Philosophy

Some where up in the brain, far below the ego, we store our beliefs and values. Some of these are just wrong, many are good, right, and true. Many of our beliefs were entrenched as children, and have not been looked at them since. Occasionally, we were likely forced into situations where we had to cross our beliefs to satisfy a need, an expectation, or a want for us or someone else who we gave power over us to. (Government, employer). At changes in our career, perhaps we need to open our minds and look at our beliefs honestly and with intention. Some will be just left, as we judge them to be good, and right and true. Other we will want to rip out like a thistle, roots and all.

This is basically the intent of Albert Ellis and Alfred Adler CBT, the Stoics, and philosophy in general, to shape out beliefs. Religions do some on this, but there primary intent is to transmit the religion to the next generation. Buddhism is the exception.

So what am I on about? Positive thinking, aka you can do or be anything you want to be, you just need to go after it, is a suitable philosophy for selling hope. Some will make it. It is good for modifying the lazy, and the unmotivated. It also increases expectation, anxiety, greed, guilt, and lower authenticity, integrity  and happiness.  Like any philosophy, it has a good side, and a less good side.

It is a short term philosophy, which is difficult for those around us. It can generate aggression, action, and similar violation of ethics to achieve an end. If this is what you desire, go for it.

Expert

In order to write a report that provides required geotechnical information to design a foundation, we need to know how to design the foundation, and what the soils are. Either part by it's self is not enough. We need to know what is to be built and how, in order to provide the proper values, without a bunch of excess. Time is money, in the engineering world. Waste of time cost somebody. When we are working on fixed price, then it costs the engineering company. Hourly rate work is rare in this industry.

I do not like to teach anyone, but those who do not know basic stuff, I find extremely frustrating. The training is all fine, but they seem to be missing the basics. 

Grinders

Grinders, people who grind on designs to reduce cost. You can either take responsibility for the design as you changed it, or build it as per design. Either one, and do not expect that I will be responsible for your modification to reduce cost. That is on you.

So if you do not like my design, find another nigger.

uls sls ws

The relationship between ULS, SLS and working stress is a construct of the collective minds of structural engineers. It has become codified and is just caca el toro in soils terms, but we geotechnical engineers must live with the government decrees, no mater how stupid they are.

Consider the centre of this diagram a number line going from low to high value.

Above ground we start out with the structure loads, and up-scale those values by partial factors of safety, as found in the building code or bridge code. these become the factored loads.

The code says that the factored loads must be less than the factored resistance, which is all fine and good, but in soils terms, the factored soils value is largely theoretical. Here, and any time Standard Penetration is used, the bearing value is empirical working stress set from a bearing value that will give about 1 inch of differential settlement, 2 inches total settlement, aka SLS value. A similar exercise is used for Cone penetration, unconfined values from Shelby tubes, or pocket pen, whether in Qu or C.

Now what happens when we have a mix of values? we need to convert all to allowable design values, and compare, and then pick our report values. We can use a factor of safety to up scale the value to some theoretical unfactored ultimate, and then apply the CFEM factors to come to a factored resistance. But now both the SLS and ULS must be checked, and for most foundations the SLS should govern. But now we are doing something odd. Some use the approach of  up-scaling working stress value by 1.35 or some number between 1.25 and 1.5, the range in load factors, and use that value. 

My preference is to provide ULS and SLS values, and let the structural engineer do twice the work of previous. Some other appear to be calling the old allowable value the factored resistance, which demands larger foundations. The bearing value in some of soils reports of late from others firms seem to be odd in relationship to soil strength and traditional values, which is of concern. Not enough test holes and high factors of safety. Not good engineering. 

Enough said.           

Basement lateral pressure

Basement lateral pressure, backfill pressure, is a tricky subject. Most books say it is Ka times the vertical, and I believe that true, right after construction. Over time I am not so sure. With high plastic clays, dessication - wetting cycles, freeze thaw cycles, for shallow fills, I think the residual stress dissipate, and the wall lateral pressure increasing over time to Ko. This is not what some of the books say. I think this condition takes 30 to 40 years to develop. Are there any long term lateral pressure studies on house basements, high plastic soils, deep frost penetration? none yet found.

After the wall has failed, the lateral repair must be stronger, because prior to failure, there was a diaphragm moment due to the end walls. During failure, the end cracks relieve this moment, hence all the lateral moment must now be taken by the vertical stiffness of the wall.

When we add potential swelling pressure and potential freeze expansion pressures, the lateral pressure becomes a large transient value. The upper bound of the pressure would be Kp; however, Kp exceeds the typical probable pressure. To use Kp for design would be excessive.

There are areas of the wall that have no lateral support, either through wall openings or through no floor diaphragm as dropped floors and stairs parallel to the wall. These may need abutments or counterbalancing exterior stairs or steps. 

Epoxy injection can reach the strength of the previous wall; however, to do that, all the cracks would need to have 100 percent penetration. The other issue is that after the wall cracked, the stresses were relieved. After epoxy injection, the critical failure start point will have changed. This results in loss of effective strength. The corners have loss the deflection necessary to develop the support it had before.

I think the only way is to do a structural design accounting for all the loss of strength, using a Ko = 1.0, plus a live load for all construction equipment, and reconstruct the wall or equivalent repair. Outside stiffeners can be used, but they must account for the actual openings in the wall and diaphragm. Typical spacing may not be adequate. There will now be no (very little) support from the end walls.

Over the years these are the methods I have seen utilized are as follow:

1. Shotcrete reinforced wall inside
2. Concrete abutment inside
3. Reinforced shotcrete wall outside
4. Wall replacement with proper reinforced design accounting for openings. One required an inside abutment.
5. PWF inside wall, without plywood
6. PWF inside wall with an plywood abutment under the beam. All the PWF were inset into the floor to existing foundations. New foundations may also be required. Bottom and top lateral support is required.
7. Exterior vertical stiffeners, back to back channel bolted through the wall to bring the wall back into line.

