Abstract
Τhis paper presents an analytical method for calculating the steady-state impedance factors of pile groups of arbitrary configuration subjected to harmonic vertical loads. The derived solution allows considering the effect of the actual pile geometry on the contribution of pile-soil-pile interaction to the response of the group, via the introduction of a new dynamic interaction factor, defined on the basis of soil resistance instead of pile displacements. The solution is first validated against a published solution for single piles that accounts for the effect of pile geometry on the generated ground vibrations. Accordingly, we show that the derived soil attenuation factor agrees well with existing solutions for pile groups in the high frequency range, but considerable differences are observed in both the stiffness and damping components of the computed impedance when the relative spacing between piles decreases. Numerical results obtained for typical problem parameters suggest that ignoring pile geometry effects while estimating the contribution of pile-soil-pile interaction in the response may lead to inaccurate results, even for relative large pile group spacings.
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Abbreviations
- r, \(\theta\), z :
-
Radial, circumferential and vertical directions in the cylindrical coordinate system 1
- \(r^{\prime}\), \(\theta^{\prime}\) :
-
Radial and circumferential directions in the cylindrical coordinate system 2
- m :
-
Number of piles in the group
- d :
-
Pile diameter
- R :
-
Pile radius
- H :
-
Pile length
- E p :
-
Elasticity modulus of pile
- A p :
-
Cross-sectional area of pile
- ρ p :
-
Mass density of pile
- C p :
-
Wave propagation velocity of pile
- mFeiωt :
-
Vertical harmonic force applied on the cap of the pile group
- ω :
-
Circular frequency
- λ*, G* :
-
Lame’s constants of soil
- \(\rho\) :
-
Mass density of soil
- \(U_{z}\) :
-
Soil displacement
- n :
-
The nth mode (n = 1,2,3…)
- An, Akn, Atn, Sk1, Sk2 :
-
Undetermined coefficients
- R n :
-
Soil reaction factor
- Z n :
-
Soil mode
- K 0 :
-
Modified second kind Bessel functions of zero order
- q1n, q2n, gn, β1n, β2n, \(\bar{u}_{pk}\), \(\tilde{u}_{pk}\), \(\iota_{n}\), \(\chi_{n}\), γk1, γk2, γk3, γt1, γt2, \(\zeta_{kn}\), \(\zeta_{tn}\), \(\varGamma_{k}\), \(\varGamma_{t}\) :
-
Temporary variables
- \(\tau_{rz}\) :
-
Soil shear stress
- f :
-
Soil resistance to pile displacement
- f a :
-
Soil resistance relevant to source pile
- f p :
-
Soil resistance relevant to receiver pile
- r a :
-
Radius of source pile
- r p :
-
Radius of receiver pile
- r k :
-
Radius of pile k
- r t :
-
Radius of pile t
- r 0 :
-
Distance between the origins of the two systems
- θ 0 :
-
Angle between the horizontal axis r and the line connecting the two origins of the coordinate systems
- ~:
-
Quantities expressed in the cylindrical coordinate system 2
- \(\psi\) :
-
Soil attenuation function
- S :
-
Distance between the centre of two piles
- \(\beta_{\text{s}}\) :
-
Hysteretic damping ratio of soil
- v s :
-
Poisson’s ratio of soil
- V s :
-
Wave propagation velocity in soil
- \(H_{0}^{\left( 2 \right)}\) :
-
Hankel function of zero order and second kind
- a 0 :
-
Dimensionless frequency
- \(\alpha\) :
-
Standard pile interaction factor
- \(\kappa\) :
-
Proposed pile interaction factor
- \(\kappa_{kt}\) :
-
Interaction factor between pile k and pile t
- F k :
-
Total soil resistance relevant to pile k
- f k :
-
Soil resistance relevant to pile k
- f t :
-
Soil resistance relevant to pile t
- \(u_{pk}\) :
-
Vertical displacement of pile k
- \(K\) :
-
Complex impedance of pile group
- \(k_{\text{G}}\) :
-
Real component of the pile group impedance
- \(c_{\text{G}}\) :
-
Imaginary component of the pile group impedance
- k :
-
Real component of single pile impedance
- c :
-
Imaginary component of single pile impedance
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant Numbers 51622803, 51708064, 51878103).
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Luan, L., Zheng, C., Kouretzis, G. et al. A new dynamic interaction factor for the analysis of pile groups subjected to vertical dynamic loads. Acta Geotech. 15, 3545–3558 (2020). https://doi.org/10.1007/s11440-020-00989-7
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DOI: https://doi.org/10.1007/s11440-020-00989-7