Civil Engineering Chapter 10: Underground Mining Methods

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Questions and Answers

What is the primary consideration when determining room sizes and pillar dimensions in room and pillar mining?

Rock conditions and predicted rock stress changes

What is the characteristic of ore bodies suitable for sublevel open stoping?

Steep dip, regular shape, and defined ore boundaries

What is the purpose of stabilized fill in primary stopes?

To prevent sidewalls from caving in when secondary stopes are mined

What is the sequence of mining in sublevel open stoping?

Primary stopes are mined first, and secondary stopes are left as pillars Signup and view all the answers

What is the main advantage of sublevel open stoping?

Increased productivity and multiple production points Signup and view all the answers

What is critical to the success of room and pillar mining?

Establishing the optimum sizes of the rooms and pillars Signup and view all the answers

What is the purpose of pillars in room and pillar mining?

To support the overhead rock mass Signup and view all the answers

What is the common mining method used for ore bodies with a dip less than 50 degrees?

Room and pillar mining Signup and view all the answers

What is the primary purpose of installing cable bolts above the stope?

To provide additional support to the rock mass Signup and view all the answers

What percentage of freshly broken ore is typically drawn from the base of the stope after each blast in shrinkage stoping?

30-35% Signup and view all the answers

What is a characteristic of orebodies that are suitable for shrinkage stoping?

They have no tendency for oxidation, hydrolysis, dissolution, or development of cementitious materials Signup and view all the answers

What is the main disadvantage of shrinkage stoping in terms of production scheduling?

Only 30-35% of the freshly broken ore is drawn from the base of the stope after each blast Signup and view all the answers

What is the primary focus of describing rock mass response to stoping activity?

Analyzing the displacement of orebody peripheral rock induced by mining Signup and view all the answers

What is the purpose of backfilling in mining?

To reuse waste for backfill material Signup and view all the answers

What is the primary difference between shrinkage stoping and VCR stoping?

VCR stoping uses larger diameter drilling Signup and view all the answers

What is the main purpose of the Room and Pillar method in underground mining?

To create a system of open rooms and pillars for support Signup and view all the answers

Which underground mining method involves the use of artificial support, such as shrinkage stoping and VCR stoping?

Artificial Support Techniques Signup and view all the answers

What is the progression direction of VCR stoping?

Vertical Signup and view all the answers

What is a characteristic of shrinkage stoping?

Most of the blasted ore remains in the stope to support the hanging wall and footwall Signup and view all the answers

What is the primary characteristic of the Cut-and-Fill Stoping method?

It uses a series of horizontal slices to extract ore Signup and view all the answers

Which underground mining method is characterized by the extraction of ore in large blocks or panels?

Block Caving Signup and view all the answers

What is the primary purpose of the Sublevel Open Stoping method?

To extract ore from large orebodies Signup and view all the answers

Which underground mining method is used for mining orebodies that are too deep or too large for other methods?

Block Caving Signup and view all the answers

What is the primary difference between Pillar-supported methods and Unsupported methods?

The use of artificial support techniques Signup and view all the answers

What is the primary characteristic of caving methods in mining?

Induced, controlled, massive caving of the ore body or overlying rock Signup and view all the answers

Which type of orebodies is block caving typically used for?

Weak and massive orebodies Signup and view all the answers

What is the primary advantage of block caving?

High production rates at relatively low cost Signup and view all the answers

What is the minimum height requirement for orebodies to be suitable for block caving?

100 m Signup and view all the answers

What process occurs when temporary pillars in an undercut excavation are removed?

Failure and progressive collapse of the undercut crown Signup and view all the answers

What is the most favorable rock structural condition for caving?

At least two prominent subvertical joint sets with subhorizontal Signup and view all the answers

What is the primary characteristic of sublevel caving?

Used in strong and massive orebodies with weak host rock Signup and view all the answers

What is the result of inducing free displacement of the country rock overlying an orebody in sublevel caving?

