Liquefaction and lateral spreading

Liquefaction occurs as a result of an increase in pore pressure caused by shear and shaking of water saturated sands. When these are overlain by an impervious layer the liquefied sand/water mix is ejected under pressure and will bubble and fountain for minutes or hours following an earthquake, starting several minutes after the passage of seismic surface waves.

Lateral spreading occurs as a result of a sideways lurching motion of the layers above fluid-saturated sediments. The surface spreads sideways especially if unconfined by lateral supporting bedrock.

The examples shown occurred on fill materials overlying sands. No liqefaction was found in sediments inland but no search was made for these.

Harbour Damage

In construction 24 january. Check back later.

 

Liquefaction and lateral-spreading were documented at the harbour and at a small fishing wharf 3 km to the north of the container unloading harbour. In the container dock the north-facing harbour wall has collapsed into the sea taking with it one small mobile crane, and leaving a second tilted at a steep angle to the south in the harbour.

Fishing wharf

No damage to the wharf occurred but the approach road contains 3 or more 20-m-long lateral fissures with no sign of sand venting. One in ten structures had collapsed on the road through Cite Soleil, but most of the strucures were single story concrete frame.

Container docks north side

Two cranes are now partially submerged and 3 containers have been tipped into the sea. Lateral spreading has extended the foundation support piers of a steel frame warehouse by at least 30 cm. The harbor wall has subsided in places 1 m and in others has toppled seaward. Numerous containers are tumbled and dented. A fire hydrant protrudes 20 cm above its former surface level.

Piled high containers and coils of steel wire have fallen into the dock. View SES from main container dock towards Port au Prince.

Lateral spreading. Three cracks (many more to te north not seen) lead toward warehouse (view west). The warehouse supporting-foundation has drifted 85 cm to the south (left) along with supporting concrete piers. The steel supports have been bent along with corrugated steel wall. The sea wall has subsided into the harbor. Local sand venting can be seen (white patches) over oil-covered tarmac. The surface has subsided 50 cm and a crane has fallen into the sea to the south. A container is about to fall to join two others in the harbor (in the distance).

This sand vent measures 2m x 3m and the tarmac crust through which it erupted has collapsed into the hole after venting ceased. A fine grey silt surrounds the rim with outgoing flow marks. Ponding to 15 cm above the original surface over an area of 7 m radius occurred. Nearby tilted containers indicate that the surface probably subsided by this amount as venting occurred.