Structure, Member Design - Geotechnics Piles XX

Transcription

1 E N G I N E E R S Consulting Engineers jxxx 1 Material Properties Characteristic strength of concrete, f cu ( 60N/mm 2 ; HSC ) 40 N/mm 2 OK Yield strength of longitudinal steel, f y 460 N/mm 2 Yield strength of shear link steel, f yv 460 N/mm 2 Type of concrete and density, ρ c 24 kn/m 3 Factor of Safety Factor of safety (overall base (effective) bearing and shaft (effective) friction 2.0 Factor of safety (base (effective) bearing), FOS 2 (usually 3.5) 3.0 Factor of safety (shaft (effective) friction), FOS 3 (usually 1.0 to 1.5) 1.5 Loading factor, K (between 1.40 and 1.60 depending on DL to LL ratio) 1.50 BS8110 Note loading factor K multiplies SLS loads for ULS loads for section (reinforcement) design; cl Soil Description Water unit weight, γ w = 9.81kN/m kn/m 3 Soil name Dry bulk unit weight, γ dry 20.0 kn/m 3 Saturated bulk unit weight, γ sat 20.0 kn/m 3 Undrained shear strength, S u (z) z kpa Note that S u can be obtained from SPT (Stroud) or SPT (Fukuoka) values; Tomlinson Effective cohesion, c' 0.0 kpa Effective angle of shear resistance, φ' 38.0 degrees Note that φ ' can be obtained from SPT (Peck) or CPT (Durgunoglu and Mitchell) values; Effective angle of friction on shaft, δ' 25.1 degrees Tomlinson SPT, N(z) z Factor for SPT, N value (base effective bearing), K SPT,b 250 Pile (drilled shaft) in sands with L 10m, Q b ' 2900kPa 57.5L/10 Quiros and Ree Pile (drilled shaft) in sands with L > 10m, Q b ' 2900kPa 57.5 Quiros and Ree Pile (drilled shaft) in sands with L 10m, Q b ' 2900kPa 100 Shioi and Fuk Pile in undrained cohesive soils 200 Neoh Pile (driven displacement) in non-plastic silts 38L/D 300 Pile (driven displacement) in sands and gravels 38L/D 380 Meyerhof Pile in drained cohesionless soils 400 Neoh Factor for SPT, N value (shaft effective friction), K SPT,s 2.0 Pile in undrained cohesive or drained cohesionless soils 2.0 Neoh

2 CONSULTING Engineering Calculation Sheet E N G I N E E R S Consulting Engineers jxxx 2 Analysis Method Undrained, drained or empirical analysis? For clays, perform undrained, drained and empirical analyses; For sands / gravels, perform drained and empirical analyses; For rocks, perform drained and empirical analyses; Gross (effective) bearing capacity limit, q flimit (z=l-l 0 ) or q flimit '(z=l-l 0 ) kpa Note that the base gross (effective) bearing capacity is limited to values up to 15000kPa because Vesic showed that at penetration depths greater than 20 pile diameters, a peak value of base resistance is reached which is not exceeded at greater penetrations depths; Note that this limiting value is D- and L- dependent, thus affecting the multi-d multi-l pile capacity charts which has thus been set to be limited by the automatically calculated value; q flimit (z=l-l 0 ) or q flimit '(z=l-l 0 ) = N q,strip.σ v '(z=20d-l 0 ) 15MPa kpa 48.9 σ v '(z=20d-l 0 ) = p surface +γ dry.(l c +20D) Invalid kpa 1 σ v '(z=20d-l 0 ) = p surface +(γ sat -γ w ).(L c +20D-z u )+γ dry.z u 208 kpa σ v '(z=20d-l 0 ) = p surface +(γ sat -γ w ).(L c +20D) Invalid kpa Tomlinson Shaft adhesion limit or shaft effective stress limit, S alimit (z) or τ alimit '(z) 89 kpa Note that the shaft adhesion or the shaft effective stress is limited to 110kPa because Vesic showed that at penetration depths greater than 20 pile diameters, a peak value of skin friction is reached which is not exceeded at greater penetrations depths; Note that this limiting value is D- and L- dependent, thus affecting the multi-d multi-l pile capacity charts which has thus been set to be limited by the automatically calculated value; ese S alimit (z) or τ alimit '(z) = K s.tanδ'.σ v '(z=20d-l 0 ) 110kPa 89 kpa ese σ v '(z=20d-l 0 ) = p surface +γ dry.(l c +20D) Invalid kpa kui σ v '(z=20d-l 0 ) = p surface +(γ sat -γ w ).(L c +20D-z u )+γ dry.z u 208 kpa σ v '(z=20d-l 0 ) = p surface +(γ sat -γ w ).(L c +20D) Invalid kpa Tomlinson Include or exclude base resistance? Note that in general, the contribution of base resistance in bored piles should be ignored due to difficulty of proper base cleaning, especially in wet hole (with drilling fluid); The contribution of base resistance should only be used if it is constructed in dry hole, if proper inspection of the base can be carried out or if base grouting is implemented; Furthermore, a relatively larger base movement is required to mobilise the maximum base resistance as compared to the displacement needed to fully mobilise shaft resistance; The base displacement of approximately 5% to 10% of the pile diameter is generally required to mobilise the ultimate base resistance provided that the base is properly cleaned and checked; Gue and Partners

