Jet grout yöntemi ile iyileştirilmiş zeminin bir boyutlu dinamik davranışının sayısal analizlerle incelenmesi
Investigation of one-dimensional dynamic behavior of improved soil using jet grout method with numerical analysis
- Tez No: 677159
- Danışmanlar: PROF. DR. RECEP İYİSAN
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2021
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Lisansüstü Eğitim Enstitüsü
- Ana Bilim Dalı: İnşaat Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
- Sayfa Sayısı: Belirtilmemiş.
Özet
Deprem yükleri sebebiyle yumuşak-gevşek nitelikteki zemin tabakalarında meydana gelebilecek sıvılaşma ve büyük kayma deformasyonları gibi olumsuzlukların önlenmesi adına zeminin dinamik mühendislik parametrelerini yükselten zemin iyileştirme yöntemlerinin uygulanması günümüzde sıkça tercih edilmektedir. Bu yöntemlerden jet grout yöntemi zemin içinde yüksek modüllü kolon oluşturarak zemin profilinin kayma rijitliğini arttırması sebebiyle Geoteknik deprem mühendisliği problemlerinde tercih sebebi olmaktadır. Bu çalışmada Sakarya ili, Adapazarı ilçesinde yer alan bir sahada farklı boy ve yerleşimde (alan değiştirme oranı) jet grout uygulaması yapılma senaryoları modellenerek kuvvetli yer hareketi sırasında zemin tabakalarında meydana gelebilecek değişimler bir boyutlu - doğrusal olmayan yer tepki analizleriyle parametrik olarak incelenmiş ve elde edilen sonuçlar tartışılmıştır. Araştırma kapsamında taban kayası derinliğinin ve alt tabaka kalınlığının etkisinin belirlenebilmesi için parametrik zemin profilleri oluşturulmuştur. Yer tepki analizlerinde kullanılan deprem kayıtları 2019 yılında yürürlüğe giren Türkiye Bina Deprem Yönetmeliğinde (TBDY) belirtilen hususlara göre ölçeklendirilmiştir. Analizler sonucunda hem jet grout kolonlarının boyunun ve alan değiştirme oranının hem de taban kayası derinlikleri ve alt tabaka kalınlıklarının analiz sonuçlarına etkisi irdelenmiştir. Elde edilen sonuçlar mühendislik bakış açısı ile değerlendirilerek yorumlanmıştır.
Özet (Çeviri)
Earthquake waves are occurred by breaking in faults and continue most of their journey through rock layers until they reach the ground surface. When they come to areas close to the surface, they pass through the ground layers and reach the ground surface. Earthquake waves advancing in the ground layers both cause changes in the structure of the ground layers that they pass through and are exposed to some changes in their own wave structure. While the changes in the soil layers are the deformations that occur depending on the shear stiffness (G) and damping ratio (D) of the soil layers, the changes in the wave structure are the amplification or deamplification in the wave amplitudes called soil amplification. One of the most important tasks of civil engineers is to design earthquake resistant structures. For this reason, it is a frequently preferred method to perform site-specific ground response analyzes where the behavior of the ground surface and soil profile at the time of earthquake can be modeled. Ground response analysis can be performed with a total of three different solution methods: linear or equivalent linear method in the frequency domain and non-linear method in the time domain. Ground response analyzes can also be performed in one, two or three dimensions depending on the field topography. Since one-dimensional analyzes are more practical than others, they are frequently preferred especially in areas with horizontal sublayers. With ground response analysis, design spectra and soil amplifications can be obtained on the ground surface, while displacements and shear strains along the soil profile can also be calculated. In order to prevent negative effects such as liquefaction and large shear deformations that may occur in soft-loose soil layers during an earthquake, it is frequently preferred to apply soil improvement methods that increase the dynamic engineering parameters of the soil. Among these methods, jet grout method is preferred in Geotechnical earthquake engineering problems because it increases the shear stiffness of the soil profile by creating a high modulus column in the soil. In this study, the changes that may occur in the soil layers during strong ground motion using the jet grout application performed with different length and area displacement ratios in a field located in Adapazarı district of Sakarya province were parametrically examined with one-dimensional - nonlinear ground response analysis and the results were discussed.Within the scope of the research, parametric soil profiles were created to determine the effect of bedrock depth and model sublayer thickness. Earthquake records used in ground response analyzes have been scaled according to the issues specified in the Turkish Building Earthquake Regulation (TBDY), which came into force