UNCERTAINTY AND RELIABILITY - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 111

intuition and experience, if any, to decide how to appreciate this outcome and what
practical maximum displacement should be adopted for a proper design.

Physical processes
In reality, all possible and relevant physical processes do play a role, always. For
a simulation or prediction the engineer has to optimise his approach by making a
selection of the dominant processes and disregard physical processes, which are not
relevant. It is recommended to support such a choice by an elementary analysis or
by specific experiments. A striking example of the effect of choices of physical
processes is found in the application of well-functions in geohydrology. For a
constant well in a semi-confined aquifer system the Hantush well-function is
commonly applied. It encompasses flow and storage in the aquifer and leakage
through the adjacent aquitard. The outcome after calibration reveals the production
capacity Q and the corresponding area of influence, the leakage factor . This

approach is applicable for (deep) reservoirs and thin or rigid adjacent aquitards.

Hantush-Jacob Hantush-Jacob Barends Barends

B B

H H Q Q

consolidation consolidation

permeable permeable permeable permeable

aquitard aquitard

permeable
storage

permeable
storage

permeable permeable

aquifer aquifer

Physical processes; producti o n well in a semi-
aquifer

Physical processes; production well in a semi-
aquifer

confined a quifer confined aquifer

aquitard aquitard

permeable consolidation permeable consolidation

1 1

Choice Choice / /

permeable storage permeable storage

1 1 yes yes yes yes no no no no 1.00 1.00

2 2 yes yes yes yes yes yes no no 1.25 1.25

3 3 yes yes no no yes yes yes yes 3.45 3.45

well-functions: (1) Theis, (2) Hantush, (3) Barends well-functions: (1) Theis, (2) Hantush, (3) Barends

Figure 8.4 Pumping test

In shallow regions where semi-permeable aquitards are relatively young
deposits, the storage is due to induced consolidation (storage) in the aquitard;
storativity of the aquifer is less relevant. By applying a special well-function
(Barends) including this consolidation process, the outcome shows a value for

being about 3.45/1.25 = 2.76 times larger than with the standard Hantush function
(see Fig 8.4, Table). That the outcome of a constant well in a shallow semi-
confined aquifer system by applying Hantush well-function represents all expected
phenomena (storage, flow, leakance), is in fact misleading, since the storage is