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By Guy Bridges, Elton Ko, Cheng Ting Ning, Owen Ng, Giovanni Chang, Robert Anderson

"PROJECT OVERVIEWThe Liantang/Heung Yuen Wai Boundary Control Point (BCP) and Associated Works will be the seventhland crossing between Shenzhen and the Hong Kong Special Administrative Region (HKSAR) of China.The project includes site formation of about 23 hectares of land for the development of the BCP and anapproximately 11-kilometre (km) long dual two-lane trunk road (the “Connecting Road”), connecting theBCP with the existing Fanling Highway. The route alignment is within a relatively rural area of HongKong, with very limited similar infrastructure works carried out nearby. It passes beneath bothmountainous terrain, and alluvial plains, and falls within an area of several major regional faults andassociated metamorphism, resulting in a complex variety of ground conditions.ALIGNMENTThe Civil Engineering and Development Department of the Government of the Hong Kong SpecialAdministrative Region carried out extensive public engagement in selecting the alignment of theConnecting Road. Over 70 consultation forums with public bodies, including the District Councils, RuralCommittees, local representatives, etc. were held during the alignment design process. In order toalleviate the concerns of various nearby villages, and to minimize land clearance and environmentalproblems, the original alignment of 10 km long (3.5 km of tunnels and 6.5 km of viaducts) was revised toits final alignment of 11 km long which comprises 5.7 km of tunnels, 4.3 km of viaducts and 1.0 km of atgrade roads.The finally adopted alignment commences at the southern end with an interchange with the existingFanling Highway, part of Route 9, which is a dual three lane expressway currently being widened to dual4 lane. Alongside the expressway is the main rail connection to the mainland of China, and theinterchange viaducts connecting to the southern portal of the Lung Shan tunnel must cross over thisrailway. The southern portal is located in the foothills of Lung Shan, and the 4.8km long tunnel is alignedin a north-northeasterly direction. The southern half passes under mountainous terrain of Lung Shan,and then crosses a valley containing the Kwan Tei river. The northern section comprises low hillsseparated by an alluvial plain and Tan Chuk Hang village area. At the northern end, the tunnel turns tothe north-west to connect with Sha Tau Kok road, an existing single carriageway road, with a newroundabout interchange. Mid-way along this tunnel there will be a ventilation building, connected to the main tunnel by a 330m long ventilation adit. To the north-western side of this interchange is the900m long Cheung Shan tunnel, and after this the remaining 4.3km of the highway connecting with theBoundary Control Point is to be constructed as an elevated viaduct. The alignment is shown in Figure 1."

Jan 1, 2016

By X. Wu

A quantitative damage evaluation caused by ground motions associated with strong roof caving is presented. The strong roofs are modeled as either cantilevering or bridging beams over continuous elastic foundations subject to an exponentially distributed vertical stress. Major factors influencing roof caveability and strain energy buildup are identified and investigated. A methodology to evaluate the strain energy accumulation caused by overhanging roof is presented. The potential for mine tremors is determined in terms of the local Richter magnitude ML which depends on the seismic energy transformed from the stored strain energy released when the roof fails. A particle velocity model is applied to estimate the damage area associated with roof collapse. A case study from a Utah coal mine shows that estimations of bump severity and damage area agree well with the field observations.

Jan 1, 1995

By Robert W. Bruhn

An investigation was made of ground response to pillar retreat mining in a 1.7 meter thick seam at 108 meter depth at a site in northern West Virginia. This paper describes mining-related stress changes and movements at mine level, displacements within the overburden, ground surface subsidence and groundwater level variations. Subsidence approached 40 per cent of the mine height and continued more than a year after mining. Water levels declined in certain deep-lying strata.

