Pipe-soil Interface Research Articles

Dynamic Responses in a Pipe Surrounded by Compacted Soil Suffering from Water Hammer with Fluid–Structure–Soil Interactions

The current literature analyzing the dynamic response of coupled pipelines neglects the crucial interplay between the pipelines themselves and these constraints. This overlooked interaction has substantial influence on the fluid–structure coupling response, particularly in scenarios involving continuous constraints. We focus on a piping system surrounded by compacted soil, which is regarded as unbounded homogeneous elastic soil that suffers from water hammer. This study established a one-dimensional model for water pipe-embedded compacted soil with fluid–structure–soil interaction. Taking fluid–structure–soil interaction into account, fluid–structure interactions (FSIs) include Poisson coupling, junction coupling emerging at the fluid–structure interface, and pipe–soil coupling (PSC) emerging at the pipe–soil interface. In this study, as soil is assumed to be a homogeneous, isotropic elastic material, the coupling responses are more complex than those of an exposed pipe, and the relevant mechanisms justify further exploration to obtain well-predicted results. To mathematically describe this system considering fluid–structure–soil interaction, the four-equation FSI model was modified to accommodate the piping system surrounded by unbounded homogeneous elastic soil, employing the finite volume method (FVM) as a means to tackle and solve the dynamic problems with FSI and PSC, which partitions the computational domain into a finite number of control volumes and discretizes governing equations within each volume. The results were validated by the experimental and numerical results. Then, dynamic FSI responses to water hammer were studied in a reservoir–pipe–reservoir physical system. The hydraulic pressure, pipe wall stress, and axial motion were discussed with respect to different parameters. With the PSC and FSI taken into account, fluid, soil, and pipe signals were obviously observed. The results revealed the structural and fluid modes. Dynamic responses have been proven to be difficult to understand and predict. Despite this, this study provides a tractable method to capture more accurate systematic characteristics of a water pipe embedded in soil.

Experimental and DEM Study on Shear Properties of Steel Pipe–Soil Interface

Experimental and DEM Study on Shear Properties of Steel Pipe–Soil Interface

Consolidation effects on pipe-soil interaction due to tunneling

Existing studies on soil-pipe interaction due to tunneling mainly focus on short-term responses. However, in areas with high water tables and low permeability soil, long-term ground movement and associated pipe responses may occur due to dissipation of excess pore pressure generated during tunnel construction. In this paper, a Winkler solution with time-varying subgrade modulus and the corresponding greenfield soil displacement formula are developed to investigate the tunneling effects on existing pipelines. The pipe is considered as an infinite Euler beam of finite width resting on a poroelastic half-space, and adhesion and drainage effects between the pipe and soil are considered using bounding techniques. The greenfield consolidation settlement is evaluated using a modified Gaussian curve. The findings indicate that the subgrade modulus decreases while greenfield soil displacement increases during the consolidation process. The time-dependent behavior of the subgrade modulus is governed by the drainage condition at the pipe-soil interface, whereas the greenfield soil displacement is primarily influenced by the drainage condition at the tunnel-soil interface. The study reveals that the bonded contact condition, hydraulic boundary condition, and displacement constraint conditions all influence the bending moment of the pipe.

Modeling pipe-soil interaction under surface loading using material point method

Considering the increasing demand for urban land resources, the construction of new structures in areas with buried pipelines poses novel challenges to both pipeline structural integrity and foundation design. Based on numerical modeling using the material point method (MPM), this paper investigates the pipe–soil interactions when the pipeline system is subjected to surface loading caused by construction activities, focusing on the failure mechanisms and earth pressure distribution around a buried pipe. The accuracy of the numerical model is verified through comparison with results from laboratory model tests as reported in the literature. The influence of both the embedment ratio and the horizontal distance ratio on the failure mechanisms is analyzed in detail. The results show that as the embedment ratio and horizontal distance ratio increase, the bearing capacity of pipe-soil systems increases significantly. The effect of buried pipes on the bearing capacity becomes negligible when the horizontal distance ratio exceeds 3 or when the embedment ratio reaches 4. The failure modes of pipe-soil systems change from Prandtl-type foundation failures to asymmetric failures as the horizontal distance increases. Both external loads and the burial position of pipes affect the earth pressure distribution around the pipe. The pipe-soil interface can provide a potential sliding surface for foundation failure, which may exhibit a suction effect on the shear band. Finally, an understanding of the failure modes of pipe-soil systems is proposed for use in the design of underground pipelines and foundation systems.

