Query: rockfall energy evaluation

title: Rock Mass Characterization of Karstified Marbles and Evaluation of Rockfall Potential Based on Traditional and SfM Based Methods; Case Study of Nestos, Greece
abstract: Rockfall consists one of the most harmful geological phenomena for the man made environment. In order to evaluate the rockfall hazard, a variety of engineering geological studies should be realized, starting from conducting a detailed field survey and ending with simulating the trajectory of likely to fail blocks in order to evaluate the kinetic energy and the runout distance. The last decade, new technologies, i.e. remotely piloted aircraft systems (RPAS) and light detection and ranging (LiDAR) are frequently used in order to obtain and analyze the characteristics of the rock mass based on a semi automatic or manual approach. Aiming to evaluate the rockfall hazard in the area of Nestos, Greece, we applied both traditional and structure from motion (SfM) oriented approaches and compared the results. As an outcome, it was shown that the semi automated approaches can accurately detect the discontinuities and define their orientation, and thus can be used in inaccessible areas. Considering the rockfall risk, it was shown that the railway line in the study area is threaten by a rockfall and consequently the construction of a rockfall netting mesh or a rock shed is recommended.

title: Statistical evaluation of rockfall energy ranges for different geological settings of New South Wales, Australia
abstract: Structures used in rockfall protection are designed on the basis of the expected impact energy. This quantity is usually assessed using commercial lumped mass models that stochastically predict possible block trajectories on a given slope. In New South Wales, Australia, it is estimated that rockfall hazard involves values of energy which are much lower than those in Europe, Canada or the USA. However, this view has not been supported by any systematic study across the whole state. Such a study is presented in this paper. It applies to the five geological situations that are the most prone to rockfall in eastern Australia. Previous experimental findings, relating to block size distribution or restitution coefficients (reviewed herein) have been used to perform this statistical analysis. A newly formulated lumped mass program, which incorporates a relationship between the normal restitution coefficient and the impact angle, allows the adoption of normal restitution coefficients in excess of unity for impact angles lower than 30deg. The results confirm that in three out of the five geological situations, the 95th percentile of impact energy is lower than 200 kJ, and less than 2000 kJ for the other two situations.

title: Optimization methods for the evaluation of the parameters of a rockfall fractal fragmentation model
abstract: In rockfall events, the falling blocks impacting the slope can experience fragmentation due to their kinetic energy. This process produces new blocks, smaller than the initial ones, moving along independent trajectories. As a result, the in situ block size distribution (related to the slope face of the source area) and the rockfall block size distribution (related to the deposit) differ. The present paper proposes and compares two optimization procedures for choosing the parameters of an iterative fractal fragmentation model based aimed at describing the rockfall fragmentation process on the base of source and deposit block distributions. To discuss the effectiveness of each approach, the two distributions are considered free of uncertainties. The influence of the number of iterations and optimization approach are discussed in terms of easiness of interpretation of the results.

title: La modellazione del fenomeno di caduta massi a piccola scala: valutazione dei parametri necessari per analisi speditive Rockfall modelling at a small scale: evaluation of the parameters needed for quick analyses
abstract: Il lavoro di Tesi Magistrale e dedicato a due dei parametri principali per la modellazione del fenomeno di caduta massi tramite il plugin QPROTO, sviluppato dal Politecnico di Torino per il software geografico libero QGIS: l'angolo di energy line php e l'angolo di dispersione laterale a. Al fine di mettere tali parametri in relazione con le caratteristiche del pendio e del masso in caduta e fornire agli utilizzatori del plugin indicazioni per la loro definizione, si e condotto uno studio parametrico su versanti 'virtuali' semplificati, ottenuti dall'unione di tre piani inclinati che definiscono la zona di distacco, la zona di transito e la zona di arresto. SU tali versanti sono state condotte simulazioni delle traiettorie di caduta massi con il software di dettaglio Rockyfor3D, al variare dell'inclinazione della zona di transito, della densita di vegetazione e della forma del blocco, che hanno permesso di valutare l'influenza di tali fattori sugli angoli php e a. L'affidabilita dei risultati dello studio e stata infine verificata tramite la back analysis di un caso reale di caduta massi effettuata ricorrendo al Plugin QPROTO.

