Soil and Foundation Principles - Lab Report Example

Introduction These tests are performed in order to determine the composition of soil, the moisture content in the soil, the liquid limit in the soil, the plastic limit and the magnitude and the rate of volume that decreases in the process of soil consolidation. The test for soil composition helps to determine the percentage composition of each component of the soil including air content and soil moisture (Handy, 2007). The liquid limit of the soil can be defined as the moisture content expressed as a percentage of the weight of the oven dried soil at the boundary between the plastic states of consistency. The moisture content at the boundary is normally defined as the water content at which the two halves of the soil cake will flow together for a distance of about half inch. The plasticity index on the other hand is the numerical difference between the liquid limit and the plastic limit and this number is normally dimensionless (Day, 2005). Both the liquid and the plastic limits are used to express the moisture content in the soil. The plasticity index is the difference between the liquid limit and the plastic limit. Plasticity index= liquid limit- plastic limit For the consolidation test, the pressure void relationship in the soil can be determined. This data is very important in the determination of the compression index of the soil and the pre-consolidation pressure (Day, 2005). Additionally, this data can be used o determine the coefficient of consolidation of the soil. The sieve test is carried out to determine the percentage of the different grains that are contained in the soil. The mechanical sieve analysis is carried out to determine the distribution of the coarse and the medium grained grains. It must be conducted within the ASTM D 422 - Standard Test Method for Particle-Size Analysis of Soils. Procedures 1. Test for soil moisture content The soil sample is weighed and recorded. The sizes of the particles are determined on a size with different sizes of the sieve holes. The soil is dried on an oven at a temperature of about 1050C -1100C. The weight of the dry soil is measured and recorded. The same procedure is repeated for the medium grained soil particles and the coarse grained particles for comparison. 2. Test for the liquid limit of the soil A sample of soil is taken and transferred to a glass plate. Water is added to the soil sample and mixed to for a paste. The soil paste is then placed in an airtight container. Using the penetration cone, the top surface of the soil is touched to and used as the starting point for the measurements. The dial gauge is then lowered to connect the cone shaft and the reading on the dial gauge is recorded. Using several samples of soil pastes, the above procedure is repeated and the readings recorded for comparison. 3. Test for plastic limit of the soil A soil sample is taken and water added to obtain a thick paste of soil. The soil paste is placed in a glass plate and allow to partially dry until it becomes plastic enough. The paste is then molded into balls of soil between the fingers and then rolled to form a thread of soil. The moisture content in the molded threads is determined. The above procedure is repeated with other samples of molded soil and the readings a taken for further analysis on the soil. 4. Compaction test on the soil A soil sample is taken and weighed. The soil is passed through a sieve and the size of the particles is determined. Using a mechanical rammer, the soil sample is hit and the number of blows done on the soil to determine the changes in the masses of the soil are recorded. This will help to determine the bulk density and the moisture content of the soil. 5. Sieve test A sample of soil is taken and its dry weight is recorded. The weight of the sieve is recorded too. After ensuring that the sieves are clean, the soil it poured on to it and shaken for about 10 minutes. The weight of the resulting soil is recorded. The process is repeated with several samples of soil and the results recorded. Results summary Lab sample M1=2533.2 g BS test sieve Actual Corrected (m) Retained (m1/m2)x100 Cumulative % passing 20 mm 60.6 60.6 2.39 97.6 Passing 20 mm (m2) 2472.8 Total (check with m1) 2553.4 Riffled (m3) 1434.4 Correction factor 1.72 14 mm 114.6 197.11 7.78 89.83 10 mm 112.6 193.67 7.65 82.18 6.3 mm 138.8 238.79 9.42 72.76 Passing 6.3 mm 1007.2 Riffled m6 273.0 5 mm 11.2 80.75 3.19 69.57 3.35 mm 19.6 141.32 5.58 6399 2 mm 25.0 180.25 7.12 56.87 1.18 mm 20.8 149.97 5.92 50.95 600 µm 38.2 275.42 10.87 40.08 425 µm 56.2 405.20 16.00 24.08 300 µm 52.2 376.36 14.86 9.22 212 µm 25.2 181.69 7.17 150 µm 11.6 83.64 3.30 63 µm 10.0 72.1 2.85 Passing 63 µm MF or ME 0.8 5.77 0.23 Total (check with m6) Table 1: Results from the sieve test 1 2 3 4 Mass of wet soil+ container 52.29 50.38 Mass of dry soil+ container 51.73 49.53 Mass of container 48.71 44.78 Mass of moisture 0.56 0.85 Mass of dry soil 3.02 4.75 Moisture content % 18.570 17.9 17.6 18.5 Table 2: Results for the Plastic limit test 1 2 3 4 Initial dial gauge reading 0 0 0 0 0 0 0 0 0 0 0 0 Final dial gauge reading 10.9 11.93 11.93 15.48 14.27 16.68 14.46 19.69 Average penetration 11.58 15.47 14.46 19.69 Mass of wet