topic four.pptx foundation Engineering f
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The document outlines the fundamentals of deep foundations in civil engineering, detailing their definitions, types, and construction techniques. It categorizes deep foundations into piles, piers, caissons, and compensated foundations, explaining their specific functions and advantages based on soil conditions. Additionally, it provides guidelines for setting out foundation trenches, excavation safety, and protective measures required to prevent cave-ins during excavation work.
topic four.pptx foundation Engineering f
- 1. CIVIL ENGINEERING COURSE CONSTRUCTION TECHNOLOGY I ChAPTER 2: FOUNDATION PRESENTER: ENG ABDIQANI FAARAH ABDILLE
- 2. 2.4 DEEP FOUNDATIONS 2.4.1 What is the deep foundation? 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 foundation can be used to transfer the loading to a deeper, more competent strata at depth if unsuitable soils are present near the surface.
- 3. 2.4.2 TYPES OF DEEP FOUNDATION 1. Piles 2. Piers 3. Caissons 4. Compensated foundations
- 4. PILE FOUNDATION Piles are relatively long, slender members that transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity. They are used when for economic, constructional or soil condition considerations it is desirable to transmit loads to strata beyond the practical reach of shallow foundations. In addition to supporting structures, piles are also used to anchor structures against uplift forces and to assist structures in resisting lateral and overturning forces.
- 5. PIERS Piers are foundations for carrying a heavy structural load which is constructed insitu in a deep excavation. CAISSONS Caissons are a form of deep foundation which are constructed above ground level, then sunk to the required level by excavating or dredging material from within the caisson
- 6. COMPENSATED FOUNDATIONS Compensated foundations are deep foundations in which the relief of stress due to excavation is approximately balanced by the applied stress due to the foundation. The net stress applied is therefore very small. A compensated foundation normally comprises a deep
- 7. PILES Types of pile Type of construction Factors influencing choice Pile groups
- 8. TYPES OF PILE Piled foundations can be classified according to: a) The type of pile: (Different structures to be supported, and different ground conditions, require different types of resistance) and b) The type of construction:( different materials, structures and process can be used).
- 9. types of pile 1. End bearing pile End bearing piles are those which terminate in hard, relatively impenetrable material such as rock or very dense sand and gravel. They derive most of their carrying capacity from the resistance of the stratum at the toe of the pile.
- 10. 2. Friction piles Friction piles obtain a greater part of their carrying capacity by skin friction or adhesion. This tends to occur when pile do not reach an impenetrable stratum but are driven for some distance into a penetrable soil, their carrying capacity is derived partly from end bearing and partly from skin friction between the embedded surface of the soil and the surrounding soil.
- 11. 3. Settlement reducing piles Settlement reducing piles are usually incorporated beneath the central part of raft foundation in order to reduce differential settlement to an acceptable level. Such piles act to reinforce the soil beneath the raft and help to prevent dishing of rafr in the centre.
- 12. 4. Tension piles Structures such as tall chimneys, transmission towers and jetties can be subject to large overturning moments and so piles are often used to resist the resulting uplift forces at the foundations. In such cases the resulting forces are transmitted to the soil along the embedded length of the pile. The resisting force can be increased in the case of bored piles by under-reaming. In the design of tension piles the effect of radial contraction of the pile must be taken into account as this can cause about a 10% - 20% reduction in shaft resistance.
- 13. 5. Laterally loaded piles Almost all piled foundations are subjected to at least some degree of horizontal loading. The magnitude of the loads in relation to the applied vertical axial loading will generally be small and no additional design calculations will normally be necessary. However, in the case of wharves and jetties carrying the impact forces of berthing ships, piled foundations to bridge piers, trestles to overhead cranes, tall chimneys and retaining walls, the horizontal component is relatively large and may prove critical in design.
- 14. Traditionally piles have been installed at an angle to the vertical in such cases, providing sufficient horizontal resistance by virtue of the component of axial capacity of the pile which acts horizontally. However the capacity of a vertical pile to resist loads applied normally to the axis, although significantly smaller than the axial capacity of that pile, may be sufficient to avoid the need for such 'raking' or 'battered' piles which are more expensive to install. When designing piles to take lateral forces it is therefore important to take this into account.
