Action Of Traffic Load Research Articles

Investigation of Water and Soil Migration and Mud Pumping of Subgrades under Traffic Load

Atmospheric precipitation leads to the increase of moisture in the subgrade. The moisture and soil migration in subgrade is a key scientific problem in evaluating the service performance of the subgrade and resolving or preventing mud pumping. Using a self-developed testing system as well as a numerical simulation model, a detailed study of the dynamic hydraulic characteristics, water migration mechanism, fine soil migration mechanism, and mud pumping properties of the subgrade was conducted. The results showed that water migrated into the upper layer of the subgrade under traffic load. Meanwhile, a pressure gradient for the pore water was generated in the subgrade. This kind of pressure gradient is beneficial for the moisture and fine soil migration. With rising groundwater level and increasing traffic load, the porosity of the subgrade soil differs at different depths. The fine soil migration is caused by water migration, which causes new migration channel for water in the subgrade. Then, a circulating system of moisture and fine soil is formed in the subgrade under a traffic load. After that, the upper layer subgrade soil is nearly saturated under the action of traffic load. Then, the nearly saturated soil liquefies instantaneously, becoming mud, under the action of traffic load. However, as the loading time progresses, the moisture and fine soil in the subgrade continue to migrate upward, resulting in the mud being pumped into the ballast and the gradual disappearance of liquefied soils at different depths.

Study on Deformation Characteristics of Low-Highway Subgrade under Traffic Load

Highway subgrade bears millions of traffic loads over the years, and its strength, stiffness, and long-term stability gradually decline. In this paper, dynamic triaxial tests were carried out to study the time evolution and spatial distribution of strain and pore pressure of highway-subgrade soil under the action of traffic load. The influence of traffic load on subgrade deformation was analyzed. Furthermore, a numerical-calculation model of the subgrade was established. The deformation characteristics of subgrade under driving load were analyzed. The main conclusions can be drawn as follows: (1) With the increase in loading times, the cumulative strain and pore pressure can be roughly divided into three stages: rapid-growth stage, slow-growth stage, and equilibrium stage. (2) The influence of traffic load on the cumulative strain and pore-water pressure of subgrade soil decreases rapidly with the increase in depth. (3) The amplitude of traffic load has a tremendous influence on the strain and pore pressure of subgrade soil, especially for shallow subgrade. (4) As the distance from the subgrade surface increases, the maximum deformation appears at the edge of the subgrade.

Fuzzy Plastic Constitutive Model and Its Application to Subgrade

The subgrade of a road is subjected to cyclic loading and unloading under the action of traffic loads. To study this mechanical response, the plastic membership function was introduced into the modified Cambridge model, and thus, the fuzzy plastic Cambridge constitutive model was obtained. With the continuous evolution of the plastic membership function from 0 to 1, the fuzzy plastic Cambridge constitutive model continuously transitions the plastic properties inside and outside the initial yield surface. The evolution of the plastic membership function can replace the complex hardening law. The reliability of the model was verified using triaxial tests and simple cyclic loading and unloading tests. Using the finite element method, the mechanical response of the subgrade under cyclic loading was calculated. The fuzzy plastic Cambridge model can explain the insignificant yield characteristics of geotechnical media. In the fuzzy plasticity theory, the stress inside and outside the initial yield surface can produce plasticity. Absolute plasticity was not observed; only different degrees of plasticity existed.

Influence of phytoncide activity of Thuja occidentalis L. on strains of microorganisms under the action of car load (Dnipro city)

Landscaping of modern cities is impossible without increasing the area of green planting, which performs the function of turning the environment into more health-friendly one. Especially valuable are the species of ornamental plants that have high volatile activity. Because volatiles regulate the balance of pathogenic microflora in the air of cities, they significantly improve people's living conditions. According to the results of a previous study it was found that Thuja occidentalis L. and Th. plicata Donn ex D. Don f. “Zebrina” had the highest bactericidal activity during the winter among members of the family Cupressaceae. Given the frost, wind, gas and smoke resistance of Th. occidentalis, the aim of the study was to investigate the dynamics of phytoncide activity of the needles of this tree species during the year in a relatively clean zone and under the influence of vehicle emissions on plants in the urban ecosystem of Dnipro. The material was collected in all seasons of the year at two monitoring points in Dnipro, which differ in the level of environmental pollution by vehicle emissions. Traffic intensity was determined by the Potichuk & Pilipaka method. Antimicrobial action of Th. occidentalis was studied by the method of placing the crops of microbial test cultures under the effect of volatile secretions of needles and evaluating the result on a scale of phytoncide activity. The test subjects were Staphylococcus epidermidis, Staphylococcus aureus, Micrococcus sp., Bacillus subtilis, Esherechia coli, Pseudomonas fluorescens, Candida albicans. Studies have shown that in a relatively clean area and under the action of traffic loads, the inhibitory effect of needles on the studied strains of microorganisms changes during the year: in winter it is the smallest, in spring begins to grow, in summer is maximum, and in autumn decreases again. Under the man-made growth conditions, the greatest volatile activity of Th. оccidentalis performs on test objects such as: S. aureus, Micrococcus sp. and E. coli. When affected by car load, there is significant inhibition of phytoncide production by needles in the presence of C. albicans, to a lesser extent – Ps. fluorescens and B. subtilis. It is recommended to use Th. оccidentalis in landscaping of urban areas with moderate traffic.

