Accumulation Of Permanent Strain Research Articles

Predicting permanent strain accumulation of unbound aggregates using machine learning algorithms

The objective of this study is to propose a machine learning-based framework for predicting the permanent strain accumulation of unbound aggregates. To develop the machine learning-based framework, material properties of 15 crushed aggregates determined at two different gradations are combined with the applied stress states on aggregate specimens during repeated load triaxial testing by considering the aggregate shear strength characteristics. Three single machine learning algorithms (K-nearest neighbor, neural network, and decision tree) and two ensemble learning algorithms (random forest and extreme gradient boosting) are used in this study. Based on the dataset obtained from 90 permanent deformation tests, hyperparameters, which are used to control the learning process, are optimized. The numerical results demonstrate that all five of the tuned machine learning models exhibit good generalization capacity and performance with the coefficient of determination exceeding 0.99. Among the five models, the extreme gradient boosting model outperforms the others, accurately predicting permanent strain accumulation even for load cycles of 10,000. The contributions of individual input features to the performance of each learning model depend on the dataset. The strength characteristics and the applied deviatoric stress are the two most important features. Therefore, the machine learning-based framework introduced in this study may be effectively used for predicting the permanent strain accumulation of unbound aggregate layer.

Undrained cyclic loading behavior of stiff Eocene-to-Jurassic plastic, high-OCR clays

Assessing foundation response to cyclic loading is vital when designing transport infrastructure, such as road pavements and rail tracks, as well as offshore, port, and tall tower structures. While detailed guidance is available on characterizing many soil types’ cyclic behavior, relatively few studies have been reported on stiff, geologically aged, plastic clays. This paper addresses this gap in knowledge by reporting cyclic loading experiments on three natural stiff UK clays that were deposited and buried between the Jurassic Age and Eocene Epoch before geological unloading to their currently heavily over-consolidated states. High-quality samples taken at relatively shallow depths were reconsolidated to nominally in situ K0 stresses in triaxial and hollow cylinder apparatus before imposing cyclic loading. The completely stable, metastable, or unstable outcomes invoked by different levels of undrained cyclic loading are interpreted within a kinematic yielding framework that is compatible with monotonic control experiments’ outcomes. The cyclic limits marking the onset of significant changes in permanent strain accumulation, pore pressure development, and stress–strain hysteresis demonstrate that the weathered Gault clay offers the lowest cyclic resistance. The experiments show that energy considerations provide a promising way of evaluating undrained pore pressure generation and stiffness degradation. They also provide a basis for developing cyclic constitutive models and analysis procedures for cyclic foundation design in stiff, high-OCR, plastic clay strata.

An experimental investigation into the behaviour of destructured chalk under cyclic loading

Low-to-medium-density chalk can be destructured to soft putty by high-pressure compression, dynamic impact or large-strain repetitive shearing. These process all occur during pile driving and affect subsequent static and cyclic load-carrying capacities. This paper reports undrained triaxial experiments on destructured chalk, which show distinctly time-dependent behaviour as well as highly non-linear stiffness, well-defined phase transformation and stable ultimate critical states under monotonic loading. The chalk's response to high-level undrained cyclic loading invokes both contractive and dilative phases that lead to pore pressure build-up, leftward effective stress path drift, permanent strain accumulation, cyclic stiffness losses and increasing damping ratios that resemble those of silts. These outcomes are relatively insensitive to consolidation pressures and are distinctly different to those of the parent intact chalk. The maximum number of cycles that can be sustained under given combinations of mean and cyclic stresses are expressed in an interactive stress diagram which also identifies conditions under which cycling has no deleterious effect. Empirical correlations are proposed to predict the number of cycles to failure and mean effective stress drift trends under the most critical cyclic conditions. Specimens that survive long-term cycling present higher post-cyclic stiffnesses and shear strengths than equivalent ‘virgin’ specimens.

Role of elastic upper limit in shakedown study for granular soils

The shakedown study for determining plastic shakedown limit is desirable for preventing geotechnical infrastructure failure under cyclic loads. The plastic shakedown limit is conceptually clear but difficult to determine experimentally since the permanent strain accumulation response is a gradual process, and the criterion for determining the plastic shakedown limit is sensitive and variable limited by lack of further understanding of mechanisms during shake down process. Motivated by the need to clarify the mechanism of shakedown limit, a new concept of elastic upper limit of quasi-elasticity extension is hypothesized in this paper. Three-stage slow cyclic triaxial tests are carried out on three types of sand to clarify this new concept. The results show that the quasi-elastic curve extends as the cyclic stress level increases until it reaches the elastic upper limit and then the deviation occurs. The objective of this study is to explore the role of elastic upper limit (the elastic extension domain limit) in the shakedown theory. It is found that the derived elastic upper limit is close to the plastic shakedown limit, especially at high levels of confining pressure. A new criterion is proposed to determine the plastic shakedown limit based on the linear dependence of the degree of elasticity on the cyclic stress level. The introduction of the concept of elastic upper limit provides new insights into shakedown study for granular soils.

