 Hello, I am Professor Dr. Satish Kumar Kashi from Walshan Institute of Technology, Sallapur presenting a topic, Standard Penetration Test for Estimating Soil Properties and Allowable Bearing Capacity. Learning outcomes of this session, students will be able to elaborate the procedure of Standard Penetration Test. Students will be able to estimate allowable bearing capacity of soil using Standard Penetration Test results. The Standard Penetration Test is the in situ test that is coming under the category of Penetrometer Test. The Standard Penetration Test are carried out in a borehole, we reach up to the level of foundation and at that level we perform this test. The test will measure the resistance of soil strata to the penetration under con. A correlation is derived between the soil properties and the penetration resistance. That way the test is extremely useful for determining the relative density and the angle of shearing resistance of cohesionless soils. It can also be used to determine the unconfined compression strength of cohesive soils. Let us discuss the tools for SPT. First is the standard split spoon sampler, then the drop hammer of weight 63.5 kg, the guiding rod, drilling rig and driving head that is also called as anvil. Let us see this figure. So here you will find this is a pulley over which a rope passes. The rope passes over a rotating drum so that the rope can be released which will release this particular do not hammer to the anvil and again it can be lifted up. So the fall of this particular hammer is 762 millimeter here. This is a slip guide pipe, here this is the anvil on which this do not hammer will fall. This is a drill rod to which this split spoon sampler is connected. This is the 63.5 kg weight which falls. This is the setup of a standard penetration test. If you take a section of this SPT sampler, so this is the open shoe, this is the tube, this is a roll pin, this is the head. The SPT sampler when assembled will look in this way. So this is the lower part, this is the upper part. When we open the split spoon sampler, we will be able to see the sample collected in this SPT in this way. When we penetrate this particular split spoon sampler in our test, so these are different positions. So here is the split spoon sampler, here there is anvil and here there is 63.5 kg drop hammer. Let us discuss the procedure for standard penetration test. The test is conducted in a borehole by means of a standard split spoon sampler as discussed. Once the drilling is done to the desired depth, the drilling tool is removed and the sampler is placed inside the borehole. By means of a drop hammer of 63.5 kg mass falling through a height of 750 mm, at the rate of 30 blows per minute, the sampler is driven into the soil. This is as per Indian standard 2131963. Then the number of blows of hammer required to drive a depth of 150 mm is counted. Further it is driven by 150 mm and then the number n is counted. Similarly, sampler is once again further driven by 150 mm and number of blows are recorded. The number of blows recorded for the first 150 mm are not taken into consideration. But the number of blows recorded for the next 150 mm intervals are added to give the standard penetration number. It is first 150 mm penetration is for a seating drives and the next is counted as a standard penetration number n. In other words, n is number of blows required for 150 mm penetration beyond seating drive of 150 mm. Sometimes it happens that number of blows for 150 mm drive exceeds 50. It is taken then as a refusal and the dust is discontinued. The standard penetration number is corrected for dielectric correction and overburden correction when it is in acceptable limits. But if it exceeds 50, one will not continue the test further. So what are the corrections? Corrections in SPT. Before the SPT values are used in empirical correlations and design charts, the field n value has to be corrected as per IS 21311981. There are two types of corrections. One is the dielectric correction and another is the overburden pressure correction. Silty fine sands and fine sands below the water table develop poor water pressure which is not easily dissipated. The poor pressure increases the resistance of the soil and hence penetration number n. So Terzaghi and Peck in 1967 recommended the following correction in case of silty fine sands when observed value n is exceeding 15. The corrected penetration number nc is 15 plus 0.5 into bracket nr that is number of blows recorded minus 15. So nr is number of recorded blows and nc is the corrected value. If nr is less than or equal to 15 then we take corrected value of n as recorded value of n. Let us discuss what is the overburden pressure correction then. From several investigations it is proved that the penetration resistance or the value of n is dependent on overburden pressure also. If there are two granular soils with relative density is same, higher n value will be shown by the soil with higher confining pressure. With increase in the depth of soil confining pressure also increases. So the value of n at shallow depth and larger depths are untimated and overestimated respectively. Hence to account this the value of n obtained from the test are corrected to a standard effect to overburden pressure. What is that correction? The corrected value n is then nc into correction factor cn into n. Now once we have the corrected value of the SPTn one can estimate about the relative density of soil as very dense, dense, medium dense, loose and very loose. And accordingly one can estimate the angle of shearing resistance phi. So for example suppose SPTn value corrected value is 30 so you can estimate the angle of shearing resistance as 36. If it is say 40 one can estimate its angle of shearing resistance as 39 and so on. Unconfined compression strength of cohesive soils depending upon SPT value say SPT value in between 4 to 8 one can expect q u that is unconfined compression test as say 50 to 100 kilo Newton per meter square. In this way soil properties can be estimated by using SPTn values. Now one can also estimate the bearing capacity of shallow foundations in sand from SPT values that is n. What we need to do? Perform SPT test according to Indian standards, decide the depth, width and length of foundation for initial calculations. Of course it is a trial and error process. The first attempt you can never get the exact size of foundation which is to satisfy all your needs. But then arrive at a suitable value and then apply the corrections to the standard penetration test values. Calculate the cumulative average value of corrected SPT values from the base level of foundation to depth equal to 2 times the width of foundation where pressure bulb extends. Calculate the above cumulative average SPT value with the figure given below to find out the corresponding angle of shearing resistance. Once we get the angle of shearing resistance 5 then one can find out this bearing capacity factors Nc, Nq and N gamma depending upon the 5 values and the nature of shear failure. Once one gets these values that is possible to arrive at the ultimate bearing capacity of soil then the safe bearing capacity of soil by applying proper factor of safety. It is also possible to estimate this is the empirical chart which gives relation between allowable bearing pressure and SPT value N for permissible settlement 25 millimeter. So Terzaghi and Peck have given this in 1967. So here depending upon a width of foundation and the N values we have these graphs. So for example suppose say N is 30 and say width of foundation is 2 meter. So one can expect allowable bearing pressure on this graph as say 330 kilo Newton per meter square. What are advantages of standard penetration test? This is a simple and economical test. It provides a representative sample for visual inspection also which can be classified further and also moisture content can be calculated. Actual soil behavior is obtained through the SPT values. The method helps to penetrate dense layers and fills of soils. Test can be applied for variety of soil conditions. However there are certain disadvantages and limitations. One is the results will vary due to mechanical or operator variability or drilling disturbances. It is also costly and time consuming. The samples retrieved for testing are disturbed samples. The test results from SPT cannot be reproduced. The application of SPT in gravels, cobbles and cohesives soils are limited. Here are some questions. In standard penetration test 54 blows were required for driving 15 centimeters beyond the sitting rail. The N value of the soil will be 54, 24, 34. The observation shall be treated as a refusal. This is the answer. The dialysis test is applied to SPT N value for saturated sand or fine silt below water table because these soils develop dash dash during the test. Options are zero pore water pressure, positive pore water pressure, negative pore water pressure. None of these. The answer is positive pore water pressure. Third question. The corrected N value obtained from SPT in sand deposit is 12. The relative density of soil may be stated as very loose, loose, medium, dense. By referring the graphs, one may come to the answer that it may be medium. These are the references which are used for drafting this PPT. Thank you.