Standardization to evaluate the lasting capacity of rubberized asphalt mixtures with different testing approaches

Under the action of traffic load, the stress and failure state of pavement structure and materials are complex and diverse. Moreover, pavement materials are multi-phase, multi-component, and multi-scale mixtures. Their mechanical properties have significant differences in tension behavior, compression characteristics, and correlations with stress states. In view of the above problems, different testing approaches were carried out in this paper. A suitable yield criterion for rubberized asphalt mixtures was proposed. Then, the strength yield surface was determined under different loading rates. Based on the fatigue test results, the concept of fatigue stress ratio was further proposed. The relationship between the rubberized asphalt mixtures fatigue life and the fatigue stress ratio was established. The results showed that the yield criterion covers the impact of the loading rates and tensile-compression strength difference on the rubberized asphalt mixtures’ mechanical behavior. The strength yield surface's shape is elliptical in the σm-σe stress space and expands outward as the loading rate increases. This paper unified the fatigue equations under different testing approaches. The established fatigue equations reflect the viscoelastic characteristics and strength characteristics of materials. The study effectively solves the difficult problem of fatigue equation selection in the structural design of asphalt rubber pavement.

The effects of suction history on the cyclic behavior of unsaturated road base filling materials

Road base is usually subjected to cyclic traffic loadings as well as environment loads. Evidence shows that excessive permanent deformation of the road base may occur under the action of traffic loads and the complicated suction history induced by climate change. Currently, how the suction history of road base affects its long-term deformation remains unclear. To gain a deep understanding of the long-term deformation of road base, cyclic loading tests were conducted on the road base aggregates (mixture of crushed tuff aggregates and clay fines) under controlled suction and suction histories. A large-size soil-water characteristic curve (SWCC) test apparatus was designed and manufactured for the water retention test of the large-size specimen, and the large-diameter cyclic triaxial testing system (LDCTTS) was upgraded with the unsaturated control system to control the matric suction and suction history during the cyclic loading test. Test results show that the permanent axial strain of the mixture has a negative correlation with the current suction and maximum suction history. The effect of drying-wetting cycles on the permanent axial strain is significant. The permanent axial strain decreases with drying-wetting cycles at the drying path, while increases with drying-wetting cycles at the wetting path. The resilient modulus increases significantly with the current suction magnitude while is independent of the suction history.

Fabrication and performance of Tile transducers for piezoelectric energy harvesting

In recent years, pavement piezoelectric energy harvesting has become one of the most promising road energy harvesting system clean energy sources. However, it is difficult for existing piezoelectric transducer structures to meet road power generation requirements. In this study, ceramic grinding and polishing techniques were used to make curved piezoelectric ceramic units with controllable curvatures. A new type of Tile transducer for roadway applications was developed in combination with an elastic metal base. Under the action of traffic load, the Tile transducer was subject to both vertical stress and a horizontal tearing force. Laboratory tests were performed on Tile transducers with simply supported and fixed boundary conditions, and the effects of concentrated and uniformly distributed loads on energy harvesting efficiency were analyzed. When the excitation frequency was 6 Hz and the load was 0.7 MPa, the output power of the Plane transducer was 0.23 mW, while that of the Tile transducer was 24.5 times as large at 5.65 mW. The ultimate compressive yield strength of a single Tile transducer could reach 2.18 kN, and the load limit was 1.5 kN at an excitation frequency of 10 Hz. This meets traffic load requirements. The open circuit voltage peak did not decrease substantially when 360 000 cyclic loading processes were performed. This indicated that Tile transducer structural performance was stable and that the transducer was durable. Based on the test results, an effective Tile transducer packaging method is proposed for application in road power generation systems.

The analysis of the factors affecting the macrotexture of bauxite clinker aggregate gradation

In this research, influencing factors on the macrotexture of bauxite clinker aggregate gradation were analyzed and the role of aggregate in the anti-skid performance of asphalt pavement was determined. AMES road texture laser scanner was used to conduct macrotexture tests. It was found that the macrotextures of single grain size aggregates were enlarged as grain size was increased, the macrotextures of mixed grain size aggregates were enlarged as the proportion of small grain size particles was decreased and both fine aggregates and mineral powder extended aggregate structure. Meanwhile, the effect of aggregate size on the macro-structure of the pavement was greater than that of percent voids in coarse mineral aggregate in the dry rodded condition (VCA). In addition, mean texture depth (MTD) was first decreased and then increased with the increase of compaction work. Under the action of traffic load, macro-structure was fluctuated. The results of this paper provide some references for road designers to consider macrotexture in gradation design.

