If you want to know why there’s a crack in your home’s foundation or if you have a bedroom door that sticks when it didn’t used to, you have to look back more than 11,000 years.It all started long before human life came to the Prairies when Glacial Lake Regina covered a significant portion of southern Saskatchewan. It formed as a giant pool of water run-off for glaciers that covered most of the province.
Thanks to educators and documents produced by the likes of the Geological Association of Canada and the Saskatchewan Geological Society, as well as the provincial and federal governments, there is plenty of published material on what many frustrated homeowners refer to as “Regina gumbo.”
The receding glaciers created a varied landscape that included rolling plains, deep valleys and vast sections of land described by geologists as “pool table flat.” The lake — that covered an area about 150 kilometres long and 75 kilometres wide, extending from north of Regina to Weyburn — drained slowly but left behind land that was uncommonly flat. But the soil had a unique chemical makeup that frustrates municipalities and homeowners to this day.
“It all has to do with the clay mineral,” said Ulrike Hardenbicker, an associate professor at the University of Regina’s geography department.
The issue with the soil has to do with sodium bentonite, a component that makes the soil eager to take on water and expand. Different versions of bentonite are used for its absorbent qualities for more practical purposes including cat litter and wine making.
“If you have 10 grams of clay, it can absorb up to 30 grams of water. And when that happens, it swells. When it’s wet, it changes its volume,” said Hardenbicker.
So the reaction to all of the mucky clay on which Regina was built is relatively straightforward — when it gets wet, the clay grows and holds onto its expanded size for long periods of time. It drains slowly and the soil similarly shrinks to its original size.
Specific rates of expansion and absorption vary depending on the chemical makeup of the clay — the amount of this mineral-infused soil differs across the former lake bed. This unique clay is anywhere from five metres to more than 15 metres deep across the former lake bed. The size and shape of the former lake bed can sometimes be seen from the air because the flat terrain is slightly lower and differs from the rolling land that’s beside it. It’s also the reason Regina’s skyline can be seen by motorists driving from Moose Jaw — because it’s on the same elevation. Motorists driving south from Saskatoon on Highway 11 don’t see Regina from the same distance because the city and the lake bed aren’t as visible.
The expansion of clay, of course, is bad for concrete foundations — the swollen earth can push against exterior walls or force basement floors to rise more than a few inches. Most homeowners in Regina and other places like Moose Jaw and Weyburn know all about this. Thousands of homeowners have required the services of engineers and foundation-repair experts to help prevent the earth’s movement from harming their house. Bracing basement walls with vertical steel beams bolted to foundation floors and ceiling joists is a common way to keep foundation walls from moving inward.
Dale Obleman, owner of AAA Solid Foundation Repair, understands how and why houses shift and heave over the years due to moisture and clay expansion. His advice is to hire an expert who can take measurements that can determine whether repairs are necessary or whether something more drastic is needed to prevent walls from collapsing.
“The clay expands and the pressure it puts on foundations is something else,” said Obleman. “I’ve seen older houses in need of bracing and I have seen brand new houses where the walls have already started to come in.”
While opinions differ among real-estate agents, house builders, contractors and homeowners, the majority agree that house shifting and clay expansion is worse in south Regina than it is in north and east Regina. However, all areas of the city and beyond have experienced shifting, Obleman said.
While there’s no foolproof method of preventing cracked basement walls or heaving basement floors, new construction methods are helping. This includes the building of piles, which are long strands of cement strengthened with rebar that extend deep into the ground to help stabilize house foundations. Some builders use piles and create voids under houses so that the movement of earth can be accommodated. However, despite the best efforts of engineers and builders, preventing shifting altogether is impossible — construction crews still build “floating walls” when they frame basements for living space. The walls are built to accommodate a few inches of movement in case basement floors rise under pressure from swelling Regina gumbo.
Regina engineer Wayne Clifton said that no building, no subdivision and no municipality within Glacial Lake Regina is immune from the effects of shifting earth. However, the amount of shifting can depend on the depth of the gumbo, as well as the efficiency of drainage and the moisture content of the ground at the time of construction, Clifton said. These are among the reasons some basements have collapses while others have remained solid.
“There are foundations in Regina that have stood up very well over the years and there are some that have done very poorly,” he said.
Engineers are regularly called into to prepare geo-technical reports before houses, subdivisions and commercial structures are built so the depth and moister content of the gumbo can be predicted and the builders know how to best limit ground shifting. The number and depth of piles also depends on the depth of gumbo, as well as the weight and size of building, Clifton added.
The shifting affects highways and sidewalks just as much as foundations — municipalities routinely send crews to repair sidewalks, streets and even lightposts that have been toppled by the shifting ground.
There is, however, an upside to living and farming on land known for abilities to attract and retain moisture. The sodium bentonite-infused soil means it’s ideal for growing; farmland on the former Glacial Lake is considered to be some of the best in the world.
“This soil retains water but it also means it retains nutrients,” said Hardenbicker.
“So in a way, it’s also the best kind of soil to have in this part of the province,” she said, adding the slow-drainage rates also means the land is susceptible to flooding.
BY ANDREW MATTE, THE LEADER-POST NOVEMBER 7, 2012
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