ground mechanics

• ground/rock support techniques
• pillar dimensioning

procedures, techniques, materials used to improve the stability and maintain the load bearing capability of rock in the EDZs

Applications: (in civil engineering projects)

• drifts
• shafts
• tunnels

• rock reinforcement (anchors)
• steel sets (meshes, arches)
• concrete (shotcrete, pre-cast)

• rock pressure and additional rock stress influence pillar and ground support design
• accurate drilling and good blasting process (minimize overbreak ad blast damage)

! keep strength in pillars, therefore preventing pillar failures !

• room size
• anchor length/size
• pillar dimension
• roof span

--> based on rock conditions

to ensure safety: cable bolts/rock bolts used

• mechanical anchored rock bolts
• grouted rock bolts

• active
• low material consumption
• mechanizable
• flexibility
• adaptability

• preload
• length
• mechanism
• material
• shape

• welded wire mesh
• chain link mesh

• relatively inexpensiv
• quick installation
• can support small blocks
• energy absorption properties
• can be used in combination with shotcrete

• quality control issues
• proper overlap can be difficult to obtain
• shear failure at the weld point
• heat-affected zone failure
• tensile failure

• energy absorption capacity
• low rigidity --> deformation capacity

• tends to unravel when damaged
• is difficult to aplly shotcrete through it
• has very low rigidity
• installation is labor-intensive, difficult to mechanize

• installed to provide exra strength
• steel straps
• mesh straps
• osro straps

1. sprayed
2. poured
3. segmental

• application of one or more shotcrete layers
• can be applied right up to the advancing face

• pumping concrete behind moveable forms
• considered to be a secondary support system
• common in modern shaft sinking operations

• installed mechanically behind advancing TBMs
• form permanent liner for the excavation
• rarely used in mine drifts

• applied to the rock surface by pneumatic shooting at high velocity
• preferred surface support method in underground mining
• often method of choice when the rock mass is heavily fractured

40-50% fine aggregates

30-40% coarse aggregates

15-20% cement

2-5% additives

water is added to hydrate the cement

dry-mix: water added at th enozzle

wet-mix: shotcrete mix prepared at custom-build concrete plant

• choice of mixing methods
• felxibility concering equipment
• availability of shotcrete

• rapid application minimizes time-dependent rock mass deterioration
• after shotcreting reinforcement installation possible
• good load transfer between surface support and reinforcement

• rock mass is covered immediately
• small opportunity for geological and geotechnical data to be collected

• maximum flexibility in delivery in terms of time
• flexibility in terms of transportation
• instantaneous control over mixing water and consistency of the mix at the nozzle to meet variable field conditions
• high suitability for placing mixtures conatining lightweight aggregates or refactory materials

• large percentage of rebound
• dusty environment created
• low application productivity
• low volume per hose size

• generally minimal quality issues
• high delivery rates
• low percentage of rebound
• minor dust generation
• easy mechanization
• high volume per hose size
• low rebound -> low waste

• transport and delivery logistics are difficult in deep mines, having only shaft access
• expensive equipment
• not suitable for small-volume applications

• a column of coal or ore left to support the overlying strata or hanging wall in a mine
• left permanently to support the surface
• much larger horizontally than rooms

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1. nut
2. domed faceplate
3. steel bar
4. expansion shell

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split set anchor

1. anchor head
2. domed faceplate
3. slotted pipe

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