Three basic ways sof installing plates in tunnels or shafts are illustrated here; each has its advantage in a particular application or ground condition.
Liner Plates Only
The most obvious advantages of this structure are that maximum support per foot of tunnel is obtained with minimum weight of steel. Liner plates, properly grouted or backfilled as tunneling progresses, form a dependable structure in either cohesive or non-cohesive ground. Liner plate structures generally require no additional support in tunnels up to 14 feet in diameter.
Ribs Inside Liner Plates
To give extra support to a liner plate structure in large diameter or heavy load conditions, ribs can be added inside the ring. Liner plates then act as lagging and are normally lighter in gage.
This additional support usually requires an increase in the diameter of the driven bore to maintain the dimensions of the finished inside diameter. This method is often used in shaft construction.
Liner Plates Between Ribs
This type of structure is less common than ribs inside liner plates because it is harder to erect. It does offer a practical trade-off under certain tunneling conditions.