Buried Concrete Pipes Research Articles

Development of a Capsule-Type Inspection Robot Customized for Ondol Pipelines

Ondol is a heating system unique to Korean homes that increases indoor temperatures by supplying hot water through pipes embedded in floor slabs. Known for its comfort and sustained heating advantages, ondol has garnered international interest in countries requiring efficient heating solutions. Given the inherent challenges faced during installation and operation, timely inspection of ondol is crucial due to difficulties in detecting and locating defects in buried concrete pipes, often leading to costly rework and removal. However, specialized inspection systems tailored to ondol pipes remain underexplored. Therefore, this paper proposes a robotic inspection system capable of assessing the conditions of ondol pipelines. We analyze the characteristics of ondol piping to establish system requirements and develop a prototype of a compact capsule-shaped inspection robot tailored for ondol pipe inspection. Subsequent laboratory testing validates system performance and usability, confirming field applications through curvature maneuverability and image reception quality tests. This study aims to motivate advancements in ondol-specific system implementation and performance validation, potentially contributing to the smartification of ondol maintenance practices.

The destructive form and response analysis of buried concrete pipes under the action of internal explosion loads

This research analyzes the damage mechanism of subterranean concrete pipelines subjected to internal explosive loads using a mix of field blasting tests and numerical simulations. The field tests reveal that, under the effect of internal explosion loads, axial and circumferential cracks occur in the concrete pipelines, with the crown, invert, and springline being damaged firstly, leading to penetrating cracks. In addition, an arbitrary Lagrangian Euler (ALE) method is used to establish a coupled model of underground concrete pipeline under the condition of internal explosion. The influence of the explosion mass on the destructive effects and dynamic characteristics of the pipeline is investigated, and the internal wall strain at the explosion center and in the central part of the pipeline is analyzed. Furthermore, the propagation and attenuation laws of shock waves in pipelines are investigated, and an attenuation law formula of shock waves inside the pipeline with two ends open is provided, which will be useful for future research.

The Efficiency of the Benefits of Tire-Derived Aggregate Backfill for Buried Concrete Pipes Beneath Paved and Unpaved Roads

Tire-derived aggregate (TDA) has been proposed in recent studies to be considered as part of backfill soil to reduce stress and strain developed in buried pipes. However, little attention is paid to checking the influence of TDA on the behavior of concrete pipes buried under trafficked roads. This research studies this topic using a verified numerical model that considers the three-dimensional nature of traffic load effects. Different road sections were considered in the analyses to cover the effect of the presence of the pavement layer and the effect of the thickness of the base and subbase materials. The results revealed that the presence of TDA decreases the bending moment induced in the pipe wall. However, the TDA performance was found to be remarkably influenced by burial depth, and it increases as the burial depth decreases. Furthermore, the TDA influence for pipes with outer diameters of 1.49 m and 2.89 m is much lower than that of 0.41 m and 0.79 m. Importantly, it was found that the highest reduction in the bending moment was achieved for the 1.0 m burial depth. The results of this research provide insight into the performance of TDA and, thus, will help practitioners make a decision regarding the use of TDA in the routine design of buried concrete pipes.

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

Age-dependent failure probabilities of corroding concrete sewer pipes under traffic loads

Concrete pipes are frequently used in the wastewater infrastructure. These buried structures are prone to ageing and deterioration, as well as damage under excessive stresses from traffic. This study presents the first set of temporal fragility models for underground concrete sewer pipes under the compounding effects of corrosion and truck loads. To address the high computational costs of fragility modeling, Bayesian Additive Regression Trees (BART) – a machine-learning based meta-model – are trained using a high-fidelity computational model of buried concrete pipes. The BART models are subsequently applied to develop age-dependent fragility models for serviceability and collapse of pipes conditional on truck loads. Considered uncertainties include statistically significant concrete and soil properties, truck load, and environmental factors that affect the corrosion of concrete sewer pipes. Results indicate that the direction of traffic stream, the degree of loss of wall thickness due to corrosion, and the maximum allowed truck load are critical factors that must be considered when planning inspection, rehabilitation, and retrofit of this underground infrastructure. According to the results, concrete sewer pipes buried in perpendicular to the direction of traffic flow are more vulnerable than those that are parallel to the direction of traffic flow. The results highlight that the probability of collapse is insignificant when it comes to vehicles weighing less than the design truck weight; however, the probability of collapse significantly increases for the moderate and severe corroded sewer pipes when it comes to the overweight vehicles. The age-dependent fragility models indicate that for sewer pipes buried perpendicular to the direction of traffic stream with service life of less than 25 years, the probability of the first major structural defect is less than 5%. This is also true for sewer pipes that have been in service for less than 45 years if the traffic stream is parallel to the buried pipe. The developed fragility models also constitute a key component of quantitative risk assessment of underground wastewater collection systems.

