 S. K. Kulkarni, assistant professor, Balchan Institute of Technology, Solapur, I am here to discuss with you on topic soil sampling. Let us see learning outcomes of this session. At the end of this session, students will be able to describe soil sampling techniques and their importance in the design of foundations. What is soil sampling? Dear friends, soil sampling is the process of collection of samples of soil in order to determine the engineering properties of soil required for the proper design of foundation. Remember, it is collection of samples. For what purpose? To determine the engineering properties of soils. This can be determined in the laboratory. Most of the tests are in laboratory, few of the tests can be conducted in situ on site. Soil samples are usually obtained by attaching an open-ended thin walled tube called a Shelby tube or simply a sampling tube to drill rods and forcing it down into the soil. A sampling tube is used called Shelby tube for this purpose. What are the objectives of soil sampling? The objectives are to obtain soils of satisfactory size with minimum disturbance for observations and laboratory tests. Remember, minimum disturbance. So, when you collect sample, the soil should get minimum disturbance. Now, this soil samples can be of two types. One is disturbed samples, another is undisturbed samples. Disturbed samples are further classified into representative and non-representative samples. Let us see what are disturbed samples. You can see in the photograph, soil sample being collected. A sample in which the natural structure of the soil gets partly or fully modified and destroyed during sampling. That is called a disturbed sample, remember. So, natural moisture content will get disturbed in this particular sampling methodology. However, by taking proper precautions, the natural water content in soil sample can be preserved. The composition and the mineral content of the soil is represented by the samples. Disturbed samples properties of the soil can be determined from disturbed samples. For example, grain size, plasticity, characteristics of specific gravity, etc. So, disturbed samples are used for laboratory testing such as grain size distribution, plasticity, specific gravity, etc. Little more details about disturbed samples. These samples are normally taken from the field for laboratory tests to characterize the physical and mechanical properties. For example, strength and deformation characteristics. These parameters are used to design foundations and to determine the use of soil as a construction material. So, these parameters are used in design of foundations by geotechnical engineers or civil engineers. Disturbed samples such as from a standard sampler are usually used for visual inspection and for tests to determine physical properties such as plasticity, grain size and shape. This we have seen. Now let us see what is undisturbed sample. A sample in which the natural structure and properties remain preserved and the water contents are retained. In the photograph you can see undisturbed sample. Water contents are preserved in this particular sample and natural properties are also preserved. It is impossible to get the truly undisturbed sample remember. The sample disturbance depends on the design of samplers and the method of sampling. Undisturbed samples are used for determining engineering properties of soil such as shear strength, compressibility, shrinkage limit, permeability, etc. So, undisturbed samples are little difficult to obtain but we can use modern techniques and undisturbed samples can be obtained and they are used for finding shear strength, compressibility, shrinkage limit, permeability these parameters. Now let us see or let us study little about samplers which are used for taking sample soil sample. Types of samplers mainly types of samplers are thick and thin wall samplers which are called thick wall samplers whose area ratio is greater than 10 percent remember and these are used for obtaining disturbed soil samples. For disturbed soil samples you can use thick wall sampler having area ratio greater than 10 percent. For obtaining undisturbed samples remember you should use thin wall samplers having area ratio 10 less than 10 percent their wall thickness will be thin right. Now what are the types of samplers? Let us see types of samplers depending upon mode of operation, open drive sampler, piston sampler and rotary sampler. These are three main types of samplers depending upon mode of operation. Now what is open drive sampler? Open drive sampler is called open because at the leading end it is open and soil enters through it. Cutting edge at leading end pushing sampler into the ground displaces the soil of equal volume of the metal of the sampler. In the photograph you can see open drive sampler and why this is how this is useful for which types of sampling undisturbed samples are obtained from bore holes by open drive sampler. So open drive sampler can be used for taking undisturbed samples remember and open drive samplers consist of thin wall tubes which are pushed or driven into the soil at the bottom of the hole and then rotated and detached lower end of the sample from the soil. Most soft or moderately stiff cohesive soil can be sampled without extensive disturbance in thin wall seamless tubes having diameter not less than 50 mm. So diameter of tubes is not less than 50 mm. The lower end of the tube is sharpened to form a cutting edge and the other end is machine for attachment to the drill rod. Lower end of the sampler is sharpened so that it can be penetrated in ground. So entire tube is pushed or driven into the soil at the bottom of the hole and is removed sample from inside. So this is an open drive sampler and its accessories. One more method is a split spoon sampler remember. This is used for obtaining disturbed samples of the soil. The split spoon sampler consists of three types. One tool steel made driving shoe about 75 mm in length. One 450 mm long steel tube split longitudinally in two walls and 150 mm long coupling at the top of the tube. The steel tube in the middle has inside and outside diameter of 34.9 and 50.8 respectively. So split spoon sampler gets split, gets split tail into two parts and it is becomes easier to take out the sample. So it is called split spoon sampler remember. And when bore hole is advanced to a desired depth the drilling tools are removed. The split spoon sampler is attached to the drilling rod and then lowered to the bottom of the bore hole by repeated blows of hammer and then withdrawn and the sample is taken and transported to the laboratory. Next type is piston sampler. Piston sampler consists of two parts sample cylinder and piston system. The pistons first is tightened in the sampler cylinder. Good quality undisturbed samples of soft and sensitive clay are obtained from piston samplers which are or which use thin wall sampling tubes with a piston inside. So remember this piston sampler is used for good quality undisturbed samples of soft and sensitive clay. So piston is used in this piston samplers. Here you can see the photograph or section of piston sampler. While the tube is being lowered to the bottom of the drill hole the piston rods and the piston are held at the bottom by different types of samplers. Next type is rotary sampler. In a rotary sampler it is a double wall tube sampler with an inner removable liner and the outer tube or the rotating barrel is provided with the cutting bit. The bit cuts and inner tubes which are stationary slides over the cylindrical sample cut by the outer rotating barrel remember and the sample is collected in the inner liner. The rotary samples are useful for sampling in firm to hard cohesive soils and they can be used for collection of undisturbed samples in stiff to hard clays remember okay. So rotary samples are used for taking samples in hard clays. So let us stop while friends here are two questions for you write their answers neatly. Thick wall sample is used for obtaining dash dash soil samples with area ratio dash dash 10 percent. For good quality undisturbed samples dash dash samplers are used. So write down your answers here are the answers. Question number one A okay disturbed samples and greater than 10 percent. Second question for good quality undisturbed samples piston samplers are used these are the answers. These are the references for today's session. Thank you.