Monday, April 18, 2011

Cognative Dissonance

Cognative Dissonance – psychological conflict resulting from incongruous beliefs and attitudes held simultaneously.

In engineering, it may be expressed in other terms.
Example, Beliefs
  1. Engineering is important; to do construction correctly is valued; I make my meager living as a “Professional Engineer”.
  2. Construction should be conducted as per the Alberta Building Code. 
  3. Some cases the Alberta Building Code is grossly wrong.
  4. Now what? We are forced to create an “artificial value” for an Ultimate Limit State soil strength, that has no physical significant, and calibrate it to the desired outcome of the building code.
Most foundation should be designed for the Service Limit State. In 40 years, I have not run across a condition that I would employ a Ultimate Limit States soil strength for design. Many of the methods of evaluation of the soil strata strength do not generate a ultimate value, largely due to the time required in clays, and the gross amount of movement that occur in such tests.
Pile load tests are as close to ultimate as we would ever come, and usually those are limited to something like 50 millimetres of movement before it is declared failed. The true pile capacity may be 1.01 to 2.0 times that amount, for discussion.
For a typical project there is a wide range of soil strengths, and all this soil data must be reduced to something that is manageable for design. That is more of an art than a science, since the reliability and variation of the data, the amount of data, the geology of the formations, and the type of foundation all play major roles in the final value. After we go through all that, then we have to fudge a number so that the final result will be correct, due to government insistence on a system of design that matches the structural concepts of how materials should behave, not reality.

Wednesday, April 13, 2011

Is there a Full Moon?

I received a call from a structural engineer, and he was looking for a way to find geotechnical information, the strength of the soil, on a specific site, on a particular pile type, without conducting a geotechnical investigation.

I suggested a load test, a procedure that will cost about twice what a geotechnical investigation would, but he could do it himself. He went away, happy.

Damn Lawyers

I was asked to do an inspection by a lawyer but they were only willing to pay if I could provide a specific outcome from that inspection. What do lawyers think engineers are? Prostitutes? Magicians? 

I declined the opportunity. 

Shrinking Clay

A problem that I see frequently in Edmonton is clay shrinkage below foundation causing substantial damage to houses, sometimes destroying the value of the house.

The typical situation is as follows:
1.      The house was built on wet high plastic clay. Much of Edmonton has high plastic clay at and below foundation level. 10 to 20% of the land was wet before development into housing.
2.      The home owners (Or the city, developers) plant trees that become large, and suck water from the soil. In dry years, there roots go to the wetter soil, often below houses. The roots extend under the exterior foundations and desiccate an amount of soil. Typically values may be 3 meters of soil shrink 3% causing a 90 millimetres of settlement. If the interior foundations are unaffected, there is a noticeable slope toward the tree, usually with cracking.
3.      Now you have a problem, without a good solution. The first part of the solution is to remove the trees. Next is to underpin, and thirdly, to level the house and repair the other damage.  As the desiccated material thickens, the depth required for underpinning increases. A geotechnical investigation is required to answer the question of how deep, and what about downdrag.
4.      We geotechnical engineers think trees are nice, but in high plastic soils, they should be at least twice the height of the tree away from the houses. That makes a city treeless.
5.      The city likes to plant elm trees along the roadways because they dry out the subgrade and improve the subgrade strength, reducing the pavement failure due to loadings. The down side is the houses on the other side of the trees suffer. Is the City of Edmonton responsible for the damage there trees cause to the private properties? How about your trees and the neighbor’s house? What about the neighbor’s trees and your house?
6.      Shrinkage is only reversible after the virgin cycle; the first time there is some nonreversible shrinkage. Most of Edmonton upper clays have been desiccated to some depth, the desiccated crust, typically 2 to 3 metres; most house foundations are in or below this. Often the desiccation results in thickening of the desiccated crust.  
7.      Watering of the trees and downspouts helps but not much. Many of the large trees will use over a cubic metre of water per day. Some 2 or 3 cubic metres.
8.      Downspouts create the other side, swelling of that clay which have been desiccated. Downspouts at trees may cause a yo-yo foundation.
9.    Now one more complication, add water after shrinkage has occurred, and we get swelling. Now swelling is pressure sensitive. The exterior foundations, interior foundation and floor slab all produce different contact pressure on the soil, so different amounts of swelling causes differential elevations across the floor. What fun the kids have chasing their marbles to the walls usually. Time   to adjust your tela-posts to keep your main floor level. If you have bearing walls in the basement, perhaps you will need to install adjustable posts. Allow for future movements by providing access to the post and slip joints in the walls or above the ceiling. 

Sunday, April 10, 2011

Alberta ABC Building Code Schedules

Ultimately, the Alberta ABC Building Code Schedules require a geotechnical engineer to make the statement that the project has been designed and constructed in accordance with the Alberta Building Code, the Geotechnical Investigation, and good engineering practices. In addition, there may be a requirement to agree with the recommendations of the geotechnical report, at least to not disagree with the report.

We will not tolerate the owner, structural engineer, or contractor withholding information required to verify that design complies with the Alberta Building Code, and provide ABC schedules. The Alberta Building code requires that all designs be conducted by ULS and checked with SLS, and the more conservative solution be adopted.

To this end we require the actual pile loads, live and dead, a site plan to verify the building is at the same location and elevation as the geotechnical investigation, and also the geotechnical investigation must generally comply with the Canadian Foundation Engineering Manual as good engineering practices.  

Ageing Is Not For the Faint of Heart

Turning off a light is a multi step process. First we must recognize that the light is on, secondly, realize that the light does not need to be on, thirdly realize that it is my responsibility to turn it off, and fourthly to make the decision to turn if off, fifthly summon the volition to make the effort to turn it off, and finally to turn it off. There may also be a requirement to not get distracted through the process, and to remember where the light switch is and why we walked across the room.

Living with someone who cannot put those steps together is an opportunity to practice love, tolerance, compassion, understanding, and a lot of other generally positive characteristics; also overcome some negative feelings, reactions, and characteristics.    

Friday, April 8, 2011

Real or Fiction

What is written on (or should that be in) this blog may be truths or fiction; I do not know. Even intended facts are questionable, as until we know everything about a subject, and do a detailed report, some facts are only approximation of the real truth. Coarse models, if you will accept the concepts of words being only a model of reality. Some fiction is intended, some is not; and is more like errors or beliefs than fiction.

Today, it is my view that gods are just concepts. I was raised with hell fire and damnation religion, so I think they and there beliefs were just fiction as opposed to the view that religious people outright lied to me. Once I realized that gods are just concepts, it allowed me to step back and separate me from my beliefs, and become more objective. I now believe that all beliefs must be reviewed, and the garbage beliefs cleaned out. Some of the beliefs will remain, even when we know they are wrong, or contain both good parts and bad, as we do not know what is better. It is better to replace beliefs with real facts.

Non of this blog should be considered advise, as I am a geotechnical engineer, and not trained in any other field; however, I do read and form opinions, which I will express openly without reservation.

The government intends to mislead us in many areas, mostly for there benefit, nutrition being just one area. It makes decision that are based on opinions of the time which are usually twenty years behind the times, and once something is started, a major correction is near impossible, even when it is badly required. Such is the case with nutrition recommendations. Until the corrections are made, each individual must decide for themselves what is best and who's advice to follow. If you think government nutrition advice is bad, consider that Building Code mess that geotechnical engineers are in in Alberta.