The Flat dilatometer is an in-situ device used to determine the soil in-situ lateral stress and soil lateral stiffness and to estimate some other engineering properties of subsurface soils. It is a relatively simple test and its use in geotechnical investigations becomes more and more common.

The FD equipment has application on:
icon Vertical drained constrained modulus M (all soils)
icon Undrained shear strength cu (in clay)
icon In situ coefficient of lateral earth pressure K0 (in clay)
icon Overconsolidation ratio OCR (in clay)
icon Horizontal coefficient of consolidation ch (in clay)
icon Coefficient of permeability kh (in clay)
icon Friction angle φ (in sand)
icon Unit weight γ and soil type (all soils)
icon Equilibrium pore pressure u0 (in sand).