Rockfall Barriers Research Articles

Introducing Meta-models for a More Efficient Hazard Mitigation Strategy with Rockfall Protection Barriers

The paper presents a new approach to assess the effecctiveness of rockfall protection barriers, accounting for the wide variety of impact conditions observed on natural sites. This approach makes use of meta-models, considering a widely used rockfall barrier type and was developed from on FE simulation results. Six input parameters relevant to the block impact conditions have been considered. Two meta-models were developed concerning the barrier capability either of stopping the block or in reducing its kinetic energy. The outcome of the parameters range on the meta-model accuracy has been also investigated. The results of the study reveal that the meta-models are effective in reproducing with accuracy the response of the barrier to any impact conditions, providing a formidable tool to support the design of these structures. Furthermore, allowing to accommodate the effects of the impact conditions on the prediction of the block–barrier interaction, the approach can be successfully used in combination with rockfall trajectory simulation tools to improve rockfall quantitative hazard assessment and optimise rockfall mitigation strategies.

The influence of high tensile bolts tightening torque on stress distribution in the bolted connection of rockfall barrier under impact load

The paper presents the finite element method approach to determine stress distribution in rockfall barrier post with end to end-plate connection, assembled with high tensile bolts under two different types of impact load. For the analysis purposes typical fixed to the foundation, rockfall barrier post is adopted with 2,50 m height and sixty degrees slope to the horizontal ground line. One post end is fixed (welded) to the base plate – anchored to foundation, the second end is supported via retaining rope. The impact load applied exactly in the post mid-height and boulder caught via net in the mid-distance between two consecutive post are discussed. Four different locations of end to end-plate connection are analysed measuring from the fixed support i.e. dimension varies in the range of 0,30 m up to 0,60 m with 0,10 m step. Six high tensile bolts, zinc coated with 12.9 grade strength have been adopted in the connection. The stated boundary problem was solved by means of SolidWorks software.

Hillslope coupled stream morphology, flow conditions, and their effects on detrital sedimentology in Garnet Canyon, Teton Range, Wyoming

Characterizing stream erosion in any steep mountain landscape is arduous, but the challenge level increases when the stream flows through a glaciated catchment frequently modified by hillslope debris. Glacial landforms and stochastic mass wasting in alpine systems may interfere with sediment delivery to downstream sites where detrital sediments are often collected to represent upstream bedrock sources. To use detrital sediments as indicators of erosion, we need to understand potential sediment accumulation in flat glaciated reaches or behind rockfall barriers. This study investigates the stream channel in Garnet Canyon, a glaciated catchment located in the central Teton Range, to describe hillslope coupled channel morphology and the subsequent effects on sediment transport throughout the catchment. Stream cross-section surveys and sediment size measurements of the surface bedload were collected in the field within a glacially flattened segment of Garnet Canyon. Calculations of shear stress conditions allowed evaluation of the importance of mineral densities on potential grain entrainment. The length of the Garnet Canyon stream observed in this study was coupled with hillslope deposits. Critical shear stresses were sufficient to move gravel-sized sediments through all sections when calculated with quartz mineral density and through most sections when applying apatite mineral density. These results verify the application of detrital sediments to evaluate erosion rates or spatial bedrock sources because snowmelt stream flow efficiently moves entrained sediment past glacially reduced slopes and potential talus barriers.

Assessment of Excavatability, Abrasivity and Slope Stability in a Sandstone Quarry in Istanbul, Turkey

ABSTRACT The Cebeci region is characterized by outcrops of Carboniferous sandstone, including diabase dykes. This region is very important area for aggregate production in Istanbul, Turkey. The aim of this study is to determine the engineering geological properties of sandstones to assess the excavatability, abrasivity and stability of cut slopes in a quarry site. Firstly, the sandstone samples were used to determine their petrographical and mineralogical characteristics. Then, physico-mechanical tests were performed on these samples. In order to determine rock mass properties, scan-line surveys were performed, and the major orientations of discontinuities were analyzed through the stereographic projection technique. Kinematical analyses were also made to determine the potential failures at the quarry site. According to the results obtained, excavatability is changed from easy ripping to hard ripping on sandstones; the carbonated sandstone is less abrasive than other sandstones. Based on the field studies and stability analyses of the cut slopes, optimum slope geometry and necessary support measures, such as wire mesh and rock fall barriers, are suggested.

