Cyclic Traffic Loading Research Articles

Analysis of Static and Cyclic Traffic Loading of an Embankment Supported by a Geogrid Retaining Structure

Abstract The article deals with a deformation analysis of a road embankment under different types of static and cyclic loading. A typical cross-section of a road embankment supported by geogrid retaining structures is considered. In the case of a design, the load is usually applied as a distributed static load. The analysis presented in the paper includes all the most loading methods used. Because there are only a few measurements for these types of construction in a given region, the analysis also includes a cyclic loading that aims to simulate real traffic loading. The cyclic loading considered the weights of cars and trucks and the distances between them, based on traffic intensity measurements. The study results showed how significant the differences in vertical and horizontal deformations of an embankment are when the different types and methods of static loading are used in a design. The results of the cyclic loading showed the deformations that can be expected from current real traffic.

Influence of Wet or Dry Conditions on the Fatigue Life of Grout Cementitious Materials under Cyclic Loading

Grouting cementing material is a kind of sealing cementing material widely used in underground space. However, the influence of the fatigue life after cementation hardening is often ignored when subjected to, for example, cyclic traffic loads. Therefore, it also often causes engineering problems such as joint cracking, leakage, and plate bottom emptiness. The prediction of fatigue life of grouting cementation material is of great significance to the stability of underground tunnel structure. In this paper, the fatigue characteristics of hardened grout specimens under different fatigue loads and cycle frequencies are studied. Test the cyclic compression load repeatedly in different environments (dry or wet). The results show that the fatigue properties of grout materials are reduced in both air and water and significantly reduced when the stress level is 65% or above of static compressive strength in wet environment, especially when the loading frequency in water drops from 10 to 35 Hz. The main mechanism of fatigue life decline is splitting effect caused by water extrusion in the sample under cyclic loading. Water washes away abrasive action in the cracks. The dry-wet fatigue aging characteristics of superhigh strength grout cement materials lay a foundation for the evolution simulation of underground foundation structures under cyclic loading.

Experimental evaluation of the usability of palm tree pruning waste (PTPW) as an alternative to geotextile

This paper focuses on serving twofold benefits for the environment by providing not only recycling of a waste material but also improving rutting performance of sand subgrade under cyclic traffic loads. In this context, a series of laboratory experiments have been conducted to benchmark the performance of commercially manufactured geotextile and palm tree pruning waste (PTPW) as soil improvement agents. Experimental results of the study were evaluated based on permanent (plastic), total, and elastic deformation, rut depth reduction (RDR), traffic benefit ratio (TBR), percentage of elastic deformation, and resilient modulus (MR). In the view of experimental results, geotextile and PTPW-reinforced sand subgrades demonstrated well performance in the sense of permanent and elastic deformations when compared to unreinforced case. It is also realized that the most satisfactory performance was obtained when geotextile or PTPW are located at a burial depth of both 50 mm and 100 mm. In that case, TBR values of geotextile and PTPW-reinforced subgrades were almost the same at 20 mm permanent deformation (i.e., 6.71 and 6.76, respectively). Furthermore, when the results were evaluated based on RDR, it is observed that geotextile and PTPW reinforcements reduced the rut depth at the rate of 49.31 % and 37.15 % at the end of 5000 load cycle, respectively.

Investigation of flexible pavement maintenance patching factors using a finite element model

Patching of flexible pavements is one of the most important functions of pavement maintenance. Although finite element modeling has become commonplace in the world of pavement engineering, modeling has not yet been significantly leveraged for maintenance applications which improve safety, ride quality, and pavement service life. The objective of this study was to model viscoelastic properties of pavement and patching materials to determine the effect of various repair factors on pavement performance using the finite element method. Specifically, surface permanent deformation, local shear stress concentration, and horizontal strain distribution were investigated. Two types of models were simulated; the first model applied static loading to a surface layer fixed on a plate and the second model applied cyclic traffic loading to a two-layered flexible pavement system. The results demonstrate the importance of patching using a semi-permanent method. The results also demonstrated the accumulated effect of repeated loading using a time-dependent material response. Results also indicated that a larger patching area resulted in less influence of the shape of the area, while a circular area proved superior to a conventional rectangular patch for sizes near the tire footprint and smaller than it. Different responses were observed depending on the type of patching material modeled, demonstrating the effect of material choice in maintenance applications. Finally, mesh optimization was performed to ensure appropriate mesh sizes are used in future studies to accurately represent the pavement layers and patches.