Jan 1, 1984

By Robert W. Bruhn

An investigation was male of ground response to pillar retreat mining in a 1.7 meter thick seam at 108 meter depth at a site in northern West Virginia. This paper describes mining-related stress changes and movements at nine level, displacements within the overburden, ground surface subsidence and groundwater level variations. Subsidence approached 40 per cent of the nine height ad continued more than a year after mining. Water levels declined la certain deep-lying strata.

Jan 1, 1984

By Louis A. Panek

Ground movements in the zone adjoining an active cave were measured at four sites in the San Manuel Mine. Measurements were made to detect extension and inclination, basic components of displacement, which can readily be duplicated by mine personnel using relatively simple equipment. The displacements demonstrated the development of a zone of strain relief surrounding the active cave, within which the ground tends to migrate toward the cave, and extension cracks develop tangential to the cave. This expansion of the ground surrounding an active cave can be exploited to promote future caving; it also creates special problems with respect to the design of an effective ground support system for mine openings in the production area.

Jan 1, 1981

By E. C. Westman, W. R. Thomas, W. J. Conrad, A. J. R. Russell

"Understanding ground control problems continues to remain a focus of the mining engineering community. To aid mine operators and engineers in identifying and responding to ground control issues, the Ground Observation System (GOS) is being developed. The GOS is an integrated, web-based graphical user interface that displays ground response data collected wirelessly from an underground mine. It presents data in an intuitive manner to assist mine personnel, who are on- or off-site, in quickly identifying hazardous areas. Geotechnical instrumentation will be connected to wireless transmitters that will relay data in real-time to a surface computer that stores the information in a database. The GOS website will then display the geotechnical data in graphical and tabular forms, as well as in conditionally formatted mine maps. Data from each measurement device will be able to be viewed in its entirety or within a time interval, and can be downloaded for further analysis. The ability of the GOS to quickly interpret and communicate mine hazards to personnel of varying technical ability should prove to be a useful tool in understanding ground control and thus improving mine safety.INTRODUCTION Computer-based data information centers that convey operating parameters and conditions are prevalent in modern underground mines. Today’s systems are popular in showing ventilation controls and monitoring equipment performance (Jyothi & Meena 2013). In ground control monitoring, Conover, Ross, and Bigby, 2010 have installed a wired telltale roof monitoring system that sends roof displacement data every ten minutes to a computer on the surface. The computer receives, stores, and displays the data in real time. Data can also be viewed remotely through a password protected internet connection. Additionally, an internet connection allowed for remote updates to the system which streamlined software development and maintenance by eliminating travel (Conover et al., 2010). Currently, no such system beyond Conover et al.’s design has been accomplished. The Ground Observation System (GOS) is being developed to fill the void of real-time geotechnical monitoring in underground mines. A wide array of data will be transmitted wirelessly and broadcasted to on- and off-site mine personnel through the internet. The GOS will incorporate geotechnical data from roof deformation, borehole scratch testing, photogrammetry, and seismic monitoring into one interface, all while achieving permissibility for the use in gaseous mines. As a result, a comprehensive view of rock movement due to mining will be available. The overall purpose of the GOS is to deliver warnings; to ensure reliable data is relayed to personnel for the identification of potential ground failures, provide mine engineers information to design more stable mines, and assist with further geotechnical research."

Jan 1, 2015

By T. J. Fenner

Surface and underground mining operations are often hindered by unknown tunnels and stopes and the precise locations of adjacent workings. Mine safety and planning are adversely affected especially in previously undermined areas where historical records are incomplete or non-existent. The results of several Ground Penetrating Radar (GPR) studies for the detection of known mine tunnels in underground coal; salt, and gold mines are presented. A case study to locate unknown, abandoned mine workings at a surface gold mine successfully located all workings to a depth of 11 meters.

