4 ms·

The shortest answer is "because people like vertical walls".

jaclaz 5y ago
Only for the record, not really vertical. Usually retaining walls (higher than 2-3 meters) have an outer slope (something like 5%) otherwise they would seem (optical effect) to be falling in.
- lmilcin 5y ago
  Even you have mentioned that "optical effect" is important. Which is exactly the point. Retaining walls are built for optical effects and looks rather than for being tough. A tough retaining wall would be a slope. Ever seen an old church arch support structure? They are not standing vertically, they are sloped. Sloped retaining walls would not be very nice to look at (they kinda look medieval) but would be much more resistant to lateral forces.
  - jaclaz 5y ago
    I don't understand your point. Retaining walls (generally speaking) are tough enough and do not fail. Those that fail were either poorly engineered/calculated or badly built (or something else in the soils/terrain behind the was overlooked or external actions - like loads and/or vibrations from trafic were underestimated). That is beyond and besides the actual shape and orientation of the wall.
    - lmilcin 5y ago
      Let me give you another analogy. Let's say Macbook keyboards fail much often than mechanical keyboards. Why is that? One could say, the reason they are failing because "they were poorly engineered/calculated or badly built" and that might be true. But another way to state this is the reason they are failing is because we like thin laptops. And making laptops thin pushes the engineering into territory where it is much more difficult to make the keyboard be designed and function reliably. Just like our love of vertical walls makes it much more difficult to engineer retaining walls that do not topple. You see, both of these do not necessarily conflict with each other. They are just different points of view on the same problem. I think that blaming the problem only on engineering is shallow thinking. It is obviously right and at the same time it gives absolutely no understanding of what is happening. It is the same kind of thinking that, for decades, blamed drivers for all accident. Obviously, it is the driver that caused the accident, but it gives no further useful understanding of the problem. Once people understood there are other factors at play some countries started introducing solutions that make the traffic much safer without messing with the driver side of equation.
      - jaclaz 5y ago
        Your analogy ends short because noone wants thin retaining walls, or - better said - the only one that decides how thick they should be is the calculating civil engineer (that normally does try to optimize thickness of the wall, in order to optimize costs). An owner/road department might decide to put some limits to the amount of land needed to build the wall and of course there may be particular cases of "narrow" areas, but we are talking of meters (and in my experience there is not that much difference in space needed for excavation between a "basic" and an "exceptionally heavy/thick" retaining wall, the difference may be at the most 1 or 1.5 meter in the base slab), and in these cases one could use gravity walls (that use much more concrete, though with less rebar and usually need less space "behind" for the excavation) or as the original article explaines anchored walls or walls on piles, or even temporary structures (micropiles and anchors usually) only to allow the building of the retaining wall. The retaining walls (under road) in the first minute of the video are not conventional cantilever retaining walls, BTW, they are one of the common ways "reinforced earth" is made (the typical rebar concrete wall is sketched, as an example, at 10:26) compare these: https://en.wikipedia.org/wiki/Mechanically_stabilized_earth https://en.wikipedia.org/wiki/Mechanically_stabilized_earth https://reinforcedearth.com/products/retaining-walls/mechanically-stabilized-earth-mse-retaining-walls/reinforced-earth/ https://reinforcedearth.com/products/retaining-walls/mechani... with a "normal" retaining wall like the gravity and cantilever sketched here: https://en.wikipedia.org/wiki/Retaining_wall https://en.wikipedia.org/wiki/Retaining_wall https://en.wikipedia.org/wiki/File:Retaining_Wall_Type_Function.jpg https://en.wikipedia.org/wiki/File:Retaining_Wall_Type_Funct... they work in a completely different manner, the MSE is more similar to an anchored wall, the "anchors" are in this case pieces of steel strips that resist the pull because of the weight and friction of the earth/soil, if the soil is not suitable or not properly compacted or you introduce a lubricant (water)there is the possibility of these strips to lose adherence, the thickness of the reinforced concrete outer slabs is irrelevant and usually fixed, independent from height of the wall or other local conditions, if I recall correctly some 14 cm. Anecdotally, I have built both kinds of walls, and actually also once "saved" a piece (some 40 or 50 mt long) of MSE-like wall that was failing (though due to other reasons, the foundation was underdimensioned), the huge difference is that traditional retaining walls are "independent" from the soil you put behind it (as long as it is within a normal weight of 1,600-2,100 kg/m3) while the MSE stability depends greatly on the quality of the soil and the way it is compacted (besides a valid calculation of the length of the strips). As a side note, MSE-like walls are usually perfectly vertical (and actually do seem like falling inward optically when they are high).

