Buried pipelines are essential for the safe and efficient transportation of energy products such as oil, gas, and various chemical fluids. However, these pipelines are highly vulnerable to ground movements caused by geohazards such as seismic faults, landslide, liquefaction-induced lateral spreading, and soil creep, which can result in potential pipeline failures such as leaks or explosions. Response prediction of buried pipelines under such movements is critical for ensuring structural integrity, mitigating environmental risks, and avoiding costly disruptions. As such, this study adopts a Physics-Informed Neural Networks (PINNs) approach, integrated with a transfer learning technique, to predict structural response (e.g., strain) of both unreinforced and reinforced steel pipes subjected to Permanent Ground Displacement (PGD). The PINN method offers a meshless, simulation-free alternative to traditional numerical methods such as Finite Element Method (FEM) and Finite Difference Method (FDM), while eliminating the need for training data, unlike conventional machine learning approaches. The analyses can provide useful information for in-service pipe integrity assessment and reinforcement, if needed. The accuracy of the predicted results is verified against Finite Element (FE) and Finite Difference (FD) methods, showcasing the capability of PINNs in accurately predicting displacement and strain fields in pipelines under geohazard-induced ground movement.

Buried water pipelines, as crucial urban infrastructure, play an essential role. However, the damage to the pipeline structure has emerged as a severe public safety hazard. Monitoring the state of the pipeline structure holds great significance for the normal operation of water pipelines. In this paper, a damage monitoring method for buried pipelines based on distributed acoustic sensing technology is proposed. Through a series of field experiments conducted on a pipeline, the feasibility of utilizing the attached fiber-optic cable to acquire vibration information has been demonstrated. The recorded vibration signals can indicate various damage statuses during the pipeline damage process, including rock/soil fall, pipeline seepage, and pipe wall failure. The results suggest that the fiber-optic cable accompanying the pipelines can be exploited as sensing resources to monitor damage risks to the pipelines, which presents advantages in the damage identification and location of buried pipelines. This research provides a valuable reference for the application of distributed acoustic sensing technology in the damage monitoring of urban buried water pipelines.

Ultrasonic guided waves are widely used in the nondestructive testing (NDT) of aboveground pipelines. However, their application in buried pipeline inspection is significantly hindered by severe soil-induced attenuation. This study proposes a method for detecting defects in buried pipelines using nonlinear chirp signals encoded with orthogonal complementary Golay code pairs. By adjusting the proportion of low-frequency and high-frequency components in the excitation signal, the attenuation of guided waves in buried pipelines is effectively reduced. Meanwhile, the use of coded sequences increases the energy of the excitation signal, and the excellent autocorrelation properties of broadband signals enhance the time-domain resolution of defect echoes. The fundamental principles of coded excitation based on nonlinear chirp signals and pulse compression methods are first introduced. MATLAB simulations are then employed to verify the approach's effectiveness in the characterization of defect echoes under various conditions and signal-to-noise ratios (SNR). A subsequent comparative analysis, using finite element (FE) simulations for buried pipelines, demonstrates that nonlinear chirp signals with a higher proportion of low-frequency components exhibit better resistance to attenuation. By fine-tuning the chirp parameters, higher defect reflectivity can be achieved than with conventional tone bursts for various defect types in buried pipelines. FE simulations further illustrate the superiority of the proposed method over tone bursts in terms of excitation signal amplitude, defect echo reflectivity, and defect location accuracy. Finally, defect detection experiments on buried pipelines with multiple defects confirm that the nonlinear chirp signals with carefully selected parameters exhibit lower attenuation rates. In the same testing environment, the coded nonlinear chirp signals outperform tone bursts by providing higher excitation amplitudes, greater defect echo reflectivity with an increase of up to 81.45 percent, and enhanced time-domain resolution. The proposed method effectively reduces ultrasonic guided wave attenuation in buried pipelines while increasing defect echo reflectivity and extending the effective detection range.