Jan 1, 1992

By R. Bishop, J. Baggett, J. Monsalve, J. Hole, N. Ripepi, A. Abassi

This work focuses on the operational and safety issues associated with karst voids in large opening underground mines. Issues include water inrush, structural instability, and engineering uncertainty in these environments. Coupled with the fracturing prevalent in folded sedimentary rocks, karsts are complex and challenging ground control risks. Traditional methods of predicting karst locations, such as probe drilling, are impeded by the inconsistent spatial distribution and variable sizes of the features. Ground penetrating radar (GPR) is a geophysical technique that transmits radio waves into a medium and subsequently detects reflected waves via a receiver. The travel time and energy of received signals are then processed and interpreted. The difference in material properties between limestone and open karsts causes strong reflections. GPR is frequently used as a geophysical surveying technique in several industries, however there is a lack of published research on underground mining GPR applications. The purpose of this work is to prove the viability of GPR in underground stone mines for karst detection, and to discuss the importance of karst detection ahead of mining. INTRODUCTION The Mine Safety and Health Administration (MSHA) currently lists 116 active underground stone mines in the United States, the vast majority of which extract limestone for crushed stone products. These limestone mines have the potential to encounter karst voids at some point in their operation, as most karstic regions of the United States develop in limestone rock masses (Kuniansky, Weary, & Kaufmann, 2016). Karsts, the cavities formed by the dissolution of carbonate rock, have long plagued the mining and tunneling industries, as well as been a hindrance on the Earth’s surface, producing sinkholes and ruining otherwise valuable land for construction and public use. The impact of karsts on the Gavarres tunnel in Spain is well documented by Alija et al; constant instability conditions, material spills into the tunnel, and unexpected cavities seriously delayed the project deadlines and “were not foreseen in the design” (Alija, Torrijo, & Qunita-Ferreira, 2013). At the water supply project in Sohngua River, China, Bin et al detail the presence of both water and sediment filled karsts which are sources of disastrous conditions at this tunnel (Bin, et al., 2017). A hydrological tunnel in Lebanon encountered numerous massive karsts in the tunneling path which required remediation via friction anchors, rockbolts, welded wire fabric, channel steel arch segments, invert steel beams, and shotcrete (Leech, Jaoude, & Ghanem, 2008). From a design standpoint, rock mass classification schemes, such as the RMR from Bieniawski and the Q-system from Barton, are not able to represent the true nature of a karstified carbonate rock mass, and therefore complex case-by-case analyses of underground conditions are necessary (Andriani & Parise, 2017).

Jan 1, 2019

By David F. Gearhart

A cooperative study was conducted between Signal Peak Energy and the National Institute for Occupational Safety and Health (NIOSH) to evaluate the behavior of a pre-driven recovery room under less than 200 ft of cover. The design of the support systems for a pre-driven recovery room must provide control of the roof and ribs during the changing stress environment experienced throughout the final advance of the longwall into the recovery room. It must also provide a stable area where mine personnel are not exposed to undue hazards during shield recovery operations. This recovery room was constructed in two phases; each phase mined a 21-ft-wide room that was heavily supported, and subsequently fully backfilled with 800-psi, cellular concrete. Instrumentation to monitor the recovery room performance included borehole pressure cells (BPCs) placed in the head gate and tailgate pillars, at four locations across the longwall panel, in the fill material, and in the first row of outby pillars near the center of the panel. Four roof-to-floor convergence sensors were installed in the back fill material and a vertical, multipoint borehole extensometer (MPBX) measured the displacement of the strata above the recovery room. Surface surveys were conducted to measure MPBX collar movement. The data show that the front abutment load was transferred onto the recovery room backfill and the out by pillars as the longwall panel was extracted. As the longwall approached the recovery area, the fender and shields yielded, but the backfill provided enough support to keep the room stable as the longwall advanced to its final position. The system worked as planned and the face was recovered in record time.

