Infrastructure: Nuclear Plants

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Infrastructure: Nuclear Plants

India has an ambitious target of power production

by Nuclear Power Reactors to meet future energy

needs of the country. Two Indian companies,

Nuclear Power Corporation of India Limited (NPCIL)

and Bharatiya Nabhikiya Vidyut Nigam Limited

(BHAVINI) are responsible organization to construct

thermal reactors and fast breeder reactors respectively

in the country. NPCIL is currently operating

seventeen nuclear reactors and constructing five

reactors. Many more reactors are at anvil. Bharatiya

Nabhikiya Vidyut Nigam Limited formed as a

company and registered under Companies Act, 1956

on 22nd October 2003 under the administrative

control of Department of Atomic Energy is presently

involved in construction and commissioning of 500

MWe Prototype Fast Breeder Reactor (PFBR) at

Kalpakkam. Kalpakkam is an important nuclear

establishment of Department of Atomic Energy of

India and this coastal site is situated 70Km south of

Chennai. The PFBR is the forerunner for the future

Fast Breeder Reactors to be constructed in various

parts of our country including two more reactors at

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Kalpakkam to meet the future energy needs of India.

BHAVINI is constructing Mega Project PFBR and

the reactor is now in advanced stage of construction.

Preface:

PFBR is situated on the south of existing twin

units of Madras Atomic Power Station (MAPS). The

centre lines of MAPS unit 2 and PFBR are only 500

meter apart. PFBR and MAPS locations on the beach

of Bay of Bengal, is shown in Figure-1.

The entire PFBR plant is divided into nuclear and

power islands. The reactor location with respect to

MAPS is governed by minimum recirculation of

water discharge from condenser to sea. The PFBR

plant located on the shore takes condenser cooling

water from sea. Sand transportation and littoral drift

are large at sandy beach profile and at sea bed near

PFBR. The intake structure in PFBR was therefore

required to be engineered to avoid the sand entering

the pump house and clogging the intake passage to

condenser cooling water. The intake structure was

Fig 2(a) Integrated layout of shore protection &PFBR Intake &Outfall

Fig-1: Location of PFBR and MAPS at the beach of Bay of Bengal

designed to draw sea water from off-shore location

above sea bed, where depth of water is approximately

10 metres. Central Water and Power Research

Station (CWPRS) has developed the scheme of

drawing condenser cooling water, the length of

intake submarine tunnel, position of intake shaft, the

depth at which the water should enter the intake

shaft, and has finalized the hydraulic parameters of

intake. CWPRS finalised these parameters based on

extensive study of several factors including the height


of tide, Highest Water Level (HWL) and Lowest

Water Level (LWL), wind velocity and sea current in

different months of the year, effect of outfall water on

the temperature of intake water for Madras Atomic

Power Station and for the intake water temperature

of PFBR. The integrated layout of the Intake and out

fall structures of MAPS and PFBR is given in Figure-

2(a) and 2(b).

General Features of Intake Structures:

The PFBR Intake structure consists of:

Ø Outlet Shaft on the shore

Ø Intake Shaft off the shore

Ø Submarine Tunnel

Ø Approach Jetty for the Offshore intake shaft

surface.

The intake is designed to draw 29m³/sec sea water

for condenser cooling for the 500 MWe PFBR. This

has been computed from the _T of 7° C across

condenser of PFBR. The approach jetty is provided to

facilitate approach to intake shaft.

For coastal sites, the Ministry of Environment and

Forest has the following guidelines:

"Temperature Limit for Discharge of Condenser

Cooling Water from Thermal Power Plant:

New projects in coastal areas using sea water.

The thermal power plants using sea water should

adopt suitable system to reduce water temperature at

the final discharge point so that the resultant rise in

the temperature of receiving water does not exceed

7oC over and above the ambient temperature of the

receiving water bodies.

Existing thermal power plants.

Rise in temperature of condenser cooling water

from inlet to the outlet of condenser shall not be

more than 100C.

Guidelines for discharge point:

The discharge point shall preferably be located at

the bottom of the water body at mid-term for proper

dispersion of thermal discharge.

In case of discharge of cooling water into sea,

proper marine outfall shall be designed to achieve the

prescribed standards. The point of discharge may be

selected in consultation with concerned State

Authorities/NIO.

No cooling water discharge shall be permitted in

estuaries or near ecologically sensitive areas such as

mangroves, coral reefs/spawning and breeding

grounds of aquatic flora and fauna".

