Elsevier

Computers and Geotechnics

Volume 78, September 2016, Pages 194-202
Computers and Geotechnics

Technical Communication
Analysis of hollow steel piles subjected to buried blast loading

https://doi.org/10.1016/j.compgeo.2016.05.015Get rights and content

Abstract

Dynamic analyses of hollow steel end bearing piles in sandy soil subjected to buried blast loading are performed herein using the three-dimensional nonlinear finite element method and the coupled Eulerian–Lagrangian technique. Parametric sensitivity studies are performed for different axial load magnitudes on the pile head, elastic moduli, mass densities, different friction angles of soil and Poisson’s ratio. The lateral deflection of the pile head decreases with increasing axial load. The peak particle velocity in soil increases with a decrease in elastic modulus, mass density and friction angle of soil and increases significantly if the soil is incompressible.

Introduction

A pile is a load bearing component of a structure that transfers the structural load to the hard soil or rock underground. The modern human civilization and smart infrastructure depend largely on the pile foundation for carrying its structural load because the pile foundation reduces the area of load distribution in the surroundings near the ground surface and thus, considered as a suitable foundation system in the regions with more congestion and a higher number of tall buildings. However, failure of a single pile can lead to disaster by causing progressive failure of the superstructure and the surrounding structures [14]. In the recent decades, terrorist attack and bomb blast have caused failure of several structures. A small magnitude of the blast, if it happens in the close vicinity of one pile may lead to progressive failure of the whole structure [5]. Moreover, the failure of the structure often starts from the soil because the soil is the weakest of all civil engineering materials. Hence, it is extremely necessary to understand the response of pile foundation in the soil when subjected to blast loading.

Disastrous events like blast inside ground creates ground shock wave that while travelling through soil gives rise to a high rate of loading (up to 102/s to 104/s) in the soil and rock [19], [5]. Drake and Little [4] experimentally studied ground shock wave propagation due to penetration of weapon and detonation of buried explosive in the saturated and unsaturated soil. Wu et al. [28] investigated the ground shock wave propagation through Granite and proposed an equation for peak particle velocity (PPV) of rock. In the Indian Standard Code of Practice, [7] an equation has been proposed for PPV given byPPV=K1W2/3R1.25mm/swhere K1 is constant and its value is 880 for soils and weathered or soft rock, W is the charge weight per delay in kg and R is the distance from the blast source in m. Many researchers have performed centrifuge and field tests for blast loading on structures. Tabatabai [24] and De et al. [3] performed centrifuge tests of underground structures under blast loading. Shim [22] carried out centrifuge tests to study the response of piles in soil under blast loading. An et al. [2] studied shock wave propagation through soil numerically using LS-Dyna and an equation-of-state model for soil. Jayasinghe et al. [9] and Jayasinghe [8] performed finite element (FE) analysis of aluminum and concrete pile subjected to underground blast loading in saturated and dry soils; however, they did not study the effect of variation of soil parameters on blast response of the pile.

The objectives of the present work are (i) to perform finite element analysis of hollow steel end bearing pile foundation subjected to blast loading, (ii) to study the displacement response of the pile subjected to blast loading under different magnitudes of axial loads on the pile head, (iii) to study the PPV in soil generated due to blast, and (iv) to investigate the stress magnitude generated in the soil due to blast. Blast response of the pile and the surrounding soil is investigated for different axial load magnitudes (Q) on the pile, different elastic moduli (Esoil), mass density (ρsoil), friction angle (ϕ) and Poisson’s ratio (νsoil) of soil. The three-dimensional (3D) nonlinear dynamic finite element (FE) analyses of pile subjected to blast loading are carried out using the commercially available FE software Abaqus version 6.11 (Abaqus manual version 6.11) and the coupled Eulerian–Lagrangian (CEL) tool. The CEL tool in Abaqus has been previously used in geomechanics problems exhibiting large deformation [21], [26], [25]. In the present analyses, the soil and the pile are modeled using the Lagrangian elements. The trinitrotoluene (TNT) explosive is modeled using the Eulerian elements. Strain rate dependent material properties have been used for both soil and pile. Soil stress–strain response is simulated using the Drucker–Prager constitutive model [13], [15]. The stress–strain response of pile is simulated using the Johnson–Cook constitutive model [10]. The pressure–volume relationship of the trinitrotoluene (TNT) explosive is simulated using the Jones–Wilkins–Lee (JWL) equation of state (EOS).