Jan 1, 2014

By Peter Zhang, Daniel Su, Essie Esterhuizen, Mark Van Dyke, Berk Tulu, Dave Gearhart

"Roof falls in longwall headgate can occur when weak roof and high horizontal stress are present. To prevent roof falls in the headgate under high horizontal stress, it is important to understand the ground response to high horizontal stress in the longwall headgate and the requirements for supplemental roof support. In this study, a longwall headgate under high horizontal stress was instrumented to monitor stress change in the pillars, deformations in the roof, and load in the cable bolts. The conditions in the headgate were monitored for about six months as the longwall face passed by the instrumented site. The roof behavior in the headgate near the face was carefully observed during longwall retreat. Numerical modeling was performed to correlate the modeling results with underground observation and instrumentation data and to quantify the effect of high horizontal stress on roof stability in the longwall headgate. This paper discusses roof support requirements in the longwall headgate under high horizontal stress in regard to the pattern of supplemental cable bolts and the critical locations where additional supplemental support is necessary.INTRODUCTIONLongwall mining is the primary underground coal mining method in the United States and currently accounts for more than 60% of the underground coal production. The longwall headgate, as a passageway for the longwall crew, intake air, material supplies, and coal belt transportation, is critical for both safety and continuous production of the longwall panel. A roof fall in the longwall headgate would not only result in substantial interruption of production but could potentially cause injuries or fatalities. Rehabilitation of failed roof in the headgate would also expose miners to the risk of injuries. Roof falls in the headgate, though infrequent, mostly occur in the belt entry near the face. Considerable research has been conducted to determine the effects of various factors on headgate roof stability, as well as effective measures to support the roof in longwall mines in the Pittsburgh seam (Mark, Mucho, and Dolinar, 1998; Chen et al., 1998; Su and Hasenfus, 1995; Su, Thomas, and Hasenfus, 1999; Su, Morris, and McCaffrey, 2002; Su, Draskovich, and Thomas, 2003; Hasenfus and Su, 2006; Van Dyke et al., 2015). Previous studies have demonstrated that high horizontal stress and transitional roof geology are primary factors that cause headgate roof failure. These studies also showed that panel orientation, retreat direction, pillar sizes, and roof support played an important role in the stability of a headgate.In underground coal mines located in the eastern United States, the magnitude of the maximum horizontal stress is typically three times greater than the vertical stress, and about 40% greater than the minimum horizontal stress. Mark, Mucho, and Dolinar (1998) studied seven cases of headgate failures caused by high horizontal stress in different coal seams in the United States and stated that roof stability is affected, to a large extent, by rock type, entry orientation, and longwall orientation. The effects of horizontal stress can be summarized in these statements: (1) A laminated roof is very vulnerable to high horizontal stress. (2) Entries that are aligned with the maximum horizontal stress will suffer less damage on development than those perpendicular to it. (3) Horizontal stress concentration and relief depends on panel orientation, the direction of retreat, and the sequence of longwall panel extraction."

Jan 1, 2018

By E. Siami-Irdemoosa, S. R. Dindarloo

Ease of excavation or rippability, also called diggability or excavatibility, is a critical decision-making parameter in the selection of both the overburden removal method and the required equipment in surface mining and geotechnical engineering projects. The most widely used method of estimating rippability is rock mass classification. Although there are different classification schemes in the literature, all of them have the two major limitations of sharp transitions at class boundaries and subjective uncertainties in decision making. In this study, the decision trees method was employed as a classification tool for estimating ground rippability, using the four rock mass parameters of weathering degree, uniaxial compressive strength, joint spacing and bedding spacing. The results were compared with those of the widely used method of diggability index rating (DIR) and a fuzzy-based DIR. The problem of subjective uncertainty was resolved in the proposed decision trees method, as the tree rules were derived automatically from the training data sets. Compared with fuzzy-DIR, a decision tree classifier is simpler, needs less computational time and is more appreciable by industry practitioners. Nevertheless, the proposed method is not flawless and, similar to both the conventional and fuzzy DIR methods, yielded poor estimations in particular instances. The limitations of the three methods are discussed.

