Rockfall Barriers Research Articles

Predictions of Localised Damage to Concrete Caused by a Low-Velocity Impact

Hillside RC barriers protected by gabion cushion layers are commonly used as passive defence measures to contain landslides and rockfalls. Gabions are expensive and require extensive maintenance. However, the design of gabion-free rockfall barriers cannot be implemented because of the lack of knowledge with the performance of a bare concrete surface when exposed to low-velocity impact hazards. The key contribution of this article is the adaptation, and experimental validation, of a theoretical model based on the principles of solid mechanics for predicting localised damage (denting and spalling) on a concrete surface. The theoretical model, which consists of closed-form expressions, can be executed using MATLAB or EXCEL for predicting the occurrence of denting and spalling in practical applications. The accuracy of predictions from the theoretical model has been validated by both large-scale impact testing and finite element simulations. The use of the model is illustrated with a worked example to facilitate the application of the presented methodology in engineering practices. The presented methodology has potential utility in the design of structural concrete which is exposed to an abrasive environment. The design of gabion-free RC rockfall barriers is an example of such utility.

A Meta-Model-Based Procedure for Quantifying the On-Site Efficiency of Rockfall Barriers

This article proposes a procedure for developing tools to quantify the on-site efficiency of any rockfall barrier. This procedure relies on meta-modeling techniques to predict the barrier ability in arresting rock blocks, whatever their trajectory. For demonstration purpose, a specific low-energy barrier for which a finite element model was available is considered. The barrier response is simulated varying six parameters describing the rock block kinematics. Six different methods are used to create meta-models predicting the simulated barrier response. The ability of each method in creating meta-models with good prediction capacities is evaluated. Meta-models created utilizing the best methods are then used to quantify the efficiency of the barrier in arresting rock blocks in two real situations. These situations exhibit very similar 95% percentiles of the block passing height and kinetic energy but very different distributions for the other parameters describing the kinematics of the rock blocks. The predictions reveal that the barrier efficiency is extremely site-dependant. The discussion addresses the meta-models performance and highlights the benefits in using such meta-models for quantifying the barrier efficiency, in particular with respect to more classical barrier design approaches. Last, the proposed eight-step procedure for generating meta-models to be used in operational contexts is described.

In Situ Block Size Distribution Aimed at the Choice of the Design Block for Rockfall Barriers Design: A Case Study along Gardesana Road

When studying rockfall phenomena, a single value of the block volume is not sufficient to take into account the natural variability of the geometrical features (orientation, spacing, persistence) of the discontinuity sets. Different approaches for obtaining cumulative distributions of potentially detachable block volumes are compared. A highly fractured rock mass outcropping along the western Lake Garda (Italy), consisting of prevailing limestone and interbedded marls, is studied in detail from geological and geostructural points of view. Then, a representative rock face has been selected and analyzed with traditional and non-contact survey methods to identify the main discontinuity sets and to collect spacing samples. Based on these data, in situ block size distributions for different combinations of sets are built following statistically-based approaches, without the use of a Discrete Fracture Network (DFN) generator. The validation of the obtained distributions is attempted based on the detached block surveyed at the foot of the slope. However, in this particular case study, the detached blocks cover only a minimal volume range compared to both theoretical values and visible rockfall scars. The fallen rock blocks have a marginal role in design block determination, since their volume depends on geological discontinuities (bedding and fractures) and could be affected by other processes after the detachment (e.g., fragmentation). The procedure here described should be standard practice in the study of rockfall events, and it should be uniform in European standards such as Eurocodes. Future developments should involve the scientific community for setting the percentiles of the probability distribution to be considered for block design definition.

Cantilevered RC Wall Subjected to Combined Static and Impact Actions

A displacement-based (DB) model is introduced in this article alongside its detailed derivations to predict the flexural response behaviour of a cantilevered reinforced concrete (RC) wall that is subjected to combined actions of boulder impact and sustained load (e.g. debris flow). In order to validate the model, a large-scale experiment was carried out by striking a 1.5 m tall, 3 m long and 0.23 m thick reinforced concrete wall using of two impactors weighing 280 kg and 435 kg to simulate different boulder impact intensities. A sustained load of 36 kN was applied to the wall using two prestressed custom-fabricated spring assemblies. Wall deflection and reinforcement tensile strain values measured from the experimental tests are shown to be within about 10–20% of predictions calculated from the proposed DB model. Errors of the predictions are consistently conservative across all the considered impact scenarios. These experimental findings are original given that no impact tests of the scale presented in this paper, which incorporate the effects of co-existing sustained lateral forces (e.g. debris flow), can be found in the literature. The proposed DB model was found to accurately predict both the deflection of the wall as well as the amount of tensile strain experienced by the reinforcement at the base of the wall. This paper concludes with a step-by-step design procedure that utilises the proposed DB model for designing RC rockfall barriers, which will be useful for practitioners aiming for a more optimised barrier design.

