Displacement Contours Research Articles

PIV TECHNOLOGY BASED EXPERIMENT FOR COMPRESSION-SHEAR FAILURE CHARACTERISTICS OF CONNECTED FISSURE ROCK MASS

Based on PIV technology,the single-through fractured rock mass specimens were prefabricated by similar materials and compression-shear failure tests were carried out to explore the influence of fracture aperture on the strength,deformation and failure process. The results show that: (1)When the initial fracture occurs,the stress of the test group with different fracture apertures decreases obviously. The plastic deformation of the hinged part of the fractured rock mass increases with the increase of the aperture. The characteristic stress value of the rock mass specimen decreases; (2)The fracture aperture affects the proportion of the deformation of the fracture and the hinge part in the total deformation of the specimen,thereby affecting the axial peak strain and the lateral peak strain of the fractured specimen. The larger the fracture aperture is,the smaller the axial peak strain and the lateral peak strain of the fractured specimen are; (3)By PIV monitoring,it is found that the initial fracture position of the specimen transfers from the middle and lower parts to the middle and upper parts with the increase of aperture degree. The specimen gradually changes from tensile shear composite failure to single shear failure; (4)Through the analysis of displacement contour pictures,it is found that the surface of the specimen needs to reach the displacement threshold k to produce cracks,and the increase of the prefabricated crack aperture will reduce the displacement threshold k of the specimen. The results provide basis for the investigation of the mechanism of water and sand mixture inrush in deep mines.

Online monitoring for floating raft structure displacement based on optimal placement of measuring points

The structure displacement of the raft of vibration isolation for ships is an important factor that affects shafting alignment accuracy and the safety of the equipment on the raft. In order to realize real-time monitoring of the raft structure displacement, which is the uncertain loadings and complex in shape, a measuring point placement strategy and an online monitoring method based on the displacement parameters to identify the displacement of the raft are proposed. FEM-based simulations for a prototyped raft have been conducted to obtain the displacement contour map. According to the displacement contour map based on displacement gradient and index evaluation, the measuring points have been combined and optimized. Displacement reconstruction principle based on a surface spline interpolation function method has been elaborated and derived. Structure displacement at any point can be obtained by a few measuring points. Finally, a case study of a certain type of floating raft is analyzed by the simulation analysis, and experimental research. The simulation and experimental results verify the validity of the measuring point placement strategy and the average of relative error with a value of less than 4% under different uncertain loadings. This method can effectively solve the problem of online monitoring of floating raft structure displacement under different changing loadings.

State Responsibility for Protracted Displacement: An International Legal Approach to Durable Solutions

Abstract Since the Second World War, displacement has become increasingly protracted and return is in decline. Despite calls for greater international responsibility sharing, many displaced people are subject to a legal limbo, lacking recognition and reparation in international law. This article seeks to establish the legal contours of protracted displacement as an internationally wrongful act that can engage the responsibility of States of origin and result in redress for those displaced. The article argues that there is evidence of a customary international law right of return, which requires States to facilitate voluntary repatriation and provide restitution. Facilitation includes refraining from preventing or obstructing return, suppressing acts of retribution or discrimination, and addressing root causes of displacement. Restitution includes property restitution, compensation for material and moral damages as well as reintegration and reconciliation measures, and offering effective models for return. The article concludes that the progressive development and codification of the law on forced displacement should address temporality, the qualities of return, and the alleviation of extant crises.

Offshore pipeline buried in Indian coastal clay: buckling behaviour analysis

ABSTRACT Buckling is a crucial phenomenon to be considered in offshore pipelines and is dependent on the resistance of the surrounding soil, which depends on the diameter of the pipe (D) and embedment depth (H). In this study, the behaviour of the failure mechanisms and the capacity factors are investigated for a practical range of embedment depth (H) and diameter of offshore pipelines (D), using Indian coastal clay properties. A 2D plane-strain model was created using a finite element package PLAXIS 2D validated against previous studies. The immediate breakaway and no breakaway conditions are analyzed. The capacity factors are observed to increase with increasing embedment depth, up to a peak value and remain constant for further increase in embedment depth. The capacity factors are observed to be decreasing with increasing pipeline diameter. The failure mechanisms are shown using displacement contour diagrams and stress contours.