This paper presents coupled thermo-hydro-mechanical finite element analyses (FEAs) of undrained uplift capacity for buried offshore pipelines operating at elevated temperature. An anisotropic thermoplastic soil constitutive model was employed to simulate mechanical behaviour of seabed soil under the combined actions of thermal and mechanical loading. FEAs investigated the influences of different parameters, e.g., pipeline embedment depth, pipe-soil interface roughness, duration of pipeline operation, and operating temperature, on pipeline uplift capacity. Time-dependent evolutions of temperature and excess pore water pressure were also tracked in soil surrounding the pipeline. For different durations of pipeline operation, FEA results revealed an improvement in normalized uplift capacity Nu of pipelines operating under elevated temperature. However, such an increase in Nu was diminished by a maximum of 7 % with increase in the ratio RTH of thermal diffusivity to coefficient of consolidation of surrounding soil. For different normalized pipeline embedment, 20-30 % enhancement of Nu was observed after six months of pipeline operation at 60 degrees C. However, after six months of operation, further improvement in Nu was negligible. Based on FEA results, this paper proposes an equation to estimate pipeline uplift capacity as a function of operating temperature, depth of embedment, and duration of pipeline operation.

Energy pile is a green, constant-temperature utilization technology with dual functions of heat exchange and load bearing. Improving its heat transfer efficiency has always been one of the main directions of scholars' research. This study discussed the optimization of heat transfer buried pipe parameters, modification of pile materials, and improvement of working fluid performance within the pipes. Additionally, based on the research achievements of the research team in recent years regarding heat transfer enhancement in energy piles, a comprehensive heat transfer enhancement system is summarized, aiming to provide new ideas and methods for the study of heat transfer enhancement in energy piles. The optimization status of different buried pipe types and pipe parameters is also summarized. The heat transfer performance and mechanical properties of different modified concrete materials are studied. A comparison and analysis of the heat transfer performance and flow characteristics of different types of circulating mediums with nanofluids are conducted, providing new approaches to improve the heat transfer performance of circulating mediums. Finally, discussions and prospects were made on the external environmental conditions around the pile, thermal interference phenomena of pile groups, energy storage concrete, the long-term stability of nanofluids, benefit assessment, and ecological evaluation. These efforts aim to promote research on energy piles both domestically and internationally.

Impact from falling objects can easily cause the local deformation of pipeline, which threatens the safe and stable operation of pipeline. In order to study the dynamic response behavior of impacted buried pipelines in cold regions, the buried pipelines, frozen soil and falling objects are taken as the object. Considering the nonlinearity of pipeline material, the contact nonlinearity between pipeline, falling objects and frozen soil, a double nonlinear dynamic analysis model of buried pipeline in cold regions is established by explicit dynamic analysis method. The rationality of the model method is verified by comparing the curves in this paper with those from the experiment. Furthermore, the changing laws of dynamic response of pipeline influenced by different factors are discussed. The results show that: when the buried depth of pipeline is 2 m, the deformation and residual stress of pipeline increase with the increase of pipeline's diameter-tothickness ratio, the impact velocity of falling object and the water content of frozen soil, and the impact velocity of falling objects influences the dynamic response behavior of pipelines most significantly, followed by the diameter-thickness ratio of pipelines and the water content of frozen soil; When the diameter-thickness ratio of the pipeline is 58, the deformation and residual stress of pipeline decrease with the increase of buried depth by 75 % and 88 % respectively. Among the four influencing factors, when the impact velocity of falling objects is 10 m/s and the buried depth of pipeline is 3 m, the deformation amplitude of pipelines caused by falling objects is the smallest. It is suggested that in the high-risk regions of falling objects, the diameter-thickness ratio, buried depth and the water content of frozen soil can be reasonably controlled under the condition of predicting the maximum potential impact velocity of falling objects, so as to improve the ability of the pipeline to resist external impact damage, which provides theoretical basis and quantitative control standards for the impact design of pipeline engineering in cold regions.

The laying of the underground pipeline in the same ditch has caused great challenges to the attractive transportation mode of hydrogen mixed with natural gas pipeline in service. The tendency to damage of hydrogen to steel increases the possibility of flammable and explosive gas entering underground engineering significantly. A leakage monitoring method for buried hydrogen-doped natural gas pipeline based on vibration signals with machine learning is proposed. Firstly, the distributed vibration sensor captures the multisource vibration signals propagating in the soil. An optimal combination of wavelet basis functions, decomposition level, and threshold parameters is selected carefully for signal denoising and accurate extraction of leakage-generated signals. Then the characteristics extracted in different frequency bands are investigated with other influencing factors, including the hydrogen-doping ratio, which affects the propagation speed of the pressure wave. The unique characteristics of vibration signal generated by pipeline leakage are extracted. On this basis, combined with the high efficiency of machine learning recognition model, a leakage monitoring model for buried hydrogen-doped natural gas pipeline is established, which achieves a 2.01 % false alarm rate at a maximum positioning distance of 70 cm. It has been successfully applied to the leak detection and location of buried hydrogen-doped natural gas pipelines, which can significantly improve the safety and reliability of underground pipeline system engineering.

