foundation design final -...
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Integrated Civil Engineering Design Integrated Civil Engineering Design ProjectProject
(Foundation Structure Design) (Foundation Structure Design)
CIVL 395CIVL 395HKUSTHKUST
By : Ir. K.S. Kwan
Date: 4/07
Foundation Structure DesignFoundation Structure Design
Foundation Control in Hong KongFoundation Control in Hong KongFoundation Design CodeFoundation Design CodeGround InvestigationGround InvestigationCommon Pile used in Hong KongCommon Pile used in Hong KongPile CapacityPile CapacityPiling LayoutPiling LayoutPile Cap DesignPile Cap DesignHorizontal Restraints to Piles and Pile CapHorizontal Restraints to Piles and Pile CapOther Consideration Other Consideration
Ground floor
SoilPile Cap
Pile
Superstructure
Building Development
Loading from superstructure to be shown on plan of foundation and loading schedule
Foundation Control Foundation Control in Hong Kongin Hong Kong
Building OrdinanceBuilding OrdinanceBuilding Department, PNAP 66Building Department, PNAP 66Geotechnical Engineering Office Geotechnical Engineering Office Register Specialist ContractorRegister Specialist Contractor (Foundation Works) (Foundation Works)
PNAP 66PNAP 66Recognized types of pile foundation Recognized types of pile foundation Piling plans submission Piling plans submission Design of pile foundationsDesign of pile foundationsPrePre--design ground investigationdesign ground investigationPrePre--drillingdrillingPost construction proof drillingPost construction proof drillingQuality supervision for piles foundationsQuality supervision for piles foundationsGroundGround--borne vibrations arising from pile driving and similar borne vibrations arising from pile driving and similar operationsoperationsPile foundations in the scheduled areasPile foundations in the scheduled areasForm BA14Form BA14Pile record plans and reportsPile record plans and reportsFurther on site testFurther on site testAmendment to approved plansAmendment to approved plans
Foundation Design in Scheduled AreasFoundation Design in Scheduled Areas
Some special requirements for pile foundations in the Scheduled Area are given in PNAPs 77, 85, 161 and 279
In accordance with the Fifth Schedule of the Building Ordinance,there are five Scheduled Areas specified in Hong Kong at present. These areas are:
Mid-levels
North-west New Territories
Mass Transit Railway Protection Areas & Kowloon – Canton Railway Protection Areas
Ma On Shan
Sewage Tunnel Protection Areas
Foundation Design in Designed AreasFoundation Design in Designed Areas
Designated areas, such as Northshore Lantau, refer to those areas with complex geology, which may impose significant constraints on the foundation design and construction. In some cases, the foundations might prove to be so costly that adjustment of the layout of the development or even site abandonment is warranted. A very comprehensive ground investigation is usually inevitable in order to identify all thegeological constraints, and it should be carried out before planning the development. Reference should be made to the relevant PNAP issued by the Building Authority for the locations and other information for the designated area
Recognized Types of Pile FoundationRecognized Types of Pile Foundation
A recognized type of pile foundation is regarded as the piling system recognized by the Building Authority prior to the approval of piling plans through the submission of relevant technical details for assessment, normally by the registered structural engineer in conjunction with the registered specialist contractor experienced in such system.. Common types of piles used in Hong Kong including :
Large Diameter Bored Pile
Drive Steel H-Pile/ Socket Steel H-Pile
Mini Pile
Barrette/ Shaft grouted Barrette
Foundation Plan DetailsFoundation Plan Details
Plan of Foundation –To show the setting out/size of all vertical elements which transmit all superstructure loading
Loading Schedule –To show the loading of all superstructure including gravity and wind loading
Foundation Foundation Design CodeDesign Code
HK Code of HK Code of Practice for Practice for Foundation Foundation
DesignDesign
ConstructionConstruction
TestingTesting
How to select suitable foundation for How to select suitable foundation for construction?construction?
Cost?Cost?Time?Time?Risk?Risk?
