RAMPUR HYDRO ELECTRIC PROJECT

IN

HIMACHAL PRADESH, INDIA

(412 MW)

“Project Description and Design of Anchor Block”

Under Guidance of: - Report prepared by:-

Er.J.P.Mahajan (Sr.Manager of Rhep cell) Nawang Chhonzer Negi

Er.Mahesh Civil Engineering Dprt.

Satluj Jal Vidyut Nigam Limited Shimla.

Introduction:-

Rampur Hydro-electric Project (412 MW) is located downstream of already executed 6 x 250 MW NJHEP and intends to use the desilted water discharged by the upstream project. As such the construction of Rampur HEP does not involve construction of any dam / desilting chambers and thus avoiding any serious environmental impact on local flora and fauna. It is proposed, to divert water from out-fall arrangement of NJHEP through a 10.5 meter diameter HRT of 15.177 Km Length. The construction of the project involves in addition to the Head Race Tunnel a 149.50 m above orifice slab. High and 38 m Diameter surge shaft, 3 numbers of pressure shafts/penstocks of 5.4 m/3.8 m diameter each and a surface Power House.

Location and layout of the Rampur project.

RHEP is located, near the town of Rampur in Shimla and Kullu districts of Himachal

Pradesh. The project area is enclosed by latitudes 77° 35’N and 77° 43’; and longitudes

31°23’E and 31° 30’E.

PROJECT DESCRIPTION:-

The Rampur Hydroelectric Project 412 MW is a tailrace development of 1500 MW

Nathpa Jhakri Hydroelectric Project with minimal social and environmental effects. Both

Jhakri and Rampur power stations are to be operated in tandem as at Jhakri tail race

pond very little storage is available.

The latter will be the master station while the former the slave. A small reservoir in the

shape of Pond of the Tailrace Outfall of NJHEP (tail pool) links the two projects. The

intake of the RHEP, which has been constructed as a part of the TRT Outfall, will draw

desilted water from the tail pool. Water leaving NJHEP will automatically enter Rampur

Intake whenever the TRT Outfall gates of Nathpa Jhakri are closed. It will utilize the

entire flow released by the latter which then flow through HRT on the same bank. The

head race tunnel, 15.08 km long will cross over to the right bank by means of a cut &

cover section, 43.2 m constructed in the river bed. An open to sky, throttled surge shaft,

38 m diameter, 140 m deep lies at the end of the HRT. Three pressure shafts take off at

the bottom of the surge shaft and emerge on the surface further downstream are of

5.40 m diameter. The penstocks continue up to the powerhouse near which they

bifurcate into 3.80 m diameter branches to supply water to six Francis turbines housed

in a surface Power House of size 138 m × 23.5 m × 48 m high. The tail water is let out in

to six draft tube tunnels leading into a collection gallery, which relays water to a 54 m

long tailrace tunnel of 10.5 m diameter, horse shoe shaped .The tailrace tunnel empties

in to open gated TRT Outfall structure. Beyond this, an exit channel leads the water to

the River as shown in figure.

The project with an installed capacity of 412 MW (6 × 68.67 MW) will generate

2025.55GWh of electrical energy in a 90% dependable year and 2182.06GWh in an

average year.

Penstock:-

The penstock, a pipe or conduit used to carry water to a water wheel or turbine. The pen-

stock can be supported in a variety of ways, depending on the existing geologic conditions

and penstock profile. The penstock can be totally buried, partially buried or supported

above ground. Generally, penstock is totally buried when either drainage is required and

when the penstock requires protection from falling tree or when dictated by economics.

And soil cover protects the penstock against the expansion or contraction. The buried

penstocks are difficult to inspect or repair. In the case of partially buried penstock

corrosion can be the problem due to contact with the soil. The above ground supports are

the better then totally buried or partially buried penstocks, and allow a better handling or

inspection or repair access. Aboveground anchor blocks and piers are used to support the

penstock.

Anchor block and Piers:-

Anchors are provided at bends to resist hydrostatic loads and accumulation of

longitudinal loads and to prevent the shift in the pipeline and to resist the vibrational

force that tend to cause displacement in the penstocks. Piers are used to support or

handle the different kind of load, such as bending stresses, concentrated loads at support,

dead load of the pipe and contained water, and resist the longitudinal force resulting from

temperature change, friction, and circumferential stresses.

Criteria for design of Anchor Blocks for the Penstock with

expansion joints:-

Note:-Design of anchor block is carried out as per IS : 5330-1984.

