how do the following changes influence the CBR?Use V to judge what the best answer is.California Bearing Ratio, CBRSignificant Significant LittleEffectIncreaseDecreaseWater content of a clean uniform gravel isdecreased by 6% from the optimum valueA"crushed limestone" is substituted for a "sandygravel", both being at optimum moisturecontentsFines (< No. 200) content of a "clean sand" isincreased from 2% to 20% at the wet side ofoptimumAn unsoaked silty clay is soaked for 96 hoursand tested at the same dry side of optimummoisture contentDensity of a "well-graded sand" is decreasedfrom100%compaction(AASHTO-T180)to95%modifiedFor a silty subgrade, depth of the water table islowered from 20 inches to 50 inchesOrganic content is increased from 15% to 30%A well-graded sand is replaced by a gap- gradedsand with fines increased from 8 to 18%how do the following factors influence “maximum drydensity"?Use v to judge what the best answer is.NoIncrease Decrease Change(a) Compactive effort is changed from "standard"to "modified" Proctor(b) Granular material gradation is changed from"poor" to "well graded"(c) Material type changes from A-3 to A-2-7(d) In-situ moisture content increases to 3%above the "optimum moisture content"|(e)Aggregatefromchangeparticles"angular/rough" to "rounded/smooth"(f) Aggregate specific gravity decreases from2.75 to 2.67

1) The cbr value and maximum dry density will reach at maximum value at optimum moisture content.…

how do the following changes influence the CBR? Use v to judge what the best answer is. California Bearing Ratio, CBR Significant Significant Little Effect Increase Decrease Water content of a clean uniform gravel is decreased by 6% from the optimum value A"crushed limestone" is substituted for a "sandy gravel", both being at optimum moisture contents Fines (< No. 200) content of a "clean sand" is increased from 2% to 20% at the wet side of optimum

how do the following changes influence the CBR? Use v to judge what the best answer is. California Bearing Ratio, CBR Significant Significant Little Effect Increase Decrease Water content of a clean uniform gravel is decreased by 6% from the optimum value A"crushed limestone" is substituted for a "sandy gravel", both being at optimum moisture contents Fines (< No. 200) content of a "clean sand" is increased from 2% to 20% at the wet side of optimum

Principles of Geotechnical Engineering (MindTap Course List)

9th Edition

ISBN:9781305970939

Author:Braja M. Das, Khaled Sobhan

Publisher:Braja M. Das, Khaled Sobhan

Chapter4: Plasticity And Structure Of Soil

Section: Chapter Questions

Problem 4.9P

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Question

100%

how do the following changes influence the CBR?
Use V to judge what the best answer is.
California Bearing Ratio, CBR
Significant Significant Little
Effect
Increase
Decrease
Water content of a clean uniform gravel is
decreased by 6% from the optimum value
A"crushed limestone" is substituted for a "sandy
gravel", both being at optimum moisture
contents
Fines (< No. 200) content of a "clean sand" is
increased from 2% to 20% at the wet side of
optimum
An unsoaked silty clay is soaked for 96 hours
and tested at the same dry side of optimum
moisture content
Density of a "well-graded sand" is decreased
from
100%
compaction
(AASHTO-T180)
to
95%
modi
fied
For a silty subgrade, depth of the water table is
lowered from 20 inches to 50 inches
Organic content is increased from 15% to 30%
A well-graded sand is replaced by a gap- graded
sand with fines increased from 8 to 18%
how do the following factors influence “maximum dry
density"?
Use v to judge what the best answer is.
No
Increase Decrease Change
(a) Compactive effort is changed from "standard"
to "modified" Proctor
(b) Granular material gradation is changed from
"poor" to "well graded"
(c) Material type changes from A-3 to A-2-7
(d) In-situ moisture content increases to 3%
above the "optimum moisture content"
|(e)
Aggregate
from
change
particles
"angular/rough" to "rounded/smooth"
(f) Aggregate specific gravity decreases from
2.75 to 2.67

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State whether the following are true or false. a. In the AASHTO classification Table 4.1, the soils that are more suitable for roadwork are located on the left than right. b. In AASHTO classification system, the better performing fine grained soils are the ones with lower group indices. c. In AASHTO classification system, sands are classified as grains with 0.075-4.75 mm diameter. d. The USCS symbol for clayey gravel is CG. e. A soil with USCS symbol SM is sandy silt.
How is the plasticity index of a soil determined?
In AASHTO, which group are the following soil likely to fail into? a. A well-graded gravel with approximately 10% fines b. A well-graded sand with approximately 10% fines c. A uniform fine sand d. A high plastic clay
Three groups of students from the Geotechnical Engineering class collected soil-aggregate samples for laboratory testing from a recycled aggregate processing plant in Palm Beach County, Florida. Three samples, denoted by Soil A, Soil B, and Soil C, were collected from three locations of the aggregate stockpile, and sieve analyses were conducted (see Figure 2.35). (a) (b) Figure 2.35 (a) Soil-aggregate stockpile; (b) sieve analysis (Courtesy of Khaled Sobhan, Florida Atlantic University, Boca Raton, Florida) a. Determine the coefficient of uniformity and the coefficient of gradation for Soils A, B, and C. b. Which one is coarser: Soil A or Soil C? Justify your answer. c. Although the soils are obtained from the same stockpile, why are the curves so different? (Hint: Comment on particle segregation and representative field sampling.) d. Determine the percentages of gravel, sand and fines according to Unified Soil Classification System.
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Refer to Problem 2.C.1. Results of the sieve analysis for Soils A, B, and C are given below. To obtain a more representative sample for further geotechnical testing, a ternary blend is created by uniformly mixing 8000 kg of each soil. Answer the following questions. a. If a sieve analysis is conducted on the mixture using the same set of sieves as shown above, compute the mass retained (as a percentage) and cumulative percent passing in each sieve. b. What would be the uniformity coefficient (Cu) and the coefficient of gradation (Cc) of the mixture?
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The subsurface characteristics for a highway pavement rehabilitation project in the southeastern United States are shown in a boring log in Figure 5.13. The highway structure consists of the asphalt pavement underlain by four different soil strata up to a depth of 20 ft, after which the boring was terminated. Some data on the grain size and plasticity characteristics are also provided for each stratum. Perform the following tasks: 1. Determine the AASHTO soil classification and the group index (GI) for each layer. 2. Determine the most probable group symbols and group names for the various layers according to the Unified soil classification system. Use Table 5.3 and the soil characteristics given in the boring log.
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