AF CONSULT INDIA PRIVATE LIMITED

10 MW, TIGA HYDRO-ELECTRIC PROJECT

METHOD STATEMENT FOR SLOPE STABILIZATION

WORK FOR THE EXCAVATED SLOPE IN POWER

HOUSE AND EXISTING IRRIGATION CHANNEL BUND

INTRODUCTION OF WORK

The construction work of Tiga HEP is in progress. During the execution,

the following conditions have been encountered:

1. The aged irrigation Canal Bund existing at site which is facilitating

other Dam in nearby area, has been observed with cracks which

may further develop in future causing seepage/percolation of

channel water towards Power house. This may also cause loss of

water supply to the aforesaid dam. Despite of available slope

protection measures viz. Boulder Pitching/cement pointing, it has

been proposed to provide “additional protection” for the existing

structure for avoiding any untoward situation. It is proposed to

provide Soil Nails in a grid of 2mtr X 2mtr in a staggered way in

the affected area of 20m width X 10mtr height followed by

Wiremesh and Shotcrete.

2. The extremely poor geology with fractured formation of rock has

been encountered which have been weaker than expectation. To

safeguard the slope against failure with the timeline, It is proposed

to provide special protection in terms of cement grouted rock

anchors followed by Reinforced Shotcrete (100X100X4 Wire mesh

within 2 layers of Sprayed Concrete). This treatment will work as

stitching of weathered rock by anchors with a layer of concrete in

the face of rock surface.

TECHNICAL PARAMETERS OF WORK

S.N Description Unit Size

Installation of Soil Nails in Irrigation Canal Embankment

1 Dia. of Tor Steel Bar coated with red oxide mm 32/40

2 Length of Tor Steel Bar coated with red

oxide

mm 3000

3 Spacing among Soil Nails mm 2000 in

staggered way

4 Welded Wire Mesh(100x100x4mm) Sqm 500

5 Shotcrete/Gunniting Sqm 500

Cement grouted Rock Anchor installation in

Rock adjoining CBU and RBU

S.N Description Unit Size

6 Dia. of Tor Steel Bar mm 25

7 Length of Tor Steel Bar mm 3000 to 5000

8 Spacing among Rock Anchors mm 2000

9 Cement Grout with non- shrinkage powder kg 400

10 Face Plate with Hexagonal bolts nos 110

11 Welded Wire mesh(100x100x4mm) sqm 385

DRAWING SHOWING TYPICAL SOIL NAIL/ROCK ANCHOR

DRAWING SHOWING TYPICAL SHOTCRETE/GUNNITE ARRANGEMENT

Procedure:

1. Surface Preparation: The surface of the excavated slope will be

cleared with loose rocks to avoid chances for falling rock piece

during course of execution.

2. Drilling of Holes: Drilling of holes shall be carried out upon surface

preparation. The depth of holes will vary from 3m deep to 5mtr

deep. The diameter of the holes shall be 40mm. The holes shall be

drilled at 10o downward inclined. Jack hammers or, drilling rigs

shall be used for the work based on suitability at field. Since the

height of the area where treatment is to be provided is almost

25m, so, suitable scaffolding shall be required to approach the rock

anchor installation place.

3. Insertion of Rock anchors: Upon successful completion of drilling,

the rock anchors shall immediately be inserted into the holes upto

the desired depth.

4. 1st Layer of Shotcrete/Gunnite: immediately after completion rock

anchor installation in a patch of 25m X 10m height, Shotcrete will

be applied on the target surface of the slope. The Mix will be of

25mPa strength designed with 10mm down aggregate

ingrediented with accelerator for fast setting of concrete. The

following will be approximate design mix adopted for the work:

DESIGN MIX FOR SHOTCRETE MIX

TYPE CEMENT (KG) WATER(KG) SAND(KG) 10MM

AGG(KG) ADMIXUTE

(KG)

M30A10 450 220.5 910.4 364.07 7.65

5. Installation of Wire Mesh: After initial setting time of

Shotcrete/Gunnite, 100X100X4mm wiremesh, made of 4mm MS

wire shall be installed on 1st layer of Shotcrete/Gunnite. The

wiremesh shall be supported by nails made of 6mm dia, 150mm

long rod in L shape to hold the wiremesh with the surface. The

Face plate and Hex Nut shall be fixed with Rock anchors keeping

the Wiremesh in between Shotcrete and face plate. Joints in

Wiremesh shall be overlapped by 100mm.

6. 2nd /Final Layer of Shotcrete: Upon fixing of Wiremesh, Faceplate &

Nut, final layer of Shotcrete/Gunnite shall be carried out to cover

the Wiremesh.

The work shall be carried out in phases of 5 mtr height, completing

the each slope in 5 cycle times.

Key Equipments involved:

1. Jack Hammer or, alternatively Drilling Rig

2. Compressor

3. Gunniting Machine with Hose

4. Concrete Mixer

5. Other Small tools & tackles

Execution Schedule / Duration:

The overall duration of the work shall be 50 days for complete execution

of the work as per the construction schedule below:

Quantities involved:

Installation of Soil Nail with Grouting : 400 RM Approx.

Installation of Rock Anchor with grouting : 1700 RM approx

Fixing of Wiremesh : 1500 Sqm

Application of Shotcrete / Gunniting : 1500 Sqm

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