Question 1

What are the three categories of lateral earth pressure on a vertical plane (wall)?&#10;A)Minor, major, excessive&#10;B)At rest, active, passive&#10;C)Static, variable, dynamic&#10;D)None of the above

Accepted Answer

The three categories of lateral earth pressure on a vertical plane are: at rest, active, and passive. At rest pressure develops when there is no lateral movement experienced by the wall. Active pressure develops when the wall moves freely outward. Passive pressure develops when the wall moves into, and compresses, the soil.

Question 2

What is the lateral pressure (in kips per square foot (ksf)) at the bottom of an 8-foot tall, 18-inch thick poured concrete retaining wall in an active pressure condition, given the backfill placed behind the wall is sandy gravel with a dry unit weight of 122 pounds per cubic foot (pcf), and an internal friction of 28 degrees? Assume the wall does not retain water and the Rankin active earth pressure coefficient Ka = 0.33.

A)0.32 ksf
B)3.2 ksf
C)322 ksf
D)Not enough information provided

0.32 ksf

Accepted Answer

The lateral force on an 8-foot tall, 18-inch thick poured concrete retaining wall in an active pressure condition with the given backfill is 0.32 ksf. Solution: Use Rankine's lateral pressure equation p_a = ? h K_a Where ? = 122 pcf h = 8 feet K_a = 0.33 p_a = ? h K_a = (122 pcf) (8 ft) (0.33) = 322 pounds/square foot x (1 kip/1000 pounds) = 0.32 ksf

Question 3

What is the lateral force against an 8-foot high retaining wall in an active pressure condition, given the lateral pressure at the bottom of the wall is 0.32 kips per square foot (ksf)?&#10;A)1.2 kips per foot of wall&#10;B)120 pounds per foot of wall&#10;C)1200 kips per foot of wall&#10;D)Not enough information provided

Accepted Answer

The lateral force against an 8-foot high retaining wall in an active pressure condition with the given lateral pressure at the bottom of the wall is 1.2 kips per foot of wall. Solution: Use Rankine's lateral force equation F_a = ½ (p_a)(h) Where pa = 0.32 ksf h = 8 feet (ft) F_a = ½ (0.32 ksf) (8 ft) = 1.2 kips per foot of wall

Question 4

What is the superimposed total lateral force resulting from groundwater pressure on a 8-foot high wall if the groundwater level behind the wall is located 4 feet below the backfill surface?&#10;A)249 pounds&#10;B)499.2 pounds&#10;C)998 pounds&#10;D)Not enough information provided to determine

Accepted Answer

the superimposed total lateral force resulting from groundwater pressure on an 8-foot high wall if the groundwater level behind the wall is located 4 feet below the backfill surface is 499.2 pounds. Solution: Use pressure area equation p = (?_w ) (h² ) (K) Where unit weight of water, ?_w = 62.4 pcf K = 1 as water pressure is equal in all directions Therefore, Superimposed lateral force from groundwater pressure =½ (unit weight of water) (height of wall - groundwater table) = ½ (62.4 pcf) (8 - 4 feet)² = 499.2 pounds

Question 5

Which of the following soil tests is performed to determine the magnitude and rate of volume decrease that a laterally confined soil sample undergoes when subjected to varying vertical pressures?&#10;A)Convection&#10;B)Compaction&#10;C)Consolidation&#10;D)All of the above

Accepted Answer

A consolidation test is performed to determine the magnitude and rate of volume decrease that a laterally confined soil sample undergoes when subjected to varying vertical pressures. Consolidation test results are used to estimate the magnitude and rate of settlement of a structure or filled earth. Compaction tests are performed to determine the optimal moisture content at which a given soil sample will achieve its maximum dry density. Convection tests are typically performed by researchers studying heat transfer, not soil sciences.

Question 6

What is the voids ratio of a compaction test sample where the mean values resulting from compaction of a large diameter sewer trench are as follows?
Moisture content, w, = 14.5%
Specific gravity, G_s , = 2.65
? = 18 kN/m³

A)0.65
B)0.8
C)1.65
D)1.8

Accepted Answer

The voids ratio of a compaction test sample with the given test results is 0.65. Solution: Use the density formula to solve for voids ratio ? = G_s ?_w (1+w) / 1 + e à e = [G_s ?_w (1+w)]/? - 1 Given ?w = 9.81 kN/m³ Therefore, e = [(2.65) (9.81 kN/m³) (1+0.145)]/18 kN/m³ - 1 e = 0.65

Question 7

Which of the following statements describes why soil testing is conducted following compaction during construction?&#10;A)Verify that the proper moisture content required by the specifications was achieved during compaction&#10;B)Verify that the soil density required by specifications was achieved&#10;C)Develop a moisture density curve to identify optimum moisture&#10;D)All of the above

Accepted Answer

Soil testing is conducted following compaction during construction to accomplish all of the listed reasons. Generally, compaction performance parameters, such as moisture content and soil density, are specified for construction projects. The Proctor or Modified Proctor Test is performed on soils to determine the maximum achievable density and to identify the effects of moisture on soil density.

Question 8

Stresses within a given soil may result from an external load or the volumetric weight of the material. In addition to these properties, which statement regarding stresses below also applies to soils?&#10;A)Soils can only transfer compressive normal stresses and no tensile stresses&#10;B)Shear stresses can only be transmitted if they are relatively small when compared to normal stresses&#10;C)Part of the stresses is transferred by water in the pores&#10;D)All of the above

Accepted Answer

In addition to stresses within a given soil that may result from an external load or the volumetric weight of the material, all of the statements listed above also apply to soils. These properties distinguish soils from other materials.

Question 9

What is the change in total stress resulting from a vacuum triaxial test that reduced the pore pressure of a dry sand sample by 4 kPa?&#10;A)- 4 kPa&#10;B)No change&#10;C)+ 4 kPA&#10;D)Not enough information provided

Accepted Answer

There is no change in the total stress resulting from a vacuum triaxial test that reduced the pore pressure of a dry sample by 4 kPA. This is attributed to Terzaghi's effective stress principal that states that total stress equals effective stress plus pore pressure. The effective stress increased 4 kPa as a result of the test, but the overall total stress did not change.

Deck 14: Soil Mechanics