Buried pipelines are one of the critical lifeline structures, and recently, efforts have been directed toward their probabilistic risk assessment. This paper explores the fragility analysis of buried ...pipelines due to permanent fault displacement. Although several studies have been carried out for the fragility analysis of buried pipelines, they are conditioned only on one significant input parameter. Unlike previous studies, the fragility curves presented in this paper are multi-dimensional, i.e., conditioned on all the significant input parameters. The fragility curves are generated using a machine learning technique called Lasso regression. This paper also explores the relative importance of various uncertain parameters on the fragility estimates. The fragility analysis results suggest that the fault displacement and fault–pipe crossing angle are the most important parameters.
Ground surface settlement is one of the critical parameters that needs to be controlled strictly during pipe jacking. The calculation model for estimating the ground deformation induced by pipe ...jacking is scarce in the literature, especially for pipes with irregular cross-section (e.g., circular pipes with flanges). In this study, considering the pipe-soil interaction, the distribution characteristics of frictions between pipe and soil, and the support force at the tunnel face, a settlement formula is proposed for a single jacked pipe using the Mindlin’s solution and the Stochastic medium theory. Based on the cavity expansion theory, a relationship for calculating the circumferential plastic zone is developed considering the effect of flanges. The distribution of the plastic zone around the pipe and the superimposition effect due to multiple pipes are discussed. Finally, a correlation is established to estimate the ground surface settlement for three types of multiple jacked pipes with different spacing. A case study of a subway station project using the Steel Tube Slab (STS) method is presented. Comparisons of ground settlement from field measurements and theoretical calculations show that the proposed approach can reasonably predict the ground surface settlement for multiple jacked pipes.
Earthen construction has attracted much attention in recent years, given that it offers many environmentally friendly features. Extensive works have been conducted to optimize the binder type or ...dosage in stabilization of raw earth, but the effects of curing and processing are often overlooked. This investigation targets to understand the strength performance of raw earth after curing and/or processing. The testing matrix contains variables of two binders (lime and sodium silicate), six densities, five curing ages, two curing conditions (natural and steam), two processing approaches (extrusion and rolling), and seven processing cycles, in which a total of 324 raw earth specimens are prepared. Analyses with scanning electron microscope are also conducted to interpret the stabilization mechanism. Results show that the strength of raw earth are positively correlated with the density. The highest strength gain is obtained at 28 days curing for both lime and sodium silicate stabilization. Upon natural curing, the mass loss increases over time, as well as the strength; upon steam curing, the mass increases with the curing age, but it can lead to a reduction in strength. The implementation of processing promotes the strength gain, and the optimal processing cycle is determined as 15–20 and 10–15 times for extrusion and rolling, respectively.
In practice, the full arrangement of sand blankets overlying soft clays could result in an uneconomic design for soft soil treatment using the surcharge preloading method. In view of this, a novel ...type of distributed drainage boundary is proposed in this investigation to improve the design. A two-dimensional plane-strain consolidation problem with distributed drainage boundary is established and solved. The sensitivity of the consolidation process to the pave rate (sand blanket area over the total area), thickness–width ratio (thickness over width of the representative element) and anisotropy coefficient (horizontal consolidation coefficient over vertical consolidation coefficient) are discussed. The results show that the negative effects of distributed drainage on the consolidation process become negligible if the pave rate and thickness–width ratio are designed adequately. Remarkably, the distributed drainage boundary becomes more efficient with the decrease in anisotropy coefficient. In addition, the increasing rate of consolidation time calculated using different parameters is presented for four average degrees of consolidation to provide a theoretical reference for engineering design.
Pipe jacking is a commonly used trenchless technology to install pipelines especially in congested urban areas or river crossings. However, the estimation of the jacking force is often heavily ...dependent on empirical calculations. The jacking force needs to be greater than the combined frictional resistance and face resistance. This investigation proposes to use a modified Protodyakonov’s arch model to compute the face resistance. A series of direct shear tests is performed to provide data of interface friction coefficient between different types of soil and pipe. The influence of slurry lubricant is also considered. A two-dimensional plane strain numerical model is conducted, where the surrounding soil is simulated as discrete particles and the lining is simplified as a single big particle. The novel modeling technique enables the evaluation of the normal force acting on the pipe. The friction resistance is then determined by multiplying the interface friction coefficient by the normal force. A ‘wavy’ shaped pipeline model is proposed to define an angular deviation influence factor to scale up the calculated jacking force due to pipe misalignment. In the end, comparison between calculated and field measured jacking force is conducted for three different drives in a pipe jacking project to illustrate the effectiveness of the proposed analysis framework.
