Effect of soil parameter uncertainty on seismic response of buried segmented pipeline

Pipelines are important lifeline facilities spread over a large area and they generally encounter a range of seismic hazards and different soil conditions. The seismic response of a buried segmented pipe depends on various parameters such as the type of buried pipe material and joints, end restraint conditions, soil characteristics, burial depths, and earthquake ground motion, etc. This study highlights the effect of the variation of geotechnical properties of the surrounding soil on seismic response of a buried pipeline. The variations of the properties of the surrounding soil along the pipe are described by sampling them from predefined probability distribution. The soil-pipe interaction model is developed in OpenSEES. Nonlinear earthquake time-history analysis is performed to study the effect of soil parameters variability on the response of pipeline. Based on the results, it is found that uncertainty in soil parameters may result in significant response variability of the pipeline

Elastoplastic indentation of unsaturated soils using a rigid cylinder

We develop a fully coupled finite element solution for elastoplastic indentations of unsaturated granular soils by a rigid cylinder by using a mortar-type contact algorithm. In the presented solution, we have employed an advanced constitutive model that allows the inclusion of the effect of matric suction and induced anisotropy in the problem. Several numerical examples in both static and dynamic scenarios are provided for validation and demonstrating the capabilities of the presented framework

Numerical modelling of sandstone uniaxial compression test using a mix-mode cohesive fracture model

A mix-mode cohesive fracture model considering tension, compression and shear material behaviour is presented, which has wide applications to geotechnical problems. The model considers both elastic and inelastic displacements. Inelastic displacement comprises fracture and plastic displacements. The norm of inelastic displacement is used to control the fracture behaviour. Meantime, a failure function describing the fracture strength is proposed. Using the internal programming FISH, the cohesive fracture model is programmed into a hybrid distinct element algorithm as encoded in Universal Distinct Element Code (UDEC). The model is verified through uniaxial tension and direct shear tests. The developed model is then applied to model the behaviour of a uniaxial compression test on Gosford sandstone. The modelling results indicate that the proposed cohesive fracture model is capable of simulating combined failure behaviour applicable to rock

Response of a plastic pipe buried in expansive clay

Failure of buried pipes due to reactive soil movement (e.g. shrinking/swelling) is a common problem for water and gas pipe networks in Australia and the world. Soil movement is closely related to seasonal climatic change, and particularly to the moisture content of soil. Although some research has been carried out to understand the effect of freezing and thawing of soils and temperature effects in colder climates, very limited research has been undertaken to examine the possible failure mechanisms of pipes buried in reactive soils. This study reports the responses of a 2 m long polyethylene pipe buried in reactive clay in a box under laboratory conditions. The soil and pipe movements were measured as the soil was wetted from the bottom of the box. It was observed that the pipe underwent substantial deformation as the soil swelled with increase of the moisture content. The results are explained with a simplified numerical analysis

Experimental modelling of coupled water flow and associated movements in swelling soils

Modelling of water flow and associated deformation in unsaturated reactive soils (shrinking/swelling soils) is important in many applications. The current paper presents a method to capture soil swelling deformation during water infiltration using Particle Image Velocimetry (PIV). The model soil material used is a commercially available bentonite. A swelling chamber was setup to determine the water content profile and extent of soil swelling. The test was run for 61 days, and during this time period, the soil underwent on average across its width swelling of about 26% of the height of the soil column. PIV analysis was able to determine the amount of swelling that occurred within the entire face of the soil box that was used for observations. The swelling was most apparent in the top layers with strains in most cases over 100%

Desiccation cracking in clayey soils: mechanisms and modelling

This paper presents a summary of the work undertaken on desiccation cracking in soils with special reference to the work undertaken by the authors and co-workers at Monash University. All areas of historical field observations, laboratory modelling and identified mechanisms are discussed briefly. Analytical and numerical approaches for modelling of the desiccation cracking and process are discussed. Cohesive crack approach is presented as a viable approach for modelling of desiccation cracking and fracture evolution catering for consistency change of soil during desiccation. It is highlighted that both tensile strength and crack opening displacement increases, thereby increasing the fracture energy of the soil as the moisture content reduces. This modelling approach can be extended to model wetting/drying cycles and to model crack dynamics. Associated moisture transfer modelling also needs to be advanced for a complete solution

Interpretation of the loading/wetting behaviour of compacted soils within the MPK framework: Part I Static compaction

