CIVIL WORKS IN THERMAL POWER PLANTS

PRESENTED BY:

GROUP B4

03-08-2012

CONTENTS

Bidding• Technical Specifications• Preparation Of Bid

Coal Handling Plant• Soil Investigation

Ash Handling Plant• Types Of Foundation• Selection Of Footing

Water Systems• Softwares • IS Codes

Miscellaneous buildings

Soil Profiles in India

Loads considered for design

Foundation Design

Design Aid:

COAL HANDLING PLANT DESIGN

The design of a coal handling plant depends upon- Station capacity: Determines the quantum of coal to be

handled by coal handling plant and the capacity of coal unloading system, crushers, coal conveying system, etc.

Coal source and quality: Quality of the coal determines the specification of coal handling equipment apart from the quantity of coal to be handled.

Coal transportation mode: Depends on the location of power plants with respect to coal mines/sources and other site conditions.

Topography and geometry: Layout of coal handling system varies with topography, geometry of the area, coal storage requirements as well as wind direction. No. of transfer points may also vary with topography and geometry of the area.

BIDDING: TECHNICAL SPECIFICATIONS

Site development works

• Site grading• Roads, drains, culverts and bridges• Storm water drainage• Sewage / waste water drainage

Construction enabling works

• Distribution of construction water beyond terminal point • Distribution of construction power beyond terminal point• Construction of Temporary Buildings including site office for Owner/Owner representatives.

Station Building & Control Room Building

• Column foundation, Plinth beams• Foundations for various equipment inside the station building • Encasements of column base• structural steel works• plumbing, water supply, drainage around building

Boiler area-

• Foundations for boilers, bunkers, elevator supporting structure• Foundation of dewatering & re-filling pumps • drainage arrangements • provision of passage way for maintenance of equipment

Transformer Yard –

• Foundations for transformers including soak pits, fire barrier wall, rail foundations including rails, foundations for other equipment and structures in the transformer yard,

• oil drainage arrangements, oil collection and separation pits, trenches and duct banks,• paving of the transformer yard including drainage arrangement for the yard, • fencing around the yard with gate for movement of equipment etc.

1.4.9 Plant Water System:

• Various pump houses (Circulation Water Pump House, Clarified cum fire water Pump House) and supporting structure for Plant Water Supply system,

• Side Stream Filtration Plant foundation, Clarified cum Fire Water Storage Sump, Foundation for DM Water Storage Tank, Portable water tank, Guard Pond, Burnt Oil Tank including foundation, CW Channel, Fore-bay, Sump, etc.

SOIL INVESTIGATION

Purpose: To obtain information on the physical properties of soil and rock around a site to design earthworks and foundations

Soil Samples Disturbed – without conserving the soil structure

Shovel/trial pits Augers – hand/machine driven, continuous flight Standard Penetration test Sampler

Undisturbed – conserving the soil structure Shelby tube sampler Piston sampler Pitcher barrel Sampler

IN SITU TESTS

Standard penetration test: IS 2131: 1981 In-situ dynamic penetration

test Bore hole dia. of 100-150 mm

and length 650 mm Diving head 63.5 Kg and height

75 cm Corrections

Overburden Dilatancy – if the stratum

consists of fine sand and silt below water table

Provides an idea of soil strength and relative density

Cone penetration test IS 4968 Method: consists of pushing an

instrumented cone, with the tip facing down, into the ground at a controlled rate

Provides soil cohesiveness data and bearing capacity

CPTu - Piezocone Penetrometer. measures the groundwater pressure as the probe is advanced

SCPTu - Seismic Piezocone Penetrometer. probe is equipped with either geophones or accelerometers to detect shear waves and/or pressure waves produced by a source at the surface.

LABORATORY TESTING

Atterberg limit to determine plastic limit, liquid limit and

plasticity index Particle Size analysis

Distribution of grain sizes Soil compaction tests

For optimum soil contest Direct shear test

For consolidates drained strength Triaxial Shear tests

Shear strength in drained and undrained conditions

FOUNDATIONS

Spread Foundation –

• The bottom part is made wider to reduce the pressure• Used in residential buildings• Design based on weight• Not suitable for heavy structures

Mat-Slab Foundation

• The load is distributed to the entire building area• Thick mats required for heavy structures

Slab-on-grade foundation

• Concrete slab, to be used as foundation, is made using a mold• Leaves no space between ground and structure• Can lead to large heat losses, exposes to flood damage due to low elevation

Shallow Foundations

• Made of wood, concrete or steel• Pole shaped members driven into soil using

large weights• Column rest on pile caps supported by Group of

piles• Monopile foundation consists of a single large

member supporting all the weight

Driven Piles

• Under reamed piles have a enlarged base and are used in firm soils

• Auger cast piles are formed by drilling through the ground using a flight auger and then pouring concrete

• Rotary bored piling can be dry bored or wet bored. Pile is encased in a temporary casing which is removed after the required depth is reached.

