Access drifts

Introduction

A drift (or access) is an excavated tunnel built for the purpose of providing a pathway for the transit of equipment, services or ore between different locations in an underground mine.

Installing Rock Bolts and Screen at Rio Tinto Diavik, 2014, Lac de Gras, NT, Canada.

Drift Types

Ore Access Drift Types

The types of ore access drifts may vary depending on the mining method, however nearly all underground mining methods can categorize their ore access drifts into the following:

• Sill (ore) Drifts
• Haulage Drifts
• Cross-cut Drifts
• Exploratory Drift

Isometric view showing haulage drifts and sill drift access.

Sill Drifts

Sill drifts (also known as ore drifts) act as the egress to the orebody in an underground mining operation. Sill drifts are usually secondary developments and act as a temporary access point while an active area in the orebody is being extracted. They are usually excavations of the orebody itself, and are backfilled or left alone after ore extraction. Depending on the mining operation, there can be many ore drifts that usually connect to a main haulage drift.

Figure XX shows several ore drifts on two levels connecting to the main haulage drift on the footwall side of the orebody. Depending on the mining operation, there can be many ore drifts that usually connect to a main haulage drift. For example, the Figure XX shows a sublevel stoping method with several ore access points, whereas a cut-and-fill mining method may have less ore access points on a single level. I am not saying this needs to get taken out but figures are referred on their own in a Wikipedia article.

Haulage Drifts

Haulage drifts are usually the source of access for an entire level from the sill drifts to a point of exit either through a ramp of shaft. Typically parallel to the strike of an orebody (dependent on mining method and orebody shape), haulage drifts see the heaviest traffic in a mining operation out of all areas of an underground mine (other than the ramp or shaft).

Figure XX shows two haulage drifts on the footwall side of an orebody with connecting sill pillars as an entryway to the orebody.

• Primary development

Cross-cut Drifts

Cross-cut drifts act as linkages between ore drifts. If mining is developing in parallel drifts on a single level, cross-cuts are made between the parallel drifts to recover more ore and leave sill pillars behind.

• Secondary development

Exploratory Drifts

Sometimes in an underground operation, a decision is made to open up drifts for to drill and gain more information of the surrounding host rock. The purpose of this could be to cover areas with low confidence of information from original drilling programs, with the hope that more ore will be found in places that were not originally accounted for. The figure below shows another example of an underground mining operation. A prospecting drift development is shown and drilling is most likely being completed to find more information about the 'undiscovered ore' zone.  

Design Considerations

Geometry

Drift Geometry is affected by:

• The purpose of the excavation
• The service requirements
• Rock Characteristics, Ground conditions in the area
• Intensity and nature of mining activity near the excavation
• Intended Life of Use
• Equipment requirements

High-traffic areas, or areas with significant auxiliary service infrastructure, may need to be larger to allow for clearance. At the design stage, the selected width and height for the excavation is designed to allow the largest perceived piece of equipment used in the area during the mine life. Transportation drifts may have damage along the walls due to equipment interactions.

Surveying drift progression at De Beers Snap Lake.

Ground control requirements in the area must also be assessed. These can influence the shape (arching) and orientation of the excavation relative to the principal in-field stresses. Another important acknowledgement is the impact of ground conditions on support consumables such as rockbolts, shotcrete, and the advance rate of the drift.

http://www.understandingunderground.sandvik.com/category/news/

Other types of ore access developments, such as drilling horizons, raisebore installations, and drawpoints, will need extra room for consumables such as drill rods.

Drawpoints will often require slashing to install remote mucking stands, provide additional void or a wider brow prior to bringing a stope on-line.

Average Excavation Sizes – NECESSARY? NOTHING HERE

Turns

Turns and Dog Legs

http://www.kamach.com/EN/ProductView.asp?ID=128 Turning development drifts is accomplished by blasting rounds with increasingly shorter holes towards the corner in the new direction. When the turn is accomplished, the face is squared off.

In designing turns, there are two main considerations:

• the ability of the development miners and equipment to develop a turn to design
• the space The angle for changing the direction of a drift requires the consideration of the turning radius of mobile equipment used.

Example An Atlas Copco E2 C operator will require 7 m of clearance (http://www.dukraft.com/wp-content/uploads/2014/09/SPECS-Atlas-Copco-Rocket-Boomer-E2C.pdf) to line up to a hole on a drill pattern. This limits the depth of a round that can be achieved on near the corners or at an angle to the face.

Another access design

(DOG LEG PICTURE AND EXAMPLE) – where is it!?!?! It doesn’t even have to be an example but an explanation would be nice.

Orientation The orientation of the drift in the mine plan should be considerate of the principal stress direction underground. Ideally, drifts should run parallel to this field. This is of extreme importance for life-of-mine infrastructure, such as for main level accesses.

