Behavior Of Buried Pipes Research Articles

Modeling mechanical behavior of buried pipe suffering from frost-heaving force based on the Winkler Elastic Foundation Beam Theory

Differential frost heaving can damage buried pipelines, with catastrophic outcomes. It is necessary to consider the interactions between the pipeline and soil as well as the stress characteristics of frost heaving. In this study, a mechanical behavior model of buried pipe suffering from frost-heaving force based on the Winkler elastic foundation beam theory is proposed. The concept of a frost heaving spring is proposed to replace the foundation spring of Winkler’s theory. The frost heaving spring is a pre-compression spring that is dependent on the relationship between the frost-heaving force and frost heaving amount, the frost heaving state is similar to pre-compressed spring resilience. Since the pipeline is continuous, soil in the non-frost-heaving area is squeezed by the pipeline and generates a corresponding elastic response. Modeling mechanical behavior of buried pipe suffering from frost-heaving force based on a linear frost heaving spring assumption provided analytical solutions under two conditions. Results show that the modeled pipeline deformation and stress values conformed well to measured data of Huang Long and Caen test. The proposed model is mathematically simple and easy to apply to studies of mechanical behavior of buried pipe suffering from frost-heaving force.

Comparative Analysis of Buried Pipe Under Heavy Train Loads

With rapid development of railway transportation and increasing demand of oil and gas in China, the heavy haul train load becomes an important factor that threaten the safe operation of pipe. The mechanical behavior of buried pipe subjected to heavy haul train load was investigated in this study. A finite element model was established to investigate the effect of train load. Finally, the multiple train loads were also discussed. Results show that the high stress area occurs under the train track. In the pipe segment below the track, the top of pipe is under compression and the bottom of pipe is under tension. The cross section of pipe is still circular. The maximum vertical and horizontal displacement are at the top and side of pipe. The maximum von Mises stress, axial strain, and displacement of pipe increase with the increase of train load. Under the multiple train loads, there are two high stress and high strain areas at the top and bottom of pipe. With the increase of multiple train loads, the maximum von Mises stress, axial strain, displacement and ovality increase.

An Investigation into the Influence of a New Building on the Response of a Sheet Pile Wall Adjacent to an Existing Buried Pipe

This paper explores a solution to safeguard buried pipes located near constructions in the Al-Bisri region of Assiut Governorate by utilizing the concept of the characteristic damage state. This issue has escalated due to the increasing rate of construction activity near pipelines, resulting in a multitude of legal disputes. This study investigates the behavior of buried pipes when influenced by newly constructed buildings using the finite element method. The paper employs two-dimensional models of a 12-story reinforced concrete building with a raft foundation and a series of piles supporting the buried pipe. In this study, we used the PLAXIS software, a 2D plane strain program, to conduct numerical investigations. The soil was idealized using the Mohr–Coulomb model with a 15-node triangular element, while the piles and structures were idealized with a five-node isoperimetric beam element. The point of contact between the beam and the soil was represented by the interface element. Our research examined the distance between the pipe and the footing edge and the distance between the piles and the footing edge. The finite element model results provided nodal displacements and element straining actions for analysis. The results shed light on the behavior of the sheet pile wall and sewage pipe in various situations. The largest bending moment in the sewage pipe was seen in the absence of piling, in contrast, to pile support at Rx = 0.75. The bending moment in the pipe expanded and always occurred at the same location as Rx rose. The clay layer next to the pipe’s lateral deformation was significantly reduced after piling, with the greatest deformation occurring at Rx = 0.