All these methods require the wall to be excavated full length and depth, exterior water proofing, good condition weeping tile to provide drainage, and some kind of vertical water drainage is recommended on the exterior wall face.

failure, who is responsible

An old, (35-40 year) sewage lagoon has "failed". It was built on clay till, (assumed, typical of the area) and affluent penetrated a dike, ran in a field and down a ditch intended for surface water. No geotechnical investigation is available, whether not done, being withheld, or just lost. The original design show how it was to be built, not the way it was. No testing data is available.

Who is responsible?

But we have no information. Piping or erosion, physical damage, muscats, gophers, water level, all unknown. Client is unwilling to pay for an investigation. So what should we do?

Only Part Residential

What is the real issue in building partly residential buildings? Our stupid building Code. Not really a safety issue, but a code writers ego, and insistence on beginning right without any reason, beyond his own collective ego bullshit.

Now the other side of the coin, the client, a builder is unwilling to spring for a geotechnical investigation, but wants pile designs for a bit of a stairs and roof overhang.

So how do I deal with this. Here is one example.

As this project is not entirely residential, the authority having jurisdiction or their agents are entitled to ask for Alberta Building Code (ABC) A, B, and C schedules. Tully Geotechnical Limited is unwilling to provide ABC A, B, and C schedules without a geotechnical investigation. The designs provide are provided on assuming the project is purely residential, and with assumed soil pile skin friction design parameters. Should the authority having jurisdiction or their agents request ABC A, B, and C schedules, the designs will be cancelled and other arrangements for geotechnical engineering will be required.  

How is that for a weasel clause?  
By the way the design parameters assumed are 15 kPa below 2.5 metres, if they can put in a pile, it will give us that. 

The PWF Solution

Last day I spoke briefly about lateral pressure failures in basement walls. There is a nice solution, and that is a PWF wall inside, if the subfloor is suitable or can be made suitable. A notch is cut into the basement slab, and the wall installed without sheathing. Nice clean solution if the wall is straightened and waterproofing is applied on the outside. This wall must be structurally designed. Excessive lengths of openings can also be an issue, where doors, windows, the like occur together. It must be attached to the floor diaphragm and the floor cut must be grouted. Also an abutting wall maybe required, for lateral support. 

Repairing Lateral house basement failures

Repairing lateral house basement failures can be conducted inside or out.

In general, the wall failed due to lateral pressure. The repair must be stronger than the old wall. When the failure was caused by impact or vertical load, the old wall was too weak, even though it served until it failed.

The steps to repair are to unload the wall, straighten, add stiffeners, water proof, and backfill. The design must account for the lateral pressure, construction lateral pressures, surcharge loading, and hydrostatic. Unreinforced concrete wall, frequently used in residential cannot be numerically justified when backfill, hydrostatic, construction and surcharge are placed on them. In short, when we do the calculations, they fail often. In reality, they fail often.

It is a simple design of a beam column problem that the code ignores by using a defective prescriptive method which ignores surcharge, hydrostatic and construction loads. It also assumes back fill soils can be compacted without providing lateral pressure on the walls. In an effort to save money, the code is allowed to stand. The reason is the code is effectively controlled by home builders, who are aware of the cost and issue, and can gently lay in fill against the basement and allow settlement to occur. Repairs cannot allow the time for settlements. As a result, repairs must be considerably stronger that the original construction.  

Procrastination verses Exhaustion

Procrastination verses Exhaustion

When we set out a list of stuff we should do today, and at the end of the day, it is not done, was it procrastination or exhaustion that stopped us, or just delusion of how much we could do in a day? It is difficult to to know along with the other stuff that comes up during the day.

When I was a young engineer, working for a testing firm, doing the dispatching, and engineering, I would start out with a pile of "engineering" to do in the morning. I would work all day, and toward the end of the day, the pile was bigger, not because I had not been working, but more was added, and I had been busy doing dispatching, and I felt it was up to me to do it all, a belief the company tried to foster in all the employees. They easily got 1.5 times the proper amount of work from us. Some of us believed the crap about how the company would look after us when the economy slowed, as it surely would. Those who got laid off after Trudeau's national energy policy came into effect know where the companies loyalty lies, with the boss man's bank account. The company and Trudeau emotionally, spiritually and motivationally destroyed many of us. No wonder there is such hatred of Liberals in Alberta.

Some of us never recovered to what we had been. Resentments, and distrust of companies, of promoter employers, kept us from performing our best for others. Companies need to be run by promoters, over optimistic, positive sorts, who can stay motivated and positive even when they as losing, just ahead of the bankruptcy trustee. Yet, at the same time, not defrauding the employees. Yes, not remitting employee deductions, and selling leased cars, and then leasing those same cars back are both forms of fraud. Producing fraudulent test results, pressing us to do likewise, and invoicing the clients is client fraud, and demoralizes the employees. Creating other companies to syphon of money for non-existent services - tax and society fraud. Running parallel companies with different ownership, one with Dick sole ownership, and all employees paid by the other, is theft from the other shareholders. We saw all those, along with theft of supplies, ordering stuff to steal for personal use, all by the share holders, who happened to be "management".

Billy and Dick, may you rot or burn, where ever you are.       

Now that I got past that rant, when I do not get my "today" list done, was the list just a delusion of what I would have time for, exhaustion, or procrastination. Did I do other more enjoyable things instead? Were those thing important and urgent? Or just important, or just urgent? We should not be doing unimportant and un-urgent things, that is just procrastination by displacement.

Important things may only be important to us, not to others. Rest and relaxation is important, and even needed, perhaps not just when it is convenient, but when it is needed. Ugly necessity. We can only do so much, and what we can do often declines with time, especially after retirement.

It is all over when the heart stops beating. Until then, we do what we do. Thank you for reading this. Please feel free to post your own thoughts or opinions on this subject or any other.

The future, retirement

Cut from the web --- not intended as humor 

The better solution then, according to a just-published IBM patent filing (US29228426A1), might be to find a way to suck knowledge out of the experts then inject it into younger, stronger, cheaper employees, possibly even in other countries.