The incline and/or decline of the drift needs to recognize the maximum slope that can be handled by mobile equipment. Changes in slope should not be so sudden so that a loaded scoop has to raise its bucket above operator height to travel up slope.

All drifts should be slightly sloped towards sumps or drain holes, to prevent water accumulation. An example ramp grade runs between 13-15%, and a drift of 17% maximum for stope accesses. For more information on ramps, see Ramp design.

Determining Service Requirements for Drift Development

The services required in a drift depend on what the drift is planned for and are tailored to equipment needs. Ore access drifts provide access to a stope during its lifecycle of drilling, blasting, mucking and backfilling and have specific service requirements. Ventilation Ventilation is one of the main limiting factors when designing and scheduling ore access drifts. Use of equipment is constrained by ventilation requirements as regulated by the Ministry of Labour for health and safety concerns. Example This calculation is the ventilation requirement for an Atlas Copco Scooptram ST7, a typical LHD that operates in ore access drifts.

Scooptram ST7: Underground Loader (LHD) Source

Ventilation planning typically uses a secondary ventilation system design to supply fresh air to ore access headings. These secondary systems usually involve attaching ventilation tubing to auxiliary fans that pull the required amount of fresh air to face of the drift from the main ventilation system. The design of ore access drifts and how they connect to other infrastructure should consider ventilation system design capabilities and limitations. Secondary ventilation system design takes in to consideration the length of the drift and how the drift connects to other openings, such as other drifts, rock passes and open stopes. The more openings in an ore access drift, the harder it is to control the flow of ventilation and hazards such as recirculated air or lengths of drift with no airflow may occur [13]. Additional ventilation challenges and design considerations are discussed in ventilation.

Equipment Selection

Equipment such as jumbo drills for development, scissor decks for bolting, LHDs for mucking and backfilling and production drills can be expected to work in these drifts. Trucks are not usually designed to operate in ore access drifts due to size and ventilation constraints. The size of planned ore access drifts is a limiting factor in scheduling equipment. A smaller access will reduce the allowable size of an LHD able to operate. A smaller LHD will only be able to extract tonnage at a certain rate and must be considered when scheduling tonnage. More detailed information about equipment sizing and equipment constraints can be found in equipment selection (is it an actual link? Has it been completed?).

Air and Water Services

Most equipment used in drift development and stope production require the use of compressed air and water. Main pipelines for compressed air and water are hung at the back of the drift in a system to service the whole mine. During development, access to these lines to operate equipment is required as the drifts advance. A system of pipelines and headers are established to provide access to the services as well as to mitigate the hazard of multiple hoses being laid out on the ground over long distances. As a rule of thumb, air and water headers are established every 50-100 feet from the pipelines to provide the miners access to attach their equipment. (WHAT IS THE AIR PRESSURE AND WATER PRESSURE PROVIDED?) Water sprays are also used in dust control to reduce health and safety hazards associated with breathing in dusts that are associated with the mine activity. For control of these substances, refer to the Regulation 822 of the Occupational Health and Safety Act [14]. During stope production, compressed air and water are required to operate the production drills and hole cleaning equipment. The use of water sprays is also practiced for dust control measures when mucking a stope. Power and Communication Services Electric power lines are run from the main substation on surface down to substations (ESS) on every level and provide a certain amount of power. Drift development scheduling must take power constraints in to consideration as a level’s ESS will only be able to support a certain number of electric powered equipment. Power connections are run from the ESS along the walls to the face of an active heading, similar to compressed air and water lines. Caution needs to be taken when hanging these power connections around wet conditions as the equipment draws a lot of current and poses an electrocution hazard.

Drift cross section view showing profile and service infrastructure, from MINE 448 course resources.

The Ministry of Labour in Canada as well as many other places require personal communication devices to be held by each person underground [cite some regulation]. The use of a leaky feeder system has provided the ability to use radios to communicate underground as well as up to surface. (MORE INFO FROM REFERENCE. HOW THEY ARE INSTALLED, NEW INNOVATIONS USING FIBRE ETC). [cite the emergency communication article on one drive] Installing Services Considerations When extending services as the development advances, appropriate sequencing must be used in order to provide the services to the heading when required but also to avoid damaging these services when blasting. As mentioned in Drift Development Constraints, the main drift on a level is typically developed first in order to access capital infrastructure required before production can begin. When cross cuts are planned to be driven off of the main drift, it is common practice to advance the cross cuts up to 12m before advancing the main drift past the cross cut. Services must be extending in to both but if the cross cut face is too close to the main drift, rock thrown from the cross cut blast will damage services if they are in the blast radius. 12m is far enough in to the cross cut that blast damage will be minimized but access to services from the main drift is still possible. The static properties of air flow will pull air from the main drift in to the cross cut to ventilate it without the use of a secondary ventilation system.