Drilled Piles

Deep Foundations

CHIMNEY CONSTRUCTION

A chimney is a structure for venting hot flue gases or smoke from the boiler into the atmosphere at sufficient heights

The stack in coal fired power plants can be tall in the range of 200 to 300 M

The stack has an outer RCC shell and a steel inner lining (Flue) for the flue gas path

The outer shell provides the strength and the inner lining protects the concrete layer from corrosive flue gases

Connection of multiple units to a single shell will have multiple inner flue gas liners

Difficulties in the construction of a tall stack – work has to be done at great height form work has to move continuously upward diameter of form work has to change continuously gap between inner and outer form has to change to

accommodate the change in thickness of the shell Methods –

Slip form method - In this method the form work for the concrete literally slips up cm by cm to produce an integrated concrete column. Continuous pouring of concrete ensures a joint free construction

Jump form method - form work jumps up to the next layer after the bottom layer is cast. This is suitable for stacks, which have lining - like refractory lining in the inside of the shell. The concrete is not continuous

LOADS CONSIDERED FOR DESIGN

Various load combinations are analyzed before the design of any structure is finalized. The following loads are considered –

Live loads (IS 875 part 2) Dead Loads

Covered in IS 875 part 1. Unit weight are specified for all the materials to be used in construction

Weights of parts and components, fuels miscellaneous are also covered

Seismic Loads (IS 1893) Wind Loads (IS 875 part 3)

Wind causes a random time-dependent load, which can be seen as a mean plus a fluctuating component.

IS 875 part 3 specifies the wind loads Design Wind Speed (Vz)

Vz = Vb k1 k2 k3 k4

Vz = design wind speed at any height z in m/s, Vb = wind velocity at any height at any specified location k1 = probability factor (risk coefficient) k2 = terrain roughness and height factor k3 = topography factor k4 = importance factor for the cyclonic region

The factor k1 is based on statistical concepts, which take account of the degree of reliability required, and period of time in years during which there will be exposure to wind, that is, life of the structure.

Selection of terrain categories shall be made with due regard to the effect of obstructions which constitute the ground surface roughness.

Category 1 – Exposed open terrain with a few or no obstructions and in which the average height of any object surrounding the structure is less than 1.5 m

Category 2 – Open terrain with well-scattered obstructions having height generally between 1.5 and 10 m

Category 3 – Terrain with numerous closely spaced obstructions having the size of building-structures up to 10 m in height with or without a few isolated tall structures

Category 4 – Terrain with numerous large high closely spaced obstructions

Topography (k3 factor) The effect of topography will be significant at a site when the

upwind slope (θ) is greater than about 3o, and below that, the value of k3 may be taken to be equal to 1.0. The value of k3 is confined in the range of 1.0 to 1.36 for slopes greater than 3o.

It may be noted that the value of k3 varies with height above ground level, at a maximum near the ground, and reducing to 1.0 at higher levels, for hill slope in excess of 17o

The factor k3 is a measure of the enhancement that occurs in wind speeds over hills, cliffs and escarpments.

Importance Factor for Cyclonic Region (k4) the speeds given in the basic wind speed map are often

exceeded during the cyclones. Structures of post–cyclone importance 1.30 Industrial structures 1.15 All other structures 1.00 The highest value may be used only for structures of post-

cyclone importance such as cyclone shelters, hospitals, school and community buildings, communication towers, power-plant structures, and water tanks

Wind pressure at any height above mean ground level

pz = wind pressure in N/m2 at height z, and Vz = design wind speed in m/s at height z.

Design wind pressure pd can be obtained as,

pd = Kd. Ka. Kc. pz

Kd = Wind directionality factor Ka = Area averaging factor Kc = Combination factor

Kd : For circular or near – circular forms this factor may be taken

as 1.0. For buildings, solid signs, open signs, lattice frameworks, and

trussed towers (triangular, square, rectangular) a factor of 0.90 may be used on the design wind

pressure.