Bench Height Research Articles

Optimization of tunnel construction parameters in soft rock section with high geostress

Large deformation and even collapse are prone to occur in tunnel crossing high geostress soft rock section, which seriously restricts the construction progress. Therefore, it is necessary to optimize the construction parameters of high geostress soft rock section by bench method. Based on the Wu Nv Feng extra-long tunnel, this paper calculates and analyzes the surrounding rock deformation and structural stress under different excavation height, excavation length and excavation footage. The analysis shows that 2 / 3 h upper bench height can balance the influence of bench height on construction mechanics and construction convenience; considering the construction mechanical characteristics and excavation support time, the excavation height and excavation footage should be reduced as much as possible. Reasonable bench parameters play an important role in controlling the deformation of soft rock tunnel under high geostress, which can provide reference for tunnels with similar engineering geology and construction environment.

Blasting Technique for Stabilizing Accident-Prone Slope for Sustainable Railway Route

Konkan Railway has many unstable slopes along the 741 km long route from Roha to Thokur in the states of Maharashtra, Goa and Karnataka in India. Frequent cases of boulder fall, slope failure and landslide used to occur on the track during the rainy season. Such cases have resulted in several severe train accidents, traffic interruptions, loss of lives and assets. Hence the Konkan Railway Corporation deployed several geotechnical measures such as wire-netting, retaining wall, rock bolting and shotcreting for stability enhancement. However, none of these measures proved effective and accidents continued. Finally, the Konkan Railway Corporation decided to redesign the cut-slopes using blasting. Excavation of hard rock for its removal without damaging the existing track (2– 3 m away from the slope) and disrupting the traffic, was a daunting task. An unplanned blast would have resulted in the closure of the route for hours. The present study explains the method in which entire cutting was redesigned by formation of 5 to 2 m wide berms at an interval of 6 m bench height from rail track level using novel direction controlled blasting technique. Further, stability of the cut-slope, before and after exacavation, has been determined using kinematic analysis and 3D numerical modelling. Similar technique can be adopted to widen or stabilize an active transportation route in hills.

Blast-Casting Mechanism and Parameter Optimization of a Benched Deep-Hole in an Opencast Coal Mine

During the research on bench deep-hole blast casting, the blast-casting parameters are directly related to the blast-casting results, so it could reveal the mechanism for improving the effect thereof. Based on the principle of the plane charge method, both the stress wave and detonation gas were considered to affect rock fragmentation and casting, a model of overburden fragmentation and casting process around the blasting hole was established, and bench deep-hole blast-casting behaviours were elucidated. By using the Factor Analysis Method (FAM), a correlation analysis model of factors influencing blast-casting results was built. The results proved that powder factor (or specific charge) ranked first in terms of its influence, followed by hole spacing, minimum resistance line, burden, and bench height. The formulae for calculating the limit powder factor value and the spacing of blasting holes were derived for different rock properties. The results showed that the optimum hole spacing was no more than 12.49 m and the powder factor was no more than 0.75 kg/m3, and it proved that an effective casting percentage (ECP) of 34% could be realized.

Dynamic capacity balance between stripping and mining of a dragline stripping system

The reliability factors of a dragline stripping system were analyzed using system reliability theory to improve its reliability and ensure the stability of surface coal mine production. The relationship between the dragline scheduled stripping volume with both the weighted average thickness of the coal seam and the height of the blast casting bench was derived. The results show that the reliability of the dragline stripping system decreases with the weighted average thickness of the coal seam and increases with a reduced casting blast bench height and monthly raw coal production capacity. Furthermore, the dynamic monthly advance distance of the dragline stripping system was found, a new concept of the dragline stripping system reliability and measurement methodology were proposed, and a prediction model for the dragline production capacity was established using a generalized regression neural network. In addition, the steps and processes of the reliability were improved. The study on the Heidaigou surface mine shows that the height of the casting blast bench should be reduced to 10.5 m when its raw coal production capacity is improved from 20 to 30 Mt/a. During the normal production of surface coal, the system reliability can be improved by dynamically determining the weighted average coal seam thickness, accurately predicting the dragline production capacity, and taking other corresponding measures.

