BİLİMSEL VE TEKNİK ÇALIŞMALARIMIZ | İksa Mühendislik | Forekazık

Tunnel Design in the Improved Ground with Deep Mixing Columns (2023)

Can, A., Gundogdu A. E. K., Gokceoglu, C.

In tunnel projects, one of the most common problems is the necessity of excavation under adverse geological and geotechnical conditions. A part of the T2 tunnel of Karaman-Ulukışla Railway System (south of Turkey) is shallow, and the ground conditions are weak and problematic. For this reason, in the study, the geotechnical problems of the T2 tunnel are described, and the engineering approaches for safe excavation of the T2 tunnel are introduced. A ground improvement with a deep soil mixing method (DSM) is selected for the safe tunnel excavation. The DSM columns before the tunnel excavation stage are designed, and all stages are analysed by employing finite element models. Based on the numerical analyses of the excavation stages, the mechanism, and the design concept of the tunnel with a ground improvement are discussed.

Comparison of Plaxis-2D and 3D Models of Improved Ground with Deep Mixing Columns (2023)

Can, A., Zengin, B., Gokceoglu, C.

In this study, the ground improvement application that applied to the foundation of a private hospital in Amasya, Turkey was investigated as a case study. The soil profile is mainly composed of silt-sand interbedded clay and under gravelly silty sand units in the study area. As a soil improvement method, the Deep Soil Mixing (DSM) technique based on the principle of simultaneous mixing the ground while injecting with cementitious, was selected. This technique is increasingly being used worldwide because of the advantages such as the variety of soil conditions that the technique can be applied, application speed, and the application’s depth. The bearing capacity of DSM columns was confirmed through five in-situ axial loading tests. In addition, core samples were taken from the DSM columns and the compressive strength tests were performed in the laboratory. For both types of tests, the results were about 25% higher than the desired values. It means that DSM columns were applied successfully. As an aim of this study, the axial load test was modelled both in Plaxis 2D and Plaxis 3D to compare their results with each other based on field data. Soil parameters that were used in numerical modelling were calibrated based on field data. This study shows us the overall physical behaviour of the soil profile can be predicted with acceptable accuracy through numerical modelling software. On the other hand, it has been observed that Plaxis 3D show more effective performance than Plaxis 2D to predict displacements.

Stability assessments of a triple-tunnel portal with numerical analysis (south of Turkey) (2022)

Can, A., Baskose, Y., Gokceoglu, C.

The Bahce–Nurdag tunnel, which is the longest railway tunnel in Turkey with approximately 10 km was planned as two tubes. During the excavation of the second tube starting from the Nurdag portal, the tunnel-boring machine (TBM) jammed at 1267 m of the excavation. The second tube was abandoned due to TBM jamming, and it was decided to build a third tube. For this construction, additional portal and tunnel excavations were needed. These excavations resulted in additional stresses. Moreover, the project was constructed in a highly seismically active region. For this purpose, the tunnel portal section was investigated numerically by finite-element analysis. Considering the results obtained from the three-dimensional (3D) numerical analysis, the existing portal was enlarged and excavation of the third tube was started. Currently, the portal construction was successfully completed, and the third tube was excavated for approximately 2200 m with the TBM. It was concluded that the suggested methodology with the excavation and support systems was found satisfactory when the analysis results were compared with in situ conditions. This study suggests that multiple tunnels and large portals to be constructed in highly seismically active regions be simulated by 3D numerical analysis for successful construction.

Paleo-Heyelan Malzemesi İçinde Açılan Tünel Portalı İçin Önerilen Mühendislik Önlemleri ve Çözümlemeleri: Bahçe-Nurdağ Tüneli, Türkiye (2022)

Ozyurek E. Y., Can, A., Acar K., Gokceoglu, C.

Son yıllarda oldukça önem kazanan hızlı tren demiryolu projelerinde, en çok karşılaşılan sorunlardan biri, olumsuz jeolojik ve jeoteknik koşullar altında tünel kazıları yapılması zorunluluğudur. Bu çalışma kapsamında, bu soruna tipik bir örnek teşkil eden ve yaklaşık 10 km’lik uzunluğuyla Türkiye’nin en uzun demiryolu tüneli olan Bahçe-Nurdağ tünelinin Bahçe Portalı incelenmiştir. Proje aşmasında tünel portal konumları seçilirken aktif heyelan alanlarından kaçınılmış, ancak Bahçe portalında paleo-heyelan kütlesinden kaçınılması mümkün olamamıştır. Bu nedenle tünelin ve Bahçe portalının güvenliğini sağlamak için ilave mühendislik önlemleri gerekmiştir. Bu çalışma kapsamında, meydana gelen yenilme mekanizmasının ortaya konulması, güvenli kazı-destek sisteminin aşamalarının sunulması ve tartışılması amaçlanmaktadır. Sonuç olarak, tasarımı gerçekleştirilen ve paleo-heyelan içinde başarılı bir şekilde imalatı tamamlanan tünel portalı, mühendislik vakası olarak sunulmaktadır. Ayrıca bu çalışmada, mühendislik çalışmaları sırasında büyük çaplı duraysızlıkları önlemede, baret kazıklı destek sistemlerinin etkin bir yöntem olduğu sonucuna varılmış ve sonlu elemanlar analiz sonuçları ile yerindeki ölçümler arasında büyük bir uyumluluk elde edilmiştir.