Numerical Investigation on Uplift Behavior for Pipelines Shallowly Buried in Sloping Ground

In practice, pipelines are inevitably buried in sloping ground, however, previous studies and guidelines of pipe-soil interaction mainly focus on level ground. In this study, the upward resistance-displacement curve for slopes with angles up to 20° was numerically investigated. To reflect the state-dependence, pre-peak hardening, and post-peak softening properties for dense sand, a modified Mohr-Coulomb model was implemented and validated by available physical tests. Numerical studies were carried out to explore the resistance-displacement curve, considering the coupling effects of slope angle, pipe-soil interface roughness, burial depth ratio. It is found that the pipeline in slopes is subjected to unbalanced lateral contact stress around its periphery. The pipeline and surrounding soil tend to move towards the slope toe during the uplift, especially for the perfectly smooth pipeline. As the slope angle increases, the peak resistance decreases for the perfectly smooth pipeline while increases for the perfectly rough one. Besides, the generally rough pipeline shows a quick post-peak reduction in the resistance. Possible mechanisms behind these phenomena were explored. Finally, considering the coupling effects of slope angle, interface roughness, burial depth ratio, a simplified method for the resistance-displacement curve based on the limit equilibrium method was proposed.

Axial pullout behaviour of fusible PVC pipes and fusion weld joints assessed using distributed fibre optic sensors

Pipes are subjected to axial pulling forces that lead to shear stresses at the soil–pipe interface and axial strain distributions from various circumstances, including pulled-in-place pipe installation and permanent ground deformations. This study investigates the axial pullout response of fusible polyvinyl chloride pipes in dense sand. Three tests were conducted using a large-scale soil chamber to assess the development of axial resistance and the impact of non-continuous pulling and fusion weld joints. The measured maximum load response was significantly underpredicted by guidelines typically used in practice. Additionally, non-continuous pulling and changes to the pull rate had negligible impacts on the load–displacement response. Pipes were instrumented with distributed fibre optic sensors (DFOS) to capture the nonlinear development of strains along these flexible pipes and the mobilization of soil friction along the soil–pipe interface. Measurements have provided insight into the propagation of axial strains along the pipe, the additional longitudinal restraint provided by fusion weld joints, and their impact on the axial force distribution along pipes. The “locked-in” strains due to residual soil–pipe friction remaining after the axial pulling force is removed have also been measured using DFOS.

Visualized direct shear test of the interface between gravelly sand and concrete pipe

The shear stress–shear displacement relationship and shear strength parameters of the interface between the pipe and the surrounding soil are important for designing the jacking force. One most commonly used method to measure the shear strength of the pipe–soil interface is the direct shear test. This paper presents the results of a series of direct shear tests conducted in the laboratory on the pipe–soil interfaces for different moisture contents. Simultaneously, digital image correlation is used to supplement the research of the horizontal displacement field of the interface. The results show that the increase of normal stress will makes the interface more prone to strain hardening during the shearing process, and the influence of the change of specimen moisture content on the interface strain characteristics gradually weakens. The shearing process of the specimen mainly involved shearing contraction, and slight shear dilation occurs only when the moisture content is small. We proposed a unified model for describing the shear volumetric change caused by the combined action of moisture content and normal stress. The shear displacement field presents a layered distribution, which is related to the shear displacement corresponding to the shear stress.

Experimental Study on Interface Frictional Characteristics between Sand and Steel Pipe Jacking

In order to study the variation law of shear frictional characteristics of the steel pipe jacking and sand interface under different working conditions, the shear stress–strain curve between five different particle sizes of sand and steel pipe jacking under different normal stress and slurry lubrication conditions was measured by using a direct shear device, and the internal friction angle, friction coefficient and cohesion of the pipe–soil interface were calculated by regression analysis. The test results show that the shear stress between sand and steel pipe jacking decreases with the increase of the average particle size of the sand, and the strain-softening phenomenon occurs. The normal stress does not change the trend of the shear stress–strain curve at the pipe–soil interface, and the peak and residual values of the shear stress increase with the increase of the normal stress. The peak and residual values of the shear stress at the pipe–soil interface under the slurry lubrication condition are smaller than those under the no slurry lubrication condition. The peak shear stress between the pipe and soil under the lubricated slurry condition decreases by about 20%. The internal friction angle and friction coefficient of the pipe–soil interface decrease with the increase of the particle size, and there is no obvious pattern between the cohesion quantity relationship and the average particle size.

