DIGGING IN

Structure is built inside an excavation

Used when tunnel profile is shallow

Used for underpasses,approach section for mines

Two types of construction employed for this

Bottom-up

A conventional method

Waterproofing can be applied to outside surface

Inside of the excavation is easily accessible for construction equipment

Drainage can be installed outside

Top-down

Allows early restoration of ground surface above tunnel

Temporary support of excavation walls used as permanent walls

Shorter construction duration by overlapping activities

SINGAPORE

Current population: 5.4 million

Projected population in 2028:

6.9 million people

Rising sea levels a worrying factor

12 km of expressways and 80 km of transit lines already below ground

Jurong Rock Caverns,a huge underground oil bunker

Located underneath the Banyan Basin,off Jurong Island on the western coast of Singapore

Southeast Asias first underground liquid hydrocarbon storage facility

Cost: US761 million

When completed,will free 150 acres,equivalent to six petrochemical plants

Two access shafts almost completed

Will be ready by 2014

Cavern itself will be up to 27 m high

Will create 1.47 million cu metres of storage space

Tankers and ship to dock overhead to allow oil to be conducted underground

Underground Science City

40 interconnected caverns for data centres and Ramp;D laboratories which would support the biomedical and life sciences industries

Estimated size is 50 acres

Will be 30 stories below a science park

Will house around 4,500 scientists and researchers

Malls on Orchard Road

Singapores shopping hub

Ngee Ann City retail complex spans 7 levels,of which one is underground

Is accessible by using underground walkways from Orchard metro station

Projected problems

Subterranean projects can be three to four times as costly as surface projects

Will need extensive soil investigations

Tricky task of weaving underground and overground utilities cables,pipes,drainage reservoirs

Could lead to psychological issues

Superstitions only dead return to the ground

Would require proper ventilation costly

As previously untouched soil is broken into,carbon dioxide would be released

OLD UNDERGROUND CITIES

Beijing,China

A network of tunnels built under the city as a bomb shelter

Has schools,restaurants,factories,theatres and a roller skating rink

Cappadocia region in Turkey

Has around 200 cities under-ground

Believed to have been built to protect in case of an invasion

Portland,US

Has a series of Shanghai Tunnels

Used to move goods,later used for smuggling,Shanghaiing abducting of people

Coober Pedy,Australia

Underground city that is still home to tens of thousands

Built to escape the heat above,is also called the worlds opal capital for its opal

Compiled by Aleesha Matharu and Joyeeta Biswas; Graphic by Pradeep yadav