MASTERING THE STANDARD PENETRATION TEST (SPT) - A COMPREHENSIVE GUIDE TO SOIL EVALUATION

The Standard Penetration Test (SPT) originated from The Reymond Concrete and Pile Company, USA, in 1927, is one of the most widely used in-situ soil testing methods in geotechnical engineering. Approximately 80-90% of geotechnical investigations worldwide rely on the SPT for soil assessment. It provides valuable information about the engineering properties of soils and is commonly used for site investigation, foundation design, and soil characterization. In this article, we'll talk about the basic concepts you need to know when performing an SPT test.?

SPT Characteristics & Procedure

To start the test, you will need to drill a hole, preferably using a drilling rig, to reach the desired sampling depth and acquire a sample of the highest quality attainable. The test uses a split-spoon sampler attached to the drill rod. This sampler has an outside diameter (OD) of 51 mm (2 inches) and an inside diameter (ID) of 35 mm (1.38 inches), and a length of 686 mm (27 inches).?

A 63.5 kg (140 lbs) hammer is dropped repeatedly from a height of 76 cm (30 inches) driving the split-spoon sampler into the ground until reaching a depth of 15 cm (6 inches). The number of hammer blows is recorded. This procedure is repeated two more times until a total penetration of 45 cm (18 inches) is achieved.

The number of hammer blows required to penetrate the first 15 cm (6 inches) is called “seating drive” and the sum of the hammer blows between the 6 inch and 18 inch interval is the Standard Penetration Resistance (N-value). The soil recovered in the split-spoon sampler is described and retained for testing. The N-value serves as a valuable tool for estimating various soil characteristics. It predicts the relative density of non-cohesive soils such as sand and reflects the consistency, and to some extent the strength, of cohesive soils such as clay.

And what if the desired sampling depth exceeds the standard penetration depth of 45 cm (18 inches)? For example, if the project involves the design of a foundation for a structure, the borehole depth may extend below the proposed foundation level to assess the subsurface conditions adequately. If this happens, the test can be extended by continuing the penetration beyond the standard depth of 45 cm (18 inches). This can be achieved by dropping the hammer repeatedly until the desired depth is reached. The number of hammer blows required to penetrate each additional increment of soil is recorded. As the penetration depth increases beyond the standard 45 cm (18 inches), the test can be conducted in increments, with the number of blows recorded for each increment of penetration. This allows for a more detailed assessment of the soil properties at different depths.

And what about the hammer used in MetaDrill Rigs? MetaDrill has designed its own Automatic SPT hammer, which includes a single acting cylinder and the SPT assembly. The hydraulic cylinder (1600mm Stroke) is used to fix the SPT assembly onto the SPT rods, the 1.6m stroke allows for greater maneuverability and control for setting up the SPT onto the rods and greater speed and efficiency.? The SPT Assembly has been developed to maximize the energy transferred to the rods. The Automatic SPT assembly from MetaDrill comes with a calibration certificate to allow accurate measurement and calculation of N value corrected.?

Moreover, MetaDrill 's commitment to quality is underscored by their rigorous technical verification process of the automatic SPT hammer. Through advanced stress analysis and meticulous modeling, MetaDrill ensures that each component, from the selection of materials to the sizing of rods and other crucial parts, meets the highest standards of durability and performance. This meticulous validation process not only guarantees the reliability and longevity of the equipment but also instills confidence in users, knowing that they are utilizing a product that has been thoroughly tested and optimized for optimal functionality in diverse drilling environments.?

MetaDrill Auto Hammer significantly enhances efficiency by automating the tedious process of assembling Standard Penetration Test (SPT) equipment, reducing human error and accelerating project timelines. Moreover, MetaDrill precision engineering ensures consistent and reliable performance, enhancing data accuracy crucial for geotechnical assessments. Additionally, the automated assembly minimizes labor costs and maximizes safety by reducing manual handling of heavy equipment, thereby fostering a safer work environment. Furthermore, the streamlined workflow facilitated by MetaDrill 's technology increases productivity, enabling drilling teams to undertake more projects with greater speed and efficiency. Overall, MetaDrill 's automatic SPT assembly presents a reliable solution, enhancing efficiency, accuracy, and safety in the realm of drilling operations.