Observations From The Instrumentation of a Micropiled and Tied Back Reticulated Grid Walter E. Vanderpool, P.E. Senior Geotechnical Engineer Terracon Consultants, Inc.
� Site: The C2K Theatre at the Palazzo � 370 kN wall load at the crest of a 15.3 m excavation � Theatre construction concurrent with excavation and tower construction
� Site excavation began 9/1/04 � Theatre construction began 11/25/04 � Secant pile installation began 12/6/04 � Underpinning installed 12/11/04 � Secant piling complete 12/16/04 � Theatre structure frame complete 3/14/05
40 N 35 30 Northing (m) 25 20 15 Secant Piles Micropiles Bonded Tie Back VW Strain Gauge 10 Inclinometer Piezometer 5 Tower shafts 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Easting (m) • Reticulated group plan • Tieback locations • VW gauge locations • Foundation shafts for cantilevered tower • Micropile locations
635 Secant Piles Viewing West FF 631.5 m VW Strain Gauge 630 Inclinometer Bonded Tie Back 625 Mat Caliche Layers Elevation (m MSL) Micropiles 620 SG 616.2 m Piezometer 615 610 605 15 20 25 30 35 40 45 50 55 60 Northing (m) • Reticulated group profile • Reticulated tieback intersections • VW gauge locations • Cemented beds • Micropile locations • Piezometer location • Tieback locations
632 Micropile, Relative Drilling Resistance, 1=very soft/loose, 3=very stiff/very dense and partially cemented, 630 5=strongly cemented 629.4 m MSL 628 626 Elevation (m MSL) 624 622 620 618 616 614 Relative Drilling Resistance, count=103 612 0 1 2 3 4 5 Drilling Resistance Rating • Relative top-drive hammer drilling resistance • Measured by rate of advance • Subjectively interpreted relative to geotechnical logging
� Flush grout injection drilling � VW strain gauge � Insertion by fiberglass rod
� Inclinometer at P1-015NS � Piezometer at P1-013S � Cemented layer at approximately elevation 626.5 m to 625 m MSL
� Notch at tower cantilever � Theatre wall 36.3 m - wide by 32 m - high by 457mm - thick � Carbonate precipitate at tie- backs
� Tower shaft group at cantilever
2250 2000 1750 M6, 6 1500 1250 1000 750 M8, 2 Gauge Microstrain Mat 500 Theatre M4, 10 M1,5 Fill Construction 250 M4, 17 Placed 0 -250 M4,17 -500 M2, 8 Curing -750 M1, 11 -1000 12/4/2004 0:00 1/29/2005 0:00 3/26/2005 0:00 5/21/2005 0:00 7/16/2005 0:00 9/10/2005 0:00 11/5/2005 0:00 12/31/2005 0:00 Date & Time • Micropile strain history • Installation 12/04 through completion 1/06 • VW strain gauge data record
60 40 Mat Placed 20 0 -20 Wall Construction Mat Fill Placed -40 M6, 6 -60 Gauge Microstrain -80 (see Figure 10) M4,17 -100 M1, 5 -120 M4, 17 M1, 11 -140 Grout Curing (see Figure 9) -160 M2, 8 -180 M8, 2 -200 12/9/2004 0:00 12/23/2004 0:00 1/6/2005 0:00 1/20/2005 0:00 2/3/2005 0:00 2/17/2005 0:00 3/3/2005 0:00 3/17/2005 0:00 3/31/2005 0:00 4/14/2005 0:00 Date & Time • Initial tension during curing and • Theatre construction excavation to subgrade 1/05 – 3/05 12/11/04 – 12/18/04 • Fill placement • Mat placement 12/24 3/14/05 – 3/20/05
-66 -67 -68 -69 Gauge Microstrain -70 -71 M4, 17 -72 2/9/2005 18:00 2/10/2005 6:00 2/10/2005 18:00 2/11/2005 6:00 2/11/2005 18:00 2/12/2005 6:00 Date & Time • Forming and concrete placement load/unload at interior location on mat
110 105 100 Gauge Microstrain 95 M2, 8 90 5/19/2005 5:00 5/19/2005 7:00 5/19/2005 9:00 5/19/2005 11:00 5/19/2005 13:00 5/19/2005 15:00 Date & Time • Tieback stressing effects • 15 Tiebacks at Level -1 stressed
• Hourly data by IPI • Inclinometer data record system 8/05 – 12/05 • Weekly record 4/05 to 8/05 and 2/06 not included
