The results obtained from a seismic study along a section of the centerline of a highway are shown below. Estimate the depths of the different strata of soil and suggest the type of soil in each stratum.

Question

What will be an ideal response?

Answer 1

From the data provided, plot the following graph:



Determine the soil type in each stratum.

u1 = 75 / (60 × 10–3)

u1 = 1,250 ft / sec

u1 = 381 m / sec

The soil in this stratum is probably sand or loess.

u2 = (150 – 75) / ((82 – 60) × 10–3)

u2 = 3,409 ft / sec

u2 = 1,039 m / sec

The soil in this stratum is probably loam or clay.

u3 = (250 – 150) / ((90 – 82) × 10–3)

u3 = 12,500 ft / sec

u3 = 3,810 m / sec

The soil in stratum is probably sandstone, limestone, or slate and shale.

Next, determine the depths for each layer of soil.

Sin ? = u1 / u2

Sin ? = 1,250 / 3,409

Sin ? = 0.367

? = 21.52º, cos ? = 0.93

OP = 35 × 10–3 sec (from graph above)

Use Equation 17.21 to determine depth,

H1 = ((35 × 10–3 sec) × 1,250) / (2 × 0.93)

H1 = 23.5 ft

Therefore, the depth for the first stratum is 23.5 ft.

Next, determine the depth for the second layer of soil.

Sin ? = u2 / u3

Sin ? = 3,409 / 12,500

Sin ? = 0.273

? = 15.83º, Cos ? = 0.962

PT = 35 × 10–3 sec (from graph above)

Use Equation 17.22 to determine depth,

H2 = ((35 × 10–3 sec) × 3,409) / (2 × 0.962)

H2 = 62.0 feet

Therefore, the depth for the second stratum is 62.0 feet.