EARTHQUAKE-INDUCED ROCKFALLS IN SANTOMERI VILLAGE, WESTERN GREECE

On the 8th of June 2008 an earthquake of magnitude Ms=6.5 occurred in Western Greece, affecting Achaia and Ilia Prefectures. According to state reports 2 casualties occurred, 214 people were injured and more than 15 villages and towns suffered extensive damages in properties and infrastructures. Among the secondary phenomena that were reported were extensive rockfalls that affected Santomeri village; a small village located on the western slope of the Scolis mountain. Large-sized limestone boulders, some reaching a volume up to 10m3 stroke houses and blocked roads, fortunately without casualties. The village was temporarily evacueated and the Laboratory of Engineering Geology was commissioned to undertake an Engineering Geological appraisal in order to investigate the extent of the rockfall events, assess the rockfall hazard and propose retention and protective measures so the area to be soon re-inhabited. After conducting a detailed engineering geological and geotechnical survey which included large scale engineering geological mapping, rockmass characterization and laboratory tests the inhabited area was initially divided in two zones of different rock fall risk level. By performing rockfall analyses in critical traverses a rock fall retention system, 325m long in total, comprising rock fall barrier was finally proposed.

Preventing and Analysis of Falling Rocks: A Case of Sarica Village (Gürün, Turkey)

Abstract: Rock fall is a common natural hazard causing significant damage to infrastructure and loss of life and property. This paper describes selection of prevention method, construction processes and the results of a rockfall hazard assessment for the village of Sarica (Gürün region, Turkey) based on an engineering-geological model. The study area is located on the lower parts of an area with very steep cliffs and 40-500 slopes with fractured sedimentary and volcanic rocks. Detailed studies have been conducted in the region to prevent the risk of any rockfalls. Maps and charts are prepared including the rock blocks that are likely to fall and the related housing area under the risk. It was found that block sizes reached 3 m3. Rockfall analyses were performed along the selected profiles using the Rocfall V.5.0 software. Kinetic energy, bounce height, horizontal location of rock end-points and velocity of the rocks along each section were evaluated separately for each profile. This data was used to select design and construction of rockfall preventing system. In this study professional type rock fall barrier (catchment fence) was used. This method was chosen because it was cheaper, more practical and reliable than others.

Dynamic response of flexible rockfall barriers under different loading geometries

Flexible steel barriers are commonly constructed on steep hillsides to mitigate rockfall. The evaluation of the dynamic response of proprietary flexible barriers is conventionally performed using full-scale field tests by dropping a weight onto the barriers in accordance with the European test standard ETAG 27. The weight typically has a spherical or polyhedral shape and cannot reproduce more complex rockfall scenarios encountered in the field. A rigid slab may load a barrier over a larger area and its effect has not been investigated. In this study, a calibrated three-dimensional finite-element model was developed to study the performance of vertically and horizontally orientated rockfall barriers under concentrated areal impact loads. A new bilinear force-displacement model was incorporated into the model to simulate the behavior of the energy-dissipating devices on the barriers. The effect of different weight geometries was studied by considering impacts by a rigid single spherical boulder and a rigid slab. Results reveal that areal loading induced by a rigid slab increases the loading on the barrier foundation by up to 40 % in both horizontally and vertically positioned barriers when compared to a concentrated load scenario with a single boulder. This indicates that barriers tested under the current test standard does not give the worst-case scenario in terms of foundation loads, and barrier designers should take into account the possible effect of increased foundation loads by reinforcing the barrier posts and/or increasing their spacing.

