Underground drill and blast

How an underground mine is drilled, the rock it is drilled in, and the development rounds worked out from both — from the design to each shift's firing.

Mining → Underground

Worked out, never assumed

Every underground design is worked out from three things the mine records: how it drills, what it drills with, and the rock it drills in. No mine's habits are built in. Two mines with different ground get different rounds from the same page, and a figure a design needs but the mine has not given is asked for rather than guessed.

You can always type your own

Anything the design works out — the hole depth, the number of relief holes, the look-out — can be typed over. What you type is filed beside the figure the design worked out, so the round shows both, and anyone reading it later can see where the mine chose differently.

How the mine is drilled

Open Underground and choose the mine.

How it is drilled asks two questions, and nothing is designed until each is answered — there is no default:

Question	Choices	What it decides
Development	Mechanised (jumbo) or Conventional (handheld)	Whether rounds are designed for a jumbo's steel and bit or for a handheld drill's
Stoping	Mechanised (long-hole / bord) or Conventional (handheld face)	Whether a stope is designed as long-hole rings or as a handheld face

Press Save methods.

Drilling machines

Drilling machines lists the machines the answers above call for, with the figures a design reads: bit and reamer diameter, steel length, angular deviation and collaring error. Leave a figure blank and the typical machine's figure is used — it shows faintly in the field, and a design marks it typical. Type the mine's own where it differs, then Save machines.

Rock domains

A rock domain is a kind of ground in the mine — a granite footwall, a sheared ore zone. Every burden, spacing and charge is worked out from the domain a design sits in.

Press Add rock domain, give it a name, and record the figures you have. Each figure says where it came from:

Source	Meaning
Measured	Tested on the mine's own core or ground
Block model	Read from the block model
Typical	A published value for this kind of rock, not yet checked here
Calibrated	Adjusted to what the mine's own blasts actually did
Stated	Given by someone on the mine, without a test behind it. A figure is Stated until you pick another source.

A development round needs the domain's rock constant (c, kg/m³) and density. A domain without them can be saved, and the round says which figure it is missing when you choose it.

Calibrate the rock constant

0.4 kg/m³ is the value most published rounds start from. Log a few firings, compare the pull and overbreak with the design, and record the constant that fits as Calibrated.

From your own blasts

Open a domain that already exists and the dialog reads the blasts fired in that rock and shows, under From your own blasts, what they say its constants are: the rock constant from the craters that were surveyed, the confined bulking from how far the ground rose around one, and the swell from the muckpile surveys. Each line carries the range the blasts gave, how far they wander either side of the figure, how many blasts it was fitted from, and what the figure was before.

Accept into this draft fills that figure in for you and marks it Calibrated. Nothing is saved until you press Save, and nothing is ever applied behind your back — the panel proposes, you decide.

Under five surveyed blasts in one domain, the figures are still shown, so you can watch a fit settle as the shots accumulate, but they cannot be accepted: one crater is one shot in one piece of ground. Blasts the fit could not use are named with the reason — no rock domain on the blast, nothing surveyed, no prediction to measure a survey against, the surveyed hole missing from the design, a crater that reads back to no reach, or a figure outside anything rock does. Where the mine has more reconciled blasts than one read returns, the panel says how many of how many it read.

How fast rock leaves the face is shown where the muck surveys fit it, but it is never offered as a rock figure: it is a muckpile constant, not a property of the rock, so the domain does not hold it.

Removing a domain asks first. Rounds already filed keep the domain's name and figures as they were designed.

Designing a development round

On Underground, press Design a development round. It stays disabled until the mine's development method is stated.

1. Choose the Mine and give the round a Round name.
2. Choose the Heading — a development design from Mine designs. Its profile is the round's width, height and arch.
3. Type the Chainage: how far along the heading the face stands.
4. Choose the Rock domain the face is in and the Explosive the holes are charged with.

The round is worked out as you choose, and drawn on the face.

