Harry E. Stewart

Numerical Modeling of Buried HDPE Pipelines Subjected to Normal Faulting: A Case Study

A systematic study is presented herein on the seismic response of buried pipelines subjected to ground fault rupture in the form of normal faulting. In this study, advanced computational simulations are conducted in parallel with physical testing using a geotechnical centrifuge. For the numerical simulations, the pipeline was modeled using isotropic 3-D shell elements and the soil was modeled using either 1-D spring elements or 3-D solid (continuum) elements. The results from continuum finite-element analyses are compared with those from a Winkler-type model (in which the pipe is supported by a series of discrete springs) and with results from centrifuge tests. In addition, via appropriate modeling of the soil-pipe interaction, the q-z relation of the soil medium is elucidated for normal faulting events. The numerical analysis results demonstrate the potential for continuum modeling of events that induce pipe-soil interaction and results in improved understanding of pipe-soil interaction under normal faulting.

Earthquake Faulting Effects on Buried Pipelines – Case History and Centrifuge Study

Permanent ground deformation (PGD) is one of the most damaging hazards for continuous buried lifelines. This hazard is especially severe when the PGD results in net compression in the pipe. In that case, buckling of pipe material can occur. If buckling is moderate, deformation of the pipe cross-section can lead to flow restriction and high friction losses, and eventually require line replacement. If buckling is severe, high localized strains can lead to pipe rupture, loss of contents, and possible pollution of surrounding soil. In this article, centrifuge tests of buried pipelines subject to abrupt ground failure in the form of surface faulting are presented. The fault movement results in mostly compression in the pipe. The test results are compared with a case history of pipe failure in the 1999 Izmit, Turkey earthquake and also with the results from the centrifuge tests which result in net tension in the pipe. The experimental setup, procedures, and instrumentation are described in detail. Suggestions for design practice are offered based on the analysis of results from both the 1999 Izmit case history and the centrifuge modeling.

Numerical Modeling of Buried HDPE Pipelines Subjected to Strike-Slip Faulting

A systematic study of buried pipeline response to strike-slip faulting was performed wherein advanced computational simulations were conducted in parallel with a series of physical tests employing split-boxes within the geotechnical centrifuge at Rensselaer Polytechnic Institute and the full-scale testing facility at Cornell University. This article describes the numerical modeling and simulations of the experimental tests. The buried pipeline and the surrounding soil are modeled using nonlinear beam (shell) elements and elasto-plastic springs distributed along the pipeline, respectively. Using the finite element method, reasonable predictions are obtained for the axial and bending strain distributions measured during the tests. It is also shown that finite element analysis using pipe beam elements and a modified soil spring model can accurately predict the pipeline seismic behavior due to strike-slip fault rupture, especially when the pipe is subjected to combined bending and tension. In addition, existing closed-form solutions are evaluated.

The effects of liquefaction-induced lateral spreading on pile foundations

Abstract Observations of pile foundation performance during previous earthquakes have shown that pile failure has been caused by lateral ground movements resulting from soil liquefaction. The recognition that lateral ground movements may play a critical role in pile performance during an earthquake has important implications for design and risk assessment, and requires that analytical models be devised to evaluate these potential problems. In this paper, parametric studies were conducted to estimate the maximum bending moments induced in piles subjected to lateral ground displacement. The results are summarized in charts using dimensionless parameters. The analyses reveal that the existence of a nonliquefiable layer at the ground surface can affect significantly the maximum bending moment of the pile. When a relatively thick nonliquefiable layer exists above a liquefiable layer, neither the material nonlinearity of the soil nor loss of soil stiffness within the liquefiable layer significantly affect the maximum bending moment. When the thickness of the liquefiable soils is greater than about three times that of an overlying intact layer, soil stiffness in the liquefiable layer must be chosen carefully when evaluating the maximum bending moment.

Seismic testing of critical lifelines rehabilitated with cured in place pipeline lining technology

Trenchless technology is well accepted for repairing critical underground lifelines with minimal ground surface disruption. The cured in place pipeline (CIPP) lining process is an application of trenchless technology that involves the installation of fiber reinforced composites inside existing pipelines. The uncertain performance of pipelines reinforced with CIPP linings in seismic areas is a barrier to the adoption of this method for seismic retrofit. This article evaluates experimentally the transient seismic response of pressurized pipelines reinforced with fiber reinforced polymer (FRP) linings. The test results show that reinforced pipelines can accommodate very high intensity ground motions and can provide substantial seismic strengthening in addition to efficient rehabilitation of aging underground infrastructure.