3 CONSULTING Engineering Calculation Sheet E N G I N E E R S Consulting Engineers jxxx 3 Pile Group Dimensions Width of pile group (pile cap) in x, B cap Length of pile group (pile cap) in y, L cap m m Pile Dimensions Pile section shape Pile shaft diameter (circular) or width (square), D 750 mm Pile shaft cross sectional area, A ps = πd 2 /4 (circular) or D 2 (square) mm 2 Pile base diameter (circular) or width (square), D b 750 mm OK Pile base cross sectional area, A pb = πd b 2 /4 (circular) or D 2 (square) mm 2 OK L c L 0 z u z L Depth of pile cap base from ground level, L c (>= 0.000m) m OK Depth of pile z=0 level from pile cap base, L 0 (>= 0.000m) m OK Depth of pile founding level from pile cap base, L (>=L 0 ) m OK Note that L 0 accounts for poor ground near surface level where no contribution of shaft skin friction capacity is adopted, in fact negative skin friction is considered over L 0 length if requested; Depth of water table from ground level, z u m Note that the soil beneath the water table has an effective submerged unit weight of about half of the soil above the water table, thus reducing the drained overall pile effective capacity; Hence use the highest water table forseeable; Enter a negative z u value for water table above ground level, this representing a flood event or a bridge pier within a sea or river with the ground level being the sea or river bed; However, a water table above ground level may unconservatively decrease the overall pile (effective) capacity utilisation, thus consider also the case when the water table is at ground level;

4 E N G I N E E R S Consulting Engineers jxxx 4 Structure, Member Design - Geotechnics Piles XX Pile Reinforcement Pile type 40 N/mm 2 Precast Driven Square RC Pile or Insitu Bored Circular RC Pile Pile compression capacity design method Cover to all reinforcement, cover 4 (usually 75) 75 mm Longitudinal steel reinforcement diameter, φ p 32 mm Longitudinal steel reinforcement number, n p 12 Longitudinal steel area provided, A s,prov,p = n p.π.φ 2 p / mm 2 Shear link diameter, φ link,p 10 mm Number of links in a cross section, i.e. number of legs, n link,p 2 Area provided by all links in a cross-section, A sv,prov,p = n link,p.π.φ 2 link,p /4 157 mm 2 Pitch of links, S p 150 mm Estimated steel reinforcement quantity 171 kg/m 3 [ A s,prov,p / A ps ]; No laps; Links ignored;

5 CONSULTING Engineering Calculation Sheet E N G I N E E R S Consulting Engineers jxxx 5

6 CONSULTING Engineering Calculation Sheet E N G I N E E R S Consulting Engineers jxxx 6 Precast (Pretensioned Spun) Driven Circular RC Pile Effective area of concrete, A eff mm 2 Effective prestress, f pe 6.3 N/mm 2

7 CONSULTING Engineering Calculation Sheet E N G I N E E R S Consulting Engineers jxxx 7 Insitu Bored Circular RC Pile (API Micropile) Yield strength of API pipe, f y,api 552 N/mm 2 Outer diameter of API pipe, OD API Wall thickness of API pipe, t API mm 9.19 mm Cross sectional area of API pipe, A API = π.[od 2 API -(OD API -2.t API ) 2 ]/4 mm 2 Cross sectional area of grout, A c,api = A ps -A API mm 2 Elastic modulus of concrete, E c = 5500.(f cu /1.5) N/mm 2 BS8110 Elastic modulus of steel, E s N/mm 2 cl API PIPE SIZES FOS str = 2.0 Grade N80 ( f y = 80,000 PSI / 552 MPa ) OD (mm) ickness (mmid (mm) Q ult (kn) Q all (kn) , , , ,247 1, ,517 1, , ,076 1, ,361 1, ,471 1, ,896 1, ,268 1, ,370 1, ,687 1, ,008 1, ,319 1, ,623 1, ,904 1, ,041 1, ,461 1, ,986 1, ,440 2, ,891 2, ,116 2, ,546 2, ,029 2, ,078 2, ,473 2, ,796 2, ,536 2, ,185 2, ,677 2, ,160 3, ,398 3,699

