Why is the leaning tower a tall structure that is not stable?

Answer 1

In 1173 the constrution workers were building a bell tower but it was originally supposed to be standing up staight but it kept tilting. Over centuries other people were helping stablize the tower and others made it worse and because the tower kept tilting they closed the tower 1990. Then they reopened the tower 2001 and they say it is expected to stay like that for the next 300 years.

It will eventually fall in the next 200 years. But it is currently being supported by protecters, (it leans 1mm a year)

the leaning tower of Pisa will fall eventually but not yet you see it leans 1mm a year.
It doesn't lean over long enough to have to do that. The centre of gravity of the tower is still vertically above the foot print (the supporting surface) of the tower.
Because it hasn't leaned far enough to become terminally unstable. Also because of twentieth century engineering work to underpin it, which has active response by hydraulic rams to counter any new movements that occur.
Pisa's Leaning Tower can lean as far as its area of support but will topple if it's windy enough or if enough resonance occurs.

Answer 2

It was built on weak unstable subsoil, as well as having a totally inadequate foundation depth for the subsoil and the weight and height of the tower subsequently built. It was built in several stages and corrections made during the second stage mean it is actually curved. Several modern attempts to stabilise the structure have been made involving lead weights and finally removing soil from the raised end to straighten it somewhat. It was decided not to try and straighten the tower completely due to tourism and merely to return it to its previous 19th century position. Two towers in Germany actually lean more than the leaning tower of Pisa, the Suurhusen (5.19) caused by its oak foundations rotting after they dried out when land was drained and Bad Frankenhuasen (4.5) as opposed to the Pisa's 3.97 degrees.

Answer 3

The lening tower of Pisa is not straight because it is eight stories high and the soil that it was built on was not solid.

Answer 4

Because it is leaning to the side. Buildings that lean to the side are not structurally stable.

Answer 5

because it is currently being supported by protectors