Lesson 2 Substructure. Dr S.Sreenath BSc Engg, MSc Engg, MSc (ICM), MBA, PhD

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1 Lesson 2 Substructure Dr S.Sreenath BSc Engg, MSc Engg, MSc (ICM), MBA, PhD

2 Outline Syllabus 1. Demolition 2. Site problems 3. Substructure 4. Basements 5. Structural Frames 6. Floors 7. External walls 8. Roofs 9. Internal Access 10. Building and Fire 11. Service Integration 12. Sustainable and Intelligent Buildings 13. Refurbishment Technologies 14. Building Services 15. Health and Safety

3 Outline 1. Types of piles 2. Low Rise Building 3. High Rise Building 4. Controlled Demolition

4 Foundations Re-cap on basic principles Must safely support the loads without moving, be unaffected by ground movement, and resist ground contaminants.

Raft Foundations Design Principles A raft foundation is heavily reinforced because there is tension in both the top and bottom of the raft and shear forces at the points of

5 Raft Foundations Design Principles A raft foundation is heavily reinforced because there is tension in both the top and bottom of the raft and shear forces at the points of heavy loads such as walls. The greater loads the stiffer the raft must be. Rafts are supported on layers of compacted hardcore after removal of the weaker surface layers of soil.

6 Raft Foundations Raft foundations are constructed in the form of a continuous slab, extending beneath the whole building, formed in reinforced concrete. Hence, the loadings from the building are spread over a large area, thus avoiding overstressing of the soil.

Raft Foundations At the perimeter, this thickening is termed the 'toe' and fulfils an important secondary function in preventing erosion of the supporting soil at the raft edges, if not prevented,

7 Raft Foundations At the perimeter, this thickening is termed the 'toe' and fulfils an important secondary function in preventing erosion of the supporting soil at the raft edges, if not prevented, undermining of the raft could occur, with serious consequences. At intermediate points within the main body of the raft the thickening will take the form of a downstand, which is effectively a thickened rib on the underside of the raft.

Pad Foundations In some instances, such as when constructing framed buildings, the loads from the building are exerted upon the foundations in the form of concentrated point loads.

8 Pad Foundations In some instances, such as when constructing framed buildings, the loads from the building are exerted upon the foundations in the form of concentrated point loads. A pad foundation is used directly under the column. Typical sizes range from about 500mm square to 1.5 metres square normally, up to depths of about 1-3 metres. Over this pile foundations tend to be more suitable

9 Pad and Strip Foundations Where framed buildings are to be clad with masonry a combined foundation is required, i.e. a pad and strip. Where the ground is however weak or subject to heave a reinforced concrete ground beam is used that will distribute the wall loads to the pads. The walls are supported by a strip foundation or a reinforced concrete ground beam. The column is supported by the larger and deeper pad foundation.

10 Pile Foundations PILE FOUNDATIONS ARE O F TEN D ESCRIBED AS CO LUMNS WITHIN THE GRO UN D, SINCE THE BASIS U PON WHICH THEY WO RK IS SIMILAR TO THAT O F A TRADITION A L CO LU MN. THEY TRANSFER LOADINGS F RO M A HIGHER LEVEL TO A LOADBEA RING MEDI UM AT A LOWER LEVEL.

1. Displacement Piles Displacement piles are set into the ground by forcing, or driving a solid pile, or a hollow casing to the required level below ground, thus displacing the surrounding earth.

11 1. Displacement Piles Displacement piles are set into the ground by forcing, or driving a solid pile, or a hollow casing to the required level below ground, thus displacing the surrounding earth. In the case of solid piles, pre-cast piles of required length may be driven into the ground using a jack or driving rig. Types: Solid precast concrete sections Solid steel sections Cast in Place piles using a driving tube and wet concrete

1a.Precast Concrete Driven Piles The use of the second of these methods, is by far the most efficient, since the length which is required may vary from pile to

12 1a.Precast Concrete Driven Piles The use of the second of these methods, is by far the most efficient, since the length which is required may vary from pile to pile, thus the use of one piece pre-cast piles inevitably necessitates adjustment of length on site. Trimming or extending of one piece piles is a difficult task on site.

13 Precast Concrete Piles The complete pile is shown as well as the typical reinforcement that is cast into the pile. Driven precast piles are typically mm wide or diameter.

14 1b. Driven Steel tube piles Steel sections can also be driven in the same manner Tubular piles can be driven with either an open bottom end or closed end. When driven open end, soil is allowed to enter the bottom of the tube. If an empty pipe is required, an auger can be used to remove the soil inside following driving. If the soil is suitable internal cleaning could also be carried out by water jetting. Closed end pipe piles have the bottom of the pile sealed with a steel plate or cast steel shoe. When driving through hard strata pile toes may be reinforced with a secondary driving shoe to assist penetration and minimise pile damage.

15 1c.Cast in place piles basic principles

16 Driven Cast in situ piling suitable in a range of weak grounds regardless of water table. Can drive through obstructions and avoids soil removal on contaminated sites

2a.Continuous Flight Auger Piling Rig There are many advantages in using CFA piling; It does not cause ground heave as the ground is not displaced.

17 2a.Continuous Flight Auger Piling Rig There are many advantages in using CFA piling; It does not cause ground heave as the ground is not displaced. It does not cause vibration and much noise, so it is ideal near existing buildings. It can be used in a wide variety of soils without the need for casings to support the borehole. They are typically able to bore to metres deep, but some can bore up to 25 metres. They are very fast compared to driven piles. They are ideal in clay soils as the friction of the clay can be used to support the pile where the concrete is cast in-situ.

2b. Large Diameter Rotary Bored Pile with Casing For piles in excess of 600mm diameter a different approach is taken to formation of the bored excavation.