Flexible Rockfall Barrier Post Support Performance: Deflection as a Positive Attribute

Rockfall has plagued infrastructure for centuries, whether generated by natural weathering of unaltered rock slopes or due to jointing and weaknesses in constructed rock slopes. Rockfall in the U.S. has been formally studied since the early 1960s, when Arthur Ritchie, chief geologist with the Washington State Department of Highways, assessed inadequacies with the state of practice relative to catchment ditch design. Since that time, rockfall analysis has become more sophisticated with the use of 3D simulation and rockfall runout models. Several international manufacturers have developed flexible rockfall barrier (fence-like) systems, the designs of which are continuously updated and improved based on testing and field performance. Most flexible rockfall barrier manufacturers also offer debris flow and avalanche barriers using similar elements.

Numerical simulation of responses of flexible rockfall barriers under impact loading at different positions

Flexible rockfall barriers have been widely used to mitigate rockfalls and protect residential buildings, railroads and highways from such natural hazard. Evaluation of the performance of flexible rockfall barriers are conventionally conducted using the full-scale impact tests in accordance with European guideline ETAG 027, in which the impact position is specified at the centre of the middle functional module. However, the trajectory of a rockfall in real case is random such that the impact position is unknown. The influence of different impact locations has not been reported in literature. In this paper, a full-scale test on a typical flexible barrier system is carried out and then used to calibrate an advanced three-dimensional finite element model, which is proposed for parametric study for the investigation of dynamic response of a typical flexible rockfall barrier under impacts at different positions. The numerical results show that the impact location will influence the residual height and maximum elongation of the flexible barrier. Although the impact position slightly affects the peak forces of support ropes, it will significantly influence the peak forces of the upslope anchor ropes and lead to unsafe anchor design. The proposed model can accurately predict the behaviour of flexible barriers and help designers to consider more practical conditions which are not specified in ETAG 027.

Experimental and Analytical Assessment of Flexural Behavior of Cantilevered RC Walls Subjected to Impact Actions

AbstractReinforced concrete (RC) impact-resistance barriers, such as rockfall barriers, often consist of a cantilever RC wall, which is expected to experience flexural bending under impact loading ...

Modelling of curtain effect in rockfall barrier with the dynamic relaxation

Flexible rockfall barriers are protection systems against risks of falling rocks. Their complex behaviour is still not well understood and the development of relevant models allowing for quick calculations is a need toward the optimisation of such structures. The key issue is the modelling of the so-called ”curtain effect”, where the cable net slides along the supporting cables. The present paper proposes hence a model of sliding cable submitted to concentrated forces. It addresses the stability conditions of the centred finite difference scheme, especially in the framework of the Dynamic Relaxation Method where estimates are found for the best possible fictitious masses at nodes. Expressions are derived in the general case, but also for monotonically curved cables and looped cable elements or rings. Elementary problems are shown for validation, before a case study based on experiments conducted during the French National project C2ROP demonstrates the accuracy and the reliability of the proposed methodology. The present study is however limited to quasi-static loadings and therefore needs further developments to be extended to realistic dynamic cases which are discussed in the conclusion.

Determination of rockfall design blocks in Upper Triassic limestones and dolomites (Dachstein Formation, Northern Calcareous Alps)

Design block size is of vital importance for rockfall countermeasure design. According to the Austrian normative document ONR 24810, the design block is specified as fractile (V95-V98) of the block size distribution depending on rockfall frequency. For rock formations, which form very large rockfall blocks (> 10 m3), the use of fractiles V95–V98 appears too high with regard to economically justifiable protective measures. The paper deals with the determination of design blocks for the Dachstein Formation on the basis of data from three Austrian test regions. The formation’s bedded limestone represents a key rock of the eastern part of the Northern Calcareous Alps and is very common along some major transport routes. A range of design blocks is derived from a synopsis of block size distributions, magnitude-frequency relations, and considerations about the rockfall barriers’ service life. In the process, the knowledge of the return period of the determinated design block is considered more important than the overall rockfall frequency. Analyzing available rockfall event data and block size distributions, it is possible to identify a return period of 21–26 years for a rockfall event ≥ 1 m3/1000 m route section. Thus, such events are rare. Events that affect the V97–V100 fractiles of the block size distribution are even rarer; they yield very large design block volumes, which show return periods > 100 years. For the bedded Dachstein limestone of the test areas, the application of the fractiles V95–V96 (0.15–2.25 m3) is useful for adapting the return period of the design block to the working life of the rock fall barrier (25–50 years).