A high-cycle accumulation model for clay and its application to monopile foundations

A high-cycle accumulation (HCA) model predicting the accumulation of permanent strain or excess pore water pressure in clay under a large number of load cycles is presented. Data from an extensive laboratory testing program on kaolin under undrained cyclic loading has been analysed for that purpose. The influence of strain amplitude, void ratio, stress ratio, overconsolidation ratio and loading frequency on the accumulation rates is considered in the constitutive equations of the HCA model. The proposed model is validated first by the simulation of element tests. Subsequently, its application to offshore wind turbine foundations under long-term lateral cyclic loading is presented by the back-analysis of a centrifuge test on a monopile in soft clay. The results are in good accordance with the measurements in terms of pile displacement and bending moment versus number of applied cycles. It is concluded that the proposed model is feasible to describe the long-term behaviour of clay subjected to high-cyclic loading.

Cyclic pseudoelastic training and two-way shape memory behavior of a NiTi alloy with small irrecoverable plastic strains:numerical modeling

Novel applications of shape memory alloys (SMAs) in various fields of medicine and engineering necessitate theoretical models that can capture non-inherent material behaviors such as the two-way shape memory effect (TWSME). Most often, this requires the use of completely different sets of models or parameters to distinguish the “virgin” material exhibiting the fundamental behaviors like superelasticity (also known as pseudoelasticity), pseudoplasticity, and one-way shape memory effect, from the “trained” alloy showing the TWSME. Although using a single model (or set of parameters) can provide much insight on the changes within the material during various loading paths and histories from the initial virgin state to the trained state, it is quite challenging. In this study, an attempt was made to use a developed general multi-mechanism material model and a single set of parameters to predict both the inherent pseudoelastic behavior and non-intrinsic two-way shape memory effect characteristics of a NiTi shape memory alloy. To this end, several simulations were carried out to investigate the effect of pseudoelastic training conditions on the corresponding actuation strain, cyclic stability, and transformation temperatures of the NiTi under zero-load TWSME. Whilst previous studies considered external indicators such as the magnitude of plastic or irrecoverable strain as a prerequisite for TWSME, the present model focused primarily on internal stresses. Based on the magnitude of the zero-load actuation strain (measured from the trained material under no external load), the model results indicated that the magnitude of the pseudoelastic training strain (in comparison to the training temperature, and the number of training cycles) has a pronounced effect on the cyclic TWSME actuation characteristics. Moreover, observations from the internal state (hidden) variables of the model, representing the intrinsic residual stress state in the trained material (under zero observable/external stress) showed the possibility for an SMA to generate TWSME even if there is no significant accumulation of permanent strains.

Assessment of RCA with RAP materials for pavement applications

Demolished concretes are being recycled to produce recycled concrete aggregates (RCA) in different scales around the world. Therefore, applications of RCA as a construction material are being popular by replacing conventional materials. Many research studies have confirmed the potential use of RCA to be applied as an unbound pavement material. However, presence of constituents such as reclaimed asphalt pavement (RAP) in RCA effects on its native properties. Therefore, this study evaluates performance characteristics of RCA with RAP under dynamic loading condition. A series of “repeated load tri-axial (RLT)” test was conducted on RAP blended RCA samples to evaluate the elastic and plastic deformation characteristics with increase of load cycles. The elastic deformation was characterised by resilient modulus and slightly dropped with increase of RAP from 0, 5, 10 to 15% in RCA. Further, it observed a trend of small increase of the plastic deformation of the RCA with the increase of RAP portion. However, presence of RAP up to about 15% in RCA did not significantly affect on the accumulation of permanent strain.

Effect of confining pressure and loading frequency on dynamic characteristics of Batu Pahat marine clay

This paper presents the laboratory study on the dynamic characteristics of marine clay subject to cyclic load over a long period of time. Remoulded marine clay samples were used to conduct the experiments using a dynamic triaxial machine. Confining pressure and loading frequency were varied while pore pressure development, resilient strains and plastic strain resulting from the application of cyclic loading were observed. The results acquired from this study revealed that as soon as the cyclic loading was introduced, it induced pore pressure that triggered the rapid accumulation of permanent strain and gradual increase in resilient strain. However, after the strain reached a stable value, the rate of accumulation of the permanent deformation started decreasing. The results also showed that an increase in confining pressure improved the marine clay resistance to cyclic loading. Similarly, when the loading frequency increased, it caused a decrease in strain generation and vice versa.

