project assignment 7302eng 2010 1

7/28/2019 Project Assignment 7302ENG 2010 1

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Project Assignment _______ ___________________ 7302ENG (2010)

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Laterally loaded piles and pile groups(Project Assignment)

Aim

To understand and analyses nonlinear response of piles and pile groups. To assist you master relevant principles studied in the course.

Question AA steel pipe pile was tested in a stiff clay near Manor (Reese et al 1975). Guo (2006)

provided the following: The pile was 14.9 m in length (L), and 0.641 m in diameter (d). The moment of

inertia, I p was 2.335 10 -3 m4, and the flexural stiffness, E p I p was equal to 493.7MN-m 2.

The undrained shear strength, C u of the clay increases linearly from 25 kPa at theground level to 333 kPa at depth 4.11 m. In the plot of p u/(d C u), however, the C u

was simply taken as 153 kPa. The submerged unit weight, s was 10.2 kN/m 3. Subgrade modulus k was estimated as 331.3 MPa. L c/r o was estimated as 10.8,thus the pile was infinitely long. Note c = 545.1, ratio of the shear modulus over the undrained strength, G s/Cu;

The pu profile was estimated by using J = 0.92, and then modified using the depthfactor suggested by Reese. The LFP thus obtained can be described by using N g = 0.961, N co = 0.352, and n = 1.0, which is plotted in Fig. 1(a) as Stiff clay ( J =0.92). Using this LFP, good predictions of the pile responses to a load level of 450 kN are achieved against the measured data (Fig. 1).

To improve the overall predictions, an excellent back-estimation was undertakenwhich rendered the three parameters N

g , N

co, and n to be adjusted to 0.854, 0, and 1.5,

respectively. The slip was initiated upon loading, thus the back-figured LFP is rational. Bending moment profiles were computed for lateral loads of 179.7, 317.7,

485.6, and 606.2 kN, respectively.With N g = 0.854, N co= 0, and n = 1.5, using the simple expressions developed by Guo(2006), such as those in Appendix I, calculate load, groundline deflection, depth of maximum bending moment, and maximum bending moment.(Hint: slip depth x p may be taken as 0.1, 0.3, 0.5, 0.8, 1.0, 1.3, 1.6, 1.9, 2.1, 2.5, 2.8)

Question B

Four of the steel pipe piles will be tested near Manor. The piles and soil are assumed to have identical properties to those shown in Question A.If the piles have a rigid pile cap, and are installed at a pile center-center spacing of 3

pile diameters. Predict pile-head loadgroundline displacement curve, and pile-head load maximum bending moment curve for the pile group. (Note the pile cap is justabove ground surface, the loading eccentricity may be taken as zero). (Hint: studycarefully the example given by Guo (2010)).


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5

4

3

2

1

0

0 2 4 6 8 10

xp

=2.71 m

(a) pu

pu

/(Cud)

x / d

Stiff clay (J =0.92)

n =1.5 &Different

c

0

250

500

750

0 10 20 30

xp

=2.71 m

wg

(mm)

P ( k N )

Stiff clay ( J =0.92)n =1.5Different cMeasured

(b) P - wg

0

250

500

750

0 500 1000 1500

xp =2.71 m

-M max

(kN-m)

P ( k N )

Stiff clay (J =0.92)n =1.5Measured

(c) P - M max

8

6

4

2

0

0 -500 -1000 -1500

(d) Bending moment profiles

IIIIIIIV

M max

(kN-m)

D e p t h

, ( m

)

n =1.5Measured

Pile-head load:I: 606.2 kN II: 485.6 kNIII: 317.7 kN IV: 179.7 kN

Fig. 1 Comparison between the calculated and measured (Reese et al 1975) responseof the Manor test


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APPENDIX I Simplified expressions (at o = 0, and N = 1)

Provided that o = 0, and N = 1 (i.e. N = 1), The following expressions may be used to predicted pile head- load, P, ground line deflection wg, and .

)2)(1)(1()]2(2)2)(1[(5.01

+++++++++=+

nne x xn xnn x

AP

p

p pn p

L

n (1)

enne x

xn x xn x

e x

x x x

nne x

nn xn x x

A

k w

p

p p p p

p

n p p p

p

p pn p

L

ng

)4)(1)(1(

)]1)(1(2)[1)(4(2

1

)122(

)4)(2)(1(

209)102(232

24

2223

+++++++++++

+++++

+++++++++= +

(2)

)1](2)2(22[)1)(2(2)1)(2()1(2)2(2)( 2

2

++++++++++++++=

nn xn xen xnnn xnen x x

p p p

p p p (3)

Under the above-mentioned conditions, constants C 1( p x ), and C 3( p x ) are given by

++++

+++

++= p p p

p

n p

p xn

xne

n xn

e x

x xC

222

121

1

5.0)(1

n p p x xC 5.0)(2 = (4)

(a) If )( p x > 0, then zmax > 0. The maximum moment M max should occur in elastic

zone, thus it locates at a depth (measured from mudline) that is equal to x p + zmax . Thevalue of M max may be estimated using Eq. (5) by replacing z with zmax , i.e. M max = M B(zmax).

]sin)(cos)([)( 21 z xC z xC e z M p p z

B += (5)

Eq. (3) allows the normalised slip depth, p x (rewritten as x ) at ( x ) = 0 to beobtained as

)2(2]12

[5.01

)2(5.0 2' +++++

++= ne

nn

en

n x (6)

The condition of p x > x will lead to )( p x < 0, thus maximum bending momentshould occur above the slip depth.The estimation using abovementioned expressions is referred to as S. Eqs. It can bereadily undertaken in a spreadsheet, similar to the form shown in Table 4 for pile A(Guo 2006).

Submission of the DesignFRI 3 PM (Week 14), in Assignment Box (Outside School Office). Latesubmission 10% off per day late. > 1 week late, zero.


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Report of the DesignThe assignment should be around 3 (A4) pages, but use plenty of diagrams, and

spread it out.Individual, not team. Weighting 45%.

Presentations Your name, subject, and name of assessment item are essential. No need for plastic pockets, folders, cover sheets etc on small assignments

project assignment 7302eng 2010 1

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