The Twenty-Eighth KKHTCNN Symposium on Civil Engineering November 16-18, Bangkok, Thailand
Performance of Contiguous Pile Wall with Raking Strut for Basement Construction of BITEC Phase 2 Project Wanchai Teparaksa1, Pongsathorn Sontiprasart22, Nitti Prachayaset2, Suraparb Keawsawasvong 1
Associate Professor, Department of Civil Engineering, Chulalongkorn University, Thailand 2 Geotechnical Engineer, Strategia Engineering Consultants Co., Ltd., Thailand 1
[email protected],
[email protected]
ABSTRACT The extended exhibition building called BITEC Phase 2 consists of 3 basements. The elevations of BITEC Phase 2 basements are -1.65, -5.50 and -8.35m. depth from ground surface. The final depth of this project is -10.65m. depth from ground surface. Because this project was constructed on the very large area, the raking strut is used as the bracing system in order to reduce the cost and time of construction. The finite element analysis was carried out to predict the movement of contiguous pile wall. The measured lateral movement of contiguous pile wall by means of inclinometer at all stages of construction is compared with FEM prediction. INTRODUCTION Bangkok International Trade & Exhibition Centre (BITEC) is located between Sukhumvit Road and Bang na-Trad Road, Bangkok. The extended exhibition building called BITEC Phase 2 was designed and consist of 7 storey buildings with 3 basements. The elevations of BITEC Phase 2 basements are -1.65, -5.50 and -8.35m. depth from ground surface as shown in Figure 1. The final depth of this project is -10.65m. depth from ground surface. The contiguous pile wall was used as the soil protection system. This paper presents the design and performance of contiguous pile wall using the raking strut as the temporary bracing system. The lateral movement of contiguous pile wall was predicted by Finite Element Method (FEM) with simulation of all construction sequences. The inclinometer was installed in contiguous pile wall in order to observe the lateral movement of the contiguous pile wall and be compared with the FEM analysis.
Fig.1. Three basements of extended exhibition building of BITEC SOIL CONDITIONS The soil investigation with 3 bored holes was carried out up to approximately 60-70m. depth below ground surface. Soil
condition consists of 12m. thick soft clay. Below the soft clay, the medium stiff clay is encountered to about 15.0m. depth. Stiff to very stiff silty clay layer was found below soft to medium clay to about 22.5m. depth. The first dense silty sand is encountered below very stiff silty clay to about 27m. depth then followed by the second layer of very stiff silty clay which was encountered to about 34.5m. depth. Finally, the hard silty clay is encountered to about 39.0m. depth then followed by the very dense silty sand. The summary of soil conditions and its properties are presented in Table1. Table 1 The summary of soil condition and property. Depth (m.) 0.0 - 4.0 4.0 – 7.5 7.5 – 12.0 12.0 – 15.0 15.0 – 18.0 18.0 – 21.0 21.0 – 22.5 22.5 – 27.0 27.0 – 34.5 34.5 – 39.0 39.0 – End
t (t/m3) 1.70 1.60 1.55 1.65 1.90 2.00 2.00 2.00 2.00 2.00 2.00
Soil Description Soft Clay (First Layer) Soft Clay (Second Layer) Soft Clay (Third Layer) Medium Stiff Clay Stiff Silty Clay Stiff Sandy Clay Very Stiff Silty Clay (First Layer) Dense Silty sand Very Stiff Silty Clay (Second Layer) Hard Silty Clay Very Dense Silty Sand
Su (t/m2) 1.90 1.60 1.30 2.60 8.20 8.30 11.40 13.70 25.00 -
N-value (Blows/ft.) 38 55
Eu/Su
E’/N
500 500 500 750 1000 1000 1000 1000 1000 -
200 200
Note: Su = Undrained shear strength, t = Total unit weight, N-value = SPT N-value, Eu = Undrained Young’s modulus, E’= Drained Young’s modulus
PROJECT DESCRIPTION The extended exhibition building called BITEC Phase 2 was constructed on a very large area. For bracing system, if the horizontal strut (Cross strut) is used as the bracing system, the cost of construction will be very expensive. So, the raking strut is used as the strut of the system in order to reduce the cost of construction. Meanwhile, using of raking strut also reduce the time of construction. The contiguous pile wall has 1.0m. diameter, 1.1m. spacing and 17.3m. long and used as the soil protection system. The first layer raking strut was braced at EL -2.5m. on the contiguous pile wall while at EL. -8.35m. on floor slab as shown in Figure 2. However, the reinforce concrete slab at the center or inner area should be constructed before the first layer raking strut was installed. Therefore, the Island excavation method was carried out by excavating the soil in middle area and the base slab was constructed, and still leaving the soil berm at the boundary of the construction area in order to prevent the movement of the contiguous pile wall. After the base slab was completed, the soil berm will be excavated and the first layer raking strut will be then installed. The different level between the second basement and third basement is about 3-4m. The inner sheet pile types FSV-III that has 12 m. long and second layer raking strut were carried out as the soil protection system of this different level. The second layer raking strut was braced between EL. -7.0m. on the sheet pile and EL. -8.35m. on the base slab as shown in Figure 2. After completion of third base slab, the second layer raking strut was removed as soon as second basement floor was completed then the first layer raking was removed as shown in Figure 3. 38000
1800
Ground Level (EL. - 0.70 m.) EL. -2.50 m.
Strut Layer 1 ( Raking) EL. -5.50 m.