DETERMINATION OF BENCH BLAST DESIGN PARAMETERS FOR LIMESTONE QUARRY AT GABLE OKHEIDER, AL AIN EL SUKHNA – WEST OF GULF OF SUEZ, EGYPT

Bench design geometry parameters are considered the important issue of rock extraction. It directly has influences on rock extraction on all surface mines and quarries operation. This paper discuss the bench height calculation according to three important considerations; the stability of slope faces, the safety of the work place and the efficiency of the work place, besides the calculation of optimum working bench level width. Also, determination of optimum blasting bench parameters such as bore hole diameter and depth, spacing - burden ratio, sub-drilling depth, stemming length, stemming material type and size, decks type and decking length, type of explosive, column and bottom charge, powder Factor for limestone quarry at Al Ain El Sukhna – west of Gulf of Suez according to field trial tests.

Prediction of Rock Size Distribution in Mine Bench Blasting Using a Novel Ant Colony Optimization-Based Boosted Regression Tree Technique

In this paper, we used artificial intelligence (AI) techniques to investigate the relation between the rock size distribution (RSD) and blasting parameters for rock fragmentation in quarries. Moreover, the ant colony optimization (ACO)–boosted regression tree (BRT) model, which is a novel AI technique for predicting RSD using the blasting parameters, is proposed based on the ACO and BRT algorithms. For predicting RSD, three well-developed models, namely the particle swarm optimization–adaptive neuro-fuzzy inference system (PSO–ANFIS), firefly algorithm (FFA)–ANFIS, and FFA–artificial neural network, were applied to the same dataset. Additionally, four benchmark AI techniques, i.e., support vector machine, k-nearest neighbors, principal component regression, and Gaussian process, and a conventional approach, i.e., the Kuz–Ram model, were employed for considering and predicting RSD. Using an image processing technique, the Split-Desktop software package was used to analyze the RSD of 136 blasting events at a quarry in Vietnam. Results were used as inputs, such as powder factor, explosive charge per delay, bench height, stemming length, and burden, and outputs, i.e., RSD, in this study. The novel scoring and color-intensity methods were used for visualizing several statistical criteria, including the correlation coefficient, mean absolute error, and root-mean-square error, to evaluate the model performance. Results indicate that the proposed ACO–BRT hybrid model yields higher RSD predictive accuracy than that obtained using any other model. The proposed model seems to be promising for optimizing the blasting parameters to increase the production efficiency while reducing the production costs.

Summary of Modelling Safety Factors of Slope Stability in A Tar-Sand Quarry: A Case Study

This research studies the importance of slope stability during open-pit mining of tar sand within the Dahomey basin, Southwest Nigeria. It involved the geotechnical characterization of the layers of Laterites and Alluvium which it underlies. In addition, SLOPE/W software of the GeoStudio package was utilized for deducing and modeling the bench face angles which had higher safety factors, through the Morgenstern Price method of slices. It was discovered that the lateritic soil layer possessed higher values of unit weight, cohesion and internal frictional angle than those of the Alluvial Sand layer. Factors of safety were generated for bench face angles ranging from 10o to 90o at 1m, 4m and above 40m groundwater levels; over a 10m bench width and 6m bench height. However, for heavy equipment, a bench width of 20m and height of 6m were assumed. This resulted in factors of safety varying between 3.58 and 1.73 for bench face angles between 10o and 30o during higher precipitation (and water tables). Thus, this suggests that stable slopes predominate at bench face angles of 10o to 30o. This can be further enhanced when sufficient drainage systems are constructed.Â

A novel artificial intelligence technique for analyzing slope stability using PSO-CA model

This study aims to develop a new artificial intelligence model for analyzing and evaluating slope stability in open-pit mines. Indeed, a novel hybrid intelligent technique based on an optimization of the cubist algorithm by an evolutionary method (i.e., PSO), namely PSO-CA technique, was developed for predicting the factor of safety (FS) in slope stability; 450 simulations from the Geostudio software for the FS of a quarry mine (Vietnam) were used as the datasets for this aim. Five factors include bench height, slope angle, angle of internal friction, cohesion, and unit weight were used as the input variables for estimating FS in this work. To clarify the performance of the proposed PSO-CA technique in slope stability analysis, SVM, CART, and kNN models were also developed and assessed. Three performance indices, such as mean absolute error (MAE), root-mean-squared error (RMSE), and determination coefficient (R2), were computed to evaluate the accuracy of the predictive models. The results clarified that the proposed PSO-CA technique was the most dominant accuracy with an MAE of 0.009, RMSE of 0.025, and R2 of 0.981, in estimating the stability of slope. The remaining models (i.e., SVM, CART, kNN) obtained poorer performance with MAE from 0.014 to 0.038, RMSE 0.030–0.056, and R2 0.917–0.974.

