Geotechnical Engineering

DHARM

88 GEOTECHNICAL ENGINEERING

40 kN/m^2. Classify the soil with regard to its sensitivity and indicate the possible structure of
the soil.

Unconfined compression strength in the undisturbed state, quu = 200 kN/m^2

Unconfined compression strength in the remoulded state, qur = 40 kN/m^2

Sensitiviy, St =

q

q

uu

ur

=

200

40

= 5

Since the sensitivity falls between 4 and 8, the soil may be soil to be “sensitive”. The
possible structure of the soil may be ‘honeycombed’ or ‘flocculent’.

SUMMARY OF MAIN POINTS

1. Certain physical properties such as colour, structure, texture, particle shape, grain specific grav-
   ity, water content, in-situ unit weight, density index, particle size distribution, consistency lim-
   its and related indices are termed index properties, some of which are useful as classification
   tests.


2. Grain specific gravity or the specific gravity of soil solids is useful in the determination of many
   other quantitative characteristics of soil and is, as such, considered basic to the study of
   geotechnical engineering. Water content assumes importance because the presence of water can
   significantly alter the engineering behaviour of soil.


3. Density index, which indicates the relative compactness, is an important characteristic of a
   coarse grained soil; it has bearing on its engineering behaviour.


4. Grain size analysis is a useful index for textural classification; it consists of sieve analysis appli-
   cable to coarse fraction and wet analysis applicable to fine fraction. Stokes’ law is the basis for
   wet analysis. Effective size and uniformity coefficient indicate the average grain-size and degree
   of gradation.


5. Consistency limits or Atterberg limits provide the main basis for the classification of cohesive
   soils; plasticity index indicating the range of water content over which the soil exhibits plastic-
   ity, is the most important index.


6. Activity, sensitivity and thixotropy are properties which are typical of cohesive soils.

REFERENCES

1. Allen Hazen: Some Physical Properties of Sands and Gravels, with Special Reference to Their Use
   in Filtration, 24th Annual Report of the State Board of Health of Massachusetts, U.S.A., 1892.


2. A. Atterberg: Die plastizität der Tone, Internationale Mitteilungen für Bodenkunde, Vol. I, no. 1,
   Verlag für Fachliteratur G.m.b.H., Berlin, 1911.


3. D.M. Burmister: Principles and Techniques of Soil Identification, Proceedings, Annual Highway
   Research Board Meeting, Washington, D.C., 1949.


4. IS: 460-1978: (Second Revision) Specifications for Test Sieves.


5. IS: 2720 (Part-II)—1973: Methods of Test for Soils—Part II Determination of Moisture Content.


6. IS: 2720 (Part-III)—1980 First Revision: Methods of Test for Soil—Part III Determination of
   Specific Gravity (Section 1 and 2).