Once again we confuse “Expert” with “Expert System”. These two things are almost diametrically opposed.

Experts understand exceptions, learn and focus on the unusual

Expert Systems codify knowledge and focuses on the common.

In fact the economic incentives for expert systems reward handling the common cases first and returns tend to decrease as the more uncommon cases are added. IBM isn’t reproducing and storing real experts, just finding a way to stamp out repeatable workers and miss labelling them.

And don’t forget: IBM perfected the step-by-step manual (repair, maintenance, and training), railroad tracks and all.

What we’re talking about, then, is a possible revolution in workplace training, one where a lifetime of experience would ideally be sucked from the mind of an experienced worker to be injected into a trainee and then the older worker discarded.

But I am an expert with experience. Every thing I learned came from books, then I tried to use that and then I started to learn what was really being done. Mind you, that was dirt and people acting like construction workers, doing what they had previously done with a twist. 

But is all that information worth anything? or is it all just smoke that will blow away? Does anyone care? Does anyone want the information? I doubt it. 

What Needs A geotechnical Investigation

What needs a geotechnical investigation? I will answer that by saying that for rational design of a foundation, we must know what the soil is verses depth and how strong it is for the depth of the foundation. Houses in a known subdivision, here, imply a competent soil at 5 feet down, so we could design piles adjacent without much risk.

Where there is no basement and foundations adjacent to look at, we need a geotechnical investigation or at least a few testholes to verify the soils are suitable. I personally would not plan an outhouse without a testhole. For an outhouse a hand auger hole would be suitable, but for a duplex, 4-  24 foot deep macro core holes with moistures and pocket pen readings ever two feet would be suitable. One in each corner, for information.

Peat, topsoil, fill, garbage, or a good lot have different values and issues. With organic materials, there is also outgassing to consider.

Negligence is such an ugly thing to be involved in, I think I will just decline to be involved, unless we know what the soils are.

Slope Instability

When we look at a big river bank and see some small movements occurring, we get a feeling that this may be a progressive failure starting. So what should we do with respect to the top of bank setbacks? The City of Edmonton has a Top of Bank Policy that requires a geotechnical engineer to provide an opinion on the slope, and have created a concept of a like of stability at some point behind the top scarp.

The first way of  providing a estimate of the required setback is to use a mature slope angle concept. That is to say that the soils are uniform along the portions of length of the river, and for that portion, the slopes should be all the same. AKA, take the longest natural distance from the river and use that as a setback from the river. OK. First approximation, OK. Expect issues. I will add to that, from any daylight, a maximum of 2.5h:1v for clays, to address sharp top scarps.

Geologically, there are two methods of producing a slope, erosion or bank slumping and toe erosion. Eroded slopes have undisturbed material at there face on the upper portions, while slumped banks have disturbed material everywhere below the top scarp. It has the shape produced by heads and minor scarps, flank scarps, fault zones, and a run out toe. It is even worse it the run out toe has been eroded by a river or ran into a river, on the outside of a bend.

A bit of erosion and channelling through general slump features shows the age. Sharpe features suggests newer, round features suggest older. Existing fresh movements suggest the hill is not stable. Repairs to the hill to prevent erosion, and provide roadway support often reduce the factor of safety on the overall hill. The city does not like to to slope analysis unless necessary, as if these show an inadequate slope, it could not allow develop above the slope without liability. As a result, the City does little short term fixes, but never address the actual cause.

Instead it put the responsibility on the home owner to find a geotechnical engineer to say it is ok to build. This one gets nervious with progressive failures, as the model to to complete failure time is not good, and before failure there is sometime considerable creep, and resulting house movements.

Client Education

Educating of clients to the reality of geotechnical / foundation engineering is an ongoing time consuming issue. Many of our clients are non engineers, often professional, well educated people. But they are often unaware of the basic principals. There expectations may exceed the engineering expected performance of the foundations.

Clay soils are about like sponges that have very sensitive pressure displacement curves that change with changes in moisture content, pressure, and time. Any foundation placed on soils will move in a response to pressure, and changes in pressure, as well as time and changers in moisture. Place two similar footings on similar soils, the one with a greater load will move more. Place an identical footing with similar loads on different soils, and we can expect different movements. Place two similar footings with similar load at different elevations within a site, we can expect different movements.

The differential movement between different unconnected foundations is the part that causes issues. Perimeter strip footings are usually tied together with a foundation wall, and some reinforcement. But was it enough and put in correctly? The interior footings are expected to move differently, and adjustable columns are now required so that the main floor can be maintained in a straight line. Adjustment must be maintained, and the structure must be build such that adjustment can be made.

Note that engineered fill is not addressed in any useful way in the building code. The building code, part 9, was developed for traditional housing, and many of the new bigger house exceed traditional; hence, the building code prescriptive portion may not be adequate to address all the issues. But the building code has an escape clause, something like; "if the code is not adequate, consider engineering the project as per the remainder of the code". How useful is that?

There are standards, but first is the standard suitable? Secondly, was the standard followed? Following an unsuitable standard will lead to problems.

Political / Media Crap

These two men, with their famous political last names, have been friends all their lives just as their fathers were – Romeo LeBlanc, the former governor-general, and Pierre Trudeau, the former prime minister. In fact, Mr. Trudeau was an honorary pallbearer at Romeo LeBlanc’s funeral; Mr. LeBlanc was an honorary pallbearer at Pierre Trudeau’s.  

an dead honorary pallbearer?

http://www.theglobeandmail.com/news/politics/justin-trudeau-grapples-with-his-authenticity-as-the-race-begins/article4593776/

Different Approaches

There are frequently different approaches to the same problem. In engineering, we frequently see different approaches, due to the time of training, place, history, or whatever. Friction in soils, for example, relative to the shear stress, may be expressed as a change in friction angle or as an absolute ratio. The numbers to get the same effect are not the same.

