Impact Forces and Energy of Flow-like Landslides Against Protection Barriers: a New MPM-validated Empirical Formulation

Full understanding the interaction mechanisms between flow-like landslides and the impacted protection structures is an open issue. In fact, while researchers have used several approaches, from experimental to numerical, it is true that the adequate assessment of the hydromechanical behaviour of the landslide body requires both a multiphase and large deformation approach.This paper firstly proposes a conceptual framework for a specific type of protection structure, namely a rigid barrier fixed to the base ground. Two different approaches are proposed: i) an advanced hydro-mechanical numerical model based on Material Point Method is tested in simulating the whole complex landslide-structure-interaction mechanism(s), ii) a more simplified empirical model is casted to estimate the impact force and the time evolution of kinetic energy. The calibration and validation of the empirical formulation are pursued, respectively, based on the MPM numerical results, and referring to a large dataset of field evidence for the peak impact pressure. Finally, the performance of the newly proposed empirical method is compared to the methods available in the literature and its advantages are outlined.

Investigating the severity of expressway crash based on the random parameter logit model accounting for unobserved heterogeneity

The present study utilized a random parameter logit (RPL) model to explore the nonlinear relationship between explanatory variables and the likelihood of expressway crash severity. The potential unobserved heterogeneity of data brought by China’s road traffic characteristics was fully considered. A total of 1154 crashes happened on Hang-Jin-Qu Expressway from 2013 to 2018 were analyzed. In addition to the conventional impact factors considered in the past, variables related to road geometry were also introduced, which contributed to expressway accidents significantly. The overall stability of the model estimation was examined by likelihood ratio test. Then, the average elastic coefficient of the significant factors at each severity level was also calculated. Several factors that significantly increase the fatal crash probability were highlighted: rainy/snowy/cloudy weather condition, low visibility (100– m), night without light, wet-skid road surface, being female, aged 41+ years, collision with a rigid barrier and some other obstacles, radius and length of horizontal curve, and longitudinal gradient. The parameters of four factors were random and obeyed normal distribution: night without light, being female, driving experience with 10 + years and with large vehicle responsible. These findings provide insights for better understanding of expressway crash severity. Some countermeasures were proposed about driver education, traffic law enforcement, vehicle and road design, environmental improvement, and so on.

Method to Correct the Velocity Variation Information of an Automatic Crash Notification System in Vehicle-to-Rigid Barrier Frontal Collisions

Automatic crash notification systems (ACNSs) play a key role in post-accident safety. To improve the accuracy and efficiency of ACNSs, a method to correct the velocity variation information of ACNSs was established. First, after the acceleration data of sled crash tests were analysed, the factors affecting the accuracy of the velocity variation information were determined, and the influence of the discrimination threshold and acceleration curve shape on the velocity variation information was examined. Second, according to the acceleration data generated by the simulation model of a sled crash, the correlation between the accuracy of the velocity variation information and influencing factors was modelled. Third, an automatic crash notification algorithm involving a velocity variation correction function (VVCF) was proposed based on the correlation model. Finally, to verify its reliability, the improved algorithm was applied to an automatic crash notification system (ACNS) terminal. The validation results show that the ACNS terminal can accurately identify collisions and transmit accident information. Moreover, more accurate velocity variation information can be retrieved.

MODELING AND ANALYSIS OF A VEHICLE DYNAMICS AT FRONTAL IMPACT INTO THE RIGID BARRIER USING A SYSTEM IDENTIFICATION TOOLBOX

The main objective of this paper is to create computer crash models (up to the level of the Kelvin model, where the coefficient of stiffness and damping is calculated by implementing appropriate numerical methods: Trust - Region, Lavenberg-Marquardt and so on) of measured real data that are obtained at the frontal impact of a vehicle into the rigid barrier. The process of modeling a vehicle crash can be done in two ways. One of them is related to CAE (Computer Aided Engineering) software including FEA. The other one (applied in this article) is based on the System Identification Toolbox, which contains MATLAB® functions, Simulink® blocks, and a special app for constructing models of dynamic systems from the measured input-output data.

Experimental Investigation on the Impact Dynamics of Saturated Granular Flows on Rigid Barriers

ABSTRACT Debris flows involve the high-speed downslope motion of rocks, soil, and water. Their high flow velocity and high potential for impact loading make them one of the most hazardous types of gravitational mass flows. This study focused on the roles of particle size grading and degree of fluid saturation on impact behavior of fluid-saturated granular flows on a model rigid barrier in a small-scale flume. The use of a transparent debris-flow model and plane laser-induced fluorescence allowed the motion of particles and fluid within the medium to be examined and tracked using image processing. In this study, experiments were conducted on flows consisting of two uniform and one well-graded particle size gradings at three different fluid contents. The evolution of the velocity profiles, impact load, bed normal pressure, and fluid pore pressure for the different flows were measured and analyzed in order to gain a quantitative comparison of their behavior before, during, and after impact.

Towards rational use of baffle arrays on sloped and horizontal terrain for filtering boulders

Baffle arrays are used to filter boulders from granular flows, such that the impact load exerted on barriers is reduced. However, current guidelines provide limited recommendations on baffle design. In this study, a calibrated Discrete Element Method modelled boulders entrained in a bulk granular assembly interacting with baffles and a terminal rigid barrier. Different baffle spacings relative to the boulder diameter (1 < s/δ < 4) were considered. A ratio of s/δ=1 is recommended for reducing the impact load by up to 80%, whilst s/δ = 4 renders an array of baffles inadequate for filtration. The optimum configuration is a staggered array with three rows of baffles on a horizontal plane in front of a barrier. This layout reduces the peak discharge by up to four times more than a similar array on sloping terrain, compared to channels without baffles. Furthermore, the transition from sloping terrain to a horizontal plane works together with the array of baffles to dissipate flow kinetic energy. On the horizontal plane, baffles attenuate the flow velocity more as the Froude number Fr increases, implying that baffles should be used if high Fr are anticipated. Finally, guidance is provided on estimating load attenuation from boulder filtration.