Deep foundation full information
5 likes1,528 views
The report explores deep foundations in civil engineering, detailing various types such as basements, caissons, and pile foundations, and comparing them to shallow foundations. It emphasizes the importance of understanding these foundations for heavy-duty construction, outlining their advantages and disadvantages, and providing insights on appropriate selection based on soil conditions. The document also recommends consulting professionals for foundation planning and construction to ensure project success.
Deep foundation full information
- 1. Salahaddin University -Erbil College of Engineering Civil Engineering Department Foundation (Deep Foundation) By Yousif Majed Yousif Imad Hanan F. Sulaqa Supervisor Zina M. Mudheher Ali Rizgar April, 2019
- 2. Page | 1 Abstract This report presents a full discussion about all of the deep foundation types. The basis of the report is to explain how this system works and why it might be advantageous or not, compared to other types of deep foundation. It will help in giving an insight on the stages of drilling. The main reason for this report is because it is important in later stages of civil engineering in specifics. As next year one of the subjects we will talk about is about foundation and most of ideas come for the 2nd year civil engineering. Our aim is to help the audience know the difference between deep and shallow foundation. Also give probable reason to why deep foundation is used. We found that deep foundation is used for heavy duty and deep construction We recommend before choosing what kind foundation to hire a professional who has to measure the depth required to sustain the construction.
- 3. Page | 2 Table of Contents Body of the report 1.0 Introduction to foundation………………………………..………….................p3 2.0 Definition of Deep foundation…………………………………………………..p4 3.0 Types of deep foundation ………………………………………………………p5 3.1 Basements……………………………………………………………..………...p6 3.2 Buoyancy rafts/ hollow box foundation…………………………………….…p6 3.3 Caisson foundation……………………………………………………………...p8 3.4 Cylinders………………………………………………………………………….p9 3.5 Shaft foundation………………………………………………………………... p10 3.6 Pile foundation …………………………………………………………………..p11 4.0 differences & advantage/disadvantage of deep & shallow foundation…… p13 5.0 calculation and equations ……………………………………………………...p15 6.0 conclusions……………………………………………………………………….p18 7.0 recommendations ……………………………………………………………….p18
- 4. Page | 3 1.0 Introduction to Foundation A foundation is a lower portion of building structure that transfers its gravity loads to the earth. Foundations are generally broken into two categories: shallow foundations and deep foundations. To make a foundation, we normally dig a trench in the ground, digging deeper and deeper until we come to subsoil, which is more solid than the topsoil that is used to grow plants and crops. When the trench is deep enough, we fill it with any strong, hard material we can find. Sometimes we pour in concrete into the trench, which we strengthen even more by first putting long thin round pieces of steel into the trench. When the concrete dries, the steel acts like the bones in our body to tie the foundation together. We call this reinforced concrete. Once the foundation has been packed down tightly, or dried hard, we can begin to build the building superstructure. This has been a brief insight about foundation and its type’s .we will branch out for more types between the two. So basically we will introduce you to all types of deep foundations and everything that concerns about it.
- 5. Page | 4 2.0 Definition of Deep Foundation Deep foundation is 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. Deep foundations are founded 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 are used where soil of adequate strength is not available is not available close enough to the surface for the use of shallow foundations. Also figure out Where the soil near the surface is unsuitable.1 Deep foundation tends to drive through more than 3 m deep underground and for that it costs more, takes more time, and more work but has more integrity for heavy duty building. These types are used for different kinds of situation as each has its specialty. 1 Building construction ,principles materials, and system ,madan Mehta ,walter scarborough ,diane armpriest,2009 update , book.
- 6. Page | 5 3.0 Types of Deep foundation 1. Basements 2. Buoyancy rafts (hollow box foundations) 3. Caissons 4. Cylinders 5. Shaft foundations 6. Pile foundations2 2 https://theconstructor.org/geotechnical/types-of-deep-foundation/7252/
- 7. Page | 6 3.1 Basement foundation 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. 3 3.2 Buoyancy rafts or hollow box foundations Buoyancy rafts or hollow box foundations also known as the floating foundations is a type of deep foundation is used in building construction on soft and weak soils. Types of buoyancy foundations, their construction methods, and advantages are discussed in this article. The decision of construction of a deep foundation is taken when the load has to be distributed to an area either with soft 3 https://theconstructor.org/geotechnical/types-of-deep-foundation/7252/
- 8. Page | 7 weak compressible soils or to reach strata that have strong soil or rock or any other special concerns. One such generally used a type of deep foundation is called as Hollow box foundations or buoyancy rafts foundation. These types of foundations are designed such a way that they behave as buoyant (floating) substructures for the net loading over it. Hence reducing the load intensity over the soil. Advantages of Buoyant Raft Foundation 1. The building is elevated to a required height, which makes them stay above high-water levels. 2. The chances of settlement are reduced. As the total weight coming is equal to the excavated soil, there is no settlement. A slight increase in this load would not bring any drastic change in exceeding the settlement limit. 3. Watertight material for foundations would help in the durability of the underground structure. 4. Foundation having a height of 3 or 4 floors are used for skyscraper construction. This construction is found for efficient than pile foundation in areas with very weak soils for a larger depth. Disadvantages of Buoyant Raft Foundation 1. As the depth of weak soil increases, the amount of excavation also increases. In construction, the excavation process is an activity found very costly. 2. Catastrophic Movement possibilities- These occur when the excavation is done beyond the critical depth of stability. 3. Support of deep foundation may undergo settlement due to the earth pressure it is subjected to, from the surrounding soft soils.
