Pipe Soil Research Articles

Investigating pipeline–soil interaction under axial–lateral relative movements in sand

This paper presents results from an experimental and numerical study on the axial–lateral interaction of pipes with dense sand. A series of centrifuge tests were conducted, with a rigid pipeline displaced in the horizontal plane in a cohesionless test bed. The relative pipe–soil interaction included axial, lateral, and oblique loading events. A three-dimensional continuum finite element model was developed using ABAQUS/Standard ( Hibbitt et al. 2005 ) software. The numerical model was calibrated against experimental results. A parametric study was conducted, using the calibrated finite element model to extend the investigations. The ultimate axial and lateral soil loading was found to be dependent on the angle of attack for relative movement between the pipe and soil. Two different failure mechanisms were observed for axial–lateral pipeline–soil interaction. This study confirms and improves on a two-part failure criterion that accounts for axial–lateral coupling during oblique soil loading events on buried pipelines.

Earth pressure measurements on buried HDPE pipe

An understanding of the stress distributions that act on buried pipes plays a key role in the development and use of design methods for these structures. The radial stresses that develop on buried flexible pipes have been investigated by a number of researchers through experimental, analytical and numerical methods. However, direct measurements of soil contact stresses acting on small-diameter pipes have not been possible, since commercial earth pressure cells are large, and the stiffness of the cell relative to the soil material is known to influence the measured stresses. A new technique is described for measuring the radial contact stresses acting on buried pipes, and experimental studies are reported that demonstrate the effectiveness of this new technique for measuring contact pressures for both loose and compacted sand backfills. Comparison of the measurements with computations from elastic soil–pipe interaction theory reveals significant discrepancies in the magnitude and distribution of radial pressure around the circumference of the pipe for both loose and compacted backfill conditions. The new measurement technology provides direct support for pressure distributions inferred in earlier studies from measurements of circumferential strains around the pipe circumference.

Three dimensional vibration analysis of a buried pipeline with slip conditions

Based on the three-dimensional (3D) elasticity theories, an analytical solution for the infinite pipeline surrounded by the infinite soil medium subjected to an incident plane wave is derived. The Coulomb frictional force is applied at the pipeline–soil interface to represent the slip condition between the pipeline and the soil medium. This applied interface interaction can be considered as the viscous damping with some considerations. The normal and shear stress distributions along the cross-section of the pipeline are obtained by solving the obtained equations analytically. Furthermore, the superposition and the corresponding principles are used to obtain the von Misses strains. The critical and maximum amplitude ranges of the incident wave for which slipping and yielding, respectively, occur are estimated. The solutions are presented for ranges of soil densities and pipe thicknesses with perfect/imperfect bonds and different incident wave angles.

Numerical analysis of an experimental pipe buried in swelling soil

This paper investigates the pipe–soil interaction for pipes buried in expansive soil when subjected to swelling soil movement due to increase in moisture content. A laboratory experiment has been undertaken on a plastic pipe in a large-scale pipe box. A three dimensional numerical model is developed to analyse the pipe response, using FLAC 3D computer program. The pipe is assumed to behave as a linearly elastic material, while the soil is modelled as a nonlinear material with Mohr–Coulomb failure criterion. The water flow and soil/pipe deformations are decoupled, where water flow is calculated using simplified capillary rise theory on the basis of measurements made. A reasonably good agreement between the experimental results and model predictions is reported.

Numerical modeling of tunneling effect on buried pipelines

The underground space in urban areas is frequently congested with utilities, including pipelines and conduits, that are affected by underground construction, e.g., tunneling. This paper carries out finite element (FE) analyses to investigate the effects of tunneling-induced ground movement on pipelines, with special attention to the different soil responses to uplift and downward pipe–soil relative movements. A series of numerical parametric studies with 900 FE simulation runs in total is performed to encompass various combinations of ground settlement profiles, pipe dimensions, material properties, pipe burial depth, and soil properties that are typical for utility pipelines and tunnel construction in urban areas. The results are summarized in a dimensionless plot of relative pipe–soil stiffness versus ratio of maximum pipe curvature to maximum ground curvature, which can be used to directly estimate the maximum pipe bending strain and (or) to directly assess the tunneling-induced risk to pipelines. The FE results and dimensionless plot are validated against field and centrifuge test results reported in the literature. Effect of pipeline orientation with respect to the tunnel centerline is explored. It might be unconservative if design analysis only considers the case that the pipeline is perpendicular to the tunnel centerline.