Studying Buried Pipeline Behavior Using Physical and Numerical Modeling

Polyethylene pipes are commonly used in new pipeline systems as well as in replacing old pipelines. When used in replacing aging pipelines, they are connected to existing old pipelines of different materials, such as cast iron. Due to a higher thermal expansion/contraction coefficient of polyethylene compared to cast iron, thermal loads may cause additional stresses in the cast iron pipelines and especially at the pipe joints. An accurate assessment of the loads transferred to the existing cast iron pipe joints requires an evaluation of the resistance provided by the friction at the soilpolyethylene and soil-cast iron pipe interfaces. The tests were performed in the laboratory and in the field to obtain soil-pipe interface friction properties. Then the interface strength properties obtained from the physical models were used in numerical modeling to investigate the overall behavior of the pipeline system, to determine the loads transferred to the pipe joints, and to assess the integrity of the joints. The results of the physical and numerical modeling are presented in this paper.

Design Guidelines for Polyethylene Pipe Interface Shear Resistance

Polyethylene pipes are commonly used in pipeline systems. Current methods used to determine the pipe pullout capacity do not consider the effects of diameter changes and cyclic movements that the pipelines may experience. Laboratory tests were performed to study the interface shearing resistance of polyethylene pipes under varying conditions. The tests were performed in a temperature-controlled room, where properties were investigated for thermal variations expected in the field. Two types of tests were performed: pull/push tests and cyclic tests. Test results indicated that reductions in pipe diameter affect the interface shear resistance that develops between the pipe and soil. As the pipe diameter gets smaller, the normal contact stresses at the interface decreases, causing a reduction in the interface shearing resistance directly proportional to the normal stress changes. Cyclic pipe movements also cause significant reduction in pipe pullout resistance. The test results indicated that the polyethylene...

A Review of Large-Scale Testing Facilities in Geotechnical Earthquake Engineering

In this new century, new large-scale testing facilities are being developed worldwide for earthquake engineering research. Concurrently, the advances in Information Technology (IT) are increasingly allowing unprecedented opportunities for: (i) remote access and tele-presence during extended remote off-site experimentation, (ii) hybrid simulation of entire structural systems through a multi-site experimentation and computational overall model, and (iii) near-real time data archival, processing and sharing. In this paper, a representative set of such state-of-the-art testing facilities is presented. Attention is focused on geotechnical earthquake engineering applications including instrumented test sites, mobile and large-scale testing laboratories, and centrifuge testing. Using such facilities, a number of collaborative research efforts are also included for illustration. The potential for further worldwide joint activities is finally highlighted.

Designing Plastic Pipelines for Thermal Loads

This paper presents a selection of design temperatures for thermal loads in buried plastic piping. Gas companies often assume that the CFR requirement for design of mechanical couplings for an instantaneous change in temperature of ∆ T = 55°C applies to all aspects of the PE system. This assumption leads to very conservative designs, and does not represent the range of temperature changes due to pipe installation and seasonal temperature variations in the ground. This paper presents data from measured ground temperatures in the northeastern United States to develop seasonal design temperature ranges. Measurements of PE pipe temperature when exposed to direct sunlight then inserted into cast iron piping are used to assess temperature changes that might occur during pipe installation. Design scenarios are identified that represent reasonable situations for the range of temperatures PE piping would be subject to, and stresses are evaluated for these conditions. Stress superposition methods are used to develop design charts for evaluating thermal loads.

PVCO Pipeline Performance Under Large Ground Deformation

Technological advances have improved pipeline capacity to accommodate large ground deformation associated with earthquakes, floods, landslides, tunneling, deep excavations, mining, and subsidence. The fabrication of polyvinyl chloride (PVC) piping, for example, can be modified by expanding PVC pipe stock to approximately twice its original diameter, thus causing PVC molecular chains to realign in the circumferential direction. This process yields biaxially oriented polyvinyl chloride (PVCO) pipe with increased circumferential strength, reduced pipe wall thickness, and enhanced cross-sectional flexibility.This paper reports on experiments performed at the Cornell University Large-Scale Lifelines Testing Facility characterizing PVCO pipeline performance in response to large ground deformation. The evaluation was performed on 150-mm (6-in.)-diameter PVCO pipelines with bell-and-spigot joints. The testing procedure included determination of fundamental PVCO material properties, axial joint tension and compression tests, four-point bending tests, and a full-scale fault rupture simulation. The test results show the performance of segmental PVCO pipelines under large ground deformation is strongly influenced by the axial pullout and compressive load capacity of the joints, as well as their ability to accommodate deflection and joint rotation. The PVCO pipeline performance is quantified in terms of its capacity to accommodate horizontal ground strain, and compared with a statistical characterization of lateral ground strains caused by soil liquefaction during the Canterbury earthquake sequence in New Zealand.Copyright