THE EVOLUTION OF FOUNDATIONS FOR OVERWATER BRIDGES

By: Ben Gerwick∗

Abstract

This paper will present a brief overview of the historical evolution of foundations

for overwater bridges from the 3,500 years old “wells” in India to the Roman cribs and

cofferdams to Caesar’s piles bridges across the Rhine. This will continue through the

medieval bridges of the Renaissance to the early pneumatic caissons and timber sheet pile

caissons. The modern period has its steel sheet pile cofferdams and tremie concrete, open

caissons, box caissons, belled piers and gravity-base structures, slurry wall cofferdams,

drilled shafts and large diameter tubular piles. Most recent in the series are the piled raft

GBS piers employed for the Rion-Antirion Bridge in Greece. From this history, an

evolutionary trend can be discerned which portends continued creativity.

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The construction of bridges, with their foundations and superstructures, began at

the dawn of history 4,000 years ago. More than fifteen hundred years BCE, the people of

northern India faced with the need to provide year-round transportation across their

seasonally-flooding rivers, extended the art of wells to bridge piers. They are still being

constructed, working in the dry season or from sand islands and they are still called

∗ Honorary Member, ACI. Senior Technical Consultant, Ben C. Gerwick, Inc., San Francisco.

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“wells”. Instead of brick circumferential wells and sinking by diver excavation in

buckets, they are today constructed of reinforced concrete and excavated by cranes with

clamshell buckets. However, backfill is still performed by human labor, mostly women

with the sand carried on their heads.

Concurrently the Babylonians constructed a bridge across the Tigris River with

foundations of large stones set in an excavated hole.

The great worry of those days was scour during flood and the tradition arose that

a human life must be sacrificed to appease the river God.

This barbaric tradition continued at least to the Roman era about 400 B.C. when a

human was sacrificed to the God of the Tiber River.

The Romans were the great Road and Bridge Builders. They developed crude

crib-like cofferdams, two parallel walls of timber filled with clay to enable them to place

pozzolanic concrete footings below water, on which to construct their magnificent stone

arches. The office of Pontifex Maximus, meaning Great Bridge Builder, was conferred

on the Chief Priest and became the highest honor in the Republic.

Caesar, invading Gaul, built a highly successful piled timber trestle across the

Rhine, using battered piles for the first time to resist the lateral force from the river. As

Emperor, he appropriated the name, Pontifex Maximus. Later, the name was given to the

Pope, a tradition which continues today.

In the Dark Ages which followed, there was a hiatus - little new was developed.

Then with the Renaissance came a flurry of activity. The art of piledriving was advanced

in Northern Italy and The Netherlands. But not until the 1700s were there any

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meaningful innovations. Then in the latter half of the 18th Century, a very sophisticated

form of construction was developed, the pneumatic caisson. This was used by Eads to

build his famous bridge across the Mississippi and by Roebling for the Brooklyn Bridge.

The story of the tragic toll on workmen is most colorfully described in McCullogh’s book

“The Great Bridge”. Pnuematic caissons, using robot excavators, were used on the new

Rainbow Suspension Bridge in Tokyo.

A pivotal development in 1910 was the use of the French process “tremie

concrete” on the Detroit River Subaqueous Tunnel. With significant improvements in

World War II and subsequently, the placement of high quality structural concrete

underwater has now become a practical reality. It has been utilized on the piers of major

bridges.

The great bridge building era in New York saw the use of the Open Caisson, a

system which has also been extensively employed on the Mississippi and concurrently is

being utilized on the Second Tacoma Bridge.

Large diameter steel cylinder piles have recently come into use to enable major

bridge piers in deep water and difficult soils to be constructed more safely, rapidly and

economically. These were employed on the Jamuna Bridge across the Brahmaputra

River in Bangladesh and are currently being used on the San Francisco Bay Bridges, both

the new Benicia and East Bay Bridges, and the Seismic Retrofit projects, as well as the

Woodrow-Wilson Bridge across the Potomac.

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This concept is being extended with a large diameter, cast-in-drilled-shaft pile, in

which a deep socket is drilled using slurry and heavy reinforcement cage and high

performance tremie concrete is placed.

The most recent decades saw the development of the steel box caissons for the

bridges across the Inland Sea in Japan, culminating with the Akashi Kailkyo Bridge, the

world’s longest span. Shortly afterward, concrete offshore platforms were developed for

offshore oil application. These gigantic box caissons are now being completed for the

piers of the Rion-Antirion Bridge across the Gulf of Corinth in Greece, which also

incorporates the concept of the pile-supported raft.

