Derin kazılarda yatay jet grout uygulamasının sonlu elemanlar yöntemi ile incelenmesi
Investigation of horizontal jet grout application in deep excavations by finite element method
Yazar: MEHMET TARAKÇI
Danışman: YRD. DOÇ. DR. BERRAK TEYMÜR
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Derin kazı = Deep excavation

Özet:
Nüfusun ve kentleşmenin hızla geliştiği günümüzde arazi maliyetlerindeki gözle görülür artış, bu alanların yer altında kalan kısımlarının da ihtiyaç doğrultusunda kullanılabilmesi düşüncesini gündeme getirmiştir. Böylelikle otopark, depo ve bazı sosyal kullanıma ayrılan birimler gibi daha geri plandaki kullanım alanlarının, inşa edilecek çok katlı yapı projesi için yer altında kalan kısmına taşınması söz konusu olmuştur. Yeraltı yapılarının inşası için yapılacak olan kazılar, çevredeki mevcut yapılaşma ve kazının geometrik sınırları nedeniyle birtakım zorlukları beraberinde getirmiştir. Bu zorluklar, derin kazı ve seçilen iksa sisteminin önemini arttırmıştır.
Bu çalışma kapsamında derin kazı iksa sistemi olarak yaygın olarak tercih edilen çok sıra ankrajlı bir destekleme sisteminde yatay jet grout uygulaması incelenmiş; jet grout enjeksiyon tekniği ile iyileştirilen ve iyileştirilmeyen zeminlerin çeşitli geometrik sınırlar için mevcut iksa sistemi üzerindeki etkilerinin araştırılması amacıyla hazırlanmıştır.
Yapılan çalışmada, bir iksa sistemine etkiyen toprak basınçlarından bahsedilerek, çok sıra ankrajlı destek sistemleri için çeşitli zemin koşulları altında oluşması öngörülen toprak basıncı dağılımlarına değinilmiştir. Öngermeli ankraj elemanlarının yatay eleman, fore kazıkların ise düşey eleman olarak seçildiği destekleme sistemleri ele alınarak tasarımda göz önüne alınması gereken temel prensipler açıklanmıştır. Bu tür sistemlerde uygulanan yatay jet grout enjeksiyonu  ile zemin ıslahı ile ilgili birtakım açıklamalara yer verilmiştir.
Tez kapsamında İstanbul ili, Kadıköy ilçesinde gerçekleştirilen örnek bir iksa uygulaması vaka analizi olarak incelenmiştir. İncelenen proje ile ilgili genel bilgiler verilerek; zemin yapısı ve karakteristik özellikleri, derin kazı iksa sistemi ve destekli kazıların gözlemlenmesiyle ilgili aletsel gözlem tekniklerinden bahsedilmiştir.
Çalışmanın son bölümünde incelenen derin kazı iksa uygulaması, geoteknik problemlerin çözümünde yaygın olarak kullanılan sonlu elemanlar yöntemi ve bu yöntemin geoteknik tasarımlar için uyarlanmış bilgisayar yazılımı olan Plaxis programı hakkında genel bilgiler verilmiştir. Daha sonra, yatay jet grout uygulamasının derin kazı iksa sistemi çalışma performansına olan etkileri sonlu elemanlar yöntemi ile araştırılmıştır. Bu kapsamda, jet grout ile iyileştirme yapılan ve iyileştirme yapılmayan zeminler, farklı geometrik parametreler belirlenerek oluşturulan geometrik modeller ile analiz edilmiştir. Yapılan analizler neticesinde; iyileştirilen ve iyileştirme yapılmayan geometrik modeller kendi içlerinde ve birbirleriyle, deplasmanlar ve düşey elemana etkiyen statik etkiler açısından mukayese edilerek sonuçlar değerlendirilmiştir.

Abstract:
As the population and urbanization have developed rapidly, the noticeable increase in the cost of land has brought the idea that the underground parts of these lands can be used when it is needed. It is thus possible to move the secondary usage areas, such as parking lots, store and some social units, to the underground part of the multi-storey building project to be built. The excavations to be carried out for the construction of underground structures brought with it some difficulties due to the geometrical conditions of the excavation and surrounding settlements. These difficulties have increased the importance of deep excavation and shoring system selected.
There is no doubt that geotechnical site investigation plays the most important role before any kind of construction project. It is needed to assess the field conditions, such as soil conditions, road and existing building situations. Taking into account the soil profile obtained from boreholes in the excavation region, groundwater level, geometry of the excavation, neighboring structures and environmental factors, shoring system should be dediced based on  safe and economy. On the other hand, the stress increase in the ground and settlements in neighboring buildings due to long-term draining of groundwater may occur. To design safe and economical shoring system, selected parameters and assumptions made should be close to reality.
