Jet grout uygulamasından sonra zemin özelliklerinde meydana gelen değişiklikler
The change in the soil behaviour after jet grouting
Yazar: TURGAY ERDOĞAN
Danışman: DR. ÖĞR. ÜYESİ BERRAK TEYMÜR
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Zemin iyileştirme = Soil improvement

Özet:
Dünya nüfusunun artmasıyla doğru orantılı olarak inşa faaliyetlerinde de artış beklenen bir sonuçtur. Bu sebeple her geçen gün inşaat yapılacak elverişli alanlar azalmaktadır. Zemin parametreleri bakımından zayıf olan alanlarda da inşaat faaliyetlerin sürdürülmesi kaçınılmaz olmuştur. Bu tür zeminlerin parametrelerini arttırabilmek için bir takım iyileştirme metotları geliştirilmiştir. Zemin iyileştirme metodu seçilirken uygulanabilirlik, ekonomiklik ve uygulama amacı bakımından çeşitli etütler yapılarak ilgili alan için en uygun olan metot seçilir. Bu tezin ana konusu olan jet grouting yönteminin, zemin parametreleri üzerindeki değişiklikler incelenmiştir. 
Jet grouting günümüzde hemen her tür zeminde uygulanabilir bir zemin iyileştirme metodu olarak kullanılmaktadır. Temel, döşeme veya dolgu altında taşıma gücünü arttırmak, oturmayı azaltmak veya farklı oturmayı önlemek, şev stabilitesinin sağlanması, zemin hareketlerini azaltmak, zemin boşluk oranını düşürmek, sızıntı bariyeri oluşturmak, sıvılaşma riskine karşı güvenlik sayısını arttırması bakımından jet grout ile zemin iyileştirme ülkemizde sıkça tercih edilen bir metot olmuştur.
Bu tez çalışmasında 1. Derece deprem bölgesinde yer alan bir bölgenin jet grouting ile iyileştirme yapılmadan önceki saha ve laboratuvar deney sonuçları ile jet grouting sonrası sonuçları karşılaştırılmıştır. SPT-N değerleri ile taşıma gücü hesaplanmıştır. Yine aynı şekilde SPT-N değerlerine bağlı kalarak sıvılaşma riski incelenmiş olup jet grouting sonrası bu riskin önlendiği görülmüştür. Temel boyutları da göz önüne alınarak hesaplanan ani oturma değeri ile iyileştirme sonrası jet kolonlarda kalite kontrol deneyleri kapsamında yapılan yükleme deneyi sonucunda elde edilen oturma değerleri karşılaştırılmıştır.
Jet grouting öncesi araştırma yapılan zeminin ani oturma değeri hesaplanmıştır. Zemin ıslahı sonrası kompozit zeminin elastisite modülü değeri kullanılarak hesap yapılmış ve çıkan sonuç karşılaştırılmıştır. Ayrıca kalite kontrol deneyleri kapsamında sahada uygulanmış bir jet grout kolona imalatından 72 saat sonra yükleme deneyi yapılmıştır. Burada okunan deplasman miktarı formül ile hesaplanan ani oturma değerleri ile karşılaştırılmıştır. 
Kayma dalgası hızı Vs ve boyuna dalga hızı Vp sahada yapılan sismik kırılma deneyi ile elde edilmiş olup, bu değerlere bağlı olarak elastik modül ve kayma modülü hesaplanmıştır. 
SPT-N ve Vs korelasyonları ile inceleme alanı verileri karşılaştırılmıştır. Jet grouting öncesi ve sonrası SPT-N değerleri farklı bilim insanlarının bağıntıları kullanılarak Vs değerleri hesaplanmıştır. Arazide yapılan sismik hız test verileri ile hesaplanan değerler karşılaştırılmıştır. Literatürde çok fazla örneği olmayan jet grout ile zemin iyileştirme metodu sonrası arazi sondajları ile laboratuvar deneyleri yapılarak zemin parametreleri elde edilmiştir. Bunun sonucunda jet grout uygulaması öncesi ve sonrası zemin özellikleri karşılaştırılmıştır.

Abstract:
The increase in construction activity, which is directly proportional to the increase in world population, is an expected result. For this reason, the convenient areas to be constructed are decreasing day by day. Sustainment of the construction activities was unavoidable in areas with weak ground parameters. A number of improvement methods have been developed to increase the parameters of such grounds. When the soil improvement is to be done, the most suitable method for the relevant area is selected by carrying out various studies in terms of applicability, economy and application. 