Caving of the host rock into the void Signup and view all the answers

What is the primary advantage of using long and subvertical blast holes in mining?

Elimination of the need for entry of operating personnel into the developing mine void Signup and view all the answers

What is the typical sequence of operations in Cut and Fill Stoping?

Drilling & blas]ng → scaling & support → ore loading & transport → backﬁlling Signup and view all the answers

What is the typical range of stope spans in Cut and Fill Stoping?

4 ~ 40 m Signup and view all the answers

What is the primary advantage of Cut and Fill Stoping in terms of environmental benefits?

Limited possibility of surface subsidence Signup and view all the answers

What type of orebodies is Cut and Fill Stoping typically applied to?

All of the above Signup and view all the answers

What is the primary characteristic of Bench and Fill Stoping?

It is a more productive alternative to cut-and-fill method Signup and view all the answers

What is the initial step in Bench and Fill Stoping?

Drilling and extraction drives along the ore length and width Signup and view all the answers

What is the main reason why Cut and Fill Stoping is suitable for low rock mass strength conditions?

Because it provides better control of rock performance Signup and view all the answers

Study Notes

Rock Mass Response to Stopping Activity

The performance of the host rock mass during mining activity is described in terms of the displacements of orebody peripheral rock induced by mining.

Pillar Supported Methods

Room and Pillar:
- A common mining method for ore bodies with a dip less than 50 degrees.
- A grid system of open rooms and pillars to support the overhead rock mass is created.
- The mining sequence can be optimized to accommodate rock conditions and ventilation demands.
- The ore is usually mined out using the same drill and blast technique as in conventional drilling.
Sublevel Open Stoping:
- A commonly used method in large-scale mining.
- Enables multiple production points in operation at the same time, offering good productivity.
- Used for large ore bodies with a steep dip, regular shape, and defined ore boundaries.
- Drills are created through the ore body to enable mining of stopes between sublevels.

Artificial Support Techniques

Shrinkage Stoping:
- A vertical stoping method conducted in a vertical or near-vertical plane.
- Most of the blasted ore remains in the stope to support the hanging wall and footwall.
- Applied to vertical or subvertical advance of mining in a stope.
- Broken ore is used as both a working platform and temporary support.
VCR Stoping (Vertical Retreat Stoping):
- A configuration method in stopes where drilling large diameter is used to detonate horizontal slices of ore.
- The method progresses vertically, as successive slices are blasted.
- Applied to cases where conventional shrink stoping is feasible, but narrow orebody width may not be tractable.
Cut and Fill Stoping:
- A method where a portion of the stope is mined, and then completely backfilled with broken rock or a mix of cement and waste rock.
- Mostly mining proceeds up-dip in an inclined orebody.
- Drilling and blasting are done about 3m thick, followed by scaling and support, ore loading and transport, and backfilling.
- Applied in veins, inclined (35°-90°) tabular orebodies, and massive deposits.
Bench and Fill Stoping:
- Developed in the early 1990s as a more productive alternative to cut-and-fill method.
- Initially, drilling and extraction drives are mined along the ore length and width.
- A bench slot is created between these two horizons at the end of the orebody.

Unsupported Methods

Block Caving:
- A method used in weak and massive orebodies, where the ore is undercut, and then the remainder of the orebody collapses into the void created.
- The host rock is fairly strong, although ultimately it tends to cave into the void created from removing the ore.
- A kind of mass mining method with high production rates at relatively low cost.
- Applicable only to large orebodies with a height of more than 100m which have a fairly uniform distribution of grade.
Sublevel Caving:
- A type of caving used in strong and massive orebodies in which the host rock is very weak and quickly caves into the void created by removing the core.
- As in block caving, the cave will ultimately reach the surface.
- Induces free displacement of the country rock overlying an orebody.
- Ore and waste are fragmented using blast holes drilled upwards from headings.
- Sublevel caving and block caving have application to inclined or vertical, massive deposits, almost exclusively metallic or nonmetallic.

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