önemli bir kısmını "çöp" olarak isimlendirilen ve değişik sınıflarda olabildiğinden "atık" da denmekte olan tüketim ve üretim yan çıktıları oluşturmaktadır. Katı ve sıvı fazda olabilen bu atıkların kontrol altında, tasarlanmış sıhhi atık depolama tesislerine tasfiyesi gerekmektedir. Genel olarak atıkların sınıflandırma biçimleri anlatılarak çöp suyu sızıntısını kontrol etmek amacıyla oluşturulan şilte ve perde sistemlerinden bahsedilmiştir, önceleri doğal kil tabakalar şilte olarak kullanılmıştır. Sıkıştırılmış kil şilteler yetersiz durumları gidermek için denenmiştir. Daha sonraları sentetik malzemeler kullanılarak daha ince ve daha geçirimsiz, emniyetli tabakalar oluşturulmuştur. Bu çalışmada, bu amaçlarla oluşturulan deponi tesislerinden bahsedilmiş ve bu tesislerin yapımında kullanılan, doğal geçirimsizlik malzemesi olan "kil" incelenmiştir. Bu tesislerde geçirimsizlik malzemesi olarak kil zeminler, sentetik malzemeler, bitümler vb. malzemeler kullanılmaktadır. Bunlardan, en fazla, doğal malzeme oldukları için tercih edilen kil zeminler, deponi yalanlarında her zaman bulunamadıkları gibi, çok kere de kompaksiyon ve diğer özellikleri dolayısıyla kullanılmaları çok güç olmaktadır. Daneleri arasındaki boşlukların çok küçük olması, hidrolik iletkenliğin (permeabilitenin) killi zeminlerde düşük olmasına sebep olmaktadır. Günümüzde ortaya çıkan, atık depolama sahalarının (deponi) iyileştirilmesi problemi, çeşitli stabilizasyon yöntemleri ile çözümlenmektedir. Bu yöntemlerde, zeminin zararlı deformasyonlar yapmadan uygulanan yükleri taşıması ve mukavemet ile stabilitelerini sonsuza dek korumaları ilkesi öngörülmektedir. Bu konu ile ilgili geniş açıklamalarda bulunulmuş ve Türkiye'nin çeşitli yerlerinden alınmış kil numunelerinin mühendislik özellikleri belirlendikten sonra, bunların şantiyede kolayca serilip sıkıştırılmasını sağlamak için belli oranlarda kum ilavesiyle, zemin numunelerinin kuru birim hacim ağırlık ve geçirgenlik özelüklerinin değişimi, deneysel çalışmalarla gözlemlenmiştir.

Material qualified as soil in Civil Engineering has very different properties from each other. Being able to analyze the behaviours of natural soils that the properties alter in wide interval, under loading on land and point out necessary parameters for planning in engineering from a more confused problem according to the other construction materials. Being able to define behaviour models and material coefficients which are current in every soils is not possible in most situations. Because of these reasons it becomes useful first to separate the soils to the specific categories according to some simple properties of them and then trying to point out engineering properties. In this kind of separation, the clay which is in the category of fine-grained is a natural imperviousness material which is in the shape of thin plate that the thickness of it is very few respecting its other dimensions. It is a kind of soil which covers the large parts of the earth. But, it is very important kind of soil that the behaviour properties must be founded and recognised in either soil types of engineering. Water films which surround the clay particles is important because particle specific surfaces are large. Because of that contained water is much. The effect of adsorpsion powers decrease according to their distance from particle surface, surface strength of the water which is in contact with particle decrease when it is far away from the surface. Being very small of the pores between clay particles causes hydraulic permeability at low rate on clayey soils. Because of that the drainage of clayey soils is very difficult. In this thesis, extensive explanations were done about clayey soils. Some tests were done about clay which is a natural impermeable soil. 7 soil samples were tested and 3 soil samples which have same propreties were choosen. These samples were mixed with sand in %10, 15, 25, 40 and 50. After that, the changing of these mixtures' permeability and dry unit weight were examined. Environmental Geotechnology has been one of the most popular subjects of geotechnological engineering in recent years. Rapid increments on industrialization and urbanization around the globe are caused vast amounts of environmental problems. Geotechnical engineers are increasingly challenged to solve these problems xiv related to waste disposal facilities and clean up of contaminated sites. The measurament of hydraulic conductivity values of compacted clays which are intensely used as a liner and cover material in waste disposal sites takes an important role in Environmental Geotechnology. Environmental geotechnologists must not only be geologists and civil engineers, but also accustomed with principles of hydrogeology, chemistry and biological processes, as well. Until recent years, hydraulic permeability of fine-grained soils could not be measured, these were accepted as impervious. But, after