Control and management of brine disposal for inland desalination plants

Desalination is a solution for a range of water supply problems. A higher recovery rate is an important goal because it increases production and improves cost effectiveness. As the recovery ratio increases, however, the concentration of dissolved ions in the brine becomes high enough to form scaling caused by precipitation of super-saturated salts. These precipitates might form a scale not only on membranes’ surfaces but also in the brine disposal line. In order to prevent scale formation, special antiscalants are added to the reverse osmosis feed. It is important to emphasize that antiscalants only delay the onset of precipitation, resulting in possible scale precipitation in long outlet pipes. In addition to the tendency of scaling, brine disposal can be a serious environmental concern that needs to be studied and considered when building a desalination plant. Marine brine disposal can cause three possible hazards: precipitation on the pipe walls, soil and marine contamination. Since 2004, Mekorot has exclusively operated and maintained a unique 30-km long brine disposal pipeline to the Mediterranean Sea with the required permission from the Ministry of Environmental Protection. The pipe is used to dispose brine streams from the Gat and Granot BWRO desalination plants, which are located in southwestern Israel near the city of Ashkelon. A brine disposal pipe was developed by Mekorot as part of a coastal aquifer rehabilitation project and was chosen as the most economic solution for these two plants. A few years ago, an experimental system was run to obtain the design parameters for preventing scale deposition from a concentrate solution. Through the design of optimal operation of brine pipes, we prevent soil contamination and avoid scale deposition from concentrate solutions from both desalination plants. This paper reviews the management and control of the brine disposal pipe, including early scale detection, as well as the standard and special monitoring programs for the long brine disposal pipe at Mekorot.

Analysis of soil conditions and pipe behaviour at a field site

Water main pipes buried in expansive soils are often subjected to severe distress subsequent to installation. Excessive stresses may be induced due to either differential movement of the soils or swelling pressures from the soils along the pipes, impairing their performance or even breaking them. Field monitoring is an important means for understanding soil behaviour and its interaction with water mains. For this purpose, field instrumentation was successfully installed to monitor the performance of a section of water main placed in a well-developed area of a city neighbourhood where more frequent pipe breakage had occurred in recent years. The instrumentation included sensors to measure pipe wall strains, pipe displacement, in situ soil water content, soil pressure, and temperature. The instruments were installed in both the soil backfill and native soil around the backfill. This paper presents the analyses of monitoring data collected during the first 3 years after instrument installation. It was observed that the soil and pipe behaviour was affected significantly by soil properties and seasonal changes and correlated closely with the change pattern of the local meteorological conditions.

Numerical analysis of the strained state of cellular pipes in inhomogeneous soil

With the help of Fourier series, we propose a method for the evaluation of the strained state of cellular underground pipes with regard for the variations of the reaction coefficient of the surrounding soil. As a result, we write, in recurrent form, the coefficients of Fourier series for the averaged components of the vector of displacements of a cellular structure. On this basis, we find the radial displacements of a polymeric pipe along its contour.

Studies on Soil Resistance to Pipelines Buried in Sand

A series of model tests were carried out to investigate the soil resistance when the buried pipe segment moved in the sand. In the tests, the pipe segments were pulled out in vertical, lateral and axial directions and the pipe segments movement and soil resistance were recorded. Observed data show that the soil resistance depends on the pipe diameters and the depth of cover. According to the uplift test results, the force-displacement relationships with smaller depth of cover are greatly different from those with larger depth of cover. The results of the lateral sliding and axial pull out tests show that the soil resistance initially increases before a peak value is reached and then keeps the same level. For the same covered depth, the lateral soil resistance is more than twice that for uplift. According to the uplift test results, the soil failure modes with smaller depth of cover are greatly different from those with larger covered depth.

