Session 15 – 16 SHEET PILE STRUCTURES Course : S0484/Foundation Engineering Year : 2007 Version : 1/0 Session 15 – 16 SHEET PILE STRUCTURES

SHEET PILE STRUCTURES Topic: Anchored Sheet Pile Braced Cut

CALCULATION STEPS ANCHORED SHEET PILE – FREE – SAND

CALCULATION STEPS ANCHORED SHEET PILE – FREE – SAND 1. Determine the value of Ka and Kp 2. Calculate p1and p2 with L1 and L2 are known 3. Calculate L3 4. Calculate P as a resultant of area ACDE 5. Determine the center of pressure for the area ACDE ( z )

CALCULATION STEPS ANCHORED SHEET PILE – FREE – SAND 6. Calculate L4 Determination of penetration depth of sheet pile (D) Dtheoretical = L3 + L4 Dactual = (1.3 – 1.4) Dtheoretical Determination of anchor force F = P – ½ [’(Kp – Ka)]L42

CALCULATION STEPS ANCHORED SHEET PILE – FREE – CLAY

CALCULATION STEPS ANCHORED SHEET PILE – FREE – CLAY 1. Determine the value of Ka and Kp In case of saturated soft clay with internal friction angle () = 0, we got Ka = Kp = 1 2. Calculate p1and p2 with L1 and L2 are known 3. Calculate the resultant of the area ACDE (P1) and z1 (the center of pressure for the area ACDE)

CALCULATION STEPS ANCHORED SHEET PILE – FREE – CLAY 4. Calculate p6 Determination of penetration depth of sheet pile (D) p6.D2 + 2.p6.D.(L1+L2-l1) – 2.P1.(L1+L2-l1-z1) = 0 Determination of anchor force F = P1 – p6 . D

CALCULATION STEPS ANCHORED SHEET PILE – FIXED – SAND J

CALCULATION STEPS ANCHORED SHEET PILE – FIXED – SAND 1. Determine the value of Ka and Kp 2. Calculate p1and p2 with L1 and L2 are known 3. Calculate L3

CALCULATION STEPS ANCHORED SHEET PILE – FIXED – SAND 4. determine L5 from the following curve (L1 and L2 are known)

CALCULATION STEPS ANCHORED SHEET PILE – FIXED – SAND 5. Calculate the span of the equivalent beam as l2 + L2 + L5 = L’ 6. Calculate the total load of the span, W. This is the area of the pressure diagram between O’ and I 7. Calculate the maximum moment, Mmax, as WL’/8

CALCULATION STEPS ANCHORED SHEET PILE – FIXED – SAND 8. Calculate P’ by taking the moment about O’, or 9. Calculate D as 10. Calculate the anchor force per unit length, F, by taking the moment about I, or (moment of area ACDJI about O’) (moment of area ACDJI about I)

BRACED CUT Type of Braced cut

BRACED CUT Type of Braced cut

PRESSURE ENVELOPE Cuts in Sand pa = 0.65HKa Where:  = unit weight H = height of the cut Ka = Rankine active pressure coefficient = tan2(45-/2)

PRESSURE ENVELOPE Cuts in Stiff Clay pa = 0.2H to 0.4H Which is applicable to the condition

PRESSURE ENVELOPE Cuts in Stiff Clay The pressure pa is the larger of Which is applicable to the condition Where:  = unit weight of clay c = undrained cohesion (=0)

PRESSURE ENVELOPE Limitations: The pressure envelopes are sometimes referred to as apparent pressure envelopes. The actual pressure distribution is a function of the construction sequence and the relative flexibility of the wall. They apply to excavations having depths greater than about 20 ft (6m) They are based on the assumption that the water table is below the bottom of the cut Sand is assumed to be drained with zero pore water pressure Clay is assumed to be undrained and pore water pressure is not considered

PRESSURE ENVELOPE Cuts in Layered Soil Where: H = total height of the cut s = unit weight of sand Hs = thickness of sand layer Ks = a lateral earth pressure coefficient for the sand layer (1) s = friction angle of sand qu = unconfined compression strength of clay n’ = a coefficient of progressive failure (ranging from 0.5 to 1.0; average value 0.75) c = saturated unit weight of clay layer

PRESSURE ENVELOPE Cuts in Layered Soil Where: c1, c2,…,cn = undrained cohesion in layers 1,2,..,n H1, H2,…,Hn = thickness of layers 1, 2, …, n 1, 2, … n = unit weight of layers 1, 2, … , n

DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT Struts Should have a minimum vertical spacing of about 9 ft (2.75 m) or more. Actually horizontal columns subject to bending The load carrying capacity of columns depends on the slenderness ratio. The slenderness ratio can be reduced by providing vertical and horizontal supports at intermediate points For wide cuts, splicing the struts may be necessary. For braced cuts in clayey soils, the depth of the first strut below the ground surface should be less than the depth of tensile crack, zc

DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT Struts General Procedures: Draw the pressure envelope for the braced cut

DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT Struts General Procedures: 2. Determine the reactions for the two simple cantilever beams (top and bottom) and all the simple beams between. In the following figure, these reactions are A, B1, B2, C1, C2 and D

DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT Struts General Procedures: The strut loads may be calculated as follows: PA = (A)(s) PB = (B1+B2)(s) PC = (C1+C2)(s) PD = (D)(s) where: PA, PB, PC, PD = loads to be taken by the individual struts at level A, B, C and D, respectively A, B1, B2, C1, C2, D = reactions calculated in step 2 s = horizontal spacing of the struts 4. Knowing the strut loads at each level and intermediate bracing conditions allows selection of the proper sections from the steel construction manual.

DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT Sheet Piles General Procedures: Determine the maximum bending moment Determine the maximum value of the maximum bending moments (Mmax) obtained in step 1. Obtain the required section modulus of the sheet piles Choose the sheet pile having a section modulus greater than or equal to the required section modulus

DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT Wales Where A, B1, B2, C1, C2, and D are the reactions under the struts per unit length of the wall

EXAMPLE Refer to he braced cut shown in the following figure: Draw the earth pressure envelope and determine the strut loads. (Note: the struts are spaced horizontally at 12 ft center to center) Determine the sheet pile section Determine the required section modulus of the wales at level A (all = 24 kip/in2)

EXAMPLE

EXAMPLE

EXAMPLE

EXAMPLE