Frye and Swelling - Shrinking under buildings

Frye is a legal standard of evidence, the lowest of which is the opinion of an expert. That would be superseded by test data, and ultimately by proof.

With foundation movements, it is impossible to go back in time to monitor moisture change in the soil below a basement so absolute proof does not exist for a specific basement. It has been shown to occur in research.

A expert can look at a structure, in a area known to have high swelling soils, note the trees, perhaps some wetter areas near downspouts, and if there is a correlation with distance from a major tree and the amount of shrinkage, that is the floor points to a tree, it is likely that shrinkage is to blame. It it point up at a drain spout, or a source of water, swelling is likely.

Now to remove doubt, one step at a time. First to demonstrate the soil has swelling/shrinkage potential. There is a good correlation between Atterberg limits, a index test for classification, and swelling. That only tells us that the soil is capable of swelling or shrinking. Add some moisture tests, and we can know that it is within the normal range that shrinking and swelling occurs. When we have condition that is dryer at the tree, wetter away from the tree, for similar soil and strata, the data would suggest that the tree is drawing water from the soil. But all trees draw water from the soil, and most draw more adjacent to the tree than away. This can get altered where there is a drain spout at the tree. Ideally the best demonstration we ever get after the fact, is a high plastic soil, and higher moisture contents at the high points of the structure. A range of moisture can usually be established.

There are odometer tests, where a "undisturbed" sample of soil is placed in a testing apparatus, the height measured, it is saturated, loaded, in steps over time, and allowed to swell, consolidate, rebound, and the results are analysed. But usually the soils in the field are not saturated to start with, so it tells more about the soil and its potential than what actually happened.

Now for the complication. Lacustrine deposits are varved, that is there is a variation in the clay/silt ratio with depth, often varying 40/60 to 60/40 in a few inches, or a foot vertically and be visually indistinguishable. The Atterberg limits, moisture content, hence the swelling potential, and the moisture holding capacity also vary. Comparing the moisture's without Atterberg limits on each sample is little better that an option mixed with some test data.

Now if we do four testhole, to 12 feet, with 12 samples per testhole, do moisture on all samples, limits on all samples, at about $100 each plus sampling, logging, field time, you have a nice bill, for a better suggestion of the possibility. Some of that data will be meaningless, or misleading, so what to do, we ignore some of the tests.  Suppose we do four testholes to 12 feet, a sample/foot , moisture on all, and say 4 limits on selected samples. Now we are introducing bias of the geotechnical engineer who is selecting the samples to conduct limits on, unless we say something like even testholes at foundation level, odd testholes at 1 foot below foundation level. Then it is biased by the person selecting the testhole order or locations.

The location must be selected to show the range, 2 in the dry areas, 2 in the wet areas. Ideally for a house, we would like two in the high area, two in the low area. This may mean 2 inside, and two out. To make matters worse we may may looking for 2 percent difference dryer hole to wetter hole, when over a few inches, the soil may vary 4 percent vertically in one testhole, so "proof" is not always obtained. The suggestion may be there in the data, or perhaps not. So now we can have a question as to what the data really shows.

One testhole in a area expected to be wet, at a downspout not near a tree, and one near a tree, not near a downspout, can be the best demonstration variability, with moistures every 1 foot, to 3 or 4 feet below the foundation may be advisable and a few limits just below the foundation level.

Now testholes on private property requires two liability wavers, one from the home owner and the insurance company we are working for must be willing to pick up the risk of a unknown utility strike. All known utilities can be located, both public and private, and avoided.  This assumes that locations are available and accessible.

Next is the other issue, the method. Inside is hand work. Coring through concrete floors is messy. Hand auguring below is tough work, and requires a skill that must be trained into people doing manual work, as well as myself to observe, and a junior engineer to sample and log the testholes. This all assumes that there are suitable locations to conduct testholes. Where the house is surrounded with trees, the outside testholes can be a issue also. Finding a "wet locations" that is clear of utilities is not always obvious, and close to the house. The front or rear lawn, well away from the house is often the only choice. Close to a tree, or within the same from the tree as the house is is often the best available choice for the "dry location".

Residential basement

Residential basements, as part 9 of the ABC allows them to be built are fragile.  They just break to easily, when anything heavy get near them. This is a problem for anyone working around these thing. They are just dangerous.
Vibration can produce lateral loads on them and fail them. They rapidly break with swelling clay or shrinking clay.

Vibration

Vibration Damage is a insurance issue, in that every time a home owners feels vibration from a construction project, the owner claims damage occurred. Frequently, the damage is obviously preexisting. But occasionally damage from vibration does occur. Any time a compaction roller gets closer than 25 feet to a residential concrete basement, built to just the minimum Alberta Building Code standards, the lateral forces are high enough to potentially cause damages. Drop weight concrete breakers and big back hoes which lift and drop concrete, pile driving operations, deep soil compaction, and well fracing all can cause damage.

Wet soils and vibration sensitive silts are particularly bad. Wet soils lateral pressures attenuation is low. Vibration sensitive silt can cause settlement at considerable distance.  

residential piles

I recently reviewed another residence in distress in which the garage piles had failed, the grade beam had failed and broken apart, the garage floor slab had heaved. Previously, the sidewalk had sunk and been replaced with unistone. The driveway was showing distress. Once more the sewer line was adjacent to the piles. What it all comes down to is eight feet of loose fill will settle 3 to 5 inches, dragging piles down when they are loaded. Unreinforced slab do not work. Unreinforced grade beams do not work. The final load was likely this winters snow load, and the piles failed rapidly, dropping one garage wall 3.5 inches at the front, and that corner of the garage grade beam bowed out 2.25 inches at the floor slabs. In addition the buck downs were 14 inches, leaving about 12 inches of concrete block under the man door.