Rockfall hazards assessment along the Aswan–Cairo highway, Sohag Governorate, Upper Egypt

The geotechnical evaluation of rockfall hazards along the Aswan–Cairo highway, Sohag Governorate, Upper Egypt has been achieved throughout a variety of field investigations and lab tests on the slopes and rock cut faces of Lower Eocene Plateau limestone. The studied Aswan–Cairo highway is located in a mountainous area and surrounded on both sides by highly sheared limestone plateau possesses steep slopes and swelling clayey hosted bands. The clayey bands are characterized by highly swelling potentiality that considered as instability and weakness planes along which the limestone blocks will be downward fallen. Based on slope height and angle, the studied slopes are mostly considered instable. Kinematically, the Lower Eocene limestone blocks have planer and wedge failure modes. According to the estimated values of the coverage distance and rebound amplitude, ditches must be dug (2 m width and 1.5 m depth) to reduce the rebound amplitude height of falling blocks and catch these blocks to avoid them to reach the highway toe. Ditches can be filled with sands to will absorb the falling blocks kinetic energy as well as rockfall barrier must be constructed at the most hazards sites to retain the falling blocks away from the road toe.

Application of Remote Sensing Data for Evaluation of Rockfall Potential within a Quarry Slope

In recent years data acquisition from remote sensing has become readily available to the quarry sector. This study demonstrates how such data may be used to evaluate and back analyse rockfall potential of a legacy slope in a blocky rock mass. Use of data obtained from several aerial LiDAR (Light Detection and Ranging) and photogrammetric campaigns taken over a number of years (2011 to date) provides evidence for potential rockfall evolution from a slope within an active quarry operation in Cornwall, UK. Further investigation, through analysis of point cloud data obtained from terrestrial laser scanning, was undertaken to characterise the orientation of discontinuities present within the rock slope. Aerial and terrestrial LiDAR data were subsequently used for kinematic analysis, production of surface topography models and rockfall trajectory analyses using both 2D and 3D numerical simulations. The results of an Unmanned Aerial Vehicle (UAV)-based 3D photogrammetric analysis enabled the reconstruction of high resolution topography, allowing one to not only determine geometrical properties of the slope surface and geo-mechanical characterisation but provide data for validation of numerical simulations. The analysis undertaken shows the effectiveness of the existing rockfall barrier, while demonstrating how photogrammetric data can be used to inform back analyses of the underlying failure mechanism and investigate potential runout.

A new discrete element model for simulating a flexible ring net barrier under rockfall impact comparing with large-scale physical model test data

Flexible barriers are one of the effective mitigation measures to intercept high-energy falling rocks in mountainous areas, owing to its high ductility and excellent energy dissipation performance. This paper presents a newly developed flexible ring net barrier model based on the discrete element method (DEM) to simulate the rockfall impact on a flexible barrier. All the input mechanical parameters were calibrated by means of laboratory tests. The capabilities of the numerical model are evaluated by comparing the results from novel designed large-scale physical model impact tests. It is found that the new discrete element model is able to reproduce the behavior of a ring net barrier under rockfall impact. A good agreement with experimental data can be found regarding to boulder velocities, net elongations and tensile forces developed between ring net elements. In addition, the effects of boulder size, impact position, barrier inclination, and barrier initial slack on barrier response in a parametric study are investigated. The results from this study provide useful guidance for future design and optimization of rockfall barriers in engineering practice.