Impact of Blast Design Parameters on Rock Fragmentation in Building Stone Quarries

Crushed stone aggregates are indispensable construction material which is produced by crushing of raw stone boulders raised from stone quarries through the process of drilling and blasting. Proper size of boulders fed to the crusher is important to eliminate congestion in the crushing circuit and obtaining the desired productivity. Drill-blast design parameters have a considerable effect on the degree of post-blast fragmentation. Bench height, spacing, burden, stemming, bench stiffness ratio and powder factor are controllable blast design parameters which considerably influence the fragmentation. By controlling these design parameters, optimum fragmentation can be achieved. Extensive field trials followed by scientific analysis have been done in this study which reveals the relation between drill-blast design parameters and post-blast fragmentation. Burden, spacing, stemming, bench stiffness ratio and powder factor were varied over a range of 30–45% which in turn caused distinctions in the mean fragment size in the range of 50–200% approximately. For optimum mean fragment size, the burden was found to be 21 times the blast hole diameter. Spacing dimension of 1.3 times the burden produced the optimum mean fragment size. Stemming length of 0.91 times of burden generated the optimum fragmentation. Mean fragment size was most optimum at powder factor of 1.02 kg/cum.

The Study of Parameters of Quarry Faces in Muruntau and Myutenbai Open Pits in Case of Applying Major Blasts

The paper presents process layouts for excavation of zones near pit envelope based on the analysis of findings of the ore loss study in case of open-pit mining, as well as the results of field measurements in the quarry faces in Muruntau and Myutenbai open pits. In the course of the field measurements, parameters of the quarry faces at Muruntau and Myutenbai open pits were determined under the following working conditions of an excavator: at full bench with shotpile height of 19–21 m; at full bench with shotpile height of 12–14 m at excavation of the “blast cap”; at heading face and taking ramp material. In all the above-listed quarry faces, the slope angles and the ore mass shotpile height when excavating were measured. Besides, the used excavator type (dragline or hydraulic) was taken into account. For each face, 2–3 measurements were performed, and the average slope angle at the ore mass excavation was determined for each type of excavator. At the next stage of the field measurements, the bench height in the rock mass and the shotpile parameters were measured before and after blasting operations under the following arrangements for preparing the rock mass for excavation: a) under normal conditions, when the ore mass blasting is performed for the selected face or relieving wall of the required thickness; b) in compression with a “blast cap” formation; c) in the marginal parts of the bench. Based on the results of the actual bench height and the blasted rock shotpile parameter field measurements, the following conclusions were drawn: a) the actual slope angles of the quarry faces were 49° when excavating the “blast cap” using dragline excavators, and 53° when excavating the ore mass at full bench regardless of the excavator type used; the slope angles of 49° for the dragline excavator and 53° for the hydraulic excavators were taken for further calculations; b) the width of the marginal (near-envelope) zone, where losses and dilution of balance ore are generated, increased from 7 to 13.0 m (at 49°) and from 7 to 11.3 m (at 53°); as a result, the areas of loss and dilution triangles have increased; c) when blasting in compression conditions, in the upper part of the shotpile, intense mixing of the involved rock and all ore grades occurs, therefore, when excavating the “blast cap”, bulk ore mass mining is only possible. The lower part of the blasted bench preserves the geological structure of the rock mass to a greater degree and can be selectively excavated with separation of the ore mass by grade; d) when blasting the rock mass, to maintain the required pulse direction and the blasting sequence, barren boreholes are included in the breaking outline, which increase the balance ore dilution, and structural dilution arises, which should be taken into account when drawing up the "Methods for determining, limitation and accounting for ore losses and dilution in the course of the Muruntau and Myutenbai (the fifth stage) open-pit mining"; e) when compiling the "Methods ...", the option of dividing a bench of 15 m high into two sub-benches of 7.5 m should be considered.