Numerical modeling of soil liquefaction and lateral spreading using the SANISAND-Sf model in the LEAP experiments

Laboratory element and centrifuge tests from LEAP-UCD-2017 and LEAP-Asia-2019 were used for model calibration and evaluation in a dynamic coupled analysis of a saturated and gently sloped deposit of sand subjected to base excitation. The paper focuses on using a recently proposed novel constitutive ingredient for modeling the post-liquefaction large cyclic shear strains in sands. An existing critical state compatible, bounding surface plasticity reference model is used, with and without this new constitutive ingredient, to explore its improved modeling capabilities. The constitutive model was first calibrated based on available laboratory element tests on Ottawa-F65 sand, and compared to the reference model showed significantly improved performance in capturing the strain-based liquefaction strength curve of a series of undrained hollow cylinder cyclic torsional shear tests. The calibrated models were used in Class-C prediction of the slope surface deformation in five centrifuge tests on a mildly sloping liquefiable ground of the same soil subjected to dynamic loading, in the three-dimensional finite difference program FLAC3D. The simulation results were compared with experiments in terms of acceleration history, spectral response, excess pore water pressure development, and horizontal displacement evolution at specified control points. The vectors and contours of displacements at the end of shaking also revealed a pattern of slope deformation consistent with that of a gently sloped liquefiable ground. Following the insights from the performance of the models in simulation of the slope response, the calibration was adjusted to more realistically account for the impact of initial static shear stress on the development of post-liquefaction shear strains. The models were again used for Class-C1 prediction of the slope deformation of the same centrifuge tests. The overall assessment revealed the capabilities and limitations of the models in simulating the soil liquefaction strength and its post-liquefaction response.

Stress-strain state of the soil mass under the uniformly distributed load action adjacent to a vertical excavation

This article provides a solution to the problem of the stress-strain state of a soil mass adjacent to a vertical excavation when applying a uniformly distributed load on its surface. The solution of the problem was obtained by the method of trigonometric Ribere-Fileon series. The final expressions for the SSS components are provided. Contours of stresses and displacements are also shown.

Three-dimensional numerical analysis of under-reamed pile in clay under lateral loading

Unlike the bearing and uplift capacities of under-reamed pile, the lateral resistance of under-reamed pile is studied by a very few researchers. Therefore, in the present study, a three-dimensional numerical analysis is carried out to study the response of under-reamed pile in clay under lateral loading. In the numerical analysis, various parameters such as embedment length to shaft diameter ratio (Lu/D), top bulb distance from the base to bulb diameter ratio (hb/Du), undrained cohesion (cu), rate of increase of undrained cohesion (m), number of bulbs, and bulb spacing to bulb diameter ratio (s/Du) are considered as variables. From the present study, load–deflection curve, variations of deflection, shear force, and bending moment, displacement contour, and soil stress in front of the pile are obtained. The lateral load-carrying capacity of under-reamed pile is estimated based on displacement-based criteria. The lateral load-carrying capacity of under-reamed pile (Qhur) is found to increase with increase in Lu/D, hb/Du, number of bulbs, cu, m, and decrease in s/Du. The deflection at the pile head is found to decrease significantly with increase in hb/Du and number of bulbs, and decrease in s/Du. It is expected that the present results will be useful from serviceability point of view.

