Underground Singapore 2011 3.2 Wall Deflections Wall deflections were monitored against the original ERSS design predictions. Figure 8 shows actual wall deflections as recorded by wall inclinometers for selected construction stages and the original design predictions which appear conservative. During the first excavation stage the wall deformed in cantilever. With successive excavation and strut installation, maximum movement tended to increase and shift downwards to form a bell shape curve. Higher deflections, particularly during stage 1 excavation, were recorded at the north wall (I2001) and largely attributed to shaft excavation commencing at this zone (Figure 1). The lowest deflection was indicated at the east wall (I2004), likely owing to nearby canal diversion excavation, as supported by an adjacent soil inclinometer recording 20mm of movement away from the excavation towards the canal. EXC to S1
EXC to S2
EXC to FEL
EXC to S4
EXC to S3
120
120
120
120
120
115
115
115
115
115
110
110
110
110
110
105
105
105
105
100
100
100
100
95
95
95
95
90
90
90
90
85
85
85
85
Reduced Level (RLm)
105
120 115
100
110 105
95
100 95
90
90 85
85
80 75
0 80
80
10
20
30 80
40
50
80
60
70
80 80
Wall Deflection (m m ) 75
75 0 10 20 30 40 50 60 70 80 Wall Deflection (m m )
Actual Predicted
75 0 10 20 30 40 50 60 70 80 Wall Deflection (m m )
75 75 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 Wall Deflection (m m ) Wall Deflection (m m ) Wall Deflection (m m )
I2001-North
I2002-West
I2003-South
I2004-East
North (design)
West (design)
South (design)
East (design)
Figure 8: Comparison of development of wall deflections and ERSS Prediction
3.2 Strut loads Consistent with wall deflections, strut loads were significantly lower than the original ERSS design predictions but indicated similar trends (Figure 9). After reaching a peak following excavation to the 1st stage, loads for the 1st strut level decreased for the remainder of excavation as deeper strut levels were added. Strut loads for the 2nd level remained relatively constant after excavation to 3rd level, whilst loads recorded at 3rd and 4th strut levels continued increasing to final excavation level.
182