Underground Singapore 2011 4 COMPARISON BETWEEN PREDICTION AND MEASURED DISPLACEMENT Figure 7 shows the diaphragm wall deflection profiles measured by in-wall inclinometer on the east wall (IW2062) and west wall (IW2061) across GL-11 when the excavation level reached RL67m. The maximum wall deflection measured was 12mm and 17mm on the east wall and west wall, respectively. Figure 8 shows the prediction of wall deflections for the design section across GL-11. The maximum diaphragm wall deflection predicted at the stage of excavation to RL67m was 27.5mm and 28.1mm for east wall and west wall, respectively. It is noteworthy that the actual wall deflection measured was much less as compared to the design prediction, especially at the level below RL80 where OA(A) was found. The over-prediction on wall deflection is attributed to the limit of 150MPa set for Young’s Modulus (E’) of OA(A) as specified in the GIBR. To better simulate the actual soil behaviour, the analysis at GL-11 was re-run keeping all the design sequence and soil parameters the same as the original design but E’ of OA(A) was increased from 150MPa to 250MPa . The predicted deflections of east and west walls with increased E’ are shown in Figure 9. The maximum wall deflection predicted at excavation to RL67m reduced to 19mm and 21mm for east wall and west wall, respectively. It can be seen from Figure 9 that even with E’ of OA(A) increased from 150MPa to250MPa, the wall deflection predicted is still larger as compared to the actual measurements. The wall deflection predicted below RL80, which is within the OA(A), is still grossly over-predicted. With the above back-analysis in mind, the construction sequence between GL-1.5 and GL-9.5 was reviewed. The two layers struts below B6, originally designed at RL68 and RL64.5 was revised to one layer strut at RL67, and the works have been sucessufully completed. 104
104
IW2062
IW2061
100
100
96
96
92 92 88 88 84 84
76 76 72 72 68 68 64
5/3/2010 (RL99)
5/3/2010 (RL99)
30/4/2010 (RL96)
30/4/2010 (RL96)
10/6/2010 (RL92)
10/6/2010 (RL92)
19/6/2010 (RL88)
19/6/2010 (RL88)
15/8/2010 (RL84.5)
15/8/2010 (RL84.5)
14/9/2010 (RL81.5)
14/9/2010 (RL81.5)
20/10/2010 (RL78)
20/10/2010 (RL78)
27/11/2010 (RL74.5)
27/11/2010 (RL74.5)
10/1/2011 (RL71)
10/1/2011 (RL71)
11/2/2011 (B6 Slab)
11/2/2011 (B6 Slab)
64 60
60 56 52 48
56 52 48 44 40
44 -4
-2
0
2
4
6
8
10
West Wall Measured Deflection (mm)
12
14
16
18
14
12
10
8
6
4
2
East Wall Measured Deflection (mm)
Figure 7: Diaphragm wall deflections measured by in-wall inclinometer across GL-11.
238
0
-2
-4
-6
Elevation (mRL)
Elevation (mRL)
80 80