Effects of liquefaction induced ground failure on bridges

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Liquefaction is process by which water-saturated, unconsolidated sediments are transformed into a substance that acts like a liquid which can undermine the foundations and base courses of infrastructure like bridges. It can cause serious damage. Liquefaction can be classified into two. They are Flow Liquefaction And Cyclic Mobility. Flow Liquefaction - Static shear stress exceeds shear strength of liquefied soil. Cyclic Mobility - Static shear stress are slightly less than liquefied shear strength, but static and dynamic stresses are greater than shear strength of liquefied soil.

Liquefaction Induced Bridge Damage

Lateral soil deformations (lateral spreading) have proven to be the most pervasive type of liquefaction-induced ground failure. Lateral spreading involves the movement of relatively intact soil blocks on a layer of liquefied soil toward a free face or incised channel. These blocks are transported down-slope or in the direction of a channel by both dynamic and gravitational forces. The amount of lateral displacement typically ranges from a few centimetres to several meters and can cause significant damage to engineered structures. Different effects on bridge are Ground Failure, Lateral Displacement, Settlement And Abutments Are Vulnerable To Seismic  Damage.

SOIL LIQUEFACTION - Caused by the loss of bearing capacity, lateral movement of substructure and dislodgement of super structure. For most bridges at river crossings subjected to medium to high intensity earthquake motions. Liquefaction is primararly cause reduced stability of earth structures, increased active pressures on abutments, loss of soil strength and the seismic inertia of the backfill and loss of passive soil resistance.

Lateral ground displacements have been extremely damaging to bridge foundations and abutments. Movement of foundation elements may create large shear forces and bending moments at connections and compressional forces in the superstructure. Subsidence and increased lateral earth pressures can also lead to deleterious consequences for bridge foundations. Waterfront retaining structures, especially in areas of reclaimed land, can experience large settlements and lateral earth pressures adjacent to bridge foundations. These movements lead to the rotation and translation of bridge abutments and increased lateral forces on pile foundations. 

A number of failure modes may occur in pile foundations, depending on the conditions of fixity, pile reinforcement and ductility. Generally, if concrete piles were well embedded in the pile caps, shear or flexural cracks occurred at pile heads, often leading to failure; if steel pipe piles were fixed tightly in the pile caps, failure was at the connection or pile cap; or if the pile heads were loosely connected to the pile caps, they either rotated or were detached.

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