2,000 ~ 3,0002,000 ~ 3,000MiniMini--pile pile 3,000 ~ 5,0003,000 ~ 5,000Socket Steel HSocket Steel H--pilepile1,000 ~ 2,5001,000 ~ 2,500Driven Steel HDriven Steel H--pile pile
10,000 ~ 30,00010,000 ~ 30,000Large Diameter Bored Pile Large Diameter Bored Pile
Cost (HK$/m run)Cost (HK$/m run)Pile TypePile Type
Selection of pile typeSelection of pile type
Common HK used piles:Common HK used piles:
Steel HSteel H--pile, pipe pilepile, pipe pileLarge diameter bored pile (LDBP)Large diameter bored pile (LDBP)MiniMini--pile, Socket Hpile, Socket H--pilepileFriction BarretteFriction Barrette
Factors to be consideredFactors to be considered
Cost Cost ( size, number, length and installation)( size, number, length and installation)
Construction difficulties Construction difficulties (plant available in market, (plant available in market, depth of pile, boulder location, programmedepth of pile, boulder location, programme…………))
Ground Ground Investigation Investigation
Ground InvestigationGround Investigation
Bored hole information to Bored hole information to identifyidentify: :
•• Pile TypePile Type•• Pile LengthPile Length•• Construction DifficultiesConstruction Difficulties•• Soil PropertiesSoil Properties•• Water tableWater table
To note the “allowable bearing pressure” which is under working load i.e. without load factor
III
II
I
How to confirm the rock head level?
5m ?
5m
Rock Head
Bored Hole InformationBored Hole Information
SPT N=100
SPT N=200
SPT N=200
SPT N=200
SPT N=150
SPT N=100
SPT N=180
SPT N=200
SPT N=100
SPT N=200
SPT N=200
SPT N=200
SPT N=100
SPT N=200
CDG Grade II/III Rock
SPT N=200
SPT N=200
SPT N=200
SPT N=200
Simple for
H-pile rest on stiff soil
Simple for LDBP bearing on bedrock
Pre-boring for
corestone layers
Pre-boring for corestone layers or rest
on corestones
Mega Tower @ Kowloon Station
• Foundation
240 nos. shaft grout barrettes, 2.8m x 1.2m & 2.8m x 1.0m, Length = 88m
How many bored holes are required?How many bored holes are required?
Large diameter bored pilesLarge diameter bored pilesAt least At least one for each pileone for each pileIn case of steep rock at base, more bore holes are required In case of steep rock at base, more bore holes are required to determine the founding level to determine the founding level
Driven HDriven H--pilepile10~20 for each blocks for normal ground condition10~20 for each blocks for normal ground conditionAdditional bored holes at locations with boulder layersAdditional bored holes at locations with boulder layers
Socket steel HSocket steel H--pile or Minipile or Mini--pilepilePile tip of every such pile should be Pile tip of every such pile should be within 5 metreswithin 5 metres from a from a prepre--drilled hole drilled hole
Common Pile Types Common Pile Types in Hong Kongin Hong Kong
Large Diameter Bored Pile
Driven Steel H-Pile
Socket Steel H-Pile
Mini-Pile
Classification of FoundationClassification of Foundation
Foundation can be classified Foundation can be classified into a number of ways, such as:into a number of ways, such as:
Shallow Shallow Pad/Strip Type/RaftPad/Strip Type/RaftBearing on soil Bearing on soil (50~300KPa)/(50~300KPa)/rock rock (3000KPa) to be used (3000KPa) to be used for highfor high--rise buildingrise building
Deep FoundationDeep FoundationPiled FoundationPiled Foundation
End BearingEnd BearingFrictionFriction
Raft foundation is large combined thick Raft foundation is large combined thick plate designed to seat and support the plate designed to seat and support the whole or a large part of a structure. whole or a large part of a structure.
Shallow raft used for highShallow raft used for high--rise buildingrise building
It is normally founding on It is normally founding on Grade III rock with allowable Grade III rock with allowable bearing pressure 3000Kpa.bearing pressure 3000Kpa.
The building average loading is The building average loading is 20KPa per floor and thus, the 20KPa per floor and thus, the shallow raft bearing on rock shallow raft bearing on rock can accommodate a building can accommodate a building up to 100 storeyup to 100 storey
Loading Supporting to Loading Supporting to PilePile
Load from a superstructure is transmitted to the Load from a superstructure is transmitted to the subsoil either by:subsoil either by:
End BearingEnd Bearing –– load is supported by resting onto a load is supported by resting onto a firm stratum such as bedfirm stratum such as bed--rock or stratum of subsoil rock or stratum of subsoil with the required bearing capacity.with the required bearing capacity.
