Dave Siciliano
Final Approach
Long post--not flying related.
The law of unintended consequences: how to build an underground wall for four times the cost of building one above grade.
It seems I have been caught again in a trap by very well meaning, highly competent professionals that have designed something for the worst case, where the implementation of what has been designed may be worse than doing nothing!!!
In the way of background, I develop single family subdivisions and have to work through a maze of city rules, other regulatory laws and regulations and regularly have to employ professionals such as engineers, architects, environmental specialists (who are usually engineers), geotechnical folks (who are engineers), accountants and attorneys.
In the case in point, I have some lots backing up near a creek. In some cases, some lots will be filled to be four feet above current grade level; in most places, the existing grade will suffice. There is a creek where the bottom is 60 feet or more from the back of the lots. We thought it would be fairly simple to put retaining walls along the back of the lots that will be raised and that would be it; then, my engineer advised me to have a slope stability study done so the walls could be properly engineered. There are expansive soils in this area and the engineer thinks we may want to put a little larger wall in to compensate for possible erosion and slope instability (expansive, clayey soils). So, the professionals take over.
Next thing I know, I’m putting six to ten foot walls in (mostly underground) to provide for possible soil erosion. First underground wall I’ve ever been asked to build. Then, someone calls a hydrologist— well, guess what; he can’t guarantee the creek won’t move. So I call and have this anal conversation about why in the world I would design to provide for the remote instance the creek could move, and even if it did, it would do it in one place— it would not be for the entire length of the wall!! Well, he says, I can’t guarantee it won’t move there, so, you need to design for it. I tell him the earth’s surface can shift too, and I don’t design for that!! (Hummm he says contemplatively, maybe we need to add that into our calculations.) So the rule of supervising engineers: the longer the engineer contemplates, the more complex, and expensive the solution will be. They never seem to find simple solutions after deep, long thought!!
Anyway, then the city engineer gets his 2 cents worth in and stipulates that over time, the grade of the slope will eventually reach 4 to 1 (a 25% grade to non-engineers) through erosion. Several cities have had wall failures, so, now everyone should design to this standard! This said while pontificating from behind a desk with no provision for inspecting actual conditions in the field. Of course the engineer recommends to that august law making body called city council and they memorialize this requirement through the passage of a city ordinance. Now I understand David Henry Thoreaus thoughts about: It is not desirable to cultivate a respect for the law, so much as for the right. Now a variance will be needed from the law if the design is to be modified.
Well the area behind where the wall will go is full of mature vegetation which includes 60 to 70 foot very desirable trees. The slopes are greater than 4 to 1, but there is a lot of very stable vegetation in the area holding the soil and it’s been this way a LONG time!!
So, my engineer tells the geologist, he must consider 4 to 1 even though that’s not existing conditions. The geologist tells the structural engineer designing the wall that the soils will not be as stable as present conditions, so, the structural engineer requires a bigger wall (deeper) and now that the creek might move, the wall bottom needs to be at the same level as the current bottom-of-creek!! Down over 12 feet from the current grade level. And, if the creek gets over there, it could undermine the wall; so, piers need to be sunk from the bottom of the wall to bedrock which is located another 13 to 30 feet below the wall (actually, the bottom of the pier needs to be four feet into the bedrock) So, now we are effectively building an underground dam!!!!!!
Now, I call the wall contractor and piering company. Of course, a ditch will have to be dug down to the bottom of where the wall will be. That’s over 12 feet in places. Then, a piering machine will have to get in the bottom of the ditch to drill the piers. The machine is eight feet wide, so the ditch must be wider. Then, the piering machine will need a place to put dirt after it bores the 24 inch in diameter holes. The machine can only go forward; no reverse, so this dirt will have to be removed before the next hole can be dug and guess what, they want a truck to be able to go side-by-side next to the piering machine which now makes the hole over 20 feet wide.
Well, digging a hole this wide will destroy all the trees and natural vegetation behind the lots. It will also remove stabilized soil that will maintain the back of the wall and stop the creek from moving over.
So, as a consequence of very well intentioned people trying to provide a retaining wall to provide stability for the back of future lots, all current natural vegetation and trees will have to be removed at great expense and a project is created analogous to the ‘big dig’ in Boston.
So, when well meaning professionals design to standards that eliminate all possible future risk by each relying upon the recommendations of another professional without examining actual field conditions; each engineers eliminates self risk by making a critical assumption that has not been verified and with each set of assumptions the complexity of the project increases (which in itself creates risk) in a proportion to the square of the number of professionals involved times the number of assumptions relied upon. What nature has done to prevent that risk for hundreds of years doesn’t matter.
Thus the law of unintended consequences: New requirements will be promulgated that will require a project to be built today that would be much less expensive and damaging if that project was left to be addressed in the future. In other words, since no one knows if the creek will move, and if it does move, when that will be, the professionals would have us install something today that will address every possible adverse outcome when funds could better be set aside to much more effectively address the issue in the future, if needed at all, at a much more reasonable cost.
