İnce daneli çimento ile enjeksiyon model deneyleri

Abstract

Bu çalışmada zeminlerin enjeksiyonu ile ilgili incelemeler ve laboratuvarda yapılan çimento enjeksi yon model deneyleri anlatıldı. Burada enjeksiyon yöntemleri, portland çimentola rı ile enjeksiyon, kimyasal enjeksiyonlar, ince daneli çimentolarla ilgili mevcut araştırmalar ve enjeksiyon da kalite kontrolü konuları incelenip ardından labora tuvarda yapılan çimento enjeksiyon model deneyleri ve deney sonuçlarının değerlendirilmesi ele alınmıştır. Enjeksiyon uygulamalarında yüzyıla yakın süredir kullanılan klasik çimentolar dane boyutu ile ilgili o- larak ancak çakıl boyutundaki iri daneli zeminlerin enjeksiyonunda başarı sağlayabilmektedir. 1980' li yıllardan sonra, gelişen teknolojinin de yardımıyla ü- retilen ince daneli çimentolar ince kum boyutundaki zeminlere nüfuz edebilmektedir. İnce daneli çimento lar düşük mukavemet, yüksek maliyet ve yeraltı suyunu kirletme gibi olumsuz özelliklere sahip kimyasal en jeksiyon malzemeleri karşısında iyi bir alternatif malzeme olarak yerini almaktadır. l.T.O. Zemin Mekaniği Laboratuvarı 'nda yapılan çimento enjeksiyon model deneylerinde kum ve kum/çakıl karışımı zemin numuneleri kullanıldı. Bu numuneler değişik relatif sıkılıklarda ve değişik düşey gerilme ler altında silindir kalıplara yerleştirildi. Değişik su/çimento oranlarında hazırlanmış ince daneli çimento ve akışkanlaştırıcı ihtiva eden karışımlar ile normal portland çimentosu, bentonit ve akışkanlaştırıcı ihti va eden karışımlar muhtelif enjeksiyon basınçları ile bu numunelere enjekte edildi. Enjekte edilmiş numune ler üzerinde 7 ve 28 gün sonra basınç deneyleri yapı larak basınç mukavemetleri ve elastisite modülleri be lirlenmiş, sonuçlar karşılaştırılarak değerlendiril miştir.