The effects of cyclic loading on the reconsolidation behaviours of marine sedimentary clays under intermittent drainage conditions

The reconsolidation settlement of marine sedimentary clay subgrade subjected to cyclic dynamic loading under intermittent drainage conditions needs to be further studied. In this study, a series of triaxial tests was conducted on natural Wenzhou soft clays to investigate the reconsolidation responses induced by staged cyclic loading under intermittent drainage conditions. The dynamic behaviours of the test specimens, such as the evolution of excess pore water pressure, variations in stress-strain hysteresis loops and resilient modulus, and cumulative strain development, are analysed and discussed. The experimental results show that during the intermittent quiescent drainage period, the dissipation of the excess pore pressure generated during the cyclic loading period results in reconsolidation of the test specimen. Hardening occurs throughout the tests, as determined by observing the variations in the hysteresis loops and resilient modulus. Throughout the tests, a higher percentage of the axial plastic strain in the quiescent period to the total axial plastic strain indicates that the reconsolidation deformation of the soft clay subgrade caused by intermittent drainage cannot be ignored. These conclusions have significant value for performing in-depth research on the dynamic behaviours of marine sedimentary clays subjected to cyclic traffic loading and predicting the settlement of roads in engineering practice.

Synthesis and characterization of calcium alginate-attapulgite composite capsules for long term asphalt self-healing

Calcium alginate capsules can gradually release the healing agent inside without rupture under cyclic traffic loading and are a promising self-healing technology for asphalt pavement. However, they have a low strength and tend to release the healing agent too fast. To enhance the strength of calcium alginate capsules and prevent them from releasing healing agent prematurely, calcium alginate-attapulgite composite capsules were synthesized with different synthesis parameters and their physical properties, morphological characteristics, release and healing behaviors were studied respectively. It was found that the incorporation of attapulgite improved the strength of calcium alginate capsules and could prevent the capsules from leaking healing agent during the drying process. The incorporation of attapulgite also slowed down the healing agent (sunflower oil) release speed of the calcium alginate capsules. Calcium alginate-attapulgite composite capsules can release 55.2% of the oil inside after 4 years of service within a medium traffic grade pavement, providing asphalt mixture with the ability to release the oil gradually to suit the cracking process of asphalt pavement. The released oil from the calcium alginate-attapulgite composite capsules improved the self-healing property of asphalt mixture and the capsules maintained their original spherical shape after releasing most of the oil inside.

Experimental study of the performance of a stress-absorbing waterproof layer for use in asphalt pavements on bridge decks

The presence of negative bending moments at the top of a continuous beam bridge can facilitate the sawing of false seams. The concrete bridge deck and its asphalt pavement will therefore develop transverse fatigue cracks under long-term cyclic traffic loads. This paper aims at preventing reflective cracks from forming in such asphalt pavements. The structure and materials used in crack prevention based on a composite stress-absorbing layer (CSAL) consisting of a geotextile and an asphalt gravel seal coat were investigated. The properties of polypropylene (PP) geotextiles were evaluated by means of differential scanning calorimetry, thermogravimetric analysis, thermal shock tests, etc. Adhesion, shear, and tensile tests were used to study the influences of factors such as the type, amount of asphalt materials, and construction temperature on the bonding performance of the pavement interface. Texas overlay tests were also carried out to explore the anti-reflective cracking and anti-fatigue performance of different pavement structures including an asphalt rubber stress-absorbing membrane interlayer (ARSAMI) and a CSAL. The results show that the PP geotextile has a melting point of about 166 ℃, a glass-transition temperature in the range of –20 to –10 ℃, and a thermal decomposition temperature of about 400 ℃. In addition, it retains good strength and deformability when subjected to thermal shock at 180 ℃, and it has high thermal stability. The modified asphalt has the highest adhesion strength to concrete slabs, followed by ordinary asphalt and then emulsified asphalt. The temperature state of the bonding layer is not sensitive to the bond strength of the bridge deck paving structure. The asphalt mixture waterproofs the surface after paving. The adhesive stress-absorbing layer imparts a secondary heating effect, thereby ensuring interface adhesion. Using a pavement structure with a CSAL can enhance resistance to reflective cracking at a low temperature by more than 5 times compared to the case not taking preventative measures. Its resistance to reflective cracking under a deformation amplitude of 2 mm at the room temperature (20 ℃) is also slightly better than that of the ARSAMI. Hence, CSALs have promising prospects for use in crack prevention.