Cost Components of Drift Development

The cost components of drift development is fairly extensive, as a large variety of work must be completed in order for the drifts to be safe and usable. The cost to develop a drift is closely related to the size of the drift, the stability of the material, and the expected life and purpose of the excavation. Labour, equipment, consumables, and ground support are the principal components needed to develop a drift and are the main components.

Labour

Depending on the size of the drift planned for development the amount of labour needed will vary. For larger openings that require short drilling depths, it may be optimal to have fully mechanized single-boom drilling. Mechanized single boom drilling can allow for the drift development steps that follow to proceed quickly as there should not be any equipment-related delays for handling drill rod extensions. It should be noted that longer rounds can result in blasthole drilling inaccuracies, which can lead to increased drilling times, increased charging and blasting times, longer muck handling times (due to larger muck volumes), and larger roof spans to be supported. [5] The alternative to mechanized drilling would be to use an air-leg drill and have the blastholes manually drilled. This situation could arise if the planned drift is too small to effectively fit a mechanized drill jumbo. The dichotomy of mechanization and manual labour becomes once again apparent with regards to how any loose rock on the excavation wall is removed. Mechanized scaling provides the advantage of not exposing mine personnel to difficult and potentially dangerous working conditions. [5]

Equipment

The size of the excavation comes into effect with regards to equipment selection. Larger openings may allow for large pieces of equipment to be used in drift development however larger openings may also necessitate more equipment (i.e. work platforms). Other factors such as ventilation and available power must be considered and accounted for.

Consumables

Consumable materials that a mine will expend during drift development are numerous and precautions should be put in place to ensure adequate supply and mitigate delays. The cost of these consumables is very much subject to the conditions of the mine and the size of the excavation. A small list has been created which includes some of the areas where materials may be expended during mine development.

Mine drift development uses:

• blasting resources
  • bulk explosives (ANFO, emulsion)

• equipment (expendable parts)
  • drill bits
  • wear plate replacement

• construction materials
  • steel (split-sets, reinforcement, rebar)
  • concrete (pillars, support)

• ground support
  • mesh screen panels
  • shotcrete
  • rock bolts (split sets, plates)
  • resin

Ground Support

Ground support normally commences after the muck has been hauled away. The type of required ground support depends on the excavation size and the ground conditions. In poor conditions it may be necessary to perform multiple ground support activities (initial and final) instead of a single activity at the end of each round. If roof stability becomes critical, initial ground support (i.e. shotcrete, mesh) can be installed immediate after scaling to stabilize the excavation before mucking out completely. Final ground support (i.e. bolting, shotcrete) can be installed after the muck has been completely removed and the exaction fully exposed for the next round. [5] Example Based on GIVE MINE NAME in Timmins, Ontario, generally it can be assumed that a cost of $2,500 - $4,000/round (3m) is a realistic cost when planning drift development for a hard rock mine in northern Ontario. [6]

Typical Development Costs as per the Mining Engineering Handbook (SME, 2011).

Scheduling Components of Drift Development for Ore Access

In the early development phase of a mine, ore tonnage targets are developed based on the calculated production rate; monthly ore tonnage targets are spread across the operating days per month to ensure that adequate tonnage is able to be sent to the mill every day. Typically, underground mines have production rates between 2000-4000 tonnes per day [8]. Daily ore tonnage sent from the mine to the mill comes from both stope production as well as from development drifts in ore. The amount of ore tonnage from development is planned for each month based on the drift development scheduling. Ore Access Development Scheduling

Long term drift development scheduling is based on stope sequencing from the life of mine schedule. From the life of mine schedule, stopes that are scheduled to begin production in the upcoming months require development access on both the drilling and mucking horizons.

It is essential to schedule adequate time to create the stope design (not completed yet, should we try to link it anyways?), drill the stope and prepare the stope for blasting and mucking in order to begin stope production as scheduled. In short term planning, the work required to complete drift development for ore access is broken down in to a three month rolling plan and monitored. Three month rolling plans look at level plans to determine how much development is required to access a stope. From these plans, the length of a drift can be seen and, based on the updated drift surveys, the remainder of the drift to excavate can be calculated [Borysenko?].

