IS:l!M4-1986
injurious compound in the ground water and soil. The site should also be
explored in detail, where necessary, to ascertain the type consistency, thick-
ness, sequence and dip of the strata.
5.3 Mass movements of the ground are liable to occur from causesinde-
pendent of the loads imposed by the structure. These include mining
subsidence, land slips,
unstable slopes and creep on clay slopes.
These factors shall be observed in detail during site investigation and
taken into account in the layout and design of the proposed works.
However, if necessary, expert advice regarding the geological and hydro-
logicai characteristics of the site shall be sought.
5.3.1 Mining subsidence is liable to occur in mining areas. The magni-
tude of the movement and its distribution pver the area of the workings
and their vicinity can be roughly estimated. Where future subsidence is
likely, care should be taken to design the superstructure and foundation
sufficiently strong or sufficiently flexible to cater for probable ground
movements. Long continuous buildings should be avoided and large
building should be divided into independent
sections of suitable size, each
with its own foundations. Expert advice from appropriate mining autho-
rity should be sought.
5.3.2 Cuttings, excavations or sloping ground near foundations may
increase the possibility of shear failure in the ground supporting the
foundations.
On sloping ground on clay soils there is always a tendency for the
upper layers of soil to move downhill, the extent, however, depends on the
type of soil, the angle of slope, ground water regime and climatic condi-
tions. Instability may develop even after a long period of apparent
stability, particularly in stiff, fissured and over consolidated clay soil.
Uneven surface of a slope on virgin ground, curved tree trunks,
tilted fence posts, tilted boundary walls, etc, indicate the creep of the sur-
face layers. Areas subject to land slip and unstable slopes shall, therefore,
be avoided.
5.3.3 Some clayey soils are susceptible to shrinkage and cracking in dry
and hot weather, and swelling in wet weather. These conditions are simu-
lated, sometimes, by extraneous agencies like trees, boiler installations,
furnaces, kilns, underground cables, services and refrigeration installations.
These factors shall be studied carefully before designing any foundations.
Shrinkage of clay soils may be increased by the drying effect produced by
nearby trees and shrubs. Swelling may occur, if they are cut down. NO
trees which grow to a large size shall be planted within 8 m of foundations
of buildings.
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