Probabilistic method for evaluating the permanent strain of unbound granular materials under cyclic traffic loading

In this study, a series of large-scale cyclic triaxial tests with different water contents (w), confining pressures (σ3), and dynamic deviatoric stresses (σd) is performed to investigate the accumulative permanent strain (εp) behavior of an unbound granular material (UGM) used in the construction of railway subgrade beds. Results indicate that an increase in confining pressure effectively inhibits the development rate of εp, and the εp behavior of stable specimens can be categorized into an initial rapidly increasing stage and a subsequent gradual stabilization stage, with different causes of material strain at each stage. The permanent strain accumulated from the first loading cycle, i.e., the model parameter a, demonstrates a power function relationship with the dynamic-static deviatoric stress ratio (η), and the model parameter b, which implies the increasing rate of εp, is strongly correlated with η and w. A probabilistic method based on a semi-logarithmic prediction model and probabilistic failure theory is proposed to evaluate the development range of εp of UGMs while considering the effects of the confining pressure, dynamic deviatoric stress, static failure deviatoric stress, and water content. Applications of the proposed method indicate that the developed probabilistic model can yield acceptable εp predictions of UGMs.

Mathematical modelling of resilient modulus response of fibre reinforced clay subgrade for pavement design

Cohesive soils forming the subgrade layer of flexible pavements undergo excessive rutting and deformation under cyclic traffic loading and therefore, polyester fibre reinforcement has been proposed in this study for increasing the strength and stiffness of the soil. Resilient modulus is a stress dependent parameter used to characterize the behaviour of pavement layers under repeated traffic loading. The resilient modulus of raw and reinforced clay was determined in laboratory under un-soaked and soaked conditions, using advanced cyclic triaxial test under pre-defined stresses that are seldom the true representative of confining stress, cyclic deviator stress and bulk stress acting in a pavement structure. Therefore, mathematical modelling of resilient response of raw and fibre reinforced soil samples was done for three models proposed in the literature and the values of coefficient of regression (R2) were determined. Fibre reinforcement resulted in significant gain in strength and stiffness of the soil. The effect of different regression coefficients was studied and the best model for estimation of resilient modulus was suggested.

Creep Model of High-Strength High-Performance Concrete Under Cyclic Loading

Concrete creep under both static and cyclic loading conditions was investigated. Four groups of high-strength high-performance concrete (HSHPC) prism specimens were fabricated, and three of these specimens were loaded periodically by the MTS Landmark Fatigue Testing Machine System. Creep characteristics and creep coefficients of HSHPC under static loading and cyclic loading, respectively, were obtained and compared. The experimental results show that the creep strains under cyclic loading with a mean stress of 0.4 fcp and an amplitude of 0.2 fcp increase significantly compared with the creep strains under static loading, and the maximum value was 1.2–2.3 times at early stages. In addition, the creep coefficient increases nonlinearly with the number of cyclic loading repetitions. The influence coefficient for cyclic loading γcyc=1.088×(N/N0)0.078 was introduced based on the previous HSHPC creep model, and then the modified creep model under cyclic loading was established. Finally, the residual method, the CEB coefficient of variation method and the B3 coefficient of variation method were applied to evaluate the modified creep model. The statistical results demonstrate that the modified creep model agrees well with the experimental measurements. Hence, it has important theoretical and practical values for accurately predicting the deflection of concrete bridges under cyclic traffic loading.

The mechanical behavior of epoxy asphalt mixture under cyclic loading

In order to investigate the mechanical behavior of epoxy asphalt mixture under cyclic traffic loading, cylindrical samples of the epoxy asphalt mixture were subjected to cyclic loading-unloading tests under varying confining pressures. The accumulation and dissipation of energy were observed in the energy evolutions. It turns out that the epoxy asphalt mixture exhibits elastic-plastic property in the first few cycles, and then the elastic property would be strengthened gradually in the cyclic loading tests. Applying a moderate confining pressure would significantly reduce the dissipated energy. The proportion of dissipated energy is about 25% from the unconfined test, and less than 15% from the confined test. As a result, more energy would be required if to produce equal permanent deformation under higher confining pressures. Therefore, a moderate increase in the confining pressure would be helpful in restraining permanent deformation, such as rutting.

Soil moisture and density monitoring methodology using TDR measurements

ABSTRACT Soil moisture content (MC) and density of pavement materials exert a great influence on pavement performance. Cyclic traffic loading with increasing MC in materials can accelerate changes in density significantly. Time domain reflectometry (TDR) is a non-destructive method for measuring MC and density of soil. In this study, TDR measurements were taken in the laboratory for a typical road material at two different conditions; at constant MC with different density and at constant dry density with different MC. Based on TDR measurements, a theoretical formulation between voltage drop occurring for the passage of an electromagnetic wave through the soil and the electrical conductivity (EC) is developed. This relationship is further correlated to develop density function providing the opportunity to obtain MC information. For the validation of the calibration functions, sensors are installed in roads to obtain field data. Laboratory results point out that the calibration models are independent of moisture and density, and the field instrumentation shows the satisfactory accuracy of the method. The newly established calibration models allow for observing the routine performance providing a better understanding of the material behaviour for example rutting of roads.

