Response of buried pipelines subject to earthquake effects

Some lifelines, such as gas and oil transmission lines and water and sewer pipelines, have been damaged in recent earthquakes. The damages of these lifelines may cause major, catastrophic disruption of essential services for human needs. Large abrupt differential ground movements that result from an active fault present one of the most severe effects of an earthquake on a buried pipeline system.

Although simplified analysis procedures for buried pipelines across strike-slip fault zones that cause tensile failure of the pipeline have been proposed, the results are not accurate enough because of several assumptions involved, such as the omission of flexural rigidity of the pipe, simplification of soil resistant characteristics, etc. Note that the omission of flexural rigidity cannot satisfy equilibrium conditions for pipelines across a ‘reverse’ strike-slip fault that causes compressions in the pipeline.

This paper presents a refined analysis procedure for buried pipelines that is applicable to both strike-slip and reverse strikeslip faults after modifying some of the assumptions used previously. Based on the analytical results, this paper also discusses the design criteria for buried pipelines which are subjected to various fault movements. Parametric responses of buried pipeline for various fault movements, angles of crossing, buried depths and pipe diameters are presented.

A refined seismic analysis and design of buried pipeline for fault movement

A large‐scale group of nine steel‐pipe piles in a closely‐spaced arrangement was subjected to two‐way, cyclic, lateral loading with water above the ground surface. The test was conducted in stiff, overconsolidated clay at a site in Houston, Texas. All of the piles in the group were extensively instrumented to allow the results to be compared with those from other piles in the group and from the testing of an isolated, single pile. The results emphasize the highly nonlinear nature of the pile‐soil‐pile interaction. A substantial reduction in ultimate soil resistance was measured in the group piles relative to that of a similarly loaded single pile for both the first cycle and for 100 cycles of load.

Cyclic Lateral Loading of Large-Scale Pile Group

The design of buried pipelines in areas of vertical ground movement is governed, in part, by the magnitude of the forces imposed on the pipe and the displacements at which they are developed. An experimental study of these effects, dealing in particular with the influence of soil density and depth of burial, is described. The results compare well with several published models for medium and dense sand, but measured values of uplift resistance are much lower than predicted for loose contractive sand. A simplified procedure that can be applied to the design of buried pipelines is given.

Uplift Force‐Displacement Response of Buried Pipe

Cyclic Lateral Loading of a Large‐Scale Pile Group

The safe and economical design of buried pipes subjected to lateral motion requires an accurate knowledge of the subgrade reaction. Too often values of the coefficient of horizontal subgrade reaction, k\dh, reported in the literature are used without understanding the author’s intentions and without thought as to whether or not the conditions in the particular application are compatible to those in the literature. A survey of the available literature discloses that the numerical values and formulations proposed were such as to underestimate the soil restraint against flexible culverts and laterally loaded piles. These values are inadequate for the safe design of buried pipes laterally displaced by settlement, thermal expansion, earthquake shaking or wave action. The results of a laboratory testing program show the complex soil-conduit interaction and the associated failure mechanisms. An analytical method is presented to determine the load-displacement curve for any size pipe embedded at any given depth. A moderate size in-situ test was performed, which confirmed that the results of the laboratory model tests could be successfully applied to in-situ conditions.

Soil Restraint Against Horizontal Motion of Pipes

Soil restraint against horizontal motion of pipes

Measurements made during and immediately after the installation of a full-sized group of nine driven piles and two isolated control piles are presented. Rates of pile set-up in saturated, desiccated overconsolidated clay, development of lateral pressures on the piles, ground movements and accumulation of residual loads in the piles are described. Note is made of the similarities between group and isolate isolated piles.

Installation of Pile Group in Overconsolidated Clay

Platforms and pipelines installed in the soil movement prone areas of the Mississippi River Delta have developed an instructive history of survivals and failures. More often than not, attention has been given to the failures, rather than focusing on the paradoxes of the survivals. Notable survivals and failures associated with platforms and pipelines installed in the Delta and subjected to soil movements are examined. Geologic, geotechnical, and oceanographic explanations for observed performance are advanced to provide a basis for analyses of performance. History indicates that careful siting of platforms and pipelines in the Delta can go a long way in providing acceptable performance. Strategies for such siting are suggested. Analyses indicate that it is possible to explain the failures that have been experienced, given that the locations and characteristics of the soil movements are understood. Thus, it should be possible to develop engineering strategies to design structures that can resist such movements, given that one can determine the locations and characteristics of the soil movements that will confront the structure.

Jean M.E. Audibert

Papers

Soil Restraint Against Horizontal Motion of Pipes

Soil restraint against horizontal motion of pipes

Installation of Pile Group in Overconsolidated Clay

Offshore Platforms and Pipelines in Mississippi River Delta

Dynamic Response Of Laterally And Axially Loaded Piles