Investigation of Backfill Compaction Effect on Buried Concrete Pipes

The present study deals with the experimental investigation of buried concrete pipes. Concrete pipes are buried in loose and dense conditions of gravelly sand soil and subjected to different surface loadings to study the effects of the backfill compaction on the pipe. The experimental investigation was accomplished using full-scale precast unreinforced concrete pipes with 300 mm internal diameter tested in a laboratory soil box test facility set up for this study. Two loading platforms are used namely, uniform loading platform and patch loading platform. The wheel load was simulated through patch loading platform which have dimensions of 254 mm *508 mm, which is used by AASHTO to model the wheel load of a HS20 truck. The pipe-soil systems were loaded up to pipes collapse. Pipes were instrumented with strain gauges to measure circumferential strains, in addition to dial gauges, for measurements of the pipe vertical deflections and settlement of the loading platforms. The test results indicated that flexure governed the buried pipe behavior. Flexural cracks formed slightly before the ultimate load. A comparison of soil backfill, between a loose and dense compaction, showed that the dense backfill improve largely the pipe installation and the strength ofpipe-soil system

Buckling behavior of buried pipe crossing stratum subsidence area

Stratum subsidence is one of the important factors threatening the pipe safety. Buckling phenomenon occurs on the pipe crossing subsidence area that may cause leakage accidents. The pipe soil coupling numerical model was established in this paper, buckling behavior of buried pipe crossing stratum area was investigated. The effects of subsidence displacement, radius-thickness ratio, internal pressure, buried depth and stratum on buried pipe’s mechanical behavior were discussed. The results show that buckling appears on the pipe when subsidence displacement is large. With the increasing of subsidence displacement, diameter-thickness ratio and buried depth of pipe, the buckling phenomenon becomes more serious. When the internal pressure of pipe increases, the buckling mode changes from concave fold to convex wrinkle gradually, and it is more serious with the increasing of internal pressure. The pipe in rock stratum is more dangerous than that in clay stratum and sand stratum. Those results can be used for the evaluation and maintenance of gas or hydrogen pipes.

Experimental Study on Uplift Mechanisms of Pipes Buried in Sloping Medium Dense Sand

Experiments are conducted to study the uplift behavior of buried pipes in medium dense sand with ground slopings of 0°, 10°, 20°, and varying burial depths. Test results show that the peak uplift resistance reduces with the increasing sloping, and up to 10% reduction is observed for 20° sloping. The displacement of pipe where the peak is mobilized, δp, also reduces for 20° sloping. The uplift resistance experiences a quicker reduction after reaching the peak due to the ground sloping. The stress level increases on the uphill side and decreases on the downhill side, resulting in lower and higher dilatancy, respectively. Consequently, the angle of slip plane to the vertical direction become smaller on the uphill side and larger on the downhill side. The slip plane extends to the ground and a complete slip mechanism develops at a pipe displacement of 2δp. The postpeak softening behavior of uplift resistance oscillates at an amplitude increasing with the burial depth and decreasing with the sloping, due to the arching effect as soil moving around the pipe periphery.

Investigation of the impact behavior when using single and double layers of geosynthetics on buried pipe structures

In this study the behavior of buried pipes under impact loading was investigated by forming protective layers with geosynthetics in various combinations in single and double layers. For this purpose, experiments were performed using a HDPE pipe with a 160 mm outer diameter, which is frequently used in the laboratory. In the experiments, Geocell, Geogrid, Geotextile, and Geonet protective layers at a depth of 120 mm were tested by laying Geosynthetic in single and double layers and then tested under the effects of impact loading by using free-weight dropping test apparatus. In the experimental study, the protective layers' energy absorption capacities were calculated by using acceleration measurements over the pipe and then evaluated together with their costs. In the experiments with a single layer Geosynthetic as a protective layer, Geonet's most successful protection structure was a 72.9 % acceleration-damping capacity. In the experiments with the combination of double-layer reinforcement elements, the most successful performance with 88.0 %, in terms of acceleration damping capacity, was obtained from Geocell and Geonet's combination with a thickness of 1 mm at a depth of 50 mm. When all the experiments with single- and double-layer Geosynthetic protective elements were evaluated as an acceleration damping ratio per unit cost, it was found that the optimum application was achieved when using a single-layer Geogrid.