Corrosion resistance of stainless steel pipes in soil

AbstractTo be able to give safe recommendations concerning the choice of suitable stainless steel grades for pipelines to be buried in various soil environments, a large research programme, including field exposures of test specimens buried in soil in Sweden and in France, has been performed. Resistance against external corrosion of austenitic, super austenitic, lean duplex, duplex and super duplex steel grades in soil has been investigated by laboratory tests and field exposures. The grades included have been screened according to their critical pitting‐corrosion temperature and according to their time‐to‐re‐passivation after the passive layer has been destroyed locally by scratching. The field exposures programme, being the core of the investigation, uses large specimens: 2 m pipes and plates, of different grades. The exposure has been performed to reveal effects of aeration cells, deposits or confined areas, welds and burial depth. Additionally, investigations of the tendency of stainless steel to corrode under the influence of alternating current (AC) have been performed, both in the laboratory and in the field. Recommendations for use of stainless steels under different soil conditions are given based on experimental results and on operating experiences of existing stainless steel pipelines in soil.

Prediction of spatial patterns of collapsed pipes in loess-derived soils in a temperate humid climate using logistic regression

Soil piping (tunnel erosion) has been recognised as an important erosion process in collapsible loess-derived soils of temperate humid climates, which can cause collapse of the topsoil and formation of discontinuous gullies. Information about the spatial patterns of collapsed pipes and regional models describing these patterns is still limited. Therefore, this study aims at better understanding the factors controlling the spatial distribution and predicting pipe collapse. A dataset with parcels suffering from collapsed pipes (n=560) and parcels without collapsed pipes was obtained through a regional survey in a 236km² study area in the Flemish Ardennes (Belgium). Logistic regression was applied to find the best model describing the relationship between the presence/absence of a collapsed pipe and a set of independent explanatory variables (i.e. slope gradient, drainage area, distance-to-thalweg, curvature, aspect, soil type and lithology). Special attention was paid to the selection procedure of the grid cells without collapsed pipes. Apart from the first piping susceptibility map created by logistic regression modelling, a second map was made based on topographical thresholds of slope gradient and upslope drainage area. The logistic regression model allowed identification of the most important factors controlling pipe collapse. Pipes are much more likely to occur when a topographical threshold depending on both slope gradient and upslope area is exceeded in zones with a sufficient water supply (due to topographical convergence and/or the presence of a clay-rich lithology). On the other hand, the use of slope-area thresholds only results in reasonable predictions of piping susceptibility, with minimum information.

Understanding soil‐pipe flow and its role in ephemeral gully erosion

AbstractThe role of soil pipeflow in ephemeral gully erosion is not well understood. Experiments were conducted on continuous soil pipes to better understand the role of internal erosion of soil pipes and its relation to ephemeral gully development. Soil beds of 140 cm length, 100 cm width and 20 cm depth had a single soil pipe of different initial sizes (2, 4, 6, 8, and 10 mm diameter) extend from a water reservoir to the outlet. Experiments were run on Providence silt loam and Smithdale loam soils under a constant head of 15 cm established for 30 min. Either the tunnel collapsed or the head could not be maintained. Soil pipes that were initially 2 and 4 mm clogged instantaneously at their mouth and did not exhibit flow, whereas, pipes initially ≥ 6 mm enlarged by 268, 397, and 699% on average for the 6, 8, and 10 mm diameters, respectively. Critical shear stress values were found to be essentially zero, and erodibility values gave erosion indexes that were extremely high. The rapid internal erosion resulted in erratic flow and sediment concentrations with periods of no flow as pipes were temporarily clogged followed by surges of high flow and high sediment concentrations. Tensiometers within 6 cm of the soil pipes did not exhibit pressure increases typically associated with pipe clogging. Flow through 10 mm diameter soil pipes exhibited tunnel collapse for both soils tested. Tunnel collapse typically occurred within minutes of flow establishment suggesting that ephemeral gullies could be misinterpreted as being caused by convergent surface flow if observations were made after the runoff event instead of when flow is first established through soil pipes. Copyright © 2011 John Wiley & Sons, Ltd.