In cohesionless soils, a change in friction angle is more traditional, but when it comes to soil acting on a surface, it is easier to understand and work with a absolute number. This absolute term of reference make life easier, but more confusing to those who training has only included friction as a change in angle.

Neither is more correct than the other, as long as one is used, and the meaning is clear. Using alpha or delta is not clear, as the nomenclature changes textbook to textbook.

The problem with university is there is too much to learn in the allotted time. Additional time would and is just filled with the professors choice of material. It takes time to absorb and learn to the point of understanding, and there is just to much material in some fields. Specialization is forced on us, even if we know a bit about many subjects.

Some of us have worked our entire lives around the field we wanted to be in, only occasionally doing the sort of projects we really wanted to do. We were forced to learn more and more around our chosen field, until we find we are generalists, no expertise in any one subfield, but generalist in the area, doing the work, and having opinions on the various methods. These opinions put us at odds with the academics.

Oh well, life goes on. We are all just learning. It is the first time through life.

  

   

Hand Calculated vs Computer

It has become apparent to me that use of the computer has become a impediment to good engineering. I started in this business with a slide rule and a Curtiss, and if you know both, you will know how I was trained. Cancel out, do the simple, and then approximate, and finally work out the mantissa. Then those expensive hand held calculators...  worth a weeks pay.
We drew graphs by hand, and remembered the values of the results.
Now the young cannot divide by three and multiply by ten on paper. Draw a graph, one minutes work, without a computer, forget it.
I feel for the next generation, when a problem arises, the young will flail for days to find a solution.
For some of these problems, I have simple numerical solution, which I learned at Uni, that produce an approximate solution. Some of them are as reliable as modern computer solutions. In one case, one of the new wonderful computer programs actually uses crappy approximate method, but provides "calibration" questions to "evaluate" parameters that are listed in the formula found in a 1923 publication. Mind you, the computer is quick at raising a number to the 0.564.

Residential Engineered fill

Engineered fill is used to create housing lots from land that was previously unsuitable. Out here, in the high plastic mud plane flats, there are slough areas that hold water most (all) years. The small ones are filled with engineered fill and turned into housing lots. No problems, usually. Bigger sloughs are usually reshaped to fit the lots better. The topsoil and/or marginal material is used to create a damn to control the water and fill is used to bring up the lots.

The primary difference between engineered fill and clean common fill is the amount of compaction and the documentation of the compaction. There is an issue with the extent of the engineered filled provided in the lots, and as the design, size, and location of the houses are not known at the time of lot construction, errors frequently occur as to the required lateral extent of the engineered fill.

After the house is put on the lot, the question becomes, was the rear of the house placed in engineered fill or into common fill? Where settlement of the back wall of the house occurs, it is likely that the engineered portion did not extend far enough into the lot.

But how do we prove the boundary of the engineered fill when the difference is compaction at the time of placement? If they used organic or marginal fill, the difference becomes apparent. But if it is good fill, now what?

Assumed Bearing Values

You may save a few dollars by using an assumed bearing value, but you take on the liability and when problem arises, and it all get dumped in the court, you become neglect. If you assume a low value, it costs the client, and if you assume a high value, you get movements.

The issue with foundations is usually to much movement. Often we expect movement, and then you have a choice, build, and allow for the movement, or not build. Some of the time, we can switch foundation types, and reduce movement to an acceptable level.

All foundations move. Movement is a response to changing  load, and to often, changing moisture regimes. It is limiting these movements to an amount that is acceptable that is the trick.

Our building codes are out to lunch in some respects. It calls for foundation design utilising ULS, which should never control in soils, SLS will always govern.  But the building code is written by a bunch of structural engineers, who do not understand soils. They force us soils types to adapt, to take what is right and bend it to fit a wrong code.

     

Engineered fill

Engineered fill is what we call the process of placing clay to support small buildings such as "traditional" houses. What is being built is far from traditional. And then there is the wet soil issues, where 0.6 metres of dry high plastic clay is placed and crusted over with a packer. The remainder of the fill is placed. Now what?

At the best, with traditional houses, we expect 2 inch of differential movement. Now a few construction problem/errors, tight basement finishes, and what do we have but houses who do not meet the owners expectations, but are within the expectations of the land developer and geotechnical engineers.

Such fun.

Tele-posts

Tele-posts, adjustable columns in the basement of most modern homes are to account for differential movement between different foundation types, and they are there for adjustment. They should be adjusted as required to keep the main floor straight. The basement walls must be constructed to allow for adjustment, and not to carry any vertical load to the basement slab. This will cause uplift of the floor, and partition cracking at doorways and other points of stress concentration.

Ice Jacking

Ice jacking is a phenomena that occurs when water is frozen, water is drawn to the freezing front through the soil, and freezes. There is also lateral frost jacking where water ingresses into a crack and freezes, producing large lateral forces. The amount of movement can  become substantial when partial melting and cyclical freezing occurs.

This can occur in a number of situations. The typical one is in old stucco homes with no insulation and vapour barrier in the joist space over the basement. Water condenses and freezes, expands, and produces lateral force. The sun hit it, it melts, runs down, freezes and expands. You get the picture. Beam pockets over basement have a similar issue. Slabs outside have the same effect happening next to houses.

This week I saw a new occurrence of this, inside a unheated insulated garage. Cars drag in snow and it melts, and condensates on the grade beam. On nice days, this melts, runs down into the space between the grade beam and slab an freezes. This provides force, and in this case, after the slab moved a bit, it pushed the grade beam out of alignment.

The solution is not cheap. Heat, to prevent freezing, is one solution. But just insulation with a vapour barrier may be enough. The thermal gradient and water may be there, but these are separated to a point where the thermal capacity is not sufficient to produce frost in quantity to cause a problem. The vapour barrier must be attached to the concrete to prevent moisture ingress with a mastic or like.   