Numerical Evaluation on Improvement Performance of Waved Connection to Reduce Damage on Buried Gas Pipeline

One of the major challenges for the oil and gas industry is to keep buried metal pipes safe from faulting. This paper discusses about a solution to keep buried pipes safe. In this study, after examining the different dimensions of the effect of wave connection on improving the performance of buried metal pipes, by changing the geometric shape of the wave connection such as doubling it, the behavior of the pipe is greatly improved. Waved connections, by their local deformation, create a rotational joint in a limited area so that other parts of the pipe remain intact. In this paper, the behavior of buried pipes due to slip direction fault displacement by modelling with Abacus software version 2017 and selection of 4-node shell element and 8-node shell element have been used for pipe and soil modelling, respectively. In this paper, by comparing to a single waved connection with a double waved connection, the performance of the pipe due to the faulting phenomenon was evaluated. The results show the improvement of the excellent performance of the double joint by reducing the plastic strain values. In addition to increasing the ductility of the pipe, the double connection has been able to reduce the strain values by about 50% compared to the single connection. In general, this paper shows that the use of wave connections can significantly increase the level of safety of buried gas pipelines without increasing the cost.

Research on the Law of Stress Development Along Backfilling Process Between Crest and Valley of Buried Corrugated Steel Pipe Culverts

Although buried corrugated steel pipe culverts have been studied intensively in the past decades, the stress development law between crest and valley during backfilling process is still not analyzed sufficiently, which is an important technical difficulty for the construction of this kind of structures. In this paper, a three-dimensional finite element model (FEM) is developed to simulate the behavior of buried pipes during construction and the stress development law within a wavelength (curvature of corrugated pipe) ranging at the crown and the spring-line inside the pipe is proposed. Based on the measured stress data of a porous continuous corrugated steel plate pipe-arch culvert, the proposed three-dimensional FEM and stress development law are verified. The results show that the stress variations in a wavelength range of corrugated steel plate are trigonometric curves. With the increase of the backfilling height, the ratio of the stress at the crest or valley, to that of the spring-line is reduced, while the axial force is increased. The absolute value of the bending moment decays and the pipe culvert tends to be ring compression as the backfilling height increased. The study verifies the "ring compression theory" and the necessity of the minimum burial depth in design. Meanwhile, some design and construction guidelines which is necessary for the structure safety during backfilling process are provided for buried corrugated steel pipe culverts.

Mechanical behavior analysis of buried pipeline under stratum settlement caused by underground mining

The stratum settlement caused by underground mining is one of the main geological disasters that threaten and damage buried pipelines. Therefore, the mechanical behavior of buried pipe under stratum settlement is investigated in this paper. Effects of pipeline parameters, mining area parameters and inclination directions of mining area on mechanical behavior of the buried pipeline are discussed. The results show that the maximum Von Mises stress and the maximum vertical displacement of pipeline are located in the middle of the pipeline during the mining process. As the excavation length increases, the Von Mises stress, the circumferential strain and vertical displacement increase. However, there is only stress concentration in the pipeline, and does not appear yield deformation. The vertical displacement of the pipeline is much greater than the horizontal displacement. The maximum stratum displacement appears on the upper surface of the mining area and it is stratum settlement. In addition, as the diameter-thickness ratio, buried depth, surrounding soil thickness of the pipeline and the height and the width of mining area increase, the maximum Von Mises stress, the circumferential strain and maximum vertical displacement of the pipeline increase, but they decrease with the increase of the buried depth of mining area. Whether the mining area is horizontal inclination or longitudinal inclination, the maximum Von Mises stress and maximum vertical displacement of pipeline are located in the middle of the pipeline. The maximum Von Mises stress, the circumferential strain and vertical displacement of pipeline decrease with the increase of the inclination angle. However, for the mining area of longitudinal inclination, the pipeline would produce horizontal displacement, the horizontal displacement of the pipeline increases with the increase of longitudinal inclination angle, and the position of the maximum strain of the pipe appears to shift. For the mining area of horizontal inclination, with the increase of horizontal inclination angle, the right side of vertical displacement curves approximately overlap, but the left side separates from each other.

