Katı atık depolarında tabii malzemelerden geçirimsiz şilte teşkili
Formation of liners by natural soils
- Tez No: 66621
- Danışmanlar: PROF. DR. METE İNCECİK
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Geoteknik Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 128
Özet
ÖZET Teknolojinin hızla gelişmesi çevre kirliliği gibi bir sorunu da beraberinde getirmektedir. Doğal olmayan malzemenin doğa tarafından absorbesi de bir o kadar zor ve uzun bir süreç gerektirmektedir. Özellikle su ile reaksiyona giren zehirli kimyasalların yağmur suyu ile teması ve bunun da insanların kullandığı suyun kaynağı olan akiferlere ulaşması ayrıca büyük bir tehlike içermektedir. İnsan sağlığım tehdit eden her türlü atığın kontrolsüz olarak istiflenmesi yerine özel amaçla tasarlanan katı atık depo tesislerinde saklanması uzun yıllardır gelişmiş ülkelerde son yıllarda da ülkemizde uygulanmaktadır. Bu tür özel tasarıma sahip depo tesisleri içerdiği atıkların doğa ile etkileşimini engellemek için, tabanda bir şilte tabakasına sahiptir. Zaman içinde şilte tabakası olarak gerek sentetik malzemeler gerekse doğal fakat özel olarak karıştırılmış ve sıkıştırılmış malzemeler kullanılmıştır. Ülkemizi, çok sayıda katı atık depo tesislerinin kurulacağı bir memleket olarak düşündüğümüzde prosesi, ekonomiklik ve uygulanabilirlik olarak iki yönden ele almak uygun olacaktır. Bu bakış açısı doğrultusunda şilte tabakası uygulamalarında doğal malzeme seçimi ülkemiz için daha uygundur. Bu noktada nasıl bir malzeme kullanılmalı sorusuna cevap olarak hidrolik iletkenliği (permeabilite) düşük, yeterli taşıma gücü ve sıkışabilirlik özelliklerine sahip bir malzeme verilecektir. Şilte tabakası, uygun bir karışımın gerekli enerji kullanılarak sıkıştırılması sonucu istenen özelliklere sahip duruma getirilecektir. Son yıllarda kirlilik ile ilgili çalışmalar yanlızca bir meslek disiplininin uygulama alam olmaktan çıkmış birden fazla disiplinin araştırma alanına girmiştir. Bu bağlamda Çevre ve Geoteknik, Hidrolik ve Kimya Mühendisliği 'nin birlikte yürüttüğü pek çok araştırma ve uygulamaların varlığından söz edebiliriz. İstenilen mühendislik özellikleri sahip malzemeleri tabiattan doğrudan elde etmek bilhassa son zamanlarda zorlaşmıştır. Buna çözüm olarak tabii malzemeleri uygun şekilde karıştırılarak kullanılan veya yapay malzeme kullanmak söz konusu olmaktadır. Yapay malzemeler pahalı olabildiği gibi, yeraltı suyuna zarar da verebilmektedir. Bu çalışmada katı atık tesislerinde şilte malzemesi olarak kullanılmak üzere tabii malzeme karışımlarının uygunluklarının tespiti amacıyla bir dizi ilgili deney yapılmış ve elde edilen sonuçlar değerlendirilmiştir. xıı
Özet (Çeviri)
SUMMARY FORMATION OF LINERS BY NATURAL SOILS By the end of the 20th century various efforts were made in the sake of providing a better and more comfortable environment for the human. However, in all the establishments that were founded for technological improvements, besides the product there is another output which is called as waste. During the time it has been understood how hazardous this waste is to the environment (as a result to the health of human) and a lot of studies were made in order to prevent this. One of these precautions is constructing sanitary fills in which waste product is kept away from the environment as much as possible. Arrangements about industrialisation and consequent pollution have taken place since 1980 by United Nations and World Heath Organization. The first official step on this subject was made in 1990 by the establishment of the Ministry Öf Environment in our country. Recently two disciplines, environmental and geotechnical engineering have come together to solve the problem of pollution of the environment. The disciplines examine the problem on the topics such as pollution of the ground water, corruption of the flow of ground water, storing of house and industrial waste in specially designed disposals. At the beginning of this century nearly all the waste was stored in uncontrolled open areas. By the 2nd World War the first sanitary waste disposals have been used. The aim of a sanitary waste disposal is to prevent the dissipation of material that is hazardous for the environment and not to let it pollute the groundwater. It is suggested to place adequate amounts of impermeable material in the liners. If natural soil does not exist an impermeable fill is constructed (by recently improved geotextiles etc.). Since 1970 the application of a liner at the bottom have taken place. It is stated that % 15-25 of the total wastes of developed countries considered as dangerous. These wastes contain highly toxic organisms that gives harm to the human life. Although success on storing the waste has been acquired it is obvious that in any case the waste can never disappear. The aim at this point is to store the maximum compacted masses of waste in a disposal with a condition that gives minimum