Skin friction Skin friction –– load is supported by the frictional load is supported by the frictional resistance so created between the contact surface of resistance so created between the contact surface of the pile and the embracing soil.the pile and the embracing soil.
Bed Rock
Pile Cap
Tower
Bed Rock
Shallow Raft
End Bearing Pile :Large diameter bored pileSocket Steel HMini pile
Friction Pile:Steel HFriction Barrette
Bed Rock
Pile Capacity Pile Capacity
LARGE DIAMETER BORED PILE (LDBP) LARGE DIAMETER BORED PILE (LDBP) CAPACITY CAPACITY
Normal size of 1.8, 2.2, 2.5, 2.75 and 3.0m Normal size of 1.8, 2.2, 2.5, 2.75 and 3.0m
BellBell--out with a gradient not exceeding 30 out with a gradient not exceeding 30 degree from vertical, and the size not degree from vertical, and the size not exceeding 1.5 times the shaft diameter may exceeding 1.5 times the shaft diameter may be permitted at the pile base to increase the be permitted at the pile base to increase the end bearing capacityend bearing capacity
The concrete strength should be reduced by The concrete strength should be reduced by 20% where groundwater is likely to be 20% where groundwater is likely to be encountered during concreting or where encountered during concreting or where concrete is placed underwaterconcrete is placed underwater
For piles subject to axial forces only, where For piles subject to axial forces only, where the concrete used is higher than grade 20Dthe concrete used is higher than grade 20D
Shaft
Base
Design capacity of LDBP Design capacity of LDBP
Capacity of base = Area of base x allowable bearing capacity of Capacity of base = Area of base x allowable bearing capacity of rock rock (i.e. either 5000Kpa, 7500KPa or 10,000 (i.e. either 5000Kpa, 7500KPa or 10,000 KPaKPa))
6902969029552235522325 T3225 T323750375025002500
5842658426467414674121 T 3221 T 323450345023002300
Allowable Allowable bearing bearing capacity capacity pile pile (D+L+W) (D+L+W) (KN)(KN)
Allowable Allowable bearing bearing capacity capacity pile (D+L) pile (D+L) (KN) (KN)
ReinforceReinforcement ment
BellBell--out out diameter diameter (mm)(mm)
Effective Effective shaft shaft diameter diameter (mm)(mm)
Bored Pile DesignBored Pile Design(Bearing at different rock level) (Bearing at different rock level)
Where steep bedrock profile Where steep bedrock profile is identified, the founding is identified, the founding levels of adjacent piles should levels of adjacent piles should not differ by more than the not differ by more than the clear distance between the clear distance between the pile bases unless the stability pile bases unless the stability of rock under the piles are of rock under the piles are checked by recognized checked by recognized engineering principles, taking engineering principles, taking into account existence of any into account existence of any adverse joints. adverse joints.
Check bearing stress due to Check bearing stress due to overlapping overlapping -- the shaft design the shaft design and base stress cannot be and base stress cannot be overstressed due to the overstressed due to the additional load additional load
Bored Pile DesignBored Pile Design-- Pile layoutPile layout
Bored Location
Walls from super-structure
Pile Cap layout
DRIVEN STEEL HDRIVEN STEEL H--PILE PILE CAPACITYCAPACITY
Common HCommon H--pilepileH 305x305x180 Kg/m3 H 305x305x180 Kg/m3 H 305x305x223 Kg/m3 H 305x305x223 Kg/m3
Founding at level with 3 consecutive SPT Founding at level with 3 consecutive SPT ‘‘NN’’ value value ≥≥200 below200 below
All steel HAll steel H--piles to be grade 55C complying with BS4360:1986 piles to be grade 55C complying with BS4360:1986 ((fyfy=415N/mm2)=415N/mm2)
For driven steel bearing piles with a design safety factor on For driven steel bearing piles with a design safety factor on driving resistance of 2, the stress in the steel at working loaddriving resistance of 2, the stress in the steel at working loadshould not exceed 30% of the yield stress. The design working should not exceed 30% of the yield stress. The design working stress due to combined axial load and bending may, however be stress due to combined axial load and bending may, however be increased to 50% of the yield stressincreased to 50% of the yield stress
