Keywords: LUSAS, numerical analysis, dynamic compaction, soil behaviour, impacting pounder, peak particle velocity.

This paper describes numerical simulation study of dynamic compaction process by using LUSAS [1] to generate a full axisymmetric elasto-platic finite element representation of soil. Examples show the analysis of a pounder dynamically impacting the soil. The cylindrical pounder (damper) is 1 m in length and has a diameter of 2.5 m. Computed results such as pounder penetration (crater depth) during impact at different drop mass and height of drop, horizontal and vertical displacements surrounding the impact point, and peak particle velocity attenuation from different distances of the impact point are presented.

The analysis of soil behaviour is materially non-linear due to the plastic deformation in the soil and exhibits boundary condition of nonlinearity due to its contact with the pounder. An elasto-plastic (optimised) Von Mises model is used to analyse the plasticity aspects of the pounder and elasto-plastic Mohr-Coulomb model is used for the soil analysis. 2D slidelines are used to specify the contact conditions between the base of the pounder and the top of the soil. Both the Mohr- Coulomb and Von Mises models are available in the library of LUSAS [1] within the material properties. The dimensions of the soil area were chosen to be 35 m by 35 m with the mesh increment has adopted to , and the time step was automatically generated by LUSAS .

The variations of crater depth with drop height and drop mass shown that significant increase of crater depth with increasing drop height and drop mass, showing a direct linear relationship. As regards to the results described in reference [2], it is worth noticing that the estimated maximum mass penetration was 310 mm for the drop mass of 10 Mg, which was between the two values of 510 mm for the force-time load solution and 260 mm for the rigid body impact load analysis. The inverse scaled distance which is the square root of drop energy, , divided by the distance, d, from the impact point versus peak particle velocity. The results showed that the best-fit line is quite similar to the upper limit line defined by Mayne [3] based on measurements at a large number of sites.

As a conclusion of these examples, it may be deduced that the crater depth due to dynamic compaction correlates well with pounder mass and drop height. It increases significantly as drop mass increases. The results confirmed some previous published data. Peak particle velocity (PPV) due to dynamic compaction attenuates with distance from drop point. As for comparison with the same distances but from different depths, higher values of peak particle velocities were found at the ground surface and decreasing with increasing depth. The curves of the peak particle velocity have oscillating forms. Under this investigation most of the peak velocity approaching a zero value at a distance of more than 20 metres from the symmetric axis of the pounder.

It is hoped to substantiate this numerical analysis with to some fieldwork on dynamic compactions. Ultimately, it is hoped that the program will contribute to the basic understanding of complex field processes, and extend available design technologies. The result obtained from this numerical study can be compared to field and laboratory situations such as: estimation of the effects of drop mass, drop weight, peak particle velocity, and other factors related to soil characteristics.

1

LUSAS©, "Powerful FE technology for specialist applications", Version 13.2-2, FEA Ltd., 2000.

2

J.L. Pan, A.R. Selby, "Simulation of dynamic compaction of loose soils", The Second International Conference on Engineering Computational Technology, Leuven, Belgium, 6-8 September 2000. doi:10.4203/ccp.71.9.1

3

P.W. Mayne, J.S. Jones, "Impact stresses during dynamic compaction", Journal of Geotechnical Engineering, ASCE, 109(10), 1342-1347, 1983. doi:10.1061/(ASCE)0733-9410(1983)109:10(1342)

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