Skip to main content

Short Note on Cohesion ans Adhesion



 Cohesion and Adhesion:
Cohesion is the property of like molecules (of the same substance) to stick to each other due to mutual attraction. The water forms a dome-like shape above the rim of the glass when filled. This dome-like shape forms due to the water molecules’ cohesive properties, or their tendency to stick to one another. Cohesion refers to the attraction of molecules for other molecules of the same kind, and water molecules have strong cohesive forces. Surface tension is the result of cohesive forces between adjacent molecules. The molecules in the bulk of a liquid are pulled equally in all directions by the neighboring molecules. But the surface molecules do not have molecules on all sides. Surface tension can cause the capillary action in the soil so that water in soil pore rises to a certain height above the ground water table.

Adhesion is the property of different molecules or surfaces to cling to each other. For example, solids have high cohesive properties so they do not stick to the surfaces they come in contact. On the other hand, gases have weak cohesion. Water has both cohesive and adhesive properties. Water molecules stick to each other to form a sphere. This is the result of cohesive forces. When contained in a tube, the water molecules touching the surface of the container are at a higher level. This is due to the adhesive force between the water molecules and the molecules of the container.
Cohesive soil is a type of soil where there is inter-particular attraction. This adds to the shear strength of the soil. The main feature of such soil types are that their particles are very fine and they are governed by the surface forces rather than by their Self weight. Clay is a very good example for a cohesive soil. In pure cohesive soils, the friction between particles will not occur and hence their shear strength will be contributed by only cohesive force and not by internal friction.

Comments

Post a Comment

Popular posts from this blog

c program to display Nepals flag

/*Programme to display Nepali flag*/ # include <stdio.h> #include <stdlib.h> void main() { int i,j; for(i=1;i<=20;i++) { if(i<=8) { for(j=1;j<=8;j++) { if(j==1||i==j&&i<8) printf("* "); else if(i==8&&j>=3) printf("* "); else printf(" "); } } else if(i>8&&i<=12) { for(j=1;j<=7;j++) { if(i==12||j==1||i-j==5) printf("* "); else printf(" "); } } else if(i>12) printf("* "); printf("\n\n\n"); } }
Post a Comment
Read more

Short Note on Group Action of PIles

  Group Action of Piles: Piles are always used in groups. This is to ensure that the structural load from a member like a column or a wall lies within the zone of influence of foundation. If single driven pile is used as foundation, one cannot be certain that pile would be located centrally below the foundation element as quite often pile moves laterally during driving. Resultant eccentricity of loading may result in development of bending stress and pile may fail. So, minimum number of three pile is used under a column. The load is transferred to pile in group through a reinforced slab or beam called pile cap. When pile cap stand clearly above the ground level the pile group is called free standing pile group. The pile spacing mainly controls the behavior of pile groups. The spacing should not be too small so that upheaval of ground surface takes place during driving into dense or incompressible material. On the other hand, if spacing is too large uneconomic pile cap may...
Post a Comment
Read more

Explain How the load carrying capacity of group of piles in clay is determined by “Block Failure Method”?

When piles are spaced at closer intervals, the soil contained between the pile move downward with the piles and at failure, pile and soil move together to give a typical block failure. Normally this type of failure occurs when the piles are spaced less than 2 to 3 times the pile diameter. For wide spacing pile in the group fails individually. In the absence of negative skin friction, the group capacity in clay is usually governed by the sum of the single pile capacities with some reduction due to overlapping zones of shear deformation in the surrounding soil. The following are design recommendations for estimating group capacity in clay: ·          For pile groups driven in clays with undrained shear strengths of less than 2,000 psf and for spacings of three times the average pile diameter, the group efficiency can be taken to be equal to seventy percent (70%). If the spacing is greater than six times the average pile diameter, then a ...
Post a Comment
Read more