in 2019. As a result of the analyzes, the effects of both the length of the jet grout columns and the area displacement ratio, as well as the bedrock depths and substrate thicknesses on the analysis results were examined. Three drilling works were carried out in the field which is the subject of this study. In the drillings, it was observed that the soil profile is generally composed of medium plasticity clays, but there is a sand band between 12 and 15 m. However, this layer, which would cause confusion in the analysis results, was not taken into account within the scope of one-dimensional ground response analysis and all layers were determined as clay layers. In SPT tests performed during drilling operations, the number of blows generally varies between 6 and 25 and tends to increase with depth. The plasticity index of the clay soil layers defined in all analysis sets was accepted as 20. The reason for this is that the plasticity index can seriously affect the behavior of soil layers under dynamic loading conditions and the effect of the plasticity index will not be examined in this study. In addition, in models with shallow bedrock depth, the bedrock layer was defined as elastic rock and the shear wave velocity of the bedrock was accepted as Vs=760 m/s while the unit volume weight was 22 kN/m3. There is no SPT-N blow data after the first 30m depth in the relevant field. In models with shallow bedrock layer, it is necessary to determine the engineering parameters of the soil layers up to the bedrock layer after the first 30m depth. Since the bedrock layer shear wave velocity is assumed to be 760 m/s in the rock layer shallow models, it is predicted that the shear wave velocity along the profile increases equally in the subsoil layers after 30m depth. In addition, in the models, the unit volume weight of the soil layers is assumed to be 18 kN/m3 at the first 10m depth, 19 kN/m3 between 10m depth and 20m depth, and 20 kN/m3 afterwards. In models with ground improvement with jet grout, the shear wave velocities of the improvement depth were changed to increase with the jet grout area replacement rate. Thus, by increasing the shear wave velocities at the improvement depths in the models, the improvement effect can be examined with one-dimensional ground response analysis. In order to use in one-dimensional ground response analysis, a total of 44 earthquake records, 2 of which were horizontal, of 22 separate earthquake records selected for models with deep bedrock and shallow bedrock, were scaled using the simple scaling method. The scaling process was scaled so that the average of 2 separate horizontal directions (H1 and H2) of 11 earthquake records selected from the station with Vs>760 m/s shear wave velocity selected for models with shallow bedrock resembles the design spectrum with ZB local design class. The average of 2 different directions of 11 earthquake records selected from the station with 180 m/s<Vs<360 m/s shear wave velocity selected for models with very deep bedrock is scaled to resemble the design spectrum with ZD local design class. Earthquake records selected for models with deep bedrock are generally scaled with coefficients between 1.5 and 3.0, and only the Coyote Lake earthquake record is scaled with a coefficient of 4. For models with shallow bedrock, the selected earthquake records are generally scaled with coefficients between 1 and 1.5, 14151344 and Iwate-1 earthquake records are scaled with a coefficient of 3. It has been determined that the spectral acceleration averages of the earthquake records are similar to the relevant local design spectrum. The obtained scaled earthquake records were used as input records in one-dimensional nonlinear ground response analyses. In order to see the effect of jet grout columns on one-dimensional ground response analysis results, jet grout lengths were determined as 10, 20 and 30 m, and jet grout area replacement rate was determined as 10%, 20% and 30%. In order to see the effect of bedrock depth, models with bedrock depths of 45m, 60m and 90m and models with very deep bedrock depth were examined. In addition, in order to see the effect of the sublayer thickness of the models on the results, depth was added to the study by examining 3 different sublayer thicknesses, thickness are being 10, 5 and 3m. As a result of one-dimensional ground response analysis, surface response spectrum, spectral ground amplification, displacement-depth and strain-depth graphs along the profile obtained in all models were compared. The results obtained were evaluated and interpreted from an engineering point of view, and relations were proposed, in which the displacement value obtained on the ground surface as a result of one-dimensional ground response analysis could be calculated with a certain error rate. The independent