Uçuçu küllerin siltli zeminlerin kayma mukavemeti üzerindeki etkisi

Abstract

Yapılan çalışmada, Gökova Termik Santralinden getirilen uçucu külle beraber toz kirecin, siltli zeminin, endeks, kompaksiyon, konsolidasyon ve özellikle kayma mukavemeti gibi mühendislik özellikleri üzerindeki etkisi incelenmiştir. Uçucu küllerin ve kirecin, üzerindeki etkisinin araştırıldığı ana zemin ÎTÜ kampus alanından alınmış olan düşük plastisiteli kumlu şilttir. Zemin, uçucu kül ve kireç karışım numunelerinin mukavemet özelliklerini belirlemek amacıyla Norveç Geoteknik Enstitüsü (NGI) tarafından geliştirilmiş olan statik basit kesme deney aleti kullanılmıştır. Bu aletle, her sette 3 deney olmak üzere toplam 1 1 set deney yapılmıştır. Deneylerin sayışım belirleyen ana parametreler, numunelerdeki uçucu kül, kireç oram ve bu numunelere uygulanan kür süreleri olmuştur. Çalışmada, zemin kuru ağırlığının %5, %10 ve %15' i kadar uçucu kül ile birlikte bazı numunelere %5 kireç katılmıştır. Kür süresi olarak ise 1 gün, 1 hafta, 1 ay ve 3 ay seçilmiştir. Deney numuneleri, daha önceden belirlenmiş olan maksimum kuru birim hacim ağırlığında ve optimum su muhtevasında olacak şekilde Standart Proktor deneyiyle hazırlanmıştır. Yapılan çalışma sonunda, zemine katılan uçucu kül ve kirecin, zeminin endeks ve kompaksiyon özellikleri üzerinde belirgin bir etkisi olduğu görülmüştür. Zeminin mukavemetinde ise katkı maddesi oranı ve kür süresine bağlı olarak %50' ye ulaşan bir artış meydana gelmiştir. Bununla beraber bu artış, killerde elde edilen artışın altında kalmıştır. ÖZET Yapılan çalışmada, Gökova Termik Santralinden getirilen uçucu külle beraber toz kirecin, siltli zeminin, endeks, kompaksiyon, konsolidasyon ve özellikle kayma mukavemeti gibi mühendislik özellikleri üzerindeki etkisi incelenmiştir. Uçucu küllerin ve kirecin, üzerindeki etkisinin araştırıldığı ana zemin ÎTÜ kampus alanından alınmış olan düşük plastisiteli kumlu şilttir. Zemin, uçucu kül ve kireç karışım numunelerinin mukavemet özelliklerini belirlemek amacıyla Norveç Geoteknik Enstitüsü (NGI) tarafından geliştirilmiş olan statik basit kesme deney aleti kullanılmıştır. Bu aletle, her sette 3 deney olmak üzere toplam 1 1 set deney yapılmıştır. Deneylerin sayışım belirleyen ana parametreler, numunelerdeki uçucu kül, kireç oram ve bu numunelere uygulanan kür süreleri olmuştur. Çalışmada, zemin kuru ağırlığının %5, %10 ve %15' i kadar uçucu kül ile birlikte bazı numunelere %5 kireç katılmıştır. Kür süresi olarak ise 1 gün, 1 hafta, 1 ay ve 3 ay seçilmiştir. Deney numuneleri, daha önceden belirlenmiş olan maksimum kuru birim hacim ağırlığında ve optimum su muhtevasında olacak şekilde Standart Proktor deneyiyle hazırlanmıştır. Yapılan çalışma sonunda, zemine katılan uçucu kül ve kirecin, zeminin endeks ve kompaksiyon özellikleri üzerinde belirgin bir etkisi olduğu görülmüştür. Zeminin mukavemetinde ise katkı maddesi oranı ve kür süresine bağlı olarak %50' ye ulaşan bir artış meydana gelmiştir. Bununla beraber bu artış, killerde elde edilen artışın altında kalmıştır. ash+5% lime by dry weight. The following procedure was used for preparing all the samples:. Dry mix the materials (soil, fly ash, or fly ash+lime) to produce a uniform mixture,. Add the required amount of water (established from prior testing of standard Proctor),. Mix until a uniform consistency is achieved,. Hand tamp three equal layers of moist mix into the Proctor mold,. Apply a pre-determined static pressure to provide the desired maximum dry unit weight,. After compaction, wrap around the specimens by aluminium sheets and placed in practically airtight plastic bags,. Keep them in the desiccators in a moisture controlled for ambient temperature curing for periods of time up to 90 days. The moisture contents of cured specimens were determined before and after they were tested. In the study, direct simple shear apparatus that is designed by Norwegian Geotechnical Institute (NGI) is used to determine the strength properties of the samples. The design of simple shear apparatus incorporates the following features: 1. The soil sample is mounted between parallel top and bottom filter caps and confined by a wire-reinforced rubber membrane. The soil specimen is consolidated under one-dimensional conditions and conditions of no lateral yield (Ko consolidation). The lateral stresses can be measured by using the wire winding of the membrane as an electrical resistance strain gauge, 2. The soil is sheared under simple shear and plane strain conditions, 3. Vertical loading can be applied either through dead loads or by coupling a manually operated worm gear to the hanger system, 4. Horizontal (shear) loading can be applied by dead loads, or through a range of constant strain rates by a multispeed motor drive that can be operated both forwards and backwards, 5. Vertical and horizontal loads are measured by proving rings. Horizontal loads can be measured in both forward and reverse direction since the ring is calibrated for compression and extension forces, 6. Reversal shear box tests to measure residual strength properties are conveniently carried out, because of the ability to reverse the direction of shear. Simple