Cyclic behavior of semi-rigid recovered plastic blends in railway track substructure

Plastic deformation of granular layers in railway tracks under cyclic loading is a key factor controlling the substructure’s stability. In particular, the granular subballast capping layer placed between the ballast and subgrade can undergo permanent deformations due to the moving wheel load of trains. This study was conducted to evaluate the cyclic behavior of recovered plastic (RP) blended at different percentages with construction and demolition (C&D) aggregates as railway subballast capping layer. Recycled concrete aggregate (RCA) and crushed brick (CB) were used as the parent C&D aggregates. Multistage triaxial compression tests were initially undertaken to determine the shear strength and the effect of RP inclusion on strength characteristics. The results of multistage triaxial compression tests were also used to find a link between static shear strength and cyclic deformation of the granular recycled materials. The plastic deformability of the RP + C&D blends was also assessed through multistage cyclic triaxial tests at three confining pressures and incremental deviator stress at each confinement. The shakedown theory was employed to characterize the changes in permanent axial and radial deformations, resilient axial strain, and permanent axial strain rate. Inclusion of RP in the RP + C&D blends was found to increase the sample’s deformability particularly in the secondary phase of deformation, reduced the stiffness, and most importantly increased the rate of permanent strain accumulation.

Strain evolution of saturated clays under cyclic loadings in three-dimensional stress condition

The strain evolution of saturated clays under cyclic loadings has been studied by means of various laboratory testing methods, aiming for the accurate simulation of engineering conditions such as the consolidation states of clays, cyclic stress paths of external loadings and boundary conditions in situ. Considering that the subgrade clays are usually overconsolidated rather than normally consolidated, the drainage condition is normally partially drained instead of undrained under long-term cyclic loadings, and the cyclic stress paths are in three-dimensional stress state, this study explores the three-dimensional strain characteristics of both normally and overconsolidated clays in partially drained condition based on a true triaxial apparatus. Emphasis are put on the effects of cyclic stress ratio (CSR), overconsolidation ratio (OCR) and coefficient of cyclic intermediate principal stress (bcyc) on the accumulation of permanent strain components including major, intermediate, minor principal strains, and volumetric strain. Test results show that the relative magnitudes of strain components are strongly influenced by both bcyc and OCR, while the accumulated directions of strain paths tend to be identical for various bcyc values. The increase of bcyc leads to a linear growth of permanent volumetric strain for both normally and overconsolidated clays, while the permanent major principal strain shows a firstly increasing and then decreasing trend versus the increase of bcyc. For the normally consolidated and overconsolidated clays, the largest permanent major principal strains are achieved at around bcyc = 0.4 and 0.2, respectively. The accumulation of permanent intermediate principal strain is always promoted by the increase of bcyc. In addition, the development of permanent major principal and volumetric strains with cycle number is analyzed in the double logarithmic plane, which are found to be combined by two linear parts.

Shakedown analysis of recycled materials as railway capping layer under cyclic loading

The permanent deformation behavior of granular materials governs the overall performance of railway track substructures. This article evaluates the cyclic behavior of construction and demolition (C&D) aggregates, namely recycled concrete aggregate (RCA) and crushed brick (CB) blended with recovered plastic (RP) as railway capping layer materials. The response of C&D/RP blends was evaluated under multistage cyclic loading using the shakedown theory. The accumulation of permanent strain, variation of resilient modulus, and changes in permanent strain rate were assessed to classify the performance of the recycled blends. The inclusion of RP in C&D materials was found to compromise the stiffness characteristics of the recycled blends. However, all the C&D/RP blends had similar or lower permanent strain than that of the conventional materials. Conversely, the energy dissipation of the recycled blends was found to increase when the RP content was increased. Thus, C&D/RP blends can be introduced as sustainable energy-absorbing geomaterials.

