Bored Pile Design [PDF]

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: :



PROJECT DESCRIPTION



FOR FINAL APPROVAL



: :



DATE DESIGNED BY



October 1, 2019 CHECKED BY :



Reference : AASHTO Standard Specification for Highway Bridges A. Ultimate Axial Capacity of Bored Pile in Soil (AASHTO 4.6.5.1) A. 1 AXIAL COMPRESSION



:



Qult = QS + QT - W



A.2 AXIAL TENSION / UPLIFT LOADING



:



Tult = 0.70QS + W



A.3 ALLOWABLE / WORKING AXIAL LOAD



:



Qall = Qult / FS



Where:



QS = Ultimate side / skin friction resistance in soil QT = Ultimate tip resistance in soil W = Weight of drilled shaft / bored pile FS = Factor of Safety ( usually FS



=



3



)



B. Ultimate Side/Skin Friction Resistance of Soils B.1 In Cohesive Soils (AASHTO 4.6.5.1.1) N



QS = p B



S



N



a i Sui Dzi



p B



=



i=1



Where:



S



fsi Dzi



i=1



B



= Pile / Shaft diameter



ai



= Adhesion factor as a function over ith depth interval



Sui = Incremental undrained shear strength as a function over ith depth interval Dzi = ith incremental of shaft diameter fsi = Ultimate unit load transfer



ai Sui



=



£ 265.00 kPa



B.2 In Cohesionless Soils (AASHTO 4.6.5.1.2) N



QS = p B



S



N



g'i zi b i Dzi



p B



=



i=1



Where:



S



fsi Dzi



i=1



g'i



= Effective unit weight of soil in the ith interval



zi



= Depth to midpoint of the ith interval



s'vi = Effective vertical stress at midpoint of ith depth interval bi



= Load transfer factor in the ith interval



0.25



£



zi · mm



= bi · s'vi £ 190.00 kPa



fsi = Ultimate unit load transfer for which,



= 1.50 - 0.00773



= g'i zi



bi



£



1.2



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PROJECT DESCRIPTION



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C. Tip Resistance of Soils C.1 In Cohesive Soils (AASHTO 4.6.5.1.3)



QT = qT · AT Where:



=



Nc · SuT · AT



Nc = Bearing capacity factor D



=



6.0 [ 1 + 0.2( D / BT ) ]



£



9.00



= Shaft / Pile length or penetration of Shaft / Pile



BT = Tip diameter of shaft / pile SuT = Undrained shear strength within 2B below shaft tip qT = Ultimate unit end bearing resistance



=



Nc · SuT



£ 3800 kPa



AT = Area of shaft / pile tip Note: If the soil within 2B of the tip has SuT < 24.00 kPa, the value of Nc shall be reduce by one-third. For drilled shaft in clays with SuT > 96.00 kPa and BT > 1900 mm, and for which shaft settlement will not be evaluated, the value of qT shall be reduced to qTR as follows: qTR = qT · Fr £ 3800 kPa Where:



Fr =



760 [ 12.00 · a ( BT·mm ) + 760 · b ]



a



= 0.0071 + 0.0021 ( D / BT )



b



= 1.45



£



1.0



£ 0.015



2.00 ( Su T·MPa )



for which,



0.50



£



b



£



1.50



C.2 In Cohesionless Soils (AASHTO 4.6.5.1.4)



QT = qT · AT



Where:



qT = Ultimate unit end bearing resistance = 0.057 · N



(in MPa) for



= 4.30 MPa for N N



N



£ 75



³ 75



= Standard penetration resistance (Blows/ft)



Note: For BT > 1270mm, qT shall be reduced as follows:



QT = qTR · AT



Where:



qTR



=



1270 · qT ( BT·mm )



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PROJECT DESCRIPTION



FOR FINAL APPROVAL



DATE DESIGNED BY



500.00



Elevation



0.00 m



Elevation



0.40 m



Elevation



1.90 m



kN



Pult = Pall =



0.00 0.000



kN kN



: :



October 1, 2019 CHECKED BY :



D. Input Data NGL



E



E 1.50 m



Tult =



: :



= Embedment of the pile top from NGL =



fs = 0.00 MPa in Cohesive soil



D



m



= Length of bored piles =



B



0.400



20.000



m



= Diameter of bored pile =



0.500



m



GWL = Ground water level from NGL QS Elevation



2.20 m



GWL



=



2.200



m



gw = Unit weight of water =



Elevation



kN/m3



19.50 m



20.00 m



B = 0.50 m



Elevation



9.810



a fs = 0.00 MPa in Cohesive soil



= Adhesion factor =



N



QT



0.550



= No. of blows/ft @ tip of the shaft =



50



NOTE 1: In cohesive soils, the upper 1.50 meters of the shaft is ignored in estimating QS to account for the effects of seasonal moisture changes, disturbance during construction, cyclic lateral loadings and low lateral stresses from freshly placed concrete. The lower 1.0-Diameter length above the shaft tip is ignored due to the development of tensile cracks in the soil near these region of the shaft and a corresponding reduction in lateral stress and side resistance.



