To prevent Big Ben from tilting further during London Underground construction, engineers injected 122 cubic meters of grout, keeping the tower's tilt within 10 millimeters over 21 months.
Grout injections to stabilize Elizabeth Tower
From January 1996 to September 1997, 24 injections of grout totaling 122 cubic meters of cement, sand, and water were carried out to prevent the Elizabeth Tower from tilting further. This work was part of the construction of the Jubilee Line extension at Westminster Station, which was built directly beneath the tower.Construction site location and impact
The construction of Westminster Station took place from January 1996 to September 1997, and involved excavating a 39-meter-deep hole 34 meters from the Elizabeth Tower. This deep excavation loosened the surrounding ground, causing the tower to tilt slightly toward the station.Monitoring the tilt
The tilt of the Elizabeth Tower was maintained between 15 and 25 millimeters at a height of 55 meters. This was a critical parameter, as excessive tilting could have damaged the connection between the tower and the Palace of Westminster. Several independent measurement systems were used to continuously monitor the tilt.Previous causes of tilt
A parking lot had already caused the tower to tilt. The underground parking lot of New Palace Yard, 18 meters deep and located 16 meters west of the tower, had caused a tilt of approximately 1/4000. This was a small but measurable displacement, similar to the lower threshold of 15 millimeters later set for the station.Compensation injection technique
The process of stabilizing the tower involved compensation injections. Holes were drilled under the foundations of tubes approximately 50 meters long, and a grout mixture of cement, sand, and water was injected into them. This technique slightly lifted the ground to compensate for its settlement, similar to using a jack to lift a vehicle.Precision and effectiveness of the work
The 24 injections took place over 21 months and prevented the tower from tilting by at least 120 millimeters. This figure is a minimum calculation at the level of the clock face, located at a height of 55 meters. The injections were done in real time, allowing for immediate adjustments.Historical significance of the tower
Big Ben actually refers to the large bell inside the Elizabeth Tower, which is officially called Elizabeth Tower since 2012. The tower is 96 meters tall and naturally tilts toward the northwest. Engineers did not aim to straighten the tower but to manage an existing slope within a tight tolerance range of 10 millimeters.
