Case Study: Caisson Foundations – MOSE Flood Barrier, Venice, Italy (2012–2014)
Engineer: Technital | Contractor: GLF
System: Automated Grouted Fabric Formwork for Caisson Foundations
Locations: Malamocco & Lido San Nicolò Inlets
Project Overview
The MOSE Project is a major flood defence system designed to safeguard Venice and the surrounding lagoon from increasingly frequent tidal surges. Venice has historically suffered from acqua alta events—extreme high tides that regularly flooded the city. The devastating 1966 flood reached 194 cm above mean sea level, and by the early 2000s, tides exceeding 110 cm were occurring more than 60 times a year, threatening Venice’s infrastructure and heritage.
To protect against these events, the MOSE system was developed using a series of mobile steel flap gates housed within precast concrete caissons placed across the lagoon’s three main inlets. These caissons required highly stable and precisely levelled foundations to maintain gate alignment and performance. Each caisson measured up to 60 m in length, 48 m in width, and weighed around 20,000 tonnes.
Due to seabed variability, limited diver access, and the non-reversible nature of the works, a reliable, high-tolerance foundation system was essential. Proserve’s remote grouted fabric formwork was selected to meet these requirements through a controlled, surface-operated installation method.
Foundation Requirements and System Selection
The seabed consisted of dredged alluvium and a crushed stone working layer, with local undulations of up to 900 mm. Manual levelling or conventional concrete infill was not viable, especially given the need for speed, repeatability, and tidal flow constraints.
Proserve’s foundation system was selected for its ability to:
- Adapt to seabed irregularities without prior levelling
- Provide uniform, high-friction contact through tailored grout infill
- Allow fully surface-operated grouting, eliminating diver involvement
- Enable vent-controlled filling with real-time monitoring from the surface
This offered a low-risk, high-control foundation method suitable for large-scale marine structures.
Design and Development
The grout bag units were fabricated from grout-tight, permeable woven fabric, pre-fixed beneath each caisson and protected within PVC sleeves. Internally compartmentalised, the system allowed controlled expansion and conformance to the seabed.
Each unit was equipped with prefixed filler sleeves and upstanding vent pipes containing embedded sensors. These allowed surface teams to monitor grout rise and pressure throughout the fill process.
The parties carried out full-scale development trials in 2009, including:
- Bag expansion under pressure in simulated trench conditions
- Grout delivery verification with neat cement mix
- CFD modelling of tow and launch forces to guide restraint design
Full Scale Grout Bag Test Filling
Installation and Execution
Caissons were cast at the Malamocco yard, fitted with grout bags, and launched using a ship lift. After being towed to the inlet, they were positioned within pre-prepared trench beds and supported on temporary jacks.
Grout Bag Fitted in Casing Hard into Recess
The grouting process followed a controlled sequence:
- Surface-mounted grout pumps delivered neat cement grout into each compartment
- Vent sensors triggered shut-off once full contact was confirmed
- A typical caisson was filled over a two-day period, without diver intervention
The system’s design allowed uplift to be controlled, washout to be avoided, and full base contact to be assured across complex seabed profiles.
Filling from Floating Barge
Project Outcome
The grout bag system performed reliably across all installations at both the Malamocco and Lido San Nicolò inlets with 719 grout bags fully filled. Full grout contact was achieved beneath each caisson, with vent feedback confirming uniform filling and no signs of overpressure or blowout. The foundations supported precise caisson placement and maintained the tight tolerances needed for long-term gate alignment.
Since activation of the MOSE system in 2020, Venice has remained protected during several high tide events that would have historically flooded much of the city. Notably, in November 2021 and again in December 2022, tides exceeded 130 cm but were fully held back—demonstrating the functional success of the gates and the foundational role played by the caisson support system.
Key outcomes:
- Full surface-based installation with no diver dependency
- Foundation tolerances met across multiple large-scale units
- Long-term structural stability established in difficult conditions
- Successful contribution to the ongoing protection of Venice from tidal flooding
The project reinforces the capability of Proserve’s automated fabric formwork to deliver repeatable, engineered foundation solutions in some of the world’s most sensitive marine environments.