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Experimental and Numerical Investigation of the Behavior of Buried Pipes Subjected to Permanent Ground Deformation Caused by Reverse Faulting

Hojat Jalali, Himan | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47450 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Rahimzadeh Rofooei, Fayaz; Khajeh Ahmad Attari, Nader
  7. Abstract:
  8. In this study the behavior of buried pipes under permanent ground deformation (PGD) ef-fects caused by reverse faulting is investigated by means of both experimental and numeri-cal approaches. A total number of 7 full-scale experiments on buried steel pipes subjected to a fault offset of 0.6 m along the slip plane is carried out and the effects of different pa-rameters such as pipe diameter (114.3 mm (4ʺ) and 168.3 mm (6ʺ)), burial depth (0.25m, 0.5m, 1 m) and soil type (SW and SM) on the response of the buried pipes are studied. Ex-perimental results show that the pipe deformation shape changes with increasing burial depth from half-sine (for shallow depths) to an S-shape (for moderate to deep burial depths). Accordingly the pipe failure mechanism changes from the more favorable beam-mode buckling to local buckling at two sections that are unsymmetrical with respect to the fault plane. At these sections, strain concentration is observed that increases with increasing fault offset. The maximum compressive strains decrease with increasing pipe diameter, decreasing soil friction angle and decreasing burial depth. Using the factor of ovality to measure the pipe cross-section distortion, it is found that the cross-section distortion in-creases by increasing the pipe diameter-to-thickness and burial depth-to-diameter ratios, and is more severe for the buckled section of the pipe in the moving part of the split box. It was also found that severe cross-section distortion occurs between 2.3 and 3.4 times the strain limit for onset of wrinkling suggested by various guidelines. In the numerical part of the study the behavior of the tested steel pipes under reverse faulting effects was investi-gated.Using the FE models that were validated utilizing the experimental results, the max-imum equivalent soil-pipe interaction forces were determined and the results were com-pared with that of American Lifeline Alliance(ALA 2005) and Pipeline Research Council International guidelines (2009).Results show that the obtained maximum bearing forcesare less than the suggested values by the aforementioned guidelines, while the maximum uplift forces slightly exceed those of ALA and are significantly larger than those of PRCI.The results indicate that for the considered cases, the uplift force is sensitive to the pipe diame-ter and its relative stiffness, while the ALA (2005) suggests a constant force for the burial depths considered in this study. Furthermore, the q-z curves for the vertical soil springs were determined. Using the proposed curves a validated simple FE modeling technique was introduced to simulate the behavior of buried steel pipes under reverse faulting for en-gineering purposes. In addition, aparametric study is carried out on buried steel and high density polyethylene (HDPE) pipelines subjected to oblique-reverse faulting. Different pa-rameters such as the pipe material (steel and HDPE), the burial depth to the pipe diameter ratio (H/D), the pipe diameter to wall thickness ratio (D/t), and the fault-pipe crossing angle are considered and their effects on the response parameters are discussed. It is found that the dimensionless parameters alone are not sufficient for comparison purposes. Based on the current parametric studies it is found that the best way to enhance the pipeline per-formance under oblique-reverse faulting effects is to place pipes with low D/t and H/D ra-tio at right angle with respect to the fault plane
  9. Keywords:
  10. Laboratary Study ; Reverse Faulting ; Buried Pipline ; Permanent Ground Deformation (PGD) ; Finite Element Method ; High Density Polyethylene ; Steel Pipe

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