•Responses of jointed rigid pipes under normal faults with various crossings are studied.•Analytical solutions for pipe bending moment and joint shear force at different crossings are ...proposed.•Excessive joint deflection dominates the pipe safety for relatively shallow burial depth and low soil density.•Increasing the burial depth and soil density, pipe failure mode changes to barrel bending and bell cracking.•Fault-crossing at around 7/10 of the pipe segment is the worst scenario for rigid pipes.
The structural safety of jointed rigid pipes can be jeopardized under abrupt ground settlements. Most previous studies have investigated the response and safety of jointed rigid pipes under abrupt ground subsidence using numerical and experimental methods at two specific positions, i.e., the shear band caused by the ground movements crosses the pipe at a joint and at the midspan of a pipe segment. In this work, a closed-form analytical solution for the deformation and mechanical response of jointed rigid pipes under abrupt ground subsidence with various crossing positions is presented. The pipe bending moment and the joint shear force are calculated, which match quite well with the results of finite element analysis. Then the maximum allowable settlements are examined, and the corresponding failure modes are identified. It shows that with the increase of burial depth and soil density, the main failure mode gradually changes from the excessive joint deflection to the barrel bending and bell cracking, and the maximum allowable subsidence distance decreases remarkably. The worst crossing position is at nearly 7/10 of the pipe length. The results offer new insights into the failure mechanism of jointed rigid pipe, and provide a basis for the protection of rigid pipes under abrupt ground subsidence.
In the history of human civilization, rammed earth has been used over thousand years to construct infrastructure, such as buildings, shelters, and defense structures. The structural integrity of ...rammed earth infrastructure can be affected by many factors over time. Abundant rainfall and typhoon can strike the World Heritage site of Fujian Tulou due to its unique geographic location in the southeast costal line of China. The effect of wind-driven rainfall on durability of rammed earth materials taken from three demolished Tulou sites with different construction history is studied. Laboratory element tests are conducted to identify that both the unconfined compressive strength and shear strength are inversely proportional to the water content. In drip tests, the maximum degree of erosion is obtained, when the rain direction falls within the range of 30–45°. In rain simulation tests, the peak erosion depth is measured for the case with a rain direction of 15–30°. Essentially, higher degree of erosion is resulted when the initial water content is higher, and lower degree of erosion is obtained when the clay content is higher.
•Interaction between DI pipelines and dip-slip faults is studied numerically.•Self-locking can cause a joint to lose its free rotational capacity completely.•Joint self-locking alters the pipe ...failure mode from kinematic- to mechanical-controlled.•Joint pull-out failure controlled by tension should be given a highest priority.•Pipe body shows a rapid growth of inward buckling at 0.65–1.27 times the pipe diameter.
Effective identification of failure modes for buried pipes subjected to earthquake-induced fault movements is crucial in the design and assessment of underground water supply networks. For bell-spigot jointed ductile iron (DI) pipes, the relationship between pipe failure mode and dip angle is still unclear. In this study, a three-dimensional finite element model of buried DI pipelines crossing dip-slip faults perpendicularly is established, based on which the joint kinematics and mechanical responses of DI pipes subjected to dip-slip faults with a dip angle between 50° and 130° are systematically evaluated. Four failure modes controlling the joint sealing performance and structural integrity of DI pipes are identified, i.e., joint pull-out failure, joint rotation failure, joint compressive failure, and excessive local buckling in the pipe segment. The results reveal that joint self-locking induced by the action of horizontal compression can reduce the joint rotational capacity greatly, rendering a segmented pipeline to behave like a continuous pipeline. Upon the occurrence of joint self-locking, the pipe mode changes from kinematic-controlled failure (joint pull-out or rotation failure) to mechanical-controlled failure (joint compressive failure or excessive local buckling). Finally, the relationship between failure mode and allowable dip angle is derived for use in design.
Compressible materials can be backfilled in the trench to reduce the soil restraints on buried pipelines at fault crossings. The potential of using tire-derived aggregate (TDA) as a backfill material ...for seismic mitigation of pipelines is investigated herein. A continuum-based three-dimensional finite element model for pipelines with trench mitigation is calibrated against experimental measurements. A comparative study is then performed to assess the impact of trench configurations and soil/pipe properties on TDA mitigation. Results indicate that TDA mitigation can generally increase the critical fault offset that a pipe can withstand by at least 20%, which is more effective than other conventional techniques, such as replacing native soils with loosely compacted soils, upgrading the pipe class, increasing the pipe wall thickness, and reducing the burial depth. Design implications of enlarging the trench and aligning the pipe at a fault-pipe crossing angle of 90° are recommended for improving the mitigation efficiency.
•A seismic mitigation measure is proposed by backfilling the trench using TDA.•3D finite element modelling is conducted to analyze pipelines at fault crossings.•Use of TDA trench increases the critical fault offset for pipelines by at least 20%.•TDA mitigation is more effective than other conventional mitigation techniques.
The hydration process during the hardening of early-age cement-based materials can lead to a considerable volume change, consequently causing considerable deformation, and even fracturing. In the ...present study, an efficient PD-FEM chemo-thermo-mechanical coupling approach is proposed with the aim of modeling fracturing in early-age concrete structures, taking into account coupled processes, such as thermal transfer, hydration heat, creep, evolution of strength, fracturing as well as hindering effect of cracks on the temperature and hydration fields. The coupled chemo-thermo-mechanical problem is solved in a staggered manner within the classical finite element (FE) and the non-ordinary state-based peridynamics (NOSBPD) framework. By doing so, fracturing in early-age concrete structures can be easily accommodated by NOSBPD featuring an elegant treatment of discontinuities. The accuracy of the proposed approach is evaluated by a benchmark problem with experimental and existing numerical solutions. The capability of the proposed approach for simulating the complex crack initiation and propagation in early-age ring and T-shaped concrete structures is demonstrated. The interaction and competition between different stress inducing mechanisms of hydration heat, autogenous shrinkage, and creep are analyzed.
