16.3 Topographic Maps, Underground Set-Out & Survey Timeliness

Survey accuracy is useful only while it represents the ground and the approved design. An open-pit surface captured last month may omit a new highwall, ramp narrowing, sump, dump lift, or stockpile. A correct but stale model can cause unsafe drill collars, wrong burden, volume disputes, water-routing error, or collision between design and actual excavation.

Topographic Surface Content

A mine topographic model should distinguish surveyed ground, breaklines, inferred surfaces, water, crest and toe, ramp edges, structures, stockpiles, dumps, drainage, utilities, control stations, and excluded or unobserved zones. Breaklines preserve sharp changes such as bench crests; a triangulated irregular network without them may smooth a highwall into a false slope.

Contours connect equal elevation. Close spacing indicates steep ground; wide spacing indicates gentle ground. Contours usually do not cross, except special representations such as overhangs. The contour interval must suit scale and required decision.

Cut-and-Fill Volume

Compare two controlled surfaces within a common boundary and coordinate system. A simple grid estimate sums cell area times elevation difference; a triangulated method calculates prismatic differences. Report:

• survey dates and cut-off times;
• boundary and excluded zones;
• in-situ or loose basis;
• density and moisture if converting volume to tonnes;
• uncertainty; and
• reconciliation with truck counts or plant feed.

If a stockpile volume is 12,500 m3 and dry bulk density is 1.8 t/m3, estimated dry mass is 22,500 t. Applying an in-situ density to a loose stockpile would overstate mass.

Risk-Based Update Frequency

Frequency depends on rate of change and consequence:

The table is a principle, not a universal timetable. Site risk assessment and governing requirements set actual frequencies.

Design Set-Out Workflow

1. confirm approved design number and effective revision;
2. verify coordinate system, units, and control;
3. load only required points and lines;
4. occupy and orient with an independent backsight;
5. set out and label points with offsets where they may be destroyed;
6. take independent check observations;
7. compare with tolerance and resolve exceptions;
8. brief the operating crew and record acceptance; and
9. survey as-built work and reconcile deviation.

Never set out from an uncontrolled screenshot or emailed coordinate list whose datum and revision are unknown.

Underground Direction and Grade

A heading set-out provides centerline, grade line, profile, and offsets. Laser alignment is useful only after survey installation and verification; a struck or moved laser can propagate error. For a planned breakthrough, use independent traverses where possible, update remaining distance, probe ahead, review ground and water hazards, and establish a controlled final-blast sequence.

Drones, LiDAR and Scanning

Unmanned aerial vehicle photogrammetry can map inaccessible pit faces and dumps. Accuracy depends on camera calibration, overlap, flight geometry, ground control/check points, surface texture, vegetation, shadows, and transformation. Keep independent check points out of the adjustment and report their residuals.

Terrestrial or mobile laser scanning produces dense point clouds but can miss surfaces behind equipment or around corners. Filter vegetation and moving objects deliberately; do not let automated classification remove real crest detail. GNSS-derived elevations may be ellipsoidal while mine plans use orthometric elevation, requiring a geoid model and validation.

Timely Release and Archiving

Every surface or plan needs a timestamp, survey extent, accuracy statement, preparer, checker, revision, and authoritative repository. Mark preliminary data clearly. Notify users when a safety-critical surface changes, and withdraw superseded models. Raw observations and processing history allow reproduction after staff or software changes.

Exam Trap

The “latest” survey is not automatically the “best” if it lacks control or excludes the critical wall. The correct choice balances recency, coverage, verified accuracy, and fitness for the decision.

A survey release should also identify areas hidden by water, vegetation, dust, equipment, or scan shadow. Users can then avoid treating an interpolated gap as measured ground.

Independent Set-Out Check

Before release, calculate a set-out from an independently controlled point or method and compare position, elevation, orientation and design offset. Record design revision and extraction timestamp on the field sheet. After installation or excavation, perform an as-built survey and reconcile the deviation with tolerance; an accurate stake placed from an obsolete design is still wrong.