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It's time to study the Vulnerabilities posed to Taj Mahal's foundation

Visual stress in the Taj Mahal

Published on 21 October 2011

Author(s): TwoCircles.net/Misbahuddin Mirza

Type:  News

The British Daily Mail’s article on the anticipated collapse of Taj Mahal in the next five years, due to its rotting wooden foundations, has put this seventh wonder of the world back under the spotlight.

The reported signs of visual distress in the tomb and minarets were immediately dismissed by the Archeological Survey of India (ASI), with an unidentified ASI official stating "We did not find any signs of stress or cracks." Some even called Agra’s Indian Member of Parliament Mr. Ramshankar Katheria’s statement to the Daily Mail as a mere publicity stunt. ASI’s statements in UNESCO documents detail the steps being taken to monitor and maintain the Taj Mahal, including the monitoring of glass strain gauges on cracks.

Regardless of the Daily Mail’s reported “Cracks appeared last year in parts of the tomb, and the four minarets which surround the monument are showing signs of tilting,” there still appear to be several valid reasons for urgently conducting a comprehensive Geotechnical Survey.

The Times of India reported that during 1987, a UNESCO-backed experts committee of B.M. Feilden and P. Beckmann expressed concern about the dearth of information about the Taj Mahal’s foundations and the nature of the sub-soil. "In a building of this supreme importance to the world cultural heritage, it is essential to have full knowledge of the foundations and the soil to assess the effect of possible changes in the sub-soil and water regimes such as industrial water extraction and the consequences of seismic activity," the committee's report said.

While a lot of information about Taj Mahal’s superstructure is readily available, the same cannot be said about the substructure. Information from sources such as archnet.org indicates that the foundation consists of well foundations spaced at 3.75 meters on centers, and that these “worked as pile foundations, and functioned even through the devastating floods of September 1978, when the water level of the river reached the mausoleum's platform.”

The Daily Mail’s statement quoted historian/Professor Ram Nath, a leading authority on the Taj, as “The Taj stands just on the edge of the river Yamuna which has now dried up. This was never anticipated by its builders. The river is a constituent of its architectural design and if the river dies, the Taj cannot survive.” Further, the Times of India (TOI) quoted an anonymous retired ASI official, as "Water in the river is an essential pre-requisite to maintain the massive foundation that supports a complex system of wells, arches and wooden spoked wheels.

Sun_set_view_of_Taj_Mahal.jpg
Sun set at the Taj Mahal

Dry ambience could fragment and disintegrate the sal wood." The TOI also quoted Professor Nath as “…..The water in the Yamuna is necessary to counter-balance horizontally the massive weight of the Taj Mahal….”

While theoretical studies like Three-Dimensional Finite Analysis of Taj Mahal Structure have been conducted on the existing super structure by Indian engineers (Viladkar, Bhandari, et al); a meaningful discussion of the Taj Mahal substructure’s integrity remains lacking. In the absence of accurate substructure information, let us look a little closely at the retired ASI official’s, and Mr. Ram Nath’s statements in an attempt to understand their rather grave sounding concerns.

In order to do this, we need to make certain assumptions based on the implied explanations in the statements of the ASI official, and Mr. Nath. The statements by these two distinguished individuals seem to indicate that:

  1. The well foundations for the Taj Mahal were apparently designed similar to how today’s bulkheads/ seawalls/ Quaywalls are designed - in which not only soil pressure from one side is considered, but various hydrostatic forces on the other side are considered; other factors such as hydrostatic imbalance in the backfill are also considered.
  2. The well foundations appear to incorporate (at least a type/combination/components of Sal) timber piles that were originally designed to stay constantly submerged in the high groundwater created by the adjacent full flowing Yamuna River.

Why is this important to the present discussion? This can be answered by comparing this to the general durability of other species of timber piles. United States Federal Highway Administration has concluded that the Southern Yellow Pine, and Douglas Fir piles, normally used in the US, will last indefinitely if submerged in groundwater; however, when used overland they will last only about 40 years in the warm southern areas of the US.

taj-mahal.jpg

Since temperatures in Agra, India, can get quite warm during summer; neglecting differences in timber species for this discussion, we could probably assume that the life of timber piles/ foundation under the Taj Mahal would probably be around 40 years - from the time the foundation was dewatered - by the lowered stream flow level in the Yamuna. Further, there are other concerns with timber piles/ foundation such as alternate wetting and drying cycles, areas of timber located above the groundwater, susceptibility to insect damage, lack of proper preservative treatments. Therefore, it is essential for an early evaluation of all these issues.

Further, we should also study the seismic vulnerability of the Taj Mahal. According to the Indian Meteorological Department’s Seismic Zoning map of India, the city of Agra – home to the Taj Mahal, falls under Zone 3, at the boundary of Zone 4 (The Indo-Gangetic basin). This map also states that: “Towns falling at the boundary of zones demarcation line between two zones shall be considered in High Zone.”

While Zone 3 with a MSK (Medvedev-Sponheuer-Karnik) value of 7 is classified as Moderate Damage Risk Zone; Zone 4 with a MSK value of 8 is classified as High Damage Risk Zone.
In it’s periodic reporting to UNESCO, the ASI has acknowledged that “Seismic shocks: Considerable number of seismic epicentres lie to the NW of Agra and two quite serious events with magnitude between 6.3 and 7.0 are recorded within 100 km of Agra. It is possible that rayleigh waves from distant earthquakes could affect the minarets and pinnacles….”

Viladkar, Bhandari, et al state that the Taj Mahal’s substructure rests on a “thin sandy layer of 9.1 meter thickness, followed by a 63.4 m thick clayey strata underlain by rock.”

The above described conditions pose a variety of potential Seismic Hazards to the Taj Mahal’s substructure such as potential for Liquefaction, Lateral Spread Displacement, Differential Seismically-induced settlement, Ground Lurching. URS Corp defines Liquefaction as a significant and relatively sudden reduction in stiffness and shear strength of saturated sandy soils caused by a seismically induced increase in pore water pressures.

Potential for seismically induced liquefaction exists whenever relatively loose, sandy soils exist with high groundwater level and/or potential for long duration, high seismic shaking. Bartlett and Youd’s (1999) publication describes conditions such as free-face, sloping ground surfaces and liquefiable layers are factors contributing to lateral spread displacement. Therefore, the ASI needs to determine if the Taj Mahal site lies inside the Liquefaction Hazard Zone.

Similarly, Differential Seismically-induced Settlement is defined by URS as occurring when seismic shaking causes one type of soil to settle more than another type. It may occur within a soil deposit with relatively homogeneous properties if the seismic shaking is uneven, which could occur due to variable geometry, for example variable depth of the soil deposit. This needs to be evaluated as well.

In summary, there appears to be sound reasons for conducting a timely, comprehensive geotechnical survey by a firm with prior experience in geotechnical work on other UNESCO listed world heritage sites.

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