Sustainable Use of Tire-Derived Aggregate in the Protection of Buried Concrete Pipes under Combined Soil and Traffic Loads

Tire-derived aggregate (TDA) has been used successfully as a backfill soil to reduce the applied stresses on buried steel pipes. The preceding study, however, paid no attention to inspecting the TDA efficiency of buried concrete pipes subjected to soil and traffic loads. In addition, it is not clear how the TDA material, traffic loading, burial depth, and road section affect the pipe-bending moment. Therefore, this paper examines the efficiency of TDA in reducing the bending moment of a 0.6 m concrete pipe subjected to combined soil and traffic loads using a validated three-dimensional finite element model. Two trench configurations have been constructed, the first is composed completely of well graded sand, and the second is similar to the first except for the 150 mm layer on the top of the pipe crown, which is replaced with TDA. Furthermore, three road sections (highway, public road, and unpaved road) have been adopted to provide an intensive understanding of the TDA effect for different road conditions. A parametric study is carried out to detect the effect of the burial depth, road section, and traffic load on the efficiency of the TDA of the buried pipe. It is observed that the TDA has no effect on the bending moment distribution around the pipe. Additionally, the TDA reduces the bending moment developed in the pipe wall with a percentage decrease range between 18% and 42% depending on the burial depth and road section. Furthermore, it is also found that the efficiency of the TDA in reducing the maximum bending moment decreases as the burial depth increases. In addition, the best performance for the TDA is found at a burial depth of 1.0 m for all road sections. Importantly, the best performance for the TDA is found for the highway section compared with the other sections, with a maximum percentage decrease of 42% compared to 27% for the public road section and 26% for the unpaved road section.

Influence of Using Tire-Derived Aggregate on the Structural Performance of Buried Concrete Pipe under Embankment Load

Induced trench method is a well-known technique usually used to reduce the soil pressure applied on buried pipes. This method involves the use of a lightweight compressible material above the buried pipe to increase the positive arching, and thus, to decrease the soil pressure applied on the buried pipe. However, little efforts have been given by previous studies to check the applicability of using tire-derived aggregate (TDA) as the light weight and compressible material in the induced trench method, where it is not clear if the TDA could be used to increase the positive arching for the case of concrete pipes with different diameters and backfill heights. Thus, this paper investigates the effect of using TDA on the structural performance of buried concrete pipes subjected to soil load using a validated three-dimensional finite element model. A sensitivity analysis has been carried out to examine the effect of the configuration of the TDA, backfill height, and pipe diameter on the performance of the TDA in reducing the pipe wall bending moment. It was found that increasing the backfill height decreases the performance of the TDA. Furthermore, increasing the pipe diameter up to 1.2 m increases the TDA performance. However, the performance of the TDA significantly reduces as the diameter increases from 1.2 m to 2.4 m. In addition, it was also observed that the TDA configuration has a remarkable influence on its performance, where it is necessary to place the TDA layer on top of the pipe crown to increase the positive arching. The results reported in this paper provide useful addition to the literature and will help designers to ensure the economic design of buried pipes using recyclable materials.