Validation of boundary PIV measurements of soil–pipe interaction

It is a well-established argument that side-wall interface friction can influence the behaviour of soil located at the boundary of physical model test chambers. This effect has a potentially significant influence on measurement techniques such as particle image velocimetry that often rely on images captured at vertical transparent boundaries. However, it is hypothesised that under kinematically controlled boundary conditions, particle image velocimetry can yield not only qualitative but highly accurate quantitative measurements of deformation. In this paper, this hypothesis is tested for the specific soil–structure interaction problem of pipelines being subject to vertical faulting. In the middle of the model, a circular model pipeline was heavily instrumented with 32 pairs of strain gauges. At the same elevation but at the window of the test chamber, an identical model pipeline was split in half axially along its centreline to give a semi-circular cross-section, and placed against the visible window. Three digital cameras were used to record deformations of the pipe and the surrounding soil during the test. After image processing and filtering, measurements of peak curvature obtained from digital image analysis on the half pipeline section are shown to be within 5% of the results obtained from strain gauges.

Reliability Estimation of Buried Pipelines Using First-Order Reliability Method

Corrugated polyethylene (PE) pipes are used widely for a variety of applications. These pipes provide substantial benefits over concrete, metal, and other traditional pipes in terms of their ability to resist environmental stresses from chemical and biological agents. Furthermore, they are easy to install, tough in the field, durable in service, and environmentally benign. In this article, the limit state function (LSF) is formulated in accordance with conventional design method. The first-order reliability method (FORM) is utilized to extract useful technical information in carrying out the effective design procedure for corrugated PE pipe. Using the three design criteria and failure probability, the methodology for reliability estimation of corrugated PE pipe is investigated. The effects of varying design parameters on failure probability are systematically studied. Of the three design criteria, it is found that the bending stress design criterion shows the smallest failure probability, and the deflection design criterion shows the largest failure probability for varying design parameters. It is recognized that the failure probability increases with an increase in the coefficient of variation (COV) of random variables. It is also noted that such design parameters as burial depth, modulus of soil reaction, outside diameter, pipe stiffness, soil density, and distance to neutral surface must be selected properly to achieve the required safety level.

Consolidation around partially embedded seabed pipelines

When a pipeline is laid on a soft clay seabed, excess pore pressure is generated. During the subsequent dissipation process, the effective stress at the pipe–soil interface and the available axial pipe–soil resistance rise. This ‘set-up' of axial resistance is an important consideration in various aspects of pipeline design, including the mitigation of thermal and pressure-induced expansion, the stability of the pipeline on sloping ground and the assessment of pipe–soil forces during installation. A set of finite-element analyses has been conducted to assess the pore pressure dissipation and consolidation beneath partially embedded seabed pipelines, extending existing solutions for strip footings. It is shown that the curved shape of a pipeline increases the normalised rate of consolidation compared with a strip footing. Dissipation curves for various levels of embedment are presented and the calculated response is shown to compare well with data from a field test conducted on a soft clay. The dissipation curves have been used to derive the development of effective contact force between the pipe and the seabed as consolidation progresses. These results highlight the significant enhancement of this force – and therefore the available axial resistance – that arises from a ‘wedging effect' related to the curvature of the pipe–soil contact surface. This wedging effect leads to a beneficial enhancement of the axial resistance.

3D FE Analyses of Buried Pipeline with Elbows Subjected to Lateral Loading

This study investigates the interaction between soil and pipeline in sand subjected to lateral ground displacements with emphasis on the peak force exerted to a bended elbow-pipe. A series of three-dimensional (3D) finite-element (FE) analyses were performed in both opening and closing modes of the elbow section for different initial pipe bending angles. To model the mechanical behavior of sands, two soil models were adopted: Mohr-Coulomb and Nor-Sand soil model. Investigations also included the effects of pipe embedment depth and soil density. Results show that the opening mode exhibits higher ultimate forces and greater localized deformations than the closing mode. Nondimensional charts that account for pipeline location, bending angle, and soil density are developed. Soil-spring pipeline analyses of an elbow-pipe were performed using modified F-δ soil-spring models based on the 3D FE results and were compared to the findings of conventional spring model analyses using the standard two-dimensional soil-spring model. Results show that the pipe strain does not change in the closing mode case. However, in the opening mode case, the pipe strain computed by the modified analysis is larger than that by the conventional analysis and the difference is more pronounced when the pipe stiffness is stiffer.