AbstractA rigid nonyielding retaining structure needs to be dimensioned to have adequate stiffness, such that it can resist mobilized lateral earth pressures. This corresponds to the at-rest ...condition, as there are, in general, negligible lateral deformations in the backfill. Measures that can mobilize higher soil shear strength and reduce lateral thrust are therefore sought to provide a more efficient design. The present study investigates the possibility of inserting compressible geofoam panels against rigid walls using physical model testing. Controlled yielding is allowed in the backfill with the occurrence of deformations in the geofoam. The mobilized earth pressures vary from the maximum at rest, to the intermediate, and finally to the minimum full active state depending on the magnitude of displacement. The effects of geofoam thickness and stiffness on lateral earth pressure reduction are explored. The measured pressure and displacement distributions form a comprehensive reference for use in calibrating design methods. Two analytical solutions are presented and compared with experimental data to evaluate their ability to calculate displacement-dependent lateral earth pressures.
Soil-cement columns are widely used to improve soft ground, and the bearing capacity of the formed composite ground is a key design parameter. The currently employed design method was developed for ...composite grounds under rigid footings, whilst the bearing capacity behavior of composite grounds under earth fills with different degrees of stiffness has rarely been investigated. Hence, the present study attempts to fill this gap. In this investigation, 1-g laboratory model tests are conducted to compare the bearing capacity behavior of composite grounds under a rigid footing and under embankment fill, based on which a numerical model that can capture the strain-softening behavior of soil-cement columns is established. The calibrated numerical model is further employed to perform 144 analyses. The results indicate that the failure mode of composite grounds differs for different types of earth fills: soil failure occurs prior to column failure under soft clay and dredged slurry, whereas column failure is the primary failure mode for composite grounds under embankment fill. This difference in failure mode of composite grounds can be explained using soil arching theories. For different failure modes, different bearing capacity efficiency factors should be used in design.
Rock shed structure is widely constructed above a tunnel portal to protect the tunnel from rockfall hazards. The damage mechanism of rock sheds under rockfall impact is crucial, but is yet still ...unclear. In this study, a dynamic peridynamic model with a relatively simple yet effective failure criterion, which considers the strain rate effect for reinforced concrete shed structures under rockfall impact and is convenient for engineering applications, is developed. After assessing the proposed method by comparing with two experimental tests, varieties of simulation cases are simulated to thoroughly investigate the influence of different factors, including the shape, mass and drop height of the falling rock, on the damage behavior of rock sheds without backfills under rockfall impact. The safety of the tunnel and the damage position for strengthening are evaluated by the proposed method. The structural damage degree of the tunnel increases with the increase of drop height and rockfall mass, but the resulting growth rate differs. The penetration ability of a round falling rock is superior to a squared or an octagon falling rock. A non-circular falling rock could induce a larger damage zone. Under the angular falling rock impact, the structure is more likely to be penetrated with a sharp impact angle. The modes of local crush and flexural failure occur firstly, and then the tunnel is sheared by the falling rock until overall collapse happens. Shear failure is more obvious when the drop height is higher or under the non-circular falling rock impact. The work suggests that all exiting analysis techniques for simplifying the impact force as a static load are not sufficient to understand the resistance of rock sheds under rockfall.
Expansive soil swells upon wetting and shrinks upon drying. During repeated drying-wetting cycles, expansive soil slope can show desiccation cracks on the slope surface to provide pathways for ...rainwater infiltration. Hence, the conventional method of cutting a slope with a gentle inclination becomes less effective for expansive soil slope, where the magnitude of rainfall infiltration outweighs the amount of surface runoff. The combination of steep slope and vegetation is proposed and evaluated in this investigation. A field test is conducted to understand the slope condition after artificial rainfalls. Controlled laboratory tests are also performed to compare the behaviour of bare and vegetated slopes for use to calibrate a numerical model. A numerical parametric study is then carried out to assess the influence of vegetation, rainfall precipitation, and soil properties. It is found that erosion occurs on the slope surface, which can be prevented by vegetation due to the interception effect. Larger leaf area and greater root depth can reduce the water content in the soil, contributing to the increase of shear strength. A steep slope is beneficial to reduce the rainfall infiltration and maximize the surface runoff.
The technique of polymer grouting is frequently used in underground projects. The life span of the grouted body needs to be evaluated carefully to guarantee the long-term performance of trenchless ...repair by polymer grouting. Cutting failure of grouting polymer by rock or soil under water pressures can occur to affect the plugging effect. In this study, the mechanism of cutting failure in polymers with different densities is systematically investigated, where the effects of cutting depth and cutting-edge radius are assessed. Phase–space reconstruction for chaotic time series and trend analysis are conducted to analyze the experimental data to understand the fluctuation nature of cutting force on polymer. It is found that the passive cutting force on polymer first increases until it reaches a transition point, after which it decreases, along with the occurrence of broken chips. The observed cutting mechanism can affect the service life of polymer grouting significantly. Critical parameters that can influence the cutting force are then determined, based on which a prediction model is proposed for selecting and optimizing the polymer grouting material in practice.
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