Evaluation of the influence of water and temperature on the rheological behavior and resistance to fatigue of asphalt mixtures

Damage caused to asphalt layers by the action of traffic load, along with water and temperature, is the main factor responsible for the progressive deterioration of pavement structures. Although many studies have been carried out and the effect of water on asphalt mixtures has been reported, this phenomenon is not yet taken into consideration in models for dimensioning the thickness of asphalt layers. This paper reports the results of a study on the effect of water and temperature on the rheological behavior, complex modulus and fatigue resistance of an asphalt mixture formulated with a conventional asphalt binder with a penetration grade of 30/45. This evaluation was carried out through 2-point bending (2PB) tests, where trapezoidal specimens were submitted to wetting-drying cycles at 60 °C and then tested with immersion in water at different temperatures. On comparing the results with those obtained from specimens tested without conditioning and immersion and employing Huet-Sayegh’s rheological model with the introduction of the damage factor (D), it was possible to evaluate the effect of the action of water and temperature on the graphical representation of the complex modulus and on the reduction in the fatigue life of the asphalt mixture. The results obtained highlight the need to take into account the action of water and temperature on the dimensioning of the thickness of the asphalt layers as well as on the prediction of the lifespan of these coatings, mainly in regions with a tropical climate.

Experimental Study on Geosynthetic Reinforced Soil Dynamic Characteristics under Cyclic Loading

The technology of geosynthetic reinforced soil has been widely used in the structural strengthening of highway subgrade. Under the action of long-term vehicle cyclic loading, geosynthetic reinforced soil can effectively improve the bearing and deformation resistance capacity of the subgrade, improve the long-term stability of the highway structure and prolong the service period of the road. At present, the quasi-static method to design the geosynthetic reinforced subgrade under the action of traffic load is not perfect enough, the research on dynamic property, design theory and parameters still lags far behind engineering practice and technology development. In this paper, we investigated the dynamic triaxial tests in laboratory with different kinds of soils (clay and silt), different confining pressures (50 Kpa, 100 Kpa and 150 Kpa), and different reinforcement layers (0 layer, 1 layer and 2 layers) to show the changes and influencing factors of dynamic elastic modulus and damping ratio. The experimental results will provide the basis for the parameter choice of geosynthetic reinforced subgrade with the influence of traffic load.

Effect of filler nature and content on the bituminous mastic behaviour under cyclic loads

The role of the filler in asphalt mixtures is particularly important because of its influence on mastic behaviour. The filler improves the resistance properties of bitumen against the action of traffic loads and temperature. However, the filler can also adversely affect bitumen in mastics excessively brittle and stiff due to inappropriate design. For these reasons, it is interesting to investigate the effect of filler type and content on mastic composition. This paper presents results from a strain sweep test applied to bituminous mastics prepared with different filler types and contents at several temperatures. The obtained stiffness modulus and failure strain results provide information to assess the fatigue behaviour of the analysed mastics.

Application of Pre-Cracking in Semi-Rigid Base to Mitigate Reflective Cracking

Because of the high strength and sound stability, the cement stabilized base has been widely used in high grade pavement in China. But shrinkage cracking are easy to occur in the cement stabilized base. Under the repeating action of traffic loads and temperature loads, this kind of cracks are easy to propagate towards the asphalt surface, being called “reflective crack”. Shrinkage cracks are not normally avertable in the cement stabilized base, in contrast with a few wide cracks of broad spacing, numerous thin cracks of narrow spacing contribute little to the severe reflection cracking. On the basis of this thinking, the pre-cracking technique as a promising approach is brought forward. Several vibratory roller passes to the cement-treated base at a short curing stage, typically 1 to 3 days after placement, to create a fine network of cracks, which avoids the wide and/or long cracks and creates the ideal crack model. Comparing to wide cracking, the degree of the stress concentration resulting from thin cracking is by far mitigated. The Finite Element Method is used to predict the ideal crack model, and then the mechanical responses of the semi-rigid pavement of single wide cracking and net hairline cracking under vehicle loading are numerically simulated, simultaneously compared and analyzed. The simulation analyses indicate that the pre-cracking technique is a very useful tool to mitigate the reflective cracks.

Influence of Design Parameters of Highway on the Deformation

Based on the geometry irregularity of pavement, an expression of the traffic load was put forward. The influence law of design parameters of each part of highway and pavement geometry irregularity on vertical deformation of highway was discussed by the three-dimension finite element numerical analysis. The research shows that the vertical deformation range of highway under the action of traffic load is generally semi-circular; the influence of surface stiffness on vertical deformation is different in different horizontal positions of surface; the influence of subgrade stiffness and foundation stiffness on vertical deformation is remarkable, but that of course stiffness is small; the rational matching of all parts of highway can effectively reduce the vertical deformation; with the increase of geometric irregularity index, the vertical deformation increases significantly.