What is the purpose of a cone penetration test (CPT) in geotechnical investigations?

The purpose of a cone penetration test (CPT) in geotechnical investigations is to provide a rapid and cost-effective method for determining the subsurface stratigraphy and geotechnical properties of soil. The CPT involves pushing a cylindrical cone with a standardized geometry into the ground at a constant rate and measuring the resistance to penetration. The cone is typically equipped with sensors that measure the cone resistance (qc), which is the force required to push the cone into the soil, and the sleeve friction (fs), which is the frictional resistance between the soil and the sleeve of the cone. Some CPT cones are also equipped with a pore pressure sensor (u), which measures the pore water pressure in the soil. The CPT data is used to infer soil type, estimate soil strength parameters (such as undrained shear strength and friction angle), and assess soil compressibility. The CPT provides a continuous profile of soil properties with depth, allowing for detailed characterization of the subsurface. The CPT is particularly useful for identifying weak layers or zones of soft soil that may be problematic for foundation design or slope stability. The CPT is also relatively quick and easy to perform, making it a cost-effective alternative to traditional soil boring methods. The CPT data can be used directly in geotechnical design calculations or it can be used to guide the selection of samples for laboratory testing. While CPT is highly useful, it does not retrieve physical samples of the soil; therefore, it is typically used in conjunction with borehole drilling to provide a more complete picture of the subsurface conditions.