Explosive compaction technology for loess embankment settlement control: numerical simulation and field implementation

Abstract

Loess covers about one-tenth of the world’s land area. While it is often used as embankment fill, loess is not an ideal construction material due to its wet collapsible nature, as it may cause significant embankment settlement and other related problems. Although explosive compaction (EC) technology has been used for many years, the challenges in experimental testing and theoretical analysis hinder its wider application. This paper contributes to the development of a design construction scheme of EC technology for loess embankment improvement through an integrated approach that involves finite element modeling, small-scale experiments, full-scale simulation and field implementation. In this study, a reliable finite element model is developed and validated through a small-scale experiment. The model is developed based on the software ANSYS/LS-DYNA®14.5 and takes into account the coupling between different materials (including soil, explosives, air and pavement). Critical performance factors such as the volume of the explosion cavity, the density of the compacted soil and the soil pressure can be obtained directly from the model. The model is then extended to simulate full-scale embankments. A sensitivity study is conducted to establish the correlations between the design parameters and the abovementioned performance factors. The relationships served as design guidelines for the successful implementation of the EC technique in an embankment section on the Cheng-Chao highway in China. The results demonstrated the feasibility of the EC technique as a ground improvement method for loess embankments, and it illustrated the effectiveness of the numerical method as a tool in design.

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Abbreviations

a, k :

Constants of soil

\(a_{0}\), \(a_{1}\), \(a_{2}\) :

User-defined constants in yield function of soil

c :

Cohesive strength

d c :

The length of its minor axis of the approximate spheroid

d v :

The length of its major axis of the approximate spheroid

e:

Void ratio

h :

Diameter of the blasting-influenced zone

r c :

Radius of exploration cavity

r e :

Equivalent radius of explosive bar

r hc :

Lateral radius of compacted zone by EC

s ij :

Deviatoric stress of soil element

w:

Water content

\(A\),\(B\) :

Linear coefficients in the JWL equation

\(C_{0}\), \(C_{1}\), \(C_{2}\), \(C_{3}\), \(C_{4}\), \(C_{5}\) and \(C_{6}\) :

User-defined constants in the linear polynomial equation of state

D h :

Depth of drill hole

D ha :

Actual hole depth measured before blasting

D hd :

Design depth of drill hole

D r :

Relative density of soil

\(E\) :

Internal detonation energy per unit volume for explosive, internal energy per initial volume for air, Young’s modulus for pavement structure

E 0 :

Initial modulus for explosive, initial internal energy per volume for air

E r :

Relative error

\(E_{\tau }\) :

Tangent modulus

G :

Shear modulus

G s :

Specific gravity of soil

H e :

Height of explosive bar

H bc :

Bottom depth of compacted zone by EC

H bcone :

Height of the bottom cone of explosion cavity

H cy :

Height of the middle cylinder of explosion cavity

H ebc :

Bottom depth of effectively compacted zone by EC

H s, H s1, H s2 :

Height of safety zone between pavement and compacted topmost point

H tc :

Top height of compacted zone by EC

H tcone :

Height of the top cone of explosion cavity

I p :

Plasticity index

K :

Bulk modulus

\(p_{\text{air}}\) :

Pressure on air element

\(p_{\text{eos}}\) :

Pressure of detonation products

P soil :

Pressure on soil element

Q :

Equivalence weight of explosive

R :

Radius of soil in model

\(R_{1}\), \(R_{2}\), \(\omega\) :

Nonlinear coefficients in the JWL equation

S r :

Saturation

V 0 :

Initial relative volume for air

V a :

Actual volume of explosion cavity

V c :

Volume of exploration cavity

\(V_{\text{rel}}\) :

Relative volume, ratio of detonation products volume to undetonated high explosive volume for explosive, ratio of the changed volume to the initial one for air

W L :

Liquid limit

W P :

Plastic limit

W :

Weight of explosive bar

W 1 :

Preliminarily designed explosive weight

W 2 :

Adjusted explosive weight

\(\beta\) :

Hardening parameter of pavement structure

\(\gamma\) :

Ratio of specific heats in the linear polynomial equation of state

\(\mu\) :

Variable in the linear polynomial equation of state, Poisson’s ratio of pavement structure

\(\rho\) :

Density, natural density for soil

\(\rho {}_{\text{d}}\) :

Dry density of soil

\(\sigma_{\text{y}}\) :

Yield strength of pavement structure

\(\varphi\) :

Internal friction angle of soil

\(\phi_{\text{s}}\) :

Yield function of soil

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Acknowledgements

The research team would like to acknowledge the support and assistance from the Chengde Municipal Bureau of Transportation. The writing of the paper is supported by the China Scholarship Council.

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Correspondence to Junliang Tao.

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Li, H., Tao, J., Wei, L. et al. Explosive compaction technology for loess embankment settlement control: numerical simulation and field implementation. Acta Geotech. 15, 975–997 (2020). https://doi.org/10.1007/s11440-019-00777-y

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Keywords

  • Embankment
  • Explosive compaction (EC)
  • Loess
  • Numerical simulation
  • Strengthening