(Source: Ministry of Environment & Forest,

Notification, New Delhi dated 22nd December

1998)

Since MAPS is the old unit, the system is

maintained in such a way that the resultant water

temperature at the final discharge point for the


Fig 2(b): Intake / Outfall Arrangement for MAPS and PFBR

Fig 3: General layout of sea water intake system

Fig 3 above shows general layout of sea water

intake structure. The off shore intake shaft is of

4.25m dia, Tunnel is horse shoe shaped submarine

tunnel of 3.6m dia and on the shore out let shaft is of

6.0m diameter. The horse shoe shape tunnel size has

been arrived based on the adequacy of cross section

even after 40 years of barnacle growth on the tunnel


combination of MAPS and BHAVINI outfall is

maintained at 10° C.

Outlet Shaft on the shore:

This is 6m diameter vertical shaft at the shore

which is 55m deep.

Intake Submarine Tunnel

Exploratory bore holes were drilled along the

centre line alignment of the proposed submarine

tunnel well before the tunnel construction was taken


Fig 5: Sectional elevation of intake structure

Fig 6a: Submarine tunnel

Fig 6b: Top view of the tunnel

Fig 6c: Inner view of the tunnel

Fig 4: outlet shaft

Intake Shaft off the shore:

This is 4.2m diameter which has a depth of 50m.

Submarine Tunnel

The submarine tunnel has a length of 556m and a

diameter of 3.6m

Approach Jetty for the Offshore intake shaft

Approach jetty has the length of 567m width is

3.52m and diameter 7.1m

Geotechnical Investigation along the length of


up. Geotechnical Investigations were carried out on

core samples from these bore holes taken along the

central line of the proposed tunnel alignment by

drilling of the 13 numbers of boreholes of 76mm dia

(NX) at 50m intervals. Boreholes were drilled upto a

depth of 65m below the sea bed for fixing the tunnel

Invert level for safe tunneling. Further, tests were

also carried out for finalizing the design of tunnel

supports, lining thickness etc. These 13 numbers of

bore holes were drilled from fore bay location to

offshore intake location (600m length). Out of 13

core samples collected along the length of the tunnel,

five boreholes namely TBH-1 to TBH-5 were on

shore boreholes and eight boreholes namely TBH-6

to TBH-13 are off shore boreholes. The intake well is

located at the bore hole No.13. The bore holes drilled

at 50m intervals indicate that the hard rock levels

closely follow the sea bed profile (expect bore hole

No.7).

Apart from these, 13 bore holes for geotechnical

evaluation, two numbers of receiver boreholes were

also drilled which are on shore bore holes, for cross

hole tests.

All the fifteen boreholes including on shore and

offshore were plugged using grout material

consisting of cement and bentonite in 1:1 proportion.


Fig 8: Original layout sea water intake structure, approach jetty, seal pit

& outfall structure

Fig 7a: Construction of approach jetty

Fig 7b: overall view of Construction of approach jetty

Fig 7c: View of construction of approach jetty from shore side

The jetty runs parallel to the submarine tunnel

and is located 15m towards north of the tunnel. Thus

the jetty axis is 15 meters north of the 13 number of

borehole alignment.

The jetty is supported on 36 sets of piles located

at 15m intervals. The piles have been taken into the

hard rock upto 2m depth for socketing. The profile of

rock encountered along the jetty alignment confirms

generally the profile similar to the bore holes along


the centre line of the tunnel and this is true even at

TBH-7 where the hard rock was found at much

deeper depth.

M/S Design Group Project Consultants (P)

Limited, Bangalore have provided the entire design

and construction detailing for the submarine tunnel

after analyzing the geotechnical investigation data.

They have also analysed the rocks, produced

geological mapping, decided on rock anchoring,

taken decision on geological issues encountered

during construction and have produced detailed

reports of the incidents.

Geological Characterisation of the Lithological

Units:

All boreholes reveal similar stratification. Four

distinct layers were noted in all the bore holes, these

are Sandy soil, Clay layer, Weathered rock and Hard

rock. Geological characteristics of the lithological

units encountered was analysed by experts and the

detailed description of the lithological units are given

below:

Upper Brown Granular Zone

This is upper most zone which comprises of fine

to medium to coarse grain brown sand, with angular

/ assorted grains of transparent and opaque quartz,

minor specks of mica flakes (biotite) and mafics

(hornblende, etc). There is a strand line close to the

shaft. This indicates that it is an area of regression.

The grain size variation is not uniform. Thickness of

this lithological unit ranges between 5.5 - 10.5 m.

Argillaceous Horizon

This lithological unit has a thickness of 2 to 9.7 m

(approx.) and its color is greyish / greenish. This clay

is highly sticky and plastic, with rare shell fragments.

