2 TYPES OF FOUNDATION a) Shallow Foundation System i) Spread Foundation ii) Mat / Raft Foundationb) Deep Foundation Systemi) Pile iii) Diaphragham wallii) Pile walls iv) Caissons
3 SHALLOW FOUNDATION Advantages Cost (affordable) Construction Procedure (simple)]Material (mostly concrete)Labour (doesn’t need expertise)
4 SPREAD FOOTING FOUNDATION Also known as a footer or footingIt’s an enlargement at the bottom of a column/bearing wall that spreads the appliedstructural loads over a sufficiently large soilarea.Each column & each bearing wall has its ownspread footing, so each structure may includedozens of individual footings.
6 The foundation consists of concrete slabs located under each structural column and acontinuous slab under load-bearing walls.For the spread foundation system thestructural load is literally spread out over abroad area under the buildingMost common type of foundation used dueto their low cost & ease of construction.Most often used in small to medium size structure with moderate to good soil condition.
7 Spread footings may be built in different shapes & sizes to accommodate individualneeds such as the following:a) Square Spread Footings / Square Footingsb) Rectangular Spread Footingsc) Circular Spread Footingsd) Continuous Spread Footingse) Combined Footingsf) Ring Spread Footings
8 a) Square Spread Footings / Pad Foundation - support a single centrally located column- use concrete mix 1:2:4 and reinforcement- the reinforcement in both axes are toresist/carry tension loads.
10 b) Rectangular Spread Footings - Useful when obstructions preventconstruction of a square footing with asufficiently large base area and whenlarge moment loads are present
11 c) Circular Spread Footings - are round in plan view- most frequently used as foundation forlight standards, flagpoles and powertransmission lines.
12 d)Continuous Spread Footings / Strip Foundation - Used to support bearing walls
13 e) Combined Footings- support more than one column- useful when columns are located too closetogether for each to have its own footing
14 f) Ring Spread Footings - continuous footings that have been wrapped into acircle- commonly used to support the walls above-groundcircular storage tanks.- The contents of these tanks are spread evenlyacross the total base area and this weight is probablygreater that the tank itself- Therefore the geotechnical analyses of tanks usuallytreat them as circular foundations with diametersequal to the diameter of the tank.
16 RAFT FOUNDATION A foundation system in which essentially the entire building is placed on a large continuousfooting.It is a flat concrete slab, heavily reinforcedwith steel, which carries the downward loadsof the individual columns or walls.Raft foundations are used to spread the loadfrom a structure over a large area, normallythe entire area of the structure.
18 It is normally consists of a concrete slab which extends over the entire loaded area.It may be stiffened by ribs or beamsincorporated into the foundation.Raft foundations have the advantage of reducing differential settlements as the concrete slab resists differential movements between loading positions.They are often needed on soft or loose soils with low bearing capacity as they can spread the loads over a larger area.
19 Mat Foundation often considered to be used when dealing with the followingconditions:The structural loads are so high or the soil condition so poor that spread footings would be exceptionally large. As a general rule of thumb, if spread footings would cover more than 50% of the building footprint area, a mat or some type of deep foundation will usually be more economical.
20 b) The soil is very erratic & prone to excessive differential settlements. The structure continuity and flexural strength of a mat will bridge over these irregularities.The same is true of mats on highly expansive soils prone to differential heaves.c) The structural loads are erratic and thus increase the likelihood of excessive differential settlements. Again, the structural continuity and flexural strength of the mat will absorb these irregularities.
21 d) The lateral loads are not uniformly distributed through the structure and thus may cause differential horizontal movements in spread footings and pile caps.The continuity of a mat will resist such movement.e)The uplift loads are larger than spread footings can accommodate. The greater weight and continuity of a mat may provide sufficient resistance.
22 f) The bottom of the structure is located below the groundwater table, so waterproofing is an important concern. Because mats are monolithic, they are much easier to waterproof. The weight of the mat also helps resist hydrostatic uplift forces from the groundwater.