Investigation of mechanical properties of corroded concrete pipes after cured-in-place-pipe (CIPP) rehabilitation under multi-field coupling

The pipeline is mainly subjected to soil load, fluid load and traffic load, the mechanical properties of corroded concrete pipes after cured-in-place-pipe (CIPP) rehabilitation under multi-field coupling have not been revealed. In this paper, a 3D numerical model of buried concrete pipes after CIPP rehabilitation under the coupled effects of the soil load, traffic load and fluid load were established based on the results of the full-scale test. The influence of cover depth, traffic load and fluid load on the maximum principal stress of the pipeline, vertical displacement of the pipeline, the von Mises stress of the CIPP liner and the circumferential bending moment of pipe-liner composite structure were analyzed. Results showed that the cover depth and traffic load have a greater influence on the crown, invert, and springline of the pipe and has a lesser influence on the shoulder and haunch of the pipe; The stress and the circumferential bending moment of the pipeline is mainly caused by the soil load, the vertical displacement of the pipeline and the von Mises stress of CIPP liner is mainly caused by the traffic load, and the fluid load has little effect on the pipe-liner composite structure.

A coupled hydro-mechanical model for subsurface erosion with analyses of soil piping and void formation

A coupled hydro-mechanical erosion model is presented that is used for studying soil piping and erosion void formation under practical, in-situ conditions. The continuum model treats the soil as a two-phase porous medium composed of a solid phase and a liquid phase, and accounts for its elasto-plastic deformation behaviour caused by frictional sliding and granular compaction. The kinetic law characterizing the erosion process is assumed to have a similar form as the type of threshold law typically used in interfacial erosion models. The numerical implementation of the coupled hydro-mechanical model is based on an incremental-iterative, staggered update scheme. A one-dimensional poro-elastic benchmark problem is used to study the basic features of the hydro-mechanical erosion model and validate its numerical implementation. This problem is further used to reveal the interplay between soil erosion and soil consolidation processes that occur under transient hydro-mechanical conditions, thereby identifying characteristic time scales of these processes for a sandy material. Subsequently, two practical case studies are considered that relate to a sewer system embedded in a sandy soil structure. The first case study treats soil piping caused by suffusion near a sewer system subjected to natural ground water flow, and the second case study considers the formation of a suffosion erosion void under strong ground water flow near a defect sewer pipe. The effects on the erosion profile and the soil deformation behaviour by plasticity phenomena are elucidated by comparing the computational results to those obtained by modelling the constitutive behaviour of the granular material as elastic. The results of this comparison study point out the importance of including an advanced elasto-plastic soil model in the numerical simulation of erosion-driven ground surface deformations and the consequent failure behaviour. The numerical analyses further illustrate that the model realistically predicts the size, location, and characteristic time scale of the generated soil piping and void erosion profiles. Hence, the modelling results may support the early detection of in-situ subsurface erosion phenomena from recorded ground surface deformations. Additionally, the computed erosion profiles may serve as input for a detailed analysis of the local, residual bearing capacity and stress redistribution of buried concrete pipe systems.

Impacts of Extreme Hydrological Events on the Behavior of Buried Stormwater Pipe

AbstractThis study focused on estimating the strength and deformation behavior of buried concrete pipe subjected to heavy rainfall-induced flooding, soil infiltration, leaks from the buried pipe, a...

Full-scale experimental investigation of the mechanical characteristics of corroded buried concrete pipes after cured-in-place-pipe rehabilitation

Cured-in-place pipe (CIPP), the most common approach employed in trenchless sewer rehabilitation technology, has been increasingly used in recent years. To examine the mechanical characteristics of corroded buried concrete pipes after semi-structural rehabilitation of CIPP, a series of full-scale tests was performed. The influence of traffic, surcharge, and fluid loads as well as cover depth on the mechanical properties of the pipe–liner composite structure was analyzed. The following results were obtained. (1) The longitudinal strain of the CIPP liner at the pipe joint is significantly greater than that at the pipe barrel. (2) The cover depth has a greater impact on the circumferential strain and a smaller impact on the longitudinal strain of the pipe-liner composite structure. (3) The above-ground concentrated loads such as surcharge and traffic loads, which will significantly increase the circumferential strain of the pipe-liner composite structure and sharply increase the longitudinal strain of the CIPP liner in shallow cover depth, greatly affect the circumferential and longitudinal strains of the pipe-liner composite structure. (4) The fluid load has little effect on the mechanical properties of the pipe-liner composite structure.