Section snippets

Lagrangian finite element modeling of soil and pile

The 3D FE model of the pile and soil are developed in Abaqus/CAE using the Lagrangian elements. A typical FE mesh of the soil, pile and explosive are shown in Fig. 1. In order to place the explosive inside the soil, a rounded hole with the same diameter as that of the explosive has been created in the soil domain. The size of the soil domain considered herein is 20 m × 20 m × 10 m. The soil and pile meshes are generated using the eight-node brick element (C3D8R) with reduced integration, hourglass

Validation studies for the FE model

The validity of the present finite element simulations has been ensured first by comparing the PPV in the geological medium for a buried blast, thus checking if the finite element tool considered herein is able to predict blast-induced stress wave propagation through soil. Moreover, the simulation results for a pile subjected to buried blast loading have also been checked with the results reported in the literature. Wu et al. [28] performed field experiment and simulation of buried blast in

Parametric sensitivity analyses

Fig. 5 shows the geometry for placement of piles and explosive as considered in the parametric analyses. Fig. 6(a) and (b) show the finite element mesh of soil, Eulerian domain, explosive, pile and also the boundary conditions. In all the analyses, steel piles with 400 mm outer diameter, 335 mm inner diameter and 10 m length have been considered. The center line of the pile is 4 m away from the center of the explosive. The spherical explosive of 50 kg TNT is placed at 0.35 m below from the ground

Results and discussions

Fig. 7(a)–(e) show head displacement time history of pile 1 for different axial load magnitudes on the pile, soil elastic modulus, density, friction angles and Poisson’s ratio. Lateral displacement of the pile subjected to blast load decreases with increasing axial load magnitude. It is observed from Fig. 7(a) that the lateral pile head displacement decreases by 55% as the axial load on the pile increases from 100 kN to 1000 kN. Moreover, the lateral displacement of the pile head increases as the

Conclusions

Dynamic analyses of hollow steel end bearing piles subjected to buried blast loading in sandy soil are carried out herein using three-dimensional nonlinear finite element procedure and the coupled Eulerian–Lagrangian technique. Parametric sensitivity studies are performed for varying axial loads on the pile, different elastic moduli, mass density, friction angles of soil and Poisson’s ratio. It is concluded from the results that the propagation of ground shock wave depends on elastic modulus,

References (28)

  • L.B. Jayasinghe

    Blast response and vulnerability assessment of piled foundations

    (2014)
  • G.R. Johnson et al.

    A constitutive model and data for metals subjected to large strains, high strain rates and high temperatures

  • Kowalsky MJ, Gabr MA. Pile bent design criteria. NCDOT research project report 2005-19. Center for Transportation and...
  • M. Larcher et al.

    Explosion in complex geometries: a comparison of several approaches

    Int J Protect Struct

    (2010)
  • Cited by (9)

    • Underwater blast response and pile failure analysis of submerged reinforced concrete piles and pile group foundations

      2022, Ocean Engineering
      Citation Excerpt :

      The study and understanding of the effects of explosions on pile foundations and combining these effects with the recorded structural damages resulting from previous explosions makes it possible to evaluate the effectiveness of the current design standards. ( Jayasinghe et al., 2013, 2014b, 2014c, 2017a, 2017b, 2018; Chakraborty, 2016; Jayasinghe, 2014). Another challenge in the investigation of the phenomenon of explosion is the study of underwater explosion or submerged explosion (Li and Rong, 2012; Zhuang et al., 2020; Wu et al., 2020; Wang et al., 2018a, 2018b, 2020; Moradloo et al., 2019; Huang et al., 2019; Barras et al., 2012).

    • Pile response subjected to rock blasting induced ground vibration near soil-rock interface

      2017, Computers and Geotechnics
      Citation Excerpt :

      Jayasinghe et al. [25] developed a fully coupled method to treat the blast response of a pile foundation in saturated soil and the effects of end restraint of pile head and the number and spacing of piles within a group were investigated later [10]. Chakraborty [26] performed parametric sensitivity studies on hollow steel piles subjected to buried blast loading in sandy soil. There are many FE codes are available that are capable of analyzing challenging engineering problems.

    View all citing articles on Scopus
    View full text