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MONITERING AND SAFETY ASPECTS IN UNDERGROUND STRUCTURES

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NECESSITY OF GEOTECHNICALINSTRUMENTATION

FINDING OUT THE ENGINEERING PROPERTIES OF THE

SOIL.

MODIFYING THE ENGINEERING PROPERTIES OF THE SOIL

TO THE DESIRED LEVEL.

DESIGN OF THE STRUCTURE BASED ON THE PROPERTIES.

MONITORING THE GEOTECHNICAL CONDITIONS OR

BEHAVIOR OF THE STRUCTURE DURING THE

CONSTRUCTION PROCESS.

CHANGES IN THE DESIGN BASED ON THE BEHAVIOR.2

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IMPORTANCE OF MONITERING INSTRUMENTS

TO OBSERVE THE BEHAVIOR OF THE STRUCTURE

MONITORING INSTRUMENTS ARE REQUIRED .

INSTRUMENTATION IS A TOOL TO ASSIST WITH THESE

OBSERVATIONS. THEY ARE OUR EYES AND EARS INSIDE

THE ROCK.

INSTRUMENTATION IS USED TO MEASURE THE RESPONSE

(DEFORMATION, STRESS ETC.) OF SOIL OR ROCK TO

CHANGES IN LOADING OR SUPPORT ARRANGEMENTS,

AND FROM THE MEASUREMENTS TAKEN, THE NEED FOR

MODIFICATIONS TO THE LOADING OR SUPPORT

ARRANGEMENTS IS DETERMINED.3

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PURPOSE OF GOOD INSTRUMENTATION

SITE INVESTIGATION.

DESIGN VERIFICATION

CONSTRUCTION CONTROL

SAFETY

LEGAL PROTECTION

PERFORMANCE

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SITE INVESTIGATION.

Instruments are used to characterize and determine initial site

conditions.

Common parameters of interest in a site investigation are pore

pressure, permeability of soil, slope stability etc.

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DESIGN VERIFICATION

Instruments are used to verify design assumptions.

Instrumentation data from the initial stage of a project may show the

need or provide the opportunity to modify the design in later stages.

For example, data obtained from NATM shotcrete cells in the initial

stretch of tunnel is used to revise the thickness of shotcrete in the

later stages.

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CONSTRUCTION CONTROL

Instruments are installed to monitor the effects of construction.

Instrument data helps the engineer to determine how fast

construction can proceed without adverse effects on the foundation

soil and construction materials used.

For example, in tunnel construction, the data obtained from the load

cells helps the geotechnical engineer to know if the stresses in the

excavated tunnel have been stabilized and how fast he can proceed

with further excavation.

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SAFETY

Instruments can provide early warning of impending failure.

In case of metro railway tunnels instruments provide early

warning through real time monitoring systems available on the

internet for any excessive and undue ground movements

affecting the adjoining premises, structure and utilities like the

railways, power lines, water lines etc.

within the zone of influence of the excavations or tunnels. This

allows for implementation of preventive remedial actions well

within time.8

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LEGAL PROTECTION

Instruments provide designers and contractors the basis of a

legal defence should resident and owners of adjacent properties

blame construction for damage to their property and life.

This aspect gains prominence in constructions in populated

areas such as for underground metro railways

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PERFORMANCE

Instruments are used to monitor the in-service performance of

a structure.

For example, monitoring leakage, pore water pressure and

deformation can provide an indication of the perform bolts and

movements within a tunnel can provide an indication of the

stability of tunnel.

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ROOF TO FLOOR CONVERGENCE MEASUREMENT

Used to measure deformation in tunnels by measuring contraction ( or elongation )Procedure : Measurements are taken by simply stretching the telescopic rodbetween the reference points, and reading the graduations on the rod. Theseindicators are useful for understanding the roof to floor closure in the advancegalleries at various stages of extraction.

TELESCOPICCONVERGENCE ROD

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Chart Type Convergence Recorder

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REMOTE CONVERGENCEINDICATOR

• For monitoring convergence in roof

• Sensor – Vibrating wire type or Potentiometric type

• Needs laying of wire from instrument location to measurement site

• Fails immediately with the failure of immediate roof

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STRATA MONITORING BY TELL TALES

• Tell tale is strata – extensometer. • It provides pre-emptive warning of roof-falling. • The dual-height tell tale provides an immediate visible

warning, distinguishing between movement above and below rock-bolted height.

TYPES• Single height tell tale• Dual height tell tale• Three point tell tale• Four point tell tale• Rotary tell tale

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SINGLE HEIGHT TELL TALE

• It comprises a strata movement indicator usually with color bands and/or graduations.