Overland Summer drainage

One of the local counties only permits overland summer drainage on road allowances. So what does one do with winter sump pump flows? Well apparently, there are not to be any within the county. So the county is trying to regulate nature? Good Luck county. Now what does one do? Build a glacier in the back yard, where it slopes to county land, so they can get a big melt in the spring, and comply with there overland summer drainage? Oh well, more government waste to tax money.

This is about like the Indiana State legislature in 19th defining the value of pi exactly, for "palatability." Or Pierre  E idiot Trudeau ramming french on western Canada. It just ain't gonna work.

Frost Heave

Frost heave is a process during freezing that causes ice lenses to be formed. Water is drawn to the freezing front. This process required three conditions; a slowly advancing freezing front, a soil that is permeable enough, yet has capillary rise, and a water table within the capillary rise. It is even worse it freezing occurs below the water table. This is all extra to the simple phase change volume increase.

Simple phase change can cause volume changes of 4 percent of the freezing depth; however, 2 percent is more typical. Frost heaves on the other hand can much large, often 150 mms to 300 mms on rural roads, and similar earth structures. Note that the frost penetration is much less in ice lens as the energy loss required to freeze water is greater. Normal soil has no laden heat, and its thermal capacity is only 10 to 15 percent of water, but the soil density is 1.5 to 2.2 time that of water, so a unit volume of soil has typically 15 to 20 percent thermal capacity plus that of contained water. For this reason, frost penetration is greater in dry soil, and typically greater in sand than clay due to the water retention properties of clays.

Silt sized material, with fine sand and small amount of clays is about the worst material for frost heave. This is usually delta sorted material or river settlements. These frequently occur in low land where water is also found. Road fills also reduce the likelihood of frost penetration, which is one thing that can help. Insulation under the pavement structure can also help.

Frost heaves, in the City's, where no frost heave has previously occurred are often indicators of water leaks, as these provide a source of water.  When opening these to expore the cause in clay tills, frequently, a water bearing crevasse infilling sand seam in east Edmonton / Sherwood Park area.  

Positive Drainage

Drainage away from your house and buildings is critical, and may require maintenance. Backfill against basements, grade beams and frost walls settle, removing drainage. Water will only run down a slope. Yup. A fellow engineer even forgot that. Oh well. The whole building drains to the elevator shaft, and the sump is just below basement floor level over one metre above the elevator shaft elevation.

The ABC building code requires a 150 millimetre vertical separation between any untreated wood and soil. This is essential to prevent rot, mould, from moisture wicking into the wood. In addition the first 1.5 metre away should drop another 150 millimetres. In new construction, we recommend 300 mms in 3 metres to allow for some settlement. Two percent is recommended beyond.

Now what do we do if there is not sufficient grade for drainage? Well, we weight for wet basements and insurance claims. Exterior sumps can be installed, usually to some depth below the weeping tile, and it may have weeping tile attached to pick up any surface ponding. These exterior sumps are high maintenance, as in this country, these pumps need to pulled out in the fall, and reinstalled in the spring, to control freezing conditions. The alternative is heat tape, insulation, and dealing with water in the winter, unless the sump goes dry. Now what about spring, when we have daily cycles of melting and thawing.

The simple solution is to allow enough grade for drainage.

Housing has become a commodity in some areas, rather than a life time investment. Many people have become detached from the care and maintenance of there houses.

Semi-Walkout

What is a Semi-Walkout basement? Well, I just do not know what else to call it. It is a walkout basement that comes out below grade. These may have interior steps that lead to the door, or open to a recessed area. These are built in water traps. The frost gets down to the weeping tile, and can produce issues. These warm weather southern designs work where there is free draining soils, no ground water within some distance, or no (little) frost penetration, or dry climates.

Wet year there are issues. Here, we can get storms that will dump 4 inches of water in one hour. The design storm. That is over 2 Imperial gallons per square foot. Now we need drains that will handle that amount of water. If you have a 500 square foot area, you need a pump system to handle 1000 gallons imperial per hour.

Any drain system with pump(s) is high maintenance. And then there is the issue of what to do with the water, and what about winter? Are you below the ground water level? if yes, will you be pumping water in the winter? now what about freezing and ice buildup? Ice kills lawns. Ice kills trees.   

Pavements over Organic Soils

Clients and non geotechnical engineers frequently want to build pavements over organic contaminated cohesive soils. Organic contaminated soils have two outstanding characteristics; they loose considerable strength when they become saturated, 1 or 2 orders of magnitude, often essentially flowing, and they are not volume stable. Much of their dry strength is due to negative pour pressure developed in the organic material when dry, aka, desiccation cementing.

Build over unknown amounts of peat organic topsoil, A horizon material, or even B horizon organic contaminated clays or silts, is possible as long as the client will accept unknown amounts of settlement. Peat will commonly settle to 25 percent of it's original volume. CNR estimates the amount of settlement over time equal to the depth of fill placed on it. Building over peat is a subject unto it'self.

Road pavements and parking lot pavements are dependent on good drainage for a good life. 2 percent grade in 2 directions is functionally the minimum grade that one can expect will maintain drainage with the typical amounts of settlement that we see in parking areas. Even this will not compensate for buried topsoil, poorly compacted trench backfill and local overloads, rutting, and the like. Any thing less than 2 percent guarantees birdbaths over time.

Pavements at 1 % is less than the paver accuracy, so birdbaths are guaranteed upon completion of paving.

To compensate for buried organic fill, at least in one direction, the grade should be increased. I would suggest 4%, however, this may be reduced and reduction will result in shorter pavement life. Anywhere water will puddle will shorten pavement life as asphalt is permeable to water, especially if the AC has low density or is cracked as a result of rutting or settlement.

For pavements to function fairly well, it is recommended that over peat or burred topsoil, a minimum of 0.9 metres of clean clay fill be placed. For heavier traffic, trucks, 1.2 is recommended. ATU requires 1.5 metres for primary highways. This assumes that 0.3 metre lift will support compacters, to achieve 98% cSPD.