GPU-Based Simulation of Dynamic Characteristics of Ballasted Railway Track with Coupled Discrete-Finite Element Method

Considering the interaction between a sleeper, ballast layer, and substructure, a three-dimensional coupled discrete-finite element method for a ballasted railway track is proposed in this study. Ballast granules with irregular shapes are constructed using a clump model using the discrete element method. Meanwhile, concrete sleepers, embankments, and foundations are modelled using 20-node hexahedron solid elements using the finite element method. To improve computational efficiency, a GPU-based (Graphics Processing Unit) parallel framework is applied in the discrete element simulation. Additionally, an algorithm containing contact search and transfer parameters at the contact interface of discrete particles and finite elements is developed in the GPU parallel environment accordingly. A benchmark case is selected to verify the accuracy of the coupling algorithm. The dynamic response of the ballasted rail track is analysed under different train speeds and loads. Meanwhile, the dynamic stress on the substructure surface obtained by the established DEM-FEM model is compared with the <i>in situ</i> experimental results. Finally, stress and displacement contours in the cross-section of the model are constructed to further visualise the response of the ballasted railway. This proposed coupling model can provide important insights into high-performance coupling algorithms and the dynamic characteristics of full scale ballasted rail tracks.

Analysis of Indentation Test Using Solid Works Simulation

The finite element analysis of spherical indentation was conducted using the SolidWorks simulation software. The relationship between the load and indention was determined, and comparison with the Hertzian solution was made. In this study, spherical indenters of diameter 5, 10 and 15 mm were used to assess the effect of indenter radius on indentation response at a specified load. The outcome of our study shows that the resulting load-indentation response does not closely correlate; as a result, a difference of 21.2% was observed between the hertz solution and simulated results. The increase in diameter was observed to be associated with the corresponding decrease in indentation depth and the indentation stress. The von Mises stress contour at maximum load was analysed and was observed to be the highest on the indented surface beneath the indenter. The resultant displacement contour shows a uniform displacement distribution.

Different aspects of slope failures considering large deformation: application of smoothed particle hydrodynamics (SPH)

Understanding the insight of slope collapse is necessary for effective hazard mitigation policy. The conventional method may not be able to capture the actual failure mechanics as these methods are based on simplified assumptions of the predetermined slip surface. Highlighting this real engineering problem, an attempt is made in this research to simulate different aspects of slope collapse numerically. Lagrangian particle-based continuum model, namely, smoothed particle hydrodynamics (SPH) has been used to develop a three-dimensional numerical slope model to understand the failure mechanics of unstable slopes. Both homogeneous and non-homogeneous slope models have been simulated, and the time history of naturally occurring failure planes has been tracked. A distinct slip surface has been seen from displacement contour of particles, which portray the innate response of a collapsed slope. The effect of soil properties on the response of slope surface has also been evaluated quantitatively by the different combination of non-homogeneous slope models. Afterwards, two conventional remedial measures have been simulated, and significant reduction of run-out length is seen, which can put a spotlight on future mitigation strategy in geotechnical hazard.

Cross-section piles in transparent soil under different dimensional conditions subjected to vertical load: an experimental study

In this study, soil pile models using transparent soil were used to study the displacement distribution law under different dimensional and loading conditions (vertical load ranges from 3 (30 N) to 50 kg (500 N)). Experiments were conducted to obtain displacement contour maps from model piles with variable diameters and lengths. Overall, the results show that side resistance increases monotonically with the pile diameter and that the pile displacement trend under the same load increases on shorter piles as well as the angle between the soil displacement direction and vertical direction. The final results were utilized to obtain displacement contour maps of rock mass and identify failure zones under different loads. It is found that the side resistance enhancement effect increases monotonically with pile diameter. The angle between the soil displacement direction and vertical direction between model piles of different lengths under identical loading conditions increases with decreasing soil volume, and the side frictional resistance and order variation resistance play a more substantial role than pile tip resistance. The findings provide a basis for constructing highways and also bridge pile foundations.