• a mechanical tell tale consists of a strata movement indicator positioned in the mouth of a drilled hole and attached to an anchor installed up the hole

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Dual height tell tale

• Dual Height tell tale is designed to be installed for monitoring the bolted strata. • They have two versions –

one for dry drill holes and the other for watery drill holes. • This is designed to be

installed following the installation of roof bolt reinforcement. 17

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SAFETY MONITORING

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ACTION LEVELS• GREEN 0 - 25 mm• YELLOW 25 - 50 mm• RED 50 mm +ACTIONS• GREEN No action required, continue routine monitoring• YELLOW Identify height of softening [HOS]. If HOS is above bolts, install longer reinforcement. If below top of bolts, install additional standard length reinforcement to increase density of support.• RED Restrict access. Investigate. Install longer reinforcement 19

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Rotary Tell tale Extensometer

• It is useful where the conventional method of Roof support system is not convenient or possible.

• Movement of the strata is indicated with a magnification of 1:15.• It gives visual indication to a workman regarding the status of

Roof stability.• Rapid and simple to install.• Rotary type are useful for variable depth.

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MAGNET EXTENSOMETER

• The Magnet Extensometer consists of a series of magnets that are installed with an access pipe.

• The magnets are anchored at specified depths.

• Measurements are taken by lowering a probe through the access pipe to detect the depth of the magnets.

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VIBRATING WIRE LOAD CELLS• The load cell is a transducer working

on vibrating-wire principle.• It has three stretched wires housed in

a metal cylinder, which are plucked by an electric pulse of high energy.

• Changes in the load exerted on the cell cause changes in the length of the wire, resulting in variations of frequency of vibration of the wire.

• As the load increases the frequency decreases accordingly and vice-versa.

• This frequency is measured by a digital read-out unit, and is converted into load using calibration charts. Efficacy and adequacy of the support system can be inferred on the basis of these load cells. 22

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ROCKBOLT LOAD CELL

• The load cell is a transducer working on vibrating-wire principle.

• The load cells should be installed under the roof bolts using specially prepared steel seating arrangement .

• The load cells should be installed at the junctions to understand the change in load over the roof bolt during the operation.

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Mechanical Load Cell

• Load cell consists of an elastic disc element sandwiched between two plates.

• The disc deflects under load and changes distance between plates.

• The deflection is measured with a dial gauge or suitable electronic transduced.

• It has limited application due to nonlinear calibration curve and restricted application.

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STRESS CELL

• Principle : These are used for measuring unidirectional stress change in the pillar. It consists essentially of a wire tensioned across a steel cylinder (38 mm diameter). As the stress within the rock/coal changes, the cylinder deforms, causing tension in the wire to change.

• Procedure : A bore hole of 38 mm diameter is required for installing the stress meters, preferably at mid height of the pillar either horizontally or slightly rising/dipping according to dip of the seam. The stress meter along with wedge and platen assembly is set in the borehole with the help of special installation tools, at a depth of about 4 to 9 m. 25

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Scope and application

The rule applies to construction of underground tunnels, shafts,chambers, and passageways. It also applies to cut-and-coverexcavations, both those physically connected to tunnels and those thatcreate conditions characteristic of underground construction. Hazardscommon to such work include reduced natural ventilation and light,difficult or limited access and egress, exposure to air contaminants,fire, and explosion

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Provisions of the standard• The standard gives employers the flexibility to select from a variety

of appropriate and effective methods of controlling workplace hazards

• In underground construction. It includes a safety program focusing on instructing workers in topics appropriate to specific jobsites

• And it gives specific duties and responsibilities to a “competent person.”

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Competent person

• A “competent person” is one capable of identifying existing and predictable workplace hazards who is authorized to take corrective

• action to eliminate them• Duties of competent person

• Monitoring air • Inspecting the work area for ground stability • Inspecting all drilling equipment prior to each use • Inspecting hauling equipment before each shift and visually checking all hoisting machinery, equipment, anchorages, and rope at the beginning of each shift and during hoisting

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Safety instruction• Employers must ensure that workers are instructed on

the recognition• and avoidance of hazards associated with underground

construction.• Instruction must include the following topics that are

appropriate to• each jobsite:

• Air monitoring • Ventilation and illumination • Communications • Flood control • Mechanical and personal protective equipment • Explosives: fire prevention and protection • Emergency procedures: evacuation plans and check-in/check- out procedures

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Access and egress

• Employers must provide safe access to and egress from all

workstations and prevent unauthorized underground entry. Completed

• Unused sections of an underground work area must be barricaded.

• Unused openings must be covered, fenced off, or posted with warning

• signs indicating “Keep Out” or other appropriate language

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Check-in/check-out• Employers must maintain a check-in/check-out procedure that

ensures above-ground personnel can maintain an accurate

count of people who are underground, in case of an emergency.

At least one

• Designated person must be on duty at the surface whenever

anyone is working underground. That person is responsible for

securing

• Immediate aid in case of an emergency

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Gassy operations• • Using more-stringent ventilation requirements

• • Using only diesel equipment approved for use in gassy operations

• • Posting each entrance with warning signs and prohibiting

smoking and personal sources of ignition

• • Maintaining a fire watch when hot work is performed

• • Suspending all operations in the affected area until all special

requirements are met or the operation is declassified

• Additional air monitoring is also required during gassy conditions

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SPECIAL AIR MONITORING REQUIREMENTS

• The employer must assign a "competent person" to perform air

monitoring. If this individual determines that air contaminants may

present a danger to life at any time, the employer must

immediately take all necessary precautions and post a notice at all

entrances to the underground site about the hazardous condition

and his responsible for checking air quality

test for oxygen first

testing for methane and other flammable gases

hydrogen sulfide levels34

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Illumination• As in all construction operations, the rule requires that proper

illumination be provided during tunneling operations, as

specified

• When explosives are being handled, acceptable portable

lighting equipment must be used within 50 feet of any

underground heading

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Fire prevention and control

• open flames and fires are prohibited in all underground

construction activities, except for hot-work operations.