This horizon can be taken as a marker horizon. It can

also be considered as an aquiclude and groundwater

below this unit is likely to occur under semiconfined

and confined conditions. This clay occurs like a plug

and its origin is not confirmed as there is no zone of

transition above and below in its spatial distribution.

This shows a break in sedimentation and deposition

environment. Because of its pale green color,

chemical composition study, plasticity, engineering

property etc., were planned to be conducted.

Weathered Rock

This zone is encountered immediately below the

clay horizon. This zone consists of broken core of

garnetiferous charnockite and chloritised charnockite

/ migmatite. Thickness of the weathered zone ranges

from 0m to 15.6 m (approx.).

Hard Basement Rock

This zone occurs immediately below the

weathered rock zone without any transition to fresh

rock. The hard basement rock has been encountered

in all the Bore holes between 10.5 m to 18 m depths

from ground level except for Borehole 7 (TBH-7),

where hard rock is encountered at a depth of 29 m

below ground level. Depth persistence and lateral

prevalence of the hard rock has been established as

seen from the correlation of the sub surface

lithological data.

Hard basement rock encountered in this strata

belongs to the Archean Charnockite group of rocks

and Migmatite complex comprising igneous intrusive

rocks and metamorphic rock. The charnockite group

of rocks is made up of quartz, pyroxene, feldspar, and

garnet. The charnockite group of rocks is also

migmatised to varying degrees resulting in

retrogression and conversion into migmatite complex

comprising different types. (Reference Geological

Survey of India (GSl) map,1998). The migmatite

complex comprises of different types of gneiss, such

as garnetiferous, biotite gneiss, hornblende gneiss,

augen gneiss and garnetiferous quartzo-felspathic

gneiss. The magmatite are generally grey coloured.

In addition to this the mineralogical composition

and its assemblage manifested in the form of micro

joints, slips, shears, slickensides, rock alteration,

fracture filling, confined only to zones of thin

partings, foliation and joints at different depths.

Excepting for these thin weak zones, the host rock /

country rock appears to be homogeneous, medium to

coarse grained, migmatitic at places; as such there is

no major zones showing any effect of intense

shearing. A deeply weathered zone encountered in

TBH-7 is an exception.



Geotechnical Stratification

All the thirteen boreholes (TBH-1 to TBH-13)

revealed similar stratification but thickness of layers

vary depending on the location. Ground water was

encountered at 2.5 to 9 m below ground level at

different borehole locations during the investigation.

General stratification of the site and its characteristics

area as follows:

Stratum 1: Loose to medium yellowish Sand

This layer is present in all boreholes. This layer

extends upto 2.5 m depth in TBH-1 & 2 to

maximum 7.0 m in TBH-7. In some boreholes this

layer is again encountered at 5.5 m and 6.75 m after

dense to very dense sand layer. SPT values vary 11 to

30. This range of N values shows loose to medium

dense relative density of cohesionless soil. The soil is

classified as SM-SP, SP and grain size distribution

shows gravel 0 to 6%, sand 88 to 98% and silt +

clay 1 to 10%.

Stratum 2: Dense to very dense Sand

This layer is present in all bore holes except TBH-

7. Thickness of the layer varies from 1.25 to 4.8 m.

SPT values varies from 30 to 71. This range of N

values shows dense to very dense relative density of

cohesion less soil. This soil is classified as SP-SM, SM,

SC, SP.

Stratum 3: Yellowish brown Silty Clay of medium

to Stiff

This is present in some bore holes like TBH-2 and

TBH-3 at depth 7.2 and 8.5 m respectively below

ground level. Thickness of the layer is varying from

1.8 to 4.0 m. SPT values vary from 9 to 12. Soil is

classified as CH. Grain sizes are gravel 0 to 4%, sand

1 to 37%, silt 23 to 41%, clay 37 to 64%.

Stratum 4: Very stiff to hard Yellowish brown

Silty Clay

This layer is present except in TBH-8. Thickness

of the layer varies from 1.1m to 9.75m. N value

ranges from 18 to 57. Soil is classified as CH. Grain

sizes are gravel 0 to 1%, sand 2 to 50%, silt 17 to

45%, clay 33 to 66%.

Stratum 5: Highly Weathered rock

This is moderate to highly weathered rock.

Thickness of this stratum varies from one meter to

15.6 m. N-value exceeded 100 and in some cases

rebound of SPT hammer was observed.

Stratum 6 : Moderately Weathered rock

A small layer of moderately weathered rock is

present below highly weathered rock. It varies from

0 to 5.5 m.

