Standard Penetration Test (SPT)Designation: ASTM D 1586History and Development:The history of SPT dates back to the early 1900s. In 1902, Charles R. Gow, owner of the Gow Construction Company in Boston, began making 1-inch boreholes using a sampler to explore the properties of the soil. After this period, engineers began using wash surveys with cuttings to obtain information on soil properties. In the early 1930s, this method was standardized by Harry Mohr, an engineer at Gow Constructions. In his experiment, Mohr used a larger sampler and counted the number of strokes per foot of penetration on an 18-inch-deep sample. He used different sample diameters ranging from 1/8 to 3/8 inches. He used a 140-pound hammer and dropped it freely from a height of 30 inches. The stroke value for the last 12-inch penetration was counted and was referred to as the SPT stroke count value. At the same time, other companies also worked on the test. They used a variety of slotted spoon and push tube samplers with outside diameters varying from 2 to 4.5 inches and hammer weights were 100 and 350 pounds. This modified split spoon sampler collected samples 1 3/8 inches in diameter. These collected samples provided important details about the soil that could not have been obtained using wash surveys. In 1945 the sampler barrel was replaced by the introduction of A-size hollow drill rods fitted with Jackbit threads. These rods replaced the old 1 inch extra pipe that was used until then. In the early 1940s, Raymond Concrete Piles Co. used a 22-inch long sampler and this device became known as the Raymond Sampler. Further research into the method was carried out by Terzaghi and Cassagrande. They used a slotted spoon for their experiment with the ASCE' media....... middle of paper ......de into large voids and low penetration resistance is observed.2- A Excessively large resistance can be expected when the spoon is blocked by a large piece of gravel or when the piece of gravel enters the spoon. Factors affecting SPT results: 1 - Effect of overburden pressure. Soils of the same density will give a lower count near the soil surface.2- Using a training shoe that is severely damaged or worn from too many drives to the point of refusal.3- Failure to properly place the training shoe sampler on undisturbed material at the bottom of the borehole. 4- Inadequate cleaning of material loosened from the bottom of the borehole.5- Driving a stone in front of the sampler.6- Variations in the 30 inch drop height of the driving weight, as this is often done by eye nu.7- Interference with the free fall of the training weight by the guides and/or the rope used to hoist the training weight during successive strokes.