The method

The round is Holmberg's four-section burn cut, as set out in López Jimeno et al., Drilling and Blasting of Rocks (1995), and checked against its worked example:

• Depth comes from the empty relief holes: a burn cut pulls only as deep as its relief lets the broken rock swell into. The round is drilled to the shorter of that and the steel, with the fewest relief holes that reach it.
• Drilling error — the machine's deviation over the depth plus its collaring error — is taken off every burden, so a hole that wanders still breaks its toe.
• The cut is four square sections round the relief holes, each breaking into the opening the last one left.
• Easers, walls and lifters take the burden the rock constant and the charge allow, with the lifters' heavier fixation.
• The back is smooth-blasted: holes closer together and lightly charged, so the arch is left sound. Switch on Smooth-blast the walls too to treat the walls the same way.

Figures you can change

Open the overrides to type your own Hole depth, Relief holes, Look-out (how far the perimeter holes angle out so the next round has room to collar), and Charges stocked — the charge per metre of each cartridge size the magazine holds. Leave any blank to have it worked out.

The figures table shows every figure with its source: derived, overridden, or as the rock domain or machine records it.

Saving and approval

Press Save the round, then Send for approval. A mine with no sign-off chain for blasts approves it at once; otherwise it goes through the same chain as the surface blasts.

An approved round that is changed goes back for approval. Say Why it changed, and the change is kept in the round's log.

While it waits, the approvers of the stage it waits on see Approve and Send back on the round. Approve asks first and signs that stage; the last stage approves the round. Send back asks for a reason and returns it to a design, with the reason shown on it. Whoever asked, or the account holder, can Withdraw the request: it returns to a draft you can change, and the approvals so far are dropped. The same buttons sit on a set of rings.

Designing and sending for approval need access level 4. In the Mining workspace, Design a round on the Blast tab, or Design a round here on a heading in the picture, docks the round designer beside the picture: see The workspace.

Each shift's firing

A round is fired shift after shift as the heading advances. Press Log a firing on an approved round and record:

• the day and shift, and the shotfirer;
• the pull — how far the face actually advanced;
• the holes actually drilled, and any misfires;
• optionally, the heading's measured width and height after the shot, which shows the overbreak.

The explosives are the design's, scaled by the holes actually drilled. With Take … kg off the magazine on, each product's kilograms are filed on its magazine item, just as a surface blast's are. The firing log's Magazine column says how each firing's filing went — Filed, Partly filed, Not filed, Nothing to file, Filing cut short, Filing unconfirmed or Not recorded — and what was not filed is listed in amber under the log, with the kilograms to add to the magazine by hand. Not recorded marks a firing with no record of its filing; it is not a failure. See The magazine for what each means.

When the heading moves on to a new round, press Retire. No more firings are logged against it, and its log is kept. A round that has been fired cannot be removed — retire it instead.

In the Blasts register

Blasts lists underground blasts beside the benches, with a Kind column: Bench, Development round, Stope rings or Stope face. Opening a development round takes you to its designer.

Designing a stope's rings

A stope's rings are drafted from a mine plan, where the stope is laid out. Compute a saved plan of stopes and headings. In Planned to fire in the selected period on the Drill and blast card, press Design rings beside a stope with none yet. A stope that already has rings still to fire drafted from the plan — designed, awaiting approval, approved, drilled or charged, even rings that drill and charge nothing yet — has Open the rings instead: a stope has one set of rings still to fire per plan at a time, and a second is refused until the first is fired or retired. Two drafts sent at the same moment are refused the same way. The ring designer opens on that stope as the plan laid it out, named after it and planned for the start of the period. Rings are drafted from the plan's first mine only.

1. Give the rings a Name, and choose the Rock domain the stope is in and the Explosive the holes are charged with.
2. Say whether the rings are Drilled up from a drive on the stope's floor or down from a drive on its back. The page starts at up, and says so beside the choice. The drive is a development design filed for the mine, when one is at the level the holes are drilled from, within 3 m of it (the stope's floor for up-holes, its back for down-holes), and has at least half its length inside the stope. Where several are, the one with most length inside is taken, cut where it crosses the stope's walls; where it leaves the stope and comes back, its longest run inside is kept. The rings are spread evenly over that length. Where it covers less than 90% of the stope's length along it, the rings say how many metres of the stope it covers, and that the rest has no rings. Where none is, the stope's long axis is assumed, and the rings say their drive was assumed.
3. Type the mine's own Holmberg–Persson K and α, fitted from its near-field monitoring. Trackapt does not assume another mine's figures, and designs no rings without them.
4. Check the Drive width, Drive height and Collar height, and the Fixation factor. It starts at 1, the figure López Jimeno et al. work Langefors' burden at for long holes, and the page says so beside the field. The direction and the fixation factor are filed with the rings and exported under Choices stated.