variables of these relations, which are different for each bedrock depth, are the jet grout length and the area replacement rate. According to all analysis results, the effect of jet grout columns on one-dimensional ground response analysis was obtained as follows. Compared to the models with ground improvement with jet grout, the maximum spectral accelerations of the models improved up to the 0.4 second period are generally higher than the models without improvement, while they are smaller after the 0.4 second period when compared to the models without improvement. In addition, the period values in which all the improved models get the maximum spectral accelerations are shifted towards smaller periods compared to the unimproved condition. In case of jet grout is applied, the spectral ground amplifications are greater than the unimproved state between 0 and 0.15 periods, and less than unimproved state after the 0.15 second period. However, the largest spectral amplification values were observed in the absence of jet grout improvement. Maximum spectral amplification is usually seen in the 3.2 second period for models with very deep bedrock depth, 1.6 seconds for models with bedrock depths of 90m, and 1.1 seconds for models with bedrock depths of 45m and 60m. Jet grouting caused a 5% to 45% reduction in displacement and a 30% to 100% reduction in shear strain on the surface, compared to the unimproved situation. Increasing the jet grout length generally increased the maximum spectral accelerations up to 0.4 second period, but decreased after this period. The maximum spectral acceleration values increased between 5% and 65% with the increase of the jet grout length, while the maximum spectral accelerations were generally observed between 0.3 and 0.4 second periods. The maximum spectral amplification up to about 1.1 second period and decreased after 1.1 second period and decreased by 5% to 20% with increasing length. Another effect of jet grout length increase is that the displacement values on the surface decrease, and the lower shear strains than the unimproved models. The displacements and shear strains showed slightly higher values than the unimproved state after the improvement depth. It is thought that this is due to the decrease in the damping ratios of the improved depths, due to the fact that the wave energy of the earthquake waves cannot be damped sufficiently at the improved depths, and thus, the unabsorbed wave energies cause a little more displacement and deformation at the unimproved depths. The increase in jet grout area replacement rate increased the spectral acceleration values by 15-50% in models with 10m and 3m sublayer thicknesses and shifted the dominant period towards lower periods. In models with a sublayer thickness of 5 m, the maximum spectral acceleration values generally did not change as the area replacement ratio increased, but as in all models, the dominant period was shifted to lower periods. The maximum spectral amplification up to the 0.30 second period and decreases it after 0.30 seconds. Ground improvement with jet grout increased the spectral amplifications by 50-70% up to the 0.30 second period, and decreased the spectral amplifications by 10-20% after this period. The increase in the area deformation rate decreased the displacement values on the surface by 10-60%, while the shear strain values decreased by 25-80%. Maximum spectral acceleration values of models with very deep bedrock depth generally have higher maximum spectral accelerations than models with shallow bedrock depth. In models with shallow badrock, on the other hand, while the maximum spectral acceleration amplitudes decrease as the bedrock depth increases between the 0-1.5 second period, they increase slightly after the 1.5 second period. In addition, in models with very deep bedrock depth, the amplitudes with the maximum spectral acceleration amplitudes are generally spread over a wider period range. Models with very deep bedrock generally showed lower spectral amplifications than models with shallow bedrock. When the models with shallow bedrock are compared among themselves, the spectral soil amplification values increase up to the 1.2 second period as the bedrock gets deeper, while it decreases after this period. The displacement and shear deformations along the soil profile is examined, the displacement values decrease by 10% to 60%, and the shear strains by 0% to 50% with the increase of the bedrock depth. When the effect of the sublayer thickness is examined, it is observed that the dominant period in the surface response spectrum expands towards the 0.1 second period as the substrate thickness decreases. However, the results did not change after the 0.3 second period for all sublayer thicknesses.
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