- 9. Page | 8 4. Space is wasted as hollow raft foundations cannot be used for any other purpose. 5. Uplift pressure would affect the whole foundation arrangement.4 3.3 Caissons Foundations: A caisson foundation also called as pier foundation is a watertight retaining structure used as a bridge pier, in the construction of a concrete dam, or for the repair of ships. It is a prefabricated hollow box or cylinder sunk into the ground to some desired depth and then filled with concrete thus forming a foundation The foundation system of and the soils beneath the building prevent the complex from moving vertically. When a load is placed on soil, most soils settle. This creates a problem when the building settles but the utilities do not. Even more critical than settlement is differential settlement. This occurs when parts of your building settle at different rates, resulting in cracks, some of which may affect the structural integrity of the building. Conversely, in some rare instances soils may swell, pushing your building upwards and resulting in similar problems. Therefore, the foundation system must work in tandem with the soils to support the building. 4 https://theconstructor.org/geotechnical/buoyancy-rafts-hollow-box-foundations/15159/
- 10. Page | 9 This figure shows how caisson foundation works: Advantages of Caissons: 1. Economics 2. Minimizes pile cap needs 3. Slightly less noise and reduced vibrations 4. Easily adaptable to varying site conditions 5. High axial and lateral loading capacity Disadvantages of Caissons: 1. Extremely sensitive to construction procedures 2. Not good for contaminated sites 3. Lack of construction expertise 4. Lack of Qualified Inspectors5 5 https://theconstructor.org/geotechnical/caisson-types-construction-advantages/503/
- 11. Page | 10 3.4 Cylinders: Small diameter concrete shafts comprising single open cells and constructed in the same manner as caissons are usually called cylinders. ... Cylinders constructed with precast concrete rings are usually filled with reinforced concrete. So basically, Cylinders are small single-cell caisson. 3.5 Shaft foundations A drilled shaft, also known as drilled pier, drilled caisson, caisson, bored pile, etc., is a versatile foundation system that is used extensively on a worldwide basis. In its simplest form, a drilled shaft is constructed by making a cylindrical excavation, placing a reinforcing cage (when necessary), and then concreting the excavation. With available drilling equipment, shaft diameters up to 20 ft (6 m) and depths exceeding 250ft (76 m) are possible. However, for most normal applications, diameters in the range of 3 to 10 ft (1 to 3 m) are typical. This size versatility allows a single drilled shaft to be used in place of a driven pile group and eliminates the need for a pile cap. In addition, normal construction practices for drilled shafts effectively eliminate the noise and strong ground vibrations that develop during pile driving operations. For these and other secondary reasons, drilled shafts have become both the technical and economic foundation of choice for many design applications. In fact, they have become the dominant foundation type in many geologic settings around the world.6 6 FRED H. KULHAWY, Ph.D., P.E. Professor of Civil/Geotechnical Engineering Cornell University
- 12. Page | 11 Advantages of drilled piers 1. A single drilled pier can take up the load of a group of piles. 2. They have higher resistance to lateral loads. 3. Compared to pile driving, equipment needed for drilled pier is lighter and there is no noise during construction. 4. Ground heaving do not exist in the case drilled piers. 5. Inspection of base and sides of pier is easier. 6. Base of drilled pier provides greater bearing capacity and great resistance to uplift. 7. They can be used even when the soil contains boulders. Disadvantages drilled piers 1. The concreting requires stricter supervision. The quality of concrete obtained is generally inferior to that in precast piles. 2. Deep excavation of drilled pier, if not properly supported, can cause substantial subsidence and damage to adjoining structures. 3. Load tests are difficult in case of drilled piers. 4. More subsurface investigations are required in case of drilled piers. 3.6 Pile foundation 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.