8 E N G I N E E R S Consulting Engineers jxxx 8 Pile SLS Loading (Including Negative Skin Friction) Surcharge at surface, p surface 0 kpa Pile SLS vertical load, F pile,v,n 3000 kn Pile group (pile cap) SLS vertical load, F pilecap,v kn Note that F pile,v,n and F pilecap,v can be positive (downward) or negative (upwards); Pile SLS vertical (compressive) NSF load, F pile,v,nsf 0 kn Note NSF = negative skin friction; Note F pile,v,nsf = ( πd or 4D).L 0. β.[ σ v '(z=-l 0 )+ σ v '(z=0)]/2; Consideration of NSF? Not Considered NSF reduction factor, β 0.30 Meyerhof Clay Garlanger Silt Garlanger Sand Garlanger Effective vertical stress at z=-l 0 level, σ v '(z=-l 0 ) 50 kpa Case when (z u L c ) >= MAX (B cap, L cap ) Invalid σ v '(z=-l 0 ) = p surface +γ dry.l c Case when 0 < (z u L c ) < MAX (B cap, L cap ) Valid σ v '(z=-l 0 ) = p surface +γ dry.l c 50 kpa Case when (z u L c ) = 0 Invalid σ v '(z=-l 0 ) = p surface +γ dry.l c Case when (z u L c ) < 0 and z u >= 0 Invalid σ v '(z=-l 0 ) = p surface +(γ sat -γ w ).(L c -z u )+γ dry.z u Case when z u < 0 Invalid σ v '(z=-l 0 ) = p surface +γ sat.l c +γ w.(-z u )-γ w.(l c +(-z u )) Note that the above equation reduces to σ v '(z=-l 0 ) = p surface +( γ sat - γ w ).L c ; Effective vertical stress at z=0 level, σ v '(z=0) 50 kpa Case when (z u L c L 0 ) >= MAX (B cap, L cap ) Invalid σ v '(z=0) = p surface +γ dry.(l c +L 0 ) Case when 0 < (z u L c L 0 ) < MAX (B cap, L cap ) Valid σ v '(z=0) = p surface +γ dry.(l c +L 0 ) 50 kpa Case when (z u L c L 0 ) = 0 Invalid σ v '(z=0) = p surface +γ dry.(l c +L 0 ) Case when (z u L c L 0 ) < 0 and z u >= 0 Invalid σ v '(z=0) = p surface +(γ sat -γ w ).(L c +L 0 -z u )+γ dry.z u Case when z u < 0 Invalid σ v '(z=0) = p surface +γ sat.(l c +L 0 )+γ w.(-z u )-γ w.(l c +L 0 +(-z u )) Note that the above equation reduces to σ v '(z=0) = p surface +( γ sat - γ w ).(L c +L 0 ); Total pile SLS vertical (compressive) load (per pile), F pile,v,comp Note F pile,v,comp = MAX(0, F pile,v,n )+F pile,v,nsf ; Total pile SLS vertical (tensile) load (per pile), F pile,v,tens Note F pile,v,tens = ABS(MIN(0, F pile,v,n )); 3000 kn 0 kn Pile ULS Loading (Including Negative Skin Friction) Total pile ULS vertical (compressive) load (per pile), F pile,v,comp,uls = K.F pile,v,com Total pile ULS vertical (tensile) load (per pile), F pile,v,tens,uls = K.F pile,v,tens 4500 kn 0 kn

9 CONSULTING Engineering Calculation Sheet E N G I N E E R S Consulting Engineers jxxx 9 Structure, Member Design - Geotechnics Piles XX Executive Summary Undrained overall pile capacity Drained overall pile effective capacity Empirical overall pile effective capacity 89% OK Pile axial compression capacity 68% OK Pile axial tension capacity 0% OK Pile detailing requirements OK Undrained overall pile group capacity Drained overall pile group capacity Empirical overall pile group capacity Overall utilisation summary 89% % Vertical reinforcement in pile 2.18 % Estimated pile steel reinforcement quantity 171 kg/m 3 [Note that steel quantity in kg/m 3 can be obtained from 78.5 x % rebar]; Material cost: concrete, c 300 units/m 3 steel, s 3500 units/tonne Reinforced concrete material cost = c+(est. rebar quant).s 900 units/m 3