The scope of this study is the research about the injection of soils and related cement injection model experiments. Here, first, injection process, injection using portland cement, chemical injections, the present research on microcement and quality cont rol in injection are examined. After these, the ce ment injection model experiments are represented. Injection process is a treatment method which is applied to the voids and cracks of soils and rocks by injecting a mixture with pressure. So, the permeabi lity of the medium is decreased and the shear strength is increased. In recent years by the help of microce ment that is produced by improved technology, impor tant developments are visible in the fields of injec tion. As known, normal cement can only diffuse to the voids of soils, that are composed of gravel. As it is noticed that, the chemical grouts used for treatment of sand where toxic and harmful for underground water the cement injections are uptodate again. Using mic rocement besides, giving no harm to underground water by toxic effects, low cost and high strength are obta ined. Generally, injection fluids are known two main types; cement based suspensions and chemical soluti ons. The difference between the two groups is that the suspensions contain particles which are held in limbo in an aqueous phase, whereas the chemical solu tions are free of particles. Consequently, the chemi cal soluble ones have the best infiltration capacity in fine cracks, and hardening is effected by the solu tion forming a gel, that sets after a certain period of time and wedges fast in crack. With the cement based suspensions, what happens is that the voids and cracks are filled with solid particles. In the case of systematic pre-injection where there is a stringent tightness requirement, in teraction between these two types of injection fluids is necessary to achieve entirely tight injection. Cement injection is hardly relevant in cracks of less than 1-2 nun. It is a good alternative in the case of injection, where the grout disappears on the conctruction, tunnels, floors on soil, dams, etc. Cement injection can be utilized in dry and water filled fissures. In all cases, the scouring and dilu ting effect of a water-filled crack must not be over looked. Taking this into consideration, the grout can also be used under water, of course. In this field, the last few years have seen the emmergence of a new option of combining cement, silicon and anti scouring agents. These are substances which are so firmly sta bilized and have a special lubricating effect so that they slip through the cracks. In addition, the danger of scouring is considerably lessened and good penetra tion down into the finer cracks is achieved without giving rise to blocking so easily. Bentonite-cement mixes may be used to form hydra ulic cutoffs by direct injection as grouts or by a variety of slurry trench techniques. It has been fo und that the properties of these materials are consi derably influenced by the way in which they are mixed. For bentonites gel strength and viscozity increase and permeability of the gelled slurry decreases continuo usly with time from mixing. Poorly mixed slurries may never develop as good cutoff properties as better mixed slurries. For bentonite-cement good mixing re duces the bleeding of the fluid material and the per meability of the set material. However, it does inc rease the strength and brittleness of the mix though this can be offset by the addition of sand or spoil. Normally speaking, %2-4 bentonite is added to the cement, the purpose of which is to stabilize the sus pension, combined with making the grout smoother and increasing the infiltration capacity. The usual procedure is to start off with a rela tively thin grout, a mix design of water/cement, 3/1 parts in weight and then gradually make the grout thicker as the pressure increases. The factor decisi ve to the mix design, however, will to a large extent be the pressure at which it is possible to operate. If higher pressure can be used, it is advantagours to use a stiffer grout. IX The roost important factors that effects the pro perties of cement mixtures are bleeding and water/cement ratio which determines maximum strength. For a long time, the term chemical grouts has been used as a synonymous of sodium silicate and the Joosten method. Sodium silicate and silicate-chloride are the basis of two-shot chemical grouts. Silicate (water-glass) injections can be applied both by two- shot (Joosten method) and one-shot methods. In last thirty years, it has been seen that many chemical grouts are used which one different from silicate, like acrylamides, lignosulfonates, phenoplasts. Chemical grouts can be silicate mixtures (water- glass) or artificial resins, plastics and polymers. Mostly silicate mixtures are used for chemical injec tions. Reasons for usage of silicate mixtures for chemical injections are their low cost and them to give not much to the underground water. Of late, cements have come onto the market which have a much finer grain than the high early strength Portland cement, called microcement. Microcements are cements produced with special mills and special mill techniques. They can be based on poor portland cement clinker or mixed with slag. The largest grain, in some microcements, is less than 20 Jim and with a fineness of 150 m2/N Blaine. While a high early strength portland cement, with a grain size of 70-90 Jim or even bigger (more than %20 bigger) and a Blaine of 40-48 mVN. This means that the the infiltration capacity in very fine fissures is considerably better than ordi nary high early strength portland cement and, through practical experience and tests, shows that they have more or less the same infiltration capacity to infilt rate into very fine fissures, just like chemical in jection f luids(solutions) such as silicate and acrylic resins. This new cement, microcement, therefore opens up new possibilities in the injection world. We now have an efficient tool based on cement materials and a tec hnique to tighten very fine fissures. In certain con sistences it can replace the chemical injection fluids completely. Practice shows that microcement can enter into fissures smaller than 0.25-0.3 mm. In connection with injecting cement suspension into fissures, it will easily build up a front in the drilling holes/ fissures. Only water, from the suspension, is able to enter through this barrier. From this barrier through to the front of the drilling/injection holes, there will be a shut down of suspension, as it gradually sediments. How good the tightness will be depends mosltly on the grain size, w/c, types of admixtures that have been used and of course the form and size of fissures. Microcement will always give a better final tightness result, because it can penetrate into the fissures better. The balancing of the design of injection process that increase parallel with the test costs, as a re sult means to lower the cost as much as possible. There are several methods to evaluate the results of an injection application. Between these, mostly pre- fered bore-hole radar and cross-hole acoustic shooting methods, are applied. While bore-hole radar method is used to determine the real position of injection mixture, cross-hole acousting shooting method is used to determine the strength(qualitatively) of the area, in which the in jection is applied. Although these two methods are being used, the experience for the evaluate of the data isn't much. In laboratory model experiments of cement injec tion, sand and sand/gravel mitures are used. Experi ments are done in three groups. In the first group experiments, the samples which are composed of diffe rent sand/gravel ratios are placed in cylinder molds with relative density of 0.30 under 20 kPa geological load. The microcement and superplasticizer mixtures which are composed of different water/cement ratio, are injected with the pressure of 150 kPa. In second group experiments, sand samples are placed in cylinder molds with relative density of 0.30 and 0.80, and by installing a rigid cover the vertical deformations of the samples are prevented. The micro cement and superplasticizer mixtures which are compo sed of different water/cement ratios are injected into sand samples with the pressure of 150 kPa and 300 kPa. In third group experiments, the samples with sand/gravel ratio 30/70 are placed in cylinder molds XI with the relative density of 0.30. By installing a rigid cover the vertical deformations of the samples are prevented. Normal portland cement and superplas- ticizer mixtures with constant water/cement ratio, different bentonite ratios are injected with constant pressure of 150 kPa. The compressive strengths of injected samples are tested after 7 and 28 days. The stress-strain relati ons, compressive strengths and elasticity moduli of the samples are determined. Besides these, the visco sity of the mixtures are measured by Marsh cone before the injection process.