• Smoking is allowed only in areas free of fire and explosion hazards.

• Employers must post signs prohibiting smoking and open flames

where such hazards exist

• Gases such as acetylene, liquefied petroleum, and methyl acetylene

propadiene (stabilized), may be used underground only for hot-

work operations.

• Leaks and spills of flammable or combustible fluids must be

cleaned up immediately.36

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Safety provisions• —IS: 4756:- 1978 – Safety Code for Tunnelling work• —IS: 3764 –1966 – Safety Code for Excavation work• —IS: 4081-1986 – Safety Code for Blasting and Related drilling

operations• —IS: 4138-1977 – Safety Code for Working on Compressed Air• —IS: 7293-1974 – Safety Code for Working with Construction

Machinery• —IS: 5878 (Various parts) – Codes of practices relating to

tunnelling and underground excavations• —Indian Explosive Act -1988• —Indian Explosive Rules -1983

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Lighting:

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• Minimum 50 lux at headings during drilling, mucking 70 m.and scaling.

• Minimum 30 lux for trolley track working area.• Minimum 10 lux for other areas inside the tunnel or on

approach cut/roads.• Emergency lights (battery operated) at the working faces and

at regular interval along the tunnel.• Proper earthling and grounding of all electrical apparatus.

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Medical facilities:• First Aid box with experienced first aid attendant with his

distinguishing badge on each shift.• Stretchers in every shift at portal.

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Protective wear:• Helmet, steel tow safety shop, gum boots for each worker. • Sign boards 1x1.5m in size to be displayed at the approach

“Construction AREA, HELMET required beyond this point”

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Notices and signs:

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Telephone System:

• For communication between control locations inside tunnel and portal (when more than 500m)

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Ventilation• Essential to make working space safe for workers by keeping

the air fresh and repairable and by eliminating harmful and obnoxious dust, dynamite fumes and other gases. Mechanical ventilation must be used for long tunnels.

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• It is essential to ensure • Temp < 40 C dry and < 29 C wet at the working place.• Concentration of gases in side the tunnel by volume a) Oxygen not less than 19.5% b) Carbon monoxide not more than 0.005% c) Carbon Dioxide not more than 0.5% d) Hydrogen Sulphide not more than 0.001%

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Sanitation and Drinking Water

• Sanitation - Unless the worksite is within 500 m of the portal of the tunnel, sanitation facilities shall be provided close by.• Drinking Water- Drinking water, at least 5 litre per person employed in the shift, shall he provided near the portal and

also inside the longer tunnels.• Washing and cleaning facilities shall be provided for all

workers near the portal.

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Risk register

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Emergency Planning & Mitigation of Risk

• to ensure safety of tunnel workers and other stakeholders• A culture of safety can be enhanced by in-house training,

communication through toolbox meetings and display of procedures and escape plans on notice boards.

• table top exercise and regular drills shall be conducted once in every six months.

• Accountability for safety performance must be appropriately allocated through the entire safety management process, in particular to the emergency plan

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Safety measures for blasting• Based on IS :4081- 1986.• No metals except approved metal truck bodies shall be

allowed to come in contact with cases of explosives. • Blasting caps, electric blasting caps or primers shall not be

stored in the same box, container or room with other explosives.

• Smoking shall be prohibited in the storage area of explosives and in its vicinity.

• Packages containing explosives shall not be allowed to remain in the sun.

• Explosives shall not be carried in the pockets or folds of clothing by any person. 51

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• All electrical wiring and equipment of storage area shall be adequately insulated and protected against mechanical damage to prevent short-circuiting.

• Children and unauthorized or unnecessary persons shall not be present where explosives are being handled or used.

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Safety measures for drilling• No drilling shall be started until previous holes in the blasted

area are flushed with air and water. • While planning drilling operations for blasting purposes,

consideration must be given to the nature of stratum and the overburden with a view to avoiding the possibilities of land-slides after blasting.

• The position of all holes to be drilled shall be marked out with white paint.

• The face of rock shall be carefully examined before drilling, to determine the possible presence of unfired explosive.

• The diameter of the bore of each hole shall be greater than the outside diameter of the cartridges of explosive. 53

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• explosives shall not be forced down a bore hole or on obstruction in a bore hole.

• A bore hole near another hole loaded with explosives shall not be sprung.

• No holes shall be loaded except those to be fired on the next round of blasting and after blasting.

• Drilling shall not be resumed after blasts have been fired until a thorough examination has been made.

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