Stratum 7 : Charnockite Bedrock

This stratum is medium to coarse grained hard

rock comprising of Charnockite and gneiss with

garnet crystals. Generally between 10 m to 18 m

depths, from ground level the hard basement rock

has been encountered in all the boreholes except

Borehole BH-7 where hard rock is encountered at a

depth of 29 m below ground level. The Rock Quality

Designation in this layer is generally in the range of

40 to 100. Weighted average of RQD in each

borehole varies from 71 to 85. Core recovery varies

81 to 90. The Rock Mass Rating of this bed rock is

63.8 and it is classified as Class II (good) rock as per

Bieniawski 1979 & IS: 12070- 1987 (Table 7).

Compression wave velocity for the rock strata varies

from 3659 m/sec to 4762 m/sec. Value of shear wave

velocity for this layer ranges from 2000 m/sec to

2300 m/ sec. Dry density and bulk density varies

from 2.66 to 2.99 gm/cubic cm and specific density

varies from 2.69 to 2.99.

Outlet Shaft on the Shore:

The excavation of the onshore shaft and the

submarine tunnel was commenced by the M/S

Gammon India Limited at PFBR site in February

2008. 3D geological log of the same was carried out

to confirm the parameters for design of lining and to

decide upon the reach where consolidation grouting

is required. The log indicated that generally the bed

rock met was Charnockite / Garnetiferous

Charnockite Gneiss with joints tight and incipient,

while the prominent joints were continuous for 5 to

10m in length in some places. These joints got

exposed as a result of blasting while excavation.



Seepage was noticed at the contact of overburden

and excavated rock surface. However, necessary

precautions were taken which included channelizing

the seepage water and monitoring of seepage in the

shaft.

The outlet shaft construction was incidence free

and was completed without major difficulty with all

the temporary supports.

Submarine Tunnel:

The horizontal horse shoe shaped excavation in

rock for submarine tunnel of size varying from 3.6m

to 4.2m is 560 meter long with Chainage 0.00

starting from centerline of vertical outlet shaft.

Conventional blasting using controlled charge was

deployed for the tunnel boring.

not have been closely maintained to submarine

tunnel axis. This conclusion governed decision

making process for further commencement of tunnel

boring.

TBH-4 was encountered during blasting on

previous day of the incidence i.e on 12.01.2009.

Small quantity sand had fallen down into the tunnel

from the hole when the zone of TBH-4 was blasted.

On 13-1-2009 at 4am further blast of 3m length was

taken up. De-mucking operation of excavated rock

was completed around 11am. At 11.15am subsidence

of sandy soil occurred at grade level (GL) exactly

above the bore hole No.TBH-4. People working on

the grade level noted that sinking of ground over

TBH-4 location and formation of a funnel shaped

chimney at the grade level, and people working in

the tunnel informed that certain slush along with

sand is falling through TBH-4 hole. On further

inspection of the tunnel it was observed that 76mm

dia TBH-4 bore has got unplugged of grouted

material (cement and bentonite in 1:1 proportion).

The slurry of grouted material along with about

12meter cube of sand has fallen down from the hole

on to the invert level of tunnel. Slight water too was

found dripping through the hole. A rod of 25mm dia

and about 4m length could be easily penetrated into

the unplugged hole of TBH-4 from inside the tunnel

bore.

Immediate action taken by BHAVINI after the

incidence-1:

Ø As a safety precaution the tunnel rock excavation

work was stopped forthwith.

Ø The matter was also referred to the experts who

arrived at site for assessment within hours of the

incident.

Decision making process following the incidence:

Ø The tunnel site was inspected by various experts.

Several rounds of reviews and discussions were

held. Experts expressed apprehension that minor

water seepage from TBH-1 and unplugged of

grouted material from TBH-4 does not provide

enough confidence that such incidence (seepage

from grout or unplugging of the grout borehole)

will not happened


Fig 9: Photos of Submarine tunnel

Two incidences were encountered during the

submarine tunnel construction.

Incidence-1:

Observation:

On completion of CH11500 on 13th Jan 2009 it

was noted that the grout in TBH-4 collapsed and

crumbled into the excavated tunnel. It also was noted

that while carrying out the rock excavation for tunnel

only 3 boreholes TBH-1, TBH-2 and TBH-4 have

been encountered within the alignment of tunnel but

not in centerline of the tunnel; rather they were away

from central axis to varying extent; from 0.5 m to

1.5m. TBH-3 could not be traced inside the tunnel.

This lead site to reach a conclusion that the boring

tool might not have taken exact gravity line while

drilling and/or the position of the drilling rig might


Hence:

Ø Either the tunnel should be diverted in further

span to avoid encountering grouted before bore

holes during the further tunnel construction.

