UNCERTAINTY AND RELIABILITY - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 113

During the 4 th conference of the Application of Stress-Wave Theory to Piles, in
1992, a similar contest was organised. Four concrete piles with different shape
were dynamically tested and 9 international experts made a prediction for the static
bearing capacity, each using his tool and interpretation method. In Fig 8.5b results
are presented. The scatter is striking. The Test Report states that the interpretation
method and type of software were more important for the variation in answers than
the difference in monitoring systems. Moreover, surprisingly, local experience was
not particularly helpful for obtaining more reliable predictions.

Slope stability
In 2008 a large dike on soft clay and peat was tested for slope stability (Fig 8.6).
An international prediction contest was organised and 40 independent experts took
a chance to estimate at which of the 8 phases the dike would collapse. The collapse
occurred in phase 4, The prediction results show (Fig 8.6, Table) that the wide
spread is mainly related to engineering choices and that the use of standard or
sophisticated models does not make much of a difference.

containers containers

IJKDIJK test IJKDIJK test

clay cover clay cover

sand core sand core

ditch ditch

peat and clay peat and clay

29 September 2008 29 September 2008

Predictions made by experts of the phase of collapse
Phase

Predictions made by experts of the phase of collapse
Phase Phase description Phase description Experts Experts Method Method

1
2
3
4
5
6
7
8

1
2
3
4
5
6
7
8

-
E
-
E S P
E S
E S P
E S
E
E: educated guess, S: slip circle analysis, P: FEM (Plaxis)

-
E
-
E S P
E S
E S P
E S
E
E: educated guess, S: slip circle analysis, P: FEM (Plaxis)

before the test
digging the ditch
deepening the ditch
waterfilling sand core
emptying the ditch
filling containers
saturating the dike
no failure

before the test
digging the ditch
deepening the ditch
waterfilling sand core
emptying the ditch
filling containers
saturating the dike
no failure

1
1
1
6
10
13
4
4

1
1
1
6
10
13
4
4

Figure 8.6 Slope stability test

Sheet piling
In 1993, in Karlsruhe, a sheetpiling test was organised (Wolffersdorff). The
behaviour of a strutted sheetpiling retaining 4 m of non-saturate sand was