All allowable stresses are to be All allowable stresses are to be increased by 25%increased by 25% due to wind due to wind effectseffects
Group reduction factor of Group reduction factor of 0.85 for a group of 5 piles or more0.85 for a group of 5 piles or more
The centreThe centre--toto--centre centre spacingsspacings are of are of more than 3 timesmore than 3 times the the perimeter of the piles or the circumscribed rectangles in the caperimeter of the piles or the circumscribed rectangles in the case se of Hof H--pilespiles
Some design capacity of steel HSome design capacity of steel H--pile pile Pile Type : 305 x305 x 223 Kg/m (55C)Pile Type : 305 x305 x 223 Kg/m (55C)
Minimum centre to centre spacing of piles in 1408mm Minimum centre to centre spacing of piles in 1408mm Design Steel Stress (Design Steel Stress (ffyy) = 415 N/mm) = 415 N/mm22
B= 325.4B= 325.4H= 338H= 338Design pile crossDesign pile cross--sectional area (A) = 28500mmsectional area (A) = 28500mm22
Capacity for 1 to 4 piles Capacity for 1 to 4 piles w/o wind = 0.3 x w/o wind = 0.3 x ffyy x A = 3548 KNx A = 3548 KNw/wind = 1.25 x 0.3 x w/wind = 1.25 x 0.3 x ffyy x A = 4435 KNx A = 4435 KN
Capacity for 5 piles or more Capacity for 5 piles or more w/o wind = 3548 x 0.85 = w/o wind = 3548 x 0.85 = 30163016 KNKNw/wind = 4435 x 0.85 = w/wind = 4435 x 0.85 = 37703770 KNKN
SOCKET STEEL HSOCKET STEEL H--PILE CAPACITYPILE CAPACITY
It is installed by inserting It is installed by inserting steel Hsteel H--piles into prepiles into pre--bored holes sunk into bored holes sunk into bedrock, and subsequently bedrock, and subsequently grouting the holes with grouting the holes with cementitiouscementitious materialsmaterials
The allowable axial The allowable axial working stress or the working stress or the combined axial and combined axial and flexural stresses should flexural stresses should not greater than 50% of not greater than 50% of the yield stress of the steel the yield stress of the steel HH--pilepile
No group effect reduction No group effect reduction factor factor
Design ParameterDesign Parameter
H section 305 x305x 180Kg/m UPB Grade 55C, Internal diameter of H section 305 x305x 180Kg/m UPB Grade 55C, Internal diameter of casing = casing = 550mm550mm
Cross section area As = 0.0229 m2Cross section area As = 0.0229 m2Perimeter of pile = 1882.6 mmPerimeter of pile = 1882.6 mmZxZx =0.002508 m3, =0.002508 m3, ZyZy = 0.000847 m3= 0.000847 m3Yield strength Yield strength fyfy = 430 = 430 MpaMpaDesign bond strength between the grout and steel HDesign bond strength between the grout and steel H--pilepile
Grout above water = 0.6 Grout above water = 0.6 MPaMPaGrout under water = 0.48 Grout under water = 0.48 MPaMPa
Design bond strength between the grout and rockDesign bond strength between the grout and rockUnder compression or transient tension = 0.7 Under compression or transient tension = 0.7 MPaMPaUnder Permanent tension = 0.35 Under Permanent tension = 0.35 MPaMPa
Design Socket Length = 4000mmDesign Socket Length = 4000mmCapacity W/o wind in compression = 3600 KNCapacity W/o wind in compression = 3600 KNCapacity W/wind in compression = 4500 KNCapacity W/wind in compression = 4500 KN
Pile capacityPile capacityAxial capacity Axial capacity
Due to steel strength = 0.5 Due to steel strength = 0.5 fyfy As = 4923.5 > 3600As = 4923.5 > 3600Due to bond strength between HDue to bond strength between H--pile & grout = 0.48 x 1882.6 x 4000/1000 = 3615 KNpile & grout = 0.48 x 1882.6 x 4000/1000 = 3615 KNDue to bond between grout & rock = 0.7x550x3.14x4000/1000 = 4838Due to bond between grout & rock = 0.7x550x3.14x4000/1000 = 4838 KN KN