The failure mechanism and construction practice of large underground caverns in steeply dipping layered rock masses

The stability of large underground caverns in steeply dipping layered rock masses is not only affected by the engineering geological characteristics of surrounding rock masses, but also by the excavation sequences and reinforcement measures. Certain places around the periphery of underground openings, such as the high sidewalls, would exhibit significant displacement increases and various failure patterns if the excavation and support were not properly designed. These issues can, according to the basic principles of structurally-controlled concept, be largely attributed to the mechanical properties of bedding planes and other discontinuities. In order to clarify the possible mechanisms behind these failures and to realize the dynamic adjustment of construction, a thorough investigation was conducted to the underground caverns of the Wudongde hydropower station throughout the excavation process. The geological conditions and mechanical properties of the rock masses in the study area were first introduced in detail. Four examples were then presented following the overall logic from geological background to failure mechanism and finally to reinforcement practice. The first example focused on the local wedge-type instability analyses, including the collection of necessary information, the identification of potential blocks, as well as the determination strategies for the factors of safety. The second example illustrated typical tensile failure mode of steeply inclined strata induced by large-scale excavation. The sudden normal unloading of bedding planes led to observable fractures along these weaknesses and considerable increases in sidewall displacements. Large quantities of extra reinforcements had to be installed to control further development of fractured range of the upstream sidewall. The third example highlighted the long-range influence of excavations on the stability of downstream roof, where multistage displacement increase and shotcrete cracking took place as a result of stress concentration and strata buckling, possibly also of the local unfavorable discontinuities. The last example was related to the failure mode of combined discontinuities on the surfaces of piers between two pits. Lessons learned from these examples mainly involve what the mechanical behaviors of the steeply dipping layered rock masses in different places after excavation will be like, and to what extent these behaviors could be predicted or anticipated, which then put emphasis on the importance of geological investigations, and how the optimization of excavation sequence and bench height as well as the timely installation of regular supports could effectively reduce the risks of instability.

Study of the Backhoe’s Digging Modes at Rock Face Working-Out

As is known from the classic works on open pit mining, the bench is a separately developed part of the rock layer, having the form of a step. It should also be noted that it is necessary to clearly differentiate the concepts of “bench height” and “height of the layer to be removed.” The benches are often divided into subbenches, developed by different excavation equipment or by the same equipment both sequentially and simultaneously, but having transport routes that are uniform for the bench. As an example, an excavator stripping of the upper and lower subbenches with loading, respectively, at the level of the excavator and above this level, is usually given, that is, the transport route (road) passes through an intermediate platform bench located in the middle of its height. Therefore, the excavation layer of any height, which is, in fact, a part of the working bench, can be considered as an independent bench with all its attributes, but in order to avoid duplication of definitions, this paper suggests the name “extraction layer”. When developing this element various digging modes can be applied. In this paper, we studied the main modes and selected the one that provides the highest performance.

Technological Indicators of Direct Dumping Zone as a Part of Combined Mining Method

Under the conditions of a combined mining system overburden is developed using a transport and non-transport technologies, specific costs for non-transport technology are lower than transport costs. The change in the non-transport bench height led to the redistribution of the volumes of transport and non-transport overburden. With an increase in the volume of non-transport overburden, the share of more expensive transport overburden is decreases, while the technical and economic indicators of the non-transport zone deteriorate due to an increase in re-excavation volumes. The change in the non-transport bench height affects the recasting ratio and the annual advance coal face line, which determine the cost of developing the overburden. This article presents the results of a study of the laws of change in the recasting ratio and the annual advance coal face line, depending on the non-transport bench height within a combined mining system of flat seam. The obtained patterns were established as a result of solving problems of substantiating typical excavation schemes of the direct dumping method and developing a mathematical model for identifying excavation schemes with the subsequent calculation of their technological indicators.