Meanwhile, cofferdams began to be extended more deeply using Wakefield

timber sheets, laminated from 3 planks and joined tongue and groove. Soon after steel

sheet piles and bracing were evolved and continue today as standard for shallow and

moderate-depth piers. The steel today is stronger and the sections now are configured to

give a higher Section Modulus, hence enabling the cofferdam to resist greater hydrostatic

heads. Cofferdams 80 feet deep are being built today on the Mississippi and tributaries.

Most recently, slurry wall cofferdams, circular in plan, have been used for very

deep water and weak soils – such as the Kawasaki Ventilation Structure in Japan. They

are planned for the anchorages of the Messina River Bridge between Sicily and Italy.

So there we have it –

• It took 2,000 years after civilization began for the first fixed bridges to be built on

piers of large stones and wells sunk in deep sands.

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• Another 1,000 years and we see the stone arches evolve along with shallow crib

cofferdams and timber pile trestles crossing rivers.

• We inexplicitly wait through the Dark Ages. Another 1,000 years before the

innovation of the pneumatic caisson.

• In the next century, the deep open caisson of steel and concrete are employed for the

great suspension bridges and the use of steel sheet pile cofferdams becomes the

standard for lesser bridges.

• Now, in only a few decades of our new era, we’ve seen an exponential growth, the

piles of steel and prestressed concrete and cast-in-drilled shaft concrete piles.

• The spectacular development of concrete offshore platforms in the North Sea has been

utilized for deep water bridge piers also, culminating in the Rion-Antirion Bridge in

Greece.

Is this the peak, the end point of historical development?

Certainly, the answer based on recent history, has to be a resounding “No!”. The

future is bright with creative engineers, exploring new possibilities for future bridges.

New materials such as Very High Strength Concrete, fiber-reinforced tremie concrete,

and advanced equipment, hydraulically-operated equipment and robotics will play a

major role in future bridges.

Technology is expanding our ability to deal with earthquakes, ship collision, and

wind dynamics. Soil structure interaction is being employed even more widely.

Prefabrication not only reduces the on-site labor but enables more sophisticated and

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higher quality structures to be achieved. Fibers and admixtures can potentially improve

our capacities in tension, compression and shear.

As to applications, these are the responses to the demands of deeper water, ever

larger and faster ships and submarines which can impact our piers and the opportunities

for floating structures.

So rather than regarding today’s achievements as a culmination, it presages to be

the dawn of a new round of evolution by which our bridges will be able to span hitherto

impassable straits such as Messina and Gibraltar, and then on to as yet undreamed of

crossings.

10/13/04

ACI “HISTORY OF BRIDGES” Title List : Pictures to accompany paper by Ben Gerwick – “Evolution of Foundations of Overwater Bridges” 1. 2.5m dia. steel tubular piles being driven for foundations of Jamuna River

Bridge, Bangladesh 2. Largest North Sea pile hammer being used to drive piles to 80m depth for

Jamuna River Bridge, Bangladesh 3. Tubular steel sheet pile cofferdam for Airport Access Bridge – Inchon, Korea 4. Rion-Antirion Bridge, across Gulf of Corinth, Greece is founded on gravity-

base structures bearing on piled-raft foundations at 70m depth. 5. Schematic of piled-raft foundation 6. Kawasaki Island concrete slurry diaphragm wall is 100m dia. ring extending

to -120m, then excavated to -80 - Trans-Tokyo Bay Highway 7. Steel box caissons form deep foundations for world’s largest Suspension

Bridge - Akashi Strait, Japan 8. Proposed gravity-base piers for 500m deep site in center of Strait of

Gibraltar

1. 2.5mm dia. Steel tubular piles being driven for foundations of Jamuna River Bridge, Bangladesh

2. Largest North Sea pile hammer being used to drive piles to 80m depth for Jamuna River

Bridge, Bangldesh

3. Tubular steel sheet pile cofferdam for Airport Access Bridge – Inchon , Korea

4. Rion-Antirion Bridge, across Gulf of Corinth, Greece is founded on gravity-base structures bearing on piled-raft foundation at 70m depth.

5. Schematic of piled-raft foundation.

6. Kawasaki Island concrete slurry diaphragm wall is 100m dia. ring extending to 120m,

then excavated to -80- Trans-Tokyo Bay Highway

7. Steel box caisson form deep foundation for world’s largest Suspension Bridge – Akashi Strait, Japan

8. Proposed gravity-base piers for 500m deep site in center of Strait of Gibraltar