Now showing 1 - 10 of 10
  • Publication
    Considerations for a District-Level, Tunnel-Risk, Screening Tool
    (Society for Mining, Metallurgy, and Exploration (SME), 2016-04-28) ;
    To more rigorously address tunneling risks to above-ground structures, vulnerability evaluation of all structures along a tunnel route is required. This multi-block area along the route can be considered a district. To fully assess each structure within a tunnel’s zone of influence, a multi-block or district-level model may provide new insights as to risk evaluation and mitigation strategies. However populating such a model with the existing geometry of the built environment poses a major challenge as measured drawings are not readily available for all structures along a tunnel’s route. Cost-effective population of such a model could arguably involve remote sensing data in the form of laser scanning or photogrammetry. However even for unreinforced masonry structures, where external, above-ground geometries can be captured, without a prohibitively expensive building-by-building, in person survey many factors would remain unknown. To consider these uncertainties in an automatic way, a performance assessment framework is proposed. Such a framework allows a more rigorous, initial, risk quantification than is currently possible within the simple empirical models generally being used in industry when tunneling risk is initially assessed. This paper introduces (within the allowable space limits of this format) considerations for auto-population and application of a district-level, tunnel-risk screening tool.
      376
  • Publication
    Steps toward a probabilistic framework for tunnelling damage
    Globally, the high rates of urbanization over the past century have spurred unprecedented levels of tunnel construction. With each tunnel installation, there is a large affiliated risk for damage to aboveground structures, especially those of unreinforced masonry. Such damage (and the subsequent costs and litigation) occur, despite huge sums committed to construction monitoring and pre-tunnel mitigation. Arguably, damage still happens because the wide range of parameters and the extent of their variability are not sufficiently considered in the risk assessment process. To address these uncertainties, a probabilistic framework for the large-scale risk assessment of existing, unreinforced masonry buildings subjected to bored tunnelling is proposed by the Urban Modelling Group (UMG) at the University College Dublin (UCD). This paper summarizes the initial steps needed to achieve such a framework.
      360
  • Publication
    Structural Reliability Analysis of NATM Tunnel Face Stability in Soft Ground
    (CIR Publishing, 2013-03-20) ;
    In spite of enhancement in modeling techniques as well as site investigation methods, uncertainty exists seriously in the process of construction of underground structure in soft soils. These uncertainties arise from limited data of geological data, measurement errors, interpolation of spatially geological properties, and extrapolation of results of experiments and natural analogue studies over times and conditions relevant to the project. Robust and optimize design of tunnel support pattern consists many important parameters including advance rate and excavation method. However, quantitative definition of these parameters is difficult because of restricting in site investigation data and uncertainties related to them. Furthermore, erroneous evaluation in these parameters can affect in incorrect projection of tunnel stability or economic loss. In this study, a probabilistic hypothetical elasticity modulus approach, based on Monte Carlo simulation algorithm (Latin Hyper Cube sampling), has been employed to evaluate the uncertainty in lining design of a NATM tunnel located in Tehran region. A parametric finite element model based on ABAQUS and a MATLAB interface program has been introduced to evaluate the performance of supporting system to limit the settlements induced by tunnel excavation in the different magnitudes of lifetime probability of failure. The tunnel has a horseshoe shape, excavating in a soft soil for subway purpose.
      409
  • Publication
    The Effect of Uncertainty on the Prediction of Building Damage Due to Tunnelling-Induced Settlement
    Prediction of the response of buildings to tunnelling-induced settlement for the extent of a tunnel route is a complex task due to the heterogeneous nature of ground conditions, variable tunnelling operations, and unknown building parameters. Consequently, there are generally uncertainties associated with building damage predictions. This paper presents a probabilistic numerical methodology to investigate the effect of uncertainties for the damage prediction of masonry buildings due to tunnelling-induced settlement. The methodology is employed to provide a Class C1 prediction for a previously documented case history. The results demonstrate the uncertainties that have a significant influence in terms of the building response prediction and, furthermore, provide a quantitative risk assessment for masonry buildings due to nearby tunnelling.  
      415
  • Publication
    Uncertainty Quantification in Tunnelling-induced Surface Settlement
    (University College Dublin. School of Civil Engineering, 2017)
    Evaluating the impact of tunnelling on above ground structures in urban areas highly relies on prediction of the settlement trough at surface level. Uncertainties in soil properties and other system characteristics for soft ground (e.g. Alluvium soil) can significantly affect the prediction. Classically, empirical formulas are used for prediction of the settlement using the experience from previous tunnelling projects. Empirical formulas do not consider the soil-lining interaction or the method of construction and lack a theoretical background for ground movement in continuum mechanics. Analytical and numerical approaches have developed to address some of these deficits, but have not to date, taken account of the many uncertainties involved in the process. This thesis introduces a stochastic method in the context of discrete random finite element theory to probabilistically predict the tunnelling-induced surface settlement. The method proposes a single mechanism (i.e. an uncertainty and sensitivity analysis framework) in which multiple sources of uncertainty can be considered within a single model (e.g. heterogeneity of the soil profile, variability in surcharge loads, and material properties). The power of the method is then examined through application to case studies involving two large-scale, shallow tunnelling projects excavated in alluvium soil. The results are compared with monitoring data, with estimations from deterministic finite element (FE) models and empirical formulas. Compared to the results of classical FEs and empirical approaches, application of the new probabilistic approach provides better understanding of the development of the settlement trough at surface level in both case studies. The output parameters for the tunnelling-induced settlement trough (volume loss and maximum settlement) are in good agreement with actual monitoring data in both case studies. Notably, the prediction result of the empirical formula in the first case study is conservative and for the second one is quite non-conservative. The new approach, on the other hand, provides more accurate predictions and insights into the effect of different sources of uncertainty.