Numerical Modeling of Wave Feature to Enhance the Performance of Buried Steel Pipelines Subjected to Faulting Displacements

Earthquake-induced permanent ground deformations are among the most important causes of damage to lifelines. Buried pipelines are longitudinal structures that are prone to be exposed to the faulting displacements. Improving the performance of these lifelines is of particular importance. This research numerically investigates the effect of a recently introduced wave feature (segments with rotational and axial flexibilities) on the behavior of buried pipes subjected to the displacement of the strike-slip faulting. Three-dimensional nonlinear finite element simulations were conducted in which the pipe and wave feature were modeled by shell element and peripheral soil was modeled by three-dimensional continuum elements. The accuracy of numerical simulations was examined by comparing the results with large-scale physical experiment. The comparison shows that the results of numerical modeling are in good agreement with experimental results. As an advantage of a calibrated numerical simulation, it is possible to extend the range of predictions and get the generalized response of the system in other geometrical and boundary conditions in which the experimental data are not available. In order to study the effect of the wave feature joint on the behavior of buried pipeline, the results were compared with a pipe with identical conditions in which the wave feature was not installed. It was found that wave feature substantially reduces the longitudinal forces and strains and preserves the cross-sectional area of the pipeline. Therefore, it considerably improves the performance of the pipe against faulting displacements.

Experimental evaluation of an expanded polystyrene (EPS) block-geogrid system to protect buried pipes

This study presents the results of experimental tests carried on buried uPVC (unplasticized polyvinyl chloride) pipes with an external diameter of 160 mm. The behavior of buried pipes in unreinforced and reinforced trenches by a single layer of HDPE (high-density polyethylene) geogrid and expanded polystyrene (EPS) geofoam block were investigated. To simulate vehicle wheel loadings, 500 cycles of repeated load respectively with an amplitude and frequency of 450 kPa and 0.33 Hz was applied to a loading plate placed over the trench surface. Pipe behavior under cyclic loadings were assessed using vertical diameter strain measurements, circumferential strains and pressures at the crown and springline. Additionally, settlement at the soil surface was measured throughout testing. The testing program is aimed at evaluating the role of different parameters influencing pipe behavior, such as embedded depth of the pipe, implementation of the EPS block and geogrid layer simultaneously and separately, and density, width and thickness of the EPS blocks. The results illustrate that the rate of changes in the pipe circumferential strain, vertical diameter strain and soil surface settlement, which increase rapidly in initial loading cycles, decreased as loading progressed. Based on the results, the density, width and thickness of implemented EPS blocks have an impact role in improving the behavior of buried pipes. The use of geogrid reinforcement with an EPS block with density of 30 kg/m3, thickness of 60 mm and width of 1.5 times the pipe diameter showed the most benefit when balancing vertical diameter strain, pipe crown strain, and soil surface settlement.

Stress Prediction of Buried Pipes Subjected to Operational Loadings in Unsaturated Soils

AbstractPipelines are used to provide variety of services in modern community and have grown rapidly in past few decades due to growing socio-economic requirements. Most of the water mains are buried in shallow depths where the soil is partially saturated with significant spatial and temporal variations. Even though the behavior of buried pipes in such unsaturated soil condition is substantially different when compared to dry or fully saturated soil, the effect of soil saturations is overlooked in the current pipe stress prediction methods, leading to unrealistic predictions of the pipe stresses. In this study, three-dimensional (3D) finite element (FE) method was employed with advanced constitutive soil models to analyze the behavior of pipes buried in unsaturated soil condition. Having validated the FE model using reported field test data, an analytical model was proposed to predict the maximum stress in buried pipes considering soil saturation effect using a series of 3D FE analyses. Results from the FE analyses reveal that the maximum pipe stress can be significantly different when soil is in unsaturated condition when compared to dry condition. The proposed formula shows a good agreement with the field data and FE results, so that the expression can be used in the prediction of maximum pipe stress when they are buried under realistic (i.e., nondry) soil conditions.

Experimental Investigation of Soil — Structure — Pipe Interaction

In this study the stress behavior of buried pipes in cohesionless soil was investigated experimentally. The parameters investigated in the laboratory tests include embedment ratio of pipe, horizontal distance of pipe to footing and the position of pipe. Hoop stresses at four positions on the borders of the pipes were measured by strain gauges. The results indicated that a significant increase in bearing capacities and decrease in pipe hoop stress when embedment ratio of pipe and horizontal distance of pipe to footing were increased. Based on the results of the laboratory model tests, the embedment ratio of pipe and the position of pipe are the main parameters that affect the hoop stresses on pipe.

