Unformatted text preview: Indian Standard (Part I) was adopted by the Indian
Standards Institution on 5 October 1981, after the draft finalized by
the Foundation Engineering Sectional Committee had been approved
by the Civil Engineering Division Council.
0.2 Raft foundation is a substructure supporting an arrangement of
columns or walls in a row or rows and transmitting the loads to the soil
by means of a continuous slab with or without depressions or openings.
Such types of foundations are found useful where soil has low bearing
capacity. This standard was first published in 1965 and revised in
1973. In this revision, besides making its contents up-to-date,
guidelines have been given to choose particular type of methods in
particular situations and giving reference to finite difference method
which will be covered at a later stage.
0.3 This edition 3.1 incorporates Amendment No. 1 (December 1988).
Side bar indicates modification of the text as the result of
incorporation of the amendment.
0.4 For the purpose of deciding whether a particular requirement of
this standard is complied with, the final value, observed or calculated,
expressing the result of a test, shall be rounded off in accordance with
IS : 2-1960*. The number of significant places retained in the rounded
off value should be same as that of the specified value in this standard.
1.1 This standard (Part I) covers the design of raft foundation based on
conventional method (for rigid foundation) and simplified methods
(flexible foundation) for residential and industrial buildings,
store-houses, silos, storage tanks, etc, which have mainly vertical and
evenly distributed loads.
*Rules for rounding off numerical values ( revised ). 3 IS : 2950 (Part I) - 1981
2.1 For the purpose of this standard, the definitions of terms given in
IS : 2809-1972* shall apply.
3. NECESSARY INFORMATION
3.1 For satisfactory design and construction of a raft foundation, the
following information is necessary:
a) Site Plan — Site plan showing the location of the proposed as
well as neighbouring structure.
b) Building plan and vertical cross-sections showing different floor
levels, ducts and openings, etc, layout of load bearing walls,
columns, shear walls, etc.
c) Loading conditions preferably shown on a schematic plan
indicating design combination of loads transmitted to the
d) Environmental Factors — Information relating to geologic history
of the area, seismicity of the region, hydrological information
indicating ground water conditions and its seasonal variations,
climatic factors like vulnerability of the site to sudden flooding by
surface run-off, erosion, etc.
e) Geotechnical Information — Giving subsurface profile with
stratification details ( see IS : 1892-1979† ), engineering
properties of the founding strata, namely, index properties,
effective shear parameters determined under appropriate
drainage conditions, compressibility characteristics, swelling
properties, results of field tests like static and dynamic
penetration tests, pressure meter tests, etc.
f ) Modulus of Elasticity and Modulus of Subgrade Reaction —
Appendix A enumerates the methods of determination of modulus
of elasticity ( Es ) and Poisson’s ratio ( µ ). The modulus of subgrade
reaction ( k ) may be determined in accordance with Appendix B.
g) Limiting values of the angular distortion and differential
settlement, the superstructure can withstand ( see IS : 19041987‡ ).
h) A review of the performance of a similar structure, if any, in the
*Glossary of terms and symbols relating to soil engineering ( first revision ).
†Code of practice for subsurface investigations for foundations ( first revision )....
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- Spring '13
- Geotechnical Engineering, raft foundation, Contact pressure