Best,
Dave
The law of unintended consequences: how to build an underground wall for four times the cost of building one above grade.
It seems I have been caught again in a trap by very well meaning, highly competent professionals that have designed something for the worst case, where the implementation of what has been designed may be worse than doing nothing!!!
In the way of background, I develop single family subdivisions and have to work through a maze of city rules, other regulatory laws and regulations and regularly have to employ professionals such as engineers, architects, environmental specialists (who are usually engineers), geotechnical folks (who are engineers), accountants and attorneys.
In the case in point, I have some lots backing up near a creek. In some cases, some lots will be filled to be four feet above current grade level; in most places, the existing grade will suffice. There is a creek where the bottom is 60 feet or more from the back of the lots. We thought it would be fairly simple to put retaining walls along the back of the lots that will be raised and that would be it; then, my engineer advised me to have a slope stability study done so the walls could be properly engineered. There are expansive soils in this area and the engineer thinks we may want to put a little larger wall in to compensate for possible erosion and slope instability (expansive, clayey soils). So, the professionals take over.
Next thing I know, I’m putting six to ten foot walls in (mostly underground) to provide for possible soil erosion. First underground wall I’ve ever been asked to build. Then, someone calls a hydrologist— well, guess what; he can’t guarantee the creek won’t move. So I call and have this anal conversation about why in the world I would design to provide for the remote instance the creek could move, and even if it did, it would do it in one place— it would not be for the entire length of the wall!! Well, he says, I can’t guarantee it won’t move there, so, you need to design for it. I tell him the earth’s surface can shift too, and I don’t design for that!! (Hummm he says contemplatively, maybe we need to add that into our calculations.) So the rule of supervising engineers: the longer the engineer contemplates, the more complex, and expensive the solution will be. They never seem to find simple solutions after deep, long thought!!
Anyway, then the city engineer gets his 2 cents worth in and stipulates that over time, the grade of the slope will eventually reach 4 to 1 (a 25% grade to non-engineers) through erosion. Several cities have had wall failures, so, now everyone should design to this standard! This said while pontificating from behind a desk with no provision for inspecting actual conditions in the field. Of course the engineer recommends to that august law making body called city council and they memorialize this requirement through the passage of a city ordinance. Now I understand David Henry Thoreaus thoughts about: It is not desirable to cultivate a respect for the law, so much as for the right. Now a variance will be needed from the law if the design is to be modified.
Well the area behind where the wall will go is full of mature vegetation which includes 60 to 70 foot very desirable trees. The slopes are greater than 4 to 1, but there is a lot of very stable vegetation in the area holding the soil and it’s been this way a LONG time!!
So, my engineer tells the geologist, he must consider 4 to 1 even though that’s not existing conditions. The geologist tells the structural engineer designing the wall that the soils will not be as stable as present conditions, so, the structural engineer requires a bigger wall (deeper) and now that the creek might move, the wall bottom needs to be at the same level as the current bottom-of-creek!! Down over 12 feet from the current grade level. And, if the creek gets over there, it could undermine the wall; so, piers need to be sunk from the bottom of the wall to bedrock which is located another 13 to 30 feet below the wall (actually, the bottom of the pier needs to be four feet into the bedrock) So, now we are effectively building an underground dam!!!!!!
Now, I call the wall contractor and piering company. Of course, a ditch will have to be dug down to the bottom of where the wall will be. That’s over 12 feet in places. Then, a piering machine will have to get in the bottom of the ditch to drill the piers. The machine is eight feet wide, so the ditch must be wider. Then, the piering machine will need a place to put dirt after it bores the 24 inch in diameter holes. The machine can only go forward; no reverse, so this dirt will have to be removed before the next hole can be dug and guess what, they want a truck to be able to go side-by-side next to the piering machine which now makes the hole over 20 feet wide.
Well, digging a hole this wide will destroy all the trees and natural vegetation behind the lots. It will also remove stabilized soil that will maintain the back of the wall and stop the creek from moving over.
So, as a consequence of very well intentioned people trying to provide a retaining wall to provide stability for the back of future lots, all current natural vegetation and trees will have to be removed at great expense and a project is created analogous to the ‘big dig’ in Boston.
So, when well meaning professionals design to standards that eliminate all possible future risk by each relying upon the recommendations of another professional without examining actual field conditions; each engineers eliminates self risk by making a critical assumption that has not been verified and with each set of assumptions the complexity of the project increases (which in itself creates risk) in a proportion to the square of the number of professionals involved times the number of assumptions relied upon. What nature has done to prevent that risk for hundreds of years doesn’t matter.
Thus the law of unintended consequences: New requirements will be promulgated that will require a project to be built today that would be much less expensive and damaging if that project was left to be addressed in the future. In other words, since no one knows if the creek will move, and if it does move, when that will be, the professionals would have us install something today that will address every possible adverse outcome when funds could better be set aside to much more effectively address the issue in the future, if needed at all, at a much more reasonable cost.
Best,
Dave
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