Soil Sampling and Soil Classification

The purpose of the standard penetration Test (SPT) is to determine the relative density and consistency of the Sub-Soils, and to obtain disturbed Soil samples for field visual identification of soil samples. Standard Penetration Tests were generally performed at 1.5 meter intervals and however were performed at 3 m intervals when achieved 100 blows. The standard penetration Test utilizes a split spoon sample tube of 50 mm outer diameter, driven into the soil by 63.5 kg Automatic hammer. The hammer was dropped from a free fall of 760mm height along a rod. The testing process consists at a seating drive of 150mm penetrations, followed immediately by a test drive at 300 mm penetrations. The number of blows count required for each 150mm penetrations and the total cumulative numbers of the last 300mm penetration is recorded as the SPT N Value. After the completion of the test, the sample tube is removed and disassembled to provide a ‘disturbed’ but representative. Test Results of SPT are shown in the Borehole log. If, however, 100 blows were reached before a penetration of 300mm was achieved, the test was stopped and the penetration achieved recorded.