soil+ container 52.28 54.35 Mass of dry soil+ container 50.83 51.52 Mass of container 44.80 40.85 Mass of moisture 1.45 2.83 Mass of dry soil 6.03 10.67 Moisture content % 24.04 26.52 26.52 28.95 Table 3: Results for the liquid limit test Location: Brackenhurst 2.5 kg *hand/mechanical rammer Layers of 27 blows per layer Volume of mould 1000 cm3 Initial sample mass 300 g Particle density mg/m3 Test no. 1 2 3 4 5 Mass of mold+base+compacted specimen (m2) 7279.8 7304.4 7329.6 7287.4 7292.2 Mass of mould+base (m1) 5321.9 5320.9 5320.6 5322.6 5322.2 Mass of compacted (m2-m1) 1938.9 1984 2009 1964.4 1970 Bulk density m2-m1/v Moisture content (w) % 15.88 16.69 18.21 22.4 22.35 Dry density pd=100p/100+w 1.690 1.704 1.706 1.605 1.610 Table 4: Results for Test for dry density Total no. of blows Penetration or protrusion Change in penetration into 4n mm 1 45 37 2 63 31 3 74 21 4 82 13 6 92 4 9 94 2 12 95 1 16 95 1 24 96 0 32 96 0 Table 5: Results for Compaction test Calibrations mean mass of sand In cone of pouring cylinder (m2) 6168.8 g 4747.6 g Volume of calibrating container 1000 ml Mass of the sand before pouring (m1) 6110 g Mean mass of the sand before pouring (m3) 4216 g Mean mass of the sand to fill the calibrating container 1473 g Bulk density of sand ra=ma/v 1.47 mg/m3 Table 6: Test for bulk density of sand Test no. 1 2 Mass of wet soil from hole (mw) 1618 1043 Mass of sand before pouring (m1) 63.2 5.725 Mass of sand after pouring (mb) 4564 4947 Mass of sand from hole 1317 857 Ratio= mw/mb 1.23 1.22 Bulk density 1.81 1.79 Moisture content 10 10 Dry density 1.65 1.63 Table 7: Results for Moisture content test Discussion The test for the water content conforms to conform to ASTM D2216-90. In all the soil samples tested for the moisture content, the natural moisture content of the soil has been determined. It is important to have the understanding of the moisture content of the soil in the determination of the mechanics of the soil particularly the bearing capacity of the soil and its ability to settle (Day, 2005). The moisture content of the soil will be important in determination of the state of the soil. The natural water content in the soil sample is normally referred to as the natural moisture content and it expressed as the ratio of the weight of the water to the weight of the solid materials in the soil sample. This value is given as a percentage as shown in the results above. The test for the liquid limit and the plastic limit of the soil is an integral part of construction engineering. These tests are used to characterize the grains of the soil and make a definite specification of the fine grained fractions of materials to be used for construction. The liquid limit, the plasticity index and the plastic limit of the soil samples are used widely either together or individually with some other definite characteristics of the soil to make a correlation of the engineering behaviors of the soils such as its compressibility, permeability, shear strength and shrinkage (Coduto et al, 2003). In the compaction test, the air voids that are present in the soil sample are removed mechanically either using a rammer or a roller. This ensures that the soil remains compact and the degree of compaction can be determined in dry unit weight of the soil. The main reasons for compaction on the soil are to increase the bearing capacity on the soil, to decrease the tendency of the structure to decrease in an undesired manner and increase the stability of the soil. It is important to note that the compaction of soil is a function of the water content (Tomlinson, 2001). Water is normally added to the soil sample during the compaction test and it acts as the softening agent for the particles. The dry unit weight of the soil is known to increase the limit of soil compaction to a point whereby beyond it, the moisture content will reduce the dry weight of the soil. From the test we can determine the compaction energy of the soil. Therefore, the compaction test of the soil tries to make the optimum density of the soil as close to zero as possible. In sieve analysis, the distribution of the different sizes of the grains has been determined and this has a major effect on the engineering properties of the soil (Whitlow, 2000). From the data obtained, the soil can be classified depending on the grain size of the soil samples. Conclusion From the tests carried out above, the moisture content, dry density, bulk density, plastic limit and liquid limit of the soil have been determined. This has been done within the set geotechnical standards and the data obtained can be used for the determination of the soil properties. References R. L. Handy, Geotechnical Engineering: Soil and Foundation Principles and Practice, Fifth Edition, McGraw-Hill London, 2007. Robert W. Day, Forensic Geotechnical and Foundation Engineering, Second Edition, McGraw-Hill London, 2005. Donald Coduto, Man-chu Ronald Yeung, William Kitch, Geotechnical Engineering Principles & Practices: International Edition 2nd Edition, Oxford University press, London (2003) M.J. Tomlinson, Foundation Design and Construction 7th Edition, McGraw-Hill, London (2001). R. Whitlow, Basic Soil Mechanics 4th Edition, Oxford University press, London (2000) Read More