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Lateral Pile Capacity Caculation using Broms's Method (Free head type)

The allowable lateral load on piles is determined from the following two criteria:

Allowable lateral load is obtained by dividing the ultimate (failure) load by an adequate factor of safety.

Allowable lateral load is corresponding to an acceptable lateral deflection.

The smaller of the two above values is the one actually adopted as the design lateral load.

Methods of calculating lateral resistance of vertical piles can be broadly divided into two categories.

- Pile Parameters

Pile Dia. ThicknessElastic

Modulus

Moment of

Inertiaec

Pile yield

Moment

Pile

Length

(b, mm) (t, mm) (Ep,kgf/cm2) ( Ip, cm

4) (ec, mm) (My, kg-cm) (D, m)

400 65.0 4.0E+05 106,435 0.0 9.2E+05 8.0

(b, in) (t, in) (Ep, psi) ( Ip, in4) (ec, in) (My, lb-in) (D, in)

15.7 2.6 5.6E+06 2,557 0.0 8.0E+05 315.0

ec : Eccentricity of applied load for free-headed piles (i.e., vertical distance between ground surface and lateral load)

1. Methods of Calculating Ultimate Lateral Resistance

1) The general soil type within the critical depth (approximately 4 to 5 pile diameters = 2.0 m) below the ground surfaconsidered to be very loose sand (cohesionless soil) from the soil report.

2) Determine the coefficient of horizontal subgrade reaction (Kh) within the critical depth for cohesionless soils.

Values of the coefficient of modulus variation Kh are obtained from the following Table.

(The values of given in following table were determined by Terzaghi.)

Kh (lb/in3)

Above

Groundwater

Below

Groundwater

Loose 7 4

Medium 30 20

Dense 65 40 Choose from the Table = 7 lb/in3 (above ground water)

3) Determine the dimensionless length factor

= 0.0137 /in : for cohesionless soils

= 0.0137 x (Embedded pile length) = 0.0137 x 315 in

= 4.31 in > 4.0 long pile caculation procedure!

4) Determine the other required soil parameters over the embedded length of the pile.

a) The Rankine passive earth pressure coefficient for cohesionless soil (Kp)

= 2.77

b) The average effective unit weight of the soil

(psi)= 1.7 t/m3 = 0.06 lb/in3

Soil Density

PC

Pile Type

5 /EIKh

D

)2/45(tan 2 p

K

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5) Determine the ultimate lateral load for a single pile (Qu)

Long free headed pile in cohesionless soil using (and for free headed case)

enter Figure 1 and select the corresponding value of and solve for

= 0 / 15.75 = 0.0

= 797741.4 / [ 0.06 15.75^4 2.77 ] = 78.04

= 30

= 30 x 2.77 x 15.75^3 x 0.06 = 19.47 kips = 8.83 ton

6) Calculate the maximum allowable working load for a single pile (Qm)

3.0 = 2.94 ton

2. Methods of Calculating Acceptable Deflection at Working Lateral Load

1) Calculate the working load for a single pile (Qa)

Calculate corresponding to a given design deflection at the ground surface (y) or the deflection correspondin

to a given design load.

Free headed pile in cohesionless soil using (and for free headed case) enter Figure 2 and

select the corresponding value of and solve for of y.

= 0.0 , = 4.31 , y = 1.0 cm = 0.39 in

= 0.55

0.39 x (5574602.1 x 2556.83)^0.6 x (7)^0.4 / (0.55 x 314.96)

= 6.12 kips = 2.78 ton

3. Determination of Allowable Lateral Capacity

Compare Qa to Qm

If Qa < Qm use Qa and y

Since Qa = 2.78 ton < Qm = 2.94 ton , use Q_allow = 2.78 ton (for Pile Foundation Design)

D

py KbM4

/ bec /

3

/ bKQ pu uQ

bec /

py KbM4/

3/ bKQ pu

uQ

/um QQ

aQ

D Dec /

DQKEIy ah /)(5/25/3

aQ

Dec / D

DQKEIy ah /)(5/25/3

aQ

a

Q

mQa

Q

mQa

Q

y a

Q

mQa

Q

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Attachment

Figure 1. Ultimate Lateral Load Capacity of Long Pile in Cohesionless Soils

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Figure 2. Lateral Deflection at Ground Surface of Piles in Cohesionless Soils

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e is

Loose Sand

Soil Type

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