Ø Or the grouting should be improved before

further blasting for tunnel bore.

Ø The bore hole size is only 76mm diameter and the

over burden over the roof of the tunnel is about

50m. In case of unplugging of borehole below the

sea water, the pressure of sea water that could

gush into the bore hole will be 5Kg.cm2, the

velocity of water will be about 25m/sec and the

discharge will be in the order of 7000LPM. If

dewatering pump capacity is augmented to suit

above as well as if the bore holes are re-grouted

from 3m before reaching such boreholes location

by injecting appropriate cement / chemical grouts

like polyurethane through horizontally or upward

inclined holes towards the roof of tunnel, it is

possible to maintain the same alignment of tunnel

in the further construction too.

However this proposal was dropped for the

following reasons:

Ø Out of balance nine bore holes yet to be

encountered during tunnel construction, one is on

the shore edge and eight are below sea water.

Ø Since no casing pipe has been left while drilling

the boreholes, it may be difficult to identify the

location of the drilled boreholes from the top

surface and take measures to grout the area

around the bore hole. Technologies / methods to

identify the borehole in advance where casing pipe

is not left are not well established.

Ø In this case, the location of borehole can be

identified exactly only after blasting and

excavating the underground tunnel.

Ø Even if the grouted bore holes are identified when

the tunnel excavation is approaching the bore hole

location using radar technology, grouting the

already plugged borehole may poses complexity.

Ø The pressure grouting from consolidation of areas

around the bore hole may not be effective as the

grouting is to be done in hard rock strata under

higher pressure than the tunnel consolidation

pressure (grouting prior to excavation of tunnel is

being done for strata to plug fissures, water

leakage etc). Therefore, tackling the situation if

the borehole in the sea location gets unplugged

during blasting for the tunnel excavation is

complex.

Ø The experience of tackling the flooding of sea

water in the tunnel is not readily available. It is

possible that more than one borehole may give in,

during the blasting / de-mucking in which case

dewatering of tunnel may become difficult.

Ø The project does not have cushion of time to face

a situation of flooding of tunnel which will involve

complex remedial measures.

Ø Keeping safety of workmen into as prime

consideration in decision making, it was decided

to take diversion for further course of tunnel.

Deviation of the alignment of the Tunnel:

Factors that were considered for deciding the

extent of deviation of tunnel are as follows:

Ø The deviation of TBH-1, TBH-2, TBH-4 opening

in tunnel from axis of the tunnel and non

detection of TBH-3 suggests that the deviation of

the axis of the tunnel should be large enough to

avoid meeting the TBH-5 to TBH-13 during

further tunnel construction.

Ø The deviation should be as small as possible to

reduce additional length of jetty required to

approach the new intake shaft.

Ø Further for the shifted location of the intake

structure, sea conditions such as littoral drift,

current etc. considered for the study for the

original design has to remain unaltered.

Ø Irrespective of the uncertainty of the bore hole

alignment (deviation from verticality) and

positional tolerance, the distance of the existing

bore hole from the blasted contour of the tunnel

should be minimum two meters (cover rock

between bore and blasted surface should be min

two meters).



Ø The tunnel has to be deviated to south-east and

after certain distance made parallel to existing

alignment as jetty on north of tunnel prevents

deviation of alignment to north.

Ø The rock profile in deviated contour should be

predictable from already completed geo-technical

studies.

Ø The water pressure drop should have only

marginal increase even after addition of two bends

in the tunnel. The existing sea water pump

supplying cooling sea water to the condenser

should be checked for its capability to cope up

with the increase flow path resistance.

Ø The bio-fouling concern should not enhance due

to the deviation in the flow path of the tunnel.

It was decided to divert the tunnel towards south-

east from the location of borehole No.TBH4 which is

at a distance of 115m towards east from the fore bay

shaft which is located on land. The straight line

lengths of the tunnel upstream and downstream of

the bends were checked for compliance to Bureau of

Indian Standard, IS 2951. Based on the requirement

of straight length between the bends as per standard

IS 2951, it was decided to deviate the alignment of

the tunnel keeping the angle of deviation as 11º from

TBH-4 and incline length to be maintained to 110m.

The tunnel bore will be again diverted by 11º at the

end of 110m diversion to make it parallel to the

original alignment. The southward

shift in the tunnel alignment thus works out to

21m. With the deviation of tunnel from the location

of borehole No.4, involving horizontally shifting the

tunnel by 21m southwards at the end of an inclined

length of 110m, the increase in total tunnel length

will be around 2m in addition to introduction of two

bends. For deviated alignment of submarine tunnel -

plan (general arrangement please refer Annexure - 1).

