When a rigid soil, embedded in sand, starts moving parallel to its original position under action of a horizontal force, it transforms soil on one side to passive state and or side in to active state.

An advantage of pneumatic caisson is that entire process of sinking well is carried out under controlled conditions and it affords easy inspection work.

It is desirable to insert wooden sleepers below cutting edge at regular intervals so as to distribute load and avoid setting of cutting edge unevenly during concreting.

The caissons are of three types: i) Box caissons ii) open caissons iii) pneumatic caissons.

According to IRC code, it is recommended that minimum depth of embankment below scour level should not be less than 2.0 m for piers and abutment with arches and 1.2 m for or types of structures.

Factor m, called coefficient of horizontal soil reaction depends on nature of soil, size and shape of area which carries load.

As a precaution to avoid tilts and shifts, radius of curb should be kept 2 to 4 cm larger than outside radius of well steining.

Strutting well method is used to avoid any furr increase in tilt of well rar than rectifying it.

The unit skin friction increases with depth, and at a given depth, skin friction is equal to coefficient of friction ? times lateral earth pressure.

The inside shuttering of well curb is generally made of brick masonry built to proper profile and plastered and outer shuttering is made by wood or steel.