- 15. 2.5 SETTING OUT OF FOUNDATION TRENCHES Setting out of foundation trenches done by the following steps: a) First of all. The corners of the building are marked and then the length of the sides are checked by diagonal measurements. b) The axial lines (center lines) of the trenches are marked with the help of profiles, sighting rails, strings and pegs. c) The off-sets are measured from axial lines and the frontage lines are placed in their correct position relative to local requirements. d) The position of cross walls should be measured along the main walls and squared from these walls if desired, the total width of trenches being carefully outlined.
- 16. The following points should be observed while setting out trenches: a) profiles, nails, strings and lime are used for setting out foundation plan. b) Sight rails may be erected at the corners of a building to determine the correct position of trenches. c) A theodolite may be used for marking accurately the axial lines or center lines. d) Strings are tied and stretched to the nails on profile or on pegs for horizontal control of dimensions.
- 17. e) Vertical reference pillars are erected at a distance of 1 meter from the edges of excavation for vertical control of building during construction. f) All the levels on site should be obtained from a fixed datum previously determined by the surveyor. The depth of trenches and other levels should also be regulated by measurements from this point. g) The bottom of all trenches should be well rammed before placing the concrete in position.
- 18. 2.6 Timbering to excavations When earth has been excavated to a considerable depth the vertical faces of the excavations need supporting by means of timber, to prevent the soil from falling in and injuring the workmen or the work upon which they are engaged. The strength of the timbering used for this purpose necessarily depends upon the nature of the soil, the depth of the excavations, and the length of time it is likely to be kept open.
- 19. 2.6.1 Excavation in firms soil The method of timbering a trench in firm ground, in which case short deal and batten ends, varying from 1 by 4 ½ inches to 1 ½ by 9 inches, and about 3 feet long, called politics or poling boards, are placed in pairs opposite one another against either side of the trench, and are held in position by means of struts, these struts, which are usually short length of 4 inches diameter scaffold poles, or 4 by 4 inch squared timbers, and cut about inch longer than the clear distance between a pair of poling boards,
- 20. Are fixed in position in the following manner: one end of the strut is placed against the middle of one poling board, and the other end is swung vertically downwards against the opposite poling board, and forced tightly against it by means of a few downward taps with a mallet.
- 21. 2.7 Excavation What is an excavation or a trench? OSHA defines as an excavation as any man made cut, cavity, trench, or depression in the earth’s surface formed by earth removal. A trench is defined as a narrow underground excavation that is deeper than it is wide, and is no wider than 15feet (4.5m)
- 22. What are the competent person responsibilities? OSHA’s trenching and excavation standard requires that a competent person inspect job site trenches daily, as the conditions change such as a rainstorm occurring, and before a worker enters the trench, to ensure elimination of excavation hazards. A competent person is knowledgeable about excavation hazards and has the authority to fix those hazards. How to protect workers in excavation or trench? All workers who enter a trench or excavation more than 5ft deep must be protected by benching or sloping of the earth, shoring, or shielding (trench boxes) to the dirction of the competent person.
- 23. Protective systems Benching: means a method of protecting workers from cave-ins by excavating the sides of an excavation to form one or series of horizontal levels or steps, Usually with vertical or near vertical surfaces between levels. Note: benching can not be done in type c soil, which is the least stable soil type. Sloping: involves cutting back the trench wall at an angle inclined away from the excavation.
- 24. Shoring: requires installing aluminum hydraulic or other type of supports to prevent soil movement and cave-ins. Shielding: protects workers by using trench boxes or other types of supports to prevent soil cave-ins. What are the general trenching and excavation requirement? Call before you dig. Request utility companies or owners to determine the location of underground utility installations before excavating.
- 25. Ensure that underground installations are protected, supported, or removed while the excavation is open. Keep heavy equipment away from trench edges and identify other sources that might affect trench stability. Keep all spoils piles and equipment at least 2ft away from the edge of the excavation. Use stairs, ladders, and ramps every 2ft, to exit the excavation. Do not stand beneath loads handled by lifting or digging equipment.
- 26. Do not work in excavations where water is standing or accumulating unless special supports are used to prevent cave-ins. Inspect excavations, adjacent area, and protective systems for evidence of possible cave-ins, indications of failure of protective systems, hazardous atmospheres, other hazardous conditions at the beginning of each workday or if the stability of the excavation cold change. Test for atmospheric hazards such as low oxygen, hazardous fumes and toxic gases hen greater than 4ft deep. Wear warning vests or other high visibility materials when working near moving equipment or vehicles
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