CCIL - Canadian Council of Independent Laboratories Soil Testing and Geotechnical Analysis Questions and Answers Flashcards

What minimum number of blows in the standard penetration test (SPT) over 12 inches of penetration defines a 'very dense' sand or gravel?

Answer: Greater than 50

An N-value greater than 50 blows per 12 inches classifies granular soil as very dense in the standard SPT relative density scale.

In a laboratory permeability test using a falling-head permeameter, what soil property is being measured?

Answer: Hydraulic conductivity (coefficient of permeability)

A falling-head permeameter measures the rate at which water flows through a fine-grained soil specimen to determine its hydraulic conductivity.

Which index property is used in the AASHTO system as the primary indicator of a soil's suitability for use as subgrade material?

Answer: Group Index (GI)

The Group Index is a numerical value computed from LL, PI, and percent passing No. 200 sieve, where lower values indicate better subgrade quality.

What does the California Bearing Ratio (CBR) test measure in pavement subgrade evaluation?

Answer: The resistance of a subgrade soil to penetration relative to a standard crushed stone

CBR measures the load-bearing capacity of a soil by comparing its penetration resistance to that of a standard high-quality crushed limestone base material.

During consolidation testing per ASTM D2435, what is the purpose of plotting the e-log p curve?

Answer: To determine the compression index (Cc) and preconsolidation pressure

The void ratio versus log pressure curve allows determination of the compression index Cc and identification of the preconsolidation pressure using Casagrande's construction.

What correction factor must be applied to SPT N-values to account for hammer efficiency when comparing results across different equipment?

Answer: Energy ratio correction (ER) normalized to 60% efficiency (N60)

Raw SPT N-values are corrected to a reference hammer efficiency of 60% (N60) because different hammer types deliver varying energy to the drill rod.