Mini pile Mini pile A miniA mini--pile usually consists of one or pile usually consists of one or more steel bars encased by grout inside more steel bars encased by grout inside a drill hole not exceeding 400mm in a drill hole not exceeding 400mm in diameter. It is mainly used to resist diameter. It is mainly used to resist compression or tension loads on sites compression or tension loads on sites with difficult access.with difficult access.The structural capacity of a miniThe structural capacity of a mini--pile pile should be derived solely from the steel should be derived solely from the steel bars. Contributions from the grout and bars. Contributions from the grout and steel casing should be ignored steel casing should be ignored The allowable capacity should be The allowable capacity should be derived from the bond strength derived from the bond strength between the grout and rockbetween the grout and rock
Mini Pile Design Mini Pile Design Number of steel bar in mini pile : 4 no. 50mm Number of steel bar in mini pile : 4 no. 50mm diadia. . Permissible compressive stress = 175 Permissible compressive stress = 175 KPaKPa(Permissible tensile stress = 230 (Permissible tensile stress = 230 KPaKPa))Socket internal diameter = 190mmSocket internal diameter = 190mmDesign bond strength between rock & grout (Ref. Design bond strength between rock & grout (Ref. CoPCoPFdnFdn 2004 Table 2.2) 2004 Table 2.2)
Under compression or transient tension = 700 Under compression or transient tension = 700 KPaKPa(Under permanent tension = 350 (Under permanent tension = 350 KPaKPa))
Design Socket LengthDesign Socket LengthDesign capacity (W/o wind) in compression = Design capacity (W/o wind) in compression = 13701370 KNKNDesign capacity (W/ wind) in compression = 1710 KNDesign capacity (W/ wind) in compression = 1710 KN
Pile CapacityPile CapacityDue to reinforcement strength Due to reinforcement strength
Compressive capacity = 1963 x 175 x 4/1000 = 1374 Compressive capacity = 1963 x 175 x 4/1000 = 1374 KN > KN > 13701370
Due to bond strengthDue to bond strengthCapacity = 700 x 190 x 3.14 x 3300 /1000Capacity = 700 x 190 x 3.14 x 3300 /100022 = 1378 KN= 1378 KN
Bond between grout & steel barBond between grout & steel barultimate anchorage bond stresses for concrete grade 30 ultimate anchorage bond stresses for concrete grade 30
and deformed bars Type 2 in compression is 3.5 and deformed bars Type 2 in compression is 3.5 N/mm2N/mm2Bond strength in compression = 3.5 x ( 50 x 3.14) x Bond strength in compression = 3.5 x ( 50 x 3.14) x 3300 x 0.4 x 4/1000 = 2901 > 3300 x 0.4 x 4/1000 = 2901 > 13701370
Soil
Rock
Negative Skin FrictionNegative Skin Friction
NEGATIVE SKIN FRICTION NEGATIVE SKIN FRICTION (NSF)(NSF)
•• Where pile foundations are installed Where pile foundations are installed through strata which are likely to undergo through strata which are likely to undergo consolidation after foundations are in place, consolidation after foundations are in place, the frictional resistance of the strata and the the frictional resistance of the strata and the overlying soils shall not be taken into overlying soils shall not be taken into account in the determination of the load account in the determination of the load carrying of the foundations. The downward carrying of the foundations. The downward frictional force exerted from the strata and frictional force exerted from the strata and the overlying soils is named as the overlying soils is named as NSFNSF. .
•• Possible additional load up to 20% of pile Possible additional load up to 20% of pile capacitycapacity
•• Possible attributed by the clayey soil Possible attributed by the clayey soil settlement with time or desettlement with time or de--watering from watering from construction activitiesconstruction activities
Pile LayoutPile Layout
Minimum pile spacing Minimum pile spacing
For driven pilesFor driven piles and other piles which derive their capacity mainly from and other piles which derive their capacity mainly from frictional resistance, the minimum pile spacing shall be not lesfrictional resistance, the minimum pile spacing shall be not less than the s than the length of the perimeter of the pile or 1m, whichever is the grealength of the perimeter of the pile or 1m, whichever is the greater, and the ter, and the piles shall be placed at not less than half the length of the pepiles shall be placed at not less than half the length of the perimeter of the rimeter of the pile or 500mm, whichever is the greater, from the site boundary.pile or 500mm, whichever is the greater, from the site boundary.