being started to be used on several areas and especially on waste disposal sites of clays the necessity of the measurement of hydraulic permeability of compacted clays occured. Especially, the permeability of clay liners which are under the dangerous waste disposal sites effects directly the groundwater and environment. So, the amount of conductivity and test methods are investigated thoroughly. The nature of clay which is different from sand and silt caused difficulty in estimating the hydraulic conductivity empirical formulas. So, these coefficients must be found in laboratory. Soil permeability can be measured in either the laboratory or the field; laboratory determinations are much easier to make than field determinations. Because permeability depends very much on soil fabric (both microstructure - the arrangement of individual particles - and macrostructure - such as stratification) and because of the difficulty of getting representative soil samples, field determinations of permeability often are required to get a good indication of the average permeability. Laboratory tests, however, permit the relationship of permeability to void ratio to be studied and are thus usually run whether or not field measurements are made. Among the methods used in laboratory to determine permeability are; 1. Falling, or variable, head permeameter, 2. Constant head permeameter, 3. Direct or indirect measurement during an oedometer test. In addition, the microstructure of clays can be altered with the effects of some chemicals and the clay liner whose permeability was low at the beginning can become pervious. Because of the conductivity tests of clay liners take much importance. The most common lining material is soil. Soil linings generally are referred to clay liners. Such linings may be constructed of clays or mixtures of sand, silt and clay. During planning a subsoil liner system, clay liners which are the parts of this system are necessary to conform on some engineering criterias. The most important one of these criterias is low hydraulic permeability. In last two decades many of the industrialized countries have been regulating the formation, disposal and management of waste. In the United States the primary emphasis has been on waste disposal rather than waste reduction. In Western European countries governments have played a much larger role in pollution management. The primary emphasis has been on waste reduction through reuse, recycling, clean up technology development, etc. xv In Turkey, Solid Waste Disposal Instructions (Turkish Environmental Regulations, 1992) says that lower level of the waste disposal sites must be covered with clay liners which has thickness not less than 60 cm. and hydraulic permeability have to be less than 10"8 m/s. The other properties that a clay liner must have are; - Low diffusion, - Elasticity, - Chemical retard, - Stability of slopes, - Stability among layers, - Long-term stability, - Feasibility. A clay liner serves as a hydraulic barrier to flow of fluids. Clay liners are used to minimize infiltration of water into buried waste (cover systems) or to control of release of leachate from the waste (liner systems). To meet these objectives, clay liners must have low-hydraulic conductivity over long periods of time. Further, one must be able to verify that the hydraulic conductivity will be suitably low, that is, often the most difficult problem to be resolved. In addition, clay liners are expected to attenuate the movement of leachate, to prolong release of chemicals in leachate, and to serve other site-specific functions. Like improvement problem of the waste disposal sites that occured in these days in the solve of the most engineering problems soil properties must be improved. In this improvement work, soil have to carry applied loading without making damaging deformation and protect stabilization eternally with strength. The main processes which are used in the improvement of the quality of natural material are drainage, particle size distribution, compaction and stabilization. The term of stabilization with its wide meaning can be described as taking to the desired level of the engineering behaviour by changing soil conditions. A stabilized soil; a- Lasting, making small deformation with loading, b- With the changing of weather conditions, it is described as protecting the properties discussed before. Discussed works with the aim of improving soil properties are; - Surface compaction, - Lime and cement stabilization, - Grouting of the soil layer, - Soil replacement techniques and mix. - Reinforced earth. XVI The other methods of improvement techniques which were not discussed in this study are; - Water table lowering, - Ground freezing, - Electro-osmosis, - Heavy tamping compaction by explosives, - Deep compaction using vibratory probes, - Soil improvement by thermal treatment, - Improvement with gravel and sand