۲۵ اسفند ۱۳۹۸
دسته:
کد : 188

» عنوان : Numerical Study of the Dynamic Compaction Process considering the Phenomenon of Particle Breakage

زبان PDF : لاتین

تعداد صفحات : ۱۱

 

ABSTRACT:

Dynamic compaction (DC) is commonly used to strengthen the coarse grained soil foundation, where particle breakage of coarse soils is unavoidable under high-energy impacts. In this paper, a novel method of modeling DC progress was developed, which can realize particle breakage by impact stress. A particle failure criterion of critical stress is first employed. The “population balance” between particles before and after crushing is guaranteed by the overlapping method. The performance of the DC model is successfully validated against literature data. A series of DC tests were then carried out. The effect of particle breakage on key parameters of DC including crater depth and impact stress was discussed. Besides, it is observed that the relationship between breakage amount and tamping times can be expressed by a logarithmic curve. The present method will contribute to a better understanding of DC and benefit further research on the macro-micro mechanism of DC.

۱. Introduction

Dynamic compaction (DC) refers to the ground improvement method in which a heavy weight is dropped onto the ground surface from a great height to increase the density of the underlying soils. The DC method has been found to be useful in improving the mechanical behavior of underlying soil layers, especially loose granular materials [۱۴]. Recently, the DC method has been widely used in many engineering fields, such as airports, seaports, dams, and railways.

Many analytical or semianalytical studies have been carried out to predict the important parameters involved in real DC treatments, including the degree and depth of improvement [۵۷], the dynamic stress distribution in depth [۸۱۰], the crater depth [۵, ۱۱, ۱۲], and the numerical simulation of DC [۱۳۱۸].

Although the topic of DC has been widely researched in geomechanics, the performance design and the application of dynamic compaction are still largely empirical in nature. This may be due to the complexity of the soil itself and the substantial challenges associated with a DC field test. Under the impact stress of a hammer, the soil foundation generates a series of complex responses, including the reorganization of local soil particles, the dramatic plastic deformation near the impact location, and the interior deformation under a stress wave. It is difficult to address all these responses in a deterministic model and collect sufficient data resources in a DC field test.

A numerical method simulation of DC attracts more attention in published literature. Poran and Rodriguez [۱۳] presented one of the earliest 2D models for simulating DC in dry sand using the finite element code. Their computed results are good when the sand is relatively loose, but when densification occurs, the computed results depart substantially from experimental data. Based on the findings of Poran and Rodriguez, Lee et al. [۱۴] and Gu et al. [۱۵] described dry sand behavior under the DC process, utilizing a finite element program. They discussed the effects of drop energy, the momentum of the falling tamper, and the tamper radius on the depth of improvement. In addition, they proposed a method for estimating the depth and the degree of improvement. Wang et al. [۱۶] developed a method for estimating ground deformation with a numerical model created in LS-DYNA.

Considering numerical studies of DC, the discrete element method, which is neither limited by the large deformation nor the constitutive model of the soil, is superior [۱۷, ۱۸]. Ma et al. [۱۸] pointed out that the improvement and the maximum influence depth of DC can be easily evaluated via the porosity changes of the gravel soil obtained by the particle flow discrete (PFC) element method. Jiang et al. [۳] conducted a series of DC tests with PFC۳D to evaluate the compacting effects via the porosity and the ground settlement.

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