It is the opinion of the author that these may be reduce 0.3 or 0.45 metres where organic contaminated clay is the offending organic. All these depths are below subgrade elevation. Standard 300 mm subgrade preparation is assumed, or cement stabilized. If the client wants to use 150 mm subgrade, then only reduce 0.3 metres, so the minimum is 0.6 metres.

These are typical rules of thumb. Specific information and detailed analysis may alter these suggestions.

Zero skin friction zones

These are general rules of thumb, first approximations, and are often broken for various reasons.

The upper portion of a skin friction has no reliable skin friction due to drying and shrinkage of the soil away from the pile, frost penetration, and potential for some fill.

Fill is unreliable, as it has two characteristics, it has unreliable strength, and unreliable settlement characteristics, most of the time. Shallow engineered fill, after one year may be suitable for light structures.

Typical recommendations for skin friction piles, drilled, cast in place concrete, are from 0 to 1.5 metres below final grade, 0 skin friction. This provides protection from drying and/or frost action. This requires a relative level site after stripping, plus/minus 1 metre, and competent native soil.

Occasionally we use 0 to x.x metres below current grade, where we have fill, or a significant slope to the site. The cause of this requirement should also be noted in the report. Occasionally elevation may be used of odd cases.

Generally, we prefer only one condition for a site, however two or more may be used if there is an clear reason, such as an old basement, utility line fill, or other special situation.

In the case where there is fill, there may also be down drag. Down drag is a load placed on the pile from fill settlement. Typically for old competent shallow fill, -10 kPa is the downdrag value assigned. New loose fill should be atleast -25, typically -20 kPa is used for fresh compacted fill. These are typical for 1 to 3 metres of fill.

Often, where less than one metre of fill below floor slab elevation, the fill is just part of the zero friction allowance and is ignored. With say 1 to perhaps 3 metres of fill, the first 2 or 3 metres of pile friction resistance, below the fill, is discounted to deal with a bit of down drag. This requires a fairly uniform condition across the site.  This requires good friction in the upper soils. Note that the surface soils can also be soft, and have lower value for other reasons, or it is specified and must be included in the structural design. That is useful  where the site has know fill areas.

Down drag can be reduced to -5 kPa by using a double polly rapped sone-tube as a friction reducing smooth surface.


Crap fill, as truck dumped winter fill, uncontrolled truck fills should all be considered as poor, and are unreliable for pile friction and slab support.  


Values and recommendations from previous projects, found in the boiler plate report, must be customized to the current situation. Any missing recommendation sections must be added. 

Engineering Education

Engineers are taught the new, hot, sexy, stuff at university, not the basics. That is becoming an issue. We have people that know about the great stuff, but not how to do the basic stuff of every day work. Sure, when they get the chance at the big stuff, they can do it, but not simple stuff, or they are just uneconomical to do the simple stuff.

Desperation cause us to make poor short term decisions. Hiring unskilled but educated workers is one such alternative that pisses off the existing experienced workers. Now, are you just turning workers, or advancing the company?

Is there need of "engineering lite" books, but there are some of these, but they prescribe ways of doing things, but not the rational, the mathematics behind the methods. But I see a need. Or perhaps videos, documentary videos.

I took a job one time out of desperation, which was not great, but I got to explore paving over ice rich permafrost, which melted out as expected, resulting in wavy undrained surface, as well as pavement failures. Such is life. Doing thing for the wrong reasons, but getting some results.

why is my road falling apart?

The story:  Underground constructed in 2007, roads 2007, no houses yet (2012), asphalt is ACB, numerous cracks, corner pushes.

ACB is a base coarse asphalt, not intended to be used as a surface course. It is open, and will allow water to penetrate. In addition, there is considerable segregation and exposed rock areas typical of cold placement of truck box corners and hopper wings. The asphalt had variable asphalt content, often to the low end. Densities were adequate.  

Separate the mechanical damage, such as the location where the crane or picker truck lifted something heavy, without adequate pads. Two rectangular spots where the rectangular pads were in contact with the AC, and is punched the structure.


Through out the project, there were issue with lift thickness, and the contractor was not cooperating with control of lift thickness. This was all reported to your man on site, but nothing changed.  

Separate trench settlements, where underground settled. Density is not enough to control; lift thickness must also be controlled. We struggled with the contractor over lift thickness when we were on site, but we were not full time. This was reported numerous time to Mr. xxx, your man. Nothing happened, the contractor continued with thick lifts.   A typical compactor has difficulty to compact the bottom portion of a 300 mm lifts, the maximum allowed. We cannot test more than 8 inches deep. A nuclear density machines density reading has surface bias, 87.5 percent of the value is in the top 50% of the depth, nearly all of the moisture reading is in the top inch. Trench settlement typically creates two longitudinal cracks, one at each side of the trench, somewhere from the straight wall to the edge. Often it shows up as three cracks where two trenches are involved. Services, and other lines that cross, can be identified by settlement in there location.

Trench settlement can also be identified by "manhold growth", which is settlement around the manholes. In several locations, it is likely that vertical ends in the backfill were created near manholes. This results in a loose column of backfill which can settle.

The lots were not graded to drain water away. There are ponds where the houses will be in portions, and water drains the rear or the curbs in locations. When subdivisions are left, it is recommended that the rear of curbs be backfilled to encourage water to drain across or away, not stand and soak in.

Traffic is more than minor. During the inspection 5 loaded trucks were noted, one loaded semi-trailer use the the 97A/89 route twice,  and on both trips, did backing practice on 97A/89 corner ( the only purpose I could think of, but I could be for other reasons)  The other truck was a tandem, hauling topsoil on Grand.


On numerous corners, the asphaltic concrete has failed by diagonal vertical shear. This is a common issue with poor compaction and pushed hand placing producing a shear plain in the asphalt during placing, which never gets knitted together without considerable rubber rolling. Thermal expansion of the mono sidewalk curb and curb produces a lateral forces on the asphalt, and the asphalt faults along the pre-existing weak plain / shear plain. 


