Analysis of rigid raft overlying the granular pile with the effect of stiffness of bearing stratum

ABSTRACT

With the use of piled raft, the load carrying capacity of the raft is enhanced and its differential settlement is reduced. As an economical alternative to conventional pile i.e. steel or concrete pile, granular pile (GP) is a reasonable option. The numerical solutions are available for floating granular pile overlaying with rigid raft. Present study deals with a method to analyse the end bearing granular pile overlying with rigid raft. A new pile settlement matrix is formulated to predict response of granular piled raft based on the elastic continuum approach. To account for the influence of bearing stratum, the mirror image approximation is used both for granular pile and raft. The results are evaluated in terms of normalised parameters such as settlement ratio, i.e. settlement of piled raft in comparison to rigid raft alone, displacement factor, percentage load transferred to tip of granular pile, percentage load shared by raft, normalised shear stress distribution along the length of granular pile and normalised contact pressure distribution beneath the raft with the variations of relative size of raft, relative length of granular pile, stiffness factor of granular pile and bearing stratum.

Abbreviations: GP = Granular pile; L = Length of pile; n = number of elements of granular pile; d = Diameter of pile; L/d = Relative length of granular pile; P = Load on granular piled Raft; D = Diameter of Raft; E_b = Deformation constant of bearing stratum; E_s = Deformation constant of soil; E_gp = Deformation constant of granular pile; D/d=relative size of raft; ν_b = Poisson’s Ratio of bearing stratum; ν_s = Poisson’s Ratio of soil; K_gp = (E_gp/E_s)Stiffness factor of GP to soil; K_b = (E_b/E_s) Stiffness factor of bearing stratum to soil; p_r = Raft stresses; p_b = Base Pressure; τ =Shear stress; z₁(=z/L) Normalised depth of GP; I_p = displacement factor; τ* = τ(πdL)/P Normalised shear stresses of a GP; γ = settlement ratio; P_b = load on base of GP; P_p = load on pile; P_r = load on raft; (P_b/P) × 100 = percentage base load; (P_p/P) × 100 = percentage pile load; (P_r/P) × 100 = percentage raft load.

KEYWORDS:

• End-bearing granular piled raft
• stiffness factor of bearing stratum
• displacement factor
• stiffness factor of granular pile
• normalised shear stress
• normalised contact pressure distribution

Acknowledgments

The author is highly obliged to convey his deep gratitude to, Prof M.R. Madhav (Civil engineering department, J.N.T.U, Hyderabad) for their contribution and encouragement in present work. Their high appreciation, invaluable guidance, comments and suggestions have played an major part in the results of this research.

Disclosure statement

No potential conflict of interest was reported by the authors.