Why an Earthquake Can't Destroy the Chenab Bridge?

Why an Earthquake Can’t Destroy the Chenab Bridge?

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The world's tallest rail bridge is built in the mountains of the Chenab River in India. The Chenab Bridge is located near seismic zone 5, one of the most earthquake-prone regions. Because of this, the bridge is designed to withstand an earthquake of up to 8.0 on the Richter scale. In this article, I will take you through the modern technologies that make this bridge earthquake-resistant.

The Role of Spherical Bearings

Did you know that the Chenab Bridge's rail deck is isolated from its substructure using spherical bearings(Fig. 1)? During an earthquake, the lower part of each bearing moves with the ground substructure, but this motion does not transfer to the rail deck. This isolation ensures that the rail deck and the train experience minimal impact from the earthquake.

Fig 1 : Spherical bearings isolate the rail deck from its substructure

Use of Expansion Joints

One question remains: how can the rail deck move relative to the piers if it is also fixed to the ground? This is where expansion joints come into play. Expansion joints allow the rail deck to move freely without significant resistance. Two expansion joints separate the bridge’s rail deck into three sections(Fig. 2), meaning the rail deck is not rigidly fixed to the ground. Instead, it rests on spherical bearings, allowing for controlled movement. Additionally, expansion joints help accommodate thermal expansion, preventing structural damage.

Fig. 2 : Expansion joints separate the rail deck into three pieces

How Did Engineers Stabilize the Mountains of the Chenab?

The mountain rocks in this area are not ideal for strong bridge construction, as they are primarily composed of dolomite. To stabilize the slopes, engineers used three techniques: grouting, anchor blocking, and shotcrete(Fig. 3).

Fig. 3 : Stabilization techniques - grouting, anchor blocking and shotcrete

Grouting

Fig. 4 : Grouting Stabilization technique

Anchor Blocking

Workers drill holes into the slope and insert special rods with multiple steel tendons inside. The rods are then grouted in place. Once the grout hardens, a block is placed on the rod. A hydraulic jack stretches the steel tendons to extreme tension. Even after removing the jack, a wedge system keeps the tendons under constant tension. The tendons try to contract, but the block prevents them from doing so, creating compressive stress that significantly increases the slope's stability(Fig. 5).

Fig. 5 : Anchor Blocking Stabilization technique

Shotcrete

After grouting and anchor blocking, engineers use a specialized machine to spray concrete onto the mountain rocks(Fig. 6). This shotcrete layer further strengthens the slopes, enhancing their stability.

Fig. 6 : Shotcrete Stabilization technique

The mountains now stable, engineers built the necessary foundation(Fig. 7), using straight steel piers to support the bridge's massive structure.

Fig. 7 : Foundation with straight steel piers

Because of these engineering techniques, nearby mountains may collapse during an earthquake, but the foundation of the Chenab Bridge will remain stable. The combination of spherical bearings, expansion joints, and slope stabilization ensures that this remarkable bridge can withstand even the most powerful seismic activity.

That's all for this article. Thanks for reading.