SUITABILITY OF NATURAL SOIL FOR ROAD WORK.

In order to determine the suitability of a particular soil it is essential to know the proportion of each material in the soil and also whether the particular material possesses the properties required of it. And for instance a road soil that is 95 percent sand will not cohere, and a clay that does not possess the property of cohesion is useless as a road material and will do nothing but make dust. The following field tests can be made. (1) To find proportion of sand in the soil:-- Dry soil sample is weighed and put it in the glass and fill with water. Agitate the same and pour off the clay and do it several times till the sand remains in the glass and dry the sand and weigh it. The result will give percentage of sand in the soil. The remainder is clay and silt. (2) To determine the proportion of clay and silt :-- Silt is generally darker in colour than clay and a sample that contains too high a percentage of silt will have not the characteristics brown colour of clay. Silt settles more rapidly than clay. If the sample is put into a glass and mixed with water and allowed to settle the clay will remain muddy while the silt will settle with in a few seconds. A sample that clears very quickly has too much silt some clay should be added to it. (3) Qualities of Clay:-- Pure clay is very retentive of moisture and becomes plastic and unstable when wet, and as it abrades easily, produces all dust when dry. The extent to which these objections occur depends on whether the clay is of the shaking or non shaking variety. The shaking variety is undesirable as it is more muddy in wet weather and more dusty in dry weather. The qualities of the various clays by shaking test may be obtained by making several balls of the same size of the different clays and dry them out and place them in water so that they are covered entirely. The balls which hold their shape longest after being placed in water have the highest resistance to shaking and that clay is preferred to be use in the road. It is important in this test that if various clays are being compared, the proportion of sand in each sample should be the same and should not exceed more than 25 percent and if sand is more it should be removed before doing the shaking test. If the clay is of the shaking variety the balls will disintegrate almost as soon as they are put in water, such a clay is not suitable for road work. Samples that contains too much silt will not show good non shaking qualities and will break up at once in the water. Clay requires to be added in such samples.