Envelopes for the soil-resistance capacity of a shallowly embedded pipeline in clay under three-dimensional combined loadings

Envelopes are developed for the soil-resistance capacity of pipelines shallowly embedded in clay subjected to combined three-dimensional vertical (V), horizontal (H) and axial (T) loading. A three-dimensional pipe-soil interface is developed to account for the effect of tension and separation between the pipeline and soil, which is used in numerical finite element modelling. Each of the 1800 finite element analyses defined a unique V-H-T condition causing failure of the soil around the pipe for a variety of pipe embedment. Using these results, a closed-form mathematical expression expresses the capacity envelope of the soil resistance to the pipe under three-dimensional V-H-T loading that is only a function of the pipeline embedment and the tension at the pipe-soil interface. Offshore pipeline engineers can use this expression to estimate the soil resistance under combined three-dimensional loading in their assessment of the stability and integrity of offshore pipelines.

Study on Improvement of Pipe-Soil Spring Model in Mountain Slope Area

For the interaction between the pipeline and the soil under the condition of large surface displacement, the displacement load is often transmitted to the pipeline through soil springs. The selection of soil spring parameters is based on laboratory research results, which may not be effective for pipe-soil interface simulation. In addition, the load and soil spring coefficient of the pipeline in the slope should vary with space and time, and these factors are ignored by the resistance formula of the current general spring model. The adaptability and temporal load distribution of the pipe-soil spring model in regions of large surface deformation are largely unknown. In this paper, we deduced the soil spring resistance formula when the surface is inclined, established an improved soil spring model for the slope, and obtained the variation law of soil spring resistance in different directions at different slope angles. At the same time, a comparison of the improved soil spring model with the standard soil spring model recommended by international associations and codes was carried out. The rationality of the improved soil spring model proposed in this paper in the calculation of the pipe-soil interaction in the slope section is further verified by small-scale physical model tests. It has a certain guiding significance for the calculation of pipe-soil interaction in slope sections.

Drained Axial Pipe-Soil Resistance at Low Confinement Using Tilt Table and Direct Shear Tests

Establishing a reliable value for the axial pipe–soil interface resistance is critical for the design of offshore pipelines. Over the last few years, several independent research groups have modified existing methodologies or devised new testing setups to further develop our understanding of the behavior of the pipe–soil interface at low contact stresses. The most common laboratory experimental methods adopted have been based on either tilt table tests or interface direct shear tests. However, a direct comparison between the results of these two testing methodologies has not been established. This paper aims at designing and fabricating a tilt table and interface direct shear setup capable of accurately estimating the drained interface resistance at low normal stresses, in addition to comparing their results under identical testing conditions. Both setups tested the drained clay–solid interface response by varying the soil composition (high and low plasticity clay), the interface roughness (smooth and rough), and the normal stress range. Results showed that the drained residual failure envelopes for the clays and clay–solid interfaces were nonlinear and could be modeled by a simple power model. The interface response was clearly dependent on the interface roughness, particularly when the roughness was normalized with the mean grain size. In the case of smooth interfaces, identical friction angles were obtained from the tilt table and the interface direct shear, whereas in the case of rough interfaces, the interface direct shear yielded lower friction angle values.

Modulating pipe-soil interface friction to influence HPHT offshore pipeline buckling

High-Pressure High-Temperature offshore pipelines laid on the seafloor are subject to large temperature and pressure variations which manifest as axial pipeline loading. Pipes become unstable in this condition and buckles form to relieve the axial stress. Considerable theoretical and experimental energy has been directed at establishing controlling mechanisms and parameters to predict buckling and design pipeline systems to be resilient and serviceable. The pipe-soil interface friction plays a pivotal role in the rate of build-up of axial loads and in controlling the critical buckling threshold. Pipes adopting smooth polymer coatings have very low friction coefficients but experimental work has shown that simple roughening techniques make greater friction coefficients available to a designer. Presented are a series of numerical analyses carried out using Abaqus to model a pipeline resting on the seabed subject to typical HPHT pipeline conditions. Global stability response is assessed with pipe-soil friction coefficients varying from 0.25 to 0.75 and differential friction regimes are adopted. It is shown that targeted application of pipe sections with greater interface friction may be a useful design tool for manipulating global buckling phenomena and could be a useful additional tool for influencing the spacing in Virtual Anchor Spacing analysis.