For miniFor mini--pilespiles, which derive their capacities mainly from bond strength , which derive their capacities mainly from bond strength between grout and rock, the minimum pile spacing should be 750mmbetween grout and rock, the minimum pile spacing should be 750mm or 2 or 2 times the outer diameter, whichever is the greatertimes the outer diameter, whichever is the greater
For bored pilesFor bored piles and the like which derive their capacities mainly from end and the like which derive their capacities mainly from end bearing, the minimum clear spacing between the surfaces of adjacbearing, the minimum clear spacing between the surfaces of adjacent piles ent piles should be based on practical considerations of positional and veshould be based on practical considerations of positional and verticality rticality tolerances of piles. It is recommended to provide a nominal minitolerances of piles. It is recommended to provide a nominal minimum clear mum clear horizontal spacing of 500mm between shaft surfaces or edge of behorizontal spacing of 500mm between shaft surfaces or edge of bellll--outs, outs, as appropriateas appropriate
Pile Layout of Driven H pile
Pile Layout of Bore Pile
Pile Cap DesignPile Cap Design
Pile layout related to the pile cap assumption Pile layout related to the pile cap assumption
•• For rigid cap, arrange the pile For rigid cap, arrange the pile C.G. to coincide the loading C.G. C.G. to coincide the loading C.G. Arrange the piles to the edge of Arrange the piles to the edge of the cap to obtain larger stiffness. the cap to obtain larger stiffness. (Less pile but more reinforcement (Less pile but more reinforcement at cap)at cap)
Rigid Cap
Flexible Cap•• For flexible cap approach, For flexible cap approach, arrange pile near the arrange pile near the column/wall. (More pile but column/wall. (More pile but less reinforcement at cap) less reinforcement at cap)
Deformed shape of Rigid Cap
Deformed shape ofFlexible Cap
Thickness of a Rigid CapThickness of a Rigid Cap(Dr. J.S. Kuang HKUST)(Dr. J.S. Kuang HKUST)
A proposed design formula for estimating the A proposed design formula for estimating the thickness of a thickness of a ‘‘rigidrigid’’ cap:cap:
t = 40 (N + 20) (mm)
where t – Cap thicknessN – Number of storey
(For 40 stories, t=2.4m)
As the “Rigid Cap Analysis”Method is based on the assumption that the Pile Cap is infinitely rigid.
The usual practice by designers in the “Rigid Cap Analysis” is to treat the cap as a beam with the applied load and solved pile reactions, calculate the shear and moments in the “beam”. The Cap is thus having a uniform bending moment or shear along the entire section of the simulated “beam”
Tf
For “Flexible Cap Analysis” , the bending moment along the mid-strip and side-strip are of different ‘signs’ as shown. So the “Flexible Cap”analysis is more realistic design for pile cap in catering for “local effects”
PilecapPilecap can be sized can be sized as one single cap or as one single cap or isolated caps to suit isolated caps to suit the signthe sign
Computer Software for Foundation DesignComputer Software for Foundation Design
The software used for foundation design mainly to find out the pThe software used for foundation design mainly to find out the piling iling load and load and pilecappilecap designdesign
CAPBSCAPBSLIFORMLIFORMSAFESAFEVDISPVDISP
CAPBS (or LIFORM)CAPBS (or LIFORM)--Rigid Cap ApproachRigid Cap ApproachConsider X and Y directions separately as a rigid beamConsider X and Y directions separately as a rigid beamLocal stress cannot be foundLocal stress cannot be foundTorsional effect consideration is calculated by equilibrium (LITorsional effect consideration is calculated by equilibrium (LIFORM)FORM)Simple data inputSimple data input
SAFE (Rigid or flexible approach)SAFE (Rigid or flexible approach)Consider X and Y directions simultaneouslyConsider X and Y directions simultaneouslyLocal stress can be found (e.g. torsional effect)Local stress can be found (e.g. torsional effect)
Horizontal RestraintsHorizontal Restraintsto to
Piles and Pile CapPiles and Pile Cap
Horizontal Restraints to Piles and Pile CapHorizontal Restraints to Piles and Pile Cap
Piles and pile caps shall have Piles and pile caps shall have adequate lateral stability and adequate lateral stability and be able to cope with any be able to cope with any allowed construction allowed construction tolerance. tolerance.
