MEXICO CITY’S MEXICO CITY’S SINKING CATHEDRALSINKING CATHEDRAL

ByByAaron AlarconAaron Alarcon

Jinghong LiJinghong Li

The cathedral has been sinking The cathedral has been sinking since the day it was built since the day it was built almost 500 years ago. almost 500 years ago.

How much the cathedral How much the cathedral has sunk?has sunk?

This pendulum is inside the Cathedral, which should be centred in the middle of the square.

It shows us how much the cathedral has sunk. This cathedral was actually worse a few decades ago.

Why is Mexico city’s cathedral Why is Mexico city’s cathedral sinking?sinking?

Why is Mexico city sinking?Why is Mexico city sinking?

• The soft clay subsoil beneath Mexico City

• The removal of water from the soil over the past years

Irregular and gradual sinking of many buildings, such as cathedral.

Geology of Mexico cityGeology of Mexico city

• Mexico is more than 2000km wide, but narrows to only 210km in the south

•The large Basin where Mexico city is located in the central part of the Trans-Mexican Volcanic Belt

• The basin, at an altitude of 2,200m above sea level, is the highest valley in the region, and is surrounded by mountains.

Mexico City PopulationMexico City Population

Water demand increases as population increase. So much water has been pumped out from the aquifer beneath it to satisfy the metropolitan area's 18 0,000,000 residents that the ground is collapsing underfoot at a stunning rate.

Reasons why the Cathedral is Reasons why the Cathedral is sinkingsinking• Construction of the Metropolitan Cathedral started Construction of the Metropolitan Cathedral started

in the second third of the 16th century. in the second third of the 16th century. • The soil where the cathedral was constructed is a The soil where the cathedral was constructed is a

land over ancient civilizations constructions. land over ancient civilizations constructions. • The layers of human occupation on the natural The layers of human occupation on the natural

crust reach down more than 15 meters, and there crust reach down more than 15 meters, and there are pre Hispanic structures more than 11 meters are pre Hispanic structures more than 11 meters deep. This emphasizes the irregularities in the soil.deep. This emphasizes the irregularities in the soil.

• The sinking of the ground in the area of the town The sinking of the ground in the area of the town reaches up to 2.4 meters relative to the point of reaches up to 2.4 meters relative to the point of the apse, while the area of the chambers have the apse, while the area of the chambers have sunk up to 1.5 to 1.6 meters from the horizontal.sunk up to 1.5 to 1.6 meters from the horizontal.

Reasons why the Cathedral is Reasons why the Cathedral is sinkingsinking• Other factors that affected the cathedral are the Other factors that affected the cathedral are the

construction of the Mexico City subway, its current construction of the Mexico City subway, its current operation, the excavations on the Templo Mayor and operation, the excavations on the Templo Mayor and the effect of a semi-deep drainage ditch that was dug the effect of a semi-deep drainage ditch that was dug in front of the cathedral.in front of the cathedral.

• Also the city has needed more and more underground Also the city has needed more and more underground water and that has made the water and that has made the phreatic horizontal to phreatic horizontal to get down, what accelerated the hardening of the clay.get down, what accelerated the hardening of the clay.

• Many efforts has been made in order to stop the Many efforts has been made in order to stop the sinking rate. Nevertheless, the sink rate between the sinking rate. Nevertheless, the sink rate between the northern tower and the apse is more than 2 cm / year. northern tower and the apse is more than 2 cm / year. These are the strongest and weakest points These are the strongest and weakest points respectively.respectively.

How to Save the Sinking How to Save the Sinking CathedralCathedral

Foundation

Cathedral

Water table

Water pump from auqifer

Foundation

Cathedral

Water table

Water pump from auqifer

Solution ProposedSolution Proposed• In 1992 the studies revealed that the In 1992 the studies revealed that the

cathedral was sinking and the reversal cathedral was sinking and the reversal process could not be postponed anymore process could not be postponed anymore so they started looking for a way to solve so they started looking for a way to solve the problem.the problem.

• Some alternatives they found were to put Some alternatives they found were to put 1500 piles under the cathedral in order 1500 piles under the cathedral in order to stop the movement of it or place piles to stop the movement of it or place piles 60 meters below and to reload the 60 meters below and to reload the aquifer.aquifer.

• The final choice was to make 30 holes The final choice was to make 30 holes about 2.6 meters in diameter under the about 2.6 meters in diameter under the cathedral. cathedral.

• Those holes were Those holes were reach down further reach down further than all the remains of other than all the remains of other constructions, down to the clay that is constructions, down to the clay that is below the natural crust.below the natural crust.

• That holes were filled with concrete and That holes were filled with concrete and were placed 15cm diameter tubes every were placed 15cm diameter tubes every 6 degrees of the circumference.6 degrees of the circumference.

Cathedral

Water table

Piles

Water pump from auqifer

Foundation

Cathedral

Water table

Piles

Water pump from auqifer

Solution ProposedSolution Proposed• The way they make the holes in The way they make the holes in

the soil is by using special the soil is by using special machines. Which make the machines. Which make the cathedral sink in that area, that cathedral sink in that area, that why they reinforced it.why they reinforced it.

• The objectives of this are to The objectives of this are to restore the geometry of 40% of restore the geometry of 40% of the sunk areas of the cathedral.the sunk areas of the cathedral.

• The movement of the hole The movement of the hole cathedral was measured cathedral was measured monthly and there was several monthly and there was several studies made after any studies made after any earthquake registered in more earthquake registered in more than 3.5 Richter.than 3.5 Richter.

• The cathedral at the end of the The cathedral at the end of the process wont be straight it process wont be straight it never was but its verticality will never was but its verticality will be improved and it will be able be improved and it will be able to resist the strongest to resist the strongest earthquakes. earthquakes.