Reduction of subgrade fines migration into subbase of flexible pavement using geotextile

Pumping in pavement is defined as traffic-induced migration of saturated subgrade fines into overlying granular layers or onto the surface of the pavement, negatively impacting the performance and service life of the pavement. The objective of this study was to assess the capability of geotextile as a separation and filtration layer in reducing subgrade fines migration. A one-third scale Model Mobile Load Simulator, an accelerated pavement testing device, was used to simulate the cyclic traffic loading on a scaled model of a flexible pavement. The results from three scaled pavement tests were compared to evaluate the effectiveness of geotextile separation and filtration in reducing subgrade fines migration. The three tests had identical configurations, except that a geotextile layer was placed at the interface of subgrade and subbase in one of the tests. The lab testing revealed that, under cyclic traffic conditions, the migration of subgrade fines into subbase was significant. However, using a geotextile at the subgrade-subbase interface significantly reduced the subgrade pumping. At the end of the test, the fines that migrated to the subbase, based on % mass of subbase, were 6.39% in the tests without geotextile and 1.81% in the test with geotextile. An approximately 30% reduction was observed in the amount of pavement rutting when using geotextile at the top of the subgrade. The subgrade soil migration in mass percentage increased with the traffic loading cycles, and more migration occurred in the bottom half than in the top half of the subbase. The study concludes that geotextile can be used as an effective means to reduce pumping of subgrade fines in pavement by providing both separation and filtration.

Cyclic behavior of natural organic clay under variable confining pressure that match traffic loading conditions

ABSTRACTOne-way cyclic loading is more typical for traffic loading and cyclic triaxial test has been recognized as a useful method for solving many engineering problems. Under traffic loading, the influence of variable confining pressure on cyclic behavior of natural organic clay subjected to cyclic traffic loading is rarely reported in the literature. In this study, a laboratory investigation on undrained cyclic behavior of natural organic clay is presented and conducted by cyclic triaxial apparatus. Tests are conducted by both constant confining pressure and variable confining pressure, to simulate the loading conditions induced by passing vehicles in actual engineering. Different stress levels are also considered in this study. By comparing between the results of constant confining pressure tests and variable confining pressure tests, it shows that the one-way cyclic behavior of organic clay is influenced significantly by variation of confining pressure, in terms of pore water pressure, permanent axial strain and stress–strain hysteretic loops.

Measuring the migration of subgrade fine particles into subbase using scaled accelerated flexible pavement testing – a laboratory study

Pavement structure typically consists of an asphalt concrete or concrete surface layer, underlying granular layers (subbase and/or base) and compacted subgrade soil layer. During wet seasons when the subgrade becomes saturated, cyclic traffic loading may result in pumping of fine particles from the subgrade up into the granular layer, which may lead to failure of the pavement. The objective of this research is to investigate occurrence of migration of fines and to determine the magnitude and rate of such migration. A one-third scale accelerated pavement testing device is utilised to simulate the cyclic traffic loading on two geometrically scaled flexible pavements representing typical collector roadways and interstate highways. The pavement sections are constructed on partially saturated aggregate subbase overlying non-plastic saturated silt as subgrade. The lab testing reveals that, under cyclic loading conditions, a considerable amount of fines migrated into the subbase. The subgrade fines migration in mass percentage increases with the simulated traffic loading cycles. The resulting gradation from the migration of subgrade fines into the subbase also varies with the depth in the subbase: more fines are deposited in the lower section (closer to the subgrade) than in the upper section of the subbase.

Influence of shear stress level on cyclic deformation behaviour of intact Wenzhou soft clay under traffic loading

Under traffic loading, the soil elements in subgrade are subjected to a cyclic cardioid-shaped stress path in the 2τvh~(σv−σh) stress plane. This significantly differs from the conventional stress paths that have been simulated using the cyclic triaxial and simple shear apparatuses, as widely reported in the literature. To date, the influence of shear stress level on cyclic deformation behaviour of intact soft clay subjected to cyclic traffic loading were rarely considered in the existing experimental investigation. For this reason, a series of cyclic hollow cylinder experiments that mimic cardioid-shaped stress paths are carried out on intact samples of Wenzhou soft clay. A wide range of vertical stress levels combined with different shear stress levels (i.e., different cardioid-shaped stress paths) are simulated in the experiments. The results show that the shear stress level significantly influences the cyclic straining and exacerbates the potential of cyclic shear failure. The difference of cyclic tests with variable shear stress level increases as the vertical cyclic stress ratio value increases. Based on the test results, an allowable cyclic stress ratio is determined to be about 0.22, which may serve as the upper bound limit of cyclic traffic loadings on soft clayey deposit. For the hollow cylinder specimens used in this study, a resilient axial strain of 3% could be a proper failure criteria value. A simplified permanent strain model that considers shear stress is proposed for the deformation behaviour of soft clay under cyclic traffic loading.

