Highway Practicals

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SOIL TESTSNATURAL MOISTURE CONTENT OF SOIL Objective To determine the amount of water present in fresh soil expressed as a percentage of the mass of the dry soil. Introduction Moisture content of soil is the amount of water within the pore spaces in soil grains. Natural moisture content is the amount of water in freshly obtained soil in its natural state. It is determined by oven-drying the soil at a temperature not exceeding greatly influences the behavior of soil. Standard reference BS 1377:1990 Apparatus Soil sample Weighing balance Metal cans Drying oven at temperature of . . Moisture content

Procedure Collect a fresh soil sample and divide into four parts by using a rifle box. This will provide the soil from which the samples for the oven will be taken. Clean and dry the moisture cans and weigh each, recording their respective weights. Fill each moisture can with soil from each soil heap and weigh the cans again. Record their weights.

Place the soils samples into the oven for a minimum of 12 hours. Remove the samples and weigh them again. Record the results in a suitable table. Treatment of resultssample Mass of soil + can (m1) Mass of dry soil + can (m2) Mass of can (m3) Mass of water Moisture content (%) 42.5 1.5 4.5 11 41 1 4 10 53.5 1 4.5 8.6 62 1 5 8.2 48.5 1 5 10.5 47 45 58 67 53.5 A B C D E

Calculation Compute the moisture content W of the specimen as a percentage of the dry soil mass from the equation:

Moisture content of the soil is 9.7%.

PARTICLE SIZE DISTRIBUTION Particle size distribution is a necessary classification of soils because it shows the relative distribution of particle sizes in a particular soil type. It makes it possible to determine whether soils are predominantly gravel, sand, clay or silt which will also affect the engineering properties of the soil. Introduction Wet sieving is performed in order to remove the clay and silt particles in the soils. The soil is first washed on a 75m sieve and the soil retained is oven-dried to obtain the soil that is passed through the series of sieves to determine the distribution. The results obtained are plotted on a graph with a logarithmic scale and the soil classified by identifying the distribution as being gravel or sand. Apparatus Test sieves Tray Evaporating dish Balance Sieve brushes Drying oven

Procedure First prepare the test sample by air drying soil for over 12 hours. Take a representative sample from the heap of about 2.5kg by rifling. Sieve the sample through the 20mm sieve. This may be skipped since the rifle box apertures are 20mm.

Take the sample and wash it through the 75m sieve. This washes out the clay and silt particles from the sample. Transfer the retained material from the sieve to an evaporating dish which is placed in an oven at for 24 hours to ensure complete drying of the sample. Weigh the dry sample.

Stack the sieves in decreasing in order of decreasing aperture size and then pass the soil through the sieves either mechanically or manually. Weigh the mass of soil retained on each sieve and then plot the particle sizes against percentage passing on a graph with a logarithmic scale. Treatment of results Obtain the total mass on all the sieves. Find the difference between the original mass and the retained sample mass.

Grade the soil from the results plotted on the graph. Classification gravelly sandweight sieve 14.0m m 10.0m m 2.36m m 1.18m m 600 m 300 m 150 m retained 86 161.5 925 148 110 156.5 104.5 % retained 4.8 9.1 51.9 8.3 6.2 8.8 5.9 % passing 95.2 86.1 34.2 25.9 19.7 10.9 5

75m Pan Total

65.5 25 1782

3.7 1.4 100

1.3 0

Discussion of results 18g of the soil was lost during the analysis. This is due to the particles that get stuck in the sieve spaces and the others that fall out of the sieves during the sieving process and transfer to the weighing pans. The soil is gravelly sand because more than 70% of the particles lie in the region of gravel and the remaining percentage is sand. Conclusion From the results of the particle size distribution it can be concluded that the soil is suitable for use as highway sub-base.