ANALISIS KESTABILAN LERENG DINDING AKHIR DI PIT BARATLAUT PADA PENAMBANGAN BATUBARA DI PT. PUTERA BARA MITRA , KECAMATAN MENTEWE, KALIMANTAN SELATAN

PT. Putera Bara Mitra used open mining system for mining operation, Yet the completion of study on the end wall slope stability that undertaken by geotechnical PT. Putera Bara Mitra in Northwest Pit and the occured a failure in the low wall on the 1st June 2012 led to the need for analysis and design the overall slope at the mine site. To analyze and design the overall slope, used value of the recommended minimum safety. The value was based on company for single slope SF ≥ 1.2 and SF ≥ 1.3 for overall slope. The calculation used Bichop method with the help of software slide v 5.0. Geometry improvements was done at the low slopes that originally single wall with a 30 m bench height and a slope 70° with SF = 0.781, into 4 levels with SF = 1.305. The analysis explained the factors that affect the stability of the low wall included the mining slope geometry, unfavorable drainase system, material stockpiles and seismicity factors. It was necessary to do prevention efforts to maintain the stability of the slope included the redesign to slope geometry, handling surface and subsurface water in a way to control slopes draining groundwater, vegetation stabilization using and monitoring slope using Total Station with Prism and Crackmeter to determine the movement of cracks visible on the surface.

Relationship of the discontinuities and the rock blasting results

The Geological discontinuities such as joint are the most common discontinuities present in the rock mass. A model scale study was carried out to evaluate the effect of the joints on rock blasting. Single hole tests at three selected burdens (optimum, less than optimum and more than optimum) were done on six different joint orientations. The joint orientation angles were 0°, 30°, 60°, 90°, 120° and 150° rotating in anticlockwise direction from the floor of the bench in a plane perpendicular to the free face. Bench models of dimensions 515x335x215 mm with a bench height of 50 mm were prepared by binding sandstone slabs of 25 mm thickness with an adhesive. The models were blasted by n°6 electric detonators. The dynamic and static properties of sandstone are given. The bench crater formed and the fragmentation produced were predominantly influenced by the position of charge with respect to the joint orientation. Severe toes were noticed in models with vertical joints and with joints dipping away from the face. Over breaks were observed in horizontally bedded models and in models with joints dipping towards the free face. Over breaks were observed in horizontally bedded models and in models with joints dipping towards the free face. The size of the broken fragments at 20 mm burden was found to be finer than the fragments obtained at 30 mm and 40 mm burdens for all joint orientations except vertical.

A New Mathematical Model for Predicting the Surface Vibration Velocity on the Step Topography

In order to control production blasting and optimize mining operation, it is important to study the step topography vibration amplification and attenuation effect in the open‐pit mine. Surface particle vibration velocity attenuation characteristics, the formation, and change rules of the terrain effect were studied by analyzing the field measured data. Results show that local amplification effect and local attenuation amplification effect of particle vibration velocity are obvious. Amplification effect associates with bench height, and the attenuation effect is closely related with the distance from the vibration source and distance from the top. With the increase of elevation, vibration magnification of the particle on the top was 1.1∼1.4. Because of the influence of the terrain effect, particle vibration velocity on the slope toe was obviously inhibitory. Based on the measured data, elevation amplification factor and clamping effect factor which influence blasting vibration velocity are put forward, and a new mathematical model considering the attenuation coefficient, the elevation amplification coefficient, and the clamping effect coefficient for predicting the blasting vibration velocity of the step topography is further improved. The regression analysis results show that the fitting coefficient of determination of the new prediction model is 0.8152 in horizontal and 0.8902 in vertical, respectively, and the prediction error is less than 20%, which is much better than other formulas. This new model provides effective reference for blasting seismic wave propagation law research of slope engineering.

Optimization of Dump Bench Configuration to Improve Waste Dump Capacity of Narynsukhait Open Pit Coal Mine

In next two years, the current waste dump of Narynsukhait coal mine is predicted insufficient to accommodate the overburden as limited of the waste dump capacity. Thus, redesigning waste dump is paramount to increase capacity of the dump in future. This paper describes current condition of waste dump of Narynsukhait coal mine and then discusses the optimization of waste dump geometry by analyzing the effect of different waste dump’s bench configuration on slope performance. Optimization of the geometry is carried out by investigating and comparing the performance of geometrical combinations of bench height, bench angles and number of safety berm by means of numerical modeling. The model shows that increasing height of bench is able to induce shear stress in the bench and may initiate bench instable. However, the shear stress can be limited by having safety berm and/or reducing bench angle to satisfy the stability criteria.

