Rock engineering and Hydropower plants

ROCK ENGINEERING

Rock engineering is the application of science of rock mechanics, engineering geology and other related discipline to the civil engineering construction.

ROCK MECHANICS

Rock mechanics is the theoretical and applied science of the mechanical behavior of rock mass.

ROCK:

Compact, indurated natural material (composed of one or more mineral) that requires drilling, blasting , wedging or other brute force to excavate is called rock.

Intact rock: Refers to the un-fractured blocks that exist between structural discontinuities.

 

Roles of rock engineering in Hydropower engineering:

a)Rock acts as platform

b)As construction material

c)As foundation

 

Rock is un-doubtly the most important material in construction of Hydropower plant where power station is located underground.

Dams are in many cases built entirely of rock and are normally founded on bed rock.

So, for hydropower engineering a sound knowledge regarding rock engineering is necessary.

 

Hydropower development includes main element of the following discipline:

1.Geological engineering

2.Rock mechanics

3.Construction engineering

In all rock engineering however the basic material is rock mass which is considered as material capable of resisting considerable loads.

Thus ,basic philosophy in modern rock engineering is to take advantage of self supporting capacity of rock mass and the positive aspect of rock as construction material.

 

 Main elements of hydropower plants  

i) Surge tank (Reservoir)

• A surge tank is a storage reservoir which is fitted at some opening made on a long pipe line or penstock.
• It helps to receive the rejected flow when the pipe line is suddenly closed by a valve fitted at its steep end.
• It helps in control of pressure variations resulting from rapid changes in pipe line flow, thus eliminating water hammer effect.
• It helps to regulate the flow in power and pumping plants by providing necessary accelerating or retarding head.

 

ii)Intake

 

•  Intake gates are structures provided with hoist to control the entry of water.
• In front of the gates trash racks are provided to prevent debris, trees, etc., from entering into the penstock.
• Rakes are also provided to clean the trash racks at intervals.

 

iii)Penstock

• They carry water to the turbines from the reservoir.
• The choice of open channel or a pressure conduit (Penstock) depends upon site conditions.
• The pressure conduit may be in the form of a flared intake passage in the body of the dam or it may be a long conduit of steel or concrete.
• Sometimes, it may be a tunnel extending for few kilometers between the reservoir and the power house.

iv)Turbine

• Turbine helps to convert hydraulic energy into mechanical energy.
• The mechanical energy developed by a turbine is used in running an electric generator.
• A turbine consists of a wheel called runner which is provided with specially designed blades or buckets.
• The water possessing large hydraulic energy strikes the blades and the runner rotates.

 

v)Generator

• The generator develops electric power.
• It is directly coupled to the shaft of the turbine.

 

vi)Powerhouse

• The purpose of the power house is to support and house the hydraulic and electrical equipment.

                                

• It is readily divided into two parts as follows:

a)The substructure: it helps to support the equipment and to provide the necessary water-ways.

b) The superstructure or building: it helps to house and protect the equipment.

 

vii)Tailrace

• The channel into which the turbine discharges in case of impulse wheel and through draft tube in case of reaction turbine is called a tail race.

                                 

 

What makes rock engineering unique in the complexity and uncertainty while interacting with the natural geological environment ?

a)Complexity 

i)Rock failure                            iii)Tensile strength

ii)Size effect                               iv)Ground water condition

b)Uncertainty

i)Geological uncertainty

• Due to unpredictability of the sites
• Due to variation of site geology

ii)Parameter uncertainty

• Concerned with spatial variation
• Rock mass strength

iii)Model uncertainty

• Arises from gap in scientific theory
• Prediction on the basis of causal reference

iv)Human uncertainity

• May be due to difference in opinion of the personals
• Simple human error

References: 

i) https://www.sciencedirect.com/topics/engineering/rock-engineering

ii) https://www.scimagojr.com/journalsearch.php?q=26268&tip=sid&clean=0

Rock engineering and Hydropower plants