Dilan Robert

Pipelines Subjected to Fault Movement in Dry and Unsaturated Soils

Because pipelines traverse large geographical areas, they frequently must cross active faults when constructed in locations vulnerable to earthquakes. In this study, the authors performed three-dimensional (3D) finite-element analyses to investigate the behavior of buried pipe subject to strike-slip fault movement in dry sand and, more realistically, in partially saturated sand. The performance of the finite-element model was first validated by comparing the computed results with the data from the full-scale experiments at Cornell University. The analysis was then extended by varying the initial conditions of the sand (e.g., sand type, density, moisture content), pipe material, pipe burial depth, and pipeline–fault-rupture inclination to assess the effect of these parameters on the soil loads applied to the pipe and the corresponding deformations. On the basis of the simulation results, the authors propose a soil–structure interaction mechanism for pipelines crossing active faults. The authors also propose design recommendations for the mitigation of ground-deformation effects at buried pipeline crossings of strike-slip faults.

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

This study investigates the interaction between soil and pipeline in sand subjected to lateral ground displacements with emphasis on the peak force exerted to a bended elbow-pipe. A series of three-dimensional (3D) finite-element (FE) analyses were performed in both opening and closing modes of the elbow section for different initial pipe bending angles. To model the mechanical behavior of sands, two soil models were adopted: Mohr-Coulomb and Nor-Sand soil model. Investigations also included the effects of pipe embedment depth and soil density. Results show that the opening mode exhibits higher ultimate forces and greater localized deformations than the closing mode. Nondimensional charts that account for pipeline location, bending angle, and soil density are developed. Soil-spring pipeline analyses of an elbow-pipe were performed using modified F-δ soil-spring models based on the 3D FE results and were compared to the findings of conventional spring model analyses using the standard two-dimensional soil-...

Experimental evaluation of bursting capacity of corroded grey cast iron water pipeline

Abstract Cast iron was used in the water industry prior to 1970 and a large number of cast iron pipes still remain as trunk mains. These pipes have been subjected to different levels of corrosion and variety of loading conditions. This leads cast iron pipes to fail in the field without prior warning. Water utilities are seeking solutions to optimise cast iron pipe renewal and rehabilitation programs for critical water mains (diameter ≥ 300 mm). A new experimental set-up has been developed at Monash University in order to perform burst testing of large diameter cast iron pipes (diameter ≥ 300 mm). A section of cast iron pipe, extracted during maintenance in Sydney, was laser scanned to determine the remaining thickness of the pipe (minimum of 7–8 mm at the most critical patches). Although the pipe was pressurised to 3.6 MPa, catastrophic failure did not occur. Water leakage from the two critically corroded patches was observed at around 3.25–3.45 MPa internal pressure. Strain results on the outer pipe surface were greater than the strain measured during tensile testing of the same pipe material. A 3-D finite element model using the scanned pipe dimensions was able to predict the maximum pressure at pipe failure (~3.7 MPa) within the range of leaking water pressure level observed in the experiment.

Modeling the Stress-Dilatancy Relationship of Unsaturated Silica Sand in Triaxial Compression Tests

AbstractIt is well known that partial saturation increases the shear strength and dilatancy of unsaturated sand. However, little research has been carried out on the actual stress-dilatancy relationship. This paper shows that the increase in peak shear strength caused by partial saturation is consistent with an increase in dilatancy, and that conventional stress-dilatancy theories are still valid for unsaturated sand. The use of state indexes as a proxy for dilatancy were investigated and extended to unsaturated sands. Additionally, these indexes can be used to establish a critical state line that is based on material properties only. The validity of the stress-dilatancy theories and the use of state indexes offer simplicity in modeling the shear behavior of unsaturated sand. This will be demonstrated in this paper with the Nor-Sand model, with which the wetting collapse can be explained as a consequence of a loss of dilatancy characteristics.

