Carbonel a#1 Introduction to Foundation Engineering 2014-2015.PDF

Technological University of the Philippines Ayala Boulevard, Ermita, Manila

College of Engineering Department of Civil Engineering

CE 521-5A Foundation Engineering

Assignment No.1 INTRODUCTION TO FOUNDATION ENGINEERING

Carbonel, Maikko Neil T. 08-205-076 June 24, 2014

Engr. Jesus Ray M. Mansayon Instructor

F O U N D AT I O N E N G I N E E R I N G , S O I L M E C H AN I C S , A N D G E O T E C H N I C AL E N G I N E E R I N G FOUNDATION ENGINEERI NG Foundation Engineering is the category of engineering concerned with evaluating the ability of a locus to support a given structural load, and with designing the substructure or transition member needed to support the construction. Source: http://www.dictionaryofconstruction.com/definition/foundationengineering.html Foundation Engineering is the engineering field of study devoted to the design of those structures which support other structure, most typically buildings, bridges, or transportation infrastructure. It is at the periphery of Civil, Structural and Geotechnical Engineering disciplines and has distinct focus on soil-structure interaction. Source: en.wikipidia.org/wiki/Foundation_engineering That branch of engineering concerned with evaluating the earth's ability to support a load and designing substructures to transmit the load of superstructures to the earth. Source: http://www.answers.com/topic/foundation-engineering SOIL MECHANICS Soil Mechanics is the branch of science that deals with the study of the physical properties of soil and the behaviour of soil masses subjected to various types of forces. Source: PRINCIPLES OF GEOTECHNICAL ENGINEERING, 7th Edition by BM Das, page 1 Soil mechanics is a branch of engineering mechanics that describes the behaviour of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids (usually air and water) and particles (usually clay, silt, sand, and gravel) but soil may also contain organic solids, liquids, and gasses and other matter. Along with rock mechanics, soil mechanics provides the theoretical basis for analysis in geotechnical engineering,

a subdiscipline of Civil engineering, and engineering geology, a subdiscipline of geology. Soil mechanics is used to analyze the deformations of and flow of fluids within natural and man-made structures that are supported on or made of soil, or structures that are buried in soils. Example applications are building and bridge foundations, retaining walls, dams, and buried pipeline systems. Principles of soil mechanics are also used in related disciplines such as engineering geology, geophysical engineering, coastal engineering, agricultural engineering, hydrology, and soil physics. Source: http://en.wikipedia.org/wiki/Soil_mechanics

GEOTECHNICAL ENGINEE RING The use of engineering soils and rocks in construction is older than history and no other materials, except timber, were used until about 200 years ago when an iron bridge was built by Abraham Darby in Coalbrookdale. Soils and rocks are still one of the most important construction materials used either in their natural state in foundations or excavations or recompacted in dams and embankments. Engineering soils are mostly just broken up rock, which is sometimes decomposed into clay, so they are simply collections of particles. Dry sand will pour like water but it will form a cone, and you can make a sandcastle and measure its compressive strength as you would a concrete cylinder. Clay behaves more like plasticine or butter. If the clay has a high water content it squashes like warm butter, but if it has a low water content it is brittle like cold butter and it will fracture and crack. The mechanics that govern the stability of a small excavation or a small slope and the bearing capacity of boots in soft mud are exactly the same as for large excavations and foundations. Many engineers were first introduced to civil engineering as children building structures with Meccano or Lego or with sticks and string. They also discovered the behaviour of water and soil. They built sandcastles and they found it was impossible to dig a hole in the beach below the water table. At home they played with sand and plasticine. Many of these childhood experiences provide the experimental evidence for theories and practices in structures, hydraulics and soil mechanics. I have suggested some simple experiments which you can try at home. These will illustrate the basic behaviour of soils and how foundations and excavations work. As you work through the book I will explain your observations and use these to illustrate some important geotechnical engineering theories and analyses.

In the ground soils are usually saturated so the void spaces between the grains are filled with water. Rocks are really strongly cemented soils but they are often cracked and jointed so they are like soil in which the grains fit very closely together. Natural soils and rocks appear in other disciplines such as agriculture and mining, but in these cases their biological and chemical properties are more important than their mechanical properties. Soils are granular materials and principles of soil mechanics are relevant to storage and transportation of other granular materials such as mineral ores and grain. 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. Source: THE MECHANICS OF SOILS AND FOUNDATION, 2nd Edition by Atkinson, page 1-3

Geotechnical Engineering is the subdiscipline of civil engineering that involves natural materials found close to the surface of the earth. It includes the application of the principles of soil mechanics and rock mechanics to the design of foundations, retaining structures, and earth structures. Source: PRINCIPLES OF GEOTECHNICAL ENGINEERING, 7th Edition by BM Das, page 1

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. The design of foundations of structures such as buildings, bridges, and dams generally requires a knowledge of such factors as a) the load that will be transmitted by the superstructure to the foundation system, b) the requirements of the local building code, c) the behaviour and stress-related deformability of soils that will support the foundation system, and d) the geological conditions of the soil under consideration. To a foundation engineer, the last two factors are extremely important because they concern soil mechanics.

