Experimental and numerical modelling of buried pipelines crossing reverse faults

Fault rupture is one of the main hazards for continuous buried pipelines and the problem is often investigated experimentally and numerically. While experimental data exists for pipeline crossing strike-slip and normal fault, limited experimental work is available for pipeline crossing reverse faults. This paper presents results from a series of tests investigating the behaviour of continuous buried pipeline subjected to reverse fault motion. A new experimental setup for physical modelling of pipeline crossing reverse fault is developed and described. Scaling laws and non-dimensional groups are derived and subsequently used to analyse the test results. Three-dimensional Finite Element (3D FE) analysis is also carried out using ABAQUS to investigate the pipeline response to reverse faults and to simulate the experiments. Finally, practical implications of the study are discussed

Experimental and Numerical Modelling of Buried Continuous Pipelines Crossing Active Faults

Pipelines are reliable and economical means of transporting water, oil, gas, sewage and other fluids. They are generally referred to as lifelines since they play a pivotal role in running a nation’s industries, services, and economy. Thus, it is essential that they remain operational at all times. Pipeline systems are located over large geographical regions and they are generally buried below ground for safety, economic, environmental and aesthetic reasons. As a result, they are exposed to a wide variety of soil profiles and hazards caused by earthquakes. Past earthquake-related pipeline damage highlighted the vulnerability of buried pipelines to Permanent Ground Deformations (PGD) caused by earthquakes. Different types of pipeline failure modes such as joint failure, tension failure, beam buckling, and local buckling failure have been observed in past earthquakes. Recent earthquakes showed that unsatisfactory performance of buried pipelines is still observed. As a result, further research is required in this subject. This thesis aims to study the response of buried continuous pipelines to faulting through physical model tests and numerical analysis. In this Ph.D. research, relevant scaling laws and non-dimensional groups for buried continuous pipelines crossing active faults are derived by using Buckingham-π theorem and governing differential equations. The physical meaning of these non-dimensional groups and their practical ranges are presented. A new physical model test setup of buried continuous pipelines crossing strike-slip faults was developed considering the non-dimensional groups and scaling laws. The working principle of the test setup and sensors used in the tests are also presented. Furthermore, a simple and scalable end connector for physical modeling based on the equivalent end springs approach in numerical modeling is proposed. The performance of the proposed end connector is assessed via physical model tests and numerical analysis. In addition, a new mitigation technique – using tyre derived aggregate (TDA) as backfill material at the vicinity iii of fault crossings- is proposed. The performance of the proposed mitigation method is assessed through physical model tests. The effects of trench shapes, trench dimensions and tyre-chip content in the backfill on pipeline performance are also investigated. Finally, three-dimensional (3D) Finite Element (FE) models of buried continuous pipelines crossing active faults are developed and these models are validated through case studies, experimental studies and analytical methods. By using the calibrated 3D FE models, a parametric study is carried out to investigate the effects of different pipe end conditions on the behaviour of buried continuous pipelines crossing strike-slip faults and to investigate the effects of non-dimensional groups on pipeline response to strike-slip faulting. The research study shows that the newly developed experiment setup is a reliable tool to capture the behaviour of buried continuous pipelines crossing strike-slip faults and to investigate the physics behind the soil-pipe interaction problem under faulting. Furthermore, the proposed end connector is capable of simulating pipe end conditions more realistically compared to conventional pipe end conditions used in earlier experimental studies. Finally, the proposed mitigation technique –using TDA as backfill material at the vicinity of fault crossings- is an effective way of protection that reduces peak bending and axial strains within the buried continuous pipelines crossing active faults

A survey of damage observed in Izmir due to 2020 Samos-Izmir earthquake

An earthquake of magnitude 6.9 hit the city of Izmir (Turkey) on 30 October 2020, resulting in 117 deaths (in Turkey) and considerable economic losses. The earthquake also triggered a tsunami. Following the earthquake, field surveys are being conducted in a Covid-secure way to study and document the damages caused. The earthquake caused significant damages to residential buildings mainly located in the district of Bayrakli and Bornova. However, no damages were observed in railway and roadway bridges or tunnels and that helped the rescue operations. The damages were mainly structural which included the so-called pancake collapse (where the entire building collapsed) and soft storey type collapse (weak storey characterised with weak columns collapsed), and in some cases, only the ground floor completely collapsed. Due to the proximity of the epicentre and the geology of the area, it seemed that the ground motions were amplified. This technical note provides a summary of the seismological and recorded ground characteristics of the earthquake together with the lessons learnt

Behaviour of buried continuous pipelines crossing strike-slip faults: Experimental and numerical study

