A numerical model to predict train induced vibrations is presented. The dynamic computation considers mutual interactions in vehicle/track coupled systems by means of a finite and discrete elements method. The rail defects and the case of out-of-round wheels are considered. The dynamic interaction between the wheel-sets and the rail is accomplished by using the non-linear Hertzian model with hysteresis damping. A sensitivity analysis is done to evaluate the variables affecting more the maintenance costs. The rail-sleeper contact is assumed extended to an area defined contact-zone, rather than a single point assumption which fits better real case studies. Experimental validations show how prediction fits well experimental data.

Minimizing the environmental impacts is a challenging task to achieve sustainability in road constructions. Although they are only temporary, the environmental burdens of building activities can have a great impact on the environment and communities, and must be properly assessed and mitigated. A comprehensive evaluation of the impacts requires the consideration of all construction activities, construction sites and the type and operation time of off-road machines and plants that will be used in each site. In this paper, a case study relating to the project of a motorway was carried out with the following objectives: (i) to estimate the dust and gases arising from the whole construction process and identify the most critical pollutants in terms of emitted quantity; (ii) to investigate the worksites, activities and processes with the greatest impact from an emissive standpoint, and (iii) to propose a rational approach for designing and putting in place effective mitigation measures. Carbon oxide (CO), nitrogen oxides (NOx), and fine particulate matter (PM10) emissions have been estimated by applying different models, methodologies and databases, depending on the construction process under analysis, and an emissive balance sheet has been produced. Results showed that CO is the pollutant released in the greatest quantity, followed by NOx. The emission of PM10, mainly due to the movement of trucks on unpaved roads, is one order of magnitude less with respect to CO and NOx, but produces the most perceived and undesired effects of the construction process in the interested communities. Tunnels and bridge are the components of a road with the greatest impact in terms of air emissions.

No abstract

International audienceIn this paper a numerical model to predict train induced vibration is presented. The dynamic computation considers mutual interactions in vehicle/track coupled systems by means of a finite and discrete elements method. The considered vehicle model consists of 7 two-dimensional discrete elements connected by spring/damper couples. The rail is modeled as finites beam elements connected to sleepers by pads areas. Supporting substructure consisting of pads, sleepers, ballast and foundation, is modelled as discrete elements. Components are connected each to others by spring/damper couples. Vertical profile of rail is considered as sum of trigonometric functions with phase and amplitude generated by a pseudo random process. The dynamic interaction between the wheel-sets and the rail is accomplished by using the nonlinear Hertzian theory. The strong point of this study consists in the model used to simulate the behaviour of pads. The rail-sleeper contact is assumed extended to an area defined such a contact-zone, rather than a single point assumption which fits better real case studies. Experimental validations show how prediction fits well experimental data

Abstract. This paper presents a numerical study of an aircraft wheel impacting on a flexible pavement. The proposed three dimensional model simulates the behaviour of flexible runway pavement during the landing phase. This model was implemented in a finite element code in order to investigate the impact of repeated cycles of loads on pavement permanent deformation.In the model a traditional multi-layer pavement structure was considered. In addition, the asphalt layer (HMA) was assumed to follow an elasto-viscoplastic behaviour.The results demonstrate the capability of the model in predicting the permanent deformation distribution in the asphalt layer.

No abstract

No abstract

The need to increase the durability of unpaved roads and the need to improve driver comfort have led to this research: to focus more attention on the use of reinforcements for this type of road. Unpaved roads are created by using an unbound granular base layer placed on compacted cohesive soils. When the subgrade is weak, due to its poor consistency and high compressibility, generally, a geosynthetic reinforcement (geogrid and/or geotextile) is placed over the subgrade, followed by a compacted granular fill layer. The use of geosynthetics can produce several benefits, such as draining, reinforcement, filtering, separation, and proofing. This paper aims to present a numerical investigation using 3-D Finite Element Modeling (FEM) to analyze the improvement, in terms of the rutting reduction of an unpaved road system, reinforced by a geogrid, under repeated traffic loads. 3-D FEM analysis was carried out on two unpaved road sections, one reinforced and the other unreinforced, with both subjected to an impulsive wheel loading. It can be concluded that a significant improvement in pavement behavior is obtained by placing a geogrid layer at the base-subgrade interface. In fact, the obtained results show that geogrid reinforcement can provide a relevant contribution to the reduction of permanent deformations.