18 2b. Large Diameter Rotary Bored Pile with Casing For piles in excess of 600mm diameter a different approach is taken to formation of the bored excavation. Generally a rotary auger or drilling bucket will be utilised. This is often mounted on the back of a mobile unit or lorry and is operated with the aid of a diesel engine driving the auger or bucket via a square section kelly bar.

19 What are some of the advantages of both driven piles and bored piles? Bored or Driven Piles Where would each be used?

20 Reinforcement cage placed in borehole prior to concreting The holes are bored either using, or by using a rotary borer or a continuous flight auger. In poor ground boreholes can be supported by temporary casings or the use of the continuous flight auger.

Placing the Reinforcement Cage The cage is lifted in position by the crane and then guided into the borehole which normally contains the in-situ concrete, if it is a bored pile using a CFA.

21 Placing the Reinforcement Cage The cage is lifted in position by the crane and then guided into the borehole which normally contains the in-situ concrete, if it is a bored pile using a CFA. Cased boreholes, on the other hand, will usually have the reinforcement placed before the concrete. This one looks like a cased borehole as someone is stood on the edge of the casing. You can again see the spacers on the reinforcement.

Completed in-situ concrete pile The reinforcement is left projecting for later connecting to the reinforcement of the pile cap or ground beam.

22 Completed in-situ concrete pile The reinforcement is left projecting for later connecting to the reinforcement of the pile cap or ground beam. The ground around the pile will be excavated prior to forming the pile cap. When piles are cast in-situ it is normal practice to cast the pile to an extended length typically 400mm above the required height. The excess concrete is then removed using a mechanical breaker to the required level. This allows reinforcement of the pile to be connected to the pile cap reinforcement.

23 Pile Reinforcement Typical sketches showing the pile reinforcement and its arrangement to the pile cap.

24 Types of Piles based on the mechanism of Load Transfer End/Point Bearing Piles Friction Piles Friction cum end bearing piles

25 Classification of Piles according to the Method of Installation of piles Driven or displacement piles Bored or Replacement piles

26 Driven or Displacement piles Advantages Durable in most environment. Easy to extend. Cheaper than steel pile. Disadvantages Cumbersome to handle and drive. Difficult to cut off. Noisy to drive. Pile can break when driven to sloping bedrock. Large displacement.

27 Advantages Bored Piles Durable in most environment. Cast to desired length to minimize cost. Can core through obstructions e.g. boulders. Allows inspection before concreting. Relatively quiet and low vibration. Can be constructed before excavation. Can be instrumented easily. Non- displacement i.e. no heaving problem.

28 Disadvantages Bored Piles Difficult to control workmanship and concrete quality. Bulging due to soil cave in means more concrete. Necking means reduced capacity. Creation of voids if concrete is placed too fast. Uncertain about end bearing. Need to dispose spoils and drilling fluid.

29 Types of Piles based on Materials Timber piles Steel piles Concrete Piles Composite piles

30 Timber Piles Advantages Easy to handle and cut off. Relatively inexpensive. Readily available. Disadvantages Decay above groundwater if not treated. Limited in size and bearing capacity. Subceptible to damage.

31 Steel Piles - Advantages Easy to handle, extend and cut-off. Available in many sizes and lengths. Can penetrate hard strata and soft rock. High tensile strength and bending moment. Can withstand hard driving.

32 Steel Piles - Disadvantages Susceptible to corrosion. Flexible pile may deviate during driving. Relatively expensive material. Heaving problem for closed ended pipe piles. Noisy to drive.

33 Construction of Bored Piles

34 Diaphragm wall A diaphragm wall is a reinforced concrete wall that is made in situ. The trench is prevented from collapsing during excavation, reinforcing and casting by the use of supporting bentonite slurry. The slurry forms a thick deposit (the cake) on the walls of the trench which balances the inward hydraulic forces and prevents water flow into the trench. A slurry made of polymers can also be used.

35 Construction of Diaphragm walls

38 Forming a large pile cap This is a pile cap for the base of a bridge support. There are 4 piles that look to be about 1.8 metres in diameter. Further reinforcement will be added to form a cage and then the void filled with concrete.

39 Pile foundations and Groundbeams Where continuous walls are to be supported, a reinforced concrete ground beam is constructed on top of the pile heads.

Pile Cap Connection When piles are cast in-situ it is normal practice to cast the pile to an extended length typically 400mm above the required height.

40 Pile Cap Connection When piles are cast in-situ it is normal practice to cast the pile to an extended length typically 400mm above the required height. The excess concrete is then removed using a mechanical breaker to the required level. This allows reinforcement of the pile to be connected to the pile cap reinforcement.

41 Pile Cap Construction The pile heads are shown with projecting reinforcement and the reinforcement of the pile cap, prior to concreting.

42 A large pile cap This pile cap will be supported on 3 piles

43 Type of soil firmer soils normally bored particularly clay, weaker soils normally driven Criteria for Pile Selection See BRE Digest 315 Choosing Piles For New Construction See also trade literature from piling contractors. Levels of water table - bored piles may require casings driven solid piles are unaffected. Proximity of structures bored piles cause less vibration and ground heave than driven piles. Depth of suitable soil driven can be to any depth. Limited diameter of solid driven piles, about 200mm. Bored piles can be over 2.4metres in diameter. Driven cast in place piles up to 600mm in diameter.

44 Thanks!

Assalamualaikum & Good Morning (May All Of You Gain A Better Understanding)

Assalamualaikum & Good Morning (May All Of You Gain A Better Understanding) Always Try To Do The Best In Your Life TYPES OF FOUNDATION TYPES OF FOUNDATION a) Shallow Foundation System i) Spread Foundation