Abstract:
Silos are one of the most common containment structures used in industrial applications worldwide
for the storage and handling of bulk granular materials such as grains, cement, coal, fertilizers,
minerals, chemicals, etc. These structures are mainly constructed in steel or concrete and consist
of a bunker and a hopper section at the bottom which can take different sizes and shapes. However,
safe operation and design of silos have become difficult to a certain extent mainly due to the
complex behaviour of infill bulk material during the discharge state. Hence, the design of silos is
governed by dynamic discharge conditions for the most part. Past studies have shown that
numerical methods such as the Finite Element Method can capture dynamic behaviour reasonably
over codes of practice. However, further optimisation of such Finite Element simulation is
necessary to improve the accuracy while reducing the computational cost.
This project studies the influence of the bulk material constitutive relationships in silo wall
pressure prediction used in numerical and theoretical techniques. Although in static conditions,
bulk materials can withstand loads in shear, in dynamic flow conditions they tend to behave
erratically leading to failure. Two of the most widely used constitutive relationships were explored
in this sense; the (i) Mohr-Coulomb relationship and the (ii) Drucker-Prager criterion. Bulk
material discharge simulation is performed using the Finite Element Method to capture the peak
wall pressure at the bunker-hopper transition of the silo.
Numerical results obtained from the Finite Element model were verified against a comprehensive
experimental study. It is found that the numerical method provides better results compared to
theoretical methods available. Eurocode predicts fairly accurate results although with some
overestimation which can be expected due to the incorporation of safety factors in design codes.
The Mohr-Coulomb stress-strain relationship can be recommended as the most appropriate
constitutive model for representing wheat as bulk material as it predicts results with almost 100%
accuracy. Contrary to that, the Drucker-Prager criterion tends to under-predict results. This needs
to be further investigated.
The influence of the lateral pressure coefficient as well as the discharge velocity on discharge
pressures have also been explored in this study briefly. It is observed that the numerical method
better predicts the lateral pressure coefficient. Moreover, when the discharge rate of the bulk
material is increased the peak pressure tends to reduce. However, these aspects will have to be
studied in detail before coming to any conclusions.
As far as this study is considered, a numerical model with the Mohr-Coulomb relationship as the
material constitutive relationship can be deemed valid in predicting discharge pressures in silos
with an acceptable level of accuracy.
Citation:
Dissanayake, T.D., & Mallikarachchi, H.M.Y.C. (2021). Pressures exerted on silo walls due to infill bulk material discharge [Abstract]. In P. Hettiarachchi (Ed.), Proceedings of Civil Engineering Research Symposium 2021 (p. 4). Department of Civil Engineering, University of Moratuwa.