Effects of longitudinal reinforcement discontinuities on the seismic response of structural walls

Lap splices and bar cutoffs introduce reinforcement discontinuities in reinforced concrete structures. A two-step approach was used to investigate the effect of longitudinal reinforcement discontinuities on the seismic performance of reinforced concrete structural walls. In the first step, six cyclic tests on small-scale reinforced concrete structural walls were conducted to study the effect of bar cutoffs. Three of the six specimens had web longitudinal reinforcement cutoffs to simulate the effects of a retrofit practice used in Japan. The test results indicated that this discontinuity resulted in approximately 50% increase in the unit tensile strains in the longitudinal reinforcing bars in boundary elements. Larger unit tensile strains caused an increase in permanent strain accumulation, increasing the likelihood of bar buckling. In the second step, the mentioned test results were combined with test results from previous tests (that investigated discontinuities related to lap splices) to calibrate equations for estimating drift capacity of structural walls with and without reinforcement discontinuities.

Experimental and ANN analysis of temperature effects on the permanent deformation properties of demolition wastes

Abstract The aim of this research is to study the effect of temperature and stress levels on the permanent strain of blends of two types of recycled waste materials, namely recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP). RAP was mixed with RCA in different percentages of up to 80% by dry mass. A three-stage repeated load triaxial (RLT) testing procedure was employed for evaluation of permanent strain of RCA/RAP blends in different stress paths and temperatures. The tests were conducted at different temperatures of 5 °C, 20 °C (room temperature), and 50 °C, to assess the behavior of blends in a wide range of temperatures. The addition of RAP was found to result in an increase of permanent strain of the blends. As the RAP content increased in the blends, the accumulation of permanent strain increased at 50 °C. The specimens with up to 40% RAP exhibited stable behavior at 50 °C in all stages of the test. With increasing RAP content, the permanent strain behavior of the specimens was found to improve for the same blends at 5 °C. Based on the results of the experiments, an artificial neural network (ANN) model was developed for prediction of permanent strain of blends and investigating the impact of the test variables. Effect of RAP content, temperature, deviator stress, and number of cycles was evaluated. Although the RAP content and temperature were found to have a significant effect on the permanent strain, the number of cycles in the RLT test was found to be the more predominant influencing factor.

Asymmetric input motion for accumulation of lateral ground deformation in laminar container shake table testing

Due to seismic response, accumulation of permanent ground deformation (lateral spreading) is an important mechanism of much practical significance. Such deformations typically occur near a ground slope, behind retaining structures such as sheet-pile and quay walls, and in mildly sloping ground. In conducting a shake table test, the generation of permanent deformations further elucidates the underlying mechanisms and allows for related ground–foundation–structure response insights. In this paper, an approach for development of accumulated ground deformations is presented, in which asymmetric inertial loading results in a biased dynamic one-dimensional shear state of stress. As such, the proposed approach allows for further insights into the soil cyclic response and pore pressure build-up, with deformations accumulating in a preferred direction. To permit a virtually unlimited number of such loading cycles, focus is placed on motions that do not cause the shake-table actuator to accumulate displacement, in view of its possible limited stroke. Using this approach, representative experimental response is outlined and discussed. This experimental response can be used for calibration of numerical models to emulate the observed permanent strain accumulation profile and associated mechanisms. In addition to liquefaction-induced lateral spreading, this asymmetric shaking approach might be beneficial for a wide class of earthquake engineering shake table testing applications.

Discrete Element Modeling of Permanent Deformation Accumulation in Railroad Ballast Considering Particle Breakage

Particle shape and mineralogy have been found to greatly affect railroad ballast response under train loading. In this research effort, the effect of particle breakage on ballast permanent deformation behavior was studied using the Discrete Element Method (DEM). Real ballast particle shapes were digitized using an inexpensive imaging tool, and agglomerates of spheres were used to regenerate those complex shapes. Particle crushing tests were carried out in the laboratory, and discrete element models simulating the crushing test were calibrated based on the laboratory test results. Model parameters established through this calibration process were subsequently used to study the permanent deformation response of ballast layers comprising complex-shaped breakable ballast particles under repeated loading. The effect of particle shape was studied by comparing the permanent deformation behavior for ballast layers comprising simplified ellipsoid particles to those comprising the complex-shaped particles simulated using agglomerates of spheres. The simulation results clearly highlighted the significance of particle breakage in ballast permanent deformation accumulation under cyclic loading. Most particle breakage was observed to occur under the initial load cycles, which also corresponded to the highest rate of permanent strain accumulation. The particle breakage as well as the rate of strain accumulation gradually decreased with increasing load cycles.