columns, - Use of lime columns. Suface compaction is the most economic and productive stabilization way that several types of instruments are used in. Soil must be compacted by being spread out in thin layers on the surface. Second stabilization style explained in practise is lime and cement stabilization. Lime and cement are the oldest stabilization instruments. Lime increase the plastic limits of clayey soils and it makes the soils drier. So, the soils can fall into small fragments and the stability materials can mix easier. This is the main advantage of lime. In cement stabilization, when the cement is mixed to make the soil more strength, the shear strength of soil reaches a high level and the soil has more resistance against penetration the water into the soil. In grouting process to increase the shear strength and decrease the permeability a liquid is sent to soil mass under a pressure. This method of consolidating ground can be used in all types of subsoil and consists of lowering a monitor probe into a 150 mm. diameter prebored guide hole As more easy stabilization methods, soil replacement by excavating the thin soil and soil mixing is discussed in this work. The poor ground is excavated, removed and replaced by compacted fills. Using this method there is a risk of differential settlement. The last method which is discussed in this work is reinforced soil which we sometimes apply that without thinking. An example of reinforced soil as a constructional material consists of frictional soil backfill reinforced by linear flexible strips, usually placed horizontally. The performance of a reinforced soil structure depends on the friction developed between the soil and strip. The choice of ribbed mild steel, instead of other metals or plastics, is based on durability, friction, creep and elastic property considerations. Another form of reinforced soil is the use of woven plastic mesh placed on and wrapped around successive layers of compacted fill in embankment construction. xvn Engineers, scientists and environmentalists have told for years that soils and groundwater are getting dirty because of the disposal to the soil. But, after these damages had occured, the instructions and the rules which contain the importance of this type of contamination and the improvement of the contaminated areas were prepared. Subjects contained in this matter can be summarized under two paragraph: - To prevent the contamination of the soil, - The improvement of the contaminated soils or to take the contamination under control. Besides improvement of the soils protecting the contaminations of the soils is an important subject. Nowadays, most important reasons which cause soil contamination are industrial and domestic disposals. The waste disposal areas which prevent the sol from contaminating wastes contain the soild or liquid wastes in a sanitary way. Barrier technologies are used to prevent the impact of the storage facilities on surface water and groundwater quality. Categories of these barriers are explained on practise as follows. 1. Natural clay layers, 2. Synthetic clay layers, 3. Compacted clay layers, 4. Admixtures, 5. Cut-off walls (diaphragm walls), 6. Natural rock beds. Geomembranes are used extensively because of their advantages in landfill construction as an impermeable layer and cover material. The vast majority of geomembranes are thin sheets of flexible plastic or rubber based materials. An other advantage of geomembranes is being able to change its properties with their usage and in this way, a layer can be form in exact way of object. When using a geomembrane as the primary liner, it is placed either directly on the prepared soil subgrade or on a previously installed geotextile. Rarely is the geomembrane left uncovered and a uniform or tapered thickness soil cover is very common. Where leak detection is important, a double liner with a drainage layer (sand or geocomposite) between the primary and secondary liners is sometimes used. Such double liners are quite common in hazardous and radioactive landfill liners. Many wastes are mixtures of materials. Any attempt to characterize such materials would be pointless; virtually all waste forms can be found. The wastes range from strongly acidic to neutral, and neutral to strongly alkaline. Some wastes are rich in metals, some are rich in organic and some are mixtures that contain both metals and organics. Although the clay has low permeability, it allows the liquids which have dangerous chemicals. The time that will pass for dangerous materials which was solved in water xvm to reach to the natural soil by passing through clay liner depens on three factors. These are hydraulic load on the clay, the thickness of the clay liners and permeability value of the clay. It is important that the load on the clay is on minimum value. Sö, it is necessary that an effective drainage system must be constructed.