10 E N G I N E E R S Consulting Engineers jxxx 10 Undrained Overall Pile Capacity Undrained shear strength at z=0 level, S u (z=0) Undrained shear strength at z=l-l 0 level, S u (z=l-l 0 ) Base bearing capacity, Q b = (πd 2 b /4 or D 2 b ).q f (z=l-l 0 ) Gross bearing capacity, q f (z=l-l 0 ) = N c.s u (z=l-l 0 ) (<=q flimit (z=l- Terzaghi Note gross bearing capacity set to 0.0kPa if base resistance excluded; Bearing capacity factor, N c = 9.0 Meyerhof Shaft friction capacity, Q s = (πd or 4D).(L-L 0 ).S a Average shaft adhesion, S a = [S a (z=0)+s a (z=l-l 0 )]/2 S a (z=0) = F.α(z=0).S u (z=0) (<=S alimit (z)) S a (z=l-l 0 ) = F.α(z=L-L 0 ).S u (z=l-l 0 ) (<=S alimit (z)) Note that S a (z=0) is the shaft adhesion at z=0 level and S a (z=l-l 0 ) is the shaft adhesion at z=l-l 0 level; Shaft adhesion factor, α(z=0) 0.80 McClelland, Nord Shaft adhesion factor, α(z=l-l 0 ) 0.80 McClelland, Nord Shaft adhesion length factor, F = function (L/D) 1.00 Note that α is 0.30 (under-reamed base piles); Note that α is (stiff over-consolidated clays); Note that α is 0.30 (heavily fissured clay); Note that α is 0.45 (very stiff clays, S u >= 150kPa); Note that α is (firm to stiff clays, eg. London Clay); Note that α is 0.45 (bored piles), 0.80 (driven piles); Note that α is 0.50 (firm to stiff clays, S u >= 70kPa); Note that α is 1-[(S u -25)/90] (soft to firm clays, 25kPa < S u < 70kPa); Note that α is (soft Malaysian Clay); Note that α is 1.00 (very soft clays, S u <= 25kPa); Tomlinson Whitaker and Co Tomlinson Neoh Tomlinson Sutton API API Gue and Partn Neoh, API

11 E N G I N E E R S Consulting Engineers jxxx 11 Co Compressive a Co Co dlund dlund ooke ers Note that B in the term L/B above is D;

12 E N G I N E E R S Consulting Engineers jxxx 12 Pile weight minus soil weight removed, F pile = A ps.l.(ρ c -γ dry ) Note under-reamed base dimensions ignored in calculation of F pile as deemed negligible; Note conservatively, dry bulk unit weight assumed for density of displaced soil; Combined base bearing and shaft friction capacity, P f = Q b + Q s Base and Shaft Capacity Factored Individually mpressive Undrained pile base capacity (factored), Q b / FOS 2 nd Tensile Undrained pile shaft capacity (factored), Q s / FOS 3 mpressive Undrained pile base and shaft capacity (factored), Q b / FOS 2 + Q s Base and Shaft Capacity Factored Together mpressive Undrained pile base and shaft capacity (factored), P f / FOS 1 Tensile Undrained pile base and shaft capacity (factored), Q s / FOS 1 Undrained overall pile capacity for vertical (compressive) load, MIN (Q b / FOS Undrained overall pile capacity for vertical (tensile) load, MIN (Q s / FOS 3, Q s Undrained overall pile capacity utilisation = MAX (F pile,v,comp / (MIN (Q b / FOS 2

13 E N G I N E E R S Consulting Engineers jxxx 13 Undrained Overall Pile (Compressive) Capacity Chart 1000 Undrained Overall Pile (Compressive) Capacity, MIN (Q b / FOS 2 + Q s / FOS 3, P f / FOS 1 ) - F pile (kn) Length of Pile, L (m) D = Db = 300mm D = Db = 450mm D = Db = 600mm D = Db = 750mm D = Db = 900mm D = Db = 1050mm D = Db = 1200mm D = Db = 1350mm D = Db = 1500mm D = Db = 1650mm D = Db = 1800mm D = Db = 1950mm D = Db = 2100mm