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.

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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.

Constructability Requirements

The third category of performance requirements is constructability. The foundation must be designed such that a contractor can build it without having to use extraordinary methods or equipment. There are many potential designs that might be quite satisfactory from a design perspective, but difficult or impossible to build. There are different types of deep foundations. One of these, a pile foundation, consists of a prefabricated pole that is driven into the ground using a modified crane called a pile driver. The pile driver lifts the pile into the air, and then drives it into the ground.Therefore, piles can be installed only at locations that have sufficient headroom. Fortunately, the vast majority of construction sites have plenty of headroom. Economic Requirements Foundation designs are usually more conservative than those in the superstructure. This approach is justified for the following reasons: a. Foundation designs rely on our assessments of the soil and rock conditions. These assessments always include considerable uncertainty. b. Foundations are not built with the same degree of precision as the superstructure. For example, spread footings are typically excavated with a backhoe and the sides of the excavation becomes the ―formwork for the concrete, compared to concrete members in the superstructure that are carefully formed with plywood or other materials. c. The structural materials may be damaged when they are installed. For example, cracks and splits may develop in a timber pile during hard driving. d. There is some uncertainty in the nature and distribution of the load transfer between foundations and the ground, so the stresses at any point in a foundation are not always known with as much certainty as might be the case in much of the superstructure. e. The consequences of a catastrophic failure are much greater. f. The additional weight brought on by the conservative design is of no consequence, because the foundation is the lowest structural member and therefore does not affect the dead load on any other member. Additional weight in the foundation is actually beneficial in that it increases its uplift resistance.

Foundations are designed to have an adequate load capacity with limited settlement by a geotechnical engineer, and the footing itself may be designed structurally by a structural engineer. The primary design concerns are settlement and bearing capacity. When considering settlement, total settlement and differential settlement is normally considered. Differential settlement is when one part of a foundation settles more than another part. This can cause problems to the structure the foundation is supporting. Source: http://en.wikipedia.org/wiki/Foundation_(engineering)

The design of foundation requires the consideration of many essential factors with regard to soil data, geology of the site, land use patterns, ground conditions and the type of structure to be built. A detailed understanding of the field situation is also very important apart from theoretical knowledge of the subject. This course seeks to provide an overview of the essential features of foundation design. The different aspects of foundation engineering ranging from soil exploration to the design of different types of foundation, including the ground improvement measures to be taken for poor soil conditions have been covered in this course. Source:http://www.cdeep.iitb.ac.in/nptel/Civil%20Engineering/Foundation_Enginee ring/Course%20Objective.html Foundation design must support different kinds of loads, such as dead load, live loads, rain and snow loads, wind loads, seismic loads etc. Foundation should be so designed that it must satisfactorily meet building requirements. The loads that a building foundation should support are: Dead Load Dead load is the combined weight of all the permanent components of the building, including its own structural frame, floors, roofs, and walls, major permanent electrical and mechanical equipment, and the foundation itself. Live Loads Live loads are non-permanent loads caused by the weights of the building’s occupants, furnishings, and movable equipment. Rain and snow loads This load is one which acts primarily downward on building roofs.

Wind Loads Wind loads acts laterally (sideways), downward or upward on a building. It is based on local wind speed. Seismic loads Seismic loads are horizontal or vertical forces caused by the motion of the ground, relative to the building during an earthquake. Other loads Other loads include load caused by soil and hydrostatic pressure, including lateral soil pressure loads, horizontal pressures of earth and groundwater against basement walls, in some instances, buoyant uplift forces from the underground water identical to the forces that cause a boat to float, and lateral force flood loads that can occur in areas prone to flooding. In some buildings, horizontal thrusts from long span structural systems such as arches, rigid frames, domes, vaults, or tensile structures also acts on foundation

A building foundation must meet three general requirements: 1. The foundation, including the underlying soil and rock, must be safe against a structural failure that could result in collapse. For example, the foundation for a skyscraper must support the great weight of the building above on a relatively narrow base without danger of overturning. 2. During the life of the building, the foundation must not settle in such a way as to damage the structure or impair its function. 3. The foundation must be feasible, both technically and economically, and practical to build without adverse effects on surrounding property. Source: http://theconstructor.org/geotechnical/foundation-designrequirement/6525/