Contribution of Cement Mortar Lining to Structural Capacity of Cast Iron Water Mains

Cast iron water mains represent a significant component of the water pipe networks in many cities across Australia. Such pipes are usually furnished with an internal cement mortar lining, mainly to act as a physical barrier to flowing liquids to reduce internal corrosion and to reduce energy losses. Although the lining is not intended to resist internal and external loadings to the pipe, recent observations of corroded cast iron water mains showed that the cement lining can withstand some internal water pressure on its own. This reveals that the lining may contribute to the structural capacity of deteriorated pipes, although the level of this contribu- tion is unknown. This paper investigates the likely contribution of cement lining to the structural capacity of deteriorated pipes. This research is undertaken through numerical modeling of pipe-liner- soil interactions. The properties of cement linings were obtained by testing actual specimens obtained from field pipes and casting simulated lining specimens of cement-sand mixtures. The study revealed that, depending on the level of pipe corrosion, cement lining can reduce pipe stress by as much as 5 to 12% or 10 to 25% if the lining tensile strength is 1 or 4 MPa (145 or 580 psi), respectively.

Degradation Prediction of Rail Tracks: A Review of the Existing Literature

In the past few decades, the railway infrastructure has been widely expanded in urban and rural areas, making it the most complex matrix of rail transport networks. Safe and comfortable travel on railways has always been a common goal for transportation engineers and researchers, and requires railways in excellent condition and well-organized maintenance practices. Degradation of rail tracks is a main concern for railway organizations as it affects the railways behaviour and its parameters, such as track geometry, speed, traffic and loads. Therefore, the prediction of the degradation of rail tracks is very important in order to optimise maintenance needs, reduce maintenance and operational costs of railways, and improve rail track conditions. This paper provides a comprehensive review of rail degradation prediction models, their parameters, and the strengths and weaknesses of each model. A comprehensive discussion of existing research and a comparison of different models of degradation of rail tracks is also provided. Finally, this review presents concluding remarks on the limitations of existing studies and provides recommendations for further research and appraisal practices.

Behaviour of unsealed stabilized road pavements using non-linear strength model

Applications of soil stabilization in unsealed road pavements are increasing being applied in Australia and worldwide. These include using standard stabilizers such as cement, flyash, polymers, resins, acids, as well as using non-standard stabilizers in the forms of enzymes. The pavement designs based on such stabilizers are predominantly based on either project experience or site specific laboratory and/or field tests based properties. The behaviour of the underlying materials, in particular partial saturation and non-linear nature, is often neglected for simplicity in the design approaches which are currently in-place. The current research investigates the behaviour of unsealed roads subjected to operational traffic using the unsaturated Coulomb-strength model. Firstly, laboratory experiments were conducted on the basis of clay soil to investigate the stabilized and non-stabilized strength properties. Having calibrated the model, 3-D FE analyses were conducted to predict the response of unsealed road pavement under traffic loads. The results showed that the response of stabilized road pavements using realistic non-linear strength envelop is substantially different from the traditional pavement response predictions. Thus, it is required to adopt partial saturation and soil non-linearity for more realistic assessments of stabilization contribution during design than are currently used.

Uplift Resistance and Mobilization of Buried Pipelines in Unsaturated Sands

Pipelines are commonly buried in depth of 1m to 2m in which the soil condition is most often partially saturated. However, the conventional design guidelines and available analytical models for predicting the uplift resistance and mobilization are based on assumption that the soil is either dry or fully saturated. In unsaturated soils, such an assumption often leads to under-estimate of uplift resistance and over-estimation of uplift mobilization. Enhanced strength and stiffness of unsaturated soils due to suction can increase the uplift resistance along with substantially different peak mobilizations as compared to tradition estimations. This can lead to under or over-estimation of remedial measures during feasibility/design stage, thus false bidding/project estimations. This paper examines the effect of partial saturation on the peak uplift resistance and mobilization of pipelines buried in sandy soils using numerical modelling. Two-dimensional finite element (FE) analyses were conducted on the basis of steel pipeline buried in unsaturated finer sand behaviour of which was modelled using modified Mohr-Coulomb model. Firstly, the numerical model was validated against the reported full scale test data, and then the analyses were extended for various pipe sizes, cover heights and degree of saturations of sands. Results showed that the peak-mobilization can be significantly different than that suggested by current guidelines, and strongly depend on the factors considered in the current study.