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During pipe bursting, a cone shaped expander is pulled through an existing pipe, breaking it, enlarging the cavity, and pulling a replacement pipe into place. The expansion of the soil cavity and axial movements of the burst head cause ground disturbance, and infrastructure such as other buried pipelines and overlying pavements may be damaged. Pipe bursting involves a complex three dimensional response of the ground surrounding the old pipe. A three dimensional numerical study has therefore been undertaken to explicitly simulate propagation of the burst head, and study the response of soil and adjacent pipelines in detail. A description of the ABAQUS modeling is presented, focusing on the analysis of pipe bursting experiments conducted using the buried infrastructure test facilities at Queen’s. The ground surface deformations, pulling forces and strains on an adjacent polyvinyl chloride pipe were computed and compared with experimental observations. On average, the computed results differ by 20% compared to experimental values. In addition, the stress and strain responses of soil were analyzed to explain the failure mechanism of soil during progression of the burst head. A parametric study was conducted by changing the burial depths, expansion ratios, trench widths, and material properties to provide a general guideline for ground movements during pipe bursting. The analysis was further extended by changing the positions (under, over, beside) and orientations (perpendicular or parallel) of adjacent pipelines with respect to the pipe being replaced. Use of the parametric study was illustrated and evaluated using a large scale pipe bursting test. The computed results are about 20% conservative compared to the experimental values of peak vertical deformations and peak longitudinal strains of adjacent pipe. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2013-02-24 16:18:16.482

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No description available.

För att förnya och förbättra den spårbundna trafiken inom Sverige är stambanor för höghastighetståg ett alternativ som utreds då det skulle innebära förkortade transporttider både för person- och godstrafik. Innan höghastighetsbanor kan etableras i Sverige finns det många faktorer som måste utredas. Eftersom tågen går med betydligt högre hastigheter än de tåg som redan används blir känsligheten för problem som kan uppstå i undergrunden betydligt högre och toleransen för sättningar och tjällyft är i princip lika med noll. På grund av klimatet som råder i Sverige finns det mycket att reda ut angående tjälproblematiken. Förutom låga temperaturer och vatten i jorden kan en trumma påverka hur tjälen utvecklas i järnvägsbanken. I den här studien analyseras påverkan som en trumma i järnvägsbanken har på tjälutvecklingen. Inverkan har analyserats utifrån ett tvärsnitt inuti järnvägsbanken för två olika köldmängder, -500 graddagar och -1300 graddagar. Innertemperaturen i trumman har antagits variera längs med trummans längd. Temperaturen har varierats inne i trumman att vara från 10 % upp till 75 % av köldmängden i uteluften. Förutom att analysera hur olika temperaturer påverkar tjälutvecklingen har den mängd material som behöver schaktas bort och ersättas med ett isoleringsmaterial för att förhindra att tjälproblem uppstår beräknats. Oberoende av trummans storlek och temperatur kommer trumman inte att kunna placeras direkt på terrassnivån utan att tjälfronten når det tjälfarliga materialet och risk för att tjälproblem ska uppstå. När temperaturen inne i trumman är 75% av köldmängden utomhus, och därmed nära temperaturen utomhus, blir tjälfronten även brantare än för lägre innertemperaturer. En brant tjälfront kan inducera större och mer ojämna tjällyft. För att undvika att problem uppstår måste ett isoleringslager av ett tjälpassivt material anläggas. Mängden material som måste ersättas ökar med trumdiameter och ökar betydligt beroende på om temperaturen inne i trumman är 10% eller 75% av utomhusköldmängden. Exempelvis ökar mängden under en trumma med 30 centimeters diameter från 1 m3 till 35,5 m3 respektive från 10,1 m3 till 58,4 m3 för en 150 centimeters diameter. Ökade mängder medför högre kostnader i både material och transporter, vilket är något som tillsammans med övriga faktorer senare måste analyseras vidare för att få mer kunskap och underlag inför en möjlig etablering av höghastighetsbanor.

