Soil improvement of runway strip and runway end safety area (RESA) through an innovative methodology

National and international regulations define requirements for bearing capacity of runway strip and runway end safety areas. Bearing capacity requirements imply the reduction of damages to an overrunning aircraft, facilitating its deceleration and allowing the easy access of emergency vehicles. In particular, international regulations from ICAO impose a maximum sinking of the aircraft nose landing gear into the soil. Hence, any functional and structural intervention in such areas should take into account this goal. Furthermore, interventions in airports infrastructures should imply minimum interference to airport activities and should comply with sustainability and environmental requirements. In this context, an innovative methodology, called "Controlled Compaction Energy Approach" was developed to stabilize soils in situ. The innovative approach does not have as main goal the maximization of density and bearing capacity as is usually the goal in traditional in situ stabilization procedures; the achievement of regulation requirements is based on the control of the compaction energy applied after stabilization, in order to develop only the required bearing capacity to obtain a surface that is not too stiff to be able to dissipate enough aircraft energy. The compaction energy needed strongly depends on different variables, such as the interstitial voids and water content and the amount of binder. A full scale test area was developed in order to set up the technique; afterwards, a real scale application of the method was carried out at Linate Airport of Milan (Italy) within the functional requalification of the runway end safety area (RESA). Such RESA is currently under operation for about two years.