Jan 1, 2015

By K. Unrug, G. Herget, A. Smith

SUMMARY Statistics on roof falls indicate that the cost of just removing the unwanted waste from roof falls in US coal mines amounts to about $20 M per year. Almost 40 percent of fatal accidents occur under permanently supported roofs, indicating that the assessment of roof stability is still a very difficult task. In an effort to obtain a better understanding of roof fall occurrences, rock strength and ground stresses were determined in the roof of one mine each in Western Kentucky, northern West Virginia, and Eastern Kentucky. Triaxial ground stress determinations clearly show that horizontal stresses were higher than vertical stresses, and that maximum stresses in the horizontal plane were concentrated between the NE-SW to E-W direction, with the exception of the Eastern Kentucky site which was above the drainage. Magnitudes of stress components may vary considerably in one drlll hole. Strength tests of roof strata materials were done on core samples. Mapping of roof falls showed that the geometry of an opening or maximum span were not the overruling factor because in the same general area, a roof fall was observed in a room (entry) which connected two stable four-way intersections. It should be noted that, in very wet areas, the roof can break up to the bed where water is carried, and a very low ratio between extent of roof fall to height of roof, fall is observed. Geometry is, however, a contributing factor because nearly 70 percent of roof falls are intersection falls. The frequency of fractures parallel to bedding in failed roof strata is much higher than that observed in the original strata, indicating a significant amount of working in the roof before failure.

Jan 1, 1984

By A. Brown

THIS P APER has been pre-pared as a progress report on Mines Branch investigations into problems of ground stress in certain co al mines of Western Canada. As such, it should be considered as a companion report to the one ( 1) presented to the Mining Society of Nova Scotia in 1956 and which dealt with similar investigations in the coal mines of Eastern Canada. For the past 50 years, dynamic incidents in the form of 'bumps' and 'outbursts' have been occurring in the coal mines of the Inner Foot-hills belt of tl1e Canadian Cordillera. As these phenomena generally become more frequent with in-creased thickness of overburden, a limiting depth of mining of 2,500 feet has been set (2) for estimating recoverable reserves of coal. If such a view were accepted, from a long-term viewpoint very large resources of coking-grade ?coal -in a part of the continent deficient in such coals -would not be available to the nation. The terrain in which these in-6dents take place may be described in geological terms as being dominated by pronounced structure in strata ?consisting of a large proportion of highly indurated rocks. The Geological Survey of Canada has co-operated by carrying out structural studies (3) at the mines, supplemented lithological by stratigraphic observations.

Jan 1, 1958

By Robert L. Sundeen, Richard V. Wenberg

INTRODUCTION Early rock-bolting practice usually consisted of ran¬domly installing bolts, using hand-held drilling equip¬ment such as air-leg mounted sinkers or stopers. As bolting technology evolved, the practice of installing uniform bolt patterns was developed, utilizing random bolt installation as required within the uniform pattern. The uniform rock-bolting technique, when used as the principal method of rock support, requires drills and jumbos designed specifically for rock bolting. This equipment is similar to conventional face drilling machines, except that the jumbos can orient the drills to obtain any necessary bolting angle; often, this means bolts may be installed at or near perpendicular to the centerline of the drift or stope opening. Fig. I shows a typical rubber-tired rock-bolting jumbo of the type commonly used in drifts and room-and-pillar mining. Modern rock-bolting jumbos are capable of drilling the required holes, inserting rockbolts, and torquing them to proper levels. Jumbos also are available for use with resin-anchored bolts. Probably the most unusual of this type utilizes a rotating bolt turret that carries the rock drill, resin charging unit, and the bolt in a single mechanism. Once the turret is loaded with the resin and bolt, further manual effort is not re¬quired. Drilling and bolt placement are accomplished by the operator from a station remote from the bolt site. Fig. 2 shows this turret device. Roof-bolting jumbos are available mounted on rail, crawler, or rubber-tired chassis. Various types of rock drills are used. Depending upon the type of rock, these may include rotary, percussion, or rotary-percussion drills. Fig. 3 shows a typical rail-mounted jumbo. CONDITIONS INFLUENCING APPLICATION General Rock Conditions Rock-bolting generally is applicable in moderately hard to hard rock. No particular type of rock is ex-