Geniş Bir Portala Ait Şevlerin Stabilitesinin Üç Boyutlu Sayısal Analizi ile Değerlendirmesi (2022)

Can, A., Baskose, Y., Gokceoglu, C.

Bu çalışmada, TCDD tarafından yapılmakta olan Bahçe-Nurdağ Fevzipaşa Varyantı projesi kapsamında inşaa edilen demiryolu tünellerinin geniş portal şevlerinin stabilitesinin üç boyutlu sayısal analizlerle incelenmesi amaçlanmaktadır. Tünel projelerinin tasarımında, yer seçimi ve tünel ve/veya diğer yeraltı yapıları boyunca olası tehlike bölgelerinin araştırılması ekonomiklik açısından oldukça önemlidir. Birçok tünel projesinde zayıf ve makaslanmış bölgeler gibi sorunlu alanlar ve aktif faylardan kaçınmak neredeyse imkansızdır. Bu çalışmaya konu olan tüneller iki tüp olarak planlanmıştır. Bahçe-Nurdağ tünellerinin Nurdağ kesimindeki çıkış portalı, Doğu Anadolu Fay Zonu’nun (DAFZ) içinde yer almaktadır. T1 ve T2 tünelleri birbirine paralel olup, yaklaşık 10 km uzunluğu ile Türkiye’nin en uzun demiryolu tünelleridir. Tünellerin kazı işleminin Nurdağ Portalı’nda başlaması ve TBM yöntemiyle Bahçe Portalı’nda tamamlanması planlanmıştır. Bahçe portal bölümünde zayıf birimlerin bulunması nedeniyle Yeni Avusturya Tünel Açma Metodu (NATM) ile belirli bir bölümün kazılması planlanmış ve T2 tüneli başarıyla tamamlanmıştır. Ancak T1 tünelindeki TBM’in sıkışması sebebiyle, mühendislik çözümü açısından uygun olan alternatifler değerlendirilmiş ve sonuç olarak Nurdağ Portalı’ndan yeni bir tünelinin kazılması alternatifi en uygun seçenek olarak değerlendirilmiştir. Bu nedenle inşaa edilen portalin genişletilmesi gerekmiştir. Bu sunumun ama konusu genişleyen portalin stabilitesinin üç boyutlu sayısal analizlerle incelenmesi ve tartışılmasıdır. Üçlü tünel kazısı için gerekli olan portal şev tasarımı, püskürtme beton ve bulonlar kullanılarak yapılmıştır. Bu tasarıma göre portal şevlerin stabilitesi ve tünel giriş bölümünün üç boyutlu sayısal analizi MIDAS GTS NX 3D yazılımı ile yapılmıştır. Yapılan analizlerde, tasarlanana şevlerin hem statik hem de dinamik koşullar için güvenli olduğu sonucuna ulaşılmıştır. Halihazırda portal inşaatı başarıyla tamamlanmış olup, TBM yöntemi ile 3. Tüpün yaklaşık 4200 m’si kazılmıştır. Bu çalışmada, projenin başarısı ve sonlu elemanlar yönteminin güvenirliliği yerindeki şartlarla karşılaştırılarak, analiz sonuçlarının performansı değerlendirilmiştir. Bu çalışma, karmaşık jeolojik ortamlardaki geniş çaplı portallerin stabilitesinin değerlendirilmesinde, saha şartlarını iyi temsil ettiği için üç boyutlu analizlerin kullanılmasına bir örnek oluşturmaktadır.

Ground Improvement of a Railway by Deep Soil Mixing Columns Against Liquefaction Problem in Manisa, Turkey (2022)

Can, A., Gundogdu A. E. K., Celenk, B., Gokceoglu, C.