CWPRS that estimated the head loss due to

shifting of the tunnel by 21m and two angular

deviations of 11º and at two end of an inclined length

of 110m as 0.023mwc (meter of water column). Thus

the head loss due to change in the layout of the

submarine tunnel is insignificant compared to the

total pressure drop computed for the original layout

which is 1.9mwc. Hence, the additional drop in

pressure because of two bends and increase in length

of the tunnel by two meters does not change the

pumping head requirement of the cooling water

pumps. The pressure drop calculations were based on

IS 2951 (Part-II). Since, the pressure drop due to the

deviation in tunnel alignment is insignificant,

increase in head loss does not result in lowering of

water level in the forebay sump. Therefore, the water

level in the forebay would not fall below the designed

minimum water level. Hence, the submergence

required for the pumps is not altered. This was also

confirmed by DCPL who had carried out initial

design of the tunnel.

M/s IGCAR assessed and confirmed that there is

no impact on biofouling due to the proposed change

in the tunnel alignment by deviation.

M/s CWPRS, Pune has confirmed that for the

shifted location of the intake structure, sea conditions

such as littoral drift, current etc. considered for the

study for the original design will remain unaltered.

With the above deviated alignment of the tunnel,

the new axis of the tunnel with perfect drilled TBH-5

would be about 10.5 meter. Even after considering

TBH-5 alignment shift by 5.5 meters towards south,

the northern boundary of the deviated tunnel will be

2.5 meter from TBH-5. Therefore any opening of

TBH-5 in the deviated tunnel path and consequent

grouting of TBH-5 was not envisaged.

The geologists confirmed that the hard rock

profile at PFBR site generally follows the natural

ground profile. The slope is only form west to east

and the rock profile follows the ground profile as

proved by the TBH bore holes. With the decision of

shifting the tunnel by 21 meter towards south

beyond TBH-5, no change is expected in the hard

rock strata or the profile compared to initial

prediction based on geotechnical investigation. It

may be noted that for the original geotechnical

investigation itself the bore holes were taken at

distance of 50m; each borehole representing the

strata over a radial distance of 25m. The new

alignment is adjudged to be safe and the deviated

alignment of tunnel will also have adequate hard



rock cover. The available rock cover for the tunnel

from the crown is expected to be 4D on south of

TBH-7 as at this location, the hard rock level is

comparatively at a lower level than the other bore

holes. Whereas at the other borehole locations

indicate rock cover of more than 6D.

Internal pressure due to water at submarine

tunnel level is about 5kg/sq.cm. (50m water

column), where as external pressure due to weight of

rock and over burden soil is about 11.4kg/sq.cm. As

per IS standard 4880 Part-IV, maximum rock cover

required is H i.e. 5Kg/Sq.cm. With this 21m shift of

the off-shore Intake structure towards south from the

original location, the jetty length has also to be

increased by another 21m towards south. The

grouting of already exposed boreholes i.e. TBH-2 &

4 located on land was also undertaken and effected

successfully.

From 13.4 m to 25.05 m the rock is highly

weathered. Further from 25.05 m to 30.0 m the rock

is highly weathered to moderately weathered

Charnockite with poor core recovery and nil RQD

had been obtained. From 30 m to the end of the hole

(65 m) slightly weathered Charnockite with good

core recovery and fair to good RQD had been

recorded.

The occurrence of deep weathering in a single

lithologically similar hole is intruguing. In view of

the completely weathered to highly weathered rock

with very poor core recovery, shattered rock and zero

RQD in TBH-7 alone, it was inferred that the reason

for this may not be lithological but structural

infirmity. With only scanty subsurface data available,

the experts took recourse to the regional geology and

also the geotechnical investigation done for Madras

Atomic Power Station (MAPS) tunnel bore holes

which is existing 500meter north of PFBR submarine

tunnel and was constructed around forty year back.

The absence of dolerite in any of the PFBR boreholes

and the occurrence of dolerite in the MAPS tunnel

bore holes was had suggested to the possibility of an

east-west fault between the two tunnels before actual

tunneling work started. Since, the dolerite rock is

now encountered after the shear zone this possibility

is now ruled out.

Possibility-1

Regionally the foliation trend in the gneissic rock

is N25º to 50º ES25º to 50º W with a dip of 60 to

80 degree in easterly direction. N30º E - S30º W

joints (Foliation joints) are dominant. Hence,

probably the shear zone encountered in TBH-7 could

be a foliation shear.

Possibility-2

Dolerite with sheared contact is reported in the

off shore bore holes drilled at MAPS. The dip of the

dyke is estimated to be 70º close to Kalpakkam, at

Punjeri a N.W.-S.E. dyke is traceable for about 1 km.

