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Brillante a#1 Introduction to Foundation Engineering 2014-2015

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  Technological University of the Philippines  Ayala Boulevard, Ermita, Manila College of Engineering Department of Civil Engineering CE 521-5A Foundation Engineering, Lecture  Assignment No. 1 INTRODUCTION TO FOUNDATION ENGINEERING Brillante, Ralph Kenneth V. 10  –  205  –  026 June 24, 2014 Engr. Jesus Ray M. Mansayon Instructor  I. INTRODUCTION For engineering purposes, soil is defined as the uncemented aggregate of mineral grains and decayed organic matter (solid particles) with liquid and gas in the empty spaces between the solid particles. Soil is used as a construction material in various civil engineering projects, and it supports structural foundations. Thus, civil engineers must study the properties of soil, such as its srcin, grain-size distribution, and ability to drain water, compressibility, shear strength, and load bearing capacity. Soil mechanics is the branch of science that deals with the study of the physical properties of soil and the behavior of soil masses subjected to various types of forces. SOIL MECHANICS  ( Geotechnical Engineering: Principles and Practices of Soil Mechanics and Foundation Engineering, by VNS Murthy, page 3 ) Terzaghi defined Soil Mechanics as follows: Soil Mechanics is the application of the laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles produced by the mechanical and chemical disintegration of rocks regardless of whether or not they contain an admixture of organic constituents. GEOTECHNICAL ENGINEERING  (The Mechanics of Soils and Foundation, 2  nd   ed. by John Atkinson, page 3) Geotechnical engineering is simply the branch of engineering that deals with structures built of, or in, natural soils and rocks. The subject requires knowledge of strength and stiffness of soils and rocks, methods of analyses of structures and hydraulics of groundwater flow. Use of natural soil and rock makes geotechnical engineering different from many other branches of engineering and more interesting. The distinction is that most engineers can select and specify the materials they use, but geotechnical engineers must use the materials that exist in the ground and they have only very limited possibilities for improving their properties. This means that an essential part of geotechnical engineering is a ground investigation to determine what materials are present and what their properties are. Since soils and rocks were formed by natural geological processes, knowledge of geology is essential for geotechnical engineering. FOUNDATION ENGINEERING  ( Geotechnical Engineering: Principles and Practices of Soil Mechanics and Foundation Engineering, by VNS Murthy, page 3 ) The subject of Foundation Engineering deals with the design of various types of substructures under different soil and environmental conditions. During the design, the designer has to make use of the properties of soils, the theories pertaining to the design and his own practical experience to adjust the design to suit field conditions. He has to deal with natural soil deposits which perform the  engineering function of supporting the foundation and the superstructure above it. Soil deposits in nature exist in an extremely erratic manner producing thereby an infinite variety of possible combinations which would affect the choice and design of foundations. II. FOUNDATION ENGINEER  The foundation engineer must have the ability to interpret the principles of soil mechanics to suit the field conditions. The success or failure of his design depends upon how much in tune he is with Nature. Source :(  Geotechnical Engineering: Principles and Practices of Soil Mechanics and Foundation Engineering, by VNS Murthy, page 3 ) III. FOUR PERFORMANCE REQUIREMENTS Strength Requirements Once the design of the loads has been defined, we need to develop foundation designs that satisfy several performance requirements. The first category is strength requirements, which are intended to avoid catastrophic failures. There are two types: geotechnical strength requirements and structural strength requirements. Geotechnical Strength Requirements Geotechnical strength requirements are those that address the ability of the soil or rock to accept the loads imparted by the foundation without failing. The strength of soil is governed by its capacity to sustain shear stress, so we satisfy geotechnical strength requirements by comparing shear stresses with shear strengths and designing accordingly. In the case of spread footing foundations, geotechnical strength is expressed as the bearing capacity of the soil. If the load-bearing capacity of the soil is exceeded, the resulting shear failure is called bearing capacity failure  Structural Strength Requirements Structural strength re quirements address the foundation‘s structural integrity and its ability to safely carry the applied loads. For example, pile foundations made from A36 steel are normally designed for a maximum allowable compressive stress of 12,600 lb/in2. Thus, the thickness of the steel must be chosen such that the stresses induce by the design loads do not exceed this allowable value. Foundations that are loaded beyond their structural capacity will, in principle, fail catastrophically. Structural strength analyses are conducted using their ASD or LRFD methods, depending on the types of foundation, the structural materials, and the governing code. Serviceability Requirements Foundations that satisfy strength requirements will not collapse, but they still may not have adequate performance. For example, they may experience excessive settlement. Therefore, we have the second category of performance requirements, which are known as serviceability requirements. These are intended to produce foundations that perform well when subjected to service loads. These requirements include:   Settlement  –  Most foundations experience some downward movement as a result of the applied loads. This movement is called settlement. Keeping settlements within tolerable limits is usually the most important foundation serviceability requirement.   Heave  –  Sometimes foundations move upward instead of downward. We call this upward movement heave. The most common source of heave is the swelling of expansive soils.   Tilt  –  When settlement or heave occurs only on one side of the structure, it may begin to tilt. The Leaning Tower of Pisa is an extreme example of tilt.   Lateral movement  –  Some foundations, such as those supporting certain kinds of heavy machinery, are subjected to strong vibrations. Such foundations need to accommodate these vibrations without experiencing resonance or other problems.   Durability  –  Foundations must be resistant to the various physical, chemical, and biological processes that cause deterioration. This is especially important in waterfront structures, such as docks and piers. Failure to satisfy these requirements generally results in increased maintenance costs, aesthetic problems, diminished usefulness of the structure, and other similar effects.
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