There are several areas that have typical failures of missed cement stabilization or deep gravel infill into some trench, producing a water source for frost heave. These can be investigated by a trench, should it be desired. This involves cutting a trench about 2 feet wide, three feet deep, and 10 feet long through the problem for evaluation. Testholes often miss the issue, as these may be small. In several of the locations, these may be gas or electrical crossings, off a bit from where the plan indicates.


There are a number of areas that appear to have structural pavement failures. This can result from a few truck overloads,  traffic volume, thin structure, or some issue with the structure. It is recommended that testholes be cored, and hand augers be conducted for evaluation. Asphalt thickness, gravel quality and thickness, cement stabilized holidays, and other issues can be identified. In some cases, these are occurring at trench settlements crack locations, which will permit the ingress of water and soften the subgrade and below.   


     

Trees Vs House Foundations

In Edmonton, and elsewhere, there are issues of tree roots causing foundation settlements via the mechanism of high plastic clay shrinkage. In most cases, we have no testholes, no real data, just typical of the area, testholes from other jobs. Opinions may change with additional soil information.


We are located in what was a glacial lake, which became a mud flat after the lake drained. Much of this area has high plastic soils. We have had a number of dryer years, the big tree now have roots through the desiccated crust, into the moister soils, drawing water from them, and in effect thickening the desiccated crust, with accompanied movements. Recent rains have created some surface swelling, with associated lateral pressures.


This is exclusively a clay dessication issue, not a tree root growth issue. Trees draw water. The amount varies greatly with season, species, heat, tree lief area, wind speed, time of day, and other factors. Several water balance studies have examined, and typically result in the trees will draw all available water in period of drought. Roots that found water will continue to grow: roots that fail to reach water growth slow or stops. 


This applies only to house foundation complying with part 9 of the ABC, 1.2 metres of cover, as it was since 1967 building code and remains in the current code. Slabs on grade and those exposed to freezing, may be underlain by fill and or organic materials, and garages on mud slabs are expected to move and the owners must just accept the movements. Consideration of the claimed damage to such slabs and landscaping is excluded from consideration. Only the house is considered. It is commonly recommended that residential foundations have at least 1.5 or 1.8 metres here, due to frost penetration and the new basement wall insulation standards, but the building codes have not caught up.


Foundation strength has little to do with movements, but does have with cracking and crack spacing. It is movement of the supporting soil that is the real issue. When the soil shrinks below the foundation, the foundation has little choice but to follow. As far as building codes go, the codes have allowed and still allow unreinforced concrete. Sure, we know how to build a foundation, and building that would not be effected by City trees, but the trees were placed after the structure was there. The cost of such a foundation and structure would cause houses to be constructed elsewhere. It is not tree roots that is causing the problem, but the dessication of the clay by the trees that is the issue. 


If the City thinks that deeper cover is required, it should be put into the building code that the City enforces. 


For movements to occur, the clays below foundation level must be wet before house construction, and near normal consolidation. In this area, we have a desiccation crust over near normally consolidated materials. In areas, the desiccation crust is thick, other areas less so. This area is old glacial lake bed. Depending on the area and reference, between 10 and 20 percent of the area was sloughs, and never dried out before man came along, trapped the beaver, drained the swamps, and made this into farm land. Development of housing, streets, sewer modified it more again. The slough areas have higher thickness's of high plastic clay, and less dessicated crust. Moisture contents are frequently 35 percent, and these clay will shrink to moistures of about 20 percent. 


Tree root spread is only one of the issues. As the tree dry's the clay, moisture also migrates toward the dry areas through the soil mass, and through the  fissures and cracks develop as part of the dessication.

The moisture a tree can take in is limited by the available moisture. In changing form 35% to 20% will give up about 0.25 cubic metres of water. The depth of dessication can be considerable, and ultimately results in thickening of the dessicated crust in areas which were wet to start with. The wet clay, and house before the trees were performing adequately. After the trees were added, the dessication occurred. This has been demonstrated repeatedly to have have occurred at other locations. 


Testholes are expected demonstrate the difference in moisture profile, if conducted adjacent to the four corners of the house. 


Note that root spread is dependent on water availability. Roots will expand and extend in the direction that the roots are encountering more water. They extend down the fissures between the soil peds,  The typical numbers are averages at best, not limits of spread. In addition, beyond the root, the moisture moves toward the dry soils. In shrinking, normal soil mass permeability fat underestimate the actual value due to moisture moving through the texture cracks.


Movements that result from frozen ground below the foundation during construction are often apparent during construction process, and first year of life. Fill, burred topsoil, construction issues or other causes usually shows up in the first five to ten years. Testholes and a soils log is required to eliminate some of these things.

The next logical step is a series of testholes to define the soil and moisture profiles to considerable depth at numerous locations. In addition, some testing could be done to define the swelling characteristics at this particular site.


The last statement "Historically the City... etc must mean that all the complaints to other city departments are not getting to their department. The City Geotechnical department is aware of the issue, and has been for thirty or forty years at least. 










   

What Should be in a GI Report

What should be in a Geotechnical Investigation report?

Essentially, the report should contain all the available information we had, and everything geotechnical the client will need to design and construct the project. Are we employing or expecting mind readers? Not quite. But anyone who is expecting to write a geotechnical investigation report will need to know how the project will be built, and what steps are involved in the process, and how the soils will impact the project, and how the project will impact the site.

This may be easier to understand by considering a part of one project, say a car parking area.

The steps of construction are as follows:

• Define main issues and the project parts
• strip the topsoil and organic B horizon material
• cut and fill to grade. All pavements should have minimum grade of 2%, including any swail. 
• install underground
• subgrade
• pavement structure
• exclude all the common errors
• include all cleanup - finish items

Now we can write the report around what is there and how it must be done, customized to that site and conditions. It must be site and project specific. To do this, we must know what the project is clearly, and all the components of the project. It is better to start knowing what is going to be required.

Report fluff is not recommended. If it add no value to the report, that is does not limit our liability, make things clearer, or provide project specific concise information to the client, leave out the fluff. 