Integration of seismic and image data processing for rockfall monitoring and early warning along transportation networks

The occurrence of rockfall incidents on the transportation network may cause injuries, and even casualties, as well as severe damage to infrastructure such as dwellings, railways, road corridors, etc. Passive protective measures (i.e., rockfall barriers, wire nets, etc.) are mainly deployed by operators of ground transport networks to minimize the impact of detrimental effects on these networks. In conjunction with these passive measures, active rockfall monitoring should ideally include the magnitude of each rockfall, its initial and final position, and the triggering mechanism that might have caused its detachment from the slope. In this work, the operational principle of a low-cost rockfall monitoring and alerting system is being presented. The system integrates measurements from a multi-channel seismograph and commercial cameras as the primary equipment for event detection. A series of algorithms analyze these measurements independently in order to reduce alarms originated by surrounding noise and sources other than rockfall events. The detection methodology employs two different sets of algorithms: Time–frequency analyses of the rockfall event’s seismic signature are performed using moving window pattern recognition algorithms, whereas image processing techniques are utilized to deliver object detection and localization. Training and validation of the proposed approach was performed through field tests that involved manually induced rockfall events and recording of sources (i.e., passing car, walking people) that may cause a false alarm. These validation tests revealed that the seismic monitoring algorithms produce a 4.17 % false alarm rate with an accuracy of 93 %. Finally, the results of a 34-day operational monitoring period are presented and the ability of the imaging system to identify and exclude false alarms is discussed. The entire processing cycle is 10–15 s. Thus, it can be considered as a near real-time system for early warning of rockfall events.

Rockfall Characterization and Structural Protection in the Siddhababa Section of Siddhartha Highway H10, Nepal

Many national highways of Nepal are periodically facing the rockfall events, causing fatal accidents. The Siddhababa section of Siddhartha Highway is a lively example of an active rockfall zone where the highly steep slope geometry in combination to the unfavourable inclination of the rock joints with the road alignment primarily cause the rockfall. Recent accidents of a jeep and a bus have created much concern on rockfall in the area. But still, we do not possess any type of structural countermeasure to overcome this scenario. To address this problem, our study aims at frstly characterizing the rockfall in the area and then on proposing structural countermeasure as rockfall barriers, rock netting and rockshed, and assisted with rock bolting, based on simulation studies and analysis of the rockfall scenario in Rocscience Rocfall® program. Journal of the Institute of Engineering, 2015, 11(1): 1-11

Применение современных геотехнологий при защите территорий от камнепадных процессов

An overview of traditional and modern engineering systems used rockfall protection is given. The main parameters which are considered in the study of stone-fall processes and in the designing of structures against rockfall are analyzed. Features of the calculation and the global experience of using flexible rockfall barriers are described.
 Keywords: rockfall, structures against rockfall, flexible rockfall protection barriers, trajectory of rockfall, impact energy of rock

A New Approach to Evaluate the Effectiveness of Rockfall Barriers

The paper addresses the response of a semi-rigid rockfall protection barrier using numerical models. The study show a large dependence of the barrier response to the impact conditions. The block size and impact position, rather than the velocity direction and magnitude induce different modes of failure of the fence, which in turn result in different values of failure energy. As a result, the barrier capacity cannot be established in a deterministic way. The effectiveness of structures as such can be more successfully evaluated through a reliability probabilistic approach. Results can be used to create a meta-model of the barrier response which can be incorporated into rockfall simulation models, enabling a reliable and comprehensive design of rockfall mitigation interventions performed with this type of structure.

Numerical Modelling of a Low-Energy Rockfall Barrier: New Insight into the Bullet Effect

This paper investigates the dynamic response of low energy, semi-rigid rockfall barriers. The study is based on a FE model that reproduces the geometry, components and connections of the existing systems that were previously tested at The University of Newcastle. The mechanical behaviour of the relevant barrier components was calibrated from simple mechanical tests and the response of the assembled system, i.e. 2 m high, 15 m long rockfall barrier, was validated against of full-scale tests results. Following a satisfactory validation of the model, further dynamic non-linear analyses were conducted to investigate the dependence of the full system performance to the size of impacting blocks. Interestingly, the total failure energy was found to evolve non-monotonically with block size because of dynamic effects that seem to prevail for impact speeds in the range of 15–20 m/s. The study also highlights the complex effects of adding intermediate longitudinal cables to the system. An improvement of the barrier performance is observed for the large blocks but the bullet effect is exacerbated for small blocks.