14 E N G I N E E R S Consulting Engineers jxxx 14 Structure, Member Design - Geotechnics Piles XX Drained Overall Pile Effective Capacity L c L 0 z u z L Effective vertical stress at pile top z=0 level, σ v '(z=0) Case when (z u L c L 0 ) >= 0 σ v '(z=0) = p surface +γ dry.(l c +L 0 ) Case when (z u L c L 0 ) < 0 and z u >= 0 σ v '(z=0) = p surface +(γ sat -γ w ).(L c +L 0 -z u )+γ dry.z u Case when z u < 0 σ v '(z=0) = p surface +γ sat.(l c +L 0 )+γ w.(-z u )-γ w.(l c +L 0 +(-z u )) Note that the above equation reduces to σ v '(z=0) = p surface +( γ sat - γ w ).(L c +L 0 ); Effective vertical stress at water table z=z u -L c -L 0 level, σ v '(z=z u -L c -L 0 ) Case when z u >= 0 σ v '(z=z u -L c -L 0 ) = p surface +γ dry.z u Case when z u < 0 σ v '(z=z u -L c -L 0 ) = 0 Effective vertical stress at critical depth z=20d-l 0 level, σ v '(z=20d-l 0 ) Case when (z u L c 20D) >= 0 σ v '(z=20d-l 0 ) = p surface +γ dry.(l c +20D) Case when (z u L c 20D) < 0 and z u >= 0 σ v '(z=20d-l 0 ) = p surface +(γ sat -γ w ).(L c +20D-z u )+γ dry.z u Case when z u < 0 σ v '(z=20d-l 0 ) = p surface +γ sat.(l c +20D)+γ w.(-z u )-γ w.(l c +2 Note that the above equation reduces to σ v '(z=20d-l 0 ) = p surface +( γ sat - γ w ).(L c +20D Effective vertical stress at pile base z=l-l 0 level, σ v '(z=l-l 0 ) Unit weight, γ' /m 3 Case when (z u L c L) >= MAX (B cap, L cap ) σ v '(z=l-l 0 ) = p surface +γ dry.(l c +L) γ' = γ dry /m 3 Case when 0 < (z u L c L) < MAX (B cap, L cap ) σ v '(z=l-l 0 ) = p surface +γ dry.(l c +L) γ' = z u /MAX(B cap, L cap ). [γ dry - (γ sat - γ w )] + (γ sat - γ w ) /m 3 Case when (z u L c L ) = 0 σ v '(z=l-l 0 ) = p surface +γ dry.(l c +L) γ' = γ sat - γ w /m 3 Case when (z u L c L ) < 0 and z u >= 0 σ v '(z=l-l 0 ) = p surface +(γ sat -γ w ).(L c +L-z u )+γ dry.z u γ' = γ sat - γ w /m 3 Case when z u < 0 σ v '(z=l-l 0 ) = p surface +γ sat.(l c +L)+γ w.(-z u )-γ w.(l c +L+(-z u ) Note that the above equation reduces to σ v '(z=l-l 0 ) = p surface +( γ sat - γ w ).(L c +L); γ' = γ sat - γ w /m 3

15 E N G I N E E R S Consulting Engineers jxxx 15 Base effective bearing capacity, Q b ' = (πd 2 b /4 or D 2 b ).q f '(z=l-l 0 ) Gross effective bearing capacity, q f '(z=l-l 0 ) (<=q flimit '(z=l-l 0 )) Terzaghi = s c.d c.n c,strip.c' + s q.d q.n q,strip.σ v '(z=l-l 0 ) + s γ.d γ.n γ,strip.d b /2.γ' Note gross effective bearing capacity set to 0.0kPa if base resistance excluded; Note for piles bored in rock, s c.d c = 1.2, s q.d q = 1.0 and s γ.d γ = 0.7; Note for piles bored in rock, q f ' = 0.3q uc, where Gue and Partn Neoh q f ' for weak rock 1500 kpa Neoh q f ' for medium rock kpa Neoh q f ' for strong fresh rock kpa Neoh D); Note typically for driven piles, N q = 20 (loose sand) to 100 (very dense sand), and for bored piles N q = 12 (loose sand) to 40 (very dense sand); Equations for bearing capacity factors Cohesion Factors Surcharge Factors Neoh Shape factor, EC7 Depth factor, Note D and B in the above equation are L c +L and D b, respectively; Bearing capacity factor, N c,strip Soils N c,strip = (N q,strip -1).cotφ' EC7 (Prandtl Rocks N c,strip Kulhawy and Goo Shape factor, EC7 Note B' and L' in the above equation are D b and D b, respectively; Depth factor, d q Self Weight Factors Note D and B' in the above equation are L c +L and D b, respectively; Bearing capacity factor, N q,strip Soils EC7 (Reissne Rocks N q,strip Kulhawy and Goo Shape factor, EC7 Note B' and L' in the above equation are D b and D b, respectively; Depth factor, Bearing capacity factor, N γ,strip Soils N γ,strip = 2.0(N q,strip -1).tanφ' EC7 (Hansen Rocks N γ,strip Kulhawy and Goo

