Comprehensive Report: USCS Soil Classification and Embankment Design

This report applies the Unified Soil Classification System (USCS) to analyze soil samples from four borrow pits (B1, B2, B3, and B4). The analysis includes determining the percentage passing through sieves, liquid and plastic limits, and calculating the plasticity index, coefficient of uniformity, and permeability. The report classifies the soils based on these properties, identifying them as gravel, sand, silty sand, and organic clay. The analysis further assesses the suitability of the soil from borrow pit B2 for embankment construction, including calculations for induced total stress distribution with depth using Boussinesq's theory and estimating seepage quantity. The report concludes with references to relevant geotechnical engineering resources.

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
Unified Soil Classification System
Name
Institution
Date

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
Unified Soil Classification System (USCS) classified soils into coarse grained and fine
grained categories. Under coarse grained soils which are those where more than 50% is retained
in No.200 sieve, soils are further subdivide into sands and gravels depending on the percentage
passing No.4 sieve. Fine grained are those that allow 50% or more to pass through No.200 sieve
and are categorized into silts and clays with a liquid limit of less than 50 and those with a liquid
limit of 50 or more. These can also be further classified into well graded and poorly graded.
Gravels that have a coefficient of curvature between 1 and 3 and a coefficient of
uniformity greater or equal to 4 are classified as well graded gravels.
Sands that have a coefficient of curvature between 1 and 3 and a coefficient of uniformity
greater or equal to 6 are classified as well graded sands.
Definitions
Plasticity Index measures a soil’s plasticity and is calculated as the difference between
the liquid limit and the plastic limit. The plasticity chart is used to classify using this.
Coefficient of Uniformity , Cu= D60
D10
Coefficient of Curvature , Cc= ( D30 )2
D10∗D60
Where;
D30 = grain diameter at 30 percent passing
D60= grain diameter at 60 percent passing

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
D10= grain diameter at 10 percent passing
Calculations and conclusions
1) Soil from borrow pit B1
D10=¿0.00002
D30 = 0.0015
D60 = 0.014
Cu= D60
D10
¿ 0.014
0.00002 =700
Cc= ( D30 )2
D10∗D60
= .00152
0.00002+ .014 = 0.016
Percentage passing the No. 200 sieve (0.075 micron) = 16%.
Percentage passing the No. 4 sieve (0.00475 micron) = 41%.
Liquid Limit was found to be 43 %
Plastic Limit was found to be 18 %
Plasticity Index = 43 – 18 = 25.
Permeability was not acquired
This soil is coarse grained and is therefore a gravel since the percentage passing sieve
No.200 is less than 50% and that passing sieve No.4 is less than 50% . It is also well graded

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
since its coefficient of uniformity is way above 6. This soil is highly plastic since PI is above 17.
The soil permeability of the soil is not indicated and thus accurate judgement cannot be made.
2) Soil from borrow pit B2
D10=¿0.00002
D30 = 0.00016
D60 = 0.0004
Cu= D60
D10
¿ 0.0004
0.00002 =20
Cc= ( D30 )2
D10∗D60
= .000162
0.00002+ .00004 = 0.00043
Percentage passing the 200 sieve (0.075 micron) = 24%.
Percentage passing the 200 sieve (0.00475 micron) = 100%.
Liquid Limit was found to be 31 %
Plastic Limit was found to be 10 %
Plasticity Index = 21%
Permeability was found to be 0.5 m/day = 0.00058 cm/s.
This soil is also coarse grained and is a sand since the percentage passing sieve No.200 is
less than 50% and that passing No. 4 sieve is greater than 50%. The soil’s permeability is

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
between 0.001 and 0.000001 cm/s and thus this soil is a silty sand. It is also well graded since its
coefficient of uniformity is above 6. This soil is reasonably stable and will be used if the core or
blankets are to be impervious (Swiss Standard SN 670 010b)
3) Soil from borrow pit B3
D10=¿0
D30 = 0
D60 = 0
Percentage passing the 200 sieve (0.075 micron) = 94%.
Liquid Limit was found to be 69 %
Plastic Limit was found to be 26 %
The plasticity index is 43 which is above the A line and thus the soil is classified under CH
Permeability was found to be 0.00001 m/day.
Soil from borrow point B3 is also fine grained and is therefore a clay or silt more so an
organic clay of high plasticity since the percentage passing is more than 50% and the liquid limit
is more than 50%. The soil has a permeability of 1.16e-9 cm/s. The soil’s permeability is more
than 1e-8 cm/s and thus this soil is silt. This soil can thus not be used in the embankment. The
soil is also not well graded and is highly plastic since PI is above 17. The coefficient of

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
uniformity that is an indicator of the grading of soil is missing and thus accurate judgement
cannot be made.
4) Soil from borrow pit B4
D10=¿0.00015
D30 = 0.0002
D60 = 0.0003
Cu= D60
D10
¿ 0.0003
0.00015 =2
Cc= ( D30 )2
D10∗D60
= .00032
0.000015+0.0003 = 0.002
Percentage passing the No. 200 sieve (0.075 micron) = 3%
Percentage passing the No. 4 sieve (0.075 micron) = 99%
Liquid Limit was not recorded
Plastic Limit was not recorded
This soil is coarse grained and is therefore sand since the percentage passing is less than
50% and that passing No. 4 sieve is greater than 50%. Permeability was found to be 2.3 m/day =
0.003 cm/s. The soil’s permeability is between 0.001 and 0.000001 cm/s and thus this soil is a

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
silty gravel. The soil’s plasticity is not known. The coefficient of uniformity is however less than
4 and is therefore poorly grained. This soil can be used in the pervious shell of the dam.
Induced total stress distribution with depth
The soil used for embankment is from borrow pit B2. The embankment receives vertical
pressure only along the center line.
Using Boussinesq and making all assumptions made in this theory (Department of the Army,
2001);
Vertical stress at any point is given by;
p
[ 1−
[ 1
1+ [ R
z
2
] ] 3
2
] where z is the depth∧R isthe radius of influence
Maximum Stress at crest = 21 KPa
Negligible weight is felt when stress = 2.1 KPa
From the graph plotted in the excel sheet attached, this is achieved at a depth of approximately
69.1 m

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
Seepage Quantity
10m
20m
Length of the dam = 800 m
Water to be retained = 60m
Negligible loss assumed
Head drops = 15
Flow channels = 6
Seepage is calculated as
Q=k × nf
nd
× H × b CITATION Dep17 \l 1033 (Department of Civil Engineering Indian Institute
of Technology, Kanpur, 2017)

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
where ;
K = coefficient of permeability
nf = Number of flow channels in the flow net
nd = Number of potential head drops
H = Total hydraulic head (No head loss thus equal to height of water to be maintained
b = width
The coefficient of permeability for soil used in embankment from borrow pit B2 = 0.5 m/day
Seepage Q, = 0.5 × 6
15 × 60× 800=9600 m3 per day

Running Head: UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
References
Department of Civil Engineering Indian Institute of Technology, Kanpur. (2017). Advance
Geotechnicnological Engineering (web). Retrieved from NPTEL:
http://nptel.ac.in/courses/105104132/Module2/lecture8.pdf
Department of the Army. (2001). FM 5 - 472: Materials Testing. Retrieved from
GlobalSecurity.org: http://www.globalsecurity.org/military/library/policy/army/fm/5-
472/apb.pdf
Swiss Standard SN 670 010b. (n.d.). Characteristic Coefficients of soils. Association of Swiss
Road and Traffic Engineers.