To meet that goal, construction crews injected what is called 'compensation grouting'-a mix of cement, sand, water and other components-into horizontal tubes drilled into the clay under the clock tower's foundation. Burland, however, prefers to talk in angles and gradients: 27.5 millimeters over 55 meters is a gradient of one in 2,000. 'We're detecting movements to an accuracy of 10 millimeters daily.'ĭuring the extension work, the goal was to keep the tower from tilting more than an additional 27.5 millimeters over the length of the 55-meter span between the ground and the center of the clock face. A second surveying instrument, an optical plumb, now makes it possible to look up a vertical line from the tower's base to a target behind the clock. Inside Big Ben's tower, a permanent automated plumb line-simply, a weight suspended on a string that serves as a vertical reference with which to compare the tower's angle of tilt-provides real-time measurements of its movement. The technology to manage building movements has become very precise. The world's major cities have nowhere to expand but downward. Burland also served in the early 1990s on a commission to stabilize the Leaning Tower of Pisa and, he says, now spends a lot of time on other projects that require building underneath sensitive, priceless buildings in built-up areas. He was called in to ensure its stability both when the Westminster station was reconstructed and extended downward to a depth of nearly 40 meters as part of the Jubilee Line Extension project and during the construction of a nearby underground parking lot in the 1970s. It bends with the weather and the time of year,' says John Burland, an emeritus professor at Imperial College London.īurland has a long, intimate history with the clock tower. No building is ever completely still: they expand, contract and sway in response to the sun and wind, and they tilt and move when the ground underneath them shifts. In fact, the builders took careful steps to ensure Big Ben's stability.

What most did not know, however, was that rumors of the tower's doom, like Mark Twain's death, were greatly exaggerated a reporter misread the final report on the extension's construction and its impact on the tower, which was filed in 2009 and released last year under the U.K.'s Freedom of Information Act. Locals instinctively blamed the London Underground's Jubilee Line Extension, which opened in 1999 and sends trains rumbling under the tower and the Palace of Westminster. Next time change is highlighted.In December 2011 British newspaper headlines warned that London's Big Ben was about to topple over. Time Changes in London Over the Yearsĭaylight Saving Time (DST) changes do not necessarily occur on the same date every year. Some other countries, such as Ireland, observe the same local time, but under a different name. The UK is the only country that observes BST in the summer. What About BST?ĭuring Daylight Saving Time, clocks in the United Kingdom are set forward one hour to British Summer Time (BST). Until 1972, time zones were defined by their offset from GMT based on mean solar time at the prime meridian in Greenwich near London. GMT is a time zone used in the UK and other European and African countries.Ī source of confusion is that GMT used to be the world's time standard before UTC was introduced.Since GMT has a UTC offset of zero, there is no time difference between the two.

Time zones are defined by their offsets from UTC.

UTC is a time standard that forms the base of time zones worldwide and is not used as a time zone in any country.However, there is an essential difference between the two: In practice, GMT and UTC share the same time on a clock, which can cause them to be interchanged or confused. London uses Greenwich Mean Time (GMT) during standard time and British Summer Time (BST) during Daylight Saving Time (DST), or summer time. The graph above illustrates clock changes in London during 2022. Business Date to Date (exclude holidays).

Big clock in london