Advancement Calculations

To determine how long it will take to complete a drift depends on how many rounds (drift cycles) are able to be taken each shift. Drift size depends on equipment requirements. For instance, a standard 5m x 5m drift that can accommodate a two-boom jumbo (Atlast Copco Boomer 282) [9]. The jumbo can drill a round of 3m - 3.5m in drift length. A drift cycle, including drilling, blasting, mucking, scaling and installing ground support typically takes one shift to complete. Assuming a day and night shift are both working in the same drift heading, up to 7m can be advanced in a 24-hr period. Based on this rate, or whichever rate of advance is planned for, the time it will take can be determined [10]. For example, a drift is planned to be 30m long and requires 30m of development. A drift round is 3m in length and a round can be taken each shift. Therefore, to complete 30m while advancing 3m a shaft, it will take 10 shifts to complete. If a day and night shift is working to develop this drift, it will take 5 days to complete. If only one shift is working to develop this drift it will take 10 days to complete.

Development Constraints

One of the main constraints when scheduling drift development is manpower and equipment resource allocation [11]. Based on the production rate, a certain number of stopes will be required to produce the necessary tonnage to meet monthly and daily targets. To meet these production targets, stope access must be completed on time. The headings that need to be advanced to provide stope access dictate the number of active heading required. Depending on how many crews and required equipment are able to be allocated to these ore access headings, the advance rate of a drift may be limited. Crews and equipment must also be scheduled for capital development headings. In most cases, capital development on a level such as refuge stations, electrical sub stations, ventilation pass and rock pass accesses need to be completed before production can begin. Therefore, when planning for a production rate and scheduling stope production, crew allocation and equipment selection must be able to meet scheduling needs. Otherwise, a smaller production rate should be considered. Ventilation requirements and constraints must also be considered when scheduling equipment and will be discussed further in Determining Service Requirements of Drifts.

Other Challenges

Drifting through Backfill Occasionally a mine plan may require development through fill to access ore. A consideration in this situation is the increased time resource needed for supporting these excavations.

https://www.minewiki.org/index.php/Sill_pillar_recovery_at_the_Louvicourt_mine

Breaking through into Other Excavations and Intersections Drift Intersections will require planning for additional ground support. At Xstrata Bruinswick Mine , mining engineers design their intersections to offset as frequently as possible, or in Ts to mitigate high stress concentrations [3]. More detail

Driving through pastefill at the louvicourt mine.

References

 Template:Refbegin
* reference 1
* reference 2
Template:Refend [1] A. Makuch, "Dynatec's Approach to Narrow Vein Longhole Stoping at Midas, Nevada," Dynatec, Midas, 2001.

[2] C. Jude, "Structural Analysis of a Mechanized LHD Trench Undercut Caving System," United States Department of the Interior, 1995.

[3] P. Andrieux and B. Simser, "Ground-Stability-Based Mine Design Guidelines at the Bruinswick Mine," in Underground Mining Methods- Engineering Fundamentals and International Case Studies, 2001, p. 206.

[4] "Shrinkage Stoping Practices at the Schwartzwalder Mine," in Underground Mining Methods, 2001, p. 197.

[5] J. Cline, "Construction of Underground Openings and Related Infrastructure," in Mining Engineeing Handbook, 3rd ed., P. Darling, Ed., Society for Mining, Metallurgy, and Exploration, Inc., 2011, pp. 1223-1237.

[6] A. Gauthier, Interviewee, [Interview]. 25 January 2015.

[7] R. Bullock, "Mechanical Excavation Methods of Development," in Mining Engineering Handbook, 2011, pp. 1203-1221.

[8] G. McIsaac, "Strategic Design of an Undergroud Mine under Conditions of Metal Price Uncertainty," Queen's University, Kingston, 2008.

[9] Atlas Copco, "Boomer 282: Face drilling rig - Atlas Copco Canada," April 2013. [Online]. Available: http://www.atlascopco.ca/Images/Technical%20specification%20Boomer%20282_9851%202500%2001_tcm795-1533190.pdf. [Accessed 2 February 2015].

[10] The Northern Miner, "The Mining cycle," The Northern Miner, vol. 90, no. 17, 2004.

[11] J. G. Hazan, "The Implications of Planning and Scheduling by CPM," in Annual General Meeting by CPM, Toronto, 1965.

[12] Ministry of Labour Ontario, "Occupational Health and Safety Act - R.R.O. 1990, Reg. 854," Government of Ontario, Toronto, 2015.

[13] C. Pritchard, "Methods to improve efficiency of mine ventilation systems," National Institute for Occupational Safety and Health (NIOSH), Spokane, 2010.

[14] Ministry of Labour - Ontario, "Occupation Health and Safety Act - R.R.O. 1990, Reg. 833," 28 January 2015. [Online]. Available: http://www.e-laws.gov.on.ca/html/regs/english/elaws_regs_900833_e.htm. [Accessed 2 February 2015].

[15] Society for Mining, Metallurgy, and Exploration, Inc, SME Mining Engineering Handbook, Library of Congress Cataloging-in-Pubilication Data, 2011.