16 E N G I N E E R S Consulting Engineers jxxx 16 Shaft effective friction capacity, Q s ' = (πd or 4D).Σ( L.τ a ') Equation for shaft effective stress Soils / Rocks τ a '(z=0) = K s.tanδ'.σ v '(z=0) (<=τ alimit '(z)) τ a '(z=z u -L c -L 0 ) = K s.tanδ'.σ v '(z=z u -L c -L 0 ) (<=τ alimit '(z)) τ a '(z=20d-l 0 ) = K s.tanδ'.σ v '(z=20d-l 0 ) (<=τ alimit '(z)) τ a '(z=z u -L c -L 0 ) = K s.tanδ'.σ v '(z=z u -L c -L 0 ) (<=τ alimit '(z)) ers τ a '(z=l-l 0 ) = K s.tanδ'.σ v '(z=l-l 0 ) (<=τ alimit '(z)) Note that τ a '(z=0) is the shaft effective stress at z=0 level and τ a '(z=l-l 0 ) is the shaft effective stress at z=l-l 0 level; Note τ a ' = σ h '.tan δ ' = K s σ v '.tan δ '; Note effective cohesion, c' ignored due to disturbed soil adjacent to pile foundation; K s.tanδ' 0.43 Calculated K s.tanδ' = k Ks.K 0.(OCR) 0.5.tanδ' = k Ks.(1-sinφ 0.22 Burland, Meyer Coefficient of horizontal soil stress, k Ks 1.25 Tomlinson Overconsolidation ratio, OCR 1.0 Effective angle, δ ' for sandy gravel 40.0 degrees Neoh Effective angle, δ ' for sand 32.0 degrees Neoh Effective angle, δ ' for silts and clays degrees Neoh Effective angle, δ ' for bored pile residual angle degrees Neoh Manual K s.tanδ' 0.43 Pile bored in very loose to dense Ksands s.tan δ (Mey ' = Pile bored in loose sands (Davies K s and.tanchan) δ ' = Pile bored in dense sands (Davies K s and.tanchan δ ' = Neoh, Meyerh Gue and Partn Gue and Partn Pile CFA in chalk K s.tan δ ' = 0.45 CIRIA574 Pile CFA in chalk with N >= 10, q uc >= K s.tan 4MPδ ' = 0.80 CIRIA86 Pile bored or driven cast-in-place in chalk K s.tan δ ' = 0.80 Pile driven in very loose to dense K s sands.tan δ (Me ' = CIRIA574 Neoh, Meyerh Rocks τ a '(z=0) = αβq uc (<=τ alimit '(z)) e and Partn l) τ a '(z=l-l 0 ) = αβq uc (<=τ alimit '(z)) e and Partn odman Note that τ a '(z=0) is the shaft effective stress at z=0 level and τ a '(z=l-l 0 ) is the shaft effective stress at z=l-l 0 level; Reduction factor, α 0.30 Correlation factor, β 0.25 Unconfined uniaxial compressive strength, q uc 1500 kpa r) odman Note typically τ a ' = 0.05q uc, where Neoh τ a ' for weak rock kpa Neoh τ a ' for medium rock kpa Neoh n) τ a ' for strong rock kpa Neoh odman

17 E N G I N E E R S Consulting Engineers jxxx 17 Structure, Member Design - Geotechnics Piles XX rhof hof ers ers hof ers ers

18 E N G I N E E R S Consulting Engineers jxxx 18 Structure, Member Design - Geotechnics Piles XX Co Compressive a Co Co

19 E N G I N E E R S Consulting Engineers jxxx 19 Pile weight minus soil weight removed, F pile = A ps.l.(ρ c -γ dry ) Note under-reamed base dimensions ignored in calculation of F pile as deemed negligible; Note conservatively, dry bulk unit weight assumed for density of displaced soil; Combined base effective bearing and shaft effective friction capacity, P f ' = Q Base and Shaft Effective Capacity Factored Individually mpressive Drained pile base effective capacity (factored), Q b ' / FOS 2 nd Tensile Drained pile shaft effective capacity (factored), Q s ' / FOS 3 mpressive Drained pile base and shaft effective capacity (factored), Q b ' / FOS Base and Shaft Effective Capacity Factored Together mpressive Drained pile base and shaft effective capacity (factored), P f ' / FOS Tensile Drained pile base and shaft effective capacity (factored), Q s ' / FOS Drained overall pile effective capacity for vertical (compressive) load, MIN (Q Drained overall pile effective capacity for vertical (tensile) load, MIN (Q s ' / FO Drained overall pile effective capacity utilisation = MAX (F pile,v,comp / (MIN (Q b