1. The foundation of anchor blocks shall be designed so that the maximum pressure

on the foundation shall not exceed the allowable bearing pressure of the soil,

which is 100 t/m2 in our case.

2. When the profile is sloping, the safe bearing capacity shall be reduced to take

into account the decrease due to non- normality of resultant to the surface in

accordance with IS:6403-1971. The angle set up by resultant with ground shall

not be less than 30° for stability of the soil below anchor.

3. Anchor block shall be designed to be safe against sliding on the foundation. The

sliding friction factor is computed by dividing the total horizontal forces by the

total vertical forces shall be less than given below (∑H/∑M<Sliding factor).

Surface Sliding Factor

Concrete on rock 0.50

Concrete on gravel 0.40

Concrete on sand 0.33

concrete on clayey soil 0.25

4. In case the anchor blocks rests on solid rock, without any weak planes

capable of sliding, the sliding factor shall be designed for 0.75. Where however,

weak seams or joints along which sliding may be apprehended in the rock below,

the stability be checked by the following formula:

µ’=co-efficient of internal friction between foundation, concrete and foundation

under saturated condition,

∑V’=total vertical force,

a”=area under compression in m3,

τ=shearing strength in N/mm2,

∑T=total horizontal forces.

Note:- The weight of the anchor block may get reduced if the anchor block and the rock

above of such a seam is anchored into the rock below the seam.

5. Anchor block shall be designed to be safe against overturning. And to avoid the

overturning of anchor block at bend, the ratio of stabilizing moment to

destabilizing moment should be greater than 2.0.

6. The design of the anchor blocks shall be such that the resultant of all the forces

falls within themiddle B/6 portion of the base where B is base width . For anchor

blocks with stepped bottom the designs shall be made so that the resultant falls

within the kern of the projection of the anchor base on the plane perpendiculr to

the resultant as shown in figure.

Figure Stability of Anchor Block with Stepped Foundation

Problem: - Design an anchor block against bend forces to stabilize the penstock at

bend considering earthquake forces taking

Notation

V=velocity,

A=Cross sectional area of pipe at anchor,

P=Dead weight of pipe from anchor uphill to expansion joint,

P’=Dead weight of the pipe from anchor downhill to expansion joint,

H=Maximum Head at any point including water hammer,

f’= friction of expansion joints per meter of circumference,

µ=coefficient of friction between packing and liner,

e=packing length,

f=coefficient of friction of pipe,

g=acceleration due to gravity.

p=weight of the pipe and contained water from the anchor to adjacent uphill pier

in N.

d diameter of pipe

e=packing length

∑V= total vertical force

∑M= total moment

Given Data

Diameter of penstock D =5.4m

Thickness of pipe t =44mm

Discharge Q=135 m3/s

Length of the penstock L =25m

Then we can calculate:-

A=3.14 X 2.72=22.8906 m2

V= Q/A

V=135/22.89 =5.9 m/s

P=wAL

P=7.5 X (AR-Ar) X L

P=7.5 X 0.7525 X 6

P=33.86 t

P’=0 (Because no piers or support is provided in downhill)

And weight of water in pipe

W=wAL

W=1 X π X 2.72 X 6

W=137.41 t

H= (1058.4 -905.3) m

H=153.1 m

µ=0.26, e=0.16

f’= 1.5µwHe

f’=1.5 X 0.26 X 7.5 X 153.1 X 0.16

f’=71.604

Load and force acting on anchor

1) Hydrostatic force:-

Fs= wAH

Fs=1X123.1X22.89

Fs=3504.459 t

Fsh1=3504.459 t ,

Fsv1=0

Fsh2=3504.459Xcos 40.15°

Fsh2=2678.67 t

Fsv2= 3504.459Xsin40.15°

Fsv2=2678.67 t

2) Dynamic force:-

Fd=QwV/g

Fd=796.5 t

Fdh1=796.5 t

Fdv1=0

Fdh2=796.5Xcos40.15°

Fdh2=608.81 t

Fdv2=796.5Xsin40.15°

Fdv2=513.57 t

3) Force due to the dead weight of pipe from anchor uphill to expansion joint

Du=0

Duh=0 and Duv=0

4) Force due to dead weight of pipe from the anchor downhill to the expansion

joint.