title: A SIMPLE ANALYTICAL METHOD FOR EVALUATION OF FLEXIBLE ROCKFALL BARRIER PART 1 WORKING MECHANISM AND ANALYTICAL SOLUTION
abstract: The flexible rockfall barrier system exhibits large deflection and complex contact behaviors such that sophisticated finite element method and full scale test are widely used to design this kind of structures, which causes inconvenient for most engineers. In this paper, a simple analytical method is proposed for fast evaluation of the performance of the flexible rockfall barrier system on the basis of system deflection characteristics observed in the full scale impact tests and, the component deflection characteristics from component tests such as the puncturing deflection of steel wire ring net, elongation of energy dissipating device, sliding movement of supporting rope and rotation of support structure. The equation for prediction of large deflection of flexible rockfall barrier system was established. The overall deflection is contributed by its components and therefore the analytical solutions for calculation of component deflections were derived based on the space geometry analysis and verified by component tests. The analytical solution for steel wire ring nets were validated by 17 puncturing tests and the maximum difference was less than 7.4% Using the discrete ring net model, an explicit dynamic method was employed to simulate the nonlinear behaviors of flexible rockfall barriers with different design energies, i.e. 2000 kJ, 3500 kJ and 5000 kJ. The deflection of each component and the overall deflections from analytical solutions were compared with the numerical simulations with the maximum difference less than 7.9% Thus, the proposed analysis solution for evaluation of large deflection of flexible rockfall barrier system is valid and ready for engineering design. A companion paper is presented in part two separately with full scale test for further verification of the proposed method.

title: A SIMPLE ANALYTICAL METHOD FOR EVALUATION OF FLEXIBLE ROCKFALL BARRIER PART 2 APPLICATION AND FULL SCALE TEST
abstract: The companion paper proposed an analytical solution for design of flexible rockfall barrier undergoing large deflection. The part one also reported that the elongation of energy dissipating device plays an important role in buffer mechanism of the system. This paper further studies the governing factors on large deflection of flexible barrier system and then establishes a deflection control based mechanical model with improved buffer performance. The factors include the matching property between the energy dissipating device and the support rope, the motion interference during sliding along support ropes, overload protection from lateral support ropes. A prototype model with a nominal energy level of 2000 kJ was designed using the analytical method introduced in part one of the paper. Both full scale test and numerical simulation were carried out to investigate the response of the prototype model under impact load. The results show that the motion interference and the braking effect during impact test are effectively controlled by the proposed deflection control based mechanical model, leading to an optimized design in terms of system buffer performance. Thus, this paper demonstrates the application of the analytical method presented in part one. The full scale test and numerical simulation prove the validity and accuracy of the proposed method.

title: A quantitative approach for the evaluation of rockfall risk on buildings
abstract: A quantitative rockfall risk analysis at local scale is a complex and difficult task because it should consider both the randomness in the natural phenomenon and the variability of the response of the elements at risk. In engineering systems, such difficulties can be tackled with logical trees. In particular, event trees allow the determination of a set of outcomes of a given event in a probabilistic manner. Following recent publications on the estimation of rockfall risk on infrastructures (roads) by means of the event tree approach, a novel framework for the quantitative evaluation of the effects of the impact of a falling rock block on a building is presented. The method considers the occurrence of a given rockfall event, the kinetic energy of the falling block, the structural response of the impacted elements and the possibility of damage propagation within the building. An example is proposed to show the capabilities of the proposed approach.

