1. CHAPTER 3
Foundations

2. Components of Building

3. Types of Foundation
Shallow Foundations
Deep Foundations

4. Shallow foundations
transfer the load to the base of columns or walls of substructure. It used where suitable soil is found at the level of the bottom of substructure.
It may be extend several feet or several stories below the ground surface.
تقوم بنقل احمال المبنى الى قاعدة الاعمدة والجدران الموجودة في substructure ويستخدم هذا النوع عندما تكون طبقات التربة عند اسفل substructure ذات قابلية تحمل مناسبة. يمكن ان يستمر الاساس الضحل من بضعة اقدام الى بضعة طوابق اعتمادا على الجزء السفلي من المبنى.

5. Deep foundation
either piles or caissons.
Penetrate the upper layers of incompetent soil in order to transfer the load to competent bearing soil or rock deeper within the earth.
تقوم بنقل احمال المبنى من الطبقات العليا ذات التحمل الغير كافي الى طبقات التربة القوية او الطبقات الصخرية الموجودة في الارض

6. Isolated (independent) footings: (column footing): square concrete footing with or without steel reinforcement, that accepts the load placed on it from above by a building column and spread the load a cross the area of soil.
عبارة عن قاعدة مربعة من الخرسانة العادية او المسلحة. يقوم بنقل الحمل المسلط عليه من عمود المبنى ويوزعه على مساحة كافية من التربة.

7. ولتقليل من احتمالية حدوث الهبوط في الاساس فان التربة التي تقع تحت الاساس يجب ان تكون ذات خصائص هندسية جيدة.

8. Continuous wall footings, (strip footings) : are commonly used where the superimposed loads are linear, generally from a load-bearing wall
يستخدم عندما تكون الحمل المنتقل ليس بواسطة العمود بل عن طريق الجدران الحاملة.

9. عبارة عن اساس مشترك من اساسين منفردين.
A combined footing is a combination of two isolated column footings.
It is used where two or more adjacent columns are closely spaced and heavily loaded. Combining them into one footing reduces the excavation cost and distributes the load over a larger area.
A combined footing is also used where an exterior column must be placed within the property line or adjacent to an existing building .
عبارة عن اساس مشترك من اساسين منفردين.
يستخدم عندما يكون الاساسين متقاربين مع بعضهما .
يستخدم عندما يكون الاساس مجاورا الى خط الملكية او الى بناية اخرى

11. Mat foundation (raft footing):
This foundation is used where the bearing capacity of the soil is low (even deep below the surface) so that isolated footings become so large that only small unexcavated areas remain between the footings.
If the excavation required for isolated footings in a building is more than 50% of the footprint of the building, it is generally more economical to use a mat foundation.
A mat foundation is also used where the bedrock is so deep that the use of a deep foundation system is uneconomical. Because of the large thickness of a mat foundation, it is sufficiently rigid to distribute loads from individual columns evenly on the underlying soil.

13. Floating foundation is a type of mat foundation.
It consists of a hollow mat formed by a grid of thick reinforced concrete walls between two thick rein- forced concrete slabs.
In this case, the weight of the soil excavated from the ground is equal to the weight of the entire building, so that the pressure on the soil is unchanged from the original condition, making the building float on the soil.
One story of excavation soil weights about the same as five to eight stories of superstructure.

15. Slab-on-ground foundation
is the most widely used monolithic foundation system because of its low cost and ease of construction.
It is the system of choice for low-rise, light frame residential or commercial buildings.
The slab functions as a foundation system and also as the ground floor of the building

16. Deep foundations
these systems include piles and drilled piers (caissons ) that are like slender columns buried in the ground.
Piles and drilled piers transfer the load either to bedrock or to soil of high bearing capacity while passing through unsuitable soil conditions.
Because the settlement of deep foundation systems is relatively small, deep foundations are also used in buildings that house items or instruments sensitive to even small amounts of settlement, which is likely to occur in shallow foundations.
Piles are generally steel, timber, or reinforced concrete elements driven into the ground.
Site-cast piles are called drilled piers or caissons. Another term used for drilled piers is bored or drilled piles. Thus, drilled piers are always of reinforced concrete.

18. Piles Foundations
Steel, precast concrete and wood are common pile materials. The material selected depends on availability, cost, below-grade environment, type of soil, the load to be supported, and the equipment required to drive the piles.
Steel and concrete piles are generally used under heavier loads. Wood piles are limited in their load-bearing capacity because of the nature of the material and the limitations on the cross-sectional area of tree trunks.
Steel piles may be H-shaped or hollow pipes. Hollow steel piles are filled with concrete after being driven. Steel piles are covered with protective coatings if used in corrosive environments. Concrete piles are made of precast concrete and are generally.
Concrete piles can be provided with a steel tip extension for easier penetration.

