Question

The time dependent settlement of ground is usually caused by the one dimensional consolidation of soil. (a) Complete the following statement by choosing the most appropriate words to fill the underlined spaces from the list of words below. "The phenomena of consolidation occur with soils in state.” List of words: both, either, mainly, only, and, or, saturated, partially saturated, wet, dry, compacted, loose, sandy, clayey. (7 marks) (b) After completing the above statement of yours, explain how the time dependent compression of an element of the soil will take place through the changes of which stresses. Use sketches if necessary. (8 marks) (C) Terzaghi's one dimensional consolidation theory is usually used to predict the time dependent settlement of ground. His theoretical equation expresses the time changes of stresses of a soil element. Then explain how this equation is used to predict the surface settlement of a soil layer which has a considerable thickness. (5 marks) There is a compressible soil layer of 3 m thickness underlain by a sand layer and will be surcharged by uniformed load of 100kPa by sand filling. Evaluate what the soil parameters are necessary to predict the total amount of settlement and the rate of settlement over the years. (5 marks) [Total: 25 marks]

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Answer 1

a) The phenomena clayey soils in of consolidation occur with saturated state. (6) Recompression for consoli dometer sample. A > Virgin compression curve x Reloading B Unloading F Role of stress history figure: Explanation of i when clay is tested in consolidometer AB the curre represents a soil that has never been subjected to compressive loads. i After the load has sleached represented by point B, the in unloaded stages. a value soil sample is

It can be seen that the unloading has not restored the soil to the original state. (iv) There will be a permanent deformation due to an irreversible alteration in the soil structure (v) The specimen is loaded again after the unloading. The reloading curve les slightly above the sebound curve and the two meet just before point B. (vii) It is observed that the reloaded soil is hot compressed as much as the soil that was not loaded before [viii) A busteresis Loop is formed between the unloading and reloading. (C) sample as shown in tigure consider a below LAV ko * tok eska figure (a) (b) Initial After state of sample compression Explanation

Then At the change in height of the consolidating over of its settlement is given by:- Hehe O teo Ан - so — Де Н іі) Iteo The coefficient of compressibility (aw) calculation can be found out by for settlement ava Ae sc = (av - Gi Ho A5 - (iv) teol mv-aveo - Ae (1) - (V) Sc=mu HAT - (vi) Thus it can be seen that magnitude of settlement is a function of soil compressibility mug boundary condition (Ho) and loading condition ardo compression index ((c) = de log (58150)

combining all the above equations, weget Sc - Ae Ho - Ho teo logo If Iteo Here, To is the present effective overburden Pressure and I tot additional stress at induced by an imposed load, thus Sco Ho log. To tar teo where, Sc - - lo - surface settlement compression index Initial voia ratio (d) the following are the parameter to predict Total settlement :- i, compression index (CC) cc = de point (o) Togo (22/5) (11) Thickness of compressible layer (H) (ii) Initial voia ratio of soil (eo) iu) overburden pressure at the particular (v) Increase in effective stress (45) (vi) Time factor (Tv) vii l length of drainage path (d) Clip coefficient of consolidation (C)