Assessment of the predictive capabilities of discrete element models for flexible rockfall barriers

This paper addresses the use of discrete element modeling approaches for predicting the impact response of flexible rockfall protection barriers. In this purpose, two different models are considered and their results are compared to detailed results from full-scale impact experiments. The studied barrier is a prototype made from a 4-contacts ring net and having a 270 kJ nominal capacity. The two discrete elements method models, developed by separate entities with different codes (Yade-DEM and GENEROCK), use different models for the ring net, the cables and cable-net connections, while other structural elements are modelled the same way : posts, anchors, energy dissipating devices, and boulder. The models for the structural elements (ring net, energy dissipating devices) are calibrated individually from quasi-static tensile tests results. The barrier model is then created assembling the structural elements, before being impacted. The tests consist in a impacting in its center a 3-module barrier, first, to one high kinetic energy impact and, second, to three consecutive impacts with a lower kinetic energy. The models results are confronted to measurements made during the experiments, considering a large set of parameters. Both models reveal satisfactory in predicting the structure response, on quantitative and qualitative points of view, and considering the boulder displacement, forces in the main cables and forces acting within the various energy dissipating devices. The quality of the prediction by each model compared to the other depends on the considered parameter. Little deviations from the experimental results are attributed to the model calibration procedure and to slight differences between the real structure and the modeled ones. In the end, the DEM approach appears suitable for modelling flexible barriers in complex loading conditions (high velocity and successive impacts).

Toward a Generic Computational Approach for Flexible Rockfall Barrier Modeling

Flexible rockfall barriers are protection structures used to mitigate rockfall hazards in mountainous areas. The complex nonlinear mechanical behavior of these structures under impacts requires powerful modeling tools to perform structural analysis. In this article, a generic computational approach to rockfall barriers analysis is introduced. First, the generic formulation and numerical implementation in the GENEROCK software are detailed. Then, two barrier models are considered and validated against experimental full-scale tests on two different technologies. This numerical investigation permits insightful numerical investigation of the barriers’ behavior. Exploratory numerical simulations are eventually performed to highlight the strengths and generality of the proposed approach. The influence of the curtain effect modeling in simulation results is presented. The effects of repeated impacts on rockfall barriers are investigated and present new insight into barrier behavior and management practices. Stochastic modeling methods are also used to study the propagation of uncertainty and variability of the structure itself in its dynamic response.

Studies on flexible rockfall barriers for failure modes, mechanisms and design strategies: a case study of Western China

A field investigation on the actual protective performance of a flexible rockfall barrier along a mountain road in western China is presented in this paper. The total area of the flexible rockfall barrier under investigation was approximately 20,000 m2. Five typical failure modes of the flexible rockfall barrier were revealed, including steel post buckling, connection failure, ring net destruction, steel cable rope breakage and anchorage point failure. In addition, component rusting, which leads to decrease in durability, was noted. Furthermore, failure mechanisms were analysed, and the main factors that were found to induce flexible rockfall barrier failure included the sliding capacity of the cable ropes at the end post support positions, the boundary conditions of the steel posts and the compatibility between the energy dissipating devices and connected cable ropes. From these observations, corresponding design strategies were proposed. In addition, an improved flexible rockfall barrier system was constructed, and its effectiveness was verified by a full-scale impact test using 5000 kJ of impact energy. Finally, the impact deflection, impact force, cable force and energy dissipation of the improved flexible rockfall barrier system were studied in combination with a non-linear numerical simulation which could be a useful tool for design of flexible barrier systems.

Rockfall Analysis and Optimized Design of Rockfall Barrier Along a Strategic Road near Solang Valley, Himachal Pradesh, India

In the Himalayan region, roadways, railways, power plants, buildings and other houses are prone to rock falls. Considering the rockfall risk in the Himalaya, this study focuses on an under construction route for Manali–Leh highway along Solang–Rohtang tunnel in Himachal Pradesh. The slopes along this road are unstable and prone to rockfall. Soon with the completion of Rohtang tunnel, this road will hit a huge amount of traffic, as it will be the shortest route to the Lahaul Spiti. So, the detailed assessment of rockfall hazard along this road is necessary. In the present study, rockfall simulation has been carried out to determine the parameters such as bounce height, maximum run-out distance, energy and velocity associated with falling rock blocks on the basis of field and laboratory analysis. The bounce height and the kinetic energy were found to be greater than 5 m and 50 kJ, respectively, in the analysis. The optimization of the ditch, slope geometry and the design of rockfall barrier have been performed duly taking slope parameters into consideration. The result shows that the optimized ditch is effective to arrest the larger number of falling rock blocks and also the kinetic energy of the rock block can be decreased by performing slope trimming. A standard barrier of 100 kJ capacity and 2.5 m height has been found suitable and proposed to make the roadway along this highway safer for travellers.