Jan 1, 1982

By G. Sauer

"More Skill is needed to avoid rather than to handle heavy ground loads." This finding, from a tunneling engineer of the nineteenth century, is still relevant today with all advanced sequential excavation and support methods available whether they are applied in the vertical or horizontal direction. Balanced contractual agreements and documents are important since they provide the spirit and climate at the site. This article aims to describe the means and measures for 'hand mined' shaft and tunnel support as they are available today. Some special construction elements and methods with a perspective in recent developments in order to avoid getting stuck in conservatism are presented as well. If we don't allow new methods, means and measures we may end up with the famous quote "Only women who have already proven they are able to give birth to a healthy baby are allowed to become pregnant!"

Jan 1, 2003

By Z Li, A Fleming, S Webster, L Snyman

Northparkes Mines is developing the E26 Lift 1 North block cave mine, which is adjoined to the existing E26 cave. This paper presents the challenges and methods used to design the ground support system during the feasibility study. Calibrated numerical simulations were conducted to forecast the levels of rock mass damage and to assist the ground support design. Generally, low to moderate rock mass damage is forecast on the extraction and undercut levels. However, poor ground conditions are expected in sheared and preconditioned zones adjacent the existing E26 cave. This will result in difficult ground conditions during development, undercutting and drawbell establishment. Empirical assessments were conducted to make sure the ground support system is able to handle both the static and dynamic load demand, and to accommodate the deformation values. A safety factor of 1.5 was used for the designs to cover the unknown rock mass conditions and potential for larger seismic events. Learnings from the E26 Lift 1 and SLC, also mining against the E26 cave, are incorporated into the design. Fibrecrete, mesh and resin bolts / mechanical anchors are the primary ground support system used, and cable bolts for intersections with a span of more than 6 m. Following undercutting and during the operating life of the mine, secondary ground support and rehabilitation will be required.

Mar 15, 2021

By J. Hadjigeorgiou, Y. Potvin

In a benchmarking paper published in the SAIMM Journal, Potvin and Hadjigeorgiou (2008) reviewed ground control strategies to manage large deformations in underground hard rock mines. Significant differences were identified in the design and acceptable tolerance between civil and mining engineering practice for squeezing ground conditions. Variations were also noted in ground support strategies between Australian and Canadian mines. In this paper we review progress in design methodology and ground support practice since 2008, including the availability of more effective deformation monitoring, new design tools, greater access to yielding ground support elements, and better installation practices. An improved understanding of technical and practical issues associated with squeezing conditions has led to the development of ground support guidelines for a range of squeezing ground conditions in hard rock mines.

Jul 5, 2023

By Bradford P. Simser

The theoretical capacity of various ground support components can be misleading, especially in bursting ground where the failure mode is often in the retainment system. Wire mesh screen seams often peel open rather than breaking the wire strands, fractured rock often un-ravels around the bolts rather than breaking the bars. If a weak link(s) in the system fails prematurely, then the potential capacity of the system may never be fully realized. Underground observations are used to show how some support systems behave in the field. Various combinations of wire mesh screen with friction bolts, rebar, modified conebolts, cablebolts, shotcrete and mechanical rockbolts are considered. A short case history is used to contrast the performance of ?just-intime? development in a high stress faulted area versus a tunnel subjected to multiple stress changes in a similar environment. The latter proved to be a serious ground support problem when the well developed fracture zone around the opening was subjected to dynamic loading from a large seismic event causing a severe rockburst. In such cases an improved mining strategy may be more relevant than higher capacity support systems.