N 20 10 8 8 16 8 8 8 6 50 50 50 50



D.1 Average Laboratory Test Results and Data Elevation (m) SOIL Friction angle from to TYPE f (deg.) 0.00 - 0.40 cohesionless 34.2 0.40 - 1.90 cohesionless 30.6 1.90 - 1.00 cohesionless 29.9 1.00 - 2.00 cohesionless 29.9 2.00 - 4.00 cohesionless 32.8 4.00 - 6.00 cohesionless 29.9 6.00 - 8.00 cohesionless 29.9 8.00 - 10.00 cohesionless 29.9 10.00 - 12.00 cohesionless 29.2 12.00 - 14.00 cohesionless 45.0 14.00 - 17.00 cohesionless 45.0 17.00 - 19.00 cohesionless 45.0 19.00 - 20.00 cohesionless 45.0 N VALUE BASED ON ORIGINAL BORE LOG DATA



Unit Weight



g' (kN/m3) 18 18 18 18 18 18 18 18 18 18 18 18 18



Cohesion c (kPa) 0 0 0 0 0 0 0 0 0 0 0 0 0



Pore Water g'w(kN/m3) 0.00 0.00 0.00 0.00 9.81 9.81 9.81 9.81 9.81 9.81 9.81 9.81 9.81



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PROJECT



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DESCRIPTION



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E. Static Pile Capacity Calculation E.1 Ultimate Side/Skin Friction Resistance



s'vi = ( svi + svi-1 )/2 Su = s'v · tan f + c



Dz = Depthi - Depthi-1 sv = Dz · (g' - g'w) svi = svi + svi-1



Formulas:



Elevation (m)



Depth



Dz



sv



s'v



-



to



(m)



(m)



0.40 1.90 1.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 17.00 19.00 20.00



0.40 1.90 1.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 17.00 19.00 20.00



0.40 1.50 -0.90 1.00 2.00 2.00 2.00 2.00 2.00 2.00 3.00 2.00 1.00



(kPa) 7.20 34.20 18.00 36.00 52.38 68.76 85.14 101.52 117.90 134.28 158.85 175.23 183.42



(kPa) 3.60 20.70 26.10 27.00 44.19 60.57 76.95 93.33 109.71 126.09 146.57 167.04 179.33



from



0.00 0.40 1.90 1.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 17.00 19.00



Su



fs



INPUT



fs(max)



QS



use fs



(kPa) (kPa) (kPa) (kPa) (kN) 2.45 4.32 190.00 0.00 0.00 12.24 24.84 190.00 24.84 58.53 15.00 31.32 190.00 31.32 -44.28 15.51 32.40 190.00 32.40 50.89 28.43 47.58 190.00 47.58 149.46 34.80 57.75 190.00 57.75 181.42 44.21 65.66 190.00 65.66 206.27 53.62 71.55 190.00 71.55 224.79 61.21 75.62 190.00 75.62 237.57 126.09 78.00 190.00 78.00 245.06 146.57 78.80 190.00 78.80 371.32 167.04 77.32 190.00 77.32 242.92 179.33 75.42 190.00 75.42 118.47 TOTAL SIDE RESISTANCE in kN, QS = 2042.43



E.2 Ultimate End Bearing / Tip Friction Resistance Soil Type @ Elevation :



20.00 m



Su @ Elevation :



20.00 m



Su @ Elevation :



19.00 m



For Cohesive Soils:



Nc =



9



\ Nc =



9



:



2850.00 kPa



a



0.0150



=



Pile Tip Area : AT =



(@ Tip of the Shaft / Bored pile)



167.04 kPa



(W/in 2B of the Tip of theShaft / Bored pile)



(For Cohesionless Soils) =



0.8684



Fr =



1.0000



for which, 0.50 qTR =



£



b



£



1.50



N/A



Note : If B > 1.27m, the value of q T shall be reduced to qTR.



7239.00 kPa 0.196



(Tip of Shaft / Bored pile)



179.33 kPa



b



= 0.868367



qTR =



cohesionless



Note : If the soil within 2B of the tip has Su < 24.00 kPa, the value of Nc shall be reduced by one-third. If Su > 96.0 kPa & B > 1.90m, the value of q T shall be reduced to qTR.



qT =



\ b For Cohesionless Soils:



:



m2



\ TOTAL TIP / END BEARING RESISTANCE, QT



=



559.5962 kN



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PROJECT



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DESCRIPTION



: : :



DATE DESIGNED BY



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E.3 Ultimate Capacity of Bored Pile / Shaft W = Weight of shaft / Bored pile



=



58.90486 kN



E.3.1 Ultimate Axial Capacity of Shaft in Compression Qult



= QS + QT - W



=



2543.12



kN



>



0.00



kN



\ OK !!!



>



500.00



kN



\ OK !!!



kN



\ OK !!!



E.3.2 Ultimate Axial Capacity of Shaft in Tension(Uplift) Tult



= 0.70QS + W



=



1488.60



kN



E.3.3 Allowable Axial Capacity of Shaft in Compression Qall



= Qult / FS



=



847.71



kN



E.3.4 Allowable Axial Capacity of Shaft in Tension Tall



= Tult / FS



=



496.20



(@ service) 0 (@ service)



kN



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