LIQUID LIMIT- CONE PENETROMETER METHOD Objective The liquid limit is the moisture content at which soil passes from the liquid to plastic state. The liquid limit provides a method of classifying fine grained soils since the smallest 10% fines determine the properties of the soil such as the shear strength. Introduction The cone penetrometer test involves determining the liquid limit of a soil sample in its natural state. The soil used is passed through a 425m sieve. The soil is penetrated using a standard cone and the penetration measured. Apparatus 425m sieve Flat glass plate Spatulas Cone penetrometer An airtight container Metal cup Wash bottle containing clean water Procedure-sample preparation Pass the soil sample through 425m sieve until about 400g of sample are collected. This is sufficient for the plastic limit, liquid limit and linear shrinkage tests. Place the sample on the glass plate and mix it with water from the wash bottle. Using the spatula, mix the sample into a paste. Store the sample in an air tight container for 16-24hours to allow the water to completely permeate the soil.

Liquid limit Take the sample from the airtight container and place it on a glass plate where it is mixed using palette knives for a few minutes. Add water to a portion of the sample and mix it again until uniformity is attained. Put some of the soil into a container using the palette knife ensuring no air is trapped by tapping it on a hard surface. Smoothen the surface with a straight edge. Place the container directly below the cone and lower it until it just touches the surface of the soil. Slight movement of the container should mark the soil surface. Lower the dial gauge to touch the cone and adjust the reading to zero. Release the cone for 51 seconds record the reading on the dial gauge to the nearest 0.1mm. Lift out the cone out clean it. Repeat the procedure for different amounts of water added to the soil. The difference between successive readings should not exceed 1mm for the same amount of water added. Carry out the procedure for about four different amounts of water (15-25mm penetration range) added to the soil and record the values obtained in a suitable table. Each time the sample is penetrated clean the container and wash it before performing another penetration. Take samples from each can for moisture content determination. Treatment of results Obtain the moisture content of the soil samples. Plot a graph of penetration against moisture content and draw a line of best fit through the points. The liquid limit is the moisture content that produces a penetration of 20mm to the nearest whole number.

Table of resultsTin no. Weight of tin + wet soil weight of tin + dry soil Weight of tin Moisture content Average moisture content Average penetration 42.3 17.05 44.2 20.03 50 21.2 48.9 23.9 BR 40 32.5 15 42.9 C A 2A 2B 23. 5 16. 5 0.5 43. 8 2C 22 15. 5 0.5 43. 3 3A 22 15 0.5 48. 3 3B 24 16 0.5 51. 6 3C 24. 5 16. 5 0.5 50. 0 4A 23 15.5 0.5 50.0 4B 25 16.5 0 51.5 4C 22.5 15.5 0 45.2

47.5 46.5 24.5 39.5 21.5 39 20 17 0.5

44.4 39.5 45.5

Moisture content at 20mm penetration = 45.5% Liquid limit = 46%

COMPACTION TEST Objective The objective of the test is to get the relationship between the moisture content and the dry density of compacted soil for a given compaction effort. These are used in specification in works involving compacting of soil. Main principles The dry density of any given soil depends on the moisture content and the compactive effort used. Compaction is the process of increasing the dry density of a soil by parking the soils more closely. This can be done by vibrating, static load compaction, tampering or kneading. Dry density of a soil increases with the increase in the mechanical effort. However for moisture content, it increases up to a maximum value and then drops. The moisture content at which the maximum dry density is achieved is the optimum moisture content. Thus with the relationship between the dry density and the moisture content for a given compaction effort, the optimum moisture content can be determined which is used in the field. Reference BS 1377: part 4 Craigs Soil Mechanics R.F. Craig Method BS heavy using a 4.5 kg rammer Equipment used Cylindrical compaction mould Metal rammer 4.5 kg heavy Balance Moisture cans Large metal tray Measuring cylinder

Oven for determining moisture content Spatulas

Sample preparation Sample was passed through a 20mm sieve and the particles larger than 20mm were removed. The sample was then dived into five representative smaller samples. Each sample was mixed with a different amount of water to give a range of moisture contents. The initial amount water for the first sample was assumed to be 8%, amount of water to be added was computed from the following equation;

Water was measured by a measuring cylinder. The each sample is mixed with water thoroughly until uniform colour is reached. Each sample is further divided into five parts. Each sample is compacted in five layers with each part of every sample receiving 27 blows Procedure The weight of the mould and the base plate were weighed and weight recorded. W1.The moist soil was placed in the mould and compacted in five layers, each layer receiving 27 blows of a 4.5 kg rammer. The rammer is dropped from a distance of about 450mm.A collar was fixed when the mould filled up before the final layer compaction. After compac