23 DEEP FOUNDATION Extend several dozen feet below the building a) Piles b) Piersc) Caissonsd) Compensated Foundation
24 PILES????? A slender, structural member consisting steel or concrete or timber.It is installed in the ground to transferthe structural loads to soils at somesignificant depth below the base of thestructure.
26 PILES FOUNDATION IS USED WHEN: The soil near the surface doesn’t havesufficient bearing capacity (weak) to supportthe structural loads.The estimated settlement of the soil exceedstolerable limitsDifferential settlement due to soil variabilityor non-uniform structural loads is excessiveExcavations to construct a shallow foundationon a firm soil are difficult or expensive.
27 LOAD CAN BE TRANSFERRED BY PILE TO THE GROUND BY 2 WAY THAT IS:End Bearing Piles OR- Pile will transmit load into the firm soil layer of the ground such as rock, gravel, very dense sandb) Friction Piles- Pile transmit the load from the structure to the penetrable soil by means of skin friction or cohession between the soil & the embedded surface of the pile.
28 There 2 type of End Bearing Piles That is Preformed Timber Pile & In-Site-Reinforced Concrete Pile
29 Friction Pile May Be Used To Support DownWard Load
31 CAST IN PLACE CONCRETE PILES Formed by driving a cylindrical steel shell into the ground to the desired depth and cavity of shell is filled with fluid concrete.The steel shell doesn’t contribute to the load transfer capacity of the pile.It’s purpose is to open a hole in a ground and keep it open to facilitate the construction of concrete pile. (same function as formwork)Vigilant quality control & good construction practice are necessary to ensure the integrity of cast-in-place piles.
32 Among the advantages of Cast-In-Place Concrete are as follows:Can sustain hard drivingResistant to marine organismEasily inspectedLength can be changed easilyEasy to handle and ship
33 PRECAST CONCRETE PILES Usually have square/circular/octagonal cross sections.Fabricated in a construction yard from reinforced or pre-stressed concrete.Disadvantages of this pile are problems in transporting long piles, cutting and lengthening.It has higher capacity than timber piles.
34 STEEL PILES It comes in various shapes & sizes Steel H-Piles are rolled steel sectionsSteel pipe piles are seamless pipes that can be welded to yield lengths up to 70m.They are usually driven with open ends into the soil.A conical tip is used where the piles have to penetrate boulders & rocks.However it needs to be treated before embedded in corrosive environment.
35 TIMBER PILES Have been used since ancient times Length of timber piles depends on types of trees used to harvest the piles,Common length are 12mIt is susceptible to termites, marine organisms and rot within zones exposed to seasonal changes.Eventhough it’s cheaper but it has low capacity and can’t take hard driving.
36 TYPES OF PILE CHOSEN DEPENDS ON FOLLOWING FACTORS: What type of pile is readily availableLocation & type of structure (magnitude of loading)Ground Condition (soil type)CostDurability
37 TYPES OF PILE CONSTRUCTION Displacement Piles- It cause the soil to be displaced radially as well as vertically as pile shaft is driven or jacked into the ground.b) Non Displacement Piles- It cause the soil to be removed and the resulting hole filled with concrete or a pre cast concrete pile is dropped into the hole and grouted in.
40 TYPES OF DISPLACEMENT PILES: Can be classified into different types base on how they are constructed and how they are inserted.There are 3 types as follows:Totally Preformed Displacement Piles(precast concrete or steel pile)Driven & Cast-In-Place Displacement PileHelical Cast-In-Place Displacement Piles
41 Totally Preformed Displacement Piles - Precast Concrete or Steel Pileb) Driven & Cast-In-Place Displacement Pile- This type of pile can be of 2 forms.- The first involves driving a temporary steeltube with a closed end into the ground toform a void in the soil which is then filledwith concrete as the tube is withdrawn.- The second type is the same except the steeltube is left in place to form a permanentcasing.