6000
EL. -18.00 m.
Strut Layer 2 ( Raking)
EL. -7.00 m. Lean Concrete t = 0.20 m., fc' = 240 ksc Distance 6.0 m. from pile wall
EL. -6.70 m.
Pile Wall Diameter 1.0 m, L = 17.3 m. Spacing @ 1.1 m. Top EL. -0.7 m. Tip EL. -18.0 m.
2000
36000
EL. -9.00 m.
EL. -10.65 m. Lean Concrete t = 0.10 m. Sheet Pile Type III L = 12.0 m. EL. -17.50 m.
Fig.2. Cross sections of the basement construction of the BITEC Phase 2 by using two layer raking struts
Lean Concrete t = 0.10 m.
2800
Ground Level (EL. - 0.70 m.) Temporary Raking (EL. -4.3 m.) EL. -3.50 m.
Block out for Raking Strut
EL. -4.30 m. EL. -5.50 m. (B2)
Lean Concrete t = 0.15 m., fc' = 240 ksc Backfill EL. -6.70 m.
Lean Concrete t = 0.20 m., fc' = 240 ksc Distance 6.0 m. from pile wall 6000
Pile Wall Diameter 1.0 m, L = 17.3 m. Spacing @ 1.1 m. Top EL. -0.7 m. Tip EL. -18.0 m.
EL. -8.35 m. (B3)
EL. -10.65 m. Lean Concrete t = 0.15 m., fc' = 240 ksc Backfill
EL. -9.00 m. Lean Concrete t = 0.10 m.
Lean Concrete t = 0.10 m.
EL. -18.00 m.
Fig. 3. Cross sections of the basement construction of the BITEC Phase 2 after the second basement was completed ANALYSIS AND DESIGN OF CONTIGUOUS PILE WALL The analysis and design of the contiguous pile wall was carried out by means of the two-dimensional plane strain finite -40.000 -30.000 -20.000 -10.000 0.000 10.000 20.000 30.000 40.000 50.000 60.000 70.000 element analysis. The construction sequence was simulated by using finite element software, namely Plaxis2D. As the basement constructed in soft clay layer, the undrained concept based on bi-linear Mohr-Coulomb failure theory was used for finite element analysis. Generally, the Young’s modulus (E) was used in terms of undrained shear strength (su) of E/su = 500 and 20.000 1000 for soft clay and stiff clay, respectively (Teparaksa 1999; 2009). The values of undrained Young’s modulus (Eu) and drained Young’s modulus (E’) divided by undrained shear strength and SPT N-value of soil layers are showed in Table 1. Figure10.000 4 presents the deformed mesh of the FEM analysis of the step of the second layer raking strut was installed. Figure 5 presents the deformed mesh of the FEM analysis of the step of the first layer raking strut was removed. A
A
0.000
-10.000
-40.000
-30.000
-20.000
-10.000
0.000
10.000
20.000
30.000
40.000
50.000
60.000
70.000
-20.000
20.000 -30.000
10.000
Fig. 4. Deformed mesh of the step of the second layer raking strut was installed
-40.000
A
A
0.000 Deformed Mesh -3 Extreme total displacement 100.98*10 m (displacements at true scale)
-10.000
-20.000
-30.000
-40.000
Fig. 5. Deformed mesh of the step of the first layer raking strut was removed
The bending moment diagrams of all steps of excavation and construction are concluded in Figure 6. The solid line in Figure 6 presents the bending moment envelope in the excavation side, while the dotted line presents the bending moment Deformed Mesh Extreme total displacement 112.80*10 m envelope in the soil side. These lines were used for design(displacements the reinforcement of pile wall. at true scale) -3
INSTRUMENTATION ANE THE RESULTS OF INSTRUMENTS The inclinometer was installed inside the contiguous pile wall to observe the lateral movement of the contiguous pile wall. The measurements of the inclinometer at various constructed stages are shown in Figure 7. In Figure 7, it can be seen that the lateral movement by FEM agrees well with field performance and it is less than the maximum lateral movement by FEM. The basement construction of BITEC Phase 2 was completed as schedule.
FEM Analysis and Inclinometer Monitoring Result 0 -2
-4
Elevation (m.)
-6 -8 -10 -12 -14
FEM Analysis
-16 -18 -20 0 10 20 30 40 50 60 70 80 90
Horizontal Movement (mm.) Fig. 6. The bending moment envelope
Fig. 7. The cooperation of lateral movements
CONCLUSIONS This paper presents the basement construction of BITEC Phase 2 located between Sukhumvit Road and Bang na-Trad Road, Bangkok. The basement construction system of 10.65m. depth was designed using contiguous pile wall with two raking struts. The finite element analysis was carried out to predict the movement of contiguous pile wall and the bending moment diagrams. The measured lateral movement of contiguous pile wall by means of inclinometer at all stages of construction is compared with FEM prediction. The FEM prediction agrees well with measured values. The deep basement was completed on the schedule. REFERENCES W. Teparaksa, (1999) “Principal and application of instrumentation for the first MRTA subway project in Bangkok” 5th International Symposium on Field Measurement in Geomechanics, Singapore. W. Teparaksa, (2009)“Usecontiguouspilewall fordeep excavation adjacent to Chao Phraya River: Case of Siriraj hospital”, ATC 18 Mega Foundation Seminar on Bangkok Recent Advance in Deep Excavation and Foundation, EIT, Bangkok