This research investigates a methodology for probabilistic life prediction of buried steel pipelines subjected to external corrosion. A unified methodology is developed considering multiple stages of degradation related to external corrosion (due to soil) and fatigue. These stages include corrosion pit nucleation, pit growth, transition from pit to short crack, short crack growth, transition from short to long crack, stable long crack growth, and unstable fracture. The methodology is useful in obtaining stage-specific forecasts for the fatigue life of buried steel pipelines subjected to external pitting corrosion fatigue. State-of-the-art computational models are used to predict damage initiation and evolution at each stage. The variability in environmental, material, and loading parameters is propagated through these models to obtain a probabilistic estimate of the remaining service life (RSL) of the pipe. Insights from probabilistic RSL prediction highlight the influence of soil type and pipe coating material on corrosion fatigue life. Global sensitivity analysis is then employed to quantify the relative importance of environmental factors (pH, pipe/soil potential, and chloride concentration), material properties (threshold stress intensity factor), and the range of cyclic stress experienced by the pipe.

Geological and topographical challenges in fault zones pose significant risks to the structural integrity of buried pipelines. Previous studies have shown that continuously buried pipelines using loose sand as backfill material experience severe damage under active fault displacement. This study proposes the use of super-absorbent- polymer concrete (SAPC) as an alternative trench backfill to mitigate structural damage in buried pipelines subjected to reverse fault movement, as opposed to conventional backfill with loose sand. This study begins with the preparation of lightweight porous concrete containing large super-absorbent-polymer aggregates, followed by mechanical property testing to establish a constitutive model of SAPC. The SAPC is then employed to backfill the trench of a fault-crossing pipeline. A finite element model is developed to analyze the pipeline-SAPC trench- soil interaction and evaluate the performance of the pipeline when the trench is backfilled with SAPC. Critical parameters such as SAPC backfill length, overlying thickness, and elastic modulus are also examined for their effects on the performance of a buried pipeline. The numerical results indicate that compared with conventional backfill with loose sand, the critical reverse fault displacement of the pipeline can generally be increased by over 100 % after using SAPC as the backfill material. Optimal pipeline performance is observed when the SAPC backfill length is approximately 60 times the pipeline diameter. Besides, a thinner overlying SAPC thickness will generally enhance the performance of buried steel pipelines under reverse fault movement. Additionally, by adjusting the sand-cement ratio and SAP volume fraction, a SAPC with a higher elastic modulus can slightly improve the performance of the fault-crossing pipeline.

Effective identification of damage characteristics and failure modes for buried pipelines subjected to fault movements is crucial for early design and disaster assessment. In the preceding companion paper, the structural responses of large-diameter prestressed concrete cylinder pipeline (PCCP) subjected to fault displacement were initially investigated under the condition where faulting crosses pipe barrel vertically, and the deterioration process and failure modes were summarized. However, the structural responses of jointed pipelines are closely tied to faulting parameters. In this paper, a study on the location and angle of the fault plane is conducted, and the damage response and failure modes of large-diameter PCCPs are analyzed in detail and compared. The results show that strike-slip fault movement causes pipeline movement through pipe-soil interaction, and the fault displacement is accommodated by several pipe segments for the large diameter-to-length ratio PCCPs. When the fault plane crosses the pipe segment at an acute angle, the primary failure modes include material damage to the pipe joints and barrel, as well as the risk of joint leakage. Material damage occurs at the joint when the fault plane passes through the PCCP joint. Given the mechanical properties and seismic resilience of PCCPs, it is advisable to avoid faulting at acute angles crossing pipeline joints. This work focuses on the structural behavior of segmented composited PCCPs crossing a fault, aiming to predict pipeline damage and failure. The findings contribute to a comprehensive understanding of the failure modes, damage characteristics, and disaster evaluation of PCCPs under strike-slip fault conditions.