Random Forest Tree Based Approach for Blast Design in Surface Mine

Blasting is one of the primary mining operations for extracting minerals and ores however, if not designed properly, may have a varying degree of environmental and socio-economic impact in and around mining areas. In Indian mining industry, blast designs are fundamentally based on the experience and capability of the blasting crew and its assessment is more qualitative in nature, based on conventional trial and error basis. With the change in site geology and geotechnical parameters, the blast design parameters also require alterations, which can be standardized with the development of an intelligent system such as neural network. In this paper, the concept of artificial neural network and random forest algorithm has been used for better blast designs. Over 120 blast results from an opencast coal mine have been used for prediction of burden and energy factor with blast hole diameter, bench height to stemming ratio, nature of strata and average fragment size as input parameters. Out of 120 data sets 85 data sets recorded at a surface coal mine was used to train the model and 20 for the validation. Co-efficient of determination and root mean square error was chosen as the indicators to identify the optimum neural network and random forest model. The root mean square values obtained for energy factor is 0.153 while it is 0.1947 for burden. Similarly, the RMSE values obtained using random forest tree algorithm is 0.48 for burden while 50.76 for energy factor. The results revealed that random forest tree network system has potential to design better blast that is not generic and can be a potential tool for blasting engineers to design optimum blast for the mines.

UI Form design considerations for ergonomists evaluating computer workstations

A professional ergonomist performing a workplace evaluation identifies risk factors and provides recommendations to mitigate these risks. This system involves analysis of the interaction between a human subject and the subject’s computer based work environment. Since the data required to be collected is more than the average person can keep in their short term memory, it is safe to say the ergonomist will need to record observations. This will have to be done while simultaneously interacting with the employee performing work. Human-computer interaction is observed by the ergonomist, but ergonomists themselves also use a computer or tablet to take records and produce a report. The interaction and interface of the data collection form for ergonomic evaluations should cater to the needs and capabilities of the ergonomist in the field (Kim, 2015) and so it is not a surprise that most forms are designed by the ergonomists themselves. These forms are also typically tailored to the type of task being evaluated (i.e. computer, laboratory, industrial) because each of their environments have particular equipment or tools these need to be recorded. For example, a computer workstation will include a chair, desk, displays, etc. while a lap will have a stool chair, bench height seating, rack, flow hood, etc. This paper will describe key user-interface form design considerations for office ergonomic evaluation forms with the purpose of optimizing the user-experience for an ergonomic professional. Applications include the use of a form on a laptop computer, tablet, or phone in a computer workstation environment. This paper will consider factors related to the working environment, reliability, input requirements, form structure and flow, and front end to back end management agents. The goal of any interface is to be intuitive enough that it would require minimal familiarization to be reliably implemented (Norman, 2002). As users gain familiarity with the form entries, the ergonomist can benefit from increased speed, accuracy and consistency of their evaluations. The report generated by these completed forms can be utilized in legal and workers compensation cases and therefore they require special consideration in the way the questions are phrased and ordered to reduce potential for error and opportunities to place blame. This added complexity makes their design more than a simple task. Guidelines are included in this article that will proactively assist ergonomists in designing effective forms.

The effect of channel restoration on ground beetle communities in the floodplain of a channelized mountain stream

Background and purpose: River regulation works, channelization and floodplain urbanization have reduced the frequency of flooding, incised river channels, and separated them from the surrounding riparian zones. This phenomenon is especially unfavourable for exposed riverine sediment areas (ERS) situated in the transition zone between terrestrial and aquatic environments, and plays a fundamental role in the functioning of riverine ecosystems. We investigated the effects of restoration practise based on eco-friendly structures on riparian ground beetle communities. Materials and methods: Carabids were surveyed in 60 sampling sites of incised and redeposited cross-sections of a mountain stream. At each cross-section geodetic measurements were surveyed and six sampling sites were randomly established at different distances from the water surface. Results and conclusions: Non-metric multidimensional scaling revealed that the dissimilarity in carabid communities between the three benches resulted mainly from differences in hydrological (bankfull discharge, period of flooding, water velocity) and geomorphological parameters (incision and erosion) in the incised and redeposited cross-sections. A GLM indicated that incision-redeposition processes had a significant effect on carabid assemblage parameters and life history traits. The effect of redeposition processes on abundance, species richness, biomass and MIB depended strongly on bench height and flood frequency. The cross-sections where eco-friendly constructions were built and bed material deposition processes were recreated showed increased abundance of ERS specialists: small predators with high dispersal power and a spring breeding strategy. However, the proportion of specialist species in the community was small, which indicates a slow rate of restoration of ERS specialist diversity.