GFRP composite footbridge series with multi-box cross section – Part 2: Local detailed design

The contribution constitutes Part 2 of research on a GFRP composite footbridge series with a multi-box cross section (Composite Structures, 2020). The 3D numerical modelling and simulation methodology was elaborated and experimentally validated on a test system in which glued laminates, rubber pads, steel plates and screw joints are applied. The test system reflects a steel post–composite platform joint applied in the footbridge series. Local detailed design calculations were carried out including the parts/joints of the case study footbridge that were omitted or modelled in a simplified manner in the global detailed design calculations in Part 1, i.e. validating the ultimate limit state (ULS) for the rubber bearings, validating the ULS for the support stabilizing systems, validating the ULS for the steel post–composite platform joints, validating the ULS for the transport-and-assembly openings. The simulation results were presented in the form of displacement contour maps, failure index contour maps and effective stress contour maps. The parts/joints in which stress concentrations appear were redesigned accordingly to meet the load capacity conditions. The elaborated methodology ensures that the local design results are applied to the entire footbridge series.

Centrifuge model studies on the settlement response of geosynthetic piled embankments

The paper aims at comparing the deformation behaviour of unreinforced embankments, basal reinforced embankments and geosynthetic reinforced embankments with floating and end bearing piles. The floating piles were terminated within the soft foundation soil, while the end bearing piles transfer the loads to a hard stratum. Four series of centrifuge model tests were conducted at gravity g = 40, using the 4.5 m radius large beam centrifuge facility at the Indian Institute of Technology Bombay. The tests were performed at constant pile spacing, and the embankment was constructed using an in-flight sand hopper. The deformations were measured using Linear Variable Differential Transformers (LVDTs). A digital image analysis technique was employed to arrive at the surface displacements, displacement vectors, and displacement contours. The geogrid reinforced embankments resting on end bearing piles and floating piles showed 88% and 44% lesser settlements respectively, compared to the unreinforced embankments. The geogrid reinforcement helps to distribute the load uniformly. A deep-seated slope failure was observed for unreinforced embankments. The piled embankments proved to be a practical solution for construction without prolonged waiting periods for pre-consolidation of the foundation soil.

Dynamic analysis of the longitudinal vibration on bottom drilling tools

With extreme complexity, the drilling process is a dynamic process which is severely influenced by longitudinal vibration. Longitudinal vibration, as one of the most important reason, is directly generated by the fatigue failure of the bottom hole assembly. In this paper, the natural frequencies of longitudinal vibration along the drillstring are analyzed by the finite element method. The deformed plot, stress nephogram, and displacement contour map under 1 to 4 ordered the natural frequency of the longitudinal vibration are obtained. The analysis results show that the maximum deformation always appears in the central part of the string so that some technological process on these positions is required to reduce the collision between the string and wellbore wall. Additionally, a time series of longitudinal vibration of a bottom rotating drillstring is extracted from real-time field data, which is measured while drilling near the drill bit. Then the time-frequency and energy spectrum analysis of the longitudinal vibration is carried out. The results of the statistical analysis show that, when the drillstring uniformly rotates, the longitudinal vibration can be considered as a kind of random vibration. However, if the stick-slip phenomenon occurs during the drilling process, the energy concentration will appear in the time series spectrum of the longitudinal vibration, by which means the vibration could be regarded as random no longer.

Simulation-Based Methodology for Determining the Dynamic Strength of Tire Inflation Restraining Devices

The article suggests and supports a simulation-based methodology for determining whether the dynamic strength of tire inflation restraining devices for tire inflation meet quality requirements and ensure operator safety during a potential tire explosion. Dynamic strength tests using an NM-600 safety shield and NK-0728 safety cage during a 29.5 R25X tire explosion at a pressure of 10 bar were presented as an example application of this methodology. The shield was subjected to destructive tests involving the use of a 2200 kg impactor, dropping it so that the minimum kinetic energy reached 20 kJ at the time of impact. Analyzed devices were constructed of S355 steel in accordance with EN 10025. The Cowper–Symonds model of material for strain rate phenomena was used in the calculations. Simulations of a 20 kJ ring impact against the cage were performed. The equivalent stress distribution was determined, and displacement contour lines for the maximum dynamic deformation value and plastic deformation were calculated. The plastic displacement obtained in numerical tests was equal to the permanent deformation recorded in the experimental test. Further, the simulations showed that the examined cage met the assumed strength criteria. The conducted tests confirmed the usefulness of the proposed methodology for assessing the dynamic strength of safety cages and shields for tire inflation. The full-scale, physical cage testing is difficult to implement because it requires placing a ring impacting the cage wall. This is a major boundary for closed cages, as considered in this publication. Thus, simulation-based methods are becoming a principal tool for safety assessment of tire inflation restraining devices.