The Manisa-Menemen Railway Project, located west of Türkiye was planned to modernize due to improving the transportation infrastructure in its area. Sandy soils with the potential for liquefaction were identified during the site investigation. Considering the project’s location in a region with high seismic activity and soil composed primarily of sand units, it is necessary to design a soil improvement methodology to mitigate the risk of liquefaction. Consequently, liquefaction analyses are conducted to design a suitable soil improvement system. A soil improvement method with deep soil mixing (DSM) columns was proposed to prevent related liquefaction problems. The factor of safety against liquefaction, the liquefaction potential index (LI), and the liquefaction severity index (LS) were calculated both for unimproved and improved soil conditions. To design DSM columns more economically, the length of the columns is reduced while still ensuring that they remained within acceptable limits for LI and LS. The performance of the DSM columns was evaluated under dynamic conditions by Finite Element Method. Based on the results obtained from the analysis, the performance of the columns was satisfactory. This study shows that a performance-based design can be used to design DSM columns in liquefiable soils. This approach can help create more efficient and cost-effective solutions for preventing liquefaction.

Design of Ground Improvement by Inclined DSM Columns for Railway Embankment (Türkiye) (2022)

Gokceoglu, C., Sirin, A., Can, A., Turk, E., Gullu, S.

In this study, the ground improvement application applied under the live railway bridge’s approach embankments in Sivas, Türkiye was investigated as a case study. The soil profile is mainly composed of orangish conglomerate, clay, silty sandy clay, and under claystone, and mudstone units in the study area. As a soil improvement method, the Deep Soil Mixing (DSM) technique based on the principle of simultaneous mixing the ground while injecting with the water-cement mix, was selected. The application of DSM columns is designed to be 45 degrees horizontal, in order to reach the deepest point of the soft clay units for better improvement against settlement. The core samples were taken from the DSM columns and the compressive strength tests were performed in the laboratory. The results were higher than the minimum designed values. It means that inclined DSM columns were applied successfully, and the excessive settlement problem was solved.

Proposed Engineering Measures and Analysis of Tunnel Portal Excavated in Paleo-Landslide Deposits (Bahce – Nurdag Tunnel, Turkey) (2021)

Ozyurek E. Y., Can, A., Acar K., Gokceoglu, C.

Due to geometrical restrictions of high-speed railways, excavation is mandatory under adverse geological and geotechnical conditions. The Bahce-Nurdag tunnel with an approximate length of 10 km is the longest among the railway tunnels of Turkey. The study area locates in Eastern Anatolian Fault Zone (EAFZ) and as the consequences of the active tectonism, the topography is steep and there are several paleo and active landslides. When selecting the portal locations, active landslide areas were avoided, but the paleo-landslide mass could not be avoided at the Bahce portal. For this reason, to the safety of the tunnel and the Bahce portal, extra engineering measures had to be taken.This study describes the problems sourced from the geological conditions of the Bahce portal, the extra engineering measures and the analysis of the measures to understand of the performance of the proposed measures. Before excavation, a retaining system with 1 m-diameter piles was constructed and the excavations were started. When the last stage of the excavation was reached, deformations up to 46 mm were detected in inclinometers. Upon this, the excavation was stopped and was backfilled immediately, thus the movements were stopped before it spreads to the buildings at close vicinity of the portal. Subsequently, a new site investigation program including boreholes was applied to understand the mechanism of failure. The paleo-landslide material in the portal region was 15 to 27 m thick sliding mass underlain by highly weathered schist. The groundwater level was measured approximately as 13 m in the new boreholes. Inclinometers were also installed in the new boreholes but all inclinometers were damaged in a short time due to movement.Consequently, the cross-section of the failure was prepared by analyzing a combination of topographic maps, in-situ observations anddata obtained from the boreholes.To providesafety of tunnel and portal construction, a new retaining system with diaphragm walls with a dimension of 1.2 x 2.8 m wasproposed and designed. Additionally, to support the retaining system against the loads sourced from the triggered paleo-landslide mass, barrette piles with a dimension of 1.2 x 2.8 m and with 2.6m of spacing per pile and steel struts with a dimension of approximately 1400 mm were selected as the support system (Figure 1). Consequently, the finite element analysis (FEA) of the slope stabilization was analyzed through Plaxis 2D software (Figure 2). The shear and axial forces and the bending moments were applied on the support system units and the analyses were performed for the static and dynamic cases because the area has a very high seismic activity. The factor of safety (k) in the slope stability analysis of the final stage of the works was also checked and the stability conditions were provided. In September 2017, the construction of the retaining walls, the support system, and the tunnel excavation were started again. The deformations of the system were monitored continuously by inclinometers which were placed in the diaphragm walls. The construction works with the suggested support system against active landslide loads weresuccessfully completedin January 2019. No significant displacements in inclinometers have been recorded over the 15-months period. In this respect, it can be concluded that barrette piles can be effectively used to prevent further landslides. This study was able to conclude that finite element analysis is a useful tool for simulating the mechanism of slope failure; the success of the project and the reliability of FEA are found satisfactory.

