NordlundNordlund Method ProcedureMethod Procedure

STEP 10 Compute the ultimate capacity, Qu.

Qu = Rs + Rt

STEP 11 Compute the allowable geotechnical pile load, Qa.

Safety ofFactor Q

= Q ua

Example 9Example 9--22

Single Piles in Cohesive SoilsSingle Piles in Cohesive Soils

ggTotal stress methodTotal stress method−−αα--method or Tomlinson methodmethod or Tomlinson method

ggEffective stress methodEffective stress method−−ββ--methodmethod

Tomlinson or Tomlinson or αα--MethodMethod

Unit Shaft Resistance, fs:

fs = ca = αcu

Where:

ca = adhesion (Figure 9-14)

α = empirical adhesion factor (Figure 9-15)

Tomlinson or Tomlinson or αα--MethodMethod

Shaft Resistance, Rs:

Rs = fs As

Where:

As = pile surface area in layer (pile perimeter x length)

Concrete, Timber, Corrugated Steel Piles

Smooth Steel Pilesb = Pile Diameter

D = distance from ground surface to bottom of clay layer or pile toe, whichever is less

Tomlinson or Tomlinson or αα--Method (US)Method (US)Figure 9-14

Tomlinson or Tomlinson or αα--MethodMethod

Sand or Sandy Gravels

Stiff ClayDb

Tomlinson or Tomlinson or αα--Method (US)Method (US)

b = Pile DiameterD = distance into stiff clay layer

Figure 9-15a

Tomlinson or Tomlinson or αα--MethodMethod

Db

Soft Clay

Stiff Clay

Tomlinson or Tomlinson or αα--Method (US)Method (US)

b = Pile DiameterD = distance into stiff clay layer

Figure 9-15b

Tomlinson or Tomlinson or αα--MethodMethod

D

b

Stiff Clay

Tomlinson or Tomlinson or αα--Method (US)Method (US)

b = Pile DiameterD = distance into clay layer

Figure 9-15c

HIGHLY OVERCONSOLIDATED CLAYSHIGHLY OVERCONSOLIDATED CLAYS

For Ψ ≤ 1.0, α = 0.5 Ψ-0.5

For Ψ > 1.0, α = 0.5 Ψ-0.25

In highly overconsolidated clays, the undrained shear strength may exceed the upper limits of Figures 9-14 and 9-15.

In these cases, the adhesion factor should be calculated according to API procedures based on the ratio of the undrained shear strength of the soil, cu, divided by the effective overburden pressure, po’. The ratio of cu / po’ is Ψ.

Tomlinson or Tomlinson or αα--MethodMethod

Unit Toe Resistance, qt:

qt = cu Nc

Where:

cu = undrained shear strength of the soil at pile toe

Nc = dimensionless bearing capacity factor (9 for deep foundations)

Tomlinson or Tomlinson or αα--MethodMethod

Toe Resistance, Rt:

Rt = qt At

The toe resistance in cohesive soils is sometimes ignored since the movement required to mobilize the toe resistance is several times greater than the movement required to mobilize the shaft resistance.

Qu = RS + RT

Qa = QU / FS

and

Tomlinson or Tomlinson or αα--MethodMethod

Example 9Example 9--33

Which pile has the highest toe Which pile has the highest toe resistance ?resistance ?

Plugging of Open Pile SectionsPlugging of Open Pile Sections

(a) Open Toe Condition

bqt qt

fso fsi

(b) Plugged Toe Condition

qt

D

fso

(a) Open Toe Condition

bqt qt

fso fsi

(b) Plugged Toe Condition

qt

D

fso

Figure 9-18

Plugging of HPlugging of H--Pile SectionsPile Sections

Figure 9-19

The DRIVEN Computer ProgramThe DRIVEN Computer Program

ggDeveloped by FHWA in 1998Developed by FHWA in 1998ggUse for calculation of static pile Use for calculation of static pile

capacitycapacity

ggDemonstration of the DRIVEN computer Demonstration of the DRIVEN computer programprogram

Piles Driven to RockPiles Driven to RockThe capacity of piles driven to rock should be based on driving observations, local experience, and load test results.

RQD values from NX size rock cores can provide a qualitative assessment of rock mass quality.

RQDRQD Rock Mass QualityRock Mass Quality90 90 –– 100100 ExcellentExcellent75 75 –– 9090 GoodGood50 50 –– 7575 FairFair25 25 –– 5050 PoorPoor0 0 -- 2525 Very PoorVery Poor

What is RQD? See Chapter 3

Piles Driven to RockPiles Driven to Rock

Except for piles driven to soft rock, the structural capacity ofthe pile will be lower than the geotechnical capacity of the rock to support a toe bearing pile. (Fair to excellent quality rock).

The structural capacity of the pile then governs the pile capacity.