A Novel Proof of Concept Experimental Setup for Seabed-Pipe Interface Friction Measurements

Abstract Offshore hydrocarbon pipelines operate at relatively high pressures and temperatures. These conditions lead to their expansion and contraction and ultimately result in pipeline buckling or “walking” after multiple cycles of operation. Such movements are typically opposed by the axial resistance of the pipe-soil interface, which has to be accurately evaluated to optimize the engineering performance of the pipelines while minimizing testing and construction costs. To date, different testing techniques have been adopted to evaluate this resistance throughout the pipeline operational life. These include laboratory soil element testing, laboratory model testing, and in situ testing using specialized, complex, and costly devices. Despite being the most reliable testing technique, in situ tests are limited by the very small number of available specialized field equipment, e.g., the Fugro SMARTPIPE and the recently developed “pipe-like” penetrometers, both of which suffer from some drawbacks related to high costs, practicality, and testing conditions. This paper presents an attempt at addressing most of the limitations that were identified in the currently available methods, leading to the development of a new in situ, cost-effective apparatus for measuring axial pipeline resistance. A laboratory proof of concept experimental setup that could be adapted in future work to become an autonomous field apparatus was designed, produced, deployed on a clay bed and tested under normal stresses in the low-pressure range. The prototype reliably captured the effects of normal stress on the drained interface resistance. It produced accurate interface friction factors that are comparable to those obtained from the direct shear tests on the same soil and interface. The results obtained are very promising and confirmed the practicality and functionality of the proposed prototype. Some areas of improvement that would enhance the efficiency and reliability of the test were identified and will be applied to future versions of the device.

Dynamic interaction of the pipe-soil subject to underground blasting excavation vibration in an urban soil-rock stratum

the When rock blasting excavation is carried out in urban soil strata, the vibration effect caused by blasting will cause the dynamic interaction between pipe and soil. If the dynamic interaction exceeds the bearing capacity of the pipe-soil system, it will cause serious damage. At present, there is no vibration velocity control standard for the buried pipeline under the influence of adjacent blasting excavation vibration, and there are few studies on the influence of internal operating pressure and pipe-soil interface on pipeline response. Therefore, we designed and implemented a full-scale blasting experiment near the buried gas pipeline, simulated the real-time process of rock blasting, and monitored the dynamic response data related to pipeline-soil interaction. The LS-DYNA dynamic finite element method (EFM) numerical calculation model was established to study the dynamic response characteristics of buried pipelines under blasting load and the influence of different working pressures. Research shows that the buried pipelines and soil layers are mainly vertical vibration, and the pipeline deformation is mainly axial tensile deformation. The dynamic peak effective stress (PES) of the pressure pipeline has three stages, which are initial stress, peak stress, and residual stress. The pressure has little influence on the peak particle vibration velocity (PPV) of the pipeline and has a great influence on the dynamic stress. The buried pipeline is mainly affected by the P wave of the blasting earthquake. Based on the interaction theory of pipe-soil interface under the action of blasting seismic P wave, the calculation model of effective stress peak (PES) of buried pipeline in soil was established, and the safety particle velocity peak (PPV) of the buried gas pipeline under different working pressure conditions was calculated.

Temperature effect on the axial behaviour of a pipeline buried in soft clay

Axial resistance is a key component to resist thermal buckling of an offshore oil and gas pipeline operating under a high temperature. The previous studies on the axial resistance of the pipeline were mostly performed under an isothermal condition, ignoring the temperature effect that would alter the strength of the seabed and modify the axial resistance of the pipeline. For this reason, a novel temperature-controlled experimental setup is developed in this study. Model tests were then carried out for simulating the axial interaction between clayey seabed and pipelines, which were heated to two typical temperatures (i.e., 15 and 55 °C) under the drained condition and then axially loaded under the undrained condition till failure. Additionally, the mobilized shear strain (and therefore mobilized shear stress) at the soil-pipe interfaces under the two temperatures are also investigated, based on a newly developed temperature-controlled interface shearing apparatus that has a transparent window for image recording and analysis. It is found that the pipeline with high temperature (55 °C) exhibits 20% larger initial axial soil resistance stiffness than the low-temperature pipeline (15 °C). This suggests the thermal consolidation has increased the soil stiffness around the high-temperature pipeline. Despite the increased undrained shear strength (s u) of the thermally consolidated clay around the high-temperature pipe, its peak axial resistance is 10% lower than that of the low-temperature pipe, the maximal normalized parameter of axial resistance α f max decreases from 0.90 to 0.70, when the temperature rises from 15 °C to 55 °C. This is attributed to the thermally induced suppression of the stick-slip (referred as “thermo-lubricity”) at the soil-pipe interface, which encourages the interface slippage prior to a full mobilization of s u around the pipes. Consequently, a temperature elevation from 15 to 55 °C has led to a reduction 36% (from 70% to 34%) of s u mobilization at the soil-pipe interface, which is observed in the interface shearing tests.

