Venice, also known as the “floating city,” is located in northeastern Italy and is characterized by a network of canals and fine palaces. Unlike other European cities, Venice’s buildings and monuments are entirely constructed on water, giving tourists the impression that the city is floating. The historical city is composed of around a hundred small islands, and buildings are built closely together, emanating from the water.
Canal in the city of Venice
Construction of Venice began in 421 AD on marshy lands, with an island created for building construction. The Barbarian invaders were the driving force behind the formation of the island, as the people of northern Italy were fearful of them. To limit the invaders’ reach, the idea of developing a city enclosed by water was conceived.
Pile foundation of the house in Venice city
Venice is a popular tourist destination and a UNESCO World Heritage Site, with visitors from all over the world flocking to see its canals, landmark buildings, and art-filled churches. The city’s unique foundation system, considered a marvel in civil engineering, is entirely responsible for its creation. In this article, we will focus on the design details and materials used to construct the foundation of Venice city, which has contributed to its worldwide fame.
1. Geology of Venice City
The Venetian lagoon, where the city of Venice was built, was formed due to the tectonic movement in the Eurasian and African plates during the Mesozoic Era. This movement also gave rise to the Adriatic Sea and the Alps mountains. The lagoon was shaped by marine deposits, melting of ice, and multiple tectonic movements. The depth of the lagoon is only 2 meters above the water level, which makes most of the land in Venice marshy.
The foundation of Venice city is made up of various materials, including clayey soil, lime-clay, sand, partially consolidated sandy-clay, and limestone, among others. Between the pavement level and a depth of 5 meters, the soil consists of sandy-clayey silts, locally medium to fine sand with silt. The foundation also contains masonry debris, trachyte blocks, wooden piles, and unreinforced concrete of varying thicknesses.
At a depth of 6 to 7 meters from ground level, a layer of soft sandy clayey silt, silty clay with organic debris, and peat is present. The compressive strength of these soils is generally between 1.0 to 2.0 MPa. From 7 to 10 meters depth from ground level, medium to fine sand with medium to high compressive strength is found, with values ranging from 7 to 15 MPa. Beyond a depth of 10 meters, an alternation of silty clay, clayey silts, and silty sands is present.
The city of Venice is located on 118 islands in the Venetian lagoon of the Adriatic Sea. The city’s foundation and geology are shaped by the tectonic movements, marine deposits, and melting of ice in the region. Due to the shallow depth of the lagoon, most of the land in Venice is marshy. The foundation of the city consists of various materials, including clay, lime, sand, and concrete, with layers of soft sandy silt and peat found at different depths. Beyond 10 meters, there is an alternation of silty clay, clayey silts, and silty sands.
2. Materials Used for the Construction of Venice City
During the initial phase of the development of Venice city, two proposals were considered for creating the foundation base. The first proposal suggested using large marble stones, but it was rejected due to the unavailability of materials and concerns about potential settlement of soil beneath the foundation. The second proposal involved driving timber into the foundation to create a stable base. Timber was abundant and readily available from the mainland of northern Italy. Specifically, water-resistant timbers such as elm, oak, poplar, and alder were brought from the forests of the mainland. These timbers were used to construct a platform for the foundation base in the ancient buildings of Venice city.
Pencil shaped piles used in the foundation of Venice city
Timber was a versatile building material that found widespread use in various architectural elements beyond just pile foundations. It was commonly employed in the construction of roofs, floors, doors, frames, and furniture. The extensive utilization of timber was evident in almost all architectural features, showcasing its versatility and durability as a preferred choice for a wide range of applications. Whether it was for structural support or aesthetic design, timber played a prominent role in shaping the built environment, with its utilization spanning across different aspects of construction and design. From providing sturdy foundations to adding aesthetic appeal, timber was a key component in the construction industry, contributing to the functionality and aesthetics of various architectural elements. Its widespread use was a testament to its versatility, availability, and durability, making it an integral part of architectural practices in many different regions and time periods.
Use of limestone blocks in the foundation of Venice city
In addition to timber, crushed stone and limestone were commonly employed in the construction of buildings for specific purposes. Crushed stone was utilized to fill the gaps between piles, preventing the accumulation of sediments and ensuring stability. Meanwhile, limestone blocks were used to create a sturdy platform above the timber piles, providing a solid foundation for the structure. As for the superstructure, bricks and stones were commonly utilized in the construction of the walls and other above-ground elements of the buildings.
3. Foundation Construction Methodology
Venice, the city built on water, has a foundation constructed using a unique methodology. The first pile driving program began in 421 AD, where piles were driven into the muddy sand until they reached the bottom of the Venetian lagoon floor. These piles were shaped like pencils, with the bottom end providing point resistance to cut through the sediments of muddy sand. The length of the piles varied between 4 to 8 meters, with an average of 6-12 piles provided in 1 square meter area. The diameter of each pile was in the range of 10 to 30 cm, and different hammers were used to install the piles into the soil.