      44
  • Publication
    Amirkabir NATM Tunnel- A case study of design challenges in a mega project of tunnel in soft ground
    (Distance and Continuing Education, Missouri University of Science and Technology, 2013-05-04) ;
    In spite of enhancement in modeling techniques as well as site investigation methods, uncertainty exists seriously in the process of construction of underground structure in soft soils. These uncertainties arise from limited data of geological data, measurement errors, interpolation of spatially geological properties, and extrapolation of results of experiments and natural analogue studies over times and conditions relevant to the project. Robust and optimize design of tunnel support pattern consists many important parameters including advance rate and excavation method. However, quantitative definition of these parameters is difficult because of restricting in site investigation data and uncertainties related to them. Furthermore, erroneous evaluation in these parameters can affect in incorrect projection of tunnel stability or economic loss. The work reported in this paper specifically dealt with Amirkabir highway tunnel with approximately 1.5Km long in each tube (i.e.,north and south tubes).It is one of the important projects excavating below one of the highest traffic region of Tehran, including the difficulty of excavating through a heterogeneous sedimentary basin mainly composed of recent alluvial. Construction has been performed by different methods i.e., Underground excavation, Cut and Cover and Top/Down methods in different sections of the project. Deformations and settlements have been monitored during and after construction in order to avoid unpredictable deformations and as a result any possible failure. Similar to other part of the project, a probabilistic hypothetical elasticity modulus (PHEM) approach has been employed to evaluate the uncertainty in lining design of a horseshoe shape NATM(New Austrian Tunneling Method) tunnel in T4 section of the project.The hybrid model, PHEM, consisting two essential parts is used to evaluate the performance of the system. A MATLAB interface program for generating the ABAQUS-based parametric model in one hand; and a Monte Carlo algorithm (Latin Hyper Cube Sampling method) to simulate the uncertainty existed in the system on the other hand are applied to produce the probabilistic density function of surface settlement of tunnel excavation and lining phases. In comparison with the monitoring data, the numerical results show that the PHEM approach introduced has had an appropriate prediction in surface settlements, improved the classical deterministic approaches.
      567
  • Publication
    Numerical modelling options for cracked masonry buildings
    In most numerical modelling of buildings, there is an assumption that the structure is undamaged. However, with historic buildings, defects often exist. Failing to incorporate such damage may cause an unconservative estimation of a building’s response. Nowhere is this more critical than in the case of urban tunnelling where hundreds of unreinforced masonry structures may be impacted by ground movements. This paper examines the effectiveness and limitations of four numerical approaches in the modelling of existing discontinuities, in the form of masonry cracking when compared to traditional finite element methods. The comparative methods include a micro-poly method, a distinct element method, a discontinuity deformation method, and a combined continuum-interface method. Particular attention is paid to the ease of model implementation, the availability of input data, applicability of crack modelling, and the ability to define the initial state of the structure as part of the model. The methods are compared to each other and finite element modelling. Relative qualitative assessments are provided as to their applicability for modelling damaged masonry.
      629
  • Publication
    Uncertainty Analysis of the Effect of Grout Injection on the Deformation of Multi-Wythe Stone Masonry Walls
    The eighteenth century Prince of Wales Fort in Manitoba Canada has experienced extensive freezethaw damage and mortar washout within the escarp walls resulting in distress and failures at multiple locations. Injection of grout could counteract this degradation of structural stability. However existing literature provides little guidance as to the improvement level that could be expected, especially with respect to out-of-plane performance. As such, the proposed treatment was modelled to include a high level of uncertainty in the system through the application of a Random Field Finite Element Micromodelling technique. A Latin Hyper cube simulation method was used in conjunction with a parametric finite element model to randomize the material properties of each stone and relevant grouting layer. The numerical results predicted that the stone-grout bond was the most critical parameter in the proposed intervention, and that in the grouted wall sections, collapse would be avoided and lateral displacements stabilized with the proposed treatment.
      235Scopus© Citations 16
  • Publication
    A semi-random field finite element method to predict the maximum eccentric compressive load for masonry prisms
    An accurate prediction of the compressive strength of masonry is essential both for the analysis of existing structures and the construction of new masonry buildings. Since experimental material testing of individual masonry components (e.g., masonry unit and mortar joints) often produces highly variable results, this paper presents a numerical modelling based approach to address the associated uncertainty for the prediction of the maximum compressive load of masonry prisms. The method considers a numerical model to be semi-random for a masonry prism by adopting a Latin Hypercube simulation method used in conjunction with a parametric finite element model of the individual masonry prism. The proposed method is applied to two types of masonry prisms (hollow blocks and solid clay bricks), for which experimental testing was conducted as part of the 9th International Masonry Conference held at Guimarães in July 2014. A Class A prediction (presented before the tests were conducted) was generated for the two masonry prisms according to the proposed methodology, and the results were compared to the final experimental testing results. The root mean square deviation of the method for prediction of eccentric compressive strength of both types of prisms differed by only 2.2 KN, thereby demonstrating the potential for this probabilistic approach.
      577Scopus© Citations 21
  • Publication
    Estimation of spudcan penetration using a probabilistic Eulerian finite element analysis
    The probabilistic approach was employed to consider the uncertainties in prediction of spudcan penetration in clay. The Latin Hypercube Sampling method was used to generate 300 sample sets of input parameters based on the laboratory and field data. Each set of input parameters was used in conducting Coupled Eulerian Lagrangian finite element analysis. The probabilistic density function of the penetration depth under the maximum applied preload was obtained. The comparison of the results to the measured data showed that the introduced method can produce reasonable prediction of spudcan penetration considering the uncertainties involved in this problem.
      470Scopus© Citations 4