Simulation study on rock slope reinforced by anti-slide pile: a case study

For the collapse of bedding rock slope in Yuqian Expressway, by using simulation software FLAC-3D this paper established simulation models bedding rock slope before and after reinforced by combined supporting, i.e., “slide-resistant pile+ diagonal bracing wall+ anchor cable”, and collected parameters such as deformation and shear stress through three monitory points established. As simulation results compared with field monitoring data, bedding rock slope before reinforced was unstable, belonging pull-type failure model, and this failure model was sudden; the displacement contour map after the slope was reinforced by combined supporting showed that there existed one bigger shear zone in the rock interface, and the shear zone was disappeared after this slope was reinforced, then maximum deformation was decreased; the displacement vector map of slope showed that this slope slipped along the rock interface before it was reinforced, but the whole slope slid along one arc after it was reinforced; shear stress concentration phenomenon in the rock interface was disappeared obviously after this slope was reinforced. As monitoring deformation compared with simulation deformation, slope deformation was less; and the slope was stable; the reinforcement measure of combined supporting has the better retaining effects.

Numerical Evaluation of Earthquake Effect on Cisumdawu Tunnel Stability

Cisumdawu Tunnel is located approximately 3.95 km southeast of the activeLembang Fault. Earthquakes induced by movement of the the active the strike-slip fault may influence stability of the twin tunnel. This paper presents results of numerical analyses carried out to demonstrate effect of a worst-case scenario of earthquake load potentially induced by the Lembang Fault on the stability of the Cisumdawu Tunnel. Static and pseudo-static tunnel stability analyses were carried out at 11 observation stations of tunnel face mapping using RS2 finite element package (Rocscience, Inc.). In the pseudo-static analyses, a 0.48 horizontal seismic load coefficient, which was obtained from a deterministic seismic hazard analysis (DSHA) based on a 6.8 maximum magnitude of estimated earthquake sourced from the Lembang Fault using Campbell-Bozorgnia (2014) attenuation relationship, was applied to the finite element models. The numerical analysis results showed that strength factors of the rock masses around the twin tunnel were greater than unity, both under the static and earthquake loads. The forepolling zones, however, appeared to be under an overstressed condition. Reduction of rock strength factor around the tunnel roof due to application of the earthquake load occurred at all observation stations. Total displacement contours of rock masses around the twin tunnel indicated an increased rock mass displacement due to the earthquake load, as compared to that due to the static load. Under the static load, the largest displacement occurred at the tunnel inverts. The predicted roof displacements obtained from this study were in a reasonably good agreement with those obtained from the field measurements. Number of yielded elements and extend of shear and tension failure zones in the rock masses around the twin tunnel also appeared to increase due to the earthquake load. Despite slight tunnel displacement as predicted in the numerical analyses, the worst-case scenario of earthquake load potentially induced by the Lembang Fault may only cause failures of the rock masses around the Cisumdawu Tunnel. To prevent the twin tunnel displacement caused by such relatively severe earthquake loads, however, stabilizing surrounding the relatively poor ground condition may be necessary.