In the area around Anaikattu about 15 km south

west of Kalpakkam several WNW-ESE dykes are

reported. In MAPS Reactor I pit a N60º W - S60º E

dyke was reported. It could be seen that the dykes in

the area trend WNW-ESE to NW-SE direction with


Depth (in m)

0.0 – 7.0

7.0 – 13.40

13.40 – 25.05

25.05 – 26.0

26.0 – 29.0

29.0 – 30.0

30.0 – 60.0

Lithological Details

Medium grained yellowish brown sand

Very stiff to hard brown sandy clay

Yellowish grey completely weathered rock

Highly weathered Charnockite. Poor recovery. RQD

Nil.

Highly weathered grey fractured Charnockite. Poor

Recovery. RQD Nil.

Moderately weathered Charnockite. Poor Recovery.

RQD 20%

Slightly weathered Charnockite. Recovery good,

RQD Fair to good.

Incidence-2 (Shear Zone Encountered between

Ch243 and Ch264)

(Rock condition at TBH-7)

From the analysis of borehole log details of 13

numbers of boreholes it was evident that low rock

will be encountered while tunneling at TBH7 and

site will have to take cautious approach during tunnel

excavation between TBH-6 and TBH-8. Rest other

bore log predicted trouble free construction while

advancing blasting for creation of submarine tunnel

bore. The following are the lithological, core recovery

percentages and RQD details of TBH-7 core samples

as prepared by M/S Geotechnics & Constructions

Pvt. Ltd.




a dip of 65º to 75º towards S30º W. The contacts of

many dykes are sheared; the shear zone trend is also

in the same trend. If the structural infirmity in TBH-

7 could also have the same trend and dipping

towards SW. Strike trend and apparent dip were

projected on to the new alignment. Thus it was

predicted that rock in the shear zone and adjacent

area will be closely jointed and could render the

crown of the tunnel weak where it intercepts.

A horizontal diamond drill hole was planned to be

drilled with double tube core barrel as tunnel

advanced. It was planned in advance that if drilling

data confirms the prognosis, tunneling in this

hazardous zone has to proceed cautiously. The zone

may be under a hydrostatic head. A similar zone in

Naptha Jhakri HEP in Himachal Pradesh (Himalaya

range) was tackled through DRESS Methodology i.e

Drainage, Reinforcement, Excavation and Support.

The method consists of drainage beyond the

heading by drilling holes with simultaneous insertion

of partly perforated steel pipes, improving the

heading by grouting and shotcreting. Before starting

the work supports (as dictated by design

considerations) was planned to be kept ready and

placed as soon as possible taking care to provide

laggings between the supports and crown. The above

details were brought to the notice of the field staff

and they were kept in readiness to face the situation.

To conform this and take precautionary measures,

a horizontal diamond drill hole was drilled with

double tube core barrel as tunnel advanced. Great

precaution and cautious approach was taken from

Ch.250 to Ch.290.

Observation during sub marine tunneling

operation:

As predicted earlier, during the excavation of

tunnel the shear zone was encountered at Ch.245

continued up to Ch.257.5. The material in the shear

zone consists of highly crushed leucocratic

Charnockite. Although most of it is granular and

non-cohesive, in places it is completely clayey. No

water seepage was notice in the shear zone portion.

From Ch: 257.5 onwards and up to the face of the

excavation at Ch.270 Dolerite was encountered. The

dolerite Dyke although hard and fresh was found to

be blocky and seamy. To the left of the crown damp

surface and dripping conditions prevailed.

The absence of dolerite in any of the bore holes (as

per data provided) and the occurrence of dolerite in

the MAPS tunnel bore holes was referred to and the

possibility of an east-west fault between the two

tunnels was predicted earlier, even before start of

tunnel excavation boring. Since, the dolerite rock is

now encountered after the shear zone this possibility

is now ruled out.

In the MAPS tunnel boreholes, the dolerite is

found to be at least 54 m wide. As per bore hole

details, dolerite was not encountered even in TBH-7,

the logs of TBH-8 also indicate only charnockite and

not dolerite. Hence, it is probable that the dolerite

now encountered is less than 50 m wide.

Remedial measures taken in PFBR tunnel in the

shear zone.

Ø The entire excavation was geologically mapped

Ø From Ch. 243m to Ch 264m (in the shear zone

and blocky and seamy dolerite portions), 75 mm

thk. shotcrete of M35 grade with wire mesh was

applied.

Ø Wherever dolerite was found blocky, it was

stitched by 10mm thick plate anchored 3m deep

into the rock using 25mm diameter rebar.

