A DECADE OF LOAD HOLD CAPACITY ACROSS WESTERN CANADA Cory J.E. Yacyshyn, P.Eng. Prepared for: International Society for Micropiles (ISM) 2009 International Workshop on Micropiles London, England May 13th, 2009 1
Micropiles Overview 1 Introduction 2 Table 1. Interface Bond Values 3 British Columbia 4 Alberta 5 Saskatchewan 6 Manitoba 7 Conclusion 2
Introduction Type of Micropile - Single, continuous thread, solid steel bars - Double corrosion protection (presence of soluble sulphates in some areas) - Axially loaded - Compression load magnitude governs over tension, if any requirement for tension - Isolated vs groups - Typically, light load requirements (25 kN to 200 kN), in Alberta, Saskatchewan and Manitoba - Higher load requirements in British Columbia (< 1,000 kN) - Commonly without permanent steel casing
Absence of Steel Casing? - Rarely is criteria been established for total pile head movement at design load levels in Owners Engineers Specifications - Low load magnitudes - Small requirement to sustain lateral loads, however, increasing trend. 3 Table 1 Interface Bond Values Intent / Description
- Intends to provide design engineers with a basic understanding of load hold capacity in Western Canada. - Description of location and geology - Table 1 shows maximum grout-to-soil/rock bond values achieved at maximum test load level. - Micropile tension test data but some soil/rock anchor tension test data - Early testing followed PTI Manual prior to publication of the Micropile Design and Construction Reference Manual (FHWA 2005)
- Data from 40 projects undertaken since 1996 - Comparison of full-scale load tests to Table 5-3 (FHWA 2005) 4 Table 1 Interface Bond Values Legend 5 British Columbia
6 British Columbia Geology - Low plastic clays - Dense sand, occasionally loose - Weak sandstone, minimal weathering - Very dense glacial tills exhibiting cement-like behavior - Presence of strong rock at the Coast Mountain Range - Cordilleran Ice Sheet, last glaciation 2 to 3 km thickness
7 Alberta 8 Alberta Geology - Typically, low or medium plastic clays, however, pockets of highly plastic clays exist in Edmonton and Medicine Hat for example.
- Dense sand some areas; Some Loess - Weak sandstone, weathered - Compact to dense glacial clay tills - Fluvial channel gravel (Calgary) Low fines content, presence of cobbles, unstable - Very weak clay shale bedrock Unconfined Compressive Strength ~ 380 kPa, varies Should be treated as a soil not rock
- Presence of soluble sulphates - Laurnetide Ice Sheet, last glaciation, 2 km thickness 9 Saskatchewan 10 Manitoba
11 Conclusion Final Remarks - Geology of British Columbia tends to be more competent vs. the prairies - Presence of highly plastic clays, soluble sulphates and loess on the prairies - Assessment of total pile head movement at design load levels needs to be addressed - Questions?
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