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.
Thursday, August 9, 2012
Friday, August 3, 2012
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.
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.
Thursday, August 2, 2012
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.
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.
Monday, July 30, 2012
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.
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.
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.
Friday, July 27, 2012
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.
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.
Friday, July 20, 2012
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.
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.
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