Environmental Engineering Reference
In-Depth Information
3.0
Equation X.8, COV = 0.4 (5% fractile)
2.5
2.0
Equation X.22, COV = 0.4
Equation X.9, COV = 0.4 (Schneider,
1.5
Equation X.21, COV = 0.1
1.0
0
10
20
30
40
50
60
Vertical extent of failure mechanism, L z
Figure 10.5 Variation in correlation factor ξ to calculate the characteristic value with the vertical extent of
failure mechanism.
It is also a Eurocode 7 requirement, as noted in Section 10.4.3.1, to take into account
other background information and data from other projects when selecting characteristic
parameter values. The use of a Bayesian analysis allows such background information and
prior knowledge of ground conditions to be taken into account.
10.4.3.4 Example 10.1: Selection of characteristic parameter values
A 12-m long pile with a diameter of 0.8 m is to be installed in a homogeneous deposit of
clay. From the results of field and laboratory tests on the clay, and also taking account of
other information and local experience, the mean undrained shear strength was determined
to be c u;mean = 40 kPa. The characteristic undrained shear strength c u;k along the pile shaft
and at the base of the pile are required for the design of the pile.
Solution
Based on the information in Table 10.4 , the COV inher of c u is assumed to be 0.4. The extents
of the failure mechanism along the pile shaft, with diameter D = 0.8 m, are L z = 12 m verti-
cally and L scurve = πD = π0.8 = 2.5 m circumferentially. Using Equation 10.16 with L z = 12 m
and δ z = 2.0 m, the reduction factor in the vertical direction Γ 2
= .1528 and using Equation
10.14 with L scurve = 2.5 m and δ
=
δ δ
=
50 0 00
.
×
.
=
50 0
.,
the reduction factor
scurve
xy
in the horizontal direction around the pile circumference Γ scurve
2
= .
9675 Using Equation
.
10.18 , the reduction factor for the pile shaft ΓΓΓ
S
. . . .
Hence, using Equation 10.22 for a log-normal distribution and with COV = 0.4, the cor-
relation factor ξ = 1.29. Using Equation 10.23 , the characteristic undrained shear strength
along the pile shaft is therefore
2
=
2
2
=
0 1528
×
0 9675
=
0 1478
z
scurve
c u;k = c u;mean /ξ = 40/1.29 = 30.9 kPa
Ignoring the lateral extent of the failure mechanism along the pile shaft, which is a con-
servative assumption, so that ΓΓ
x
==. and adopting Schneider and Schneider's (2103)
Equation 10.19 with L z =12 m and δ z =2 m gives Γ 2
2
2
10
y
= .
1574 Using Equation 10.22 with
.
 
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