harm to the environment. In the designed waste disposal water containing highly toxic xmcompounds which is formed at the bottom of the waste must be drained and kept away from ground water. During the planning of a subsoil liner system, compacted clay liners which are the parts of this system are necessary to match some engineering criterion. The most important criterion is considered to be the permeability. In the last two decades many of the industrialised countries have been regulating the formation, disposal and management of the 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 bigger role in pollution management. The primary emphasis has been on waste reduction through re-use, recycling, clean-up technology development, etc. In Turkey, Solid Waste Disposal Instructions (Turkish Environmental Regulations, 1992) says that the lower level of the waste disposal sites must be covered with clay liners which has a thickness not less than 60 cm and hydraulic conductivity must be less than 10'8m/s. It is required to place the waste disposal away from the aquifers that supply water in order not to let it pollute in case of any negative condition. The base of a soil liner should supply the following conditions;. adequate bearing capacity. adequate impermeability. limited compressibility. characteristic to serve as barriers to hazardous material. characteristic no to be affected by hazardous material The construction steps of a waste disposal can be given as follows: 1. constructing liners 2. constructing sealing foils 3. setting up drainage blanket 4. positioning waste material 5. placing lime basement 6. placing protective layer 7. installing the cover layer The quality-control program employed during construction can be the most important factor affecting the hydraulic conductivity of a compacted soil liner. Experience has shown that, even if acceptable soil is used (e.g., sufficient clay content, plasticity index, and activity) and sound principles have been employed during construction control may yield liners with high hydraulic conductivity. However, if the design is sufficient and quality control is ensured, the probability is high that low hydraulic conductivity will be achieved. Sampling and testing is performed as part of quality control. Testing may include hydraulic conductivity, or other soil properties (such as water content, dry unit weight, and plasticity index) that are correlated to hydraulic conductivity. xivThe use of cut-off slurry walls as containment systems for polluted subsoils has increased considerably. The main backfill materials for this kind of containment barrier in Western European Countries are cement-bentonite mixtures. In addition many types of construction equipment and procedures together with special additives for the cement-bentonite mixtures have been used and patented by specialised contractors in order to obtain the best sealing, deformability, and durability performance for cut-off slurry walls used as containment barriers against pollutant migrations. The main concern of containment barriers for polluted areas is the check of the actual in-situ effectiveness in terms of hydraulic conductivity, pollutants diffusion and sorption, deformability, and durability. Among the features to be checked, hydraulic conductivity or permeability place a fundamental role. Compacted fine-grained soils are often used in landfill liner and covers as hydraulic barriers. Because of the inherent risk of ground-water pollution from landfills, statistical methods are being developed to analyse quality of constructions and the reliability of compacted soil liners. Compacted soil liners are used to minimise infiltration of water into buried waste (cover systems) or to control of the release of leachate from the waste (liner systems). To meet these objectives, clay liners must have low hydraulic conductivity for long term stability. In addition, compacted clay liners are expected to attenuate the movement of leachate, to extend the release of chemicals in leachate, and to serve other site-specific functions. Large-scale field tests are often conducted on test pads or trial sections to asses the field-scale hydraulic conductivity of compacted clay liners. During testing, The effective stress is typically low («lOkPa) and is not necessarily representative of the effective stress that will exist when the actual liner is loaded with waste (50-300 kPa). As a result, the reported hydraulic conductivity that will exist during operation and after closure of the facility. One method to extrapolate hydraulic conductivities measured in the field to higher levels of effective stress is to apply a reduction factor determined from results of laboratory tests conducted over a range of effective stresses. However, because specimens commonly used for laboratory testing can be too small to adequately represent the network of pores controlling