18-07-2013, 02:54 PM
THE SINKING OF WELL FOUNDATIONS IN DIFFICULT SITUATIONS
THE SINKING OF WELL.pdf (Size: 118.33 KB / Downloads: 218)
ABSTRACT
Well foundations are quite appropriate foundations for alluvial soils in rivers and creeks where maximum depth of scour
can be quite large. In India technology of well foundation for design and construction is quite well developed. Still there
are situations where serious problems are encountered at site during construction of well foundations. Some of the typical
problems have been identified and solutions adopted by the author and also elsewhere in some earlier jobs have been
presented in this Paper.
INTRODUCTION
In the Indian subcontinent there are many rivers
where the depth of alluvial deposits is very high and the
scour around the pier foundations can be very deep if
the piers are located within the active channel of river.
For such condition well foundation is a very appropriate
type of foundation.
To the author’s knowledge one 3 km long Railway
bridge crossing a creek was supported on pile
foundations. After some years, the sway of the pile
foundations was so large when the mail trains crossed
the creek; the Railways not only reduced the speed of
the trains substantially but constructed another bridge
adjacent to this bridge on well foundations. Thus under
certain situation, well foundation is a highly desirable
type of foundation.
SINKING WELL THROUGH STIFF CLAY STRATA
If a very stiff clay layer is encountered during the
sinking of a well, the engineer has to face a very tough
and challenging situation if the well becomes stationery
and does not move at all.
At that time due to the action of horizontal water
current force, the well may start tilting. The well becomes
more vulnerable due to tilt if a step is provided on the
outside face of the well steining to reduce the thickness
of the steining. At the initial stage if the tilt is not brought
under control, the tilt goes on increasing making the
situation very difficult to control. This leads to a very
expensive and time-consuming affair for attempting to
make the well straight and vertical within practical limits.
CONCLUSION
On this paper a list of difficult situations, which bridge
engineers normally encounter during sinking of well
foundations, is presented. In some cases the author
himself devised some solutions to some perennial
problems, which have been described in this paper. The
problems like the formation of hump inside the dredge
hole of a well foundation or wells cracking due to sand
blow, or in a stiff clay layer wells becoming stationary
and not sinking down are quite common situations. In
several major projects where such situations developed
the author as the Technical Head of that organization,
developed methods and adopted them to overcome those
problems and these methods are presented in this paper.