CCIL CCIL - Canadian Council of Independent Laboratories Soil Testing and Geotechnical Analysis Questions and Answers 5

Question 1

In geotechnical engineering, what does the term 'preconsolidation pressure' (σ'p) represent?

Accepted Answer

The maximum past effective vertical stress a soil has experienced

Answer

Preconsolidation pressure is the highest effective stress the soil has ever been subjected to, determined from the e-log p' curve using Casagrande's construction.

Question 2

Which CCIL/ASTM test is used to determine the California Bearing Ratio (CBR) of compacted soils in the laboratory?

Accepted Answer

ASTM D1883

Answer

ASTM D1883 covers the laboratory CBR test, which measures load-penetration resistance used in pavement subgrade design.

Question 3

What is the significance of the A-line on the Casagrande plasticity chart used in the USCS?

Accepted Answer

It separates clays (above) from silts and organic soils (below) at a given liquid limit

Answer

The A-line equation PI = 0.73(LL − 20) divides inorganic clays (C soils, plotting above) from silts and organic clays (M/O soils, below).

Question 4

During a Standard Proctor compaction test (ASTM D698), how many layers of soil are compacted into the mold?

Accepted Answer

3 layers, 25 blows each

Answer

ASTM D698 Method A specifies 3 equal layers compacted with 25 blows of a 5.5-lb hammer dropped 12 inches into a 4-inch diameter mold.

Question 5

What does a negative pore pressure (suction) in an unsaturated soil sample during shearing indicate?

Accepted Answer

The soil is dilating, generating negative excess pore pressure

Answer

Dense or heavily over-consolidated soils tend to dilate when sheared, causing negative excess pore pressures that increase effective stress.

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL CCIL - Canadian Council of Independent Laboratories Soil Testing and Geotechnical Analysis Questions and Answers 5