Remaining topics in V.N.S MURTHY 2

1. THIXOTROPY OF CLAYS When clays with a flocculent structure are used in construction,

these may lose some strength as a result of remoulding. With passage of time, however, the strength increases, though not back to the original value. This phenomenon of strength loss-strength gain, with no change in volume or water content, is called ‘Thixotropy’. This may also be said to be “a process of softening caused by remoulding, followed by a time-dependent return to the original harder state”.The loss of strength on remoulding is partly due to the permanent destruction of the structure in the in-situ condition, and partly due to the reorientation of the molecules in the adsorbed layers. The gain in strength is due to the rehabilition of the molecular structure of the soil. The strength loss due to destruction of structure cannot be recouped with time.

‘Thixis’ means the tough, the shaking, and ‘tropo’ means to turn, to change. Thus, thixotropy means “to change by touch”; it may also be defined, basically, as a reversible gel-sol-gel transformation in certain colloidal systems brought about by a mechanical disturbance followed by a period of rest.

The loss in strength on remoulding and the extent of strength gain over a period of time are dependent on the type of clay minerals involved; generally, the clay minerals that absorb large quantities of water into their lattice structures, such as montmorillonites, experience greater thixotropic effects than other more stable clay minerals.

For certain construction situations, thixotropy is considered a beneficial phenomenon,since with passage of time, the earth structure gets harder and presumably safer. However, it has its problems—handing of materials and equipments may pose difficulties. Thixotropic influences have affected piles, a type of foundation construction, driven in soils. The disturbance may cause temporary loss in strength of the surrounding soil. Driving must be fully done before thixotropic recovery becomes pronounced. Thixotropic fluids used in drilling opoperations are called ‘drilling muds’2. MAJOR SOIL DEPOSITS OF INDIA

The soil deposits of India can be broadly classified into the following five types:

o Black cotton soils, occurring in Maharashtra, Gujarat, Madhya Pradesh, Karnataka,parts of Andhra Pradesh and Tamil Nadu. These are expansive in nature. On account of high swelling and shrinkage potential these are difficult soils to deal with in foundation design.

o Marine soils, occurring in a narrow belt all along the coast, especially in the Rann of Kutch. These are very soft

Prepared by: Krishan H.Pandya ,B.E 5th Sem Civil (GTU) , 4/11/2023

Remaining topics in V.N.S MURTHY 2

and sometimes contain organic matter, possess low strength and high compressibility.

o Desert soils, occurring in Rajasthan. These are deposited by wind and are uniformly graded.

o Alluvial soils, occurring in the Indo-Gangetic plain, north of the Vindhyachal ranges.

o Lateritic soils, occurring in Kerala, South Maharashtra, Karnataka, Orissa and West Bengal..

Prepared by: Krishan H.Pandya ,B.E 5th Sem Civil (GTU) , 4/11/2023