A standard inclinometer or plain tube is securely fixed in the element to be monitored, i.e. a pile, diaphragm wall or soil mass.

A series of individual electro-levels (ELs), [precise tilt sensors], are mounted on carriages and positioned at known intervals inside the tube. The monitoring axis of the ELs must be in the plane in which the movements are required.

In piles or diaphragm walls the tube would be mounted vertically, in a soil mass or dam it could be at any angle.

Deflection of the tube and hence the structure it is fixed to can be determined by either summing the movement determined from each EL,

= the change in angle monitored, and L = the length over which it applies.

Alternatively a polynomial can be fitted to the slopes and the deflection determined through integration of the polynomial.

The ELs monitor change in slope that can be integrated to determine deflection. y = s + C. Where C is the constant of integration determined from known end conditions, fitting a polynomial to the slopes allows the following to be determined:

Bending Moment = ds/dz x EI
Shear Force = d2s/dz2 x EI
Soil reaction = d3s/dz3 x EI