observations from the instrumentation of a micropiled and ... - vanderpool... · observations from...
TRANSCRIPT
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 Palazzo370 kN wall load at the crest of a 15.3 m excavationTheatre construction concurrent with excavation and tower construction
Site excavation began 9/1/04Theatre construction began 11/25/04Secant pile installation began 12/6/04Underpinning installed 12/11/04Secant piling complete 12/16/04Theatre structure frame complete 3/14/05
• Reticulated group plan• VW gauge locations• Micropile locations
• Tieback locations• Foundation shafts for
cantilevered tower
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40 45 50 55 60 65
Easting (m)
Nor
thin
g (m
)
Secant Piles MicropilesBonded Tie Back VW Strain GaugeInclinometer PiezometerTower shafts
N
605
610
615
620
625
630
635
15 20 25 30 35 40 45 50 55 60
Viewing WestEl
evat
ion
(m M
SL)
Secant Piles
VW Strain Gauge
Inclinometer
Bonded Tie Back
Mat
Micropiles
Piezometer
Northing (m)
SG 616.2 m
FF 631.5 m
Caliche Layers
• Reticulated group profile• VW gauge locations• Micropile locations• Tieback locations
• Reticulated tieback intersections
• Cemented beds• Piezometer location
• Relative top-drive hammer drilling resistance• Measured by rate of advance• Subjectively interpreted relative to geotechnical logging
Micropile, Relative Drilling Resistance, 1=very soft/loose, 3=very stiff/very dense and partially cemented,
5=strongly cemented
612
614
616
618
620
622
624
626
628
630
632
0 1 2 3 4 5
Drilling Resistance Rating
Elev
atio
n (m
MSL
)
Relative Drilling Resistance, count=103
629.4 m MSL
Flush grout injection drillingVW strain gaugeInsertion by fiberglass rod
Inclinometer at P1-015NSPiezometerat P1-013SCemented layer at approximately elevation 626.5 m to 625 m MSL
Notch at tower cantileverTheatre wall 36.3 m - wide by
32 m - high by 457mm - thick
Carbonate precipitate at tie-backs
Tower shaft group at cantilever
• Micropile strain history• VW strain gauge data record
• Installation 12/04 through completion 1/06
-1000
-750
-500
-250
0
250
500
750
1000
1250
1500
1750
2000
2250
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 12/31/20050:00Date & Time
Gau
ge M
icro
stra
in
M4,17Curing
M6, 6
M4, 10
M8, 2
M2, 8
M4, 17
M1, 11
MatFillPlaced
Theatre Construction
M1,5
• Initial tension during curing and excavation to subgrade12/11/04 – 12/18/04
• Mat placement 12/24
• Theatre construction 1/05 – 3/05
• Fill placement 3/14/05 – 3/20/05
-200
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
20
40
60
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
Gau
ge M
icro
stra
in
M6, 6
M4,17
M1, 5
M1, 11
M2, 8M8, 2
M4, 17Grout Curing(see Figure 9)
Mat Fill Placed
Mat Placed
Wall Construction
(see Figure 10)
• Forming and concrete placement load/unload at interior location on mat
-72
-71
-70
-69
-68
-67
-66
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
Gau
ge M
icro
stra
in
M4, 17
• Tieback stressing effects• 15 Tiebacks at Level -1 stressed
90
95
100
105
110
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 15:00Date & Time
Gau
ge M
icro
stra
in
M2, 8
• Inclinometer data record• Weekly record 4/05 to 8/05 and 2/06
• Hourly data by IPI system 8/05 – 12/05 not included
• Piezometer data record 12/04 – 1/06
• Head rise during tieback grouting• Head drop during drilled shaft
construction
Secant Pile P1- 013,S
608
610
612
614
616
618
620
622
624
626
628
630
632
634
11/9/20040:00
1/4/20050:00
3/1/20050:00
4/26/20050:00
6/21/20050:00
8/16/20050:00
10/11/20050:00
12/6/20050:00
Date and Time
Gro
undw
ater
hea
d (m
)
Head (m MSL)
O. G. 630.3 m
S. G. 616.2 m
F. F. 631.5 m
Tieback Grouting(see Figure 14)
Shaft Drilling
• Tieback grout placement at Level – 2
Secant Pile P1- 013, S
615.0
615.5
616.0
616.5
617.0
617.5
618.0
618.5
619.0
619.5
620.0
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
Gro
undw
ater
hea
d (m
MSL
)
Head (m MSL)
Elastic Analyses vs. Observations
• Boussinesq elastic analyses by superposition• Instrumented micropile locations and depths
-250
-200
-150
-100
-50
0
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
Vert
ical
Str
ess
(kPa
)
M1,5 M2,8 M4,17 M8,2
M6,6 M1,11
Embedded straingauge depths (D/B)
14.8 m
2.7 m 2.7 m
36.3 m
4.9 m
B=10.1 m
30.8 m
Excavation subgrade 616.2 m MSL
Secant pile tip elevation610.1 m MSL
PLAN (sketch)
RowM1
RowM8
Line 1 Line 22
M6,6
M4,17
M8,2
M1,17
M5,1
M2,8
Ground/Micropile Load Sharing Pre-Excavation, April 1, 2004
17.1 %5.62-33.4-30.260.80.58M6,6
11.8 %5.64-49.4-32.940.50.37M4,17
10.9 %5.64-43.3-26.550.80.60M4,10
47.0 %2.70-50.9-64.710.50.47M8,2
16.6 %4.18-72.0-50.000.50.30M2,20
28.1 %3.70-67.3-69.930.50.30M2,14
5.6 %3.70-67.4-14.020.50.30M2,8
73.2 %2.02-34.0-50.321.10.66N2,2
50.4 %1.96-43.2-42.620.80.57M5,1
50.9 %1.62-58.7-55.050.50.30M1,17
88.3 %1.62-36.7-52.411.10.66M1,11
37.6 %1.62-67.5-41.080.50.30M1,5
Stress Ratio %
Tributary Area (m^2)
Boussinesq Stress (kPa)
4/1/05 Load (kN)
D/BD/LLocation
37.6% to 88.3% at perimeter5.6% to 73.2% at 1st interior row10.9% to 11.8% near middle of mat (row 4)17.1% at back edge of mat (row 6)Prior to stressing
Ground/Micropile Load Sharing Post Construction January 31, 2006
139.5 %*5.62-33.4261.760.80.58M6,6
11.4 %5.64-49.4-31.710.50.37M4,17
83.0 %*5.64-43.3201.220.80.60M4,10
184 % *2.70-50.9252.840.50.47M8,2
29.0 %4.18-72.0-87.140.50.30M2,20
79.6 %3.70-67.3-198.270.50.30M2,14
6.7 %3.70-67.4-16.600.50.30M2,8
86.12.02-34.0-59.431.10.66N2,2
66.4 %1.96-43.2-56.180.80.57M5,1
26.6 %1.62-58.7-25.220.50.30M1,17
115.5 %1.62-36.7-68.561.10.66M1,11
20.8 %1.62-67.5-22.770.50.30M1,5
Stress Ratio %
Tributary Area (m^2)
Boussinesq Stress (kPa)
1/31/06 Load (kN)
D/BD/LLocation
After tieback stressing20.8% to 115.5% at perimeter6.7% to 184% (tension) at 1st
interior row11.4% to 83.0% (tension) near middle of mat (row 4)139.5% (tension) at back of mat (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.