Ø ISMB 600 @ 600 c/c with steel lagging was

provided in this stretch of submarine tunnel. The

entire inner surface (top, sides and bottom

surfaces) of this dolerite region was supported

with the above referred structural members.

Ø After the 3D geological logging of the submarine

tunnel, consolidation grouting was carried out

between Ch.15m to 30m, Ch.75m to Ch.85m and

Ch 240m to Ch 270m.

Ø Before any blasting for the tunnel, probe holes,

6m deep were drilled from the blasted face to

determine the rock strata ahead of tunnel face.

This was done either by diamond drilling or jack

hammer drilling.

The work of tunnel excavation is under progress

and as of 15th September, 2009, 515 meter out of



560 meter of tunnel was already excavated.

Concluding Remarks:

The PFBR intake structure is a design andconstruction marvel. True to the type of activity, the

construction has met several surprises which werequickly addressed with the help of experts withinIndia. The job has progressed well as per schedule

despite the above mentioned difficulties.

Acknowledgement:

This detailed technical paper is prepared after

drawing technical contents from various reportsprepared by experts and organizations engaged byBHAVINI for intake structure design, construction,

trouble shooting and remedial actions. This reporthas also major inputs from the agencies who havecarried out geo-technical investigation, construction

and inspection activities. The authors thankfully

acknowledge them.

The credit of this report goes to:

Ø Dr. S.K. Jain, Chairman and Managing Director,

M/s Nuclear Power Corporation of India Limited

& M/s Bharatiya Nabhikiya Vidyut Nigam

Limited

Ø Dr. Baldev Raj, Distinguished Scientist and

Director, Indira Gandhi Centre for Atomic

Research, Kalpakkam

Ø Shri S.C. Chetal, Director, REG, Indira Gandhi

Centre for Atomic Research, Kalpakkam

Ø M/S IGCAR who have conceptualised and

conceived entire scheme. Carried out bathymetric

studies, analysed the results produced by various

experts

Ø The entire civil team of M/S BHAVINI Ltd

Ø M/S CWPRS, Pune have designed and done

model studies of Intake Structures and finalised

blasting charge

Ø M/S Gammon India Limited who have finalized

construction and inspection schemes and done

field construction of Intake Structures

Ø M/S DGPCL, Bangalore who have provided the

entire design and construction detailing for the

submarine tunnel after analyzing the geotechnical

investigation data. They have also analysed the

rocks, produced geological mapping, decided on

rock anchoring, taken decision on geological

issues encountered during construction and have

produced detailed reports of the incidents

Ø M/S DBM Geotechnics and Constructions Pvt

Ltd., Bombay who carried out Bore Hole drilling

and Geotechnical Investigations

Ø M/S Anna University, Chennai who gave expert

analysis on geotechnical analysis.

Ø M/S NGRI who carried out cross hole tests

Ø M/S Indian Institute of Technology, Chennai

Ø M/S National Institute of Ocean Technology,

NIOT, IIT, Chennai who have done HWL and

LWL studies

Ø Dr. D.N. Seshagiri, an experienced Engineering

Geologist and Dr. S.R. Gandhi, a Senior Geologist

and Professor at IIT Chennai, who have

contributed significantly in preparation of this

paper. Few names of organisations and experts

have been brought out above. The contribution of

those whose names do not appear is also not less

and is thankfully acknowledged.

References:

Ø Geotechnical Investigation Report for Sea Water Intake

Structure at Kalpakkam in Tamilnadu State for FBR-Project,

BHAVINI-DBM Geotechnics and Construction Pvt.Ltd.

Ø Report from Design Group, Bangalore Titled Paper on

Geotechnical Problems faced during execution of Submarine

Tunnel and Remedial measures carried out.

Ø Physical Thermal Model Studies for Locating Intake/ Outfall of

500MWe Fast Breeder Reactor Project (PFBR)-CWPRS

Ø Mathematical Model Studies for Location of Intake/ Outfall of


Ø Flow Model Studies for Intake Structure of Fast Breeder

Reactor Project (PFBR)- CWPRS

Ø "Supplementary Mathematical Model Studies for Littoral Drift

and Thermal Recirculation for Sea Water Intake/ Outfall of

500MWe Fast Breeder Reactor Project (PFBR)-CWPRS"

Ø Physical Wave Model Studies for Sea Water Intake/ Outfall of


Ø Field Data Collection and Analysis for Condenser Cooling Sea

water System (CCWS) of 500MWe Fast Breeder Reactor

Project (PFBR)-CWPRS


Documents

Infrastructure: Nuclear Plants