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Micropiles Save Drilled Shafts. Allen Cadden, P.E. Problem. Settlement of up to 25 to 50 mm Cracks in supported floors Work stopped before last 2 floors were constructed. Subsurface Conditions. New Fill. Alluvial Soils. Residual Soils. Partially Weathered Rock. 10-40 ft. 3-12 m.
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Micropiles Save Drilled Shafts Allen Cadden, P.E.
Problem • Settlement of up to 25 to 50 mm • Cracks in supported floors • Work stopped before last 2 floors were constructed
Subsurface Conditions New Fill Alluvial Soils Residual Soils Partially Weathered Rock 10-40 ft 3-12 m Diabase Rock
Strain Gauge Configuration 7 inch, N80 0.5 inch wall 178 mm, 12.5 mm wall 56 kg/mm2 Steel 10 ft (3 m) Segment 1 Strain Gauge 10.9 ft 2 13.9 ft 3 14.4 ft (4.4 m) 16.9 ft 4 23.4 ft
9 mm 1070 kN 2140 kN 3210 kN Load Test Results
1070 kN 2140 kN 7.4 m
Average Shear Stress vs. Cycle @ 300 ton (2700 kN)(assumes nonmoving pile tip) 1150 kPa, 165 psi
Caisson Connection to Drilled Shafts High Load, Large Shaft
Connection to Drilled Shafts Low Load, Small Shaft
Conclusions • Micropiles fixed the problem • Loads well in excess of 300 tons can be carried by a 7 inch pile • The load transfer in a rock socket is not constant under cyclic loading