634 Secant Pile P1- 013,S F. F. 631.5 m 632 O. G. 630.3 m 630 628 626 Groundwater head (m) 624 622 Tieback Grouting 620 (see Figure 14) 618 S. G. 616.2 m 616 614 612 610 Shaft Drilling Head (m MSL) 608 11/9/2004 1/4/2005 3/1/2005 4/26/2005 6/21/2005 8/16/2005 10/11/2005 12/6/2005 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Date and Time • Head rise during tieback grouting • Piezometer data record • Head drop during drilled shaft 12/04 – 1/06 construction
620.0 Secant Pile P1- 013, S 619.5 619.0 618.5 Groundwater head (m MSL) 618.0 617.5 617.0 616.5 616.0 615.5 Head (m MSL) 615.0 7/1/2005 11:00 7/1/2005 12:00 7/1/2005 13:00 7/1/2005 14:00 7/1/2005 15:00 7/1/2005 16:00 7/1/2005 17:00 Date and Time • Tieback grout placement at Level – 2
Elastic Analyses vs. Observations 0 M6,6 Secant pile tip elevation -50 610.1 m MSL M4,17 Excavation subgrade M1,11 M8,2 M6,6 616.2 m MSL M2,8 Vertical Stress (kPa) -100 M1,5 Embedded strain M2,8 gauge depths (D/B) M4,17 Line 1 Line 22 M8,2 36.3 m -150 Row M1 14.8 m B=10.1 m -200 M5,1 30.8 m Row 4.9 m M8 M1,17 PLAN (sketch) 2.7 m 2.7 m -250 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Depth (D/B) - D/B 0=629.3 m MSL, D/B 2=609.1 m MSL • Boussinesq elastic analyses by superposition • Instrumented micropile locations and depths
Ground/Micropile Load Sharing Pre-Excavation, April 1, 2004 D/L D/B 4/1/05 Boussinesq Tributary Stress Location Load Stress (kPa) Area Ratio % (kN) (m^2) M1,5 0.30 0.5 -41.08 -67.5 1.62 37.6 % M1,11 0.66 1.1 -52.41 -36.7 1.62 88.3 % M1,17 0.30 0.5 -55.05 -58.7 1.62 50.9 % � 37.6% to 88.3% M5,1 0.57 0.8 -42.62 -43.2 1.96 50.4 % at perimeter � 5.6% to 73.2% at 1 st interior row N2,2 0.66 1.1 -50.32 -34.0 2.02 73.2 % M2,8 0.30 0.5 -14.02 -67.4 3.70 5.6 % � 10.9% to 11.8% M2,14 0.30 0.5 -69.93 -67.3 3.70 28.1 % near middle of M2,20 0.30 0.5 -50.00 -72.0 4.18 16.6 % mat (row 4) M8,2 0.47 0.5 -64.71 -50.9 2.70 47.0 % � 17.1% at back edge of mat M4,10 0.60 0.8 -26.55 -43.3 5.64 10.9 % (row 6) M4,17 0.37 0.5 -32.94 -49.4 5.64 11.8 % � Prior to stressing M6,6 0.58 0.8 -30.26 -33.4 5.62 17.1 %
Ground/Micropile Load Sharing Post Construction January 31, 2006 D/L D/B 1/31/06 Boussinesq Tributary Stress Location Load Stress (kPa) Area Ratio % (kN) (m^2) M1,5 0.30 0.5 -22.77 -67.5 1.62 20.8 % � After tieback M1,11 0.66 1.1 -68.56 -36.7 1.62 115.5 % stressing M1,17 0.30 0.5 -25.22 -58.7 1.62 26.6 % � 20.8% to 115.5% M5,1 0.57 0.8 -56.18 -43.2 1.96 66.4 % at perimeter � 6.7% to 184% N2,2 0.66 1.1 -59.43 -34.0 2.02 86.1 (tension) at 1 st M2,8 0.30 0.5 -16.60 -67.4 3.70 6.7 % M2,14 0.30 0.5 -198.27 -67.3 3.70 79.6 % interior row M2,20 0.30 0.5 -87.14 -72.0 4.18 29.0 % � 11.4% to 83.0% M8,2 0.47 0.5 252.84 -50.9 2.70 184 % * (tension) near middle of mat M4,10 0.60 0.8 201.22 -43.3 5.64 83.0 %* (row 4) M4,17 0.37 0.5 -31.71 -49.4 5.64 11.4 % � 139.5% (tension) at back of mat M6,6 0.58 0.8 261.76 -33.4 5.62 139.5 %* (row 6)
CONCLUSIONS � The micropiles accumulated 10 to 90 percent of the load as it was applied in proportion to the relative stiffness between the soils and the micropiles. � Instrumented micropiles responded with strains consistent with their location within the group and the forces applied. � The micropiles provided confinement and resistance to axial deformation during tieback stressing. � Tie back stressing caused micropiles to act in tension at the tieback bond zone.
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