Suffusion, also called internal instability, is an internal erosion mechanism that occurs in embankment dams when fine-grained particles are washed out of the core soil matrix by seepage. Initiation of internal erosion depends mainly on three major factors: grain size distribution of the soil, stress conditions and hydraulic load; whilst its continuation depends of the filter properties. Broadly graded moraines, as glacial tills, are more susceptible to internal erosion by suffusion than other types of soils used in dams. Most embankment dams in Sweden consist of a central core of glacial till built more than 50 years ago. At the time of its construction, the available guidelines did not include specific grain size boundaries for the core and the filter related to internal erosion susceptibility. Today, several Swedish embankment dams have experienced incident of internal erosion such as leakages and sinkholes, making internal erosion an important safety issue. This circumstance allows raising the questions: How safe are the Swedish embankment dams and what conditions are needed for internal erosion by suffusion to initiate? This research aims to contribute to the assessment of dam safety by giving inputs regarding the characterization of internal erosion by suffusion and the relation among the main factors involved on its occurrence (geotechnical characteristics of soil material, degree of compaction and hydraulic load). This in order to increase the knowledge regarding the critical hydraulic gradient needed to develop suffusion in a given till material with a known degree of compaction. The research includes a laboratory program consistent on suffusion tests, which is an extension of the standard permeability test, and considers post-test examination and diagnosis of the samples. Two main groups of tests were performed: small and large suffusion tests. The small tests serve as a reference of the expected behaviour of soil samples under different boundary and test conditions, which allows optimizing the number of test to be performed in large tests. Results show that suffusion mechanism can be classified as internal suffusion (or filtration) and external suffusion (loss of soil particles from the soil matrix). The influence of compaction degree on the initiation of suffusion is limited in internally stable soils. However, poorly compacted specimens exposed to high hydraulic gradients could develop both internal and external suffusion if the filter is not capable to retain the eroded particles. The hydraulic conductivity of specimens with internal suffusion tends to decrease with a step wise increase of the hydraulic gradient. Such tendency is the result of the matrix of soil reaching equilibrium with the new seepage stresses. The hydraulic conductivity of specimens with external suffusion tends to increase with the increase of the hydraulic gradient.

Granular materials have a “discrete” nature whose global mechanical behaviors are originated from the grain scale micromechanical mechanisms. The intriguing properties and non-trivial behaviors of a granular material pose formidable challenges to the multiscale modeling of these materials. Some of the key challenges include upscaling of coarse-scale continuum equation form fine-scale governing equations, calibrating material parameters at different scales, alleviating pathological mesh dependency in continuum models, and generating unit cells with versatile morphological details. This dissertation aims to addressing the aforementioned challenges and to investigate the mechanical behavior of granular materials through multiscale modeling. Firstly, a three-dimensional nonlocal multiscale discrete-continuum model is presented for modeling the mechanical behavior of granular materials. We establish an information-passing coupling scheme between DEM that explicitly replicates granular motion of individual particles and a finite element continuum model, which captures nonlocal overall response of the granular assemblies. Secondly, a new staggered multilevel material identification procedure is developed for phenomenological critical state plasticity models. The emphasis is placed on cases in which available experimental data and constraints are insufficient for calibration. The key idea is to create a secondary virtual experimental database from high-fidelity models, such as discrete element simulations, then merge both the actual experimental data and secondary database as an extended digital database to determine material parameters for the phenomenological macroscopic critical state plasticity model. This expansion of database provides additional constraints necessary for calibration of the phenomenological critical state plasticity models. Thirdly, a regularized phenomenological multiscale model is investigated, in which elastic properties are computed using direct homogenization and subsequently evolved using a simple three-parameter orthotropic continuum damage model. The salient feature of the model is a unified regularization framework based on the concept of effective softening strain. The unified regularization scheme is employed in the context of constitutive law rescaling and the staggered nonlocal approach to alleviate pathological mesh dependency. Lastly, a robust parametric model is presented for generating unit cells with randomly distributed inclusions. The proposed model is computationally efficient using a hierarchy of algorithms with increasing computational complexity, and is able to generate unit cells with different inclusion shapes.

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This thesis describes research efforts toward the development of a wireless sensor node, which can be employed in durable and expandable wireless sensor networks for remote monitoring of soil conditions in areas conducive to slope stability failures. Commercially available soil moisture probes and soil tilt sensors were combined with low-power, wireless data transmitters to form a self-configuring network of soil monitoring sensors. The remote locations of many slope stability hazard sites eliminates the possibility of real-time, remote monitoring instrumentation that relies on AC power or land-based communication methods for operation and data transfer. Therefore, various power supply solutions and data transfer methods were explored during this research and are described herein. Additionally, sensor modification and calibrations are discussed. Preliminary evaluations of field durability of the pilot instrumentation were undertaken during this research. Geotechnical engineering instrumentation must be able to withstand extreme weather related conditions. The wireless, solar-powered soil moisture and tilt sensor node was installed on the Texas A&M University campus, allowing evaluation of system reliability and instrument durability. Lastly, potential future research and conclusions arising from this research are presented. This research has shown that commercially available wireless instrumentation can be modified for use in geotechnical applications. The development of an active power management system allows for sensors to be placed in remote locations and operated indefinitely, thus creating another option for monitoring applications in geotechnical and environmental problems.