LIQUEFACTION

FAILURE OF FOUNDATION - STRUCTURE COLLAPSE

CLASSIFICATION

FLOW LIQUEFACTION

CYCLIC MOBILITY

Static shear stress exceeds shear strength of liquefied soil.

Static shear stress are slightly less than liquefied shear strength,but static+dynamic stresses are greater than shear strength of liquefied soil.

The risk to public safety.

2. The importance of the structure (lifeline, economic recovery, military).

3. The cost of the structure (capital investment and future replacement costs).

4. The cost of mitigation measures. The policy further specifies that, “All bridges should be evaluated for liquefaction and lateral spread potential and the possible effects of these conditions on the structure.” Consideration is given to the magnitude of the anticipated lateral soil deformation, the influence of piles on embankment deformations, and tolerable deformation limits of the structures under consideration. Close coordination between the geotechnical engineer and the bridge design engineer is required.

LIQUEFACTION-INDUCED BRIDGE DAMAGE Lateral soil deformations (lateral spreading) have proven to be the most pervasive type of liquefaction-induced ground failure (Youd 1993). 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 centimeters to several meters and can cause significant damage to engineered structures.

EFFECTS ON BRIDGE

GROUND FAILURE

LATERAL DISPLACEMENT

SETTLEMENT

ABUTMENTS ARE VULNERABLE TO SEISMIC DAMAGE

SOIL LIQUEFACTION

LOSS OF BEARING CAPACITY

LATERAL MOVEMENT OF SUBSTRUCTURE

DISLODGEMENT OF SUPER STRUCTURE

LARGE SCALE DEVELOPMENT - SEISMIC RISK

60% INDIA’S LAND HIGH SEISMIC ZONE

EARTHQUAKE

DAMAGE TO STRUCTURE

AFFECT SOCIAL & FINANCIAL STATUS

LOSS OF MANY LIVES

•For most bridges at river crossings subjected to medium- to high-intensity earthquake motions -liquefaction primary cause

•reduced stability of earth structures

• increased active pressures on abutments

•loss of soil strength and the seismic inertia of the backfill

•loss of passive soil resistance

impacts from liquefaction

Lateral ground displacements have been extremely damaging to bridge foundations and abutments.

2. 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.

5. 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.

PILE FAILURE