Mechanics of chain-link wire nets with loose connections

Chain-link wire nets are used for slope stabilization, natural hazard protection systems, mine and tunnel safety and many other important applications. In rockfall protection barriers the nets are designed to withstand dynamic, impulsive loadings. As they are composed of ultra-high strength steel wires with loose three-dimensional connections, the high resistance nets are very flexible and serve to efficiently distribute loads throughout the structure. Rockfall barrier design requires accurate numerical simulations. In this work, a Finite Element model of chain-link nets is developed. To treat the complex contact interactions among chain-link elements and rockfall barrier components we develop a computational scheme relying on a general contact algorithm. The non-linear force displacement response of the net obtained in tensile quasi-static laboratory tests is successfully reproduced by the numerical model. The model parameters are obtained by optimization techniques. The calibrated chain-link model with contact is shown to successfully simulate a full-scale test of a flexible rockfall protection barrier. The computational schemes allow us to accurately model the mechanical behaviour of chain-link wire nets with loose connections.

Parameter identification of rockfall protection barrier components through an inverse formulation

Rockfall barriers are key protection systems in mountainous regions worldwide. They are designed to intercept and capture falling rocks. Most systems are composed of flexible steel wire-nets connected to wire-rope cables which are in turn attached to steel posts and anchored to the ground. Additional energy dissipating devices can be connected to the cables to enhance the performance of the barriers. The composition and geometrical arrangement of wires forming net components and cables are a severe limitation to realistic finite element (FE) modeling of rockfall barriers. Detailed models are computationally expensive. Therefore, macroscopic models reflecting the system behavior on a coarser scale, i.e., the global behavior, need to be derived. In this work, macroscopic FE models pertaining to the modeling of the wire-ring net and the spiral cables have been developed and investigated. Material plasticity, damage initiation and ductile damage are taken into account. The non-linear force displacement response obtained in laboratory tests has been successfully reproduced by introducing additional parameters. An inverse optimization process based on the multi-island genetic algorithm is used for the determination of model parameters. The developed numerical approach succeeds in modeling rockfall barrier connections in a manner that is more refined than previous attempts, yet of low computational expense. The accuracy of this approach is verified by the match between simulation and test results of a full scale rockfall barrier prototype that was tested according to the ETAG027 standard.

A case study on an open hillside landslide impacting on a flexible rockfall barrier at Jordan Valley, Hong Kong

A case study on an open hillside landslide impacting on a flexible rockfall barrier at Jordan Valley, Hong Kong is presented in this paper. The landslide occurred sometime in June 2008. This is so far the only case history of landslide debris having been intercepted by a flexible rockfall barrier in Hong Kong. The landslide scar is 10 m wide and 7 m long, and the landslide volume is about 110 m3. The landslide debris was largely retained by the barrier but two of the barrier posts were severely damaged and failed. Debris mobility analysis and structural analysis of this case history have been undertaken with a view to obtaining a better understanding of the possible landslide dynamics and behaviour of flexible barrier upon debris impact. The analyses appear to have reproduced some of the salient field observations. The probable key contributory factors to the failure are highlighted and discussed. Through the study, the possible range of equivalent pseudo-static impact pressure exerted on the flexible barrier by the landslide debris is assessed. The site observations and results of the analyses provide insights pertaining to the importance of robustness in the design and detailing of flexible debris-resisting barriers.

Practical design of rockfall catchfence at urban area from a numerical analysis approach

This paper presents a numerical approach for the design of rockfall catchfence based on the study of the rockfall stabilization works at Route 5 state highway in NJ, US where severe rockfalls have been periodically occurring. For the optimal design of rockfall catchfence, statistical rockfall analysis has been performed to estimate critical impact conditions and impact energy in the study area. Then, the design criterion of the rockfall catchfence has been validated by means of 3D finite element analysis featuring explicit dynamic capabilities. A series of parametric studies indicate that the rockfall barrier system can be optimally designed by controlling the design parameters such as the stiffness and configurations of net barrier system and impact conditions. The paper illustrates how detailed numerical analyses can be applied practically to optimize the design of the rockfall barrier system under a given field condition.