Large-scale experimental evaluation of soil saturation effect on behaviour of buried pipes under operational loads

The behaviour of pipelines in unsaturated soil is fundamentally different from that of pipelines buried in dry or saturated soils. However, the effect of soil saturation on buried pipe behaviour has been overlooked in past research mainly due to the very limited large-scale experimental studies available. Most of the available studies on buried pipes in unsaturated soil are based on numerical modelling that analyses the pipe behaviour using a calibrated soil model developed on the basis of fundamental unsaturated soil characteristics. Investigations with such approaches may not be acceptable owing largely to unverified or complicated pipe–soil interactions and three-dimensional stress re-distributions. In this paper, the effect of soil saturation on buried pipe behaviour is investigated using a comprehensive large-scale experimental setup. A detailed methodology of large-scale testing, which was used to obtain pipe deformations as well as soil stresses with reference to a cast iron pipeline buried in low-plasticity clay under different soil saturation levels, is presented. The results obtained from large-scale experiments are compared with those of three-dimensional finite element analysis. Results produced in this paper reveal that the degree of water saturation of backfill soil can significantly affect the pipe deformation under internal and external loadings.

Numerical Analysis of Mechanical Behavior of Buried Pipes in Subsidence Area Caused by Underground Mining

The buried pipe crossing the subsidence area is prone to failure. The mechanical behavior of buried pipe in subsidence area was investigated in this paper. Effects of subsidence displacement, pipe parameters and soil parameters on the mechanical behavior were investigated. The results show that high stress appears on the pipe's surface and exceeds the yield strength after the strata subsidence. As subsidence displacement increases, the ranges of high-stress area and displacement increase, and the pipe section changes from a circle to an ellipse. The maximum axial strain occurs on the pipe in no-subsidence area. The maximum plastic strain and ovality of the pipe increase with the increasing of subsidence displacement. The displacement, plastic strain, and ovality of the pipe increase with the increasing of diameter–thickness ratio and buried depth. Internal pressure and friction coefficient has a little effect on the pipe displacement. The ovality decreases as internal pressure increases. The plastic strain and ovality increase with the increasing of the friction coefficient. As the elastic modulus and cohesion of soil increase, the displacement, plastic strain, and ovality of the pipe increase. The effect of Poisson's ratio on the deformation of pipe is small.

Behaviour of buried pipes in unstable sandy slopes

Significant forces can be applied to embedded pipelines in sloping grounds due to soil instabilities, which potentially might lead to leakage of hazardous fluids into the environment. The soil-pipeline interaction in sandy slopes has been investigated experimentally using small-scale physical models tested in geotechnical centrifuge. A novel method is developed in this paper to estimate the ultimate external forces, induced by slope failures, acting on buried pipes at various locations inside the slope. Instabilities were triggered by surcharge loading on the slope crest in the centrifuge tests. Six dense coarse sandy slopes were tested with different pipe locations with respect to the slope crest. Moreover, two medium dense fine sand slopes were tested in the same manner to study the effect of the grain size distribution on the soil-pipe interaction. The external forces on the pipe induced by the surrounding soil movements were calculated based on the measurements of four strain gauges installed on the pipe. The shape of failure surface and pipe movements were monitored with the aid of advanced image analysis techniques. The results indicate that a buried pipeline has the potential to affect the slope failure mechanism. Normalised force-pipe displacement relationships were derived and compared to the estimation methods suggested in previous studies, which were mainly done on pipes installed in flat grounds. A new prediction method is introduced in this study, which considers the pipe burial distance to the slope crest. Moreover, the slope angle effect on the ultimate force applied to the pipe is also investigated, and a generalised formula is developed. Finally, two examples of the application of the new method are presented for pipelines installed at the toe of two large-scale subarial and submarine slopes.