F O U N D AT I O N AN D I T S T Y P E S A foundation is the lowest and supporting layer of a structure. Foundations are divided into two categories: shallow foundations and deep foundations. HISTORIC FOUNDATION TYPES Earth fast of post in ground construction Building and structures have long history of being built with wood in contact with the ground. Post in ground construction may technically have no foundation. Timber pilings were used on soft or wer ground even below stone or masonry walls. In marine construction and bridge building a crisscross of timbers or steel beams in concrete is called grillage. Padstones Perhaps the simplest foundation is the padstone, a single stone which both spreads the weight on the ground and raises the timber off of the ground. Staddle stones are a specific type of padstones. MODERN FOUNDATION TYPES Shallow foundations Shallow foundations, often called footings, are usually embedded about a metre or so into soil. One common type is the spread footing which consists of strips or pads of concrete (or other materials which extend below the frost line transfer the weight from walls and columns to the soil or bedrock. Another common type of shallow foundation is the slab-on-grade foundation where the weight of the building is transferred to the soil through a concrete slab placed at the surface. Slab-on-grade foundations can be reinforced mat slabs, which range from 25 cm to several metres thick, depending on the size of the building, or post-tensioned slbs, which are typically at least20 cm for houses, and

thicker for heavier structures. Deep foundations A deep foundation is used to transfer the load of a structure down through the upper weak layer of topsoil to the stronger layer of subsoil below. There are different types of deep footings including impact driven piles, drilles shafts,cassions, helical piles, geo-piers and earth stabilized columns.The naming conventions for different types of footings vary between different engineers. Monopile foundation A monopile foundation is a type of deep foundation which uses a single, generally large-diameter, structural element embedded into the earth to support all the loads (weight, wind, etc.) of a large above-surface structure. A large number of monopile foundations have been utilized in recent years for economically constructing fixed-bottom offshore wind farms in shallow-water subsea locations. For example, a single wind farm off the coast of England went online in 2008 with over 100 turbines, each mounted on a 4.7-meter-diameter monopile footing in ocean depths up to 18 metres of water. Source: en.wikipedia.org/wiki/Foundation_(engineering) When determining which foundation is the most economical, the engineer must consider the superstructure load, the subsoil conditions, and the desired tolerable settlement. In general, foundations of buildings and bridges may be divided into two major categories: 1. shallow foundations and 2. deep foundations. Source: PRINCIPLES OF FOUNDATION ENGINEERING, 7th Edition by BM Das, page 1

T Y P E S O F S H AL L O W F O U N D AT I O N 1. Strip Footing: A strip footing is provided for a load-bearing wall. A strip footing is also provided for a row of columns which are so closely spaced that their spread footings overlap or nearly touch each other. In such a case, it is more economical to provide a strip footing than to provide a number of spread footings in one line. A strip footing is also known as continuous footing.

2. Spread or Isolated Footing: A spread footing (or isolated or pad) footing is provided to support an individual column. A spread footing is circular, square or rectangular slab of uniform thickness. Sometimes, it is stepped or haunched to spread the load over a large area.

3. Combined Footing: A combined footing supports two columns. It is used when the two columns are so close to each other that their individual footings would overlap. A combined footing is also provided when the property line is so close to one column that a spread footing would be eccentrically loaded when kept entirely within the property line. By combining it with that of an interior column, the load is evenly distributed. A combined footing may be rectangular or trapezoidal in plan.

4. Strap or Cantilever footing: A strap (or cantilever) footing consists of two isolated footings connected with a structural strap or a lever. The strap connects the two footings such that they behave as one unit. The strap is designed as a rigid beam. The individual footings are so designed that their combined line of action passes through the resultant of the total load. a strap footing is more economical than a combined footing when the allowable soil pressure is relatively high and the distance between the columns is large.

5. Mat or Raft Foundations: A mat or raft foundation is a large slab supporting a number of columns and walls under the entire structure or a large part of the structure. A mat is required when the allowable soil pressure is low or where the columns and walls are so close that individual footings would overlap or nearly touch each other. Mat foundations are useful in reducing the differential settlements on nonhomogeneous soils or where there is a large variation in the loads on individual columns.

T Y P E S O F D E E P F O U N D AT I O N Deep foundations are required to carry loads from a structure through weak compressible soils or fills on to stronger and less compressible soils or rocks at depth, or for functional reasons. These foundations are those founding too deeply below the finished ground surface for their base bearing capacity to be affected by surface conditions, this is usually at depths >3 m below finished ground level. Deep foundations can be used to transfer the loading to a deeper, more competent strata at depth if unsuitable soils are present near the surface. The types of deep foundations in general use are as follows: 1. Basements 2. Buoyancy rafts (hollow box foundations) 3. Caissons 4. Cylinders 5. Shaft foundations 6. Piles Basement foundations: These are hollow substructures designed to provide working or storage space below ground level. The structural design is governed by their functional requirements rather than from considerations of the most efficient method of resisting external earth and hydrostatic pressures. They are constructed in place in open excavations. Buoyancy rafts (hollow box foundations) Buoyancy rafts are hollow substructures designed to provide a buoyant or semibuoyant substructure beneath which the net loading on the soil is reduced to the desired low intensity. Buoyancy rafts can be designed to be sunk as caissons, they can also be constructed in place in open excavations. Caissons foundations: Caissons are hollow substructures designed to be constructed on or near the surface and then sunk as a single unit to their required level.

