SPT Test (Standard Penetration Test)

The SPT test (Standard Penetration Test) is one of the most widely used field tests in India for evaluating soil strength. When clients ask “Is soil testing really needed?”, the simplest answer is: SPT N-values directly influence your foundation design.

What is the SPT test?

SPT is performed inside a borehole. A standard sampler is driven into the soil using a hammer of standard weight dropped from a standard height. The test measures how many blows are needed to penetrate a fixed distance—this becomes the N-value.

What does the N-value mean?

In simple terms:

• Low N-value → loose/soft soil → higher settlement risk

• High N-value → dense/stiff soil → stronger bearing support

Your geotechnical engineer uses N-values (with corrections) to estimate:

• Bearing capacity

• Settlement

• Soil consistency/density

• Foundation type & depth

Why SPT is important in Bengaluru/Karnataka

Many sites have variable strata: filled land, clay pockets, sandy layers, weathered rock. SPT helps identify these changes with depth so the foundation is designed safely.

What should a good SPT report include?

• Borehole depth & location

• Soil strata description

• Groundwater level (observed)

• Raw and corrected N-values

• Lab test summary (Atterberg limits, gradation, etc.)

• SBC recommendation + settlement consideration

• Clear foundation recommendation

Common mistakes to avoid

• Doing “one borehole for a big site” (insufficient coverage)

• Missing groundwater details

• Not correlating lab results with field data

• Using generic SBC without site interpretation

Need an SPT-based soil investigation for your project? Edge2 provides field investigation + lab testing + clear foundation recommendations.