Rock slope stability and design in Arafat–Muzdalifa area, Saudi Arabia

The present contribution is a complete study extending before, during, and after the excavation of the mountain side that lying north of road 7. It includes slope stability analysis, rock cut design, and rockfall modeling for natural slope and rock cut face. Neoproterozoic granodiorite and biotite granite forming the slope body have medium to very high strengths. Mineral compositions and textures of these intact rocks control the strength values. These rocks are intensively dissected by fractures that are filled with montmorillonite and chlorite. The high plasticity and slippery nature of these filling materials represent the main problem that may face a rock cut designer because they damage the mechanical properties of these fractures. The problem begins with the selection of the rock mass classification that deals with the fracture fillings and extends during the stability analysis and the suggestion of mitigation and supporting measures. The rock masses building the natural slope are suffered by plane, wedge, and toppling failures. Therefore, two rock cut designs are suggested to avoid the hazards related to these failures and considering the construction cost as well. Rockfall modeling for the natural slope and rock cut designs was done to assess the hazards related to these falling of the blocks. The kinetic energy of falling blocks is represented on the roadway by the coverage distance and block rebound amplitude. Slope height has a positive effect on the values of these distance and amplitude, whereas the steepness of berm height has a negative effect on them. Coverage distance is a function to the location of rockfall barrier and to the width of road ditch, while the amplitude controls the barrier height.

Perforation of Flexible Rockfall Barriers by Normal Block Impact

Flexible rockfall barriers are a common form of protection against falling blocks of rock and rock fragments (rockfall). These barriers consist of a system of cables, posts, and a mesh, and their capacity is typically quantified in terms of the threshold of impact (kinetic) energy at which the barrier fails. This threshold, referred to here as the “critical energy,” is often regarded as a constant. However, several studies have pointed out that there is no single representative value of critical energy for a given barrier. Instead, the critical energy decreases as the block size decreases, a phenomenon referred to as the “bullet effect.” In this paper, we present a simple analytical model for determining the critical energy of a flexible barrier. The model considers a block that impacts normally and centrally on the wire mesh, and rather than incorporate the structural details of the cables and posts explicitly, the supporting elements are replaced by springs of representative stiffness. The analysis reveals the dependence of the critical energy on the block size, as well as other relevant variables, and it provides physical insight into the impact problem. For example, it is shown that bending of the wire mesh during impact reduces the axial force that can be sustained within the wires, thus reducing the energy that can be absorbed. The formulas derived in the paper are straightforward to use, and the analytical predictions compare favorably with data available in the literature.

Experimental Testing of Rockfall Barriers Designed for the Low Range of Impact Energy

Most of the recent research on rockfall and the development of protective systems, such as flexible rockfall barriers, have been focused on medium to high levels of impacting energy. However, in many regions of the world, the rockfall hazard involves low levels of energy. This is particularly the case in New South Wales, Australia, because of the nature of the geological environments. The state Road and Traffic Authority (RTA) has designed various types of rockfall barriers, including some of low capacity, i.e. 35 kJ. The latter were tested indoors using a pendulum equipped with an automatic block release mechanism triggered by an optical beam. Another three systems were also tested, including two products designed by rockfall specialised companies and one modification of the initial design of the RTA. The research focused on the influence of the system’s stiffness on the transmission of load to components of the barrier such as posts and cables. Not surprisingly, the more compliant the system, the less loaded the cables and posts. It was also found that removing the intermediate cables and placing the mesh downslope could reduce the stiffness of the system designed by the RTA. The paper concludes with some multi-scale considerations on the capacity of a barrier to absorb the energy based on experimental evidence.

Prediction of the Bullet Effect for Rockfall Barriers: a Scaling Approach

The so-called “bullet effect” refers to the perforation of a rockfall protection mesh by impact of a small block, which has a kinetic energy lower than the design value, where the design value is determined through tests with relatively large blocks. Despite playing a key role in the overall performance of a flexible rockfall barrier, this phenomenon is still poorly understood at present. An innovative approach for quantitatively characterizing this effect based on dimensional analysis is proposed in this paper. The analysis rests on a hypothesis that the relevant variables in the impact problem can be combined into three strongly correlated dimensionless parameters. The relationship between these dimensionless parameters (i.e., the scaling relationship) is subsequently investigated and validated by means of data generated with a finite element model. The validation process shows that the dimensionless parameters are apt and that the proposed scaling relationship characterizes the bullet effect with a reasonable level of accuracy. An example from the literature involving numerical simulation of a full rock barrier is considered, and satisfactory agreement between the calculated performance of the barrier and that predicted by the established scaling relationship is observed.