A comparative study of the effect of the soil constitutive model on the seismic response of buried concrete pipes

No attention has been given in previous studies to understand the influence of the sophistication of the soil constitutive model on the response of buried concrete pipes subjected to transverse seismic effect. This research, therefore, has been conducted to address this gap in knowledge by analyzing the behavior of a buried concrete pipe subjected to transverse seismic shake employing the linear elastic (LE) model, elasto-plastic Mohr-Coulomb (MC) model, hardening soil (Hs) model, and hardening soil model with small strain stiffness (Hs small) to provide a benchmark study that helps the designers and the researchers to select the most suitable and less computationally demanding soil constitutive model. The cases of good and poor installation conditions have been considered in the analyses. In addition, numerous earthquake records have been used to allow the consideration of wide range of earthquake intensities to aid general conclusions. It was found that all of the considered constitutive models produce the same trend of the circumferential bending moment (BM) that is developed around the pipe. In general, the maximum BM produced using the LE and MC models is significantly lower than that produced using the Hs and Hs small models with one exception for the LE model for a predominant frequency of 0.66 Hz. Furthermore, the maximum BM produced using the LE and MC models is not sensitive to the increase of the peak ground acceleration (PGA). More importantly, the Hs and Hs small models produce almost similar results with a percentage difference ranges between 1% to 9%. In addition, the Hs and Hs small models show a decrease of the maximum BM as the predominant frequency rises and an increase of the maximum BM as the PGA rises.

Effect of Bedding Compaction on the Behavior of Buried Plain Concrete Pipes

Plain Concrete pipes serve as effective underground infrastructure lines especially as sewer lines and culverts. The installation quality has a high effect on the performance of the buried pipe-soil system besides the pipe material strength. In this research, experimental investigation of buried plain concrete pipes installed in gravelly-sand soil and subjected to strip loading platform as surface loading to search the effect of the bedding compaction on the pipe. Granular soil bedding is a traditional material surrounding concrete pipes. An experimental testing program for two precast plain concrete pipes has 300 mm inner diameter was conducted in a laboratory soil box test facility. Loading on a pipes-soil system were applied up to collapse. Circumferential strain in pipes was measured by means of strain gauges in addition to the measurements of displacement developed in the vertical direction by means of a linear variable differential transformer (LVDT’s) and dials gauges. It is concluded that in case of loose bedding, a higher bedding factor of 1.83 is produced in comparison with dense bedding which produces a bedding factor of 1.49, thus yields that the quality of installation is improved with relatively loose bedding under the pipe.

A high-fidelity computational investigation of buried concrete sewer pipes exposed to truckloads and corrosion deterioration

As wastewater systems are reaching critical levels of aging and deterioration, simulation of realistic pipe behaviors is ever more needed to analyze and manage the associated risks. Developing such models is challenging, in part due to the complexity of aging and deterioration impacts on the structural and functional performance of pipes. This study investigates the impacts of a number of design and uncertain variables on the serviceability performance of concrete sewer pipes throughout their service life. This is facilitated by a high-fidelity three-dimensional Finite Element (FE) model of concrete sewer pipes, surrounding soil, and pavement layers in ANSYS platform. The FE model is capable of capturing nonlinear behaviors of concrete, soil, and pipe-soil interactions, in addition to simulating crack formation and crushing of concrete pipes. Corrosion impacts are simulated by sequentially removing concrete layers inside the pipe so that corrosion effects from previous years are taken into account. The influence of linear versus nonlinear assumptions for soil and pipe-soil interactions on the performance of the pipes especially crack width are investigated for cases where the models are subjected to external truckloads. Moreover, impacts of most common trench installations in terms of bedding, side-fill configuration, and soil properties are analyzed for the entire service life of the pipe. Results reveal that the soil surrounding the pipe needs to be modeled as a nonlinear material regardless of the soil grain size. It was observed that the error associated with modeling soil and soil-pipe interactions as linear increases as the pipe ages and the extent of corrosion increases. Results of this investigation can guide the development of reliable and computationally efficient numerical models for deteriorating underground concrete sewer pipes.