20 E N G I N E E R S Consulting Engineers jxxx Drained Overall Pile Effective (Compressive) Capacity Chart Empirical Overall Pile Effective (Compressive) Capacity, MIN (Q b ' / FOS 2 + Q s '/ FOS 3, P f ' / FOS 1 ) - F pile (kn) Co Compressive a Co Co Length of Pile, L (m) D = Db = 300mm D = Db = 450mm D = Db = 600mm D = Db = 750mm D = Db = 900mm D = Db = 1050mm D = Db = 1200mm D = Db = 1350mm D = Db = 1500mm D = Db = 1650mm D = Db = 1800mm D = Db = 1950mm D = Db = 2100mm

21 E N G I N E E R S Consulting Engineers jxxx 21 Empirical Overall Pile Effective Capacity SPT at z=0 level, N(z=0) 5 SPT at z=l-l 0 level, N(z=L-L 0 ) 305 Base effective bearing capacity, Q b ' = (πd 2 b /4 or D 2 b ).q f '(z=l-l 0 ) 0 kn Gross effective bearing capacity, q f '(z=l-l 0 )=K SPT,b.N(z=L-L 0 ) (<= 0 kpa Note gross effective bearing capacity set to 0.0kPa if base resistance excluded; Shaft effective friction capacity, Q s ' = (πd or 4D).(L-L 0 ).τ a ' 6985 kn Average shaft effective stress, τ a ' = [τ a '(z=0)+τ a '(z=l-l 0 )]/2 49 kpa τ a '(z=0) = K SPT,s.N(z=0) (<=τ alimit '(z)) 10 kpa τ a '(z=l-l 0 ) = K SPT,s.N(z=L-L 0 ) (<=τ alimit '(z)) 89 kpa Note that τ a '(z=0) is the shaft effective stress at z=0 level and τ a '(z=l-l 0 ) is the shaft effective stress at z=l-l 0 level; Pile weight minus soil weight removed, F pile = A ps.l.(ρ c -γ dry ) 106 kn Note under-reamed base dimensions ignored in calculation of F pile as deemed negligible; Note conservatively, dry bulk unit weight assumed for density of displaced soil; Combined base effective bearing and shaft effective friction capacity, P f ' = Q 6985 kn Base and Shaft Effective Capacity Factored Individually mpressive Empirical pile base effective capacity (factored), Q b ' / FOS 2 nd Tensile Empirical pile shaft effective capacity (factored), Q s ' / FOS 3 mpressive Empirical pile base and shaft effective capacity (factored), Q b ' / FO 0 kn 4657 kn 4657 kn Base and Shaft Effective Capacity Factored Together mpressive Empirical pile base and shaft effective capacity (factored), P f ' / FO Tensile Empirical pile base and shaft effective capacity (factored), Q s ' / FO 3492 kn 3492 kn Empirical overall pile effective capacity for vertical (compressive) load, MIN ( 3386 kn Empirical overall pile effective capacity for vertical (tensile) load, MIN (Q s ' / F 3492 kn Empirical overall pile effective capacity utilisation = MAX (F pile,v,comp / (MIN (Q 89% OK

22 E N G I N E E R S Consulting Engineers jxxx Empirical Overall Pile Effective (Compressive) Capacity Chart Empirical Overall Pile Effective (Compressive) Capacity, MIN (Q b ' / FOS 2 + Q s '/ FOS 3, P f ' / FOS 1 ) - F pile (kn) Length of Pile, L (m) D = Db = 300mm D = Db = 450mm D = Db = 600mm D = Db = 750mm D = Db = 900mm D = Db = 1050mm D = Db = 1200mm D = Db = 1350mm D = Db = 1500mm D = Db = 1650mm D = Db = 1800mm D = Db = 1950mm D = Db = 2100mm

