UNDERGROUND

1
UNDERGROUND

• WHAT IS DIFFERENT?
• IT IS DARK
• Difficulty in sighting targets. They are usually
  illuminated
• Using the instruments. Modern electronic
  equipment usually has a lit LCD display.
• POOR CONDITIONS
• Water. Standing water on the floor and falling
  water.
• High temperatures.
• Poor visibility
• Mine machinery.
• ROCK MOVEMENT
• Makes survey stations unstable
• Health hazard to surveyors

2
UNDERGROUND

• WHAT IS DIFFERENT?
• MINES ARE 3-DIMENSIONAL
• The transfer of bearings, levels and co-ordinates
  from surface to underground can be difficult.
• The sightings are often very steep or vertical!
• Problem of converging vertical lines!
• TRAVERSE IS THE ONLY CONTROL
• Traversing is the only means of carrying a
  control survey throughout underground workings,
  i.e. you cant use triangulation, trilateration,
  resections or GPS etc.
• SURVEY STATIONS
• These are usually positioned on the roof or back
  of the working to avoid problems with bad floor
  conditions.

3
UNDERGROUND

• SETTING UP UNDER A ROOF STATION
• TRIPOD
• Use plumb bob suspended from station to get
  tripod under station.
• Check height to get line of sight to next
  station.
• Make sure tripod is firm and protected from
  running water.
• THEODOLITE
• Level as normal.
• Set the telescope to horizontal so that the
  VERTICAL CIRCLE reads 90 or 270 degrees, and
  centre instrument under bob using dot on
  telescope.
• Check level and centre.

4
UNDERGROUND

• MEASURING
• Use the standard procedure, but
• ILLUMINATION
• x-hairs - light at an angle in front of scope.
• Plumb bob string.
• Lamp to illuminate circles.
• Illuminated target.
• INSTRUMENT HEIGHT
• This is the distance from centre of trunnion axis
  to base of roof station
• OBSERVERS
• In restricted roadways, you may need one either
  side.

5
UNDERGROUND

• LEVELING
• The procedure is the same as normal BUT the staff
  is inverted and the levelling point is the base
  of the roof station.
• DISTANCES
• As with surface measurement, EDM should be used
  for simplicity and accuracy, but steel tapes can
  be used.
• Remember to adjust for Mean Sea Level.

6
UNDERGROUND

• CORRELATION WITH SURFACE
• For all mines it is necessary to tie in the
  underground plans with surface plans. This is
  vital for features which rise to the surface
  (e.g. access points, ventilation shafts,
  prospecting boreholes) but also important for
  records and planning mine development.
• We need to transfer bearings, co-ordinates and
  levels.
• There are three different situations
• ADITS, LEVELS AND INCLINES lt30deg
• INCLINES gt 30deg INCLINED SHAFTS
• VERTICAL SHAFTS

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UNDERGROUND

• ADITS, LEVELS AND INCLINES lt30deg
• Standard precision traversing should be possible,
  starting and finishing on a surface station,
  using surface R.O. The traversing technique
  using EDM should also give the correct levels,
  but a levelling survey could also be carried out
  reasonably easily.
• INCLINES gt30deg INCLINED SHAFTS
• Normal traversing from surface becomes more
  problematic, with difficulties in setting up and
  sighting. Levelling becomes very difficult
  because of the the short distances required.

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UNDERGROUND

• VERTICAL SHAFTS
• BEARINGS COORDINATES
• i) OPTICAL OR LASER METHOD
• There can be a major problem with refraction of
  light/laser.

Known Co-ordinated points
Line of Sight/Laser
Targets are moved to coincide with beams/sight
9
UNDERGROUND

• ii) WIRES
• Weighted piano wire suspended down shaft.
• Fluid damped with oil/water to prevent swaying.
• But there are problems with air currents from
  vent fans.

Surface Control
Piano Wire
Wires weighted and damped in oil/water filled
buckets.
Underground Control
10
UNDERGROUND

• ii) WIRES
• OBSERVATION TECHNIQUES

Co-Plane. Line up the two wires so that the
bearing at the base is the same as the top.
Weis-Bach. Set the theodolite slightly off line
so that two angles are measured, less than 1 deg
apart.
Weis-Quad. Braced Quad method where the
theodolite is set up in two locations and a
series of angles measured.
11
UNDERGROUND

• iii) MAGNETIC METHOD
• Another method of fixing the bearings underground
  is to determine magnetic orientation. This is
  not very accurate and magnetic deviation (angle
  of magnetic north from grid north) varies with
  time, so it can be difficult to relate back to
  the grid system. Accuracy of only /- 1 at best.

12
UNDERGROUND

• iv) GYROSCOPE METHODS
• The theory behind using a gyroscope is that it
  will naturally attempt to align itself with TRUE
  North. Because no Gyroscope is perfect it will
  actually find Gyro North, but this is usually
  relateable to Grid North.
• The instrument is a spinner which rotates at more
  than 20,000 rev/min. in the horizontal plane. It
  works by the fact that the spinner will try to
  maintain its initial spatial position, but the
  rotation of the earth will pull the spinner out
  of this plane into the meridian. The Gyro will
  oscillate for some time before aligning on the
  meridian and so accurate readings will mean
  waiting for a while.
• One of the early Gyro Compasses was the Wild GAK
  which gave accuracy of 20 after 20 minutes.
  Now, instruments can give 2 or 3 after 1 or 2
  minutes.

13
UNDERGROUND

• VERTICAL SHAFTS
• LEVEL
• i) Steel Tapes. Tapes can be 300m long. Not
  often used.
• ii) Trigonometric Levelling using EDM.
• iii) Wire Method.

Surface Control
Marks on Wire
Piano Wire
Underground Control