Tunnel

Tunnel

A tunnel is an underground passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube construction techniques rather than traditional tunnel boring methods.

A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. The central portions of a rapid transit network are usually in the tunnel. Some tunnels are used as sewers or aqueducts to supply water for consumption or for hydroelectric stations. Utility tunnels are used for routing steam, chilled water, electrical power or telecommunication cables, as well as connecting buildings for convenient passage of people and equipment.

The options may include demolishing the arch and replacing it with a more substantial structure, building a cover slab on new supporting piles above and independent of the existing arch, or find a lightweight material for the embankment that would be substantially lighter than general class 1 fill. These options were analysed for cost, design capacity and the time required to keep the programme on schedule. 

Leca® LWA proved the most effective solution in all three parameters and the joint venture contractor welcomed the fast build solution it provided.

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Pull Out Resistance of LECA LWA

The ‘pull out’ resistance of LECA® Lightweight Expanded Clay Aggregate makes it an ideal solution for reinforced soil retaining walls and bridge design. Particularly when constructed over weak sub-soils or voids, this method has been proven to cut overall construction costs considerably. LECA® Lightweight Expanded Clay Aggregate is used extensively to reduce vertical loading.

Tunnel Development with LECA
Tunnel Development with LECA
Tunnel Development with LECA
Tunnel Development with LECA

Pull Out Resistance

The ‘pull out’ resistance of LECA® Lightweight Expanded Clay Aggregate makes it an ideal solution for reinforced soil retaining walls and bridge design. Particularly when constructed over weak sub-soils or voids, this method has been proven to cut overall construction costs considerably. LECA® Lightweight Expanded Clay Aggregate is used extensively to reduce vertical loading.

Reducing Earth Pressure

Structures such as underground parking, tunnels or roof garden benefit greatly from the reduction in pressure and avoid additional costs of strengthening. Being light weight and round in nature, LECA® Lightweight Expanded Clay Aggregate can be transported and placed more easily than that of traditional fill in these difficult to access areas.

Earth pressure of fill soil affects a supporting structure on a boundary surface between the supporting structure and earth. Supporting structures loaded by earth pressure include among others, retaining walls, sheet pile walls, back fill of bridges, basement walls, and foundations.

Minimise Earth Pressure

When Leca® Lightweight Expanded Clay Aggregate is applied to improve stability; the following design aspects shall be taken into account:

  • Properties of underlying subgrade and its loading history
  • Pore water pressure
  • Groundwater and/or perched water level and possible open  water level
  • Inclination of ground surface or soil layers and possible river bed located beside the structure
  • Required safety factor of structure against collapse
  • Highway Embankment Widening
     

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Sustainability with LECA

Environmental and sustainable issues which were probably not the main focus 75 years ago, is certainly a concern today in the modern world.