A comparative study of the response of buried pipes under static and moving loads

Abstract The buried pipes should be designed properly to withstand the loads imposed by the backfill soil weight and traffic loads. However, a thorough literature review has shown differing opinions on the effect of static and moving traffic loads on buried pipes. Some studies have shown that moving loads produce higher displacement in buried pipes compared to static loads, while other studies have shown contradicting results. These differing opinions have created confusion among researchers who are studying the response of buried pipes under traffic loads, where most of the studies have been conducted using either static or moving loads without proper justification to the selection of the loading type. To clarify this confusion, this paper presents a rigorous study on the behaviour of buried pipes under static and moving traffic loads using a robust finite element analysis. The static and dynamic finite element models have been developed and validated using high-quality field data collected from the literature. The developed models were then used to investigate the effect of the truck speed, pipe stiffness and loading conditions on the maximum displacement of buried pipes. The results showed that the displacement of buried pipes due to static loads is always higher than the pipe displacement due to moving loads. In addition, it was found that the ratio of the static to dynamic pipe displacement decreases as the pipe stiffness increases and increases to a lesser extent as the truck speed increases. Hence, future studies should consider the static loads in designs as these are the most stringent loading condition. This is actually very helpful for designers if they are using numerical methods in their designs, because static analyses are much more straightforward to conduct and less computationally demanding compared to dynamic analyses.

Protection of Buried Pipe under Repeated Loading by Geocell Reinforcement

With increase in cities’ population and development of urbane life, passing buried pipelines near ground’s surface is inevitable in urban areas, roads, subways and highways. This paper presents the results of three-dimensional full scale model tests on high-density polyethylene (HDPE) pipe with diameter of 250 mm in geocell reinforced soil, subjected to repeated loading to simulate the vehicle loads. The effect of geocell’s pocket size (55*55 mm and 110*110 mm) and embedment depth of buried pipe (1.5 and 2 times pipe diameter) in improving the behaviour of buried pipes was investigated. The geocell’s height of 100 mm was used in all tests. The repeated load of 800 kPa was applied on circular loading plate with diameter of 250 mm. The results show that the pipe displacement, soil surface settlement and transferred pressure on the pipe’s crown has been influenced significantly upon the use of geocells. For example, the vertical diametric strain (VDS) and soil surface settlement (SSS), in a way that using a geocell with pocket size of 110*110 mm reduces by 27% and 43%, respectively, compared with the unreinforced one. Meanwhile, by increasing buried depth of pipe from 1.5D to 2D, the use of geocell of 110*110 mm delivers about 50% reduction in SSS and VDS, compared with the unreinforced soil.

Structural behavior of buried pipe bends and their effect on pipeline response in fault crossing areas

Pipe bends, often referred to as “elbows”, are special pipeline components, widely used in onshore buried steel pipelines. They are sensitive to imposed deformations and their structural behavior is quite flexible and associated with the development of significant stress and strain, which may lead to failure. In the present paper, the mechanical performance of buried steel pipeline bends is investigated first, using rigorous finite element models that account for the pipe-soil interface. Three 36-inch-diameter pipe elbows are considered, subjected to pull-out force and embedded in cohesive soils. The elbows have bend angles equal to 90°, 60° and 30°, and bend radius-over-diameter ratio (R/D) equal to 5. The results show the increased flexibility of the pipeline bend with respect to the straight pipe, and are reported in the form of force–displacement diagrams. Furthermore the deformation limits of each elbow are identified in terms of appropriate performance criteria. The second part of the paper investigates the effect of pipe bends on the response of pipelines crossing active faults using a three-dimensional rigorous finite element model. The numerical results refer to a 36-inch-diameter pipeline crossing a strike-slip fault, and show that the unique mechanical response of pipe bends, in terms of their flexibility, may offer an efficient tool for reducing ground-induced deformations. The three-dimensional model employs the load–displacement curves of the first part of the paper as end conditions through nonlinear springs. Furthermore, the results show that there exist an optimum distance of the elbow from the fault plane, which corresponds to the maximum allowable ground displacement. Therefore, pipeline elbows, if appropriately placed, can be employed as “mitigating devices”, reducing ground-induced action on the pipeline at fault crossings.