Feb 1, 2008

By Bob Munz, Ry Stone

To facilitate the installation of the longwall equipment for each extraction panel, West Elk mine develops set-up room roadways that are between 26.5 and 30.5 feet wide. Historically at the mine, the set-up room roadways have been driven in a single 20-foot-wide pass, then incrementally widened to the required width during installation of the longwall shields. The first pass roof is supported with a generic roof support plan consisting of partially encapsulated roof bolts and point-anchored cables. This ground support plan was utilized regardless of the geotechnical conditions encountered in the roadways or consideration of the required stand-up time of the roadway before the longwall shields were installed. This "blanket" approach tends to result in over-conservative or inappropriate roof support designs, particularly in changing geotechnical environments. Guided by the desire to optimize the ground support plans and increase mining efficiency for future set-up rooms, the West Elk mine and Agapito Associates, Inc. have developed and implemented a strata management program. Strata management, as a formal and structured process, allows ground support and mining methods to be tailored to the anticipated and encountered geotechnical environment in a con- trolled manner (Thomas 2007). To arrive at adequate site-specific ground support plans for the set-up rooms at the mine, several struc- tured processes were utilized. Firstly, the geotechnical environment was characterized by examining the roof lithology and geomechanical properties from nearby rock core obtained from exploration boreholes. To increase both mining efficiency and continuity, and to achieve longer stand-up times before the longwall shields are installed, a multi-pass approach was implemented into the design. During mining, the geotechnical conditions of the roadway are mapped, and the roof is strategically surveyed with a borescope. This process was used to ensure that the encountered ground behavior was in alignment with the design standards used for the roof support design. To support this process with measured data, roof extensometers were strategically installed throughout the roadway. This data was used to monitor the magnitude of roof displacement at various horizons and record displacement rates up until the longwall shields were installed. Lastly, a Trigger Action Response Plan (TARP) was used during mining to cater for any unforeseen changes in ground conditions that would warrant additional con- trols such as increased monitoring or the installation of additional ground support. This paper presents two case histories at the mine where the above strata management approach was implemented to arrive at a site-specific ground support plan. The main changes to the mine's ground control plan included a multi-pass mining approach, the utilization of fully encapsulated roof bolts, and the transition to a stiffer roof support system. The geotechnical mapping, the roof borescope results, and the roof extensometer data will be presented to demonstrate the effectiveness of the ground support system up until the longwall shields were installed in both presented cases.

Jun 25, 2024

By R Varden

This paper summarises the process taken to simplify 35 ground support standards accounting for the multiple development profiles, dynamic geotechnical environment and the practical safety implications of a large-scale change in the ground control standards. This reduction was required after an incident involving incorrect standards being issued. The subsequent investigation identified that: • Selection of ground support standard for a mining instruction (MI) is not straightforward due to multiple standards, standards not reflecting current reinforcement used and complex geotechnical environment being encountered. Instead, site-specific ground control instructions were being issued. • Ground support standards were hard to follow and confusing, errors were present and not all standards to scale. • Ground support standards being used did not reflect what was being installed, ie bolt type incorrect and mesh orientation different. • No process or tier action response plan (TARP) for operators to follow for ground control standard noncompliance. • No justification for ground support standards being used in the current geotechnical environment. • No process for ground support standard selection and thereby no paper trail to document and assess adequacy of performance. A project was undertaken to reduce and simplify the ground support standards, produce a justification document to support ground support design and develop a process for site practitioners to identify the type of ground support standard required for the mining instruction. The exercise of rationalising the ground support was met with some challenges, including: • Technical aspects to determine the level of demand and the capacity for each ground support scheme. • Training the geotechnical engineers how to determine the level of risk for each area. • Winning over other technical services staff and the underground mining contractor of the new approach and then implementation. One of the major successes was the acceptance by the underground operators who found the system simplified their work and gave them increased confidence in management of seismicity. The rationalised ground support standards have now been successfully in place for over two years.

Mar 29, 2023