Design and construction of Tunnel by TBM and

Underground stations by cut and cover method

Submitted by:-

Divyam Garg

UNDERGROUND STATION

1. Open excavation

Excavation in which no shores, piles, or sheeting are used to hold back the soil at the edge of the excavation. This method of excavation is adopted in the region where large open area is available .

2. Confined

• Area required for excavation and construction is less. • Adopted in highly populated areas. • Costlier than open excavation.

This can be carried out in 2 ways:

• Top-Down • Bottom-up

Choice for adoption of either of the two methods depends upon the depth of rock underlying.

• If the rock is found at smaller depth bottom up is adopted ,or

• if larger depth top down is adopted. This is due to problem in trenching in case of rock.

CUT AND COVER

This method also called soldier piling (part of bottom up) involves excavation that is to be carried out in stages casting • base slab, • concourse slab • roof slab at approximate level until formation level is reached.

• In Soldier Piling, first of all coordinates are located on ground using total station.

• Then the boring is done in the soil using drilling tool.

• The full length UB (universal beam) section for soldier pile is lowered in drilled bore hole.

• After lowering the section in the bore approx. 500mm to 600mm concreting is done of mix

1:2:4.

• To this UB section a BRACKET of 900mm length is welded on which a WALER BEAM is

attached.

• Waler beam is of 610*229 mm and length 12m.

• To this Waler beam, STRUT are arranged along the width of section to support the UB

section in retaining soil.

DIAPHRAGM WALL

The diaphragm wall is a structure cast in a slurry trench by tremied concrete.

The construction sequence is illustrated in Fig.

(A) Trenching under slurry, (B) End stop inserted (steel tube or other), (C) Reinforcement

cage lowered into the slurry-filled trench, (D) Concreting by tremie pipes.

• GUIDE WALLS are inverted ‘L’ shaped continuous RCC walls forming a support to earth.

Its purpose is to provide permanent alignment and prevention of collapsing of soil.

• In continuation trenching is done by the grab attached to the telescopic kelley which

are mounted on hydraulics rigs. Excavation by grabbing will be in presence of

POLYMUD solution.

• After completion of grabbing stop end are lowered in trench.

• After the lowering and fixing of the stop ends the reinforcement cage can be lowered.

With steel reinforcement in place the tremie pipe of 200/250mm dia is lowered.

Immersion depth inside concrete will not be less than 2 metres.

• EXTRACTION OF STOP END is carried out using Jacking arrangement method.

TOP-BOTTOM CONSTRUCTION:

• Top slab is casted with opening in the slab.

• After roof slab attains required strength, mini backhoe is lowered trough

opening in slab to carry out further excavation.

• Then concourse slab and base slab is laid.

• Checking of all final formation will be carried out with survey instruments

CASTING YARD

• Here precast segment rings are casted which are going to be installed in tunnels.

• Ring segments are prepared in universal mould.

• It is having 5+1 parts named as A, B1, B2, C1, C2 and a Key (K).

• Reinforcement bars used are of grade Fe-500 of 12mm main bars and 8mm stirrups.

Since these are supposed to be highly precise therefore each cage is needed to be

checked for:

undercut

Spacing =195mm with tolerance of ±4mm

Over bent

Over weld

• Concreting is done directly through transit mixer each with capacity of 6m3and

subsequently mould is vibrated.

• Strength required to be gained by the segments is 12MPa. And is checked through cube

compressive strength made out of the same material. Then the piece is demoulded by

special vacuum device attached to the over head crane.

• Curing of these segments is done by steam. Temperature is raised at 22ºC/hr. Max.

Temperature that can be taken is 60 ºC. It is retained at max. Temperature for 1hr.

TUNNELING

The methods involved in this work are:

1. Preparation of work site.

2. Setting out and layout as per approved drawing.

3. Construction of Guide wall.

4. Construction of permanent and temporary D’wall.

5. Dewatering to lower water table.

6. Sequential excavation and fabrication and installation of steel frame/struts to support

D’wall.

7. Installation of gantry cranes, cooling ventilation system and battery charging room,

backup units.

8. Construction of temporary base slab.

9. Then TBM cradle is installed upon which its components are received and installed.

10. After installation and proper checks tunnel excavation is commenced in a cyclic

manner.

At the start and other D’walls through which TBM have to cut through are provided

with Glass Fiber Reinforced Plastic Bars (GFRP) instead of steel reinforcement. This

portion is called Soft Eye.

Technical Specification for TUNNEL BORING MACHINE (TBM)

1. Tail outer diameter 6610mm

2. Tail inner diameter 6410mm

3. Tail thickness 100mm

4. Overall length 12,265mm

5. Total thrust 40000KN

6. Extending speed 71mm/min

7. Cutter head dia. 6650mm

8. Cutter head Power 900kW

9. Cutter head speed 1.5-3rpm

10. No. of injection port 43

THANK YOU