flow at field scale, hydraulic conductivities estimated in this manner may not necessarily be representative of field conditions. Mineral sealing layers should not be subject to settlement to such an extent that their barrier function is compromised by deformation. Such deformations can cause cracking or shearing mechanisms in mineral sealing layers. Systems which seal the body fall within the external stability zone. The basal lining and capping system can comprise different materials with varying friction and shear behaviour. This behaviour determines resistance to sliding along the liner elements and/or subgrade contact interfaces. xvWaste body deformation (vertical or lateral) must not result in damage to lining systems or other structures within the waste body. In particular, an assessment of differential settlement and spreading deformation is necessary. Unacceptable stresses or strains on capping systems due to differential settlements have been observed in the following situations: ? Close to the landfill surface wastes with widely differing composition (that means waste of different consistency and settlement potential) have been placed. B The waste surface forming the subgrade of the capping system exhibits large variations in age or pre-loading. An unacceptable influence on the barrier function caused by the settlement-induced deformation can be expected when the tensile strength of the mineral sealing material is exceeded and open cracks develop. If deformation action leads to shear mechanisms without open cracks, no significant increase in leakage rates through the liner will occur. In particular, this situation will occur when overburden pressure prevents cracking and under these circumstances sealing performance will not be affected. Many wastes are mixtures of materials that can be in various states. Any attempt to characterise such materials would be pointless. The wastes range from strong acidic to neutral, and neutral to strongly alkaline. Some wastes are rich in metals while some are rich in organic and some are mixtures that contain both metals and organics. In this study laboratory tests are performed to achieve an ideal material to be placed as a soil liner system. The aims to be fulfilled are adequate impermeability, adequate bearing strength, incompressibility and adequate long term stability. In order to accomplish the desired values that are expressed in various standards several laboratory tests are done. Material chosen for testing comprised of sand-gravel mixture plus two different kinds of bentonite (bentonite A, wL=270, wP=28, IP=242, bentonite B, wL=570, wp=58, IP=512). A highly plastic clay (wL=75, wP=33, Ip=42) was added in percents of %5, %10, %15 consecutively. The material specifications are given in the appendix sections. The grain size distribution of the coarse material is calculated and plotted in a log- normal chart. To have a well-graded material a few trials were made and materials having the best grain-size distribution were chosen. A portion of %3 (by weight) of bentonites (A and B) were added to the coarse material. To the final material %5, %10 and %15 (by weight) of clay was added in consequence. Standard Proctor Tests were done in order to estimate the maximum dry unit weight-optimum water content. The specifications for the data are given in the appendix sections. xviFor the samples at maximum proctor compaction permeability tests were performed. The permeability tests done at the laboratory are falling head tests which are generally performed to test the permeability of the fine grained soils. Details for the tests are given in the tests section and data for the calculations are given in the appendix. Deformation-controlled shear box tests were accomplished for each of the samples in order to calculate the maximum shear strength. The ideal mixture percentages are given in the conclusions section. In order to find the unconfmed compression specialities of the samples oedometer consolidation tests were performed for the mixtures containing %10 clay. Further details about the tests can be seen in the conclusions section. In the tests which were performed on the material that comrised bentonite A, the mixture containing %10 clay is considered to be the ideal for permeability and the shear stress. During the tests which were performed on the material that comprised bentonite B, the region remained somehow narrow. The ideal mixture for permeability, maximum dry unit weight, and shear strength is considered to be the sample containing %15 clay. Further details about the tests can be seen in the conclusions section. It is observed from the applications that no matter how precisely the tests in the laboratory are performed, in-situ tests must also be done in order to get a more reasonable aspect for the durability of the construction. xvn
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