Observations From The Instrumentation of a Micropiled and Tied Back - - PowerPoint PPT Presentation

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

• Reticulated group plan
• VW gauge locations
• Micropile locations
• Tieback locations
• Foundation shafts for

cantilevered tower

5 10 15 20 25 30 35 40 5 10 15 20 25 30 35 40 45 50 55 60 65

Easting (m) Northing (m)

Secant Piles Micropiles Bonded Tie Back VW Strain Gauge Inclinometer Piezometer Tower shafts

N

605 610 615 620 625 630 635 15 20 25 30 35 40 45 50 55 60

Viewing West Elevation (m MSL)

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 1 2 3 4 5

Drilling Resistance Rating Elevation (m MSL)

Relative Drilling Resistance, count=103

629.4 m MSL

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

• Micropile strain history
• VW strain gauge data record
• Installation 12/04 through

completion 1/06

• 1000
• 750
• 500
• 250

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 12/31/2005 0:00 Date & Time Gauge Microstrain M4,17 Curing M6, 6 M4, 10 M8, 2 M2, 8 M4, 17 M1, 11 Mat Fill Placed Theatre Construction M1,5

• Initial tension during curing and

excavation to subgrade 12/11/04 – 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

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 Gauge Microstrain M6, 6 M4,17 M1, 5 M1, 11 M2, 8 M8, 2 M4, 17 Grout 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 Gauge Microstrain

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 15:00 Date & Time Gauge Microstrain

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 11/9/2004 0:00 1/4/2005 0:00 3/1/2005 0:00 4/26/2005 0:00 6/21/2005 0:00 8/16/2005 0:00 10/11/2005 0:00 12/6/2005 0:00

Date and Time Groundwater head (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 Groundwater head (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 0.2 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 Vertical Stress (kPa) M1,5 M2,8 M4,17 M8,2 M6,6 M1,11 Embedded strain gauge 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 elevation 610.1 m MSL

PLAN (sketch)

Row M1 Row M8 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
• 30.26

0.8 0.58 M6,6 11.8 % 5.64

• 49.4
• 32.94

0.5 0.37 M4,17 10.9 % 5.64

• 43.3
• 26.55

0.8 0.60 M4,10 47.0 % 2.70

• 50.9
• 64.71

0.5 0.47 M8,2 16.6 % 4.18

• 72.0
• 50.00

0.5 0.30 M2,20 28.1 % 3.70

• 67.3
• 69.93

0.5 0.30 M2,14 5.6 % 3.70

• 67.4
• 14.02

0.5 0.30 M2,8 73.2 % 2.02

• 34.0
• 50.32

1.1 0.66 N2,2 50.4 % 1.96

• 43.2
• 42.62

0.8 0.57 M5,1 50.9 % 1.62

• 58.7
• 55.05

0.5 0.30 M1,17 88.3 % 1.62

• 36.7
• 52.41

1.1 0.66 M1,11 37.6 % 1.62

• 67.5
• 41.08

0.5 0.30 M1,5 Stress Ratio % Tributary Area (m^2) Boussinesq Stress (kPa) 4/1/05 Load (kN) D/B D/L Location

37.6% to 88.3%

at perimeter

5.6% to 73.2% at

1st interior row

10.9% 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

• 33.4

261.76 0.8 0.58 M6,6 11.4 % 5.64

• 49.4
• 31.71

0.5 0.37 M4,17 83.0 %* 5.64

• 43.3

201.22 0.8 0.60 M4,10 184 % * 2.70

• 50.9

252.84 0.5 0.47 M8,2 29.0 % 4.18

• 72.0
• 87.14

0.5 0.30 M2,20 79.6 % 3.70

• 67.3
• 198.27

0.5 0.30 M2,14 6.7 % 3.70

• 67.4
• 16.60

0.5 0.30 M2,8 86.1 2.02

• 34.0
• 59.43

1.1 0.66 N2,2 66.4 % 1.96

• 43.2
• 56.18

0.8 0.57 M5,1 26.6 % 1.62

• 58.7
• 25.22

0.5 0.30 M1,17 115.5 % 1.62

• 36.7
• 68.56

1.1 0.66 M1,11 20.8 % 1.62

• 67.5
• 22.77

0.5 0.30 M1,5 Stress Ratio % Tributary Area (m^2) Boussinesq Stress (kPa) 1/31/06 Load (kN) D/B D/L Location

After tieback

stressing

20.8% to 115.5%

at perimeter

6.7% to 184%

(tension) at 1st interior row

11.4% 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.