For driven piles and small For driven piles and small diameter piles, adequate diameter piles, adequate horizontal restraints in at horizontal restraints in at least 2 directions shall be least 2 directions shall be provided to individual piles provided to individual piles or pile capsor pile caps
The allowable horizontal The allowable horizontal movement is about 25mmmovement is about 25mm
Soil passive load
Wind shear force from super-structure
Drag Wall/ Wing Wall to resist lateral loadDrag Wall/ Wing Wall to resist lateral load
Pile Cap on Plan
Drag Wall Wing Wall
Pile foundation near Pile foundation near slope slope
Where the Where the foundation has foundation has imposed additional imposed additional loads on slopes or loads on slopes or retaining walls, or the retaining walls, or the groundwater regime groundwater regime has been affected, the has been affected, the stability of the stability of the affected slopes or affected slopes or retaining walls should retaining walls should be checked as part of be checked as part of the foundation designthe foundation design
Flexible material to avoid any lateral
pressure on slope
Slope
Other ConsiderationOther Consideration
Where piles are required to provide anchorage Where piles are required to provide anchorage resistance against uplift, overturning and/or resistance against uplift, overturning and/or buoyancy, it should be demonstrated that the buoyancy, it should be demonstrated that the piles and the supporting ground have adequate piles and the supporting ground have adequate anchorage capacities to satisfy the anchorage capacities to satisfy the requirementsrequirements
The above requirements may be deemed to be The above requirements may be deemed to be satisfied by demonstrating that each pile in a satisfied by demonstrating that each pile in a pile foundation satisfies the following pile foundation satisfies the following condition individuallycondition individually
DminDmin + 0.9 + 0.9 RuRu –– 2.0 2.0 IaIa --1.5U 1.5U –– 1.5W 1.5W ≥≥00DminDmin = Minimum dead load= Minimum dead loadRuRu = Ultimate anchoring resistance of the pile= Ultimate anchoring resistance of the pileIaIa = Adverse imposed load including live and soil = Adverse imposed load including live and soil loadsloadsU= Uplift due to highest anticipated groundwater U= Uplift due to highest anticipated groundwater table table W= Wind loadW= Wind load
Piles Providing Resistance Against Uplift,Piles Providing Resistance Against Uplift,Overturning and BuoyancyOverturning and Buoyancy
Pile in tension
Anchor come from the friction between rock and grout of pile
Rock
The average settlement is The average settlement is limited at 20mm and limited at 20mm and differential is controlled by differential is controlled by 1/10001/1000
Pile bearing on rock Pile bearing on rock Differential settlement come Differential settlement come from elastic shortening of pilefrom elastic shortening of pile
Pile by friction on soilPile by friction on soilThe average settlement can The average settlement can be estimated by Tomlinsonbe estimated by Tomlinson’’s s Equivalent Raft approach or Equivalent Raft approach or computer modeling (computer modeling (e.ge.gPIGLET, VDISP)PIGLET, VDISP)
Settlement of FoundationSettlement of Foundation
Foundation near Foundation near MTRMTR’’ss Structure Structure PNAP 77PNAP 77
The protection boundary is about 30m outside the outer surface of the MTR structure but it encompasses the whole of any lot where any part lies within the 30m distance.
No pile, foundation, borehole, well, soil nail, horizontal drain or other geotechnical installation should be driven or constructed within a distance of 3m from any point of the underground railway structures
The vertical or horizontal pressure change on any underground structure due to the above works, including filling. Dewatering etc. and due to additional loads transmitted from foundations shall not exceed 20 KPa
MTR
Foundation on ground Foundation on ground with abandoned pilewith abandoned pile
ReRe--access the capacity of access the capacity of existing pile for reexisting pile for re--useuse
Select space for new pile Select space for new pile location in particular the Hlocation in particular the H--pile pile
Raking Pile Raking Pile
Where raking mini piles are used to resist lateral forces, care should be taken to ensure equilibrium of forces and moments are maintained, taking into consideration the lack of bending stiffness of the piles and the effectively hinged conditions at the pile heads and bases
Besides providing additional space below ground level for a building, loads from the superstructure are also transferred through the structure of a basement to the foundation
Such arrangement provides considerable rigidity to tall buildings base on the principle of buoyancy, that is, the basement box will displace the soil embedding it and balance the combined weight of the entire structure
Foundation with basement Foundation with basement
Q Q && AA
If you have any questions about the structural design, please forward email (with your Name and Student ID no.)
to : [email protected]