Modelling and analysing failure modes of buried pipelines perpendicularly crossing landslide boundaries

The pipeline response to shallow translational landslides is investigated using semianalytical and numerical methods. The orthogonality of a pipeline and the landslide boundary is considered in this study. In the finite element (FE) analyses, ground movements are simplified as spatially distributed horizontal transverse deformation. The pipe-soil interaction is modelled accounting for large ground deformation, inelastic material behavior, and special contact conditions at the soil–pipe interface. Pipeline failure patterns are summarized based on a series of FE models with varying diameter thickness ratios of the pipe and soil conditions. According to the FE analysis results and the published literature, the existing failure criteria are evaluated and extended to cover new failure modes. The dynamic evolution in the predominant failure modes due to the pipe elongation effects is investigated. A semianalytical solution for the sliding distance to the onset of pipe wall wrinkling is given. In addition, a pipeline failure criterion is proposed based on the relative stiffness. This dimensionless parameter is correlated with failure features, including failure modes, sliding distances to failure initiation, and failure positions. The reliability of the proposed FE model and failure prediction methodology is validated using published results from centrifuge tests and FE analyses. Simple charts for failure prediction in terms of relative stiffness parameters are provided. The proposed approach allows efficient and reliable safety evaluation on X65 steel pipelines subjected to horizontal transverse ground deformation without conducting numerical modelling.

Study and Analysis on Stress Safety Judgment Method of Heavy Vehicle Rolling on Long-Distance Pipeline

With the rapid increasing mileage of China’s long-distance oil and gas pipelines, the intersection construction with other civil engineering, encroachment by invading the pipeline route, and other third-part problems occurred occasionally. Heavy vehicles rolling the serving pipeline have become one of the inevitable safety risks. The field test method of three in-service long oil and gas pipelines under heavy vehicle rolling is elaborated. The pipeline stress and soil pressure during tests are monitored and analyzed. The parametric model of pipe mechanical response under heavy vehicle rolling and stacking load is established, and the quantitative feedback of each parameter on pipeline stress safety response under heavy vehicle rolling is formed. The results show that the influence factors such as vehicle weight, vehicle speed, buried depth of pipeline, horizontal distance and cover plate on the stress state, vertical displacement state, and contact stress of pipe soil interface are highly consistent with the finite element method and test method, which could be a guideline for the safety assessment at rolling site.

Discussion of “Experimental Study on the Pipe-Soil Interface under the Influence of Pipe Jacking Stagnation Time” by Tianliang Lia, Wen Zhaoa, Run Liua, Jianyong Hana and Cheng Chenga

Jacking forces which exceed expectations constitute a risk for tunnelling contractors. One scenario in which high forces may arise is when jacking of lubricated pipes is temporarily halted, which was considered by Li et al. using a programme of direct shear testing. While recognising the importance of the topic to the profession, the purpose of this Discussion piece is to highlight some of the limitations of the study.

An Experimental Study on Frictional Properties of Concrete Pipe–Soil Interface

An Experimental Study on Frictional Properties of Concrete Pipe–Soil Interface

Experimental Study on the Influence of Slurry Concentration and Standing Time on the Friction Characteristics of a Steel Pipe-Soil Interface

In pipe jacking, the continued growth of friction resistance around the pipe may cause problems, such as an insufficient jacking force, soil collapse, and even land subsidence, which seriously endangers the structural safety of the pipe and surrounding structures. Bentonite slurry is often used as a lubrication material, but the friction resistance increases due to the inappropriate slurry concentration, and this may cause construction safety problems. In addition, the slurry standing time increases the difficulty of re-jacking construction. To further study the above problems, the friction characteristics of a steel pipe-soil interface under different slurry concentrations and slurry standing times were studied using direct shear tests. The test results show that the peak shear stress and friction coefficient of the interface first decrease and then increase with the increase in the concentration, which is less than or equal to 20%. The peak shear stress and friction coefficient increase with the increase in the concentration, which is greater than 20%, and the position of shear failure changes from between the slurry soil mixture and pipe wall to between the slurry and pipe wall, and finally to the slurry interior. The influence of the slurry standing time on the friction characteristics of the interface is as follows: For the same slurry concentration, the peak shear stress and friction coefficient of the interface increase with the standing time, approximately increasing first and then stabilizing; for different slurry concentrations, the amplification of the peak shear stress and friction coefficient increase with the increase in the concentration.