Excavation in moraine and dense non-cohesive soil : Numerical analysis of soil behavior

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: Excavation and moving of soil are common civil work tasks connected to the construction of buildings, roads and railways. In construction projects large amounts of soil have to be handled with different machines, tools and working methods. Soils are more or less difficult to excavate depending on their properties. The ability to excavate the soil (the excavatability) in combination with the type of work performed affects the choice of machines and tools being used. It also affects the time it takes to perform the work. The handling of soil volumes is a large part of the project cost. The cost depends on the machines and tools being used, the amount of soil being excavated and the ability to excavate the soil.The main objectives of this study are:• to identify parameters affecting the excavatability of soil through a literature review.• to study and describe the excavation process in soil.• to evaluate parameters affecting the horizontal resistive force on a wide blade with the finite element method.• to compare and discuss the magnitude of the horizontal resistive force obtained in the finite element study with calculations using an analytical model.• to propose a platform for further research in this area.The excavation process and the analysis of a tool working through the soil have been studied for three types of machine-tool sets. Earlier studies from different authors have provided important parameters that affect the resistance of soil as well as form a basis for the analysis of excavation and moving soil. A two-dimensional finite element analysis of a wide blade moving horizontally in a soil mass has been performed. The purpose of the numerical analysis was to analyse and discuss the effects of different soil and soil-tool parameters on the resultant resistive force acting on the blade.Based on the literature review, it was found that the particle size, the content of cobbles and boulders, the shear strength and the denseness of the soil affects the excavatability of the soil. When defining a model for predicting resistive forces on an excavation tool, it is necessary to study the total excavation process, including how the tool interferes with the ground, how the machine and tool moves and the methodology used for excavating and moving the soil.Based on the numerical analysis, it was found that, for undrained cohesive soil, the resistive force increases linearly with undrained shear strength and adhesion. For non-cohesive soil the resistive force increases non-linearly with the soil friction angle and the soil-tool friction angle, and linearly with dilatancy. Extended interfaces as well as different mesh sizes significantly impacted the magnitude of the resistive force.In order to determine the excavatability of soil and to present a new system for classification of excavatability, related knowledge is needed about the excavation process and the effect of the cobble and boulder content on the excavatability. Theoretical results obtained in this study must be verified by field tests.

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