Stress–strain response of soft clay to traffic loading

Approximately 25% of China's 120 000 km of expressway, as well as many new metro lines and airports, rest on soft clay deposits. However, service settlements are proving larger than expected, especially in southeast China. This note describes laboratory experiments on K0-consolidated intact samples of soft clay taken near Wenzhou, south-east China, that explore whether cyclic traffic wheel loading contributes significantly to the observed settlement trends. Cyclic triaxial (CT) tests are reported together with cyclic hollow cylinder (CHCA) experiments that imposed cardioid-shaped 2τzθ − (Δσz − Δσθ) stress paths. Cyclic principal stress axis rotation is shown to have an important influence on vertical straining. Once a certain threshold has been exceeded, the resilient and permanent strains developed in the CHCA tests become progressively larger than their counterparts in CT tests conducted at the same vertical cyclic stress ratio, with trends that diverge progressively as vertical cyclic stress ratio increases. Critical cyclic stress ratios can be defined that divide the response into (a) stable, (b) metastable and (c) unstable cyclic ranges. The novel experimental approach and high-quality data reported should aid practitioners and modellers in developing new analyses to address this economically significant geotechnical problem.

Resilient modulus for unbound granular materials and subgrade soils in Egypt

Mechanistic Empirical (ME) pavement design methods started to gain attention especially the last couple of years in Egypt and the Middle East. One of the challenges facing the spread of these methods in Egypt is lack of advanced properties of local soil and asphalt, which are needed as input data in ME design. Resilient modulus (Mr) for example is an important engineering property that expresses the elastic behavior of soil/unbound granular materials (UGMs) under cyclic traffic loading for ME design. In order to overcome the scarcity of the resilient modulus data for soil/UGMs in Egypt, a comprehensive laboratory testing program was conducted to measure resilient modulus of typical UGMs and subgrade soils typically used in pavement construction in Egypt. The factors that affect the resilient modulus of soil/UGMs were reviewed, studied and discussed. Finally, the prediction accuracy of the most well-known Mr Prediction models for the locally investigated materials was investigated.

Alkali-Silica Reaction in Concrete Pavements

A significant number of German concrete motorway pavements have shown damage only a few years after construction. The alkali-silica-reaction (ASR) is often one of the reasons for this damage. German guidelines and regulations focus on the optimisation of the concrete composition to avoid damage due to ASR. Moreover, diverse research projects have dealt with the development and optimisation of ASR performance test methods with and without external alkali supply. However, the influence of other parameters on the occurrence and intensity of a damaging ASR had not yet been taken into account. Such parameters include, e.g., insufficient curing and the modifications of concrete’s porosity due to the use of slip form pavers. Likewise, the increased traf-fic loading had not yet been considered. The Federal Institute for Materials Research and Testing (BAM) assesses these parameters and processes in a number of projects. These projects aim primarily to increase the durability of the concrete pavements, in particular by improving preventive measures that may be taken before or after the construction of concrete pavements. This paper gives a short overview of BAM’s projects concerning ASR in concrete pavements. Furthermore, results regarding the influence of the cyclic traffic loading on ASR are presented.

Simulating the cyclic behaviour of unsaturated soil at various temperatures using a bounding surface model

Soils in many earth structures are often unsaturated and subjected to cyclic loads (e.g. subgrade soil in pavement under cyclic traffic loads) under various climatic conditions. Although many constitutive models have been reported for modelling unsaturated soil behaviour, none of them is developed purposely to capture the cyclic behaviour of unsaturated soil at various temperatures. In this note, a new cyclic thermo-mechanical model for unsaturated soil is developed using the bounding surface plasticity theory. Differently from conventional elastoplastic models, plastic strain is allowed inside the bounding surface to capture cyclic stress–strain relations. The new model is developed in terms of mean Bishop's stress, deviator stress, suction, temperature, specific volume and degree of saturation. Thermal, hydraulic and mechanical behaviour of unsaturated soil are fully coupled. Computed results from this model are compared with measured data from suction- and temperature-controlled cyclic triaxial tests on an unsaturated silt. It is shown that computed and measured plastic strains are generally consistent at various numbers of cycles, suctions and temperatures.