title: Full Scale Testing and Performance Evaluation of Rockfall Concrete Barriers
abstract: Rockfall hazards are present throughout the state of Ohio. The Ohio Department of Transportation (DOT) employs Test Level 3 standard concrete barriers along the edges of roadways to contain rockfalls in high risk areas. The performance of these barriers under impact from rocks on the ditch side and their effectiveness for rockfall catchment are relatively unknown. Full scale impact tests were performed on concrete barriers to simulate the effects of impacts from rocks of various sizes and shapes. Numerous impacts were made at different sections and levels of the barriers to test their structural integrity and energy absorption capacity. The results from this study revealed that 32 in. high precast concrete barriers with current Ohio DOT details had an impact energy absorption capacity of up to 24 kJ under a single impact. The corresponding energy absorption capacity of 42 in. high cast in place concrete barriers was about 56 kJ under a single impact. Moreover, these barriers experienced severe cracking and spalling of concrete under impact loading. Several design modifications were studied in this test program. These modifications included reducing the spacing of rebars and rebar sizes, using welded wire fabric, and using different types of fibers in the concrete. The tests conducted on the modified concrete barriers showed an impact energy increase of more than 100% with the modifications suggested in this study. Barriers made from the modified designs also experienced significantly reduced extent and severity of cracking and a reduction in spalling and splashing of concrete under impact loading.

title: Rockfall Concrete Barrier Evaluation and Design Criteria
abstract: Rockfall is the movement of rocks down a slope which may be in the form of freefall, bouncing, rolling and sliding based on the characteristics of slopes and nature of rocks. When the rockfalls reach the roadway, they are hazardous to roadway users. Standardized precast concrete barriers (PCB) or cast in place (CIP) concrete barriers are commonly used by Ohio Department of Transportation (ODOT) to protect the affected highways against rockfall hazards. Impact tests were conducted on full scale PCB and CIP concrete barriers to determine the impact resistance of these types of barriers against rockfall. Manufactured or natural rocks of different sizes and shapes were dropped from ranges of drop heights based on the desired impact energy to capture the performance of these barriers under impact loading. Current ODOT standard details were modified to improve the impact resistance of such barriers. The test results indicated that impact energy absorption capacity of the revised barriers can be increased by more than 100% compared to that of the barriers with the current ODOT standard details. The rollout tests were conducted on three different slopes with CIP concrete barriers constructed at the bottom of these slopes. The first slope was made to an inclination of 30 degrees, the second slope with 45 degrees, and the third slope with 55 degrees. The test rocks were dropped on the top of the slope to roll down and impact the concrete barriers constructed along a ditch at the bottom of the slope. The impacting velocities, the trajectories of the rocks while rolling down the slopes and bounce heights were digitally captured with high speed cameras. The results obtained from rockfall simulation programs such as CRSP were validated using the field measurements obtained from these rollout tests. The results indicated that the predictions obtained from rockfall computer simulation programs generally underestimate the bounce heights and velocities, and consequently the energies delivered by the rocks at the impact location.

title: Evaluation of the Effect of Sand Pack Coverings on Rockfall Protection Fences Using Numerical Approach
abstract: Flexible fences have been used widely for protection against rockfall impact and have garnered considerable attention from engineers and researchers due to their effectiveness and adaptability to various types of topography and impact energy magnitude. Generally, friction braking devices are widely used for absorbing impact energy and external support cables are added to enhance structure stability. The utilization of sand packs as impact absorbing components in the fence structure is considered a new and rational idea. This research was conducted to gain better understanding of the structural behavior of a fence without any braking device or external support cable, and the absorption performance of sand pack to cushion rockfall impact. The fence studied in this research consist of three spans of cable net covered by 14 sand packs, and was subjected to impact load by a vertical free fall of weight. The sand packs covering the fence were considered for a numerical study using the finite element method of LS DYNA to simulate the behavior of the complete fence structure, including the sand pack cushion. The numerical model was adequately validated through a comparison between the results of the model analysis and those of the fundamental experiment. The examination and discussion of the structural dynamic behavior of fences by applying the validated model clearly revealed the effects of the sand pack and impact energy magnitudes on the structural characteristics of the fence. These effects led to the revelation that the absorption performance of the sand pack coverings to absorb the impact and redistribute its load are expected to result in the practical application of sand packs as absorbing elements in rockfall protection fences.