In the case of a deep excavation, it is necessery to select the appropriate support system based on  the data obtained from the construction site. Today, deep excavation can be made with various shoring systems. Most prefered ones are bored piles, mini piles, diaphragm walls, well curtains and sheet piles. These systems can be defined as vertical supports and also be increased in terms of bearing capacity by horizontal supporting systems like prestressed anchors, soil nails and struts.
In this study, horizontal jet grout application is investigated in a multi-row anchorage system which is widely used as a shoring system in deep excavations. Different geometric models were created with different diameter and length of jet grout coulumns and  strength reduction factors for interface between structural elements and soils layers affect of these on soils treated with jet grouting injection were investigated. The study aims to  to investigate the effects of jet grout application on the displacement of an excavation system with finite element modelling.
In order to be able to design the retaining structures with sufficient level of safety, the lateral forces acting on the system must be analyzed and calculated correctly. Generally, loads that influence shoring system can be defined as lateral earth pressure, thrust from surcharge loads and hydrostatic pressure. In the scope of the study, detailed explanations of soil pressure distributions for various supported systems under different soil conditions are given.
Shoring systems in which prestressed anchors are selected as horizontal elements and bored piles as vertical elements are discussed, and the basic principles to be considered in design are explained. An overview of the system's general stability assessments is provided, including information on the assesment of bearing capacity of anchors and bored piles and on the state of collapse of these structural elements.
Soil properties in anchorage systems directly affect the anchorage load capacity. As a result, improving the soil properties can be an alternative solution for such structures. In this study, soil improvement technique with jet grout injection applied horizontally in anchorage support systems is mentioned and importance is given for the system.
In this thesis, an example of a shoring aplication constructed in Istanbul is analyzed as a case study. By giving general information regarding the project investigated, the soil structure was determined by examining borehole datas obtained from the site. Then, idealized soil profile was created. In determination of soil parameters in the soil profile, various field and laboratory experiments conducted within the scope of the geotechnical studies conducted in the field of investigation and literature studies was used.Additionally, details of the application of the horizontal and vertical elements of the deep excavation system examined are explained. A summary of instrumental observation techniques used for the safety of the excavation and shoring system is given.
In the last part of the study, general information is given about deep excavation application, finite element method widely used for solving geotechnical problems and Plaxis program which is a computer software adapted to geotechnical design.In the following it is aimed to investigate the effect of horizontal jet grouting on the performance of the deep excavation system performance by using the finite element method.
Plaxis was used to analyze the design and calculation methods of the design parameters required for the analysis. The accepted parameters for the jet grouting column and existing soil layers are obtained from the geotechnical investigations conducted on construction site and from literature studies. Design parameters have been calculated considering all geometric models created and the improved soil unit behind the shoring system taking into account the areas that anchoring or anchorage groups have in the system.
The displacement capacity of the excavation system studied by Hardening Soil model in the analyzes has been examined in detail. The maximum horizontal and vertical displacement ratios that occur in the soil and region in which they occur are expressed together with the plaxis output. As well as the vertical displacement distribution on the soil surface and horizontal displacement distributions on the vertical element are also included.
The dimensioning of the structural element is directly connected to the order of the elementary static forces. For this reason, bending moment, shear force and axial load values acting on vertical element are calculated for all models created were compared to determine the optimal load distribution for the most unfavorable case. 
The results of the analysis acquired from finite elements method, Plaxis, can be useful to give a prediction to the designer before construction. Additionally, it should not be forgotten that the results depend on the parameters entered in the programme. Therefore, it is important to compare the values obtained from software analysis with the instruments placed in the field. For the safety of the excavation, instrumental analyses are essential.
Within the scope of the thesis, geometric models designed to investigate the effect of horizontal jet grout application on the system were analyzed and evaluated in terms of static effects acting on vertical element and displacement levels. The results acquired from analysis can be summarised as follows:
- In the untreated soil, the root of anchors was not able to provide adequate adherence during the reaching of the target prestress load.
- Application of the jet grout significantly reduced displacements and the shear force, axial load and bending moment values acting on vertical elements under the same project prestress load.
- Since increasing the jet grout column diameter will increase the friction surface between the soil layers and the jet grout columns, a relatively larger portion of the prestressing load will encounter the interface friction.Thus, it is likely to increase static forces acting on vertical element and the displacement levels under the project prestressing load.
- It is obvious that during the horizontal jet grout application, the surface of shoring system will be exposed to high pressure and this pressure will create additional displacement and cross-sectional effects on the vertical element. For this reason, the continuity of jet grout columns must be terminated at a certain distance or reduced in pressure value. In the analysis which  jet grout columns are terminated 5 meters behind from surface of shoring system, there is a visible increase in displacement rates and static forces acting on the vertical element.
- The increase or decrease of the Rinter coefficient defined for the interface element between the jet grout columns and the ground shows parallel behavior in the shear force and axial force values acting on the vertical element. The opposite is true for bending moment values when parallel behavior is shown. It is also observed that the displacement of the increased Rinter value on the vertical element is further shifted in the direction of the excavation area.