Countermeasures for Uneven Settlement such as Jacking-Up - Technologies for Offshore Airports(4) -

If the land settles uniformly, there is no impact on airport facilities. However, in cases of differential settlement, where the amount of settlement varies by location, structural distortion can occur. Buildings are particularly susceptible to differential settlement, and even slight variations can cause serious problems. Therefore, Kansai International Airport has implemented the following countermeasures.

Jack-up System

The jacking-up system is a mechanism used to correct slight tilting of a building caused by differential settlement. Each column of the structure is individually lifted using jacks, and steel plates are inserted to adjust and restore the building's level alignment.

Impact of Constructing a Basement

The central main building of the terminal, which is one of the most prominent structures at the airport, contains a large basement. To construct this basement, it was necessary to excavate soil. However, since the weight of the building was expected to be lighter than the weight of the removed soil, iron ore was placed beneath the main building as ballast to compensate for the difference. Even so, the central main building remains slightly lighter than the surrounding sections. As a result, the central main building has settled less than the surrounding areas, causing a slight incline between the main building and the side wings. To correct this, jacking-up was performed to level the floor.

Automatic Monitoring System

The first terminal building has 900 columns, and the settlement of each column is measured using an automatic monitoring system. Based on this data, the columns that need jacking-up are identified, and operations are carried out accordingly.

Regular Jacking-up Operations

Currently, as ground settlement has gradually stabilized, differential settlement has also decreased. The resulting tilt is now so slight that it is no longer visible to the naked eye. However, jacking-up operations are still carried out every few years as a precaution.

A three-stage diagram showing a process that uses a jacking system to correct uneven building settlement. In the initial state, the passenger terminal building sits horizontally on the ground. In the differential settlement process, the ground sinks unevenly, causing the center of the building to sink more than the wings on either end and the building to become curved. In the state of completed correction, the entire building has been lifted up using jacks and restored to a horizontal position.

Basic concept of the jack-up system 1

A three-stage diagram showing a technical process of jacking up a building column.In the diagram on the left, the building's column is on pile foundation. In the diagram in the center, a hydraulic jack is used to lift the column, creating a gap, into which steel plates are inserted. In the diagram on the right, the construction work has been completed, with the hydraulic jack removed and the column securely elevated by inserted steel plates.

Basic concept of the jack-up system 2

A graph showing the uneven settlement of the passenger terminal building and the effectiveness of jacking up as a remedial measure. The top is a schematic diagram of the terminal building (south wing, main building, north wing), and the graph below it corresponds to the location of the building, with two curves showing the state of subsidence. The amount of uneven settlement is indicated by a red line. The foundation of the building has sunk unevenly, with the south wing in particular sinking the deepest. The first-floor level is indicated by a blue line. The floor has been raised by jacking up in response to the settlement indicated by the red line. The blue line shows that the floor has been corrected to be almost level.

Measures against unequal settlement under the passenger terminal (as of December 2007)

A worker is carefully inserting height-adjusting steel plates one by one by hand into the gap on the foundation of a jacked-up building.

How the pillar under the passenger terminal is jacked up

An enlarged view of a worker carefully inserting each height-adjusting steel plate by hand.

Other Various Countermeasures

Countermeasures other than Jacking-up

If the overall weight of the island remains uniform, it helps minimize the potential for differences in ground settlement.
Therefore, in addition to jacking-up, Kansai International Airport implemented the following countermeasures during the initial construction phase.

Specific Measures

Raft foundation A construction method in which a concrete foundation is placed directly on the ground. This method has the characteristic of allowing the entire structure to settle uniformly in the event of differential settlement.
Compaction of the reclaimed layer Ground compaction was carried out on the 30-meter-deep reclaimed ground to prevent compression during earthquakes.
Adjusting the balance through soil removal To minimize the load difference between the building and the surrounding ground, soil volume was adjusted as necessary.

As a result of these comprehensive countermeasures, the settlement on Phase 1 island is now primarily attributed to the deep and uniform subsidence of the diluvial layer.
As a result, differential settlement causing operational issues has been minimal at essential facilities such as runways and taxiways.

Technical Initiatives (Related Links)