S048436854.PPT

Session 15 16 SHEET PILE STRUCTURESCourse: S0484/Foundation EngineeringYear: 2007Version: 1/0

SHEET PILE STRUCTURESTopic:Anchored Sheet PileBraced Cut

CALCULATION STEPSANCHORED SHEET PILE FREE SAND

CALCULATION STEPSANCHORED SHEET PILE FREE SAND1. Determine the value of Ka and Kp2. Calculate p1and p2 with L1 and L2 are known3. Calculate L34. Calculate P as a resultant of area ACDE5. Determine the center of pressure for the area ACDE ( z )

CALCULATION STEPSANCHORED SHEET PILE FREE SANDDetermination of penetration depth of sheet pile (D)Dtheoretical = L3 + L4Dactual = (1.3 1.4) DtheoreticalDetermination of anchor forceF = P [(Kp Ka)]L426. Calculate L4

CALCULATION STEPSANCHORED SHEET PILE FREE CLAY

CALCULATION STEPSANCHORED SHEET PILE FREE CLAY1. Determine the value of Ka and Kp2. Calculate p1and p2 with L1 and L2 are known3. Calculate the resultant of the area ACDE (P1) and z1 (the center of pressure for the area ACDE)In case of saturated soft clay with internal friction angle () = 0, we gotKa = Kp = 1

CALCULATION STEPSANCHORED SHEET PILE FREE CLAYDetermination of penetration depth of sheet pile (D)p6.D2 + 2.p6.D.(L1+L2-l1) 2.P1.(L1+L2-l1-z1) = 0Determination of anchor forceF = P1 p6 . D4. Calculate p6

CALCULATION STEPSANCHORED SHEET PILE FIXED SANDJ

CALCULATION STEPSANCHORED SHEET PILE FIXED SAND1. Determine the value of Ka and Kp2. Calculate p1and p2 with L1 and L2 are known3. Calculate L3

CALCULATION STEPSANCHORED SHEET PILE FIXED SAND4. determine L5 from the following curve (L1 and L2 are known)

CALCULATION STEPSANCHORED SHEET PILE FIXED SAND5. Calculate the span of the equivalent beam as l2 + L2 + L5 = L6. 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 STEPSANCHORED SHEET PILE FIXED SAND8. 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 CUTType of Braced cut

BRACED CUTType of Braced cut

PRESSURE ENVELOPECuts in Sandpa = 0.65HKaWhere: = unit weightH = height of the cutKa = Rankine active pressure coefficient = tan2(45-/2)

PRESSURE ENVELOPECuts in Stiff Claypa = 0.2H to 0.4HWhich is applicable to the condition

PRESSURE ENVELOPECuts in Stiff ClayThe pressure pa is the larger of

Which is applicable to the conditionWhere: = unit weight of clayc = undrained cohesion (=0)

PRESSURE ENVELOPELimitations: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 cutSand is assumed to be drained with zero pore water pressureClay is assumed to be undrained and pore water pressure is not considered

PRESSURE ENVELOPECuts in Layered SoilWhere:H = total height of the cuts = unit weight of sandHs = thickness of sand layerKs = a lateral earth pressure coefficient for the sand layer (1)s = friction angle of sandqu = unconfined compression strength of clayn = a coefficient of progressive failure (ranging from 0.5 to 1.0; average value 0.75) c = saturated unit weight of clay layer

PRESSURE ENVELOPECuts in Layered SoilWhere:c1, c2,,cn = undrained cohesion in layers 1,2,..,nH1, H2,,Hn = thickness of layers 1, 2, , n1, 2, n = unit weight of layers 1, 2, , n

DESIGN OF VARIOUS COMPONENTS OF A BRACED CUTStrutsShould have a minimum vertical spacing of about 9 ft (2.75 m) or more.Actually horizontal columns subject to bendingThe load carrying capacity of columns depends on the slenderness ratio.The slenderness ratio can be reduced by providing vertical and horizontal supports at intermediate pointsFor 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 CUTStrutsGeneral Procedures:Draw the pressure envelope for the braced cut

DESIGN OF VARIOUS COMPONENTS OF A BRACED CUTStrutsGeneral 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 CUTStrutsGeneral 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, respectivelyA, B1, B2, C1, C2, D = reactions calculated in step 2s = 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 CUTSheet PilesGeneral Procedures:Determine the maximum bending momentDetermine 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 CUTWalesWhere A, B1, B2, C1, C2, and D are the reactions under the struts per unit length of the wall

EXAMPLERefer 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 sectionDetermine the required section modulus of the wales at level A (all = 24 kip/in2)

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