Effect of blow frequency and additional static force on the vibro-percussion pipe penetration rate in soil

The authors describe and discuss experimental investigation of the effect exerted by blow frequency and additional static force on penetration rate of a pipe under vibration-percussion by a pneumatic hammer with using a measuring and recording instrumentation developed at the Institute of Mining, Siberian Branch, Russian Academy of Sciences. The penetration velocity ranges are found for the real blow frequencies of the test pneumatic hammer equipped with additional static load. Determination of static force sufficient to press the pipe in soil in hammer-free regime is reported.

Lateral Breakout Resistance of Shallowly Embedded Offshore Pipelines

Stresses induced by thermal expansion of unburied seabed pipelines can be designed to be relieved through controlled lateral buckling, which requires accurate and reliable assessment of the lateral breakout resistance. The lateral breakout resistance is strongly dependent on the pipe embedment, soil strength and loading history of the pipe. In addition, prediction of the pipe movement during the breakout process is essential as it subsequently determines the lateral resistance at large displacement. Theoretical solutions based on plasticity theory are available for combined vertical and horizontal loading on partially embedded pipes. These solutions however ignore the pre-failure pipe displacement and the associated change in soil geometry which could have significant influence on the failure load. A series of 1g model tests has been conducted to examine the lateral breakout resistance for a shallowly embedded pipe in a soft clay. Two types of tests, (1) sideswipe tests and (2) probe tests, were conducted to examine the effect of pipe embedments and loading history on the breakout resistance of a partially embedded pipeline. Results were compared with other proposed predictions in order to provide a more rigorous basis for the prediction of the breakout resistance of a partially embedded pipeline.

Three‐dimensional responses of buried corrugated pipes and ANN‐based method for predicting pipe deflections

AbstractThis study investigated localized responses, such as circumferential stresses, on corrugation and pipe deflections. Also, this study examined the effect of corrugation geometry on the overall and localized response of corrugated pipes with refined three‐dimensional modeling of the entire soil–pipe interaction system, including corrugation. To investigate the availability of the traditional two‐dimensional method, the results from the three‐dimensional finite element method (FEM) were compared with those from the two‐dimensional FEM. The soil–pipe modeling techniques of this study were verified by comparing the FEM results by Utah State University and analytical results. An artificial neural network (ANN)‐based model to predict vertical deflections of buried corrugated pipes was developed to overcome the shortcomings of existing methods and obtain results that are close to the level of accuracy of FEM results. In order to train an ANN, analyses on a large amount of data were executed with various standardized pipe geometries and burial depths regulated by the Korea Highway Corporation using the two‐dimensional FEM verified in this study. The widely used back propagation algorithm was adopted. The ANN‐based model developed in this study was shown to be an effective tool by comparing the results with test data and sensitivity analyses were executed based on the data from the developed ANN. Copyright © 2010 John Wiley & Sons, Ltd.

Steady flow-induced instability of a partially embedded pipeline: Pipe–soil interaction mechanism

The steady flow-induced instability of a partially embedded pipeline involves a complex process of pipe–soil interaction. In accordance with the hydrodynamic loading and the dimensionless analyses, a series of pipe–soil interaction tests have been conducted with an updated pipe–soil interaction facility including a load–displacement synchronous measurement system, to reveal the underlying pipe–soil interaction mechanism. The effects of pipe surface roughness, end-constraint and initial embedment are investigated, respectively. The values of lateral-soil-resistance coefficient for the rough pipes are bigger than those for the smooth pipes. For a fixed value of non-dimensional submerged weight, the values of lateral-soil-resistance coefficient for the anti-rolling pipes are much larger than those for the freely laid pipes. The effects of initial embedment on the ultimate soil resistance get less with the decrease of the submerged weight of the pipe. A comparison is made between the results of the present mechanical-actuator tests and those of the previous water-flume tests, indicating that those results are quite comparable. For the equivalent level of dimensionless submerged weight, the directly laid pipe in currents has higher lateral stability than in waves.