Soils - Exam #1

What is the range of grain sizes that are classified using U.S. Standard sieves?

0.075 mm to 75 mm

List the five main objective of compaction.

1) Detrimental settlements can be reduced/prevented 2) Soil strength can be increased (and slope stability improved) 3) Bearing capacity of pavements is increased 4) Hydraulic conductivity can be decreased 5) Undesirable volume changes can be controlled

The zero air voids curve represents _____ saturation.

100%

Specific gravity of solids

Gs

Density

p

Define effective stress and how it is calculated.

Effective stress is the intergranular stress and is calculated as the total stress minus pore water pressure.

Data can plot above the ZAV line a. True b. False

False

Compaction of fine-grained materials is a function of what four variables?

Dry density, water content, compactive effort, and soil type (gradation and % fines)

The solid phase of soil is comprised of what six particle types differentiated by grain size? (HINT: Review Table 2.3 and Figure 2.4)

Boulders, cobbles, gravels, sands, silts, clays

Define "compaction"

Compaction is the densification of soils and rocks by the application of mechanical energy.

Impact Compaction

Compaction/densification from a falling weight

Vibratory Compaction

Compaction/densification from particle vibration

Kneading Compaction

Compaction/densification from shearing fine grained soils

Dynamic Compaction

Compaction/densification resulting from a falling weight.

Static Compaction

Compaction/densification resulting from pressure.

What is/are the name(s) of the plot(s) that the proportional distribution of different grain sizes is/are commonly shown?

Cumulative frequency diagram Histogram Gradation curve

For a similar average grain size soil (e.g., sand), Wopt _______ and Pd-max _______ when the soil changes from poorly graded to well graded.

Decreases, Increases

Explain, in words, the difference between density and unit weight. What is the equation for converting density to unit weight?

Density is the ratio of mass to volume, while unit weight is the ratio of weight to volume. The equation is: (density times gravity equals unit weight).

Compactive effort

measure of mechanical effort applied to a soil mass

Review Table 5.1. What differences between Methods A of the Standard and Modified Proctor compaction tests contribute to the difference in compactive effort?

Hammer weight, hammer drop weight, and number of layers

What device is used to determine grain size of particles less than 0.075 mm in equivalent diameter?

Hydrometer

Review Figure 5.4. As average grain size decreases in grain size, Wopt _____ and Pd-max ______.

Increases, Decreases

Review Figure 5.4. As average grain size decreases, the compaction curve width _____ and height ______.

Increases, Decreases

Compactive Effort

Measure of mechanical energy applied to a soil mass

Compaction is a _____ soil stabilization method

Mechanical

PI

Range of water contents over which the soil behaves as a plastic.

Densification

Reduction in void ratio

What is the difference between Relative Density and Density Index?

Relative Density uses void ratio and Density Index uses dry density or dry unit weight to characterize soil with respect to maximum and minimum density.

Read Section 5.7.1. What is relative compaction, how is it determined, and why is it necessary?

Relative compaction is an end product specification that is based on the ratio of the field dry density to maximum dry density for a soil, and is used to control the density achieved in the field (provides a baseline criteria to ensure soil is within density specification).

The texture of a soil is related to its appearance or "feel". What three things does the texture depend on?

Relative particle size, relative particle shape, and range/distribution of particle sizes

Degree of saturation

S

3 components or phases of soils

Solids, water, air

The degree of saturation, S, is defined as Vwater/Vvoids as a percent. What does this tell us about the voids within a soil mass?

The total percentage of void space that contains water.

Most of the mass-volume relationships for soils are independent of sample size and are often dimensionless a. True b. False

True

The line of optimums (curve drawn through optimum water contents for different compactive efforts) is parallel to the S=100% curve. a. True b. False

True

Water content can be calculated using either the ratio of mass or ratio of weight of water to solids. a. True b. False

True

LL

Water content representative of a lower limit of a soil's viscous flow

PL

Water content representative of the soil's lower limit of a soil's plastic state

Define, in words, what constitutes as Well Graded soil vs. a Poorly Graded soil.

Well graded soil has a normal or near normal distribution of a wide range of grain sizes, while poorly graded soil has either an excess or deficiency of certain sizes.

Under what conditions is a soil assigned a dual symbol under the USCS rubric?

When the fraction of soil that is fines (<0.075 mm or #200 sieve) is between 5% and 12%.

0<LI,1

When the natural (e.g. field) water content is such that the soil behaves as a plastic

LI<0

When the natural (e.g. field) water content is such that the soil has brittle behavior

LI>1

When the water content is such that the soil behaves as a liquid

Compaction is a function of what four things

dry density, water content, compactive effort, soil type/gradation

Void Ratio

e

How is the distribution of different grain sizes plotted? Describe the parameter and the scale used. Give answer in (x,y)

grain diameter in logarithmic scale, percent mass (or weight) on linear scale

LL > 50

high plasticity L=low

LL < 50

low plasticity H= high

Porosity

n

Void ratio is calculated as volume of _____ divided by volume of ___________.

voids, solids

Water Content

w

Water content is the ration of the amount of ______ present in a soil volume to the amount of soil grains based on the ______ mass of the soil, not the _____ mass.

water, dry, total