This document discusses techniques for constructing structures on swelling soils, including using a cohesive non-swelling (CNS) soil layer. It provides details on the CNS soil method proposed by Mr. Katti in 1978 to reduce the effects of swelling soil. The key steps are to remove the top layer of expansive soil and replace it with a CNS material like gravel. The CNS layer develops cohesive forces that help counter heaving from the soil below, while avoiding damage from the swelling soil above. Tests are needed to determine the optimal thickness of the CNS layer for different soil and material conditions. When using this method, the CNS layer should be non-swelling with low maximum swelling pressure and stabilized to

1. -Prepared by Mr. Pratik U. Mashale
(B.E. CIVIL A-28, NKOCET)
-Guided by Prof. S. B. More (CIVIL), NKOCET

2.  Introduction
 Causes of Swelling
 Remedies
 Cohesive non-swelling soil
 CNS Materials
 Construction procedure
 Conclusion

3.  Swelling soil or expansive soil are those soil which
have tendency to increase volume when water is
present and to decrease the volume when water is
not present.
 The soil which are not only cohesive but also having
swelling property, damages the structures.
 Foundations constructed on this type of soil are
subjected large uplift pressure caused by swelling.

4.  Structures like residential buildings, canal
linings, pavement of roads etc are severely
damaged due to alternative expansion and
shrinkage of cohesive swelling soil.
 Causes cracks, heaves and breakups of
structural parts.

7.  While constructing structure over such soil one
of following alternative can be used
 Extending foundation to larger depth
 Removal and replacement of soil
 Temporary surcharge (preloads)
 Vibro-compaction
 Chemical stabilization

8. There are many other techniques to
minimise swelling pressure but following
are the main techniques among them:
oCushion sand Method
oUse of under-reamed piles
o Cohesive Non-swelling soil

9.  In 1978, Mr Katti had proposed concept of using
cohesive non-swelling layer to reduce effect of
swelling.
 Cohesive forces develop up to a depth of 1.0 m
to 1.2 m with saturation of expansive soil, which
help to counter heave in the soil beneath even
through the soil within the zone itself swells.

10.  Actually, It is necessary to conduct large scale
tests to determine the optimum thickness of
CNS layer with available CNS material.
 The top layer of expansive soil is removed
and replaced by cohesive non-swelling soil
(CNS) layer, which was saturated later. .

11.  Gravel is good CNS material.CNS material may be
having cohesion but must not have
swelling/expansive property.
 Mr. Katti (1996) recommended the use of a
mechanically stabilized mix (MSM) to be placed on
the top of the CNS cushion to make soil strong
enough to bear the load.
 CNS material should be non-swelling with a
maximum swelling pressure of 10 kN/m2.

13. Construction
procedure

14.  While during construction, we should avoid
swelling/ expansive soil.
 CNS soil method is good and economic
method amongst other.
 CNS material should be of gravelly material.

15. Thank you !