Your building your dream home in the Greater Winnipeg Area and today is piling day. The concrete piling contractor shows up and starts drilling but the bore holes are collapsing in and/or filling with water. Dang it! What now?
Collapsing holes due to sand, silt or muck or a hole which is quickly filling with ground water will often require an engineered re-work. The most likely solution is a switch from a cast in place concrete friction piles towards an end bearing driven pile such as H-pile, timber pile or precast concrete pile. All of these traditional alternative piling solutions tend to increase the cost of piling your home by 3 to 6 times what may have been budgeted for C-I-P (cast in place) sonotube style piles. OUCH!
I wish this was an article about an everyday alternative piling solution that is always cheaper or the same price as concrete friction piles. For residential projects with loads of 20,000lbs (89kN) to 30,000lbs (133kN), Winnipeger’s on a budget love the economy of concrete friction piles. Unfortunately, in Winnipeg clay on a residential project with loads in excess of 20,000lbs, there isn’t an alternative piling solution that beats the economy of concrete friction piles.
Traditionally in Winnipeg, the most economical alternative to concrete friction piles has been driven timber piles. At a typical budget of 3 to 4 times the price of concrete friction piles, this most economical alternative still is a very expensive and tough pill to swallow. Although, only popular the past few years in Manitoba, there is a 185 year old engineered piling solution that has replaced timber piles as the most economical solution in sloughing soils around Winnipeg. It’s not a miracle alternative and it likely means budget pains but at a typical cost of 1.5 to 2.5 times residential concrete friction piles, helical screw piles are an effective lower cost alternative to other driven, end bearing piling solutions.
Below is a brief comparison of driven timber piles and helical screw piles for residential projects with typical loads of 20,000 lbs (89kN) loads.
|TIMBER PILES||HELICAL SCREW PILES|
|AVAILABILITY||Typically ordered custom resulting in weeks of delay.||Stocked and ready within days.|
|INSTALLATION||Pounded in the ground with massive equipment resulting in vibration which could impact neighbouring structures and that is loud. Often, when installed near a neighbouring structure, consultants must be retained to monitor the neighbours’ foundation(s) for damages.||Turned in the ground with small or mid sized equipment, little to no vibration and no louder than an idling engine (difficult to hear from inside a neighbouring home).|
|LONGEVITY||Life expectancy of ~100 years, ground water generally improves life expectancy.||Minimum life expectancy of ~140 years and average of 340 years if hot-dip galvanized, divide life expectancy by 2.5 if not HDG.|
|ESTIMATE ACCURACY||Lengths are predetermined, they can’t be lengthened, generally they are ordered longer than expected and cut off to height. If they are not long enough, the short pile is abandoned in the ground and longer piles have to be ordered resulting in delays and higher costs.||Can be lengthened as required to achieve design criteria, a pile that is estimated too long will thus be cheaper and piles estimated short are quickly and easily lengthened at nominal cost.|
|COMPRESSION||Predictable performance means very low probability of failure.||Predictable performance means very low probability of failure.|
|LATERAL||Shaft is generally 16″ in diameter and provides high resistance to lateral pressures.||Shaft is generally 3.5″ in diameter resulting in lower resistances to lateral pressures. Lateral loads for a house are typically well within the lateral resistance of a 3.5″ shaft helical pile.|
|COST||Typically 3 to 4 times the cost of CIP piles||Typically 1.5 to 2.5 times the cost of CIP piles|
|LENGTH||Limited to 75 foot length using very large equipment. Note, this is likely long enough in Winnipeg although not guaranteed.||Can be lengthened as deep as necessary using small or mid sized equipment such as a mini or midi excavator or skid steer|
|MOBILIZATION||Materials are large and bulky and equipment is large to massive, mobilization is typically thousands of dollars using semi trucks and heavy duty trailers||Materials are sleek, lightweight and easily stacked while equipment can be moved with standard pick up trucks and trailers.|
It is important to note that the reinforcing detail of a concrete friction pile used for a commercial application is much more robust than a comparable CIP pile for residential applications. Therefore, a 20,000lbs capacity friction pile in a commercial application is substantially more expensive. Postech Screw PIles are already commercial grade piles. Used for commercial purposes in the Greater Winnipeg Area, helical screw piles have a much higher probability of being a cost effective alternative to not only driven end bearing piles but also concrete cast-in-place friction piles.
The friendly and professional team at Postech Screw Piles Manitoba is always happy to discuss your project needs. We will quickly prepare information so you can determine if helical screw piles are the best solution for your piling project needs. Contact us today at 204.793.0653 or visit www.screwpiling.ca to request that our team connect with you.