- 13. Page | 12 7 Types of driven pile Types of driven pile Suitable condition Unsuitable condition Timber driven pile Suitable option for temporary works or when the load is small Cannot be used when loads are large. It may suffer decaying if water level fluctuates, and it is not suitable for heavy driven since it may experience unseen splitting. Concrete driven pile Extra reinforcement ration is needed to make the pile withstand driven force, it needs time after casting to obtain necessary strength and hence there is a gap between casting and driven, and it may suffer from unseen damage due to driven forces. Suitable for all loading conditions, it can withstand corrosive soils Steel driven pile It is suitable for all It is subjected to 7 https://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwjg_cDWu- bgAhVjMewKHcv8DVAQjRx6BAgBEAU&url=https%3A%2F%2Ftheconstructor.org%2Fgeotechnical%2Findi an-standard-codes-on-pile-foundations%2F7331%2F&psig=AOvVaw2Lxj- 8PwDw8tf1cz3gTcMI&ust=1551719437789179
- 14. Page | 13 loading condition, it does not suffer damages due to driven forces, it can be extended and cut down. Considerable long driven pile can be used by welding on additional length. corrosion in marine condition above soil level and subsequently it needs protection, And long piles may go off the line during driving8 This table helps us to distinguish which type of driven pile to use and is suitable for certain. Shallow foundation and deep foundation have several differences. In the following table the main differences between shallow and deep foundation are given: Sources Shallow Foundation Deep Foundation 1 Definition Foundation which is placed near the surface of the earth or transfers the loads at a shallow depth is called shallow foundation. Foundation which is placed at a greater depth or transfers the loads to deep strata is called deep foundation. 2 The depth of foundation The depth of shallow foundation is generally about 3 meters or the depth of foundation is less than the footing with. Greater than shallow foundation. 3 Cost Shallow foundation is cheaper. Deep foundations are generally more expensive than shallow foundation. 8 https://theconstructor.org/geotechnical/selection-of-type-of-pile-foundation/20751/
- 15. Page | 14 Sources Shallow Foundation Deep Foundation 4 Feasibility Shallow foundations are easier to construct. The construction process of a deep foundation is more complex. 5 Mechanism of load transfer Shallow foundations transfer loads mostly by end bearing. Deep foundations rely both on end bearing and skin friction, with few exceptions like end bearing pile. 6 Advantages Construction materials are available, less labor is needed, construction procedure is simple at an affordable cost etc. Foundation can be provided at a greater depth, Provides lateral support and resists uplift, effective when foundation at a shallow depth is not possible, can carry huge load etc. 7 Disadvantage s Possibility of a settlement, usually applicable for lightweight structure, weak against lateral loads etc. More expensive, needs skilled labors, complex construction procedure, can be time-consuming and some types of deep foundations are not very flexible etc. 8 Types Isolated foundation, strip foundation, mat foundation, combined foundation etc. Pier foundation, pile foundation, caissons etc. 9 9 https://civiltoday.com/geotechnical-engineering/foundation-engineering/180-difference-between- shallow-and-deep-foundation
- 16. Page | 15 5.0 Calculation and equations Vertically Loaded Piles The total pile resistance may be split into components from the base and the shaft. Consideration of static equilibrium then gives the ultimate capacity as: Pu = Psu + Pbu – W Pu Ultimate load capacity of the pile Pbu = Ultimate resistance at the base of the pile (Base resistance) Psu = Ultimate side shear resistance on the pile shaft (Shaft resistance) W = Self-weight of the pile Base Resistance In analysing pile behaviour it is conventional to express the ultimate base resistance by Pbu = Ab ( fb + po)
- 17. Page | 16 Ab = Plan area of the pile base fb = Net ultimate resistance per unit area of the base po = Overburden pressure at the level of the base If the pile does not extend above the soil surface it is found that the pile weight is usually similar to the force due to the overburden pressure. Thus W ≈ Ab po and Pu = Psu + Ab fb Side Resistance As = Surface area of pile shaft in contact with the soil = Average ultimate side resistance per unit area In general, the side resistance will be a function of depth below the surface, because both the undrained strength su (short term undrained analysis) and the effective stresses (long term analysis) increase with depth. The average shear stress can be expressed mathematically as where L is the length of the pile
- 18. Page | 17 Base resistance This is a simple bearing capacity problem, that is Where of is the ultimate bearing capacity. For a soil with fu = 0 the ultimate bearing capacity can be written qf = Nc su + g D = Nc su + po The net ultimate resistance is simply fb = Nc su and the ultimate base resistance approximately Pbu = Ab (Nc su + po) It is conventional to take cu = cub where sub is the undrained shear strength of the soil at the pile base and to assume fu is zero. The value of Nc can then be obtained from Skempton’s chart (p28 Data Sheets) which is applicable for Φu = 0. When using this chart it is important to check the length to diameter ratio L/D (D/B on the chart). It is normally assumed that pile bases may be treated as deep foundations and that Nc = 9. However, if L/D is less than 4, Nc will be lower than 9 as shown in the chart below and the ultimate capacity will be similarly reduced.
- 19. Page | 18 6.0 Conclusion From all the researches that were done, the researches give an insight on what deep foundation is and how it subdivides to have certain amount of types which are used for specified situations. It can also show the differences between deep and shallow foundation in detail to why one might be better put to use than the other, as each has its functionalities. 7.0 Recommendation As for every project to be done, we would propose for a professional to equate the cost, time, and amount of work /needed work in order to determine when to use deep or shallow foundation .Also a planner, who calculates cost and time because this information will help a lot as to when investors might consider the construction of the project.