shear apparatus differs in a major respect from the conventional direct shear box, the top and bottom halves of which are moved with respect to each other, strains are non-uniform and failure occurs in the indeterminate zone. In the simple shear apparatus, the sample is placed between loading caps in a rubber membrane XIll of circular cross section, reinforced by a spiral wire winding. This provides lateral restraint against horizontal shear strains, but possesses a very small resistance to horizontal shear strains. When the loading caps are displaced relative to each other, horizontal cross section remain horizontal and undergo no horizontal linear strains. Vertical cross sections normal to the direction of shear remain plane but tilt through an angle equal to the shearing strain. An element of the soil will therefore undergo deformations corresponding to a condition of simple shear in the direction of the shear force, and plane strain in the transverse direction. All elements undergo the same strain, excluding boundary effects near the rubber membrane, which are minimised by making the sample height small in relation to the sample diameter. The apparatus thus offers the possibility of loading a sample to a failure in a manner which differs from the triaxial tests. It offers an advantage over the former test in that the whole sample is strained uniformly, and the maximum shear resistance is less influenced by any tendency to progressive failure than it would be with a less homogeneous condition of stress and deformation. A further advantage is found in constant volume tests. In these tests, drainage leads are kept open and hence pore water pressures are zero, but volume change is prevented by adjusting the external stresses. These tests can be carried out with greater precision since, because of the type of deformation, the requirements of no volume change can be met simply controlling the sample height. This is done using the manual worm gear to adjust the vertical pressure. An advantage which simple shear apparatus offers over the triaxial test is that the conditions of uniform simple shear and plane strain simulate more closely the conditions on the failure plane in certain types of field problems. The results of the tests performed for determining the effects of contents of fly ash and lime on index, compaction, consolidation and shear strength of silty soil, and curing times on shear strength are summarised below: 1. The original liquid and plastic limit of untreated soil were 26% and 20%, respectively. There is a general increase in these properties with increasing fly ash content. The addition of 5% of lime together with 15% of fly ash resulted in a smaller increase in the liquid limit, when compared with the mixes treated with of 15% fly ash. This mix had no plasticity. The values of specific gravity reduced from 27.4 kN/m3 to 26.3 kN/m3. 2. The compaction characteristics of soil, soil+5% fly ash, soil+10% fly ash, soil+15% fly ash, soil+15% fly ash+5%lime were determined. The optimum moisture content increased with increasing fly ash content but opposite trend was observed for the maximum dry unit weight. An addition of 5% of lime also caused a further increase in the optimum moisture content from 13% to 25%, but a decrease in the maximum dry unit weight from 18.9 kN/m3 to 15. 1 kN/m3. 3. Three oedometer tests were conducted at their maximum dry unit weights and optimum moisture contents in order to observe the effect of fly ash and lime additive to the soil on consolidation and permeability characteristics. Results of these tests indicated that the samples compressed very little, because of small XIV values of air void ratios of them. Coefficients of consolidation were from 1.32xl0"3 cm2/sec to 2.96X10"4 cm2/sec. Coefficients of permeability of the specimens were between 1.13xlO"5 ~7.25xl0"6cm/sec. 4. The shear strength tests were conducted on soil specimens containing fly ash and fly ash+lime. It was observed, contents of fly ash and lime and curing times were important parameters on shear strength. At first, the effect of fly ash content on shear strength were investigated. The results of these series of tests showed that content of fly ash in the samples caused no noticeable strength increase. Then, the effects of curing times up to 90 days on the samples that have soil+15% of fly ash content were studied. In these samples, shear strength increased about thirty percent with respect to the specimens prepared by using pure soil. Lime addition together with 15% of fly ash content to the soil also caused increase in strength. The amount of strength increase was 50%. This is the maximum value in shear strength increase determined during all tests for silly soils. It was also observed that the samples saturated under hydraulic conditions, have less strength than unsaturated samples. i The values of cohesion and angle of internal friction of the samples changed by relating to the contents of fly ash and lime, curing times and type of test. The values of cohesion ranged from 37.6 kPa to 57.8 kPa. The other shear strength parameter, angle of internal friction was varied from 20°.9 to 28°.7.