Thursday, August 21, 2014

Geotechnical vs Structural

The dividing line between structural and geotechnical becomes blurred some of the time.

The structural engineers have come up with a closed form solution, that if they had a suitable "soil" value, slab on grade design would be totally numeric. This value they would like is termed a "modulus of subgrade reaction", and it was derived theoretically by creating a term for everything the structural engineers do not know about slab on grades. It is a abstract term, which is also a system dependent number.

Now it seems that they have done the same for screw piles, but even worse. They have used a typical test value result as a system parameter in cohesive soils. This will not be given by any geotechnical engineer in a report, for it is potentially dangerous if miss-used, and lowers geotechnical to technician work. In cohesionless soils, they are using typically assumed parameters for design, not measured values. They are going from measured values to classification, and estimating from those the closed form solution values. When this get into court, the screw pile guys should be held responsible.

It is time to hang my shingle in the garage, and retire. Put my sliderule on blocks. what would be the correct euphemism? Not put out to pasture, for that was what was done to old unwanted horses. They we not put in the pasture, where they would need to be feed all winter. They were put out by the cruel bastards, to starve, eat the neighbors hat, or become coyote food. Most of those who use the expression do not understand what it means.     

Monday, August 18, 2014

Solar Panel on roofs

Solar panels should be installed at fairly steep angles to be effective on roofs. In fact, in northern areas they may need to be sun tracking. 30degrees off perpendicular drops the out put to 70%. so all this increases roof snow load.

There is also an issue that these need to be cleaned frequently.

I saw one roof yesterday that hsd three rows of pannels, spaced and at raised angle. That will collect snow.

So now what is the snow load plus dead load? was 1 Kpa, but now perhaps 2.5 plus panels. Expect deflections, if not failures.

Friday, August 15, 2014

volumetric behavior of wet high plastic clay during and after freezing.

This is not a rigorous treatment of this subject, but rather an administrative overview.  

Volumetric behavior of wet high plastic clay during and after freezing is important to understand when building small surface structures which are partly supported on such conditions. When adjacent structures are attached and founded below the effect of freezing soils and moisture change, there will be differential movement that occur annually. In addition, if some of the clay is uncontrolled back fill and or fill, more variation is introduced.

There are two separate issues of volume change with freezing, phase change and secondly the development of ice lenses or frost heave.  The second requires freezing front, as "frost susceptible" soil, and a source of water. High plastic clay is not normally considered as frost susceptible soil since the hydraulic conductivity is quite low; however, if organics are present, all bets are off. 

For this mental exercise we need to consider the soil as a five phase system, rather than the normal three. Solid, liquid and void, as normal, but the water is also ice, liquid and water vapor. Water increases in volume about 9% in the phase change. Water vapor moves through the soil toward the freezing front; it is drawn by substantial thermodynamic forces; the vapor freezes at the freezing front, and shows up as ice crystals. The same happens in a frost susceptible soil, except it is liquid water that moves, and forms ice lenses. This thermodynamic force draws water into the soil, increasing the saturation. This suction has very little impact on the void ratio, at this stage.  Also, in most cases, water is found with depth.

Where saturation occurs before freezing, the water turns to ice, and increases in volume by 9 %. This does not happen abruptly but rather as a rapid change, as there is a temperature gradient, and super cooled liquid water due to water-soil adhesion. Very soon, as cooling continues, the water is fully frozen. The amount of expansion can be best understood by considering the void ratio (volume of voids/volume of soil solids) and the degree of saturation (approximately volume of water/volume of voids). All the physical state properties; density, moisture content, are directly linked to void ratio and degree of saturation. In the end, wet clay expands on freezing. If a soil was 50% voids, and fully saturated, the expansion would be 4.5 %. Where the ground is laterally restrained, the only it can go is up, therefore in this case the amount of uplift would be approximately 4.5% of the depth of frost penetration. The amount of expansion is dependent on the soil, moisture, and depth of freezing, which in turn, is dependent on ground cover, amount and duration of cold, wind, building heat loss, and other factors.

Buildings are designed to stay more or less stable, while everything on the ground outside will move seasonally with the frost. This includes grade supported slabs, steps, walkways. Building supported steps typically do not move as much. The design and construction of these units does not account for these movements, when combined with settlements.

Fill and loose materials settles. It is dependent on moisture, grain to grain stress and strength. When it is wet, saturated, the settlement is time dependent, and is termed consolidation, and is characterized with the expulsion of water, greater density, lower void ratio, lower moisture content, greater strength and the like. When it is less than saturated, it compacts with the expulsion of air. It tends to stay in lumps with voids between the lumps until it gets water and then settles quickly to some degree. It is never finished until it becomes saturated and consolidates. Now for the ugly part, consolidation has pressure dependent end point; it consolidates until the strength is equal to the imposed load. It will change end points when the pressure changes. It may also dry, which increases the strength and stop consolidation. The whole process is water supply dependent, which is not predictable. Consolidation it's self is time dependent, but not the supply or removal of water.

Now that we know what consolidation is about, during freezing, water is drawn in, and some expansion occurs. Each spring, after melting, drainage may occur, and the frost moved materials can consolidate back to a new state of equilibrium. One area is not necessarily the same as the next. Ramps may be high in the center, like the center swelled, another trick of high plastic clay, when it gets water. It may be that the edges were backfilled after the retaining walls were constructed, while the center was native or well compacted clay.

Wednesday, August 13, 2014

Supernatural God

The handle of god has been used for a long time and has many definitions. In many religions, it is a supernatural being, which cannot exist. To the Phoenicians it was the creator of the heavens, the natural process, that they did not understand. OK, now we understand a bit, but not all, but enough to say it is all natural.

The stoics said that we had a bit of divinity in us all; that was logic, reason consciousness. Logic was the stoic god, and for some also nature and the forces of nature. They did not understand forces yet, but they did understand the unseen pushes and pulls of nature. As Zeno put it "All is controlled by the pushes and pulls of nature". 

The Greeks carved chunks of stone to represent Gods, which stood for a specific group of natural forces, or behaviors. They gave a specific group of forces a name. Somebody had to, and one more to rule over them all.

Now we modern humans should know and accept that nothing supernatural can exist. You can have concepts and live as though those concepts were real physical objects, speak of them as such, but if you do, you are just fooling yourself into an illusion or delusion. You are a sick puppy. Go hug a statue. Do it in winter, naked, just to prove how tough you are.

Gods have been used long enough to explain what you, we do not understand. Enough already.

So how does AA function. After reading DiCemente on Change, AA provides 8 of the 10 processes of change in the final three stages. It does this unknowingly, without a plan, without order, without intention. The first two stages are not present in AA, happily drinking, and getting into a bit of bother. It is not until they need or want to change that they darken the door at an AA meeting. There God is irrelevant, well not quite, it forces and attitude that is necessary for recovery.