Depending on the state paths, loading/wetting of compacted unsaturated soils can exhibit complex volumetric behaviour such as swelling, collapse, collapse followed by swelling, swelling followed by collapse, and swelling pressure development. Microscopically, these behaviours arise from complex interactions among applied stresses, air-water pressure deficit or suction at the water menisci, moisture content or degree of saturation in the voids and the nature of the micro- and macro-soil aggregates of compacted soils that depend on the level of suction (Alonso et al., 1999). While significant advances have been made in modelling the hydromechanical behaviour of compacted unsaturated soils taking these interactions into account, input parameter determination requires advanced testing equipment and the testing processes can be very time-consuming. Recently, a relatively simple and practical framework within the void ratio-moisture ratio (volume of water/volume of solids)-net stress space (referred to as the MPK framework) was proposed by Kodikara (2012) to explain/predict these state paths. A desirable feature of this framework is that it identifies a direct link between the well-known compaction curve and the compacted soil constitutive behaviour. The current paper presents a comprehensive series of tests on statically-compacted soils, the results of which are in close agreement with this framework. Two soil types, namely lightly reactive kaolin and more reactive clay, referred to as Merri Creek soil, were used in the testing. The soils were prepared with different moisture contents from the dry state and statically compacted at constant water content to obtain void ratio-moisture ratio-net stress constitutive surfaces, as well as soil specimens for state path tests. The state path test results of yielding under loading, collapse under wetting, swelling pressure development and change in yield pressure due to wetting are explained within this framework. In addition, some published data on a silty soil mixture were also analysed, highlighting that the framework is valid, regardless of the degree of reactivity of the soil. Suction was not measured in the authors’ experiments, as it was not required to explain the above state paths according to this framework. However, it is recognised that suction is the conjugate state variable to the moisture content. Therefore, in future experiments, suction will be measured and its role will be fully explained within the framework, adding more generality.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Numerical analysis of an experimental pipe buried in swelling soil

This paper investigates the pipe-soil interaction for pipes buried in expansive soil when subjected to swelling soil movement due to increase in moisture content. A laboratory experiment has been undertaken on a plastic pipe in a large-scale pipe box. A three dimensional numerical model is developed to analyse the pipe response, using FLAC(3D) computer program. The pipe is assumed to behave as a linearly elastic material, while the soil is modelled as a nonlinear material with Mohr-Coulomb failure criterion. The water flow and soil/pipe deformations are decoupled, where water flow is calculated using simplified capillary rise theory on the basis of measurements made. A reasonably good agreement between the experimental results and model predictions is reported

Shrinkage development during soil desiccation

Clayey soils undergo shrinkage during desiccation. When shrinkage is restrained by the boundary conditions or by internal stresses, tensile stresses are generated within the soil body. These stresses eventually produce tension crackswhich create problematic situations in many engineering applications. Presence of shrinkage cracks is significant in many applications such as earth embankments, landfill clay liners, foundations, and road pavements. Desiccation or thermally induced induced shrinkage cracks cause problems in other disciplines as well, for example in mining engineering, agricultural engineering and materials engineering. It is important to understand the shrinking behavior of soil in order to study the desiccation crack development in clayey soils. Free shrinkage of slurry clay was observed in laboratory experiments. Image analysis, along with Particle Image Velocimetry (PIV) technique was used to analyze the data obtained. Relatively small specimens 100 mm longwere used so that strains could be measured to high accuracy.Werribee clay, an expansive clay found in West Melbourne, was used in the experiments. Basic clay properties include liquid limit of 127%, plasticity index of 101 and linear shrinkage of 22%. This paper discusses the relationship between strains (vertical, horizontal, and volumetric), displacements, water content, degree of saturation and void ratio. Shrinkage strain development prior to crack initiation was examined to identify crack failure condition

Investigation of desiccation cracking using automated digital photography

Desiccation cracking can be heavily detrimental on the performance of clay soils in various engineering applications. Typical engineering applications include compacted clay barriers in waste containment, dam cores, canal liners and road pavements. The evolution of desiccation cracks has not been clearly understood and explained. A series of laboratory tests were conducted using Merri-Creek clay and potato starch. The evolution of cracks was captured by automated digital photography and presented in a time-lapse video format similar to the phenomenon of a blooming flower. To the authors’ knowledge, this is the first time such a video has been produced. Both simultaneous and sequential types of cracking are investigated. The relationship between desiccation rate, average cell area, thickness of the specimen and etc are examined and discussed