Significant variables for leakage and collapse of buried concrete sewer pipes: a global sensitivity analysis via Bayesian additive regression trees and Sobol’ indices

Identifying key variables that influence crack formation in buried concrete sewer pipes and impact their structural integrity is crucial for evaluating the leakage and collapse vulnerability of these underground structures. The present study performs a comprehensive global sensitivity analysis for these critical pipe responses considering various uncertainties associated with material properties and loading. A high-fidelity three-dimensional nonlinear Finite Element (FE) model of a typical pipe is developed and used to capture pipe behavior. Considering the significantly high computational demand of the generated FE model, a surrogate model using Bayesian Additive Regression Trees (BART) is developed to accurately approximate input-output relationships in this high-dimensional problem. Significant variables are subsequently determined via a global sensitivity analysis based on Sobol’s theorem through the application of Markov Chain Monte Carlo simulation to the trained BART model. Results indicate that concrete and backfill soil properties and variables associated with truckloads contribute significantly to the variation of key pipe responses, thereby affecting the likelihood of leakage and collapse. Findings of this study can benefit the design and management of sewer pipes in large wastewater networks and significantly reduce the complexity of assessing the reliability of sewer pipes.

New insights from the Ölfus case study concerning the seismic performance of buried concrete wastewater pipes in the vicinity of a severe earthquake

The correlation of earthquake damage to underground wastewater (sewage and drainage) pipelines and measured intensity measurements is described in this paper. The study is based on pipelines consisting primarily of segmented concrete pipes in Hveragerði, Iceland. This town experienced a Mw 6.3 earthquake on 29 May 2008, originated in its near field. Subsequently, the interior conditions of all the pipelines were thoroughly investigated by a robot camera. All the pipeline damage detected was analysed and documented. While damage in segmented pipelines is assumed to occur primarily at the joints due to axial ground strains, the predominant damage in Hveragerði was circular cracks at the centre zone of the pipe barrels. This suggests that (1) ground curvature plays a greater role in the seismic response of the pipelines, and (2) the stiffness and strength of the pipe barrel should be considered in a seismic analysis. The pipe damage observed in the sewage lines, close to the engineering bedrock, was half as much as the damage observed in the drainage lines resting on a thicker backfill material. A relationship between non-minor damage rates and the intensity measurements was observed for the drainage pipeline only, where the best overall correlation results were obtained for peak ground velocity. The commonly used fragility curves greatly underestimate the damage rate observed in the study area. This may apply to the potable water systems, where the majority of segmented pipelines consist of brittle pipes of cast iron, asbestos or concrete (HAZUS, NIBS 2003).

Multi‐sensors in‐line inspection robot for pipe flaws detection

In-line inspection (ILI) robot has been considered as an inevitable requirement to perform non-destructive testing methods efficiently and economically. The detection of flaws that could lead to leakages in buried concrete pipes has been an area of great concern to the oil and gas industry and water resource-based industry. The major problem is the difficulty in modelling the detection of cracks as a result of its irregularity and randomness that cannot be easily detected. This work covers the study of defect detection of non-destructive testing methods using fusion inspect sensors, light detection and ranging, and optic sensors. Studies on ILI robots are also reviewed to construct an efficient gauge. Nevertheless, the study on current support vector machine (SVM) technique is centred as the main classification engine for the combined sensory data. The prototype robot has been designed and successfully operated in a lab-scale environment. Intuitively, the obtained data described the status of inspected pipe clearly. Sensors from the proposed list also well integrated as attaching to the robot. The experiments with SVM techniques to evaluate the feasibility of defects detection also achieved remarkable results.