An Equivalent Continuum Approach to Efficiently Model the Response of Steel Wire Meshes to Rockfall Impacts

Steel wire meshes are a key component of rockfall protection barriers. The efficiency in reproducing the structure response with numerical methods relies upon the specific modelling technique employed to capture the wire mesh behaviour. The fabric of some rockfall meshes, such as chain-links is quite complex, which leads to sophisticated and costly numerical models, if modelled accurately. This paper presents an efficient approach to model the response of steel wire meshes to rockfall impacts by using shell elements to develop an equivalent continuum model. An elastoplastic behaviour is prescribed to the shell elements to reproduce the results of a set of experimental data, carried out on mesh portions under various load paths and boundary conditions. The idea is that simple laboratory tests can be used to calibrate an effective numerical model of the steel wire mesh with a significantly lower computational cost if compared to other effective solutions. The model’s ability in yielding consistent results when implemented at the structure scale is then assessed, based on the data of full-scale impact tests on a three-span low-energy rockfall barrier. The method can be extended to other wire mesh types and can find convenient application on exploring the response of a rockfall barrier with a cost-effective tool.

Effect of impact velocity, block mass and hardness on the coefficients of restitution for rockfall analysis

One of the most significant input parameters in rockfall trajectory modelling is the Coefficient of Restitution, which controls block rebound. In particular, in the design of rockfall barriers, it can significantly affect their height. In practice, the coefficients of restitution are acquired by field or laboratory tests, back analyses of known events, experience or, most commonly, suggested values connected to the slope material. Furthermore, to account for the effect of impact velocity or block mass, scaling factors are available. However, the suggested values are based on a qualitative description of the slope material, and the scaling factors are not well documented, nor do they account for the effects of impact velocity and block mass simultaneously. In this paper, a semi-empirical correlation is proposed that takes into account the Schmidt hammer rebound value of both the slope and block material as well as the impact velocity and block mass. This was derived by an extensive laboratory experimental study (445 impact tests) of a one-dimensional drop of spherical blocks onto planar surfaces. The semi-empirical correlation proposed adequately describes the responses observed under the circumstances imposed in the laboratory.

Use of explicit FEM models for the structural and parametrical analysis of rockfall protection barriers

This paper illustrates the experimental test procedure and results of two flexible barriers of low and medium energy, the so-called IBT-150 and IBT-500. For this purpose, ETAG 027 European Guideline is used. All the requirements for the tests performance are followed and the two energy-level tests performance requirements have been fulfilled in both rockfall barriers. Numerical modelling helps to understand and predict the behavior of these barriers with different configurations drastically reducing the costs of performing real tests. The results of the real test on IBT-150 and IBT-500 have been taken as references to validate two numerical models using Abaqus Explicit software. Afterwards, a presentation of some alternatives of the barrier IBT-150 are stated, which allow a more economical design removing some components that do not affect the energy level of 150 kJ set by the manufacturer. Also, a parametrical analysis of the IBT-500 numerical model has been performed varying the geometrical characteristics, such as the net grid dimension, the diameter of the perimeter cable, the length of the functional modules and its height. The aim of this analysis is the enhancement of maximum energy capacity of the barrier related with the amount of material used to build it. Following the ETAG recommendation, the maximum energy level (MEL) test is achieved if the barrier is able to retain the block. Thus, the MEL level for each numerical model was determined by increasing the initial speed of the block until it trespasses the barrier.

Reconnaissance of geotechnical aspects of the 2016 Central Italy earthquakes

Between August and November 2016, three major earthquake events occurred in Central Italy. The first event, with M6.1, took place on 24 August 2016, the second (M5.9) on 26 October, and the third (M6.5) on 30 October 2016. Each event was followed by numerous aftershocks. The 24 August event caused massive damages especially to the villages of Arquata del Tronto, Accumoli, Amatrice, and Pescara del Tronto. In total, there were 299 fatalities, generally from collapses of unreinforced masonry dwellings. The October events caused significant new damage in the villages of Visso, Ussita, and Norcia, although not producing fatalities, since the area had largely been evacuated. The Italy–US Geotechnical Extreme Events Reconnaissance team investigated earthquake effects on slopes, villages, and major infrastructures. The approach adopted to carry out post-earthquake reconnaissance surveys was to combine traditional reconnaissance activities of on-ground evidences and mapping of field conditions with advanced imaging and damage detection routines enabled by state-of-the-art geomatics technology. Presented herein are the outcomes of the post-event reconnaissance surveys conducted after both the August main shock and the October events, focusing on geotechnical aspects, such as earthquake-triggered slope failures, mud volcanoes, performance of different geotechnical structures (i.e., dams, retaining walls, rockfall barriers, road embankments) and building damage patterns related to site amplification.