The paper examines the behaviour of buried continuous pipelines crossing strike-slip faults using experimental and numerical modelling. A newly developed experiment setup is presented along with the derivation of relevant scaling laws and non-dimensional terms governing global response of continuous pipelines to strike-slip faulting. Four model tests are carried out to understand the performance of the pipelines and the results are presented through the derived non-dimensional framework. Three-dimensional (3D) Finite Element (FE) model is also undertaken to simulate buried continuous pipelines crossing strike-slip faults and is calibrated against the model test results and a field case record for validation and verification. A parametric study is also carried out to better understand the parameters influencing the response of buried continuous pipelines to strike-slip faults and to also investigate the effects of pipe end conditions on their behaviour. API 5L X70 steel pipe with 490 MPa of yield strength was used in the numerical parametric study. Two different scenarios based on fault crossing angle of the pipe (β) were considered in the parametric study: (a) pipelines in tension and bending; (b) pipelines in compression and bending. The experimental and numerical results show that the longitudinal pipe strains under strike-slip faulting are strongly dependent on six parameters: (a) normalized fault displacements (represented by δ/D where δ is the fault displacement and D is the pipe diameter which is also an indication of soil strain in the mobilised zone); (b) ratio of pipe diameter to wall thickness (D/t); (c) fault crossing angle of the pipe (β); (d) relative soil-pipe stiffness (kD4/EI); (e) ratio of burial depth to pipe diameter (H/D) and (f) pipe end conditions. Finally, practical implications of the study are discussed

Influence of consolidation properties on the cyclic re-liquefaction potential of sands

The relative density can be used as the main indicator to assess the liquefaction resistance of clean sands. As relative density of the sand deposit increases significantly following the initial liquefaction, one should expect that the soil can improve its liquefaction resistance. However, earthquake records indicate that densified sand can be liquefied again (re-liquefied) at smaller cycles by the similar seismic loadings. This work aims to clarify the counterintuitive finding that, after the first liquefaction, the resulting significant increase in relative density (induced by settlements and variation of the water level) do not necessarily imply an increase in the number of loading cycles for re-liquefaction. In this paper, we present a series of experimental results concerning the cyclic liquefaction and the following re-liquefaction of clean sand deposits. The experimental setup is performed by a shaking table, transmitting one-degree of freedom transversal motion to the soil within the 1.5 m high laminar shear box. At four different seismic demands, the input excitation was imposed three times to examine the influence of the initial distributions of the relative density and the consolidation characteristics on the liquefaction potential of the sand. The re-liquefaction cycles of the sand, which previously experienced liquefaction under the same seismic loadings, show that post-liquefaction reconsolidation of the sand deposits affects the re-liquefaction resistance.TUBITAK Project 111M43

Usage of Tyre Derived Aggregates as backfill around buried pipelines crossing strike-slip faults; Model tests

Buried pipelines crossing active faults are exposed to excessive loads under fault movements due to large relative movement between pipes and the soil surrounding them. As a result, extreme longitudinal strains develop within pipelines under large fault movements and this leads to pipeline failures. Several seismic mitigation techniques were proposed to improve the performance of buried pipelines crossing active faults. In this study, the potential of using Tyre Derived Aggregates (TDA) as a backfill material for mitigating the effects of strike-slip faulting are investigated through physical model tests. First, the details of the physical model test setup and model configuration are presented. Then a comparative study is carried out to study the effect of TDA content in the backfill and trench configurations on TDA mitigation. Model tests revealed that using a sloped trench with 100% TDA content in the backfill can decrease peak axial pipe strains up to 62% and peak bending strains up to 19%. It is observed that enlarging the trench and using an inclined trench improve the performance of the TDA mitigation technique

The weight and ghrelin changes of fecal microbiota transplantation in rats

Background: Fecal microbiota transplantation is a promising method to solve obesity. Our study's aim was to investigate the changes of weight and ghrelin levels in obese rats receiving fecal microbiota transplantation from lean rats. Methodology: Twenty-one rats were divided into three equal groups: Group 1: Obese control group; group 2: Obese recipient group; and group 3: Lean donor group. Feces which was collected from donor group was transferred to the rats in recipient group, orally by gavage, 3 times every other day. The weight and ghrelin levels were measured from each rat at the beginning and end of the study. Results: There was statistically significant weight gain in donor group (p: 0.001), but there were no statistical significant weight chances was detected in control and recipient groups (p: 0.82, p: 0.12, respectively). There was an increase in donor and control groups, but a decrease was observed in the recipient group at ghrelin levels. However, there was no significant difference at ghrelin levels in any groups (p: 0.05, p: 0.2, p: 0.4, respectively). There was a significant relation in control group in weight and ghrelin changes (p: 0.007), but no significant relation was detected in either recipient or donor groups (p: 0.29, 0.53, respectively). Conclusion: Metabolism changes of obese rats were observed after fecal microbiota transplantation, and it was the only group that decreasing ghrelin levels