Time is money, in engineering, especially with fixed prices. We need to both do the work right and make money. Fluff has no revenue, and a considerable cost.

Hide, not identify the true need.

I have a client which we have done a few footing inspections on house for. On this one, he actually requires a geotechnical investigation for piles, and he tried to slip it in as a footing inspection. Clients just cause me stress. OH well, shit happens.

Control Freaks - Tyrants

We all see these, occasionally. Pit the poor people who work under them.

Tyrants are impotent without people to prey on.

I am not talking about the over confident, like the typical surgeon. They need to believe that they know it all to overcome the natural human reluctance of cutting into someone. This is all ego built up in the mind. The reflection of there training, the reflection of the overgrown collective egos that are the medical community.  We often work with collective superegos, - municipal governments planning and development departments.

I was asked for stamped and sealed design notes, and this time I declined to provide them. The last time I provided them and the individual started to pick them apart, and it became apparent that he knew less about the subject than I, by far. He was a tyrant, as it turned out.

The other reason to ask for design notes is at the suggestion of a lawyer. The collection of legal information, in preparation for a lawsuit before the work is done, in my opinion is dealing in bad faith. I do not want to work on projects like that.

Another reason is to ask for design notes is to learn the method, so that you can do the work in the future. I am not about to train my clients to do me out of work.

Regardless, providing design notes is leading with your chin. We can make a decision if they insist: Do we want to work for a tyrant, a big ego, a litigious, or a information thief anyway?

hunting with a pencel

In an evolutionary scene, we engineers hunt with a pencil. We consulting engineers are the storehouse of designs, concepts, ideas, computing models, formulas, data, and some theories, and many approximations of the physical world as it was, which we pull off the shelf, add a bit of site specific data, adjust the model, turn the crank three times to the left, flick the accumulator switch, once to the right, put in a bit more data, or take some out, turn the crank a few more times, and come up with an answer (If you are old enough to remember the Curta Calculator).  The final step is to communicate the answer to the client. Before this can happen, we must know what we are hunting for, and where to find it.

We had better know the answer in a general way at least, or what data we will need and where to get it before we take on the project. If it is reclamation, we had better know the cause of the original failure, and how to avoid it, or if we are dealing with time and wear, what the clients current and expectations are.

Traffic loads are increasing, not only in volume, but the governments have and are increasing legal loads. This has a tremendous impact on the cost of roads, at public expense.  These legal loads come onto private property, and pavements must be thicker to support them. The equipment that loads and unloads them is large, more heavy pavements. The building that house them are large, heavier loads. Buildings  in general are large, heavier, and the clients are only looking at dollars in most decisions now.  

It has become a much more difficult struggle to operate a small firm. The specialization has made it difficult to find suitable replacement personnel. Burnout of senior people, myself in particular, is the issue.    

Asphalt Pavements

How do we repair asphalt pavements that are in need of overlay and there is no money?
Well that is a hard question. Water is the main issue. Overlay patch anywhere that water stands after a shower. Truck dumped and grader leveled asphalt is the best solution, equivalent to a leveling course. Seal to prevent water ingress. Water softens the support and hastens failure.

Expect heavier overlays.

Cracking will continue at a faster rate. New cracks and old cracks growing in length and width will create additional issues, so annual sealing via spray chip seal is the best patching method, where water is draining.

It becomes repeat the truck dump patching and spray seal annually until the road/pavement has been evaluated, and a structural over lay has been applied.

Most of the roads that I have designed the pavement thickness on were constructed with less asphalt and gravel than I recommended. This reduces a 20 year design, that should be overlayed at 15 years, to something less. When the next government administration asks why it is failing at 10 years, all involved have mover on. Say la vie.      

High Bearing Values

High Bearing Values and ABC Geotechnical Schedules

Here is one response that can be placed in the cover letter that sets out the limits where the bearing values are a bit on the high side.

The bearing value provided in the geotechnical investigation report (GI) is higher than we would typically provide within that formation and area. There is no test data contained within the GI report support such a value based on conventional data conversion for typical construction. The value is acceptable for flexible construction.

We are therefore proceeding on the basis that we are accepting the bearing value at face value; however, differential movements may be excessive for some styles of construction and suitable for others. No information has been provided on the structure or performance expectations.

Insurance and Foundation Movement

In general, home insurance does not cover foundation movements. Some insurance may cover damage due to foundation movement. You fix your foundation (the big cost) they may cover the damage to interior (drywall patches, painting).

We are located in what was a glacial lake, which became a mud flat after the lake drained. Much of this area has high plastic soils. We have had a number of dryer years, the big tree now have roots through the desiccated crust, into the moister soils, drawing water from them, and in effect thickening the desiccated crust, with accompanied movements. Recent rains have created some surface swelling, with associated lateral pressures.

We can do an inspection of the damages and provide an opinion as to the probable cause(s). With residential construction, there are often additional problems to the foundation movements. Poor design, that the expected performance is not satisfactory, wrong construction, poor construction, incomplete construction, poor repairs, and may other problems exist. Inspections are conducted at a hourly rate, including travel time, inspection time, any research time digging through archives, and report writing time.

We can also conduct a geotechnical investigation to determine soil index parameters, or actual values, and an indication of the swelling potential a number of ways. The next step is typically a minimum four deep macro-core test holes, with moisture contents, Atterberg limits, remaining linear shrinkage to oven dry estimates, hand auger holes inside the structure, site surveying, house level survey, drafting of the collected data, and a engineering report. The current cost are typically $7000 to $15000.

Out to Lunch

How should one handle the situation when the "authority having jurisdiction" is out to  lunch on a particular topic?

We see this in the building code, in nutritional recommendations, in medical recommendations, and in the past religion, when it had real influence. One way is to write a book, do a blog, or a web site and publish it. The information is then out there, in the public domain, where people are free to chose to understand or not.

This is considered dissonance of some kind, in the past it might have been treason or heresy. Now it is rebellion, but what is the best solution?