ВЫДАВЛИВАНИЕ СЛАБОГО СЛОЯ ГРУНТА ИЗ СЖИМАЕМОЙ ТОЛЩИ ОСНОВАНИЯ ФУНДАМЕНТОВ КОНЕЧНОЙ ШИРИНЫ

The paper provides a quantitative assessment of the deflected mode of foundation stratum of finite width foundation, in the compressible thickness of which there is a slack clay soil layer. A number of criteria for assessing the possibility or impossibility of extruding a slack layer depending on its strength and rheological properties, as well as the relative thickness of the layer to its length (h/l) and the relative depth of the layer (h/d) have been given. Closed analytical solutions are given to determine the rate of Foundation precipitation depending on the rate of extrusion of the weak layer, including taking into account the damped and undamped creep. The analytical solutions in the article are supported by the graphical part made with the help of the Mathcad program. Plots of changes in shear stresses in the layer along the x axis at different distances from the axis and at different values 0, contours of horizontal displacement velocities in the weak layer at different distances from the x axis, plots of horizontal displacement velocities in the middle of the weak layer and plots of horizontal displacement velocities in the weak layer at different distances from the x axis are given. As a calculation model for describing the creep of a slack layer, rheological ones of the soil using power and hyperbolic functions and their modifications have been considered. In addition, most modern rheological models that take into account soil hardening during creep have been considered. Based on these models, the problem is solved by means analytical and numerical methods using the Mathcad PC and the PLAXIS PC according to the Soft Soil Creep model. The graphical part shows the isofields of horizontal displacements for 300 days and 600 days and the corresponding contours of horizontal displacements.

Stress analysis of double-lap bi-material joints bonded with thick adhesive

Mechanics of double-lap Steel-to-CFRP adhesively-bonded joints loaded in tension are investigated experimentally using Digital Image Correlation (DIC) and Acoustic Emission (AE), analytically using a one-dimensional closed-form solution and numerically with Finite Element analysis. The double-lap bi-material joints are fabricated of a steel core adhesively bonded to two CFRP skins with adhesive thickness of ~ 8 mm, using an Epoxy-based and MMA-based adhesives. In order to capture the in-plane deformation of the joint, full field strain/displacement maps are obtained using DIC. This data is used to validate the shear-lag model predictions of the adhesive shear stress/strain distribution as well as the linear-elastic Finite Element Model (FEM) results. In addition, they are used to capture the susceptible damage locations and their effect on the displacement contour maps, strain distribution and load transfer between the joint's different constituents. A correlation between the DIC displacement and the AE signals is obtained for damage detection in both joints. Moreover, a good agreement amongst the analytical, FE and DIC strain/stress distributions along the bond-line is observed. This study introduces the analytical shear-lag model as an alternative to predict the stress state in thick-adhesive double-lap joints, with an acceptable level of accuracy and robustness.

Small- and large-scale analysis of bearing capacity and load-settlement behavior of rock-soil slopes reinforced with geogrid-box method

This paper presents an investigation on bearing capacity, load-settlement behavior and safety factor of rock-soil slopes reinforced using geogrid-box method (GBM). To this end, small-scale laboratory studies were carried out to study the load-settlement response of a circular footing resting on unreinforced and reinforced rock-soil slopes. Several parameters including unit weight of rock-soil materials (loose- and dense-packing modes), slope height, location of footing relative to the slope crest, and geogrid tensile strength were studied. A series of finite element analysis were conducted using ABAQUS software to predict the bearing capacity behavior of slopes. Limit equilibrium and finite element analysis were also performed using commercially available software SLIDE and ABAQUS, respectively to calculate the safety factor. It was found that stabilization of rock-soil slopes using GBM significantly improves the bearing capacity and settlement behavior of slopes. It was established that, the displacement contours in the dense-packing mode distribute in a broader and deeper area as compared with the loose-packing mode, which results in higher ultimate bearing load. Moreover, it was found that in the loose-packing mode an increase in the vertical pressure load is accompanied with an increase in the soil settlement, while in the dense-packing mode the load-settlement curves show a pronounced peak. Comparison of bearing capacity ratios for the dense- and loose-packing modes demonstrated that the maximum benefit of GBM is achieved for rock-soil slopes in loose-packing mode. It was also found that by increasing the slope height, both the initial stiffness and the bearing load decreases. The results indicated a significant increase in the ultimate bearing load as the distance of the footing to the slope crest increases. For all the cases, a good agreement between the laboratory and numerical results was observed.