When will home buyers be protected? Not under the current system of codes, permitting, and no quality enforcement. The government is only interested in the appearance of enforcement, the political necessary part. Mind you, this was a 27 year old house. Yard drainage was less than ideal.

Ultimately, the builder must held responsible for the structure for a long time. How can we do this? Ultimately, an independent third part should provide a code adherence certification, to be registered on the title. The code would need revision that no one would be happy with. This would produce a requirement that each excavation, and back fill, every bit of work on the property be tracked on the title; hence, the owner would know what he was getting, not if it was going to hold up. All the common shortcuts would not be permitted.

Many of the contractors are not even aware of the problems of common construction methods. Steel on the bottom of the concrete slab, unreinforced concrete construction, permitted in the building code is just wrong, for long life. The building code, federally created, modified and adopted by provinces, municipally sort of enforced model we have now does not work. Inspection is by "permitting companies", that can only make money by paying their "build code inspectors" less that the government would be required to pay, to do the same work for less money, or do less work. It is not logical to be able to do the work "profit" less than the government.

Difficult Clients

Difficult clients occur. They just want what they want, even though what they want is impossible, or not what they need, or just not what we provide. That may be the easiest way to look at it, as simply not what we provide. If we provide something that will not work for them, it is difficult to get paid. That is what makes working with armatures so difficult. By armatures, I mean first timers, virgins, at what ever they are doing, property development, privates building house, home builders doing custom homes, or commercial work, commercial contractors moving to industrial or institutional work, or from the oil industry to our construction field.

We do what we do, but are willing to change as long as it does not compromise our own standards, ethic, or logic. We work on paper and in the real world. The two must match.

Some client are just not worth having. The liability is just to much for the money it will provide.

Extrapolation Beyond the Testhole Area

Extrapolation beyond the testhole area is dangerous and must be totally at the clients risk. A situation has arisen where the client want advise on a site adjacent to a building for a parking area. It was not included in the original investigation.  Any additional advice should be an extra.

The first recommendation should be testholes are required to provide the requested recommendations. We only know the soils at the testhole locations, and there may be only soils classifications that are relevant. Soil varies rapidly across a site.  Fluvial deposits vary rapidly across the direction of water flow, less along the flow, and the flow is constantly changing, so the direction is changing. As sediment is placed, the channel is filled in. When old braiding and oxbows occur, peat will grow. So when we find peat, is it a channel or bog? How uniform do you expect the geology to be?

We expect that there is peat on this site. With peat, they need to be aware that movement, settlement, will occur, and that the settlement can be substantial. Grades are important when settlement is expected, and a 1.5 metre pad over the peat is require, remember that peat is associated with water, so what do we really have?

Next, as fill will be required, we will need to confirm the clay is suitable, and is consistent with the clay assumed in the fill design. Settlement of any remaining peat will occur. How much settlement? Rule of thumb 50% +_ 25% of fill depth. OK. Another one for deep muskegs-- 1/2 the depth of the fill placed. Peat is fibrosis, shearing is often not the issue, just compression of the peat. Fabric or grid can also spread the load better, but does nothing for settlement. Low weight fill has been utilized a few times. Artificial foam has been proposed to be floated, but I have never seen. 

One more thing to think about.
   

Routine Buildings, required number of testholes for preliminary investigation.

Ultimately, the purpose of any geotechnical investigation is to obtain information about the unknown conditions that lie below the surface. Often the geotechnical investigation is the first information on the site, often before even the sight survey. We are exploring the unknown. After exploration, we only know the conditions at the testhole locations, but that can imply a variation between the testholes. We can have tremendous variation in short distances both vertically and horizontally.

The information required is to provide input into the type of foundation, design parameters, and other issues that can be expected. Two large “unexpected” costs often encountered are unsuitable fills and poor foundation conditions, requiring expensive foundations. The more information we provide, the better the owner can estimate the cost and performance before construction is started.

With fills, additional testhole may be required to examine the extent and depth of the fills. Environmental cleanup can be dangerous due to fill settlement downdrag on piles. Redevelopment sites often have old fill over old utilities. Old fill compaction was often poor, and old fills often contain garbage.

Heavy buildings, high retaining structures, elevators, and similar are not included in this section: heavy buildings may have special requirements. This is intended for one story industrial buildings, three storey or so apartments, motels, and other buildings, but may apply to others in a general way. Areas with complex geology may require additional testholes. Thalwegs, stream erosion channels, occur in bedrock and clay till formations. Native buried peat moss formations occur in geologically recent river and delta deposits.

The testholes are intended to provide an indication of the vertical and horizontal variability of the strength and settlement characteristic of the various geological strata to sufficient depth to support the expected loads. One testhole tell the conditions only where the testhole was at: we have no clue as to the variation across site. One testhole is suitable for lift stations, or similar very small structure.

Two testholes are suitable for linear structures, 100 to 200 metre long sewer, roadways;  50 metre short height retaining walls, add one per each additional 200 metres of roadway or sewer, 1 per each 50 metres retaining wall.

Three testholes is the minimum required to describe a plain in geometry; however, the contact between strata is seldom plainer, and especially water lain strata. Three testholes is suitable for buildings to 500 square metres, add 1 per 250 m2 to 1000, 1 per 500 thereafter. Personally, I would not build a house without 4 testholes.

Should something odd or expensive to deal with be found, additional testholes for clarification may be required. Old coal mines, undocumented environmental cleanups, any industrial use, or redevelopment site can be hazardous.