23 E N G I N E E R S Consulting Engineers jxxx 23 Pile Reinforcement Design Precast Driven Square RC Pile or Insitu Bored Circular RC Pile Pile Longitudinal Reinforcement Design Percentage of reinforcement A s,prov,p /A ps x 100% 2.18 % Axial compression capacity, N cap,pile,comp 4418 kn SLS Design N cap,pile,comp = 0.25f cu.a ps 4418 kn e and Partn ULS Design N cap,pile,comp = 0.35f cu.a ps + (0.67f y -0.35f cu ).A Note alternatively, SLS design including steel reinforcement can be estimated by N cap,pile,comp = 0.275f cu.a ps f y.a s,prov,p with 0.55f y limited to 175N/mm 2 ; Total pile vertical (compressive) load (per pile), F pile,v,comp,(uls) SLS Design F pile,v,comp 3000 kn 3000 kn BS8004 ULS Design F pile,v,comp,uls Axial compression capacity utilisation = F pile,v,comp,(uls) /N cap,pile,comp 68% OK Axial tension capacity, N cap,pile,tens 2442 kn SLS Design N cap,pile,tens = 0.55f y.a s,prov,p 2442 kn ULS Design N cap,pile,tens = 0.95f y.a s,prov,p Total pile vertical (tensile) load (per pile), F pile,v,tens,(uls) 0 kn SLS Design F pile,v,tens 0 kn ULS Design F pile,v,tens,uls Axial tension capacity utilisation = F pile,v,tens,(uls) /N cap,pile,tens 0% OK Pile Shear Reinforcement Design Note that pile shear design to be performed as per column design; Pile Detailing Requirements All detailing requirements met? OK Min longitudinal steel reinforcement number, n p (>=6 circular; >=4 square) 12 OK Min longitudinal steel reinforcement diameter, φ p (>=12mm) 32 mm OK Percentage of reinforcement A s,prov,p /A ps x 100% (>0.4% and <5.0%) 2.18 % OK Longitudinal steel reinforcement pitch (>=75mm+φ p but >=100mm+φ p for T 143 mm OK Circular pile bar pitch = π.(d-2.cover 4-2.φ link,p -φ p )/n p 143 mm Square pile bar pitch = 4.(D-2.cover 4-2.φ link,p -φ p )/n p mm Min link diameter, φ link,p (>=0.25φ p ; >=8mm) 10 mm OK Max link pitch, S p (<=12φ p, <=300mm, <=D) 150 mm OK Require an overall enclosing link.

24 E N G I N E E R S Consulting Engineers jxxx 24 Precast (Pretensioned Spun) Driven Circular RC Pile SLS axial compression capacity, N cap,pile,comp = 0.25.(f cu -f pe ).A eff SLS total pile vertical (compressive) load (per pile), F pile,v,comp Axial compression capacity utilisation = F pile,v,comp /N cap,pile,comp Insitu Bored Circular RC Pile (API Micropile) ers SLS axial compression capacity, N cap,pile,comp Reinforcement only N cap,pile,comp = f y,api.a API /2.0 Composite section (strain compatibility) N cap,pile,comp = 0.5f y,api.(a API +A c,api 04 cl Concrete filled CHS N cap,pile,comp = (0.91f y,api.a API cl. 11. SLS total pile vertical (compressive) load (per pile), F pile,v,comp Axial compression capacity utilisation = F pile,v,comp /N cap,pile,comp

25 E N G I N E E R S Consulting Engineers jxxx 25 Structure, Member Design - Geotechnics Piles XX Accounting for Tolerance in Pile Installation Moment induced at head due to out-of-position, M = 0.075F pile,v,comp,uls Lateral force induced at head due to out-of-vertical, H = F pile,v,comp,uls / knm 60 kn

26 E N G I N E E R S Consulting Engineers jxxx 26 Group Pile Design Undrained Analysis Consideration of NSF? Total pile group SLS vertical (compressive) NSF load, F pilegroup,v,nsf Tomlinson Note NSF = negative skin friction; Note F pilegroup,v,nsf = B cap.l cap. γ dry or sat.l 0 ; Pile group capacity, Tomlinson Note D, B, L, s and s b in the above equation are L-L 0, B cap, L cap, S a, S u (z=l-l 0 ) and D, respectively; Undrained overall pile group capacity for vertical (compressive) lo Undrained overall pile group capacity utilisation Note utilisation is (F pilecap,v + F pilegroup,v,nsf ) / (Q u / FOS 1 );

27 E N G I N E E R S Consulting Engineers jxxx 27 Drained Analysis Note there is no risk of drained overall pile group failure if FOS of individual piles are adequate; Gue and Partn Empirical Analysis Note perform undrained or drained analysis;

28 E N G I N E E R S Consulting Engineers jxxx 28 Scheme Design (Cohesive Soils) ers

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30 E N G I N E E R S Consulting Engineers jxxx 30 Scheme Design (Non Cohesive Soils)

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