ESE-078 – Standard Penetration Test Apparatus

The Standard Penetration Test (SPT) Apparatus is a widely used tool in geotechnical engineering for assessing the properties of soil, primarily to determine its density, strength, and compaction. The SPT is a field test used to obtain soil samples and measure the penetration resistance of the soil, which is critical for foundation design, seismic analysis, and soil classification.

The SPT is typically conducted by driving a split-spoon sampler into the ground using a drop hammer. The number of blows required to drive the sampler a specific distance (usually 300 mm) is recorded, and this N-value is then used to estimate the soil’s engineering properties.

Key Features and Specifications:

1. Hammer System:
   • The SPT apparatus includes a hammer weighing typically 63.5 kg (140 lbs), which is dropped from a standard height of 760 mm (30 inches).
   • The hammer drives the split-spoon sampler into the soil, with the number of blows per 300 mm of penetration recorded.
   • The hammer is dropped 30 times (or as per standards) to penetrate the first 300 mm of soil, and the N-value is calculated based on the total blows recorded.
2. Sampling Spoon:
   • The split-spoon sampler is a hollow cylindrical tube designed to collect a soil sample as it is driven into the ground.
   • It has a split design, allowing easy retrieval of the sample after penetration.
   • The standard sampler length is 610 mm, with a diameter of 50 mm, and it is typically used in both dry and wet conditions.
3. Rod Assembly:
   • The rods used in the SPT apparatus connect the hammer to the sampler and are designed to extend the depth of penetration as required.
   • Extension rods (like the 1.5-meter extension rod) are often used to extend the reach of the apparatus when testing deeper layers of soil.
   • The rods are made of strong, durable materials such as steel or alloy.
4. Drive System:
   • The SPT apparatus can either be manually operated or attached to a drilling rig. Drilling rigs are commonly used in deep testing or for working in tough soil conditions.
   • The drive system can also include a winch or pulley for hoisting and dropping the hammer.
5. Safety and Precision:
   • The system is designed for reliable operation under tough field conditions, and modern versions often include automated counters to precisely record the number of blows.