Şişen zeminler ve bir kilin şişme basıncına kireç katkısının etkisi

ÖZET Şişebilen zeminlerin su alması veya zeminin üzerindeki basıncın herhangi bir nedenle azalması sonucunda şişme adı verilen önemli hacim değişiklikleri oluşmaktadır. Bu hacim değişikliği bir çok mühendislik yapısı için önemli derecede tehlike arz etmektedir. Zeminlerin şişme davranışının önceden belirlenmesi ve etki eden faktörlerin incelenmesi ile oluşabilecek zararlara karşı önlem alınması mümkün olacaktır. Bu çalışmada şişen zeminler üzerine yapılmış literatür çalışmaları incelendikten sonra İstanbul ili Çatalca ilçesi yöresinde bulunan bir araziden alınan örselenmiş numuneler üzerinde İ.T.Ü Zemin Mekaniği laboratuvarında bir seri deneyler yapılmıştır. Deneylerin birinci kısmında farklı başlangıç su muhtevasının ve kuru birim hacim ağırlığında kompaksiyon numuneleri üzerinde konsolidasyon deney aletinde şişme basınçları belirlenmiştir. Elde edilen deney sonuçlarına göre çizilen grafiklerden su muhtevasının artması ile şişme basıncının azaldığı görülmüştür. Bununla beraber kuru birim hacim ağırlığının artması ile şişme basıncı artmaktadır. Fakat su muhtevasının çok düşük değerlerinde elde edilen düşük kuru birim hacim ağırlıkları için çok yüksek şişme basıncı değerleri elde edilmiştir. İkinci kısımda, belirli oranlarda kireç katılarak aynı şartlarda numuneler hazırlanmış ve deneyler tekrarlanmıştır. Bu şekilde kireç içeriğinin şişme basıncını ne şekilde etkilediği incelenmiştir. Deneylerin sonuçlarına göre kireç katılması ile şişme basıncının azaltılabileceği tesbit edilmiştir. v SUMMARY EXPANSIVE SOILS AND EFFECTING OF LIME ON THE SWELLING PRESSURE OF A CLAY In this study, a summary of the state of the art knowledge of expansive sous were outlined and a number of laboratory tests were conducted on the samples which were prepared by Modify Compaction mold. The possibility of damage to structures due to swelling of clays is complicated by the problem of idendifiying, at the outset of an expansion characteristics. in many parts of the world, the possibility of demage to structures due to the swelling of clays constitutes a severe problem in design and construction. In recent years, considerable progress has been made in clarifying the mechanism of swelling in soils, in understanding the behavior of expansive soils, and in developing technigues for handling swelling soils in engineering practice. However, the problem of identifying, at the outset of an investigation, those soils likeiy to posses undesirable expansive chracteristics remains one of the most throublesome phases of the subject. Identification of expansive soils is very useful! for understanding of the swelling behavior of soils. There are three different methods of identification, of the expansive soils. These are mineralogica! identification, indirect methods and direct measurement. Expansiveness of a soil is related to the clay mineral type of soil and amount of the clay. Hence, the swelling potential of any clay can be evaluated by identification of the clay mineral type. VTindirect methods of identification of expansive sous have been approached by many investigations around the world. Such methods may include *lndex Properties *USBR Classification *Aktivity.P.V.C. Meter *Soil Suction The Plasticity index and the Liquid Limit are usefull indices for determining the swelling characteristics of most clays. The swell potential is presumed to be related to the opposite property of linear shrinkage measured in a very simple test. The grain size and the amount of clay content have a bearing on the swelling potential of expansive soils. The clay content as wel as the Atterberg Limits should be included in the routine laboratory investigation on expansive soils. USBR Classification and P.V.C. are usefull methods for understanding the swelling behavior of expansive soils. Another term that is being increasingly used to explain expansive soil behavior is Soil Suction. But the actual aplication of soil suction in geotechnical consulting practice is stiiriimited. Soil suction is a parameter describing the state of soil and indicates the intensity with which it will attract water. The techniques available for the perdiction of swelling potential and swelling pressure fail into three groups. These are swell oedometer test, soil suction and emprical techniques. Recently, American Society for Testing Materials (ASTM) standardized the swell oedometer test procedures under the designation. VIIThis standard describes three alternate oedometer testing procedures to evaluate the anticapeted volume changes. ASTM defines swelling pressure as the pressure which prevents the specimen from swelling or that pressure which is required to return the specimen back to its original state (Void Ratio, Height) after swelling. The main factors effecting volume change are : * Soil Type * Structure * Dry Density * Moisture Content * Permeability * Thickness of Soil Stratum * Insitu Stress Conditions * Externally Applied Loads Method of Compaction for Remolded Samples Time Required for the Tests * Degree of Saturation * * Many empirical correlations have been made between routinely determined soil properties, such as Atterberg Limits, and magnitudes of from case histories or laboratory swell tests. This approach fails distinguish between the two major components involved, and actually attempts to correlate the Atterberg Limits, which should reflect the clay mineralogy and thus intrinsic expansiveness, with the observed swell which is due to the particular moisture change used in test procedure. However, a significant degree of success has been achieved with some of these methods. vmOn the other hand, the high degree of swelling is harmful! to engineering strustures and it may be required to control. A lot of stabilization methods have been developed for reducing of swelling. One of them that has been known to engineers all over the world is the use of lime. Lime is a favourable agent to reduce the swelling of soils. It is generally recognized that the addition of lime to expansive clays reduces the plasticity of the soil and, hence, its swelling potential. The chemical reaction occuring between lime and soil is quite complex. The amount of lime required to stabilize the expansive soil ranges from two to eight percent by weight. The basic lime stabization process includes in-place mixing, plant mixing and pressure injection. In this investigation, clayey soil sample which show high swelling have been tested. The clay used in laboratory test was brought to the laboratory from a construction area in Çatalca. The properties of the sample such as the Atterberg Limits; colloid contents, dry density and optimum water content were obtained by utilizing routine laboratory tests. The sampie which were used in the consolidemeter swelling test have been prepared by Modify Compaction Mold. The swelling pressures of ail samples which were at different initial moisture content and dry density were obtained. In the second part of the laboratory studies, the effect of lime on the swelling pressure was investigated. At the above initial conditions, samples included different percent of lime were prepared and the swelling pressures were obtained in consolidemeter test. Also, for each percent of lime content, the index properties of the samples were obtained. When the reieationship between initial moisture content and swelling pressure was plotted, it was seen that when initial moisture content increases, swelling pressure decreases. However, acording to the variation of initial dry density versus swelling pressure; when dry density increases, swelling pessure increases. IXThe same graphics were plotted for test results were obtained for lime included samples. The resuls of the laboratory tests indicate that the use of lime reduces swelling pressure. When percentage of lime increases, swelling pressure decreases. x 64