42 c) Helical Cast-In-Place Displacement Piles - This type of construction is performed using a special type of auger.- The soil is however compacted, not removed as the auger is screwed into the ground.- The auger is carried on a hollow stem which can be filled with concrete, so when the required depth has been reached concrete can be pumped down the stem & the auger slowly unscrewed leaving the pile cast in place.
43 METHOD OF INSTALLATION Dropping Weight or Drop Hammers- commonly used method of insertion of displacement pilesDiesel Hammers- Most suitable to drive pile in non cohesive granular soilVibratory Hammers or vibratory method of pile driving- very effective in driving piles through non cohesive granular soilJacking Method Of Insertion
44 Diesel HammerRapid controlled explosions can be produced by the diesel hammer.The explosions raise a ram which is used to drive the pile into the ground.Although the ram is smaller than the weight used in the drop hammer the increased frequency of the blows can make up for this inefficiency.This type of hammer is most suitable for driving piles through non-cohesive granular soils where the majority of the resistance is from end bearing.
45 Vibratory Method of Pile Driving Vibratory methods can prove to be very effective in driving piles through non cohesive granular soils.The vibration of the pile excites the soil grains adjacent to the pile making the soil almost free flowing thus significantly reducing friction along the pile shaft.However the large energy resulting from the vibrations can damage equipment, noise and vibration propagation can also result in the settlement of nearby buildings.
46 Pile Driving Rig - raise and temporarily support the pile that being driven and to support the pile hammer.
48 Dropping Weight / Drop Hammers A weight approximately half that of thepile is raised a suitable distance in a guideand released to strike the pile head.When driving a hollow pile tube theweight usually acts on a plug at the bottomof the pile thus reducing any excessstresses along the length of the tube duringinsertion.
50 Jacking Method Of Insertion Jacked Piles are most commonly used inunderpinning structuresBy excavating underneath a structure shortlengths of pile can be inserted and jackedinto the ground using the underside of theexisting structure as a reaction.
52 NON DISPLACEMENT PILES THERE ARE 4 TYPES THAT IS:Small Diameter Cast-In-PlaceLarge Diameter Cast-In-PlacePartially Preformed PilesGrout or Concrete Intruded Piles
53 PIERS It’s a vertical bridge support. It’s a foundation for carrying a heavystructural load which is constructed in sitein a deep excavation.
54 Among the things to be taken in consideration during construction of pier are as follows:Drilling through wet or caving soils may need use of temporary steel casing. May also require the use of a tremie & a pump to dewater the hole & place concrete. This is more expensive and require a large diameter hole.For the purpose of reinforcing, it’s difficult to get bars to the full depth of the pier with the proper concrete cover in deep holes.Use centralizes. Use large diameter bars versus more bars.
55 c) Don’t leave holes open for any length of time even in dry condition c) Don’t leave holes open for any length of time even in dry condition. Cuttings fall in or etc. Have concrete on site and fill right after drilling and cleaning.
65 WHAT IS CAISSONS? It’s a prefabricated hollow box or cylinder. It is sunk into the ground to some desireddepth and then filled with concrete thusforming a foundation.Most often used in the construction of bridge piers & other structures that require foundation beneath rivers & other bodies of water.This is because caissons can be floated to the job site and sunk into place.
66 Basically it is similar in form to pile foundation but installed using different wayused when soil of adequate bearing strengthis found below surface layers of weakmaterials such as fill or peat.It’s a form of deep foundation which areconstructed above ground level, then sunk tothe required level by excavating or dredgingmaterial from within the caisson.
67 A caisson foundation consists of concrete columns constructed in cylindrical shaftsexcavated under the proposed structuralcolumn locationsCaissons are drilled to bedrock or deep intothe underlying strata if a geotech eng. find thesoil suitable to carry the building load.
68 It’s created by auguring a deep hole in the ground.Then, 2 or more ‘stick’ reinforcing bar are Iinserted into and run the full length of thehole and the concrete is poured into thecaisson hole.The caisson foundations carry the buildingloads at their lower ends, which are oftenbell-shaped.