The 6th International Geotechnical Symposium on Disaster Mitigation in Special Geoenvironmental Conditions Chennai, India, January 21-23, 2015
NUMERICAL STUDY ON ANCHORED PILE WALL DEFORMATIONS Chavda Jitesh1 PG Student, Applied Mechanics Department, S.V. National Institute of Technology - Surat 1
[email protected]
Solanki. C. H.2, Desai. A. K.3 Professor, Applied Mechanics Department, S.V. National Institute of Technology - Surat 2
[email protected] 3
[email protected] ABSTRACT: Urbanization has set forth a challenging trend to go deeper into the ground to meet the space requirement for basement parking, public amenities, housing utilities, etc. The Pile walls are commonly used in urban area as retention systems for deep excavations. The Numerical analysis was carried out using 3-Dimensional Geotechnical FEM software “PLAXIS-3D” on Anchored pile wall retention system. The effect of anchor location, Inclination of anchor, spacing of anchor, effect of stage wise excavations on deformation of ground and pile wall was studied. The analysis results show that anchoring at the depth of 25% [0.25H] height of excavation [H] from top and anchoring at an inclination of 25 to 30 degree to horizontal is most effective. This paper presents the results and findings of parametric study performed. Keywords: Anchored pile wall, Deep excavations, FEM analysis 1. INTRODUCTION:
1.1 Geometrical inputs for Anchored Pile wall:
The number of deep excavations in city is seen to increase exponentially so are the problems associated with their construction. Structures in the immediate vicinity of excavations, dense traffic scenario, presence of underground obstructions and utilities have made excavations a formidable task to execute. Clearly, deep excavations are posing mounting problems that demand a site specific and tailor made retaining solution. Even in complicated urban settings, deep retaining systems have been deployed successfully by overcoming construction challenges. This article describes s tudy on one of the retaining system called Anchored Pile Wall that is successfully executed in the urban areas. Item Model Drainage condition Soil unit weight – Dry (kN/m3) Friction angle, Ø (o) Cohesion, c (kN/m2) Elastic Modulus Poisson ratio, υ
Sand Mohr– Coulomb Drained 16
Pile Linear Elastic Non porous 25
30 1 35Mpa 0.25
--------30Gpa 0.15
Table 1: Parameters used for modelling of Pile wall in PLAXIS-3D
The length of wall is taken as 16m, diameter of pile = 750mm, Capping beam of 750 x 375 mm considering same properties of pile, height of excavation is up to 8m with stage-wise excavation of every 2m, 3D model of 30m x 3m x 20m (X,Y & Z) having pile wall at distance of 20m. In order to discard the effect of pore water pressure, modelling is done considering no water table i.e. dry soil.
Fig. 1 FE model used in the analysis (deformed mesh after excavation)
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2. ANCHORED PILE WALL STUDY:
Fig. 2 Model of anchor in PLAXIS-3D Anchor properties Length
5.66 m
EA
650,000 kN
Fig. 3 anchoring at various angles 0
5
10
15
20
10 5 Ground Deformations in (mm)
For medium dense sand soil, wall height of 16m and Pile diameter of 750mm, effects of anchor location, Inclination of anchor, spacing of anchors on wall and soil deformations were studied. Using the basic numerical model shown in Fig.1, with properties of soil mentioned in Table 1 and anchor properties mentioned below, a parametric study was performed to investigate the effect of parameters considered on wall and soil deformations. Analyses were performed using the finite element method. The analysis results show that anchoring at the depth of 25% [0.25H] height of excavation [H] from top and anchoring at an inclination of 30 degree to horizontal is most effective and gives less Pile wall deflection. While having multiple anchor levels is the most efficient way to reduce wall and soil deformations. The anchor spacing of 4d is kept as a basic model for analysis, were d is diameter of pile. Modelling of Anchor in PLAXIS comprise of node to node anchor having EA value, and to gets frictional reaction embedded pile is connected to anchor as shown in Fig. 2
0 -5 -10
no anchor
-15
anchor at 45 degree
-20
anchor at 35 degree
-25
anchor at 25 degree
-30 -35
Distance from pile wall axis in (m)
Grout – embedded pile Fig. 4 Effect of anchor on Ground deformation
Length
4.25 m
Density
24 kN/m3
E
30 GPa
0
Diameter
150 mm
-2
Skin resistance - Linear
Ttop max = 200 kN/m Depth of wall in (m)
Table 2: Anchor properties and Grout – Embedded pile properties
4
In order to study effect of anchoring on ground deformation and pile wall deflection, anchoring at angle of 0, 25, 30, 35 and 45 degrees to horizontal was done as shown in Fig. 3.
8
10
12
-4 -6 -8
-10
2.1 Anchoring at various angle
6
-12 -14 -16
anchor at 45 degree anchor at 35 degree anchor at 25 degree anchor at 0 degree anchor at 30 degree deformation of pile wall in (mm)
Fig. 5 Effect of anchor inclination on Pile wall deformation
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0.15 0.14 0.13 0.12 0.11 0.1 0.09 0.08
δmax/H %
From Fig.4 and Fig.5, ground deformation and pile wall deflection is reduced with installation of anchors. Anchoring at an inclination of 25 to 30 degree gives less ground deformation and pile wall deflection as shown in Fig. 6.
deformation at tip of wall in (mm)
angle of inclination of anchor to horizontal in (degree) 0
10
20
30
40
50
0.10
6
0.20
0.30
0.40
0.50
Depth of Anchoring (xH)
7 8
Fig 8 Maximum wall deflection
9 10
In Fig 8, δmax is maximum deflection and H is height of excavation.
11 12
2.3 Spacing of anchors
2.2 Installation depth of anchor The depth at which anchor has to be install is important parameters. The anchors were installed at height of 1m, 2m, 3m and 4m i.e. at 12.5%, 25%, 37.5% and 50% of height of excavations. From Fig 7 and Fig 8, at depth of 2m anchoring is most effective. 4
6
8
10
12
0 Pile wall depth in (m)
-2 -4 -6
4
1m depth
-10
2m depth
-12
3m depth
-14
6
8
10
12
0 -2 -4 -6 -8 -10 -12 -14
-8
-16
The anchors were installed with horizontal spacing of 2d, 3d, 4d, 5d and 6d (d=diameter of Pile). Fig.9 shows that with less horizontal spacing, pile wall deformations reduces.
pile wall depth in (m)
Fig. 6 Deformation at tip of wall with anchor at depth 2m
-16
2d 3d 4d 5d 6d Deformation of Pile wall in (mm)
Fig. 9 Effect of spacing of anchor on deformation of wall
4m depth Deformation of Pile wall in (mm)
Fig 7 Effect of anchoring depth on deformation of Pile wall
CONCLUSIONS 1) With progress in excavation, the ground deformation increases and the settlement value becomes larger and larger as the excavation deepens. According to numerical analysis, a distance range of 0 m to 10 m from the foundation excavation is the main influence
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area, and then away from the excavation, there is less influence on surface settlement 2) With the application of anchor, the Pile wall deformation and ground deformation reduces. 3) Anchoring at various depth shows that at -2m from ground level i.e at depth of 25% height of excavation the deformation of wall is less. 4) The anchor inclination of 25 to 30 degree to the horizontal, gives considerably less ground and pile wall deformations. 5) With increase in horizontal spacing of anchors, wall deformation increases.
Chang-Yu Ou, Pio-Go Hsieh, Yi-Lang Lin, (2013), “A parametric study of wall deflections in deep excavations with the installation of cross walls”, Computers and Geotechnics 50, 55–65
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