The rings are laid out once you stop typing. A figure no ring is drilled at is refused in words until it is put right: a burden outside 0.5–10 m, a toe spacing outside 0.5–15 m, a drive outside 1.5–20 m, a collar height outside 0–5 m, or a fixation factor outside 0.5–1.5. The stope's stoping method must be stated first. Where the mine cannot be read for want of the network or the server, the page says so and offers Read again.

The method

• Burden and toe spacing follow López Jimeno et al., Drilling and Blasting of Rocks (1995, ch. 24): Langefors' burden at a toe spacing of 1.25 burdens, less the drilling deviation. Myers et al. (1990) is shown beside it as a cross-check. The published toe spacing rules disagree, and a toe spacing outside them is warned of.
• Uncharged collars follow Onederra & Chitombo (2007). Each hole takes the longer of the caption's collar sequence and the collar its damage zone needs, from the near-field vibration at the mine's K and α. The Collar set by column says which. A caption collar is shortened, with a warning, to keep ten charge diameters charged, and never less than 0.5 m, the shortest column loaded. At a bit of 50 mm or less, the 0.5 m decides it. A hole too short for its damage collar and that least charge is not loaded.
• Metres in rock. Each hole is collared where it leaves the drive, not at the rig. Its length, the drilled metres, and its uncharged collar are measured from there, and the sheet and its export say in rock. A hole lying wholly in the drive is not drilled, and a hole shorter in rock than the least charge is neither drilled nor counted.

Type your own Burden or Toe spacing to redesign around them; the worked-out figure is kept beside it.

Saving and firing

Press Save the rings, then Send for approval, Mark drilled and Mark charged as the stope is prepared. Fire opens the firing dialog: the day the rings went, the shotfirer, any misfires, a note, and whether the explosive comes off the magazine. A ring blast is fired once, and the dialog says it cannot be undone. Fire does nothing more while the dialog is open or the firing is being sent, and a firing that still reaches the server twice is recorded and filed once. A firing dated later than now is refused. Where Fire is refused because the rings changed or were fired elsewhere, the page reads them again and shows them as filed.

Retire stops the rings being drilled, charged or fired from here on, and keeps their record. Rings are retired while designed, approved or drilled. Charged rings are not retired: there is explosive in the holes, which is fired, or made safe under the mine's misfire and recovery procedure. Fired rings are the record of their firing. The page offers Retire only where it is taken. Fired and retired rings no longer stand for their stope, so new rings may be drafted for it: a stope is often fired a few rings at a time, and the next rings are drafted once the last set has gone.

An approved set of rings whose holes, charges or design figures change — including a save of rings redesigned from today's figures — goes back to Designed and must be sent for approval again. Rings already drilled or charged keep their status, and the change is logged.

Save any changes before Send for approval or Mark drilled: both act on the rings as filed, so they wait while the page shows changes not yet saved.

Reopening rings

Rings that are designed or approved are still open to change. Reopened, they are designed again from today's rock domain, rig, explosive and drives, with the choices and typed figures they were filed with. Where that gives other rings, holes, metres or kilograms than those filed, the page says so and counts it as a change not yet saved: save to file the new design, or leave without saving to keep the rings as filed.

Rings that are drilled, charged, fired or retired are shown and exported as filed: their rings, holes, charges, figures and warnings, exactly as the charge-up crew and the magazine work from them. They are not designed again, even where the rock domain has been recalibrated or removed since.

Only the figures you type are filed as typed. A figure that moved because you typed another — the toe spacing under a typed burden — is filed as worked out, so it follows the design when the rings are reopened.

In the mine plan

A mine plan of stopes and headings charges each heading at its own round: the drilled metres and kilograms per tonne of the round approved last (or, with none approved, the round filed last), scaled to the plan's rock density where it differs. A heading with no round, or with a round that drills and charges nothing, keeps the processes' typed rates, and the plan names it. See Each heading drilled and loaded as its round is. A saved plan charges each stope at the rings drafted from it for that stope, and lists what each period fires. See Each stope charged at its rings.

Not designed here

Handheld stope faces are recorded in the register but are not designed from the rock on this page.