There are various type of soil which is different in physical and chemical composition like sand, silt, and clay.
Also there are different use of soil testing for plant growth, mining, and construction related activity like buildings and dams.
The various test on the soil can be categorize into two types:
1/ classification test:
Which provide information about the general soil characteristic as well as mechanical properties like strength, size grading, permeability etc, these tests help to classify soil sample into different types.
2/ soil test to determine engineering properties:
Which evaluate the usefulness or the suitability of particular soil specimen for construction works.
Beside the above types of tests, other tests are also conducted to be determining other various parameters.
The investigation program included drilling boreholes and collection soil samples at desired intervals for subsequent observation and laboratory testing.
The investigation program will consist of soil boring and sampling and field testing.
Boreing and sampling:
The boreholes will be made by the rotary drilling machine. The borings shall be drilled vertically undisturbed and disturbed samples will be taken at different interval according to soil type.
Standard Penetration Testing:
Standard penetration tests (SPT) will be carried out to provide an indication of the density and/or consistency of the group and to obtain disturbed samples for visual inspection and laboratory testing and classification.
Atterberg limits will be determined on representative soil samples of cohesive soils. The atterberg limits refer to arbitrarily defined boundaries between the liquid and plastic states,
and between the plastic and brittle states of grained soil , expressed as water content , in percentage .
The liquid limit is water content at which a part of soil placed in a standard cup , cut by a standard grooving tool , will flow together at the base of the groove when the cup is subjected to 25 standard shocks. The one-point liquid limits test is usually carried out and distilled water may be added during soil mixing to achieve a desired consistency.
Particle Size Analysis
Particle size analysis will be performed by means of sieving; sieving is carried out for particles that are being retained on 0.063 mm sieve. In sieve analysis, the mass of soli retained on each sieve is determined and expressed as percentage of the total mass of the sample. The particle size is plotted on a logarithmic scale so that two soils having the same degree of uniformity are represented by curves of the distribution plot. In hydrometer analysis is based on the principle of sedimentation of soil grains in water. When a soil specimen is dispersed in water, it is assumed that soil particles are spheres and the velocity of soil particles can be express by Stokes law.
Water Content Determination
Water content is determined by oven –drying a moist/wet soil at a constant temperature of 105 C for 18-24 hours.
The oedometer consolidation test is used for the determination of consolidation characteristics of low –permeability soils when subjected to vertical loads. The results may be used to calculate and estimate settlements of structural foundations when placed on the ground. The two parameters normally required are:
The compressibility of the soil: Coefficient of volume compressibility, mv
The time related parameter: Coefficient of consolidation, cv
Particle density is the term used instead of specific Gravity of particles. Knowledge of the particle density is essential in relation to other test , especially for calculating porosity and voids and for computation of particle size analysis from a sedimentation procedure (Hydrometer analysis). It is also important when compaction and consolidation properties are considered.
The objective of this test is to obtain relationship between compacted dry density and soil moisture content, using two magnitudes of manual comp active effort. The test is used to provide a guide for specifications on field compaction.
California Bearing Ratio (CBR)
The strength of the sub grade is the main factor in determining the required thickness of flexible pavement for roads and airfield. The strength of sub grade ,sub-base and base course materials are expressed in terms of their California Bearing Ratio (CBR) value.
The CBR – value is a requirement in design for pavement materials of natural gravel.
The Triaxial test is primarily designed to determine the shear strength parameters of a soil sample either in terms of total stresses , i.e. the angle of shear resistance (?), the cohesion (c), and the undrained shear strength (cu ). Or in terms of effective stresses, i.e. the angle resistance and cohesion (c).
These values may be used to calculate the bearing capacity of a soli and stability of slopes.
The shear box allows a direct shear test to be made by relating the shear stress at failure to the applied normal stress. The objective of the test is to determine the effective shear strength parameters of the soil, the cohesion (c') and the angle of internal friction. These values may be used for calculating the bearing capacity of a soil and stability of slopes.
The fundamental soil property involved in water flow is permeability. The permeability is especially relevant for engineering problems like determination of rate of leakage through an earth dam.
It depends mainly on the particle size , void ratio , density and degree of saturation.
Soil testing is well recognized as a sound scientific tool to assess the power of the soil to supply plant nutrients.
Analytical methods for estimation of physical properties and available nutrients:
1/ soil texture:
Soil texture or particle size distribution is stable soil characteristic which influences physical and chemical properties of the soil.
To estimate the content of the various sizes of soil particles, the soil sample has to be brought into dispersed state by removing various types of binding forces.
The particles below 2 mm diameter are separately determined which constitute sand, silt and clay.
2/ caution exchange capacity (CEC):
The total number of the exchangeable cautions a soil can hold is called cation exchange capacity. The higher CEC, the more cations can retain. It can be expressed in terms of milliequivelant/100g soil or centimoles of positive charge /kg of soil (c mol /kg). The CEC of the soil depends on the kind of clay and organic matter present.
/3 Soil moisture:
Gravimetric method of moisture estimation is most widely used where the soil sample is placed in an over at 105 C0 and dried to constant weight. The difference in weight is considered to be water present in the soil sample.
The soil ph is the negative logarithm of the active hydrogen ion (H+). It is the measure of soil sodicity, acidity or neutrality. The procedure for measurement of soil PH is by using the pH meter.
5/Soil Electrical Conductivity:
The electrical conductivity (EC) is a measure of the ionic transport in a solution between the anode and cathode. The (EC) is normally considered to be a measurement of the dissolved salts in a solution.
6/ gypsum Requirement:
In the estimation of gypsum required to replace the sodium from the exchange complex. The soil treated with gypsum become dominated with sodium in the exchange complex.
7/ Organic carbon /Organic matter:
Organic matter estimation in the soil can be done by loss of weight on ignition, also it can be expressed as the content if organic carbon in the soil. Organic carbon / organic matter can be estimated by volumetric and colorimetric methods.
8/ Total Nitrogen (kjeldahl method) (N):
Total N includes all forms of inorganic N, like NH4 NO3 ..... and also urea and organic nitrogen compounds like protein, amino acids and other.
9/ Available phosphorus (P):
The estimation of (P) in the soil depends on specific coloured compounds are formed with the addition of appropriate reagent in the solution.
10/ Available Sulphur (SO4 ):
SO4 in the soil can be determinate in cacl2 extract. It can be estimated turbid metrically.
11/ Exchangeable cations:
Are usually determined in a neutral normal ammonium a acetate extract of soil. The extract ant mixture determined by titration method or by atomic absorption spectrophotometer.
For estimation of micronutrient, different extracant have been developed for assessing plant available nutrient content is the soils. The elements so extracted can be estimated quantitatively through chemical methods or instrumental techniques.