Soil improvement techniques involve changing soil characteristics by a physical action, such as vibration, or by the inclusion or mixing in the soil of a stronger material. The aim of this process is to increase the load bearing capacity or the shear strength, to reduce both absolute and differential settlements or in certain cases, accelerate them, to remove the risk of liquefaction in the event of an earthquake or major vibrations. Vibro-compaction is a ground improvement technique that can be used to transfer structural loads to suitable levels in poor ground conditions. The effect of vibration consolidates and strengthens the ground, helping to compact non-cohesive soils such as sand that would otherwise be unsuitable for construction. Since cohesive soils don't respond to vibration, this process is not suitable for those ground conditions. In the vibro-wing method, a steel rod, which is provided with 0.8m long wings spaced 0.5m apart in the vertical direction, is driven down by a vibratory hammer to the required depth of the compaction. The shaft is pulled out slowly as the soil is vibrated. The withdrawal rate depends on the time required to reach the required relative density. The rate is mainly governed by the permeability of the soil. A higher withdrawal rate can be used for coarse sand than for fine sand. Dynamic compaction is a method that densifies soils and fills by using a drop weight. The drop weight, typically hardened steel plates, are lifted by a crane and repeatedly dropped on the ground surface. The drop locations are typically located on a grid pattern, the spacing of which is determined by the subsurface conditions ad foundation loading and geometry. This technique has been used to increase bearing capacity and decrease settlement and liquefaction potential for planned structures. Compaction grouting is well established method of in-situ soil improvement and can also be used to lift and level structures founded on poor foundation soils. It is primarily used to densify weak foundation soils, although is often used for many other treatment objectives, including lifting and releveling of structures, filling sinkholes and solution cavities, increasing capacity of piles, mitigation of soil liquefaction potential. Inherent in the compaction grouting process is the ability to work in and around existing structures and infrastructure elements, allowing for subsurface soil improvement without the need for structure demolition. Prefabricated vertical drains also known as wick drains consist of channeled synthetics core wrapped in geotextile fabric. They are flexible, durable, inexpensive and have an advantage over sand drains which is that they don't need drilling. Prefabricated vertical drains is best suited in clay, silt, organic layers, clayey and silty sand. The drain is placed into steel mandrill then the mandrill is pushed into the ground to the determined depth with a mast mounted on back hoe. Anchor plate is attached to the wick material to hold it in place as mandrill is removed. Then the prefabricated vertical drain is cut off a little above the ground. It is used to reduce surcharging process time and accelerate settlement not reduce it. Pore water will move laterally to the nearest drain instead of moving vertically to the permeable layer. Therefore, the drainage distance decreased. Stone column is a ground improvement technique used to improve the load bearing capacity and reduce the settlement of the soil. It is also called as granular columns or granular piles. This technique is also known as vibro replacement. In this technique dense aggregate column (stone columns) is constructed by means of a crane suspended downhole vibrator. Water can easily pass into the stone column. So, stone column helps in excess pore water pressure mitigation and accelerates the consolidation process. 
Jet grouting is a soil treatment technique for stabilizing soft ground by mixing cement slurry with in-situ soil. The jet grouting involves the injection of cement slurry under high pressure from a nozzle fixed on a rotating monitor into the ground. The resulting high speed fluid jet erodes the in-situ soil and simultaneously mixes it with cement slurry to form a soil-cement column. Jet grouting is now used as a practicable ground improvement method on almost all types of grounds. Ground improvement with jet grouting is used in order to increase bearing capacity, reduce settlements or prevent different settlements, provide slope stability, prevent ground movements, reduce void ratios, create leakage barriers, increase the number of safety against liquefaction risk, jet grouting has become a frequently preferred method in our country.
The main problem in the field of examination, which was the subject of the thesis, was the improvement of the weak ground. At the first stage, it was planned to excavate 5m depth of the weak ground layer and then to improve the ground with controlled fill with 30 cm thickness. In order to do this deep excavation, mini piles were modeled around the excavation. However, in contrast to the ground studies, it was determined that underground water level in the mini pile drilling was at 3 metres not at 10 metres depth. Since the groundwater level is close to the ground, mini-pile drilling has not been carried out and this method has been abandoned. As a result of calculations made, it has been decided that the most reasonable improvement method that can be done in this area is jet grouting. It has been seen that the improvement of the soil will be successful by application of jet columns with a diameter of 60cm in a length of 9m in 1.70m x 1.70m squares in the calculations made by considering the project load and soil parameters. In order to obtain the necessary diameter of jet column, Jet-2 method was found to be suitable for the diameter measurement made on the test columns which were made on the field.
Liquefaction is the loss of strength of saturated sandy and silty soils under transient and cyclic loading due to excess pore water pressure. In this thesis, the field and laboratory test results before jet grouting and the results after jet grouting have been compared for a region located in the 1st degree earthquake zone. The bearing capacity is calculated with SPT-N values. Also risk of liquefection factor is calculated with SPT-N values and seen that it is prevented after jet grouting.
The settlement of a shallow foundation can be divided into two major categories; elastic, or immediate, settlement and consolidation settlement. Immediate, or elastic, settlement of a foundation takes place during or immediately after the construction of the structure. Consolidation settlement occurs over time. Pore water is extruded from the void spaces of saturated clayey soils submerged in water. The total settlement of a foundation is the sum of the elastic settlement and the consolidation settlement. The elastic settlement, that is calculated with the values of the modulus of elasticity and the dimensions of foundation, is compared with the settlement values obtained as a result of the loading test performed within the scope of quality control tests on the jet columns after improving. 
The elasticity and the shear modulus are calculated by the values of Vs and Vp that are obtained by the seismic refraction survey. The SPT-N and Vs correlations were compared with the datas from the study area. Soil parametres have been obtained by the field and laboratory experiments after jet grouting which has a very few examples in the literature. As a result, the soil parametres before and after were compared.