A Soil Improvement Methodology for a Shallow Tunnel Excavated in Extremely Weak Clay: A case study from Turkey (2021)

Gundogdu A. E. K., Can, A., Acar K., Gokceoglu, C.

Shallow tunnels excavated in weak ground conditions have serious engineering problems because excavations in weak ground conditions result in high deformations. These deformations occurring in shallow tunnels also cause serious settlements on surface.In this study, the problems encountered in a railway tunnel are described and the proposed engineering measures are presented. The length of T2 tunnel of Karaman-Ulukısla Railway Project (south of Turkey) is about 2.5 km and the exit parts of the tunnel is rather shallow because the overburden in this part varies between 15-25 m. The tunnel is excavated inclay having low to high plasticity (CL-CH). Groundwater level isabout 4.5 to 9 m.Another important problem is the presence of an oil pipeline passing through the tunnel. Oil pipelines are very sensitive to ground settlements, and the damage to the pipe creates serious problems. Due to these difficulties, this part of the tunnel must be excavated with no or minimum deformation and without any failure. However, if a tunnel is excavated in weak ground conditions with New Austrian Tunneling Method, high deformationscan be expected. To avoid these deformations, a soil improvement method, deep soil mix (DSM), is proposed to improve the ground conditions before excavation. DSM columns improve the ground, increase the NATM class and decrease deformations. The proposed improvement methodologyis evaluated with numerical analyses. The DSM method is a widely used technique in geotechnical engineering applications. Performance of this method mainly depends on increasing the stiffness of natural soil by adding a strengthening admixture material such as water/cement injection by mechanical mixing. By using DSM columns, it is aimed to increase the soft soil properties to soft rock class, thus the improved ground of the tunnel section can be classified as B2 NATM Class.The DSM columns are designed with a dimension of 1 m and with 0.85 to 0.90 m of spacing per column at the center and at the sides of the tunnel, respectively. Additionally, the stability of the B2 Class tunnel is needed to support system. For this class, Store Norfors (SN) type bolts with 6 m length and shotcrete with 0.20 cm thickness were selected as the support system of the tunnel (Figure 1). Consequently, to verify and check the validity of the suggested support systems with the improved ground four different critical tunnel sections were analyzed numerically by Plaxis 2D software which is a finite element analysis (FEA) program, In the Plaxis 2D analysis the deformations, the shear and axial forces, and the bending moments were applied on the tunnel excavation were determined. The results of the FEA (Figure 2) show that the maximum deformation in natural ground conditions is 608 mm while that in the improved ground is obtained as 40 mm. It is concluded that the suggested improvement methodology, excavation and support systems are found satisfactory. This study is significant as it is one of the first examples of a NATM project with ground improvement by using DSM columns.

Performance of Diaphragm Walls Supported by Anchorage and Struts in Deep Excavations (2019)

Avcı, S. and Can, A.

A Case Study of Wet Soil Mixing for Bearing Capacity Improvement in Turkey (2014)

Maghsoudloo, A. and Can, A.

This paper presents aground improvement implementation case under a raft foundation of a local hospital. The selected ground improvement method is Wet Soil Mixing (WSM) technique. Soil mixing is increasingly applied to environmental applications and ground stabilization in geotechnical projects. In this technique, weak soil is mixed with cementitious slurry to improve the characteristics of the soil.The investigated case is one of the pioneering WSM ground improvement technique implementation cases in Turkey. The soil profile is mainly consisted of low plasticity clay. The effect of ground improvement is verified by a series of laboratory tests and four in-situ pile loading tests.The results of in-situ pile load tests on constructed soilcrete columns showed an acceptable factor of safety for the bearing capacity of the WSM columns. Measured bearing capacities in all four tested columns were nearly 20% higher than calculated values. In addition, a set of samples are obtained from the constructed columns and unconfined compression tests have been conducted.The laboratory test results indicate that the selected cementitious slurry has a sufficient efficiency to form the stabilizing columns.

Can, A., Gundogdu A. E. K., Celenk, B., Gokceoglu, C. (2022), “Ground Improvement of a Railway by Deep Soil Mixing Columns Against Liquefaction Problem in Manisa, Turkey”