Permanent ground deformation induced by surface faulting can seriously threaten the structural integrity of buried pipelines. The failure mode of fracturing in pipe wall is somewhat difficult to be ...simulated by the classical finite element method. In this work, brittle damage of buried pipelines subjected to different dip-slip faults is investigated by using peridynamics, where the pipes are characterized as peridynamics shell structures and the surrounding soil is simulated as Winkler springs. Three sets of experiments are simulated using the proposed modeling strategy, and good agreements between experimental and numerical results are achieved, in terms of progressive brittle damage features (deformation and crack patterns). The first crack initiates under a certain fault displacement, and then it propagates inwardly to penetrate through the cross section on the footwall side. A new crack then occurs on the other side in a later stage. Pipeline failure is more prone to occur within the zone of three times the pipe diameter from the fault plane, showing three broken segments by the two dominant cracks eventually. Parametric study suggests that reverse faulting is more harmful to the pipeline than normal faulting. The most unfavorable dip angles for pipelines under normal and reverse faulting are 65° and 75°, respectively. The pipeline with a thicker pipe wall or a higher critical energy release rate, being buried in a smaller burial depth or a looser sand condition, shows a higher capacity to resist the dip-slip fault.
In practice, it is vital to know the propagation law of settlement in soil induced by tunneling. In this paper, a novel two-dimensional subsurface settlement propagation model is established based on ...the stochastic medium theory. The governing equation is solved with the assumed settlement profile at the tunnel crown using the Fourier transform method. Subsequently, the sensitivity of the subsurface settlement to the model parameters B and N is discussed. A database containing 12 case histories is used to establish the relationship between the elastic modulus of soil and the model parameters B and N by the linear fitting method. Results show that the model parameters B and N can reflect the vertical propagation ability and the compression (or swelling) performance of the overlying soil, respectively. Finally, the applicability of the proposed model is demonstrated with a case study of tunneling in clays. It is concluded that the model presented in this paper is highly effective and convenient for use in practice.
The downward resistance between pipes and soils dominates the serviceability and structural integrity of buried rigid pipelines when geohazard conditions such as ground subsidence and normal faults ...are encountered. This study first presented a numerical investigation on the interaction between buried rigid pipes and soils under downward relative movements, based on which a novel mathematical representation of the bearing force-displacement curve was derived. Sand backfills in the numerical model were characterized using plane-strain shear strength parameters, and the increment of elastic modulus with depth was accounted. Simulated results showed that the bearing resistance kept increasing with the relative displacement and the failure resistance was analogous to the local shear, rather than the general shear bearing capacity. The proposed force-displacement relationship consisted of a nonlinear region before the mobilization of failure resistance and a linear post-failure region. The rationality of proposed method was evaluated against experimental measurements reported in published studies and calculations from the commonly used method, which can provide a basis for assessing performance of buried rigid pipes under downward relative movement conditions.
Real-time prediction of excavation-induced displacement of retaining pile during the deep excavation process is crucial for construction safety. This paper proposes a modified back analysis method ...with multi-objective optimization procedure, which enables a real-time prediction of horizontal displacement of retaining pile during construction. As opposed to the traditional stage-by-stage back analysis, time series monitoring data till the current excavation stage are utilized to form a multi-objective function. Then, the multi-objective particle swarm optimization (MOPSO) algorithm is applied for parameter identification. The optimized model parameters are immediately adopted to predict the excavation-induced pile deformation in the continuous construction stages. To achieve efficient parameter optimization and real-time prediction of system behavior, the back propagation neural network (BPNN) is established to substitute the finite element model, which is further implemented together with MOPSO for automatic operation. The proposed approach is applied in the Taihu tunnel excavation project, where the effectiveness of the method is demonstrated via the comparisons with the site monitoring data. The method is reliable with a prediction accuracy of more than 90%. Moreover, different optimization algorithms, including non-dominated sorting genetic algorithm (NSGA-II), Pareto Envelope-based Selection Algorithm II (PESA-II) and MOPSO, are compared, and their influences on the prediction accuracy at different excavation stages are studied. The results show that MOPSO has the best performance for high dimensional optimization task.
Surcharge preloading consolidation of soft soils often implements a layer of fully arranged aggregate materials. The volume of drained water is abundant at the early stage of consolidation, but it ...reduces at middle and later stages, during which the fully arranged sand blanket will be a waste. In this investigation, a concept of distributed sand blankets is proposed to save aggregate materials. A series of finite element analyses have been performed on layered soils with distributed sand blankets. A mixed type of drainage boundary is assigned to a representative model, where a half sand blanket is perfectly pervious and a half width of soil among sand blankets is impervious. From parametric study, it has been found that a pave ratio between sand blankets and the total soil width can be selected in a range of 40%-60%, which will save aggregates by approximately 50% but cause an increase of consolidation time by less than 10%. For a fixed pave ratio, more evenly spaced sand strips with smaller width should be employed to optimize the design. The effectiveness of distributed sand blankets is not influenced by the anisotropy of hydraulic conductivity, elastic modulus, Poisson's ratio, and thickness in multiple soil layers.
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Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