A study on slip activation for a coarse-grained and single crystalline CoCrNi medium entropy alloy

The new CoCrNi medium entropy alloy (MEA) has emerged to be one of the most promising systems which provide extraordinary ductility and strength at cryogenic temperatures. In this study, utilizing both polycrystalline and single crystal specimens, as well as advanced optical strain measurements, the deformation mechanisms dictating the mechanical behavior at the onset of plasticity were detected and precisely quantified. Independent of deformation temperature, the accumulation of permanent strains at the microstructural level was attributed to plastic slip at the onset of yielding and at low levels of deformation (<10%). The resolved shear stress for slip activation was measured to be 78 MPa at 298 K and between 140 MPa and 160 MPa at 77 K. These unique measurements were used to provide an estimate of the temperature dependent resolved shear stress for slip at temperatures ranging from 77 K to 575 K. In addition, strain heterogeneities at the grain-scale were measured to study the nucleation of slip at the micro-scale in polycrystalline specimens. In summary, the present study aims to quantitatively assess the accumulation of plastic strain and reveal the underlying deformation mechanisms (i.e., slip or/twinning) leading to the buildup of plastic strains at the microstructural level.

Shallow chalk quarry stability using an original shear strength reduction approach

Unexploited underground quarries may represent a potential hazard for the surrounding urban environment. In this context, this work presents a stability study of quarries in North France. A shear non-uniform non-homogeneous degradation approach is proposed for the stability study. The presence of joints in the chalk continuum is considered by using an anisotropic plasticity model accounting for the accumulation of permanent strains along these joints. Stability analysis using proposed degradation approach is performed and compared with the conventional shear strength reduction approach. The comparison shows that the proposed degradation approach might be an alternative to conventional shear strength reduction approach.

A review on permanent deformation of granular material

Long-term behavior of a granular material under repeated loading plays a vital role to understand the behavior of rutting in pavements. Many researchers observed the behavior of permanent strain accumulation in the granular material under cyclic loading condition. The permanent deformation of granular material caused by numerous factors varies with the degree of each factor influence on granular material. This paper summarizes and discusses the impact of individual factors on permanent deformation of granular material through reference to published scientific data. As well, this paper outlines the different constitutive models to find the permanent strain and discusses the permanent strain modelling using shakedown theory.

Dense-graded aggregate base gradation influencing rutting model predictions

Abstract This paper presents findings from an ongoing research study at the University of Illinois focused on developing and calibrating an improved permanent deformation model for unbound aggregate materials through laboratory testing and characterization. The project scope included testing sixteen aggregate materials, commonly used in the state of North Carolina for pavement base courses, in the laboratory through monotonic and repeated load triaxial testing. This paper primarily focuses on quantifying effects of aggregate gradation on permanent deformation behavior. To accomplish this, four materials were tested at both: (1) “source gradations,” i.e. original gradations from quarry, and (2) an “engineered gradation,” i.e., standard reference gradation at which aggregate specimens were prepared for testing. Predictive rutting models were developed to consider the influences of shear strength and applied stress states on permanent deformation accumulation. Rutting model parameters obtained from testing aggregate specimen at one gradation could be used to reasonably predict the permanent deformation accumulation in another sample given the shear strength properties did not show notable differences. For specimens corresponding to significantly different amounts and/or plastic nature of fines, the permanent strain levels predicted using one set of model parameters differed significantly from those predicted using another set of model parameters developed for another gradation. Moreover, the effects of gradation on permanent strain accumulation were significantly more pronounced at the higher shear stress ratios (e.g. 0.75), compared to lower shear stress ratios; which is defined as the ratio between the shear stress applied to a specimen during repeated load triaxial testing compared to the corresponding shear strength under the same confinement.

FATIGUE RESISTANCE OF SURFACE TEMPERATURE REDUCING PAVEMENT UNDER FIXED-POINT LOAD

Asphalt and concrete pavements cover a high percentage of urban area. In the summer season,the surface temperature of asphalt pavements exposed to the solar radiation increases to 60°C or more. Thisis one cause of the urban heat island phenomenon. In the field of road engineering, cool pavements have beenconstructed to decrease the surface temperature and to improve the road environment. We have previouslystudied the cement-based grouting material containing cement, ceramic waste powder, and natural zeolite forcool pavements. This cool material is poured into voids in porous asphalt pavements. The constructionmethod for this cool pavement is the same as that for water retaining pavements. The temperaturemeasurements show that the surface temperature was lower by 15-20°C than the conventional porous asphaltpavement temperature of 60°C. On the other hand, the accumulation of permanent strain in the asphaltpavements causes rutting under passing traffic loads in the hot summer season. In this study, the fatigue testsunder a fixed-point load were conducted to evaluate the fatigue resistance of the surface temperaturereducing pavement at 40°C. The fatigue resistance of pavements under various loading levels is evaluated atsinking displacements of 15 and 20 mm. The test results show that the surface temperature reducingpavement has a higher fatigue resistance than conventional porous asphalt pavements.