Soil Penetration Tests and Site Investigation Methods

Penetration Tests and Site Investigation Methods

Penetration test: A rod is driven into the ground. Soil resistance to the penetration of the rod is related to soil consistency. Different layers of different consistency are identified. A very short time is needed to carry out this test. We use it to establish a relationship between resistance to penetration and various soil parameters. It has a direct application to design. Two types: discontinuous (SPT) and continuous (dynamic and static).

Standard Penetration Test (SPT)

The Standard Penetration Test (SPT) is carried out at the bottom of a borehole. A falling weight of 63.5 kg is dropped into the drill rods from a height of 760 mm. N: number of blows to advance 300 mm (30 cm). If the number of blows for the first 150 mm (15 cm) drive exceeds 50, record the penetration length for 50 blows (R).

There is a correlation with strength (φ) and deformability (E) in granular soils. A disturbed soil sample is obtained.

Correction factors:

• Ncore = fN
• WGL (questioned)
• Efficiency

Dynamic Cone Penetration Test

The dynamic cone penetration test is a continuous test. It is performed by driving a rod with a conical tip into the ground by blows. A falling weight is dropped onto the drill rods from a given height. The number of blows for a given penetration (mm) is recorded.

Static Cone Penetration Test (CPT)

The static cone penetration test (CPT) is suitable for sands and is a continuous test. It is performed by pushing a rod with a conical tip into the ground by pressure. The main difference between the three tip systems (Gouda, Begemann, electric) is the way the penetration is performed.

We obtain:

• Gouda tip: tip resistance and frictional resistance in the rod.
• Begemann tip: tip resistance and frictional resistance at the depth of the test.
• Electric test: tip resistance, frictional resistance at the depth of the test, and pore water pressure.

Geophysical Methods

The interpretation of geophysical methods is performed by an expert in these techniques, not necessarily by a geotechnical specialist. A source sends waves through the soil and receivers record the wave velocities. We obtain information about the soil by studying the velocity of the waves and can derive deformability parameters. In general, velocity should increase with depth; different layers will show different velocities.

Two types:

• Cross-hole
• Down-hole

Site Investigation Program

The type, number, and minimum depth of exploration depend on the nature of the work and the soil properties. Guía de cimentaciones: used to classify the soil and the work. CTE: we need to know the type of construction and the type of soil.