The piles were selected in such a way that they could easily penetrate the layer of loose muddy sand and reach the layer of compressed clay for better frictional resistance. Without this frictional resistance, the structures built above the pile foundation would have sunk and collapsed. However, the installation of piles into the soil was a costly and labor-intensive task, taking more than a month to construct a single building.
Once the piles were installed at the top level, they were cut horizontally to form a leveled platform for the foundation base. Crushed stones and stone debris were filled between the piles to prevent soil erosion, and limestone blocks were layered on top of the piles base. These blocks acted as a subfloor and provided support to resist the massive superstructure load.
One of the most significant pile driving programs was performed for the construction of San Zaccaria, a church in the center of Venice. This church was built in the mid-1400s, and around 7000 piles were installed into the ground, with 6000 wooden planks used in its construction. The piles were delivered in two stages for its construction as enough area was not able to stock the piles around the church site. All the piles were installed at a close spacing, ensuring that the top of all the piles formed a stable base.
Researchers suggest that there are around 40,000 to 80,000 timber piles beneath the two major islands (Venezia and Murano) of the city. The overall density of the piles in these islands is around 1.35 to 2.75 piles per square meter. As the area of the Venice city is around 5,909,000 square meters, there would be at least 11 million timber piles below the city if the pile density is taken around 2 piles per square meter.
4. Modern-Day Foundation Construction in the Venice City
Venice is home to many historic buildings and monuments, most of which were constructed after the 16th century. However, older buildings are now becoming unstable and difficult to maintain, leading to the demolition of many of these structures. Despite this, the wooden pile foundations of these older buildings are still intact and are often reused in the construction of new buildings. By reusing existing foundations, significant amounts of money, material, and time can be saved.
When constructing new buildings, additional piles are added to the existing foundation if the building’s footprint changes or if there is a significant increase in superstructure load. The San Marco tower is a prime example of this methodology, as it was built on the foundation of a building that was destroyed by fire in 1485. However, the wooden piles were still able to support the new tower without any remediation or rehabilitation. These existing wooden piles are capable of withstanding fires, adverse weather conditions, and massive superstructure loads.
The use of wooden foundation in the development of Venice’s 118 islands is a testament to the city’s civil engineering marvel and resilience. However, the foundation industry has since progressed, and new buildings in Venice are now constructed using reinforced concrete piles. These concrete piles have a greater compressive and uplift capacity than wooden piles, occupying the same surface area. Nonetheless, Venice’s construction methodology using wooden piles continues to inspire and teach us valuable lessons.
FAQs
Which is the world’s largest floating city?
Venice is known as the biggest floating city in the world.
Why is Venice city famous in the world?
Venice is a popular destination for tourists from all corners of the globe. The city is known for its stunning canals, which are a major attraction for visitors. People come from far and wide to take a boat ride along the canals, enjoying the picturesque views and unique atmosphere of this beautiful city.
One of the most notable features of Venice is its architectural landmarks. The city boasts a wide variety of historical buildings, each with its own unique style and character. Visitors can marvel at the stunning architecture of the Doge’s Palace, St. Mark’s Basilica, and many other iconic structures that have stood the test of time.
For those interested in art and history, Venice is also home to many impressive churches that are packed with beautiful works of art. These churches are not only places of worship but also cultural treasures that showcase the rich history and artistic heritage of the city.
In short, Venice is a city that has something for everyone. Whether you’re interested in architecture, art, history, or just want to experience the unique atmosphere of this beautiful place, there are plenty of reasons to visit and explore all that it has to offer.
Why were wooden piles used in the foundation of Venice city, especially in the marine environment?
The wooden piles had been completely submerged in water, with no part of them visible above the water’s surface. As a result, there was no opportunity for the wood to come into contact with the air or oxygen. This lack of exposure meant that the decomposition of the wooden piles by bacteria and fungi was highly unlikely to occur.
What is the reason behind the strong foundation of Venice city?
Venice, the historic city built on a group of small islands in northeastern Italy, has a unique foundation made of wooden piles. These piles were driven deep into the muddy lagoon floor and serve as a base for the city’s buildings and structures. Over time, the timber piles have undergone a petrification process due to prolonged exposure to seawater. This process has transformed the wooden piles into a hard stone-like material that has helped to preserve the ancient buildings of Venice. As a result, many of the historic structures in the city still stand today, despite the challenges of being located in a watery environment. This petrification phenomenon has helped to protect and maintain the cultural heritage of Venice for future generations.