Only for the record, not really vertical. Usually retaining walls (higher than 2-3 meters) have an outer slope (something like 5%) otherwise they would seem (optical effect) to be falling in.

lmilcin 5y ago
Even you have mentioned that "optical effect" is important. Which is exactly the point. Retaining walls are built for optical effects and looks rather than for being tough. A tough retaining wall would be a slope. Ever seen an old church arch support structure? They are not standing vertically, they are sloped. Sloped retaining walls would not be very nice to look at (they kinda look medieval) but would be much more resistant to lateral forces.
- jaclaz 5y ago
  I don't understand your point. Retaining walls (generally speaking) are tough enough and do not fail. Those that fail were either poorly engineered/calculated or badly built (or something else in the soils/terrain behind the was overlooked or external actions - like loads and/or vibrations from trafic were underestimated). That is beyond and besides the actual shape and orientation of the wall.
  - lmilcin 5y ago
    Let me give you another analogy. Let's say Macbook keyboards fail much often than mechanical keyboards. Why is that? One could say, the reason they are failing because "they were poorly engineered/calculated or badly built" and that might be true. But another way to state this is the reason they are failing is because we like thin laptops. And making laptops thin pushes the engineering into territory where it is much more difficult to make the keyboard be designed and function reliably. Just like our love of vertical walls makes it much more difficult to engineer retaining walls that do not topple. You see, both of these do not necessarily conflict with each other. They are just different points of view on the same problem. I think that blaming the problem only on engineering is shallow thinking. It is obviously right and at the same time it gives absolutely no understanding of what is happening. It is the same kind of thinking that, for decades, blamed drivers for all accident. Obviously, it is the driver that caused the accident, but it gives no further useful understanding of the problem. Once people understood there are other factors at play some countries started introducing solutions that make the traffic much safer without messing with the driver side of equation.
    - jaclaz 5y ago
      Your analogy ends short because noone wants thin retaining walls, or - better said - the only one that decides how thick they should be is the calculating civil engineer (that normally does try to optimize thickness of the wall, in order to optimize costs). An owner/road department might decide to put some limits to the amount of land needed to build the wall and of course there may be particular cases of "narrow" areas, but we are talking of meters (and in my experience there is not that much difference in space needed for excavation between a "basic" and an "exceptionally heavy/thick" retaining wall, the difference may be at the most 1 or 1.5 meter in the base slab), and in these cases one could use gravity walls (that use much more concrete, though with less rebar and usually need less space "behind" for the excavation) or as the original article explaines anchored walls or walls on piles, or even temporary structures (micropiles and anchors usually) only to allow the building of the retaining wall. The retaining walls (under road) in the first minute of the video are not conventional cantilever retaining walls, BTW, they are one of the common ways "reinforced earth" is made (the typical rebar concrete wall is sketched, as an example, at 10:26) compare these: https://en.wikipedia.org/wiki/Mechanically_stabilized_earth https://en.wikipedia.org/wiki/Mechanically_stabilized_earth https://reinforcedearth.com/products/retaining-walls/mechanically-stabilized-earth-mse-retaining-walls/reinforced-earth/ https://reinforcedearth.com/products/retaining-walls/mechani... with a "normal" retaining wall like the gravity and cantilever sketched here: https://en.wikipedia.org/wiki/Retaining_wall https://en.wikipedia.org/wiki/Retaining_wall https://en.wikipedia.org/wiki/File:Retaining_Wall_Type_Function.jpg https://en.wikipedia.org/wiki/File:Retaining_Wall_Type_Funct... they work in a completely different manner, the MSE is more similar to an anchored wall, the "anchors" are in this case pieces of steel strips that resist the pull because of the weight and friction of the earth/soil, if the soil is not suitable or not properly compacted or you introduce a lubricant (water)there is the possibility of these strips to lose adherence, the thickness of the reinforced concrete outer slabs is irrelevant and usually fixed, independent from height of the wall or other local conditions, if I recall correctly some 14 cm. Anecdotally, I have built both kinds of walls, and actually also once "saved" a piece (some 40 or 50 mt long) of MSE-like wall that was failing (though due to other reasons, the foundation was underdimensioned), the huge difference is that traditional retaining walls are "independent" from the soil you put behind it (as long as it is within a normal weight of 1,600-2,100 kg/m3) while the MSE stability depends greatly on the quality of the soil and the way it is compacted (besides a valid calculation of the length of the strips). As a side note, MSE-like walls are usually perfectly vertical (and actually do seem like falling inward optically when they are high).