19. Driving of Piles
pile-driving machines come in different types, depending on the type of soil and the pile material, they basically consist of a heavy weight placed between guides so that it can move up and down in a straight line.
The driving force comes from the repeated hammering action as the weight is dropped on the pile head, raised, and dropped again, using diesel, hydraulics, or compressed air for the operation

21. Drilled Piers (Caissons) Foundations
Drilled piers are often used individually (as opposed to a cluster of piles) because they can be made almost as large as required.
The drilled pier diameter generally varies between( 450 – 900) mm.
Larger-diameter piers (1800 in diameter or larger) are used for bridges or high-rise structures. Another reason for using individual piers is that their vertical alignment is almost assured.
Drilled piers may either have a straight shaft or be belled at the bottom
A belled pier has a straight shaft with an enlarged bottom that bears on a high-capacity soil. However, belled piers are not practical in non cohesive soils because of soil caving.

22. Construction of Drilled Piers
Piers are generally constructed by first drilling a hole of predetermined diameter into the soil.

23. After the hole has been drilled to the required depth, a steel reinforcement cage is lowered into the hole, and concrete is placed in the hole. Placement of concrete is generally done using a tremmie, which is a steel pipe topped by a funnel, Figure. The tremmie takes the concrete close to its intended location and prevents separation of concrete particles, which would occur if the concrete were dropped from a distance. The tremmie is gradually brought up as the hole is filled with concrete.

27. Drilled Pier Termination Where a pier is used to support another concrete member (a grade beam or concrete column), steel reinforcing dowels that extend beyond the top of the pier are placed in the member before concreting is completed.

28. Piles Versus Drilled Piers
Piles and piers have their own unique applications.
Piles are ideally suited for marine and coastal sites, where drilled piers are not suitable because of the presence of water, a high water table, or the presence of a sandy soil with cave-in potential. As the pile is driven, an assessment of the soil’s bearing capacity is obtained from the blow count and the resulting pile penetration.
Piles can be used immediately, with no wait time for the concrete to cure. However, pile driving is noisy and requires heavier equipment. It also disturbs the surrounding area with vibrations caused by the driving operations.
Piers are particularly suited for urban locations where vibrations and noise from pile driving are unacceptable. They can also support a much larger load than a pile and, unlike piles, do not require capping.
The technology required for piers is less complex; hence, drilled piers are generally more economical than driven piles. For this reason, piers are popular for foundation systems for low-rise buildings in expansive (clay) soils.

29. Foundation Settlement
All foundation systems require a determination of the bearing pressure created by the loads on the underlying stratum (soil or rock). This bearing pressure must be less than the stratum’s allowable bearing capacity.
In addition to having an adequate bearing capacity, foundations must resist settlement. This is generally of greater concern for shallow foundations because they bear on a more compressible stratum than deep foundations.

30. Immediate and Consolidation Settlement
Settlement occurs as the soil compresses under the loads. The greater the soil’s compressibility, the greater the settlement.
In coarse-grained soils, settlement is immediate; that is, it occurs as the load is applied. Therefore, most of the settlement in coarse- grained soils occurs during the construction of the building.
In fine-grained (particularly clayey) soils, part of the settlement is immediate, and the remainder (called consolidation settlement) occurs over a period of several months or years. Consolidation settlement occurs when the water held between clay particles is squeezed out by the load, and the soil consolidates and shifts.

31. Uniform and Differential Settlement
Settlement may be uniform over the entire structure or non uniform (referred to as differential settlement).
In uniform settlement, the entire structure settles by the same amount.
Differential settlement is more serious. It leads to deformation of the structural frame, imposing stresses on the structure for which it has not been designed and possible structural failure
Building codes specify the maximum permissible amount of differential settlement of footings.
Properly designed and constructed foundation systems with a monolithic base (mat or raft foundations) have negligible differential settlement due to their rigidity.
Differential settlement is an important design consideration in foundation systems consisting of multiple footings because of the local variation in soil’s compressibility, uneven compaction, and uneven bearing pressure induced on the soil by the superimposed loads. Therefore, footing dimensions are determined not merely on the bearing capacity of the soil but also on footing settlement to ensure that all footings in the building have approximately the same amount of settlement.

33. Underpinning
Underpinning is the process of strengthening and stabilizing the foundation of an existing building. It may be required for any of several reasons:
The existing foundation may never have been adequate to carry their loads, leading to excessive settlement of the building over time.
A change in building use or additions to the building may over load the existing foundations.
New construction near a building may disturb the soil around its foundations or require that its foundations be carried deeper.
Whatever the cause, underpinning is a highly specialized task that is seldom the same for any two buildings.  

34. Three different alternatives are available when foundation capacity needs to be increased:
The foundation may be enlarged.
New, deep foundations can be inserted under shallow ones to carry the load to a deeper (strong stratum of soil).
The soil itself can be strengthened by grouting or by chemical treatment.

35. Geotextiles
Geotextiles are flexible fabrics made of chemically inert plastic that are highly resistant to deterioration in the soil.
They are used for a variety of purposes relating to site development and the foundations of buildings. As in earth reinforcement or soil reinforcement, a plastic mesh fabric or grid is used an earth embankment.
The same type of mesh may be utilized in layers to stabilize engineered fill beneath a shallow footing, or to stabilize marginal soils under driveways, roads and airport runways, acting very much as the roots of plants do in preventing the movement of soil particles.

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