Dd=0

Ddh=0 and Ddv=0

5) Sliding friction of pipe on piers due to expansion or contraction uphill from

anchor

Spu=98.037 t

Spuh=98.037 t

Spuv=0

6) Sliding friction of the pipe on piers due to expansion or contraction downhill

from anchor

Spd=0

Spdh-0

Spdv=0

7) Sliding friction of uphill expansion joint

Sev-1.234 t

Sevh=1.234 t

Sevv=0

8) Sliding friction of downhill expansion joint

Sed=0

Sedh=0

Sedv=0

9) Hydrostatic pressure on exposed of pipe in uphill expansion joint.

Fu=0.785X10-3 t

Fuh=0.785X10-3 t

Fuv=0

10) Hydrostatic pressure on exposed end of pipe in downhill expansion joint

Fd=0

Fdh=0

Fdv=0

11) Longitudinal force due to reducer above anchor

Lu=wH(A’-A)

Lu=0

Luh=0 and Luv=0

12) Longitudinal force due to reducer below anchor

Ld=wH(A’-A’’)

Ld=0

Ldh=0

Ldv=0

Net horizontal force Rx

Rx=1112.75 t

Net vertical force Ry :

Ry= -2773.21 t

Resultant R:-

R=√(Rx2+Ry

2-2RxRy cos Ѳ)

R=2988.127 t

Now let’s assume the

Length of anchor block=25m

Width of anchor block=12m

Height of anchor block=18 m

Then self-weight of concrete= L X W X H X 2.4

=25 X 12 X 18 X 2.4

=12960 t

Net weight of the concrete= 12960-cross sectional area of penstock X L X 2.4

=12960-π X 2.7442 X 25 X 2.4

=12960-1419=11541 t

Weight of the penstock= π X (R2-r2) X full length X w

=3.14(2.7442-2.72) X 25 X 7.85

=147.68 t

Weight of water in penstock= π X 2.72 X 25X 1

=572.56 t

Now:-

Self-weight of anchor + weight of penstock +water

=11541+147.68+572.56

=12261.124 t

Term Force L.A Moment about toe

Self-weight of anchor + 12261.124 (↓) 12.5m 153264.05 tm

Block + penstock + water

Net horizontal force 1112.75 (→) 9m -10014.75 tm

Net vertical force -2773.21(↑) 12.5m -34665.13 tm

Seismic force (horizontal) 17716.56(→) 9m -15449.04 tm

Seismic force (vertical) -1144.37(↑) 12.5m -14304.64 m

Total: - ∑v=8343.54 ∑M=78830.54

∑H=2829.31

1) Check for the resultant from toe :-

Eccentricity=L/2 – (∑M/∑V) < (L/6)

E=25/2 – (78830.54/8343.54)

E=3.052 < (L/6) =4.17

Hence proved, safe against tension at base.

2) Check for Bearing pressure:-

Toe stress= (∑V/A) X (1+6e/L)

Toe stress= {83434.54 /(25X12)} X (1+6X3.052/25)

Toe stress=48.17 t/m2 <100 t/m2 in our case, in Rhep.

3) Check against stability:-

(∑H/∑V) <0.4

=2829.33/8343.54=034 <0.4

Hence safe against sliding

4) Check against overturning:-

(Stabilizing moment/destabilizing moment) > 2.0

= (153264.05/74433.76) =2.059 >2.0

Hence proved, the anchor block is safe against overturning.

Without considering the seismic force:-

Term Force L.A Moment about toe

Self-weight of anchor + 12261.124 (↓) 12.5m 153264.05 tm

Block + penstock + water

Net horizontal force 1112.75 (→) 9m -10014.75 tm

Net vertical force -2773.21(↑) 12.5m -34665.13 tm

Total:- ∑v=9487.914 t ∑M=108584.175 tm

∑H=1112.75 t

1) Check for the resultant from toe :-

Eccentricity=L/2 – (∑M/∑V) < (L/6)

E=25/2 – (108584.175/9487.914)

E=1.05 < (L/6) =4.17

Hence proved, safe against tension at base.

2) Check for Bearing pressure:-

Toe stress= (∑V/A) X (1+6e/L)

Toe stress= {9487.914 /(25X12)} X (1+6X1.05/25)

Toe stress=39.596 t/m2 <100 t/m2 in our case, in Rhep.

3) Check against stability:-

(∑H/∑V) <0.4

=1112.75/9487.914=0.117 <0.4

Hence safe against sliding

4) Check against overturning:-

(Stabilizing moment/destabilizing moment) > 2.0

=(153264.05/44679.87) =3.43 >2.0

Hence proved, the anchor block is safe against overturning.