Standard Penetration Test (SPT) Designation: ASTM D 1586 History and Development: The history of SPT dates back to the early 1900s. In 1902 Charles R. Gow, owner of Gow Construction Company of Boston, began drilling 1-inch boreholes through a sampler to explore soil properties. Engineers later began using cutting-wash surveys to obtain information about soil properties. In the early 1930s this method was standardized by Harry Mohr, engineer at Gow Constructions. In his experiment Mohr used a larger sampler and counted the number of strokes per foot of penetration on a sample 18 inches deep. He used several sample diameters ranging from 1/8 to 3/8 inch. He used a 140-pound hammer and free-dropped it from a height of 30 inches. The shot count value for the last 12 inches of penetration was counted and called the SPT shot count value. At the same time, other companies also worked on the test. They used a variety of split-spoon and push-tube samplers with outside diameters ranging from 2 to 4.5 inches and hammer weights ranging from 100 and 350 pounds. This modified split-spoon sampler recovered samples as small as 1 3/8 inches in diameter. These guided samples were able to obtain important terrain details that could not be 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 extra 1 inch tube used up to that point. In the early 1940s, the Raymond Concrete Piles Co. used a 22-inch long sampler and this apparatus became known as the Raymond Sampler. Further research on the method was conducted by Terzaghi and Cassagrande. They used a split spoon for their experiment with the support of ASCE'...... in the center of the paper ......d in the large voids and low resistance to penetration is observed.2- You can expect excessive resistance when the spoon is blocked by a large piece of gravel or when the piece of gravel gets stuck in the spoon. Factors influencing SPT results: 1- Effect of overload pressure. Soils of the same density will provide a lower count near the soil surface.2- Using a guide shoe that is severely damaged or worn from too much driving to rejection.3- Failure to properly place the sampler on undisturbed material at the bottom of the survey. 4- Inadequate cleaning of material loosened from the bottom of the survey.5- Placing a stone in front of the sampler.6- Variations in the 30 inch drop height of the drive weight, as this is often done by eye.7- Interference with the free fall of the transmission weight through the guides and/or the rope used to lift the transmission weight for subsequent shots.