 I am here to discuss with you on topic soil exploration. Learning outcomes of today's session. At the end of the session, students will be able to describe soil exploration and its importance in the design of foundations. What is soil exploration? Dear friends, soil exploration is a methodology which consists of determining the profile of the natural soil deposits at the site, then taking the soil samples and determining the engineering properties of soils using laboratory tests as well as in situ testing methods. In the photograph, you can see a soil in exploration being carried out. Let us go ahead. Now soil exploration program usually involves taking test pits or soil borings, boreholes. Now a detailed soil exploration program consists of, what it consists of? Number one, determining the need for and extent of geophysical exploration. Then preliminary location of each borehole or test pit. Then numbering the boreholes or test pits, plan at a depth of each borehole or test pit. All these details are there in soil exploration program. Number five, methods and procedures for advancing the boreholes, sampling instructions for at least first borehole, determining the need for and type of in situ tests. What is in situ tests? In situ tests are those tests which are carried out at site. Then requirements for groundwater observations. So all these points are included in detailed soil exploration methodology which is followed. Then here you can see the photographs of soil exploration being carried out. In the first photograph, auger boring you can see. In the second photograph, the details of pit, like depth of different strata etc., is visible. Now dear students, there are different methods of soil explorations. Generally, soil exploration is classified into two methods, direct and indirect. Direct methods consist of using, taking trial pits or test pits. Then using wash boring method, using rotary rigs method. Indirect methods consist of some geophysical explorations. In today's session, we will focus ourselves only on direct methods. In direct methods, we will study in some other session. So direct methods, one by one, we will see how these methods are employed. First is trial pits or test pits. How these trial pits are taken? See a pit is dug by hand using shovel or a machine such as backhoe. Here in the photograph, you can see a backhoe used for taking a trial pit. Also you can take pit by using shovel, remember, using hand. Now this method provides excellent shallow depth soil stratigraphy. Direct method can be used for a limited depth, see there is a limitation around 6 meters. We cannot go beyond that and this gives excellent shallow depth soil stratigraphy. Now which are the equipment used for taking trial pits? Those are called augers, hand or power augers. Power augers are called mechanical augers also. So hand operated augers are used for relatively smaller depth, say less than 3 to 5 meter. And power driven augers are used for greater depths, say up to 60 to 70 meter. Here in the photographs, you can see the augers. These augers how they are advanced in soil by rotating while pressing into the soil. And you will get a pit in ground. Now next method is wash boring method. This is the simple and fast method for advancing holes in all types of soils. The resulting chopping and jetting action of the bit and water disintegrates the soil. The cutting is forced up to the ground surface in the form of soil water slurry through the annular space between the drill rod and the casing. Water is pumped through a hollow rod that may or may not be equipped with a drill bit to remove soil from a bore hole. The washings can be used to estimate the soil types. Here you can see photograph of wash boring. Water is used to disintegrate the soil and this bit can easily progress or proceed due to disintegration of soil at the tip. There is a sharp edge to this bit which advances in soil. Now there is one more method called rotary rigs method. Rotary rigs are the mechanical devices generally mounted on trucks. These are massive structures, housing equipments used to drill water wells, oil wells or natural gas extraction wells and they can be small enough to be moved manually also by one person and they use augers. So manually used drilling rigs are also there and mechanical devices which are mounted on trucks they are also there. And they are useful in case of highly resistant strata and related to finding out the rock strata and also to access the quality of rocks from cracks, fissures and joints etc. can conveniently be used in sands and sills also. Here the bore holes are advanced in depth by rotary percussion method which is similar to wash boring technique. Here also water is used so that soil gets disintegrated and aids in advancement of this particular tool or bit. Now there are certain guidelines on number and depths of bore holes given by IS code and these are governed by experience based on geological character of the ground, the importance of the structure, the structural loads and the availability of equipment also. Which are those guidelines? For buildings of area less than 100 square meter, minimum 2 bore holes must be taken. For buildings having area less than 250 square meter, minimum 3 bore holes must be taken. For buildings with less than 500 square meter area, 4 bore holes are necessary. For 1000 square meter of area, 5 bore holes are must. So the list is here, for 10,000 square meter of building, minimum 10 bore holes must be taken. So these guidelines should be followed so that the soil sample is available, sufficient soil sample is available to test the site. And for subdivisions like area less than 4000 square meter, minimum 2 bore holes are necessary. Likewise, these guidelines must be followed and the bore must be taken. Now there are guidelines on depth of bore hole also. For shallow foundations for buildings, minimum depth is equal to breadth of foundation or 3 times breadth of foundation or 5 meter. Then deep foundations like pile foundation, 25 meter to 30 meter depth should be there. For retaining walls, 1 to 2 times the wall height. All these depth specifications must be followed while taking bore holes in ground. Now dear students, let us pause a while here. Here are two questions for you, solve them. First is for a proposed residential building to be built on a plot of 600 square meter, dash dash number of bore holes must be taken for soil investigation as per codal provisions. Pick up the correct option. Then power augers can be used for drilling soil up to dash dash meter, write down the correct option, come on do it. Here are the answers. First question, D is the correct option means 5 number of bore holes must be taken for a plot of 600 square meter. And power augers can be used for drilling up to 60 to 70 meter, so C is the correct option. I hope you have written the correct answers, all of you. Now these are the references for today's session. Go through all these, thank you.