Dynamic analysis of concrete pipes under the coupled effects of traffic load and groundwater level fluctuations

AbstractFluctuations in the groundwater level make the working conditions of concrete pipes below the groundwater level more complex than those of concrete pipes above the groundwater level. This paper describes the application of a three‐dimensional (3‐D) refined finite element (FE) model to the analysis of a buried concrete pipe subjected to the coupled effects of traffic load and groundwater level fluctuations. First, the dynamic responses of the concrete pipes buried in dry soil were investigated with a full‐scale test and an FE model. The results show that the FE model predicted results similar to those observed in field pipes. Then, the dynamic responses based on the numerical results of pipes buried in dry soil under a traffic load and those of pipes buried in saturated soil under the coupled effects of a traffic load and groundwater level fluctuations were compared. Finally, a parametric analysis of the effects of the void ratio, permeability coefficient, and fluctuation period in the groundwater level in relation to the dynamic responses of the pipes was conducted. The results show that the mechanical behaviors of the pipes in dry soil were substantially different from those of pipes in saturated soil. Compared with pipes in dry soil under a traffic load, the stresses at the crown, springline, and invert of the bell under the coupled effects of the traffic load and groundwater level fluctuations were lowered by 44.8%, 52.0%, and 50.3%, respectively, while those of the spigot were lowered by 42.0%, 50.3%, and 49.6%, respectively. The maximum principal stress and the vertical displacement were proportional to the void ratio and the permeability coefficient, while their relationship to the groundwater level fluctuation period was less straightforward.

Seismic response and design of buried concrete pipes subjected to soil loads

Concrete pipes are a crucial element in sustaining contemporary life because they afford appropriate means to transport drinking water, sewage, and storm water. Thus, these useful assets must be designed correctly. The current methodology to design these assets is based on factors called the bedding factors; these factors have been developed considering only static loads. Evidences from previous studies showed that buried structures, including concrete pipes, are vulnerable to failure due to seismic shake. However, no study has been found in the literature to address the response and the design of buried concrete pipes subjected to seismic shake. Thus, this research aims to study the seismic response and seismic design of underground concrete pipe subjected to soil loads. The combined influence of the seismic shake and diameter of pipe, burial depth, installation condition, and intensity of the seismic shake have been studied using a carefully developed finite element model. The results showed that the seismic shake noticeably rises the maximum bending moment; however, the percentage increase remarkably influenced by the diameter of the pipe and the burial depth. Furthermore, the percentage rise of the maximum bending moment declines as the installation quality becomes poorer. The results also showed that the maximum bending moment rises nonlinearly as the acceleration rises. Comparisons with the current AASHTO bedding factors illustrated that these factors either conservative or unsafe. The reasons for these inaccuracies in the current design bedding factors have been discussed and novel equations to predict bedding factors that consider the seismic shake have been derived using novel intelligent data mining technique. The accuracy of the proposed equations has been demonstrated and thus, these equations can be used by practitioners/designers to implicate the effect of seismic shake in the design of buried concrete pipes.

Finite element analysis for deeply buried concrete pipes in proposed imperfect trench installations with expanded polystyrene (EPS) foams

The objective of this study was to evaluate the performance of imperfect trench installations incorporating a soft material zone for buried concrete pipes. Traditionally, imperfect trench installations locate highly compressible lightweight materials such as expanded polystyrene foams, baled hay or straw above buried pipes in order to induce positive soil arching without trenches and hence reduce vertical top pressure and horizontal pressure. However, bottom pressure is not significantly reduced due to the additional downward shearing forces induced by transferring top pressure to the adjacent sides. Previous FE models that take account of plane strain elements suggest that soft zones surrounding pipes can markedly reduce bottom pressure, as well as the top and lateral pressures, but these models have not yet been validated by field tests and there have also been difficulties in evaluating the longitudinal behaviors of pipes. This study revisited the proposed use of soft zones using three-dimensional finite element analyses and validated the modeling methodologies using Valsangkar’s field tests. The results confirm that soft zones are a highly effective way to reduce the surrounding pressures on deeply buried concrete pipes, and the new finite element models presented here successfully overcome the limitations of the previous plane strain approach.