Cylinders: Cylinders are small single-cell caissons. Shaft foundations: Shaft foundations are constructed within deep excavations supported by lining constructed in place and subsequently filled with concrete or other pre-fabricated load-bearing units

Pile foundations:

Pile foundations are relatively long and slender members constructed by driving preformed units to the desired founding level, or by driving or drilling-in tubes to the required depth – the tubes being filled with concrete before or during withdrawal or by drilling unlined or wholly or partly lined boreholes which are then filled with concrete.

Source: http://theconstructor.org/geotechnical/

Importance of Foundation in Civil Engineering Structures Foundation is the bottom most part of a structure which is hidden inside the soil in most of the cases. Therefore more quality control is required as it is possible to hide the mistakes underground. Unfortunately foundation will have given less importance compared to externally visible portions of the structure in most of the cases. It is a normal practice to provide the foundation without proper Geo technical assessment. More importance is given to structural aspects and foundation is provided from a structural point of view only. Repair of failed foundation is not an easy matter and it involves complicated engineering techniques with high cost in most of the cases. It is also seen that damaged portion of the highways is repaired from the top leading to the failure at the same location in a case where the failure is occurred in the foundation portion. Special care is required in cases of weak compressible soils and water table variations. It is required to have a combined assessment of Geo technical and structural engineering with equal importance in providing foundation for Structures. Also the Soil assessment laboratories with experts shall be made available to common people to solve their foundation issues.

Source: http://fphzus.wordpress.com/2012/08/30/importance-of-foundation-in-civilengineering-structures/ ` G E O T E C H N I C AL P R O P E R T I E S O F S O I L The geotechnical properties of a soil—such as its grain-size distribution, plasticity, compressibility, and shear strength—can be assessed by proper laboratory testing. In addition, recently emphasis has been placed on the in situ determination of strength and deformation properties of soil, because this process avoids disturbing samples during field exploration. However, under certain circumstances, not all of the needed parameters can be or are determined, because of economic or other reasons. In such cases, the engineer must make certain assumptions regarding the properties of the soil. To assess the accuracy of soil parameters—whether they were determined in the laboratory and the field or whether they were assumed—the engineer must have a good grasp of the basic principles of soil mechanics. At the same time, he or she must realize that the natural soil deposits on which foundations are constructed are not homogeneous in most cases. Thus, the engineer must have a thorough understanding of the geology of the area—that is, the origin and nature of soil stratification and also the groundwater conditions. Foundation engineering is a clever combination of soil mechanics, engineering geology, and proper judgment derived from past experience. To a certain extent, it may be called an art. Source: PRINCIPLES OF FOUNDATION ENGINEERING, 7th Edition by BM Das, page 1

Soil properties Some of the important properties of soils that are used by geotechnical engineers to analyze site conditions and design earthworks, retaining structures, and foundations are:  Unit Weight Total unit weight: Cumulative weight of the solid particles, water and air in the material per unit volume. Note that the air phase is often assumed to be weightless.  Porosity Ratio of the volume of voids (containing air, water, or other fluids) in a soil to the total volume of the soil. A porosity of 0 implies that there are no voids in the soil.  Void ratio is the ratio of the volume of voids to the volume of solid particles in a soil. Void ratio is mathematically related to the porosity.  Permeability A measure of the ability of water to flow through the soil, expressed in units of velocity.  Compressibility The rate of change of volume with effective stress. If the pores are filled with water, then the water must be squeezed out of the pores to allow volumetric compression of the soil; this process is called consolidation.  Shear strength The shear stress that will cause shear failure.  Atterberg Limits Liquid limit, plastic limit, and shrinkage limit. These indices are used for estimation of other engineering properties and for soil classification. Source: https://en.wikipedia.org/wiki/Geotechnical_engineering

S I G N I F I C AN C E O F F O U N D AT I O N E N G I N E E R I N G Foundation Engineering is an important component of any construction project. The structural loads of buildings, bridges, towers, and other civil engineering works must be transmitted to the underlying natural soil or rock material using a foundation system that is safe, stable, and economical. The course provides participants with the necessary geotechnical engineering skills to analyze shallow and deep foundation systems under different loading conditions. Source:http://www.mcgill.ca/continuingstudies/programs-and-courses/engineering0/engineeringce/foundation

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